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You seem to have this strange fascination with keeping the outward appearance of some parts of airframe while totally redesigning the interior structure.
You don't actually save much. Keep fuselage from the cockpit back (if you are lucky) and the outer wing panels?
Regardless of what you do with the nose the wing from engine nacelle to engine nacelle will have to be redone. To fit the landing gear if nothing else. Changing the location of major weights changes stress loads even if total weights are the same.
For a couple of light plane single to twin conversions look at the Beechcraft Bonanza and Travel air and the Piper twin Comanche.
With Whirlwind, it's the combination of (almost) clear view canopy, Fowler flaps, slats and retractable tailwheel, all in a single plane - unparalleled in ww2? That's fascinating to me
I save more than when Typhoon was developed in Tempest, P-51D in -H, Fw-190 in Ta-152, Bf-109E into -F.... Even the P-36 grew steep in weight to become mid-war P-40, like K for example.
added: more frugal than turning the Hurricane production lines into Typhoon production lines
I'm trying to do the opposite - turn the twin into a single
The need for the slats is dubious. Especially with the Fowler flaps. Slats do a lot more for keeping aileron control at really low speeds (like landing) than they do for turning. I am not sure if they were wired shut in operation of the Whirlwind, accounts may differ.
True in some cases but they had a lot more invested is some of those production lines. And a question is how much some of them were changed, a lot for the P-51s or a little for the P-36/P-40, It gained a lot of weight and may have needed some parts beefed up but could you build a P-40 wing using many of the same jigs/fixtures as the P-36 wing? how much of the fuselage structure changed?
The Travel Air replaced a 225-240hp six with pairs of 160-200hp fours, kept the same cabin/payload area. It Borrowed the main spar from a bigger twin and the landing gear from the T-34 trainer ( two seat trainer/narrow fuselage Bonanza). T-34 could land on carriers so the landing gear was heavier duty than the regular Bonaza landing gear. Beech already had some of the bits and pieces laying around.
And they weren't trying to change the payload area (cabin) which for fighter planes is the gun location.
Given what we NOW KNOW about the Sabre they might have been better off keeping the Whirlwind and junking the Typhoon
At the time the decisions needed to be made the Allies were UK and France. The USA was 4 years away from defending democracy. The RAF was intending to be dependent upon the Tornado/Typhoon. Continuing Hurricane production and Spitfire developments were to fill in the gap when that programme was failing.Sensible post
The Allied war effort was not dependent on Typhoon/Tornado, so, even if those weren't around, the Allies would've done pretty much the same.
It was intended as the future way, to have a 1600bhp power day fighters now (ie when the decision was made in 1935) and a 2,500bhp day fighter in the mid 1940's using known (ie Kestrel based) power units and a future proof armament. In the initial enthusiasm it was seen as the future standard and the Tornado/Typhoon as a back up, as was the Sabre.
The Spitfire was not, initially, intended as anything more than a better Hurricane supplement pending Whirlwind or Tornado production and there were doubts there would be another production contract after the first one.
The Whirwind was never intended to replace the Spitfire or Hurricane. .
I desperately try to find where I found that Merlins would fit and the airframe could take them, Westland stated in January '41 they could fit merlin XX's into the whirlwind if they wanted it
Not to mention larger radiators, large oil coolers, quite possibly larger fuel tanks, different props, change in center of gravity. How much closer the twin Merlin Whirlwind would have been to a short wing Welkin is an interesting subject