Effectiveness of the P-38 (3 Viewers)

[GregP]

Maybe he named his P-38 "Hoyt-Clagwell?"

... which was the brad of tractor they made up for the show. The real tractor was Fordson Model F.

 

[Barrett]

As is so often (semi-eternally) on the internet:
THERE WAS NO SUCH THING AS "THE P-38"
anymore than there was such a thing as THE 109 or THE Spitfire. All came in various flavors. Usually LOTS of flavors.

I knew a bunch of 38 pilots, mainly when I was secretary of the aces assn. The s/e guys kidded them for flying "light bombers." Every Lightning pilot I knew loved the airplane though they distinguished between the early models (through G) and the J and L models.

Maneuverability: my friend John "Shady" Lane flew with Tommy Lynch in the 39th FS. When they transitioned from P-39s they began experimenting. Found that they could enhance turn radius to the left, for instance, by retarding the inboard throttle somewhat while cramming on the outboard, and vice-versa. No appreciable torque with contra-rotating props.

 

[MIflyer]

Ward Duncan, maintenance chief of the 9th PRS, said there were two significant problems with the P-38.

Early ones did not have much range, because they had planned to use 50 gal drop tanks mounted close to the inner wing, like everybody else did. Not only did the drop tanks not have enough fuel, but they contributed a lot of drag. Using the much larger 160 gal tanks on long pylons solved that.

You could not see the ground from altitude, which made lining up for a photo run a challenge. The engines and nose kept the pilot from seeing the target and they could never figure out how to install a sight to enable the pilot to look down because the NLG was in the way. They even tried making a slant angle camera so take pictures from a distance. Note that Lockheed put a Drift Sight in the U-2 so the pilot could look down and see the ground.

Ward thought the Japanese Dinah was a better recon airplane than the P-38.

 

[tomo pauk]

Early ones did not have much range, because they had planned to use 50 gal drop tanks mounted close to the inner wing, like everybody else did. Not only did the drop tanks not have enough fuel, but they contributed a lot of drag. Using the much larger 160 gal tanks on long pylons solved that.

Manual for the early P-38s (including the early recon birds) makes no mention the 50 gal tanks; the 75 gal tanks being the smallest.

You could not see the ground from altitude, which made lining up for a photo run a challenge. The engines and nose kept the pilot from seeing the target and they could never figure out how to install a sight to enable the pilot to look down because the NLG was in the way. They even tried making a slant angle camera so take pictures from a distance. Note that Lockheed put a Drift Sight in the U-2 so the pilot could look down and see the ground.

Were the PR Spitfires and/or recon Mustangs ever outfitted with the look-down sight, with the even worse look over the nose?

 

[MIflyer]

Ward worked with F-4's, (no suffix) based on the P-38E and were a bit different from the later models, although with generally better fit and finish.

Recon Mustangs were used for TAC-R, shooting pictures sideways. With Spits you could look over the front edge of the wing, which was not possible with the P-38.

 

[Peter Gunn]

The P-38 can dive as well as it needs to. Just throttle back as you nose over, then hose the crap outa them and pull up! 440 Knots was the safety limit imposed by HQ, but the plane could safely go to 460 Knots! Thats 506 MPH to 529 MPH Given the extremely long effective range of the plane's guns, it should never be a problem!

I'm no P-38 expert by any stretch, but as I recall diving was NOT the Lightnings strong suit. I also question it clocking 526MPH and still keeping some empennages.

However I am open to enlightenment.

 

[Shortround6]

I think there is some confusion between knots and mph and indicated air speed vs true airspeed.

The Early P-38s were placard for 3 different altitudes and different speeds for different G loadings, They also had different placards for a nose mounted pitot tube and a wing mounted pitot tube. The early P-38s were placarded at 420 mph IAS at 10,000ft with the wing mounted pitot tube. They were placarded at 290 mph IAS at 30,000ft.

I would imagine (not being a pilot) that few pilots were doing the mental mathematics to convert IAS to true airspeed in combat or in steep dives.

 

[pinehilljoe]

Warren Bodie devotes many pages to the compressibility issue with early P-38s while diving.

 

[GregP]

Nobody did conversions in combat. Hence, placards were in IAS is every WWII cockpit I have ever seen, and that's a few, including some axis airplanes.

 

[tomo pauk]

Recon Mustangs were used for TAC-R, shooting pictures sideways. With Spits you could look over the front edge of the wing, which was not possible with the P-38.

Looking at this picture, it seems that there was some elbow room for the pilot to look over the LE of the wing.

I'm no P-38 expert by any stretch, but as I recall diving was NOT the Lightnings strong suit. I also question it clocking 526MPH and still keeping some empennages.

However I am open to enlightenment.

I'd say that you have your stuff right. See this 10 year old thread, for example.
Mr. Stewart has a lot of homework to do (= provide sources) to back up his claims. Not that I'm holding my breath.

 

[Holtzauge]

I'm no P-38 expert by any stretch, but as I recall diving was NOT the Lightnings strong suit. I also question it clocking 526MPH and still keeping some empennages.

However I am open to enlightenment.

I'd say that you have your stuff right. See this 10 year old thread, for example.
Mr. Stewart has a lot of homework to do (= provide sources) to back up his claims. Not that I'm holding my breath.

Yes, it seems they never really fixed the P-38's dive problems a 100%: And even as early as in November 1941 Lockheed test pilot Ralph Virden was killed in a dive test with the YP-38. Apparently there is an internal Lockheed report from May 1942 where Kelly Johnson outlines problems in dives and dive recovery which I've only heard about but not seen myself (anyone has that?).

And no one seems to have been even close to figuring out why this was happening at the time: Even the famous NACA aerodynamicist Theodore Theodorsen was off the mark and championed stabilizer icing as the main culprit at a NACA conference as late as in 1943. So quite a long time after the problems started to appear. However, it was one of the NACA's younger engineers, John Stack, who correctly identified the problems as related to compressibility effects that resulted in a loss of lift on the inboard sections of the wing which in combination with the reduced downwash on the stabilizer caused the "Mach tuck" problems.

So the dive brakes fitted later on the later P-38 was not there primarily to keep the speed down, but actually put there to maintain the lift on the inner portions of the wing (which also helped with the downwash on the stabilizer). But it still seems this never really solve the problem completely, and the limit Mach number in dives for the P-38 continued to be lower than for both the P-51 and P-47 for its entire service life as far as I know.

PS: Thanks for linking back to that old thread tomo pauk. Seems to contain a lot of good information on dive limits!

 

[GregP]

The P-38 was never fitted with dive brakes.

It was fitted with dive flaps. The dive flaps were two rectangular pieces of aluminum about a foot or so wide that were hinged at the front and placed on the lower surfaces of the inner wing between the boom and fuselage, and hinged at the back with a more narrow strip acting as a sliding actuator. The front hinge line was in front of the center of lift. When the dive flaps were deployed, they hinged down from the front and forced the airflow under the wing to deflect downward in front of the center of lift, thereby imparting a nose-up pitching moment to the airplane even if the elevators were blanked by the shock wave.

Yanks Air Museum has a photo-recce P-38 with the dive flaps installed on it. They also have a P-47D with dive flaps installed on it. Again, these are rectangular flaps, hinged at the front, placed directly behind the landing gear wells, inboard of the gear pivot, and also in front of the center of lift. They operate the same way.

 

[MIflyer]

I would not call them flaps. And I would not call them brakes, since that conjures up what you see on SBD and SB2C. What they did was modify the wing profile to put the center of lift back toward the front, since at transonic speeds it moves aft. The F-106A had a system that responded to this condition so that at about Mach 1.05 it automatically transferred fuel to
retrim the airplane. The P-47 was equipped with them as well.

 

[MIflyer]

it seems that there was some elbow room for the pilot to look over the LE of the wing.

What they like to do is approach the target with it off to one side, at a near 90 degree angle, and then roll onto a heading that will take them over it, exactly like I did this morning when I turned onto base leg and then onto final. The P-38's engines kept them from being able to do that.

 

[drgondog]

Boosted Ailerons give the P-38 the highest Rate of Roll of All common combat aircraft of WW-II. In spite of the highest Polar Moment of Rotation! You are absolutely correct when you state 60 Degrees left to 60 Degree right is important, it is the single most important part of dog fighting! But Maximum Continuous Throttle speed is more important, and no other plane can match the P-38 at altitude! None! The P-51 is close at 25K' and the P-47 is close at 30-33K', but no other plane is close! Speed is life! (A Famous fighter pilot statement!)
Secondly, it was far and away the single best gun platform of all fighters in the war! (Caused by the complete absence of "P" effect caused by those counter rotating props and CL mounted guns with high RoF and MV/BC!) PBR =800 Yards and maximum effective Range 1,800 Meters!

Respectfully, the only part of the flight regime (P-38L) that seems close to P-51D w/1650-7 is at Max Continuous 20000 feet. At 25K the 51D at Max Continuous exceeds the L at Combat power,and opens the gap at 30000. My sources for the moment are the flight tests on Spitfireperformance.com

 

[Holtzauge]

The P-38 was never fitted with dive brakes.

Absolutely. Bad mistake on my part to call the dive flaps dive brakes.

When the dive flaps were deployed, they hinged down from the front and forced the airflow under the wing to deflect downward in front of the center of lift, thereby imparting a nose-up pitching moment to the airplane even if the elevators were blanked by the shock wave.

Interesting interpretation of how the dive flaps worked aerodynamically. Where does it come from? The only one I'm familiar with so far is the one from NACA report 767 (Which references the P-38 dive flap solution in NACA report WR A 66) which uses the same terminology as I did, i.e. that the cause of the pull out difficulties in the P-38 is due to a loss of lift and the resulting loss of downwash on the stabilizer.

 

[drgondog]

Absolutely. Bad mistake on my part to call the dive flaps dive brakes.



Interesting interpretation of how the dive flaps worked aerodynamically. Where does it come from? The only one I'm familiar with so far is the one from NACA report 767 (Which references the P-38 dive flap solution in NACA report WR A 66) which uses the same terminology as I did, i.e. that the cause of the pull out difficulties in the P-38 is due to a loss of lift and the resulting loss of downwash on the stabilizer.

The primary benefit to the dive flap was to generate an instantaneous pitch up Moment, followed by increase in CL and change in lift distribution as the shock wave dissipates.

 

[Holtzauge]

The primary benefit to the dive flap was to generate an instantaneous pitch up Moment, followed by increase in CL and change in lift distribution as the shock wave dissipates.

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?

 

[pbehn]

No, I think you have a very valid point: Some time ago I saw a compilation of production costs and as I recall it the P-38 was darn close to being twice as costly as a P-51 IIRC. Can't swear to the exact numbers but they did not come cheap. Then there are the added maintenance and operational costs for a twin as well of course. OTOH, twin safety when flying long range missions over water like in the Pacific is of course a plus and given the square-cube law it's always easier to design in long range into a large plane compared to a small one.

In my opinion financial costs were the least of the issues, compared to all other costs. The requirement for fighter escort created the need for an additional air force, that was around the size of RAF fighter command in around a year and in spite of all other expansion plans for all other types. The P-51B/C didnt take any engines from any US type, and the Packard Merlin was already a massive expansion, it may have meant fewer engines for Lancasters but Packard production under lend lease was much higher than the original ordered quantities. The P-51B didnt have a "day job" in mid 1943 because it was still in transport. The P-38 and P47 were already in service with assigned tasks, even if all three types were the same in performance it would still make sense to use the P-51 for escort work, because that avoids switching the others, re training and transporting planes and pilots etc.

 

[Frog]

In my opinion financial costs were the least of the issues, compared to all other costs. The requirement for fighter escort created the need for an additional air force, that was around the size of RAF fighter command in around a year and in spite of all other expansion plans for all other types. The P-51B/C didnt take any engines from any US type, and the Packard Merlin was already a massive expansion, it may have meant fewer engines for Lancasters but Packard production under lend lease was much higher than the original ordered quantities. The P-51B didnt have a "day job" in mid 1943 because it was still in transport. The P-38 and P47 were already in service with assigned tasks, even if all three types were the same in performance it would still make sense to use the P-51 for escort work, because that avoids switching the others, re training and transporting planes and pilots etc.

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