Bf-109 vs Spitfire vs Fw-190 vs P-51

davparlr · Aug 24, 2010

drgondog said:
A stffer wing will flex less but also have a higher natural frequency - the latter, when approximating the frequency of say a prop/engine combination or turbine blade rpms, could cause resonance, fatigue - and ultimately structural failure - (i.e. Comet)

Small point of clarification. While the Comet did have a problem with fatigue, it was not the wing flex. The issue was with the pressurization and depressurization cycling of the fuselage, a relatively new design feature after WWII. This pressure cycling caused fatigue failure around the rectangular windows among other places.

Fighter aircraft, with their rather short, strong wings probably have an insignificant flex.

Interesting note. The B-2 bomber, even with much fuel in the wings has almost no wing flex. The wing is 100% composite and composite material does not like to move in that direction. The composite wings are extremely strong.

drgondog · Aug 24, 2010

davparlr said:
Small point of clarification. While the Comet did have a problem with fatigue, it was not the wing flex. The issue was with the pressurization and depressurization cycling of the fuselage, a relatively new design feature after WWII. This pressure cycling caused fatigue failure around the rectangular windows among other places.

Fighter aircraft, with their rather short, strong wings probably have an insignificant flex.

Interesting note. The B-2 bomber, even with much fuel in the wings has almost no wing flex. The wing is 100% composite and composite material does not like to move in that direction. The composite wings are extremely strong.

Agreed - I wasn't clear with the 'connector' between Comet and fatigue failure versus Comet and wing flex versus Comet and resonance. I should have been more explicit - or referred to other ships that had accelerated fatigue (in wing root/spar regions) due to stiff wings - like the F-4.

Strictly speaking the pressure/depressure cycle is another chapter in aeroelasticity although it has nothing to do with wing flex.

Composites do not behave like aluminum in context of properties of materials. I have been away from composite design for a long time but when I was in the biz, composite structures properly bonded/treated were far stronger (and brittle) than aluminum or steel in weight comparison

OTOH repairing battle damage on the composite tailbooms of Hueys were extremely difficult. IIRC composites have elasticity in strict context - but there is no 'yield point leading to elastic deformation - it simply fails.

In high frequency, reversible load design analysis (Helicopter a good example) the limit load stress was designed at 25kpsi for 2024 - far below the elastic yield point - simply because of the fatigue factor.

VG-33 · Aug 25, 2010

davparlr said:
davparlr said:

Which means the entire wing would stall at he same time.

Click to expand...

No, it would only occure if you have constant thikness profile section for an elliptical wing.
On trapezoidal wing it depends on general geometry and taper ratio. If you're on very triangular wing, your tip will stall first. If your wing is rectangular or has no much high taper ratio (over elleptical category), no problem: it would first stall from the center, to exterior.

To avoid aileron stall, on so called under elliptical wings (very triangular), you can also reduce wing thikness profile on a higher rate. There are old abaccus/tables for that, based on pressure field studies...

That could be sporting, slats or no slats. However, the slats extending would certainly give warning to the nearness to stall, however, after slat extension, aircraft could uncontrollably depart at any time.

Click to expand...

Not at all, critical AoA is always higher with opened stalts than without. So central wing section of the Me-109 will stall first. Even without slats i guess. Exactly on the aera of it's shitbag profile of it's wing, where you can see radiators. They're destroying NACA2R1 geometry and both lift and drag with it.
In general case, avoid to put radiators on lifting aeras.

claidemore · Aug 25, 2010

Isn't the lift created on the top surface of the wing? If so, would that be the reason the radiators are on the undersurface, not the top? Of course a wing mounted radiator creates other problems, but how much effect (detrimental) would it actually have on lift? The changes on the Spitfire radiators from Mk V to Mk IX didn't seem to have much detrimental effect, at least none that I've heard of.

On another note, if adding twist causes one part of the wing to stall first, (allowing to pilot to feel an impending stall and either correct or hold the plane at that point without stalling), would it be accurate to say that adding the twist would have a net effect of the wing stalling sooner than it would have otherwise? If so, might that be the reason W. Messerschmitt didn't have any twist in his wing? Wingloading was high already, why 'hasten' the stall? Particularly when you have LE slats.

parsifal · Aug 25, 2010

fantastic stuff guys, though I struggle to comprehend even the basics of the discussion. Without trying to re-ignite the controversy, I have to pose the question, of the four types we are looking at, which one had the best or most advanced wing form.

I suspect the answer will be along the lines of "it depends on the mission profile" In anticipationof that, I guess I have to ask a series of more complicated questions.

Of the four types which was the better at

i) High altitude (above 20K)
ii) Medium Altitude (10-19.9K)
iii)Low Altitude (below 10K)

assuming two scenarios for each of those altitude ranges firstly a turning knife fight, at say average speeds of 250 knots, and combat mainly in the horizontal. Alternatively, which is the better wing form in a high speed fight, say above 300 knots, in which the emphasis is on straight line speeds and the combat is mostly in the vertical.

Maybe this original question...which type is the better depends heavily on the combat situation under which the hypothetical combat is being fought...

I believe, though I know there are many w2ho will disagree that as a geneneralization, the spit, with its elliptical wing was better in the horizontal at lower speeds, than the Me109 under those same conditions. Conversely, the 109 was better at higher speeds, with its thinner smaller wing, and was better in the vertical plane, though i have read it had some problems in a dive (I dont think those problems relate to the wing however).

Would be interested to read your opinions....

VG-33 · Aug 25, 2010

claidemore said:
Isn't the lift created on the top surface of the wing?

Not only, but it's about for 80% of it. My "on" was in general sense of language, it also meant "under"
The lift is created not by itself, but because of a particular circulation relationship between superior and inferior flow. If you perturbate it, you reduce the total output. Look at thin curvated and plate profile wing tunnel result. Not terrific, isn't it? Your top surface is not working as an hoover...

If so, would that be the reason the radiators are on the undersurface, not the top? Of course a wing mounted radiator creates other problems, but how much effect (detrimental) would it actually have on lift?

Just imagine your Me-109 with underwings radiators running from the Karman to tips. How good would it fly, in your opinion?

The changes on the Spitfire radiators from Mk V to Mk IX didn't seem to have much detrimental effect, at least none that I've heard of.

Compare the Spit (22.48 m²) and Me-109 (16,05) wing aera to radiators one. How much dtrimental, difficult to say...But much higher than probably prof Willy end sir Reginald had ever imaginated. The same as for Ju-52 corrugated skin. It's easy to criticize owerdays. But for 1933, did anywone ever saw published studies on that time, about the question? Back to radiators: obviously they were not aware from tests leaded in TsAGI wind tunnel with SB-2 radiators (at the end of the 30ies), that finally went inside the wing thikness of the SB new-look, called Ar-2. This solution being at far, the best.

On another note, if adding twist causes one part of the wing to stall first, (allowing to pilot to feel an impending stall and either correct or hold the plane at that point without stalling), would it be accurate to say that adding the twist would have a net effect of the wing stalling sooner than it would have otherwise?

Yes and no. It depends of the twist value first. But you can sometimes win by increasing oswald number in twisted wings, that you loose by partly decresing your critical AoA on some wing section, before the others, as you have previously suggested.

If so, might that be the reason W. Messerschmitt didn't have any twist in his wing? Wingloading was high already, why 'hasten' the stall? Particularly when you have LE slats.

You also have a little drag gain on small AoA for fast speeds and dives, if you don't use twist.

Regards

Milosh · Aug 25, 2010

Back to radiators: obviously they were not aware from tests leaded in TsAGI wind tunnel with SB-2 radiators (at the end of the 30ies), that finally went inside the wing thikness of the SB new-look, called Ar-2. This solution being at far, the best.

deHavilland put the radiators in the wing of the Mosquito and I doubt they were aware of the TsAGI tests.

tail end charlie · Aug 25, 2010

Milosh said:
deHavilland put the radiators in the wing of the Mosquito and I doubt they were aware of the TsAGI tests.

The spitfire was originally designed to have evaporative cooling in the leading edge of the wings. The radiators were put on when the evaporative system didnt work. Supermarine used the wings and floats as radiators on their race planes.

from
wikipedia
Ahead of the spar, the thick-skinned leading edge of the wing formed a strong and rigid D-shaped box, which took most of the wing loads. At the time the wing was designed, this D-shaped leading edge was intended to house steam condensers for the evaporative cooling system intended for the PV-XII. Constant problems with the evaporative system in the Goshawk led to the adoption of a cooling system which used 100% glycol.

Colin1 · Aug 25, 2010

tail end charlie said:
The spitfire was originally designed to have evaporative cooling in the leading edge of the wings. The radiators were put on when the evaporative system didnt work. Supermarine used the wings and floats as radiators on their race planes

Well, sort of
the Type 224 was a different beast to F37/34 and evaporative cooling, though they possibly didn't know it, was on the cusp of obsolescence. The Type 224 gave 'a good performance, attained by the inclusion of leading edge evaporative cooling and a Rolls-Royce Kestrel S engine in a clean monoplane design'.

The evaporative cooling system worked by means of a steam separator mounted directly behind the engine outlets and the steam is led from there to the leading edge of the wing. The steam chamber is formed by the spar and metal covered leading edge. The condensate drains to a hotwell at the lowest part of the wing and is returned to the header tank by two turbine-driven pumps, the turbines being driven by the steam supply from the engine. Alternatively, the engine hotwell pump can be used. If preferred a normal type of honeycomb condenser can be fitted under the fuselage, the increase in weight of the aircraft being approximately 200lbs. Wind tunnel tests show that the increased weight and resistance results in a sacrifice of 12mph top speed and 300ft/min climb.

Unfortunately for evaporative cooling and fortunately for the Spitfire, the invention of glycol and its higher boiling point than water meant that powerplants no longer needed cumbersome, unwieldy evaporative systems, they could now be cooled with a fraction of the coolant volume and more efficiently; radiators weren't 'put on when the evaporative system didn't work' (it did work), it's just that the radiators were part of a different and more effective method of cooling.

tail end charlie · Aug 25, 2010

Colin1 said:
Well, sort of
Unfortunately for evaporative cooling and fortunately for the Spitfire, the invention of glycol and its higher boiling point than water meant that powerplants no longer needed cumbersome, unwieldy evaporative systems, they could now be cooled with a fraction of the coolant volume and more efficiently; radiators weren't 'put on when the evaporative system didn't work' (it did work), it's just that the radiators were part of a different and more effective method of cooling.

I suppose at the time supermarine, from their racing experience preferred not to have radiators but then with the meredith effect radiators producing some thrust to compensate for the radiators drag it made it a no brainer. Since the guns fired in the wings I dont know how the evaporative system would have worked anyway.

Colin1 · Aug 25, 2010

The USAAC had been using glycol for about 10 years prior to Supermarine's travails with a product called Prestone but it was applied 'neat' and like all neat glycol, it pretty much ate the gaskets; the Americans did suffer many leakage problems with their powerplants.

It wasn't until just prior to the outbreak of war that someone came up with the idea of a mix ratio of 70:30 water to glycol mix, this was applied to the Merlin and proved superior to the neat glycol application at atmospheric pressure whilst considerably reducing the seepage through the gaskets.

The system was introduced to all Merlins after the II and X.

drgondog · Aug 25, 2010

parsifal said:
fantastic stuff guys, though I struggle to comprehend even the basics of the discussion. Without trying to re-ignite the controversy, I have to pose the question, of the four types we are looking at, which one had the best or most advanced wing form.

Form or airfoil or combined features of an integrated wing? The 51 seems to have the wing with th eleast drag while retaining desirable flight and handling characteristic. The Spit wing started out as the planform with the least induced drag until all the necessary real life additions were made. The 109 wing offered a very innovative and useful feature in the slats. Can't think of any unique novelties on the Fw 190 wing save the zero twist on the outboard section. All performed very well in air to air combat.

Short answer is that offhand I don't know how I would award a 'suprior' wing design as there were many other factors that went into air superiority

Only one (of the four named fighters) had significant range AND comparable combat performance at all altitudes. The wing was lergely responsible for the success of the Mustang... but many other factors contributed to its balanced qualities

I suspect the answer will be along the lines of "it depends on the mission profile"

In anticipation of that, I guess I have to ask a series of more complicated questions.

Of the four types which was the better at

i) High altitude (above 20K)
ii) Medium Altitude (10-19.9K)
iii)Low Altitude (below 10K)

assuming two scenarios for each of those altitude ranges firstly a turning knife fight, at say average speeds of 250 knots, and combat mainly in the horizontal. Alternatively, which is the better wing form in a high speed fight, say above 300 knots, in which the emphasis is on straight line speeds and the combat is mostly in the vertical.

Maybe this original question...which type is the better depends heavily on the combat situation under which the hypothetical combat is being fought...

I believe, though I know there are many w2ho will disagree that as a geneneralization, the spit, with its elliptical wing was better in the horizontal at lower speeds, than the Me109 under those same conditions. Conversely, the 109 was better at higher speeds, with its thinner smaller wing, and was better in the vertical plane, though i have read it had some problems in a dive (I dont think those problems relate to the wing however).

Would be interested to read your opinions....

It depends on the mission - as far as selecting the wing. As far as which was 'better' at different altitudes and which version (i.e Fw 190A-8 or Fw 190D-9). If you select speed and roughly comparable climb and turn, the Mustang was pretty much slightly superior to the Fw 190 although the 190 rolled faster. The 51 would outdive all except the comparable version Spit with the thinner wing (t/c) at transonic speeds.

If you select climb and turn, the Spit (IMO) pretty much triumphs all else being equal at all altitudes in general (two speed/two stage characteristics permitting some performance gaps - depending)

The 109 wing design with slats gave it excellent manueverabilty at high AoA from low speed to high G manuevers but as VG pointed out the wing/airframe design demanded radiator position in a placement sure to increase drag and reduce lift over the inboard wing section.. Ditto Spit.

Another way to look at it. The 51 was the heaviest (by significant percent) but it was faster and flew farther because the heavier airframe also carried a lot more fuel and was signigicantly less 'draggy' then the other three. A factor that should be discussion, having not much to do with wing planform is the design of the control surfaces. The 51 was perhaps the most responsive at high speed.

Of the 4 (109, Spit, Fw 190 and P-51) the 51 was the cleanest and the 109 was the draggiest. The 190D supassed the Spit and was closer to same drag as Mustang B/D. Arguement rage regarding the Meridith Effect as thr primary reason for the difference in performance but the fuselage/wing combination was nevertheless lower in drag than the other three.

The Spit, Mustang and 109 all had about the same ceiling with the Spit and 109 having better Lift Loading than the Mustang - pointing back to the reduced drag of the Mustang giving it compensation for its higher lift loading - and the Meridith Effect may have contributed another significant thrust component at high altitude..

So, could the 109 have benefitted with an under fuselage radiator design and laminar flow wing (while retaining) the slats? Probably in speed and range, but slower in climb due to extra weight.. Ditto for Spit vs Mustang.

Milosh · Aug 25, 2010

The 109A>E would be draggy but why would the 109G>K, excluding the 109s with bulges, be draggy?

drgondog · Aug 25, 2010

claidemore said:
Isn't the lift created on the top surface of the wing? If so, would that be the reason the radiators are on the undersurface, not the top? Of course a wing mounted radiator creates other problems, but how much effect (detrimental) would it actually have on lift? The changes on the Spitfire radiators from Mk V to Mk IX didn't seem to have much detrimental effect, at least none that I've heard of.

On another note, if adding twist causes one part of the wing to stall first, (allowing to pilot to feel an impending stall and either correct or hold the plane at that point without stalling), would it be accurate to say that adding the twist would have a net effect of the wing stalling sooner than it would have otherwise? If so, might that be the reason W. Messerschmitt didn't have any twist in his wing? Wingloading was high already, why 'hasten' the stall? Particularly when you have LE slats.

VG answered the questions but I though I would make one addition. First - wing twist doesn't cause the inboard part of the wing first, it enables the more twisted section to remain at a slightly lower AoA than the inboard wing. In effect when the inboard section relative AoA reaches stall, the outboard section still has an AoA below the stall value. Altough I didn't know that the 109 wing had no twist until yesterday, it is easy to assume that as the entire wing approached AoA for CLmax (stall), the slats have already deployed due to the stagnation pressure buildup of the impending stall and immediately provides additional CL for that portion of the wing. Happily (and by design) the ailerons were behind the slats and remained effective as the bottom was dropping out on the inboard sections.

Brief background re: Twist and airfoil/wing properties - The wing of constant section/infinite span has no induced drag and the entire wing (theoretically since infinite span is impossible) would altogether stall at the same AoA.

Airlow around a lifting surface requires that a streamtube 'particle' separated by the leading edge must re-join that particle at the trailing edge. When the 'particle' on one surface must travel faster (i.e on the upper surface of an airfoil with the most curve) then Bernoulli's Principal kicks in - faster velocity and lowest pressure on that curved surface than it's 'slower cousin' below. Airplanes fly and curveballs curve based on these principles

Your airfoils in such publications as Abbott and Dunhoff (sp?) which publish airfoil sections have the twio dimensional values of the perfect constant section infinite wing CL, CD and Cm for each airfoil. They must be corrected for such factors as AR and Tip Geometry

Airflow in a three dimensional wing will have a spanwise component of velocity which results in the flow at the wing tip to move from the lower surface to rejoin it's 'cousins' traveling on the upper surface. We now have a vortex, which causes inviscid drag, which we call INduced Drag

Make a wing finite and the lift distribution varies based on the planform. An elliptical planform (induced drag exists but it is lowest possible value -compared to a different wing planform with same AR, Oswald efficiency constant) starts with the 'best' Lift Distribution and the 'Lowest' induced drag. Add twist to the perfect wing and you increase drag (slightly). The inviscid drag due to twist is calculable and it is additional to the inviscid induced drag of the untwisted wing.

Twist can only degrade an Elliptical Wing's Lift Distribution spanwise, and increase induced drag as a result. The rectangular wing plan form with a well designed tip and a modest degree of twist will tend to shift the Lift Distribution inboard to make it more closely approach the elliptical.

Everything VG stated is dead on..

drgondog · Aug 25, 2010

Milosh said:
The 109A>E would be draggy but why would the 109G>K, excluding the 109s with bulges, be draggy?

Because the wing in all variants was draggy, the paint was draggy, the exhaust stacks were draggy, the slats and sheet metal gaps behind the slats were draggy, the radiators were draggy, the tailwheel was draggy. The open wheel wells were draggy

The nose/oil cooler of the 109F/G/K was less draggy than the E, the lack of tail struts were less than the 109E.
The bulges of the G was draggier than the E.The K was the cleanest and it was still draggy in comparison to the Mustang and fw 190/190D.

The basic airframe of the 109 was a 1935 design with many operational changes but kept the wing and same general lines/control surfaces, etc.

tail end charlie · Aug 25, 2010

drgondog said:
It depends on the mission - as far as selecting the wing. As far as which was 'better' at different altitudes and which version (i.e Fw 190A-8 or Fw 190D-9). If you select speed and roughly comparable climb and turn, the Mustang was pretty much slightly superior to the Fw 190 although the 190 rolled faster. The 51 would outdive all except the comparable version Spit with the thinner wing (t/c) at transonic speeds.

If you select climb and turn, the Spit (IMO) pretty much triumphs all else being equal at all altitudes in general (two speed/two stage characteristics permitting some performance gaps - depending)

It is clear the mustang was cleaner in aerodynamics than the spitfire but I'm sure read somewhere that the spitfire had a higher limiting mach number, are the two not related or was I reading bollocks.

Some spitfires had wings clipped did that make them more like a trapezoidal wing as regards drag or is it more complicated than that (I think I already know the answer)

parsifal · Aug 25, 2010

If Soren were here now........

Milosh · Aug 25, 2010

drgondog said:
Because the wing in all variants was draggy, the paint was draggy, the exhaust stacks were draggy, the slats and sheet metal gaps behind the slats were draggy, the radiators were draggy, the tailwheel was draggy. The open wheel wells were draggy

The nose/oil cooler of the 109F/G/K was less draggy than the E, the lack of tail struts were less than the 109E.
The bulges of the G was draggier than the E.The K was the cleanest and it was still draggy in comparison to the Mustang and fw 190/190D.

The basic airframe of the 109 was a 1935 design with many operational changes but kept the wing and same general lines/control surfaces, etc.

How can the paint be draggy when it was a finer grain than American paint? That means it not as orange peely as American paint.

How can the radiators be draggy when they had a boundary layer separator?

Why would the exhaust stakes be draggy?

Only the G-6 and G-14 had noticeable bulges.

Njaco · Aug 25, 2010

tail end charlie said:
......
Some spitfires had wings clipped did that make them more like a trapezoidal wing as regards drag or is it more complicated than that (I think I already know the answer)

I'm no expert but I believe that was for carrier Spitfires (Seafires) - space concerns.

parsifal · Aug 25, 2010

Ive read that clipped wing versions wer built for better low altitude performance. I guess with the denser air at lower altitudes, less wing was needed to get the necessary lift, and with less wing comes less surface area, and hence less drag

The equation becomes intersting in the midwar period. Putting aside the more exotic subtypes for both the 109 and the Spit, I would say that for most of the war the Spit and the 109 were more or less equal adversaries. Perhaps the lowest point in comparability occurred in early 1941, with the large scale introduction of the Me109f subtype. In the battles over Francein early to mid 1941, the fighter sweeps by FC were mainly against Me 109e types. Fighter Commands SpitII, Vs and Hurricane IIs were hard pressed by the4 Me 109es, achieving exchange rates somehat worse than 2 for1. Against the Me 109f, the exchange rates were even worse, perhaps as high as 3:1 against the RAF. SpitV versus Me 109F were a bit better, due mostly to the firepower advantage I think held by the later cannon armed subtypes of the Mark V.

What i find intriguing however, is that the general consensus held by many is that the 109 was superior to its stablemate the 190. Yet while it is arguable that the Spit V could at least hold its own against the Me 109f, it is generally acknowledged that aginst the FW 190, the Spit V was badly outclassed. The conventional histories then say that it was not until the ontroduction of the Spit IX in the latter part of 1942 that this qualitativfe imbalance was addressed. In combat against the Spit V at least, the FW 190 appears to be superior. Perhaps it has something to do with the altitudes (most of the combats over France and southern England were at low level) or the low firepower of the f subtype, or paerhaps we are looking at yet another urban myth.

I dont have figures for the FW190, introduced in the fall of 1941, but I have read that it outclassed s, rtThe FW

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