DougT

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Hello engine nuts,

For a few years I've wanted to build a unique 4-stroke gas engine for RC airplanes. Would anyone be interesed? I've ordered some books and equipment and am thinking of a 30cc single or 60cc opposed twin. No camshafts, rockers, pushrods, etc. Dry sump oiling, electronic ignition, 4 valve heads, possible crankcase supercharging similar to YS's. My target for a single would be about 42 oz and a twin about 52-55 oz.

I see what specialty 2-strokes sell for any how many people have them and think people would be interested. I know I love new and unique things.

Doug

H. Wayne S

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Wow, and the cost of such a beast ? I personally think the 50 to 80cc range would provide a wider market.

rsallen13

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Look at the new 3w radial. If you could build a crank and case for one or two of those cylinders you might have a winner.

tango28charlie

I would be VERY interested in any 4-stroke gasser that had a wet sump and therefore did not require a mix of gas and oil. I would be categorically UNinterested in any 4-stroke gasser that did still require a mixture of gas and oil. If any such 4-stroke gas engines were available in the normal sizes I'd never buy another 2-stroke gasser, even if I needed an engine one size bigger than a 2-stroke to get the same power.
Charlie

rmh

Go ahead - build it -
PS I ain't saying you can't do it - but at this point in time -after looking at the various other attempts at providing "revolutionary" model engines -- you have your work cut out for you.
Let's see-- sleeve valve/rotary head valve /wobble plate / sliding vane /sliding sleeve/miter gear /etc..
I too would like to see an approach that really differs from the myriad of stillborn attempts over the last 100 yeas.
So far the only truly acceptable one has been the Wankel--and it is a horror story to make correctly.
Good luck

DougT

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H Wayne.

Thanks for the recomendation. I was also eyeing the 50cc single/100cc twin size range.

Tango,

I fully intend on it being a true 4-stroke(no pre-mix).

I should be getting the manual on sandcasting today or monday along with some more books on boring/machining and metallurgy.

The engine that's given me inspiration is a 12.5cc, 2 valve head and it turns up to 13,000 rpm. I'm thinking of the 7-8,000 rpm range but more torgue. The only thing I don't have a handle on yet is how to build a wet sump oil pump. Any suggestions/references?

Doug

ZAGNUT

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thought you were going for a dry sump? if so then look at the gear pumps used for fuel on the model turbines. you'll need more than one scavenge pump for inverted flight. stack a few of these together, each one taking oil from wherever it can collect in the case and returning it to through a check valve to the tank. one pump in the stack takes oil from the tank and feeds the engine.


dave

rmh

Modern aerobats use dry sump (essentially)
the reason being for sustained inverted flight and side G loads -
Ditto for race cars - 'cept for the inverted part----
oiling systems are an art form all of their own ----

tango28charlie

Doug, I'd suggest taking apart a Honda GX25 to see how they lubricate that. With engines this small you probably can rely mostly on splash lubrication rather than full pressure. Are you sure about the sleeve valves though? In full scale engines such as the Napier Sabre, they seem to be problematic. A more conventional 4-stroke design, either OHC or push rod might be easier to build.
Charlie

ZAGNUT

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where did you see sleeve valves mentioned? i think Doug wants to use regular poppet valves but without cams, rockers or timing gears...


dave

Willdo

DOUG, all of the answers so far have been good, - Dick has probably been around (like me) for quite a while and has seen them all (as I have).
They never fail to intrigue me, and I keep going back over them again and again, like an amateur gold panner going over the tailings in a disused goldmine.

I admire your enthusiasm, but casting metal from a book! - a good start, yes, - no doubt, - but not unlike trying to practice sex with the manual by the bedside! - it's a bit of an art, and can really only be learnt through practice and having all the right equipment, (and getting lucky). - same thing goes for designing, machining and welding.

I guess what I'm trying to say is, learn the casting and machining techniques first, then while you are learning these, you can be thinking about exactly what is practicable in the engine design department.

As Zagnut said - poppet valves ( maybe he'll have to enlighten me about the no cams bit ??),
- sleeve valves have always been difficult, machining wise, material wise and lubrication wise.

I have always been against using fuel/oil mixture in four strokes, but it does have some merit, in that it can offer simple supercharging from the crankcase pumping. (turnaround for me!).

No matter what you do, the four stroke will always be more complicated, heavier and more expensive than the two stroke, so live with it.

Having said all this, I am really only trying to stop you from making the mistakes I made, all over again, - at the same time not destroying your enthusiasm, - the main thing is, one step at a time, and a lot of thought into each step.

As a friend of mine ( who keeps me straight on airframes) says, and as RCIGN always says, use the KISS principle! - I know they are right, and I have to be brought down to earth now and again!

Good luck with your efforts.

Willdo

Doug the drawing on this link may, or may not interest you, but worth a look.

http://fvkma.tu-graz.ac.at/eng/Desig...nProject4.html

SilverEagleBW

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Some 20 or so years ago there was a gentleman by the name of Merit Zimmerman that lived in the Cleveland area.He designed,built and sold a small four cylinder inline four stroke engine.The engine purred like a kitten,and flew a 1/4 scale great lakes trainer with gusto.The sound of that engine was something to be heard,one word comes to mind,beautifull!It ran on gasoline and every chance (every weekend!lol)i had i went to see that plane fly.I would say go for it on a four stroke gasser,i would be highly interested.

BiplaneCrasher

Wow! what a great discusion. I also would love a four stroke gasser but isn't there a good reason they don't make them now?

Here are some Zimmerman pics...

Ed

SilverEagleBW

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ED!!OMG!! You have one of his engines!,,,They are masterpieces!Tell you,I became friends with Merit and Dee Harwell (the pilot!)during that timeframe.Great people the both of them.Truely Merit was a master of the craft in those days,and i have not seen the detail and attention that he gave to his engines since then.Granted he sold his engines for a nice price but they are worth every red cent!Alot of thought and engineering went into that engine,i know,i witnessed alot od thier testing.In the future i would love to buy one of his engines if one can be found for sale.

rmh

Beautiful engine---
It looks like a full scale racing engine-- Offenhauser type.
The Italians made some incredible stuff like this - some engines had the head and block as an integral unit -- dual ovehead cams etc..
The English also had some terrific engines - as well. Nothing sounds like a Jaguar.
I have some single cylinder model stuff made by a friend (dec.) that was all done on a drill press and an Atlas lathe--plus lots of plain old filing and fitting.
I did some twin engines on a single drive setups--
When someone notes that they can't use a particular engine because they would have to make a hole in the firewall - I shake my head at our model plane hobby and how it has changed into a buy and fly thing.
I assembled my first car from parts -not by choice -but I have never regretted a moment of it.

DougT

My Feedback: (1)

ZAGNUT:

Thanks, I did not mention sleeve valves. I'm planning on using OH poppet valves. "Electronic cam". You mentioned a fuel pump from a turbine. Isn't that similar to a electric glow fuel pump to fill a tank? Or is it different? Also, I saw a Yak-55 at our latest aerobatics show here and the owner says the engine uses a dry sump system with a header tank feeding the pump. He can run at any attitude(verticle) for up to 30 seconds before he needs to drop the nose. I don't know how practical that is considering all the 3D flying people do. Maybe this won't be a true 3D engine? I could have 2-3 different scavenging ports to collect oil for the header tank.

Willdo:

Thanks for the link. Very interesting. That looks similar to the Stihl 4-mix except the "oil separation case?". Thanks for the heads up on the casting. I'm sure I won't be a pro. I just want to get something close that I can turn and mill to dimension.

Doug

Willdo

That's the spirit Doug, but just remember - thoroughly learn one thing at a time - that's where I always came unstuck!

That Zimmerman engine is a beauty, would it be possible to produce anything like that today under a couple of thousand bucks?
Don't know about the power to weight though, but the double overhead cams suggest it had a bit of power, and I couldn't help but notice the radiator, ( something I want to perfect).

BiplaneCrasher

I think they could produce these engines on a large scale over there on the Isle of Sushi, but they would be more than a couple of thousand. More like four or five thousand. There is already a company that builds a V8 for the spoiled super rich folk and that engine is five grand.

I do not own a Merrit gem, but would love to! Anyone finance?

DougT

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Yes, that engine is nice. I'd love to hear it run.

I think Connely? makes scale engines that are in the 5K range.

I've been reading issues of "Strictly I.C." These engines in this magazine are just as nice. That is where I've got some of my ideas and motivation. I might have to order more of the back issues.

Doug

Willdo

Looks like I'm a bit out of touch with reality on pricing! . - but the thought is nice.

Meantime, I think I'll stick with modifying single cylinder production engines! - that Zimmerman engine looks so good I'd be afraid to fly it, and that defeats the purpose of the sport.

dannafinance

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http://www.carrprecision.com/Pages/prod02.htm

Check out this web page.

Antique

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Just got back from Scale Masters, saw a 34cc 4 stroke wet sump, used a 22-6/10 prop, WW1 bipe, flew scale, supposedly a Fuji prototype...They said it was made for airplanes only..Was cowled in, through the hole I could see some casting machined off where the mag coil was originally bolted to the cylinder...It had electronic ignition... If it were only for airplanes they would not have extra casting on it.
You think a large company would invest $$$$$ in a new engine for a small market ?
Color me SKEPTICAL...
Suspicions confirmed...It's a Briggs and Stratton Fource 4 34cc string trimmer engine...

GoeKeli

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That sounds interesting Ralph. Well, sort of! haha. Is there a enough power in one of these engines to sping a gear drive? Why would it be worth it? I don't know. I guess for scale applications a 4 stroke would be nice, but for me I need things very simple.
I wonder what kind of RPMs they were getting on the trimmer? 3k or 4k?

Joe

Antique

My Feedback: (4)

Couldn't tell, but a 22-6/10 prop on a 34cc wouldn't turn all that fast...It flew the plane very well and was very quiet...a gear drive would work but unless you turned the engine about 8000 the prop would have to have LOTS of pitch....The main advantage of the 34 is just that it's stronger because of the additional cc displacement..I'm quite sure the new Honda 35cc 4 stroke will be just a strong, probably stronger..The GX25 I converted was nice and light and had a belt driven overhead cam, gotta be stronger than a flathead....Maybe when it gets advertised for sale there will be some numbers we can look at..You can see some info on it if you look up the Briggs and Stratton website, Fource 4 weedeater...Couldn't find a price there, must be one on a dealer website somewhere...The Honda GX25 is $175 retail.....Willdo in New Zealand is testing mine on a plane..It made about the same power as a G23.....
Rpms? The website shows a comparison chart between the Fource 4 and some other 2 cycle engine..I think peak rpm was around 7800, but the 22 inch prop on the plane was nowhere near that...A Poulan 46 turns that prop about 6300...Can't see a 34cc flathead doing that...
Good power plant for a WW 1 bipe for scale applications...IF they can keep the price somewhat reasonable....