WesWorld

Something that I'm thinking about for some time now.
In history we have some examples of air frames with radial and inline engines, LaGG-3/ La-5,Yokosuka D4Y1/D4Y3,Focke-Wulf 190A/D and Kawasaki Ki-61/Ki-100
(there are more but ones that did not enter combat I'm omitting as there are not enough data on them) that I know of.
That are the best examples as Jug vs Mustang debate is not too useful for me as those were vastly different planes. Design with vastly different principles in mind,although both were long range escorts.

So far I have those pro's and con's on each engine

Radial engines have simple construction which in it self is an enormous bonus, less parts means less things to go wrong less things to make and maintain.
(Simple also means that when You shoot at it it wont blow up that easily)
Con that I know is that they have large frontal surface there of more drag, more drag equals to less speed.
Also some thing that is both pro and a con.
Air-cooling although it simple it also less effective that liquid-cooling.
Trying too increase it(cooling) effectiveness will also increase the mass dramatically.

Inline engines have smaller cross section(less drag etc...)
But are complicated and require liquid cooling.

That is all I know about the engine design it self.
As for practical application.
Inline engine powered planes performed better at altitude, many planes had a cannon up to 45mm in caliber firing thou propeller hub,some thing one cannot do in a radial powered plane.Inline engines are much less resistant to damage there cooling systems radiators and coolant lines can be destroyed and the whole engine will die.
That is not a problem with radials as they are air-cooled and don't have delicate cooling.

I found debates of inline vs radial with the Thunderbolt vs Mustang debates. Jug was better suited for ground attacks,P-47 had a heavier and tougher airframe and it was not all about the engine althou it helped.We cannot forget the Tempest a great British fighter by many consider best ground attack platform of WWII which had a liquid-cooled inline engine.Il-2 Sturmovik and it successor Il-10 also had inline engines.During the war soviets did make a radial powered Il-2 variant but supply problems with AM-82 engine force them to abandon the project,That may support the "Inline no good for attack plane" argument, but when the war was ending and a Il-10 successor was developed and there was no problems with radial engine supply, it retained the inline liquid cooled power plant.
As for In-line are better interceptors well J2M Raiden build from start as an interceptor had a radial engine, that is not saying much as it effectiveness was never proven or disproven for that matter.


As for the above mentioned planes with radial and inline power plants

LaGG-3 was a plane that had its down sides it was too heavy and was loosing air speed fast in continued maneuvers.Time and time again I found a claim that with attaching a AM-82 radial to the frame a poor fighter was made a great fighter.
What those who claim that are forgetting is that La-5FN the plane that outclassed early Bf-109G and Fw-190A's that had a long development behind it. It first incarnation the La-5 was considered inferior to LaGG as was it next model the La-5F only on the third try did the Lavochkin bested the LaGG-3 and the production of the in line variant was droped.

D4Y Suisei dive bomber with started it life with a in-line later was equipped with a radial that was do the fact that Aichi Atsuta engine was so hard to maintain(the fact that japanise personnel was not familiar with in-line liquid cooled engines didn't help)With the switch of the Atsuta for Kinsei the ceiling and rate of climb improved, higher fuel consumption resulted in shorter range and a slower cruise speed, while the bulky engine obstructed the forward and downward view of the pilot, hampering carrier operations.

As for the Focke-Wulf 190 perhaps the most famous engine switch in aviation history.The D model "was intended to improve on the high-altitude performance of the A-series enough to make it useful against the American heavy bombers of the era"and,compared with the FW 190A-8, Dora-9, had a greater level speed, climb rate, and ceiling.Was much quieter - the Jumo 213A vibrated much less than the BMW 801(It may appear unimportant but less noise less vibration less vibration the longer it will take for some thing to brake of.

The Kawasaki Ki-61-I was a good plane and it next version Ki-61-II equipped with an upgraded engine enterd production. Then a really annoying thing happened the factory that made He-140 engines got bombed by B-29,
So the jap's were sitting with a factory full of airframes with no engines for them. So they did the same thing they did with Judy they put a Keisei in it.
This aircraft build out of necessity turned out to be one of best fighter aircrafts of WWII.
Compared with Ki-61-II it was some 300kg lighter and had the same horse power, there for better everything apart from diving speed.

So do you have an opinion in this matter? Thank for the help.

You get people who are in favour of one or other but really it depends on the application. If you want something to go fast then the liquid cooled inline is probably a better choice. Reading discussions on the subject on the internet you'd think that radials are invulnerable to damage but this is definitely not the case.

The radial is invulnerable to damage... unlike the rest of a plane.


I seem to remember reading something somewhere on the internet about the radials performing better over sea while the inlines perform better over land. Can't remember where exactly I read that and how much of that is true...

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Originally posted by Rooijen10
I seem to remember reading something somewhere on the internet about the radials performing better over sea while the inlines perform better over land. Can't remember where exactly I read that and how much of that is true...

Not really true. So far as damage, a US study of radial engined planes found only 25-30% returned to base after any hit to the engine and only 20% for any hit to a fuel system. There are some examples of radials surviving after having cylinders shot away but they are fluke events in a massive data sample.

I was referring to engine performance, not survivability. Sorry if that was not clear.

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Originally posted by Rooijen10
I was referring to engine performance, not survivability. Sorry if that was not clear.

Performance differences from over land or sea makes no sense. The sea salt tends to corrode things a fair amount (the R-3350 engines on the P2V at Cosford are awful) but that would give an advantage to the liquid cooled type as you simply replace the exterior parts but the engine block remains fine. With an aircooled engine its a case of replacing the engine rather than replacing the fins.

Liquid cooled engines are cooled more effectively and so are able to make a greater specific power and have lower fuel consumption. Power/weight ratio is less obvious as theres a large choice of data to make comparisons from.

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Originally posted by Red Admiral

Not really true. So far as damage, a US study of radial engined planes found only 25-30% returned to base after any hit to the engine and only 20% for any hit to a fuel system. There are some examples of radials surviving after having cylinders shot away but they are fluke events in a massive data sample.

The question I have regards the additional vulnerability of having a liquid cooling system. Some of the rounds that hit a liquid cooling system would have continued to hit the engine, coolant or fuel system

My understand is basically a hit of any type = engine will seize later.

If that means a radial has the following critical systems :
Pilot
Engine
Oil ?
Fuel (partial with sealing tanks)

While the in-line adds an additional critical system,
coolant

So it comes down to if a round would have perforated the cooling system (would 20mm shell fragments?) what would it have hit in the same spot in a radial.
Even if the answer is the engine, that is a drop of ~25-30% on the loss rate. Now if in some cases the answer is "frame" or "air" etc, that difference could rise.


As for Sturmoviks, the data set presented is insufficient to draw a conclusion. Those 10,000 ground fire losses may be from a pool of 100,000 hits. The pilot quality or planes or maintenance could respond worse to damage. Limited training could lead to poor doctrine and taking a higher number of hits, their lower speed and altitude could mean more hits in the same period of time, any number of potential reasons.

I agree, too tenuous a link is claimed between Sturmovik losses and engine type; if we could compare a radial and in-line Sturmovik over the same period over the same types of actions, I would be more willing to draw a conclusion.

Its a very tenuous link thats proves absolutely nothing. P-47s and Il-2s are not flying the same missions and they're not against the same targets so its difficult to compare. Then how do you judge whether it's been hit in the engine or not?

Its interesting to note that the Typhoon and Tempest were the main RAF fighter-bombers, both with liquid cooled engines but their vulnerability is not apparent. Mostly, anecdotes are with regards to how durable they were.

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My understand is basically a hit of any type = engine will seize later.

It might seize later. It is unlikely that a single hit to the radiator will drain all the coolant and even then there is a fair amount of heat that is able to be rejected from other means. In cruise condition around 25-30% of the heat is rejected through the radiator (around 12-15% at full power but total heat transfer greater). Throttling back to lower powers will prolong the engine life. There are a couple of examples of P-51s having their radiators shot away over Germany but making it home.

Liquid cooled engines are more vulnerable but take into account the smaller size and lessened chance of hitting, the greater ease of armouring and there's very little difference.

Another data point on the subject are the ground-attack variants of the Fw-190, the F, G, and D-12. The first two are modified versions of the radial-engined (BMW-801) Fw-190A series, while the last is a modified version of the inline-engined (Junkers Jumo 213) D series.

Radials, generally, offered more total horsepower, in a less aerodynamic package, and had one less system to go wrong. Depending on what radials vs inlines a country had, either or both would be used in any role.

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The British did not have good radials despite their Napiers and Bristols.

What nonsense, the Hercules and Centaurus were excellent engines. Napier didn't make any radials. Armstrong-Siddeley and Alvis also produced good designs but for smaller applications.

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Not true. Spitfire was a classic case in point;. One hit in the radiator and down she went. Same for any Messerschmidt of any make.

Again nonsense, you have no proof.

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Radials, generally, offered more total horsepower,

Thats simply because they were larger. The specific power they are able to produce is considerably less.

Spitfires v Zeros over Australia has nothing to do with inline vulnerability. It has a great deal to do with a massive tropical filter robbing power, dust destroying the engines, having no spares and limited numbers of trained mechanics. Then you push the engines far over their limit by doing fast full power climbs in hot conditions to high altitude.

That is not evidence. The Australians moved to P&W because those engines were more available.

To get the same power, the cylinder dimensions and displacement have to be larger for an air cooled engine. Thats in addition to being larger overall because of the general arrangement.

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Why did Pratts outperform the Bristols and Napiers?

But the P&W engines didn't outperform the Bristol radials or the Sabre.

Centaurus v. R-2800; Centaurus is more powerful, lighter and has better fuel consumption but is a few litres larger

Centaurus v. R-3350; Centaurus is more powerful, much lighter, has better fuel consumption and considerably more reliable. Engines almost the same displacement

Sabre v. anything, more power, excellent p/w ratio, good fuel consumption, small size, very reliable by 1944/45

Bristol had their own 28-cylinder four row radials with a variety of cylinder dimensions with power up to around 4200hp (and easily more)

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2. The Merlins failed later. Seafires were wiped out over Balikpapan in 1945! This time it was by Oscars when the BPF tried to do a raid. Those were FAA and they didn't have any Darwin excuses, then.

Meanwhile Merlin powered Mustangs were eating, much better, Japanese aircraft for breakfast over Tokyo.

The probelm wasn't with the engine, it was with the crappy airframe. *ducks behind concrete wall*

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The Australians moved to Pratts because Bristol hadn't worked the bugs out of their radials.

No. It was because the P&W engines were available.

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2. The Merlins failed later. Seafires were wiped out over Balikpapan in 1945! This time it was by Oscars when the BPF tried to do a raid. Those were FAA and they didn't have any Darwin excuses, then.

More nonsense.

All I've got to say is that you're incredibly biased and in denial of fact yet again.