So I recently put together one of my first speed-build kits from flite test, an FT Viggen. I was super excited to get it in the air using the 70mm edf setup from Grayson hobbies. When I finally got out to a field by my house to fly it, I ended up crashing and wrecking the airframe on takeoff. Shortly after takeoff, my Viggen rolled twice to the right, then spiked into the ground. When I reached it, I found that the edf had seperated form the mounts, and I assumed that this was what caused the problem. So I rebuilt the plane from scratch (with the same electronics) and got back out to the field, only to have it perform another uncommanded roll and crash on takeoff, however this time the mounts and airframe were still intact. I was wondering if anyone else has had this kind of problem and how I might be able to fix it (I couldn't find anything like this anywhere not the forums). By the way, my transmitter is the fs-t6 from fly-sky.
FT Viggen Crash-Causing Problem
- Thread starter Nsims4400
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- crash problem speed-build viggen
So I recently put together one of my first speed-build kits from flite test, an FT Viggen. I was super excited to get it in the air using the 70mm edf setup from Grayson hobbies. When I finally got out to a field by my house to fly it, I ended up crashing and wrecking the airframe on takeoff. Shortly after takeoff, my Viggen rolled twice to the right, then spiked into the ground. When I reached it, I found that the edf had seperated form the mounts, and I assumed that this was what caused the problem. So I rebuilt the plane from scratch (with the same electronics) and got back out to the field, only to have it perform another uncommanded roll and crash on takeoff, however this time the mounts and airframe were still intact. I was wondering if anyone else has had this kind of problem and how I might be able to fix it (I couldn't find anything like this anywhere not the forums). By the way, my transmitter is the fs-t6 from fly-sky.
Have you flown RC long? What flitetest planes have you flown before the viggen?
Sounds like too much throws or reversed elevons. I just built and maidened a speed build version myself and even while testing it on 3s, which was way underpowered (1kg auw) and want enough to get airborne, it was still really stable and controllable.
If the throws are correct then I don't know what could have cause the problem. The torque from the fan shouldn't really be enough to roll the airplane that fast. Were your trims neutral when you launched the plane?
Is your tail warped?
I have a 90 mm edf in mine and have never had any torque issues. Make sure the wings aren't warped and quadruple check your control directions. The Viggen is a very docile flyer. Since you've been flying for 2 years, I'm sure its not a "newbie" issue. Sounds like something is definitely amiss!
My wing surface was flat and i checked my rail with a 90 degree angle. My trims were completely neutral at launch as well. If anyone would like to see the video (I can't post it) please feel free to email me at nsimmons4400@gmail.com
How did you connect the aileron servos? Y cable or dual aileron setup? Did you double check the mixing on the TX if you setup for dual aileron to ensure you have the directions correct -- no reversing needed, etc? When you give full left roll, how much does the left aileron travel up vs the right aileron travel down? What about right full roll?
Oops... I forgot that the Viggen is a elevon plane! My only question next is if the plane is balanced on it's long/roll axis? Seems odd for an EDF to have such a roll tendency if all the surfaces are neutral/straight, and you've verified the elevon control directions and mixing is correct. I've had fixed wing planes behave oddly, acting out of trim on the roll axis, when the CG between the left and right was off enough and I had to land and shift the battery from one side to the other a bit more.
I've used an even more powerful EDF than that grayson hobby set up and have had no issues with torque roll on the Viggen, and on 4s too. Can you post a video of your control surfaces with coordinated info on what your stick movement looks like?
The only things that would explain the behavior you're seeing is:
1. Setting the trim way off
2. Tail heavy
3. Control surfaces set wrong
4. Your build came out drastically disproportional
The only things that would explain the behavior you're seeing is:
1. Setting the trim way off
2. Tail heavy
3. Control surfaces set wrong
4. Your build came out drastically disproportional
Unfortunately I cannot uploa a video of the control surface due to the limitations of the device I'm using, and I have already ruled this out as a problem. However, I think the cg might be the issue. How far off would the cg have to be to cause the plane to roll drastically?
That's a hard question to answer, but a cg that is too far aft will make a plane do very squirrelly things. The recommended cg is 5.25" (133 mm) forward of the leading edge of the rudder. Check to see if that matches your plane's cg.
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