AA5BY

While I certainly don't need another plane, I do need a winter project so have concluded to do a junk box winter build. In the junk, is a Ryobi conversion bought several years back from a pilot forced to get out of RC for health reasons. I don't know if the engine was new or used when converted, only that it has never been fitted to a plane.

I did run it once, but don't recall what prop or stats it produced, only noting that if decelerated too rapidly, it suffered a vibration zone so not giving much for the engine, it was set aside and never considered. With current radios with servo speed adjustment, I believe the deceleration vibration can be avoided.

I'm wanting to scratch out a Fly Baby and the Ryobi seems would be an engine choice for the lazy flier with its Clark Y foil. I've a Cub cowl which the Ryobi with its rear carb and exhaust would fit well and given a scratch build, the fire wall can be set back the needed amount to make the long Ryobi work with the cowl.

Size is the big question and I'd be happy to build anything between 1/4 and 1/3 or 84 -112 inches, whatever would best suit the Ryobi for lazy slow flying. Other considerations are whether to convert to EI or stay with mag. The mag will work in the cowl. It might be that decision would better be made after finishing the build and let balance needs dictate.

I'll try to bench run the engine and get some prop and rpm numbers. What is a typical prop to use and what numbers are typical? Any rough guidelines on size and weight limitations for a Ryobi? Any guidance would be appreciated.

AA5BY

The Ryobi started easily (with a starter) and ran without problem (not even any of that remembered deceleration vibration so that may have been prop related).

Prop used was an APC 18x6W.
Top 6800
reliable idle 1500 (probably due to the heavy APC wide prop)

I don't know if that was too much prop. Temps ran up to 260-80.
Top rpm fluctuates between 6500-6800.

Are those numbers normal for a Ryobi?
I suspect it would run slightly cooler without the coil blocking a large part of the front of the jug.

AA5BY

A second run session this morning provided a little increase. Leaning the LS to the point of spool up stumble and then backing off slightly, allowed tuning the HS for sustained and smooth high end of 7200 rpm without any heating issues.

av8tor1977

My Feedback: (6)

That's a good prop size for it loadwise, and the numbers suggest the engine is probably in good condition. That prop would also be a good one for the plane you envision. The only other thing to know about a Ryobi is that they should never exceed 7500 static rpms. Below that, they work great.

Weight for them is really based more on wing loading desired. For what you want, I suggest a minimum wing area of about 1200 square inches. You could go larger. For reference, this engine would fly something like a Great Planes Giant Stik for general sport flying. Not 3d mind you, nor unlimited vertical, but definitely sufficient for sport aerobatics in a plane that size. I presently have a Ryobi 31 in a big, 76" span Tiger Moth biplane, and it is a "Match made in Heaven"! Takes off at less than half throttle, does large round loops, and tall Hammerheads.

I convert all my engines to CDI for better appearance, a good bit less weight, more power, and easy starting. However, there is one thing to check before you go chucking the magneto. In 15 years of converting engines, I have only run into ONE of them, but some of the older Ryobis are externally balanced, and if run without the mag flywheel will shake like hell. So pull off your flywheel and check the balance of the flywheel. (I just use the large Dubro prop balancer.) Those flywheels are mass produced and likely won't show a true zero balance, but if it is significantly off, then you know your engine is one of the rare externally balanced engines and would need to be run WITH the mag flywheel.

A couple of side notes: If you change it to electronic ignition, which I do recommend if possible, I believe the only place that sells the cool ignition sensor setup for Homelites and Ryobis is Adrian at www.ch-ignitions.com. (Engine converting has gone way down with the invasion of Chinese engines, and thusly many of the conversion parts suppliers have been forced out of business.)

Secondly, you will notice two threaded bosses on the front of the engine. I find these convenient to add weight to if needed for adjusting the weight and balance. Just saw the ends off of large fishing weights. Then flatten them slightly with a hammer, drill a hole in them lengthwise, and bolt them to the engine. Be SURE to use Loctite, as the soft lead will compress and not keep the bolt securely tight.

Hope this helps,
Have fun!
AV8TOR

AA5BY

Much thanks for the helpful answers to my questions.

As you might imagine, the length of the Ryobi conversion requires a firewall set back to work with most cowls so to some degree a clear road ahead was/is desired.

av8tor1977

My Feedback: (6)

Sounds like a nice project. Keep us posted. Any thoughts of getting extra ambitious and making it a Flybaby bipe?? That would be cool and unusual...

www.bowersflybaby.com/pix/biplane.html

I can't wait to get back active in the hobby. Two major back surgeries and other life problems have kept me away too long. Hopefully I will at least get to fly a bit when I go visit my daughter next month.

AV8TOR

AA5BY

I scratch built a 90" bipe two winters ago powered by an OS GT40 four stroke. It has 2700 sq in and weighs 20 lbs even and still is lightly loaded at around 17 oz sq ft. It is a slow flier but yet fairly aerobatic with symmetrical foils. It is really cool to watch the slow flyer roll slowly but not drop altitude.

I think I've decided on around 94 inch span for the Fly Baby making it about a 28%. That would give it about 1300 sq in.

btw... this afternoon when the temperature increased, rpms on the Ryobi dropped 200 back to 7000. The carb has a 7.9 mm venturi. Should I consider a slightly larger carb?

I hope you get some flying in soon.

av8tor1977

My Feedback: (6)

Very nice! I love that red!

I keep thinking about building a stand WAY off scale Fokker D7. I have a Stihl 36cc four stroke gasser all converted and needing a home. I always thought WW1 planes with a screaming 2 stroke to be somewhat of an anachronism, and this Stihl four stroke putt putting away would be the answer to that. But I love aerobatics, so I would make it stand off scale and use symmetrical airfoils. Actually, I might cheat and use some ARF Big Stik wings, and just scratch out the fuse and tail feathers. Should be fun.

I wish I could have teased you into a Flybaby Bipe. When I looked up that link for you, I was impressed once again with how cool and classic they look. As far as your carb, yes, the original carb on the Ryobis is quite small. It would do better with a 10 or 11mm carb. I wouldn't go any larger than that for a Ryobi. Also, does your setup have an extra metal carb spacer? Converted Ryobis need the carb spaced out slightly in order to obtain full linkage movement/travel.

Off topic, I just bought an SDR-RTL dongle to play with here while I'm recovering. It allows you to pick up radio signals from 100khz to 1.7Ghz on the computer. (Possibly as high as 2.2ghz) Only cost 20 bucks! That ought to be interesting. Ever played with one?

AV8TOR

AA5BY

The 36cc four stroker would make a great engine for a classic bird. When I built the big red bipe... I wanted four stroke sound and literally fell into it. A fellow flier at the field was frustrated with and had thrown the towel in on the OS 40cc. I asked about it... and he offered it to the project but didn't think it would work.

It had two problems. When I first ran the engine, thrust was 8lbs static. The ball and spring check valve was missing on the positive crankcase ventilation system, which reduced fuel pump pressure. Once they were added, thrust came up to about 11lbs.

The OS ignition had failed, and he had substituted in a RCexl unit. A timing check showed it firing at 15° btdc. It seems that the OS ignition scheme was different than RcExl... it fired at a given time lapse after acquisition of dwell, rather than release of dwell, thus the pickup sensor would not adjust to suit the RcExl ignition. Timing to 28° raised static thrust to a little better than 16 lbs and enough to fly the 20 lb bipe well. So... the bipe got cool four stroke sound.

Yes... the Ryobi does have the spacer to allow the butterfly to fully open. I've another 8mm carb and will drill it to 9 -10 mm and try it.

No... I've not played with a radio receiver for a computer. Years ago, I did use a sound card as an A to D converter for sat imaging and in fact built a rather expensive TAPPER DSP (digital signal processor) for digital satellite work but I've not messed with a computer spectrum analyzer. I've a poor boy SA made using a very old tube scope... but last time I powered it... it failed to come alive and I've not dug into it.

I'm an inactive ham now and an inactive sailor. Our local flying field is a ten minute drive and friendships there go back forty years... so RC has captured my time, energy and resources.

Your question about the receiver... caused me to remember that my son handed me a box of stuff to tinker with... I'll have to check it out. (note: just took a look and it is some digital motor control stuff)

Thanks again for your help with my project. Wish and hope that your back mends well.

av8tor1977

My Feedback: (6)

Thanks. And you're welcome! Any time.

Yes, I was thinking that OS was pretty small for that plane, and would need to be on top tune to haul it around. With the very high density altitudes here in Arizona, I have always "over" powered my planes, before doing so became the rage as it is now. A while back a guy at the field brought and flew a quite large 3 channel Sunday Flyer type plane. It was a polyhedral, cabin monoplane, and looked to be about 90" span. It was powered by a .15 glow engine, which seemed ridiculously small. I flew it though, and it actually flew quite well. A relaxing flyer, and it made me want one!

Keep us updated on your project, and have a good one,
AV8TOR

AA5BY

According to a Wiki page... the Fly Baby can be a convertible in that a top wing can be fitted to the low wing airframe. I'm kinda intrigued by that. I might be willing to tackle such.... after giving it due thought.

A local story has it that one of the area pilots had a Phaeton 90 years ago and the top wing departed and the pilot flew it around the circuit a few times before landing without a problem... so obviously... the idea is not far fetched and the Wiki site offers that there have been convertible Fly Babys.

I've opened a build log on RGG with some pre build chatter going on now. Right now it is titled Junk Box Build, in the balsa builders forum. If we get some other junk box builders, it might stay so named, otherwise eventually when building begins, it will be renamed to reflect a Fly Baby build.

https://www.rcgroups.com/forums/show...%29&perpage=10

AA5BY

The Ryobi is getting an ignition change to EI. The mag flywheel and coil combine for something better than 15 ounces, which is 1/4 the weight of the engine so it is going on a diet.

A suitable EI was in the junk box including a spark plug bushing so no cost is incurred. A timing hub is completed except for installing the magnet when its position is determined. Yet to do is disassemble the engine to drill and tap for the pickup mount screws.

The timing hub required a taper cut that proved a bit tedious because of the need to grind a small tool bit. A key had to be made and the key slot required the greatest effort using a small jewelers file.

Is 28° a good number for the timing?

av8tor1977

My Feedback: (6)

Yep, 28 is fine. What we usually do on the Ryobis, Homelites, and McCulloch engines is use the hose clamp style sensor assembly from CH Ignitions, though there's nothing wrong with drilling and tapping the crankcase snout for the newer RCEXL type setup. The only thing is the CH style makes magnet positioning less critical, and you don't have to disassemble the engine and remove the front bearing to drill and tap sensor mount holes. (The CH sensors work fine with RCEXL ignitions.)

Adrian at ch-ignitions.com doesn't show the hose clamp style sensors separately on his website, but he sells them if you're interested.


AV8TOR

av8tor1977

My Feedback: (6)

Now that you've gone to all that nice work on the hub....

I often cheat. I take a hole saw, and saw the center out of the mag flywheel. I then chuck that in the lathe and dress it true, mount a magnet in it, then polish it. Saves a bunch of time. Then I just make the prop hub itself just like for a magneto engine.

AV8TOR

AA5BY

If I'd had another flywheel... that is the route I'd gone but didn't want to burn the bridge.

Thanks for the confirmation of 28° timing.

av8tor1977

My Feedback: (6)

Remember to prop that Ryobi for 7500 rpms or less static. The Ryobi is a good, and useful engine and I've had a ton of good use and fun with them. It is the only easily found rear intake, rear exhaust conversion engine. They made a bizillion of them. They respond very well to an 11.1 mm venturi carb in place of the miniscule original carb, and a free flowing exhaust. Some of them had a very low exhaust port timing of only 120 degrees. A healthy power increase can be had by raising it to 150 degrees.

The reason for the rpm restriction is because they use a weak, stamped steel connecting rod. I've threatened many times to machine up a stouter rod for them, but as usual, I have many more "bright ideas" than time or energy! Anyway, they hold up fine if held to 7500 static rpms, and I have briefly buzzed my modified ones to 8500 with no explosions. (Be assured though that I was quite ready for an explosion when I did that, and wouldn't have been the least bit surprised had it happened!)

AV8TOR

av8tor1977

My Feedback: (6)

WOW!

Just made a jaunt over to RCG and took a gander at your posts. You made that hub out of FLAT STOCK??!! Man! You have more patience than I do, plus my poor back would never allow me to stand at the lathe that long! I keep various diameters of aluminum round stock on hand, though 1", 1 1/2", and 1 3/4" round stock handle 99% of my needs. I'm even going to order some split rings and set screw collars because they are available ready made so cheap it doesn't pay to stand at the lathe and make them. Nice work though. Are TOM, Antique, and Jedi Jody still active over there at RCG? Tell 'em I said hi. Great engine guys!

AV8TOR

AA5BY

It occurred to me late last night that I'd not responded to your question about the engine gurus. I think they moved over to Flying Giants. I enjoy reading their post but have not had interchange with them. I read some amount there, but rarely post there.

The Ryobi got two bench runs today, one at the field and the other after returning home.
The EI provided easy hand starting and it gained a couple of hundred rpms but it suffered an occasional shaking problem at idle, that seemed not to be mixture related. It was packed home for further checking.

The prop had varnish on it but was double checked and found to be in very good balance but flipping over, it would fall off each direction so had a heavy sided hub. It was given a mark and returned to the engine and positioned opposite the timing magnet, which fortunately provided a one o'clock position. No more shaking. I guess the combination of magnet and heavy hub were the cause. Will check it out with another prop.

Will be on the hunt for a larger venturi carb having a choke.

aspeed

Just thought about your back problems. I have a fairly high stool that I use for my lathe. It is a Hardinge chucker with a slight indentation to get my knees under. I always used one at work and could barely make it through the day (evening shift usually) without. My feet were the problem, not my back. Being 6' 3'' it is harder for me to stoop down to see what is going on if standing. My favourite chair had a back on it. It was from the 1950's, likely older than me. The last time I was recalled to work after a layoff, someone threw it out and put it in an auction. The *******s. Nevertheless, an adjustable height stool may give you some more time on the machines. I bought a new stool with padding for my home workshop.

AA5BY

Occasionally tall women will demand kitchen counters raised above the standard 36" to counter back strain. My lathe spindle height is 4' even and I'm 5' 11" and consider it ideal. Should your spindle height be 50-52 inches?

yasir_ali

Perfect!

av8tor1977

My Feedback: (6)

Thanks. Yes, I am 6' 3" as well. (Well, I was before these back surgeries; now I am 6' 2".) I have always constructed my work benches higher than standard. Tends to aggravate anyone else that uses them.

AV8TOR

av8tor1977

My Feedback: (6)

Yep. CDI is the way to go for sure.

The Walbro carbs have a number cast into the carb throat entry. This number is the venturi size in 64's of an inch. You want a # 28 for your Ryobi. Use caution when searching e-bay, etc. for carbs. Many newer carbs have only one mixture adjustment needle and are not suitable for our use.

AV8TOR

aspeed

My lathe is 47" spindle height. I drop 8" when I sit down on my stool. That is about right for me. I put 2"x4" s under my milling machine to get it a bit higher. It is a Hartford, Bridgeport copy. At work we had a horizontal TOS mill and all the midgets could not work on it, so they built a heavy 10" platform. I hated that. To get somewhat on topic. I have a McCulloch motor that I wanted to change for a model plane. It came with two coils, and they both give no spark. It has been sitting for many years now. I am not crazy about big planes, so will likely let it sit another while. It looked like it had very little use, and now they are out of business. I thought about glow/gas or some ignition system. Since then, I got quite a few Homies, just in case I make a boat.

av8tor1977

My Feedback: (6)

Unless a person screws up really bad, (like forgetting to mix the oil in the gas or something), it rather doesn't matter if one of these engines is out of production and you would like to use it. They all use standard bearings, seals, etc. I get all my bearings and seals from Boca Bearings, I get my rings from custom ring makers like Frank Bowman or his new protege, and I make my own gaskets. Ignitions are are CH, RCEXL, or RCAP. With proper use, all the other important hard parts will outlast you yourself! The Chinese engines are a bit of a different story, as many of them will eat a crankshaft or something sooner or later.

AV8TOR