1:5 Spitfire Balsa Kit - Custom Control Horn Design: Length?

[Nick Stock 2]

I've been working on the tail section of this kit - planing and sanding to necessary profile. I just have some tidying to do before glassing the Horiz stab and covering the elevators before final assembly.

I plan to cut my own control horns by hand from pre-cured carbon fibre sheet.

Can anyone advise on my current design (pictured below) - whether long enough hence resultant pushrod travel or else?

 

Thanks

Nick

Edited By Nick Stock 2 on 13/08/2018 10:30:54

Edited By Nick Stock 2 on 13/08/2018 10:43:58

[Jon H]

Im sure it would be plenty. You certainly wont be using 20 degrees deflection so i cant see a problem with this.

[Nigel R]

Looks good to me. I make it 20 degrees when:

1. Servo travel is 50 degrees

2. Servo horn attachment is 15mm from centre of servo disc.

I assumed the elevator is about 25mm thick, ie total hinge to linkage is (1/2 x 25mm) + 19.5mm.

[David Ovenden]

Just a thought. Is the elevator hinge point really where you show it in the diagram? Aren't they normally hinged at the centre of the circle that forms the radiused leading edge, rather than at the leading edge itself? If so, that would affect the geometry of your diagram.

Edited By David Ovenden on 13/08/2018 13:41:05

[Nick Stock 2]

Thanks you both. Together with this and Tim's Seagull Model Hurricane setup, I committed to a vertical distance of 25.4mm/1" from lower surface of the elevator to the hinge point.

This I hope will err on the side of 'big servo arm movement = less control surface deflection' which I understand is vital to warbird setups - particularly Spits.

[Nick Stock 2]

Posted by David Ovenden on 13/08/2018 13:35:26:

Just a thought. Is the elevator hinge point really where you show it in the diagram? Aren't they normally hinged at the centre of the circle that forms the radiused leading edge, rather than at the leading edge itself? If so, that would affect the geometry of your diagram.

Edited By David Ovenden on 13/08/2018 13:41:05

David good point - perhaps in the actual full size the hinge point was/is some distance within the leading edge. However my Robart hinges have their hinge points effectively dead in the middle between the outer most part of the leading edge and the trailing edge of the horiz stab, perhaps at most within a few mm. So I take the view now that as long as I'm in the right ball park, I can adjust surface deflection with the position of the pushrod at the servo end (inwards or outwards) and then fine tune with my transmitter (end point).

N

[Tim Flyer]

Nice bit of carbon cutting there too Nick😊