Propeller problems perhaps?

[David Davis]

I recently participated in a light-hearted competition, La Coupe Des Barons, an event for a three-channel trainer. My model, pictured below, is powered by an OS 48 FS Surpass.

La Coupe Des Barons has four flying tests two of which call for accurate flying close to the ground, the other two are speed events. The week before the competition I experimented with different propellers. The model flew well on 13x4 and a 10x8 propellers.

In the competition my motor cut out twice in flight while using the 13x4. I had no problems with it on the 10x8. The first cut occurred just after take off when I had turned with the wind. The second occurred after I'd flown four circuits.

I am quite prepared to admit that I may have over-leaned the mixture and that caused the engine to cut out on two occassions but do you think that the 13x4 is too big for an old 48 fourstroke?

Edited By David Davis on 11/09/2019 08:36:31

[Denis Watkins]

You are in the correct range of prop David, it is not your prop deadsticking the motor.

10 x 7, 11 x 6, 12 x 5, 13 x 4, is the correct choice

[Jon H]

I would say 13x4 is a bit small. I would use 13x5 and not worry. I know ASP52's run well on that and in my experience they perform much like an os48.

[Don Fry]

But is there a possibility that the low speed mixture is upset by the prop change. Or it is a sub optimal adjustment, OK for one prop but not OK for the other.

[David Davis]

Thank you for the advice gentlemen. I'll try running it without the cowling once I've repaired it but that won't be till the weekend at least as the French Army is holding excercises in the area until Friday. Not that I've seen hide nor hair of them yet!

[David Davis]

Thank you again for all of your advice gentlemen. It appears that a 13x4 propeller is not too big for the OS 48 Surpass and given that the engine did not cut out at all while I was using the 10x8 propeller, I assume that the cowling cannnot be causing the engine to overheat.

Therefore, I think that the most likely reason for the engine cutting out while fitted with the 13x4 was that I had adjusted the mixture too lean on the day. I'm not normally a needle twiddler so that'll teach me!