High-Drag Areas on the Supermarine Spitfire

[wuzak]

I`ve got a really nice report on special "aero Spitfire canopy" (not the speed-spitfire but wartime report, Sept 1943) which wasnt putting the armour inside but a total redesign (wasnt a bubble canopy though). Sadly I cant post the pics as its copyright infringement.

I can quote from it though !

It raised top speed from 410 to 415mph (in level flight in a Spitfire IX reg "EN 498"), when dived at 550mph it put +12mph on top speed.

It was called the "Conical Screen", the sliding bit was identical but the front bit was totally rounded off.

You can get it at Kew Archives in London ref "AVIA-6-10404"

I also have another report on Spitfire aero, which stated that basically the fit of the panels was awful and resulted in (they reckoned) 7.5mph differences production models depending on how well it was fitted together at that particular factory.

Also from Kew, ref "AVIA-6-10367" and was also 1943

There were also larger studies conducted when the Mustang arrived as the air ministry was incredulous about where the speed difference had come from, but I dont have time to go trawling through those tonight. I seem to remember that it was a big mix of panel gaps, radiator installation, wings, paint and so on.

I believe that screen was not adopted because it distorted the pilot's view, and so was deemed unsuitable for combat aircraft.

PR Spitfires did adopt a rounder profile screen, without armoured glass, for extra high altitude performance. They may have been related to the screen you mention.

Also, don't forget that the two cannon barrels cost ~8mph in speed.

Delete the cannon (presumably for 4 x 0.50"), add the super screen and improve panel fit and finish, and you would not be far shy of P-51 performance. But with less firepower than a regular Spitfire.

 

[pbehn]

The Spitfire radiator was designed to use the Meredith effect, but in practice it wasn't that well done.

The P-51's duct was also not ideal, with the expansion from the intake being uneven from top to bottom, with the roof of the duct changing directions quite sharply.

That said, Supermarine did propose a similar radiator system for the Spitfire, but the Air Ministry rejected it in favour of production. Because in WW2 production was king!

Edit: There were a lot of small areas that the Spitfire was in deficit to the P-51, drag wise. While the radiator and the wing were the most significant factors, they weren't as big a difference as is often thought. Just a lot of small bits of extra drag adding up.

You would almost think that' someone looked at the Spitfire and Bf109 and thought how to improve on them.

 

[Reluctant Poster]

You can have extra HP even with a blended ram air intake, but not pay as much of price in drag that will come with an intake that is protruding away from airframe.
Seafire 47 vs. Seafire 45

According to Spitfire by Morgan and Saleslady the Mark 47 was slower than the Mark 46 due to the relocated air intake

 

[tomo pauk]

According to Spitfire by Morgan and Saleslady the Mark 47 was slower than the Mark 46 due to the relocated air intake

Indeed, by 3 mph.

 

[Zipper730]

Maybe I have it all wrong but I think the splitter plate works by "splitting off" the turbulent layer of air next to the aircraft skin and allowing the air that is flowing more smoothly to enter the radiator opening. This allows a higher volume of air for the same size opening and the less turbulent air flows better through the radiator also consuming less drag.

I didn't think it was about changing the divergence angle so much as simply getting rid of the turbulent airflow going into the ducts. Regardless, I prefer the term "diverter" but that's a term used in jet-powered aircraft.

nobody was really using splitters in the mid to late 30s.

The P-38 used them on the radiator scoops.

On the Spitfire there was limited room to work. . . . The radiator is already shoved as high into the wing as it will go. and you have limited space in between the radiator and landing gear to get a nice curve in the duct.

Wow, I never realized they had such little room. A belly-radiator would have definitely fixed this, but you wouldn't want to belly in with it...

Notice the date on this communique.

August 10, 1942...

Then there was a constant barrage of advice and instruction issued by the RAF to Fighter Command and its squadrons about MAINTAINING the finish on service aircraft. Generally, even in the UK, this was not done very well.

Out of curiosity -- how did the US & Germany compare?

I`ve got a really nice report on special "aero Spitfire canopy" (not the speed-spitfire but wartime report, Sept 1943) which wasnt putting the armour inside but a total redesign (wasnt a bubble canopy though). Sadly I cant post the pics as its copyright infringement.

Do you have a link to the page -- I don't think that qualifies...

I can quote from it though !

It raised top speed from 410 to 415mph (in level flight in a Spitfire IX reg "EN 498"), when dived at 550mph it put +12mph on top speed.

Impressive

I also have another report on Spitfire aero, which stated that basically the fit of the panels was awful and resulted in (they reckoned) 7.5mph differences production models depending on how well it was fitted together at that particular factory.

So workmanship sucked?

 

[Shortround6]

The P-38 used them on the radiator scoops.

I don't believe the early ones did. The J model certainly did. I am not sure of the H model.

 

[Deleted member 68059]

Do you have a link to the page -- I don't think that qualifies...

There isnt really a link as its an archive paper I photographed myself in London ... sorry.

Discovery | The National Archives

Search for

AVIA 6/10404

All that gets you is the index listing for it though....you CAN order copies but they cost an absolute fortune. So most people visit.

 

[Reluctant Poster]

The Seafire XVII and 47 had curved windscreens
Seafire Mk.XVII SX336

 

[Ivan1GFP]

Washout to avoid a harsh stall doesn't do much for drag.
There was also the issue of landing gear that didn't quite fit into the thin wing and some of it had to hang below the wing surface.

 

[wuzak]

Washout to avoid a harsh stall doesn't do much for drag.
There was also the issue of landing gear that didn't quite fit into the thin wing and some of it had to hang below the wing surface.

Funny that the prototype initially had fully enclosed main landing gear. The Mk III also had fully enclosed landing gear, IIRC.

The landing gear did not protrude from the wing, but some of the wheel well was open, which would cause some drag. Though the decision to remove the covers was made in testing the prototype.

 

[Ivan1GFP]

Funny that the prototype initially had fully enclosed main landing gear. The Mk III also had fully enclosed landing gear, IIRC.

The landing gear did not protrude from the wing, but some of the wheel well was open, which would cause some drag. Though the decision to remove the covers was made in testing the prototype.

My understanding was that the mid production Spitfires had large enough wheels that their gear doors were very slightly below the wing's lower surface. This was corrected with the change in the wing with the last marks.

 

[BarnOwlLover]

The Spitfire radiator was designed to use the Meredith effect, but in practice it wasn't that well done.

The P-51's duct was also not ideal, with the expansion from the intake being uneven from top to bottom, with the roof of the duct changing directions quite sharply.

That said, Supermarine did propose a similar radiator system for the Spitfire, but the Air Ministry rejected it in favour of production. Because in WW2 production was king!

Edit: There were a lot of small areas that the Spitfire was in deficit to the P-51, drag wise. While the radiator and the wing were the most significant factors, they weren't as big a difference as is often thought. Just a lot of small bits of extra drag adding up.

I thought I saw something on here to this effect. It may be a bit off topic, but I've seen references to what is suspected to be RJ Mitchell's last major design he worked on before his death, which was the Supermarine 312. From what little I could glean from it, it was basically a Spitfire but much modified, namely with a ventral radiator and standard cannon armament. Outside of that, though, I've been quite frustrated to find other details about this design.

But it does show that it may be possible to fit such a radiator onto a modified Spitfire design, but, one, Mitchell died before the design was 100% complete or built, and two, as you hinted at, Joe Smith (Mitchell's associate/design assistant and successor) may've been inspired by that design and maybe even the P-51 later to try and modify the Spitfire, but he was turned down by the RAF and the Air Ministry. Which IMO is odd, given how much the Spitfire already evolved (though I did read that for the most part, the fuselage between the front firewall and tail was little modified from the Mk V on until the 22/24 line).

 

[BarnOwlLover]

I also found this drawing of a Spitfire that tested a ventrally mounted Meredith ramjet engine.

There was also the Supermarine 338, which was a heavily modified Spitfire IV (used to test the Griffon engine and lead to the Spitfire XII) that had a gull wing, butterfly tail and a ventral radiator.

 

[pbehn]

I also found this drawing of a Spitfire that tested a ventrally mounted Meredith ramjet engine.

View attachment 693642

There was also the Supermarine 338, which was a heavily modified Spitfire IV (used to test the Griffon engine and lead to the Spitfire XII) that had a gull wing, butterfly tail and a ventral radiator.

View attachment 693643

From my understanding of things, a ventrally mounted radiator caused compressibility issues mounted there, it has to be further back behind the area of max cross sectional area, as on a P-51, also on that arrangement the frontal area is increased, on a P51 the inlet is visible on a frontal view, but the "splitter" isnt..

 

[BarnOwlLover]

I wonder how well the Spitfire would've done if it used radiators similar to the Spiteful? I'd bet that's probably a big part of why the Spiteful was nearly 40 mph faster than the Spitfire 14.

 

[Graeme]

Supermarine 312.

Source...

 

[Shortround6]

I am not sure the Spiteful radiators really did that much.

A lot wider than the Griffon Spitfires but shallower. More of the radiator could be hidden inside the wing rather than sticking out. Now notice where the intake flap hinge is and barely visible in the exit hinge.

Both flaps open at least part way. Granted this set up does not have the air making large excursions in the vertical and rejoining the exit flow. BUT you don't have the depth front to back to expand the airflow, get it through the radiator, and squeeze the heated air down to the higher pressure. May be it did work but you had nowhere near the depth front to back that the Mustang, CA-15, MB-5 and P-82 have

The only way to truly know is for somebody to have mounted instruments in the airflow coming out through the exit nozzle/flap and recorded the exit speed vs the intake speed.
That will tell you if you actually achieved positive thrust. Wither the thrust is worth the drag of the size of the scoop is another story.

 

[tomo pauk]

Hmm - is it just me, or the Spiteful was also with a windscreen set at the shallower angle than it was the case with Spitfires?
W wuzak Wurger etc - help

 

[Wurger]

The prototype (the second pic in #57 ) VG471 is the Supermarine Sea Fang F.31 while the RB515 in the first image above is the Spiteful, the first production aircraft.

Here is comparing of the Spiteful prototype NN664 and RB518 of the production series and the MV259, a Spitfire PR Mk. XIV. It looks like the angle of the windscreen was slightly different if compared to the ealier one. However it could be a trick because of the different windscreen frame for both types. IMHO the Spiteful and Sea Fang got the longer front glass.

NN664-RB518

NN664-MV259

the pic source: the net

the source: Supermarine Spiteful and Seafang Fighters

 

[BarnOwlLover]

To be honest, I do wonder how much the Meredith effect is fact vs myth. Obviously, there's something to it, as with laminar flow wings. But I don't think that theory 100% paid off in terms of real world results. It's like comparing the P-51 with the Spitfire. When powered by similar engines, the P-51 was a good 30 mph or so faster on top end than the Spitfire, and it took the Griffon engined Mk 14 at least 300-400 more bhp to reach the same speeds.

Overall, I think that P-51 was just a cleaner airframe than the Spitfire. The fit and finish above all on the Mustang was seemingly miles ahead of a lot of Spitfires. You have to remember that it seemed that Spitfires didn't go fully to flush riveting for all external panels until sometime in 1943. The Mustang did this basically all along going back to the NA-73X prototype.

I do believe that the laminar flow wing and Meredith radiator done well helped, but they weren't the sole magic bullets. I'd bet that a lot of why the Spiteful was so fast was just lessons learned from designing the Spitfire and gains in manufacturing and aero made since the mid 1930s.

That's why sort of my "dream" fighter would have the best attributes of the Mustang and the Spitfire. IMO, we got pretty close with the XP-51F and G, and sort of approached that with the P-51H. Or maybe if the P-51B/C/D/K was able to keep the weight to NA-73X or P-51/Mustang I levels.