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Ryobi 31cc

Old 05-03-2004, 02:02 PM
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3DP
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Default Ryobi 31cc

I'm thinking about using a Ryobi 31cc in a 25% lanier extra or laser. What kind of performance could I expect from this combination? How much actual power can you get out of a 31cc Ryobi engine? I plan on using some sort of electronic ignition so I can save some weight by removing the flywheel. Another reason for this is I wonder what kind of forces the flywheel would put on the crankshaft when flying somewhat agressively due to the gyroscopic effect.
Old 05-03-2004, 03:42 PM
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CrazyHerb
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Default RE: Ryobi 31cc

3DP,
It all breaks down to wing loading...

While the Ryobi is a very reliable motor, it has a few major drawbacks for your intended purpose.
First is weight, even with electronic igntion you will sit around 4 lbs ready to fly. This ties directly in to wing loading.
I couldn't find any info on the 25% but if I remember correctly it MAY just barely have 1000 sq inches of wing area.
You will be lucky to get the plane under 12-13lbs ready to fly and still have an airframe strong enough to support a gasser.
http://www.gsal.org/tools/Wing_Laoding.htm

That brings your loading up to about 28 oz ft. Flyable, yes....perfomance...no...you'll have to keep power on it until you land...it will be a tip stalling nightmare.
Imagine the waste of a good aerobatic airframe that flies like a heavy trainer...with faster roll rates....and a snap tendency...

The most thrust you'll get from the Ryobi (even converted to ignition) will be 14-15 lbs.

It really depends on how you want to fly it....but I don't recomend anything under 1200 sq inches for a Ryobi. My Big Pink (with ryobi TWIN ring version) is 16 lbs with over 18 sq FT of wing area... loading is around 13-15 oz sq ft. A very happy combo....

Recommended airframes for the Ryobi (Stinger 1.20, or UltraStick 1.20)....notice both have generous wing area.....
Recommended motor for the 25% - any glow 1.20-1.60 or maybe the newer generation of gassers like RCS 1.40/1.80 MVVS 1.40-1.60

I have the RCS 1.40 and its awesome...worth every penny....swings a 16x8 Bambula at 9100 rpms and whole setup is 3lbs with muffler and ignition.
Currently bolted to a GSP/CMP Katana.

So....I would seriously think about what direction to go from here....
Keep the Ryobi? - Get a different airframe
Keep the Laser? - Get a glow motor (or new generation lightweight gasser if you want gas)

I hope this helps....and I'm not saying don't try it....but be prepared that you more than likely will not get the results your looking for with this combo.
This airframe deserves a good strong, light motor...and the ryobi deserves a light 1200+ sq in plane.....
Good Luck!
Hope this isn't too much of a downer.....
CrazyHerb
www.crazyherb.com
Old 05-03-2004, 05:39 PM
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3DP
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Default RE: Ryobi 31cc

Great, this is exactly the response I was looking for. I rather have someone tell me how it really is. If I get a stinger 120 instead, what would the performance of that combination be like?
Old 05-03-2004, 07:14 PM
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Rejean Boucher
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Default RE: Ryobi 31cc

What a timely post. thanks 3DP and thanks CrazyHerb for your detail response. I myself have been trying to figure out what airframe to slap this motor on, I have seen your video of your Big Pink Foamy; sure is impressive.
Yesterday, I was bench running my Ryobi 31CC at our local field for the second time and we were totally impressed with its power output. Initially I had a 16x10 Master Airscrew Classic series and it was topping 9200 RPM! I quickly switched over to a larger 18x8 Dynathrust and now it runs 7200. I recall reading somewhere that you should not run the Ryobi 31cc over 8000 or you might snap the connecting rod. So far I have 70 minutes on the bench, will place a couple of more hrs prior to flying. Since I am new to this gas stuff, I don't have much to compare it too, other then what I am reading here on RCUniverse. Anyways I am very impressed with the power output. Only negative so far, is trying to maintain the exhaust secure. I am going to re-tap the holes to fit a helicoil insert and lock wire the bolts in place, hopefully this works. My timing is set to 28 degrees advance, CH ignition and was running 87 octane with the standard ryobi oil mixed at 32:1. Short shaft, dual rings and those controversial vertical slits in the inside of the cylinder wall. This weekend I will update my web site with more details to my conversion project.

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