Light fighters alternatives, 1935-1945

Shortround6 said:

The Sabre wound up having a problem with boost limits. Building a cylinder wall to hold the pressures in the cylinders of a late WW II engine was not easy but building a strong cylinder wall that moved up and down and side to side and had parts of the cylinder unsupported at times during it's travel was very, very hard. Sabre's were using 12-15lbs of boost when Griffons were using 18-21lbs? Sabre VII used 17.5lbs with ADI while a Griffon 69 used 21lbs with 100/130 fuel and 25lbs with 100/150 fuel.

RR does not get some of the credit it deserves for basic materials development. In the 1930s and 40s (and later?) there were a bunch of different Steel, Aluminum and high temperature alloys that carried an RR as part of their code. Developed by, for, or in partnership with Rolls-Royce. You can't make great engines without good materials.

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The British aircraft industry as whole owed a lot to Rolls Royce's basic research into metallurgy. RR developed aluminum alloys were used by all of the British engine manufacturers.

The following quote is from:

"At this time the aluminium-alloy forging industry was a comparative newcomer in the field of metallurgical technology. By the late 1920s Rolls Royce, in its development of high speed aero engines, was finding that the alloys then currently available, primarily Duralumin and Y alloy, were simply not good enough to withstand the far higher stresses now being encountered in the latest engines. Clearly new alloys were required. In addition, although HDA was producing components in these metals by early 1928, it had no proprietary control over them. Subsequent development work, undertaken initially by Rolls Royce metallurgists Hall and Bradbury, resulting in the famous RR series of alloys.
This new series of alloys was first announced in 1928-1929 and in the early days was confined to just four 'versions':
• RR 50 (Al - 1.1%Cu - 0.9%Ni - 1.0%Fe - 2.4%Si - 0.13%Mg)* which served as a sand and die casting alloy for general purposes;
• RR 53 (Al - 2.0%Cu - 1.3%Ni - 1.3%Fe - 1.5%Si - 1.6%Mg - 0.07%Ti) was a high strength die casting alloy for pistons, cylinder heads, etc., for operation at elevated temperatures;
• RR 56 (Al - 2.2%Cu - 1.0%Ni - 0.9%Fe - 1.0%Si - 0.9%Mg - 0.1%Ti) a high strength forging alloy for general purposes; and
• RR 59 (Al - 2.3%Cu - 1.0%Ni - 1.2%Fe - 1.0%Si - 1.5%Mg - 0.1%Ti) a high strength forging alloy for pistons and other components operating at high temperatures.
However, Rolls Royce was not keen to manufacture and market these alloys themselves."

Rolls Royce material specifications are listed on the following site:
The entire website is very comprehensive, well worth a look.

And of course the Concorde was clad in RR58

Trying to get back to the light fighter concept during 1935-45 we have a change in concept in 1939-40 in most nations that throws a wrench in things.
This is in addition to actual combat seeming to take two different directions, which took a while to sort out.
And a 3rd thing is the evolution of aircraft tended to make them heavier as time went on (quickly) so the dividing line for weight of a light fighter shifted very quickly.

The French were the big proponents of light fighters, with finances being a big motivator.
The French were pretty good at getting decent (or more than just decent) speed out of the prototypes. The planes were small, which is part of the light fighter concept.
Problems were they used small wings which meant a high wing loading for not great turns in 1940, Small size and good streamlining does not cure poor power to weight which means poor climb. The Potez 230 and the Cauldrons have problem with view over the nose. You can raise the cockpit but that creates drag.

The change to pilot and fuel protection in 39-40 is a bit of bump for the light fighters. Pilot protection is pretty much the same regardless of aircraft size while fuel protection depends on level of protection desired, materials available and size/shape of the tanks. But adding 100kg of protection to an 1900kg fighter is going to hurt performance more than adding 100kg to a 2800kg fighter. Adjust weight of protection as needed to suit.
Some countries took to high speed combat (boom and zoom) faster than others. Other countries stayed with maneuver combat. Light weight fighters using maneuver combat may have been possible (don't copy small wing French fighters) but that may require a lighter armament than the French fighters used, no protection and slower speed (larger/higher drag wing).
Some light fighters may have been possible to upgrade, but larger engines may be a problem. Even engines of the same nominal size from the same manufacturer. The Curtiss CW-21s used the same engine as the F2A-1 Buffaloes and because of the lack of reduction gear and the older engine construction the engine was several hundred pounds lighter than later R-1820s. A more powerful engine also needs a larger propeller.
Some lightweight fighters that made it into service were a little too light and had structural problems (so did some not so light fighters).
Lightweight fighters with small wings and small engines may not be the best idea for turning into ground attack planes. Might depend on the guys building the runways?
But getting to two 500lb bombs was probably not going to happen with small wings and under 900hp engines.

Shortround6 said:

The change to pilot and fuel protection in 39-40 is a bit of bump for the light fighters. Pilot protection is pretty much the same regardless of aircraft size while fuel protection depends on level of protection desired, materials available and size/shape of the tanks. But adding 100kg of protection to an 1900kg fighter is going to hurt performance more than adding 100kg to a 2800kg fighter. Adjust weight of protection as needed to suit.

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That math lacks the accounting for the power increase the 1940-41 light fighter will have vs. it's earlier version that entered the service in 1937-38.
It also does not account for the fact that the protection added does not mean that drag is also increased (at least not until people start clamping the BP glass in front of the winshield instead of aft the windshield); no added drag despite the improvement of the A/C = great.

Shortround6 said:

Lightweight fighters with small wings and small engines may not be the best idea for turning into ground attack planes. Might depend on the guys building the runways?
But getting to two 500lb bombs was probably not going to happen with small wings and under 900hp engines.

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So we want that a small fighter carries almost double the load than the bombed-up Bf 109 carried?
Shaking my head.

tomo pauk said:

That math lacks the accounting for the power increase the 1940-41 light fighter will have vs. it's earlier version that entered the service in 1937-38.
It also does not account for the fact that the protection added does not mean that drag is also increased (at least not until people start clamping the BP glass in front of the winshield instead of aft the windshield); no added drag despite the improvement of the A/C = great.

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Power increases depend on the starting engine. Renault was not going to get much more power out of the air cooled V-12. Changing to a V-16, even if they had gotten the crankshaft to survive adds some challenges of it's own.
Up grading G-R 14M engines is also a bit problematic.
Problems with other engines?
The drag is not the problem with most of these light fighters. They had the thrust to drag numbers down pretty well. It is the change in wing loading for turning/maneuvering and the change in power to weight for climb and accelerating that was the problem.
Just look at the American F4F-3 and F4F-4 or the changes from the P-40 through P-40C (Or the E)

tomo pauk said:

So we want that a small fighter carries almost double the load than the bombed-up Bf 109 carried?
Shaking my head.

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Well I keep getting told how good the P-40 was at carrying a pair of 1000lbs bombs
So adjust as you see fit, one 500 or 441lb or a pair of 220lbs bombs or four 110lbs bombs.
Or single 220 and a pair of 110s to follow the path of the Spitfire with one 500lb and a pair of 250s.
Point is that the "light fighter" cannot carry the war load of a bigger fighter and as result you need more of them which kind of kill the whole "cheap" argument.
Plenty of air forces used less than optimum aircraft because that is all they had. Planning on building large numbers of less than optimum aircraft to begin with may very well be false economy.

yulzari said:

The pre Sabre Napier engines were designed around the idea that running an engine at twice the speed as opposed to twice the capacity will give you more power per weight. Did not quite work out but that was the guiding principle.
Rolls Royce went down the road of stuffing in twice the air at higher pressure which did work as chemistry and metallurgy progressed. It was not for nothing that Rolls Royce was known for the triumph of development over design I think that I may be quoting from LJK Setright The Greatest Engines of All Time by LJK Setright.

Of course I am grossly generalising a far more complex situation, but it summarises the two approaches.

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I decided to read Setrights article and immediately spotted an egregious error typical of the man
"with all bearings (thinwall shells, to be copied by Vandervell),"
Vandervell do NOT copy Napier.
The real story from The Valiant Vanwalls
"The epiphany that changed Tony Vandervell's life was the 1930 news that Clevite in Cleveland, USA had developed what it called a "thinwall" bearing."
"With the help of his father, who backed him in buying the necessary production equipment, Tony Vandervell successfully acquired the British rights to make the new-fangled bearings. By 1936 he was manufacturing them in quantity at the new factory of Vandervell Products Ltd. in the west London suburb of Acton. He was up and running just in time to help with wartime rearmament, working closely with Acton neighbor Napier, producer of advanced aircraft engines."

The article is also chalk full of unsubstantiated inuendo such as
"sequestration of all the best and most suitable airscrews for use only on R-R engines"

Shortround6 said:

Power increases depend on the starting engine. Renault was not going to get much more power out of the air cooled V-12. Changing to a V-16, even if they had gotten the crankshaft to survive adds some challenges of it's own.
Up grading G-R 14M engines is also a bit problematic.
Problems with other engines?

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Most engines gained about 20% between the mid-1930s and the ww2. British (and Polish) can move from the ~600 HP Mercury in 1935/36 to the 840 HP version come 1937/38. Even more can be gained with the Kestrel/Peregrine, 640 -> 745 -> 885. Another ~150 HP can add the 100 octane fuel.
For the French - a more sane engine policy on their part would've seen Renault making the 700 HP HS 12X, if not the 840 HP 12Y by the mid-1930s, and the HS not making a single radial engine.
Germans can go from the 600 HP Jumo 210 to the 700 HP versions, and by mid-1939 try the HS 12Y they just have gotten in their lap.

Shortround6 said:

Well I keep getting told how good the P-40 was at carrying a pair of 1000lbs bombs
So adjust as you see fit, one 500 or 441lb or a pair of 220lbs bombs or four 110lbs bombs.
Or single 220 and a pair of 110s to follow the path of the Spitfire with one 500lb and a pair of 250s.
Point is that the "light fighter" cannot carry the war load of a bigger fighter and as result you need more of them which kind of kill the whole "cheap" argument.

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Stick a 500 lb or a 250 kg bomb - or whatever is the equivalent in the light bombs - under a light fighter and call it a day.

Shortround6 said:

Plenty of air forces used less than optimum aircraft because that is all they had. Planning on building large numbers of less than optimum aircraft to begin with may very well be false economy.

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Soviets did that - building the large number of less than optimum aircraft - with the biplane fighters by the time I-16 was a thing. Italians did the same. British were not such the offenders, still the Gladiator gotten to be mad in the hundreds. Many times the optimal fighters ended up as flops (due to the A/C itself or the engine choice), or were too late. So having a good and elaborate plan to make the stuff that your industry is well set-up, despite the design not being the latest and bestest, might've been prudent. Improve the aircraft later with better engines and whatnot.

Shortround6 said:

The Sabre wound up having a problem with boost limits. Building a cylinder wall to hold the pressures in the cylinders of a late WW II engine was not easy but building a strong cylinder wall that moved up and down and side to side and had parts of the cylinder unsupported at times during it's travel was very, very hard. Sabre's were using 12-15lbs of boost when Griffons were using 18-21lbs? Sabre VII used 17.5lbs with ADI while a Griffon 69 used 21lbs with 100/130 fuel and 25lbs with 100/150 fuel.

RR does not get some of the credit it deserves for basic materials development. In the 1930s and 40s (and later?) there were a bunch of different Steel, Aluminum and high temperature alloys that carried an RR as part of their code. Developed by, for, or in partnership with Rolls-Royce. You can't make great engines without good materials.

Click to expand...

Watch it. The Napier Sabre had a high compression ratio compared to other supercharged engines, 7:1. The Rolls Royce Merlin and Griffon were 6:1. Your cylinder pressure at top dead centre (TDC) should be atmospheric pressure, plus supercharger boost, all sort of multiplied by the compression ratio. Adiabatic compression is not simple. A Sabre ought to have lower manifold boost pressures as a result. I don't know how they decide on compression ratios for supercharged engines. There must be a sweet spot somewhere. I have worked out the brake mean effective pressures (BMEP) for an Rolls Royce Griffon_65 at 2050HP at 2750RPM (262psi), and for a Sabre_V at 2850HP at 3800RPM (265psi). I would assume that both engines are making good use of 130_octane fuel. The numbers effectively are equal.

Read Bill Gunston's book By Jupiter, all about Roy Fedden at Bristol. They switched their sleeves from some form of carbon steel, to what Gunston describes as an "austenitic Ni-Cr-Mo steel", which I interpret to be similar to 300 series stainless steel. 300 stainless steel has a much higher coefficient of thermal expansion than 400 (ferritic) series stainless steel, or carbon steel. Combined with low-expansion aluminium alloys, you can maintain an accurate fit between your pistons, sleeves and cylinders through a wide range of temperatures. Rolls Royce was a bigger organization than Bristol, and likely Napier as well. They may have had an easier time getting the alloys they wanted.

Howard Gibson said:

Watch it. The Napier Sabre had a high compression ratio compared to other supercharged engines. The Rolls Royce Merlin and Griffon were 6:1.

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True, except the Sabre was 7:1 which is not all that high compared to most Allisons' or P&W or Wright engines (these were all around 6.65:1 to 6.7:1)
DB engines were higher and Jumo 213 was about 6.5:1.
Actual compression ratio does depend on the valve timing somewhat.