GrantR
Well-Known Member
Is it possible to build a 3 axis airplane that is incapable of spinning?
The reason I ask is because I have a radio controlled model that will not spin or enter a decent stall.
Does airfoil thickness have anything to do with stalls and spins?
I just built a new electric r/c plane and this one will not hardly stall and will not spin at all. I can land this airplane will full up elevator with a easy sink rate and full control.
I have resized the rudder to 4 different sizes with the same results no spin.
When I attempt the spin I have full up elevator to stall and full rudder to attempt a spin. As the plane spirals down I add in a tad of opposite aileron to try and flatten the spiral and make it spin. Instead of flatting the spiral it will actually turn the plane in the direction of the aileron deflection.(opposite direction of the rudder)
I have built 2 other planes using the same motor and radio gear and building method. These two would spin very well. One had a 9X36” wing and the other a 6.5X36”. Both of these would spin fine.
The fuselage on 9X36” was 36 inches long. The fuse on the 6.5X36” was 24” inches long.
The fuse on this airplane is 30 inches long and the wing is 8X40”.
The H and V stabilzers are 20% and 10% of the wing area respectively. The rudder has been changed in size even tripled in size and still no spin.
These wing is symmetrical blue core ¼ inch foam insulation folded over a ¾ inch tall spar to make the wing. The ailerons are cut with a 45o bevel and tapped to the bottom skin so the bevel faces upward.
I am wondering if this may be causing some kind of air bubble keeping the wing from stalling all the way. I have even changed the wing incidence to a very positive setting to give the tail more down force. I moved the cg back so far the tail would drop when the power was pulled. Still no spin.
The wing thickness is 15.6% thick.
The other plane with the 9X36” inch wing was build the same. It has a 1” spar so 1.5 thick or 16% thick
It would not spin until I put it on the long fuse that was the same length as the wing.
So in conclusion:
Problem Airplane does not stall well. More or less mushes and will not spin.
While in a spin attempt opposite aileron over powers the rudder and turns the plane. Plane spirals down and does not spin.
Rudder sizes changes did not help.
My though as to what may be the problem: The aileron bevel being on the top side may be causing some type of air bubble. Or the wing is too thick.
I have attached a drawing of how the wing looks. The wing skin is ¼ thick house insulation folded over the .75 tall spar the brown line. The top and bottom skin meet at the trailing edge where they are glued together so this is ½” thick there and the Aileron (red) is tapped to the bottom wing skin and the 45o bevel faces upward. Aileron is also ¼ thick foam.
Any ideas?
Grant
The reason I ask is because I have a radio controlled model that will not spin or enter a decent stall.
Does airfoil thickness have anything to do with stalls and spins?
I just built a new electric r/c plane and this one will not hardly stall and will not spin at all. I can land this airplane will full up elevator with a easy sink rate and full control.
I have resized the rudder to 4 different sizes with the same results no spin.
When I attempt the spin I have full up elevator to stall and full rudder to attempt a spin. As the plane spirals down I add in a tad of opposite aileron to try and flatten the spiral and make it spin. Instead of flatting the spiral it will actually turn the plane in the direction of the aileron deflection.(opposite direction of the rudder)
I have built 2 other planes using the same motor and radio gear and building method. These two would spin very well. One had a 9X36” wing and the other a 6.5X36”. Both of these would spin fine.
The fuselage on 9X36” was 36 inches long. The fuse on the 6.5X36” was 24” inches long.
The fuse on this airplane is 30 inches long and the wing is 8X40”.
The H and V stabilzers are 20% and 10% of the wing area respectively. The rudder has been changed in size even tripled in size and still no spin.
These wing is symmetrical blue core ¼ inch foam insulation folded over a ¾ inch tall spar to make the wing. The ailerons are cut with a 45o bevel and tapped to the bottom skin so the bevel faces upward.
I am wondering if this may be causing some kind of air bubble keeping the wing from stalling all the way. I have even changed the wing incidence to a very positive setting to give the tail more down force. I moved the cg back so far the tail would drop when the power was pulled. Still no spin.
The wing thickness is 15.6% thick.
The other plane with the 9X36” inch wing was build the same. It has a 1” spar so 1.5 thick or 16% thick
It would not spin until I put it on the long fuse that was the same length as the wing.
So in conclusion:
Problem Airplane does not stall well. More or less mushes and will not spin.
While in a spin attempt opposite aileron over powers the rudder and turns the plane. Plane spirals down and does not spin.
Rudder sizes changes did not help.
My though as to what may be the problem: The aileron bevel being on the top side may be causing some type of air bubble. Or the wing is too thick.
I have attached a drawing of how the wing looks. The wing skin is ¼ thick house insulation folded over the .75 tall spar the brown line. The top and bottom skin meet at the trailing edge where they are glued together so this is ½” thick there and the Aileron (red) is tapped to the bottom wing skin and the 45o bevel faces upward. Aileron is also ¼ thick foam.
Any ideas?
Grant
