Undercart in relation to c of g

[Harry Glover]

On a  "tail dragger" monoplane, where should the undercarriage be mounted?

A. In front of the c of g?

B. On the c of g?

C. Behind the c of g?

The question may seem basic to many, but I am in conflict with my self as to the best position.

 Any guidance is appreciated.

[GrumpyGnome]

Not being an aerodynamicist, I'd suggest in front of the c of g or it won't drag it's tail...... 

[john stones 1 - Moderator]

In front or it'll tip when powers added.

 

[Geoff S]

In front, but not too much or it'll squirm about on take off like a very squirmy thing.  Under carriages on vintage models are too far forward for rise off ground and are very prone to being difficult to take off. I think it's because they were originally intended for hand launch and the undercarriage is primarily intended to protect the propeller on landing.

 

Just about at the l/e of the wing seems to work.

[Cuban8]

QED.

[kc]

U/c should be on the position shown on the plan!   Of course if it's an own design then the question is relevant and most answers would be 'slightly in front of CG '.  

On a low winger an u/c mounted on a wing is inconvenient ( transport, storage & also strength of mounting )so a fuselage mounted u/c is easier.

It's not always critical but when the u/c is bent back a little after some landings it can be noticeably trickier, so just bending forward a bit by hand works on piano wire u/c.  I like piano wire u/c formed into a torque rod type. See many of Peter Millers designs for RCME recently where the wire goes across the fuselage to opposite side then  into vertical retaining slots.  The horizontal part twists to act like a torque rod ( as in car suspension - Morris Minor, Beetle etc ) giving some springing effect.  Simple, effective and removeable for covering.

[leccyflyer]

1 hour ago, Harry Glover said:

On a  "tail dragger" monoplane, where should the undercarriage be mounted?

A. In front of the c of g?

B. On the c of g?

C. Behind the c of g?

The question may seem basic to many, but I am in conflict with my self as to the best position.

 Any guidance is appreciated.

Definitely in front of the CG for a taildragger monoplane. For a low winger a position at, or just in front of the wing leading edge is good for reducing the chance of tipping up on starting to roll for take off. Not too far forward though, or the ground handling can suffer.

[Andy Gates]

Whenever I build or modify machines I generally place the axle of the undercarriage 30 degrees forward of the vertical from the CoG. Not fool proof but pretty close.

[Harry Glover]

Thanks gents for your answers. Answer A seems to be the logical correct one.