Historical Comments

“REDUCING FLIGHT TEST TIME FOR AIRCRAFT PERFORMANCE EVALUATIONS THROUGH THE USE OF MODELING AND SIMULATION,”

by Frank Brown

E-MAIL TO THE EDITORS EDITORS’ NOTE: The following e-mail ‘thread’ was generated as a result of last month’s technical paper, If you missed it, you need to sign up for electronic distribution of Flight Test News. Sign up today by emailing your request to sfte@hughes.net Darcy and Lee,

The technical paper that Frank wrote on performance modeling & simulation has an error in it that I feel needs to be corrected. He states that I developed the AFFTC Digital Performance Simulation (DPS) program for use on the C-5A test program. That is not correct. The DPS was developed much later than the period of C-5A testing.

However, his main point of stating that performance M&S was used on the C-5A is absolutely correct. Performance M&S used at the AFFTC was really pioneered by Lockheed concurrently and independently on the SR-71 and the C-5A.

Dick Abrams (SFTE Kelly Johnson Award Winner and Fellow) did the work on the SR-71 for the AFFTC and I worked on the C-5A program under the tutelage of Clay Houston (SFTE Fellow) from the Lockheed Georgia Company. Ron Hart worked for Lockheed at that time and worked on the propulsion elements of the model. The test program was an actual implementation of the current DoD STEP guidance, it simply was accomplished about 30 years before the guidance was issued. The performance test program was designed and flown specifically to validate the model and the test report both documented the fidelity of the model as well as the performance of the airplane as calculated by the model. The C-5A contract included performance guarantees. The flight test validated model was used to calculate the aircraft performance for use in determining guarantee compliance.

I was not involved in the SR-71 program but from my discussions with Dick Abrams, they did about the same thing that we did on the C-5A.

I might add that this pioneering M&S work was not in accordance with the “standardization” methodology being used by the AFFTC at the time and was resisted by AFFTC management! As a result, we used the model to develop a standardization technique which consisted of calculating performance at test conditions and at standard conditions.

We applied the difference in these two calculated values to the measured test performance in order to develop the “standardized” level. This technique was later used by the AFFTC (Mike Leone, Larry Gordon, Charlie Van Norman & Jim Papa) to develop the original UFTAS program used on the AX Competition (YA-9A vs YA-10A).

Unfortunately UFTAS and “standardization” has lasted for nearly 30 years and M&S has only recently been rediscovered. It’s too bad the AFFTC establishment did not recognize the potential of M&S 30 years ago and the remarkable work pioneered by the Lockheed/AFFTC teams on both the SR-71 and the C-5A!

I simply wanted to correct the documentation of some ancient history.

Charlie [Van Norman, “Kelley” Johnson Award Winner, SFTE Fellow]

Charlie, you’re right on. What I’m especially proud of on the C-5 was we developed the model jointly with Lockheed; it was used not only for guarantee compliance, but for building the Flight Manual as well. We, the Air Force, knew and approved the level of performance in the manual. Also the most difficult and time consuming part of the “model’ was not the up and away part but the runway performance. We completely modeled the C-5 characteristics very thoroughly in this critical regime. I don’t think a complete a job had ever been done before. Unfortunately, I have not heard of it done since. You, Clay, Ron, and Pete Smith did a great job. Our only minor failing was preservation of the documentation of the methods and results. V/R, Ken Martin

Ken, I think the fact that the report was published by Lockheed contributed to the lack of knowledge of the work. There were limited copies available (I don’t even have one) and it was thus not used as an AFFTC reference for subsequent flight test programs. Charlie

Charlie, I whole-heartedly agree with your comments. To the best of my knowledge, DPS at the AFFTC was “invented” by Wayne Olson. I am not sure what time frame, as I pitched all my reference material at retirement.

As I remember it, it was in the days of punched cards, (I know I am dating myself). I can remember coming in to work early and running DPS in the back room of Bldg. 1400 before everyone came to work and I got kicked off the card reader. I believe this was on the C-141B stretch program I took the liberty of forwarding your e-mail to Wayne, so expect to hear from him. Ron Hart

Ken, see my comments in e-mail to Charlie WRT Newsletter item. With regards to C-5 documentation, I had saved the C-5A joint reports on Performance and on Propulsion, throughout all these years, probably because my name and blood was on them. Anyway, when I retired I took them both to the tech library and gave them to Pat Henrich to put in the system.

Needless to say, the library was not happy, the reports weighed about 20 pounds each, and, as I am sure you will recall, and numerous foldout plots. If someone ever gets to the Tech Library I would be interested to know if the reports are still there. The reports came in handy over the years, and I wished I had saved the FQ reports too. One interesting incident occurred not too long ago when the YF-22 or F-22 folks said they were going to put out a joint AF-contractor report-the first one in AF history! Ron Hart

EDITORS’ NOTE: Ron, we checked – the report, “C-5A Category 1 & 2 Performance Test Program,” is still there in the Bldg. 1400 Technical Library! (3 large volumes, #81472)