Rotax engine/gearbox/prop combinations

[acwishing]

I am building a Loehle Parasol (first build and little knowledge!). At this point I am planning on a Rotax 503 and would like to use a wood prop (just because it would seem appropriate for the parasol). I don't understand the engine/gearbox/prop combinations and what would be the best safety/efficiency option. Can anyone direct me to a source of information on this subject.

[Frank Giger]

Get ready for a lot of math and then some easy answers.

But first, it doesn't matter what the prop is made of - one has to keep the tips of the prop from going super-sonic or they unravel.

Here's some math to chew on:

http://www.experimentalaircraft.info/articles/aircraft-propeller-3.php

But if you're going to get a wood prop cut for you, the easiest answer is to talk to experts (for example, I told Valley Engineering/Culver Props that I wanted a 1915cc VW direct drive engine and they spouted a prop size appropriate for it with no math needed on my end).

But there's at least one chart talking about it:

http://www.ultralightnews.ca/articles/rotaxproprecommendation.htm

[Timm Bogenhagen]

I used a 2-blade Tennessee 60X42 for my Rotax 503 dual carb, 2.58 ratio B-gearbox powered MiniMAX. This combination gave a good all around performance. If you want better climb you could go 60X40 or if you want better cruise consider 60X44. The 2.58 gearbox is the most common ratio for the Rotax B-box. Ground clearance is an important consideration. Generally, the larger diameter you can get, better thrust results.