Sidevalve single

[Niels Abildgaard]

Hello Hopper

In racing it is the cubic that give the class to race,but from a technical point of view it is much more relevant to compare mass of engines.Is it unrealistic that a flathead 750 with racing crankwebs was same mass as the 500 ccm OHC competitors in racing trim ,engine plus gearbox?

 

[Hopper]

Niels, hard to compare really. The Harley flathead used cast iron cylinders whereas the BSA Goldstar 500 used all aluminium alloy. Doubtless the Harley engine was heavier. But what Harley did was lighten the whole bike and engine to compensate. Because it produced the same power as a 500 OHV, the chassis and the engine components were pared down to what woiuld be run on a 500, not a normal 750 OHV.

Same could be said for building a flathead model engine - if a 15cc sidevalve engine is producing the same power as a 10cc OHV, then you can make all components of the sidevalve engine such as con rods, piston, casings etc to the thicknesses and weight of a 10cc OHV engine. You should then end up with a 15cc engine that weighs just slightly more than a 10cc OHV and puts out about the power of a 10cc OHV.

 

[Niels Abildgaard]

Hello Hopper

Thank You for reflections that are very close to my own.That is always nice.
These fellows

http://www.d-motor.eu/nl/fuel-consumption-110.htm

are making a SV aircraft engine and claims 260 gram of petrol per kWh.
The watercooled Continental that went around world unrefueled was 240 and the Rotax 912 is 280.

 

[Hopper]

Hi Niels
Thanks for the link. That is fascinating stuff.it
With 2700cc engine producing about 90hp, it is obviously tuned for economy and reliability and not maximum performance -- which is good in an ultralight!!
I see it has 8:1 compression listed. This would limit performance on a flathead by reducing gas flow between valves and bore.

Compare this with the Harley KR producing 50-60hp from 750cc at 6:1 compression. That's, say, 80hp per litre. Compared with with the D-Motor at about 32 hp per litre at 8:1 compression.

A huge difference. But of course the Harley racing engine might last only a race or two between major overhauls -- not something the ultralight owner wants.

However, for a model engine, I think some of the Harley head/cylinder breathing designs may be of interest to play with. Also the cam profiles. They used very high lift cams with long duration and overlap. No worry about valves hitting the piston or hitting each other, so the cams looked almost square, and in some cases hourglass shaped, slamming valves straight to full open and keeping it there until closing time then slamming it shut.

The two cams on the left are the race cams, compared with stock cams on the right, in the pic below. (All these cams are used with roller cam followers, which influences the shape to be less pointy than with flat tappets.)

 

[Hopper]

PS, plus of course the D-Motor flathead compares well with the Rotax 912 by producing about the same HP from an engine of about the same weight as the 1200cc Rotax. A big capacity but lightly built motor with flathead simplicity. Perfect!
Perhaps we will see the return of the flathead to general useage?? Who knows, strange things happen.

 

[Cogsy]

I have been following this thread with interest, but I must admit I'm missing something. These power figures being tossed around seem incomparable to real world OHV engines. For example, the 2011 Kawasaki ZX10 displaced 998cc and supposedly made around 210bhp at speed and over 200bhp without ram air effect. This is a road bike, built and intended for high mileage between rebuilds, not a highly stressed racing engine.

I realise you guys are primarily focused on model aircraft engines but I can't see the flatheads getting close to this type of possible performance.

 

[Niels Abildgaard]

Hello Al
To compare flying engines on cubics is not right.
TBO,mass per power unit and specific fuel consumption at 75% max power is better.

 

[Cogsy]

Fair enough. I know nothing about the bike's fuel consumption, nor relative engine weight for it's displacement. I do know the whole bike, frame, wheels, lights, brakes, seat, gearbox, etc, weighed only 198kg which seems light for 200+hp, but the aero engines may well have equal power to weight ratios.
The only reason I asked was because of the discussion of the harley's vs 500cc OHV bikes. I thought it only fair to throw the ZX10 specs into the mix as a more modern example of a normal OHV bike.

 

[Hopper]

HI Cogsy, I think the OP's intent is to build a simple, compact, lightweight engine for model aircraft, which the sidevalve suits admirably. Miniaturizing the technology that gives a Ninja 200hp is not really do-able for the average home-shop builder. Harley flathead technology though was so basic and simple it is not hard to repllicate.

I think the link that Niels posted to the D-Motor aviation flathead and comparison to the Rotax engine is pretty encouraging. The Rotax is putting out only 90-100hp from a 1200cc. And Rotax do know how to build high performance engines if they want (viz BMW, Aprillia, Buell etc etc) but for aircraft engines weight and size and fuel economy are also a big factor, not just straight horsepower. The Flathead D-motor by comparison is putting out 90-100hp from an engine that is 2700cc but the same weight and physical size as the Rotax.

Is an interesting point though -- 210hp per litre is a far cry for the racing bikes' 80hp per litre of 1968. Of course the fastest road bike of that year was the 60hp Triumph Trident/Rocket 3 -- about the same as Harley's flathead racer.. How times have changed. Pity the Harley riders who try to drag race me off the lights when I am on my sportbike don't realise that!

 

[Niels Abildgaard]

Hello Richard

Here is my proposed fourstroke beater with lowest possible parts number count,but no first order balance.I am working on that but need the piston weigth.
Am asuming around one gram per ccm ie 11 gram for yours.

 

[mu38&Bg#]

Niels doesn't your software figure at least volume for the piston?

The D-motor is an interesting result. Because it runs slow, it doesn't have to breathe particularly well, so the flat head design isn't as much of a problem. Surprisingly, it's efficient at 260g/kWh. I wonder what hydrocarbon emissions are like.

Greg

 

[Niels Abildgaard]

Hello Greg
The problem is that I have never constructed a piston for sale,but many others have.That means that a rule of thumb is better here but it interest me what Richard has dared to come down to.
One of the SV advantages is that piston mass can be low as pressures are not that high.
Considering emissions You should rather be concerned what comes out of american engines over Your head.
Lead is criminal and unnessecary.

 

[ownthesky2010]

This is some excellent discussion. I am soaking it all up here and its really showing me the gaps in my knowlege.
Thanks to everyone who has made a contribution.
I have started on an air bleed style carb and got as far as machining most of the main body and made a complete mess of the air bleed holes.
I drilled them 2mm instead of 1mm and now they intersect which makes having 2 of them pointless.
I cant decide if I should scrap it and start again or try to sleeve one of the holes.
Niels
I finally managed to weigh the parts you asked about.
Piston: 10g
Con rod: 6g
Wrist pin, ring and clips together: 2g
The total is 18g
A bit more than I thought but not too bad considering the only 4 stroke engines I have ever seen the inside of were motorcycle engines and none of them were sv engines.
Incidentally the spare conrod that I have without the bearings/bushes installed is 3g.
I think I will do some more weight elimination on the piston. The walls could be thinner. I have already re-designed the crankcase and timing module to lose some weight there.

 

[ownthesky2010]

This is some excellent discussion. I am soaking it all up here and its really showing me the gaps in my knowlege.
Thanks to everyone who has made a contribution.
I have started on an air bleed style carb and got as far as machining most of the main body and made a complete mess of the air bleed holes.
I drilled them 2mm instead of 1mm and now they intersect which makes having 2 of them pointless.
I cant decide if I should scrap it and start again or try to sleeve one of the holes.
Niels
I finally managed to weigh the parts you asked about.
Piston: 10g
Con rod: 6g
Wrist pin, ring and clips together: 2g
The total is 18g
A bit more than I thought but not too bad considering the only 4 stroke engines I have ever seen the inside of were motorcycle engines and none of them were sv engines.
Incidentally the spare conrod that I have without the bearings/bushes installed is 3g.
I think I will do some more weight elimination on the piston. The walls could be thinner. I have already re-designed the crankcase and timing module to lose some weight there.

 

[Hopper]

Hi Niels,
I think one area you will need to look at carefully on your "fourstroke beater" is the exhaust valve. Because of the poor combustion chamber shape, flathead exhaust valves and ports get very hot.
On a four stroke, the exhaust valve gets a rest every second revolution but on a two stroke will get heated every revolution. I think it will need some serious cooling fins or even liquid cooling, ala D-motor, in that area.

 

[Niels Abildgaard]

Hi Hopper

I had not realized that so thank You for warning.It will be eased somewhat as two strokes exhaust is a mix of hot real exhaust and cool fresh charge.
I am wondering how the inlet ports shall be placed around cylinder to minimize this air/fuel loss as much as possible.
The bst cylinder material is probably aluminium with an inserted bronce valve seat ring.
Bang went the low cost goal.

 

[Niels Abildgaard]

.
Niels
I finally managed to weigh the parts you asked about.
Piston: 10g
Con rod: 6g
Wrist pin, ring and clips together: 2g

I think I will do some more weight elimination on the piston. The walls could be thinner. I have already re-designed the crankcase and timing module to lose some weight there.

Hi Richard
Thank You for numbers.Amazing good engineering yourside.
Have been scheming a firstorder mass balancing system using Your numbers and it can be easily done without tungsten or unobtanium.

 

[ownthesky2010]

Hi all
I have this thing about where I want it now. Been through a few carbs and finally settled on a slide carb from an rc car with a modified low speed needle. This engine likes the fuel metered up to around 80% throttle so the lsn had to be re-profiled a few times. The high speed needle only affects the last 20%. I still have a bit of tuning to do but I'm confident that this carb will work and give me a stable 7800rpm on top.
I have also managed to get it running well without glow power constantly attached.
The head is a quick and dirty test part with a bigger combustion chamber and lower compression, hence the lack of cooling fins.
I'm going to stop working on this engine now and start on the twin version.
Then build a carb based on the rc car model with a few of my own tweaks.
Thanks a lot for all the contributions everyone, its great to have a place to go to for advice.

[ame]https://www.youtube.com/watch?v=Z1zmY6bEN8Q&feature=youtu.be[/ame]

 

[Niels Abildgaard]

Hello Richard
Very nice engine sound and your devellopment speed is impressive.
What kind of twin and crankshaft is next?

 

[ownthesky2010]

Thanks Niels.
I'm planning a flat 180 degree twin with shared crankpin.
The cylinder, cams, piston etc from the single will be reused.
I only built the single to test the design.
After the twin I will build a 7 cylinder radial.