Build the perfect air-cooled engine

tomo pauk · Feb 7, 2013

The historic R-2600 has 3 thing against it, vs. an 18 cyl engine of the same displacement I propose:
-it has no turbo, meaning the internal supercharger need to do all the work, so it will use much more engine power than a turbo-supported version
-it has no water injection installed, that means at least 10 % less power
-it is, as you've noted, a 14 cyl engine, and the RPM will not be as high as in 18 cyl engine of same displacement.

Why the R-3350 was unable to go above 2200 HP is a mystery to me - maybe Wright and AAF were trying to have the B-29 really working (= engines don't blow up), the 2200 HP being enough to propel it? Several engines were down-rated in order to work as they should (Vulture, BMW-801D, V-1710) until the issues are fixed. The Bristol Cenaturus was making 10% more power, without turbo, without water injection.

There was nothing special about the versions of the R-2800 that were making 2800 HP - those would be the C series with turbo and ADI, produced from late 1944 on. We can note that 1st B series, turbo + ADI in P-47, were making 2300 HP from late 1943 on, and, in mid 1944, 2600 HP.

riacrato · Feb 7, 2013

Shortround6 said:
C-46 could carry about double the payload and carry it further.

Sure, but often enough you don't need that payload or range and with 2/3 the maintenance costs (according to wiki) and much lower fuel consumption, the C-47 becomes very attractive for many applications. There are reasons it was much more successful and cost efficiency was one of them.

wuzak · Feb 7, 2013

tomo pauk said:
The historic R-2600 has 3 thing against it, vs. an 18 cyl engine of the same displacement I propose:
-it has no turbo, meaning the internal supercharger need to do all the work, so it will use much more engine power than a turbo-supported version
-it has no water injection installed, that means at least 10 % less power
-it is, as you've noted, a 14 cyl engine, and the RPM will not be as high as in 18 cyl engine of same displacement.

Why the R-3350 was unable to go above 2200 HP is a mystery to me - maybe Wright and AAF were trying to have the B-29 really working (= engines don't blow up), the 2200 HP being enough to propel it? Several engines were down-rated in order to work as they should (Vulture, BMW-801D, V-1710) until the issues are fixed. The Bristol Cenaturus was making 10% more power, without turbo, without water injection.

There was nothing special about the versions of the R-2800 that were making 2800 HP - those would be the C series with turbo and ADI, produced from late 1944 on. We can note that 1st B series, turbo + ADI in P-47, were making 2300 HP from late 1943 on, and, in mid 1944, 2600 HP.

The turbo in WW2 aircraft was used to normalise the air pressure to sea level. In other words, the engine at 25,000ft could makethe same power as as 0ft. The turbo didn't make for more powerful engines - they were just able to holdonto power to altitude.

If you hooked up a turbo to the R-2600 it would be unlikely to make any more than the 1900hp it already did.

Re the R-3350, I believe it was a case of making it reliable first.

wuzak · Feb 7, 2013

riacrato said:
Sure, but often enough you don't need that payload or range and with 2/3 the maintenance costs (according to wiki) and much lower fuel consumption, the C-47 becomes very attractive for many applications. There are reasons it was much more successful and cost efficiency was one of them.

So half the payload/range but 2/3 the maintenance costs? "Much lower fuel consumption" would also not be less than half that of the C-46. This would suggest that the C-46 was more cost eficient.

davparlr · Feb 7, 2013

riacrato said:
Sure, but often enough you don't need that payload or range and with 2/3 the maintenance costs

twice the load and and only a 50% increase in maintenance cost? Sounds like a deal to me.

and much lower fuel consumption,

I doubt the fuel cost was twice the C-47.

the C-47 becomes very attractive for many applications.

It is true that the cheaper to operate C-47 would be the selected choice for some missions but the same could be said about the C-45. The C-47 itself was limited in applications due to its limited payload. I suspect that, except maybe for short/unimproved field performance (maybe not), the C-46 could do any job the C-47 could do. True, it could be more inefficient for lighter loads at short distances but it would do okay.

There are reasons it was much more successful and cost efficiency was one of them.

The C-47 was and is a great aircraft. It was rugged, dependable, and economical but I suspect the major reason for its broad success was availability.

If I was flying the hump, I would definitely want to be in a C-46.

tomo pauk · Feb 7, 2013

wuzak said:
The turbo in WW2 aircraft was used to normalise the air pressure to sea level. In other words, the engine at 25,000ft could makethe same power as as 0ft. The turbo didn't make for more powerful engines - they were just able to holdonto power to altitude.

The turbo R-2800, with ADI, was offering more power than mechanically driven two-stage with ADI. 2300-2600 HP vs. 2200 for B series, or 2800 vs. 2450 for C series, all for sea level. The V-1710 was also providing more power in turbo versions than in non-turbo ones, some 100 HP plus in TO, and 200-300 more in military rating, F series.

If you hooked up a turbo to the R-2600 it would be unlikely to make any more than the 1900hp it already did.

It depends - if the engine-stage supercharger is smaller, or/and with decreased drive ratio, hence using less power, the BHP should be increased for same IHP? It worked for V-1710.
Then install ADI, it was used in Cyclone 9 and 18, but unfortunately not in Cyclone 14.

Truth to be said, I'd prefer the P&W design 'my' engine, though.

Re the R-3350, I believe it was a case of making it reliable first.

Agreed.

riacrato · Feb 7, 2013

davparlr said:
twice the load and and only a 50% increase in maintenance cost? Sounds like a deal to me.

Many times you won't need twice the payload, but be making the run anyways.

I doubt the fuel cost was twice the C-47.

Did I ever say so?

It is true that the cheaper to operate C-47 would be the selected choice for some missions but the same could be said about the C-45. The C-47 itself was limited in applications due to its limited payload. I suspect that, except maybe for short/unimproved field performance (maybe not), the C-46 could do any job the C-47 could do. True, it could be more inefficient for lighter loads at short distances but it would do okay.

Real world proves me right I don't doubt the C-46 was a good aircraft for what it needed to do. But the C-47 was many times more successful, numbers reflect that. Apparently the load was adequate and the costs spoke for it.

If I was flying the hump, I would definitely want to be in a C-46.

And if I was going to bomb Tokio, I want a B-50. And if I was going to land on the balcony of some Italian castle I want a Storch. Right tools for the right job, that was my point all along.

riacrato · Feb 7, 2013

wuzak said:
So half the payload/range but 2/3 the maintenance costs? "Much lower fuel consumption" would also not be less than half that of the C-46. This would suggest that the C-46 was more cost eficient.

Like above: I said maintenance costs, not costs for fuel.

davparlr · Feb 7, 2013

riacrato said:
Many times you won't need twice the payload, but be making the run anyways.

and I would guess that many more times you need multiple planes or sorties because you don't have enough load carrying capacity. It is typically better to have too much than not enough.

Did I ever say so?

I guess have no idea what you said. You seem to imply a fuel savings in the C-47 but that only applies if the load can be placed in one aircraft. If there is more than one aircraft load, it probably would be more efficient to us a C-46.

Real world proves me right I don't doubt the C-46 was a good aircraft for what it needed to do. But the C-47 was many times more successful, numbers reflect that. Apparently the load was adequate and the costs spoke for it.

I think numbers reflect more of the fact that there were hordes of these very capable airlifters at the start of the war and the assembly line was humming whereas the C-46 was still problem solving and starting an assembly line. Typically, for airlift, more load is better.

baldo · Oct 28, 2013

wuzak said:
The turbo in WW2 aircraft was used to normalise the air pressure to sea level. In other words, the engine at 25,000ft could makethe same power as as 0ft. The turbo didn't make for more powerful engines - they were just able to holdonto power to altitude.

If you hooked up a turbo to the R-2600 it would be unlikely to make any more than the 1900hp it already did.

Re the R-3350, I believe it was a case of making it reliable first.

As what I've learned and correct me if I'm wrong: A supercharge will 'stole' HP from engine output to work, while a turbo NOT,it just recover energy from exhausted gas. And 2nd, more pressured air-fuel mixture means more power. So a turbo charged R-2600 would probably produce more power at sea level, and even more power at atitude.

OldSkeptic · Oct 28, 2013

baldo said:
As what I've learned and correct me if I'm wrong: A supercharge will 'stole' HP from engine output to work, while a turbo NOT,it just recover energy from exhausted gas. And 2nd, more pressured air-fuel mixture means more power. So a turbo charged R-2600 would probably produce more power at sea level, and even more power at atitude.

A Turbo is not a magic act, it steals power too, directly and indirectly (as applied to aircraft). You lose power from the back pressure on the exhaust, you lose exhaust thrust (significant at higher altitudes), given the technology of the time they were huge therefore you had a huge weight penalty. The P-47 (weighed as much as a twin engined Beaufighter) was built around the turbocharger and as such was huge and despite being single engined cost nearly as much as the twin engined P-38 ... and twice as much as a P-51.

Turbos in cars have many advantages over superchargers, but that is at sea level ... in a car. In an aircraft, well there are issues. One thing that helps current aircraft with turbos is modern oils and materials. They can run at RPM and temps that were science fiction back in WW2.

Shortround6 · Oct 28, 2013

baldo said:
As what I've learned and correct me if I'm wrong: A supercharge will 'stole' HP from engine output to work, while a turbo NOT,it just recover energy from exhausted gas. And 2nd, more pressured air-fuel mixture means more power. So a turbo charged R-2600 would probably produce more power at sea level, and even more power at atitude.

In part it depends on when (what year) in WW II and the engine in question. Most radials were were limited in cooling and so you can't just up the pressure and get more power without cooking the engine. A 1900hp R-2600 used completely different cylinders and cylinder heads than 1700hp R-2600 with a LOT more fins. As fuel got better or water injection was introduced things got better for some engines.
In WW II NO engine had just a turbo. ALL turbo equipped planes had a turbo supercharger feeding an engine driven supercharger. A Wright R-2600 to make 1700hp was already running just over 7lbs of boost.

Now IF you had pulled the engine driven driven supercharger and replaced it with a turbo only the increased back pressure would have cost you power on the ground and about 8% at 20,000ft. You also would have lost the exhaust thrust which does get better with altitude and speed but varies quite a bit from plane to plane with radials due to the exhaust systems used. The Turbo was heavier than the engine driven supercharger. It also required a more sophisticated control.
The Supercharger part of of the turbo was limited to about a 3 to 1 pressure ratio so it could only supply 44.5in of pressure to about 18,000ft, after that the lower outside air pressure cuts into the manifold pressure and power.

Shortround6 · Oct 28, 2013

OldSkeptic said:
A Turbo is not a magic act, it steals power too, directly and indirectly (as applied to aircraft). You lose power from the back pressure on the exhaust, you lose exhaust thrust (significant at higher altitudes), given the technology of the time they were huge therefore you had a huge weight penalty. The P-47 (weighed as much as a twin engined Beaufighter) was built around the turbocharger and as such was huge and despite being single engined cost nearly as much as the twin engined P-38 ... and twice as much as a P-51..

The P-47 gets quite a bum rap for it's turbo and stuff like this does not help. A P-47 D was about 13,000lbs 'clean'. The Beaufighter VI was 19,750lbs or about 50% heavier. Compare empty weights or empty equipped if you want.

The single engine comparison is a little off too. The P-47 was designed as a 2000hp fighter. The P-38 was designed as a 2000-2200hp fighter, The P-51 was designed as an 1100hp fighter. When all three were designed 100/130 fuel did not exist. just plain 100 octane. Try comparing the P-47 to the F4U for size and cost seeing as how they used the same basic engine with a different supercharger solution.

tomo pauk · Oct 28, 2013

The Corsair and Hellcat were about same weight as P-47, so the turbo unit seem to be well worth it. Once we consider that it took two piston engines to beat what one turbo R-2800 was capable for (1000 miles combat radius, with enviable high speed and useful punch), it starts looking like a bargain.
A half of P-38J's powerplant weighted 2915 lbs (including prop, lubricating, turbo, ducts, all coolers etc). Once above 5000 ft, it was providing more power than Fw-180As powerplant (again, with prop etc, but without lubricating) that weighted 3663 lbs and a have had a bigger drag (should cancel out any advantage of having the exhaust thrust).

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