3 ms·

I worry when there is a hidden assumption that people were dummies for the choices they made. That tends to be more true for policy than engineering. Distilled

I worry when there is a hidden assumption that people were dummies for the choices they made. That tends to be more true for policy than engineering. Distilled impression. Water cooled inline engines. Small frontal area means lower drag. Water cooled provides a forgiving flexible operating envelope. What you want in a fighter. Downside, more complicated. Upside better performance means kill enemy better. Air cooled radials. The drag penalty is less as the engine size increases. More reliable as long as you stay inside the design envelop. Scales up better than inline water cooled engines. Better suited for multi-engined bombers with a well defined mission profile. At the end of the war though it was obvious that turbojets were the future for fighters. Which is why water cooled engines went away. Radials though are more efficient at lower speeds than early turbojets which is why they persisted.

jabl 4y ago
I don't think it's that simple. Inline engines have less frontal area, yes, but then you need a radiator which will add back quite a bit of drag. Further, as Kurt Tank demonstrated with the, at the time, revolutionary FW 190, it's possible to make a very low drag radial engine installation. These ideas were then used in the Tempest II and Sea Fury, which were among the fastest piston engined planes ever made. Further, I'd say in history there's a lot of path dependence here (in aviation engine development as well as elsewhere, obviously) as well rather than 'pure' arguments based on the best option for a from scratch design. As it wasn't clear at the time which engine type would 'win', major powers developed both lines in parallel, if for no other reason but to not be so much behind their competitors in case some development would cause one of the engine types to clearly pull ahead. WWII showed that both air cooled radial and water cooled inlines could be used for top of the line fighters for the entire conflict. After the war, it was clear that for speed jets were going to be the future and there wasn't the wartime pressure to keep any and all production lines going at maximum capacity, so aircraft designers had more leeway in choosing powerplants. Perhaps it was because US multi-engine aircraft designers were familiar with radials and it was clear to them they were plenty good enough, perhaps it was better reliability, but radials they chose (with some exceptions, obviously).
- tengwar2 4y ago
  Radiators can add drag, but they can also add thrust which exceeds that drag. (https://en.wikipedia.org/wiki/Meredith_effect https://en.wikipedia.org/wiki/Meredith_effect).
samatman 4y ago
Generally engineers don't make dumb decisions, there are exceptions, they make plenty of hard ones. The difference between the Thompson M1928 and the M1A1 isn't that the M1A1 is superior, and yet they cranked the handle on the latter as hard as they could during the war. So "If something were better than something else, why did they make more something else during WWII?" doesn't persuade me. Nor does it eliminate other arguments which would make sense.
p_l 4y ago
Funnily enough from RAS (Reliability, Availability, Serviceabilty) British liquid cooled engines beat American radial engines so hard it wasn't funny. Mostly it was due to end to end design of entire engine pod which made all operations better. Meanwhile USA had, well, a lot of radials and radial making manufacturing lines and people who had experience with radials but little idea about much more complex liquid cooled engines.
- jabl 4y ago
  > Funnily enough from RAS (Reliability, Availability, Serviceabilty) British liquid cooled engines beat American radial engines so hard it wasn't funny. Presumably you mean the Merlin and not, say, the Sabre? :) But anyway, that's interesting, haven't heard of that before. Do you have some more information on this topic? From what I've read Americans were shocked to find out how 'hand built' the Merlins were, with pretty large differences between each engine, engines being delivered with metal filings in the crankcase requiring inspection and cleaning and whatnot. So a large part of the work Packard did for the license produced Merlin was tightening up the design so it could be mass produced much faster on production lines. Of course this doesn't prove the RAS point you made one way or the other, but it seems strange that if Americans put so much more emphasis on efficient production that they wouldn't have put similar effort into serviceability?
  - p_l 4y ago
    The issue with Merlins was that Rolls Royce was manufacturing them whenever and by whomever by the time war got into full swing, which easily explains the differences between individual engines. As for serviceability, the difference was in design - American engines were effectively "thrown over the wall" to airplane designers, resulting in such beautiful designs like B-17, where IIRC inspecting or changing a sparkplug started by removal of propeller because apparently even good idea fairy was out drinking when they designed it. In comparison Rolls Royce designed a standard "pod" for the engine that would be then minimally adapted by plane designer, with an eye towards servicing and commonality. So the tolerances might have been tighter on US production lines, but little thought was placed at least in some designs on how to support operations on the planes instead of just building them. (Something that arguably is present today with F-16 at least, and possibly F-35 too)

jabl 4y ago

I don't think it's that simple. Inline engines have less frontal area, yes, but then you need a radiator which will add back quite a bit of drag. Further, as Kurt Tank demonstrated with the, at the time, revolutionary FW 190, it's possible to make a very low drag radial engine installation. These ideas were then used in the Tempest II and Sea Fury, which were among the fastest piston engined planes ever made. Further, I'd say in history there's a lot of path dependence here (in aviation engine development as well as elsewhere, obviously) as well rather than 'pure' arguments based on the best option for a from scratch design. As it wasn't clear at the time which engine type would 'win', major powers developed both lines in parallel, if for no other reason but to not be so much behind their competitors in case some development would cause one of the engine types to clearly pull ahead. WWII showed that both air cooled radial and water cooled inlines could be used for top of the line fighters for the entire conflict. After the war, it was clear that for speed jets were going to be the future and there wasn't the wartime pressure to keep any and all production lines going at maximum capacity, so aircraft designers had more leeway in choosing powerplants. Perhaps it was because US multi-engine aircraft designers were familiar with radials and it was clear to them they were plenty good enough, perhaps it was better reliability, but radials they chose (with some exceptions, obviously).

tengwar2 4y ago
Radiators can add drag, but they can also add thrust which exceeds that drag. (https://en.wikipedia.org/wiki/Meredith_effect https://en.wikipedia.org/wiki/Meredith_effect).

samatman 4y ago

Generally engineers don't make dumb decisions, there are exceptions, they make plenty of hard ones. The difference between the Thompson M1928 and the M1A1 isn't that the M1A1 is superior, and yet they cranked the handle on the latter as hard as they could during the war. So "If something were better than something else, why did they make more something else during WWII?" doesn't persuade me. Nor does it eliminate other arguments which would make sense.

p_l 4y ago

Funnily enough from RAS (Reliability, Availability, Serviceabilty) British liquid cooled engines beat American radial engines so hard it wasn't funny. Mostly it was due to end to end design of entire engine pod which made all operations better. Meanwhile USA had, well, a lot of radials and radial making manufacturing lines and people who had experience with radials but little idea about much more complex liquid cooled engines.

jabl 4y ago
> Funnily enough from RAS (Reliability, Availability, Serviceabilty) British liquid cooled engines beat American radial engines so hard it wasn't funny. Presumably you mean the Merlin and not, say, the Sabre? :) But anyway, that's interesting, haven't heard of that before. Do you have some more information on this topic? From what I've read Americans were shocked to find out how 'hand built' the Merlins were, with pretty large differences between each engine, engines being delivered with metal filings in the crankcase requiring inspection and cleaning and whatnot. So a large part of the work Packard did for the license produced Merlin was tightening up the design so it could be mass produced much faster on production lines. Of course this doesn't prove the RAS point you made one way or the other, but it seems strange that if Americans put so much more emphasis on efficient production that they wouldn't have put similar effort into serviceability?
- p_l 4y ago
  The issue with Merlins was that Rolls Royce was manufacturing them whenever and by whomever by the time war got into full swing, which easily explains the differences between individual engines. As for serviceability, the difference was in design - American engines were effectively "thrown over the wall" to airplane designers, resulting in such beautiful designs like B-17, where IIRC inspecting or changing a sparkplug started by removal of propeller because apparently even good idea fairy was out drinking when they designed it. In comparison Rolls Royce designed a standard "pod" for the engine that would be then minimally adapted by plane designer, with an eye towards servicing and commonality. So the tolerances might have been tighter on US production lines, but little thought was placed at least in some designs on how to support operations on the planes instead of just building them. (Something that arguably is present today with F-16 at least, and possibly F-35 too)