"Jumo 222" and "DB 606/610" made in H16 form instead of being 24 cyl types - what gives?

[Peter Gunn]

You may be right. But there was a lot of stuff going on and sometimes studies or comparisons are done for engines of the same power. The 16 cylinder engine/s that Tomo is proposing has 1/3 more power than the V-12 which makes things a little more difficult, Much like most people would not want to use the same weight crankshaft in a 36 liter engine as they would in a 27liter engine assuming both engines were making the same power per liter.
H-S used a rather light crankshaft for a 36 liter engine (about 50KG) but then they were only getting around 900-1000hp out of the engine in it's 1930s forms. Sauer changed to an 80 kg crankshaft when they tried to get 1400-1500hp out of the engine.
Not only were they putting a greater load on the crankshaft with more pressure in the cylinders (more force on the piston per firing impulse) but they were running the crankshaft at a higher speed. Going from 2400rpm to 2600rpm is 8.33% faster but the rotational loads go up with the square of the speed (so do the loads on the connecting rods just from stopping and then going back in the opposite direction hundreds of times per second) so these forces go up 17.3%. Junkers was pulling a miracle getting the 213 over 3000rpm
V-16 also has a crank about 1/3 longer which means more flex and for torsion that extra 1/3 length can mean a lot with the last pair of cylinders trying to twist the crankshaft and then unloading.
Our intrepid engine designer can opt for the H-16 and dodge the V-16 problems and pay for it with the 2nd crankshaft/crankcase and came drives. It might actually not wind up that different as far as weight goes. I don't know. But there is no getting away from the increased frontal area. This aspect had greater and lesser importance over the years.
1919 and the 20s it didn't really matter what shape the engine was (mostly), This 60.3 liter X-16 engine was huge
View attachment 784235
Don't even want to figure out the firing order on that thing
But they hid it well two of these
View attachment 784236
Another Blackburn product so frontal area was not a consideration. Fuselage was over 11ft deep.
In the 1930s size of the engine became a lot more important. During WW II it became a little less so, with 1700-2300hp engines and the fuel to operate them the planes hade gotten larger and with added length and decent streamlining a fairly large engine could be put in a fast plane with good streamlining (Do 335, a 13.8 meter fuselage can hide a lot of "stuff").

An H-16 engine may have been very useful as a bomber engine even if it would have given the 109 boys conniptions.

I realize you have to walk before you can run and the guys between the wars were really striving to get more speed/power/endurance/whatever out of both aircraft and engines but...

How did it come to pass that so many of them seem to have been dreamt up (and acted upon) after one too many at the pub?

"Hey... I know, if we mash three or four banks of cylinders together..."

On the bright side, at least whatever that thing is has a three bladed prop instead of two blades.

 

[Shortround6]

On the bright side, at least whatever that thing is has a three bladed prop instead of two blades.

Without delving into the witchcraft that is prop design................A 1000hp engine in a 115mph airplane with a 2 bladed prop needs a huge propeller. Truly huge.

 

[z42]

I realize you have to walk before you can run and the guys between the wars were really striving to get more speed/power/endurance/whatever out of both aircraft and engines but...

How did it come to pass that so many of them seem to have been dreamt up (and acted upon) after one too many at the pub?

"Hey... I know, if we mash three or four banks of cylinders together..."

In retrospect it's easy to see which approaches are workable and which aren't.

Though arguably even at the time it would have made sense to spend more on improving the basic engines. But the revolutionary potential of jets weren't clear (or well, the potential was known, what wasn't clear was whether it would be possible to build something in practice that would tap into said potential), so it was understandable to have something next gen in the pipeline to prepare for the day when the V-12's and 18 cylinder radials run out of steam.

 

[Reluctant Poster]

Slap a couple .303s in front of the cockpit and bolt on a tail hook and ya' got a great carrier based interceptor. It'll take up almost no space.

An excellent companion to the Curtiss SB2C which also is missing the rear fuselage.

 

[Shortround6]

How did it come to pass that so many of them seem to have been dreamt up (and acted upon) after one too many at the pub?

"Hey... I know, if we mash three or four banks of cylinders together..."

It sometimes made sense at the time. 1920s when fuel didn't support much boost (if any) you had two choices for more power. More displacement or more rpm.
Adding a bank of existing cylinders offered about a 50% increase in power, assuming the crankshaft held up. Beefing up the crankcase and crankshaft seemed easy to do.

Going from a 2000 rpm engine to a 3000 rpm engine (same 50% potential power) may have been harder. ALL of the rotating. reciprocating parts (includes valves, valve springs, rocker arms, etc) increases the stress loads by 125% over existing loads. The existing engine is not quite of verge of breaking down but the just run it faster school could be in big trouble.
If you are trying to plane for a future engine (3-5 years down the road) you may come up with a different answer than trying to come up with an engine for next years race.

And in the 20s they were still trying to figure out sodium cooled valves, better valve seats, more reliable springs. better oil systems and so on. An extra bank of cylinders may have been the low risk option.

 

[peceed]

In his excellent book "Classic Racing Engines" Karl Ludvigsen has chapters on the Porsche 753 1.5 litre Flat-8 and the BRM P75 3 litre H-16.
For the H-16 he writes:
" Severe torsional vibrations affected the output gear train's centre gear and bearings, which received twisting impacts from both crankshafts at alternating intervals and in opposite directions. As a palliative the mass of four of the crank counterweights was increased by 2lb (0.9kg) apiece by bolting and welding a steel inertia ring to each one. "This modification, crude though it was, proved effective' recalled Tony Rudd,' and it was then possible to install the engine in a car."
"A major change allowed the H16 to run as a sequential 16, with one cylinder firing every 45 degrees of output shaft rotation. This required new crankshafts with eight individual throws to give a firing order that allowed tuned scavenging exhaust pipes to be used."

The truth is that H16 engine can always be perfectly balanced without using any counterweights. The key requirements is a full synchronization of shafts that acts as their own counterweights, offsetted by 180 degrees. It cancels both primary and secondary imbalances.
For example Napier Sabre has exactly the same amount of firing intervals as V12 engine.
So perfectly balanced balanced H16 would fire every 90 degrees. 45 degrees is not viable.
Having this in mind, one can use customized layout of crankshaft, that won't work for V8 or Flat-8 engines, that cancels all forces locally in groups of 8.


It is not true that the H16 engine will limit visibility, quite the opposite. The pilot always sits high enough to have a view over the engine, and the shorter engine body can improve the forward viewing angles. The H engine can move accessories to its lower part, guaranteeing a very small upper width. The only disadvantage is that in the case of a fighter, the higher position of the cabin will slightly increase the overall drag compared to the inverted V12. But the frontal area increases no more than the power, which may ultimately bring benefits. In the case of bombers, the benefits are immediate, but I still think it is better and much easier to make the H24 engine right away.

 

[peceed]

Mercury to Pegasus is a 25mm change in stroke. For some reason (rounded off numbers?) this was only worth 47mm in listed diameter

There was around 3 inches of difference between diameters of Jupiter (138.4 cm) and Mercury (130.7 cm). Later their heads became bigger and Pegasus (Jupiter with superchae grew to 140 cm, and Mercury to around 131.5 So everything is quite consistent and minimized.