Would it have been cheaper to....

[Thorlifter]

One of the major advantages to the P-51 was the laminar flow wing. So, instead of developing a whole new plane, would it have been cheaper to just put that wing on a P-40 and also given the same upgraded engines the P-51 had ? Would that big chin of the Warhawk still be a hindrance?

 

[wuzak]

You'd be talking about the XP-53/XP-60.

 

[wuzak]

Double post.

 

[GregP]

I like the XP-40Q better than the XP-53/XP-60 myself. It was a beautiful thing and had good performance. It was a VERY good fighter but, in the opinions of the people in charge, not good enough to warrant production. I think they made a mistake and should have switched the Curtiss line over to P-40Q's and sent them as repalcements for the P-40's. The roll performance was better than the P-51 as was the climb performance. The top speed was less than 1/2% slower than the P-51 and it would have been a nasty surprise for people used to engaging P-40's.

In the end, it didn't get to show it's capabilities and was relegated to prototype status. Thus history speaks.

The Curtiss CW-21 Demon looked good, too, but had an abysmal showing when it had a chance to shine, so you never know what might have happened. The P-40Q might have done very well and might have been another hard-luck case ... it's all in the eye of the person imagining the scenario.

 

[OldSkeptic]

One of the major advantages to the P-51 was the laminar flow wing. So, instead of developing a whole new plane, would it have been cheaper to just put that wing on a P-40 and also given the same upgraded engines the P-51 had ? Would that big chin of the Warhawk still be a hindrance?

Not really. There is a mythology about the Mustang's low drag being because of its laminar flow wing, which is simply not true.
The slightest manufacturing defect, dents from use, or dirt or even just a insect splat on the leading edge destroys the laminar flow.

That's why no current plane has a laminar flow wing, you can do it in the laboratory, but not in real life.

The Mustang's low drag came from it's advanced radiator design, which offset 90% of radiator drag, plus careful attention to the design and manufacturing of the all the leading edge surfaces.

Thinness matters more in terms of drag and mach limit. Take the rewinged Typhoon, the Tempest, it was 25+mph faster on the same engine, plus a much higher mach limit, but that that was due to it being much thinner (and being semi-elliptic didn't hurt either).

 

[Shortround6]

The Mustang's advantage came from both (and perhaps a few other minor points, fully enclosed landing gear for one)

True laminar over the entire surface of the wing was only obtained in the Lab (wind tunnel).

Dirt,dents, chipped paint and insect splat degrades the airflow (increases drag) on regular wings too.

ALL wings start with laminar flow on the wing leading edge. The difference is at what point the airflow breaks down and goes turbulent. Most conventional airfoils had this happen around 20% of cord. The Davis wing on the B-24 extended this by around 5%? and the wing on the P-51 could extend this to around 40%. Now I would think that reducing the drag on even 15% of the surface of a 240sq ft wing might cause enough drag reduction to affect performance. How about a 5% reduction?
Something was going on because the Airfoil on the P-51 was 15.9% at the root and according to some of the amateur aerodynamicists on this site that should have doomed the Mustang to performance on a par with the Hurricane (unless that radiator was very, very good).
The Mustang might NOT have gotten a major reduction from laminar flow, it may have been from the shape of the airfloil with it's max thickness moved back to 39/40% of the cord instead of the more common 25-30% of cord. This may have allowed for that thicker wing to have more volume (room for fuel, guns, ammo) than a thinner wing with the same drag. But they wouldn't have designed that moved back thickness at the time unless they were looking for laminar flow.

Airflow on an airplane is very complex and is one reason (along with lack of large wind tunnels) that 'tuft'experiments are still going on.

Singling out one feature on a plane and proclaiming it to the difference between Plane A and plane B leaves out too many other variables.

You might want to tell Honda that their new Business Jet doesn't have laminar flow either.

Maybe it has some, maybe it has a little and maybe it has none and it is just advertising hype

 

[Shortround6]

One of the major advantages to the P-51 was the laminar flow wing. So, instead of developing a whole new plane, would it have been cheaper to just put that wing on a P-40 and also given the same upgraded engines the P-51 had ? Would that big chin of the Warhawk still be a hindrance?

Going back to original question.

It might have but part of the problem was the expectations of the AAC (army air corp). They were looking for major increases in BOTH performance and payload and the higher payload was in direct conflict with higher performance. You also have the whole wing loading/field performance thing. Loading down a plane with a heavy gun armament was bound to cause problems with limited power engines. British Mustangs with cowl guns were carrying 108lbs less ammo than the P-40C was for it's cowl guns.

Next is how much cheaper it actually would have been (and forget about the chin radiator, that was the least of the P-40s problems, a number of experimental P-40s flew with the radiators in other positions), Saving the Fuselage from the firewall back (or front of cockpit if you prefer) and changing wings, fuel tanks, landing gear, engine mounts, engine/powerplant/cowl is actually saving only a small percentage of the aircraft. Major changes in engine power, canopy and airflow often required a least some modification to the rear fuselage, tail fin/rudder, horizontal stabilizer further reducing commonality with original versions.
Changing the wing too much can affect the fuselage, and while you can modify just about anything with enough time and money a "Mustang" style wing could very well require a different attachment point (or two) to the fuselage compared to the original wing. This might only require modifying a Bulkhead/frame or two but again, lowering the commonality of the airframe runs up the cost.
The Second Me 209 was supposed to use a large number of Bf 109 parts/jigs/fixtures and make for an easy switch over in production but as the plane progressed through development performance not only decreased from original proposals but commonality of airframe from dropped to 30% or under which rather undermined the whole concept.

 

[gjs238]

If it were so easy to change wings, the effort would have been better spent on an earlier wing with fuel cells for the P-47.

 

[GrauGeist]

They tried all sorts of variations on the P-40 to improve performance.

XP-46: slightly smaller than the P-40, it incorporated changes like redesigned landing gear, clean fuselage lines (it actually looked similar to the MiG-3) and several other features.

XP-53: laminar flow wing and a Continental XIV-1430-3 engine

XP-60: Rolls Royce Merlin engine

XP-60A: Allison V-1710-75 engine with turbosupercharger (B14)

XP-60B: Allison V-1710-75 engine with turbosupercharger (SU-405-2)

XP-60C: P&W R-2800-53 equipped with contra-rotating prop

XP-60D: Packard V-1650-3 engine

XP-60E: P&W R-2800-10 engine

YP-60E: P&W R-2800-18 engine and bubble canopy

 

[nuuumannn]

One of the major advantages to the P-51 was the laminar flow wing.

It's worth remembering that across the Mustang's entire design, drag reduction was a key issue; in terms of wing and tailplane to fuselage fairing, placing of the radiator, the wing profile, fuse cross section; all that stuff, so a major rework of the P-40 would be required. As Greg pointed out, the P-40Q had good performance, even though of the ones that were built, each was different from the next, but the thing with the Mustang was the time it appeared with the performance it had, entering service in early 1942, development going on in 1940/41. Could Curtiss have produced a good reworked P-40 in that time? Look at what Dave posted above and how successful its attempts at producing a good P-40 replacement. The P-40Q would not have entered production and service until late '44, early '45.

The reason the Mustang came about was because Curtiss did not have the production facilities to build P-40s for the Brits; NAA was in the best position to build a new fighter from scratch because they did not have the same fighter production commitments.

 

[wuzak]

The P-60 could have been in production, depending on supply of the V-1650-1. It didn't happen because the performance improvement didn't justify changing the production lines.

 

[Shortround6]

The P-60 could have been in production, depending on supply of the V-1650-1. It didn't happen because the performance improvement didn't justify changing the production lines.

Pretty much hit's the nail on the head.

From Joe Baugher's website;

" The performance of the XP-60 was disappointing as well, with a top speed of only 387 mph at 22,000 feet. It took 7.3 minutes to reach an altitude of 15,000 feet, and service ceiling of 29,000 feet. Some of the reason for the disappointing performance was due to the wing surface not being finished to the degree of smoothness required for the laminar flow wing. Another factor was the fact that the Merlin engine did not deliver the guaranteed output. Empty weight was 7008 pounds, gross weight was 9277 pounds, and maximum takeoff weight was 9700 pounds. Dimensions were wingspan 45 feet 5 1/4 inches, length 33 feet 7 1/2 inches, height 12 feet 4 inches, and wing area 275 square feet."

The speed really isn't bad, actually rather good, considering the size of the airplane. However even a good running Merlin is going to have trouble with a plane that weighs about 700lbs more than a P-40F using the same engine. That shows up in the climb and ceiling.

 

[nuuumannn]

That's the point I'm making. In the time specified, Curtiss couldn't build a fighter as good as the Mustang.

 

[Shortround6]

In part due to the USAAC

They asked for eight .50 cal MGs in the P-53 and P-60 to start with.

If North American had been told to build a fighter carrying about 50% more weight in guns and ammo than the one they built ( close to 400lbs more) they might not have come up with quite the same design.

 

[nuuumannn]

In part due to the USAAC

The Mustang was designed for the British, not the Americans for starters. How could the Americans ignore the Mustang even with a P-40 derivative? Even if Curtiss could have gotten the P-60 into production, it's pretty likely the P-51 as it became with the USAAF i.e. a long range escort fighter, would have come about at any rate. It was a part of NAA's requirement for building the Mustang for the Brits that airframes were made available for evaluation by the USAAC.

 

[Shortround6]

I don't know if sanity was prevailing at the time the P-51 was adopted by the US but many of the requirements issued in 1940-41 called for totally unrealistic weapons loads to get the performance they were asking for. Almost every one of these "super" fighters turned into flops to a varying degree with the P-61 being the most successful.

The Mustang was designed to beat the P-40C, or it's upcoming version the P-40D (four .50 cal guns) NOT as alternative to the P-47 or P-53 (eight .50 cal guns).
What planes evolve into in later models when they get more powerful engines, stress factors are lowered, landing and take-off distances relaxed and so on are not good grounds for saying what the design would have looked like in the beginning with those extra requirements in force.

 

[drgondog]

Not really. There is a mythology about the Mustang's low drag being because of its laminar flow wing, which is simply not true.
The slightest manufacturing defect, dents from use, or dirt or even just a insect splat on the leading edge destroys the laminar flow.

Ah, no. There is more to it than that. Both the 45-100 and the 66-(.18) 015 (P-51H) had section Drag Coefficients of ~.0038 to .0045, and the NACA 23015 had section drag coefficient at .006 to .007, at same RN ranging from 6x10^^6 to 3x10^^6

The Max CL for the 23015 however was ~1.6-1.7 while the NACA/NAA 45-100 was 1.4 to 1.5.

These are Wind Tunnel Results on real airfoils - not 'theoretical',. The 'Laminar Flow' airfoils used on the P-51 did Not achieve their theoretical potential, but the carefully filled, sanded and painted upper and lower surfaces of the leading edge to about 30% yielded significant parasite as well as profile drag reduction due to delayed boundary layer separation over a conventional 23015 for example

That's why no current plane has a laminar flow wing, you can do it in the laboratory, but not in real life.

What you can't do with a laminar flow wing is push boundary layer separation from the AC to the Max T/C position (absent suction). In the case of the Mustang the T/C location was at 50%[ As to "Today"? virtually all conventional airfoils for mid to high end subsonic aircraft are doing fine with 64 and 65 and 66 series airfoils with max T/C of 35 to 50 percent. In other words 'laminar type'.

The Mustang's low drag came from it's advanced radiator design, which offset 90% of radiator drag, plus careful attention to the design and manufacturing of the all the leading edge surfaces.

Amusing as you go right to the heart of the matter with respect to achieving benefits (surface and leading edge treatment when you stated above that the tiniest disruption, etc "destroys the laminar Flow". In addition a real benefit was the low velocity gradient of a laminar flow wing and max T/C at 40-50% resulted in a huge delay to transonic shock wave formation - certainly a huge drag factor at high speed at altitude and dives. Had you said that placing a sandpaper strip on the leading edge would nullify medium Reynolds number regime drag reduction you would have been entirely correct.

Thinness matters more in terms of drag and mach limit. Take the rewinged Typhoon, the Tempest, it was 25+mph faster on the same engine, plus a much higher mach limit, but that that was due to it being much thinner (and being semi-elliptic didn't hurt either).

Nice to get it completely right. You are correct that T/C is the single most important factor in wing drag. But having said that a 64-009 will have significantly lower section drag than a 23009

 

[OldSkeptic]

It's worth remembering that across the Mustang's entire design, drag reduction was a key issue; in terms of wing and tailplane to fuselage fairing, placing of the radiator, the wing profile, fuse cross section; all that stuff, so a major rework of the P-40 would be required. As Greg pointed out, the P-40Q had good performance, even though of the ones that were built, each was different from the next, but the thing with the Mustang was the time it appeared with the performance it had, entering service in early 1942, development going on in 1940/41. Could Curtiss have produced a good reworked P-40 in that time? Look at what Dave posted above and how successful its attempts at producing a good P-40 replacement. The P-40Q would not have entered production and service until late '44, early '45.

The reason the Mustang came about was because Curtiss did not have the production facilities to build P-40s for the Brits; NAA was in the best position to build a new fighter from scratch because they did not have the same fighter production commitments.

That's right. One of the annoying things about the Mustang 'myth' is that it takes credit away from NA and their whole design team. Every part of the design was carefully done to reduce drag, from the nose backward. This included fit and finish as well. Very, very clever people.

We know from all sorts of examples that even slight imperfections on all the leading surfaces can have major speed impacts. The classic being the Spitfire and their 'pea fitting', to work out what areas to smooth rivet (expensive) and the ones they could use normal ones. The other example was the Crossbow work, they found they could add 10+mph to just about any plane just by taking a normal one and tidying it up.

 

[GrauGeist]

We know from all sorts of examples that even slight imperfections on all the leading surfaces can have major speed impacts. The classic being the Spitfire and their 'pea fitting', to work out what areas to smooth rivet (expensive) and the ones they could use normal ones. The other example was the Crossbow work, they found they could add 10+mph to just about any plane just by taking a normal one and tidying it up.

Sure, and the P-40 had quite a number of drag-inducing features well beyond the cooler intake cowl flaps and carb intake. For example, look at the canopy and it's structure as a source of drag...including the canopy slide track.

Lots of work to be done on the P-40's airframe if one were to try and create a streamlined finish.

 

[Aozora]

Can anyone point to a report on the effects of removing the O/D - Neutral Gray camouflage from the P-51? I would assume that removing any extra layers of paint from laminar flow wings would have been of some benefit.

Conversely, it would be interesting to know whether the addition of the D-Day stripes, field applied camouflage, or other identification markings to the P-51's wings also affected performance.