1、Lessons Learned Entry: 1263Lesson Info:a71 Lesson Number: 1263a71 Lesson Date: 2002-07-01a71 Submitting Organization: LARCa71 Submitted by: Grant WatsonSubject: Sting Deflections Contributed to Model Failure Description of Driving Event: While testing at Mach 0.8 in the 16-ft Transonic Tunnel, a ful
2、l-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 damaged the wind tunnel blades. The sting was also damaged
3、. 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 test envelope, F-15 cowl traveled past intended angle, sti
4、ng deflection, and dynamic loads.THERE ARE 6 LESSONS IN LLIS FOR THIS DRIVING EVENT.Lesson(s) Learned: As outlined below, sting deflection can cause the angle of attack to change. This can result in the aerodynamic forces increasing in an unanticipated manner. The planned test conditions at the time
5、 of the mishap (M = 0.8, move the cowl down to an angle of 8*) had not been properly reviewed and assessed. Data recorded at a test condition just prior to the mishap (M=0.8, cowl fixed at 8*) indicated that these conditions resulted in a sting roll moment (26,487 in-lbs) above the allowable limit (
6、26,000 in-lbs). Also, at M = 0.8, the cowl moved down quicker than expected. This meant the operator response time to activate the cowls brake was critical. As the cowl moved down, the operator did not activate the brake quick enough to stop the cowl at 8*; consequently, it traveled to its maximum a
7、ngle of 13*. Note, conditions of M = 0.8, 13* had not been analyzed prior to testing. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-With the cowl at 13*, M = 0.8, the aerodynamic loads resulted in sting loads that exceeded the stings limits and cau
8、sed the sting to deflect downward. This deflection decreased the angle of attack by a few degrees (i.e., it became more negative), which increased the aerodynamic forces even more. In other words, excessive aerodynamic forces caused sting deflection that resulted in increasing the already excessive
9、aerodynamic forces. At this point, the aerodynamic forces caused sting loads that far exceeded the sting limits, resulting in ultimate failure of the sting. Recommendation(s): Static aerodynamic analyses should take into account the sting deflecting under load. Evidence of Recurrence Control Effecti
10、veness: To ensure that sting deflection under load conditions remain with safe tolerances, the structural analyst double checks the sting loading against expected test condition aerodynamic loads. Based on these data, the maximum load limits are established prior to the test runs.Documents Related t
11、o Lesson: N/AMission Directorate(s): a71 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-,-,-
