Are we discussing climb or power loading? The Tempest had laminar wings and was extremely heavy.
Question about RoC of Spitifire IX, XIV vs late BF 109's.
- Thread starter MaxPower
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J L Atwood one of the P51's designers attributes Shenstones work on refining of the radiator duct to make best use of the Meredith effect as the greatest drag reducing component of the P51's design, as does Ludwig, in his writings you could almost assume he dismisses the laminar flow wings contribution to lowering drag. In the famous Spitfire pea test of 1937 the Spit in question did 365mph @ 18,000ft yet could only do 343mph with the pea's glued on. I can't help but feel the P51 benefited from all over flush fitting rivets and a well designed and refined radiator ducting system for it's reduction in drag over the use of laminar flow wings, even more so considering it was only the outer wing section that was designed to make use of laminar flow.
As I understand it the P-51 was better than the Spitfire in 3 areas, wing profile produced less drag at most speed. Cooling drag was lower again at most speeds. Overall cleanliness fit and finish was better, it was designed that way. My point was about generalisations, a thin wing is generally less draggy than a thick one, but not in all cases, it depends where the thickest part is and what the overall profile is.
The wings of Spitfire probably produced less drag than that of Mustang?
However, Mustang have had other things going for him (or, Spitfire have some sore spots, drag-vise) - radiator design (especially once Spitfire gotten better engines than 1-stage Merlin), fully retractable & covered U/C, fit & finish (not always), absence of rear view mirror, slope of windsrcreen. Amament-related drag was probably also lower on Mustang. On earlier Spitfires (rouhgly pre-1943) external BP glass, carburetor choice and draggy exhausts also prevented Spitfire reaching it's full performance potential.
However, Mustang have had other things going for him (or, Spitfire have some sore spots, drag-vise) - radiator design (especially once Spitfire gotten better engines than 1-stage Merlin), fully retractable & covered U/C, fit & finish (not always), absence of rear view mirror, slope of windsrcreen. Amament-related drag was probably also lower on Mustang. On earlier Spitfires (rouhgly pre-1943) external BP glass, carburetor choice and draggy exhausts also prevented Spitfire reaching it's full performance potential.
Not what I meant, is that how it came across? A thin wing should have less drag but only if it uses the same profile as the thicker one. That's why Mitchell wanted a thin wing but later research into profiles produced thicker wings which had less drag at most practical speeds.
The use of laminar wings reduces parasitic drag but it does not reduce lift induced drag. The Drag Coefficient on the wing consists of Cd0 = CdA + CdL. The reduced drag of the laminar wings makes the aircraft faster and leaves more power in reserve for climbing. In other words it improves the L/D ratio not by improving lift but by improving drag.
The Spitfire had the thickest portion of its wing 2213 (root) and 2209 (outer aileron hinge point) about 2206 where the wing tips attached at 20% of chord. By contrast the thickest portion of the P-51 wing was way back at 50% and it was 14% thick most of the way to the tip.. This preserved a positive pressure gradient across the first 50% of the wing and was supposed to maintain laminar flow. The trailing 50% thereby had a more aggressive negative gradient that would rapidly lead to a loss in laminarity but the disadvantage was minimal and the gain easily outweighed the loss and was not so significant. It was also handled by a fish tail reflex curve. (P51 wing cross section looks like a tuna fish viewed from above)
The reality however was that the Laminar wings had a higher critical Mach and it was the reduction in shock drag, not laminarity that made these more efficient.
The Germans had a laminar wing on the Me 309, all their own work, but essentially the Germans believed correctly that these wings weren't laminar in real life and designed for higher critical Mach, which had the same effect. Me 262 wings were at 11% thick at 45% chord at the wing root and 9% thick at 35% of chord at the wing tip. The Germans didn't have an opportunity to put a new piston engine fighter type in production anyway.
The performance shortfall of the Me 109G6 relates to
1 Power Limitation due to boost limits of the DB605A engine to 1.3 ata until October 1943 when 1.42 ata became available.
2 The failure to retain a retractable tail wheel (Me 109F, Me 109G1 and Mustang had retractable tail wheel)
3 the failure to retain wheel well covers (Mustang had them)
4 gun bulges (these could have been smoothed over and streamlined but weren't till the Me 109G6AS onwards.
The above would need to be 'fixed' before you thought about laminar flow. These aerodynamic mods would probably have added 25kmh but production rate was prioritised.
(leading to higher pilot attrition). They werent properly fixed till the Me 109K4 in November 1944 through the Me 109K1 was ready in 1943.
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Shortround6
Major General
My own, admittedly unschooled, belief is that the Mustangs wing in an absolute sense, didn't differ in drag much from the Spitfires wing.
However for the around the same drag the Mustang was able to accommodate a considerable amount of fuel in it's thicker wing, which was a large advantage.
How one wishes to interpret that in consideration of drag I don't know.
More volume/payload for same drag? does that equal lower drag?
However for the around the same drag the Mustang was able to accommodate a considerable amount of fuel in it's thicker wing, which was a large advantage.
How one wishes to interpret that in consideration of drag I don't know.
More volume/payload for same drag? does that equal lower drag?
Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
I think you could revise that view, I have Supermarine papers from the war discussing putting a laminar flow wing on the Spitfire, they calculated a significant potential gain (I dont have it in front of me but I think if I remember rightly +10>15mph).
Do you remember, per chance, the thickness-to-chord ratio of the laminar-flow wing Supermarine was discussing?
That's not my understanding. As I understand it the P-51 profle delays the onset of turbulent flow and therefore has less drag at lower Mach numbers, at higher mach numbers P-51 has supersonic flow before the Spitfire because of the thickness. This is largely theoretical because it means the Spitfire has less drag at speeds where the propeller is about to fall off. My point was about generalisations which "power loading" is. The wingspan of a standard P-51 and Spitfire were almost exactly the same, but the Spitfire could remove 4ft to improve roll at the expense of climb and altitude performance, or add extended tips to increase altitude performance. Take 4 ft of the P-51 and you lose a lot of area and aileron. They are completely different wings they just happen to have a span in common, almost nothing else.
All true but only in terms of performance in speed, RoC etc. things like rear view mirrors and the Malcolm hood and addition of cannon reduced performance but were accepted to see better and hit harder.
cherry blossom
Senior Airman
- 524
- Apr 23, 2007
Wikipedia says: The wing area has been reduced from 242 sq ft (22.5 m2) to 210 sq ft (20 m2) and a thickness chord ratio of 13% has been used over the inner wing where the equipment is stored. Outboard the wing tapers to 8% thickness/chord at the tip.
This is referenced to Morgan, Eric B. and Edward Shacklady. Spitfire: The History (5th rev. edn.). London: Key Publishing, 2000. ISBN 0-946219-48-6 on page 493.
The Incomplete Guide to Airfoil Usage gives the aerofoil of the Spiteful as Supermarine 371-I at the root and Supermarine 371-II at the tip.
Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
Annoyingly its just a memo-file, so all I know is "new laminar flow wing" and the speed advantage.
I know where the files will be, but I cannot get to them right now due to "the predicament"
That was the 'theory' that Melville Jones at Oxford had and that Eastman Jacobs from the NACA followed when he developed the 'laminar flow wing' of the Mustang. It worked only in the wind tunnel under ideal conditions. In real life the natural imperfections in metal wings as well as accumulation of damage and various insect strikes make laminar flow break down at about the same point. Jacobs understood that his new aerofoils had much better 'compressibility' characteristics.
True laminar flow required the development of glass fibre wings. On one German sail plane that has a genuine laminar flow wing it uses this has a wiper mounted on a rail on the bottom of the wing that runs along the leading edge to clean it periodically.. DASA and Airbus will use a slat that protects the leading edge at low altitude and secretion of a cleaning agent at high altitude to keep the wing clear on its 'blade wing'.
So basically it was the reduced compressibility that made these wings have a lower drag from about Mach 0.4 onwards. It's also important to realise that transonic wings (ie laminar flow) don't just reduce shock drag. They have better pitching characteristics. A shock wave generates lift father back on the wing thereby pitching the nose down, possibly into an irrecoverable drive known as Mach tuck.
I rather doubt the spitfire wings had a higher Mach limit. The P-51D had problems with its bubble canopy rather than its wings in a dive.
Below I've puts some pictures of wing profiles of the P-51, Spitfire, Corsair, Me 109
Note Spitfire wing was 2213 at the root and 2209 at the outer aileron hinge and 2206.4 where the wing tips attached.
The 2209 means wing thickens of 09% at 20% chord.
Note as explained the breakdown of laminarity occurs at about the same point on the laminar flow wing as the standard 4 or 5 digit due to surface imperfections despite the above theoretical illustrations The laminar wing still has lower drag due to a higher compressibility rating and it has far more internal space for fuel etc allowing the fuselage to be reduced.
Its important to note that the spitfire wing was very well designed. It's also important to note that the mustangs speed advantage over the spitfire IX with the same engine came from much more than the wings
1 P-51 had fully covered wheel wells
2 P-51 had a retractable tail wheel
3 P-51 had a better radiator pressure recovery
4 P-51 Probably had better tolerances due to new construction techniques.
5 P-51 guns were fully imbedded.
6 "Laminar wing" profile was but one. Fix the above and the gap closes.
From memory a P-51 could manage 440-444 mph high altitude whereas the Spitfire IX could manage 416. At low altitude the difference was more like 45mph than 24mph due to P-51 better aerodynamics.
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Laminar flow wings were first fitted to a MkVIII fuselage as a mock up for a Spitfire replacement then later to a MkXIV to test them for the Spiteful, the prototype crashed and by all accounts the handling was rubbish, especially near the stall but it was fast, how much can be attributed to the wings or the 2,375hp Griffon is hard to say.
If you add up all the drag inducing components on the Spitfire, the cannon barrels stubs and bulges uncovered wheel wells non retractable tail wheel rear view mirror they all cost approx 20 or so mph in top speed, plus tests done on in squadron MkV's found that simply refinishing the worn paintwork added as much as 10mph to the speed.
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Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
The +10mph for Laminar flow wings was estimated here for the Valiant (i.e. Mk23) - the fact it didnt handle well has no relevance to the drag question.
As I`ve already laboured elsewhere on the forum, even the Germans knew perfectly well that a Laminar profile would be highly beneficial
and made similar estimates for the 109, and were deeply impressed by the Mustang wing drag values (I`ve got the wind-tunnel reports).
The 109 didnt get the new wing for various reasons, the biggest issue was that for the Laminar wing to work well, you need flawless build standards,
the leading edge slats would have ruined this and so Messerschmitt had to design a totally new wing 15% bigger to make up for deleting the
slats, this was such a big revision, and the forced labour methods produced such bad finish that they judged it wasnt worth it.
Winkle Brown didn't much care for the laminar flow wing, the prototype crashed because the handling especially near the stall was abrupt, if you wanted an extra 10mph fit wheel well doors and a retractable tail wheel and give the thing a nice paint and polish.
I only know what I read here, I am not talking about level flight but the extremes in a dive. WW2-fighter and critical Mach speed
