sellener

I would like to understand induced drag a bit better.

I am fully capable of spitting out phrases I have heard in handbooks, and circulers. For instance.... for a checkride oral I might say induced drag is the penalty an airfoil pays anytime its generating lift.

Or

Wing tip vortices are the source of induced drag

Or

Vortices create downwash behind the trailing edge which effectivly increaseing the angle of the relative wind which also directs the lift vector (which acts perpindiculer to the relative wind) back.

Or

Something about upwash in front of the wing which also changes the relative wind a bit bending the lift vector back

bottom line, I dont truly understand what all causes induced drag....

my best understanding to date is.....

air travels high to low from under the wing towards the wingtip and then combines with the air their to impart a rotation to the air (vortice) the spiraling down motion over the trailing edge makes the effective relative wind angle a bit more and thus the drag vector tilts back to stay perpindiculer to the relative wind.

But I think there's a bit more to it than that if thats even an accurate statement.

250 or point 65

have you used the search function? I believe that ryan1234 and one or two others had a pretty extensive discussion about this months ago.

ryan1234

You pretty much have most parts of it. If you really want to break it down technically there are two parts of induced drag: Inviscid and viscous.

...But... to start simple....most cases lift is 90 degrees from the relative wind. The airfoil's force of lift may not be generated 90 degrees from the relative wind, it may be slightly aft angle - inclined (like at 95 degrees say). The difference of the 90 degree lift and the actual airfoil force created is an induced angle of attack - it is induced by lift caused by circulation flow (upwash, vortices,etc).....
It is a lift component in the drag direction, thus called induced drag

I'm not sure if the examiner wants you to explain circulation flow - but if he does.. you could probably be pretty simplistic about it. Key factors are tip vortex strength depends on angle of attack and wing design and are a result of lateral flow. It is basically a convergence of higher pressure from the bottom moving laterally and upwards to the lower pressure on the top which is moving downward and lateral at the wing tips. The energy contained in that flow determines the induced angle of attack. The greater the pressure differential, the greater the energy in the vortex. Aircraft with higher aspect wings generally have lower induced drag. High altitudes require high angle of attacks so generally the induced AoA (and induced drag) is high... that's why the U-2 has a high-aspect wing.

sellener

i did some searching didnt seem to find it, could you post a link if you know the thread?

thanks

slipped

I always thought of it like this:
Think of a blade going through water. if the blade is feathered eg slicing sharp through the water there is little drag, a wing is very similar.
A wing slicing through the air at a low AOA creates little drag AND little lift.
When you increase the AOA to get more lift the knife/wing is harder to move through the water= Induced drag

Stringer

I'm in the process of studying for my JAA ATPL exams. They have a module entitled Priciples of Flight, the book for this has great explanations about most areas of aerodynamics in good detail but not too overwhelming. PM me if you are interested in details of the book, I might even have a copy you can have...

Cubdriver

I started a thread on this a year or two ago here- NPR's Explanation of Lift- probably one of many on APC if you look around. Some other threads that come to mind recently are listed below.

Ground effect- Cessna Versus Piper Trainers
Ground effect- Lift in Ground Effect (II)
Lift on takeoff- When Lift Starts and Stops

I would talk about it some more myself, but I am very busy these days, and aerodynamics is my favorite subject. Don't feel bad if you have to struggle with it to understand. Top scholars continued to struggle with details of aerodynamics theory well into the 20th Century. They studied and researched the subject their whole lives- why should it be surprising how hard it is for us mere mortals.

sellener

That is how I thought of it too. Easy to understand/visualize that way, however none of the literature seem to support it. They're always talking about vortices and downwash and bending the lift vector blah blah.

I agree that that concept is simple to grasp and understand. Your hand out of the window of a car.... hand flat no lift not much drag....tilt hand arm goes up and back.....lots of lift and lots of drag....muscle (thrust)needed to keep arm from moving back, but arm otherwise floats.

This example demonstrates something about aerodynamics, but I dont think it really is induced drag (wish it was, then I could say i understand induced drag)

Now, I would like to understand what we just described if it is not induced drag??

ryan1234

If you don't have a copy already, I suggest... as a few others on this forums have... Aerodynamics for Naval Aviators - It is a great book for breaking down things in non-engineering terms, really easy to understand.

Da Magic

It's PFM and thats all you need to know.... haha PM me if u need to know what that is.