Torque Roll

[Nigel Heather]

Hi, this question is something that got raised when discussing funfighters but I have posted here as it is a more general issue.

 

I want to build an electric powered funfighter, they are usually just aileron and elevator, but for EP I was advised to add rudder because of the torque roll.

 

So some questions:

 

• Why would torque roll be an issue for electric power but not IC power
• How would rudder help - these are hand launched - with undercarriage it should exhibit as turning to one side so you would correc5 with rudder but with a hand launch wouldn’t it roll, to be corrected with aileron
• And would you not address this with side and down thrust.

 

Would someone explain what happens to me.
 

Cheers,

 

Nigel

[Outrunner]

Nigel, that sounds a load of rubbish to me. I have an electric Balsacraft Spitfire and a Slec Coyote also electric that have no rudders and both hand launched and excellent handling. Why should being electric powered make any difference to flight characteristics? 

[Shaun Walsh]

Can't see how IC or electric power would make a difference to a models susceptibility to torque roll. The only time I've ever seen a model suffer badly from torque roll was many years ago when a friend of mine put a 60 two stroke in a KK Outlaw, it had to be hand launched at half throttle otherwise it would roll wildly in the opposite direction to the prop, once you built up some airspeed you could throttle up and keep control but it would spin much quicker to port than starboard.

[leccyflyer]

Never noticed this being an issue with any of my funfighters, when they were IC powered, or after they were converted to electric flight. The Spitfire didn't have a rudder, The Bf109E did have a rudder, but they both launched the same.  TBH I think you are seriously overthinking this. They are simple models that are made to be handlaunched and thousands of them get handlaunched without any obvious issues.

 

An exception that I've noted in this type of model- don't know why - is the Ripmax Bf109E.  Our Ripmax Spitfire and Ripmax Mustangs all go away dead straight from a handlaunch. The Ripmax Bf109E on the other hand definitely rolls to the left on launching and both myself and my pal Derek launch the 109 with a bootful of right rudder to counteract that, having been caught out early on.

[Simon Chaddock]

It does seem odd to use rudder to correct torque roll in an hand launched plane if it has ailerons as well.

In terms of roll control the rudder only has a secondary effect whereas the ailerons are primarily for roll.

On the other hand a ground take off with undercarriage the torque and "P" yaw effects can only be controlled with the rudder until the plane is actually flying.

 

Just an observation from someone who due to field conditions has to hand launch practically everything whether or not it has a rudder.😉   

[PatMc]

1 hour ago, leccyflyer said:

An exception that I've noted in this type of model- don't know why - is the Ripmax Bf109E.  Our Ripmax Spitfire and Ripmax Mustangs all go away dead straight from a handlaunch. The Ripmax Bf109E on the other hand definitely rolls to the left on launching and both myself and my pal Derek launch the 109 with a bootful of right rudder to counteract that, having been caught out early on.

Some marks of the full size Bf109 fin & rudder had an asymmetric airfoil with the camber on the right side to counteract torque roll. The characteristic may have had something to do with the higher tailplane position when compared with other fairly similar layout fighters of the time.

A number of full size aircraft to have the fin mounted at a slight angle or the rudder permanently offset for the same reason.  

[PatMc]

51 minutes ago, Simon Chaddock said:

It does seem odd to use rudder to correct torque roll in an hand launched plane if it has ailerons as well.

In terms of roll control the rudder only has a secondary effect whereas the ailerons are primarily for roll.

On the other hand a ground take off with undercarriage the torque and "P" yaw effects can only be controlled with the rudder until the plane is actually flying.

 

Just an observation from someone who due to field conditions has to hand launch practically everything whether or not it has a rudder.😉   

The main problem isn't actually "torque roll", in fact its a yaw caused by it the rotating slipstream striking one side of the fin.    

Edited June 27, 2023 by PatMc

[Nigel Heather]

7 hours ago, leccyflyer said:

TBH I think you are seriously overthinking this. They are simple models that are made to be handlaunched and thousands of them get handlaunched without any obvious issues.

To be fair, I don’t think I am over-thinking this.  I had no intention of fitting a rudder - it was the manufacturer who advised that as I was going with EP I should fit a rudder because of the torque roll when launching.  I didn’t understand why an EP would torque roll when an IC would not, nor did I understand how a rudder would help torque roll when hand launching - so I came here for a second opinion - how is that over-thinking.

 

Cheers,

 

Nigel

[Nigel Heather]

5 hours ago, PatMc said:

Some marks of the full size Bf109 fin & rudder had an asymmetric airfoil with the camber on the right side to counteract torque roll. The characteristic may have had something to do with the higher tailplane position when compared with other fairly similar layout fighters of the time.

A number of full size aircraft to have the fin mounted at a slight angle or the rudder permanently offset for the same reason.  

 

5 hours ago, PatMc said:

The main problem isn't actually "torque roll", in fact its a yaw caused by it the rotating slipstream striking one side of the fin.    

 

These make a little more sense.  It is a BF109 that I have gone for and both of these suggestions make more sense than a torque roll.  But even so, why would either of those be a problem with EP but not IC.

[paul devereux]

6 hours ago, PatMc said:

The main problem isn't actually "torque roll", in fact its a yaw caused by it the rotating slipstream striking one side of the fin.    

Why would that be a thing with EP but not with IC? Edit: just saw Nigel posted the same question. The only setup difference I can imagine is that the EP prop is different, but I still can't see how the airflow would have a different effect on the plane.

Edited June 28, 2023 by paul devereux

[MattyB]

Agreed, the only reason I can think of for the torque effect being greater on the EP va IC model is if it uses a significantly bigger and heavier prop. Is that the case based on the powertrain recommendations for your model, @Nigel Heather? Even if it is, I still call the manufacturers recommendation as a load of rubbish tbh; I’ve never seen a fun fighter that can’t be reliably hand launched with a bit of practice, irrelevant of the whether it has a rudder or the powertrain used.

 

Edited June 28, 2023 by MattyB

[J D 8]

 At take off with a hand launched model the reason having a working rudder can help with a flight deviation [ caused by wind gust, bad launch ] is because it is in the slipstream from the prop, where as the ailerons are not so effective because the model has yet to reach flying speed.  A good straight launch is all most need.

[leccyflyer]

1 hour ago, Nigel Heather said:

To be fair, I don’t think I am over-thinking this.  I had no intention of fitting a rudder - it was the manufacturer who advised that as I was going with EP I should fit a rudder because of the torque roll when launching.  I didn’t understand why an EP would torque roll when an IC would not, nor did I understand how a rudder would help torque roll when hand launching - so I came here for a second opinion - how is that over-thinking.

 

Cheers,

 

Nigel

Aaah, you didn't say it was the manufacturer's recommendation. Might be worth asking them for clarification.

 

As Pat has pointed out the term torque roll is something of a misnomer, one of long discussion in online fora for years, what is being described is due to the rotational slipstream from a large prop acting on the fin which is a yaw to the left in conventional airframes. It's conceivable, even likely, that an electric powered funfighter will have at least a 10x7" prop, or even an 11x7" prop, if fitted with a "typical" outrunner. In it's IOC guise it will probably have had something like a 9x6" prop if fitted with a .25 cu in glow engine.  Coupled with the smaller fin on the Bf109, compared to the Spitfire, that might provide some explanation. However, like I said, I didn't notice any difference of adverse effects when moving up from IC to a brushless motor onb my Cambrian Bf109e.

 

 

[leccyflyer]

22 minutes ago, MattyB said:

Agreed, the only reason I can think of for the torque effect being greater on the EP va IC model is if it uses a significantly bigger and heavier prop. Is that the case based on the powertrain recommendations for your model, @Nigel Heather? Even if it is, I still call the manufacturers recommendation as a load of rubbish tbh; I’ve never seen a fun fighter that can’t be reliably hand launched with a bit of practice, irrelevant of the whether it has a rudder or the powertrain used.

 

Well you say that, Matty,  but in your avatar picture you are clearly chucking that poor little funfighter directly at the ground! 😉

 

You posted while I was typing and there could possibly be something in prop size, the only thing is whether that is due to the specific airframe and that might be related to the size of the fin?

[Jon H]

Given how small, light, and inexpensive servos are these days i would fit the rudder. Its better to have it and not really need it than to need it and not have it. 

[leccyflyer]

Agreed - it's nice to have a rudder anyway and a 9g servo and lightweight pushrod isn't going to hurt.

[Jon H]

11 minutes ago, leccyflyer said:

Agreed - it's nice to have a rudder anyway and a 9g servo and lightweight pushrod isn't going to hurt.

 

Well exactly. i use my rudder almost as much as the ailerons and elevator so i would rather have it

[MattyB]

1 hour ago, leccyflyer said:

Well you say that, Matty,  but in your avatar picture you are clearly chucking that poor little funfighter directly at the ground! 😉

 

 

Torque roll was definitely not a problem in that case - that was my old Paul Janssen's PSS Macchi 202 Folgore. It was the original proto built by Paul and flew absolutely beautifully; now sadly sold on as I no longer had the room for it, though I do have a Janssen's Spit fuselage in the loft somewhere for when I retire...!

 

 

Edited June 28, 2023 by MattyB

[PatMc]

3 hours ago, paul devereux said:

Why would that be a thing with EP but not with IC? Edit: just saw Nigel posted the same question. The only setup difference I can imagine is that the EP prop is different, but I still can't see how the airflow would have a different effect on the plane.

Sorry Paul, I didn't make myself clear. I wasn't refering to any difference between EP & IC but, as Leccy has pointed out, to the misuse of the term "torque roll". 

[PatMc]

There's IC, EP & BS. When folk who primarily fly IC give advice on EP they often include BS in large dollops. 😁

[Chris Walby]

Difference between IC and EP...well IC will be ticking over a 2000 rpm and WOT at 10,000 so difference of 8,000 and most like launched at WOT. EP typically 4S and 1100KV so off load motor speed of 16,280 rpm and probably around 15,000 rpm with the prop on. Hence the prop will be accelerated by nearly 50% more rpm.

 

EP most likely launched before the motor has got to full speed so the accelerating prop has a greater torque effect with EP than IC hence the greater tendency to roll. With very over powered funfighters etc I have found launch at less than wot and waiting until the motor has stopped accelerating helps with the launch.

 

Open to any other theories though 🙂 

[leccyflyer]

Personally I pretty much never launch at full throttle - drives Derek mad, as he's usually doing the chucking - I power up to about 3/4 throttle then pour on the coals as I'm climbing out.

 

That's a superb video Matty - love it. 😎 Interesting how the glider completely disappeared when it entered that rear 3/4 end view going away, then reappeared as it turned.

[leccyflyer]

2 hours ago, Jon - Laser Engines said:

 

Well exactly. i use my rudder almost as much as the ailerons and elevator so i would rather have it

I find I'm often using rudder even when there isn't one there. Old habits die hard. 🙂

[Martin Harris - Moderator]

16 minutes ago, Chris Walby said:

 

 

Open to any other theories though 🙂 

One factor that comes to mind (although the effect may be debatable) is that in a typical outrunner there is a significant rotating mass at a larger diameter than an IC engine’s rotating components. Maybe where the idea of EP producing more torque effects came from?

 

At model sizes I would agree that helix effects probably outweigh torque effects but ask a Sopwith Camel or high powered WW2 piston engined aircraft’s pilot whether they are significant!

Edited June 28, 2023 by Martin Harris - Moderator

[PatMc]

6 minutes ago, Chris Walby said:

Difference between IC and EP...well IC will be ticking over a 2000 rpm and WOT at 10,000 so difference of 8,000 and most like launched at WOT. EP typically 4S and 1100KV so off load motor speed of 16,280 rpm and probably around 15,000 rpm with the prop on. Hence the prop will be accelerated by nearly 50% more rpm.

 

EP most likely launched before the motor has got to full speed so the accelerating prop has a greater torque effect with EP than IC hence the greater tendency to roll. With very over powered funfighters etc I have found launch at less than wot and waiting until the motor has stopped accelerating helps with the launch.

 

Open to any other theories though 🙂 

For the same power, torque is greater aat lower rpm.