Scaling gears 1.5x Vega V Twin

[DurhambuilderParticipant @durhambuilder]

In my idle moments I’m sketching up re-dimensioned plans for a 1.5x Vega V twin glow ignition aero engine. It will never be ‘flown’ but hopefully will actually run. The original design by David Parker (Model Engineer Jan 1986 onwards) was for a 9cc engine and scaling everything up by 1.5 times would give a 30cc engine. The original timing gears are 48dp 12T and 24 T which gives 0.75″ between centres. To get 1.125″ between centres for my bigger engine I could keep the tooth count the same and go for 36dp or alternatively I could stick with the  48dp and go for 18T and 36T. Is there any advantage in either solution?

FWIW both combinations of gears are widely available in hardened steel for the radio control car enthusiasts and only a few pounds each, I probably won’t be cutting them myself.

[JasonBModerator @jasonb]

I can’t see it making much difference either way, just make sure there is plenty of material between the root of the pinion’s teeth and the hole through it.

[Peter Cook 6Participant @petercook6]

The question piqued my curiosity as to the difference. In an idle moment I found this online gear strength and power calculator  and after guessing some reasonable parameters it calculated the allowable power transmission.

Changing only the DP and tooth count  – for 36DP 12 & 24 it gave an allowable power transmission of 0.14hp , while at  48DP 18 & 36 gave 0.18hp or about 30% more power transmission capability.

 

[Roderick JenkinsParticipant @roderickjenkins93242]

Keeping the larger number of teeth will give a little more sensitivity to tweeking the timing.

Rod

[DurhambuilderParticipant @durhambuilder]

Thanks guys, 3 nil to the 48dp so that’s what I’ll go for.

[Author]

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