CanDo

BTW, my Honda (FWD) had a small amount of toe in after Honda aligned it. Getting back to planes, because the main gear designs varied greatly over the years and the landing surfaces ranged from asphalt, concrete, grass, dirt, wet/dry, etc., it seems like the quickest way to get valid data for our model planes is to experiment a bit and try a little toe in or toe out and see what results we get. Just as the Wright Bros found out, debating can only get you so far, testing gave them the answers they needed.

otrcman

That was the best comment yet in answer to the OP's question.


I have long puzzled over toe-in vs toe-out. And I'm still not sure. This issue has puzzled me for an entire career as an aeronautical engineer (BS & MS), 35 years as a professional flight test engineer, and few years as a landing gear designer. In my retirement years I have spent more than a few hours as a full size flight instructor, specializing in training people to fly vintage tailwheel airplanes. I'm checked out in 41 different makes and models of tailwheel airplanes, some of which have had toe-in and some have had toe-out. Most have the main wheels straight-ahead.

What have I concluded from all this practical experience? Toe-in or -out doesn't seem to make much difference. If you have had a positive experience with one or the other, you may find that your experience probably won't generalize out to other models. There are so many other dominating factors. On my models I generally just set the main wheels straight and worry about the important stuff.

The big deal is to have lots of lateral force capability at the back. At low speeds, the tailwheel or skid provides that force. At higher speeds, the tail is off the ground and the fin/rudder provides stability and control. If you jam the throttle from a standing start, the horizontal stab will provide enough lift to immediately reduce the downforce on the tailwheel and you will be left without tailwheel control before you have enough airspeed for rudder control. Holding a little bit of aft stick before applying power can delay the tailwheel lift just enough to get you started on a straight track and allow enough speed to build up for aerodynamic control. Just remember to ease off the back stick before the model lifts off prematurely.

On landing, it is important to keep the stick fully back once the plane is on the ground. This keeps the pressure on the tailwheel. If you do a stall landing (three-point), then don't let off the aft stick until you stop engine. If you do a wheel landing, remember to smoothly pull the stick fully aft as the tail begins to settle. Then, as in a stall landing, keep the stick fully back until the prop stops. There is a tendency among both full scale and model pilots to breath a sigh of relief and relax as soon as the wheels touch down. Watch some videos of models landing. Its pretty common to see a ground loop on landing in which the elevators return to neutral soon after touchdown. It's much rarer to see a ground loop with the elevators fully deflected throughout the landing.

Does all this guarantee a nice straight takeoff or landing? Nope. Other factors do dominate. Top heaviness (biplanes & triplanes) is a big factor in the stability of a tailwheel plane. Pitch attitude on the ground is another important factor. WWI planes typically sit very nose-high and this makes things more difficult. All you can hope for is to minimize problems within the constraints of the scale model that you are flying.

Dick

CanDo

Dick, well said my friend. Good to hear from you!
-Les-
(22 years-RC planes, 17 years-UAVs, 47 years-cars/hot rods, 42 years electronics)

dionysusbacchus

My Feedback: (25)

What I have found is that the closer the axle is to the C of G, the less likely the plane is to ground loop, no amount of elevator or rudder input will stop this if the wheels are positioned poorly in relation to the C of G. Of course the closer the axle gets to the C of G the more likely it is to have a tendency to nose over. The trick in all of this is to find the sweet spot, where the best of both worlds resides. Slight toe in I find very effective in tracking, even for tricycle landing gear set ups. Toe in alone will not correct improperly positioned wheels in relation to the C of G.

Most modelers think that getting the wheels as far forward as possible is the goal, this is a mistake. Even off of grass fields with the proper use of elevator you can make excellent take offs with the wheels in a good location for proper ground handling.

I know this because I conducted tests with an actual model by changing the landing gear location at the field, with the landing gear way forward the model was uncontrolable on take off.