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

z42 said:

but generally improved performance and a two-stage supercharger doesn't seem completely unfeasible.

Click to expand...

Two stage superchargers need (demand?) intercoolers.

We have two conflicting problems. The more boost you use, the hotter the intake charge is and the more likely the intake charge is to detonate in the cylinders.
The higher octane fuel you have the more boost you can use before detonation.
Germans used lower boost limits and so needed lower octane, then they jacked up the cylinder compression which needed more octane (knock resistance).

If you want 1.42 Ata at 25,000ft you have to compress the air at 3.8 times the air pressure. If you want to higher or use more boost you need to compress the air more and the intake aid is going to be even hotter.
At 20,000ft if you want 1.42 you only have to compress the air 3.09 times.

The two stage supercharger is feasible, but you need everything that goes with it. The size intercooler you need depends on what you are trying to do. It is on a curve and you get get modest results using an equal amount of air to the intake charge, You can get about 50% more cooling by doubling the amount of cooling air but things go down hill fast. You need over 3 times the amount of cooling air to get just under twice the cooling of the modest result. You have low performance fuel and you are trying to use more than modest boost you need a big intercooler.
Good superchargers are around 70% efficient. There is a certain amount of heat just from compression even if everything was perfect. In the 70% supercharger 30% of the power going to the supercharger does nothing to compress the intake charge/air and winds up as extra heat in the air of the intake charge.

Shortround6 said:

Two stage superchargers need (demand?) intercoolers.

Click to expand...

Yes and no?
A lot depends on the fuel available (LW is better using the C3 fuel on 2-stage engines than on the BMW 801s?; however, the B4 fuel was found workable on the German engines with 2-stage S/C), compression ratio, as well as on the availability of the water-alcohol injection system.
Thing might be that even a not-ideal 2-stage S/C (as in case of Jumo 213F, DB 603LA, 605L, as well as with Allison 2-stagers) is still better than the best 1-stage supercharger setups.
There is also a thing of German engines being much bigger than the usual suspect (= the 2-stage Merlin), so even a non-ideal 2-stage S/C will still see a very usable power at high altitudes.

Shortround6 said:

Two stage superchargers need (demand?) intercoolers.

Click to expand...

Maybe you do, maybe not. From TSHPR, page 390, about the two-stage supercharger developed for the DB 603L:

Kollmann and his supercharger calculation engineer Rothe had expected to have to install a charge-cooler but, after testing the DB 603 L supercharger, found that the efficiency of 73% was higher than expected, and that therefore the added weight and drag of the cooler and its external radiator didn't offset the power gained by enough of a margin.

Click to expand...

I'm not aware of whether there were similar considerations for the 603N supercharger, or whether it was indeed using a substantially different supercharger? Presumably some changes were needed, as the engine produced significantly more power than the 603L..

z42 said:

Why should prototypes not count?

Click to expand...

So teh Rolls-Royce Merlin RM.17SM producing 2,600hp+ counts?

wuzak said:

So teh Rolls-Royce Merlin RM.17SM producing 2,600hp+ counts?

Click to expand...

If you can make a cogent argument for modest and plausible alterations to history leading to this ending up as a service engine during WWII, sure why not?

wuzak said:

Maybe the stroke wasn't the limiting factor for the engine diameter, but the space required between cylinder barrels at their base.

Click to expand...

For Allison's proposal (and Arsenal's version) of H24, they put the propeller shaft right in the center, so the distance from crankshaft to crankshaft was determined by the diameter of the reduction gears e.g. If reduction gears were 10" center to center on the V-12, the centerlines of the crankshafts of the H-24 were 20" apart. This allows using common intake manifolds, common heads, common cylinder block (Crankcase is unique and rather substantial). Which as I understood tomo pauk 's original premise was desired for this what if - he's wanting to just fancy up the manufacturing machines to handle either I-4 or I-6 components based on what is being built that shift. A bit of PIA for the manufacturing engineer - you need to make the machine so it doesn't a. damage itself when the wrong component is selected, b. damage the component. A challenge but not that complex.

The Napier Sabre uses 4 double reduction shafts; this allows the crankshafts to be very close (with appropriate timing, they wouldn't even need to be stroke distance apart.) This allows a combined cylinder block and head - which saves weight and the combined head stiffens thing up...which might allow further weight reduction, but there are issues with cooling if both banks exhaust are using same ports, routing coolant around cylinder barrels and manufacturing is going to need unique machines for the unique parts.

wuzak said:

So teh Rolls-Royce Merlin RM.17SM producing 2,600hp+ counts?

Click to expand...

I was going to use the Allison V-1710-127 of 2,980hp as what prototypes are capable of. But again Germans didn't have materials (cobalt, nickel) to build the VDT. Like the "Speed Spitfire's" Merlin/early DB603, companies could mix up brews that would provide much better power for prototypes, but those concoctions weren't something that could be used in service engines.

Shortround6 said:

Two stage superchargers need (demand?) intercoolers.

We have two conflicting problems. The more boost you use, the hotter the intake charge is and the more likely the intake charge is to detonate in the cylinders.
The higher octane fuel you have the more boost you can use before detonation.

If you want 1.42 Ata at 25,000ft you have to compress the air at 3.8 times the air pressure. If you want to higher or use more boost you need to compress the air more and the intake aid is going to be even hotter.
At 20,000ft if you want 1.42 you only have to compress the air 3.09 times.

Click to expand...

I'm going to reference Callum's book too:

A two stage supercharger needs efficient compressors for each stage, otherwise it really isn't buying you much.
The other part of the equation - the huge cylinders (>160mm bore/180mm stroke) are more susceptible to detonation.

There is also the problem of needing to crawl before walking/walking before running. tomo pauk needs a V-12 running so all the work of selecting everything from supercharger to crankshafts (bearing sizes, finishes, etc) to heads to reduction gears production ready, before committing to the H-16 or he risks throwing everything away. What Junker's didn't know about pressurized cooling through '40, they didn't know. In a time warp scenario, yes, we could provide them with that; but this was just try an H-16 instead of coupled V-12s.

Having an OK working engine today is better then terrific engine after the war is over.

wuzak said:

Maybe the stroke wasn't the limiting factor for the engine diameter, but the space required between cylinder barrels at their base.

Click to expand...

don4331 said:

For Allison's proposal (and Arsenal's version) of H24, they put the propeller shaft right in the center, so the distance from crankshaft to crankshaft was determined by the diameter of the reduction gears e.g. If reduction gears were 10" center to center on the V-12, the centerlines of the crankshafts of the H-24 were 20" apart.

Click to expand...

I was talking about a radial engine.

In the history of aircraft engines, flat 8's are relatively rare. They are found in General Aviation, Lycoming, Continentals and Jabiru, but they are rare. The vibration characteristics are not the same as those of a 12 cylinder. Developing an H16 requires a crankshaft of 8 single rod journals, is more flexible and is a bit more complicated per cylinder than a V12 or 180 degree V12. Five main bearings or nine? The frontal area of the H16 is going to be very close to the frontal area of the H24. Gearing the two crankshafts together is the same difficulty or greater for the H16 due to the greater torque fluctuations. Given all these costs, a one third power increase for a more than one third weight increase seems to be a unappealing pitch to the funding sources.

sotaro said:

In the history of aircraft engines, flat 8's are relatively rare. They are found in General Aviation, Lycoming, Continentals and Jabiru, but they are rare. The vibration characteristics are not the same as those of a 12 cylinder. Developing an H16 requires a crankshaft of 8 single rod journals, is more flexible and is a bit more complicated per cylinder than a V12 or 180 degree V12. Five main bearings or nine? The frontal area of the H16 is going to be very close to the frontal area of the H24. Gearing the two crankshafts together is the same difficulty or greater for the H16 due to the greater torque fluctuations. Given all these costs, a one third power increase for a more than one third weight increase seems to be a unappealing pitch to the funding sources.

Click to expand...

A H16 would have the same frontal area as a H24 if they are based on the same design.

An H16 will have two crankshafts, each with 4 rod journals. They will use fork and blade type rods.

Only if they went for a boxer type engine would they need 8 throws per crankshaft.

sotaro said:

Developing an H16 requires a crankshaft of 8 single rod journals, is more flexible and is a bit more complicated per cylinder than a V12 or 180 degree V12. Five main bearings or nine? The frontal area of the H16 is going to be very close to the frontal area of the H24. Gearing the two crankshafts together is the same difficulty or greater for the H16 due to the greater torque fluctuations.

Click to expand...

Covered by wuzak.

sotaro said:

Given all these costs, a one third power increase for a more than one third weight increase seems to be a unappealing pitch to the funding sources.

Click to expand...

The BMW 801 have had an even worse power-to-weight ratio vs. the Jumo 211s and the DB 601/605s (as well as the reliability issues), the RLM still kept buying it because they were interested in total power of the engine. The 801 made the Fw 190 and Do 217 possible as we know them.

The H16 will be providing no worse power-to-weight ratio than the BMW 801 or the coupled engines, and, unlike the 801, it will still be making a good power on 87 oct fuel. It will also represent a less risky thing than the Jumo 222, whose failure meant, among other things, that Ju 88 family remained the mainstay of the LW bomber force, despite the limitations, like the low speed when bombed up since the bombs of the preferred size will not fit on the restricted bomb bay, as well as due to the low power of the Jumo 211s.

Shortround6 said:

Well, they had to fit it on the existing airframe. Even with 5 blades it was not big enough to handle the power of the 24 cylinder engine.

Just tying to give a context of the size. It is roughly the size (diameter) of an R-2800/R-3350/Centaurus but a little skinner.
The 211 H-16 is 46.7 liters (2847cu in) so it is not a surprise. Frontal area of the R-2800 is 15.2 sq ft, frontal area of the Arsenal H 24 is 14.1 sq ft.

Click to expand...

Because the shape of a H engine is basically square, its frontal area needs to be encased in an oval, or circular cowling to get any kind of decent streamlining! So, it's true frontal area needs to be calculated off of the longest dimension, typically between the top left and bottom right cylinder heads. Just look at the huge probiscis of a nose on the Typhoon! It puts a Corsair, P-47J or Boeing XF-8B to shame with is muscular bulge! That was funny, but true.
There is only one reason to make a small fighter plane in WW-II. It's harder to see sneaking up behind you and this IS THE SINGLE MOST IMPORTANT TRAIT for a WW-II fighter plane to have. The potentially best fighter plane of the war ever flown was the Bell XP-77! But the most effective one ever to actually serve was the P-38. For a whole host of other reasons!

Frank Stewart said:

There is only one reason to make a small fighter plane in WW-II. It's harder to see sneaking up behind you and this IS THE SINGLE MOST IMPORTANT TRAIT for a WW-II fighter plane to have.

Click to expand...

Interesting, but I think this flies enough in the face of conventional wisdom that some more substantial evidence than proof by assertion in ALL CAPS is warranted before it is believable.

Frank Stewart said:

Because the shape of a H engine is basically square, its frontal area needs to be encased in an oval, or circular cowling to get any kind of decent streamlining! So, it's true frontal area needs to be calculated off of the longest dimension, typically between the top left and bottom right cylinder heads. Just look at the huge probiscis of a nose on the Typhoon! It puts a Corsair, P-47J or Boeing XF-8B to shame with is muscular bulge! That was funny, but true.

Click to expand...

Here's a picture of a Sabre in a Vickers Warwick, an aicrfat that normally carried a Centaurus or R-2800.


As you can see, the engine doesn't fill the cowling compleely like the radias did.

Frank Stewart said:

*SNIP*
There is only one reason to make a small fighter plane in WW-II. It's harder to see sneaking up behind you and this IS THE SINGLE MOST IMPORTANT TRAIT for a WW-II fighter plane to have. The potentially best fighter plane of the war ever flown was the Bell XP-77! But the most effective one ever to actually serve was the P-38. For a whole host of other reasons!

Click to expand...

The single most important trait of a WWII fighter is to be small? While I agree, many kills were of the "Boom and Zoom" type where the target never saw it coming, I highly doubt the size of the attacking fighter had much to do with that.

Care to elaborate on the "But the most effective one ever to actually serve was the P-38. For a whole host of other reasons!" statement? That's quite a sweeping generalization, I'd say the P-51 (for starters) would have something to say about that.

The Sabre is a poor example.
It used small, 93.3 cu in cylinders. The Jumo 211 used 177.8 cylinders.
The Sabre actual was sort of a hybrid. It used two crankshafts but in only used two cylinder blocks. In crankshaft had 1/2 it's pistons operating in the right hand block and 1/2 in the left.
Both sets of cylinders on each side exhausted through a common manifold. Basic engine was very compact. However there was all sorts of stuff piled on top or hanging underneath.

Jumo cylinders use 44mm more stroke than a Sabre. Unless you use really short rods you have to put the cylinders further away from the crankshaft. You are going to wind up with an engine around 50-52in height. Indeed the post war French H-24 built Jumo was 59in high but had some "stuff" higher and lower than the cam boxes.

Missed this one.

Frank Stewart said:

The potentially best fighter plane of the war ever flown was the Bell XP-77!

Click to expand...

Ok, it had potential.

All it needed was a new engine (like twice the power), better armament, protection, more fuel to go with the more powerful engine. Larger wing wing so it doesn't play lawn dart at low speeds. A view over the nose so deflection shooting didn't need the "By Guess and By God" (prayer) method of aiming.

But it had potential. So did the Christmas Bullet.

Shortround6 said:

Missed this one.

Ok, it had potential.

All it needed was a new engine (like twice the power), better armament, protection, more fuel to go with the more powerful engine. Larger wing wing so it doesn't play lawn dart at low speeds. A view over the nose so deflection shooting didn't need the "By Guess and By God" (prayer) method of aiming.

But it had potential. So did the Christmas Bullet.
View attachment 782690

Click to expand...

Given it was previously stated that THE SINGLE MOST IMPORTANT TRAIT in a fighter plane is the size (that still packs a decent engine?), my vote goes to the Gee Bee.

Every see how the pilot gets in and out?
The canopy does not move.

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.

tomo pauk said:

Covered by wuzak.



The BMW 801 have had an even worse power-to-weight ratio vs. the Jumo 211s and the DB 601/605s (as well as the reliability issues), the RLM still kept buying it because they were interested in total power of the engine. The 801 made the Fw 190 and Do 217 possible as we know them.

The H16 will be providing no worse power-to-weight ratio than the BMW 801 or the coupled engines, and, unlike the 801, it will still be making a good power on 87 oct fuel. It will also represent a less risky thing than the Jumo 222, whose failure meant, among other things, that Ju 88 family remained the mainstay of the LW bomber force, despite the limitations, like the low speed when bombed up since the bombs of the preferred size will not fit on the restricted bomb bay, as well as due to the low power of the Jumo 211s.

Click to expand...

Tomo, having looked at a few other threads, I realize your interest in an H16 is long lasting. There is a reason that there was only one production H16, that was installed in only 70 aircraft. Wuzak, Shortrounds and a few others have already commented on the difficulties of creating an H16. The largest unknown is the resonance from the firing order and that impact on the gears that connect the crankshafts and the prop speed reduction unit. The alternative is to have more primary order vibration. As the 18 cylinder radials showed, vibration was the great bugaboo of WW2. There is no guarantee in 1939 that an H16 would be buildable on schedule at specification. An H24 would be significantly easier to develop. It is not just history that tells us that, but a pair of flat crankshafts are not going to make a smooth engine.

"The H16 will be providing no worse power-to-weight ratio than the BMW 801 or the coupled engines"
This seems to be a bit tenuous.