# Build the perfect air-cooled engine



## wuzak (Jun 17, 2011)

We have had a long discussion, not always on point, about the merits of different liquid cooled piston aero engines.

Now we should look at the flipside - what is/was/could have been the best aircooled engine for all around service (ie used in bombers, fighters, attack, whatever). Or perhaps we should look at ones for specific duty.

I personally don't think production numbers give the answer to what was best, and there were several engines that didn't reach production, or only gained small production orders.

For example. The Armstrong Siddeley Deerhound. This was a 21 cylinder 3 row radial, with ohc and 2 valves per cylinder. 

The Mk I had difficulty meeting the targeted 1500hp, and the chief engineer resigned as a result. Stewart Tresilian, formerly of Rolls Royce, was recruited to take over the job, modified the Mk II so that it was able to produce 1340hp, still short of the projected target. The modifications brought capacity up to 41l (2,505cid) from 38.19l (2,259.75cid).

Bore and stroke was 140mm x 127mm. This was carried over to the MkIII, which was a total redesign by Tresilian. He added reverse cooling to the design, and the engine was able to demonstrate 1800hp on the bench.

The engine was compact, with a diameter of 44 inches, giving significantly lower frontal area than the major radials of the period - the R-2800 was between 52 and 55 inches (depending on version), as was the R-4360, the Centaurus was 55.3 inches, the Hercules 55 inches. The smaller Taurus was slightly bigger at 46 inches in diameter. The R-1820 was over 54 inches in diameter, the R-2600 was 55 inches, and the R-3350 nearly 56 inches in diameter.

The R-2600 is probably closest in power output to the MkIII in its initial development status, and very similar in capacity. Had the Deerhound project been continued it may have been on par for power with the R-2800 by war's end. It was, however, cancelled mid 1941, and the company instructed to concentrate on gas turbines.

A further development, the 28 cylinder Wolfhound, never left the drawing board.


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## Shortround6 (Jun 17, 2011)

Lots of engines showed potential on the bench. A down fall of the Deerhound could have been cooling. They showed a lot of ingenuity in the cooling arrangements but they were complicated. Three cylinders in a row means air has to be directed between the rows, turned sideways, travel through the row (cylinder fins), get collected on the other side and then move back out of the space between the rows. Even an R-4360 used a simpler pattern than that. Another potential source of problems in cooling is the is the overhead cam. how much potential cooling area is blocked by the cam box?
Using the same size cylinders as an two row 18 a 3 row 21 gets a 1/6 increase in displacement but adds a heavier crankcase and crankshaft. The overhead cams may be heavier than push rods. 

A sleeve valve Deerhound might have been interesting. The sleeve drives wouldn't have been much more coplicated than the overhead cams and might have even required less gearing than than the 14cylinder Hercules. It would also have freed up the head area for a more unobstructed airflow.


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## Trilisser (Jun 17, 2011)

My perfect air-cooled engine would be (assuming at least 2000 hp power class)
-18-cylinder radial
-with sleeve valves and copper alloy heads
-two stage supercharger with infinitely variable drive plus aftercooler (i.e. RR type blower)
-direct injection

I see that Centaurus is the closest to that ideal.


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## Shortround6 (Jun 17, 2011)

All good ideas but the after cooler design is very hard to implement on a radial. on a V-12 the air comes out of one outlet on the supercharger case and you can put an after cooler between the outlet and the intake pipe/manifold that runs ito the V before it branches off to the individual cylinders. radial engines had multiple out lets from the supercharger ( the R-2800 may have had nine, see: R-2800 Overhaul Manual) which calls for either fancy duct work or multiple small aftercoolers. 
I believe at least one experimental radial used one aftercooler for each cylinder or pairs of cylinders. It is not impossible but it is a lot harder than on a V-12. 

Remember that the engine is only as powerful as the cylinder with weakest/hottest mixture


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## Lighthunmust (Jun 17, 2011)

wuzak said:


> . He added reverse cooling to the design, and the engine was able to demonstrate 1800hp on the bench.


 
What is "reverse cooling". Is it the changes in direction of airflow that Shortround6 mentions?

You and Shortround6 are really making great posts here and on the water cooled thread. Thanks.


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## Trilisser (Jun 17, 2011)

SR, excellent points. In fact, you got me pants down in this at first. But, when I think it more closely, it would be doable. First, the supercharger unit would not be integral with the engine. Instead, it would be driven off a short entension shaft and the aftercooler unit could be located between the engine proper and the supercharger unit. from that aftercooler unit the induction air would then be delivered to cylinders via brached piping. Of course, this would make direct injection mandatory.


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## Readie (Jun 17, 2011)

The Centaurus was the logical end to power house aircooled radial design along with some of the American designs.Huge power available.
It is just me or do you find that the radial just does not have that the je ne sais quoi...the iconic sound of a liquid cooled inline?
It may just be the exhast arrangement, I'm not sure...
But, I expect Soundround will know.
Cheers
John


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## Trilisser (Jun 17, 2011)

One annoying thing in radial sound may be when they start: the clanking due to crankshaft pendulum counterweights swinging to and fro. But it is a matter of taste.


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## davebender (Jun 17, 2011)

It appears to me the benefits of air cooling disappear by the time you reach about 1,200 hp. After that air cooled engines become rather large and heavy relative to power output. They also become a lot more expensive to produce.

I nominate the R1830 as being close to perfect for an air cooled radial engine. Add fuel injection and it would be even better.
1,250 lbs. Dry weight.
1,200 hp.
Reliable and inexpensive.


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## wuzak (Jun 17, 2011)

Lighthunmust said:


> What is "reverse cooling". Is it the changes in direction of airflow that Shortround6 mentions?



Reverse cooling for a radial is taking the cooling air over the rear cylinders first and then moving forward.







That is, the air flows right to left in the picture above, not left to right as is convention.

The R-2800 and R-4360 both adopted fans to provide reverse cooling when specified in pusher configurations (XP-56 and B-36).


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## wuzak (Jun 17, 2011)

Shortround6 said:


> Lots of engines showed potential on the bench. A down fall of the Deerhound could have been cooling. They showed a lot of ingenuity in the cooling arrangements but they were complicated. Three cylinders in a row means air has to be directed between the rows, turned sideways, travel through the row (cylinder fins), get collected on the other side and then move back out of the space between the rows. Even an R-4360 used a simpler pattern than that. Another potential source of problems in cooling is the is the overhead cam. how much potential cooling area is blocked by the cam box?
> Using the same size cylinders as an two row 18 a 3 row 21 gets a 1/6 increase in displacement but adds a heavier crankcase and crankshaft. The overhead cams may be heavier than push rods.
> 
> A sleeve valve Deerhound might have been interesting. The sleeve drives wouldn't have been much more coplicated than the overhead cams and might have even required less gearing than than the 14cylinder Hercules. It would also have freed up the head area for a more unobstructed airflow.


 
In the case of the Deerhound, it had 50% more cylinders than other radials of similar capacity (R-2600, Hercules).

Mks I and II did have a lot of difficulty with cooling, hence the redesign and the move to reverse cooling. The cooling arrangement would be little different to an air-cooled in-line in that the air would be introduced on one side of the cylinder bank and taken from the other. It is also basically what the R-4360 did.

The cam boxes were no more of a problem than air-cooled in-lines. Though, it has to be said, such beasts tended to be small, low powered engines.

A sleeve valve version would have needed 7 drive shafts for the sleeves, maximuim, compared with 14 for the Hercules and Taurus, and 18 for the Centaurus. It may have been possible to do with 4 shafts - 3 servicing 2 cylinders and the 4th taking the last. The sleeves would then be driven by skew gears, as per Sabre.


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## wuzak (Jun 17, 2011)

Here is an aircraft with a reverse cooling arrangement.

The de Havilland Albatross






The holes in the leading edge are for the cooling air. The air is forced (by ram air pressure) down the outsides of the engine, inside the cowling, then crosses the cylinder bank to provide cooling and ending up in the vee. It then exits via the panell beneath the engine. (at least that's the way I surmise the flow goes. (Often in the vee engine the air will go into a plenum in the vee and is pushed outwards to provide cooling, but the outlets beneath the engine look more likely to take the air from the vee.)

The engine used is the inverted V12 Gipsy Twelve






I couldn't find a picture of the Armstrong-Whitworth Whitley, but one did fly with the Deerhound installed.


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## Shortround6 (Jun 17, 2011)

davebender said:


> It appears to me the benefits of air cooling disappear by the time you reach about 1,200 hp. After that air cooled engines become rather large and heavy relative to power output. They also become a lot more expensive to produce.
> 
> I nominate the R1830 as being close to perfect for an air cooled radial engine. Add fuel injection and it would be even better.
> 1,250 lbs. Dry weight.
> ...



It depends on how you measure power. A DB605D would be useless as a bomber engine. While it's peak 3-5 minute power may rival a R-2800 it's continuous, max rich, run it till the fuel runs out power level does not. A "B" series R-2800 can run at 1650hp at 2550rpm until it runs out of fuel as long as the cylinder head temp is within limits. There is no 5 min or 15 min or 30 min time limit. It does burn a tremendous amount of fuel doing this but it can be done. Cruising power in lean settings are going to be greater too. 

A 1200hp R-1830 offers about 95hp per sq ft of frontal area, A 2000hp R-2800 offers 131 hp per sq ft of frontal area. 

A 1200hp R-1830 also weighs over 1400lbs, not 1250lbs. 

Adding fuel injection will give freedom from backfires and carburetor icing, I am not sure what else it does for the R-1830.


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## davebender (Jun 17, 2011)

> fuel injection will give freedom from backfires and carburetor icing, I am not sure what else it does for the R-1830.


Fuel injection is inherently better when a P-36 or F4F fighter aircraft is flying upside down.


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## Shortround6 (Jun 17, 2011)

Wuzak. You have the cooling arrangements of the de Havilland Albatross described perfectly.
While there may have been nothing wrong with the Gipsy twelve it does show a lot of the limits of aircooled V-12s. It was just a bit smaller than a R-R Kestrel in displacement (18.4litres vs 21.2 litres) it was wider, higher, longer, heavier and offered about 70% of the power. This doesn't include the size of the radiator although the cooling arrangements on the Albatross were a ways from simple light or compact 

It sure does look sleek and pretty though. 

The Gypsy 12 was under the disadvantage of using cylinder assemblies common to the company's 4 and 6 cylinder engines. While this meant that the cylinders were cheap and easy to provide spare parts for it also meant that the cooling fins were marginal for the duty they were asking of it. They were trying to get about 25% more power per cylinder than the unsupercharged 4 6 cylinder engines gave. 
It also weighs 7lbs less than an 820hp Mercury radial. which, despite it's better streamlining probably explains why it wasn't used much.


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## Shortround6 (Jun 17, 2011)

davebender said:


> Fuel injection is inherently better when a P-36 or F4F fighter aircraft is flying upside down.



Why?


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## wuzak (Jun 17, 2011)

Here is another ai-cooled in-line - the Napier Dagger






You can see the inlets that lead to plenums between the cylinder banks for coling. The air exits to th eoutside of the cylinders.

Here it is in action in the Handley Page Hereford





It was also used on the Martin-Baker M.B.2





Data from Wiki

Specifications (Napier Dagger III MS)Data from Lumsden[3]

General characteristics

Type: Twenty-four-cylinder supercharged air-cooled H engine
Bore: 3.813 in (96.8 mm)
Stroke: 3.75 in (95.25 mm)
Displacement: 1,027 in³ (16.8 L)
Length: 80 in (2,032 mm)
Width: 22.5 in (584 mm)
Height: 45.125 in (1,146 mm)
Dry weight: 1,358 lb (616 kg)

Components

Valvetrain: One inlet and one exhaust valve per cylinder
Supercharger: Single-speed centrifugal type supercharger, 5.04:1 reduction
Fuel system: Napier-Claudel-Hobson carburettor
Fuel type: 87 Octane petrol
Cooling system: Air-cooled
Reduction gear: Spur, 2.69:1

Performance

Power output:725 hp (541 kW) at 3,500 rpm for takeoff
794 hp (592 kW) at 4,000 rpm at 5,000 ft (1,520 m)
Specific power: 0.77 hp/in³ (35.13 kW/l)
Compression ratio: 7.75:1
Specific fuel consumption: 0.43 lb/(hp•h) (261 g/(kW•h))
Oil consumption: 0.18-0.35 oz/(hp•h) (7-13 g/(kW•h))
Power-to-weight ratio: 0.62 hp/lb (1.02 kW/kg)

Less powerful than the Peregrine, but some 200lbs/90kg heavier. Although a later version was reportedly good for about 1000hp.

The sound was also, apparently, quite horrific.

A model of the Napier Dagger

The Dagger was developed from the H-16 Rapier.


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## Lighthunmust (Jun 17, 2011)

Thank you for answering my question Wuzak, and with photos no less! Great stuff you and Shortround6 are posting. The rest of us should be paying you two for the education.


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## wuzak (Jun 17, 2011)

Actually, to me the Pennine would be the best air-cooled engine. In early development it was capable of 1hp/cu.in, which the R-2800 could only do with a lot of boost and ADI, while the R-4360 only did so in VDT engines, which had to be continuously monitored and adjusted by hand (no control system existed at that time). The R-3350 could do more than 1hp/cu.in when in turbo-compound form.

In terms of power to weight it was about 1hp/lb, similar to most versions of the R-2800 and better than most other air-cooled engines.

Slightly longer than an R-4360 it could have fitted into an F2G (ie F4U with R-4360), and would have been a great bomber engine.

Data from Wiki

General characteristics

Type: 24-cylinder supercharged liquid-cooled 90 degree X layout aircraft piston engine
Bore: 5.4 in (137.1 mm)
Stroke: 5.0 in (127 mm)
Displacement: 2,791 in³ (45.73 L)
Length: 106 in (2692 mm)
Width: 39 in (991 mm)
Height: 37.5 in (952 mm)
Dry weight: 2,850 lb (1,293 kg)

Components

Valvetrain: Sleeve valve
Supercharger: Gear-driven centrifugal type supercharger, single stage, two speed
Fuel type: Petrol
Cooling system: Pressure air-cooled

Performance
Power output: 2,740 hp (2,043 kW) at 3,500 rpm, +12 psi boost at sea level
Power-to-weight ratio: 0.96 hp/lb (1.58 kW/kg)


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## Shortround6 (Jun 17, 2011)

The later Daggers were rated at 955hp for take off at 4200rpm and 6lb of boost. Also 1000hp at 4200rpm at 8,750ft. Cooling problems seem to be endemic though. Those air scoops came with the engine, Napier apparently not trusting the air frame manufactures to provide proper airflow for cooling. Most Herefords did not see combat (if any actually did?) and some accounts say a number of them were re-engined with Pegasus engines.


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## Readie (Jun 18, 2011)

Shortround6 said:


> Most Herefords did not see combat (if any actually did?)



Some did apparently in 1940 -41.

Handley Page H.P.53 Hereford - bomber

Albeit with little success.
Cheers
John


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## Shortround6 (Jun 18, 2011)

When all is said and done the ultimate air-cooled engine is probable going to be an 18 cylinder 2 row radial of about 53-57 litres displacement. supercharger to suit employment and Sleeve or poppet valve to suit initial cost or maintenance requirement. 

A VERY interesting article can be found here: http://www.flightglobal.com/pdfarchive/view/1937/1937 - 0507.html?search=Fedden

While everything in it may not be 'gospel' it does show what at least one great engine designer was thinking and why at the time. It also shows that multiple layouts were at least being considered although perhaps with a view of justifying their own position?


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## Trilisser (Jun 18, 2011)

A most interesting article! BTW, I wonder how would it pan out if the ultimate air cooled radial was a CI engine with pure turbocharging...


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## basil (Feb 6, 2013)

Ad ultimate aircooled aircraft piston engine - a very interesting project was the Junkers O-32 (P 130) project which was designed 1945/1946 (already under soviet occupation) by Junkers engineers under the leadership of Dr. Cordes and Dr. Scheibe. It was an aircooled two stroke compression ignition radial in two versions - one 10 cylinder double row radial (34 liter) and one 12 cylinder double row radial (36 liter), each with about 4.000 hp. It would have powered a fan (derived from the Jumo 012 turbojet) instead of a propeller without reduction gearing at a speed of 6.600 rpm - resultig in a thrust of 2.000 kp (19,6 kN) and was proposed to have a fuel consumption of less than a third compared to the Jumo 012. Work was terminated in 1947 because of work on turboprops which finally resulted in the Kusnezow NK-12.


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## wuzak (Feb 6, 2013)

34l/36l, 4000hp, 6600rpm Diesels seem a bit far fetched for WW2 time frame.


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## merlin (Feb 6, 2013)

The Deerhound is an interesting engine, though by making it a three-row you'd have thought 'cooling problems' could have been anticipated! 
Having said that the performance of the Mk I, is that different to what happened to the Hercules - similar power target, with the initial one being lower than expected - what happened - it took till Mk III to get there! 

Might it have helped focus their minds if the Air Ministry had stipulated either engine. Imagine Bristol's loss of 'face' if they were forced to have Deerhounds in a Bristol aircraft instead of an under performing Hercules.


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## tomo pauk (Feb 6, 2013)

Wonder how well the Homare would've been doing, built maintained by Western standards, while using 'good' fuel. And then install some auxiliary supercharger stage, maybe a fan to cool it while the cowling is made tight...


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## davebender (Feb 6, 2013)

How can any piston engine be considered "perfect" if it arrives too late to matter?

An acceptable air cooled engine will be reliable and in service NLT 1942 (i.e. WWII half over). A perfect air cooled engine will be reliable and in service during 1939.


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## Shortround6 (Feb 6, 2013)

"A perfect air cooled engine will be reliable and in service during 1939"

And will have been designed to run on 87 octane fuel, no water injection and using 1938/39 manufacturing techniques. In other words, _totally obsolete_ by 1944. 

The Wright R-1820 was giving about 1100hp for take-off in 1939. By 1945 it was good for 1425hp for take-off and post war went to 1525hp. Not only did the fuel change but so did just about everything else _EXCEPT_ the bore and stroke. Different crankcase and crankshaft, different pistons, different cylinder construction, different cylinder head construction, different number of cylinder hold down bolts, and so on. Engine weight changed by around 200lbs. 

Versions of this late model air cooled engine powered an awful lot of helicopters (several thousand) but I guess it was far from perfect because the jet engine was already on the scene?????

Piston engines powered the majority of the worlds transport planes for a good decade after WW II ended. Last Lockheed Constellation was rolled in 1958, last scheduled passenger airline flight ( not charter or cargo) was in 1967 as just one example.


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## tomo pauk (Feb 6, 2013)

Perfect engine means that timing is right, among other stuff. Maybe Dave was having that in mind? Even the engines that were in service later than 1939 (R-2800, BMW-801, Hercules) received plenty of upgrades, if not complete redesigns, by 1945.


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## Shortround6 (Feb 6, 2013)

That they did but Mr Bender seems to be saying that any aircooled aircraft engine after 1939 was less than "perfect" because it won't be in "time". For "what" he isn't saying.

Nobody was using the air cooled engines in fighters in 1944/45 that they were using in 1939. 

And while the jet engine was an indicator of the future it was far from perfect in 1944/45 for fighters and far, far, far, from perfect for many other aircraft propulsion duties.


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## riacrato (Feb 6, 2013)

There's no such thing as one perfect engine, radial or inline- It all depends on the applications you're going for. A 14 cylinder with ~40l displacement might be good for a lot of applications but will run into limitations and is inefficient when the plane gets really big. And an 18 cylinder or even larger engine can be overkill for a smaller aircraft.


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## wuzak (Feb 6, 2013)

merlin said:


> The Deerhound is an interesting engine, though by making it a three-row you'd have thought 'cooling problems' could have been anticipated!
> Having said that the performance of the Mk I, is that different to what happened to the Hercules - similar power target, with the initial one being lower than expected - what happened - it took till Mk III to get there!
> 
> Might it have helped focus their minds if the Air Ministry had stipulated either engine. Imagine Bristol's loss of 'face' if they were forced to have Deerhounds in a Bristol aircraft instead of an under performing Hercules.



Armstrong-Siddeley wanted the Deerhound to be liquid cooled. The Air Ministry wanted an air-cooled radial manufacturer to compete with Bristol, so insisted that the Deerhound be air cooled.

Radials with more than 2 rows faced cooling problems, regardless of whether the rows were staggered or not. The solution used for the R-4360 was shrouds to guide air around cylinders, and that should work for the Deerhound. The solution Armstrong-Siddeley chose was reverse flow cooling.


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## tomo pauk (Feb 6, 2013)

riacrato said:


> There's no such thing as one perfect engine, radial or inline- It all depends on the applications you're going for. A 14 cylinder with ~40l displacement might be good for a lot of applications but will run into limitations and is inefficient when the plane gets really big. And an 18 cylinder or even larger engine can be overkill for a smaller aircraft.



I agree that a big engine can make the job harder for the airframe designers; hard, but not impossible to build a not-so-big airplane. The renown Bearcat was an example of big engine in a modestly sized airframe. But even the Fw-190 was carrying around some big powerplant, on a wing area smaller than of P-51, let alone Spitfire. We also know the other small airframes with big engines, eg. La series (900 kg dry weight of engine), or maybe Yak-3U, or that 109 prototype with BMW 801.
The ~40L engine can still provide plenty of power, if it has 2 stage spercharger, while using good fuel. Even more power should make 18 cyl engine of such a displacement, smaller pistons mean more RPM.

As for the airplanes that are getting really big, how big would that be? The Lanc, Stirling Halifax were flying with radials displacing under 39 liters, the engines being humble single stage ones. Many German US planes were using 41 or 42 liter radials, again single stagers, to a good effect. If those engines were running into limitations, that was only at high altitude, because none of them were using multi-stage supercharging.


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## wuzak (Feb 6, 2013)

tomo pauk said:


> As for the airplanes that are getting really big, how big would that be? The Lanc, Stirling Halifax were flying with radials displacing under 39 liters, the engines being humble single stage ones. Many German US planes were using 41 or 42 liter radials, again single stagers, to a good effect. If those engines were running into limitations, that was only at high altitude, because none of them were using multi-stage supercharging.



The "under 39l" engine would be the 2360ci Hercules.
The "42l" radial would be the R-2600.

Note that the B-17 and B-24 both used radials under 30l - the R-1820 and R-1830. These, too, were single stage units but equipped with turbochargers.


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## wuzak (Feb 6, 2013)

How useful would the Deerhound IIi have been?

About 1800hp, 44" (1118mm) in diameter, around 41l (2500ci). Basically the same power class as an R-2600, but much smaller frontal area. Maybe a bit heavier, though.


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## riacrato (Feb 7, 2013)

tomo pauk said:


> I agree that a big engine can make the job harder for the airframe designers; hard, but not impossible to build a not-so-big airplane. The renown Bearcat was an example of big engine in a modestly sized airframe. But even the Fw-190 was carrying around some big powerplant, on a wing area smaller than of P-51, let alone Spitfire. We also know the other small airframes with big engines, eg. La series (900 kg dry weight of engine), or maybe Yak-3U, or that 109 prototype with BMW 801.
> The ~40L engine can still provide plenty of power, if it has 2 stage spercharger, while using good fuel. Even more power should make 18 cyl engine of such a displacement, smaller pistons mean more RPM.
> 
> As for the airplanes that are getting really big, how big would that be? The Lanc, Stirling Halifax were flying with radials displacing under 39 liters, the engines being humble single stage ones. Many German US planes were using 41 or 42 liter radials, again single stagers, to a good effect. If those engines were running into limitations, that was only at high altitude, because none of them were using multi-stage supercharging.


 
When I said limitations I was thinking about B-29s, Me 323s and the likes.

Also, while a big radial can be fit into a smaller airframe, why would I power my C-47-class aircraft with a high-class and expensive R-2800 when in the end an inexpensive R-1830 will do just as fine. Granted the engine costs is not all in that decision, but look at C-46 vs C-47.


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## tomo pauk (Feb 7, 2013)

wuzak said:


> The "under 39l" engine would be the 2360ci Hercules.
> The "42l" radial would be the R-2600.



Indeed 



> Note that the B-17 and B-24 both used radials under 30l - the R-1820 and R-1830. These, too, were single stage units but equipped with turbochargers.



That would technically qualify them as a two stage engines - engine stage + auxiliary (turbo, in this case) stage.



riacrato said:


> When I said limitations I was thinking about B-29s, Me 323s and the likes.



Okay, I see what you mean. 
If, for example, US have had the 2600 cu in, 18 cyl engine, it would've been, in turbo installations, a 1800 HP in early war, 2000 HP in 1943, and maybe up to 2500 HP in early 1945. More than enough to carry the Grand Slam, let alone the nuke, in a 4 engined plane. The engine being small enough to power a fighter of modest size?



> Also, while a big radial can be fit into a smaller airframe, why would I power my C-47-class aircraft with a high-class and expensive R-2800 when in the end an inexpensive R-1830 will do just as fine. Granted the engine costs is not all in that decision, but look at C-46 vs C-47.



Maybe your transport aircraft with 2 big engines would be able to carry more payload at greater distances, with less pilots needed per ton-mile?


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## Shortround6 (Feb 7, 2013)

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


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## wuzak (Feb 7, 2013)

tomo pauk said:


> If, for example, US have had the 2600 cu in, 18 cyl engine, it would've been, in turbo installations, a 1800 HP in early war, 2000 HP in 1943, and maybe up to 2500 HP in early 1945. More than enough to carry the Grand Slam, let alone the nuke, in a 4 engined plane. The engine being small enough to power a fighter of modest size?



Not sure that is a safe assumption Tomo.

R-2600 only got up to around 1900hp (ok, so it is a 14 cylinder engine). The R-3350 really only got to 2200hp by the end of the war.

In contrast, some special versions of the R-2800 were able to get 2800hp by the end of the war, but that was really stretching things.


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## 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.


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## 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.


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## 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.
> ...



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.


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## 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.


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## 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.


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## 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.


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## 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.


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## 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.


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## 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.


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## 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.
> 
> ...



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.


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## 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.


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## 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.


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## 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.

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## 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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