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FT Racer uncontrollable

samwise

Junior Member
#1
I took my FT Racer out for a maiden today and it was uncontrollable. It was fine on the straightaways but upon banking to the left it uncontrollably continued to bank to the left until it was vertical and fell out of the sky. I saved it a couple of times and tweaked my DR/Expo settings several times and it all ended in a dirt nap. Please help! I love the look of this plane and I am a decent pilot, but if it doesn't do the business then its worthless. Thanks in advance and i'm sure I have broken forum rules as this is my first post. Sorry.

-SL
 

samwise

Junior Member
#3
I really wasn't using all that much elevator for the turn as I was planning on it being a gentle bank to the left, but as I said the left wing just dropped. The deflection on full rates goes all the way to the limit of the foam cutout. ftracerelevator.jpg
 

samwise

Junior Member
#6
Possible Motor Torque

I am running a Turnigy Aerodrive D2838/8 1100KV spinning an APC 8x6E. When it does decide to pitch all the way over it certainly always chooses to go opposite of the props direction. There isn't much space to move the battery left or right. I guess I will try moving the battery all the way to the right and reduce elevator throw.
 

samwise

Junior Member
#7
Well I went out and flew (read: crashed) the plane again and it's definitely torque. Anything above 1/4 throttle and the left wing points toward the ground with the rest to follow. Its not like i'm running some crazy prop, just the one that they suggested. I wasn't bashing the throttle around either. Decided to tear her to pieces and salvage the electronics while they still worked. Too bad such a beautiful plane flew like a limp noodle. Thanks for trying to help guys. Back to my RCPowers Extra...
 

samwise

Junior Member
#10
Nope! Was that in the build video? I just centered it. Second try I put the battery all the way to the right. And had a bunch of trim and low throttle it pitched right from trim and anything above low throttle she pitched all the way left. For future reference how much offset is needed?
 

nerdnic

nerdnic.com
Mentor
#11
That's very odd. I've never had that issue with any of the FT planes and I've run small and overly huge motors on all of them. If you are willing to give it another go, try a FT Spitfire, it's a much better plane than the racer.
 

JohnRambozo

Posted a thousand or more times
#13
I just checked the build video and they made sure to center the wings. Perhaps the motor you're using has too much torque for centered wings. When they launch it in the video it does a slight bit of roll before it picks up speed as with any plane, even the might spitfire. But there are no issues after that.
 

samwise

Junior Member
#14
Might be the motor during acceleration but it seemed like even at constant throttle settings above half it would still roll, just less violently. A prop at constant angular velocity should provide the same torque for any motor. That being said it's pretty odd it was so unflyable with the recommended prop. Is the spit a good option for something to try next? Will it handle my apparently overpowered motor?
 

Foam Addict

Squirrel member
#15
Was the motor put on straight, or did it have a slight right or left angle?
A slight right tilt is excellent, a left tilt is often catastrophic.

Also, if your rudder trim was off to the left, the motor torque would be amplified, and that would cause the same problem as you experienced.
 

nerdnic

nerdnic.com
Mentor
#16
Might be the motor during acceleration but it seemed like even at constant throttle settings above half it would still roll, just less violently. A prop at constant angular velocity should provide the same torque for any motor. That being said it's pretty odd it was so unflyable with the recommended prop. Is the spit a good option for something to try next? Will it handle my apparently overpowered motor?
I've had my spit near 100mph with no issues, so I think you're fine with you're 28/38 motor.
 

samwise

Junior Member
#17
Rudder and motor were straight. Thought about trying to change the motor angle but I decided to try other things. How much angle would you suggest? An extra washer on one side of the mount or more than that?
 
#19
When you built it, did you remember to offset the wing to correct for the motor torque?
It's the old speedster, not the racer/ slinger that has the wing offset.

I don't have any clever ideas beyond that, since the racer is not overly notorious for it's torque roll. Of course you'll have to real wizh its relatively high base speed below which some controls may become unresponsive
 
#20
Usually if you are having problems with torque, a little right hand thrust will do the trick. As mentioned earlier, a couple of washers under the left side of the motor mount will usually get it. Another possibility is wing incidence. As you bank into a turn, the inside wing slows down. When you execute a slow turn, you have to compensate for the reduced lift with quite a bit of elevator. So you effectively have shorter wings (the "lifting" length of the wing is always measured parallel to the horizon) and a high angle of attack. If there is any warp or twist to the wing, or if the wing incidence is all-around too high you get into a tip stall. The inside wing tip is just flying too slowly for the high alpha. So, it loses lift first causing it to drop before the outside wing loses lift also. That sounds like what you were experiencing.

Finally, there is down thrust. With a "high lift wing", that is one that generates a lot of lift per inch, often the wing climbs so quickly that it leaves the tail behind. Imagine holding your airplane level by the wing balanced right at the center of gravity. Now imagine rapidly lifting it straight up twenty or thirty feet. The wind drag pushing on the top of the horizontal stabilizer would cause the tail to "weather-vane" down in relation to the wings. This is more or less what can happen with wings that lift efficiently at low speeds. Especially if the motor is really powerful. The fix is to add a couple of degrees of down thrust to the motor in the form of a couple of washers behind the top of the motor mount. That way, as the thrust and thereby speed and lift increase, the motor is effectively pulling the nose down even as the tail is trying to pull the nose up. Balance is good!

Why that matters in a turn not always obvious. But it gets back to the tip stall problem. If the plane has a tendency to pitch up, and the wing incidence is too high (or twisted), and there is no compensation for torque, you will have a perfect storm of conditions that combine to make flying no fun.

In short (too late!), if a plane won't behave its self, check wing incidence (angle of wing chord center-line relative to H-Stab center-line). 1 to 2 degrees is usually adequate. Then experiment with thrust angle. I find that with planes that are designed to glide well on little or no thrust, two washers behind the left upper corner (facing into the prop) of the motor mount, three or four under the upper right, two under the lower right and none under the lower left, often gives just the right balance of forces. the motor should be pointed to the right and down at the same time. You will have to experiment, its part of the fun.

Good luck!