misterpanda

Dar, Ed:

Good news !! I installed the Zinger 14x8, nicely balanced with a pair of stong magnets. The G90 is now running much more smoothly, very good transition considering it's new, and LOADS of power.

I tried the following plugs with these results:

OS A5-- the engine barely started
OS # 8: good power, much less vibration with the new prop.
OS F: It ran but not very impressively, engine vibrated more due to weak running.
K&B with idle bar: The best of all four tested, yielding the smoothest (vibrationwise) run of all.

Therefore the K&B is staying with the engine.

My fuel is FAI home mix. Our elevation (above sea level) is 8,600 feet (=30% hp. loss). Our year-round day temp. averages 65 Fahrenheit . These data to give you an idea of our flying environment.

The Zinger 14X8 is quite light but sturdy. I always sand smooth the front and back of my props because I've seen that rough faced props, believe it or not, cut down the RPM. Glossy-faced props (Grish) really whip up the revs. Hope I don't break it, being it's the only one I have, and you don't see many of those around here.

One thing that irks me is that the Super Tigre engine manual (page 14) recommends a prop range for the G90 which is ridiculous: Starting with 11x8 (which is for a .46), ending with 13x7 (for a good- powered .75).

So the engine is now running quite well, not totally smoothly, but quite acceptably (my rating from 1 to 10 = 8). I have to mention that the engine mount has rubber shock-absorbing inserts. Let's see how it flies mu 7.5lb plane once its fully broken-in.

So "the props have it" basically. The plug change affected somewhat too. Thanks all for your comments and info. I'm a much happier G90 owner now.

Regards,
Misterpanda

NM2K

My Feedback: (14)

Very good. I'm glad that you are happy.

The rubber mounts contribute a lot to engine shaking. Unless you are competing where noise abatement is a requirement, vibration isolation mounts are to be avoided. They rob your engine of power, kill glow plugs faster and make your engine more prone to lose parts (hard to keep screws attached).

Not all vibration mounts are the same. The various types have their own characteristics. I have been known to use the Dubro system without problems. The system used by J-Tec (one of my favorite vendors) caused me some problems when the rubbers pulled through the firewall, even with properly drilled/sized holes in the firewall. A friend built the model for me and he is an excellent builder, so I doubt that it was anything that he did. Maybe they weren't tightened sufficiently. Who knows. Anyway, I don't use isolation mounts any longer, since I don't fly in competition that requires them.

People have been flying G90's with the suggested props for at least a couple of decades, if you count the S90K in the group. Those were normal prop sizes before 3D came along. I always argued that it should have been a list starting with the 11x9 and going up to a 14x6, with the 13x8 in there too. Tigres were designed to rev up.

Good luck with yours.

Ed Cregger

XJet

Light prop, less vibes, point proven, case closed

(big smirk)