Jabiru - Page 2

gpiney · #11 01-20-2010, 09:59 AM

Don't forget to add in the weight of the prop and spinner. That may move you back an inch or so. You may also gain a pound with engine sensors. There are a lot of 'add-ons' which the engine manufacturer does not include. And don't forget it is DRY weight which does not include the weight of the oil.

Canadian_JOY · #12 01-20-2010, 02:10 PM

I've got to say the Jab3300 is one of the sweetest-sounding engines on the market today. We have a couple of them on Sonex aircraft in the local area and they produce some very nice ear-candy at takeoff power.

I'd suggest you take a look at what Sonex builders are doing. Keep in mind they went to a spinner machined from billet aluminum in order to put more weight forward. A local builder put a Jab2200 in a 601 and ended up having to add massive lead weight trays atop the engine to get the CofG in limits. Obviously that's not the right way to go.

With a need to move weight forward you may also wish to consider an engine-mounted fire extinguisher, and of course a bigger battery mounted as far forward as you can get. The idea of putting the Dynon remote compass sensor up front is a non-starter - too much ferrous metal up there, plus it only weighs an ounce or two. But ensuring the engine sensors are mounted right up front will be a big help - my Van's oil pressure sensor is surprisingly heavy, as is the tach sensor and adaptor.

David Paule · #13 01-09-2011, 06:23 PM

Hate to revisit something that finished a year ago, but it could well be that if you hang that 3300 on it, moved forward the right distance, that the mass inertia for pitch and yaw increase significantly.

This is because the inertia is the mass times the distance from the CG squared.

An increase in mass inertia apparently adversely affects the RV-3's handling characteristics. However if you don't do aerobatics, including spins, that might not matter.

The static stability will decrease with the increased side area forward, as well as the prop being moved forward.

Hate to be all negative, but there it is.

Andy Hill · #14 01-11-2011, 01:21 AM

As per David, suggest also allow for:

Top / Bottom engine mount / firewall fittings. Take 280lbs x X" (Dist) and compare to 180lbs x X+20". You may find the moment at that point much higher, which will either require a redesign of the engine / firewall mount, or restricting to +/-4g say
Empennage size. Increase ia "area" fowrard of CG due to extra cowling (+~20") - and that area x dist from CG = moment. You should probably look look at increasing the fin / HS (and control surface?) sizes to compensate or you could have pitch/yaw instability problems (in turn compounds CG problems).

Andy

smokyray · #15 02-07-2011, 05:38 PM

Hi Bill,

Many years ago when I was building my RV4, I was flying a friend's RV3 with an 0-235, wood prop, nose tank, no electrics. It had a tow hitch built into the lower rear fuselage so you could prop it, get in, release the tow hitch and go. I loved it, a really great airplane! Having just crunched the weight numbers, the 0-235 with no accessories, flywheel or anything else hanging on it and a light prop is within 30 pounds of the Jabiru with all the trimmings.
The math formulas presented show me you just might be able to keep it within the stock cowling and not have to add any weight other than necessary items. If yours has a nose tank, fuel helps alot more than wing tanks. With an Odessey PC-925 battery firewall mounted (28 lbs), 3 blade composite or MT 3 Blade electric constant speed prop out front (57 lbs) you will be close without having to move it significantly forward. Worth a try!

Good on ya!
Smokey

I watched my friend Jim Swick scratch build a clip-wing T-Craft with a Rotec Radial up front (his 14th scratch-built airplane). He hung the engine from a chain in front of the airplane and put angle iron brackets into the fuselage engine mount holes. He then lowered the engine carefully onto the iron bars with the airplane supported at the struts in level flight. When it balanced, he marked the braces and measured the distance. He then welded an engine mount up with the engine hanging in the proper position and simply made the tubes match the holes.

RVjim · #16 02-08-2011, 08:34 AM

From Smokey Ray,
(stuff cut)
MT 3 Blade electric constant speed prop out front (57 lbs) you will be close without having to move it significantly forward. (end quote)

The MTV-18 3 blade electric CS propeller assembly (includes attached spinner) weighs about 45 pounds.

I believe Smokey Ray was referencing the weight of the larger hub MT 3 blade electric CS propeller assembly which does weight about 57 pounds.

BTW, MT propellers are limited to 2800 RPM maximum.

Regards,
Jim Ayers

steve lenne · #17 02-08-2011, 10:52 PM

thats a lot of weight to put on the end of a jabiru motor

kymjon · #18 02-09-2011, 04:48 AM

Not sure I would want to be hanging heavy weights off the prop drive as they were designed with wooden props. I believe that Airmaster in New Zealand have now developed a version of their electric in flight adjustable for the Jab motor.

They can also be hard to start when it is cold as the ignition spark is quite weak and cold fuel does not atomize well and one thing to do is to close up the spark plug gaps more than the manual says and they do start much better.

Mine stopped in flight and the resultant forced landing in windy conditions behind trees did not go well and the aircraft was written off. My wife laid down the law and said I could only have another aircraft if it had a real aero engine and a stall warning. Agreed rapidly and I now have a beautiful RV6A with Lycoming 0-320 and stall warning. Sometimes good things come out of bad landings

smokyray · #19 02-09-2011, 08:11 AM

Guys,
Couldn't agree more. That is alot weight on the nose, however comma, I was just running numbers that show you can put enough weight up front without significantly changing the airframe.
I personally would put a big battery up front and install a ground adjustable Sensy or Whirlwind composite.
The RV-3 owners list shows two with 0-200's in them, should be close in weight similarity

Smokey

sjarrell · #20 02-09-2011, 08:42 AM

Quote:

Originally Posted by smokyray

Guys,
Couldn't agree more. That is alot weight on the nose, however comma, I was just running numbers that show you can put enough weight up front without significantly changing the airframe.
I personally would put a big battery up front and install a ground adjustable Sensy or Whirlwind composite.
The RV-3 owners list shows two with 0-200's in them, should be close in weight similarity

Smokey

One other thing to consider that makes putting a larger battery in a really good idea.... I had a Jabiru J230 with the 3300 engine and it required a strong battery to spin it fast enough to start when it was cold. Hot it started just like a car.... very quickly in a blade or two. I forget how many RPM it was that you had to be spinning before it would start but it wasn't trivial, and I ran the battery down more than once in cold weather (30-40 degree F) trying to start it. I'm sure this problem (high rpm start) would be exacerbated with a heavier prop.

Also, if you use the Jabiru ignition coils (which are actually Honda industrial coils) be sure to put blast tubes on them to keep them cool, and keep a spare handy as they're not something that you're going to find locally. They do get hot and burn out (even with the blast tube.... ask me how I know... :-)