I am preparing to build a Sig 1/4 scale Spacewalker II. I want to use a gas engine and am trying to decide which one. I am considering a Brilelli 26cc but I also have a Homelite 25cc weed eater and a Ryobi 31 cc that I could convert at minimal cost. What sounds like my best option in terms of what will fit best in the plane? Does anyone have any dimensions on the converted ryobi or homelite. I am concerned that it will be too long to fit in the cowl. I also know where I could get a Quadra 35 at a good price. How would that fit? Any help appreciated!

Brian

Get a G26 from RCIGN1 and don,t look back. A very fine engine. Regards, Capt,n

Fireman,
How deep is the Spacer Walker cowl? About six inches? I think that the shaft can stick out some since it doesn't use a large spinner. The Quadra is about 6" like the Homelite depending in the mount used, but much bulkier. It would give the best performance of the cheap choices. The Ryobi is 7" long with the carb enclosed in a mount or standoffs. If you make a hole in the firewall for the carb, it can be about 5" or so. Since they are conversions, the choice of parts and type of block determine the exact lenghts. If you could get a good running Quadra 35 or 41 for under $100, it would be great. The plane has a short nose, so the 4.5 lbs of the Quadra would help balance. The other two conversions will weight about four pounds on magnito ignition anyway and swing small props. The light weight high dollar choices, could be easier starting, but will just cost more in this application.

Dave

The Quadra like Dave says is also a good engine. It kinda depends too on the other planes you may get in the future to use same engine. If you do not plan on light-weight aircraft in the future....the Quadra is a good choice...if it runs good and is not crash damaged (bent crank). Good luck, Capt,n

The Quadra is new (older but un-run). I can get it pretty cheap. A lot cheaper than the Brillelli. The depth in the cowl is about 6" from the nose ring to the firewall so the Quadra would be tight. Width shouldn't be a problem. I have a feeling the Quadra would swing a bigger prop than either of the conversions.

Brian

I have a 31cc Ryobi that I converetd and it swings an 18x10 Master Airscrew at 7600 rpm. The carb and muffler are behind the engine so it fits well in a narrow cowl. I used a Walbro Wt644 big bore carb. and CH Ignition. Good luck!

The Quadra will swing an 18 inch prop with no problem. The others will depend on the quality of the conversion and swing a 16" to 18" accordingly.

Dave

I have both a converted Homelite and Ryobi engine. The Ryobi has not flown but the Homelite did until I snapped the magneto coil off (now swapping crankcases).

Both engines are near identical in size when converted (subject to variations in conversion kits and whether electronic is fitted).

The Ryobi is a smaller case and narrower is width, given the muffler and carb are on the rear. For the Homelite it will be wider due to side carb and exhaust.

Take into account that while Homelite and Ryobi flywheels differ slightly, they are essentially the same dimension wise.

Length wise, that will depend on the conversion method used but it would be easier to make a shorter Homelite conversion simply because there is no requirement to leave carb (and breathing) space at the rear. Other than the carb issue, both engines are probably similar in overall length.

If you want, I can measure my Ryobi tomorrow morning and then give a rough measurement for a Homelite (noting my Homelite engines are currently disassembled).

One thing I will say is that I think the Homelite is a better built engine (excluding the coil mounting) than the Ryobi. It at least has a proper alloy connecting rod and crank counterweight whereas the Ryobi makes do with stamped steel pieces laminated/rivetted together (Note: based on the engines I've had apart....perhaps Ryobi has changed this).

Raven, thanks for the info. One reply here said that the Ryobi is 7" long once converted. Does this hold true for yours as well? Maybe I could figure an average and go from there. I think a 7" engine would fit okay with some minor mods. If you would be willing to take some quick measurements I would sure appreciate it.

Thanks,
Brian

With a 1 inch clearance between the carb and the firewall (so the carb can breath) the total length of my engine is 8 1/4inches from firewall to the prop nut face.

Now, my conversion uses a prop nut that may be slightly longer than other aftermarket units as it was made on a friends lathe (very nicely done). If you are going electronic ignition (no flywheel) you can probably get the engine down to 7inches long without a problem.