• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Help! FT Simple Cub

#1
Just completed my build of the Simple Cub this morning (1st ever build) and took it out this evening for a little testing. Tried taxiing around the tennis court and was unable to control it. If left alone, it will take a hard right turn. With full left rudder, it will slowly turn to the left, then wants to stay to the left. Adjusting trim did not correct the problem. Tried getting the tail off the ground, but it did the same thing. I'm at a loss as to what to look at/for to correct the problem. The only thing I can see out of alignment is the horizontal stabilizer is shifted about 1/8" to the left when looking from the front of the plane.

Any help anyone can provide on how to troubleshoot this will be gratefully accepted.
 

Ketchup

4s mini mustang
#2
The problem you have is called a ground loop. It happens to all planes that are in tail dragger configuration and it happens because the main gear is in front of the cg. I’m not exactly sure how to explain the rest (I hope somebody else can), but just know that this is normal. If the problem gets severe though, check to see if your wheels are aligned.
 
Last edited:
#3
Severe. is what I would call it. If you give enough throttle to really start rolling, but before the tail lifts, it will turn tight to the right. This happens before you can do anything. It probably happens in about 4 or 5 feet.

I will check the wheel alignment.

Thanks
 
#5
Checked the wheel alignment and found a little bit of toe-out. Tweaked the axels to have a tiny bit of toe-in. Will reports results when I get a chance to test it tomorrow. Thanks for the help.
 

Arcfyre

Well-known member
#6
Do the wheels spin freely on the axle? If the right wheel has more rolling resistance than the left, it could be acting like a brake, causing the plane to turn.

You may also try a steerable tailwheel mod, I have done this to all of my taildragger models with great success. It makes ground handling much easier and is very simple to do.

I use a slightly larger version of this (I used thicker wire and a 30mm diameter wheel) on my cub and storch and they love it:

https://www.flitetest.com/articles/steerable-tailwheel-for-your-mighty-mini
 

Hai-Lee

Old and Bold RC PILOT
#7
You definitely need to assure that the wheels are free to rotate and that they track straight.

You also need to assure that the Vertical fin is properly aligned and that you have sufficient rudder travel.

Finally you need to know that when taxiing you should do so with full "UP" elevator so that the tail does not lift or generate any lift that might lighten the load on the tail skid or wheel. With the skid/wheel firmly planted the plane is dragged straight unless forced sideways by the rudder forces or even "P" factor. Side thrust should remove all "P" factor effects!!

With the tail held down the plane should be more easily steered. If taking off Keep the tail firmly planted until there is a reasonable amount of forward speed so that when you lift the tail the rudder has sufficient effect to control the plane's direction.

It works for me and my students!

Have fun!
 
#8
Stability this morning was much better, but still not as good as I wanted. I used some small washers that just fit the axel, 3 sizes of heat shrink to build up the axel to match wheel size, and modified as shown in the attached photos. The wheels are very stable and do not vibrate or shift side to side. Plane stability while taxiing is greatly improved. I assign the remaining instability to pilot error.

Thanks for all the help.
Jake
IMG_1405.jpg IMG_1406.jpg IMG_1409.jpg IMG_1410.jpg