Pete S-RCU

I have a Zenoah G62 in a TF Giant scale Corsair.
This is my first time with a gas engine.
Stock magneto engine, brand new.
It has a bad vibration at about half throttle.
Used two different props, both balanced.
It's mounted solidly to a 3/4 inch laminated plywood firewall.
Mounting bolts on the engine stay tight, but other things shake loose in the plane.
How much vibration is normal with this engine?

Capt Jim

My Feedback: (168)

Hi Pete....Zenoah G-62 uses a Walbro carb. They are well known to have a poor mid-range...however, that only makes for a rough transition, from low to high RPM, but not necessarily a vibration.
Big gas engines sure do make a lot more vibration than glow engines, but it is typically most noticeable at very low idle settings. It should be smooth enough to fly above 2000 RPM's.
What was vibrating loose?... and was it secure to begin with. It is not unusual to see screws backing out, nuts working loose, etc, on a big gas set-up. Lok-Tite is one product that helps keep things all together, but it is no substitute for good regular inspection and maintenance.
If your prop and spinner, (if you use one) are properly balanced that motor should be fine. It would be rare to find one that had a bad (radically unbalanced) crankshaft...unless it had endured a prop strike the ground at sometime, or any number of bad crash scenarios. Bent cranks can be straightened though. All it takes is a fixture to hold it firmly in position (like a lathe) while you rotate it by hand using a dial indicator to detect the location and amount of run-out. Then you just set it in a big vice and whack it appropriately in the correct spot until you get it all back in line again. I hope this is helpful to you.
Have fun, and good luck.
PS: By the way, I have a big ocean going sailboat docked here that has "Lake Prior" as its hailing port. From what I hear, Lake Prior would not be big enough or deep enough to hold this one. She's 50 feet long, and 7 feet deep!
jim

Big_Bird

My Feedback: (1)

Pete, I think that what you are experiencing is pretty normal. You probably have an air frame/engine resonance problem near mid throttle. The most common cure for this is to determine where that throttle setting is and not run the engine there for very long during a flight. The other thing to do is to use Loctite on the screws and keep everything tight.

Pete S-RCU

Thanks for the replies guys.
The engine is mounted solid, I was told soft mounts aren't the way to go for this setup?
I do have lock-tite on the engine mounting bolts, they stay tight, although I have only run one tank of gas thru it.
The engine is brand new, so I assume everything is straight.
It seems to hit a resonant spot about 1/2 throttle, just wanted to know if I had a problem.
It vibrated the fuel tank back and the clunk line inside fell off.
I have put clamps on the tygon lines and put foam padding behind the tank to make sure it doesn't move.
I just rebalanced the prop, wood 20-8-14 and an APC 20x10.
Both seem to vibrate equally, so it's probably just the nature of the beast.

Thanks again for the help.

Big_Bird

My Feedback: (1)

Pete, sounds you are doing the right thing. I usually put a layer of foam rubber on the tank floor and use nylon tie wraps to hold the tank down. Gasoline doesn't have the foaming problem that methanol has so vibration is not much of a problem with the fuel. I always use nylon tie wraps inside and outside the tank.

The props that you are using with the G-62 may be a little small. You might like the 22x10 size better. The G-62 seems to be best when it is propped for 7000 - 7300 on the ground. I like the NX and Menz standard 22x10. The best thing about the NX is that they are always in stock at Airwild. At least that is what I've found.

Soft mounts cause more problems than they are worth. You sure won't find many people using them. Solid is best.

Pete S-RCU

Hi Ken,
Just ran it with the 20-8x14, runs good, vibration seemed exceptable.
Peaked it about 6500 and then richened it up till it was 6300 rpm.
Maybe will pickup a few rpm as it breaks in.
Idles around 1700 reliably.
Did range test, OK with the engine running.
Am going to try it with the cowl on and see how it runs, heat wise.
How long do you think it will run on 24 oz fuel. I ran it a long time and didn't run out of gas?

Pete S-RCU

Ran it with the cowl on, cowl vibrates at the resonant point.
I have the heavy FTE resin dummy engine mounted in the cowl.
I glued it in with Zappa dappa goo, might be too flexible?
I will have to investigate to see if I can mount it different.
Makes a hell of a racket when it starts vibrating.

Big_Bird

My Feedback: (1)

Pete, sounds like you are about ready to fly it. Remember to transition through the rough point pretty quickly. I have 6 planes with gasoline engines and they all have a little rough spot due to resonance. This really hasn't been too much of a problem.

Homepylon

My Feedback: (1)

Hi Pete:
I've got a new G-62 with CH Ignition in a 1/3 scale Jungmeister bipe and the characteristcs you describe are the same as I've encountered. I ended up mounting my dummy engine with small brass brackets and 1-72 bolts in addition to epoxy putty. This seems to be holding up OK. The engine does shake quite a bit around 4500, but other than loosening the dummy engine it hasn't been a problem.

You should be fine with a 24 ounce tank. I put a 32 in the Jungie and am always landing with about a third of a tank left after a 15 minute flight at various power settings.

I think the G-62 is pretty good value for the money. It sure hauls around my 30lb bipe with authority. I'm running a 22x10 XOAR prop. Started with a Zinger (big mistake) and can't believe the difference with the XOAR. I'm getting 6300rpm with about a gallon and half burned so far. Everyone at the field says I should be getting 7k, but I think the engine needs more running time.

Good luck with your Corsair

Brad

Tired Old Man

My Feedback: (1)

Running time will not bring you the 700 rpm. Maybe 50 or 100 but not 700. You need a different prop, or better tuning, or a better muffler, or all three. The muffler for certain if you are using the stock unit.

Zippi

My Feedback: (10)

Pete S-RCU,

I'm running a G62 with CH EI with a XOAR 22X10 prop. The first time out to the field it was running about 6700 rpm so I tweaked the high end 1/8 leaner and it tached at 7000 rpm. really sounds and runs good. We just had a Warbird meet and a lot of guys are running the Top Flight 22X6X10 wood prop on their G62's and the are getting better performance and it really makes a good sound in the air. I just ordered one from Tower. The XOAR props from Chief Aircraft are $28.50 and the Top flight props from Tower are $17.99. I'm going to give one a try and see what happens.

Pete S-RCU

Thanks for the advice guys.
I'm going to remount the dummy engine today with epoxy and maybe some brackets.
I think I didn't roughen up the inside of the cowl good enough.
It'sready to fly, soon as we get a day without 30 mph winds I'll give it a shot.