Radial vs liquid cooled engines

[swampyankee]

Depends on what? Horsepower? Design?

Power, design, installation, operation. Engines for commercial and civil aircraft were mostly air-cooled; cost of operation, including cruise fuel consumption would be highly important. These factors would be less important to air forces, which were the main customers for liquid-cooled engines.

A complicating factor is that a large portion of the large radials were in multi-engine aircraft, which frequently had a flight engineer, whose job involved monitoring and tweaking engine performance.

 

[Clayton Magnet]

The verdict of history? Air cooled radial wins. Almost all of the post war heavy hitters, DC-7, Stratocrusiers, Constellation, C-124, Brabazon, used air cooled radials.

Wouldn't this be better explained by the fact that post war aviation was almost exclusively dominated by American types, and they for the most part stopped developing in-line aero engines after the Allison? Aircraft piston engine development kinda leveled off and stopped in the 1950's, so whatever was popular then is what tended to stick. The vast majority of aircraft with piston engines today use American air-cooled designs, without any real advancements since the 40's or 50's. A O-360 in a brand new Piper or Cessna today is about the same thing as an O-360 from 1955.

 

[Clayton Magnet]

I don't think anyone would argue that in general, air cooled engines are more damage tolerant, but the degree of which gets blown out of proportion. Was the Corsair not known to have a "glass jaw", in the form of oil cooler placement? And what kind of blow-torch effect would a punctured component in a P-47's elaborate turbo ducting cause?

 

[swampyankee]

Wouldn't this be better explained by the fact that post war aviation was almost exclusively dominated by American types, and they for the most part stopped developing in-line aero engines after the Allison? Aircraft piston engine development kinda leveled off and stopped in the 1950's, so whatever was popular then is what tended to stick. The vast majority of aircraft with piston engines today use American air-cooled designs, without any real advancements since the 40's or 50's. A O-360 in a brand new Piper or Cessna today is about the same thing as an O-360 from 1955.

US dominance, especially in transport aircraft, is certainly one factor, but the USSR followed the same trend.

 

[KiwiBiggles]

With all the anecdotes in this thread about P-47s, F6Fs etc making it home having lost a pot in combat, it has to be asked, was the R2800 especially prone to losing cylinders due to combat damage? Maybe the lack of stories about Spitfires coming home with pistons hanging out the top of the engine just reflects that the Merlin didn't lose cylinders.

 

[BiffF15]

Or that they didn't make it home when they did.

I have a bud who used to fly at Stallion 51. He lost a cylinder and ended up landing immediately at Avon Park. Obviously the prudent thing to do due to fear of losing the engine and or the aircraft.

Cheers,
Biff

 

[Shortround6]

An air cooled engine, the vast majority of the time, used separate cylinders. You can have one shot off or blow one off with detonation (or crappy maintenance?
and the rest of the engine is relatively unaffected (valve trains, intake and exhaust manifolds, cooling for the most part). Granted you are losing oil by the bucket and the engine is hardly running smooth/even which does not bode well for long term (15-20 minutes?) life.

Liquid cooled V-12s used 6 cylinders to a block, you aren't going to lose one cylinder. A "Hit" that takes out one cylinder on a radial is going to put a really big hole in the cooling system, it may take out part of the oil system, If it hits in the valve area it may take out the camshaft which can stop several cylinders (up to six) or maybe just a few rockers on adjacent cylinders (they are closer together than on a radial). IF the cylinder head starts to lift for any reason you may lose compression in several cylinders.

One wonders at the resistance to combat damage of other radials. Excluding the French Hispano Suiza radials (which were known to lose their propellers with absolutely no help from the enemy.) did the Wright R-2600 have a reputation for getting back with missing cylinders? Or the Hercules?
Please note that the Armstrong Siddeley Tiger in early Whitleys was banned from overwater flights before the shooting even started. Gnome Rhone engines and their derivatives (Russian M-88 and Italian Piaggio ) had no center bearing on the two throw crank so their ability to run for very long with a cylinder and piston gone is rather suspect.

I am also sure that plenty of R-2800s didn't make it home after taking hits to the engine.

 

[fastmongrel]

The Fairey Swordfish was also known for coming back with its Bristol Pegasus missing a pot. Mind the Peggy made such a noisy clatter I bet sometimes the crew didnt notice they had an 8 cylinder

 

[RCAFson]

Some PR for RR:

View: https://www.bbc.com/news/av/uk-england-derbyshire-45220185/how-ernest-hives-merlin-engine-powered-the-spitfire

 

[Reluctant Poster]

The USN did a study of "aircraft loss and damage in relation to components affected by Japanese fire". The table I have attached is from the Rand Corporation Study "Aircraft Vulnerability in World War II" dated 12 July 1950.
There is a lot of fascinating reading in this document. I was surprised to learn, as Clayton Magnet mentioned, that the Corsair did have a "glass jaw" with a higher loss to hit ratio than any other single engine navy aircraft.
A lot of it is as expected
The B-24 was more vulnerable than the B-17
Don't get hit by 20 mm cannon
Aircraft are deadlier than AA
Bombing Germany was much more dangerous than bombing France
The P-47 was much more resistant to AA than the other 2 but the P-51 is only a bit worse than the P-38
The P-47 was somewhat better than the P-51 in air to air but the P-38 was significantly worse
The B-26 was a lot tougher than the B-25
The most vulnerable part of a heavy bomber was the engines. Sadly a lot of B-17s were lost because the emergency prop feathering oil reserve was deleted to save weight
" With only 10% of P-38's returning after one engine was disabled , it is evident that in most cases the disablement of either engine led to the loss of the aircraft. Thus contrary to what might be expected , the second engine of the P-38 probably increased the vulnerability of the airplane."

 

[swampyankee]

I think it's likely that a twin-engined fighter that loses one engine in combat is going to be extremely vulnerable, as the aircraft's performance is severely degraded. In addition, since early P-38s also only had a generator on one engine, losing that engine means that little things like radios and radio navigation equipment are running off battery, which may not last quite long enough.

Even with aircraft with liquid-cooled engines, details of the cooling system design can make a huge difference. An aircraft with a nose-mounted radiator, like the V-12 FW190s and the P-40, are less likely to suffer damage to the cooling system from fighters, at least, than an aircraft with a radiator mounted in the wings or in the rear fuselage, first simply because fighters are going to be attacked by other fighters most often from behind, and secondly, because the nose-mounted radiator will have much shorter coolant lines.

 

[Shortround6]

On the P-38s the propellers were electric which means on the early ones (and early means somewhere into the 'J's) if the battery failed after the engine with generator was lost you could no longer adjust the pitch of the prop on the remaining engine. A long flight home could mean turning off the radios and other stuff (panel lights?) and only turning them back on periodically to save the battery. Electricity was also needed for the aux fuel pumps, turbo regulators, oil cooler and intercooler exit flaps (on the later P-38s) pitot tube heating, and instruments.

There were instances in the CBI theater of P-38s making return flights of 600 miles on one engine. However there were only a few squadrons in the theater using P-38s so perhaps the number of times this was done is not statistically significant ?

 

[Clayton Magnet]

I used to work on pipeline monitoring aircraft, specifically Piper Navajo's, and it was known that losing an engine at that altitude meant that the other one would just carry you to the crash site. So having two engines just meant we were twice as likely to crash

 

[PWR4360-59B]

I used to work on pipeline monitoring aircraft, specifically Piper Navajo's, and it was known that losing an engine at that altitude meant that the other one would just carry you to the crash site. So having two engines just meant we were twice as likely to crash

Sure glad the FAA doesn't agree with you, if they did all the jet passenger aircraft would have 4 engines again.

 

[swampyankee]

Sure glad the FAA doesn't agree with you, if they did all the jet passenger aircraft would have 4 engines again.

Or one

The single engine rate of climb rules for light twins are quite a bit laxer than those for largish jet commercial aircraft.

 

[Clayton Magnet]

if they did all the jet passenger aircraft would have 4 engines again.

Jet passenger aircraft generally don't operate below the tops of trees, looking for gas leaks in pipelines. A Navajo that loses an engine at that altitude, while in a 30 degree bank is going to crash.

 

[PWR4360-59B]

So would almost any plane. In a 30 degree bank at 50 feet off the ground. And besides that sounds like a job for a Cessna 150 not a fast twin.

 

[Clayton Magnet]

Agreed. That's why the company reverted to modified 172's for the role. Far better downward visibility, and far lower maintenance costs, even with the extra fuel tank STC's. But somebody had the brilliant revelation that a twin would be safer. And they then selected an aircraft with props swinging in the same direction, so if you lose the right engine, you lose rudder authority.

 

[swampyankee]

Agreed. That's why the company reverted to modified 172's for the role. Far better downward visibility, and far lower maintenance costs, even with the extra fuel tank STC's. But somebody had the brilliant revelation that a twin would be safer. And they then selected an aircraft with props swinging in the same direction, so if you lose the right engine, you lose rudder authority.

Quite few modern twins have handed propellers. Lack of rudder authority is because the fin and rudder were too small.

 

[PWR4360-59B]

I have flown only single engine stuff, but I do know when you have an engine out on a twin you also pull out the running engine as well, back to low to no power and recover then slowly add the power. And not doing so is why an engine out on a twin can bring it down.