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I've hand propped and started my "532" on many occasions when the old battery was just not holding a charge. I've hand propped 150hp Lycomings but I'm a bit leary of hand propping my 80hp Rotax if the need should ever arise. Don't know if its age and wisdom or I've become a "Wuss" in my old age. Has anyone hand propped a 4 stroke Rotax and been able to tie their own shoes afterwards?
I don't think hand propping is a big deal if done properly. That said I think it would be difficult to hand prop a 912. I seem to recall that it takes 200+ rpm to excite the ignition circuit. With the gearbox that would take something like 80 rpm at the prop. My fear is that you would be reaching for the next blade when it did start if you could get it to turn that fast. Maybe somebody who has successfully done it can chime in but I've never heard of it being done.
If you can actually turn the prop fast enough to excite the ignition, you will surely loose a hand as the next blade comes around.
These motors should NOT be hand propped or even attempted to be propped.
Rotax 912 engines should not be hand propped.
1. The ignition module does not excite until somewhere between 200 and 300 RPM (Info on this figure varies but it’s still faster than a magneto system).
2. The gear box makes it twice as hard to pull the prop through the compression.
3. The compression strokes do not occur in the same prop position each revolution.
4. Typical props on Rotax 912 engines are light weight and have very little inertia.
There are reports of a few owners that have done it successfully, and a few reports of serious injuries. I would rather read reports of a helpful pilot showing up with jumper cables.
Stay safe guys and gals.
John Pitkin
Greenville, Texas
I agree with John on this issue - I'd prop a supercub engine, but not a 912. I have had enough trouble with my table saw - rather not mess with bigger blades like a warp prop attached to 100 hp.
One of the strategies I came up with when building our kitfox was inspired by prior experience that most of the airplane troubles I have suffered having had to do with electrical and charging systems. We went for redundancy - meaning two electrical systems - two alternators (the rotax & the optional belt driven alternator), two e-busses one for essential and the other for the high draw stuff I wanted anyway; and, two batteries. Normal operation is with the two systems functioning separately; but, there is a cross tie switch/solenoid that enables a person to power both systems from either side separately and disconnect the bad alternator - This also allows a person to start the aircraft from either or both batteries if one pukes in the outback. The only issue would be if the 40 amp alternator dies and you need to live with the rotax alternator - some load has to go but the essential stuff will still work.
One thing we have going on a rotax system is that it is a 12/14 volt system which can be jump started from a car - some day I hope to install some simple connectors to make a jumpstart from a car easier in case both master switches get left on for a few days.
I know adding 50 # to a kitfox is not something everyone wants to do - but this way the extra e- load I wanted can be taken care of and I figure there is some hope of getting the engine started without being tempted to hand prop if one battery croaks. I try to make up for the added weight of the system by eating lots of broccoli..........:rolleyes:
Sincerely,
Dave S
Kitfox 7 Trigear
912ULS Warp