Monday, 8 October 2007

A prop - er job!

Before I can get started on building the frame I need to build a reduction gear mechanism and buy a propeller. A reduction gear is needed to reduce the speed of the propeller so it spins at its optimum rpm, above 3000rpm and the propeller becomes inefficient. The KT reaches 15hp at 10.500 rpm, so I need to reduce this at the propeller by 4.1 this will get the propeller spinning at 2625 rpm, which should be just about right.

But before I start work on the reduction gearing, I need to decide on a prop, sounds simple enough but there are a lot of variables to consider to gain maximum thrust. An adjustable pitch prop is the ideal solution because you can tweak the prop until you find the optimum pitch for your engine. Unfortunately these are too expensive for my budget so I'm going to have to find an alternative.

Weeks of research and lots of questions later, I've decided on a 48" x 23" pitch wooden propeller from tp-propellers. The prop is designed for the Top 80 PPG and as luck would have it, has the same rotational direction as the KT, I've had it made with slightly more pitch than the standard Top 80 prop, that way if I find that the engine doesn't get up to speed I can trim a little of the end a bit at a time until it reaches the sweet spot, (thanks Jeff).

So I ordered the prop and 2 weeks later it arrived and what a lovely thing it is too. Suwicha, from tp-propellers has been very patient in answering my million and one emails and I would have no hesitation recommending their services, and the price? £77.00 delivered, a real bargain in my opinion.

Next step, building the reduction gear.

Build cost so far £260.45

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