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GlenP

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So, basically, the Angle of Attack, influenced by the Angle of Incidence of a Horizontal Stabilizer ( conventional "Stab" or a Canard ), determines what the Glider "sees", as being "upright".

What happens on a Delta planform, zero-dihedral, "flying wing" ( without any Horizontal Stabilizer) and symmetrical, vertical Rudder(s) that are above and below the Wing ? ( Think a fuselage-less Delta-Katt, without a Canard )

I am assuming that some type of "Elevator Flap" would be necessary . . .

Dave F.

View attachment 441797

View attachment 441798
Yes, you need to balance the lift of the wing longitudinally with either a down force on an aft tail or an up force on a lifting canard to keep the nose pitched up in an attitude where the wing generates lift. Flying wings with no moveable control surfaces would require a special non-symmetric airfoil to trim for flight, ie trailing edge reflex is required to cancel out the pitching moment.

The fuselage stick on that particular delta-katt, according to the plans, has the incidence of the canard relative to the wing fixed to ensure you have a trimmed and balanced condition, they are not both at the same incidence angle. If you toss is upside down it will loop nose down until it uprights itself or hits the ground.
 

Rktman

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Flying wings with no moveable control surfaces would require a special non-symmetric airfoil to trim for flight, ie trailing edge reflex is required to cancel out the pitching moment.
Is this why the old Estes Nighthawk requires that unusual airfoil? IIRC it's beveled "down" (thinner) toward the leading edge and "up" on the underside trailing edge.

nighthawk airfoil.jpg


nighthawk wing.jpg
 

GlenP

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Is this why the old Estes Nighthawk requires that unusual airfoil? IIRC it's beveled "down" (thinner) toward the leading edge and "up" on the underside trailing edge.

View attachment 441849


View attachment 441850
Yes, essentially the mean camber line, the average of the upper and lower airfoil surface has a slight change in curve at the trailing edge. Here is another example of a reflex trailing edge, from the Wikipedia page on camber,



I think some of the confusion as to how does a glider "know" which way is up, is that folks are confusing the lateral directional stability of roll and yaw with longitudinal stability for pitch. When inverted, the glider won't roll over along the axis, it is basically flying inverted at the top of a loop, it will continue to fly in the loop until it pulls out at the bottom of the loop. The wing dihedral really has nothing to do with pitch attitude control, that is more for roll & yaw. Granted there are some coupled modes where these all interact, so this is just a very simplified explanation.
 
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Ez2cDave

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Is this why the old Estes Nighthawk requires that unusual airfoil? IIRC it's beveled "down" (thinner) toward the leading edge and "up" on the underside trailing edge.

View attachment 441849
Eric,

Very interesting . . . I had forgotten all about the "special airfoil" used on the Astron Nighthawk . . . Great memory !

See steps #9 - #10 :

1607621558067.png


Dave F.
 

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Aeronerd

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Eric,

Very interesting . . . I had forgotten all about the "special airfoil" used on the Astron Nighthawk . . . Great memory !

See steps #9 - #10 :

View attachment 441856

Dave F.
Saw the catalog picture when I was 13 and fell in love with it. It was the first glider I ever built and was a defining moment for me. Been a rocket/boost glider fanatic ever since (though I took a many decades break in between).
 

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