Converting

[Arron Davison]

Good afternoon all,

I have a question when sizing engines from 2stroke to 4stroke how much more do you allow for 4stroke?

Say a size 52 2stroke would be a ?? 4stroke?

[Jon H]

In general a 70 4 stroke would be considered a match but its not quite that simple as the nature of the power delivery on the 4 stroke is quite different and far larger props are normally used.

Do you have a specific model in mind that you want to run with a 4 stroke?

[Simon Chaddock]

Arron

The conventional 'rule of thumb' is go up one size for a 4 stroke but it also makes sense to make use of the 4 stokes lower revs and higher torque by using a .larger. prop.

Of course it also depends on what you are starting with. There are better or worse 4 strokes just as there are with 2 strokes!

[Arron Davison]

It is for the Nick Ziroli, Lockheed P-38 Lightning.

Power required 38 - 52 i take it that this is 2stroke?

[Jon H]

ummm...i think that is 38-52cc. The model is about 120 inch if i recall correctly, or does he do a smaller one?

[David Ovenden]

Arron, I think the Ziroli P-38 is 114" span and weighs in at around 40lbs. So it will need engines around 50cc or 3cu.in (300 size 4-stroke)

Jon - Maybe it would suit two laser 300V twin 4-strokes; what do you think?

[Jon H]

Posted by David Ovenden on 24/08/2017 15:26:19:

Arron, I think the Ziroli P-38 is 114" span and weighs in at around 40lbs. So it will need engines around 50cc or 3cu.in (300 size 4-stroke)

Jon - Maybe it would suit two laser 300V twin 4-strokes; what do you think?

Yes 300 or 360. We have had someone do this but i cant remember who. In any case it didnt end well as the tail departed in flight. I think he built another and it suffered the same fate

[Arron Davison]

That is the model i am talking about 114"

I like the look of the 300V 4 stroke very nice!

[Arron Davison]

Posted by Jon Harper - Laser Engines on 24/08/2017 15:31:48:

Posted by David Ovenden on 24/08/2017 15:26:19:

Arron, I think the Ziroli P-38 is 114" span and weighs in at around 40lbs. So it will need engines around 50cc or 3cu.in (300 size 4-stroke)

Jon - Maybe it would suit two laser 300V twin 4-strokes; what do you think?

Yes 300 or 360. We have had someone do this but i cant remember who. In any case it didnt end well as the tail departed in flight. I think he built another and it suffered the same fate

Was this due to vibration?

[Alan Gorham_]

Steve Rickett built two Ziroli p38s, but I think he used 2 off Laser 360Vs.

Be aware that there is a structural weakness in the tail of the Ziroli design (hence why Steve built two after no.1 disassembled itself) so you might want to speak to someone who has built one to get the gen on modifying the tail..

[Arron Davison]

Thank you Alan

That is great advice! Much appreciated.

[Jon H]

Thanks for filling in the blanks Alan. Now i remember the whole story. It was an issue with the model not the engines. The V's ran very smoothly and offered far less wobble than an equivalent single. Be careful if you go for the same model without any mods to the tail.

The engines he used were 360v's and they now live in his A20 as seen below.