What was the problem with the allison engine?

[wuzak]

The Continental was intended to be used with a turbo charger and had a single speed supercharger drive to the engine supercharger in most versions (there were at least 13 different versions) there were one or two two speed versions and a 2 speed two stage version but many of these models never made it into an airframe for flight testing.
I don't believe the Ford engine ever made it out of the test cells to be installed in a test mule aircraft so it's actual configuration is also pretty open ended.

There was only one type of IV-1430 engine cleared for test flight, and it flew in both the XP-49 and XP-67. Both used a single stage, sea level rated engine with turbosupercharger. It was rated at around 1350hp, and 1600hp WEP, but in flight tests it is unlikley to have made much more than 1000hp, hence the disappointing (and near identical) performance of both the XP-49 and XP-67.

It is interesting to note that the IV-1430 had more hours on single cylinder development than the whole Merlin testing program until production started! The IV-1430 program started around the same time as the V-1710 and Merlin.

The IV-1430 had several variants of supercharger proposed, as well as two speed gearboxes for propellor drives. But this was wasted effort while the core engine was not running and nowhere near production.

Late in the war an IV-1430 was tested to 2300hp, apparently. But by then the program was being wound down.

 

[davparlr]

Power is one thing, but how much power is translated into forward motion is another.

At such altitudes the performance of the prop falls off, unless the prop is designed for such altitudes. And if the prop is designed for high altitudes it will be less effective down low.

Apparently the P-47M was quite able to convert the massive horsepower into forward motion. At 35k, the much cleaner Ta-152H was capable of 459 mph, the P-47M, 475 mph. In fact the P-47M was faster than the Ta-152H all the way up until the nitrous kicked in.

 

[davparlr]

Until I saw one at the Yanks Museum in Chino,CA the P-47M seemed like a mythological beast. Seeing your location davparir I am guessing you have seen it. If not, make time, you will enjoy Yanks.

I have been there. Their airshow in May is something to behold. Watching an F6F chase a Zero around the field, and a F-86 and a Mig-15 play catch-me-if-you-can is absolutely stunning.

 

[wuzak]

I think the Lancaster (and the follow-on development, the Lincoln) was handicapped by being Merlin powered.

Four turbo charged Allisons (basically the whole engine package from a P-38J/L) would have been more effective. More allitude capability compared to the Merlin 20 series in the Lancaster (equal to the Merlin 85 engines in the Lincoln) to help get above the flak and fighters. The stronger Allison power section could handle more power longer than the Merlin (good for the long climb to allitude) with less maintenance. Most importantly, the turbocharged Allison burned less fuel than a Merlin for the same horsepower, so more bombs for the same takeoff weight.

If Bomber Command wanted better altitude performance from the Lancaster then surely they would have put 60- or 70-series engines into pace, a much simpler exercise than converting to the Allisons.

FWIW a B-17E (IIRC) was converted from Wright R-1820 power to Allison V-1710 power by Lockheed Vega, who were one of the factories producing the B-17. This was the XB-38. It had better performance than the standard version, but was deemed too much work to stop the production lines and change over. The engine installation owed much to that of the P-38, though the turbo remained in the standard B-17 location (bottom of nacelles). the coolant radiators were located in the leading edge between the engines.

Griffon power in the Shackleton (another Lancaster follow-on) was also less than ideal. Allison had a turbocompound V-1710 running in their test cell. A single stage single speed version of a gas sipping Allison turbocompound would have been a better match to the Shackleton than the Griffon. (Note, this assumes that Napier misfires with their diesel work. They already had data and blueprints for the Jumo 205 diesel, a Deltic version of a Jumo 205 would have been could have been winner for long range patrol aircraft. Even the 'simplified' second version of the Nomad was wayyyyy too complicated. As with the Sabre, Napier reached too far).

Allison was unwilling to invest in the TC V-1710 without orders. The TC needed a better turbine - an air-cooled turbine was required as the exhaust was too hot for the standard GE turbine used for the prototypes (the turbine was from a C-series turbo - which is used for R-2800 applications, rather than a B-series turbo usually coupled to a V-1710). Additionally, Allison wanted to concentrate on jet power.

Napiers were building Jumo Diesels under licence before WW2, IIRC. The Deltic version would have been too heavy and been to draggy for an aircraft installation.

In any case, the Shackleton was post war, and as Britain was very cash strapped they could not afford to buy American engines, and preferred to use and develop engines from their own country.

As the Shackleton was designed as an ASW aircraft, altitude performance was not necessary, and its range and endurance was more than sufficient for the task.

I'd also add that a better alternative would have been the turboprop engines that began appearing after the war.

 

[fastmongrel]

As the Shackleton was designed as an ASW aircraft, altitude performance was not necessary, and its range and endurance was more than sufficient for the task.

I'd also add that a better alternative would have been the turboprop engines that began appearing after the war.

There was a proposal to fit RR Dart turboprops on the Shackleton but as usual the proposal was dropped because "it is going out of service soon it would be a waste of money". This was in the early 60s the Shack was still rattling along nearly 30 years later

My Brother in law flew many hours on Shacks as a Warrant officer electronics specialist and he says one Shack MR3 flew with a Rolls Royce Dart turboprop on an inside engine position to test the installation. The Dart was plumbed into the Viper turbojet booster engines fuel tank.

He reckons his hearing is permanently damaged by the racket inside a Shack and he was heartily glad when they transferred to the warm, draught free, quiet and vibration free Nimrod.

 

[gjs238]

FWIW a B-17E (IIRC) was converted from Wright R-1820 power to Allison V-1710 power by Lockheed Vega, who were one of the factories producing the B-17. This was the XB-38. It had better performance than the standard version, but was deemed too much work to stop the production lines and change over. The engine installation owed much to that of the P-38, though the turbo remained in the standard B-17 location (bottom of nacelles). the coolant radiators were located in the leading edge between the engines.

I wonder how this would have held up to German attacks, compared to the air cooled engines.

 

[Lighthunmust]

I wonder how this would have held up to German attacks, compared to the air cooled engines.

It would have been a huge mistake. No additional performance would have balanced the increased mechanical vulnerability.

 

[wuzak]

It would have been a huge mistake. No additional performance would have balanced the increased mechanical vulnerability.

Note that the USAAC had considered in-line liquid cooled engines essential for bombers because they could give more power for a certain capacity.

Not sure how much more vulnerable a B-17 would have been with the Allisons. The performance gain would have been totally lost by the tactics of mutual defensive fire, as this meant that the B-17s could rarely perform as well as it was able.

The B-29 could have had reduced "mechanical vulnerability" had they adopted the V-3420 installation of the XB-39 - some 30mph faster, more takeoff power, and proven and reliable engines (V-3420 was basically two V-1710s). The XB-39 used an engine installation, first trialed on the XP-19, which was specifically designed to bolt up to the same bulkhead as the R-3350. All cooling requirements were handled within the power egg.

 

[johnbr]

Me I would have gone with the saber on the B-29

 

[Lighthunmust]

Note that the USAAC had considered in-line liquid cooled engines essential for bombers because they could give more power for a certain capacity.

Not sure how much more vulnerable a B-17 would have been with the Allisons. The performance gain would have been totally lost by the tactics of mutual defensive fire, as this meant that the B-17s could rarely perform as well as it was able.

The B-29 could have had reduced "mechanical vulnerability" had they adopted the V-3420 installation of the XB-39 - some 30mph faster, more takeoff power, and proven and reliable engines (V-3420 was basically two V-1710s). The XB-39 used an engine installation, first trialed on the XP-19, which was specifically designed to bolt up to the same bulkhead as the R-3350. All cooling requirements were handled within the power egg.

When did they consider liquid cooled engines essential? Who in USAAC/USAAF thought they were essential? I am well aware of various studies and trials, but do not recall hearing anything on the essential need for liquid cooling.

How much more vulnerable? As much as billions of coolant system piercing pieces of flak can create. Liquid cooled engines may have made a stronger case for the use of more HMG instead of more cannon on Luftwaffe fighters. More bullets to pierce versus less shells to burst.

The only thing wrong with the mechanical vulnerability of the B-29 power plant aside from the engine cowling was that its first name wasn't P&W and its last name 2800.

 

[Shortround6]

It was in the 30s that liquid cooling was considered essential. Part to it was theory. They hadn't really done much for trials. Aircooling wasn't developed as much as it was just a few years later. This liquid went along with the "hyper" cylinder or engine and we know how that turned out.

The P&W R-2800, fine as it was, may not have been able to power a B-29. There is not only take-off power and Military power but Cruising powers to consider. The R-3350 may have had a max cruise power using auto-lean settings of several hundred horsepower more than the R-2800. Considering that these max auto lean settings produced power down around 1200hp an extra couple of hundred HP is actually quite a percentage change.

 

[Readie]

I must admit that I had always thought that liquid cooling was preferable for internal combustions engines as it provided a more stable temperature and therefore allowed the engine to develop more power and reliability.

In all combustion engines, a great percentage of the heat generated (around 44%) escapes through the exhaust, not through either a liquid cooling system nor through the metal fins of an air-cooled engine (12%). About 8% of the heat energy finds its way into the oil, which although primarily meant for lubrication, also plays a role in heat dissipation via a cooler
Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust inhibitors. The industry term for the antifreeze mixture is engine coolant. Some antifreezes use no water at all, instead using a liquid with different properties, such as propylene glycol or a combination of propylene glycol and ethylene glycol. Most "air-cooled" engines use some liquid oil cooling, to maintain acceptable temperatures for both critical engine parts and the oil itself. Most "liquid-cooled" engines use some air cooling, with the intake stroke of air cooling the combustion chamber.

Comparing air and water, air has vastly lower heat capacity per gram and per volume (4000) and less than a tenth the conductivity, but also much lower viscosity (about 200 times lower: 17.4 × 10−6 Pa·s for air vs 8.94 × 10−4 Pa·s for water). Continuing the calculation from two paragraphs above, air cooling needs ten times of the surface area, therefore the fins, and air needs 2000 times the flow velocity and thus a recirculating air fan needs ten times the power of a recirculating water pump. Moving heat from the cylinder to a large surface area for air cooling can present problems such as difficulties manufacturing the shapes needed for good heat transfer and the space needed for free flow of a large volume of air. Water boils at about the same temperature desired for engine cooling. This has the advantage that it absorbs a great deal of energy with very little rise in temperature (called heat of vaporization), which is good for keeping things cool, especially for passing one stream of coolant over several hot objects and achieving uniform temperature. In contrast, passing air over several hot objects in series warms the air at each step, so the first may be over-cooled and the last under-cooled. However, once water boils, it is an insulator, leading to a sudden loss of cooling where steam bubbles form (for more, see heat transfer). Unfortunately, steam may return to water as it mixes with other coolant, so an engine temperature gauge can indicate an acceptable temperature even though local temperatures are high enough that damage is being done.
An engine needs different temperatures. The inlet including the compressor of a turbo and in the inlet trumpets and the inlet valves need to be as cold as possible. A countercurrent heat exchange with forced cooling air does the job. The cylinder-walls should not heat up the air before compression, but also not cool down the gas at the combustion. A compromise is a wall temperature of 90°C. The viscosity of the oil is optimized for just this temperature. Any cooling of the exhaust and the turbine of the turbocharger reduces the amount of power available to the turbine, so the exhaust system is often insulated between engine and turbocharger to keep the exhaust gases as hot as possible.

The temperature of the cooling air may range from well below freezing to 50°C. The cooling system is designed to vary cooling so the engine is neither too hot nor too cold. Cooling system regulation includes adjustable baffles in the air flow (sometimes called 'shutters' and commonly run by a pneumatic 'shutterstat); a fan which operates either independently of the engine, such as an electric fan, or which has an adjustable clutch; a thermostatic valve or just 'thermostat' that can block the coolant flow when too cool. In addition, the motor, coolant, and heat exchanger have some heat capacity which smooths out temperature increase in short sprints. Some engine controls shut down an engine or limit it to half throttle if it overheats. Modern electronic engine controls adjust cooling based on throttle to anticipate a temperature rise, and limit engine power output to compensate for finite cooling.
Finally, other concerns may dominate cooling system design. As example, air is a relatively poor coolant, but air cooling systems are simple, and failure rates typically rise as the square of the number of failure points. Also, cooling capacity is reduced only slightly by small air coolant leaks. Where reliability is of utmost importance, as in aircraft, it may be a good trade-off to give up efficiency, durability (interval between engine rebuilds), and quietness in order to achieve slightly higher reliability — the consequences of a broken airplane engine are so severe, even a slight increase in reliability is worth giving up other good properties to achieve it.

Cheers
John

 

[gjs238]

Right from Wikipedia

 

[Readie]

Right from Wikipedia

Yes, I couldn't find a more succinct source. Other than a degree in Physics !
Cheers
John

 

[Lighthunmust]

It was in the 30s that liquid cooling was considered essential. Part to it was theory. They hadn't really done much for trials. Aircooling wasn't developed as much as it was just a few years later. This liquid went along with the "hyper" cylinder or engine and we know how that turned out.

The P&W R-2800, fine as it was, may not have been able to power a B-29. There is not only take-off power and Military power but Cruising powers to consider. The R-3350 may have had a max cruise power using auto-lean settings of several hundred horsepower more than the R-2800. Considering that these max auto lean settings produced power down around 1200hp an extra couple of hundred HP is actually quite a percentage change.

As you frequently are, I think you are correct about the R2800 being marginal. I admit I have a bias toward P&W over Wright.
It is my understanding that the primary problem with the R-3350s on the B-29 was insufficient cooling due to cowl design. The result being failures and fires. The fires burning through the wing in less than a minute with catastrophic wing failure occurring.

 

[Readie]

As you frequently are, I think you are correct about the R2800 being marginal. I admit I have a bias toward P&W over Wright.
It is my understanding that the primary problem with the R-3350s on the B-29 was insufficient cooling due to cowl design. The result being failures and fires. The fires burning through the wing in less than a minute with catastrophic wing failure occurring.

I copied this from Wiki for interest and my learning...

By 1943 the ultimate development of the new bomber program, the B-29, was flying. However the engines remained temperamental, and showed an alarming tendency of the rear cylinders to overheat, partially due to minimal clearance between the cylinder baffles and the cowl. A number of changes were introduced into the aircraft production line in order to provide more cooling at low speeds, and the planes were rushed to operate in the Pacific in 1944. This proved unwise, as the early B-29 tactics of maximum weights combined with high temperature airfields produced overheating problems that were not completely solved, and the engines had a tendency to swallow their own valves. Because of a high magnesium content in the crankcase alloy, the resulting engine fires were often so intense the main spar could burn through in seconds, resulting in catastrophic wing failure.
Early versions of the R-3350 were equipped with carburetors, though it was the poorly designed elbow, or entrance to the supercharger that led to serious problems with inconsistent fuel/air distribution. Near the end of World War II, in late 1944, the system was changed to use direct injection where fuel was injected directly into the combustion chamber. This change improved engine reliability immediately. After the war the engine was redesigned, and became a favorite for large aircraft of all designs, most notably the Lockheed Constellation and Douglas DC-7.

Got there in the end
Cheers
John

 

[Lighthunmust]

Right from Wikipedia

Yes, I couldn't find a more succinct source. Other than a degree in Physics !
Cheers
John

What search terms are you using on wikipedia?

I don't doubt your veracity, considering all the individuals in positions of power within the USAAC during the 1930's with certitude on so many ideas that the events of 1939-45 quickly showed to be very wrong.

If the "Brass" was fixated on liquid cool performance it is the same thing narrow vision that resulted in the battlecruiser. I'm sure you know how unsuccessful those faster, similarly armed, but more vulnerable, battlecruisers fared when facing slightly slower, similarly armed, but less vulnerable battleships. The idea that they were enamored with inlines is especially interesting considering that radials were used on every major design after 1935. Perhaps this is more due to availability than desire, but thank goodness it happened.

When I first posted the issue of mechanical reliability I was also implying mechanical reliability under fire. B-17s and B-24s with liquid cooled engines would have resulted in many more loses from enemy fire.

 

[Readie]

What search terms are you using on wikipedia?

I don't doubt your veracity, considering all the individuals in positions of power within the USAAC during the 1930's with certitude on so many ideas that the events of 1939-45 quickly showed to be very wrong.

If the "Brass" was fixated on liquid cool performance it is the same thing narrow vision that resulted in the battlecruiser. I'm sure you know how unsuccessful those faster, similarly armed, but more vulnerable, battlecruisers fared when facing slightly slower, similarly armed, but less vulnerable battleships. The idea that they were enamored with inlines is especially interesting considering that radials were used on every major design after 1935. Perhaps this is more due to availability than desire, but thank goodness it happened.

I just put my question /thoughts etc onto google and see what comes up. Or, I read my books...

The RN made some howlers with HMS Hoods armour. Its 3 knot advantage was no match for her 1918 designed armour. Central magazines was another blind alley.
Mind you, all of this is said with the benefit of hindsight.

I couldn't agree more that we were lucky to have the stalwarts we had in WW2. Liquid or Air cooled are two approaches to achieve the same thing. The ultimate piston engined aircraft. I have favoured liquid for the reasons I rather clumsily tried to show in an earlier post but, I fully accept that the last double radials had their measure in power / weight .

The USA radials and Bristol Centaurus are superb.

Cheers
John

 

[Shortround6]

I don't doubt your veracity, considering all the individuals in positions of power within the USAAC during the 1930's with certitude on so many ideas that the events of 1939-45 quickly showed to be very wrong.

If the "Brass" was fixated on liquid cool performance it is the same thing narrow vision that resulted in the battlecruiser. I'm sure you know how unsuccessful those faster, similarly armed, but more vulnerable, battlecruisers fared when facing slightly slower, similarly armed, but less vulnerable battleships. The idea that they were enamored with inlines is especially interesting considering that radials were used on every major design after 1935. Perhaps this is more due to availability than desire, but thank goodness it happened.

Not really a good analogy. Battlecruisers were quite successful when used for what they were designed for, fighting armoured cruisers. They were not intended to be fast battleships no matter what the press releases said.

The decade between 1930 and 1940 was one of tremendous development in aircraft engines and fuel. Any boob can supercharge the crap out of an engine and get a lot of power for a few seconds. The trick is getting th engine to last for several minutes at such power, and even more important, getting the engine to go several hundred hours between overhauls. The big enemy of high performance engines is heat. the cooler you can get an engine to run the more boost you can use for more power. Many engine designers of the time started by designing a cylinder to get the most power they could from it and then laid out the engine/multiplied the cylinder to get the desired power for the complete engine. Liquid cooled cylinders could make more power for the same size as aircooled engines could. part of this was just the levels of technology of the time ( which actually changed almost by the year). A high powered aircooled engine needs cooling fins, lots of them and big ones. In a lot of cases the depth of fin and the spacing was beyond the state of the art in casting technology so fins had to be machined. As casting, forging, machining technologies improved more and deeper fins could be put on cylinders (and heads) to allow for better cooling and more power. A few figures from P &W will show the trend. The 1927 wasp cylinder was 149 cu in and good for about 45hp with a total fin area of 1200 sq in. By 1932 the 131 cu in twin wasp cylinder was good for about 67hp and had 1500 sq in of finning. By 1940 the R-2800 cylinder of 155cu in had 3100 sq in of finning for its roughly 100hp per cylinder and the "C" seies cylinder of 1945 had 4300 sq in of finning for it's 125 hp per cylinder. Sq in of fin per HP varied from 26 on the wasp to 34 on the "C" series R-2800.
Wright engines showed similar massive increasing in finning ending with the famous sheet metal fins rolled and caulked into machined grooves. The Bristol Hercules went through at least 4 different cylinder head designs with increased finning as it's power went up.
Without these manufacturing break through's in casting, forging and machining the aircooled engine could have hit dead ends. At times during the 30s the future of the aircooled engine's ability to compete with the liquied cooled engine didn't look good. The air cooled makers managed to keep pulling tricks out of their bag but betting on what would happen 3-5 years down the road was never a sure thing.

 

[davparlr]

The P&W R-2800, fine as it was, may not have been able to power a B-29. There is not only take-off power and Military power but Cruising powers to consider. The R-3350 may have had a max cruise power using auto-lean settings of several hundred horsepower more than the R-2800. Considering that these max auto lean settings produced power down around 1200hp an extra couple of hundred HP is actually quite a percentage change.

Spitfireperformance has good data on the R-2800 under P-47M performance however I could only find rudimentary info on the 3350. What I found was that the 3350 max continuous power at 28k was 2050 hp, the R-2800 in the P-47M had a max continuous power of 1650 hp there, and at most altitudes up to 33k. Now, I think the 3350 was supercharged, not turbocharged, if so, power might drop off quicker than for the turbocharged 2800, which did not drop off.