Online Community of Zenith Builders and Flyers
Hello Jabaru Owners!
I have a 3300 Jabaru sitting on the front of a Zenith 750 and I am about 7 weeks out to first start. I know I need a prop on the front before I turn the key! I have 2 quotes from prop manufacturers and I am wondering what you have on the front of your 750.
The factory has a Whirlwind GA200-J2B that would be my first choice seeing that it fly's well on the prototype. It comes in a 65 inch and a 63 inch.
So here are the questions I have:
Why would Whirlwind have 2 sizes for the 750 and which one is better for STOL flight. I would prefer climb performance over cruise.
Are there any other props that you have found to work well with the Jab / 750 combination? What kind of prop are you flying with?
Anyone have a used prop you would like to sell?
Joe in Oshkosh
i have that engine w a Sensenich Wooden Climb Prop... i would go w the Whirlwind Ground Adjustable as well.
Jabiru should answer your question regarding diameter, i.e. directly coupled and max engine rpm... tip speed being so critical. they have done prop studies w their 'approved' vendors... from what i've read.
they run perfectly and smooth... always watch for head/valve deterioration by removing the valve covers frequently... all valves should look exactly the same without dark/hot... this will indicate problems way early. Also, i've read they have a newer cowl for the oil cooler. i'd be interested in photos of that...
Your install looks great so far! Keep us posted for future installers.
Geo, thanks for the advise. What kind of hose did you use between the airbox and the carburetor? I was thinking a cut down radiator hose with a 90 degree bend but their must be a better way!
Here's a pic of the new cowl design (photo taken May, 2014 - I don't know if there has been another design change since) It's supposed to prevent turbulence, especially at high angles of attack, from interfering with the exhausting cowl air and provide a better exhaust air path from the oil cooler:
The new design looks much more efficient with less drag - I have the original cowl design and flush-riveted a 2" aluminum extension on the lip:
As far as the carb/airbox duct, I originally used SCAT but had uneven EGT's. I switched to a 90 degree bend smooth-bore radiator hose with a "straightener" between the hose and the carb. This resulted in more balanced EGT's. Pete at Jab USA gave me the "straightener." It was a section of aluminum tube with 4 internal vanes 90 degrees apart to smooth and straighten the airflow ... I don't know if Arion has them or not, but it wouldn't be too hard to fabricate one.
I've run a Sensenich carbon fiber ground adjustable prop for about 300 hrs and have been very pleased with it. This prop is specifically designed for the Jab 3300. Each blade is molded in one piece with a hollow internal cavity so it is very light and strong. About the only criticism I have is that the pin/cylinder system that simultaneously adjusts the pitch of both blades is not precise enough to suit me - I turn the blades to the approximate pitch and then use a digital protractor to fine-tune the pitch (13 degrees for best cruise on my STOL 750) separately on each blade. It pays off since I was able to do a DynaVibe prop/engine balance and got it down to 0.03 ips !!! (< 0.1 ips is considered "good" and < 0.07 ips is supposedly below the limits of human perception of vibration).
While this prop isn't exactly cheap (I bought a slightly used prop fresh from a factory refurbishment, so it was same-as-new for a fantastically low price!), it has been superseded by an even more expensive model "for some applications." I "think" however, the prop I have is still the appropriate one for the STOL 750, so thankfully it is less-expensive!
If you have any questions, don't hesitate to call Sensenich. They'll usually put your call right through to an engineer or technician and are very patient answering questions and even willing to fabricate custom parts such as prop spacers, drive lugs, etc.
BTW, Cummins Spinners makes a beautiful aluminum spinner for this prop. Not exactly cheap, but it is a bolt-on and go part and saves hours of finishing and painting a fiberglass spinner. I bought my first Cummins spinner for my Sensenich wood prop from Jabiru USA (don't know if Arion, the new Jab dealer, has them or not) but bought the second Cummins spinner for the carbon fiber prop directly from Cummins for less $$, even though they're in Australia!
BTW, there's nothing wrong with the Sensenich W68CK36 that is the base model for the FWF kit from Jabiru USA. Certainly not adjustable (but much less expensive, especially used!), but since it is wood, it is inherently smooth and certainly beautiful to look at! :>) Here's my original prop (just sold it this week!) with a Cummins spinner:
John, I have a wood prop I am going to sell but it's for the 650 with a Jabaru. Seeing that you have flown behind the wood prop and the carbon fiber prop, which one did you feel was better for performance?
Since the wood is fixed-pitch, it's obviously a compromise between climb and cruise - a good "all around" prop. However, it's no contest vs the carbon fiber, since it is ground adjustable - you can set the pitch for either extreme or somewhere in-between.