I agree... they're "torqueier"- will turn more prop for their weight & horsepower than just about any of the competition & hence outperform in climb & cruise, perhaps the lightest weight "package" available, ceramic coated cylinders giving very low oil consumption & negligible wear throughout their life, 2000 hr TBO with examples going far longer before teardown, absence of shock-cooling issues... I could go on & on. I never knew too much about them & therefore wasn't a big fan, but I'm convinced that they are a great engine now.
Sorry if this post should be in the Rotax category
John Evens
Arvada, CO
Kitfox SS7 N27JE
EAA Lifetime
Chap. 43 honorary Lifetime
The Jabiru is a great engine. Runs smoother, simple to maintain, and has great power without a gear reduction, multiple carbs, cooling system, etc to worry about.
I investigated my options before spending $20k plus on an engine. Hopefully you have figured out that the Rotax is not the lightest package by any stretch of the imagination, nor is it cheap to operate over a 10 year period. Look at fuel consumption, annuals, and overhauls in the total picture. Reliability is equal since neither engine is causing planes to fall out of the sky. I think the rotax is passed over by those of us that hate a PSRU and high maintenance costs.
OBTW - you can hand prop a Jab in the back country if your battery goes dead.
The single most expensive purchase will be your engine. It costs more than a kit so be careful. Like the plane, you will have to live with your decision. Forget about shock cooling and step climbing. IMHO, anytime you are zoom climbing or quickly descending you are flying unsafe. Just because a rotax handles those two scenarios better doesn't make that sort of flight safe.
I hope we can keep this thread civil as it is a good discussion. As Tim pointed out your engine is a big investment so folks get pretty passionate about their decisions. I, for one, am glad there are options, the more the better. Which is best is likely to be one of those debates that will go on forever hopefully with ocasional new choices thrown into the mix. I chose the Rotax because it was the most common and best understood power plant for this plane. I also don't like having a reduction unit but it does provide one solution for the following engineering challenge. To optimise the prop based on desired performance envelope will result in the best length, pitch and RPM. To optimise an engine for best HP/weight and other considerations will also result in a best RPM it just wont be the same as the best RPM for the prop. A direct drive engine will compromise these two in exchange for simplicity (a very real advantage in an airplane engine). Consider the following relationship (this has a bunch of hand waving but I believe basically correct). For constant tip speed and static thrust HP needs to increase linearly with the prop RPM at which it is produced. This is to say that if you have 20% more HP at 20% higher prop RPM (and therefor a 20% shorter prop) it should be about a wash in static thrust.
Last edited by Dorsal; 11-04-2012 at 06:23 AM.
Dorsal ~~^~~
Series 7 - Tri-Gear
912 ULS Warp Drive
Dorsal, Thanks for the info. That is why I started the thread. I just want all the info I can get. This is for sure the 2nd biggest investment on our project. Or as may wife said, the reason she upped my life ins. as you said, hope we can keep this civil because some rotax people are closed minded on this subject. Thanks again, Eddie
Not wanting to quibble about things, but a few posts back it was mentioned that you can hand prop a Jabiru. The standard Jabiru ignition needs about 300 RPM to make spark. I know I was never able to spin my 2200 that fast by hand. Kind of interesting though, the 582 Rotax also needs about 300 rpm to make spark. Having the gear box will let you hand prop it if you really flip it fast. Good thing to, my battery was nearly dead today, and so I fired it up by hand. Got some nice flying in afterall! Take care, Jim Chuk
PS I've never heard of anyone handproping a 912 even though it has a gearbox. Anyone done it?
Yes. I've done it twice on the 80 hp but that was before I read you couldn't do it. Now of course I wouldn't even try. I was much younger then too.PS I've never heard of anyone handproping a 912 even though it has a gearbox. Anyone done it?
BTW, I've been living with my Rotax decission for 14 years and 2,500 plus hours of reliable, cost effective , fuel efficient, low maintenance very enjoyable flight. My engine decission worked out great. Hope yours does too.
DesertFox4
Admin.
7 Super Sport912 ULS Tri-gear
I wouldn't even want to try hand-proping a 912. They say a minimum of 200 rpm to make the Ducati boxes fire. Besides with the style of charging system these motors use, you need some battery to make it charge. Running without a battery in the loop will ruin the rectifier/regulator.
I don't know how the Jabs work, but you can prop a 2-stroke Rotax. A member of our chapter has a 503 powered Ridge Runner and he always props it. Here it is being done by one of our own (DaveF) on a 582.
http://www.youtube.com/watch?v=W867v6beoo4