Has a Merlin ever been put into a P-39?

[MikeGazdik]

I have been reading through old posts, and digging up some nice newfound information on the P-39, one of my pet favorites. ( I like underdogs I guess)

Has anyone ever seen or heard about the P-39 having a Merlin installed? For racing or any other reason? That might be quite an airplane!!

 

[Colin1]

As far as war production goes

I don't think the P-39 was ever even conceptualised with a Merlin but the USAAF placed an order on 27Jun41 for two prototypes of the P-63 powered by the same V-1710-47 engine. The serials were 41-19511 and 41-19512.
A third prototype was also ordered, 42-78015, this one fitted with the Packard Merlin.
The first prototype, 41-19511, flew for the first time on 07Dec42, the first anniversary of Pearl Harbour. It was destroyed on 28Jan43 when its landing gear failed to extend.
The second prototype, 41-19512, followed 05Feb43. It too was destroyed, this time due to an engine failure.
The Merlin-engined 42-78015 was later delivered with another Allison instead, as the Merlins were primarily needed for the P-51.

and as far as air racing goes

A P-63C-5 (44-4181/NX73744, race no 53) in natural metal finish was brought to the 1948 air races by Frank Singer. A year later, Singer returned with a P-63C-5 painted dark grey and trimmed in red.
Decades later, it is not clear whether Singer had one Kingcobra or two. Re-registered (B9009/race no 90) this ship was extensively modified and distinguished by a tiny bubble canopy when flown in the 1971 San Diego air races piloted by Larry Havens.
This aircraft had a shortened wing, concave wing tips, and a V-1710-135(G4) engine.
Plans existed to convert the craft to a Merlin engine but before they could materialise, it was lost on a trials flight on 07Sep72 when Havens bailed out.

And that's about as much as I can find concerning Merlin interest for the P-39.

Sources
Bell P-39 Airacobra
Robert F Dorr Jerry Scutts
Crowood Aviation Series
ISBN: 1 86126 348 1
Page 130

 

[MikeGazdik]

Wow, very detailed, thanks for the info Colin. I didn't think the Air Corps / Bell had had ever tried. I had figured some racer would have attempted the conversion. With the amount of P-39 /P-63 airframes being found on the increase, I wonder if anyone would try it in the future.

Which leads me to two more seperate thoughts. 1) Is a P-39 / P-63 lighter than a P-51 and if so, would that translate to more speed around the pylons? 1b) A P-63 does have laminar airfoil wings correct? 2) If the Allisons were orginally better at low altitude, and the Merlins at high altitudes, why are the Merlins THE inline for Unlimited racing? Couldn't the Allison be tuned to equal or greater performance since the racing is on the deck. Or is the Allison still limited by its single stage supercharger even down low when racing?

 

[claidemore]

There are low alt rated Merlins, as well as high alt ones.

 

[Colin1]

1) Is a P-39 / P-63 lighter than a P-51 and if so, would that translate to more speed around the pylons?

1b) A P-63 does have laminar airfoil wings correct?

P-39
Empty: 5,600lbs (2540Kgs)
Loaded: 7,780lbs (3530Kgs)
Max speed: 380mph

P-63
Empty: 6,375lbs (2892Kgs)
Loaded: 10,500lbs (4763Kgs)
Max speed: 410mph

P-51 (Allison)
Empty: 6,300lbs (2858Kgs)
Loaded: 8,600lbs (3901Kgs)
Max speed: 390mph

P-51D
Empty: 7,125lbs (3230Kgs)
Loaded: 11,600lbs (5,206Kgs)
Max speed: 437mph

The P-63 was outwardly similar to the P-39, the lineage was obvious and unmistakeable but it was a completely different aircraft. Unfortunately, most of the novel design features were set prior to Pearl Harbour; at the time the design must have looked as good as anything.
The P-63 did indeed employ a laminar-flow wing section but I have my doubts as to the efficacy of the technology as applied to any WWII fighter, not just the P-63.

 

[MikeGazdik]

I guess what I am getting after is this thought. P-51 and P-63 both have laminar wings. The 63 is a little lighter, and I may suspect a little more aerodynamically clean. Put a race Merlin in one with the right prop, you might have a tough racer!

 

[Colin1]

I guess what I am getting after is this thought. P-51 and P-63 both have laminar wings. The 63 is a little lighter, and I may suspect a little more aerodynamically clean. Put a race Merlin in one with the right prop, you might have a tough racer!

Yes
I can see what you're driving at, the fly in the P-63 ointment for me was the retention of the awful, car-door/canopy arrangement that must have dragged at the a/c's aerodynamics.
A few were fitted with a teardop-style canopy a la P-51D, other than that it looked a beautifully clean a/c that has features I'm surprised weren't more extensively emulated throughout the industry. The use of leading-edge radiator cooling, vented at the trailing edge exploiting Meredith Effect and doing away with boxy, under-wing coolers and ventral scoops. This, admittedly, might have proved tricky for a/c using Fowler flap arrangements but then again, maybe not, the vent being blended into the upper wing possibly.

The other is the mid-engined layout, contentious maybe but like performance cars, it distributes the a/c's weight beautifully, gets it up on tricycle undercarriage for better ground-handling visibility and puts a big, punchy armament in the airscrew. I don't know how comfortable a pilot would feel sitting so close to the airscrew but he could conceivably have been moved much further forward giving him an unparallelled view of his own battlespace, instead of the enemy a/c 'disappearing' behind his engine cowl; it wasn't until planes like the Me163, the Ar234 or the Meteor that this was exploited. I discount the P-38 pilot because he doesn't have airscrews in front of him to worry about.

Fitted with the Packard Merlin, I see no reason why it couldn't have competed with the P-51 in everything but long-range escort - the only viable internal tankage area being occupied by the engine.

As a racer, I agree, it would have made a tough opponent but neither the P-63 nor the P-51 were fast enough in level flight to truly exploit laminar-flow technology - it wouldn't have helped.

 

[FLYBOYJ]

YesA few were fitted with a teardop-style canopy a la P-51D, other than that it looked a beautifully clean a/c that has features I'm surprised weren't more extensively emulated throughout the industry

Agree...

 

[drgondog]

P-39
Empty: 5,600lbs (2540Kgs)
Loaded: 7,780lbs (3530Kgs)
Max speed: 380mph

P-63
Empty: 6,375lbs (2892Kgs)
Loaded: 10,500lbs (4763Kgs)
Max speed: 410mph

P-51 (Allison)
Empty: 6,300lbs (2858Kgs)
Loaded: 8,600lbs (3901Kgs)
Max speed: 390mph

P-51D
Empty: 7,125lbs (3230Kgs)
Loaded: 11,600lbs (5,206Kgs)
Max speed: 437mph

The P-63 was outwardly similar to the P-39, the lineage was obvious and unmistakeable but it was a completely different aircraft. Unfortunately, most of the novel design features were set prior to Pearl Harbour; at the time the design must have looked as good as anything.
The P-63 did indeed employ a laminar-flow wing section but I have my doubts as to the efficacy of the technology as applied to any WWII fighter, not just the P-63.

Hard to pin down. What we do know is that airfoil had a very low Cd0. We debated (on this site) quite extensively Gene Lednicer's VSAERO modelling paper for the P-51B and D, the Fw 190A and D-9 and the Spit IX with excellent graphics demonstrating pressure distribution and drag results very closely approaching the wind tunnel results.

The only limitation that VSAERO had from any theoretical modelling approach I have seen is the inability to introduce surface roughness and any non-steady indicial velocity components to test separation conditions for AoA below critical.

Interestingly again, from one of the NACA Charts Lednicer presented, the 51 was second only to the P-80 (of US) in total parasite drag - and definitely superior to both the 190s and the Spit and 47 and F4U and P-38 - all of which were in the Spit IX range, above the Fw 190D-9.

 

[Colin1]

Hard to pin down. What we do know is that airfoil had a very low Cd0. We debated (on this site) quite extensively Gene Lednicer's VSAERO modelling paper for the P-51B and D, the Fw 190A and D-9 and the Spit IX with excellent graphics demonstrating pressure distribution and drag results very closely approaching the wind tunnel results.

The only limitation that VSAERO had from any theoretical modelling approach I have seen is the inability to introduce surface roughness and any non-steady indicial velocity components to test separation conditions for AoA below critical.

Interestingly again, from one of the NACA Charts Lednicer presented, the 51 was second only to the P-80 (of US) in total parasite drag - and definitely superior to both the 190s and the Spit and 47 and F4U and P-38 - all of which were in the Spit IX range, above the Fw 190D-9.

I've not read that report
it sounds interesting and I'd like to dig it up and go through it.
I'm a big fan of the late Lee Atwood, a US aeronautics and later astronautics engineer; the man was a god and I have huge admiration for him, a genuinely clever guy.
He did some paper on laminar-flow and how it was there on the Mustang, it just didn't do much (what chance of finding that, I wonder?); I seem to remember something about laminar-flow being key to a WWII combat pilot in the dive.

 

[Marshall_Stack]

How about putting a turbosupercharger in the P-39 as originally designed? I know that Bell fought to keep the turbosupercharger on the plane despite the USAAF and NACAs infinite wisdom to delete it (either because of drag or problems with the turbo). If I was Bell, I would have continued testing on that configuration.

I wonder what would have the higher gas consumption; the turbo and Allison or the Merlin 61?

 

[Colin1]

I wonder what would have the higher gas consumption; the turbo and Allison or the Merlin 61?

Looking at it purely from a mechanical data point of view;

Allison
Weight: 1340lbs (608Kgs)
Displacement: 28 litres (1710 cu in)

Merlin 61
Weight: 1320lbs (600Kgs)
Displacement: 27 litres (1650 cu in)

the Merlin looks to shade the Allison on fuel; 'ain't no replacement for displacement' holds but it costs fuel. The weight of any supercharger would also need to be added to the all-up weight of the Allison.

 

[davebender]

'ain't no replacement for displacement' holds but it costs fuel

I am under the impression that newer versions of the DB605 were more fuel efficient then newer versions of the RR Merlin despite having a greater displacement.

 

[Colin1]

I am under the impression that newer versions of the DB605 were more fuel efficient then newer versions of the RR Merlin despite having a greater displacement.

You're probably right
but as a rule of thumb it does hold some water...

my previous post doesn't unequivocally state that the Merlin was better on fuel than the Allison, I used basic, mechanical data to present my assumption that it probably was

 

[drgondog]

I've not read that report
it sounds interesting and I'd like to dig it up and go through it.
I'm a big fan of the late Lee Atwood, a US aeronautics and later astronautics engineer; the man was a god and I have huge admiration for him, a genuinely clever guy.
He did some paper on laminar-flow and how it was there on the Mustang, it just didn't do much (what chance of finding that, I wonder?); I seem to remember something about laminar-flow being key to a WWII combat pilot in the dive.

http://www.ww2aircraft.net/forum/polls/allied-tests-captured-bf-109-s-12456-4.html

Colin - Here is where I posted it last year..last link, bottom page, post 60

 

[Colin1]

Colin - Here is where I posted it last year..

Thanks fella
I'll be taking a look at that

 

[MikeGazdik]

Ok guys, in laymen terms. On Laminar flow, you are saying that at the speeds these fighter used, it did not add speed? Even the Mooney uses this airfoil. I thought that the laminar flow wings of the Mustang and others greatly attributed to the speed these aircraft could obtain.

 

[SoD Stitch]

Ok guys, in laymen terms. On Laminar flow, you are saying that at the speeds these fighter used, it did not add speed? Even the Mooney uses this airfoil. I thought that the laminar flow wings of the Mustang and others greatly attributed to the speed these aircraft could obtain.

Laminar flow wings did contribute somewhat to an aircraft's top speed but, IIRC, they were more effective at making the airfoil more efficient, not just faster; the airflow over a laminar-flow wing was "less disturbed" than the airflow over a "normal" wing, making the wing slipperier and, therefore, more efficient, since there was less turbulence over the airfoil. However, laminar-flow wings also had to be kept in much better shape (i.e.: cleaner) than a normal airfoil, since any disturbances in the airflow negated the benefits of the laminar-flow wing.

This is from Alfred Price's Combat Development In World War Two: Fighter Aircraft:

"One important airframe change which was not incorporated in the Spitfire during the Second World War was the so-called 'laminar flow' wing. This was a wing with an exceptionally fine finish; the surface roughness had to be less than .0005 of an inch and the maximum wave allowance was .0001 of an inch in any two inches of surface. The fineness of the finish was combined with a high-speed aerofoil section, with it's thickest point about half way back from the leading edge (rather than a third of the way back, in a conventional aerofoil). The first aircraft operational with the laminar flow wing was the North American P-51 Mustang, which entered service in the RAF in the summer of 1942. Later, re-engined with a Rolls-Royce Merlin with a two-stage supercharger, the Mustang became one of the outstanding fighters of the war. The effect of the laminar-flow wing can be seen if the performance of the P-51B Mustang is compared with that of the Spitfire IX; the comparison is valid, because the two aircraft were powered by almost exactly the same type of Merlin. In terms of wing span and area the Mustang's wing was closely comparable with that of the Spitfire; the latter's wing was 2 inches longer and about 4 per cent greater in area. Yet in spite of the similarity in wing dimensions and engine power, and the considerably greater weight of the Mustang (about a quarter greater), the latter was approximately 20 mph faster than the Spitfire IX for any given cruising power setting of the engine, and about 30 mph faster at maximum speed. The main factors responsible for this were the laminar-flow wing and the high-speed aerofoil."

 

[Colin1]

The effect of the laminar-flow wing can be seen if the performance of the P-51B Mustang is compared with that of the Spitfire IX; the comparison is valid, because the two aircraft were powered by almost exactly the same type of Merlin. In terms of wing span and area the Mustang's wing was closely comparable with that of the Spitfire; the latter's wing was 2 inches longer and about 4 per cent greater in area. Yet in spite of the similarity in wing dimensions and engine power, and the considerably greater weight of the Mustang (about a quarter greater), the latter was approximately 20 mph faster than the Spitfire IX for any given cruising power setting of the engine, and about 30 mph faster at maximum speed. The main factors responsible for this were the laminar-flow wing and the high-speed aerofoil."

I doubt it
the 20 - 30mph difference is more realistically attributed to the outlet for the radiator cooling. North American engineers designed this to allow heated air to exit the a/c under pressure, thus providing the Mustang with, effectively, a rudimentary tail pipe.

To say that the comparison is valid because both a/c share the same engine is a wee bit shy of good science, the prominent carburettor air intake and boxy under-wing coolers on the Spitfire were not present on the Mustang.

Any advantage of the Mustang over the Spitfire was down to the thrust designed into the radiator cooling by exploiting Meredith Effect.

Laminar-flow would have made its presence more felt if the Mustang had been able to go faster but this wasn't going to happen, the propeller itself was beginning to impose drag and the fact that the wings of a WWII fighter stuck straight out to either side (ie unswept) were the new limiting factors in piston-engined development.
Sure, there were later versions of the P-51 but they weren't fast enough either, they were just banging up against the limits of what you could do with a piston-engined a/c.

Laminar-flow could overcome the turbulence along the lift surfaces of the wing but it couldn't overcome the frontal, cross-sectional area of a straight-winged, propeller-driven a/c trying to move forwards faster.

 

[drgondog]

I doubt it
the 20 - 30mph difference is more realistically attributed to the outlet for the radiator cooling. North American engineers designed this to allow heated air to exit the a/c under pressure, thus providing the Mustang with, effectively, a rudimentary tail pipe.

While I fundamentally agree your point regarding the outlet (and inlet) design for the radiator, there are analytical studies recently which downplay the thrust effect of the design - reference the Lednicer report as an example for the analytical VSAERO approach on some design details for the racer STREGA..On the other hand the drag of the 51 inlet design was substantially lower than the spit (and 109) designs

To say that the comparison is valid because both a/c share the same engine is a wee bit shy of good science, the prominent carburettor air intake and boxy under-wing coolers on the Spitfire were not present on the Mustang.

Any advantage of the Mustang over the Spitfire was down to the thrust designed into the radiator cooling by exploiting Meredith Effect.

I would tend to disagree on this point. I would pose that both the reduced parasite drag of the airframe and wing of the Mustang were the primary speed factors - looking to a.) Cd0 of the airfoil, b.) radiator and carb inlet design and c.) canopy windscreen.

Colin - I was particularly interested in the VSAERO pressure distribution comparisons for flow over the wings and canopy windscreens between the two ships. I suspect that the model results are of course idealized with respect to the wing and probable boundary layer separation points that would occur in real life - but nevertheless the plots were an excellent example of potential flow model results in a frictionless environment.

Laminar-flow would have made its presence more felt if the Mustang had been able to go faster but this wasn't going to happen, the propeller itself was beginning to impose drag and the fact that the wings of a WWII fighter stuck straight out to either side (ie unswept) were the new limiting factors in piston-engined development.
Sure, there were later versions of the P-51 but they weren't fast enough either, they were just banging up against the limits of what you could do with a piston-engined a/c.

I thoroughly agree this point - in fact I would further postulate that the a/c was experiencing drag from the propeller disk at the point it started positive velocity on taxi roll... and continued to the point where it may have been the dominant 'parasite drag' component along with wave drag in the ~ .8-.85M range for the Mustang.

Laminar-flow could overcome the turbulence along the lift surfaces of the wing but it couldn't overcome the frontal, cross-sectional area of a straight-winged, propeller-driven a/c trying to move forwards faster.

Again - totally agree

Not to be too picky - strictly speaking, the introduction of the boundary layer increase in the spanwise direction is the factor which causes laminar flow to transition to turbulent flow. The Laminar flow wing of the P-51 had its max thickness at ~ .4C versus the Spit (and most others at .3-35C). As you know the longer you maintain laminar flow over an airfoil, the later (and farther along the chord) the turbulent flow is created to introdue positive pressure gradient - chordwise - and therfore a profile drag component added to the wing when the airflow separates.

In the Lednicer model, even with his iterative steps to introduce a positive pressure gradient build up at trailing edge, the wing shows lift for what looks like ~ .9C - and that ain't gonna happen in real life.

Having said that his (Lednicer) model yielded very nice results to compare with the NACA wind tunnel and NAA flight tests made without prop (in dives to .75M).

Colin - At this point you may not agree what I said, and I am perfectly fine with leaving it at that rather than take this thread off course. Good to have you on the forum.