1、Lessons Learned Entry: 1266Lesson Info:a71 Lesson Number: 1266a71 Lesson Date: 2002-07-01a71 Submitting Organization: LARCa71 Submitted by: Grant WatsonSubject: When Maximum Load Limits are Exceeded, Testing Should be Terminated Until it is Proven Safe to Continue Description of Driving Event: While
2、 testing at Mach 0.8 in the 16-ft Transonic Tunnel, a full-scale F-15 inlet model separated from the sting. The model traveled downstream and impacted the catch screen and turning vanes. The impact resulted in total loss of the model and damage to the screen. Some debris got through the screen and d
3、amaged the wind tunnel blades. The sting was also damaged. An investigation team concluded that the aerodynamic loads on the model resulted in sting loads that exceeded the ultimate strength of the sting. Possible reasons the large loads occurred are: operating at a Mach Number not in the original t
4、est envelope, F-15 cowl traveled past intended angle, sting deflection, and dynamic loads.THERE ARE 6 LESSONS IN LLIS FOR THIS DRIVING EVENT.Lesson(s) Learned: At a test condition just prior to the mishap (M=0.8, cowl fixed at 9*), a red light indicated that the sting roll moment, which equaled 28,1
5、77 in-lbs at the time, exceeded the maximum limit of 26,000 in-lbs. In response to this, the test team decided to limit the maximum cowl angle to 8* so that the roll limit would not be exceeded again. The test data shows that at M=0.8, cowl fixed at 8*, the sting roll moment was 26,487 in-lbs, which
6、 slightly exceeds the allowable limit (26,000 in-lbs). No action was taken to this condition. The lesson learned was that the test teams response to the limit was not congruent with the nature of the test conditions. At M=0.8, the model was in a region that had not been analyzed. The response to exc
7、eeding a load limit should have been to stop testing and analyze the issue in detail. Also, the test team did not monitor a condition that they believed to be safe (i.e., cowl at 8*) close enough to Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-rea
8、lize that it still exceeded the maximum limit. Recommendation(s): Establish a policy of test termination at test conditions where maximum loads limits are exceeded until it is proven safe to continue. If it cannot be shown to be safe, testing should not continue. Evidence of Recurrence Control Effec
9、tiveness: The branch has implanted new policy guidelines, which define specifically the operator and test engineer response to these limits. This is a branch policy for standardized response to balance dynamic display unit (BDDU) overload conditions. It provides the distinction between cautionary an
10、d limit “stop“ conditions. If conditions, based on additional analysis by the force measurement engineer cannot be shown to be safe, then test conditions are modified to stay within the safe allowable load boundaries and established limits.Documents Related to Lesson: N/AMission Directorate(s): a71
11、Exploration Systemsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Test FacilityAdditional Info: Approval Info: a71 Approval Date: 2002-07-22a71 Approval Name: Leslie J. Johnsona71 Approval Organization: LARCa71 Approval Phone Number: 757-864-9409Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
