rare bear engine problems?

[Howard]

V-12 gear reduction.

Can you compare the RPM's on a radial with the V-12's?? The are so mechanically different.
Yes, I should have known that was a separate reduction to drive the prop. Have seen V-12's where that reduction was "hollow" so that a gun could fire thru it and thru the centerline of the prop. The gun was placed approximately between the V of the cylinders. On the P/F-39 where the engine was behind the pilot; driveshaft between his legs to a "hollow" gear reduction in the nose that drove the prop, allowing gun to fire thru center of gear reducer. One of the lo local "restoration" organizations here has several of the bare frames with the engine/driveshaft/gear reduction in place. Howard..

[Unregistered]

Re: V-12 gear reduction.

Originally posted by Howard
Can you compare the RPM's on a radial with the V-12's?? The are so mechanically different.
Howard..

Of course you can, much as you can compare the RPM of a NASCAR v8 to a Formula 1 V12 :-)

There are many factors that affect how any given engine develops power as a function of crankshaft RPM, but cylinder arrangement really doesn't factor into it all that much. There is a subtle connection in the fact that radials have a master rod with articulated rods which puts a lot of bob-weight on the crank throw, but I would argue that this is a lesser factor than the simple difference in the size of the individual cylinders given that both radials and aircraft V12s run at very low RPM compared to other types of non-aero engines (8000+ for NASCAR v8s, 14,000+ for F1 or CART V12s, for example).

The V12's run higher RPM simply because they have less reciprocating mass per cylinder (lighter weight pistons and connecting rods) and have shorter strokes (less piston acceleration at a given RPM) than most radials. Conversely, that means that they HAVE to run a bit faster to develop similar horsepower ratings, since the combustion forces are acting ona smaller piston surface area and over a shorter piston stroke. Radials tend to have have BIG bores, BIG strokes, and rely on moderate cylinder pressures at low RPM, whereas Merlins rev higher and operate at higher cylinder pressures. On the other hand, the Merlin looks a bit tractor-like if you were to compare it to, say, the Napier Sabre which had 24 small cylinders instead of 12 medium-sized cylindersl, so really there is a continuum of design options.

Where the rubber meets the road (bad analogy, should be 'where the torque hits the air' :-) is the fact that regardless of the engine's optimum RPM, its output must be geared so that it can turn the propellor at an optimum RPM for its design. Given that you can build strong enough gearing(*), it doesn't matter all that much whether the engine design needs the crankshaft to spin at 2800 RPM, 3600 RPM, or 7000 RPM to achieve full power.

(*)- the caveat is that its typically somewhat easier to make reduction gearing reliable if it doesn't have too wide a ratio, giving a bit of advantage to an engine design that needs on the order of 1.5:1 reuction instead of 3:1, but again this can be overcome with engineering.

FWIW...

Steve L.

[Unregistered]

connie in question

I believe the Connie in question that used the slow nose cases according to a Lockheed engineer that I spoke with was called the Starliner. If I recall correctly, it had a number 1049 or 1149. He said they didn't make very many of them as they were the last ones built to compete with jets quiet by slowing the props for noise reduction and efficiency.
george lakes iii

[Unregistered]

Re: connie in question

Originally posted by Unregistered
I believe the Connie in question that used the slow nose cases according to a Lockheed engineer that I spoke with was called the Starliner. If I recall correctly, it had a number 1049 or 1149. He said they didn't make very many of them as they were the last ones built to compete with jets quiet by slowing the props for noise reduction and efficiency.
george lakes iii

L-1649. This web site says only 44 were built, and that jibes with my memory from reading about them years ago: http://www.starliner.net/specs.html

As for efficiency, an old bit of trivia is that the Constellations, Douglas DC-7s, and Boeing Stratoliners were ALL far more fuel-efficient than jets of the day. But when kerosene cost pennies per gallon and a jet could many many times longer without an overhaul while flying 150-200 mph faster, the jets won anyway. Jets later became more fuel efficient, but some vague spark of a memory is telling me that no passenger airliner has yet ever actually beaten the DC-7C for absolute lowest amount of fuel used per passenger mile. Don't hold me to that, though, some of the more modern jets may have finally beaten it.

[Unregistered]

(8000+ for NASCAR v8s, 14,000+ for F1 or CART V12s, for example).

Don't mean to nitpick here but most F-1 engines are V-10 nowadays and CART use V-8's. Ferrari has been boasting 17,000+ rpms for a while now. At the US GP last week some of the guys were turning close to 20,000 rpm (Yikes) at the end of the long straight. Technology is a wonderful thing.

GP

[Race5]

To me the crazy thing about F1 motors is the idle speed. They mentioned it at one race this season as being near 9k, as that is how fast it must spin to keep the hydraulic pumps working. The throttle, brakes,clutch, and parts of the traction control are all hydraulic on those thinge.