shann

My Feedback: (12)

I have done some research and have not found what I am looking for. I have a zenoah GT-80 on a H9 Extra 330L. It has a 3W 24X10 wooden prop and twin bisson mufflers (they look like bisson best I can tell) . I have read that it should turn around 7200rpm. I can just get 6200rpm peaked. Is there a problem with the engine or is the prop too big? I don't know how new the engine is only that I was told it has been bench run and thats it. I don't know that I believe that. I want as much static thrust (3D) as I can get with out spending a fortune on the prop. I also don't have the funds to experiment with props. Changing the engine out right now is not an option unless some one wants to swap a ZDZ80 or 100cc twin for it I will consider electronic ignition here pretty soon but I don't think that is going to make a huge difference in top end power. So bottom line is: What prop do I use?


Thanks
shan

Tired Old Man

My Feedback: (1)

The electronic igniton will not provide more power, but it will reduce weight. Reducing weight effectively increases power because the same engine now has to work less hard to do the same job it did before, leaving the difference available for greater flight performance.

Try a 24-10 PT or Mejzlik carbon prop. A Menz in the same size would be a good wood alternative. Don't try a Vess until you know your engine better. The wrong one can put a lot of load on that engine that it doesn't need. That 3W is a lot of wood. Another item that comes to mind is engine tuning. Being bench run does not mean it's been tuned for the location it will be flown at, just simply made to run. Something else. RPM numbers are different for every single engine and prop combination. No two are ever the same. If you end up only getting 6,800, 7,000, or whatever, if you did everything else correctly that last number is the correct one for the engine.

Truckracer

My Feedback: (19)

Yes, your tach readings seem a bit low for that engine. I usually expect somewhere between 6800 and 7200 with similar props to what you are running. The 3W wood props do load an engine quite a bit but not to the extent you are seeing. A Menz or Xoar will usually turn up more than a 3W. RPMs will vary quite a bit just from one prop to another of the same stamped size and brand. The Zenoah twins like to turn up so you might try something like a 23-10 also. These engines require a compromise between what they like to run well and what your airplane likes to perform well.

If those are the Bisson mufflers, do they still have the crimped ends (tapered to a smaller diameter on the end) exhaust stacks? If so, cut the tapered end off and enjoy a bit of performance improvement. Maybe the engine just needs more run time to come around .... how does the compression feel when you turn it over? I have one Zenoah twin with stock ignition, one with a rcign conversion .... they run pretty much the same at full throttle .... the EI version idles and starts extremely well and weighs well over a pound less that the stock one.

Rcpilot

My Feedback: (78)

Run a 23-10 on the motor for 5 or 6 gallons. Let it spin.

Then switch out to the 24-10.

shann

My Feedback: (12)

I just ran a master airscrew scimitar profile 22X10 and clocked 8200rpm. Is this too many rpm for this engine? I have been adjusting the high speed at top end to peak and backing it off 300 to 400 rpm. So this is not bench run settings. Also the plane has been flown three times now. I do notice it sounds fine straight and level and drops a very noticable amount of rpm on vertical. My Tarus 3.2 does not do that. I know different engine prop combo. My point is I think the engine is way over proped. The only affordable prop I can find right now is the menz 23X10 profile. Do you guys think that will be all right? Or can I use the 22X10

I also want to thank all of you for your time and thoughts responding to this thred.

Shan

Rcpilot

My Feedback: (78)

8200RPM is a cake walk for a GT-80. It's perfectly fine to run it at 8200RPM. That same motor--unmodified internally--is run on methanol fuel in GS racing planes at well over 10,000RPM. Only thing different is the carb and a glow plug is fitted. Nothing about the crank, bearings, rings, pistons, rods etc.. is changed.

That engine is laughing at you. "8200RPM? HAHAHAHAHAHAHAA bring it on!!"

If it will fly the plane, then run that prop until it breaks in a bit.

Tune the engine, as you have already done. Now you should be able to fly it for 3 or 4 gallons without touching the needles. As the engine breaks-in, it will turn more RPM and require that you open the high speed needle some more to prevent lean running.

When it hits 8500--8700RPM, slap a 23-10 on it and tune for that prop. Fly it. It should run fine for another 3 or 4 gallons. It will pick up RPM as it loosens up and gets comfortable. Richen the high speed needle to prevent lean running and let it spin.

The 23-10 should peak out somewhere over 7500RPM after a few gallons. It will eventually stop gaining RPMs and settle in. At that point, you can opt to keep your 23-10 or prop it up to the 24-10 again and check RPM. Tune again. Keep it over 7000RPM and you'll be happy.

shann

My Feedback: (12)

Now that's what I am talking about. Thanks Rcpilet

Rcpilot

My Feedback: (78)

You will know when it's time to re-tune the engine. As it breaks in and begins to turn more RPM--it will start to act lean. Just fatten the high speed needle a bit and fly it some more.

SPACE COWBOY

Cool info! Thanks, guys!