Qualities that made for a great aircraft that don't show up in performance stats.

Schweik said:

Like I said, there is some subjectivity in this which is why we will probably never agree. And yes I do think an aircraft is actually a new design sometimes within a specific aircraft model type. Personally (as I said already) I'd say Fw 190D is different from the A for example, or the Spit I from the Spit XXI, and the Allison Mustang from the Merlin ones, but I wouldn't insist on it.

I guess I would draw the line when it's both substantially different in terms of capabilities and performance, and has a different official designation. Admittedly somewhat arbitrary.

Defining exactly what makes a truly different aircraft when they are clearly of the same development lineage is tricky and I don't think there is any "official" criteria we would all necessarily agree on. I would argue it was usually a combination of factors, some dramatic (new type of engine, changes in the number of crew or a substantially changed wing), some more incremental like changes in armament, pilot or fuel system protection, fuel capacity, landing gear, modified control surfaces, and so on.

In the case of the P-36 / P-40 it's the combination of substantially increased performance (esp. top speed and dive acceleration) and overall carrying capacity. At the risk of repeating myself I believe the P-36 hit a wall in the 30's.

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I think most of us would agree that the Spitfire XXI is different than a Spitfire I. You do have a different wing in addition to the different engine and the somewhat different tail. Early Spitfires used three different wing tips but they were interchangeable from the last rib station out, no change to rest of the wing.
With the change from an Allison powered Mustang to a Merlin powered one things are only slightly more difficult. Pretty much the same wing but the fuselage got a splice put in it so you can't really take a P-51A airframe a put a Merlin V-1650-3 in it and get a real P-51B.
P-47D to P-47N gets a little tough. They extended the wing root area but kept the same airfoil and cord to accommodate fuel tanks. Then clipped the wing tips to reduce the wingspan to near original

New design or??????.

The basic difference between a P-36/Mohawk and a P-40/Tomahawk is the engine and the drag reduction/increased speed it provided. It came a cost in weight which affected maneuverability a bit. The majority of the plane was unchanged except to accommodate the increased weight.

Elmas said:

A Friend of mine, Ten. Alberto Scano, was among the Pilots to fly in the last Operational Training Unit on piston fighters in the early '60.
Here his memories.

Memorie di un pilota: le immagini e i ricordi del Tenente Alberto Scano - Aviation Report

Alberto told me several times that while G-59s had a wonderful stall behaviour, that of P-51 as awful.

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I'm wondering if the poor stall behaviour of the P-51 was due to the laminar flow wing. IIRC the Supermarine Spiteful/Seafang which were also laminar flow had vicious stall characteristics.

"You can't have a drunk wife and a full barrel" says a proverb of my own Country.
An aeroplane is a result of a lot of compromises and, if some parameters are stretched, the blanket becomes a little bit short somewhere.
So, using a profile with less resistance at high speeds (I should not say exactly "laminar", for various reasons) had as a result poor performances at stall. With computers today that could be sufficiently predictable, but Schmued and his Team, considered they had just a slide rule in their hands, made certainly the right choice at the right time.

Elmas said:

"You can't have a drunk wife and a full barrel" says a proverb of my own Country.
An aeroplane is a result of a lot of compromises and, if some parameters are stretched, the blanket becomes a little bit short somewhere.
So, using a profile with less resistance at high speeds (I should not say exactly "laminar", for various reasons) had as a result poor performances at stall. With computers today that could be sufficiently predictable, but Schmued and his Team, considered they had just a slide rule in their hands, made certainly the right choice at the right time.

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I think part of the idea of Laminar flow wings was to get simultaneously a large wingspan and low drag - presumably the big wing still providing benefits of lift and thereby, maneuverability. But the effect seems to be mainly for low drag and not much else. For the size of the wing it usually seems to end up somewhat lacking in lift. Of the few examples I know of which seems to have possibly succeeded in threading that needle were the elliptical Spitfire wing and the semi-elliptical wing of the Re 2005, also from the same country as that hilarious proverb.

Schweik said:

I think part of the idea of Laminar flow wings was to get simultaneously a large wingspan and low drag - presumably the big wing still providing benefits of lift and thereby, maneuverability. But the effect seems to be mainly for low drag and not much else. For the size of the wing it usually seems to end up somewhat lacking in lift. Of the few examples I know of which seems to have possibly succeeded in threading that needle were the elliptical Spitfire wing and the semi-elliptical wing of the Re 2005, also from the same country as that hilarious proverb.

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In the Mustangs defence I would point out that it was faster than the Spitfire by circa 30MPH. With additional tanks in the rear and on the wings it was possible for a P-51 to go into combat at 30,000ft with full main tanks. Also I believe the use of a small amount of flap improved turn performance. For much of a Mustang mission on escort it was grossly overloaded compared to its original design.

Of course - the tradeoff in speed (and cruise efficiency) was worth it at that point in the war, especially since Luftwaffe planes were mostly of high wing loading too and in the Pacific Theater, most Japanese aircraft were so much slower by then as to be at a marked disadvantage. Speed is life for fighters.

But if I know I was going to get into a dogfight and range wasn't an issue I might have preferred to be in a Spit IX or XIV personally. Not that that matters much.

Schweik said:

Of course - the tradeoff in speed (and cruise efficiency) was worth it at that point in the war, especially since Luftwaffe planes were mostly of high wing loading too and in the Pacific Theater, most Japanese aircraft were so much slower by then as to be at a marked disadvantage. Speed is life for fighters.

But if I know I was going to get into a dogfight and range wasn't an issue I might have preferred to be in a Spit IX or XIV personally. Not that that matters much.

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It was pure serendipity that the P-51 could take huge amounts of internal and external fuel and that it could fit a Merlin engine, it was just designed as a fighter and generally US fighters had longer range than their European counterparts.

Schweik said:

Of course - the tradeoff in speed (and cruise efficiency) was worth it at that point in the war, especially since Luftwaffe planes were mostly of high wing loading too and in the Pacific Theater, most Japanese aircraft were so much slower by then as to be at a marked disadvantage. Speed is life for fighters.

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The late-war Japanese fighters were anything but slow and were on a par with anything the Allies had.
KI-84, KI-100, N1K and J2M were all dangerous adversaries.

GrauGeist said:

The late-war Japanese fighters were anything but slow and were on a par with anything the Allies had.
KI-84, KI-100, N1K and J2M were all dangerous adversaries.

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In theory yeah. But from what I have read, those weren't the planes encountered for the most part. Built in relatively low numbers and mostly grounded due to mechanical problems, spare parts shortages and fuel shortages. And none of them were apparently very good at high altitude. Only the Ki-84 and the (very rare) J2M were really competitive in terms of speed. The main issue though is that from what i understand most enemy fighters encountered in 1943 & 1944 were still Ki-43 or A6M, with a few Ki-61 and Ki-44 and the occasional hapless twin-engined Ki-45. The ones you list above could be very dangerous when encountered but seemed to be pretty rare in the field.

I agree though those were very good designs, particularly the N1K and Ki-84. So were some of their later make Naval bombers like the Aichi B7A (352 mph, two 20mm cannon and supposedly more maneuverable than a Zero), Yokosuka D4Y (342 mph) and Nakajima B6N though they were a bit too fragile for the real world and didn't get to reach their full potential.

There was also declining pilot quality to contend with. Somebody posted a thread here a while back showing some Japanese statistics for air combat in Burma and Ki-84 squadrons apparently came out on the losing end against late model P-40s a couple of times.

I wonder how good of a fighter the B7A might have made. If it could manage 352 mph with a tail gunner and bomb handling gear, one would imagine it might have been a pretty good land based fighter. It doesn't seem to have been used much because it was meant for very large aircraft carriers which didn't become available (the only one big enough- the Taiho, was sunk in 1944). It probably came out too late to make much of a difference regardless.

ktank said:

I'm wondering if the poor stall behaviour of the P-51 was due to the laminar flow wing. IIRC the Supermarine Spiteful/Seafang which were also laminar flow had vicious stall characteristics.

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No. Airfoil behavior—despite Riblett — is not well-corrrelated to wing stall. Check out the stall of the 23012 airfoil, used on the Bonanza, which does not have a vicious stall, by any standard.

How to compare the P-51 (390 mph) airfoil

P-51D ROOT (BL17.5) AIRFOIL (p51droot-il)

Airfoil database list(P) p51droot-il to pw98mod-pw

with that of the Beech Bonanza (180 ktas)?

NACA 23012 12% (naca23012-il)

Quite two different profiles, aren't they?

And of course it is not a matter of "just" wing profile, being involved (very important) wing incidence and specially "wash-out", interferences between wing, tailplane and fin, etc.

And, probably, the flight envelope of P-51 was quite different ( and probably more demanding) from that of Bonanza.

Elmas said:

How to compare the P-51 (390 mph) airfoil

P-51D ROOT (BL17.5) AIRFOIL (p51droot-il)

Airfoil database list(P) p51droot-il to pw98mod-pw

with that of the Beech Bonanza (180 ktas)?

NACA 23012 12% (naca23012-il)

Quite two different profiles, aren't they?

And of course it is not a matter of "just" wing profile, being involved (very important) wing incidence and specially "wash-out", interferences between wing, tailplane and fin, etc.

And, probably, the flight envelope of P-51 was quite different ( and probably more demanding) from that of Bonanza.

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Nonetheless, stall properties of wings are not strictly determined by the stall properties of the airfoil. There were numerous high performance fighters with decent stall properties. Also, many laminar flow airfoils have fairly benign stall.

swampyankee said:

Nonetheless, stall properties of wings are not strictly determined by the stall properties of the airfoil. There were numerous high performance fighters with decent stall properties. Also, many laminar flow airfoils have fairly benign stall.

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Stall behavior is a property of the entire airframe, not just the wing, and varies with the G acceleration at which it occurs. A Bonanza with an entire Mustang replica wing would not likely acquire a nasty stall reputation simply because it would seldom if ever be stalled at high speed and high G.
Let's face it, most "nasty stall behaviour" results from asymmetric stalling resulting in some variety of a snap maneuver. This is exacerbated if the lift/drag deterioration is very sudden (this IS a function of the wing's airfoil and planform), and further worsened by elevator and rudder blanking in the disorganised airflow.
A plane with a "docile" wing (lots of tips-down wing twist and a relatively "thick" cambered airfoil), and tailfeathers clear of the high AOA wing downwash will give you a smooth controllable stall, even at high speed and high G. Trouble is, such a plane is not going to give you best speed, maximum cruise efficiency, or best ACM maneuverability on the available power. It WILL, however, help you keep your nugget aviators alive outside of combat situations. As you've probably guessed, I've been describing my sweetheart here, the T-34, the ultimate Walter Mitty fighter-Bonanza.
Another factor to consider is pilot behavior. Most relatively inexperienced pilots have a tendency to reflexively "steer" the airplane with ailerons at high AOA, no matter how much they've been barked at by their instructors. Any aileron deflection on the verge of a stall will almost certainly induce an asymmetric stall opposite the direction of the control input. Low, slow, and dirty in a snappy machine like the P-51, this will likely lead to fatal consequences.
This scenario brings up another facet of the stall/spin phenomenon, getting behind the power curve. For a heavy, high performance plane like the Mustang there yawns below safe approach speed a deep, dark abyss called the back side of the power curve. It starts when you get a little slow and your sink rate picks up. Deck angle stays the same, so you don't notice, but your increasing vertical velocity is causing your AOA to increase significantly. This increases drag, and you slow still further, AOA increases more and you're still fat dumb and happy until you notice the ground rushing up, dump the nose to gain speed, drastically reducing lift, so sink rate and AOA increase yet again, and you are on the verge of a stall. There are three alternative endings to this episode.
1) You realize you're too slow to add power which would induce a "torque roll", so you ride it into the mangroves short of the runway.
2) You try to stretch your glide to the runway, remembering your instructor's admonitions to be gentle on the rudder when slow, so you steer with the ailerons, snap inverted and arrive at the same spot in the mangroves somewhat more spectacularly.
3) You realize you desperately need power, cob the throttle, the torque roll takes over despite full opposite aileron and rudder, and you arrive at the same spot in the mangroves even more spectacularly.
Speed is life.
Cheers,
Wes

swampyankee said:

Nonetheless, stall properties of wings are not strictly determined by the stall properties of the airfoil. There were numerous high performance fighters with decent stall properties. Also, many laminar flow airfoils have fairly benign stall.

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But of course. As I said before (or, better, as Ten. Alberto Scano said to me) stall of G.59 was a piece of cake in comparison to that of P-51.

I used to believe the Spitfire had a poor rate of roll until someone put a chart on the forum. The Spitfire had its wings clipped to improve rate of roll, but that doesn't mean it was poor, the Spitfires problem was it usually came across the Fw 190 and that was about as good as it gets in WW2 roll rate. The issue is whether you are making a judgement or a comparison. The performance of aircraft was increasing all the time and compromises were made, if this compromise resulted in a plane that stalled in level flight at 100MPH then don't try to fly at 90MPH, much of it is an issue of pilot training. In combat the Fw 190 would stall so quickly it would sometimes tumble, much worse than the more benign Hurricane, that doesn't mean that any pilot would prefer the Hurricane. From the war years to present day pilots have flown both the Spitfire and the Mustang, are they making a judgement on the Mustang or a comparison with the Spitfire because the Spitfire was 30MPH slower with the same engine and most would choose speed over stall characteristics. The P-51 maybe wasn't the best in turn and stall performance, I am sure the designers were aware that it wouldn't be, there isn't a free lunch in engineering, however there wouldnt be so many flying today if it was intrinsically dangerous.

A P-51 is NOT dangerous unless it is the first high-performance aircraft you have ever flown. Then it is a downright killer.

But so is ANY 1,300+ hp WWII fighter. Fighter pilots required primary, basic, and advanced training before being strapped into a worn-out P-40 for fighter transition. If you put a new, baby P-51 pilot into a B-29 with no transition training, he would not survive for very long, either.

GregP said:

A P-51 is NOT dangerous unless it is the first high-performance aircraft you have ever flown. Then it is a downright killer.

But so is ANY 1,300+ hp WWII fighter. Fighter pilots required primary, basic, and advanced training before being strapped into a worn-out P-40 for fighter transition. If you put a new, baby P-51 pilot into a B-29 with no transition training, he would not survive for very long, either.

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Of course. My Friend Ten. Alberto Scano went from T-6 to G-59 two seater, then to G-59 single seater and then to P-51.

GregP said:

A P-51 is NOT dangerous unless it is the first high-performance aircraft you have ever flown. Then it is a downright killer.

But so is ANY 1,300+ hp WWII fighter. Fighter pilots required primary, basic, and advanced training before being strapped into a worn-out P-40 for fighter transition. If you put a new, baby P-51 pilot into a B-29 with no transition training, he would not survive for very long, either.

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It reminds me of a Tommy Cooper joke, Tommy goes to the doctor and puts his arm behind his back.
Tommy : Doctor every time I do this it hurts.
Doctor : Well stop doing it then!

One major factor beyond performance stats, is the ability to keep them flying. Wars are not won by the best airplane, tank, or rifle, but through logistics. Having equipment that is robust, simple to maintain, in large quantity, operator friendly, with well trained crews, pays greater dividends than individual performance characteristics. Great example, the Tiger and Panther tanks. Compared to allied tanks, T-34 and M4 Sherman for example, they were regarded as the better vehicles. But when looked at through the logistics lens, they failed miserably. Harder to produce, highly technical and complex, difficult to maintain (without adequate spare parts), not in great enough quantity, and a host of other factors, reduced their combat effectiveness.