Is there a formula for locating the landing gear when converting from tri-cycle to tail dragger? I'm converting a PT 40 trainer. Any other things I need to know for conversion. Thank You.

Midwesterner

I just move the main gear forward until the axle is inline with the wings leading edge, and added the tailwheel at the very end of the fuselage. You will probably need to add so plywood to use as mounting plates.

Diito. That is the way I set up a tail dragger also.

I have a PT-60 built as a tail dragger. My axle centerline is slightly behind the leading edge. We fly off grass and the plane does not try to nose over.

It will not hurt to be a bit out ahead of the leading edge. I have low-wing models with the gear attached with the axle 3/4" or better in front of the leading edge. The center of gravity factors in more than the leading edge. Too far ahead of that and you can't get the tail up on the rollout. Too close and you do face plants coming and going.

And, although you balance the model dry, you usually try to take off with a full tank of fuel ahead of those main wheels.

Absolutely infront of the leading edge. Directly under the front windscreen for example.

I have a PT60 and I am converting it into a tail dragger and I am having a problem with the gear gear as my elivader sticks out past my tail rudder and I want a steerable rear wheel because my plan is to make it a float plane once I get it flying and tuned right. any ideas would be appreciated.

I converted a Avastar and my CG changed a lot. I would make sure to do another balance. May not change on your plane but did on mine. Made a better plane out of the Avastar. gphil

I prefer the wheels center hub to be 1/4 to 1/2 inch in
front of the L.E. JMO<

Bob

Here's a PDF document that might help you.

Mike

Thanks for the great ideas  I was wonderinging about the front gear I will move it a little farther forward of the CG. But I still have the problem of the steerable tail wheel. As my Rutter is forward to my elivator.

There are a couple of ideas about how to position the main gear on a tail dragger.

The simple one is to locate the axles directly below the wing leading edge. It's simple and works with your average model airplane. If it's a really simple model, there is no LE sweep and it's easy to see where the wheels should be. If the LE sweeps aft, it's not so easy. Most people would use the Mean Aerodynamic Chord location to work out where to place the axles. The picture below shows where the MAC would be on the swept LE of that airplane. The verticle thin blue line that touches the LE about half-way out shows where that MAC would be on that model.

Aeronautical engineers go beyond simple to figure out where to put the axles. The work a lot of numbers and such to come up with a location based on where the CG of the airplane is in the airplane. They don't go from where the CG cuts the wing, but exactly where it is. It's usually above or below the centerline of the wing chord. The model in the picture is a mid-wing and it's CG is very close to being mid-wing. So the yellow and red lines were drawn assuming the CG is where those two lines cross each other. The engineers also work out where the rubber meats the road instead of where the axels are. They know the rubber should roll on the runway about 15degrees forward, as shown in the picture. Oh wait...... the picture shows a 27degree angle, not a 15 degree one......... hhmmmmmmmmmmmmmm

That model had an annoying habit. When the wheels first hit the runway, the sucker porpoises. The wheels would hit and pitch the nose up and the model would BOUNCE. It's really tough to grease that baby in. Why?

When those tires hit dirt/grass/pavement, the model is coming down. The tires hit ground and the ground starts pushing up. The CG keeps going down. The nose starts going up. The tail comes down twice as fast as the CG does. That model's tail wheel often hits the rudder. It needs to be bent out every so often. It lands like a salmon going to spawn.

Why not move the wheels directly under the CG? Drag generated by the tires rolling along the ground introduces a nose down pitch. A grass runway throws a bit more drag into the equations. Moving the wheels forward a touch balances the drag. 15-20 degrees forward works.

anyway..........

I just finished converting a Hobbistar 60 to a tail dragger - you can check out the thread here.

I am finishing up a PT.60 for my son's first trainer. It will have an XYZ 20cc and is also a taildragger. I bent up my own main gear and they are placed just a hair in front of the leading edge. I added a ply mounting plate at the rear of the fuse for the tail gear and it will be linked to bottom of rudder via a bungee system. I like doing them this way to keep loads off the rudder servo. The PT.40 was my very first plane.

BTW, I enlarged the rudder and elev. and made the wing in between the trainer and sport version. Should be a great flyer!