American aversion on spinners + cooling gills

[Pasoleati]

Why were Amis so reluctant to adopt spinners in their radial-engined aircraft while everybody else had them?even supposedly clean designs like the F8F lacked one.

Another question is why Amis stuck to the crudish outward opening circumferential cooling air flaps with their radials while many others adopted e.g. sliding cooling gills with much less drag?

 

[riggerrob]

Radials were perceived as inherently 'draggier' ergo little point to installing spinners or refining cowlings.

Mind you, the first Grumman Wildcat prototype had such a crude cowling and performance so slow that it lost the first round of tests to the Brewster Buffalo. Grumman repeatedly tested Wildcat prototypes in a NACA wind tunnel until its performance exceeded that of the Buffalo. A major change was re-angling cooling air so that it exited the cowling parallel to boundary layer airflow.

The US Navy preferred radials for simplified maintenance. Never installing spinners meant one fewer component to mess with in a cramped hangar onboard an aircraft carrier.

Full-circle cowling flaps were the norm until Royal Navy pilots tied down the top flaps on F4U Corsairs - to improve visibility during landings.
Grumman Hellcat had bottom exit exhaust stacks while the later Bearcat got side exhaust stacks.

 

[Pasoleati]

To be frank, the excuse of simplified maintenance without a spinner is laughable. It would imply that American fitters were worst of the lot since everybody else could handle spinners.

Aa for the F2A-3 vs. F4F-4, the figures provided in their respective SAC sheets point to a very trivial differences in speed and climb while the F2A-3 has significantly better range.

 

[southwestforests]

To be frank, the excuse of simplified maintenance without a spinner is laughable.

Actually, according to my Grandfather who worked on USN aircraft in and after WW2 it does matter and especially matters in wartime.
Also a factor is manufacturing time and costs when you are building multiple thousands of a thing in a hurry; 3 minutes saved for each spinner not used on a production line making 10,000 of the engine adds up to make a difference.
An even more important resource to not expend is the raw material, time, transportation, and manpower which it would cost to inventory and transport the spinner parts to the production line and at the production line.
And that factor is a thing which my Grandfather dealt in after the war when he designed, built, and maintained machines for factories.

 

[sferrin]

Given the various USN and USAAF did fine without them maybe their utility is oversold.

 

[Pasoleati]

Virtually everybody else used them for without a spinner an optimal cooling isn't possible. But then Americans also were far behind in automatic engine controls too. The radial installation of the La-7 was much cleaner than that of the F8F.

 

[Nicknick]

I guess the idea behind it was, that unlike in an inline engine, the air in a radial engine will not flow smoothly after the spinner but hit the crankcase and accessories quite violently. The benefit of a spinner in an air-cooled radial is surly lower than in a water-cooled engine, nevertheless, all later model were equipped with a spinner, so that it must have added a benefit. I guess it was because, the airstream is more gently pushed outwards in front of the airplane when a big spinner is used.

 

[riggerrob]

I guess the idea behind it was, that unlike in an inline engine, the air in a radial engine will not flow smoothly after the spinner but hit the crankcase and accessories quite violently. The benefit of a spinner in an air-cooled radial is surly lower than in a water-cooled engine, nevertheless, all later model were equipped with a spinner, so that it must have added a benefit. I guess it was because, the airstream is more gently pushed outwards in front of the airplane when a big spinner is used.

Some of the last radial-powered airplanes (late 1940s) had both external and internal spinners. The external spinner is obvious and usually a parabolic curve similar to those installed on in-line engines. However, the internal, fixed spinner is not as easy to see because it is between the spinning spinner and the fixed crankcase. The crankcase does not need much cooling air. Try to think of the internal spinner/fairing as the rear half of a teardrop.

Can we even call it a "spinner" if it does not rotate?
Hah!
Hah!

Anyways, the internal spinner/fairing smooths airflow from the flat, spinner back-plate towards the crankcase. It also helps direct cooling airflow towards the baffles around the cylinders.
For example, when Rohr added an internal, rear spinner to their 2-175 prototype, climb rate increased by 50 percent, meaning that the 'excess power' increased by half. IOW internal drag (inside the ducted fan) dropped by half.
Internal airflow through radial cowlings is far more complex than it appears at first glance. Next time you see a radial engine un-cowled, take a close look at all the baffling that directs cooling air across cylinder fins, carburetors, oil-coolers, etc.

 

[Nicknick]

Great, I will definately take a closer look at the next opportunity. I always thought, air flow in radial is quite complex, but its nice to learn something new.