chall

I built a .40-size glow trainer, but decided to switch it to a tail dragger configuration. The plane flies and lands swell, but it's ground-handling is terrible.

As you gain speed taxiing the plane wants make a sharp turn to the right (or left, I've tried so many variations I don't know what it's doing right this minute). I am currently using DuBro's fiberglass landing gear, so I know it's straight and not bent. I've also tried to bend the axles slightly to give it "toe-in". I've tried a million tweaks on the tail wheel and finally just disconnected it so it swivels freely.

Here are my suspects, but feel free to suggest others!

- Some fellow fliers feel the 2-1/2" main wheels are too small for our grass field.
- Too much toe-in. The books recommend 3 degrees, but how in the world would you measure 3 degrees toe-in on a 1-inch axle?
- Replace tail wheel with a plain skid. Maybe the wheel is getting stuck or something.
- Add a spring-connected or shock-absorbed rear wheel.

But I'm really at a loss. I've been fighting this problem for a month, with no real success. It mis-behaved the same way with my old metal landing gear. I am presuming (maybe I shouldn't) that the fore-and-aft placement of the gear is correct since it lands so well.

By the way, slow speed taxiing is poor too, but seems to be unrelated to the take-off speed problems.

Help!

eaglelope

How far forward of the CG is the main gear? If you get it too far forward then it will have a tendency to ground loop. Even with the wing LE seems to be about right.

You may also want to try a toe-OUT of the main gear. I've seen this argued on RCU several times with arguments for toe-in as well as toe-out. For whatever reason, I have had better luck with toe-out on my 40-size taildragger trainer.

Mark

Red B.

Eaglelope is right about not positioning the landing gear to far forward. You have to strike a compromise betwen nose-over and ground-looping tendencies.

As for toe-in or toe-out, in my experience it doesn't matter much when flying from grass fields. My reccomendation is to set the wheels with zero toe-in/toe-out.

Do you use a steerable tail-wheel? If so, do not use too big a throw. Try using a wheel deflection that is about 1/2 to 1/3 of the rudder deflection. Too much wheel deflection often cause over sensitive ground handling.

Wheel size usually doesn't have a big influence of the ground tracking but big wheels reduce rolling friction which may be a consideration if you are flying off a long grass.

If the aircraft consistently weers of in one direction during the take-off run you should consider increasing or decreasing engine side thrust.

Another thing: Throttle management! When using a nose gear configuration it is usually O.K. to slam the throttle but this is not so with a taildragger configuration. Increase throttle gradually and apply full throttle only after the tail wheel is off the ground.

I hope this is of some help.

/Red B.

khodges

My Feedback: (1)

I think you'd be better off with a steerable tailwheel instead of the free-castering one, because: as small and light as your plane is, the least crosswind will have it "weathervaning" or turning into the wind when it's on the tailwheel, and the prop blast , p-factor and engine torque are going to make it squirelly also. A steerable tailwheel will provide resistance to turning unless you make a rudder input. I had a Sig Kadet MkII that I tried converting to a taildragger and used a free castering tailwheel because I would have had to re-do the whole tail to make a sterable one, and all the above things I mentioned happened. I tried a skid and things improved a little, but steering on the ground was still very difficult. I finally put it back to tricycle config. and bought a Rascal 40. Damn good airplane to learn taildragging on.

Even if you put a steerable wheel on it, the problem with the tail coming around will still be there once the tailwheel lifts, it's just the nature of taildraggers, and you have to learn to make rudder corrections to keep the plane pointed down the runway until it lifts off. If you have a computer Tx, program about 60-70% exponential into the rudder and see if it helps you to not overcontrol. As you get the feel for how much rudder you need, start taking expo out. The other thing to try is to feed throttle in gradually when you start the takeoff roll, rather than nailing it, this will also allow you to feed rudder in a bit at a time and see how much you need ( the amount of rudder needed will increase with increased throttle).

Toe-in might help some, but larger wheels will make it more effective, and the placement of the mains, as others have said, is important. The rule of thumb is even with the leading edge of the wing, but I'd go a bit further than that; the longer the nose of the plane, the further in front of the leading edge. You want enough weight on the tail so that it doesn't lift immediately, but not so much that it wants to stay planted until the mains lift off. The tail should fly before the rest of the plane, and should continue to fly after the rest has landed

practicepracticepracticepractice.

chall

Thanks for all the suggestions Here's a photo so you guys can see what you think. I'm under the leading edge. So moving the gear forward might reduce ground looping?[img][/img]

chall

[img][/img]

khodges

My Feedback: (1)

I think that looks pretty close, definitely don't go any further back, maybe as much as an inch further forward. Someone mentioned toe -out, definitely not. Toe in tends to make a plane correct to its center. When the plane begins to veer to one side, that wheel is then "parallel." to the direction of travel, while the other one is toed-in more, which creates more rolling drag on that side, which causes the plane to veer in that direction, straightening it up. My L-4 has scale gear that has the toe-in built in, and it works. There also needs to be a bit of positive camber to the wheels for toe-in to work (the top of the wheel leans out when looking at it from the front)

JohnBuckner

My Feedback: (1)

Normally I would also agree that in most cases folks put the gear to far forward but after seeing the photo I think the real culprit is the gear that is far to tall for the airplane with a resultant severe deck angle when in the three point attitude. On takeoff intitally while in the three point attitude there will be excessive 'P' factor aggravated by that high deck angle. This of course must be delt with by the pilot and just as he gets this in hand as the tail raises he will also have to deal with much more gyroscopic precession as the nose is lowered through a greater arc and the left turning tendency is compounded.

Make or Get some lower gear and and the problem will go away.

John

By the way Moving the gear further foward of the CG will destabilize ground handling. The closer it is to the Cg, the better will be the directional stability. On a taildragger the most stabile position possible is with the gear at the CG. Of course this must be limited by the need to prevent noseover. Many early full scale sailplanes acturally had this arrangement and they inculuded a tailwheel and a nose skid.

bingo field

http://www.rcuniverse.com/forum/m_21...tm.htm#2118831

This was my post using my experiences converting an Alpha to a taildragger. It has some pictures that may be helpful, along with the posts from the reponses that I recieved. Maybe a little bit helpful to you. Good luck, and you will get a kick out ot the changes you make to it.

britbrat

JohnBuckner has hit it right on the head -- the gear is correctly positioned, but it is much too tall. Shorten the legs & re-connect the tailwheel steering.

chall

OK guys! I dug up some old landing gear and bought some 3" wheels. This looks better doesn't it?

Won't know if it works until Sunday at the field, but I'll be sure to report back.

Thanks so much for all the ideas and advice.

[img][/img]

chall

Finally got out to the flying field yesterday. Yes, I think the lower landing gear height helped. Only got one take-off in due to a very rough landing :-( But the period of ground loop vulnerability seemed small enough to get past.

Now to re-attach the landing gear, install a new prop, bend the tail wheel back in place, and patch a hole in the fuselage!

Thanks again, I never would have thought of this.

Woodpile

Just a thought, because I didn't see it mentioned... Are you holding full-up on the elevator while taxiing? Gotta keep that wheel in good contact with the ground until the tail lifts...

Flypaper 2

Another help is to put a longer tailwheel wire on it to make the tail sit higher. Makes the tailwheel stay on the ground longer. The nose high attitude sitting on the ground was why the DR1 triplane was notorious for groundlooping.

chall

SUCCESS! Finally got a perfect take-off. The final tweak was to adjust the tail wheel so the plane actually tracked right at low speed, but at take-off speed would be tracking straight. The old engine torque thing I guess. It hadn't occured to me until a fellow flier at the field suggested it.

I'm sure I've heard about engine torque before, but never thought about it in quite this circumstance.