Jabiru
 

I have a Jabiru 3300 engine that, hopefully, will find its way to the business-end of my RV-3. A new conical mount just arrived from Vans. An extension of some yet to be determined length will mate the Lycoming conical mount to the 3300. The 3300 weighs about 180 pounds. An O-320 weighs about 280. Comments are requested regarding the correct method of determining how much forward the Jabiru will have to be located.

Thanks

Bill Newkirk

Hi Bill...
 

I'd start with a datum, like the leading edge of the wing and measure that distance to the liftiing eye of an 0-320. Multiply the weight of the engine by the distance to find a value for the moment/arm.

Then divide the weight of the Jab into said moment and the answer should give you a close distance to locate the Jab.

Best,

Jabiru
 

Thanks, Pierre. I did as you suggested and the result is that with everything else being equal, the motor should be pushed forward about 20". Wow.
Of course, the location and size of the battery is just one of many variables.

Bill Newkirk

You probably can shorten the distance...
 

...by using something heavy, like the Landoll harmonic balancer on the prop flange. Either that, or some lead attached to the motor mount near the front.

The caveat here is unnecesary added weight, plus the downward stress on the motor mount under higher 'G' conditions, like aerobatics or turbulence.

Best,

Wow, 20"! If you don't add some accessories up there to bring it back some, you're going to have to add spray bars behind the wings and rent yourself out as a cropduster.

Hmm... Let's see... What could go ahead of CG to help? Battery, Smoke system, Remote compass for a Dynon? Might be too close to the engine for the compass. Metal prop? Constant speed prop maybe?

RV-3 Jabiru
 

Depending on how far you are in building of your 3, I would suggest that you look at the design of the 3 with the 0-200 continental engine.

Jabiru
 

Hi, Tony. I'm the really good-looking guy that was interested in how you built the roll-bar on your beautiful 3.
I already have the Jabiru engine and really want to use it. It is nice and narrow, so it will not require "cheeks". AND a couple of us are coming up with a plan to attach Wittman Tailwind wingtips to my quickbuilt wings. Some of the Tailwind guys at Oshkosh told me that those tips reduced the sink-rate almost 400 ft/min. Please don't stone me, it is an experimental after all.

Bill Newkirk

More power to you.
 

Bill,
I think it is great that you are enjoying the beauty of what experimental aviation is about. If you want to experiment with this engine, I say go for it. I've heard good things about the jab 3300.

Just play it safe in your testing.
I personally am not the type of individual that has the patience and know how to design things, but I am greatful for those of you that do.

It will be nice if you can make this work. A little competition for lycoming and rotax engines can't hurt us as consumers.

best of luck,

The Jab 3300 is a good engine, at least in my experience (50 hr behind it). Single Bing altitude-compensating carb, 6-cyl smoothness, simple fuel and electrical systems, standard automotive spin-on filter, likes MoGas, etc. I think it's only configured for a FP prop, so the Sensenich composite ground-adjust might be the prop of interest. Price is decent at $18k.

The 3300 and the -3 are an interesting pairing. The Jab is light and simple, what the -3 is all about. Narrow too, probably smaller "cheeks" on the cowl. Down sides are lower Hp output, less support in the US, no support from Van's for the install.

Kudos to you for trying something new!

TODR

We do this type of CG check all of the time flying model airplanes. You want to use the actual center of the CG to make your new calculations for the motor moment. The center of the CG on most models ia about the wing spar. I do not know what it is on a RV :confused: With models we call this the balance point. Using the new measurements I believe you will move the motor back just a little from the 20 inches. You need to double check with new calculations using the WB formula for your aircraft to make sure the new CG is where you want it.

Dave (Swift driver)