ajcoholic

My Feedback: (10)

For the guys who know, I am currently working on a rotary valve four stroke of my own design. Its a 1.20, based on the old Webra T4-40/60/80 design.

The past few days I have been wondering what a scaled DOWN version would be like! I do have plans for a .074 poppet valve 4 stroke, but with the gear and cam drive, etc it is probably heavier than I would want, not to mention a lot of work (time I dont have this winter). However, the basic design of a rotary valve 4 stroke is so simple, only a few more parts than a 2 stroke. I took apart an old printer of mine, and the miniature toothed belt and cogs got me wondering.... an .049 or .061 rotary valve 4 cycle, driven off the crank like the webra would be so simple, lightweight and just probably sound so cool!

In all my engine books, travels and speaking to many people the only miniature 4 strokes have been poppet valve ones, and they are rare. I think this may be an easy experiment... and wouldnt it be cool to have one of your 1/2A planes powered with an engine that sounds so different than a screaming 2 stroke?

AJC

Bipe Flyer

What a great idea! That would be incredibly cool.[8D] I recently bought my first 4 stroke and I have to admit, I like it more than I thought I would.

Consider this a pre-order if you ever decide to build and sell.

Ooh, you could anodize the case black and the head gold... sort of a mini Golden Knight; or a Golden Squire, if you will.

ajcoholic

My Feedback: (10)

Funny thing... just worked this out. If I take the Webra T4-40 (.40 size) and exactly halve the bore and stroke to .4134" and .3661" respectively, you get....

dun dun duhhh... .049!!!!!

It was meant to be I tell you....

There is but one problem I have to figure out. The stock head has the glow plug sitting at an angle in the head, and the valve is running right through the centre of the head. The combustion chamber is a sort of wedge head. I dont think there is enough room for the standard plug if I scaled it down directly. Have to figure it out, maybe move the valve off to one side. Oh well, to the drawing board I go.... pencil and paper for me, I am too slow at CAD

AJC

ajcoholic

My Feedback: (10)

I was thining about this thing a lot tonight, while I was out walking my dog.

New idea... for a prototype, I can take a cox td crankcase, and use the crank/crankcase. This will save me some time. Just put an aluminum cover over the front (where the plastic carb housing usually is). The new backplate I can make up to thread into the case, and drill/extend the crankpin to turn the shaft that will drive the belt.

The cylinder I can turn up from leaded steel (same as cox uses) and then lap, so I can use an existing cox piston.

So if I use the cox crankcase, crankshaft, prop drive washer, etc, and piston/rod allmost half the work is done!

Just have to make the new backplate, cylinder, and head, and of course the rotary valve. I can use one of my Tarno carbs feeding directly into the head...

Any other ideas??? Please feel free to share....

AJC

Rick Lindsey

Oooh ooh oooh... count me in for one!
I'm afraid I don't have a clue how our engines work, so I wont' have any useful input, but I would love a 1/2a four-stroke engine. The 2-stroke scream is actually something that would turn me away from 1/2A stuff, even though I am attracted to the smaller scale.

fastlash

My Feedback: (7)

wouldnt it be easier to, rob the belt cog wheel off the printer, and cut back the plastic housing and key the cog wheel on the crank over the intake cut away , or use a product eng. and machine the front down to the point that you still have a bearing to support the crank, just a thought, are you thinking about a tensioner or you going the belt stretch method, i.e. exact fit plus a small percent figured in for wear and stretch

ajcoholic

My Feedback: (10)

That all depends upon the sizes of belts I can get. I can machine my own cogs as needed (I have a rotary table on my mill and can make gears and toothed wheels no problem). I dont think there is room up front on the td shaft, but its something to look at.

I just like the belt being in back anyhow. Thats how I am making my big one (here is a shot of what I have so far - just think miniature )

AJC

ajcoholic

My Feedback: (10)

Also, you need a 1:2 ratio to drive the valve off of the crank. The orinter stock cog wheels are no where near that, most are 1:1. But I think I can work with the belts...

AJC

LS171Malibu

My Feedback: (16)

Have you looked at the rotating sleeve that the RCV 58 uses. It looks so simple and no space in the head is for valves. I WANT ONE, however you go about it!

ajcoholic

My Feedback: (10)

I have an RCV 58, yes, the rotating sleeve is a neat way to approach the idea, but it is much more difficult due to the need for bevel helical gears, something I cannot cut... yet. Also, the engine cylinder must be much more boxy in order to hold the sleeve bearings. I think the horizontal rotary valve in the head is the simplest way, and should be the lightest.

AJC

sturmvogel

Rather than face the difficulty of making a glow plug that's unique, how 'bout a 4 cycle diesel??
Bob Peterson

ajcoholic

My Feedback: (10)

I will use a regular plug, just have to find a different place for it. I will probably make the combustion area more like a cox glowhead, ie, trumpet shaped and put the valve off to one side, and the plug in the center. Rather than like the Webra that has the plug off to one side, in the side of the head block.

4 stroke diesel - thats also on my list of things to try. I am getting there maybe in 2008 by the way things are going...

AJC

ballgunner

My Feedback: (1)

One of the greatest ideas to come down the pike in years. Sign me up too, especially if you develope the diesel. I like models of all sizes but I have to rely on the inventive types to get anything other than shake the box, install the prop and off to the field. Used to design a lot of my own airplanes. If the little four stroke becomes a reality I'll go that way again.

ajcoholic

My Feedback: (10)

Woh now guys! I havent even starte dto make one yet and I allready have a bunch of "orders"...

Like most of my stuff, I am afraid if this does work, it will be a one-of, but rest assure if I do make it and it runs I will share my plans and details with everyone...

AJC

boberos

Hi Andrew,

I don't want to complicate things but I have a HP VT21 rotary vave 4 stroke that runs just great. It has no belts just gears & a shaft running up the rear. I think the rotary valve runs in the other plane to the Webra. Not sure though.

Bob G

ajcoholic

My Feedback: (10)

Yes, the HP engines (there were 3 of them, now RJL makes just the.21 and .49) have a rotary valve that runs vertically in the center of the head. The valve is run by a pair of pinion gears, and a shaft up the rear of the engine. The valve also open the glowplug to the combustion chamber, unlike the Webra style that has the plug allways in contact with the chamber.

Probably harder to get the gear train down, and tolerances are defintely more critical than with a belt. But it would probably make a good miniature also.

For now I will run with the horizontal valve.

AJC

wild fred-OLD

interesting! but who's gonna make a monosoupape like the lerhone or gnome with cox cylinders and one valve....

Bipe Flyer

Weren't those the best sounding engines?
Here's a link to a sound clip of a Gnome.

http://www.lincolnbeachey.com/gnome1a.mov

ajcoholic

My Feedback: (10)

Wild Fred.
Well, I can lend you my book on making the Bently rotary engine, and you make one up for us, how about a mini using .020 size cylinders?

Me, I'll stick to one cylinder for the time being...

AJC

Bipe Flyer

How about a flywheel that could be put on a .40 right behind the prop, that is made out of 7 .020 cyls? Cheating, I know, but it sure would look good.

ajcoholic

My Feedback: (10)

George Luhrs is making a run of .015 single cylinder 4 strokes, and a 5 cylinder radial with a total displacement of .061!! The only thing, the price will be out of this world, he currently sells one of his single cylinder stationary .074 four strokes for allmost a grand US$$..

But what a master of the art.... WOW!

http://www.minimodelengines.com/ComingAttractions2A.htm

ballgunner

My Feedback: (1)

A few years past there was a functioning 1/4 scale rotary advertised or at least reviewed in the model mags. If I remember correctly the price was about $3500.00 each. I haven't seen anything concerning that engine for some time now. Probably just as well. If I bought one and couldn't manage the airplane because of torque and bent the engine I'd be looking for a cliff for jumping purposes. There was also a modeler who developed a radial crankcase and rods using Cox cylinders, about 7 cylinders I believe. Don't know anymore about that one either as I haven't seen his ads for some time.

LS171Malibu

My Feedback: (16)

This ain't show-n-tell(cool stuff though)...it's AJC's four stroke thread!

Randy W.

During my days at Cox back in 1984 a fellow Customer Service employee named Kevin Kline and I decided to build a 4-stroke .049. We used a stock crankcase, and an unported cylinder we had to get from Kustom Kraftsmanship as we had none in the warehouse. Kevin milled a standard glowhead to accept a brass tube aspen valve assembly and secured it with JB Weld. The drive gears were borrowed from the then popular Scorpion R/C car and were driven off the prop drive plate. We mounted a 7 x 3 glass filled prop to provide flywheel action. We ran the engine several times. It hand started easily sounded like a larger 4-stroke engine, but very faint. Due to the very small valve required to clear the glow plug element, the engine put out very little power. We had hoped to fly an EZ-Bee with it, but I doubt it would have done much. Kevin still has the engine, though I believe the valve assembly came apart one day when he tried to use an electric starter on it.

ajcoholic

My Feedback: (10)

To my understanding, an Aspen type valve is an "inverted cone shape" that spins in the head, with ports cut into it. I dont understand how it was mounted with the glowhead element in the centre, where the valve "axle" would be...?

ANy further description? Sounds neat!

AJC