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 Flight Testing A forum for test pilots, flight test engineers, observers, telemetry and instrumentation engineers and anybody else involved in the demanding and complex business of testing aeroplanes, helicopters and equipment.

 23rd Mar 2010, 23:55 #1 (permalink) Join Date: Jul 2008 Location: Sydney, Australia Posts: 37 CL help I am trying to find the Coefficient of Lift for a Dash 8 Q400 for my A/C engineering studies at Uni. I am pretty new to the world of aircraft engineering so need some clarification in what I am doing exactly. If Cl = W/(1/2PV^2S) and I have a mid cruise weight, cruise altitude and cruise velocity should I sub into the V a value of true or indicated airspeed in m/s? How do I find my true airspeed at altitude? Any help is much appreciated, Cheers
 24th Mar 2010, 09:48 #2 (permalink) Join Date: Jun 2002 Location: east ESSEX Posts: 2,046 Try `www.luizmonteiro.com`,and use imperial units.,IE feet/ft/sec etc
 24th Mar 2010, 11:30 #3 (permalink) Join Date: Feb 2000 Location: UK Posts: 10,333 You'll get the same answer if you use CAS and standard sea-level air density (1.225kg/m^3), or TAS and actual air density at altitude, and both will be correct. If you are given IAS instead of CAS, there should be a small difference but don't worry about it for this level of academic work, just assume that IAS=CAS (just don't ever do that if you start working in a flight test department.) You should also get the same answer whether you use SI or Imperial units, so long as you use the proper engineering form of the units and don't go near unwanted bastard units such as inches, centimetres or (worst of all) kilogrammes-weight. G
 24th Mar 2010, 20:09 #4 (permalink) Join Date: Jul 2008 Location: Sydney, Australia Posts: 37 Thanks G, much appreciated
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