1、Lessons Learned Entry: 1261Lesson Info:a71 Lesson Number: 1261a71 Lesson Date: 2002-01-01a71 Submitting Organization: LARCa71 Submitted by: Grant WatsonSubject: Worst-case Conditions Involving Wind Tunnel Test Conditions and Model Configurations Not Properly Identified, Reviewed and Assessed Descrip
2、tion of Driving Event: While 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
3、got through the screen and damaged 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
4、Number not in the original test 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: As outlined below, failure to properly identify, review and assess worst-case test conditions can result in a
5、chain of events that result in a major mishap. The planned test conditions at the time 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
6、conditions resulted in a sting roll moment 26,487 in-lbs, which was above the allowable limit of 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 ac
7、tivate the brake quick enough to stop the cowl at 8*; consequently, it traveled to its maximum angle 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*
8、, M = 0.8, the aerodynamic loads resulted in sting loads that exceeded the stings limits and caused 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, excessi
9、ve aerodynamic forces caused sting deflection that resulted in increasing the already excessive 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): All worst-case test conditio
10、ns need to be identified, reviewed and assessed using state-of-the-art codes or other recognized and accepted methods prior to performing wind-tunnel tests. Evidence of Recurrence Control Effectiveness: Pretest and pre-run meetings are now in place along with a check list that properly identifies an
11、d documents worst case test conditions and limits. Worst-case test conditions and failure mode analysis are now included as part of a new branch position “AST Facility Systems Safety Engineer“. This function specifically looks at each wind tunnel test as a system, to identify all possible failure mo
12、des or undesired events. Based on identified failure scenarios, additional countermeasures or state-of-the-art analysis is performed prior to the Facility Safety Head approving test runs to begin.Documents Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Aeronautics ResearchA
13、dditional Key Phrase(s): a71 Facilitiesa71 Test & Verificationa71 Test FacilityAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2002-06-22a71 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-,-,-
