Bristol Hercules sleeve valve radial engine plans drawings

[Laurentic]

Mike - reference your post (Reply No.38) I have pm'd you rather than detract further from your thread here.

Chris

[Art K]

Mike,
I didn't realize Aquila was SC'd. Here is the website for Strictly IC  http://www.strictlyic.com/index.htmlclick on special engine articles and the last one is the Barr & Stroud issues 83 & 84.
Art

[Vixen]

Thanks Art

You and everyone else on the MEM forum are so helpful, it's truly amazing. 

Cheers

Mike

[AVTUR]

If anyone wants to know more about full size sleeve valve engines the Newcomen Society has published a book "The Piston Engine Revolution" that includes a chapter on Bristol's work on the sleeve valve. This was written by a late member of the Bristol RRHT. There is also about a quarter of a chapter on Napier's work with the valve. Don't expect much technical information. The book is free to members, otherwise it is £36. Their website is www.newcomen.com

While all the work was done by Bristol it was paid for by the Air Ministry and they owned the technology. They could give details to other companies.

I attach a little picture (simple, is it not).

AVTUR

[john mills]

Mike
in the edition i have i can not see much reference to specific port timing  the drawings in reply 34 are on page 341 in my book the same.
  john

[Vixen]

 

Thanks for looking, John

Mike

[john mills]

Mike
i find were he says he does not intend to deal at any length with the geometry of the sleeve valve and its porting arrangements as it will be obvious to any one who cares to set it out on drawing board .
John

[Vixen]

Mike
i find were he says he does not intend to deal at any length with the geometry of the sleeve valve and its porting arrangements as it will be obvious to any one who cares to set it out on drawing board .
John

Ha ha, that's a good one John. 

And no doubt most obvious if you happen to be Sir Harry Ricardo KBE, Fellow of the Royal Society, President of the Institution of Mechanical Engineers, consultant to the Royal Aircraft Establishment (ARE) and disposed to be rather arrogant.    Others may struggle an bit.

Time to get out that roll of Mylar tracing film

Cheers

Mike

[cnr6400]

I don't plan on gettin' my old mechanical pencil and erasing shield out any time soon Mike and John! it might have been a minute's job for Sir Harry before his morning coffee, but somehow I doubt it would go so easy on my paper and drafting board!   

(especially since I stopped manual drafting professionally in about 1987 per my employers' instruction and have used various flavours of CAD for various employers at the day job since...)

[Laurentic]

I would presume that Sir Harry's "rather arrogant" manner may have came from having to deal with the politicians and the Air Ministry in the run up to and including into WW2, from what I have read of those times, but even so, I would have to sit and ponder for some quite considerable time sat before my drawing board before it became anything like obvious how to set it out!!

Chris

[Admiral_dk]

I can only see two ways to check the values without committing to material - either paper, film etc., or CAD.
There are one reference on the drawings from Lohring about the port height influence on the timing and I'm guessing that the other ones (overlap), has to do with how wide / narrow the ports are.

I think that I would start with the later, as the drawing has quite a long overlap for a slow runner with normal aspiration 

Best wishes

Per

[Vixen]

Per has it spot on. It's quite straight forward to visualize the motion of the sleeve with respect to the cylinder, either by using CAD or with two strips of mylar film moved in a circular motion. One strip would show the sleeve ports, the other the exhaust ports. This will show you the positions where the ports open and close.

For a model sleeve valve engine to run nicely, it is important to choose the optimum timing for these opening and closing events. If we consider a racing engine (sleeve valve or poppet valve) both the inlet and exhaust ports (valves) open as early as possible and close as late as possible, overlapping in between. This produces a high revving engine, with a narrow power band and often incapable of running at tick over speeds. For a round town runabout, a wider powerband is needed, giving good engine response from tick over to full speed. For this the port (valve) opening and closing times will be much reduced with very little overlap. A supercharged aircraft engine is closer to the racing engine than the town engine. They run continuously at altitude, at a constant cruising speed with slightly higher power and speed during take off and climb. The port (valve) events are optimized for these running conditions. Also a longer overlap, where both ports(valves) are open, allows the supercharger to scavenge more of the exhaust gasses from the cylinder and improve fuel efficiency.

For the model sleeve valve engine, the scaled down supercharger will not actually produce any boost; unless you run it at jet engine speeds. The model engine effectively becomes a normally aspirated engine, and the valve events need to change to reflect this. The 'hot' port (valve) timing of a racing engine would be undesirable. Likewise the port (valve) timing associated with a supercharged engine, operating at altitude would not be ideal either. For a well mannered and reliable normally aspirated model engine, running on the bench, a 'milder' port timing; with shorter opening times and lower overlap are called for. Just as Per recommends above. You can now see the reason for my interest in the Barr and Stroud engine port event timing.

Once the 'Ideal' port timing is decided upon, it becomes relatively straight forward to use the CAD or your mylar strip drawings to define the revised port shape, where the ports open and close to meet the new 'Milder' operating conditions. The sleeve ports will tend to be smaller in all directions than those of the full size supercharged engine being copied.

Mike

[AVTUR]

I had hoped my last posting would  be it as far as sleeve valves for the moment. But...

Mike

I have just had a look at the National Archives catalogue for "sleeve" between 1920 and 1950. There are 204 papers of which about 20 concern IC engines (both 2 stroke and 4 stroke). They include papers from Fedden and Ricardo. None of them has been digitized.

I suspect Fedden, or more likely his designers, used a lot of cardboard and wood before any serious drawing was done.

I am a bit lost on increasing the overlap for a supercharged engine. I would have thought one reduced it since the boost is helping the scavenge. I know a few supercharged racing engines had large overlaps but that was for cooling with methanol. I know I could be very wrong here.

AVTUR

[Vixen]

Hello AVTUR

It's difficult to encompass all the port timing possibilities in one short paragraph. However, I still believe that a more conservative, 'milder' port event timing (i.e smaller ports) will lead to a better running model engine.

Mike

[RReid]

As an engineer (retired) with an interest in engines but no real education or experience in detailed IC engine dynamics and design, I'm really enjoying this discussion, though I have nothing to contribute.