Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Indeed, you're right. It would've been cool if someone has the good data covering the rigidity of the boxer engine crankcase whole engine.
Almost all modern (after the 60's) light aircraft engines are flat fours and sixes. But they are large engines compared to car engines. over 8 litres for 300hp. They are separate cylinder air cooled engines over 90% of the time. and for the most part, the bigger ones are being fitted to aircraft that have side by side seating, width isn't that big a concern. A 100hp Lycoming four has an overall width wider than a Merlin.
Just because an engine works as a Six doesn't mean it will work as a twelve without a little beefing up. with a crankshaft twice as long the twelve with suffer more from torsional vibration, which is not a vibration that a pilot or driver would really feel.
It is perfectly possible to design a flat twelve with enough strength to handle the load the designer wants. It is just that because of the shape of the engine it will be heavier than an equivalent V shape engine. The designer may go for the flat engine anyway because of other considerations that trump the weight difference.
The propellor shaft was positioned so it was in the centre of area of the engine when looking from the front. When it wa sinstalled in the airframe it gave less frontal area than otherwise, and thus less drag.
Already posted in this thread (the rounded red rectangle shows approximate layout of engine block, in boxer configuration); the variant with coaxial drive would've neatly served in Mosie
Getting back to the original idea the "ideal" liquid cooled engine is going to be a V-12 (either upright or inverted) or an H-24 (more than likely horizontal) of between 35 and 45 litres displacement. 4 valves per cylinder if poppet valves or sleeve valves. If it is to be used for a variety of roles then it should have the ability to use several supercharger designs or configurations.
Now we get into 'trade-offs':
What is the configuration more likely to cost less per engine,
What is the configuration that will be easiest to service.
What will be the TBO hoped for.
Is there a maximum or minimum desired weight.
Please give me a reality check:
The Vee would probably cost less due to simplicity. A 12 is going to cheaper than a 24
The Vee would probably be easiest to service because of easier access to all parts. A 12 is going to be easier to service than a 24
A poppet valve engine would be easier to service for minor repair but a sleeve valve engine for major repair. This one is debatable, the sleeve valve should make it to major overhaul without any work on the valve train excluding battle damage)
The time between overhaul would be greater for the poppet valve engine. Sleeve valve engines (the radials) wound up with much longer TBOs but that was post war
I am not sure which configuration would be lighter for the same displacement or power, I assume the Vee. the Griffon and the Sabre were about 1 cu in difference in displacement so make a good comparison. With single stage two speed superchargers the Sabre was more powerful, depending on version much more powerful, it could also be 600lbs (31%) heavier.
You know I am never going to get around to finishing the reading of those engine books I bought if you guys keep this up.
I am still not seeing what this gets you. Unless you can come up with a bunch of very tiny pilots
If you move the propeller down more in line with engine you wind up hitting the ground or using a lot of small blades.
Or having some really strange landing gear.
If you leave the prop where it is you don't gain much in making the frontal area smaller.
Yes you do get room for a cannon but that is a lot of hoop jumping to go through.
A few dimensions for your consideration.
Width of the Merlin ........30in.
Width of the Sabre ........40in.
Width of O-1230............44in.
height of Arsenal 24H..... 59in.
height of Hispano 24Z.....54.5in
Width of Potez 12D.........37.2in
Height of Potez 12D........32.7in
The Lycoming engine was one of the US hyper engines and was good for about 1200hp at 3400rpm from it's 20.2 litres, later doubles into a 24cylinder H engine. used a 120mm stoke.
The Arsenal 24 used Jumo 213 cylinder blocks in an H arrangement and if lair flat a few inches could be trimmed from the height but 165mm stokes don't go with flat engines very well.
Same for the Hispano, a 24 cylinder H engine using Hispano Z cylinder blocks. 170mm stoke, again a few inches could be saved if laid flat.
Potez is air cooled but uses a spur gear to offset the propshaft to the top. It is also a 17.6 liter engine with a 120mm stoke. It used push rods and had the supercharger horizontal underneath the crankcase.
The Sabre used a a 121m stoke and half a one is going to give an 18.4 litre engine with about 1000hp for most of the war.
BTW, the Mossie still has to fit the landing gear behind the engine
Lighthunmust, it would be highly likely that sleeve valves provide much longer TBO as far as valve gear is considered. Harry Ricardo found out in his tests that in high time engines the cylinders of a sleeve valve engine had much less wear. Plus as in the sleeve mechanism there no compnent that is subject to pure reciprocating movement the stress would be lower there as well. E.g. the standard Merlin valve gear is no good for long TBO.
As for servicing, I would say the same.
Please read, I don't think I can type several hundred pages