enginehistory.org

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

Hmmmm.
I suppose that means mountain men, being at higher altitudes, have a
different measurement ??
(best I shut up now, or this will be moved to separate thread!)

gryan · Guest

I don't know what measurement the mountain-men use! I hope altitude does not affect the calculation at all.

In the race engine organisation I consulted for the mean piston velocity (MPV) was the favoured number. RPM was ignored unless you were the gearbox designer. Whenever designing up piston engines for boats and cars for competition (or everyday use) mean piston velocity (MPV) was the guide to how long the engine would last. Higher MPV usually means more power but shorter engine life (less TBO). This is a reasonable guide.

The relationship between piston velocity and rpm is dependent on the stroke length. For a constant rpm the piston velocity goes up with increasing stroke length. And if the piston speed gets high enough, down comes engine life (reliability). If you sacrifice stroke length you can run high rpm reliably and for a long time. That usually liberates more power.

Most engines run into reliability problems at similar piston velocities but the rpm when this occurs may be very different. For example I would be happy to run a road race engine with 54mm stroke at 16,000 rpm or more (it would be very reliable for several races) but an engine with 106mm stroke would not be safe even for a few seconds at that rpm (its MPV would be very high). Comparing the values of MPV in the two cases it is clear the 104mm stroke engine is far more highly stressed than the 56mm unit.

Turing to the Nagel Engine. The engine has short stroke, modest bore and lots of cylinders. It makes power at slightly elevated rpm (by aviation standards, but by automotove or marine standards it is a low rpm device). If you calculate the MPV it is nothing special so the engine should, in theory, be reliable enough.

It has a 2.5:1 reduction box which is OK. Most WW2 piston engines had redction boxes anyway so there's no inherent trouble with that surely?

I think they could usefully run the Nagel much faster without too much trouble.

Conclusion:
MPV is the indicative number and not RPM.

Why not build a super high rpm engine and gear it back? Should be lighter than a bigger unit of the same power (more efficient use of mass).

This leads to an idea for another topic.... the ultimate engine. I'll post on that shortly.

jjuutinen · Joined: 13 Jul 2003 Posts: 180

First, I´d rather have an engine with rpm ranging from 500 to 3000 than one with a range from 1000 to 6000.

I have calculated piston speeds for lots of engines. For example, in terms of MPV the Sabre isn´t anything particularly spectacular. Now, please do not check sources: which mass produced (thousands) WW Two aircraft piston engine had the highest MPV?

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

I'll take a guess at one of the later Merlin marks.

jjuutinen · Joined: 13 Jul 2003 Posts: 180

No. More guesses?

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

OK, time for some psychological guesses.
In this thread (and others), you seem to like sleeve valve engines.
So, given that I can't recall anything that says the Bristol sleeve-valves were slow-revving and they did have a long stroke...
Hercules ?

jjuutinen · Joined: 13 Jul 2003 Posts: 180

Let´s say you are getting closer but not close enough. It is not Hercules nor Centaurus. But, the Cent did have high MPV, later marks with their rpm of 2800 return MPV of 16.6 m/s (Merlin less than 16 m/s). The engine I mean
-is a European one
-has an MPV of 17.9 m/s
-is a V-engine
-has wet cylinder liners
-has spark plus located near the ideal position (central)

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

OK, I'll admit I looked around a little. DB 603 ?
(not sure if it had wet liners, though, but I do see MPV of ~18m/s quoted).

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

Re your ideal engine,
I'm interested in what you mean by wet liners in a sleeve valve engine.
Unless the sleeve is running in a ferrous block, wouldn't all sleeve engines have the sleeve running in a liner, and due to the complexity of inlet & exhaust ports necessitate a wet liner ?

(certainly the guy who made the model Eagle engine seemed to think so,
-hard to argue with someone who's built one from scratch).

jjuutinen · Joined: 13 Jul 2003 Posts: 180

Nope, not DB 603. It has dry liners BTW:)

Re wet liners in sleeve valve engines. This is my scew up. As the sleeve itself is a sort of liner, having separate liners is overcomplicating things. I.e. the block itself would have the water passages. Regarding the Eagle model, while the article doesn´t clearly state it, the original did not have separate liners but the model does keep things "simpler".

One thing of interest: the TM article on RR testing mentions that "...the Eagle...had, typical of sleeve valve engines, very good detonation resistance."

In view of this it would be interesting to know how much boost can the Centaurus take? I remember reading a pilot comment in a British aviation magazine in an article on the Airspeed Amabassador that you could simply pull back the rpm level at full boost without the engine getting cranky in the process. Perhaps a good pointer is that the Centaurus 373 achieved 3000 hp + with 100/130 fuel which is much more than the similar sized R-3350 achieved on the same fuel.

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

Alright, if a Jumo 213A doesn't have wet liners, then IDK!

jjuutinen · Joined: 13 Jul 2003 Posts: 180

WE HAVE THE WINNER! It is indeed the Jumo 213. It couples quite a long stroke of 165 mm (bore is 150 mm) with highish rpm. The 213 is also an interesting engine in having variable inlet guide vanes.