14x6 or 15x6 prop

[Rocker]

Have a Seagull Bower Flybaby 

I have a Laser 80 up front but find this is a bit to powerfull with the 14x6 prop on .If I put a 15x6 prop on the the Laser 80 will the 15x6 prop tone it down a bit or would it make it worse ???

[Jonathan W]

I can't speak to the Laser 80 specifically, but generally you would go up in diameter and down in pitch if you wanted to "calm things down".

[Don Fry]

Why not just set the throttle arm to give 80 % power. 

[Nigel R]

Or use less throttle stick?

[Rocker]

I am flying around on under a third throttle .Just wondered if a bigger prop would help 

[J D 8]

 As with @ Jonathan W above less pitch, so try 15x4. Model will accelerate faster but top speed and speed at other settings will reduced.

[Don Fry]

15 x 4 will work, just make sure the throttle cut works. Occasionally the efficiency of the big prop produces enough power to keep the thing aloft. You can also try differential on the throttle, so it’s less sensitive in the positions you are flying in, so reducing workload. 

[Cuban8]

Yes, a combination of throttle setting and prop when I've played around with a friend's over powered vintage style model. Master Airscrew props are intrinsically less efficient than other makes so might be worth experimenting with. They are easy to cut down with care, and providing they're balanced well each time, you could try a certain amount of cut-and-try to get the performance you're looking for. Either that or a big box of props!

[GrumpyGnome]

Or even a smaller engine ..... 🙂

[911hillclimber]

Please forgive this intrusion gents:

I am trying to build a 5cc diesel and I read a 15 x 6 prop is right for this vintage (low revving?) engine.

This prop is HUGE to what I'm used to.

 

What is the ideal prop size for a 5cc deisel?

[Jon H]

On 04/04/2024 at 22:00, Rocker said:

Have a Seagull Bower Flybaby 

I have a Laser 80 up front but find this is a bit to powerfull with the 14x6 prop on .If I put a 15x6 prop on the the Laser 80 will the 15x6 prop tone it down a bit or would it make it worse ???

 i would go for 15x6

 

 

[Jon H]

6 minutes ago, 911hillclimber said:

Please forgive this intrusion gents:

I am trying to build a 5cc diesel and I read a 15 x 6 prop is right for this vintage (low revving?) engine.

This prop is HUGE to what I'm used to.

 

What is the ideal prop size for a 5cc deisel?

 

it seems a bit excessive to me but is in line with the max recommended for a paw 29, which is about the same size. I would probably use something smaller like 11x6 for the first bit of running. Once the engine is running well with this lighter load start pushing it a bit harder with 12, and then 13x6. See how the engine handles and responds. 

[911hillclimber]

Thank you Jon for the speedy reply.

 

[Engine Doctor]

I have just looked at the Spectre 1950 engine test for the DC Wildcat , a 5cc longstroke engine , not unlike your engine. The test was done by  L. H. Sparey for Aeromodeller  in the April 1950 edition.

The recommended prop for that  is 13 x 6 . It might spin a 15 x 6 when its run in but its a bit of an ask and unlikely to be of any real advantage for thrust . 

As Jon says start off with a lighter load . Once running and up to temp stop it and allow to cool a few times. If at any time it starts to overheat and labour  stop it and allow  it to cooI completely then start again .It should start to loosen up after a few stop start cycles. Gradually increase speed and adjust comp and fuel for max revs. Once it can hold its rpm without overheating or labouring then try experimenting with props.  The Wildcat tested said that it would spin a 13 x6 at between 9k an 10 k rpm but that was a Mk 3 so DC had done some homework to get there. 

[jeff2wings]

It's quite capable of swinging a 16 " prop but not that one as it's for a modern petrol engine ,probably one about 20-25cc

second run on a 16x6 airflow wood 3,900 rpm with incorrect port timing, l will see what rpm my Mk3 wildcat and ETA 5 do on this prop