I have a fun fly precedent with a .46 thunder tiger on it. When I throttle up for take offs it starts fishtailing down the runway (have done 360,s more than once) does anyone know what a good cure for this might be, or maybe something else I can try?? Thanks

I just started flying a 4 star and Im experiencing the same sort of thing. Make sure it rolls relatively straight at low throttle (or just roll it with the engine dead). It will try to go left as soon as you give it throttle ( I mean immediately). I am still having trouble, but I have found that if you give it just a touch of right as you throttle it up it helps. Just let up as soon as you see it starting to go right. Give it throttle slowly and dont over correct, that is my problem. I have managed to take off with out running off the run way the last few times. I still am not that good at it. I know the principle, but reaction is a different story. I guess practice makes perfect.

Slowly advance the throttle. Use every inch of runway you have while learning to take-off a taildrager. it should take from 5 to as much as 10 seconds to move the throttle from idle to 75% (and most light models should be off the ground by then) If you slap the tick to full throttle, you WILL ground loop.

Use a full up elevator briefly, to help keep the tail down, making the tailwheel more effective until the rudder gains some authority. (as it gains speed, let off of the elevator)

A LITTLE toe-in can help. Too much makes the plane want to nose-over.

If possible, shim or shift the landing gear to put the axles directly under the leading edge of the wings when the airplane is level. That can often cure a "squirrly" model.

As you gain experience with taildraggers... you can apply the throttle faster. The coordination of rudder, elevator and throttle becomes automatic.

I agree it takes time to develope the feel of tail wheel to rudder transition. And if you are patient you will become a much better pilot. Learn how to use the rudder during take-off. Best of luck--

Using rudder is about the only way to get most tail draggers off the ground, and that's what you'll have to learn do Killer Clam.

Seriously, it's just as FH described; hold full up and start advancing the throttle. Once the plane is rolling at a fast walking speed, relax the elevator to neutral and the tail will lift a bit. Once the plane gets to flying speed, a gentle application of up elevator will let it lift off the ground.

At some point shortly after the tail lifts, you'll probably have to start feeding in some right rudder. Just remember to go easy, on both the throttle and the rudder.

Good luck. It will come to you.
Dennis-

Killer Clam,

Your in "good hands" here at RCU. Listen to DB and Huber and you will do just fine.

Remember!!!! PRACTICE...PRACTICE...PRACTICE...

Before you know it, IT is automatic.

Happy(takeoffs&)Landings,

Sean

I did forget to mention... make certain your wheels turn FREELY. Ever do a Cub Scout soap box derby car? remember how freeely the wheels turned on the ones that went fastest? You want your model's wheels just as free turning if possible.

If you have threaded screws as your axles.. it helps to drill the wheels out and put brass tube bushings in the wheels if you have plastic hubs. The plastic grabs the threads and that makes the wheels catch. The brass won't catch. (make sure you de-burr the ends...)

I agree with the posts... especially a little toe in. While not necessary, it is essential that your plane isn't toe-out.

Also, remember to always try to take off into the wind. Cross winds will certainly help to derail your takeoff line

KillerClam,

You're not having a torque problem, you are having a propwash problem. Torque would
be causing your plane to roll to the left. What you are seeing is yaw to the left, which you
try to correct with rudder, probably overcompensating, causing the fishtailing. This is caused
by the spiraling airflow from the prop hitting the vertical stabilizer. Picture the swirling flow
moving back along the fuselage, and then hitting the fin. If your fin had as much area on the
bottom as on the top, then the propwash would not cause any yaw. This is usually not practical,
so the top part of the fin is much bigger, and the propwash only hits the fin above the center line,
pushing the fin to the right, steering the plane to the left. I have an overpowered Goldberg Eagle
that I built as a taildragger, and it suffers from this problem also.

There are several things you can do to help with this problem. The main one, as several people
have mentioned, is to learn the skill of using rudder to compensate. This will happen in time,
and will involve some hairy, possibly scary, takeoffs. You can also reduce the steering effect of
the propwash. One way is to ramp up the throttle gradually. This way, the propwash is weaker
early on, when the plane is moving slowly. As the plane gains airspeed, the air moving backward
past the fin gives a 'weathervane' effect, preventing yaw. You will notice that when the plane is rolling,
or flying, fast, the propwash has no noticeable effect on yaw, because the weathervane effect is
stronger than the effect of the swirl on the fin. Another improvement you could make is to add some
fin area below the center line. Even though you can't add as much below as above, you can probably
add enough to reduce the yaw effect of the propwash. To keep the bottom part of the fin from extending
too far below the fuselage, you can extend it along the fuselage, to get some additional area. You
could also clip the top of the fin, to reduce the amount of area above the center line. If you do this,
be careful not to get carried away, and to preserve enough rudder area. One other thing you can
try is to use a prop with less pitch. Generally, a lower pitch prop will generate less swirl in the
propwash than a higher pitch prop. If you aren't using a very low pitch prop already, give it a try.

Good luck,

banktoturn

Gradual rise in throttle is very good advice. You need to use your rudder until just before lift off and then start transitioning to ailerons to control the roll as it lifts off the ground. At least this is what solved my problem. I had this problem with a trainer and I found that I wasn't transitioning properly from ground control (rudder and throttle) to air control (aileron and throttle). The rudder control and aileron have to overlap a little on takeoff, especially in a cross wind.

I don't miss trainers for this reason.

Joe

I am glad you explained that. I have been using the "right hand rule" on the axis of the prop, and for the life of me I could not figure out why that would cause the plane to yaw. Now it is all clear.

hi folks -

i am also going through first time taildragger take off rudder control. i just finished building a 4-star 60 and am experiencing the same things you have been talking about. on acceleration, the plane wants to yaw hard to the left and i've been experimenting with getting "the feel" of rudder/elevator compensation.

anyway, the reason i am adding a post here is because i am also experiencing some weird stuff on landings that i did not have to deal with on my old tricycle gear trainer:

landings come in good and slow with the engine running at low idle of around 1900-2100 rpm's - so i don't think much is going on torqe-wise

when i land and roll down the runway, just before the tailwheel comes down and makes contact, the plane begins to yaw to the RIGHT. and so while it's yawing to the right, i am feeding in almost full left rudder. eventually, the tailwheel makes contact and once rubber to pavement control takes over, the plane ends up doing a 360 left donut because i've been pushing the rudder to keep it from going right initially.

i am using one of those sullivan tailwhels with a spring connecting the tailwheel steering to the rudder. they give you two choices of springs to use - stiff & flexible.

at first, i had the flexible spring on and i thought that may be the problem. i figured that at moderate speeds where the tailwheel is in contact, there was just too much decoupling of the steering from the rudder which would create instability.

so i switched out springs for the stiff one.

although i will still do 360 left donuts, the effect is less severe but the plane still wants to yaw to the right initially and full left rudder has little effect until the tailwheel makes contact.

i don't think it could be that the rudder is trimmed to the right - i've checked this. also, since the engine is basically idling, prowash over the rudder is minimal.

maybe the front wheels need to be toes in as suggested above ?????? but when i push the plane across pavement by hand, it seems to track straight.

anyway... any ideas welcome.
thanks

-paul.

How about forcing the tail-wheel on to the runway sooner?

The plane looses a lot of speed n the runway. When there is not enough speed left for flying, but before the plane "yaws" right, just add up elevator. This will force the tail down, and give you all the authority you need.

gus

I agree with gus. I have a GP Shoestring and even the mfg. calls for 3-point landings. This means getting the tailwheel on the ground ASAP. I have found it is much easier to control the roll out if you get the tail wheel down as soon as the plane loses flying speed.

i'll try that.

i'm pretty close to doing 3 point landings and i will have to mentally see whether i was releasing the elevator flare in landings or not by repeating what i was doing before. i may very well have released the flare too soon causing a right yaw situation

i'm confused as to what is the mechanism for the right yaw however. i don't remember a crosswind.

Yaw on touchdown is usually a sign that the wheel it yaws toward is not turning freely. I would be looking fr why the right wheel s not turning freely if it yaws right on toughdown, forcing heavy rudder use.

You should be able to set it down on the mains in a higher speed dead-stick landing and if the wind is straight down the runway... just let go of the sticks and let it coast to a stop. (if the runway is smooth)

Another cause of yaw on touch-down is use of ailerons to counter a roll. If hte airplane is not laterally balanced, or if the rudder and ailerons are cross-corrected, you can have a bit of this problem. (usually not as severe as you describe.) I have demonstrated adverse yaw on touchdown by slowly feeding in aileron and rudder to the point that full rudder could not correct for the adverse yaw, but that was on purpose... It is "interresting" to watch a plane turn right with full left rudder and aileron.

thanks guys,

i've now got clean takeoffs. i had severe left yaw because i needed to trim the rudder slightly right from mechanical center. i discovered this when doing a vertical stall - the plane wanted to yaw left while going straight up.

for the landing right yaw, i did notice that the wheels needed to be toed in. i also took out the tension in the fuel line i put around the axle to limit slip. although it still yaws right slightly, it is much better. i am also getting used to not letting off the elevator flare (all the way) in order to push down a bit on the tail wheel to aid in steering control.

i'm getting more consistent now [sm=lol.gif]