Gryohead

I have a dual ring 31cc Ryobi that is turning a Master airscrew 18x8 at 8400 rpm which I think is a little high for this engine, I would like to get this in the 7500 rpm range, should I go with a 18x10 or a 20x6 prop? Gryohead.

captinjohn

I would just fly it the way it is for now. Just do not use full throttle....good to have reserve! By the way...can you tell us what carb and exhaust...ect you are using on that Ryobi? Capt,n

av8tor1977

My Feedback: (6)

That's a really strong Ryobi. Is it modified? Are you sure your tach is correct? My 42cc Poulan turns an 18 x 8 at about those rpms...

If your tach is correct, then personally, I would prop it a little heavier to get closer to 7500 static as you say. The prop unloads in the air, and the consequent rpms will be high for a Ryobi.

As far as which prop, that depends on both you, and the airplane. A big slow airplane would like the 20 x 6, as would an airplane used for some 3D flying. A faster, sleeker airplane used more for traditional aerobatics would probably do better with the 18 x 10. You prop the engine according to the airplane, and also according to it's intended use.

Have fun,
AV8TOR

Gryohead

The engine does run strong and has been modified, carb. is a Walbro WA 40 A two needle and was opened to 11mm, Bennett mufler, the flywheel has been turned down with all the fins removed, a paper gasket between the cyl. and crankcase to increase C/R, the intake and ex. ports have been reworked and has Bowman rings, so I guess you could say it has been modified a little. The airplane is a large sport Aerobatic 81" wingspan, 13.5 lbs. mid wing scratch built. A real little ***** cat when it comes to flying.

Gryohead

captinjohn

Do you know what the port timing is now? I still say with throttle management...the prop you have is fine. Capt,n

Gryohead

154 deg. on the exhaust and 143 deg. on the intake. Gyrohead

Ralphbf

My Feedback: (27)

Do you like the speed the plane has now?

If so go with the longer prop.

A prop with a 6 pitch is pretty slow. And a prop with a 10 pitch is pretty fast.

av8tor1977

My Feedback: (6)

How can the intake timing be 143 degrees when it is a reed valve engine??? Did you change it to a rotary intake valve?

AV8TOR

Gryohead

The transfer ports in the cylinder were raised to 143 degrees. Groyhead.

av8tor1977

My Feedback: (6)

I saw on a website a while back where a guy made a rotary valve setup for a Ryobi. I'd like to try that sometime. Oh well.... too many ideas/projects/experiments, too little time...

AV8TOR

Gryohead

The only problem with the Ryobi is the stamped steel connecting rod that's why you have to watch the rpm. I had one eat the rod on a test stand, it must have been turning around 9 grand when the engine just stopped dead and thru the prop down in the dirt, luckly it went stright down and not out. Gryohead

av8tor1977

My Feedback: (6)

Yeah, that's why it's best to keep the static rpms down to around 7500 with the Ryobi. I imagine it still unloads to well over 8000 in certain flight modes, but they seem to hold up ok as long as the static is about 7500.

AV8TOR