WHAT ARE THE CHALLENGES (IF ANY) WITH FITTING A GAS ENGINE 20CC TO 35CC , INTO A CMP T-34 MENTOR ...PLEASE SHARE YOUR THOUGHTS ( I'M A 13 YEAR MACHINIST)

You are going to have so much weight in the plane that it will be a poor flyer

Pick a lighter weight engine to start with. Echo are powerful for their size/weight. Get rid of the magneto flywheel and coils and go to gas/glow to minimize weight. Trim all of the excess mental from the engine. Get a light weight muffler. Use a wood prop. Even then it may be too heavy an engine, like W8YE says. Good luck.

Regards, Richard

Thanks agin for the speedy replies .....My main goal is to fly this craft with only one battery , given the limited resources where i live ...so i really want to keep the magneto and fly-wheel ,however i will try to source a smaller engine ....as for the echo engines : non-existant where i live ....in reality the smallest engine i may get away with  is a 20cc weadeater feather-lite ......has anyone tried this modification on the aircraft in question ? (CMP T-34MENTOR)....THANKS.

Look into gas/glow, it eliminates the magneto, and only needs a battery to the glow plug for starting. Uses one part glow fuel to three or four parts gasoline. There is a forum here on RCU on the subject with all the details.

Regards, Richard

Personally i think the gas glow idea is brilliant ....except that it still will be difficult for me to locate this one part glow fuel .....otherwise it is a really good idea

With your fuel restrictions, it would have been best to pick the engine first and then an airplane to fit the engine?

Absolutely .....it was like a rock and a hard place ....i really wanted the "cmp t-34 mentor " in question and i am hoping that my knowledge as a machinist and access to a machine shop would also help my case ....that said ...I still need the help of you guys to kinda walk me through this process....thankyou.

My job summons me .....gotta go do a dash-8 run throughout most of the caribbean till midnight this evening (christmas blues) ....I thank you-all for your valuable contributions ....I would appreciate some indepth insight into my proposed project .....and some ideas as to the equipment you would have chosen for this aircraft ...ie. ,servos , receiver and battery , gas engine, carburretor, muffler , prop and spinner ...and also wheel size......

thankyou again and talk to you guys in a bit.....cheers.</p>

the featherlite 20cc could work, but on a 40 size plane it really needs to be on electric ignition (or gas/glow, if you look through the thread there are options in what you can use) to work. Like I said in your other post, those featherlites are super light, but are also dogs unless you modify the exhaust port duration (they come at around 110 degrees when it should be 150 degrees for better power). With that plane and a magneto engine you would have to chop the nose of the plane (I wasn't talking about the engine before) down to just in front of the wing, with electric ignition you can move the ignition module and battery back behind the engine where the fuel tank normally goes to get the COG back further. And for a battery, it doesn't have to be complex, I've taken cordless phone batteries apart and made myself a receiver pack, a 800mah battery should last around 3 flights before a charge is needed. Trimming down aluminum from the engine doesn't add up fast at all, you could work for a few hours and only get a couple ounces, the weight is in the crankshaft...

good luck, I'm actually trying to put a 18cc featherlite on a 40 size stick, need to get my bandsaw going before I get any further on that.

Is the weight of the several sizes of Featherlite engines the same? I there any weight advantage of using an 18cc vs a larger one? Thanks.

Sincerely, Richard

they have a slightly different casting for each, so it's just a small change in weight between any of them. I should strip an 18cc, 21cc and 25cc and see what the difference is... and maybe the old style 25cc versus the new style 25cc since I have all of the above

I put a 20cc stihl conversion on a 60 size four star. It flies fine but is a bit heavy. I think that lighter will fly better even with a bit less power. We'll see, I am currrently messing with an old Magnum .91 2-stroke. I got it running and will put in in the four star and see how it goes.

I did a Weed Wacker 25 cc featherlite a while back. Even with porting, open exhaust, bigger carb and electronic ignition, it was no power house. I chopped off everything I could and it is not very light given the power output.

It seems like smaller conversions work best on short nosed slow planes, Cubs and WW-1 war birds.

For a 40 size plane I woulld look for a ringed glow engine and install a rimfire plug and RCEXL ignition. Install the magnent on the hub and go. Run the ignition on AAA size NIMH batteries. The Super Tigers are very reasonable. The 51 and 61 ringed might be pretty good?

http://www.supertigre.com/engines/

Perhaps even some other 60-ish sized ringed engine that is at hand? If a tiny walbro carb show itself then go ahead and make an adapter. Otherwise it will run wih the stock carb. Just run lots of oil in the mix to protect the big end of the con rod. Yes it would be nice to have bearing on the con rod but it is not necessary. Hey, they always did it that way on the old ignition engines. Wasn't he most concearned about the price of fuel. This solution would work. Yep, the plane would get slimed but, that was not the issue for him.

Thanks for your input ....just need to get you straight on this one .....your proposal is a .61 glow with rimfire plug and rcexl ign. ....would this require drilling and re-threading the head to fit the rimfire plug ?.....also are you suggesting that there is more compression to be had in these glow engines compared to ...say a string trimmer engine modified in the same manner ....(using same rcexl ign. ) ?

Get some input from some of the other guys here on my idea before proceeding and/or spending money. It is my understanding that a 1/4 x 32 plug will fit in a glow plug hole. Do check on the length for whatever engine you get of have . RCEXL makes an igniton for those little plugs. I suggest you shop for an ignition vender and ask him what will work with your engine. It is also my understanding that you can run a ringed glow engine on gas with lots of oil, some of these guys can give input on how much. I would guess 20% castor oil would work fine.

The string trimmers are low compression. A glow engine will be higher. During the 50s a lot of conversions were done on ignition engines by simply installing a glow plug. I do not think that is a central issue in this project though. IF you go with a spark plug to light the fire instead of compression you set the timing with the spark. Glow and diesels set the timing based on the compression ratio. As far as power output goes rasising the compression is not going to be major factor either way.


W8YE can probably answer specifics. I have never done this kind of "conversion". I think I read about his experiences with this very thing on this or other some forum.

The Rimfire sparkplug referred to has a 1/4-32 thread just like a glow plug. So, no rethreading is needed. I think the premise is that the lighter weight of a 2 stroke glow converted to gas with an electronic CDI will result in a more power per unit weight than the weedeater engine. Be careful, because the converted glow will run hotter than on glow and has less cooling fins and mass than the gas engine. So, insure you hae adequate cooling if going this way. Running a gasoline engine on gas/glow will not have cooling problems because it was designed for hotter running gasoline. It will be heavier for the same reason, more cooling fins, and because it has a heavier crankshaft and connecting rod with roller bearings etc. The Walbro gasoline carb will be heavier than the glow fuel carb also. You will need to run heavier percent of oil with the converted glow engine because it does not have roller bearings in the con rod. These are all just general considerations when thiinking glow vs gas vs gas/glow and the conversion permutations involved in each. I think more research and experimentation is needed to see if anyhing but a glow engine will be ok for your designed-for-glow application.

Have you considered electric power? I don't do electric myself, but many do.

Good luck.

Sincerely, Richard

There's another reason to forget a magneto gas engine. In the case of the T-34, the cowl would require some serious and ugly surgery to accommodate a flywheel up front. I'm eventually going to build a 120 size Tiger Moth from NitroPlanes. I'm powering with a Ryobi 31 and it required conversion to CDI to deal with the cowl. With CDI, the entire engine will easily fit inside, with only the exhaust stacks coming out the bottom. With the flywheel, the cowl would have been a disaster.

Thanks for your contribution , I realise that no one really supports the magneto being used with this project .......and I must agree that i do NOT want to chop down the nose of my aircraft NOR make a mess of my cowl to allow for the magneto .

But you guys have to bear with me ...as Ireally wanted this plane to be as efficient as possible ...ie. normal gas mixed with a little oil and only one battery to power the receiver. Now I can see that the argument has been greatly enhanced to support the use of the CDI , particularly considering the unsightly modifications which have to be made to support the magneto set-up.

So in my quest to achieve this partially green "MOD" I suspect I may have to lean towards using a cdi ......so I have a few questions for those used to the cdi set up ...: cant it be powered by "AA" rechargeable batteries and what sort of flight time can i expect with these batteries ....or the normal battery pack ?

I like the simplicity of magneto and there's really no or very little weight advantage, once you account for the extra battery pack, etc. with the CDI. Some of my motors are still magneto, and I will use them on uncowled planes, like stiks. In fact I have a 19CC weadeater motor that runs great and is a candidate for smaller planes w/o cowl. Also have a few Homies, same deal.

the weight advantage on CDI isn't in loosing weight, it's being able to move it from right behind the prop to behind the engine alltogether.

with CDI, you can use a standard 4 cell AA receiver pack and get 3-4 flights like you would using it for the receiver on a 40 size plane.

I've been using the AAA size and even smaller sized cells with 1200 Mah capacity in my 40 sized planes on ignition for many years. It gives you the weight reduction without the fear of the batteries dying early in the flying session. I was flying a Goldberg Falcon-56 for many years with a K&B 40 on ignition with a short Rimfire 1/4-32 thread plug and my ignition module from the New CDI forum. Also flew a .60 sized Ugly Stick for many years on ignition with great results. Reducing the weight was always a factor in my considerations with ignition. Usually I would only place a 4 ounce tank in either sized plane using the economy of gasoline and 20% oil to make many hundreds of successful flights. Just make sure if you go to ignition, that you shield the spark plug lead and have that well grounded to eliminate any RFI that would interfere with the radio of course.

Also of interest in engine choices would be the 18cc and 21cc Echo and featherlite weedeater motors. I have converted hundreds of these over the last 20 years with great results. While keeping in mind that you are looking for a high power to weight ratio for a smaller plane, a correct sized converted glow engine would be probably the best choice here for the Mentor. I have "stuffed" a .60 in a .40 sized plane many times to overcome any slight power loss from running a heavily oil ladened fuel mix. As proof that this method works, I am still flying an Ugly Stick with a K&B .61 on ignition with a 4 ounce fuel tank that gives me better than a 15 minute flight time...and I really tear up the sky. So if you can find the right combo of engine with a ringed piston and correct gas-oil mix, you'll do just fine...

John

You still may want to consider gas/glow. You do have to mix gasoline and glow fuel and use a glow plug in your gasser, but then, just connect a battery as in glow to start and then disconnect the battery to fly. No CDI, no magneto, no sparkplug, no on-board battery for ignition. Fuel cost much much less than glow. Mess much much less than glow.

Over and out.

Sincerely, Richard

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You still may want to consider gas/glow. You do have to mix gasoline and glow fuel and use a glow plug in your gasser, but then, just connect a battery as in glow to start and then disconnect the battery to fly. No CDI, no magneto, no sparkplug, no on-board battery for ignition. Fuel cost much much less than glow. Mess much much less than glow.

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Indeed another brilliant idea , however over here on this microscopic (3rd planet) island , there currently is a guy selling glow fuel at a discounted price of USD47.20 per gallon (I'd have to resort to flying my craft butt naked after selling all my clothes and belongings to pay for my glow fuel

Except for the glow problem ...I really do love the No CDI, no magneto, no sparkplug and no on-board battery for ignition. And besides there doesnt seem to be much benefit weight-wise as compared to a CDI + battery, which dont weigh that much.

What about the cooling fins on the string trimmer engine blocks: are they absolutely necessary , considering that this is an airplane , which supposedly will always be in foward flight , allowing for air rushing past the engine through the cowl..thereby cooling it ?

Now it seems like this project's difficulty is in choosing the powerplant for modification ....alas I must choose soon so the quest can begin :

-Mentor + Weedeater engine +Magneto= FLYING BRICK
-Mentor + weadeater engine + CDI = Many Batteries on a "not electric craft"
-Mentor + converted glow engine + all the parts to make it work = Me becoming a Grandpa before I fly craft
-Mentor + gas/glow engine + expensive small part glow fuel = Me flying with maybe an underwear (as i alreaady sold most of my stuff)
-Mentor + Normal glow engine + expensive full part glow fuel = Me flying "no gas" Mentor with a rope tied to it and swinging like crazy to keep it airborne....
also Butt naked , after being kicked out by wifey after selling everything to pay for GLOW.

Hence my predicament......

you don't have to break the bank to get the batteries all set up. Get yourself a decent multi purpose charger (I have a Triton, I use it for nearly everything in my garage) and scavenge to find batteries that fit your needs. If you look in the right places you will find batteries that you can modify to fit your airplane. I've been scouring goodwill around here (there's one where everything is $1.59 a pound) for cordless phone batteries, many of these are 500-800mah AA 3 cell packs, the other day I went there and found two brand new packs for Shark cordless vacuums, 7 C cell pack. I got those two batteries along with a handful of phone packs for $5, with the triton I can rejuvenate the packs and charge them appropriately and be sure they still cycle to cull capacity. My Triton charger being a 12V charger is portable, I take it flying with me, in the garage I have a modified computer power supply mounted to the wall that it plugs into. If you know your way around a soldering iron it isn't too hard to modify most of these batteries to your needs.