Spitfire Documentary 1976

[Charge]

Evaporative system can be lossy or lossless but ablation is entirely another kind of system and not used in any aircraft, not even in SR71 let alone some WW2 birds.

I really thought that given the size of the radiator system (in floats and in fuselage) the Supermarine racer could simply rely on dissipating the heat via this surface area alone. Interesting to learn that it actually used such a refined cooling system.


"Also this is incidentally why the Spitfire has very strong wings given their thin section."

It doesn't have particularly strong wings. Even that they were 13% of thickness the wing was large so it also had a quite big "wet area" dragwise. They were also floppy enough to cause aileron reversal in high speed and required a very strong steel spar to absorb vertical loading which leads me to conclude that the box structure didn't really contribute much. The spar was not rigid but more like a spring for endurance. Of course this is not good for the wing structure in the long run but these planes were made for war not for years of peace time flight.

In this picture you can see that the spar has many rectangular tubes inside one another:

http://i130.photobucket.com/albums/p274/rum_monster/MK356/Spars_0421.jpg

-C+

[GScholz]

Pointless.

[nrshida]

It doesn't have particularly strong wings. Even that they were 13% of thickness the wing was large so it also had a quite big "wet area" dragwise. They were also floppy enough to cause aileron reversal in high speed and required a very strong steel spar to absorb vertical loading which leads me to conclude that the box structure didn't really contribute much. The spar was not rigid but more like a spring for endurance. Of course this is not good for the wing structure in the long run but these planes were made for war not for years of peace time flight.

In this picture you can see that the spar has many rectangular tubes inside one another:

http://i130.photobucket.com/albums/p274/rum_monster/MK356/Spars_0421.jpg

Yes thank you I have seen the spar. I'm fairly sure they are aluminium alloy and not steel. I understood the sectional taper was to reflect the reduction in stress towards the wingtips rather than to act as a spring but I might be wrong.

Of course especially in aircraft strength should also be balanced with consideration to weight. The structure is especially strong given its weight is what I meant. You could also add additional spars or other structure but that would of course add weight.

I don't know the figures off the top of my head but despite the larger wing area the impression I had was that the Spitfire was very slippery compared to the 109, wetted area being a factor but not all important when it comes to drag.

[GScholz]

The 109F and early G were very slippery and generally faster than their contemporary Spitfires at similar engine power. Later 109s not so much.

For example 109F-4 (1,332 hp) vs. Spit V (1,440 hp):






That's Marseilles btw.

[nrshida]

The 109F and early G were very slippery and generally faster than their contemporary Spitfires at similar engine power. Later 109s not so much.

For example 109F-4 (1,332 hp) vs. Spit V (1,440 hp):

(Image removed from quote.)


(Image removed from quote.)

That's Marseilles btw.

I'm sure you are right but the messerschmitt does have much smaller wings and is lighter too I think? You could write a very interesting comparative design article about the differences and similarities between the 109 and Spitfire. There's an awful lot going on under the skin of both and they arrive at a similar position from some very different design thinking.

[GScholz]

Indeed.

[nrshida]

I just mean that if you blew up the 109 design to make a similar wing area the top speeds would be very different.

[GScholz]

For sure. The Cd of the 109 is larger than the Spit. Total drag of the 109 is less. However, scaling becomes difficult as designing a slippery small plane is more difficult than designing a slippery large plane; many of the parts that need to stick out into the air stream don't scale very well, like radiators, various air scoops for the engine, antennae, canopy, gun ports etc. If we scaled the 109 up to Spit size its Cd would become smaller. Perhaps not matching the Spit, but still.

[nrshida]

I agree, but then we have the Mosquito to compare which makes things interesting again.

[GScholz]

The bigger they are the slicker they get compared to their size. Brunel discovered that back in the day.

[Jabberwock]

The 109F and early G were very slippery and generally faster than their contemporary Spitfires at similar engine power. Later 109s not so much.

For example 109F-4 (1,332 hp) vs. Spit V (1,440 hp)

Cleaning up a Spitfire Mk V and some detail changes could make a big difference, and close that comparative speed gap to the 109F-4 noticeably. In 1943, the RAE took an old, battle worn Spitfire Mk V that was underperforming (topping out at about 354 mph). The stripped and repainted the wing leading edges, cut the exhaust ejector chutes clean with the wing, fit a whip type aerial, filled and sanded the panel gaps, deleted the rear vision mirror and replaced the fish-tail type ejectors with multi-ejectors.

End result, the Mk V reached 389 mph. That's 35 mph better than when it came to the RAE and 14 mph better than the Mk V as originally tested.

[Scherf]

Ejector exhausts certainly did good things for the Mossie (thanks HTC!).