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Home✈️Aircraft🚁HelicopterHIROBOOther › New 8.9 gear ratio
04-25-2009 01:53 PM  10 years ago
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Quickster

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Victoria, Australia

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New 8.9 gear ratio
Is anyone using the new 89 tooth main gear for the sceadu? Would love to hear some feedback on performance!
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04-26-2009 06:56 AM  10 years ago
IYKIST

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London united kingdom

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Is Hirobo gradually going back to the high gear ratios.
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04-26-2009 05:14 PM  10 years ago
BJames111

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San Diego, California

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89 tooth main gear and the 10 tooth pinion gear gets you an 8.9:1 gear ratio. The O.S. 50 hyper for example, makes 1.9hp at 17,000 rpm. So IF you divide 17,000 rpm by 8.9, you get 1,910 rpm headspeed. MOST 50 kits have an 8.5:1 gear ratio, and with the same engine can run 2000 which for 3d flying, seems to be a better choice. As far as I can see, there is no benefit of going to a higher (numerically) gear ratio, unless perhaps you are wanting to reduce the headspeed.
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04-27-2009 03:06 AM  10 years ago
Jafa

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Sydney, Australia

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But the thing is we run a HS that results in an engine speed of 17,800 to 18,200 so that when we load the engine it falls back to peek power where it will hopefully hold the RPM better than falling to a lower RPM below peek power

AgileFalcon used to like 8.9 gearing for the OS50 - it's certainly an engine that loves to rev
The Century 50 sized heli's had fairly low gearing as well

Personally I think the stock 8.7 gearing works fine and is good for running 2100 on the head

Protos | Logo 400 & 500 | Sceadu Evo | Freya Evo | Trex600N | Avant FX
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04-27-2009 04:32 AM  10 years ago
BJames111

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San Diego, California

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in my opinion, 8.9 to 1 is too high. 8.5-8.7 is really where modern 50 size engines seem to work best. I have a feeling we are going to see larger "50" size engines coming, and they will likely work better with the lower g/r's
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04-27-2009 06:53 AM  10 years ago
Quickster

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Victoria, Australia

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Fair enough! It sounds like the 8.7 is the choice. I wonder why Hirobo have just come out with this new main gear as being for 3D?
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04-27-2009 04:14 PM  10 years ago
MRC-Hirobo

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Edison, NJ

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The Stock 87T main is the best. You will get the right head speed that you are looking for in 3D (2100).MRC Host
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