Rotax "B" box; "C' box

[Will Crisp]

:) Hey Rotorheads!

I've done lots of reading, but my resources come up lacking. I'd like to know what Rotax "B" box or "C" box stands for? :confused: I do understand that it represents the mechanical geared/ratio connection between the crankshaft and the prop. What the specific designations stand for is what I'm interested in knowing. I'd appreciate your input!

Thanks in advance for the reply! :)

[GyroRon]

B box is one type, C box is another. The C box is stronger and has a better dampening system built in, it is also more expensive than a B box. Both do the same thing, so either will work. Only one is better and more expensive than the other!

There is also a E box which is basically a C box with built in electric starter.

And there is a A box but it is no longer produced. It predates the B box and is not as strong.

[Will Crisp]

Hey Ron ,

Thanks for the quick, informative reply! Now get some sleep! :)

[steveb]

Take a look at http://www.skydrive.co.uk/sd_re_gb.asp

"B" boxes are fine, but rattle like a bag of spanners on tickover.

"C" boxes have a rubber doughnut in the drive which helps to dampen out the power pulses, which makes the box quieter on tiockover and can help avoid vibration problems, particularly with heavier props.

The gearbox offsets are also slightly different - something which need to be taken in to account of you are swapping one for the other.

Both boxes can be supplied with a variety of reduction ratios.

I use a "B" box driving an IVO - seems to work fine.

[gyropilot]

When considering which gearbox to use, keep in mind the following:

B model gearbox weighs 9.9 pounds.
C model gearbox weighs 17.6 pounds.
E model gearbox weighs 24.7 pounds.

These are approx. dry weights. The gear oil = even more weight.

Every pound of excess weight you can leave on the ground means that much more extra performance in the air.

John L.

[Will Crisp]

Steve,

Part diagrams are great and help solve the mystery! Thanks for the URL and your observations. :)

John,

Thanks for the numbers and the reminder. The power to weight battle is never won....only forgotten...until the next modification. :)