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Nov 12, 2001, 08:13 AM
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Steve McBride's Avatar

Why you should not run an MP Jet planetary gearbox in reverse......

Decided to give a different motor a try in a pusher model and had a Hacker B20-12L on an MP Jet 3.8:1 planetary gearbox available.

I reversed the motor direction, slapped a 7x4 APC prop on it and checked everything out. Handlaunch and 2 complete circuits before the prop came fluttering down.

A deadstick landing and I find the housing had unscrewed itself due to the prop torque. It was secured but somehow came loose. In a normal rotation (for tractor use) this would not have made a difference. However as the reverse prop torque tends to 'unscrew' things, use as a pusher should only be attempted if you are sure things are tight and secure.

I lost all the planetary gears and assume I need to buy a complete new box.

Oh well - live and learn I suppose.

You have been warned

Steve McBride
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Nov 12, 2001, 05:07 PM
NipponDave's Avatar
Hi Steve,

Just FYI, you don't need to throw away the gearbox. I'll have the pinions in stock when we open the shop next year. I'll be back in Japan early March, so send me an email and I'll get them out to you if needed. Shipping will only be about $2 - the set of gears and washers will probably be priced around $5.


Air Craft Japan


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