Hi

I'm stuck doing this project on aspect ratio and I fonud out using my wind tunnel data that wings with higher aspect ratio stall at lower angles of attack and more abruptly, can anyone tell me why this happens, because I have till tomororw to hand this in and I can't find anything on the net about it

Cheers in advance

It looks like you are going to have to say the dog ate your homework!!

Not to be mean or anything but don't you think asking the forum to do your homework is a bit like cheating, maybe, kinda. I guess it's because when I walked backwards in the snow at Purdue to go to class we didn't have the internet so I hate for anyone else to be able to take advantage of it.

Best of luck, do the search on aspect ratio, wing stall characteristics, flow separation, etc. I have yet to find a topic that I couldn't find some data on the subject. Look for the old NACA reports. There is a site

http://www.aeromech.usyd.edu.au/aero/

that has your answers but you have to pull it out.

Good luck,

Scrooge Ben

Give us some more info and we'll see if we can't point you a bit closer to the mark. And are we talking higher aspect ratio with constant chord and thus increasing wing area or constant area and thus reduced chord?

Bruce "feeling generous but not gonna spoon feed ya because I don't really know either" Matthews

lol, not asking you to do my homework, it's just small, (excuse the pun), aspect of the project. I just noticed on my Cl vs AOA graph the higher aspect ratio wings stall at lower angles of attack and quite adbrutly too. I searched for about 2 hours on why, but could only find out that they do. Lower aspect ratio wings produde more lift past the angle of stall than higher aspect ratio's too.
This explains why lower aspect ratio wings are more manourverable because they still produce quite a bit of lift past the stall, so for fighters such as the Eurofighter and F22 they can carry on in their turn, even though the wing is stalled ( a high speed stall) this forms the clouds over the top of wing. But as the drop in lift is not as big as with higher aspect ratioi wings they still carry on in the turn, where as if it was a higher aspect ratio they would fall out of the turn earlier. However the drawback is hell of alot of drag is created which is why power is so important in fighters, enabling them to keep the speed up in the turn for longer.
I just wanted a little explanation as to why a higher aspect ratio wing stalls faster, but I still haven't found no good reason, (not even on the website you gave me Ben)

Anyway I can miss this bbut out, explained enough about it I think now

Interesting, the data on this site toward the bottom of the page, I might have misread the listing though, is given for several different aspect ratios

http://www.aeromech.usyd.edu.au/aero/

The data doesn't show much difference in stall alpha. See if it correlates with what you have.

I'll give you a hint, it is an effect of tip vortices.

I'll attach the figure from Martin Simmon's Book, he is very good at presenting accurate data.

I can't find anything on the net about it, but I had a "eureka" moment while I was bored and was watching the landing of concorde that I recorded about a year ago. Hope this is right ben.

Concorde lands at a very high angle of attack compared to most planes, and the lift is generated by huge vortices which form over the top of the wing, vortices like tornados have very low pressure in them, so if a low aspect ratio wing's flow starts to seperate, the wing tip vortices get bigger and cover a greater percentage of the wing. This vorticy then allows the wing to fly for that couple of degrees more, horay!!!!!!

Probably to late for your project, but you're on the right track. Remember that on an infinite wing the stall angle is a function of the airfoil shape only and is independent of aspect ratio. Of course, you don't really have an AR since the wing's infinite, but you get the idea. So it must be something to do with the interaction of the wing tips.

Think about this, too. Under some circumstances it's good to "trip" the boundary layer thus creating turbulent flow. The turbulent flow while creating more drag will "stay" with the wing longer. So you can think of the wing tip vortices as turbulent flow (because it is) and it will stick to the wing longer than a laminar flow before separating.

The funny thing is I asked my lectuere after I handed my project in, and they didn't know, sure one of them will though

You got it foofydoo (foofydoo??) In the figure you see the stretching out trend of the low aspect ratio wing.