Effectiveness of the P-38 (1 Viewer)

[pbehn]

Along with Packard Merlins, all Continental produced V-1650-7 Merlins served as P-51s engines.

That doesnt change my point, the P-51 being produced in large numbers didnt affect any USA type. By mid 1944 Packard Merlins were being put in Spitfire Mk XVIs and sent to Russia under lend lease.

 

[drgondog]

As per the description in the NACA summary from report 767 below, the problem stems from a loss of wing lift which in turn results in a loss of downwash on the stabilizer. This in combination causes the pitch down moment.

My understanding of how the dive flap works is this: The deflection of the dive flap alleviates this by changing the flow field around the wing, increasing the lift and modifying the lift distribution, thus restoring lift (See NACA report WR A 66 figure 8). The change of the pitching moment Cm is then the integration of the restored lift in combination with the effects of the increased downwash of the tail. This in combination creates a positive pitch up moment, not the other way around.

"The primary benefit to the dive flap was to generate an instantaneous pitch up Moment, followed by increase in CL " That sounds backward to me: What would be the physics behind such an instantaneous pitch up? Is that your own theory or did you find such a description somewhere?

Dive CLs are near zero, but the lift distribution is relatively normal until the shock wave dramatically reduces the lift distribution aft of the shock wave. This is how CL and Lift distribution are connected.

The Pitch up moment caused by the flap deployment at 30% chord, increased lift due to the change of angle of attack. The phenomena of 'loss of lift' was synonymous with totally separated and highly turbulent flow aft of the shock wave which rendered the elevator useless to provide pitch authority.

For the P-38 and P-47D specifically, the increase in both lift and drag of the wing had the immediate effect of reducing airflow speed over the pre-shock wave location and therefore below the transonic shock wave velocity, restoring the pre-shock lift distribution, which resulted in near normal downwash over the horizontal stabilizer.

Not my own theory. That said Corky Meyer anecdotally described the phenomena while dive testing a P-47 IIRC, further stating that he wished Vought would apply the same mod to the F4U.

View attachment 785155

 

[Holtzauge]

Dive CLs are near zero, but the lift distribution is relatively normal until the shock wave dramatically reduces the lift distribution aft of the shock wave. This is how CL and Lift distribution are connected.

The Pitch up moment caused by the flap deployment at 30% chord, increased lift due to the change of angle of attack. The phenomena of 'loss of lift' was synonymous with totally separated and highly turbulent flow aft of the shock wave which rendered the elevator useless to provide pitch authority.

For the P-38 and P-47D specifically, the increase in both lift and drag of the wing had the immediate effect of reducing airflow speed over the pre-shock wave location and therefore below the transonic shock wave velocity, restoring the pre-shock lift distribution, which resulted in near normal downwash over the horizontal stabilizer.

Not my own theory. That said Corky Meyer anecdotally described the phenomena while dive testing a P-47 IIRC, further stating that he wished Vought would apply the same mod to the F4U.

I think the way you describe it now aligns much better with my understanding as well based on the NACA reports. But there is still one thing I would like to point out: The added lift from the dive flap deployment comes directly and is not dependent on a change in the angle of attack as you wrote. You can see this is the figure below from NACA WR A 66 which is for a fixed -1 degree angle of attack. So from whatever angle you are trimmed to in the dive, deploying the dive flap will as a first effect give you added lift at whatever trimmed angle of attack you may have. And it's this initial change of lift due to the deployment of the dive flap that then sets in motion the nose up pitching moment due to the added/restored wing lift in itself, in combination with the added/restored down sweep on the stabilizer.

 

[drgondog]

I think the way you describe it now aligns much better with my understanding as well based on the NACA reports. But there is still one thing I would like to point out: The added lift from the dive flap deployment comes directly and is not dependent on a change in the angle of attack as you wrote. You can see this is the figure below from NACA WR A 66 which is for a fixed -1 degree angle of attack. So from whatever angle you are trimmed to in the dive, deploying the dive flap will as a first effect give you added lift at whatever trimmed angle of attack you may have. And it's this initial change of lift due to the deployment of the dive flap that then sets in motion the nose up pitching moment due to the added/restored wing lift in itself, in combination with the added/restored down sweep on the stabilizer.

View attachment 785335

before belaboring the 'chicken/egg' question of the time valued changes caused by P-38 dive flap, are you presenting trailing edge flap CL at very low Mach number?

 

[Holtzauge]

before belaboring the 'chicken/egg' question of the time valued changes caused by P-38 dive flap, are you presenting trailing edge flap CL at very low Mach number?

No, the figure is for the deployment of the dive flap.

 

[MIflyer]

the P-51 being produced in large numbers didnt affect any USA type

Well, except for the P-40. Not only did they not build any more P-40F and P-40L, but those built with Merlins were re-engined with V-1710 wen their Merlins wore out.

I have wondered about how many P-51 had British-built Merlins. One of my college professors flew P-51 in WW2 and said his had a RR Merlin rather than a a Packard and that the RR was much smoother. Of course once I was talking to a Scotsman who said he heard that the Packards were smoother ("That's toooo smooooth to be a RRRRRolls RRRRoyce."; he rebuilt RR motorcars as a hobby so he may have known what he was talking about.

 

[SaparotRob]

Cool shot.

 

[Admiral Beez]

I really like the P-38, but "the most effective fighter?"

Not of the singles, but there's no other WW2 twin engined prop fighter I'd want to take up against the Axis' best fighters than the P-38L. If we can stretch out the war past-VJ Day I'd maybe give the DH Hornet or Grumman Tigercat a try, but otherwise against the latest Fw-190, Bf 109, Ki-84, C.205, Kawanishi N1K, Me-262 or anything else, it's the Lightning vs. allcomers.

 

[bf109xxl]

By mid 1944 Packard Merlins were being put in Spitfire Mk XVIs and sent to Russia under lend lease.

In the book "Aviation Lend-Lease" by V.Kotelnikov (2015), which is the most detailed description of aircraft deliveries to the USSR under the lend-lease program, Spitfire XVI is not mentioned at all, as well as in other sources known to me. According to Kotelnikov, only modifications VB (143), IX (1183 LF, 2 HF) were delivered to the USSR. Several PR IVs were transferred to the Soviets after British pilots flew combat missions over Norway. Could you please provide a reference to your source?

 

[pbehn]

In the book "Aviation Lend-Lease" by V.Kotelnikov (2015), which is the most detailed description of aircraft deliveries to the USSR under the lend-lease program, Spitfire XVI is not mentioned at all, as well as in other sources known to me. According to Kotelnikov, only modifications VB (143), IX (1183 LF, 2 HF) were delivered to the USSR. Several PR IVs were transferred to the Soviets after British pilots flew combat missions over Norway. Could you please provide a reference to your source?

Lend-Lease to USSR in WW2

 

[bf109xxl]

Lend-Lease to USSR in WW2

The web page under link contains no references to primary sources (archives, monographs) and cannot be recognized as reliable. Any reference to primary sources would be appreciated.
The appearance of nine Mk.XVI in the USSR could not pass without a trace, there would be necessarily documents on the tests, as for the other models. But there is no mention of them still.

 

[Thumpalumpacus]

Not of the singles, but there's no other WW2 twin engined prop fighter I'd want to take up against the Axis' best fighters than the P-38L. If we can stretch out the war past-VJ Day I'd maybe give the DH Hornet or Grumman Tigercat a try, but otherwise against the latest Fw-190, Bf 109, Ki-84, C.205, Kawanishi N1K, Me-262 or anything else, it's the Lightning vs. allcomers.

Easily the best twin-prop fighter of WWII.

 

[Yew Staff]

This interesting, though primarily about the P-51, it also covers the P-38 impact

View: https://www.youtube.com/watch?v=0BSuh16ouaE

 

[Geoffrey Sinclair]

AIR 22/310 British final position of aircraft shipped to USSR as of 30 June 1945. All Hurricanes shipped from Britain.
1st, 2nd, 3rd protocols
P-39 202 arrivals, 53 losses
P-40 30 arrivals
On British account from USA, 2,744 P-39, 300 P-40, 85 P-63, including 28 aircraft that crashed before hand over.
Hurricane IIA 154 arrivals, 22 losses
Hurricane IIB 1,412 arrivals, 278 losses
Hurricane IIC 967 arrivals, 46 losses, another 117 arrivals rejected by USSR
Spitfire IX 190 arrivals

4th protocol
Spitfire IXe 985 arrivals
Spitfire IX 11 arrivals
Spitfire HF.IXe 1 arrival

Extra to protocols:
pre 1st protocol, 41 Hurricane IIA, 159 IIB, 141 P-40, 10 P-39, 4 P-51 from Britain, 59 P-40 shipped from US plus 1 Hurricane IIA and 35 IIB handed over by 151 Wing.
Offered October 1942 shipped to Basra 150 Spitfire Vb
Handed over in North Russia 25 Hampden torpedo bomber and 3 Spitfire IV in October 1942, 3 Spitfire IV in June 1944.
Offered in April 1943, 60 Hurricane IID of which 14 rejected as they had over 40 hours flying time
Flown out by USSR ferry crews from UK, 14 Albemarle, 1 Mosquito
Offered in January 1944 as replacements for rejected aircraft, 52 Hurricane IIC on convoy JW58, 30 Hurricane IV handed over at Basra
Force landed aircraft handed over in September 1944, 5 Lancaster I and 1 Lancaster III
Offered in October 1944, 1 Typhoon 1B shipped on convoy LS.2595 in March 1945 handed over at Basra, plus 1 Stirling III flown out in February 1945 and handed over at Adaban.
Shipped to Basra in error and believed handed over to USSR 1 P-39.

 

[Admiral Beez]

Now a twin Griffon Lightning? That would be fun.

Griffon powered P-38?

Would the Rolls-Royce Griffon been a good choice/evolutionary step for the P-38?

ww2aircraft.net

 

[tyrodtom]

Well, except for the P-40. Not only did they not build any more P-40F and P-40L, but those built with Merlins were re-engined with V-1710 wen their Merlins wore out.

I have wondered about how many P-51 had British-built Merlins. One of my college professors flew P-51 in WW2 and said his had a RR Merlin rather than a a Packard and that the RR was much smoother. Of course once I was talking to a Scotsman who said he heard that the Packards were smoother ("That's toooo smooooth to be a RRRRRolls RRRRoyce."; he rebuilt RR motorcars as a hobby so he may have known what he was talking about.
View attachment 785366View attachment 785367View attachment 785368

I worked on a 69 RR Silver Shadow, off and on for two years, had a stack of RR manuals over a foot high.
Replaced the roof, and a lot of bodywork. ( a roof fell on it)
I also had to rebuild brake system, fuel system, and other mechanical parts.

I may have learned a lot about that Rolls Royce, but I doubt that taught me anything about a RR Merlin.

 

[drgondog]

No, the figure is for the deployment of the dive flap.

I should have seen that due to the Mach No. columns. That said I interpret the CL vs M plot as indeterminate with respect to 'first' reaction, without a plot of CMac as a function of time when dive flap deployed, overlayed with CL change as function of time.

 

[drgondog]

Well, except for the P-40. Not only did they not build any more P-40F and P-40L, but those built with Merlins were re-engined with V-1710 wen their Merlins wore out.

I have wondered about how many P-51 had British-built Merlins. One of my college professors flew P-51 in WW2 and said his had a RR Merlin rather than a a Packard and that the RR was much smoother. Of course once I was talking to a Scotsman who said he heard that the Packards were smoother ("That's toooo smooooth to be a RRRRRolls RRRRoyce."; he rebuilt RR motorcars as a hobby so he may have known what he was talking about.
View attachment 785366View attachment 785367View attachment 785368

You raise good questions. The strike at Packard circa June 1943 affected the 1650-3 as well as deliveries of 1650-1. Mat.Cmd had issued orders for 1000 1650-1 for delivery as spares for Q1/44 but was overruled at AAH Hq in favor of converting those orders to 1650-3 to try to catch up with NAA delivery of engineless P-51B.

The NA-110 (Australian order) were intended as Rolls engined at assembly in Australia. Suspect your professor was RAAF.

 

[Reluctant Poster]

Well, except for the P-40. Not only did they not build any more P-40F and P-40L, but those built with Merlins were re-engined with V-1710 wen their Merlins wore out.

I have wondered about how many P-51 had British-built Merlins. One of my college professors flew P-51 in WW2 and said his had a RR Merlin rather than a a Packard and that the RR was much smoother. Of course once I was talking to a Scotsman who said he heard that the Packards were smoother ("That's toooo smooooth to be a RRRRRolls RRRRoyce."; he rebuilt RR motorcars as a hobby so he may have known what he was talking about.
View attachment 785366View attachment 785367View attachment 785368

The converted P40s were restricted to training only. That freed up Merlins for front line duty.
Bill Marshall can correct me, but the only P51s with RR built Merlins were conversions by RR used in testing programs.

 

[SaparotRob]

This interesting, though primarily about the P-51, it also covers the P-38 impact

View: https://www.youtube.com/watch?v=0BSuh16ouaE

I don't watch this guy's videos. I must be old. His clickbait titles piss me off.