Which ratio for C Box

[gertcoetzee]

For a new prop, Pieter de Necker needs to know the reduction of the gear box - on all the trikes it is at the back where I have put the red circle on the picture. Mine has no number or ratio - now what?

On a web site I found "Reduction Box "C" box with ratios: 2.62 to 1, 3.0 to 1, 3.4 to 1, 4.0 to 1"

Please help!

[Tjoek]

It is more than likely a 3.47:1.

IIRC - The 4:1 ratio was mostly used with the 6-blade IVO combination, which is not that common anymore. The 2.62:1 is mostly used where you swing a small diamater prop (e.g. due to tail boom restrictions).

[Wargames]

It is more than likely a 3.41:1.

Do you mean 3.41 or 3.47?

The options is the following for the C/E box: 2,62 | 3,0 | 3,47 | 4,0

Gert, my bet is still on the 3,47 ratio. It is the most common ratio for the C box, and your prop pitch would also indicate that.

We could always measure it!! Roadtrip??

[Morph]

Put a tippex mark on the side of the rubber coupling (look through the hole in the side of the box). Mark a line on the prop and some where on the engine so that you can rotate it exactly one revolution.

then get someone to turn the prop (mags off) slowly. Count the amount of times the tippex comes past the window. It will be multiple times per one revolution of the prop.

2,62 two and a half times
3,0 exactly 3 times
3,47 three and a half
4,0 exactly 4 etc

[Duck Rogers]

Or just borrow an Optical Tachometer from one of the model RC boys and measure the prop revolutions with the engine at say, 3000 rpm. Whatever reading you get on the optical tach, just multiply by 3.47 and see if the result is 3000, matching the engine revs. If not, multiply by the next ratio, say, 4 and see if the result is 3000. And so on.......

[Boet]

I like Oupa Morph`s plan!