os.35max two stroke

[philip pember]

am fitting above motor to a super 60 after removing electric motor, what size prop can this swing, will it cope with a 12x6 ??. cheers lads.

[Gary Binnie]

Hi Philip,

 

 9 x 6 to 10 x 6 according to a free card given away with RCM&E some years ago.

 

Will see if I can get permission to post photos of it.

 

     Cheers

 

         Gary

[Frank Skilbeck]

I would say a 12 x 6 would be too much, I am currently running a OS40 FSR on an 11 x 6 and a 12 x 6 would be too much for that. But you don't need speed on a Super 60, so a 12 x 5 or 11 x 5 would be a better fit, my Super 60 in it's time flew on a OS40 FS, PAW 35 and an Irvine 25.

 

Which OS 35 Max is it?, you can find a selection of engine tests here

Edited May 18, 2021 by Frank Skilbeck

[Gary Manuel]

Propeller selection chart by scrolling down and selecting from here:

https://www.modelflying.co.uk/rcme-extra

 

or direct from here:

https://forums.modelflying.co.uk/sites/3/documents/prop guide.doc

[Jon H]

That chart seems to lean a bit on the small side. I used to use 10x6 props on my ASP 36, OS 30/35fp etc and they were just fine. Its not a bad base guide but certainly not set in stone. 

 

In the specific case of the OP i would be leaning towards 11 or 12x5 as Frank suggests. A great deal depends on the engine in question. 

[john stones 1 - Moderator]

Reckon the guides are just that myself, never stuck rigidly to them suck it and see is my thinking, may not be happy with a 12x? on, but reckon it'll turn a low pitch 11x ?.

[PatMc]

I used to generally use a Graupner grey 12x6 on an (pre-schnuerle) OS 25 Max powering a Junior 60. Later when an OS LA 25 was fitted I found it best to use a much smaller prop - IIRC 10x6.

Bottom line - IMO if the Max 35 is a pre-schnuerle ported engine the 12x6 should be fine.    

[Nigel R]

I'd use 12x4 myself, without knowing whether it's a 1960s crossflow or a later 35FP.

[David Davis]

If it's one of these, you'd better be careful! ?

 

 

Edited May 18, 2021 by David Davis

[PatMc]

Nigel a 4" pitch will tend to run out of thrust as the model reaches flying speed whereas, although turning at lower rpm with 6" pitch, the prop is more likely to maintain a decent margin of thrust. 

[Jon H]

Just now, PatMc said:

Nigel a 4" pitch will tend to run out of thrust as the model reaches flying speed whereas, although turning at lower rpm with 6" pitch, the prop is more likely to maintain a decent margin of thrust. 

 

Depends on the flying speed and engine rpm I flew a pilot twin ace on a pair of 25fp 2 strokes throwing 10x4 props and it wasnt slow. They did rev though, sounded great ? 

[philip pember]

3 hours ago, Jon - Laser Engines said:

That chart seems to lean a bit on the small side. I used to use 10x6 props on my ASP 36, OS 30/35fp etc and they were just fine. Its not a bad base guide but certainly not set in stone. 

 

In the specific case of the OP i would be leaning towards 11 or 12x5 as Frank suggests. A great deal depends on the engine in question. 

it is a os 35 fp and will start with 10x6 and have 11x5 handy. thanks for the info lads.

[PatMc]

I was reckoning on it being a cross flow OS 35 Max. I would agree that a 35FP is best ran at much higher rpm on a smaller prop.

[Gary Binnie]

Have permission to post images of the card.

 

1.  The propeller selector, upper part is 35 mHz radio channel numbers. Above that is a CC to cubic inch conversion scale.

 

 

2. Don't leave home without....! I use the 'Notes' gadget on an iPhone to make sure I have everything (one glider flying session I left the tailplanes at home and at one comp I left a transmitter at home).

 

 

3. Pre-flight checks.

 

 

[Engine Doctor]

If its anything like my old J60 then a 12 x 4 will be fine. They are not meant to tear around the sky and most flying will probably be done at less than full throttle.

My old 60 flew on a clapped out OS max 25 with I think from memory a 10 x 4 prop . It was a long time ago. 

[Peter Christy]

Many years ago, I used to fly a Super 60 on six channel reeds with a Merco 35. I used an 11x6 prop, which the Merco swung just fine. This is a slow, draggy model, so you don't want the engine screaming. Diameter is everything here! I would go for an 11x6, and if the engine struggles, reduce the pitch, NOT the diameter.

 

--

Pete