P-38 vs P-51: Full internal fuel dogfighting

[drgondog]

I'm 99.9% sure that B-29 missions from the Marianas were escorted only by P-51s attached to 20th AF.

P-47Ns based at Okinawa and Ie Shima flew escort missions over Japan and Formosa but not for B-29s.

 

[Conslaw]

The "N" Thunderbolt flew very few B-29 escort missions. I think I have read one group's unit history that recorded one escort mission. Of course there may have been others by the few other groups. The P-47N was still a hell of a plane and if the US had invaded Japan, the "N" would have been a true star.

Going off on another tangent, I spoke to a veteran once who worked on the ground crew for a B-17 unit in Italy. He said late in the war they stripped their B-17s down so they could fly bombing missions from 30,000, like the early (Pre-E) B-17s. I have never read any unit histories or confirmations on this. If anybody has any info please post. I wish I knew the number of the bomb group.

 

[drgondog]

Greg - the mission tasking in the ETO was not dogmatic in that bomber altitudes were primarily based on weather/flak considerations later in the war. That said, the 2nd BD B-24s were always flying lower when the B-17s were at 25000 feet (average). Early in the ETO experience the relative high altitude handling characteristics of the B-24, combined with best cruise speed advantage of the B-24 dictated an average formation altitude of 21-22000 feet.

When using radar for 10/10 cloud cover expectations the formations dropped as low as 18,000 feet for several missions.

As to fighter cover, the high squadrons frequently were as high as 5,000 feet above the high boxes of B-17s and so came to target as high as 30-32,000. I have not read every 8th AF mission Summary so can't comment if any fighter cover went as high as 35,000 but have read encounter reports where flights climbed to engage 109s observed at 35,000 feet. I doubt that very many P-51s or 47s or 38s bothered to climb that high with a full load of fuel.

The CBI/PTO/SWP bombing altitudes for B-24s was more often at 15-18,000 feet and frequently escorted by a range of fighters including P-40, F4U, P-38. I would be curious to know what missions, if any, ever flown by B-24 (or B-32) were at ETO/MTO altitudes.

 

[drgondog]

The "N" Thunderbolt flew very few B-29 escort missions. I think I have read one group's unit history that recorded one escort mission. Of course there may have been others by the few other groups. The P-47N was still a hell of a plane and if the US had invaded Japan, the "N" would have been a true star.

Going off on another tangent, I spoke to a veteran once who worked on the ground crew for a B-17 unit in Italy. He said late in the war they stripped their B-17s down so they could fly bombing missions from 30,000, like the early (Pre-E) B-17s. I have never read any unit histories or confirmations on this. If anybody has any info please post. I wish I knew the number of the bomb group.

Conslaw - in the waning months of ETO/MTO flak was the primary threat and several tactical mods were made to improve high altitude performance, including having the Navigator or Engineer toggle on lead crew and leav the bombardier home. including removing the ball turret and finally, cutting in half the ammo load of common practice during 1943.

It could have the effect of increasing effective cruise altitude for equivalent load of bombs, but late in the war the mission planners would have increased bomb loads more frequently for lower altitudes to improve % of bombs on target.

 

[GregP]

I'll buy that, Bill.

The B-29 mission I never did investigate since the Navy war was what I was following. I assumed they used P-47Ns, P-51Ds, and P-38s just because all were avialable, and chose whatever fighter was suitable for the mission at the time, but didn't consider that perhaps ALL the B-29 missions were a bit long for the P-38s.

They chose the P-38 for the Yamamoto mission specificvally because the P-38 had the range ... so I never really thought about it as I was mostly a "fighter guy."

 

[drgondog]

Greg - I think it was a combination of three factors, maybe more. The first was organizational. Only Mustang groups were assigned to 20th AF. The second reason, perhaps linked to the first is that every drop of fuel was 'imported' via shipping and the B-29s used a lot more fuel than comparable B-17/B-24 fleet. The P-51D was far more economical than the P-38 and 2/3 cost of P-47N to operate - That combined with proven track record of escort (for Lemay) made a choice, if he had to make one, a no brainer.

Logistics with respect to single type versus multiple type (say P-38 and P-47 along with P-51) IMO also contributed to the decision.

 

[Zipper730]

if they didnt burn down the fuse tank the center of gravity was off and they were limited on some of the maneuvers. that is why they ran it down to 25-30 gallons right after take-off.

Oh, I thought one would want to burn out the whole tank; then switch to the drop-tanks until you had to punch 'em off?

Regardless from what I remember the P-38J you had to burn off a little bit of the wing tanks first before switching to drp-tanks

All subsequent Mustangs had the 85 gallon tank until the P-51H - which carried a 50 gallon tank, and had increased fuselage length and re-designed tail to eliminate the stability issues inherent in the Merlin powered Mustang combined with increased gross weight and 85 gallons/500+ pounds aft of the CG on take off.

I though the center tank was had the CG just on the aft limit...

 

[BiffF15]

Oh, I thought one would want to burn out the whole tank; then switch to the drop-tanks until you had to punch 'em off?

Regardless from what I remember the P-38J you had to burn off a little bit of the wing tanks first before switching to drp-tanks

I though the center tank was had the CG just on the aft limit...

Zipper,

In the Eagle we would burn out the external wings first, external centerline, then internal. The plane would do that automatically (bleed air pressure to the wings was higher than to the center bag) so that when you jettisoned external tanks the internals where as full as they could be. In the Mustang, and I'm guessing here, the mentality was the same except for the CG problem. Get the CG under control, keep as much gas internally as possible until the situation drives you to jettison the external tanks, then fights on. Your burn rate in combat is so high, even in a Mustang, that you want to start a fight with as much fuel on board as possible (long ride home). This is a consideration that the Bf-109s / Fw-190s did not have which in turn is a serious performance advantage. Like Colin Chapman said, "Add lightness".

I also flew the OV-10 Bronco. We usually flew with a centerline bag (1500lbs) and could carry 1500lbs internal. Engine out climb performance in the summer was so anemic we would adjust fuel loads to compensate. In the morning "go" (bank) we would fly the planes with both internal and external full. The pilots would then burn most of the internal fuel out, then sip from the external. They would land with about 300-400lbs internal, and about 1k in the external. The next flight was in the heat of the day with the previously poor engine out performance, and should the pilot lose and engine he could jettison almost all his fuel (excess weight) to increase his odds of a safe recovery.

The big picture I'm trying to convey is some planes in certain conditions require unusual operational considerations.

Cheers,
Biff

 

[drgondog]

Zipper - find one of the texts I recommended earlier. Look up Neutral Point, Static and Dynamic Stability and Static Margin. I'm not going to dive into this but here is a simple concept in context of the issues arising from the addition of the 85 gallon fuselage tank. The center of mass for a full tank is well aft of the CG and in fact, very near the Neutral point, Note that the Tank is an addition to all the other masses contained in the Design for the Mustang - all of which contribute to the Center of Gravity and in fact establish the Neutral Point..

The CG MOVES depending upon the load out. When Dry, the CG is at a 'forward location'. When fully loaded, the 'new' CG moves aft but hopefully short of the Neutral Point. When fully loaded with 85 gallons the CG has moved very close to the Neutral Point (a well defined term that you need to research) rendering the aircraft Statically unstable.

One of the major design changes for the P-51H was to design it with a Neutral Point aft (relative to P-51 through P-51K) as well as increase the tail areas to address the stability issues the earlier Mustang experienced even prior to the 85 gallon fuselage tank introduced into the Merlin Mustang.

 

[Zipper730]

Zipper - find one of the texts I recommended earlier. Look up Neutral Point, Static and Dynamic Stability and Static Margin.

Dynamic stability has to do with oscillations like phugoids, Static stability is what most people think of with stability (i.e. if I pull back on the stick, g-load goes up to 1.5 fro 1.0 it should return back to 1.0 if the stick is centered), and neutral point I just checked... its the point where stability becomes neutral.

 

[KiwiBiggles]

One of the major design changes for the P-51H was to design it with a Neutral Point aft (relative to P-51 through P-51K) as well as increase the tail areas to address the stability issues the earlier Mustang experienced even prior to the 85 gallon fuselage tank introduced into the Merlin Mustang.

Do you (or anyone else) know if giving the P-51H a larger static margin like this caused it to be slower on the controls than the D/K etc? My understanding has always been that stability and responsiveness are each other's inverse; that increasing static stability by providing a larger static margin leads to slower responses to pilot input.

 

[GregP]

Are the control surfaces the same size on the D/K and H? I haven't checked. But it might make a difference.

 

[drgondog]

Two factors - difference between the P-51B thru K had adjustable aileron throw from 10, 12 to 15 degrees, whereas the P-51H was 12 degrees max. The P-51H ailerons (and tail surfaces) were also larger. The Roll rates were approximately the same in flight tests but rigging data is not available for the tests that I have looked at, nor in NAA Performance Calculations.

As to static margin. I don't have the data on the stated aft cg location as percent of MAC for either. What Was different is that the center of mass for the 50 gallon fuselage fuel tank was closer to the normal take off CG AND within the static margin (and neutral point) for All load outs - contrast with all 85 gallon fuel tank installations.

 

[Zipper730]

As to static margin. I don't have the data on the stated aft cg location as percent of MAC for either. What Was different is that the center of mass for the 50 gallon fuselage fuel tank was closer to the normal take off CG AND within the static margin (and neutral point) for All load outs - contrast with all 85 gallon fuel tank installations.

So the P-51H was more docile for long-range operations

 

[BiffF15]

Zipper,
I think you could say long range or full internal fuel load ops. I imagine (Drgondog please correct me if I'm assuming incorrectly) that carrying either external tanks or bombs along with a full fuselage tank in the P-51H was safer due to the changes from the B/C/D models.
Cheers,
Biff

 

[tomo pauk]

Are the control surfaces the same size on the D/K and H? I haven't checked. But it might make a difference.

Two factors - difference between the P-51B thru K had adjustable aileron throw from 10, 12 to 15 degrees, whereas the P-51H was 12 degrees max. The P-51H ailerons (and tail surfaces) were also larger. The Roll rates were approximately the same in flight tests but rigging data is not available for the tests that I have looked at, nor in NAA Performance Calculations.

As to static margin. I don't have the data on the stated aft cg location as percent of MAC for either. What Was different is that the center of mass for the 50 gallon fuselage fuel tank was closer to the normal take off CG AND within the static margin (and neutral point) for All load outs - contrast with all 85 gallon fuel tank installations.

Looking at Gruenhagen's book, pg. 176, the -H have had smaller ailerons - 6.35 sq ft vs. 6.7 sq ft on previous in-service variants; both values include tab. Travel was also incresed to 15 deg both up and down, being 10 deg up and down previously (greater travel + greater area = greater rate of roll?). AIleron tabs were movable 10 deg up and down in all versions.
P-51H was with horizontal stabilizer of greater area, but of smaller span; however the area of the elevators was reduced a bit. Vertical tail was with greater area on the P-51H, too.

 

[wuzak]

The P-51H was also longer by about a foot.

Increased leverage for the elevators?

 

[drgondog]

Tomo - I think Bob transposed the D/H data on ailerons and Elevator data. The NAA data has 10-12-15 degree throw for all P-51B/C/D and P-51H at 10 for ailerons and the areas Bob presented are also 'opposite' for Elevator data.

Warbird Tech Series posts AN-60-60JE-2 Three View extracted from NAA top drawing three view. I will check my drawing package.

 

[bobbysocks]

Oh, I thought one would want to burn out the whole tank; then switch to the drop-tanks until you had to punch 'em off?

Regardless from what I remember the P-38J you had to burn off a little bit of the wing tanks first before switching to drp-tanks

I though the center tank was had the CG just on the aft limit...

I think ( and only my opinion ) was they were hedging their bets. when they dropped their tanks they were on internal fuel and sometimes ( depending on the mission ) a LONG way from home. as missions started to go to berlin and points beyond, having enough fuel so they didn't have to ditch or bail out in enemy would be a concern. I have read several accounts where the plane's engine died due to fuel starvation almost as soon as the pilot plopped her on the runway. on a mission to Munich my dad and his wingman ran out of fuel before they hit the channel. by that time there were 9th AF and RAF bases in France and Belgium so it was no big deal...had that happened before D-day they would have had to break off the engagement they were in earlier or would have become POWs. that extra 30+ gallons might mean the difference between sleeping in your own bed or floating in a dingy in the north sea OR an all inclusive vacation to stalag luft ???...

 

[Zipper730]

The P38 was never designed for dog fighting. It was an interceptor.

It was called an interceptor to circumvent armament restrictions that the USAAC put on pursuit planes, as well as possibly allow two engines.

It was intended to climb and accelerate fast, fly quickly, and at high altitudes, but it was intended to be able to fly as a traditional interceptor and a fighter.

A couple of observations - the P-38J tested at 15000 pounds is 2699 pounds under full internal combat load. -------> 85% of full internal GW. If you 'grow' the P-38J GW to Normal full combat load you divide the recorded turn radius of 838 ft by 0.85 ------------>985 ft

The P-51B at 9000 pounds GW is 611 pounds under full internal combat load - the equivalent of flying without 85 gallon tank fuel ----------> 93% of full internal GW. If you then divide the presented turn radius of 883 ft by 0.93 -------> 949 feet, less than the comparably loaded P-38.

Wait, I thought the P-51D was listed?

It is further documented in Dean's "America's Hundred Thousand". He also documents the turn performance of the P-38J/L as less than the P-51D - and the P-51B outperforms the P-51D.

The B was a little cleaner with the razorback and had a slightly different wing; the P-51B was lighter also.

The "N" Thunderbolt flew very few B-29 escort missions. I think I have read one group's unit history that recorded one escort mission. Of course there may have been others by the few other groups.

Why did it fly so little?