I have just completed building a SIG Kadet Mark 2 (from a kit) and I have it powered with a Magnum 40. I have modified the planes landing gear to a tail dragger. My problem is this..... when I taxi, the plane tracks straight. As soon as the tail wheel lifts off, the plane will pull to the left, and just spin in circles! If I give it some up elevator (to keep the tail wheel down longer), the plane will pull up very quickly then as it starts to climb, it will again pull to the left, and usually ends up doing a beautiful arch, and hit the dirt! On the few occaisons when I have been able to wrestle it up into the air, I have been able to trim it for level straight flight. It will not pull to the left in flight, even when going from idle to full throttle. The planes flies great, but is a little sluggish on the ailerons.
Everything looks straight, CG is right, and I'm running out of ideas.
I have tried to do a slower takeoff (at 1/2 to 2/3 throttle) but as soon as it picks a speed ...... here we go in circles!
Before I decide to strip the plane, and make it a static model, Any Ideas or suggestions?

Try some right thrust....when taking off a tail dragger, hold some up elevator as to throttle up release some of the up elevator, the tail rises and should track straight...as it continues down the runway release all up elevator...then just add a little up and it should take-off. Need to add right thrust before you try this.

Larry
AMA 11269

Thanks, I'll give that a try. Any idea as to how much? 2 degrees?

On any tail dragger, the rudder must be used to keep the plane going straight during the take off run. Learn how to use the rudder, and your problem will be solved. Do not try to hold the elevator down too long to keep the tail down, as the plane will lift off prematurely, as you have already found out. There is a technique for taking off a tail dragger:

1) Hold full up elevator while slowly advance the throttle.
2) Be prepared to use the rudder to keep the plane going straight.
3) When the plane is rolling and increasing speed, slowly release the elevator to let the tail up while continuing to advance the throttle.
4) Use the rudder to keep the plane going straight.
5) When the plane reaches flying speed, it will lift off the ground.

Watch some of my take off videos to get an idea:

* [link=http://whitetyphoon.com/rc/dymond_f8f/take_off.wmv]F8F Bearcat Take Off[/link] - 933K

* [link=http://whitetyphoon.com/rc/vq_p40/movies/take_off_17.wmv]VQ P-40 Take Off[/link] - 1.0M

* [link=http://whitetyphoon.com/rc/tf_p40/movies/take_off.wmv]Top Flite P-40E Take Off[/link] - 1.2M

* [link=http://whitetyphoon.com/rc/kyosho_corsair/take_off.mpg]Kyosho Corsair Take Off[/link] - 1.9M

* [link=http://whitetyphoon.com/rc/h9_corsair/movies/TakeOff01.mpg]Hangar 9 Corsair Take Off[/link] - 2.0M

Again, right thrust is not necessary if the "Rudder" is properly used on the take off run.

Hey ozzie,

that is normal. A little trick I might suggest. Bend your tail wheel to the left. When you taxi you will have to hold right rudder, just like when taking off. It makes the transition a little easier.

Thanks for the feedback. I had tried right rudder, but it didn,t really seem to help. The only way to stop was to back off completely. Now this is my first tail dragger, so I know that there is a lot of pilot error here. I will add some right thrust, (to help compensate for my lack of skill) any suggestions as to how much? My senior has a 1/8 inch shim on the left side of the mount, I assume the same will work?

Maybe a combination of things. Is your main gear tracking straight, or are your wheels bent outward, inward, or a combination? If the wheels roll straight it may improve takeoffs. I had to fix my first tail dragger when the wheels were toed out a lot.

Wheels should be toed in a bit.

One of the fellas at my field improved the ground handling of a plane tremendously by moving the main wheels back a little bit. That is, toward the tail. It doesn't seem to make sense, but he explained that with the wheels closer to the C/G, there's not so much tendancy for the mass behind the wheels to want to swing around forward. Or something like that...

Your friend is right. Rule of thumb is to prop the plane up level. Wheel axles should be directly below the lead edge of the wing. Try not to over-control with the rudder too. Hope this helps.

Right thrust is not going to help solve your problem. It takes pilot skill to take off a tail-dragger, that is why trainers have tricycle gear. What you are experiencing is "P-factor". When the plane is setting on the ground in the normal tail down attitude, the propellor blade traveling down or the right side of the plane hase more angle of attack than the blade on the left that is traveling up. Thus you have more "effective" pitch on the right side and it pulls the plane to the left. When the plane levels out, (tail rises) this creates eaqual angle of attack on both sides. There are also some forces created by the props slipstreeam swirling around the fuse and striking the fin and forcing it to right and makes the plane pull left. I think I said all that right.
You just need to learn the correct apllication af rudder elevator, and throttle. Once you get it down, it becomes second nature. Dont give up.

Here are some links on P-Factor:

* [link]http://home.earthlink.net/~x-plane/FAQ-Theory-PFactor.html[/link]
* [link]http://www.djaerotech.com/dj_askjd/dj_questions/propeffects.html[/link]
* [link]http://www.qmfc.org/school/yaw.htm[/link]

Some quotes from those links:

"This is one of the reasons why most real prop planes need a certain amount of right rudder to keep them straight during takeoff and climbout."

"rudder is typically required on takeoff and climb in most airplanes"

So again, using the rudder is the key to success. With proper technique, a plane with toe-out wheels, no right thrust, or wheel axles in front of the wing leading edge, can be taken off straight down the runway.

Again, thanks for all the input. I will try the suggestions, and as soon as the snow clears, I'll work it out.
Yuo guys are awesome!

Another band-aid is to put a longer tail wheel wire on it to set the tail higher off the ground. Helps the P factor element. High ground angle is why the Fokker DR1 was so notorious for ground-looping.

Be careful here, this is usually not the best idea. If the gear is too close to the CG on a tail-dragger, it the plane will have a very bad tendency to nose over on takeoff and landing. The closer the gear is to the CG, the more critical the elevator control becomes. Use of right rudder for takeoff is most likely the answer to ozzie65's problem. Also be sure the main wheels are straight and slightly toed in.

A 1/8" change in your firewall or mount is a LOT of change in the thrust angle --- too much. It would be better to practice more on holding a straight track.

I wouldn't mess with the gear and I wouldn't mess with the firewall, just learn to use the rudder on take off.

P- factor, the same way in full scale learn to use the rudder

Thanks for all the input. I haven't had a chance to take the plane out yet... too much snow on the ground. In the meantime, I have checked my CG, 3 inches form LE. The wheel axels are approx 1 inch forward of the LE, ie 4 inches in front of the CG. Could this be contributing to the problem, or is this OK? Remember, this was originally designed for trike landing gear, and I modified it to a Tail Dragger. The tail is up approx 1 1/2 inches, due to the tail wheel, so the angle is only very mild. I have adjusted the tail wheel to turn left slightly, so I will be forced to apply right rudder while taxiing (per one of the earlier suggestions.)
Any input appreciated.

I think moving the gear back to the leading edge will help a good bit. I have seen planes with gear too far forward that were a handfull on the ground. I have also seen planes that were set-up exactly right that were a handfull .

To each his own but I wouldn't go that route. Why try to correct something that you need to learn with a misaligned tail wheel? It's only gonna make taxiing at slower speeds a PITA, especially when the plane is coming toward you. Straighten the tail wheel and learn to fly the plane. You'll be a much better pilot in the long run, unless you plan on installing a crooked tail wheel on all of your future tail-draggers.

The only thing I would suggest changing is installing a tail wheel that places the wheel to the rear of the rudder like the Sig tail wheel. I have this tail wheel on several planes and it makes for very straight take off runs. I'd leave your main gear where its at, moving them back may cause your plane to nose over on landings.

As Terry says, move it back to the LE. It's a balance thing. The further back you move it, the less it will groundloop But if you go to far, as said above, it will nose over when you apply throttle. I have a Mustang with retracts which are to far back and cannot be moved ahead, so I hold about half elevator till it gets moving at a good speed before letting it back to neutral before lift off.

pulling to the left is a natural tendecy due to motor torque,use trim on the rudder to compensate while on the ground,then reajust in the air.See I do my RCU universe home work..lol