Hi, I have a Tower Hobbies 40 size trainer with an OS 46 FX engine. I am having the hardest time taking the plane off. When I begin taxiing I have to give it heavy right rudder to keep it straight and when its gather speed it shoots to the right towards the fence. I have tried putting over sized wheels and toeing in the rear wheels. I have also tried and made the nose gear as stable as possible. Please help with suggestions or solutions. Thanks!!

Hmmmm...

If the nose wheel is straight and solid (IE, no wiggling of the wheel OR gear wire) The first question I would have to ask is: Is the plane sitting with a slight nose-up attitude (1 or 2 degrees)? Also, are you flying from grass, dirt, or pavement?

chances are if you plane is acting like that on the ground, you are have to compensate by trim in the air also. Sounds to me like you need to add some right and down thrust to the engine.


Looking at your engine from the prop.. remove your motor mount and put (1) NO.6 washer under the lower right corner, put (2) washers under the upper right corner, and (1) washer under the upper left corner. On most 40 size mounts, this will give about 2 degrees right thrust and 2 degrees down thrust.

Sounds crazy but it will make you plane handle lots better on the ground and in the air!! TRy it!

Dang_it

Some trainers have landing gear that is well.. crap. Make sure that the nose gear is straight, and then adjust it so that there is very little travel on the nosegear. Most of the time what happens is that we tend to overcontrol when trying to steer the plane. Add to this the speed needed to take off and the plane usually ends of veering off the runway. Your best bet is to cut power, abort the takeoff, and try again. I would try adjusting the landing gear before making any thrust changes to the engine.

Seems to me that you need to line your nose wheel
up with your rudder. Yoy say that you have to put
a lot of 'right' in your steering on the ground to
keep it straight. When you leave the ground, the
rudder makes it take the right turn...

you may also have slack in your control rod to the
nose wheel.

Thanks everybody for your feedback. In response to Minnflyer's questions. The plane does sit slightly nose up and my club has a grass runaway. Thanks!!

asraox,

It sounds to me like the swirling prop wash is pushing your fin to the right, which steers the plane to the left. This problem is most evident when the airspeed is low, and the throttle is wide open. In these conditions, the prop is generating lots of swirl in the prop wash, and the airspeed is so low that the fin does not have a stabilizing effect. I have this same problem with a somewhat over-powered Goldberg Eagle. One thing that would help is to add some fin area below the thrust line. You may not be able to add enough to make a noticeable difference without dragging the tail on take-offs and landings. You can also practice giving lots of left rudder at the beginning of your takeoff run, and gradually easing off as you get some airspeed ( by airspeed, I mean speed relative to the air, even though the plane may still be on the ground ). This is what experienced pilots do without having to think too much about it. Another thing you can do is to gradually ramp up the throttle as you takeoff. This lets the amount of swirl build up at the same time the airspeed is building up, so you don't get such a large steering force from the propwash until you have some airspeed to help keep the plane straight. My favorite copout, which my instructor did not like, is to simply takeoff directly away from the pits, ignoring the runway, at full throttle, so the plane could happily steer to the left for the 15 feet that it takes my Eagle to get airborne. This, of course, is not appropriate if other pilots are expecting you to be taking off in the more conventional pattern. By the time you are in the air, you should be fine, unless you are still over-correcting with the rudder. One other possible help would be a prop with lower pitch.

Good luck,

banktoturn

First, remove wing, then set (bend the rear gear to where it looks as straight as possible. Then, change the nose gear from as steerable as possible to the least steerable .It doesn't take much movement to turn a plane on the ground. Make sure it's straight buy finding a slop, (sidewalk or something) and give it a coast test. When it look's like it will track straight then go to the field (wing off) and taxi test it. When its all groovy make sure the rudder is straight by adjusting the linkage. Leave the front wheel alone after its tracking good. And remember after a hard landing it may be tweaked a bit. No prob , just bend it back and test it out again.

some of my students have the same set up and plane,taking off we need very little right rudder ,,the plane is balanced?It has 2 or 3 degrees of right thrust?The plane sets level or just a tad down in the nose,right?The nose gear is tight with no slop? The nose gear control is secure and not just flexing? The nose gear should move very little compared to the rudder,is the nose gear and rudder turning the same direction,checked all that?That plane will almost land and take off by itself,dought the problem is toe in or wheels,we fly off both.

They are right, it doesn't take much movement of the nose wheel to steer it, seems like I read once that the nose wheel should be set so that at full deflection the plane will taxi in a 10 foot circle. Try this and I agree hole hartedly that it is a good idea to practice
taxiing with the wing off if your not working with an instructor. I
would suggest that you find a good qualified instructor tho.

I noticed that the push rods connecting my servo to the steering arm is very weak and bends easily. I think thats whats causing my plane to behave erratically on the ground also it seems to be interfering with my throttle push rod. So I went out and bought Sullivan gold push rods 2/56" size which are far more rigid. I am also going to reposition the throttle servo arm so it doesn't interfere with the steering arm. I hope that will fix it, since it was quite a bit of work un-mounting the engine and drilling holes in the firewall for the larger push rods. Lastly I am going to take everyones advice and make sure that the nose wheel has very little travel compared to the rudder (10ft turning radius) and also test taxiing without the wing. Thanks for all your help!!

Ah haaaaaaaa!!!!! So much for being solid!

I hate the steering setups on some of those trainers. Just chop the nose wheel off, move the main gear forward and mount a tailwheel (lol).

Buy a Sig LT 25, it's a taildragger and I like it as a trainer better than the Sig LT 40.To me it handles like a PT40.

Welcome Asraox: Well, leave it to me to think of the simplest thing. We had a guy at our Field that had the same problem with his plane. After all was said and done, about an hour and a half of all us experts dissecting this poor guy's plane, it turned out to be the right side wheel on the main gear, was not rolling freely. Just a thought, I don't have them often so be gentle. Always glad to help if I can. Garry

Another thought here is to find a nice smooth surface like concrete or something like that and dont even start the engine up. Just center your rudder and then give the plane a nice push and see if it goes straight or veers one direction or another, then adjust your linkage to track straight. I used to do this in my basement so the things would track straight. Also, the wheel dragging is a good suggestion to check out too. I got one collar too close one time and it drug, and made the plane track to the tight wheel side. I fly from buffalo grass, and one thing that really helped was to put a Fults dual strut nose gear on my trike planes, as that would take a lot of stress and movement off of the servo and control arm assembly.

Hi Guys, Thanks for all your valuable input. It seems like the problem was a number of things all of which you guys brought to the light.
1) The push rods were very weak and were bending causing the nose wheel to behave erratically when the push rod snapped back into place. - So I replaced the push rods and reduced the left to right movement of the nose wheel considerably. It now has very little throw. (about 10 ft turning radius)
2) The the right wheel and front wheel were very tight compared to the left wheel, so I sanded the wire gear so that all 3 wheels turn very smoothly.
3) I then took it to a flat surface and pushed it hard and kept adjusting the nose wheel till it tracked straight. Finally I had to give very slight right rudder trim to keep it dead straight. I then adjusted the rudder so that it was dead straight even though I had a little right trim for the nose gear.

Tomorrow I take it to the field and will test taxi it without the wing,Hopefully it will not give me any more problems. Thanks again for all your help!!

asraox,

If you find that the adjustments you have made don't eliminate the problem, try the following experiment: Take off at full throttle ( or however you have been ), and then do a more gradual takeoff roll, gradually advancing the throttle as the airspeed goes up. If, as I suspect, you have a propwash problem, this will allow the "weather vane" stability of the fin to kick in before you get up to full throttle.

Good luck,

banktoturn

Hi Bankoturn, I am new to the hobby so I am not yet well versed with all the lingo, could you further elaborate on the propwash theory and explain what you mean by weather vane and fin stability. Thanks!!

asraox,

Yeah, sorry about that. The vertical stabilizer, or fin, is just that: a vertical surface that stabilizes the plane, by keeping the front pointed to the front. It does this the same way that a weather vane stays pointed into the wind. As long as the plane is moving fast enough, if it gets turned sideways ( yawed ), the fin will then be at an angle to the incoming flow, and it will be pushed back toward the centerline, straightening the plane out. If the plane is moving too slowly, relative to the air, then the push on the fin is weak, and it may not be enough to straighten it out. This is why it is easier to keep the plane rolling straight after it gets up to higher speed.

The effect of propwash depends more on the type of plane. Because the propeller has to spin to generate thrust, it not only pushes air back, but it also gives the air some 'swirl' ( like a tornado ). If you look at your plane from the front, the prop is spinning counterclockwise, and so is the air that it pushes back along your plane. When this swirling air hits your fin, it exerts force on it. Since your fin is almost entirely above the centerline of your plane ( this is true on most trainers, the counterclockwise swirling air pushes your fin to the right, which steers your plane to the left. If you have a strongly swirling propwash, and the plane is moving slowly, you have a situation in which you have a fairly strong steering effect, and a fairly weak stabilizing effect. This is the situation if you give your plane full throttle at the beginning of your takeoff run, while it is barely rolling forward. If you throttle up gradually, you will find that you don't need to give as much rudder to keep it straight, and by the time the plane is rolling pretty fast, you may not need any. If you manage the propwash carefully, your tricycle gear may keep you going straight with no rudder at all. My plane is a taildragger, so the back lifts up, and my tailwheel doesn't help me roll straight at all. A prop with lower pitch will give you less swirl for a given amount of thrust, so this might help as well. If you feel like modifying your plane some more, you could add some fin area below the centerline, so that the propwash on the bottom can partially cancel out the propwash on the top.

Of course, it is possible that all your problems were with your gear. You will find out tomorrow.

Good luck,

banktoturn

Wow!! I just had a Physics 101 flashback. Thanks for the excellent explanation. It now makes sense to me. I don't think I want to modify my plane anymore, so hopefully the landing gear fixes should sort out the bulk of the problem. I will do as you say and try a gradual take off instead of a starting with full throttle. Thanks again Banktoturn.