B-29 Escort: P-38, P-47N or P-51H ? (1 Viewer)

Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules

Lets not forget our highest scoring pilots, Bong and McGuire, used P-38s. I would have to go with the P-38, mostly cause I can't swim :p ALSO, the P-38 has no critical engine and twin rudders. You have positive airflow over the rudders no matter which engine quits. The Mustang did it's job admirably albeit maybe not comfortably. I would be very nervous flying behind a Merlin over all that water. VMC for most WWII types is between 125 and 145mph, which gives a safe margin in single engine cruise. For example, the VMC of a B-25 is 145mph, with an engine feathered you can still cruise at 160-170mph.

jim

Agree 100%
 
If what I have read is true, P-38 Glacier Girl has working turbos. I was lucky enough to see, and touch that gorgeous and historical plane. (sorry for the drool marks!)

My question is this, if the turbos on most of the turbo aircraft are not working, why are they still so much quieter? Is the exhaust plumbed through hollow shells of the turbo? I have heard Thunderbolts, Lightnings and B-17's first hand, and they are very quiet.
 
I don't want to be a stickler for details but only the Turbo Chargers are non functioning on some aircraft. They may be installed for looks but are easily rendered inop. The Superchargers are still an essential functioning part of the engine. The Turbo used on the P-38 and P-47 is the same used on the B-17 and B-24.

jim
 
Last edited:
The extra exhaust noise from the Merlin on a P-51 may be that it is more highly supercharged than most non-turbo Allisons, and is an indicator of the energy in the exhaust.

Or it may be that the design of the ejector stubs, which Rolls-Royce spent some time on, make for louder exhaust. The ejector stubs were designed to maximise the exhaust energy at certain speeds and engine power settings.
 
I am not sure but I don't think the P-47 at Chino has a turbo either. GregP or anyone else can you confirm this?

Greg has told me before that the P-47 has its turbocharger, but that it is inoperative. The reason it remains is to maintain the weight balance in the aircraft, as the C-series turbocharger with intercooler and associated plumbing has more than a little weight.
 
The Mustang is noisy because the exhaust stacks are only around 10" long and is not dampened by exhaust plumbing. Next time you see a P-40 run take note of the noise, same engine as the P-38 but, same style of short stacks like the Merlin. The P-47 and P-38 noise is dampened by exhaust plumbing, essentially like a muffler. Round engines have an exhaust "collector ring" that routes engine emissions to a specific outlet, either to the Turbo, or to a common outlet. We had the decibel levels of our B-25 measured a few years ago. The 25 has really short exhaust stacks and is extremely noisy. At cruise it was in the neighborhood of 120db. The B-17 and B-24 were relatively quiet at 90-100db, given they have full collector rings routed to the turbo.

jim
 
I don't want to be a stickler for details but only the Turbo Chargers are non functioning on some aircraft. They may be installed for looks but are easily rendered inop. The Superchargers are still an essential functioning part of the engine. The Turbo used on the P-38 and P-47 is the same used on the B-17 and B-24.

jim

Please be a stickler. Many of the books I have read through the years used supercharging as a generic term, which caused alot of confusion for me as to what was and what was not supercharged, turbocharged, or both. Im a gearhead / car racer, and know what they all mean, but I did not know what to believe as far as what I was reading. Until the internet came along and you can speak "directly" with folks like this forum.

I don't know the specific differences of each, but could the Merlin have a little more "boost" even in low stage than an Allison? A Merlin has a snappier sound to it to me, from idle, and up on throttle, than an Allison as installed in a P-40 or P-39. ( never heard a P-39 first hand ) In my experience with drag race engines, the 3 biggest things that change the sound is camshaft, exhaust valve size, and cylinder pressure, which a supercharged engine has in spades.
 
No worries Mike, alot of people are in the same boat. The B-29 also used the same Turbo. The turbo is a pilot operated, exhaust driven, power inducer. The function of the turbo is simple, pump sea level air pressure into the engine to maintain sea level manifold pressure at high altitudes. As an aircraft climbs the air gets thinner and Manifold Pressure slides off. The pilot controlled turbo waste gate can be closed, forcing exhaust the through the turbine, and turning the compressor mounted via a shaft to the turbine. This forces compressed air into the engine and therefore regulating a stable Manifold Pressure. The B-24 and B-17 both have optimum cruise settings of 30" of Manifold Pressure. Here is a great YouTube video from WWII. We differentiate the Turbo Supercharger and the Engine Driven Supercharger by simply saying Turbo, or Supercharger.


View: https://www.youtube.com/watch?v=mzcP1IYHJmc

jim
 
Thanks Jimh. I understand the works of both systems. I was wondering if the Merlin has either more static compression or more boost from the supercharger than an Allison,(in P-40 /39) which would make it louder and contribute to its "snappier" sound.

Going back with this original thread question, of the aircraft offered, the P-38L is the choice. Only to be bettered by a Tigercat or a Twin Mustang............maybe!
 
Lets not forget our highest scoring pilots, Bong and McGuire, used P-38s. I would have to go with the P-38, mostly cause I can't swim :p ALSO, the P-38 has no critical engine..
Both engines on production P-38's were critical, stbd engine righthanded, port engine lefthanded. IOW failure of either engine caused both yaw and torque effect to want to roll the plane over to the left/right if the left/right engine failed. The original YP-38 had a no critical engine arrangement (stbd engine lefthanded, port engine righthanded) but the flow pattern in normal operation was not favorable.

As far as general advantage of two engines, the P-38's problem in ETO/MTO was that air combat loss of one engine made the plane so vulnerable to further fighter attack that the effect on total loss rate wasn't clear, in fact the P-38 had the highest loss rate of USAAF fighters in E/MTO though that was partly a product of more difficult operating circumstances than other types (P-39 had the lowest rate, because a lot of its missions in that theater were defensive patrols considered combat missions but no contact). So it depends to a considerable degree what kind of Japanese opposition is assumed in 1945. In the actual case the P-51 (D's, but using high octane gas and high boost, so considerably outperforming 1944 vintage ETO P-51's) units on Iwo Jima flew only a few escort missions with B-29's (though a couple involved large and furious dogfights with Japanese interceptors) before it was decided it was more worthwhile to have them sweep and strafe against Japanese airfields. Many B-29 raids then were at night anyway (though sometimes also daylight unescorted as the fighter threat diminished). But those P-51's could escape basically any Japanese fighter if they were in trouble; even P-38L's could not do that as reliably v a/c like the Type 4 (aka Frank); P-47N likewise could and P-51H even more so assuming just the Japanese types which reached operation by the end of the war.

Also besides a pilot POV a P-38 represented much more cost to produce and resource to maintain than a P-51; the P-47 had that disadvantage v Mustang too though not as much as the P-38 did.

Joe
 
Last edited:
I thought about the critical engine controversy before I posted that. The definition of critical engine is one that most adversly affects handling and performance. The P-38 featured outward turning contra-rotating propellors (as you correctly pointed out) that eliminated torque when both were running normally. I tend to believe the story that the inward rotating propellors caused an area of turbulence between the booms and affected elevator stability, therefore were switched to outward. The power to weight ratio of the P-38, combined with positive rudder and rudder trim authority no matter which engine failed, eliminates the conventional critical engine theory. Watch this video, it is thorough in it's single engine performance parameters.
View: https://www.youtube.com/watch?v=ilArlZzLW-U

During WWII, high performance multi engine flying was in its infancy. Commonly referred to as "single engine flying speed" rather than VMC or critical engine inop, it was taught that there was no reason to fly below this speed for the particular airplane being flown. The P-38 can be flown normally above 120mph, as seen in the Lockheed training film. I've got around 350 hours of PIC in the B-25 Mitchell. Part of the Type rating check ride is a VMC demonstration (at altitude). There are alot of contributing factures to the definition of VMC, which culminates with loss of directional control. The accepted VMC for the B-25 is 145mph. During my flight training and on the checkride itself it was possible to get the airplane down to about 110mph before I could no longer hold heading or alititude. This is well below 145, and the airplane behaves well but it is not what you want during takeoff if there is an engine failure, it will roll over into the dead engine. Which is why it is taught to retard the throttles and land straight ahead in the event of an engine failure on takeoff if single engine flying speed is not attained. see this video of an A-26...
View: https://www.youtube.com/watch?v=QvplU_5ysjk This is what happens when VMC is not attained before liftoff and you have an engine failure.

I had the good fortune of seeing Lefty Gardner do his P-38 routine on several occasions and he did single engine rolls into the dead engine quite successfully. The P-38 was truely ahead of its time and there is a reason our top scoring aces had success with this machine. It was a reliable, stable gun platform. I would rather be a sitting duck with one engine running than riding down the silk to an awaiting German pitchfork.

The Mustangs that were built in 1944 were the same as the ones built in 1945. In reality there isn't a whole lot of differences between the B and the D models. Add two guns, a bubble canopy, you have essentially identical gun platforms. They certainly fly the same. Alot of blood was shed to get the base up and running on Iwo. If the P-38, P-47, or P-39 were capable of doing the job of escorting they would have been used in that role. The superiority of the D model was proven during Korea, as it was chosen over the H model to serve in country. anyway...thats my .02...this and quarter will get me a cup of coffee.

jim
 
Both engines on production P-38's were critical, stbd engine righthanded, port engine lefthanded.
Not really depending how you look at it. Like saying a glass of water is half empty as opposed to being half full. Engine out procedures were identical on each engine and although it has been mentioned that the YP-38 flew better than production models during engine out operations, you were still trimming the aircraft in some form to compensate for the dead engine. One could argue that because the left engine on earlier models carried the generator, that was considered the critical engine. I've had this question posed to many multi engine pilot, some of them being test pilots and it seems to come back as a "split decision."
I thought about the critical engine controversy before I posted that. The definition of critical engine is one that most adversly affects handling and performance. The P-38 featured outward turning contra-rotating propellors (as you correctly pointed out) that eliminated torque when both were running normally. I tend to believe the story that the inward rotating propellors caused an area of turbulence between the booms and affected elevator stability, therefore were switched to outward. The power to weight ratio of the P-38, combined with positive rudder and rudder trim authority no matter which engine failed, eliminates the conventional critical engine theory. Watch this video, it is thorough in it's single engine performance parameters.
View: https://www.youtube.com/watch?v=ilArlZzLW-U

During WWII, high performance multi engine flying was in its infancy. Commonly referred to as "single engine flying speed" rather than VMC or critical engine inop, it was taught that there was no reason to fly below this speed for the particular airplane being flown. The P-38 can be flown normally above 120mph, as seen in the Lockheed training film. I've got around 350 hours of PIC in the B-25 Mitchell. Part of the Type rating check ride is a VMC demonstration (at altitude). There are alot of contributing factures to the definition of VMC, which culminates with loss of directional control. The accepted VMC for the B-25 is 145mph. During my flight training and on the checkride itself it was possible to get the airplane down to about 110mph before I could no longer hold heading or alititude. This is well below 145, and the airplane behaves well but it is not what you want during takeoff if there is an engine failure, it will roll over into the dead engine. Which is why it is taught to retard the throttles and land straight ahead in the event of an engine failure on takeoff if single engine flying speed is not attained. see this video of an A-26...
View: https://www.youtube.com/watch?v=QvplU_5ysjk This is what happens when VMC is not attained before liftoff and you have an engine failure.

Great post Jim! One of the pilots I posed this question to summed it up with great simplicity in something like this "if you have to do more work shutting down or flying on one engine as opposed to another, that's you're critical engine." BTW Tony LeVier also maintained the P-38 didn't have a critical engine.
 
Last edited:
1. The power to weight ratio of the P-38, combined with positive rudder and rudder trim authority no matter which engine failed, eliminates the conventional critical engine theory.

2. The Mustangs that were built in 1944 were the same as the ones built in 1945. In reality there isn't a whole lot of differences between the B and the D models.

3. The superiority of the D model was proven during Korea, as it was chosen over the H model to serve in country.
1. I guess it's a matter of semantics but what you are saying is that the P-38 handled satisfactorily on one engine, which a lot of twin bombers of that time didn't, agreed. However AFAIK the definition, not theory really, of a critical engine is one which if lost will leave the torque and yaw of the remaining engine reinforcing one another to roll the plane in one direction, ie usually referring to twins with both engines of same hand, port engine critical if both engines are righthanded, stbd engine if both are left handed. But by the same standard definition, neither engine is critical with counter-rotating engines turning inward, and both are critical with counter-rotating engines turning outboard.

But even if one assumes the standard definition of criticial engine goes out the window with counter-rotating engines, some counter-rotating twins fly better on one engine than others, and the P-38 a relatively good one, but it never matters much which engine fails on any counter-rotating twin (well except maybe a push-pull twin), just as far as flight characteristics.

2. The planes were basically* the same but the fuel wasn't and WEP boost setting was higher on 7th AF D's at Iwo Jima than what the 8th AF had used, w/ noticeable increase in speed.

*late block D's as used in PTO in '45 had some other bells and whistles like APS-13 tail warning radars, etc.
3. The F-51D was used in Korea rather than any of the somewhat different lightweight Mustangs (H) or morever the apparently more suitable F-47D or N because not only did more F-51D's remain in total USAF inventory (though the difference between total F-47 and F-51 in June 1950 wasn't as great as is sometimes portrayed) but those in ZI were concentrated on the West Coast, and moreover the FEAF still had a small number of F-51D's in inventory in Japan (though not distributed to units). Those were the a/c sent to Korea in late Jun for the ROKAF but which flew some missions w US pilots. Also it had spares stockpiles and remaining maintenance and pilot experience with the F-51D, not with the H nor the F-47. The H would have offered little advantage in Korean conditions anyway, D being adequate in the handful of combats pitting F-51's against NK prop a/c and any prop fighter was heavily outperformed by the MiG-15 later on. But FEAF later regretted the decision of 51 v 47 as F-51 losses soared especially in 1951 v more heavily AA armed Communist field armies by that time. But, the USAF wasn't willing to support operation of multiple prop fighter types in Korea and (commanding general) Stratemeyer was told to forget it when he broached the idea of adding the F-47 later on (see "Stratemeyer Diary").

Joe
 
Last edited:
1. I guess it's a matter of semantics but what you are saying is that the P-38 handled satisfactorily on one engine, which a lot of twin bombers of that time didn't, agreed. However AFAIK the definition, not theory really, of a critical engine is one which if lost will leave the torque and yaw of the remaining engine reinforcing one another to roll the plane in one direction, ie usually referring to twins with both engines of same hand, port engine critical if both engines are righthanded, stbd engine if both are left handed. But by the same standard definition, neither engine is critical with counter-rotating engines turning inward, and both are critical with counter-rotating engines turning outboard.

But even if one assumes the standard definition of criticial engine goes out the window with counter-rotating engines, some counter-rotating twins fly better on one engine than others, and the P-38 a relatively good one, but it never matters much which engine fails on any counter-rotating twin (well except maybe a push-pull twin), just as far as flight characteristics.

But you're still trimming either engine after it is lost/ shut down regardless of prop direction, the aircraft is still going to roll. A little easier if the prop turns inward, so semantics perhaps?
 
3. The F-51D was used in Korea rather than any of the somewhat different lightweight Mustangs (H) or morever the apparently more suitable F-47D or N because not only did more F-51D's remain in total USAF inventory (though the difference between total F-47 and F-51 in June 1950 wasn't as great as is sometimes portrayed) but those in ZI were concentrated on the West Coast, and moreover the FEAF still had a small number of F-51D's in inventory in Japan (though not distributed to units). Those were the a/c sent to Korea in late Jun for the ROKAF but which flew some missions w US pilots. Also it had spares stockpiles and remaining maintenance and pilot experience with the F-51D, not with the H nor the F-47. The H would have offered little advantage in Korean conditions anyway, D being adequate in the handful of combats pitting F-51's against NK prop a/c and any prop fighter was heavily outperformed by the MiG-15 later on. But FEAF later regretted the decision of 51 v 47 as F-51 losses soared especially in 1951 v more heavily AA armed Communist field armies by that time. But, the USAF wasn't willing to support operation of multiple prop fighter types in Korea and (commanding general) Stratemeyer was told to forget it when he broached the idea of adding the F-47 later on (see "Stratemeyer Diary").

Joe

I may be wrong but wasn't it a fact that most (or all) F-47's in 1950 were assigned to Air National Guard units? I always thought that the Air force didn't want to use the Air Guard units who were familiar with the 47 in the conflict so they went with the more plentiful front line F-51. Whatever the case may be I think that the F-47 would have been the better choice, whether flown by Guard or front line units.
 
P Factor is a function of speed. The slower you go the more negative effect Torque has, Spiraling Slipstream, and Gyroscopic Procession. High performance aircraft are slaves to the propellor. With gear and flaps down at 120mph in a P-51 you don't shove all the power into it, you ease in what you need. Otherwise you are just a passenger for a pretty neat roll. A P-47, Hellcat, Corsair, P-38 etc, are no different. A critical engine is critical when if affects directional control (or as Flyboy noted a loss of generator or hydraulic pump) at slow speed, like takeoff or a missed approach. The 38 doesn't suffer from the traditional spiraling slipstream because it has no fuselage and as the air spirals back over the booms and rudders it is actually forcing the nose straight ahead. If you lose an engine while in cruise, or being shot at in an engagement the loss is negligable because of the speed over "Blue Line" and "VMC"...be it a B-17, B-24, B-25 or P-38. You will be more vulnerable no doubt, but controlling the airplane would not be an issue.

I would love to see your sources for the Mustang. I am always looking to learn more. AFAIK all Mustangs, even today are rated to 61" of MAP, 67" for temporary war emergency power. The Merlin can operate with octanes as low as 87 and as high as 145. The power settings are the same, no manual I have read indicates otherwise. We operate under the instructions dictated by Jack Roush. His shop has produced some of the finest running Merlins in recent times. For longevity we limit the engine to 55" for takeoff...most of us use 45-50". Cruise and aerobatics are done with 35-40". The only time you will see higher MAP's are from the transport series Merlins and Reno racers. Anyway, I'd love to see the source. Thanks

jim

PS I agree...the P-47 would have done much better in Korea than the 51...it was a poor choice by the powers that be.
 
Last edited:

Users who are viewing this thread

Back