Prop

[gordon bubbParticipant @gordonbubb68746]

My Billings Kadet lists more and more to the right as the speed increases, presumably a torque effect. Currently running a 35mm two bladed prop. Will a 3 bladed one of the same size be better?

Gordon

[gordon bubbParticipant @gordonbubb68746]

[Chris EParticipant @chrise]

The list is because of the torque that you are putting out between the motor and the prop. Changing the prop to one of the same size but with a different number of blades will only reduce the list if it reduces the power and thus the thrust.

Which prop / motor / battery are you using?

 

Edited By Chris E on 04/12/2022 16:05:40

[gordon bubbParticipant @gordonbubb68746]

This is an old build from way back, as per an earlier post. The instructions show a three bladed prop but with no indication of the size. It came out of the loft with a two bladed one fitted so I guess I never had the official one. It has a MFA 360-1 motor, S35 two bladed prop and 2S Li-Po battery. With this she goes faster than I need but possibly useful for escaping from angry ducks and geese! According to the MFA data sheet it is a 6v motor so I am probably overdoing things a bit and just need to limit the use of full power.

I had read somewhere that a 3 bladed prop might help mitigate the torque effect.

Maybe I could just drop a size.

Thanks,
Gordon

[Chris EParticipant @chrise]

A Rs-360 6v with a 7.2v battery and a 40mm 3Bl Plastic Prop are what, I think, was recommended by Billings.

3 blade plastic props tend to have much less pitch than an S pitch 2 blade so that might well help.

[Dave Cooper 6Participant @davecooper6]

Extreme engineering department – how about a lead weight on a beam-wise traveller. A small auxilliary motor drives the traveller in opposition to the list and proportional to the applied main motor torque ?

I like tinkering with such things and would probably use a 'rack and pinion' as found in a car buggy's steering.

Too silly to contemplate ? Think about a racing sailing dinghy where the crew leans out to balance the applied wind force….

Have fun,

Dave

[Colin BishopModerator @colinbishop34627]

I would go for a 30mm three blade prop if you are putting up to 7.4volts through the motor. The smaller diameter will allow the prop to spin faster and, together with the the reduced pitch, will lessen the torque effect. Those two bladers are a bit brutal in that respect!.

Youn could probably get away with a 35mm three blader as well though but the smaller prop has 3 blades so it's a bit suck it and see!

Choosing props is an art rather than a science!

Colin

[gordon bubbParticipant @gordonbubb68746]

Looks like some good advice, thank you all. I'll get a couple of 3 blade props and give them a try.

I do like the rack & pinion idea!

There won't be an update on this for a while due to other commitments and the weather. Nearly froze my fingers yesterday.

Gordon

[Dave ReedParticipant @davereed72029]

My thoughts: As the list increases with speed, a solution will need to do the same. How about a small wedge on the bottom of the hull near the stern, right hand side? My theory is that as speed increases, pressure on the wedge will increase and level the boat. Size and shape might need tweaking.

Someone with more boating experience can probably tell you why this won't work or is a bad idea – I invite comments…

Dave

[Ray Wood 3Participant @raywood3]

Hi All,

Yes real boats have trim tabs, so I'd use a soft aluminium tab glue to the transom so you can adjust it to get her running level.

These havn't been bent down yet but the principle is the same

Regards Ray

Edited By Ray Wood 2 on 07/12/2022 14:46:34

[ashley needhamParticipant @ashleyneedham69188]

Great picture, Ray !

Ashley

[Ray Wood 3Participant @raywood3]

Hi Ashley,

Yep she looks scary, brand new with a Zenoah 26cc engine, next years boat to run at Mote Park Maidstone they allow IC !!!!

Regards Ray

[James Hill 5Participant @jameshill5]

That`s a very busy stern Ray, what does the rest of the boat look like?

Jim.

[Dave Cooper 6Participant @davecooper6]

Yes, trim tabs should work, but a couple of extra considerations :-

1. Would they spoil the appearance of the model ? (Non-scale effect).

2. They may need to be speed-sensitive ie. dynamically adjustable when the boat is in motion.

Just a thought…

Dave C

[ashley needhamParticipant @ashleyneedham69188]

Some wedges underneath the hull would work, and be invisible….?

Ashley

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