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I received my CH 750 kit here in the UK and I think it's great - and I have been making steady progress with it ever since. As I am building for the English climate I am degreasing and epoxying as I go.
I have not ordered an engine or a propeller yet but I have the Firewall Forward kit for a Rotax 912 and am planning to fit the 100 HP engine.
This is the first CH 750 to be built in the UK - so obviously there is not a lot of local experience of this aircraft on this side of the Atlantic. I can see that there are large numbers of CH 750s flying in the USA and Canada.
The thing that I don't know - is what propeller and what pitch and diameter to fit. Obviously there is variation in whether one optimizes for climb or cruise and it would be useful to know which is best for which purpose. From my previous building and flying experience I know that there can be lots of variations and subleties in propeller selection. At the moment I have no idea what ball park I am in, at all.
Would some kind person be so good as to tell me which propeller works for the aircarft in his / her experience. I should be most grateful.
All the best,
I am also planning to install a 912 in my CH750 so I don't have any first hand information but there are several on this site that have the 912. Until they chime in, you could go to John Gilpin's Stolspeed website and look at some of the work that he has done. He loves to experiment with these high drag light STOL aircraft and we are lucky enough to have him document and publish on his site. The prop comparison can be seen here: http://www.stolspeed.com/id/62
Thanks for the advice - really appreciated. My decisions can be some way off - but from my earlier building experiences it does seem an art as well as a science, and it's a challenging area that needs a lot of thought and research. It was the big area I had absolutely no feeling for as I have always been a VW, Continental and Lycoming user. Your advice really appreciated. Tony Oliver
Hi Oliver. Sensenich designed a new 3-bladed, ground adjustable, composite prop specifically for the Rotax a few years back and is receiving very good reviews. Conventional wisdom would normally have a large 2 bladed prop for low and slow flight but the new Seni prop 3 bladed seems to have addressed both good torque for T/O, climb, floats etc as well as good high speed (tongue in cheek) performance.
I found the prop to be of outstanding craftsmanship and very easy to install. The pitch adjust is straight forward only requiring one wrench and no protractors etc.
If nothing else the scimitar tips add a definite cool factor to your plane.
The only reservation I have is the use of a composite prop in the bush. The prop comes standard with leading edge protection and the company advised the hollow construction provides significant impact protection but Ill be sure to test the theory this summer.
Lots of good props out there but the primary consideration that I used for selecting my prop is the Rotax requirement to keep the mass moment of inertia under 6000 kg.cm2. The Seni is 3000 kg.cm2 and total weight is only 9 lbs.
Check this web page for the installation and demo test by zenith on a CH-701.
Specs and pic for the Seni below
Many thanks for the reply. Again, this gives me some very good leads to follow up. Much appreciated - particularly as I am starting from ground zero in propeller selection - and being the first CH 750 build in the United Kingdom, there aren't too many people around here I can ask. All the best - Tony Oliver
WARP 70" or 72" diameter. 2 or 3 blade prop its a builder choice. Very tough and relatively cheap prop. Setting pitch is easy with the protractor that comes with every prop. Rotax 912S install is easy 3 day install... bolt in go flying. I have a 68" 3-blade taper tip (constant speed platform) on my Rotax 80 hp CH601HD and 72" dia 3 blade on my CH750.
Greatly appreciate your steer on this. I am learning fast - thanks to all the help I'm receiving from all you helpful guys. Best Regards
Perhaps consider the new Rotax 912iS 100Hp - very interesting and I am sure that Skydrive can help with ideas for the installation... The 750 is a great platform for the new engine - and should be economical in the long run (less maintenance, less fuel)...
Thanks for the contribution. To make a little bit of a contribution in return for all the helpful advice I am receiving - I would like to add that my quest for information on this theme is in part a result of my earlier experiences with the FRED I built in 1983. Like the CH 750 the FRED was a very high drag, high wing aircraft, but - unlike the CH 750 - fitted with the engine of its day, a VW engine - it was a very marginal aeroplane. It would do 60 kts and that was it. And, this combined with what would be taken to be extemely low rates of climb. I won't mention how low. I must have tried about 8 or 9 different propellers on it and was continually shaving inches off the tips to give me higher RPMs, etc. I know that I am in a different league with the CH 750 performance in terms of power-to-weight ratio, modern engines like the Rotax, etc, but my experiences left me with an awareness that the selection of an appropriate propeller is an matter on iteration and experience. I do know what it is like to take off and not go up.... Many thanks for the advice. Best regards. Tony Oliver
I have heard that Sensenich is now offering a 72 inch 3-blade prop for the Rotax. Their website still does not show it. Can anyone confirm this rumor? Is anyone using or considering using this prop?
I have a Woodcomp Klassic 3 blade 68" ground adjustable prop. on my 701/912uls. No problems in 11 years and 400 hours.
I sent it back to the factory last year for a check over. They do some kind of frequency / resonance test. They replaced the leading edge protection tapes and put new nut plates and better screws on the spinner and backplate. The cost was very reasonable and the guys are good to deal with.
They have a website with loads of different models to choose from. The UK agent is Kevin Dilks of Special Aviation Services, he's also a Rotax expert.
The only drawback is that adjusting the pitch is a bit fiddly, you have to do each blade individually. The Sensenich prop mentioned above would certainly be attractive from that point of view, although I think it's more expensive.
Best of luck,