I've been around RC planes for many years (most recently sailplanes and dynamic soaring) but I only recently got back into glow.

I am having major problems controlling my plane (a low-wing Stick taildragger) on the takeoff roll. The plane will make a 90 degree turn to the left at full throttle that is barely correctible.

Is this "normal" for this type of plane? I know some amount of right rudder is necessary on takeoff, but this is truly ridiculous.

Also, could my landing gear/wheels be at fault? There is quite a bit of play in both the main wheels (Du-Bro low-bounce) and the tail gear.

THe plane, for those who were wondering, is a .46 size Sport Stick from Hobby People (pretty good flyer, actually)

Try some toe-in on your wheels. Also, SOME torque to the left is normal. Apply a little right rudder from the start as you roll your throttle.

Please don't take this the wrong way.
Why are you using full throttle to take off.
I bet that plane will take off at half throttle with no problem.
Why are you gunning the engine to full throttle.
If you did that to a car with an oversized engine (rear drive) you would be spinning all over the place.
A plane will not be any different.

Apply throttle slowly and when you get to half, stop
Let the plane build speed. If it needs more speed, then give it a couple of clicks.
You don't need full throttle to take off so don't use it.

Not taking it the wrong way at all! This is exactly the type of advice I need!

The next thing I was going to try was pushing the throttle up gradually and slowly instead of gunning it...Bad habit I picked up from flying electrics.

Thanks!!

What size engine? Full throttle on T/O isn't necessary as Giestware noted.

Engine is an OS .46. I noticed when flying that there isn't much difference between 1/2 throttle and full throttle, but at full there is plenty of power to do most any non-3D manuever. I am not sure if the engine is performing up to snuff, however. It is 20 years old, but had only 10 hours or so of time on it when I took it out of my last glow plane. I took it apart and cleaned it, and am still fine-tuning it.

I've found that for me a little bit of up elvator at the start of takeoff roll seems to keep the tailwheel on the ground and effective until enough air is over the rudder. You'll want to neutralize it quickly though.

My Piper cub .20 is a handful on the ground. As Geistware said I have to roll in to it and then it does`nt handle so bad.

Many items can contribute to this problem:

Try this checklist;

Add 2-4* right thrust.

Use some tubing to eliminate any slop in the wheel bearing surfaces. if flying off grass loose is better, if off hard surface not loose but not tight.

Any slop in a stearable tail wheel will give you grief. Free coaster tailwheels will give you more grief, if you have any crosswind, especially at the initial roll of the take-off and the slowing down of the landing roll.

Technique wise: Start your TO with a slow advance of the throttle with very light up elevator, concentrating on rudder steering. As soon as the model is moving with response to the directional control, go neutral on the elevator to allow the stabilizer to seek the level air stream. Concentrate on keeping straight with rudder. With a good head of steam up, apply a very light up elevator pressure and establish a climb. CONTINUE STEERING WITH RUDDER. USE ONLY ENOUGH AILERON TO MAINTAIN WINGS LEVEL. IF A WING DROPS MUCH USE RUDDER TO PICK IT UP. MAINTAIN ELEVATOR TO KEEP NOSE ATTITUDE DOWN BELOW 15* CLIMB OUT for at least 50 feet after TO. Use of aileron at liftoff or just before or after only creates adverse yaw and causes violent roll tendencies, especially with excessive elevator inputs after TO.

Good straight Take Offs are an art and require good skills. The usual overpowered jump-offs with the left-turn uncontrolled what-cha'call-it maneuvers don't really define the purists' form.

OTOH some of the ARF trainers of today have so much right "rudder" built into the vertical stabilizer that it is difficult to get them to go left. These guys get soloed, never learn to make real take-offs, jump to some hot P-51 and wonder why it was "built wrong"!

Well, there are now two planes to cross off your list. A Texan and a Cub.

Hossfly's advice is excellent. I speak as someone who has caused club members to slide behind their vans when they saw me try to take off. (G) Try this. On a non-busy day at the field and with the understanding of all, set your plane down on the centerline of the runway at the end of the runway. (You want a lot of room.) Stand directly behind the plane. Very slowly open the throttle and concentrate on the alignment of the fuselage. Anticipate any shift and give some rudder as needed. You must be on top of the situation or all is lost. Once the plane veers things will only get worse. It it goes way out of align shut the throttle and try again. Have a spotter stand with you whose duty is to yell "cut" if the plane is wacky. (His brain will be functioning while the pilot's is a little fuzzy! I know.) Take your time and good luck.

> Well, there are now two planes to cross off your list. A Texan and a Cub. <

A Cub is a terrible choice for a trainer and I have not seem many pilots keep them in a straight line on a takeoff. And the Texan, like its full scale version, can show serious vices.

Every plane handles differently even if they are identical planes. Some you can "punch it marge" and some you can't and need to start off slow.

Well everyone assumes that you are well past "step one"...

Step One:

On a lightly inclined (preferably asphalt) location, turn on the TX and RX but not the engine.
Center the controls.
Gently push the plane forward as you stand from behind.

Does the plane veer to one side? If so adjust the tail wheel until the plane stops doing this with the controls centered.

Then move on to the runway test previously stated.

Try holding right rudder to keep take off roll straight, and advance throttle smoothly through takeoff roll. Allow the tail to rise and achieve takeoff speed before you lift it off. This is where you need to apply right rudder to keep it straight. It just takes practice and you will get it.

Check your latteral ballance

You mentioned that there isn't much difference between 1/2 throttle and full throttle.
On most engines this is normal, most of the throttle control is in the low end.
If you have a computer radio you may be able to set a non-linear throttle curve which for one click on the transmitter will move the throttle arm less on the low end and more as you get into the high end.
If you do not have this feature you can do it to some degree mechanically.
Set your end points to max and move your linkage on the servo arm and the throttle arm so you can use all of the available travel.
Next adjust the way the servo arm sits on the servo so the low end is almost straight forward or back depending on your plane.
Each click on the transmitter will move the servo a specific number of degrees, the distance the push rod moves is determined by the length of the servo arm and where the arm is in the arc. As the arc of servo arm approaches 90 degrees to the pushrod the amount of movement on the push rod per click is maximum. If you can get the throttle to fully open when the arm is just past 90 degrees this is the area where each click moves the push rod the most.
Hope this makes some sense, if you want to try to get some RPM change for each click on the throttle you might try messing with it.

All good suggestions, but I say start basic.

with the motor off check to make sure it tracks straight when you push it.

with the motor on as you start the takeoff roll you need to apply a little up elevator, this pushes the tailwheel
down. typically I start with right rudder and up elevator as the plane starts the roll you can reduce both inputs.

The keys are track straight to start with, then right rudder and up elevator, slowly adding power I woould
try idle - 1/2 wait a bit, reduce inputs, full power wait a bit, lift off.

One other learning point also. Torque, by the laws of physics cannot cause a plane to YAW to the left. You are dealing with a phenominon called P-factor.

I took some measurements this morning and discovered that the plane apparently has a considerable amount of LEFT thrust built in.

Not only are the engine mounts off center on the firewall and mounted about 5mm or so to the LEFT of the centerline, from the tips of a 12 inch prop to the wingtips, the distance is almost 1/4 inch GREATER on the right than on the left, indicating a lot of left thrust.

My plan for tonight it to remove the engine and mounts, and shim the left mount with washers until the thrust angle is at least neutralized.

YIKES...

Looking from behind the plane, as an on-board pilot would, does the front of the engine angle to the right or to the left?

Most planes have a degree or two of RIGHT thrust, not left thrust.

Check the angle of the firewall.

I find it hard to believe that the plane was manufactured with left thrust, maybe this merely a problem with the mounts.


If so... washers will tend to wear into the plastic mounts causing a loosening of the mount over time and lessening the effect.

I find it better to sand the mount bottom down, by running the mount on medium sandpaper at a very slight angle (more force on one side really) or for an even quicker solution I use a belt sander or bench grinder to do the work.

This permits me to adjust the thrust line and keep the entire base of the mount in contact with the firewall as it should.

Of course things are different with metal mounts....

Looking at the engine from the pilot's perspective, the engine is angled to the left, and is off-center towards the left. Bad, bad, bad...

Good suggestion re sanding the mount. They are plastic. I will try tonight.

Soresoar, what kind of plane do you have?

Andy

What is "P-Factor"?

P-Factor is an aerodynamic effect that causes propellor-driven planes to yaw when they are flown at high power and low speed (takeoff and climbout, for example.)
At low speeds, the plane flies at a substantial angle of attack, and so the airflow is not parallel to the plane's axis. Relative to the plane, the airflow is directed several degrees upwards. Now the prop axis is normally parallel to the plane's axis. As the prop rotates, on one side the blades are travelling upwards and on the other side they are travelling downwards. (On most planes, the prop turns clockwise, as seen from behind, so the left side goes up and the right side goes down.)

The upwards angle of the airflow causes the downward (right) side of the prop to have a greater airspeed and angle of attack than the upward (left) side. So the downward (right) side of the prop generates more thrust. Pull harder on the right side of the plane than on the left and the plane will yaw to the left.

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.

The other factor that requires right rudder on takeoff (in planes with clockwise props) is spiral propwash. The sideways component of the spiral propwash strikes the vertical stabilizer from the left (in conventional single engine configurations), also causing a yaw to the left. In general, the spiral propwash effect is a lot stronger than P-factor.

You also need right aileron to keep the plane straight to counteract the rotational torque from the engine(s).

This is soresoar, logging in from a different computer -

The plane is a Sportsman Aviation (Hobby People) Sport Stik .40. I tried easing up the throttle to take off and it was even worse. Consensus at the field is that my tail gear is a piece and needs to be replaced. I have a new one on order.

We tried an experiment at the field, which was to have a helper hold the plane while I gunned it to WOT, and then let go. At that point, there was airflow over the rudder and the takeoff roll was perfect, requiring just a touch of right rudder.

The major problem time is above the speed when the miserable tail wheel is effective, and below the speed when the rudder is effective.