Determining Aircraft Performance
 

I've been following this forum for a while, and decided it was time to finally ask a question.

My basic understanding of aircraft testing is that much of the performance data found in the AFM is determined by means of flight test, such as stall speeds for example. Specifically, I'm talking about a light aircraft, such as that used in General Aviation. I was wondering if it is possible to get this performance data by means of a test in a wind tunnel using a scale model.

The reason I ask is that I am a currently a BSc Student in Mechanical Engineering, looking for an undergraduate thesis idea. I am also a pilot, more specifically a Flight Instructor in Canada with around 1000hrs or so, so I at least understand the basic concepts of performance figures... My career ambition is to get into flight testing, so I've been looking for thesis ideas that might teach me a thing or two in that area. Alternatively, if anyoone has any other ideas that makes for a good thesis, I'm completely open to it. I'm probably the least creative person I know.

Thanks in advance for the help.

RSC, firstly welcome to Pprune and the FT forum.

Performance figures are not derived primarily from WT data, but what is not uncommon is to generate Cd/Cl/Cm curves from WT data and to then make a first stab at aircraft performance data from that. This is then validated and refined in FT. The same is true to a greater extend of aircraft handling data.

Now for an undergraduate thesis you need two elements for a good mark - theoretical and practical so here's one idea for you.

- Take a light aircraft with well documented performance data (plenty of those), make a model of it (I'd buy an airfix kit and modify it). Create some theory which would derive basic aircraft performance (don't shoot yourself in the foot trying to be too ambitious, just pick one thing - TORR for example). Then create wind tunnel tests to generate the data, and see how well the theory+WT match up with manufacturer's scheduled data. That, plus a good argument as to any inconsistencies could get you a good mark at BEng level.

- If you are still flying, do something similar with (say) glide performance at different speeds and flap settings, then do the same in an aeroplane. Generate the theory to cross-validate them.

There are a few other ideas, some of which might be more mechanical here, which might be worth a look at.

G

Further to Genghis' reply -
the reason for not using WT data is that the thing the pilot must refer to for all flying, the airspeed indicator, is not going to be indicating completely accurately - wind tunnel data would use absolutely accurate airspeed.
So, even if the wind tunnel data were completely valid, it would be necessary to find a way to translate that to the real aircraft, with the real pitot static system, and no-one has found a way to do that.

Performance Data from WT
 

Deriving performance data from WT data is possible, but it is unreliable. Big Aircraft manufacturers (A... and B...) do it (for projects of a new aircraft, for example), but still they apply quite big factors just to be on the safe side. To do the same with a GA aircraft and achieve high precision will probably cost more than building the whole thing, then flying it....

I agree with Genghis' ideas, but don't use TORR. It is awfully difficult to predict, with all those dynamics, ground effect and stuff going on all at the same time.