High-Drag Areas on the Supermarine Spitfire

[Metrallaroja]

I was discussing the in service fury.

Ah ok. Yeah many radials had the oil coolers in the LE.
The Corsair for example had almost all configurations possible. It had the oil coolers in the LE (F4U-1, F4U-4, F4U-5), the oil coolers in the engine compartment with air from the LE (F4U-6 (AU-1)) and it had a bigger oil cooler in the engine compartment with air from a nose inlet (F4U-7).

 

[pbehn]

Ah ok. Yeah many radials had the oil coolers in the LE.
The Corsair for example had almost all configurations possible. It had the oil coolers in the LE (F4U-1, F4U-4, F4U-5), the oil coolers in the engine compartment with air from the LE (F4U-6 (AU-1)) and it had a bigger oil cooler in the engine compartment with air from a nose inlet (F4U-7).

The Griffon needed a lot of cooling, not only for the engine oil and water but also the intercooler, the scoops on Spitfire Mk XIV and later are like buckets, they are huge.

 

[elbmc1969]

Yes, I'm aware of those. I guess my question is more of a theoretical nature. What is the aerodynamics of a wing with LE radiators? And given they are such an obvious idea that even yours truly can imagine them being a good design, why didn't world+dog adopt them?

If the air goes into the wing, it doesn't go over and under the wing. Not a scientific analysis, but you don't get something for nothing. You could make the wing much thicker and then possibly get the effect of a thing wing because of the reduced air flow over the top and bottom of the wing--possibly.

There is also a lot that can be gleaned from NACA reports, or RAE/DVL stuff too but that isn't as easy to get. For example with LE radiators NACA found that they are more sensitive to AoA than other installations, so they can work really well in level flight but are probably a bad option for an aircraft that needs to climb rapidly.
--https://www.secretprojects.co.uk/threads/drag-of-radiators.37145/post-456493

 

[elbmc1969]

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.

naca.central.cranfield.ac.uk/reports/arc/rm/1683.pdf

Summary here: Meredith Effect: Fact or Fantasy "Meredith Effect: Fact or Fantasy"

Enter Gruenhagen's book "Mustang. The story of the P51 fighter", 1969. This text gives a rather full account of the cooling duct development. This was a very comprehensive series of trials to determine the design parameters and performance for the duct. Consider this: your boss comes in and says "we have mounted a P51 in the wind tunnel. Pick your best mate, go and sit in it while we run the tunnel up to 500 MPH, and do some measurements for us. Don't bother the life insurance companies, when we told them you are upwind of a 5000 HP fan drawing air through the tunnel, they declined your application". But that is what they did, and not only did they survive, but the data they measured is on page 79 of my edition.


Now at first glance, the only interesting part of the data are the sketches showing various arrangements of ducts for coolant and oil cooling. The numerical data is hard to read: the print is so small. But being half-blind anyway, I thought I better put on my 2.5 binocular magnifier and see what the column headings were. I was immediately revolted by the unit "slug": but as this turned out to be 1 slug equals 32.172 pounds, then that was not so bad. After all, the number 32.172 seemed to be related to the acceleration due to gravity, so some nameless old fossil was trying to separate the concepts of mass and weight. Of course, I am not yet a fossil, as I have not yet gone underground!

If you have any interest, read the web page. It has some interesting tidbits of its own.

 

[pbehn]

If the air goes into the wing, it doesn't go over and under the wing. Not a scientific analysis, but you don't get something for nothing. You could make the wing much thicker and then possibly get the effect of a thing wing because of the reduced air flow over the top and bottom of the wing--possibly.

On the Mosquito the air enters the lower part of the leading edge and exits underneath, however the leading edge is extended forward, so the air exits approximately where the wing leading edge is,. I am sure de Havilland knew what they were doing.

 

[z42]

On the Mosquito the air enters the lower part of the leading edge and exits underneath, however the leading edge is extended forward, so the air exits approximately where the wing leading edge is,. I am sure de Havilland knew what they were doing.
View attachment 702251

Radiator outlet on the top surface of the wing sounds bad from a lift perspective, but on the underside of the wing the outlet would be in the high pressure zone below the wing, creating back pressure in the radiator? From that POV a Mustang style belly scoop sounds like a good idea, with the inlet in line with the high pressure under the wing and the outlet in the lower pressure zone well behind the wing?

 

[pbehn]

Radiator outlet on the top surface of the wing sounds bad from a lift perspective, but on the underside of the wing the outlet would be in the high pressure zone below the wing, creating back pressure in the radiator? From that POV a Mustang style belly scoop sounds like a good idea, with the inlet in line with the high pressure under the wing and the outlet in the lower pressure zone well behind the wing?

The only think I really know about the subject is that I dont know much at all. You need a degree in thermodynamics or similar to fully understand all the ins and outs of it. It took NAA a long time with many versions of inlet to perfect the P-51. The "exhaust" of the Mosquito system like the P-51 is adjustable. Then it is an issue of airflows, temperatures, density and depth of radiator matrix, relative volumes of plenum either side of the radiator. It is generally acknowledged that the P-51 had a great set up, but no one else did the same or copied it. I think that is because you have to start with that in mind at the first stage of design, or it doesnt work.

 

[Shortround6]

The main problem with the Mosquito's radiator (and it wasn't much of one, the system did cool the engine/s without much trouble at different speeds and altitudes rather well, which was it's main job) was that the air traveled different distances depending if it was at the bottom or top of the duct. Most other radiator set-ups are going to have that to some degree.
The exit duct had a rather abrupt taper and turn to the bottom but you can't move it back much without hitting the main spar.

you may be able to "fix" that by extending the wing root forward but that comes at the cost of worse view from the cockpit and more skin area for more drag and a bit more weight.
What are you gaining for what it will cost you?

 

[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.

Correct

On the Spitfire there was limited room to work.
View attachment 527247
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.

I'd have to see a profile view of the radiator, but I'd suspect that you'd have to shape the area in front of the wing in such a way as to carve in a little more area so the splitter could be put between the normal radiator's flow path and the additional carved-in area would handle the turbulent flow.

Of course, this would potentially eat into the skin and could have serious effects on structural or aerodynamic matters.

View attachment 702385

It looks like the inlet area is about twice that of the outlet area. I'm not sure what the P-51's inlet/outlet ratio is (or the XF-12) but part of me does wonder if it'd be possible to have taken the Mosquito's shape and sort of "wrap it" it into an annulus with a spinner in the middle. It might be simplistic but it'd produce a radial inlet with low cooling-drag.

 

[elbmc1969]

It looks like the inlet area is about twice that of the outlet area. I'm not sure what the P-51's inlet/outlet ratio is (or the XF-12) but part of me does wonder if it'd be possible to have taken the Mosquito's shape and sort of "wrap it" it into an annulus with a spinner in the middle. It might be simplistic but it'd produce a radial inlet with low cooling-drag.

"The exit area was 0.019 m^2, just 29.5 square inches"

So ratio is fairly large. Someone will have to supply the inlet area, or measure it, to get an accurate ratio, but this indicates a minimum of 2:1.

 

[Zipper730]

"The exit area was 0.019 m^2, just 29.5 square inches"

What was the inlet area?

 

[z42]

"The exit area was 0.019 m^2, just 29.5 square inches"

So ratio is fairly large. Someone will have to supply the inlet area, or measure it, to get an accurate ratio, but this indicates a minimum of 2:1.

From the article you posted just a little bit higher up in this thread: the inlet area is 0.08948 m^2
That makes the inlet area a factor of 4.63 larger than the outlet (using 0.01929m^2 for the outlet area in that same article).

 

[z42]

I'm not sure what the P-51's inlet/outlet ratio is (or the XF-12) but part of me does wonder if it'd be possible to have taken the Mosquito's shape and sort of "wrap it" it into an annulus with a spinner in the middle. It might be simplistic but it'd produce a radial inlet with low cooling-drag.

Is there some particular advantage of an annular radiator vs. a more traditional scoop? Germany did use them extensively so evidently they thought there was some merit to it..
I wonder if it would be possible to make a P-51 style radiator making use of the Meredith effect for a power egg installation for multi-engine aircraft? Say put the inlet scoop under the engine, then the radiator itself could be tucked partly behind the engine itself, and the outlet in the rear end of the nacelle. Of course might interfere with the landing gear..

 

[SeaWorldOrBust]

Is there some particular advantage of an annular radiator vs. a more traditional scoop? Germany did use them extensively so evidently they thought there was some merit to it..
I wonder if it would be possible to make a P-51 style radiator making use of the Meredith effect for a power egg installation for multi-engine aircraft? Say put the inlet scoop under the engine, then the radiator itself could be tucked partly behind the engine itself, and the outlet in the rear end of the nacelle. Of course might interfere with the landing gear..

Hawker experimented with an annular as well and had good results, especially in conjunction with a ducted spinner (though that added a fair bit of weight). However that's in comparison to the normal Tempest V which has probably the draggiest radiator installation of any of its contemporaries. They also tried leading edge wing radiators and had similarly promising results. The Tempest I, with Sabre V and wing radiators was actually ordered into production with 700 units, however with the end of the war in sight, that was cut to 300, and then later changed to chin-radiator Tempest VIs using the same engine. The related Fury I, also with wing radiators, was also ordered into production, but later cancelled, as the radiator configuration was considered unsuitable for ground attack, which was to be the Fury's main role in post war service.

As far as the 190 D is concerned, obviously the annular radiator did well enough there to allow it to achieve pretty good performance, but it's hard to compare with other potentially competitive installation types, given that the only other power plant used on the 190 airframe was air cooled. Worth noting though that the annular radiators on the Jumo 213 E and F were significantly different from the A model in the D-9, so there may have been further room for improvement there. I'm not sure how either of these installations compare to the Hawker design.

E elbmc1969 As far as wing radiators at high angles of attack are concerned, I don't think it's a huge concern for climb, given the performance of the DH Hornet in that respect, perhaps it's a matter of the particulars of the design.

 

[elbmc1969]

E elbmc1969 As far as wing radiators at high angles of attack are concerned, I don't think it's a huge concern for climb, given the performance of the DH Hornet in that respect, perhaps it's a matter of the particulars of the design.

Wait, I said something about high angles of attack? What did I say? When?

 

[pbehn]

E elbmc1969 As far as wing radiators at high angles of attack are concerned, I don't think it's a huge concern for climb, given the performance of the DH Hornet in that respect, perhaps it's a matter of the particulars of the design.

They are different issues. A high "angle of attack" as in a tight turn changes the airflow into the radiator inlet. A high rate of climb has the engine working at full power but the cooling system having a reduced airflow because airspeed is lower.

 

[wuzak]

The main problem with the Mosquito's radiator (and it wasn't much of one, the system did cool the engine/s without much trouble at different speeds and altitudes rather well, which was it's main job) was that the air traveled different distances depending if it was at the bottom or top of the duct. Most other radiator set-ups are going to have that to some degree.
The exit duct had a rather abrupt taper and turn to the bottom but you can't move it back much without hitting the main spar.

That is true, even more so, for the P-51's radiator scoop.

For the Spiteful there were tests done on a radiator mock-up. They found under certain conditions that there was a boundary layer build-up, and a portion of the radiator area was effectively blanked off.

 

[wuzak]

I wonder if it would be possible to make a P-51 style radiator making use of the Meredith effect for a power egg installation for multi-engine aircraft? Say put the inlet scoop under the engine, then the radiator itself could be tucked partly behind the engine itself, and the outlet in the rear end of the nacelle. Of course might interfere with the landing gear..

Like a chin radiator?

 

[wuzak]

Thats a logical development of the Spitfire like MB3 and 4 to reduce the high drag from underwings radiators - as per the P-51, that design utilises the Meredith Effect to improve cooling, significantly reduce drag and actually gain some thrust.

The Spitfire had Meredith radiators - just not that effective.

 

[wuzak]

The Hawker examples were the Griffon Fury and the Sabre Fury. Not the Centaurus Fury

The Griffon Fury didn't have leading edge radiators. It had a great big chin scoop.