Ryobi 31cc Gasser Build

[offaxis]

This weekend when I was at an auction a Ryobi 31cc string trimmer came up for sale and no one bought it. It was thrown on the junk pile to be discarded. I couldn’t let a good motor go to waste so I asked if I could take it home and was given the ok.

It had a note on it for parts only but I figured I would at least try and see if it starts. I gave it a few pulls and it puttered to life. After some playing with the choke settings and a few restarts, the motor came to life and appeared to run fine. I’m excited to tear it down and convert it to a RC engine and build my first gasser.

What I’ve learned about this motor when used in a RC Plane:
Displacement: 31cc
Expected RPMs: 7000-7200
Typical Prop Size: 18x8 or 16x10
Typical Thrust: 11-13lbs
Use a resistor type of plug: NGK BPMR6F
Mount bracket can be made from a 3x3 aluminum tube.

Conversion parts available here: http:[//]www.carrprecision.com/Pages/prod02.htm [Balu: Link removed, Domain is now hosted by a Domaingrabber and contains malicious ads. Visit at your own risk.]

I’m looking for inspiration and will store all the information I need here for when I will finally get to this build. What plane should I build for this motor? SPAD UltraStick, an oldtimer, old warbird. It would be cool to put it into a 3D plane but I’ve read that the heavy motor makes them too nose heavy and don’t have enough power. I also don’t know how to fly 3D yet either.

This project will be drawn out for a long time because my wife says I’ve use up my 2015 annual RC hobby budget money on a zmr250 build. She’s right and it’s only the end of March. It’s going to be a long year.

 

[PJaussie]

Just do a few extra cash jobs around the place and gradually buy the balsa a few bits at a time and go from there, the balsa is cheapish but its the time that costs, and that you can afford from the sounds.

I've always liked the oldies, maybe a Sopwith Camel?

 

[sconner]

Google "weeder boat". I was going to use my old Ryobi weed eater for a boat, just never did it. I would think for a plane it would just weigh to much to be very fun. The plane would have to be massive to carry the load. But hey, if you do it, I want to see it!

 

[offaxis]

Does any one have recommendations on coroplast planes to build. Want something high wing and fun to fly.

 

[sierra_bravo]

How about a SPAD ultra stick I already started the build on one for my 30cc homelite.

I've never flown it myself but I have heard great things about them. Also the original plane used a 31cc ryobi so your motor would work great. For conversion parts you could always do what I did and get the prop hub made by a machine shop. My local machine shop made me the hub and also re-threaded the crank shaft for free.

-Sam

 

[offaxis]

I think I'm going to give this a try. http://www.instructables.com/id/8-Ft-Wingspan-Coroplast-RC-Piper-Cub/

 

[Frequent crasher]

with 2016 right around the corner, are you still looking for an airframe? if so look up my BAD SPAD. the ultraspadstick looked a little complex for me as a first spad build.

 

[Flyin Farm Boy]

The ryobi 31 is a great motor. With a bigger carb and electronic ignition it becomes a powerhouse. (at least for a throwaway weedeater) My neighbor gave me one and I spent a lot of time tinkering with it. Finally got it to turn an apc 18x6w (recommended prop btw) at 8100 rpms! That pulls my 15# spad straight up pretty well. I can hover on a good day. Here is a link to some pictures. Check post #729. http://www.rcgroups.com/forums/showthread.php?t=221347&page=49

 

[offaxis]

The ryobi 31 is a great motor. With a bigger carb and electronic ignition it becomes a powerhouse. (at least for a throwaway weedeater) My neighbor gave me one and I spent a lot of time tinkering with it. Finally got it to turn an apc 18x6w (recommended prop btw) at 8100 rpms! That pulls my 15# spad straight up pretty well. I can hover on a good day. Here is a link to some pictures. Check post #729. http://www.rcgroups.com/forums/showthread.php?t=221347&page=49

Cool. Where did you source the bigger carb and ignition. Hop up parts are getting harder to find for these motors.

 

[Flyin Farm Boy]

http://www.ebay.com/itm/New-Poulan-...814832?hash=item33af9fc230:g:HQwAAOSwpDdVTxbb

Ebay. They have pretty much everything if you look long enough. Walbro makes so many different models it is hard to know which one to get. The ones with a 11.11mm venturi are the right size. I think the stock size venturi was like 8mm. Also helps to gut the muffler if you still are using it. Or if you are handy with a welder just make a straight pipe out of thin walled pipe about 10" to 12". Get a tachometer if you don't have one. That way you can fiddle with different things and compare the rpms to see if it helped.

http://www.hobbyking.com/hobbyking/...or_Single_Cylinder_Gas_Engines_14mm_Plug.html

http://www.hobbyking.com/hobbyking/store/__10783__Turnigy_Multi_Blade_Micro_Tachometer.html

 

[offaxis]

Cool thanks.

 

[Flyin Farm Boy]

No problem. I'm glad to pass along the info. Been doing these weedy conversions for a while. Its a lot of fun. I almost enjoy the conversion part more than actually flying them....almost. With the electronic ignition you can just flip start these by hand. Or a chicken stick if you prefer. You will probably lose a pound or two of flywheel and magneto which always is good. Another thing I always do is remove the choke lever and flap. I don't have proof, but in theory it would increase airflow. You also don't need an inline primer bulb. Just hold your thumb or finger over the carb intake and crank the prop until you feel gas on your thumb. If you have spark it should fire right up even without the choke. I am working on a 120cc 2 cycle snowblower conversion now. Got it to turn a 30x20 at 5700 rpms. Yikes! Here is a cool tool I use a lot for calculating thrust and horsepower.

http://personal.osi.hu/fuzesisz/strc_eng/

Be safe and have fun.

Ben

 

[smashed2bits]

i have 2 of these engines and am getting ready to do this myself. thats a nice looking spad Farm Boy looks like a great flyer. how does that ignition system work or is it just an upgrade? also, how did you do your prop hub and motor mount?

 

[Frequent crasher]

What kind of plane are you looking to build Smashed2bits?

 

[smashed2bits]

i just want to build a nice simple trainer, maybe slightly aerobatic. i am thinking about a 200% coroplast cessna based on timmyp's plans. but I do have a new hotwire i just built, maybe something foam and glass or a biplane.... i should just make it swappable

 

[Frequent crasher]

Sounds fun! If you want, check out my BAD SPAD on YouTube or this forum, it would do great with that ryobi!

 

[smashed2bits]

I think I have decided to build a quarter scale tiger moth. 7'4" wingspan. The 16" prop I have should be perfectly to scale. I will build floats too. I plan to take my time and build this thing over the next year. Planning has begun and when I start to build a whole build thread will be in order. Maybe I'll even enter next year's scale build off.... so excited.

 

[Frequent crasher]

Ok, if you want a plane for the second ryobi, let me know and I'll give you the latest updates that haven't made the forums/online plans yet.

 

[Frequent crasher]

The airframe costs well below $200...

 

[Do335Dave]

When one of our weed eaters died of a broken shaft I took the motor out as a matter of principle because, hey: free gas motor. It's stuff like this proves I was under divine guidance.