Fury Expert gear ratio!

[david.read]

Gent's,

I have a Expert with a tired OS70 SZ-H. ( It was a self inflicted tiredness, but thats life i guess.

I have thought about the old YS 80 ST as a replacement (Only because it fits straight in) but due to the lack of units selling them in the UK i'm reluctant to go in that direction.

The OS 70 (On the right fuel) produces 2.5HP at 16000 Rpm. With my 9.3:1 ratio on the Fury, that gives me a main blade head speed of 1720 Rpm optimum.

Q: Would i be better to change the pinion to the 11T so the ratio would change to 8.45:1 giving me the option of running the head up to 1890 Rpm?

Q: Would the YS 80 be the way to go on this ratio as well?

Q: I know that i would need the 11T pinion to change ratio, but would i need different side plates as well?

Hope to hear - Regards,

David

[Alfred]

I am about to do exactly that David.
I purchased a 2nd hand YS 80.
I am just waiting for my conversion parts to arrive.
Yes you will also need the conversion plates.
And if you go YS 80 then you will also require the collars to clamp the fan onto the engine.
Mine will be running with a MP2.
The OS70 will continue it's duty in an older X-Cell.

[david.read]

Do any of you guys run a 9:1 ratio on a Fury with an OS70?

Could a New OS70 pull a 8.45:1 ratio, i.e blades at 1890 RPM with the engine at the optimum 16,000 RPM?

To get 1820 head speed from a 9.3:1 ratio you need to rev the engine to 17,000 RPM - (Is this not on the high side for the engine?).

Just trying to get to grips here with some of the ratios out in the park.

Regards,

David

[kthane]

Practical RPM Range for an OS70 is 2,000 - 18,000 RPM. The one I had in my fury ran great at ~1830HS with 9.3 and SB70 muffler. The difference between it and my next engine (YS80) was subtle to say the least. I found the 70 to have a very sharp drop off in power with respect to RPM. Keeping your 70 above your calculated peak HP rpm will likely result in a heli that appears to have a whole lot more power. Onlyraptors was having a sale on the YS91 for 239. If you gonna go that route, go all the way. To convert to 8.45 you need to shave 30 thousands off the engine mounts and drill out holes in clutch plates or just replace the clutch plates. Also need 11 tooth pinion ofcourse.