Why Do Airplane Wings Have a Natural Forward Pitching Moment?

[fog37]

Thanks CWatters. That is awesome and impressive. I am trying to make a RC model high-lifting airplane (that can carry a lot of weight, given a certain take off speed, etc.). I see how I can determine the minimum take off speed given a certain wing areas, and motor power. I wonder how quickly the plane will reach that speed. That will determine the minimum takeoff distance (runway). Do you have any insight in that?

Just to make sure, you mention that the CG of the entire airplane should be placed at distance, from the leading edge of the wing, that is 25%-33% the mean chord line (starting from the trailing edge of the wing 25-33$ of the chord backward).

Thanks and happy Easter!

 

[anorlunda]

I flew fast electric powered competition gliders some years ago

Wow, that sounds like fun. But you don't say if the gliders were remote control models, or full size with you on board as pilot.

 

[CWatters]

They were F5B class RC models. I also flew full size gliders for awhile but not long enough to go cross country, all local flying.

There are quite a few videos of F5B models on YouTube. An example...

 

[CWatters]

Thanks CWatters. That is awesome and impressive. I am trying to make a RC model high-lifting airplane (that can carry a lot of weight, given a certain take off speed, etc.). I see how I can determine the minimum take off speed given a certain wing areas, and motor power. I wonder how quickly the plane will reach that speed. That will determine the minimum takeoff distance (runway). Do you have any insight in that?

For that sort of aircraft you want a thick wing section with quite a bit of camber and possibly flaps. It's tricky working out how fast it will accelerate to that speed. More power the better. A fine pitch prop will also accelerate faster but don't go too fine or the top speed will be too slow.

Just to make sure, you mention that the CG of the entire airplane should be placed at distance, from the leading edge of the wing, that is 25%-33% the mean chord line (starting from the trailing edge of the wing 25-33$ of the chord backward).

Thanks and happy Easter!

Yes 25-33% of the chord back from the leading edge.

 

[FactChecker]

I guess the aerodynamic moment is due to the lift force, always applied at the CP.

This is wrong and I don't know if it is clearly corrected later. There is a torque on the wing that has nothing to do with the location of the wing versus the CP. In creating lift, airflow is diverted down. That produces a twisting torque on the wing which is different from the leverage arm that the lift is applied to. Both must be accounted for.