Bearcat vs Corsair

[drgondog]

So, Greg - illustrate your grasp of Physics and Aero (I presume you are one of the 'everyone who knows aero' per your comments above as well as physics) and start where you should start.

Two equations are necessary when iterating climb, acceleration and top level speed when the a.) Thrust HP is known, b.) the propeller efficiency is known for ALL Ranges of Thrust HP, c.) Drag (Base parasite plus parasite drag of miscellaneous items (including friction) plus increments of angle of attack parasite drag) multiplied by the CDm/CDp ratio related by increase in R.N. along the velocity plot, c.) Induced Drag

Force = Mass*Acceleration
Thrust = Drag

Why, you ask?

Well the P-51H is about 8.5% cleaner in parasite drag and the W/L for level flight is 40.5 for Combat load versus 43 for the P-51D at 10,300 pounds (Report uses 9700 for W/L=41.6)) meaning the Induced Drag for the P-51H is also lower than the P-51D.What this should suggest to you is that the P-51H Performance Chart and Report from NAA has accounted for all the above and extrapolated the Performance envelope for the correct Gross Weight but the P-51D values must be re-calculated based on a lower Gross Weight from a true load out equality AND a different THP rating all along the profile.

You didn't do this.

You then pick a velocity slightly different and iterate based on T=D and F=Ma as you move from excess Thrust to insufficient thrust for the top speed calculations until T=D.

It (The resulting top speed comparison with same engine and boost envelopes) is less of an effect on change to top velocity for the slightly different airframes as it is to acceleration and climb performance calc where the 6% in Gross Weight increase to move the P-51D from the NA 'model' state to an new analysis will yield significant advantage for the P-51H.

 

[rochie]

i will add that if we are talking fragilility during servicing and turn around or maintenance then would i be correct in thinking a P-51's Laminar flow wing is more fragile than the conventional wing on a Spitfire ?

 

[drgondog]

No, Rochie. The Mustang wing was very strong - so was the Spitfire wing.

I imagine that you are referring to the fact that the NACA/NAA 45-100 never truly achieved 'laminar flow' and that minor imperfections on the surface of the wing degraded some aerodynamic benefits.

Having said this the surface treatment at the NAA factory was to fill the flush rivet imperfections forward of the 30% chord line, prime, sand and paint to achieve a smoother surface than the Spit.

 

[wuzak]

Having said this the surface treatment at the NAA factory was to fill the flush rivet imperfections forward of the 30% chord line, prime, sand and paint to achieve a smoother surface than the Spit.

I think this is the point that Rochie is making - that the filling and paint are relatively easily damaged and have more of an effect on performance for the Mustng thsn they do for the Spitfire.

The arrangements for reloading ammunition were changed on the H compared to the D.

Armament was the same as in the P-51D. Removable ammo boxes and a redesign of the ammo doors were added. This saved time reloading and must have eased up on the laminar flow killing scratches and scuffs on the wings. The earlier models had to be loaded by hand out of portable ammo boxes. The top surfaces of the wings were taking a huge beating and disrupting the true laminar flow of the wing surface. I honestly doubt the crews in the field either knew or cared much about that.

In that way, the H could be described as less fragile than the D.

 

[rochie]

Thanks Bill, wuzak is right, it was laminar flow properties of the P-51's wing I was asking about, wondering if it was as difficult to maintain as is sometimes wrote about ?

Never doubted the physical strength of the actual wing structure

 

[pbehn]

All prop planes are fragile, If you take a P51 at max speed and fly downwards the wings and prop fall off very quickly. The design of all these aircraft was a compromise, strength costs weight.

 

[drgondog]

"To Be Laminar Flow or Not to Be Laminar flow". The NAA 45-100 never achieved hoped for results for "Laminar" flow to the max T/C point at ~ 38%, and shuffling about on the leading edge of the wing sure affected surface roughness, along with hail, operating on a dusty runway, etc.

Having said that, the wing still achieved a remarkable reduction in drag due to the shape and the benefits continued for delay of Mach wave formation as well continued performance of the wing in comparison with the classic types such as NACA 230xx with mac T/C of ~25%.

Any scuffling aft of the spar - as in the ammo box section was in an area where the region was immersed in an adverse pressure gradient or large build up of the boundary layer. IWhile I agree most of Joe's points, I see the ammo storage and resupply and stiffer door to serve faster operational turnaround with portable ammo containers, than preserving any laminar flow illusions in that section of the wing. IIRC the wing aft of about 30-35% was not treated with putty, primer and paint - just primer and paint as it was immersed in a boundary layer stage that negated any 'laminar flow' attributes.

Another point - the theoretical transition point from Laminar fluid flow to Turbulent fluid flow, based on the Mean Aerodynamic Chord is in the R.N. range of ~ 500,000 which is barely moving. The R.N. range of 9x10^^6 is about 150 mph at SL densities.

Then to add to the point I was making above, the P-51H was significantly 'stronger' with respect to target G limits at Combat Gross weight simply because the airframe never grew any heavier due to modifications while both the Mustang and Spitfire grew significantly as new engine and extra fuel, etc was added.

I don't know that Supermarine engineers did Not beef up any part of the Spit to conform to original Stress vs G load but I do know that NAA did Not alter any structure to accommodate the original 8 G target for limit load as the airframe continued to grow. The XP-51 wing through the P-51B was exactly the same and the very first opportunity to re-design the spar/root chord/carry through structure came with the D - but it is clear from the Pilot Handbook that 8000 pounds remained the GW standard for Mark I, P-51, P-51A, A-36, P-51B/C, P-51D/K - all designed at 8G Limit and 12G Ultimate for 8,000 pounds GW.

 

[rochie]

thanks for the explanation Bill

 

[pbehn]

Then to add to the point I was making above, the P-51H was significantly 'stronger' with respect to target G limits at Combat Gross weight simply because the airframe never grew any heavier due to modifications while both the Mustang and Spitfire grew significantly as new engine and extra fuel, etc was added.

I don't know that Supermarine engineers did Not beef up any part of the Spit to conform to original Stress vs G load but I do know that NAA did Not alter any structure to accommodate the original 8 G target for limit load as the airframe continued to grow. The XP-51 wing through the P-51B was exactly the same and the very first opportunity to re-design the spar/root chord/carry through structure came with the D - but it is clear from the Pilot Handbook that 8000 pounds remained the GW standard for Mark I, P-51, P-51A, A-36, P-51B/C, P-51D/K - all designed at 8G Limit and 12G Ultimate for 8,000 pounds GW.

From what I have just read on the net modifications to the Spitfire wing were more for torsional strength and performance in dives the later marques of the Spitfire and the Spiteful looking increasingly like a Mustang in the wing department.

from wiki

Redesigned late wing[edit]
As the Spitfire gained more power and was able to fly at greater speeds the possibility was that pilots would encounter aileron reversal so the Supermarine design team set about redesigning the wings to counter this possibility. The original wing design had a theoretical aileron reversal speed of 580 mph (930 km/h),[8] which was somewhat lower than that of some contemporary fighters. The new wing of the Spitfire F Mk 21 and its successors was designed to help alleviate this problem; the wing's stiffness was increased by 47%, and a new design of aileron using piano hinges and geared trim tabs meant that the theoretical aileron reversal speed was increased to 825 mph (1,328 km/h).[8][9][10]


and for the Spiteful

Design and development[edit]
By 1942, Supermarine designers had realised that the aerodynamics of the Spitfire's wing at high Mach numbers might become a limiting factor in increasing the aircraft's high-speed performance. The main problem was the aeroelasticity of the Spitfire's wing; at high speeds the relatively light structure behind the strong leading edge torsion box would flex, changing the airflow and limiting the maximum safe diving speed to 480 mph (772 km/h) IAS[nb 1]. If the Spitfire were to be able to fly higher and faster, a radically new wing would be needed.[1]

Joseph Smith and the design team were aware of a paper on compressibility, published by A D Young of the R.A.E, in which he described a new type of wing section; the maximum thickness and camber would be much nearer to the mid-chord than conventional airfoils and the nose section of this airfoil would be close to an ellipse[nb 2]. In November 1942 Supermarine issued Specification No 470 which (in part) stated:

A new wing has been designed for the Spitfire with the following objects: 1) To raise as much as possible the critical speed at which drag increases, due to compressibility, become serious. 2) To obtain a rate of roll faster than any existing fighter. 3) To reduce wing profile drag and thereby improve performance.


The wing area has been reduced 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.[1]

Specification 470 described how the wing had been designed with a simple straight-tapered planform to simplify production and to achieve a smooth and accurate contour. The wing skins were to be relatively thick, aiding torsional rigidity which was needed for good aileron control at high speeds. Although the prototype was to have a dihedral of 3° it was intended that this would be increased in subsequent aircraft.[1] Another change, to improve the ground-handling, was replacing the Spitfire's narrow-track, outward-retracting undercarriage with a wider-track, inward-retracting system. (This eliminated a weakness in the original Spitfire design, giving the new plane similar, safer landing characteristics, comparable to the Hurricane, Typhoon, Tempest, Mustang, and Focke-Wulfe 190.) The Air Ministry were impressed by the proposal and, in February 1943, issued Specification F.1/43 for a single seat fighter with a laminar flow wing; there was also to be provision made for a wing folding scheme to meet possible Fleet Air Arm requirements. The new fighter was to use a fuselage based on a Spitfire VIII.[2]

 

[drgondog]

That summary strongly suggests changes to the wing such as increased skin thickness to create stiffer torque box (which would also de facto increase beam cap thickness for the spars) resulted in raising the Spit back to a 7.2/11.0 Load capability at the 1942 GW.

 

[rochie]

great bit of info pbehn, thanks

 

[wuzak]

I don't know that Supermarine engineers did Not beef up any part of the Spit to conform to original Stress vs G load but I do know that NAA did Not alter any structure to accommodate the original 8 G target for limit load as the airframe continued to grow. The XP-51 wing through the P-51B was exactly the same and the very first opportunity to re-design the spar/root chord/carry through structure came with the D - but it is clear from the Pilot Handbook that 8000 pounds remained the GW standard for Mark I, P-51, P-51A, A-36, P-51B/C, P-51D/K - all designed at 8G Limit and 12G Ultimate for 8,000 pounds GW.

I'm not entirely certain, but I think the "universal wing", which was used on Mk V and subsequently the Mk IX, was strengthened from the wing that Mks I and II had.

The VIII also got an upgraded wing, which had small leading edge tanks in board of the cannon bays. These wings were used on the XIV too.

Griffon variants were strengthened with new longerons, among other things, to take the higher loads from the heavier engine.

 

[pbehn]

That summary strongly suggests changes to the wing such as increased skin thickness to create stiffer torque box (which would also de facto increase beam cap thickness for the spars) resulted in raising the Spit back to a 7.2/11.0 Load capability at the 1942 GW.

I see your "beam cap thickness" with cold working, and raise you with the "Bauschinger effect".

I know very little about aerodynamics above that of an interested layman. Once in Italy we had a problem with Yield, every high result was blamed on "cold working" every low result was blamed on the "Bauschinger effect", the true cause was the external water quench which wasnt admitted until it was replaced. Basically what I am saying is I haven't a clue what beam cap thickness is.

 

[drgondog]

I see your "beam cap thickness" with cold working, and raise you with the "Bauschinger effect".

I know very little about aerodynamics above that of an interested layman. Once in Italy we had a problem with Yield, every high result was blamed on "cold working" every low result was blamed on the "Bauschinger effect", the true cause was the external water quench which wasnt admitted until it was replaced. Basically what I am saying is I haven't a clue what beam cap thickness is.

If we use an "I" Beam as the cross section of a spar the upper and lower flange are part of the individual 'caps' and the vertical web is the material that takes out the shear due to the bending loads placed on the spar when one cap absorbs compressive load and the other a tensile load.

When sheet metal is effectively 'affixed' to a spar as described above, a specified portion of the cross section can be considered as 'additive' to the cross sectional area of the original I beam caps... thus the Stress = P/A is reduced by the effective increase in Area. Having said this, the skin attached to the spar must also carry shear loads imposed by the bending and subsequent deformation of the spar at the cap, even as the web between the caps carries the shear between the compression and tensile portions of the cap.

During the analysis phase, the cap region must first be analyzed for compressive and tensile loads/divided by the area for allowable stress, the web must be analyzed for buckling while carrying the shear transfer, then the skin/rivet design must be analyzed to determine whether the stress is a.) too high on the rivet cross section within the skin, then b.) look for rivet hole deformation/failure due to the rivet/fastner and c.) look to the spar cap for the interaction of the rivet attaching skin to spar cap as above.

 

[drgondog]

I hope that makes sense

 

[swampyankee]

In the air to air role, the Bearcat is the superior performer.

An armament of four .50's though is pretty marginal though.

Which is why they upgraded to 20 mm pretty quickly

The Corsair was, however, a more versatile aircraft, probably the closest thing to a WW2-eral equivalent of the fighter/attack F-18.

 

[swampyankee]

Don't forget that the Allies (except the Russians) not only had superior numbers, but had better quality pilots to boot. Yes I know that there were still many German aces who flew the ME-262 jet fighter and the T-152, but a few good men really can't turn the outcome of a doomed war anyway. Most of the German and Japanese pilots were mostly hastily trained young men who could barely fly the plane they were in, let alone fight, and had practically no combat experiance to boot.

I think that by 1944, certainly 1945, the Soviet pilots were quite good, if for no other reason than the bad ones had all been shot down.

 

[pbehn]

I hope that makes sense

It does Drgondog, I don't know how I missed it years ago, apologies.

 

[drgondog]

Some years ago I read an account of the only Bearcat vs Mustang encounter known to me. Shortly after hostilities ceased on VJ day, a carrier with a squadron of F8Fs was in the Gulf of Mexico and called on the port of New Orleans as a PR exercise. Nearby, on shore, was based a squadron of P51s. The guy relating the story was one of the Bearcat pilots. He said that several times both units would go up and "happen to" meet for simulated dogfights. He pointed out that no F8F was ever bested in these encounters. Who can say what the relative quality of the pilots was, flight time, etc., but it is the only example of such an encounter I'm aware of. Another account by a pilot who flew both planes said the 'Cat was clearly the stronger performer - that its throttle response was instantly felt seat-of-the-pants, while the Mustang first made more noise, then began to accelerate. The Bearcat would have been an excellent anti-kamikaze device, though that was not its initial designed purpose. The Mustang proved superb as a long range bomber escort and many B-17 aircrew survived the war because the P51 could go all the way there and back on the long missions. Hats off to William Overstreet, who passed in 2014. He flew 100 P51 missions, survived being shot down 3 times, flew a FW190 back to England for one of his escapes, and chased a 109 under the Eiffel Tower, shooting it down over Paris. Many eyewitnesses corroborated this event.

The Bearcat in flight comparisons with a P-51D should always win at low to medium altitude. Different missions. The XP-51F/G and P-51H on the other hand, carrying as much fuel as the F-8F in every category except turn and maybe roll. The XP-51G with full internal combat load of 205 gallons had a 7500 fpm climb rate and 497mph dash speed at WEP at 22,000 feet. The XP-51F/G didn't go into production because without a fuselage tank, it didn't have the desired Combat radius of the P-51B/C - but it would have much better range, climb, dive, acceleration, ceiling, speed in all power settings - than the F-8F.

 

[Peter Gunn]

Would the P-51G have been based on the razorback P-51B/C or would it have been the new bubble top model?

EDIT - Nevermind, sorry, a quick search on the intewebz answered that.