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        Is there such a thing as motor being too powerful/prop being too big?

#1 simingx Jan 26, 2003 10:41 PM

Is there such a thing as motor being too powerful/prop being too big?
 
I installed a Mega 16/15/5 with a Master Airscrew 7x4 (gas) prop on my Wattage F-22, gave it a launch... and round it went, rolling RIGHT INTO the ground 2 meters in front of me! No amount of right aileron could save it :(
It has a broken stabilator now... I wonder if the torque produced was too much for it to handle?
The motor is turning the prop at about 12,500 RPM.

#2 Andy W Jan 26, 2003 10:45 PM

Sure, it can happen.
..a

#3 ShredAir Jan 27, 2003 12:40 AM

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Sure. If the tail wags the dog or the prop spins the plane... :o)

Dieter Mahlein,
http://shredair.com

#4 shaneyee Jan 27, 2003 01:20 AM

Sounds like what happened to my PicoJet the first time I flew. I launched it upwards with a moderate throw like a parkflyer and it stalled and ate dirt so fast I couldnt even blink -just a few metres in front of me. Dont think it was the torque but rather a stall. You have to throw it hard and straight ahead. Next time we fly and if KP brings the Picojet around .. I'll show you how I throw it. You use as much strenght as you would throwing a football or a softball.

Shane

ShredAir: Thats really outrageous...

#5 vintage1 Jan 27, 2003 04:45 AM

Yup. If the plane stalls at full throttle, torque nearly always turns it against prop rotation under power, so it looks like a nasty tip stall whether it is or not. The key is to have the model going fast enough so the ailerons actually work :)


You aren't going to ever run into torque problems on direct drive.

However, if you have put in a heavier or more powerful motor, sometimes its wise to re-check downthrust/upthrust and CG.

#6 tim hooper Jan 27, 2003 07:10 AM

I think the potential problem is worse on a pusher set-up, as there's no propwash over over the control surfaces to give authority at low airspeeds.

tim

#7 Sparky Paul Jan 27, 2003 10:47 AM

Prop too big, motor smells bad after flight.
F-22.. BAD airplane for models!
The verticals get blanketed by the large wing.
Unless you have a LOT of speed all the time, it will do exactly what you saw, all the time.

#8 DaveW Jan 27, 2003 10:09 PM

Yes, the torque of a powerful motor can sure do that.

As Sparky said, the problem is even worse in pushers as there is no prop blast over the control surfaces to help at low ( launch ) speed.

When you go into high power systems, you NEED to have things like dual rates on the transmitter so you can have large throws for low speeds and switch to smaller ones for flying. As you found out, "flying" throws may not be able to handle the takeoff torque.

Try launching at partial throttle and throwing it as hard as you can.

Hope its repairable.

Dave

#9 mkirsch1 Jan 28, 2003 07:28 AM

Have you checked to make sure your ailerons weren't reversed? If the ailerons were reversed, the more you tried to correct the roll, the worse you made it.

#10 Thomas Nelson Jan 28, 2003 07:36 PM

I have a similar setup on my smallish pusher ...
 
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Quote:

Originally posted by simingx
I installed a Mega 16/15/5 with a Master Airscrew 7x4 (gas) prop on my Wattage F-22, gave it a launch... and round it went, rolling RIGHT INTO the ground 2 meters in front of me! No amount of right aileron could save it :(
It has a broken stabilator now... I wonder if the torque produced was too much for it to handle?
The motor is turning the prop at about 12,500 RPM.

A few less rpm. Same prop - in fact I've used an 8x3.8 as well. 24" WS, 20.6 ounce AUW. Same pusher config. Same stabilator control - no ailerons. No right/down thrust. Approximately 17 ounces static thrust. Never a hint of torque problems during launch. And I don't heave it nearly as hard as my TwinJet.

A maneuver I enjoy watching (more than flying) is to do a slow circuit at eye level & at high AoA and then punch it for a steep, slow climbout. Again, never experienced any appreciable torque reaction with this application of full throttle.

I dunno if this helps or not. But I plan to use EXACTLY the same motor/prop combo as you in the next iteration of my '27, and nothing I had read or experienced to THIS point was suggesting that I would be making a mistake.

I'm always ready to learn, though! If others think this really is a torque problem, I may need to rethink things.


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