View Full Version : Bernoulli equation: perhaps not significant ?
bultaco
2nd Mar 2006, 09:10
I'm studying for the ATPL "principles of flight" exam. The Bernoulli equation is used to describe how an aircraft wing generates lift. However, I came across this very interesting website (below) that posits a physical description of lift. It suggests that the action:reaction of directing air downwards is the main contribution for lift generation and the Bernoulli lift contribution is small. It says that a Cessna 172 at 140kts displaces 5 tonnes of air downwards per second to produce lift. It's well worth reading but I don't know wheather to trust the information. Does anyone have an opinion on this ?
http://www.aa.washington.edu/faculty/eberhardt/lift.htm
Interesting stuff, but while studying for exams, I'd stick to the syllabus and basics, otherwise you could confuse yourself in the exams.
The examiner won't be trying to disprove Bernoulli !!
High Wing Drifter
2nd Mar 2006, 09:37
I started this thread in Tech Log for that very reason: http://www.pprune.org/forums/showthread.php?t=207289
The Bernoulli doesn't add up as a principle means of lift for me either. Some good comments in the thread.
EGBKFLYER
2nd Mar 2006, 11:17
My Bristol notes do mention the Newton III theory if only in passing. Neither Newton nor Bernie made an appearance in the exam though.
Oddly enough, I do teach it in my notes, but with a big warning to go back to it after you've spurted out the Bernoulli stuff in the exams. It makes complete sense, but Stick and Rudder said that too, many years ago. Bernoulli is what the examiners want, though. Go back to that site after you've passed!
Phil
hughesyd
2nd Mar 2006, 13:57
You are pretty much right. Bernoulli theorm has a minimum contribution to lift and virtually none with speeds above Mach2. I dont have my notes with me at the moment so please dont ask me to go into detail!:eek: , but my lecturer here in Spain is from one of the top proffesors in Aerodynamics and boy is he good!, he has the same theory of the limited contribution to lift.
scroggs
3rd Mar 2006, 07:06
This topic is currently being discussed (http://www.pprune.org/forums/showthread.php?t=207289&highlight=bernoulli) in Tech Log, the appropriate forum for this kind of discussion. As this thread has nothing to add to that I've linked to, I shan't move it but I shall close it. Please continue your discussion on that thread.
Scroggs