INVESTIGATION OF ACCIDENT TO U-2F SERIAL NO. 342

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP74B00447R000100010066-9
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 39
• Document Creation Date: December 12, 2016
• Document Release Date: February 5, 2002
• Sequence Number: 66
• Publication Date: March 21, 1966
• Content Type: MEMO

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To:
From:
Subject:
Ref:
21 March 1966
INVESTIGATION OF ACCIDENT TO U-2F SERIAL NO. 342
a.
dated 18 March 1966
b. Static Test Report, LR 10571, 15 October 1955
The accident involving the U-2F Aircraft Serial No. 342 occurred following
practice refueling hook-ups with a tanker at an altitude of 35,000 feet
and resulted in the break-up of the aircraft. Witnesses in the tanker
stated that apparently the left wing failed as the pilot pulled up and
away from the tanker from a position alongside.
At the time of the incident the subject aircraft weighed 17,160 lbs. with
a center of gravity at 28.4 percent MAX. This center of gravity is at
the aft limit as given in the Flight Manual. The speed at the time was
approximately 210 to 220 knots calibrated airspeed which corrects to 200
knots equivalent airspeed. The Mach Na. at this speed and altitude would
be .66.
The fuel loading consisted of 530 lbs. in the sump tank, 2000 lbs. in the
auxiliary tanks and about 200 lbs. in the main tanks. Slipper tanks were
on, but empty. The aircraft was in the gust configuration; that is, the
flaps and ailerons were "shifted" up, thereby reducing tail load.
Usingthe specific weights, speeds, altitude etc. at the time of the acci-
dent, loads were calculated along the wing as a function of load factor
for a symmetrical pull-up maneuver. From this study, it was concluded
that the most critical item was up-bending in the wing root section.
Figure 1 is a plot of wing root bending moment (W.S. 36) versus load factor.
Also shown is the calculated ultimate allowable moment corresponding to a
symmetrical pull-up load factor of 4.2 3 and the static test failing moment
corresponding to a factor of 4.5 g (Ref. LR 10571).
Hence, the capability of the airplane in this particular configuration for
a symmetrical pull-up maneuver would be from 4.2 to 4.5 g at failure. If
the pull-up was combined with aileron action in roll, the center of gravity
load factor would be reduced to 80% of the above or about 3.5 g.
Structural and metallurgical examination of the wreckage resulted in the
conclusion that the initial failure had occurred in the left hand wing root
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INVESTIGATION OF ACCIDENT TO
U-2F SERIAL NO. 342
Page 2 21 March 1966
lower surface as shown in Figures 2 and 3. Metallurgical analysis of the
fracture surfaces proved that the failure was a typical static, ductile
failure with no evidence of fatigue, stress corrosion or prior damage of
any kind. Mechanical properties of the skin and striaters were equal to
or higher than specification requirements (Ref. to
dated 18 March 1966). The above is particularly interesting
wnen considering the fact that the subject airplane was over ten years old
and had approximately 3000 hours of flight time.
Referring to the static test report, LR 10571, it is noted that the failure
shown in Figures 2 and 3 is very similar to the failure which occurred at
110% of ultimate maximum wing up-bending during static test. Excerpted
from this report are Figures 4 and 5. Figure 4 shows the wing defelction
at 100% of ultimate, and Figure 5 shows the failure at 110% of ultimate
load.
From the foregoing it is concluded that the subject airplane failed s cal
in the left wing root lower surface in a rolling pull-up maneuver of atleas
3.5 to 4 g's. The Flight Manual states that the airplane has a limit capa-
bility, shifted, of approximately 2.5 g's. It is recommended that an addi-
tional statement be inserted calling attention to the fact that pull-ups
combined with roll are traditionally limited to a portion of the symmetrical
flight load factors.
FRMCH:jwb
Attchs. Figures 1 thru 5
cc: C. L. Johnson
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PREPARED BY.-1
DATE a ?-?5
CHECKED BY
LOCKHEED-CALIFORNIA COMPANY
A DIVISION OF LOCKHEED AIRCRAFT CO"ORATION
PAGE
MODE! /-???/::
REPORT NO
CHNICAL PAPER NO
PRINTED IN U.S.A. ON CLEARPRI
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FORM 5278
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FIG. 2 - LEFT HAND WING ROOT - FWD. PORTION.
LOOKING DOWN AND INBOARD ON LOWER
SURFACE INITIAL FAILURE.
FIG. 3 - LEFT HAND WING ROOT - AFT PORTION.
LOOKING DOWN AND INBOARD ON LOWER
SURFACE INITIATOR FAILURE.
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FIG. 4 - WING AT 100% MAXIMUM UP BENDING ULTIMATE
COND II B. REF. REPORT LR 10571.
FIG. 5 - WING ROOT LOWER SURFACE FAILURE AT 110%
ULTIMATE COND. II B. REF. REPORT LR 10571.
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25X1A TO*
FROM:
SUBJECT; METALLURGICAL ANALYSIS OF SECTIONS OF FAILED WING,
MODEL U-2, S/N 342
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March 18, 1966
Three sections of failed wing which were submitted for metallurgical
analysis are shown in Figures 1-3.
Specimen "A!' (Figure 1) is a portion of lower skin of left wing at in-
board end. Forward (chordwise) portion of primary failure is shown at right in
photo. Enlarged view of typical surface of fracture in lower skin is shown in
Figure 4. Photo-macrograph of a section cut normal to surface of fracture in skin
is shown in Figure 5. This fracture was ductile in nature and resulted from single
application of tensile overload. Microstructure (Figure 6) of skin material is
normal for 7075-T6 sheet. Al]. fracture surfaces in lower skin were similar in ap-
pearance. No evidence of fatigue, stress - corrosion or material defects was found
in skin fractures.
Enlarged view of fracture in lower skin stiffener is shown in Figure 7.
Photo-macrograph of a longitudinal section of stiffener taken normal to surface of
fractures is shown in Figure 8. These fractures were also ductile in nature and
resulted from single tensile overload. Microstructures shown in Figure 9 are nor-
mal for 7075-T6 extruded material. No evidence of fatigue, stress - corrosion or
material defects was found in stiffener fractures.
Tensile test coupons were machined from akin and stiffener material
in specimens A and B (Figures 1 and 2) and tested with the following results:
ftu
Spec. A - Skin 76.6 SCSI 69.9 ESI 9%
76.2 69.3 9
76.3 69.5 10
Spec. A - Stiffener 89.8 XSI 88.2 KSI 10%
89.6 79.5 10
91.4 85.7 a
Spec. B - Skin 76.4 'SI 70.0 En 10%
76.5 69.9 10
76.8 70.3 10
Spec. B - Stiffener 93.6 lea 85.7 LSI 10%
91.7 83.1 9
These data satisfactorily meet or exceed specified m
7073-T6 materiel.
tiCK:wrn
mm values for
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FIG. 1 =- LEFT WING. LOWER SKIN, FORWARD PORTION OF PRIMARY. TENSION FAILOE
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4411 / 7151/ ,1,4R 1 i196P
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7,5s
AMR
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FIG. 4 - APPEARANCE OF FRACTURE SURFACE IN LOWER $KIN AT LOCATION INDICATED BY
AMON IN FIGURE 1. APPEARANCE or AM SKIN FRACTURES WAS SIMILAR. 2-X
FIG. 5 - MACROGRAPH OF SECTION CUT NORMAL TO
0N PL A-A XII FIGURE 4. jO><
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FIG. 6 - MICROGRAM OF TN SI IN FIGURE 5, IvaailOSTRUCTURE IS NORMAL FOR
7075-T6 SHEET MATERIAL. -12.4-cj
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FIG. 7 - APPEARANCE OF FRACTURE SURFACE IN STIFFENERS AT LOCATION INDICATED BY
ARROW IN MITRE 1. APPEARANCE OF FRACTURES IN ALL LOWER SURFACE
STIFFENERS WAS SIMILAR. 2--3(
FIG. 8 - MACROGRAPH OF SECTION CUT NORMAL TO FRACTURE ON PLANE A-A IN FIGURE 7. 0 k
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