Liquid cooled aero engine with <12 cylinders?

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Something sounds a little off.

Half an Allison would be 855 cu in (OK make it a bit smaller) which was rather large for a "family" plane even in the late 20s.

Popular engine in the late 20s in the US was the Wright Whirlwind 7, (there was also a 5 cylinder version) of about 225hp from 760 cu in, Used by Lindbergh and was also the early engine on the Lockheed Vega.

Another part of the story that changes is the army interest. The Army was interested, very interested, but had no money, the Navy had money so the Army suggested Allison try to get navy funds to keep the project alive. Army hoping to get more funding in later years and get involved then.
 
Very interesting, thanks for sharing. I wonder if this six cylinder engine was air or liquid cooled?
 
Admiral Beez said:
Very interesting, thanks for sharing. I wonder if this six cylinder engine was air or liquid cooled?
Click to expand...
I don't know, but the reason I posted it was to show the effect of the great depression, from talk of having aeroplanes almost as popular as cars were, they quickly went to the only "market" being for an airship engine, how close did the USA actually come to not having the Allison and therefore P38, 39 and 40? The Scneider Trophy was won by a watercooled in line six cylinder in 1921, after that all were V12s from many countries and makers.
 
Siemens-Halske made an 11 cylinder rotary during WW1. A 11 cylinder radial was thus possible. The small cylinders probably aided head cooling around the valves as well as smoothness and combustion stability.



A 12 cylinder single row radial was surely possible as it was balanced due to being simply two 6 cylinder radials staggered 30 degrees but I suspect two rows of 6 cylinder radials was more attractive. Siemens and halske evenually became Siemens Schukert, then BRAMO then folded into BMW.
 
Allison had been involved with several engine "projects" during the 1920s including fitting their bearings to Liberty engines which dramatically increased overhaul life.
They overhauled and modernized between 2,000 and 3,000 Liberty engines
They also did an air cooled conversion. Fitting air cooled cylinders instead of the water cooled ones. This required a smaller bore and dropped the Displacement from 1650 cu in to 1410 cu in. At least 8 upright and 4 inverted engines were built.

Allison was also involved with a flat twin (hoped for expansion to 10 or 12 cylinder versions) and a "small" radial for "flivver" planes. The "Flivver" planes were a government project with a targeted price of $700 in the late 20s or very earlier 30s. The Above pictured Arrow with converted Ford V-8 was one result (at a price of $1500). more details on the small radial are lacking.
 
If we're going to less than 12 cylinders liquid-cooled engine - that would probably be a V8 engine - then better choose cylinders as big cylinders as possible. Something along 2/3rds of DB 603, Jumo 213, AM-38 or Griffon, that will give around 1100-1200 HP for the starters. Employing all the tricks (at least 130 grade fuel + ADI + better S/C with intercooler) will make those doing ~1400-1500 HP. Same tech produces 1800-2200 HP on a Merlin, V-1710 or DB 605 of the day?
The V10 will give more than V8, some 25% more, but mature V10s are wide and not well (or at all) understood in 1940s.
 
A V-12 gets a power stroke every 60 degrees of crankshaft rotation IF it has a 60 degree angle between banks.
A V-8 gets a power stroke every 90 degrees of crankshaft rotation with a 90 degree Bank angle.

If you try to use a V-8 with a 60 degree bank angle either to keep the engine narrow or use existing tooling you get an uneven firing order. Some impluses will be 60 degrees apart and others 120 degrees apart. This makes for a rough running engine with extra vibration.
Bolting such engines into 25-30 ton tanks was no problem, especially considering that with no supercharger the firing impulses were less strong and the engines were limited to about 400 less rpm.

A large V-8 may be shorter and lighter than an equivalent V-12. But it will be wider, a bit taller, and probably vibrate more. With the larger cylinders the large V-8 will turn less rpm than an equivalent displacement V-12.
 
The three markets for aero engines, air transport, general aviation, and military aviation, had somewhat disparate requirements, which drove most land-based air forces to liquid-cooled V-12s but drove air transport and general aviation away from liquid-cooling, as both general aviation and air transport were more sensitive to first cost, operating cost, and dispatch reliability than military aviation and less sensitive to power density and maximum output.
 
All radial engines have an odd number of cylinders Radial engine - Wikipedia
 
The Hispano Suiza V8 was the most successful engine of this type in WW1. It was fairly powerful and relatively light. As higher power levels were required, people started building V12s. Note that one advantage of a V12 is that one can easily get even firing intervals with a 60 degree angle between the cylinder banks - this offers a good compromise between providing space for manifolds and engine accessories between the cylinder banks and frontal area.
 
Radial engines based on 4 stroke concepts practically always have an odd number of cylinders in each bank. The very few exceptions were either unsuccessful or multi-bank inline engines, such as the Jumo 222 (albeit not really an example of a successful engine).
 

6 cylinders, 12 pistons, 2 crankshafts.
The 207 turbo version form the Smithsonian website linked to.

Power rating: 746 kW (1,000 hp) at 3,000 rpm Displacement: 16.6 L (1,526 cu in.) Bore and Stroke: 105 mm (4.1 in.) x 2 x 160 mm (6.3 in.) Weight: 648.6 kg (1,430 lb)

Bolding by me, weight is dry weight, does not include coolant, oil, radiators and oil coolers and accessories.
It worked in some special applications but was not anywhere near a first rank engine for general use.
Yes it did exist and got good fuel mileage
 
From wiki

Anybody who thinks "balance" is easy has only to look at a parallel twin (two cylinders in a row) designer can have both pistons going up and down together with the cylinders firing alternately (360 degrees apart) with whacking big counter balances on the crankshaft.....or........have one piston going up while the other is coming down. Doesn't need as much counter weight but now the cylinders go........#1 fires then 180 degrees of crankshaft rotation then #2 fires then 450 degrees of rotation then repeat. You also get a rocking couple where instead of the whole engine jumping up and down you get it jumping up down less but rocking from side to side (or inline with the crankshaft).
 
I have owned both of exactly the same displacement, Triumph 750 (360 crank) and Kawasaki 750 (180). The Triumph was much more "rideable" especially in the wet, the Kawasaki vibrated less but the vibrations were far more annoying despite it having balance shafts to reduce it. I went as a pillion on both a Ducati 860 and a Moto Guzzi 850, despite all the noise they make they hardly vibrate at all.
 
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