GMI UNSOLICITED PROPOSAL NO. E-1106 - LOW ALTITUDE AIRSHIP

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03639A001200100001-0
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 89
• Document Creation Date: December 23, 2016
• Document Release Date: October 25, 2012
• Sequence Number: 1
• Publication Date: February 6, 1959
• Content Type: MISC

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4Bd11-044 :P.,t4,044H
MECHANICAL DIVISION
2003 EAST HENNEPIN AVENUE ? MINNEAPOLIS 13, MINNESOTA ? ? FEDERAL 2- 81
February 6
1959
IF ENCLOSURE (8) IS/ARE WITHDRAWN
(OR NOT ATTACHED) THE CLASSIFICATION
OF THIS CORRESPONDENCE WILL BE CAN-
CELLED WITHOUT REFERENCE. TO THE
ORIGINATING AUTHORITY.,
.GMljtJnsolicitedTroposal No. E-1106 -.Low Altitude Airship
Gentlemen:
General Mills, Inc. is pleased to submit herewith five (5) copies of our
unsolicited proposal No. E-1106 for a low altitude airship.
We have elected to submit budgetary costs, for your planning purposes; how-
ever we would be happy to submit a complete breakdown of costs if you so
deem it necessary at this time. The estimated cost to design and develop
a system in accordance with the technical discussion is $100,000. A budgetary
figure for each vehicle in quantities of twenty (20) is $7,400 which includes
$1,400 for batteries. The hardware items and batteries on the airship are
reusable if they are recovered undamaged. We anticipate this recovery for
at least 80 percent of the flights thereby reducing the total cost of the
twenty units. One set of ground equipment will be required for each launch
50X1
point which will include IR, transmitters, etc. costing approximately $5,000.
If you have any questions during your evaluation of subject proposal, please
feel free to contact us and we will be happy to forward any additional informa-
tion you may require.
,
/.1,?r 4'1
D
Very truly yours
Mechanical Division of
GENERAL MILLS, INC.
50X1
50X1
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February 3, 1959
LOW ALTITUDE AIRSHIP
Technical Proposal .E-1106
Prepared by:
Mechanical Division of
GENERAL MILLS, INC.
1620 Central Avenue
Minneapolis 13, Minnesota
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This document consists of t54 pages, and is number of ,/
C opies.
"This document contains information affecting the National defense
of the ?United States within the meaning of the Espionage Laws, Title 18,
U. S. C. , Sections 793 and 794 . . Its transmission or the revelation
of its contents in any manner to an unauthorized person is prohibited
bylaw."
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TABLE OF CONTENTS
I.
INTRODUCTION
A. Background
Page
3
6
1. Detailed Requirements
2. Typical Mission
B. System Description
C. System Capabilities
II.
TECHNICAL DISCUSSION
8
A. Design Considerations
8
1,
Design Parameters
8
a. Envelope Shape
8
b. Envelope and Tail Material
8
c. Tail Surfaces
9
d. Pressurization
10
e. Airship Volume
11
f. Static Stability Considerations
13
2.
Propulsion System
23
a. Propeller Analysis
24
b. Motors
26
c. Motor Mounting
27
d. Flight Duration
30
3.
Maneuverability
32
C. Navigation and Controls
40
1.
Preset System
42
2.
Command System
44
3.
Command/Preset System
47
4.
Other Systems
47
5.
Prototype Airship Navigation and Control System
49
D. Operations
51
1.
Launching Procedure
51
2.
Guidance Procedure
52
11
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TABLE OF CONTENTS (CONT.)
Page
III. PROGRAM AND SCHEDULE
54
?A. General
54
B. Program on Guidance and Control
54
IV. PROGRAM ORGANIZATION
62
V. FACILITIES AND EXPERIENCE
65
A. Balloon Facilities and Experience
65
I. Design Engineering
65
2, Plastic Film Fabrication
.66
3. Flight Operations
.66
B. Guidance -Facilities and Experience
66
C. Radio ,Communications
68
D. Additional Facilities
68
E. Additional Experience
6.8
VI, PERSONNEL RESUMES
7.0
APPENDIX A
APPENDIX B
APPENDIX C
Al
A5
A8
ill
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LIST OF ILLUSTRATIONS
Figure
Title
Page
1
Mission Profile
2
2
Horizontal Flight Path Limits
2
3
Low Altitude Guided Airship
4
4
Mission Time for 'Various Winds
7
5
Distribution of Operational Effort
6
6
BaLlonet Pressurizing System
12
7
Bailonet Placement
14
8
Static Stability
15
9
Helium Exhau.st Valve
18
9A
Liquid Ballast System
19
10
Descent Curve
21
11
Ascent Curve
22
12
Motor Mounting Method
28
13
Flight Duration vs. Wind Direction
31
14
Turning Radius as a Function of Torque and
Forward Velocity
34
1 5
Turning Time as a Function of Torque and
Forward Velocity to Turn 180?
35
16
Turning Rate (rad/sec) as :a Function of
Torque and Forward Velocity
36
17
Slipstream Diverting Devices for Heading Control
38
1 8
Aft Propeller in Heading Control
41
19
Preset Airship Control System
43
20
Command Airship Control System
45
21
Command/Preset Control System
48
22
Prototype Control System
50
23
Summary of Program Schedule
55
24
Schedule - Guidance and Control Equipment
56
25
Schedule - Vehicle and Ground Equipment
57
26
Project Organization Chart
63
27
"Aerocap" Balloon Similar to Proposed Airship
67
iv
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LOW ALTITUDE AIRSHIP
Technical Proposal
I. INTRODUCTION
This document is an unsolicited proposal for the development of an auto-
matic package delivery airship system. General Mills, Inc. believes that a
requirement for such a system exists, and this proposal defineS our approach
to the development of the system.
A. Background
In December 1958, General Mills, Inc. (GMI) determined that a require-
ment may exist for an automatic package delivery airship system. This sys-
tem should be capable of being transported in a small motor vehicle to a
launch point, of being inflated and launched in the field, and would deliver a
25 pound payload to a remote area and then return to the vicinity of the launch
point.
1. Detailed Requirements
The airship should possess the following flight requirements:
Payload
Range (launch point to target)
Maximum airspeed
Altitude (maximum)
Launch Altitude
25 pounds
1 mile minimum
5 miles maximum
20 knots
2,000 feet MSL
0-1500 feet MSL
The airship will operate silently to prevent audible detection, and it will be
colored to provide minimum visual detectability. The weight and helium
content of the airship will be held to a minimum consistent with the load
carrying requirements to facilitate field launching by a small crew. The
entire airship system will be transportable in a small truck.
2. Typical Mission
A possible mission of the system may be as follows: A crew in a
small truck drives to a field location near a closed danger area. They stop,
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remove the airship from the truck, inflate it and ready the simple guidance
system. The payload is attached, the motors are started, and the airship
takes off. It rises 500 feet above the terrain, silently crosses a danger area
and then descends to low level. It flies a few feet (25) above terrain until it
reaches the desired destination. The payload is then released and the airship
rises 500 feet and returns to the vicinity of the launch point. This operation is
illustrated in Figure 1.
500 Feet
Launch
/if
Out
/1
Point
///
1 to 5 Miles
Return
// ////
.4About 1/4 Mile
Release
Payload
///
Destination
Figure 1. Mission Profile
The navigation requirements for the airship are simple because the destina-
tion or target is long and narrow, such as a road. We can assume that navi-
gation within a 30 degree wedge is aatisfactory, as sketched below.
Launch
Point
Figure 2. Horizontal Flight Path Limits
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The airship need not return precisely to the launch point; however, it should
return across the danger area and it is desirable that it be located and re-
covered.
It has been indicated that experienced personnel will be utilizing the equip-
ment involved in this system, and that such personnel have handled and inflated
polyethylene balloons under field conditions.
Line-of-sight radio command control guidance of the airship is permissible,
if such is required.
B. System Description
This paragraph contains a general description of the proposed system.
The configuration of this system has been established on the basis of our
limited knowledge of the application and operational requirements of the sys-
tem, and it is possible that a more detailed understanding of these require-
ments will make an alternate system more desirable. This is particularly
true of the airship guidance system. A more detailed technical discussion,
including alternate versions which were considered, will be found in later
paragraphs of this proposal.
The configuration of the proposed system is shown in Figure 3. The
airship has the following characteristics:
Length
Diameter
Gross Volume (including
tail fins)
Helium Volume
Balloon System Weight
Material
Propulsion
Speed
34 feet
11 feet
2330 cubic feet
2.190 cubic feet (sea level)
102 pounds (not including payload)
2 mil polyethylene
Two 1/2 HP DC motors
2 foot diameter propellers
20 knots
Side mounting of the motors permits azimuth control and keeps the pro-
pellers away from vegetation and personnel. The vertical fin has been placed
above to keep it out of the way also. The fins are pressurized with helium.
The "gondola" suspended below the airship contains the payload, the alti-
tude control rope (drop-line), the ballast, the guidance and control system and
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?.mignabeinfajallginkilaPRz,6
Figure 3. Low Altitude Guided Airship
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the batteries. The gondola is made of cloth and is suspended by nylon harness
lines. Such construction reduces packaging problems and aids portability.
The airship system will contain a simple guidance system which will
establish the proper ground track for the airship at altitude. Changes of
direction of flight are accomplished by turning the side mounted motors on
and off, thereby eliminating the need for movable control surfaces. Pro-
visions will also be included to allow the ground crew to track the progress
of the airship constantly as long as it is within line-of-sight. We believe
that this capability is necessary to speed the mission and thus help insure
its success.
The elements of the guidance system are:
1) Altitude, sensed by a pressure altimeter and controlled
at high altitude by valving helium or dropping ballasts.
At low altitude, the drop-line maintains terrain clearance.
2) Direction, sensed by a compass in the airship.
3) Ground track, sensed by tracking the vehicle with an
infra-red "sniper scope" or IR viewers which are com-
mercially available. To aid in tracking, the vehicle
will carry an infra-red light, which will be shielded to
prevent radiation in all directions. Range to the air-
ship can be measured by using two "sniperscopes" and
by triangulating with the aid of a small navigation plotter.
Ground track will be corrected after launching by a command radio link
which directs a corrected azimuth heading to the airship. Once established
as a directional memory, the airship will continue to fly this heading until
the payload is released.
Upon release of the payload, the airship rises to 500 feet above terrain
and heading command is transmitted which returns the vehicle to the launch
area.
If it were possible to assume that operation would occur only under very
light wind conditions, then the guidance system can be greatly simplified. No
means of determining ground track would be necessary. The airborne guidance
system would include a compass to maintain heading, and airship descent would
be initiated by a simple timer instead of by radio command.
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C. System Capabilities
The system described herein can be launched under field conditions.
Unpacking, assembly and inflation can be accomplished by 2 or 3 men in 1
hour or less. Although a top speed of 20 knbts should permit operation in
winds up to 15 mph, field inflation should not be attempted if surface winds
are in excess of 10 mph. Surface winds at night are usually low, and night-
time operation should be possible most of the time.
The airship with 33 pounds of silver cell batteries has a duration of
about 60 minutes. This duration will theoretically permit delivery to a line
5 miles from launch point and will permit return with head or tail winds as
high as 17 mph, (assuming perfect guidance) and winds as high as 21 mph at
90 degrees to the flight path. This operation is shown in Figure 4. With no
wind at all, the 5 mile mission can be accomplished in 26 minutes, and a
1 mile mission in about 5 minutes.
The normal mission should be complete, including inflation, flight and
recovery, in less than 2 hours. This time may be divided as fqllows:
Prepare
and
Launch
Flight
Figure 5. Distribution of Operational
Effort
The above is based on a reasonable expectation of 60 minutes for asSembly,
inflation, operational check,. and launch; 30 minutes for flight (both ways);'and
20 minutes for recovery.
Operation of the airship will be quiet, and the infra-red light will not be
visible to the naked eye. This, coupled with small size of the vehicle, will
minimize the probability of detection.
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0
co
0
ao.
CP, 00 N
NIri
714 c\1 c. oo r- .1;) 7t4
_4" r7,1 1=-4
qdux - pUtAP
Mission Time for Various Winds
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II. TECHNICAL DISCUSSION
A. Desigil Considerations
The basic criteria used in the design of this airship are high reliability,
ease of launching and flying, and a low unit cost. Therefore, the system
components will be items which are proven and which are commercially
available rather than components which must be developed.
1. Design Parameters
a. Envelope Shape
The navy,,Class Cu" shape with a 3 to 1 fineness ratio has been
selected for the envelope shape. GMI has used this shape for its captive
balloons, a number of which were in the same volume range as this airship,
and has found it to be highly satisfactory. It has a low drag coefficient, a
high volume-to-surface area ratio, and has a favorable position of the center
of buolyatfcy.
b. Envelope and Tail Material
The general requirements for the materials are 1) low elonga-
tion, 2) low gas permeability, 3) high strength-to-weight ratio, and 4) abra-
sion and handling injury resistance. The material elongation must be held
to a minimum to prevent shape distortion and subsequent deterioration of
the envelopes aerodynamic characteristics. Low gas permeability losses
give the balloon a longer flight time, while a high strength-to-weight ratio
allows a relatively smaller gross envelope volume for a given payload be-
cause less lifting gas is required to lift the envelope. The material must
be tough to prevent leaks from developing during normal handling procedures.
A two-mil polyethylene film most adequately meets the specifications
and will be used. Polyethylene is recommended insteacl of Mylar because
polyethylene is much easier to fabricate and Mylar has such a very low tear
resistance.
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c. Tail Surfaces
An ellipsoid has its stable direction of translation through the
atmosphere when its shortest axis lies tangent to its path. This results in
the body tending to turn broadside to the direction of movement through the
fluid medium and results in 'themaximum drag or energy being dissipated '
into the slipstream. Therefore, airships are fitted with stabilizing fins to
produce a moment counteracting -this tendency of streamlined bodies of revo-
lution to turn broadside to the wind. The attachment of fins nearthe aft-end
of the airship which are parallel to the major axis of the airship results in
their having a restoring .moment which is .minimum when the wind flow is
parallel to the major axis and which increases rapidly as the flow is dis-
placed from this axis. The fins also disturb the theoretical pressure distri-
bution around the hull allowing the production of some stabilizing forces on
-the hull itself.
The desired airship flight characteristics must be specified and the
tail efficiency defined before- the 'actual tail fin area can be specified. If
the tail fins are too.small, the airship will have the tendency to turn broad-
side to its direction of translation which means that power would always have
to be expended to bring the airship back to the desired course. If the tail
fins are .too large, the airship will be so stable that it cannot be maneuvered
without expending a great deal of power.
The 'efficiency of the tail fins is a function of their 'aerodynamic charac-
teristics and their placement on the envelope. A rigid fin such as an airplane
wing can be made so that it has a high restoring-force through .small angles
of displacement. Such a fin' should not be packaged with the balloon envelope
because of the danger of it punching holes in the envelope during shipping
It would probably have to be mounted on the 'envelope in the field after the
airship has been inflated. An inflatable fin can be made which does not have
as effective aerodynamic properties, but which possesses certain other ad-
vantages. Inflated fins are recommended for the following reasons:
I) Lower weight.
2) May be fastened to the envelope at the factory.
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3) Simplifies ground handling during inflation.
4) The base of the fin may be made relatively broad reducing
the stress in the envelope with a minimum weight penalty.
The force acting on the tail fins produces a moment of torque which tends
to rotate the airship about its center of rotation. Therefore, as the length of
the moment arm increases, the forces acting on the fins may be reduced.
Because the center of rotation is near the middle of the balloon, the fins
should be placed as far aft as practical.
A review of references 1, 2 and 3 and the analysis in this report on
maneuverability indicates that a tail surface projected area of . 5 (balloon
2/3
envelope volume) divided equally into an inverted "Y" form tail and
placed as shown in Figure 3 is satisfactory for the recommended inflated
tails.
The tails will be inflated with helium and pressurized to the same pres-
sure as the envelope by having free circulation between the tails and the en-
velope. The estimated volume of the tail fins is 110 cubic feet.
d. Pressurization
The airship must be pressurized to prevent deformation by the
dynamic pressure of the air and bending moments produced by the payload
and propulsion system. The common method of maintaining a constant
pressure differential between the lifting gas and the outside air is by using
?a ballonet. A ballonet is a compartment within the airship envelope which
may be inflated or deflated with air, thus varying the volume occupied, and
hence, the pressure of the lifting gas. As the airship rises, the pressure
of the external air decreases so that air must be evacuated from the ballonet
to allow the lifting gas to expand and reduce pressure. The converse is true
when the airship descends. A more complete discussion of this problem is
included in the static stability and the altitude control sections of the proposal.
1. Bairs tow, L. Applied Aerodynamics Second Edition, New York, Longmans
Sreen, and Company, 1939.
2. Burgess, C. P. Airship Design, New York, Ronald Press, 1927.
3. Blackemore, T. L. Pressure Airships, New York, Ronald Press, 1927.
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The ballonet will be pressurized by a two blower system with each blower
stalling at 1/2 inch of water pressure. One small blower will operate con-
tinuously to maintain the pressure in the ballonet to overcome leaks and minor
changes in altitude. This blower willhave a flow rate from 0 to ZOO CFM.
During the valving operation, a larger blower will operate to place air in
the ballonet at the same rate that helium is being valved. This blower will
have a capacity of about 700 CFM. An airtight flap-type valve will lie over
the top of this large blower when it is not operating to prevent air loss from
the ballonet. The valve will be gravity operated for closing while the pres-
sure generated from the blower will open the valve during operation. See
Figure 6 for the blower arrangements.
e. Alt ship Volume
The airship must hay. ..a large enough volume of helium to sup-
port its weight buoyantly at the maximum design altitude. Since the airship
must fly to an altitude of 2000 feet MSL, the required volume may be ca3cu-
lated from the relationship: system weight = airship volume times helium
13...!oyant lift, pounds per cubic foot.
The following is an estimated breakdown for
Payload and release mechanism
Propulsion system
Navigation and controls
Wiring
Drop line and ballast
Batteries, including rack
Ballonet blowers, helium valve
Balloon weight, including harness,
ballonet, etc.
the system.
25 pounds
20 pounds
16 pounds
3 pounds
20 pounds
_33 pounds
7 pounds
.1201 vol2/3 pounds
The lift of helium at 2000 feet based on the NACA standard atmosphere
is .0622 pounds per cubic foot. As previously stated, the volume of the tail
fins is about 110 cubic feet, hence they will have a lift of about 7 pounds. The
volume relationship may now be expressed as .0622 vol = .1201 vol2/ 3+117.
Therefore, the minimum balloon volume is 2220 cubic feet. The length of
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Valve Opens when
Fan is Running
Ballonet
Pressure
Relief Valve
Continuous
Running Blower
Intermittent Fan
Figure 6. Ballonet Pressurizing System
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Air ship
Envelope
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this balloon is 34 feet and the maximum diameter 11.3 feet. The estimated
balloon weight is 20.4 pounds.
f. Static Stability Considerations
The airship is in equilibrium when the sum of the external
moments is equal to zero.
The balloons position when it is in equilibrium is significant because
any transient forces acting on the balloon will result in perturbations about
this position. For the present case, the two most significant components
of the airship's position are its angle of attack and its altitude above the
ground.
(1) Airship Angle of Attack - The angle of attack of the airship
is defined as the angle between the major axis of the airship and the wind or
relative motion of the atmosphere. The drag of the airship is minimum when
this angle is zero and it increases by a factor of the angle squared as the
airship is displacedfrom this position. Therefore, the airship flies at a
zero angle of attack, it will'result in the minimum dissipation of power to
complete the mission.
The major forces acting on the airship are the buoyancy of the lifting
gas and the gravity forces acting in the vertical plane and the drag and the
thrust acting in the horizontal plane. (The airship is symmetrical and
proper tail fins will be applied so that there will be no aerodynamic pitching
or yawing moments at zero angle of attack.) For steady state flight, the
thrust equals the drag, so the moments from the horizontal forces can be
made equal to zero by placing the propulsion force at the same level as the?
effective center of drag of the airship. The moments from the vertical
forces will be zero if the center of buoyancy is directly above the center
of gravity of the system. The gravity forces on the airship change when
ballast is dropped and when the payload is released so these or any other
varying weights should be placed directly below the center of gravity to
avoid shifts in the position of the C. G.
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When loads are dropped, the buoyant forces must be reduced to maintain
airship equilibrium. Buoyancy is reduced by valving helium. As helium is
valved, air is forced into the ballonet to maintain a pressurc: differential acrosr
the envelope. Since the center of buoyancy is defined as the point where the
surn of the moments of the lifting gas is equal to zero, the helium released and
the air added to the ballonet must be symmetrically placed with respect to the
C. G, This will be accomplished by placing a cylindrical ballonet in the air-
ship with the major aids on a line passing through the center of gravity and
the center of buoyancy (See Figure 7).
'Completely Inflated Ballonet
Batteries, Payload, etc.
Figure 7. Ballonet Placement
Based on preliminary estimates? the center of buoyancy of the proposed
system is 15.8 feet from the nose and along the center line of the airship.
The center of gravity is also 15. 8 feet frorn the nose and 6. 9 feet below the
center line before the rda.d is dropped; and 51 8 feet below after the load
has been dropped.
With the center of gravity located below the center of buoyance at zero
angle of attack, the system acts as .a pendulum2with the center of buoyancy as
the pivot point (See Figure 8) The weight of the airship system gives a re-
storing moment of N = wL Bina if it is displaced from its equilibrium posi-
tion tending to return the airship to its zero angle of attack position.
(2) Airship Altitude - The airship maintains altitude in the at-
mosphere by the buoyance principle. If the weight of the displaced air is
equal to the weight of the airship, the vertical forces will be in equilibrium
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CB
Figure 8. Static :Stability
and the airship will remain, at its present altitude. If the weight of air dis-
,
placed exceeds the airship weight, it will rise; and if the airship weight ex-
ceeds the weight of the displaced air, it will descend.
Obviously, the airship gets its buoyant lift from the fact that a cubic
foot of helium gas weighs less than a cubic foot of air at the same tempera-
ture and pressure. Therefore,, the buoyant lift of the airship may be lowered
by valving off helium into the free air and replacing the helium by air in the
ballonet. This method allows the volume of the airship to remain constant
while varying the lift.
(a) Ballonet Volume - The ballonet must have enough
volume so that an adequate amount of air may be inserted to pressurize the
airship at all points on the flight profile. The maximum helium volume in
the airship is 2220 cubic feet. This volume exists 'When the airship is at
2.000 feet MSL on the way to the target area. The minimum helium volume
occurs as the airship approaches the ground when it returns to the launch
area. If this area is at sea level, the volume at this point is approximately
1420 cubic feet; therefore, the ballonet must have a volume of 800 cubic feet.
(b) Helium Valving Rates - Helium must be valved 4 times
on a flight mission. The airship will have excess free lift when it is released
from the launch point and after is has dropped the payload. It must lose lift
to approach the ground at the target area and again when it returns to the
launch site. The valving rate can be specified as the rate required to cause
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the airship to come into equilibrium before it rises more than 500 feet after it
has dropped the 25 pound payload, the time of maximum free lift.
The airship obeys Newton's second law or F = ma where
m =
a =
F
effective mass of the airship; includes airship mass plus
entrained air; slugs
acceleration; ft per seC2
free lift minus drag where drag may be expressed as KV2;
pounds
If helium is valved at a constant rate of volume, the decrease in free
lift is given by F - ct, if thermodynamic effects are neglected, where F' is
the initial free lift, c is the valving rate in pound lift per sec, and t is time
in seconds. The differential equations of motion then become:
dv
+ KV2 = - ct
dt
or
d2h + K dh 2
) ?
(dt = F - ct
dt
where
h = balloon altitude, feet
V = balloon velocity, FPS
K = balloon drag factor
Neither of these equations can be solved in terms of elementary functions
because of their non-linearity, so they must be evaluated on a computer or by
numerical methods. The following section shows a numerical analysis for 2
cases showing the flight profiles with a valving rate of 3/4 pounds per second.
This rate proves satisfactory and will be used as present design criteria.
This rate of valving and the exact length of time the valve must remain open
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at each position in the flight profile will be solved on our analog computer
during the engineering phase of the proposed program.
The valving rates are quite critical for a satisfactory ascent and descent
profile, and the valve must be accurately calibrated. The proposed system
consists of an orifice and an electrically driven valve. They are mounted as
shown in Figure 9. The large blower on the ballonet will start to function as
the valve is opened so that the pressure differential across the orifice is con-
sta.nt. This constant pressure principle allows calibration tests to be run in
the laboratory to determine the optimum orifice size and shape.
(c) Altitude Control Ballast - The flight profile of this
system requires that the balloon fly at varying :altitudes, and some type of
ballast system will be required to facilitate an abrupt change in rate of de-
s-cent to prevent collision with terrain.- Fortunately, the application of the
sys.tem results in the disposal of part of the gross load at a time that addi-
tional altitude or free lift is required, and ballast is not required at this
point of operation. The ballast system will be controlled by an automatic
activating device. The preliminary design of the system allows 9 pounds
of weight for the ballast.
The simplest system would consist of a small tank containing a liquid
ballast such as wafer, kerosene or :any other available liquid. The dropping
of this ballast would be controlled by an electric solenoid valve that would
be activated by the altitude control circuit. To avoid over control, this
ballast would be released through a restricted orifice of a size determined
from experimental testing of the system. (See Figure 9A).
An alternate to the liquid ballast system would be one utilizing steel or
lead shot for ballast. This system requires that the'ballast material be clean
and completely free of any foreign matter to prevent any stoppage or mal-
function of the control valve. With this system, ballast would have to be
furnished as part of the field package and would be contained in sealed,
moisture proof containers. This system also would use an electric sole-
noid valve to regulate the flow of ballast,;
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Lifting Mechanis
Motor
Valve
Calibrated Orifice
Figure 9. Helium Exhaust Valve
Airship
Envelope
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Poly Bag
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Orifice Plate to',
Regulate Rate of Flow
Figure 9A Liquid Ballast :System
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Solenoid Valve
To Altitude
Control'
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(d) Drop Line - The use of a drop line or drag rope is com-
mon for very low altitude balloon flights. This allows a balloon to float at a
near constant low level without the use of large quantities of ballast to correct
for small changes in altitude. This method is not practical in areas that are
forested or covered by brush or hedges because of the possibility that the rope
may become tangled and stop the progress of the balloon. By proper selection
of the drag rope material, this probability may be minimized but cannot be
eliminated entirely. Tentatively, the drop line is 50 feet long and consists
of a light, hollow plastic tube which will be shot loaded to a 5 pound weight
in the center and at the lower end. This method presents a more decisive
force in controlling the airship's variations than a line with a uniform weight.
Another major reason for using a drag rope for this application is to
provide a handling line to aid in launch and recovery of the vehicle. It is
mandatory that the airborne system return to its launch area for recovery,
and the use of a drop line would make the recovery more certain.
(e) Analysis - Figure 10 shows the resulting altitude and
velocity-versus-time curve for the 500 foot descent approach to the position
for dropping the payload. To start the descent, helium is valved from the
airship at a rate of 3/4 lb/sec for the first 16 seconds. During this period,
the loss of helium creates the necessary force to accelerate the airship down-
ward. After the valving is stopped, the airship reaches an equilibrium velocity
of 8.4 ft/sec. When it has descended to an altitude of 100 feet, a ballast of
9 lbs is dropped to lower the descent velocity. To reduce this velocity to
zero, a 50 foot drop line is utilized. The drop line is alight, hollow plastic
tube of negligible weight with 5 lb masses located at its middle and end positions
As the drop line touches the ground, the airship experiences a reduction in
weight of 5 lbs and the velocity is reduced from 5.6 ft/sec to 4.1 ft/sec in 5
seconds. Then the second 5 lb mass touches the ground with the resultant
effect of reducing the descent velocity to zero at an altitude of 17 feet above
the ground. This maneuver takes approximately 80 seconds.
Figure 11 shows the resulting altitude and velocity-versus-time curve after
the payload has been dropped. When the payload is dropped, the airship ex-
periences an upward accelerating force due to the excess lift. To stop this
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C.)
0
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I.
bO
g
rtf
o (I) rd
Pi 4-4
' g
.o P :a' ?
r
d
?
a, N
0
4.4 tn'r.
.
Stop Valving
?o
(DA/ 4j) AlTopTaX
(U) aPn1T1TV
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0
0
Descent :C urve
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0 0 00
0
apn4Tliv "
(oaspj) AlpoTaA
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ascent, helium is valved from the airship at the rate of 3/4 lb/sec for 33. 3
seconds. After the valving ,stops, the ascent velocity is reduced to zero by
?the opposing drag force at an altitude of 500 feet in 230 seconds.
The graphs were plotted by solving the following differential equation.:
rn.2 L7 +Kv2= F ct (See Page 16)
dt
If the term (f-ct) is assumed constant over, small time intervals, the
following solution can be used:
TK
V = lefF/K tanh + constant
Vm
This equation was solved numerically, assuming F to be constant over
5 second intervals.
2. Propulsion System
Before a propulsion system can be specified, the requirements of
the system must be known. The first of these requirements to be investi-
gated is the thrust needed to propel the airship at a speed of 20 knots.
Balloon Drag = :CD V2 .vol2 3
drag coefficient
air 'density, slugs/feet3
V = airship velocity, fps
vol = airship volume, feet3
.05
1.3 lb/ft2 (velocity of 20 knots)
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vol2 / 3
= (2220)2/3 = 170
drag = -(. 05) (1. 5) (170) = 11 pounds
Since the thrust must equal the drag
= 11 pounds.
The required propulsion system must therefore be capable of producing
a total thrust of 11 pounds. The two systems which have been considered are
a propeller system and rocket or jet system. Some of the factors that enter
into the evaluation of the two are efficiency, heat, visibility, noise, cost and
controllability. The advantages of a propeller system indicate that it would
be more practical for the application in question. Cost, which is an important
determining factor, would be extremely high for developing a rocket system,
and at the low velocities required, the efficiency of such a system would be
lower than that of a propeller 'system. In addition, a rocket would produce
excess heat which would be detrimental to the fabric of the airship. If rocket
engines were used they would have to be mound at an unreasonable distance
from the surface of the ship. The glow from the rocket would make it easily
visible during night flights and the noise produced would also aid in the detec-
tion of the vehicle
A propeller system can be developedwhichwillbe of relatively low cost
as compared to a rocket development and will be difficult to detect both visu-
ally and aurally during night flights.
a. Propeller Analysis
Based on the momentum theory, a small propeller of the model
aircraft type would have the following characteristics.
where
T = thrust, pounds
A = propeller area, feet2
(1)
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.air density, -.si.ugifeet3
Vd = airship speed, _fps
Vs. = slipstream velocity, fps
Vo = free stream velocity, fps
_Let V = Vd
if the .prop radius r, = 1.foot; .1" = 5...5 pounds; and Vd = 33. 8 fps.
5. 5
Vs =A + 33.8 =55. 6 fps.
Vd
0)2 (.00238) (33. 8)
I . EfficiencyS.= . Vd ,
= ? ' 7-z" 75. 5%
Vs -N.d 89.4
IFor "a propeller running .at 6000 rpm and Vs = 55. 6,fps, the advance should
be .. 55 ft/turn or 6.66 inches/ turn,
I The effective hp required is -given by
I H =
P T x V
'd
III = 11 (20) (1. 69)
HP = . 675 HP
550
IIf two propellers are used, - each propeller must supply,
1 .675
? .338 HP
2
The momentum theory neglects .energy losses resulting from vorticie-s in
the slipstream. If some allowance is made for these losses and the propellers
are assumed to be 67.5% efficient, then the motor
. 338
hp=
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b. Motors
The motors used to drive the propellers can be either internal
combustion or electric. An internal combustion engine would be heavier than
an electric motor at the low horsepower needed and would also present spe-
cial problems. A clutch might have to be used between the propeller and en-
gine to facilitate maneuvering the airship since the engine could not be turned
off during flight. A muffler -system would also be needed to reduce the noise.
All factors point to an electric motor as the power source for driving the pro-
pellers. Such a motor would be quiet running, light weight, and easy to control
for maneuvering.
One difficulty in using electric motors is that of finding a satisfactory
source of power. If the motors are assumed to 60% efficient,
Power required = 2 x .5
= 1. 67 HP = 1245 watts
.6
?A table of some of the batteries considered is _sliown below.
Irate
Weight
Nominal
Capacity
Watt Hours
Lb. Per
Watt Hours
?Type
(lb)
Voltage
Amp. Hrs.
Per lb.
24V
Per Dollar
Lead Acid
15
12
12 @ 5 hr
rate
9.6
30
4.83
Lead Acid
51
12
70 @ 20 hr
rate
.16.47
102
43. 80
Silver 'Zinc
. 825
1.51
20 @ 10 hr
36.6
13.2
0,95
Silver Zinc
1766
1.51
60.@ 10 hr
rate
51.3
28.3
1.15
Silver
?Cadium
2.565
1.10
70 @ 13 hr
rate
30
56.4
.89
Since a battery with the greatest watt hours per pound is needed, the
second silver zinc battery would probably have to be used. The weight for
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-a 27 volt system would be 3,./1.8 pounds. .The watt hours available are
31. 8 x 51. 3 = 1630 watt hours
This would be enough to handle the motor requirements and the require-
ments of the navigation and control equipment for approximately one hour.
The disadvantage of this battery is its relatively high cost.
c. Motor 'Mounting
The next point to consider is the mounting of the motors. The
simplest method would be to mount two motors, one on each side of the air-
ship along an axis passing through the center of gravity. This method would
produce a better static balance than if the motors were mounted elsewhere.
If they were mounted beneath the ship they would possibly interfere with the
fastening of the payload. Also, by placing the motors -on each side, a greater
torque will be available for turning since they will be at a greater distance
from the center of the ship than if they had been mounted underneath.
The proposed method of mounting is shown in Figure 12. The center of
each motor should be approximately 15 inches from the skin of the airship to
provide proper clearance for the propeller. The method of mounting the
motor must be such that the complete unit can be easily and safely packaged
and that the airship can be quickly launched with the least amount of adjust-
ments being made in the field. These requirements are in addition to the
requirement that the motor be mounted as rigidly and securely as possible.
To meet this last requirement, the motor should be supported by at
least three cables. The three cables will be oriented as shown in Figure 12,
two providing vertical support and one providing horizontal support. The
motor will be attached to two aluminum tubular beams, which in turn will be
attached to a thin aluminum plate fastened to the skin. The purpose of this
plate :is to hold the motor away from the airship. The area of the plate shall
be such that the internal pressure will provide an outward force sufficient to
offset the inward force due to the motor weight and mounting cables.
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Support Cable
1/2 Hp - 27 Volt
(-D.C. Motor
Aluminum Plates
1
Support Cabl
Support Cable
Top View
Aluminum Tubes
Support Cables
Front View
Figure 12. Motor Mounting Method
upport Cables
Support Cables
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With the dimensions? given, a pressure differential of 1" of water and a
motor thrust of 5.50 pounds, the required plate area can be calculated. The
weight of the motor cables and tubing is taken as 7 pounds.
Force due to weight of motor:
7
tan 54? = 5.05 pounds
,Force due to thrust of motor:
5. 5 lbs
F2
= 54 degrees
0 = 14.5 degrees
- F2 =. 5. 5 tan 14. 50 = 1. 42 pounds
Total force = F1+ F2 = 6. 47 pounds
= .1 inch of water = 0361. psi
Plate area = FT= 6?47 ? 179 in2
Po . 0361
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To have a sufficient factor of safety, the plate area should be at least
250 in2. It is suggested the plate be approximately 10 inches high and 25
inches long. A rectangular shape such as this will provide additional sup-
port in the direction of the axis of the airship.
The motor cannot be too difficult to package. Likewise, the plates can-
not be mounted at the launch site since too much valuable time would be con-
sinned. The best arrangement from both points of view is to have a combi-
nation of the two.
The manner in which this is accomplished is to attach the aluminum
plates to the airship at the factory. This could be done by using a pressure
sensitive fiber tape. The aluminum plates would have two sockets welded
to them into which the aluminum tubes would fit. The airship could then be
easily packaged with only the plates attached. The motors can be packaged
separately along with the tubes, cables, and propellers.
The tubing and cables
would be attached to the motor at the factory.
When the vehicle is unpacked in the field, the motor can then be mounted
and readied in a few short steps by first placing the aluminum tubes into the
sockets on the plates and securing them by pinning or bolting. The cables
would then be attached to the airship and the propellers would be fastened.
The final step would be to connect the electrical system to the motors.
d. Flight Duration
The total flight duration should be one hour or less since the
batteries will last that long when the motors are running continuously and
the other equipment is in intermittent operation. The airship will be capable
of traveling at a velocity of 20 knots. The total flight time depends upon the
velocity and direction of existing winds but with a 15 knot wind, a flight to a
destination 5 miles away and a return to the starting point can be made in less
than 1 hour regardless of wind direction. A plot of flight duration versus
direction of a 15 knot wind is shown in Figure 13. This plot is based on a
straight line flight, which means the vehicle is pointed in the proper direction,
and then maintains a 20 knot velocity output. This will not occur in the actual
case because of variations in the wind velocity and direction. With a condition
of no wind the total flight time is .434 hours.
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Time Requirements with 15 Knot Wind
Velocity of Airship 20 Knots
Velocity of Wind 15 Knots
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S .111. 0 H UI Tj,
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Wind Direction
Flight Duration vs.
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It is thus apparent that before a launching of the airship is made, the existing
wind conditions must be known to insure the possibility of a successful flight.
3. Maneuverability
When the airship is flying on a straight, unaccelerated flight path,
all forces acting on the vehicle are in static equilibrium. In order to curve
the flight path, this equilibrium must be upset in such a way that the resulting
unbalanced forces operate perpendicular to the flight path. Various methods
can be employed to supply the force or torque required to curve the flight path,
and several schemes are discussed in later paragraphs.
The acceleration of the airship in response to the unbalanced forces per-
pendicular to the flight path results in a curvature of the flight path and a ro-
tation of the airship about the Y axis. This rotation produces damping mo-
ments which tend to stop the rotation, and which require additional torque to
produce the desired curvature. This damping effect, caused by the angular
velocity of the airship about its Y axis, gives it additional stability over un-
accelerated flight conditions.
The following -equations (see appendix) can be utilized to determine the
turning radius as a function of required torque for the proposed airship con-
figuration:
where:
g = n/K - (KII)t
- n I/K2
n/K _
n = required torque, ft. lbs.
K = damping term, ft. lb. sec.
I = total moment of inertia, ft. lb. sec. 2
= angle of yaw, radians
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The results of the above equablons are shown in Figures 14, 15 and 16.
(It should be noted that these curves were developed on the assumption of a
horizontal turn with the forward and angular velocities remaining constant.)
From these curves the time required to turn 180 degrees, the angular velocity,
and the radius of turn for a particular velocity and torque can be obtained.
From the preceeding equations, it can be shown that, other things being
equal, this radius is proportional to the velocity squared. Thus:
This relationship concludes that in order to minimize the turning radius,
the forward velocity should be reduced.
Of the various devices which could be used to produce the unbalanced
force necessary to cause a curved flight path, the following axe considered
practical from a design standpoint:
1) Movable surfaces
2) Rotatable aft propellers
3) Propeller controls
A movable surface in the form of a rudder could be attached to the trail-
.' ing edge of the top fin of the inverted Y tail configuration. By deflecting the
rudder, the pressure variation over the fin is changed, creating the neces-
sary force to turn the airship. The fins of the proposed airship are pres-
surized and are, therefore, subjected to deflection for relatively light air
loads. As the rudder is deflected, the dynamic pressure of the air will
create a pitching moment tending to twist the fin. This moment varies with
the speed squared, and thus, as the speed increases, the fin twists in a direc-
tion tending to reduce the turning moment. At low speeds, the torque pro-
duced by the rudder, unless it is prohibitively large, is insufficient to pro-
duce the required turning radius.
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..?????????
V =10 Knots
10 20 30 40 50
Figure 14. Turning Radius as a Function of Torque and Forward
Velocity
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200 ?
160 ?
120?
w
E-1
80-
40?
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V 20 Knots
V= 10 Knots
10 20 30 40 50
Torque (ft lbs)
Figure 15. Turnin.g.Time as a Function of Torque and Forward.Velocity
to Turn 1800
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. 08 ?
V = 10 Knots
0
10 20 30
Torque (ft - lbs)
40
Figure 16. Turning Rate (rad/sec) as a Function of Torque and
Forward Velocity
50
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All control surfaces are more effective at high speeds, since the forces
acting on the surfaces vary as the square of the velocity. To take advantage
of the increased velocity of the propeller slipstream, a movable surface could
be positioned immediately behind the propeller. Proper 'deflection of these
surfaces would create the required torque to turn the airship. Using this
scheme to curve the flight path, the following configurations would utilize
the largest moment arm and contribute the maximum torque:
I) Two propellers positioned one on each side of the
maximum diameter section.
2) A propeller positioned on the aft end.
With the propellers positioned at the section of maximum diameter, the
most efficient control surface would be a flat plate. This arises from con-
sideration of the forces acting on the surface. From Figure 17, it is ob-
served that the moment contributed by the drag is much larger than that
contributed by the lift component. Since this surface must be designed to
create maximum drag, a flat plate, utilizing turbulence and eddy flow,
would be practical. However, the deflection of this surface would merely
cancel the thrust of the corresponding propeller, resulting in a "sluggish"
system.
With a propeller positioned at the aft section, a symmetrical airfoil
would give best results. From Figure 17, it is observed that the lift com-
ponent is the major force contributing to the required torque. If a flat
plate were used, as the airstream strikes against the inclined plate, tur-
bulence and eddy currents would destroy the lift and increase the drag. Since
the drag force does not contribute to the turning moment, it must be mini-
mized. Thus, a symmetrical airfoil, limited to a plus or minus 16 degr ee
deflection, would be practical..
From the calculations given below, it is shown that for a particular torque,
more control surface area is required when the propellers are located at the
section of maximum diameter than at the tail, primarily because of the dif-
ference in the moment arms.
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4-3
4C4 41)
1-4 rd
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From Figure 17,
where:
n1
2
L
=CD
SECRET
/2 S V
2
1
= (1.28) P/2 S1 V2 (6)
S2 V2
= (1'6) P/2 2 V2 (18)
= drag coefficient for a flat plate
-= lift coefficient for a typical airfoil
density of air
S1' ? required areas
V = velocity of airship
11'12 ? respective lever arms
Thus, ,for'a given torque:
n ? n
.1 7 2
1.28
1,6
(6) (1. 28) p/2 Si V2 = (1. 6) pi 2 s V2 (18)
= (l.6)(18)
(6)(1.28) ? 3'75
In either case, this system, besides increasing the total weight of the
airship and reducing its payload, requires an additional power supply to
activate the surface and hold it in place. Also, the drag of these surfaces
?reduces the efficiency and over-all performance of the airship.
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A propeller positioned aft of the airshipwould eliminate these inefficient
control surfaces. Using the moment arms as a criteria, this scheme would
supply the maximum torque possible, resulting in the minimum radius of
turn. However, when the propeller is positioned for maximum torque (see
Figure 18), the air flow strikes it in its plane of rotation, causing a very in
system. Also, the auxiliary equipment necessary for such a con-
figuration would add considerable weight and complexity to the airship.
The third possible method is to apply propeller controls. To produce
the necessary force to curve the flight path, the thrust of the propeller is
decreased by reducing its rotational speed. With this arrangement, it is
possible to obtain a maximum torque of 30 ft. lbs. by stopping the required
propeller. Utilizing this torque, the following results are obtained:
Minimum Time to
VForward Turning Radius turn 1800
20 Knots 400' 77 sec
10 Knots 100' 38 sec
This sys.tem combines the advantages of efficiency, lightweight, low cos t,
and.siMplicity, and because of these benefits it was selected.
C. Navigation and Controls
The preceding paragraphs have 'considered .the basic airship design, its
propulsion system and the mechanisms for steering and altitude control.
This section is devoted to the system necessary to impart the required
guidance information to the steering and altitude controlling mechanisms.
To satisfy the operational requirements of the airship, it will be necessary
to control the heading of the airship, the cruising altitude and the point at
which the airship begins its descent prior to dropping the payload. It will
also be necessary to control the airship so that it returns to the launching
area. The general design objectives of the control system are simplicity,
reliability and low cost.
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Streamlines
Figure 18, Aft Propeller. In Heading Control
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In operation the airship will be required to perform the following:
1) Ascend to a cruising altitude
2) Cruise to a predetermined point
3) Descend to a low altitude
4) Cruise at a low altitude
5) Release the payload
6) Ascend to a cruising altitude
7) Fly to the vicinity of the launching point.
8) Descend
A number of different control systems are suitable to this application,
and each system possesses certain advantages and disadvantages. A few of
these possible control systems are discussed in the following paragraphs.
1. Preset System
With this system, the various parameters of heading, elevation and
range are preset prior to launching the airship. Figure 19 is a block diagram
of this system. A magnetic compass is employed as a reference for the air-
ship steering- system. The magnetic comp.ass has a synchrotel output device
which is connected to two control transformers. The. shaft of one control
transformer is set to the desired heading for the airship on the outbound course.
The shaft of the second control transformer is set to the heading for the return
course. The output of the control transformer is a voltage with an amplitude
proportional to the error in the heading of the airship from the reference
heading. The phase of the error signal with respect to a reference voltage
indicates the direction in which the airship is off course. The error 'signal
is supplied to a phase sensitive rectifier which operates a polarized relay.
If the airship is on the desired course, the output of the phase sensitive recti-
fier is zero and the polarized relay operates one set of contacts fora left
error, and the other set of contacts for a right error. The relay contacts,
in turn, control motor contactors which control the flow of current from the
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0--00
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>s
czt Cd
?10 -8 711)
? 43 ?
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battery to the drive motors. Thus, if the airship is off course to the left,
the right motor is stopped until the heading error is corrected, at which time,
the right motor resumes operation.
The altitude control for the airship employs an altitude monitor which is
preset on the ground to the desired cruising altitude. A vertical speed indi-
cator is also employed to optimize the altitude control. The output of the
altitude monitor and the vertical speed indicator are combined and sent to a
phase sensitive rectifier which operates a polarized relay. In this case the
two sets of contacts on the relay are connected to a helium valve and to a
ballast valve. To maintain the preset altitude, helium is valved off to cause
the airship to descend and ballast is dropped to allow the airship to rise. A
timing device which is preset prior to launching the airship determines the
sequence and duration of the various phases of flight such as the time at which
the steering system begins operation, the time at which the altitude system
begins operation and the time at which the airship is caused to descend to
the low cruising altitude. These various times will have to be calculated
on the basis of desired flight path, estimated wind speed and estimated wind
direction over the flight path of the airship.
As soon as the payload is released, a signal causes the steering system
to switch over to the return course heading and causes the altitude system
to begin valving helium for a preset length of time to compensate for the loss
of the payload. Upon reaching cruising altitude, the regular altitude control
system takes over. The final operation of the timer is to cause the airship
to descend to the launch point after completing the return course.
The advantage of this system is that it requires no control communica-
tions during the flight of the airship. The accuracy of the system is dependent
upon the ability of the ground crew to estimate wind speed and direction ac-
curately along the path of the airship and to estimate the pertinent times to
be set into the timer.
2. Command System
A command system for controlling the airship involves two links --
an information link and a command link. Figure 20 shows a block diagram
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co)
?C
0
4.a
a
0
0
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of the command systerr In this system the magnetic compass output is trans-
mitted to the launch po:z.c,.t with a telemetering -transmitter. An altitude monitor
in the airship produces signal proportional to altitude, and this information
also is transmitted to he ground station by the telemetering transmitter. A
receiver on the grourW picks up the transmitted signal with a directional an-
tenna. The receiver Octects the transmitted signal and displays heading' and
altitude information orna pair of meters at the ground station, The directional-
antenna.is rotated for roaximum signal, and the bearing of airship .rela-
tive to the ground station is determined by the position of the antenna. Know-
ing the heading of the rship, the altitude, and the bearing of the airship from
the ground station, the ground station personnel can transmit appropriate
commands to the airshi.p with a command transmitter. A command receiver
in the airship receives the signals and operates appropriate relays to control
the drive motors and tie helium and ballast valves.
To measure the range to the airship, both the command and information
links are used. From the ground station, a reference tone is transmitted
through the command transmitter to the airship where it is picked up by the
command receiver. The output of the receiver is then filtered appropriately
and sent to the telemetering transmitter. The telemetering transmitter then
transmits the reference tone back to the ground station receiver, and a phase
angle meter compares the phase of the received tone with that of the trans-
mitted tone. The phase shift between the return signal and the transmitted
signal is a direct function of the range between the airship and the ground sta-
tion, Time delays in the various equipments can be compensated by adjust-
ments at the ground station prior to launching the airship.
Other -means of determining airship bearing from the ground station and
the range between airship and ground station are feasible, For example, an
infrared optical system could. be used to determine the relative bearing and
the range to the airship providing -a suitable infrared source was carried on
the airship.
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The principal advantage of the command system is that ground station
personnel can transmit corrections to the airship and can compensate for
changes in wind speed and direction from those values measured at the time
of launch. The disadvantage of the system is that it requires considerable
equipment in operation by the ground personnel during the flight of the air-
ship. Also it requires 2-wa:y communication while the airship is cruising at
low altitude.
3. Command/Preset System
The command/preset system combines features of both the preset
system an-d the-_,cornmand system discussed earlier. Figure 21 shows a
block diagram of the system. In this. system, a magnetic compass with a
synchrotel output is connected to a control transformer, and the shaft of
the control transformer is adjusted to the desired heading before launch.
Once in flight, the heading reference can be changed by command from the
ground station. As in the preset system the control transformer output
provides an error voltage resulting in the control of the right or left motor.
Altitude control may be either automatic as in the preset systexn, or
by direct control of the helium and ballast valves as in the command sys tern.
? Information of heading and altitude is telemetered back to the ground.
A range reference tone transmitted from the ground to the command re-
ceiver is re-transmitted to the ground with a telemetering transmitter.
The descent phase prior to dropping the payload is commanded from the
ground station. An indication of the payload release is telemeterd back to
the land station so that the return course heading can be commanded. Once
the airship is returned to the vicinity of the launching point, a command is
given to cause the ship to return to earth. The prime advantage of this sys-
tern.is its flexibility. Should any of the automatic systems fail, the ground
station personnel can take over control of the airship by direct command link,
and this would be an advantage should it be necessary to abort the mission.
4. Other -",Systems
A number of other systems could be used, including beam riding or
simultaneous lobe comparison techniques. These involve the use of considerably
47
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V.C.O.
V .0 . O.
CRUISE
ALTITUDE ALT
ALITEUDE
moNrroR
VERTICAL
SPEED
MONITOR
Jr -1
-
PRASE
SENSITIVE
RECTIFTEN
POLAR
RELAY
HEIAUM
VALVE
PAYLOAD
RELEASE
SIGNAL
TRANSMTITER
Jr
BALLAST
VALVE
SYNCHRAMENTAL
PRE-SET
BEADING MOTOR
MAGNETIC
COMPASS
JrJr Jr
CONTROL
TRNISPOIVER
PHASE
SENSITIVE
RECTIFTP11
1 1
POLAR
RELAY
TI
L ATONING
RELAY
CONTROL
RELAY
MOTOR
CONTACTOR
COTTROL
REL AY
MOTOR
CONT ACTOR
LEFT
MGM
RICHT
MANOR
COMAND DECEIVER
A/FG/III,
ALTITUDE READING PAYLOAD MOE
ERROR DROP
? Figure 21. Command/Preset Airship Control System.
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more complex ground and airborne equipment and hence will not be described
in detail, however, they will be given consideration d.uring the design phase
of the program.
5. Prototype Airship Navigation and Control System
The following is a description of the system to be used in the proto-
type airship. It features simplicity and flexibility. Figure 22 is a block di-
agram of the system. This system is a combination of the preset and the
command systems des.cribed earlier.
In this system the ground station personnel have complete control over
the airship by means of a command transmitter. In addition, a magnetic corn-
"' pass aboard the airship serves as a heading reference, and the desired head-
ing is preset into the system. During flight, an operator at station A observes
the IR beacon on the airship through his IR viewer. With his viewer set to the
desired flight path, he can determine if the airship is going off course, and
he can jog the _reference heading in the airship either left or right with the
command transmitter.
The cruising altitude is 'controlled by a system using aneroid sensors
and helium and ballast valves such as that used in the preset system.
The operator at station B also observes the IR beacon on the airship.
When the relative bearing of the airship from station B reaches a precalcu-
lated value, the automatic altitude control is removed by a radio command
and a timer programs the helium and ballast valves to bring the ship down
to the low altitude drop level.
Once the airship begins the descent phase, it can operate without ground
command and steers the last commanded reference heading. The drop rope
holds the airship at an equilibrium altitude. Once the payload drops, the
helium valve opens for a preset period of time and then the regular altitude
control begins functioning. The return course heading is commanded by
?the operator at station A upon seeing the airship return to altitude. Operator
A observes the airship during its return flight and transmits course correc-
111 tions as before.
1
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Altitude
Monitor
SECRET
Vertical
Speed
Monitor
Phase
Sensitive
Rectifier
Polar
Relay
Helium
Valve
A
Timer
Synclira-
mental
Motor
Ballast
Valve
A
_yload Dump
Signal ?
A A
Magnetic
Compass
Control
Transformer
Phase
Sensitive
Rectifier
Polar
Relay
Latching
Relay ?
Control
Relay
Motor
Contactor
Control
Relay
V
Motor
Contactor
Command Receiver
Figure 22. Prototype Control
System
cretin
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Upon reaching the launching area, the helium is valved off and the 'motors
are stopped by radio command.
This system is reasonably simple -to operate under the expected conditions
of a mission. - All of the automatic controls ,can be disconnected and direct
command given from the ground station. .Since the airship is not radiating
radio signals, it cannot be tracked 1:37 D/F stations, The operating radio fre-
quency, power and ground antenna size can be chosen to give optimum in -
suranc.e against detection.
D. Operations
Operational problems are minimized for this _system because of the small
size of the balloon. This system can be transported complete with inflation
gas by a jeep or other similar small vehicle.
The inflation gas for this system can be contained in 10 standard, 22 0
cu. ft. helium cylinders. These cylinders form the major part of the opera-
tional equipment.
Additional equipment will include the following:
1) Cylinder manifold with gage
2) Inflation hose and diffuser
3) Ground cloth (15 x 40 ft.)
4) Handling lines
5) Ground control instrumentation for control of flight
6) 0-100 lb. spring scale
A balloon as small as this may be successfully launched by a crew of
three or four men depending on surface wind conditions.
1. Launching Procedure
1) The helium requirements are determined and the cylinders
gaged at the staging or 'supply area to insure that sufficient
helium will be provided at the launch site.
2) The launch site must be a cleared area at least as large as
the ground cloth.
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3) The ground cloth is spread so that its longest dimension
will be along the direc tion of the wind.
4) The balloon is removed from its box and is spread out
so that its nose points into the wind. (Launchings should
not generally be considered in surface winds in excess of
15 mph.)
5) The inflation gas cylinders are ma.nifolded together and the
inflation hose and diffuser connected to the inflation tube on
balloon.
6) The balloon is inflated with sufficient gas to lift the complete
airborne system as determined with the spring scale.
7) The tail and ballonet blowers are started to pressurize the
tails and the balloon envelope.
8) Attach load and make final check out of the control system.
9) Release balloon for flight.
After completion of mission, the balloon will be returned to the general
launch area for recovery. When the balloon reaches this area it will be de-
flated and the controls and other hardware recovered.
2. Guidance Procedure
The ground guidance equipment should be checked prior to the mis-
sion. The transmitter will be tested for power output and frequency, and the
infra-red viewers will be examined for satisfactory operation.
Two men are required to operate the guidance system after the airship
is aloft. The first man measures the azimuth angle to the airship with an
infra-red viewer and controls ground track by commanding right and left
corrections with the command transmitter. The second man, located some
distance away, tracks the airship with a second infra-red viewer and measures
the azimuth angle to the airship. With a known base line between the two
viewers, the azimuth angles define the position of the airship.
The length of the base line between the two veiwers can be established
by one of two methods.
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1) The two observing ,positions can be established with
map coordinates, or:
2) The second man can be displaced from the first man
by a distance measured with a line.
In the first case, communication be the observers could be established
with a "walkie-talkie" radio. In the second, the measuring line could be a
telephone line which would serve the dual purpose of communications. The
azimuth of the base line would be obtained by supplying the second viewer
with an infra-red light source, and then sighting on that source from the first
viewer.
A compass or sighting on stars with :a transit will give north reference.
In our present concept, this optical sight is mounted on the same tripod as
the infra-red viewer.
After the "descend" signal is given to the airship, the second viewer is
no longer required. This operator can be returning to the vehicle while the
airship is proc-eediiig on its mission.
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.'.SECRET
ILL. . PROGRAM.:;..464p,?ip-/-/EP-LTI,?, , ;":6(,)
A. General
The program necessaryAgicleliver ;a:satisfactory Warkingmodel of this
low altitude airship covers 9 months time. A summary of this schedule is
shown in Figure 23. More .etailed schedules are shown in Figures 74 and
25;
,omodelscifithe air-borne gbitrance 'sy steth
?
mus t_ be ?fabric ate d one 4_11 iexp eri-rnentaLbreadboard and the fcifheLr. a. de
liverable prototype. We also forsee the fabrication of six balloons, icone...being
the final and deliverable model. All ,six balloons will not be complete; the
, . ; cr_ :1?? -
first five consisting mainly of the plastic fabrication. We anticipate that, -
all five will be damaged during the flight tests. It is expected that the hardware
such as motors, etc. will be recovered and reused on the others.
The ground guidance equipment is expected to be
' 4_ ? ,
ment, either purchased or GFE. Only one mode/ should be necessary for the
development program.
As the schedule shows, we anticipate an extensive flight test program.
This is required to adjust the design and performance of the airship and
guidance system and to insure its satisfactory operation under field conditions.
In addition to the ground guidance equipment, there will be a minority
of ropes and hoses, a ground cloth, and a suitable container. This is called
"ground equipment" in Figure 25. It will be fabricated in time for the flight
tests and will be subject to minor additions and modifications as we learn more
during the flights.
The delivery of the equipment can be followed 30 days later by a technical
report.
B. Program on Guidance and Control
The program of guidance and control equipment is based on the fabrication
of a breadboard model and testing, followed by the design, fabrication and test
of the prototype. The program is detailed in Figure 24 and explained below:
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???????
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_Fabricate Prototype
Deliver Prototype
Cl)
;-1
bi)
0
$.4
0
.0
Lf) U)Lf)
r.17.1
0 en.
c
'14
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(NI
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Analytical Studies
Selection of Components
Fabricate Breadboard Model
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Bench Tests
?Co nfiguration
.I?co
and Other Tests
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Preliminary Design
4-04
a) a)
0 0
0
4-4
0
cn
a)
0
? v-i
t4)
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Fabricate First
Flight Test
SECRET
Model-Fabric a tion
Lt
Nt4
cn
57
?cc
? s
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Analytical Studies
The guidance function is reviewed with the customer to make sure we
have the correct requirements. Possible GFE equipments are considered.
Some REAC studies are performed to study the closed loop performance of
the vehicle and guidance and control equipment in azimuth and elevation.
Gust effects are considered. The compass requirements are determined.
Selection of Components
This phase involves writing of brief specifications and determination of
tolerances on components, discussion with vendors, and determining the
applicability of existing equipment. The problem here is not so much of
finding equipment and components that will do the job, but rather finding
satisfactory low cost components.
Procurement of Components
Once components .are located, 6 weeks should be adequate allowance
for delivery.
Fabricate Breadboard Model
The sensors, relays, controls, motors and propellers are assembled
into an operating model for bench performance tests.
Bench Test
The breadboard model is checked for electrical and mechanical operation.
Measurements are made on sensors.
Design Prototype Configurations
The information gained in the design and test of the breadboard model,
and the data from vehicle flight tests which utilized components of the control
equipment permits the design of the prototype system and its proper packaging.
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Procurement of Components
This time is allowed for delivery from suppliers and fabrication in the
model shop.
.Fabricate Prototype
The prototype is fabricated, using a limited amount of engineering
drawings.
Bench and Other 'Tests
The prototype is checked for functional operation and given a limited
environmental check. Certain sensors should operate properly (altitude)
and the equipment should withstand a. fair temperature range and the vibra-
tion and handling during transport.
Flight Tests
The prototype vehicle and guidance system are assembled and checked
together as a system. A mission is simulated.
C. Program on Vehicle
A detailed schedule of the program for the development of the vehicle
and associated ground equipment is shown in Figure 25. The following work
is anticipated during the various phases of the system.
Preliminary Design
Stress, aerodynamic configurations, weight and balances, electrical
power required, helium valve rates, ballonet fan sizes and flow rates, verti-
cal turning rates, acceptable propeller noise, selection of envelope material
are all typical of the problems to be considered here.
Selection and Test of Components
Actual motors, propellers, valves, and other components will be se lected
based on consideration of their characteristics and will be tested. Thrust tests
will be made. Propellers will be checked on a truck to determine optimum rpm
at cruise speed. A volume calibration will be made on helium valve.
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Flight Test
The first vehicle will be inflated and flight tested initially in a hangar.
Harnessing will be checked and the vehicle put in limited motion utilizing
?various portions of the control equipment as they become available. Main-
tenance of pressure by ballonet fan will be checked.
Other Models
Four additional experimental models will be fabricated, each one em-
bodying successive changes as design knowledge improves. These models
will be successively utilized and expended during the tests.
Flight Tests
Models will be flown outdoors, weather permitting. Rise rates, alti-
tude control, drag coefficient, maneuverability, operation of ballast sys tem
and other information will be obtained.
Build Prototype
A prototype vehicle utilizing prototype hardware will be constructed
based on information obtained from the design and construction of experi-
mental models.
System Flight. Tests
The final prototype model with the final prototype guidance system will
be checked by performing a simulated mission.
Design and Fabricate Ground Equipment
During this time the auxiliary equipment will either be designed and
fabricated or located within our existing inventory. This consists of tie
down ropes, hoses, valves, container and other things necessary to con-
duct the flight tests and permit proper operation of the delivered prototype.
Flight test instrumentation will be fabricated at the same time.
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Modify Ground Equipment
The 'ground equipment which was assembled for the flight tests will be
modified and changed. to make it suitable for use during the test of the proto-
type. No ground equipment (except guidance) will be delivered.
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IV. PROGRAM ORGANIZATION
The proposed project will be carried out under the direction of personnel
of the Engineering Department. Services of personnel from the Balloon and
Research Departments will be enlisted as necessary. A simplified organi-
zation chart of the Mechanical Division of General Mills is shown in Figure 26.
The chart shows the relationship of this project to the existing organizations
of the Engineering and Balloon Departments. The blocks in the project organi-
zation which are duplicated as heavy blocks within the division organization
indicate where most of the effort will occur.
The project will be under the direction of the Special Vehicle Systems
Group in the Systems Engineering Laboratory of the Engineering Department
of the Mechanical Division.
The Special Vehicle Systems Group is a new organization that has been
and is being introduced to old and potentially new customers and users of
General Mills' balloons and services. This group is staffed with personnel
formerly with the Research Department who have done preliminary design
on balloon vehicles and with system engineers from the Engineering Depart-
ment. This group is located in Plant 5 of the Mechanical Division and thus
has access to the facilities of the Engineering and Research Departments and
to the services of several hundred scientists, engineers and technicians
working there. The function of this group is to be responsible for designs
of new balloon systems which involve the use of more than just a gas bag,
such as power plants, instrumentation, payloads, dynamics, guidance,
control, special effects, etc.
Since this program involves the use of a power plant, guidance, and
dynamics, it will be directed by the Special Vehicle Systems group. All
preliminary vehicle design, guidance and control design, analysis using
REAC and digital computers, and analysis of test data will be done by this
group. Certain ground equipment and airborne instrumentation and flight
operations and equipment associated therewith will be designed and fabricated
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by the group at Plant 6 under J. Swisher. Construction of the production vehicle
and the early models including detailed design will be done at Plant 7. General
Mills has successfully used this organization and method of operating on pre-
vious projects.
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V. FACILITIES AND EXPERIENCE
The facilities and experience required for the completion of the proposed
airship program fall into three categories:
Balloons -- Guidance -- Radio Communications
The Mechanical Division of General Mills, Inc. is ideally suited to this program
because it possesses an engineering staff experienced in all three areas, and
it has laboratories and manufacturing facilities already engaged in similar work.
It is impossible in a short discussion to describe all facilities of the
Mechanical Division which may be useful in the proposed program. Aside
from the purchase of standard parts and devices, General Mills, Inc. is
completely independent of outside suppliers for a program of this type and
this magnitude. The entire program will be handled within the framework
?of our existing organization.
A. Balloon Facilities and Experience
The facilities of the Balloon Department of the Mechanical Division en-
compass three areas -- Design Engineering, which is engaged in the design
and construction of balloons and balloon flight control and data collection
equipment; Plastic Film Fabrication, which handles a vast array of balloon
production jobs; and Flight Operations, which handles the flight preparation,
launching and tracking of GMI balloons. All three of these activities are
staffed with experienced experts, and are generously supplied with electronic,
mechanical, and plastic film manufacturing equipment.
I. Design Engineering
This group possesses broad experience in the fields of electrical,
mechanical and aeronautical engineering coupled with .a sound background in
physics related to balloon applications. Its accomplishments include design
of such components as preset-timed controls, remote controls', .telemetering
devices., automatic :.c-utdown-devices for terminating flights, barographs for
.determining time-altitude .data, bar acoder s?and transmitters for relaying
.data to ground site.s, and a variety of other specialized instruments .and de-
vices.for specific ?app.lications.
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The services of two shops are available to this group. A well equipped
instrument development shop is capable of constructing and testing both
electrical and mechanical prototype units, and a machine and welding shop
fabricates special fittings and components dictated by a particular design
need.
2. Plastic Film Fabrication
The capabilities and facilities of the film fabrication group for
handling a vast array of production jobs are second to none. This group
has produced balloons in every configuration from hundreds of thousands of
small Pillow Balloons? Liuch as those used for dropping propaganda leaflets
behind the Iron Curtain, to gigantic 212 foot diameter balloons of 3,750,000
cubic foot capacity used for upper altitude research and high altitude rocket
launching. In fact, Figure 27 shows a more elaborately constructed "AEROCAP"
balloon which closely resembles the configuration and dimensions of the air-
ship proposed in this document.
The plastic film fabrication group has combined four important ingredients
necessary to the production of plastic balloons: flexibility, speed, efficiency,
and painstaking care. The inspection, production control and methods sections
have integrated their efforts in such a way as to guarantee the customer maxi-
mum product reliability.
3. Flight Operations
Flight operations has a threefold activity: 1) flight preparation, 2)
inflation and launching., and 3) tracking and recovery. This group has at its
disposal modern direction finding radio equipment, recovery trucks and both
single and multi-engine aircraft for tracking.
B. Guidance Facilities and Experience
Aside from the facilities of the Balloon Department, the Engineering
Department of the Mechanical Division operates a Guidance and Navigation
Laboratory which is engaged in the development of precision electronic, elec-
tromechanical, and mechanical analog devices for use in missile guidance
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systems, bombing .and navigation computers and other types of guidance and
control systems used in missile and aircraft installations. Although this
work is far more complex and detailed than the requirements of the guidance
system for the proposed airship, the experience and the fabrication facilities
of this laboratory may be of value in developing the optimum airship guidance
system. The engineers of the Guidance and Navigation Laboratory are experi-
enced in the requisites of any airborne guidance system: namely, accuracy,
low cost, reliability, light weight, and low power consumption.
The Guidance and Navigation Laboratory is also staffed with personnel
who are engaged in the development of complex surveying and automatic
tracking systems. These personnel are well qualified in the fields of optics
and infra-red radiation. Again, while the complexity of their work exce eds
the requirements of the tracking system for the proposed airship, their ex-
perience will be helpful in formulating the optimum tracking system.
C.
Radio Communications
The Engineering Department operates a Communications and Controls
laboratory which has broad experience and facilities in radio and microwave
communications, and in control systems. The services of this group are
available to assist in the development of radio command and radio range
systems for the proposed airship.
D. Additional Facilities
The Computer Laboratory of the Engineering Department possesses a
Reeves C400 (REAC) analog computer which will be helpful in achieving an
optimum airship design, and which will aid in the analysis of flight control
devices.
E. Additional Experience
During the past decade plastic balloons have evolved from experimental
toys to highly reliable scientific stratoplatforms. Innumerable military oper-
ational and reseaxchprograms currently employ balloons. General Mills, Inc.
has been at the forefront of this work for many years, and has developed a
wide variety of balloons for a multitude of applications.
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In response to continuing and widespread requirements to suspend scien-
tific equipment or advertising material at relatively low (a few thousand feet)
altitudes and in average meteorological conditions, GMI has accomplished
the successful design, construction and operation of aerodynamically shaped,
lighter-than-air captive vehicles. These vehicles, sold under the trade mark
"AEROCAP", are aerodynamically shaped with tail fins.
Units up to 39 feet in. length have been successfully operated and have
proven themselves reliable at altitudes up to 1500 feet above terrain in winds
of up to 40 knots. The "AEROCAP" Balloon deploys itself almost vertic ally
above the mooring point throughout a wide range of wind conditions. A brief
flight was made with one of these units to an altitude of 4500 feet above ter-
rain with no difficulty experienced. Rapid progress has witnessed flights of
units up to 65 feet in length, fabrication of vehicles more than 130 feet long,
and development of balloons in excess of 200 feet capable of 20,000 lbs. lift.
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? VI. PERSONNEL RESUMES
The following pages contain resumes of personnel who will be assigned to
the Low Altitude Airship project.
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APPENDIX A
Sound Detection
A test was conducted by General Mills to determine the sound intensity
of a 2 foot propeller rotating at 6000 rpm. The test was made indoors in a
large room where the original sound-pressure level (SPL) was recorded ?as
55 decibels (db). The reference point for the SPL is . 0002 microbar. The
power level (PWL) is also given in decibels and has a reference point of 10-13
watts. The relationship between SPL and PWL is given below:
where:
PWL = SPL + 20 logio r +10. 5
PWL and SPL are in decibels
r = the distance in feet from the sound source to the point
where the SPL is measured.
(1)
If the SPL is measured at .a point the SPL at a point r can then be pre-
dicted from equation (1).
SPL = SPL, - 20 log10 (2)
The sound intensity of the 2 foot propeller rotating at 5900 rpm was re-
corded by a General Radio'Co. sound-survey meter placed 2-1/2 feet from
the propeller. The SPL reading recorded was 83 Db. Because the test was
run near a wall, the reading obtained is slightly higher than the actual read-
ing due to sound reflections. A correction factor of -2 Db was used to c orn-
pensate for the room reflections. The SPL reading at 24/2 feet is then
given as 83-2 = 81 Db. Since the airship will be flying -at an altitude of 500 ft
the sound intensity at that distance should be known.
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= SPL - 20 lo
SPL2
r2
g10
5
= 81 - 20 1?g10 00 2.5
= 81.- 46 = 35 Db.
A SPL of 35 DB is classified as a faint sound and is equivalent to a
quiet residential area ora quiet home. This 35 Db SPL occurs directly
below the airship. At any other ground station the SPL will decrease as
the distance from the airship increases.
The loudness level is somewhat different from the sound-pressure
level. It is the SPL at a frequency of 1000 cycles per second. The units of
loudness level are phons. Sounds of various frequencies are compared to
a sound of equivalent _loudness at a frequency of 1000 cps. In the case of
a propeller rotating at 5900 rpm, the frequency of the sound waves would be
approximately 200 cps. A SPL of 35 Db at ZOO cps is equivalent to 14 Db at
1000 cps,. or a loudness level of 14 phons. About 50 percent of the population
can hear sounds that exceed 20 phons and the percentage decreases rapidly
as the loudness level drops below 20 phons.
The results of the test indicate that the proposed airship would not be
easily detectable due to noise. Although the test was not made under actual
conditions or even under ideal conditions, it is believed that a fairly repre-
sentative value of sound intensity was obtained.
Figures Al and A2 show the sound-pressure level and loudness level as
a function of propeller rpm.
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85
80
75
70
65
60
55
"r;
72 50
45
ca 35
20
15
10
5
0
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At 2.5 Fee.t
At 500 Feet
1000 2000 3000 4000 . 5000 6000
-.Propeller rpm
Figure Al. Sound Intensity vs. Propeller Speed
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25
20
15
'Fos
o 10
a,
5
r-I
cu
Ili 0
-5
-10
-15
0
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90 Percent of Population can detect 30 Phons
50 Percent of Population can detect 20 Phons
1000
2000 3000
Propeller rpm
4000
5000
. Figure ?A2. Loudness Level vs Propeller RPM at Di stance
of _500 Feet
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APPENDIX B
Equations of Maneuverability
Direction of X axis
when t = 0
X Axis
43
Flight
Path
From trigonometry:
ds = Rd/ii
Rearranging:
ds ds/dt
R
dy) /dt
However, from the geometry of the figure:
20 =
where:
R = radius of turn, feet
P1 position of airship at t 0
P2 =position of airship at t t
0 =angle of yaw
je =angle of sideslip
S =distance which airship has
moved in time t along circle
y=angle between positions
P and
1
V =forward velocity, fps
(1)
(2)
(3)
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Taking the derivative with respect to time:
2d0
cit dt
Upon substitution of (4) into (2)
V
R-2
(4)
(5)
The required yawing velocity, 6, can be obtained from a differential
equation developed from dynamic considerations.
where:
n- KA I ad
(6)
n torque, ft lbs
K = damping turn, ft lb sec
I =total moment of inertia, ft lb sec2
angle of yaw, radians
Re arr anging
Thus
'Equivalent integral form
0=
a { - 1-1/
- K/I at
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Solving
or
Thus
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log (6 n/K) C ?K t
n/K c e-(K/I)t
n/K [
Equivalent integral.form
Solving
or
Thus
1 e.1) t]
idt =-_ n/K
- e-(K/I)
dt
? Evaluating C
at t = 0
0-= 0
C -n/K
(7)
= n/K [t eat]
C
K/I Evaluating C
at t
0
C - nI/ K2
n/K (t -+- I/K e4K/1/t) ? C
A= nKt -F n I/K2 e-(K/I)t- n I/K2
Al
(8)
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APPENDIX C
Solutions of Airships Vertical Motion
The free lift of an airship must be changed 4 times to successfully com-
plete its mission. To determine the relationship between the various para-
meters after the free lift has been changed, the following differential was ob-
tained from Newton's second law and was programmed for a REAC:
where:
4di, 2 =
M f
dt
de
airship mass, slugs
drag term, slugs/ft
free lift, lbs
a valving rate, lbs/sec
valving time, sec
altitude, ft.
When the airship reaches the desired position and drops its payload,
it experiences an upward acceleration due to the excess free lift. To stop
this ascent, helium is valved from the airship at .a constant rate until
f - at= 0. Then the drag force reduces this ascent velocity to zero at the
required altitude.
Figures A3, A4, and A5 show the results of the above procedure from
18 REAC solutions. These results were obtained from the above differential
equation, assuming m = 5. 5 slugs and varying the parameters, k, a, and f.
From these figures, it is observed that the valving rate adjustment is very
critical to reach the desired altitude, since the other parameters are rela-
tively fixed for a particular configuration.
These curves were plotted to show how the various par ameters affec t the
desired altitude and peak velocity. For an analysis of our configuration, see
Figures 10 and 11 of Section 3-B
A8
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700
500
re)
@ 3 Minutes
100
700
500
100
a = .5 lb/sec
f = 25 lbs
f = 20 lbs
f =15 lbs
.10 .15 .20
a = .6 lb/sec
f '= 25 lbs
f = 20 lbs
f =: 15 lbs
. 10
.15
Figure A3. Altitude Variation
.20
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.10
.15
.20
a = . 6 lb/sec
= 25 lbs
f = 20 lbs
15 lbs
.10 .15 .20
Figure A4. Peak Velocity Variation
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600
400
4.1
a)
-0
200
600
4-4
? 400
200
1
2
Time (min)
3
f 25 lb
a =.6.1b/sec
1 2
'Time (mm)
Figure A5. Altitude Variation with Time
3
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