CNC Radial Engine

[MMT]

Hello everyone. I have always wanted to build a radial engine, so about 3 weeks ago I finally started one.
I thought I would post some pics, and get some input. The project started out as a 4 stroke, but midway through I decided to go 2 stroke.
The bore and stroke are 1" x 1.125" and the displacement is 130cc.
I started to duplicate the 5 bears hodgson radial. The bore and stroke dimensions are the same and that is all. I have completely designed all parts from scratch, including the supercharger.So far all parts are machined from 6061 AL except the jugs they are 12L14, and the crank is 4140 PH.
I hope this is durable and reliable enough to power an rc aircraft, but I'm not sure what to expect. Anyone have any experiance in this area?
Thanks for your input. I will keep posting progress.

[balsaman]

Nice

A 2 stroke requires alternating high and low pressures in the crank case. How will you achieve that?

Eric

[One of Many]

Nice work for 3 weeks. It might take me 3 years to get that far at the rate I am moving on my Morton. My trouble is no time and plenty of talent. Too many other priority projects on the books.

A few things I would have as a concern. The 12L14 might be a bit soft for cylinders unless you have planned for cast iron liners. Best not run it lean for fear of galling in the bores. I think my Morton uses 4130 tubing. I can't imagine your engine doing more that 5000 rpm, but large 2 strokes radials do run higher. If you are not looking for long term service then it may be fine. I know my plans are to fly the M5 a few times and shelf it. At least I can say it did fly something then....

As to the point of rpm. I wonder if the idle will be reasonable for so many jugs on glow. If you carb it direct rather than crank case induction could be better. I have heard some super charges this small do struggle to even be effective at low RPM. Then there is the issue of lubrication in the crank.

That is good news that you will keep posting on your progress. I know the magazines don't come often enough. So, my function in this hobby is to be building engines just like yours......vicariously through the works of others.

DC

[RotarySMP]

Nice work MMT. I will also be interested in hearing how you make it breathe.

[RICHARD ZASTROW]

MMT Good luck on the engine. Depending on how much you want to spend, there are coatings that can be applied to cylinders, pistons etc. NASCAR & dragster guys use them all the time. I assume the supercharger will have enough capacity to remove the need for cylinder scavanging. You may have to solve a pressure problem created by piston blow-by into the crankcase from combustion pressure. All solveable. Again, Good Luck.

[MMT]

2 stroke engine pressure does not require alternating pressures. They simply require some sort of crankcase vacuum (i.e. alternating pressure created from pistons) or a fuel/air mixture forced into the crankcase (i.e. supercharger) to replace the fuel/air mix that is being consumed in the combustion chamber.
I will have to ensure that the impeller will create sufficient pressure to make this happen. It may have to be underdriven to may this happen but hopefully not.
As for the 12l14 cylinders, that seems to be the material of choice with home builders of i.c. engines. I also thought this would be too soft at first, and then I remembered that Briggs & Stratton and many other manufacturers use aluminum cylinders.
My experience with 12L14 is that it has much better anti-galling properties than most other grades of low carbon steel.

[Stevie]

Originally Posted by MMT 2 stroke engine pressure does not require alternating pressures. They simply require some sort of crankcase vacuum (i.e. alternating pressure created from pistons) or a fuel/air mixture forced into the crankcase (i.e. supercharger) to replace the fuel/air mix that is being consumed in the combustion chamber. .

I don't know where you got this idea; but without a positive pressure in the crankcase the mixture will not be forced through the transfare ports up into the cylinders
2 stoke twins have a crank arranged so both piston are at BDC to create this pressure; or you can do it with one up; one down as long as the 2 are sealed from each other
The more cylinders you add the worse this gets as pistons are going up as other are going down; so there will not be an significant pressure difference to pump the charge into the cylinder needing it
Best would be to omit the transfare ports; directly charge the cylinder after the spent gases have mostly gone with a supercharger (it will have to be powered by something other than the motor) you still might have to scavenge the cylinder with a baffle across the piston crown

This is why most radial engines are 4 stroke; tough to make it work as a 2

[RICHARD ZASTROW]

MMT You are almost there. By supercharging directly through the transfers, you can have a sealed crankcase like a conventional 4-stroke. This is how many deisel 2-stroke engines operate. In fact, I believe that was the method for the Orbital/Neon 4-cylinder was arranged. As far as Briggs & Stratton and all the other aluminum 2-strokes, they are plated with hard chrome and run soft rings or other coatings such as Porsche developed "Nikasil" nickel-silicon. Others have been developed since, mostly ceramics of one type or another such as aluminum oxide. These have been used since the mid-1970's. As far as 12l14, I'd still coat either the pistons or the cylinders to avoid galling. I personally would check into the best grade of aluminum for coating of choice, machine out of aluminum and then coat the aluminum.
Of course, this is the place for you to say "I'd rather do it my way." Good Luck.

[RICHARD ZASTROW]

MMT Here's a follow-up. If you are interested in leading edge useable IC engine technology,you might want to look up Delta Hawk aircraft engines. These are both turbo and supercharged combined deisel 2-stroke v-4's They have line drawings etc. on their site.

[MMT]

In my earlier post when I said "crankcase vacuum", I meant "crankcase pressure". I think Richard knew what I meant. Sorry for the typo. As far as the 12L and Al pistons I will look into different types of plating. Thanks for the info Richard.

[RICHARD ZASTROW]

MMT You were correct. There is crankcase vacuum and pressure. Both happen in every complete cycle. What I was refering to is the isolation of the crankcase from the cylinders such is done on the old "screamin' Jimmy's" supercharged 2-cycle deisel truck engines. The old GMC superchargers were attached to the side of in-line 6's blowing thru the transfers at the bottom @1/3 of stroke. This allows the typical oil sump in the crankcase. The other item is having the transfers covered by long skirts on the pistons, long cylinder walls and good piston rings to keep control of oil and combustion pressure blow-by. This would also negate the need to seperate cylinders for the otherwise required pumping action. I see no reason not to proceed with your idea. Personally,I'd make it direct injected deisel capable of burning jet fuel readily available at any airport along with the deisel fuel available at most filling stations. (Biodeisel?)
Keep on keepin' on

[itsme]

Hi there,

Several people have built 2 stroke radial engines for models and they do generally work very well (assuming they are designed and built properly). They normally use a vane-type supercharger that is driven off the back of the crank. This is then used to pressurise the crankcase and porting is as it would be for any 'normal' 2 stroke. The engine then runs on standard model fuel. There was a commercial attempt at this in the 1990s sometime called the Berger Radial with 7 cylinders, however I'm not sure what ever happened to it.

I have a feeling that the engine may start to get impractical for a model aeroplane if you start trying to have seperate induction on each cylinder along with a 'conventional' bottom-end lubrication system.

As far as diesel goes for model aeroplane engines, again this is not very practical when using direct injection. Almost all 'diesel' (or compression ignition) model engines operate like glow engines (in that they take a fuel/air mixture in), however they rely entirely upon the compression for ignition. ie. they don't have any ignition plug - as you would expect. These engines rely on fairly large quantities of ether in their fuel (normally around 30%). A direct injection diesel model engine was built some time ago (I have a feeling it was in the 1940s), however, it was reported to be exceptionally fiddly to set up and too complex for what it was intended for.

Just a few thoughts....

Keep on going and hopefully you'll have a running engine in the near future!

Regards
Warren