It has been a long time since i have been in the hobby, but this leaf blower motor has got my mind a spinning. the side blew out on it and now i want to use it to power my model airplane. it is a 25CC 2 cycle motor and I have a few questions i am unable to answer myself.

1st. i plan on building a j-3 cub style aircraft for it completely from scratch. now i will be able to do this without much difficulty, but i need to know how big to build it. i don't plan on doing more than lazily flying it around, and it would be nice if i could put floats and skis on it without it wanting to fall out of the sky.

2nd. I want some opinions about whether to leave on the pull start. it would be nice to leave it on and just be able to pull start the airplane, but at the same time i know that is a decent amount of wait at the extreme front of the airplane. I just feel it would be more convienent to have it on there so i don't have to drag around my starter.

3rd. I have heard of people having problems with radio interference with these 25cc conversion motors. is there anyway to test if i will have this before i take the plunge into flight??? are there ways to reduce the radio interference?

4th. has anyone done this before with a Sam's club leaf blower. it is a propol leaf blower. worked good for 4 seasons untill the side of the impeller chamber blew out. the motor has always run like a champ, but i was curious if anyone had used this particular motor before for a conversion.

5th. and i know this will create some debate. what kind of prop should i use. i would like to use a 3 blade prop as i have never used one before, but if enough people recommend the slandered 2 i will use that instead. also what kind of pitch should i use.

and lastly. should i try and build a new muffler for it or can I adapt the one that came with it. this is the only part of the motor that i'm iffy about. it was used for several seasons, but this is the only thing showing it's age the rest will clean up nicely.

Any help you could give would be greatly appreciated. below are photos of it, also i don't know how much it weighs right now.

There are many companies making conversions for leaf blower motors and weedwacker engines, or you could take it to a machine shop and ask them to make a prop adapter for you and modify it for you. mounting them is sometimes tough, standoffs are usually hand fabricated to mount them.

You might try your post in this forum http://www.rcuniverse.com/forum/forumid_92/tt.htm and have better luck.

If your looking for good, cheap engines, check out kinghobby.com, they have 25cc gassers with electronic ignition for around $150, thats a fair price, mine from them runs great and it's light, with the pitts muffler included.

First let me say welcome back to the hobby and welcome to RCU!

1) I would plan on a 1/4 scale cub. I would also recommend building a clipped-wing version . A clipped-wing Cub flies just as gentile as a full-wing version, but frankly, the full-size wing is too big. It was designed around an engine that was barely big enough to get the plane off the ground and due to it's length, it makes turning difficult (Lots of adverse yaw).

2) Take the pull-start off. It would be nice to pull-start it, but as you said, it's excessive weight - not to mention the fact that it would be impractical (Where would the handle be sticking out?) and it would be very difficult to conceal under a cowl.

3) Keep your radio at least 12 inches from the engine and use a non-metallic pushrod for throttle.

4) I have not used this particular engine, but I have converted weed wacker engines and they work great.

5) Gassers have a pretty wide range of props. You COULD use a 3-blade, but it wouldn't look very scale, and 3-bladed props lose some efficiency, I would try something like a 16x8 2-blade

6) That muffler should work just fine.

yeah i was going to end up forging my own mount i see no other way to do it. there is a plate in the back i am going to take off and cast a new one in plaster-of-paris with a engine mount included. and then poor in a metal. will either use aluminum or nickle. as you all can tell i am still in the planing phase, but i appreciate all the help as i start to build i will post pictures in here

No need to forge a new mount. Just grind off those two things on the side of the back plate and attach a 1/4" aluminum plate with the 4 existing bolts (Of course, you may need to replace the bolts with longer ones due to the thickness of the plate).

A hole in the center of the plate will allow whatever that is in the middle of the back plate to protrude.

Hang on a minute with your casting plans. Plaster of paris is not a suitable bold compound. It is just plane dangerious. Plaster of Paris will break down at a high temp. You have to have the mold hot, at least 300 degrees or more to drive off the moisture in the mold before pouring molten metal into it. Even if you are pouring into a metal mold, it has to be hot. I got in a but of a hurry one day when pouring a billet of gold. THe billet mold is steel. I didn't get it warm enough and when I poured the molden gold in, the steam blew it right back out. Nothing like having a 1/4 oz of melted gold spraying out like a gyser. That was with a steel mold and only the moisture in the air. If you try that with plaster of paris, all the moisture in the plaster will instantly turn to steam and blow.

One other point, if you have the ability to cast and then machine a new case, why not must machine one from a billet? In any case, you final cost and the reliability of the engine, and the overall weight will be much better with a comercial engine as suggested before.

Don

In general, to make castings for metal, use casting sand, but it's more work than having a mount made from a single piece of aluminum billet. Plus, if I were going to give it a try, I'd remove all the cooling fins from the flywheel,the starter pawls shave as much metal from the front housing as possible but still hold the magneto coil. The shaft may or may not unthread, if it does, then it would be easier to replace it with a bolt and buy or make a prop shaft coupler for an already existing engine that could be centered up and drill the holes and bolt it to the flywheel. But after all this, it may be cheaper to just buy one of those king hobby units or skim the classifieds here for a good used zenoah or us engine. The old US 25 could be bought for real cheap sometimes.

You need to remove the pull start. Imagine that thing kicking back and pulling your hand right into the prop. Plus, what if it starts, and you let go of the rope, then the rope ends up lashing into the prop disc...just dangerous.
1/4 scale is just right for that sized engine. Maybe a 90 to 100 inch wing????
Also, I wouldn't use a 3 bladed prop on a cub.....it would just not look right.
you need to machine a lot of the extra weight off of the engine. Shave the flywheel down-take off the cooling fins. Also, shave down some of the cooling fins on the head itself. Get a free-flowing header, or make one from aluminum stock. You'll have to have a prop driver machined for the engine as well.
All in all, I would think the afore mentioned 150 dollar 25 CC with EI is a better deal, unless you are just wanting to tinker with this thing. I would guess you'll have at least 100 bucks tied up in the conversion in both cash and time.

That looks like a good conversion engine, as mentioned above cut off all excess aluminum and i too would grind down those tabs on the back and use the 4 backplate bolts to mount it. Your shaft on that engine is just like mine, all what i did was cut it down a bit and rethread the end and for the prop driver all i did was take a pc of 1" aluminum rod with a 5/16" hole drilled thru it and used a nyloc and washer to attach the prop. I wanted mine lite and i too was worried about interferance so i went the GAS/GLOW way, this saves lots of weight as you can remove the flywheel, coil, and sparkplug, and the best part is no interferance as the engine runs off a 4 stroke glow plug like a normal glow engine. Here is my weedeater 21cc conversion.

As for props i was using a TF 16x8 @ 6900rpm and an APC 17x6 @ 7200rpm.

How much did you spend to do that, including engine purchase, I know the cheapest you could get a weedwacker for is about $75.00, used is a whole different story.

Tell me about this Gas/Glow setup. I thought that there had to be a high percentage of alcohol in the fuel to react to the platnum in the glow plug to ignight the mix. Are you saying that you can get a good running engine on a standerd 40-1 gas mix with a glow plug. Do you have to keep a glow driver on while it's running?? What about the low end and transistion? This sounds to good to be true.

Don

yeah i am very interested in this too, because if i can go with glow i can cut the weight by almost half i speculate.

I think he ment it runs off of a 4 cycle glow plug and glow fuel, I don't think the compression is enough to light off gas with a little glow plug. If he is using glow the wieght savings went down the tubes due to the volume of fuel that must be carried to get the same flight time you would using a gas engine on gas.

Nope, the magic mix to run GAS/GLOW is 1 part 10%nitro / 10% oil glow fuel mixed with 2 parts PREMIUM gasoline, Zenoah makes an adapter to go from a standard sparkplug thread to a glow plug thread and an OS F 4 stroke glow plug is used. Most ZAMA carbs do not like the alcohol but a Walbro handles it just fine, the only thing you really have to do to the engine is richen up the needles a bit. Run time is close to running straight gas, and on most engine you will see an RPM increase over straight gas/oil. For more info scroll down to the ENGINE CONVERSIONS forum, there's lots of good reading in there about this. This set up runs just like a normal glow engine, lite plug, start engine, remove plug ignitor and go, you get very low idle running GAS/GLOW, no onboard batteries for ignition, no RX interferance, and #1, less weight.

As for how much i have in this engine, i'd say about $18, the weedeater was found at the curb on garbage day ( FREE ), glow plug adapter ( $9.99 ), OS 4 stroke plug ( $7.99 ) and a few hours cutting and shaving the excess material off ( FREE on most days ). The prop adapter was made from a pc. of 1" aluminum rod that i had laying around the shop and the mounting plate was from a scrap of 1/8" aluminum i had laying around. It's kinda funny the most expensive thing on that engine is the prop ( $10.99 ).

aaahhh, using the glow for the catalyst, and letting the ignition of the glow fire off the gasoline, lots of oil to lube the engine and keep it cool. Smart!

I usually consider a 25cc engine capable of flying a 12 to 14 pound airplane, which will have about 1,000 sq. in. wing area.

I prefer leaving the pull start on the engine. However your pull start is on the prop end of the engine, which is dangerous.

I would always bench run an engine first to make sure that it can be started and then to determine a satisfactory prop. Start with props in the 16� diameter range and plan on buying many different props. Most blowers turn 8,000 rpm and should turn the prop at least 7,000 rpm.

The original muffler will work. You can always purchase or make another muffler after you are successful.

Bill

Actually when using the 1 part 10% nitro / 10% oil glow fuel to the 2 parts Premium gasoline the oil content after mixing is only 3% which equate to about 32:1 which is just a little more than the standard 40:1 that most gassers run. If you are going to try this do not use regular unleaded as most people are having problems with seperation of the mix and gasoline does vary from station to station, i used Sunoco ultra 94 and had no problems with seperation. And yes that amount of glow fuel added to gasoline is enough to keep the plug lit but most people have the best sucess with the OS Type F four stroke plug.

Here the the test plane for my engine, it ran great on the ground but after 2 min in the air it kept deadsticking on me, dumb ***** me flipped the carb to make the throttle linkage easier but unknown to me at the time there is a small hole for the impulse line to run the fuel pump, that explains the deadsticks, i did some damage to the wing and gave the plane to a friend, he now has a Stihl 26cc GAS/GLOW engine on it and wow that's tons o power for a 6lb plane.

Funny thing was this plane is a .40 sized trainer, but it balanced perfectly with my 21cc on it, by the way my engine came in at 32oz with motor mount and the factory steel muffler.

WARNING: Beginners do not put this large of a motor on a trainer plane unless you really, really know what your doing ( Read as NOT A BEGINNER )

surprised the motor fir inside the trainer

I'm suspised it held together. That was my first trainer and I was kept busy gluing things together, The must have been short on glue the week they built it. It was a bad flying plane, This was with a o.s. 52 four stroke. I'm not susprised it balacned out OK, I had to ad 10 oz under the engine to balance it.

Don

Actually my OS .40LA looked so small on the nose of this trainer i knew i just couldn't use it, the 21cc fit right in nicely and believe me there was no lack of glue when i was done with this plane, i went over everything with CA, i added triangle stock inside the nose of the plane, i epoxied on a pc. of 1/4" ply on top of the original firewall and also ran some extra beads of epoxy around the nose, after 6 flights with the 21cc and about 16 with the 26cc there is no signs of anything coming apart. The explorer flies quite good and from experience it glides in quite nicely, here's one of the maidens from last year with a deadstick where i used to fly, i now have joined a club and prefer having a large flat grass runway to land on. http://www.rcuvideos.com/video/EXPLORER40-wmv

aldentwc Some good advise and some that would frighten me to consider given so far. Go spend some time reading in the Engine Conversion forum mentioned above. There are two threads on gas-glow useage that have been compiled over the last few years. An electronic Ign will get a Homie lightened and easily started in a easy manner. I have two CH igns. that I move between planes. I doubt the 'shaft' will unthread; every one I have seen are an extension of the crankshaft. 1000sq inches is good wing size more is better. 10-13 lbs is a good weight target for scale flight. If you keep the magneto ign, DO NOT Mess with the flywheel other than shaving/breaking off the cooling fins. This is a safety concern. If you could locate a 25 or 30 cc Homelite mounting will be simplifed. Go read and enjoy.