AA5BY

I've had a Saito 1.25 on the shelf for several years, it being taken out of service for a couple of reasons. It was hard to hand start and would bark the fingers till they hurt. To use an electric starter required 24v and I'd have to drag up another battery to get it started. Consequently it didn't get flown often and that brought on another problem... the exhaust valve would be stuck from inactivity and that would require pulling the jug off. So, it got traded for a gas engine and stored.

The recent desire to build a Cub brought a need for the engine, as four stroke sound was a priority with a lesser desire that it be gas. So, the engine was given ignition to cure the starting difficulties with the hope that it would tune for gas. I knew the plane's cowl would yield full jug frontal air flow and that full power would be needed only a small percentage of flight time.

To my surprise, the stock carb showed promise on gas. The single difficulty was getting the idle low and smooth. Initial efforts yielded a rich and rough but reliable idle at 2,650 rpms. Leaning the LSN more would smooth out and increase the idle allowing the barrel to be closed to a more typical idle position and thus lowering the idle, but it brought spool up stumble problems. With guidance from Brutus (Bert) from the Netherlands, a one second servo speed was programmed in the transmitter. That stopped the spool up problem which often resulted in the engine quitting. Drawing the LSN out of the spray bar more slowly, prevented the dumping of fuel before engine rpms started accelerating. It worked. The current idle is likely too slow in combination with the 17 x 4w APC prop that yields strong braking for those no head wind landings. Idle will likely need raised some.

I've now eight flights on the Cub with the conversion and couldn't be happier. Running gas, I don't believe the exhaust valve will freeze up. And, fuel cost are considerably less than with glow fuel with a contrast of 25 cents per 10 min flight compared to $ 2 or more. And... there is little clean up. Best of all... the Cub has that wonderful Saito four stroke sound.

Fuel: regular gas w/ 15:1 Stihl HD 2 stroke oil
Timing: 28° BTDC
Ignition: RCexl
Prop hub: self made
Pickup sensor: mounted to a bracket mounted to the aluminum motor mount
Engine mounted: inverted
Fuel tank: 12 oz
Fuel consumption: .5 oz per minute
RPM: w / APC 17x 4w - 7, 950
Idle rpm: 1,700 - 1,800
Max temperature: w/ not more than 30 sec duration wot - 220F ( measured with sensor bolted to rear jug screw and sensor positioned behind the jug and out of the air flow)

av8tor1977

My Feedback: (6)

Glad it worked out so nicely for you. Do keep an eye on temperatures however. Purpose designed gas engines have more cooling fin area because gasoline burns hotter than glow fuel. Even the factory Saito gas engines tend to run warm. When I do glow conversions, I generally run them on ignition and Methanol instead of gasoline because Methanol runs much cooler and only costs around $4.00 a gallon. Also, if running the original glow fuel carb, it will be much less finicky to adjust when using Methanol.

AV8TOR

AA5BY

Very true about the hotter temperatures. Gas engines are critical about having full jug prop blast to cool them and even so, the air can't linger there, it has to then easily flow out of a cowl. Careful attention was given to the cooling. Not only does this installation have full frontal impact to the entire jug, but the whole of the bottom of the cowl is cut away for exit area and the cowl has air scoops to insure that no stagnant air exist to heat up any where in the cowl. A temperature telemetry sensor is bolted to the aft jug screw and the sensor positioned aft of the jug and out of the air flow. The temperature does not rise after killing the engine so I don't think it is influenced by cooling air.

Perhaps a criteria for a conversion to gas, is fitting the conversion to a plane that does not require WOT for other than short burst for an aerobatic maneuver. This conversion is fitted to a 91" Cub weighing 11.5 lbs and needs only half throttle to cruise.

Time will confirm one way or the other the success... so far, it looks good. I've eight flights on the plane so far so those plus bench running and plane testing, I've likely two hours on it.

AA5BY

Some update on the conversion. After the last post, the very next flight incurred a broken big end. The cause is uncertain but does not appear to be from lack of lubrication as the bearing surfaces remained good and crankcase seemed to be getting well lubed. I also do not think heat was a factor. The engine does run hotter on gas, but I don't think it is running too hot.

The rear bearing (ten years old or more) after cleaned up and spun would sometimes go into oscillation so may have fatigued the rod. Also, two flights earlier, a wheel axle had broken on takeoff and with the loss of a wheel, the WOT engine running a composite prop was stalled by the grass runway. The incident may have stressed the big end.

At any rate, the engine was given a replacement rod and bearings and reduced compression and now has eight more flights and time will tell if the broken rod will repeat.

I'm in hopes that it will hang in there on gas but if not, will be returned to glow with spark ignition. It is super easy to hand start, consumes four ounces of gas mix in ten minutes and sounds fantastic in the Cub. It will idle very low and runs great.

After reading all of the travails of the Saito gas carbs, who would have thought that the stock methanol carb would do so well by simply slowing the throttle servo down a bit. It is important to note that throttle servo slow down does not mean that spool up is slower.

The conversion is running muffler pressure, but that is a good thing as it makes it very easy to prime the engine to start. No choke or starter are needed. Not having a pump or regulator in the carb also keeps things simple and in time will avoid likely aging issues.

This conversion really surprised me at how easy it was to do and how well the outcome though that depends on what caused the big end failure. Again, time will tell and a log is being kept of flights.

av8tor1977

My Feedback: (6)

If indeed the rod big end failure was definitely not lube related, it might have been caused by detonation. Gas has a much lower octane than the methanol in glow fuel, and this along with burning hotter as well may have caused detonation to occur. Look closely for pitting on the old piston crown, and look for signs of heat/overheated oil deposits on the underside of the piston crown. Lowering the compression was a good move, but you might also try pulling a couple of degrees of ignition timing out of the engine.

Then again, it is possible that the prop strike over-stressed the rod....

AV8TOR

AA5BY

Nothing was noted on the top of the piston and I didn't know to look for oil baking on underside of crown. The .013 shim cost 300 rpm but on the Cub, the loss didn't hurt too much, stripping about ten feet off the vertical climb of a wing over. Most of the time, it is flown a good bit below full throttle.

btw, on another subject, years ago during the hot days of weed conversions, I did one conversion that ran well until losing the ignition and bought one other completed conversion of a Ryobi from a guy getting out of the hobby. On the bench however, it had a deceleration stumble that would shake like the dickens and sometimes die but if slowing the deceleration just slightly, it never reared its head. Unable to tune the problem out, the engine was never used and now that servo speed adjustment would now probably solve the problem, a Ryobi is doubtfully considered practical conversion.... unless of course someone is doing it themselves for the pleasure.

av8tor1977

My Feedback: (6)

I happen to have a Ryobi 31 on a giant 76" span Tiger Moth biplane. It's a match made in heaven! And due to the rear exhaust/rear intake layout of the engine, I have no cutouts in the sides of the narrow cowl, which looks great. It really is a super sweet combination. It takes off at about 1/4 throttle, putts around the sky at less than half throttle, and at full throttle it does fantastic verticals and aerobatics. Fun setup that I am proud of...

AV8TOR

AA5BY

No doubt. It is highly gratifying when ones efforts produce great results.

av8tor1977

My Feedback: (6)

I have had a TREMENDOUS amount of fun and sucess converting engines for airplane use. Doing so added a whole new dimension to the hobby for me, and I very much enjoy it. I presently have 5 airplanes flying with various engines I converted, and would put them up against any "store-bought", purpose built engines. I even have a couple of 50cc twins that I make out of two 25cc Echo weedeater engines. It's a lot of fun for sure, and some of the fun comes from the amazed looks on peoples faces when, after seeing one of my planes fly, I tell them the engine came from a (weedeater, leaf blower, chainsaw, etc.) This part of the hobby has come a very long way from the old early gassers that were heavy, vibration prone, and sometimes unreliable, though interest has dropped way off with the introduction of the cheap Chinese import engines.

Add: I have one cool little engine I made that I am particularly proud of. It is made of highly modified 26cc Zenoah clone racing parts. It weighs 1lb. 14oz. Including muffler, mounting bolts, etc., and turns a 16 x 8 prop at 10,200 rpms on a muffler; no tuned pipe!

AV8TOR

AA5BY

Impressive numbers.... you have every right to feel good about such an effort. And... finding enjoyment in whatever phase of this or any hobby or interest is of great value. I certainly enjoyed the Saito 1.25 conversion to gas and last fall the conversion of a Saito 1.82T.

My only other conversion effort was a weed conversion, that was run for a few years on a Phaeton Bipe. It was gratifying to take a discarded engine and do a conversion at no cost. No doubt it is enjoyable to enhance performance and explore the limits of what can be accomplished and develop the skills and knowledge towards those ends.

I'm currently commissioning a 1/4 Aeronca Champ that will be powered by the 182T so we'll see how that conversion goes.
regards,
arlyn

av8tor1977

My Feedback: (6)

Wow, an old Phaeton biplane! I had one of those many years ago. Fun airplane.

Ok, good luck on your projects.

AV8TOR

AA5BY

I've now twenty flights on the conversion since the repair, 28 total. No dead sticks in that time. It has handled upper 90's temperatures. When my bench is cleared of the current build project, the plan is to do an engine check and if all looks good, to raise the compression back to original and regain the 300 rpms lost. They enabled larger loops and higher hammer head climbs.

Construction on a 1/4 Aeronca Champ is nearing completion, powered by a Saito 182T converted to gas.



.

av8tor1977

My Feedback: (6)

Looks great! I would love to see/hear a video of that engine running. Does it have a slightly more "throaty" sound on gas? Re- your 1.25, you might try experimenting with both compression AND ignition timing. Backing off the timing a bit might let you run the higher compression without getting into detonation, but with possibly less loss of power. And I assume you are running premium gas. I hesitate recommending trying 100LL Avgas due to the distinct possibility of lead fouling the valves. Do you have temperature telemetry? If not, you might invest in one of those inexpensive recording temperature units. Detonation causes CHT's to skyrocket and monitoring them would be a good tool in your experiments. Like you, I hate leaving any power "on the table" as they say.

Man, I just happened to take real notice of your AA5B(y) "handle". That is one of my favorite airplanes of all time, and I have hundreds of hours of great flying time and adventures in them. I also used to pick them up at the Grumman factory in Georgia, and ferry them to Tucson, Az. Great times, great memories. Do you get many comments on your handle? I imagine not many would recognize it, like I didn't 'till just now.

AV8TOR

AA5BY

The handle is my Ham radio call sign.

I had heat telemetry for a while but the sensor gave out. My current system is the old feel the hub for heat comparison.
Not knowing whether detonation was happening or the exact cause of the big end failure leaves me in the dark. I had the goal of 20 flights and then examine the engine and follow your suggestion and examine the underside of the piston crown for baked oil deposits.

The engine has run really well and is delightful to the ears in the Cub.

I'm in hopes of good results with the 182T in the 1/4 Champ. The 182 has a single crank pin so at low rpms has a notable unsteady gait. I've fitted it with an 18x6W prop for a try.

Ladyflyer

My Feedback: (2)

The "lag" you speak of is most likely not due to a slug of gas too soon. Actually , the gas delivery lags behind . This is why we had accelerator pumps for carburetors in automotive use .

av8tor1977

My Feedback: (6)

Very true. Some of the Walbro carbs actually have an accelerator pump and I like using them. When using a carb without an accelerator pump, it is almost always necessary to tune the idle mixture richer than optimum in order to avoid a stumble, or sometimes an outright "flameout" upon quick throttle up situations. Many people use various mechanical and/or electronic methods to help with this inherent problem by slowing down the throttle movement, but really that is just a "bandaid" and you tend to never know when you might accidentally hammer the throttle too suddenly, and be rewarded with "the sound of silence". Never a good experience when flying a model plane.<br /><br />The science of it is that when the throttle is opened from idle, especially suddenly, due to inertia the airflow into the engine is able to accelerate much faster than the fuel, causing a sudden leanout and a resulting engine "stumble" or even flameout.<br /><br />AV8TOR

AA5BY

Yep, my comment of why the stumble had it wrong.

Regarding servo slow down being a band aid.... that is true, but we use all sorts of counter efforts to solve problems. Down thrust is a band aid for using a Clark Y foil, etc. An accelerator pump is a counter effort to a sudden drop in vacuum and inadequate fuel to air ratio. Servo slow down allows leaning and smoothing an idle and avoiding the stumble that sometimes comes with it..

On the Saito 1.25 conversion, if it was leaned up enough to close the barrel to obtain a low and smooth idle... it wouldn't just stumble... it would die. However, using a servo delay completely solved that. In twenty eight flights, there has been no dead sticks nor has there been any sense of slowness to power up. The counter measure or band aid has no ill effects that I can tell.

av8tor1977

My Feedback: (6)

Oh, don't get me wrong, band aids are sometimes necessary! (Just ask my 11 year old daughter! She uses them by the boxful!) Maybe "band aid" was a poor choice of words. I think it stems from my aggravation that they don't produce a carb that would make a "band aid" unnecessary. (I would "kill" for a Walbro carb with a really efficient accelerator pump and a midrange mixture adjustment!)

Anyway, I too use both the mechanical and electronic methods of slowing down the throttle action. You have to do so.

AV8TOR

carcas87

Hi body, did you hade problems of overheat?? in your saito engine??

AA5BY

No problems with the Saito 1.25A overheating but I should add, that it had really good cooling with air directed at the full jug and air scoops bringing air into the top of the cowl which then produced a downward flow to aid the back of the jug.

I also converted a Saito 182T and it needed some sheet metal curved baffles to direct air down the back side of the jugs.

Cooling with gas can be done with some effort but I wouldn't use a converted gas engine in a situation that doesn't have good cooling.

AA5BY

Too often follow up reports are not given, leaving questions about the outcome of some endeavor.

The Saito 125a gas conversion has now logged a total of 48 ten min flights and continues to perform flawlessly. I couldn't be happier with the outcome.

av8tor1977

My Feedback: (6)

Great. To paraphrase the guy on "A-Team"; Don't ya just love it when a plan comes together?!

(I also agree that more people should be more diligent about follow on updates.)

AV8TOR

carcas87

i had made some experimetns by me, and i get some issues with the temp, that is a little video of a 2st engine,, but with some modifications..

carcas87

****,,, the page dont permit to upload the link for the video..

AA5BY

I would agree that one of the criteria of a conversion to gas is a good cooling environment.

A few more thoughts. The cost of the conversion was right at $90 (ignition, plug and opto switch). 48 flights has provided enough fuel savings that I'm now even so going ahead, savings become real.

It is important to note, this is an engine that I'd taken out of service several years ago due to several glow fuel issues and had no plans to put it back into service again using glow fuel.

btw.... The success with this engine prompted also converting a Saito 182T. That conversion also went well using the stock carb with a servo speed slow down. It is fitted to a 1/4 Champ and now has 17 flights. I've not calculated the cost pay back on doing it as it involved two ignition units but it will eventually pay its way.

It was a bit more challenging in regard to the cooling. Even though it has separate carbs, it would not tune for equal jug temps, the starboard running 20-30° hotter than the port. This had me perplexed until a very knowledgeable Saito guru shared that for some reason, Saito provided different valve timing for the two cylinders. Consequently, I chose to provide air flow directors that wrap around and provide air flow over the back of the jugs. Doing so dropped temps on the starboard cylinder from 250° down to 220°. The port side now runs 200°.