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Handed props?


chris evans 9
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Hi folks, I am currently building an "AV10 Bronco " with hot wire cut foam. Span 0.950 m.  to my own design. I will use handed props but I am wondering which goes where?  Is there a specific side for the different rotations ? for example: which side should I place the Counter clockwise prop?

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In all honesty i wouldnt bother wasting time with it. Torque swing on model twins is not a big deal and you just make your life more difficult with prop selection. Admittedly its easier with electric, and the variety of props is better, but it will not make a significant difference to the model. 

 

Over the years i have operated/beg/stolen/borrowed at least 7 twin and 1 4 engine model. All of them had same rotation props and none of them gave trouble. 

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IMHO there is another issue to consider.

You say you are building your plane out of hot wire cut foam so I presume it will a 'lightweight' rather than a 'heavyweight'.

You only have to look at full size to find that really high power twins (eg DH Sea Hornet, Grumman Tiger Cat) used handed props that rotated inwards over the top. This was done primarily for a benefit in single engine operation but it also meant that a recovery anywhere near the stall under power was much safer.

So the question is will your 'light weight' twin be in the really high power category bearing mind that most RC planes are likely to have a higher thrust to weight and thus motor torque than full size. Electric in particular can generate high torque virtually instantly and well before the plane's aerodynamic control has caught up.

If you can find suitable handed props I would suggest you fit them.

 

As a builder of some lightweight scale RC 'twins' I have more than once had to apply full power in a low and slow situation but was safe in the knowledge that the limited aileron control would not be aggravated by any net motor torque.

 

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The best place to find handed props for electric is for quadcopters and the bonus is you get two sets. After saying that I have built several twins and fours and I didn't see any difference between either set up, with electric you are unlikely  to have one side fail,which is as Jon hinted is the real reason for handed, but it is so easy change motor direction, why not?

Edited by john davidson 1
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  • 3 weeks later...
On 13/08/2021 at 20:54, Simon Chaddock said:

IMHO there is another issue to consider.

You say you are building your plane out of hot wire cut foam so I presume it will a 'lightweight' rather than a 'heavyweight'.

You only have to look at full size to find that really high power twins (eg DH Sea Hornet, Grumman Tiger Cat) used handed props that rotated inwards over the top. This was done primarily for a benefit in single engine operation but it also meant that a recovery anywhere near the stall under power was much safer.

So the question is will your 'light weight' twin be in the really high power category bearing mind that most RC planes are likely to have a higher thrust to weight and thus motor torque than full size. Electric in particular can generate high torque virtually instantly and well before the plane's aerodynamic control has caught up.

If you can find suitable handed props I would suggest you fit them.

 

As a builder of some lightweight scale RC 'twins' I have more than once had to apply full power in a low and slow situation but was safe in the knowledge that the limited aileron control would not be aggravated by any net motor torque.

 

 

 

This demonstrates a bit of a misunderstanding of this whole question. 

 

Yes our models have high thrust-weight, but this means our models accelerate really fast and aerodynamic effectiveness of controls is available more or less instantly. The lighter the model, the lighter the wing loadings so our models are more inclined to float than a full size so an actual stall is less likely in the first place. A heavy model will be more vulnerable to torque effects as it accelerates slower and can actually stall. My big warbirds are more impacted by torque than my small ones. Its just the way it is but they are nowhere near as big a handful as full size. 

 

Our models simply do not have the same torque reaction's as full size aircraft. 

 

I am not saying torque is never a problem, just that we have far more control authority and far less 'torque' to deal with that our full size friends. 

 

The final point would be flying style. Its daft to firewall the throttle from near stall speed in any case and while handed props might make this safer on a twin, they cant help on a single and its not a good practice. Even on electric, ESC's  can loose timing etc so slamming throttles open is never something i will recommend. 

 

 

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On 13/08/2021 at 15:25, chris evans 9 said:

Hi folks, I am currently building an "AV10 Bronco " with hot wire cut foam. Span 0.950 m.  to my own design. I will use handed props but I am wondering which goes where?  Is there a specific side for the different rotations ? for example: which side should I place the Counter clockwise prop?

 

As Jon says with IC there is not much choice so both in the same direction (or all 4!) and then there is the case of the P38 (they rotate top away from the fuselage) but that's to solve other aerodynamic issues.

 

I have a Woohoo (twin electric plank) with both rotating in the same direction and even at stall it won't yaw/roll if I slam the throttle open + its got no tail so work that out? Oh and I ran out of normal props on Sunday so put two pushers and swapped the motor wires over...didn't make a difference 

 

My Grumpy Tiger Cub (twin electric) has props in both directions but the original was IC and known for its very good behavior if one quit.

 

In conclusion (IMHO) if you can find good quality props in tractor/pusher then use them, but not at the expense of correct prop size. If that means both in one direction then that's the better option. Oh and as one very competent designer said to me throttle and rudder are best used to manage swing on takeoff.  If its scale flying then either will work just fine.

 

PS - just because its electric does not make it immune from one motor failing so motor and ESC cooling are paramount if you are tootling about and working the SC's really hard. 

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