Ailerons - theory of operation, and a general discussion of lift

Peter wrote:

I never said it is “all” about deflection. I said the picture (of lift) is made up of several things, and all of them are required for it to work.

But your list was not comprehensive, if you list the facts you must be reasonably comprehensive.

IMHO if you say

airflow redirected downwards

you should add something like: simultaneously with other ‘half’ of the airflow redirected upwards.

EuroFlyer wrote:

Let me try to understand that.

It always seemed so easy to understand. When I tilt the hand slightly, the air which blows at the lower side is being compressed and deflected downwards. And of course, this creates a cushion of air on which the hand then glides upward. And, because the air which is being blocked from blowing over the upper side of the hand (which it does when the hand is level with the surface), automatically creates sort of a mini vacuum or area of lower pressure which helps the hand to move up. This, of course, works similar the other way round, when I tilt the hand down, it moves down because the cushion of air being created on the upper side.

Your explanation, is probably sufficient for a passenger. for a pilot I’d argue it’s not comprehensive enough as there doesn’t seem much room to explain a stall.

Similarly trying to explain lift in terms of downwash or deflection, might be sufficient for some but for an engineer trying to calculate the size and shape of the wing, using that approach you might design it with ‘twice’ as much wing than needed. Or since we supposed to be discussing ailerons, he or she might design them much bigger than necessary…

Peter, this is the bit of your post I found objectionable:

Because you must have a net downward deflection on the airflow to generate a net lift.

Peter is right. Another thing is that without viscosity, almost no lift would be created. The cambering of the wing is a way to play with the viscous effects to get a large amount of lift in wide range of AOA.

LeSving wrote:

Peter is right.

I don’t agree, but we will have to wait to hear what he really meant.

Ted, I did write “as a child”, didn’t I. So give me a break. I don’t want to diminish the wonderful work of brave engineers ;)

EuroFlyer wrote:

So give me a break.

My understanding as a young adult who had proudly passed his license exams, was only slightly more sophisticated and of course partially wrong. I don’t have any formal training in the topic, but it’s taken me at least twenty years to build a reasonably correct understanding that matches reality.

Both bernoulli and newton (bernoulli is just newton’s laws restated) can be used to explain lift, it’s just that you have to do it correctly. Neither of those two fellows actually described how lift works, though I read somewhere that newton said it couldn’t be done

I have given up trying to understand or explain all this in terms of simple cause and effect, my advise to those that have passed their exams and seek enlightenment is that there will always be part of the puzzle that you won’t understand, which is what cobalt’s graph sums up so nicely.

Both bernoulli and newton (bernoulli is just newton’s laws restated) can be used to explain lift

Bernoulli is not Newton. Force and energy are related, but different concepts. If you want to understand lift, then force, energy, continuity and the basics of fluid dynamics (rotation and viscous effects in particular) are all needed.

Lift itself is only a force.

LeSving wrote:

Bernoulli is not Newton

I’ve no idea what Bernoulli had in mind other than he wasn’t trying to figure out how birds fly however you can derive his formula from newtons second law, which is what I meant.

Peter wrote:

There is no way to get lift with less than all three of these things happening. All three will always happen at the same time. All are parts of the same picture.