Do you have any questions in designing an airplane?

[baronbernie]

Many of us have a hunger to fly a plane of our own design, and some like to modify a plane to fly a different way.

I have one design question, how is the dihedral for a T-28 Trojan determined. The wings are so much different (dihedral) than most planes do?

 

[rockyboy]

Dihedral has a stabilizing effect on a plane - it helps it roll back to level flight.

When a plane with no dihedral rolls to the side, both wings lose lift in the same amount - and if it goes too far it will stall and just fall out of the sky sideways. Ask me how I know

Adding dihedral creates an effect where the plane rolls to the right, the right wing actually becomes more level while the left wing is at a higher angle. The level wing creates more lift than the wing at the high angle, which pushes the right side of the plane back up till the wings both have the same angle when the plane is level. Pretty neat, eh?

So when you want to design a plane think about how you want it to fly. If you want it to be very acrobatic and able to do super fast rolls and turns, use very little or no dihedral at all. If you want to be very stable - perhaps even just a 3 channel without any ailerons, use a pretty high amount of dihedral. If you want a sort of fun flying ability that's not crazy to try and control but can still zoom around, use just a couple degrees of dihedral.

You can do any of these on a T-28 design - it might not be as scale as finding the exact measurements of the full size plane, but you will have a model that flies like you want it to.

 

[Hai-Lee]

Dihedral is normally set so that the centre of mass is balanced with the centre of lift in a vertical sense when looking in level flight.
This counteracts the effects of a large mass being above the wing strucutre and hence making the plane effectively top heavy and being dynamically unstable.

That is the warbird need for dihedral for aerodynamic balance. As for small aircraft and various trainers dihedral is added to provide the extra stability and self righting behaviours.

The dihedral being used to balance the mass can be seen even where the centre of mass is below the lift centre and this negative dihedral, (called anhedral), is easilt seen in the Harrier and a number of the later american and russian heavy lifters.

The reason the trogan has so much dihedral is that the big heavy fuselage and motor are sitting atop the wings. As a trainer it needed more than neutral stability so a portion of the dihedral is to overcome the mass Vs centre of lift effects and then more was added to give the self righting required for a trainer aircraft.

Too much dihedral will give rise to nasty handling effects such as "Dutch Roll". So as you can see the amount of dihedral and hence stability is something of a dark science!

have fun!

 

[baronbernie]

Thanx for all your help. Does anyone have any questions concerning the designing of there own plane? Go ahead and ask away and let others help you reach your design goal.

 

[jimklupar]

Does anyone know of a book or article that outlines basic design parameters for RC planes. i.e. weight, motor, prop, wingspan, wing loading....

 

[Hai-Lee]

Try this link. http://www.airfieldmodels.com/infor...f_model_aircraft/rc_aircraft_design/index.htm

I found it useful when I started into my own designs.

Have fun!