Radial vs in-line engines

[reflected]

I was thinking about WWII planes and I realized that most radial engines were much more powerful than in-line engines.
Let's take the Corsair or the Thunderbolt for example, with their 2000+ HP P&W, whereas Spits and 109s were a little above 1000. Is there a technical explanation for that?

[Davedog74]

because your comparing 1940 engines with later engines,

[reflected]

Is that so? OK, I was wondering about that too.

Then, what decided between an in-line and a radial engine when they designed these machines? I guess radials were easier to cool but they produced more drag, but I might be wrong.

Wait, I'm not sure those late war Griffons or DB-s ever reached the 2200 HP of a P&W ? So there might be something after all?

[Tacoma74]

The way I've always looked at it is that a big radial may produce a lot of power and be very torquey, but they're is enivitably a quite larger amount of drag introduced to the nose of the plane. A 109 on the other hand for example has a more "bullet shaped" nose with the inverted v-12, thus being more streamlined and needing less power to pull it through the air.

[Davedog74]

seafire 47 had 2300 hp but was post war most fighters were radials post war,so i guess radials were the way to go,im pretty sure they took more of a beating,im sure the real experts on here will tell us why

[Welshman]

MK 14 spit was 2035hp

[Sternjaeger II]

the debate Radial VS Inline is as old as the planes they were installed onto.

They both come with pros and cons, here are the most common ones:

Radial PROs
Very high TBO/extremely dependable
Resistent to damage/gives protection to pilot
air cooled, no need for cooling ducts/radiators etc
huge displacement/HP

Radial CONs
lotsa drag/bad forward visibility
oil thirsty
strong gyroscopic torque (the rotating crankshaft counterweight and big prop blades can cause the plane to torque itself out of delicate situations like pre-stall if full throttle is applied, still present on inline engines, but not as strong)
avgas thirsty
needs big supercharger
heavy

Inline PROs
streamlined engine
lighter than radial
more fuel efficient
lighter superchager
better fwd visibility

Inline CONs
needs liquid cooling/radiators
more susceptible to damage (can't fly with one or more pistons damaged)
shorter TBO


I suppose it's down to pilot's preferences and for the tasks assigned.

One of the bigger question marks in the history of warfare for me was the use of Mustangs in Korea, when P-47s would have probably done a better job.

[Crumpp]

Good summary, Sternjager II and all.

larger amount of drag

In general, yes but as long as the designer pays attention to the installation of an aircooled motor, the Cd0 is not necessarily higher. Look at the Zeke, Corsair, F6F Hellcat, or Focke Wulf series. All have average to below average Cd0 for the period. In fact very few inline installations approached the Cd0 of the Zeke.

Consequently there are inline installations that have much higher drag than radials.

heavy

Only when comparing dry weights. Add in the radiators and coolant and their is little to choose in terms of weight.

In terms of TBO, liquid cooling wins out. Temperatures are much more stable across the engine in comparison to air cooled engines. Air cooled cylinders can vary over 100 degrees in normal operation just from fuel metering alone.

http://www.liquidcooledairpower.com/lc-longertbo.shtml

[Sternjaeger II]

Originally Posted by Crumpp

Good summary, Sternjager II and all.

In general, yes but as long as the designer pays attention to the installation of an aircooled motor, the Cd0 is not necessarily higher. Look at the Zeke, Corsair, F6F Hellcat, or Focke Wulf series. All have average to below average Cd0 for the period. In fact very few inline installations approached the Cd0 of the Zeke.

Consequently there are inline installations that have much higher drag than radials.

yeah, but in the end of the day you need a higher number of HP to compensate for the drag, and even if you implement ram fans like on the FW190, you still need air to go through the cyl heads and out from the sides in a very turbulent fashion. No matter how "polished" your radial design is, it's still a radial

Only when comparing dry weights. Add in the radiators and coolant and their is little to choose in terms of weight.

I suppose it depends on the specific plane really. A Thunderbolt would have a chunky turbo supercharger installed in the fuselage and oil coolers in the engine cowl, that adds a lot of weight as well. Let's not forget that the Merlin has a higher power to weight ratio other than a lighter dry weight.

In terms of TBO, liquid cooling wins out. Temperatures are much more stable across the engine in comparison to air cooled engines. Air cooled cylinders can vary over 100 degrees in normal operation just from fuel metering alone.

http://www.liquidcooledairpower.com/lc-longertbo.shtml

mmmmh, again, it really depends on engines. It's not a good idea to run a Merlin, even with transport heads, beyond 600 hours, while a well maintained radial has more than double that TBO. In fact, apart for certain non certified ones, I can't think of any radial with a TBO below 500 hours, while there are many many many inlines that are below that (the DB family being the extreme example).

Temperature is not the only factor, and whilst a coolant system failure can be catastrophic, a radial can survive prohibitive temperatures, thermal shock and component failure, and still do its job.

[Igo kyu]

The Sabre http://en.wikipedia.org/wiki/Napier_Sabre was a 2,000 hp inline.