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Nov 30, 2019, 09:00 AM
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Discussion

EDF torque roll?


Newbie question. Building large B2 as a cruiser, likely 4 fans. Coming from a prop world, I would ensure half are rotating clockwise and the other half counter. Is there any such need in EDF? I am assuming so, but not seeing the right choices. Thanks.
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Nov 30, 2019, 11:29 AM
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Ed Waldrep's Avatar
The do have some torque, but not enough to notice usually. Opposite direction fans are rare, I can only think of one from 20 something years ago, and it had two rotors rotating in opposite directions.

I had a 90mm F-18 that was a kit and it had huge inlets, they were 178% of the fan swept area, which is really much larger than you want, but this was the days before lipos and I wanted to make sure the fan had plenty of air. The plane had full inlet ducting and it got plenty of air.

I would make a speed run, pull vertical and stay there and as the model was slowing down I'd cut all power, and when it was just about to stop going up, if I hit full throttle, the jet would torque roll about 3/4 of the way around and then flop over as it fell. It was kinda cool but not scale at all.

Later I rebuilt most of the fuselage of that jet after a pcm lockout and re-designed the ducting to scale sized inlets that were smaller at 100% Fan Swept Area. I don't think it would do the torque roll anymore but it's been 12 or so years ago so my recall is a bit fuzzy.

The big thing to worry about with a B-2 is getting the nose to yaw into a turn. I saw video of a big 4 fan model recently and I noticed the nose was favoring the outside of the turn, the jet was slipping. I don't know if they needed more "drageron" on the inside wing or not, but probably did.

You could modify the plans with a Prandtle type wing but that's a bit of work.
Nov 30, 2019, 12:06 PM
Registered User
4 smaller fans have less net torque effect than the same thrust produced from a single big one so the answer is no except, as ED points out, under condition of a full stall.

I suspect the complex aerodynamics of the B2 will be much more significant than the torque effect from the fans.
Nov 30, 2019, 01:39 PM
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Comrade_D's Avatar
There are more left turning tendencies in props then just torque.
Torque of the EDFs is pretty much negligible, but it’s there.
Nov 30, 2019, 06:14 PM
Classic jets rule
AIR SALLY's Avatar
The stators in a fan help to negate torque or "P" factor. If you use outrunner motors you may cause some torque effect ... so just plan on inrunner motors.
Nov 30, 2019, 07:35 PM
jofro
I find there is still considerable torque roll with EDF models, the more power the the worse it gets.
Easy to to take control while having both hands on the TX but different story when self hand launching EDF jet, I'm learning at the moment with my latest creation of one of the smallest twin powered one. "Mini Twin Widow"
It would be wonderful if there was a counter rotating unit avail to compensate for twin set ups as this model.
Nov 30, 2019, 08:09 PM
If it flies, I can crash it.
rocketsled666's Avatar
Very few multi-engine full-scale aircraft have counter rotating props. The P-38 is famous for it. But I only barely remember of a couple of others. Building engines and props that turn the other way around adds cost both to the original manufacturing and also to maintenance. And aerodynamically it's not really all that critical.

But for for model airplanes motor torque can be a significant issue (because we're generally overpowered compared to scale). EDFs included. If they're not flying fast enough for control surfaces to be effective in countering the motor torque, the plane will roll in response to that torque. I have a couple of larger prop planes that will lift a wheel if I jam the throttle to WOT while the plane is sitting on the ground. Hand launching a larger EDF can be challenging because of this, too. You don't necessarily want to toss it at WOT. My old Horizon FJ2 Fury is pretty much impossible to hand launch at WOT, it'll roll inverted before it's going fast enough to fly. But on wheels I can slam the throttle open and it doesn't care at all, the motor torque isn't enough to be a problem on the roll out and once the plane is moving fast enough it doesn't matter.
Nov 30, 2019, 08:36 PM
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Comrade_D's Avatar
If you can’t manage torque of an EDF — you should be doing model trains instead.

Just saying...
Dec 01, 2019, 03:25 AM
jofro
Just another useful post from a "Comrade" !
Dec 01, 2019, 09:19 AM
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Thread OP

Thanks


Super helpful suggestions/info/explanations. Thanks for the effort - is why I love this group.
Dec 01, 2019, 04:57 PM
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Comrade_D's Avatar
One plane that I can really feel any torque on — is a fiberglass Avanti S. It has a larger JP Hobby metal fan and a good size outrunner.

To demonstrate, I do a slow, minimum airspeed, 15 degree of flaps pass over the runway and then rapidly apply max thrust and watch airplane bank a few degrees to the left.
Dec 01, 2019, 05:28 PM
jofro
Quote:
Originally Posted by Comrade_D
If you canít manage torque of an EDF ó you should be doing model trains instead.

Just saying...
Comrade, you can tell me anything about "torque rolls", just one of my RC daily specialty I start first thing in the morn.
Dec 02, 2019, 03:12 PM
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Comrade_D's Avatar
Sorry. I don’t classify those as airplanes.
Might as well, staple a picture of an airplane to a string and dangle it off the building.
Dec 02, 2019, 04:46 PM
If it flies, I can crash it.
rocketsled666's Avatar
General definition of "Airplane": any of a class of craft with fixed wings propelled through the air by a propeller, jet or gravity, which is supported in flight by the flow of air over the wings.

So when they're hovering, they're not airplanes (neither is any 3D aircraft). But on the way to a hover and when landing (assuming no hand launch/catch while vertical) they are airplanes.
Dec 02, 2019, 05:04 PM
Pro Hoarder
turbonut's Avatar
Well I dont see what they have to do with and EDF torque roll as the OP asked..But that is just me
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