Jabiru 3300

[avidflyer]

I agree that the different props affect the cooling on the ground more than in the air. Here are pics of two different props I ran on my plane and you can see how the wood prop would push more air into the cooling ducts on the ground than the Warp drive prop would. As I said, I didn't have problems with my Warp Drive and cooling, but up here in MN. it is seldom more than 80 F when I'm flying.... maybe 20F to 50F more likly. Take care, Jim Chuk

[kitfox5v]

Thanks guys, Keep them coming. Any information will help us all. I love this forum. It's nice to have fellow builders input. I'm not ready yet so maybe they will have all problems solved by then. I just don't believe running a 912 5000 plus just to spine a prop 2000rpms is cost effective in the long run. just seems like alot of wear to me.Thanks Eddie Kitfox5v

[Av8r3400]

I just don't believe running a 912 5000 plus just to spine a prop 2000rpms is cost effective in the long run. just seems like alot of wear to me.

Over 40,000 of them sold with millions of hours of flight time would disagree with that.

I can't understand why these engines are hated so much for being efficient and reliable.

[jrevens]

Over 40,000 of them sold with millions of hours of flight time would disagree with that.

I can't understand why these engines are hated so much for being efficient and reliable.

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

[TahoeTim]

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.

[Dorsal]

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.

[kitfox5v]

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

[Esser]

Thanks guys, Keep them coming. Any information will help us all. I love this forum. It's nice to have fellow builders input. I'm not ready yet so maybe they will have all problems solved by then. I just don't believe running a 912 5000 plus just to spine a prop 2000rpms is cost effective in the long run. just seems like alot of wear to me.Thanks Eddie Kitfox5v

There are a few differences you have to look at with that too. The biggest one being displacement. A 912 is roughly 1200cc and a O-200 is 3300cc yet they run the same horsepower. The 912 has a shorter stroke and because of this can run at a higher RPM easier (Due to easier balancing, slower piston speed, etc). It gears down its high RPM to a lower shaft speed and gains a mechanical advantage for this. Because of this mechanical advantage I wouldn't say there is anymore wear and tear than an engine with a long stroke/low rpm that is doing all the work off the cylinders. The one trade off with the high rpm is you usually gain peak power but lose torque.

It is just two different ways of skinning a cat. Much like a 4.3lFerrari engine that makes 500hp and a 7.0l corvette engine making 500 hp.

[War Eagle]

While the gear box reduces the engine speed so it can keep the prop tip speed at a reasonable number it also multiples the torque out put of the engine.

As an example: if your engine generates 100 hp and 50 ftlbs of torque at 5800 rpm and you add a gear box with a 3:1 ratio then you now have 150 ftlbs or torque delivered to the prop. Horsepower doesn't change but the torque to drive the prop is multiplied by the gear ratio.