Radial vs liquid cooled engines

[Timppa]

What's the difference? Frontal area, drag? For the same hp, that is.

Ultimately, well designed radial engined plane did not have more drag. The most obvious examples are airframes that used both types:
Tempest V - Tempest II
LaGG3 - La7 (in this case the latter had actually less drag)

Of the early war planes you may compare Bf109E and A6M3, both with about the same power and same speed.

 

[wuzak]

Corect me if I'm wrong, but the LaGG 3 had susbtantially less power than the La 7.

And there were some liquid cooled installations that weren't well designed.

When using leading edge radiators the Tempest I was some 20mph faster than the Tempest II with less power. And a Tempest V with an annular radiator was also about 20mph faster than the Tempest II. One Fury prototype was also fitted with the Sabre with annular radiator, an was about 25mph faster than the Centaurus version. In both those examples the Sabre had a bit more power (about the same difference between Tempest II and standard Tempest V).

I don't know much about the A6M3 to compare. E had a top speed of around 355mph.

 

[Shortround6]

There are definite limits as to how big you can make a cylinder, either air cooled or liquid cooled without resorting to trickery like triple ignition. There are limits on stroke, both in piston speed and from a fuel burn stand point. This rather restricts engine configurations.

The DB 603 and the Russian AM-35/38 series were about as big as you could make a V-12. 18 cylinder engines are pretty much limited to radials and triple banked inlines (arrow head engines?). Going to 24 cylinders solves the displacement problem for the inline ( read liquid cooled) but leaves the choice of one crankshaft or two. One didn't seem to work well. The more cylinders the higher the maintenance load.

The Griffon and the Sabre were almost the same displacement, the Sabre was more powerful (maybe/depending?) but was about 500lbs heavier for a single stage Sabre vs a two stage Griffon. That is without cooling systems. Power available over 20,000 is a lot closer than power down low.
The Centaurus is about 150-200lbs heavier than the Sabre but has no cooling system (ok a bigger cowl and cowl flap set up) Power at altitude may favor the Sabre, Max cruise may favor the radial.

When comparing top speeds it is nice to know the altitudes. Changing altitudes by even 2,000ft can mean around a 4% difference in drag.

Comparing identical or near identical airframes with different engines is hard enough. trying to draw conclusions from different airframes with different engines introduces too many variables.

On a small scale the Fairchild 24 cabin monoplane was available for a number of years with either the inline 6 air cooled Ranger engine and the Warner radials. over the years the HP of the engines did vary but in general given engines of the same power the Rangers were faster but the Warner radial powered planes, being lighter, climbed better.

 

[gjs238]

A question here, civilian airliners before the Jet Age all seemed to be radials. Was there a reason for this? Were there any liquid cooled airliners? I know fighting and flying and just flying are different goals but the radial engine era seemed to last until jets took over.

Didn't blimps and Zeppelins use water cooled engines?

 

[gjs238]

Did the U.S. Navy ever use a liquid cooled engine on the planes operating from carriers?
I'm not aware of a single one.

Didn't that have something to do with storing ethleyne glycol on ships?

 

[stona]

Didn't that have something to do with storing ethleyne glycol on ships?

Why would that be? It's not particularly flammable,certainly when compared to aircraft fuels,nor is it difficult to store. Typical flash point of petrol (gasoline)is around -40 C whereas ethylene glycol is over 100 C.

I'm just wondering,it maybe the US Navy had a good reason I'm unaware of. You wouldn't want your matelots drinking the stuff

Steve

 

[Shortround6]

A question here, civilian airliners before the Jet Age all seemed to be radials. Was there a reason for this? Were there any liquid cooled airliners? I know fighting and flying and just flying are different goals but the radial engine era seemed to last until jets took over.

The only liquid cooled airliners were a Few Canadian and British plane using Merlins. At the time the British (including the Commonwealth) had one heck of a trade deficit problem and foreign (meaning US) engines simple could not be afforded. That left the Merlin, Griffon, Sabre, Hercules and Centaurus engines. The Sabre and Griffon found no takers at all in the commercial field and Rolls, by expending a fair amount of effort and trading a bit on the Merlin reputation did make the above mentioned sales. Commercial Hercules ( even licence built in France) and Centaurus engines filled the British commercial aircraft until the jet and turbo prop.
The Americans, for a variety of reasons, dominated the post war commercial aircraft market and so did American engines, which after the Allison stopped production, meant air cooled radials.
One less system to fool with and maintain and with acceptably low operating costs ( and airline owners are a hard headed tight fisted bunch) the air cooled radial did the job.

 

[Shortround6]

Some, but the US Navy had a lot of bad experiences with water cooled engines in the 20s, Liberties, Curtiss and Packard engines and decided enough was enough. A broken water pipe over land is bad enough, a broken water pipe or leaky radiator over water is a lost aircraft and probably a lost pilot/crew. The Navy was not adverse to looking at or even funding an occasional water/liquid cooled project in order to keep abreast of the state of the art or even move for adoption should the gap between liquid and air cooled become to great.
It didn't.

 

[CobberKane]

Ultimately, well designed radial engined plane did not have more drag. The most obvious examples are airframes that used both types:
Tempest V - Tempest II
LaGG3 - La7 (in this case the latter had actually less drag)

Of the early war planes you may compare Bf109E and A6M3, both with about the same power and same speed.

The 109 had about 17% more power and 20mph more speed than the zero, so hard to draw conclusions from that. The Tempest is a good example though - I think they pinched the idea of the contra-rotating fan behind the prop from the Fw190. The 190 was probably the most influentual fighter of the war in terms of demonstrating that the radial was still right up there with LC engines.

 

[cimmex]

I think they pinched the idea of the contra-rotating fan behind the prop from the Fw190. The 190 was probably the most influentual fighter of the war in terms of demonstrating that the radial was still right up there with LC engines.

The fan behind the prop of the Fw190 has the same turning direction as the propeller but around three time the speed.
Cimmex

 

[CobberKane]

The fan behind the prop of the Fw190 has the same turning direction as the propeller but around three time the speed.
Cimmex

Sorry, I was thinking 'counter-rotating props'.

 

[CobberKane]

Sorry, created in error

 

[CobberKane]

What's the difference? Frontal area, drag? For the same hp, that is.

Yes, by saying 'for the same horsepower' you are restricting yourself artificially in the same way a motorcyle manufacturor is by saying 'we must not go beyond 750cc'. In practice the designer of the figher aircraft is going to use the engine that gives the best balance of performance, fuel consumption etc, irrespective of whether it is defficient in one particular area like drag. The fact that radial engine fighters were matching the performance of the best inline engines right up to the end of the war indicates that their disadvantage in terms of drag was not enough to place the radial engine at a disadvantage compared to the inline V in practise .
I guess in theory it would be possible to build a mile-long V-100000 with no more frontal area than a V-12, whereas a radial of increasing capacity would have to get wider and wider. In practice all that was laid aside by the jet engine, and even if for some hypothetical reason the jet could not be made to work other alternatives eventually came along for driving airscrews.

Oh, I note that someone posted yet another 'urban myth' example of a radial engine fighter gettin home with smashed cylinders (plural). Still waiting for a similar account of an LC engine doing that...

 

[gjs238]

...whereas a radial of increasing capacity would have to get wider and wider.

The radials grew in length as well as rows were added.

 

[wuzak]

Oh, I note that someone posted yet another 'urban myth' example of a radial engine fighter gettin home with smashed cylinders (plural). Still waiting for a similar account of an LC engine doing that...

I never said it was an urban myth - I said those who managed it were extremely lucky.

Drgondog already gave you an account of a P-51 which returned to base with 3 "smashed cylinders".

 

[wuzak]

Yes, by saying 'for the same horsepower' you are restricting yourself artificially in the same way a motorcyle manufacturor is by saying 'we must not go beyond 750cc'. In practice the designer of the figher aircraft is going to use the engine that gives the best balance of performance, fuel consumption etc, irrespective of whether it is defficient in one particular area like drag. The fact that radial engine fighters were matching the performance of the best inline engines right up to the end of the war indicates that their disadvantage in terms of drag was not enough to place the radial engine at a disadvantage compared to the inline V in practise .

There are practical limits to anything.

Adding length to a V engine will lead to diminishing returns because of crankshaft flexibility, and other associated issues. Adding cylinders to air-cooled radials can increase the diameter (more cylinders per row) and/or length (more rows). After a cerain number of rows it will be getting very difficult to cool the rear cylinders.

Note that liquid cooled engines can be radials too - R-2160 Tornado, Lycoming, XR-7755, BMW 803, for example. Granted, these never went beyond prototype stage.

You will notice that the air cooled engine powered fighters late in the war which matched liquid cooled ones were generally more powerful.

 

[wuzak]

Yes, by saying 'for the same horsepower' you are restricting yourself artificially in the same way a motorcyle manufacturor is by saying 'we must not go beyond 750cc'.

Thought I had better look to see what my post was in response to. And there it was - you were the one that introduced the same power level stipulation.

Having said that, if a thirty litre aircooled engine running at a lower state of tune can return similar figures to a more highly tuned twently litre liquid cooled engine, what's the difference? Unlike car or motorcycle manufacturers of today, producers of WWII aero-engines has no incentive to restrict themselves to arbitrary capacity limits

What's the difference? Frontal area, drag? For the same hp, that is.

 

[tyrodtom]

The fan behind the prop of the Fw190 has the same turning direction as the propeller but around three time the speed.
Cimmex

How much power was consumed by that cooling fan ?
If it was so successful in cooling the engine, why did no one else copy it?

 

[Shortround6]

How much power was consumed by that cooling fan ?
If it was so successful in cooling the engine, why did no one else copy it?

It was "copied". Some Martin Mariner patrol bombers used fan cooled R-2600s. The P-47J used a fan cooled R-2800 ( dropped for the P-47M&N) I am not Sure if the Russians had a few fan cooled installations of the Ash-82. At least one Bristol Hercules commercial installation post war used fan cooling. I am not sure about the Hawker tempest II or Fury.

That is off the top of my head, there may certainly well be others without getting into buried or pusher installations.

 

[cimmex]

Power needed to drive the fan was 80 to 100hp depends on 12 or14 blades.
Cimmex