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Compare total drag of wall to wall wing vs wing(open tips) in wind tunnel,AT SAME AoA.

My first intuition is that wall to wall wing has higher pressure drag at outward parts of wing,because side-walls "act" as big endplates,so that makes difference.Reslut is higher total drag.

But

enter image description herewall to wall wing

If aerodynamic force1 =70N and angle A = 75° Drag1 =cos75 x 70N=18.1N

wing

Aerodynamic force2 has lower magnitude lets say 60N and reduced effective AoA is 1° ,then angle B=74° Drag2= cos 74 x 60N =16.5N

(even if I choose 65N(only 7% reduction in aerodynamic force)drag will be smaller at wing ,cos74 x65N=17.9N)

I think Peter Kampf has best opinion,this can not be prove with data because we dont know how much is magnitude of aerodynamic force at wing is reduced compare to wall to wall wing..

Wing has tilted aerodynamic force back but in same time has lower magnitude ,so it cant be prove is drag higher or lower,it can go in both directions. Vector tilt back at wing is usualy very small,maybe 1°,so my general oppinion is that vector tilt back has less contribution than reduction of aerodynamic force magnitude at wing...

What is your opinion?

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    $\begingroup$ This wall-to-wall (or theoretical infinite span) wing is a recurring theme here. I would encourage you to do a little research before asking what seems to me a repetitive question... $\endgroup$ Sep 8, 2020 at 20:25
  • $\begingroup$ @MichaelHall I think this topic must be reviewed and make final common accepted answer.From posts and comments I see that exist difference in opinions between members who are aerodynamics experts.For example PeterKampf think that this cant be prove with data,others think wing has higher drag etc...I hope we can clear things $\endgroup$
    – user52248
    Sep 8, 2020 at 20:35
  • $\begingroup$ But what is new and different about your question? $\endgroup$ Sep 8, 2020 at 23:53
  • $\begingroup$ @MichaelHall, there are some questions that discuss wall-to-wall/infinite span and they are not actually consistent with each other at the moment. It definitely does deserve some focused clarification. $\endgroup$
    – Jan Hudec
    Sep 9, 2020 at 19:49

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I agree with your conclusion that the wall-to-wall wing has more drag than a free-flying wing at the same angle of attack.

But what is the point of this comparison?

People build wings to create lift. These wings might be on airplanes, but also on helicopters, propellers, the fin keels of boats or the blades in turbo machinery. Their purpose is in all cases to create lift. Not drag. Drag is an accepted price for that lift creation, but not their purpose.

So it is pointless to ask for a drag comparison when disregarding lift at the same time. This is akin to asking if a wing that is not moving creates no drag.

You don't even let us know the wingspan of those hypothetical wings. Are they in the same windtunnel, so the free-flight one has less aspect ratio, span and surface? Or is it the same wing, with the windtunnel removed?

So please stop repeating the same pointless and insufficiently specified question over and over. You will not get useable insights because the answers can not be helpful.

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  • $\begingroup$ See? I was right! $\endgroup$ Sep 19, 2020 at 9:10
  • $\begingroup$ For sure I will continue to warn if I notice wrong answers.This is useful for others members.Indeed it is everyone's duty. $\endgroup$
    – user52248
    Sep 19, 2020 at 9:15
  • $\begingroup$ @Сократ say what? $\endgroup$ Sep 19, 2020 at 9:21
  • $\begingroup$ @PeterKampf But what is the point of this comparison? Example:Goal at rear wing at race car is to produce as much downforce(lift) and with the least drag.So aero-engineer must know if he add end plates to given wing ,downforce will increase but DRAG will also INCREASE ,compare to open tips-wing at SAME AoA. If he doesnt know such basic thing,for sure he will get fired. I know this is not 100% same test as in wind tunnel ,because end plates cause additional own drag etc,but final conclusion is same.. $\endgroup$
    – user52248
    Sep 19, 2020 at 14:14
  • $\begingroup$ @Сократ Goal at rear wing at race car is to produce as much downforce(lift) and that's why we want endplates. cause though they increase drag, they increase lift even more. So your car can do with a smaller rear wing, producing LESS drag! I thought you had this figured out. $\endgroup$ Sep 19, 2020 at 15:38
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You're not looking at the problem from the right point of view... Your conclusion is the same as saying that a Ferrari will use less fuel while going down a hill than a Toyota prius going up.

In real life you need to keep the lift constant and equal to the gravitational force to keep the airplane airborne. In order to have an intuitive answer your experiment should thus keep the lift constant. And in that condition you'll see that drag increase for open tips wing.

The physics behind that is the following. The wall bounded wing as well as the infinity wing have the same working principle, the flow around it is bidimentional, the free stream flow is perpendicular to the airfoil and thus the velocity in the lift equation is equal to the free stream velocity. In the open tips or finite length wing case the flow becomes three dimensional. As there are no boundary at the tip, the high pressure air from the lower side can go around the corner to the upper side of the wing. This creates a lateral velocity going outwards (to the tip) on the lower (pressure) side and inwards (to the fuselage) on the upper (succion) side. This effect can be seen in the vortex wake left behind. This has two effect. It gives lateral momentum to the flow which is energy lost and thus increase drag but also reduce the relative velocity seen by the airfoil and thus decrease lift. To maintain lift constant you'll need to increase the AOA and therefore drag will increase furter.

In conclusion and open tip / finite length wing is less efficient as the lift to drag ratio also known as glide ratio is smaller. In order to keep lift constant you'll require to produce more drag.

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  • $\begingroup$ In real life you need to keep the lift constant and equal to the gravitational force to keep the airplane airborne˛ Who tell you that I am talking about wing at aircraft?Wing is using in lots of applications,F1,foil,fin,sail....So lift=gravity force doesnt have to be case. You must start thinking "out of book",aerodynamics is not just aircrafts. $\endgroup$
    – user52248
    Sep 18, 2020 at 19:22
  • $\begingroup$ Well my point is that your conclusion "so it cant be prove is drag higher or lower,it can go in both directions." is wrong and I tried to give you an example that is intuitive. Of course wings are used somewhere else but the principle is the same. What you require from the wing is lift, what you get in return is drag. For your f1 it's related to down force, a foil to the sustentation force of the ship (very close to aircraft wing) and for a sail it's the propulsive force of the ship. In all configurations the answer is the same I tried to give one particular example that I find intuitive. $\endgroup$
    – MaximEck
    Sep 18, 2020 at 19:29
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Your conclusion that the endplated wing has more drag for a given AoA is correct. This really is the answer. You can stop reading here. But:

In real life, when using the foil in a wing, you cannot keep the same AoA. While drag reduces for the same AoA, lift reduces even more, as seen clearly from your diagram. And that is unacceptable for a real airplane. You will therefore want a higher angle of attack to get enough lift. And that higher angle of attack will create more drag.

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  • $\begingroup$ JanHudec and YZYL tell that wall to wall wing has less drag...They dont agree with my conclusion aviation.stackexchange.com/questions/77573/… $\endgroup$
    – user52248
    Sep 18, 2020 at 16:18
  • $\begingroup$ unless it is also very close to the bottom (in ground effect), it should have non-zero induced drag. Jan Hudec. $\endgroup$ Sep 18, 2020 at 17:16
  • $\begingroup$ That looks like an agreement. $\endgroup$ Sep 18, 2020 at 17:17
  • $\begingroup$ In fact, it seems to me that JZYL's answer is not relevant to this question. $\endgroup$ Sep 18, 2020 at 17:28

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