OS 40 Surpass Propeller Choice.

[David Davis]

At the risk of boring you all to death, for those few of you who don't know, my entry for this year's Coupe Des Barons has been accepted. This is what my Baron looks like.

The Baron is a well-known trainer here in France which was first produced in the early 1970s. The maximum sized fourstroke engine eligible for the competition is 0.42 cu ins. Users of two-strokes are limited to a 35 and those opting for electric power to 825 Watts.

The event takes the following form, after a Concours D'Elegance there are four flying tests:

1. Baguettes. Where you have to hit 1 metre high balsa sticks stuck into the ground.
2. Pylon. Which is a straight forward pylon race, then after a typical French lunch....
3. Renard. Where you have to cut off a streamer towed by a trainer.
4. ...and finally Limbo where you have to fly between an enormous "goal post."

My Baron is powered by an OS 40 Surpass and is currently fitted with a 11x6 propeller. I realise that this engine does not have the power of an OS 35FX for example, but what would be the best propeller for me to use on this engine-airframe combination bearing in mind that the model features a radial cowling of 12 cms ( 4.75" ) in diameter? According to my old Traplet Plans Guide a 40 four-stroke may use anything from a 10x7.5 to a 12x6.

I want the model to fly as quickly as possible with this engine to give me the best chance of doing well in events 2 and 3.

Edited By David Davis on 03/04/2018 08:06:31

Edited By David Davis on 03/04/2018 08:07:01

[Peter Miller]

I always use an 11 X 6 prop on my OS .40 Surpasses and a 12X 6 on the 48 Surpass

[Jon H]

12x5 might work too. Even a 13x4 should be ok.

I would test the 12x5 first and see how you get on

[Denis Watkins]

Flying the 40 surpass, with 5% nitro on an 11 x 6 is very comfortable, with 10% making quite a big difference, if required.

If you can get a 2200 - 2400 tickover for comfortable landings with either prop is a bonus, the 12 x 5 larger disc being preferable

[Trevor Crook]

As I recall, I used an 11x7 on my .40 Surpass in a Flair SE5 many years ago, and it flew well.

[Geoff S]

That sounds like a very enjoyable competition. I just wonder about the typical French lunch before the second part of the contest ... red wine included?

Geoff

[David Davis]

Posted by Geoff Sleath on 03/04/2018 11:03:11:

That sounds like a very enjoyable competition. I just wonder about the typical French lunch before the second part of the contest ... red wine included?

Geoff

Haven't you seen the video of last year's event Geoff?

Sixty-one started and thirteen remained in flying condition at the end of the event including two which were flown by two young girls!

**LINK**

[Former Member]

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[Former Member]

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[Jon H]

Posted by Percy Verance on 03/04/2018 21:03:09:

Jon

I used a Graupner 12x5 on my OS .48fs. It was much better in the verticals than a 6 inch pitch prop. It does depend what the engine's bolted too of course........

Yea absolutely. My dad taught me to fly on a flair pup with an OS 48 in it and usually it flew on 12.5x6 graupner super props. Seemed happy enough.

I do have an FS 40 kicking about and was actually considering joining the hurricane winter build and doing a glow conversion on it just for fun. If the weather wasnt so awful i would dig the engine out and see how it revs on a 12x5...im sure i have one somewhere