The ‘magic number’ of Flight Test


Do you believe in “magic numbers”? Are magic and arithmetics two completely different and by definition uncombined concepts or maybe not? Either ways, there are numbers that in certain disciplines are encountered more often than others. So what would be the “magic number” of flight test?

I finally think I have an answer to that question, and that number is seven (7)! It is the number that answers all of the following questions:

  1. How many test points are required for PEC certification of a single configuration?
  2. How many speed points are required to define a level performance curve?
  3. How many stalls should be performed per configuration to determine stall speed?
  4. How many TO/LD per config are required to define TO/LD distances?
  5. What is the theoretically ideal number of pilots for HQ tasks?
  6. How many speeds points are required for the determination of a climb performance curve?
  7. How many different altitude level accels are required for the generation of a SEP plot (Altitude vs. M)?
  8. What is the average number of test points per test flight? (Ref. Lockheed Martin 2013)
  9. What is the number of weapon shots required to determine CEP?
  10. Which is the minimum HQR that you should be grounding an airplane?

Bonus: Which Section of the SFTE Corporate Bylaws establishes ‘Flight Test News’?

This common encounter of number 7 in flight test, is not something unexpected. 7 can be described as the the minimum/convenient number that can adequately capture nonlinearities across a region, as well as indicate deviations from a normal distribution in statistics, and that is what flight test is looking for!

Bottom line: If you are asked to recommend a number in flight test and you are unsure, just say “seven” … it usually works :-)

Disclaimer: This post includes a mix of technical accuracy, approximation and humor. It is not intended as technical advice as each test is unique and should be treated as such.

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