With the P-38K, was the P-51 and F4U even necessary?

[swampyankee]

Would a laminar type wing have helped the P-38.

That's not an easy question to answer. First, laminar flow airfoils of that era, like NACA's 6 series airfoils, could not maintain laminar flow in service (indeed, even today it's considered normal practice to use the lift and drag characteristics with a tripped boundary layer, i.e., one that is turbulent), so there is not likely to be much drag reduction. However, because some of the 6 series airfoils were designed to have maximum flow velocity (maximum Cp​) fairly far aft, they had higher critical Mach numbers than other airfoils.

So, the answer to the question is "maybe yes, maybe no." I'd vote for probably no.

 

[wuzak]

Would a laminar type wing have helped the P-38.

First, laminar flow airfoils of that era, like NACA's 6 series airfoils, could not maintain laminar flow in service (indeed, even today it's considered normal practice to use the lift and drag characteristics with a tripped boundary layer, i.e., one that is turbulent), so there is not likely to be much drag reduction.

I would think that there was a lot of scope in the P-38's wings for drag reduction. They were quite thick and had a low critical mach number.

However, because some of the 6 series airfoils were designed to have maximum flow velocity (maximum Cp​) fairly far aft, they had higher critical Mach numbers than other airfoils.

Tell that to RJ Mitchell, whose Spitfire wing had a higher critical mach number than the Mustang's laminar flow wing.

So, the answer to the question is "maybe yes, maybe no." I'd vote for probably no.

You would end up trading top speed (improved with laminar flow wing) for climb rate.

 

[davebender]

Unfortunately P-38 engines required 5 years to fix (1939 to 1944). By then the war was almost over.

Spitfire first flew during 1936. Britain would have been up a creek without a paddle if engine technical problems required 5 years to fix. So would Germany if Me-109 engine required 5 years to fix. Even the problem plagued BMW801 engine was fixed in less then 5 years.

 

[swampyankee]

Some caveats are needed here, I think. First is that most of the reviewers are Navy and almost all military pilots are highly bias for one, their aircraft, and two, their service. Second, I am sure all the reviewers were single engine pilots. As such, the plane is big, complex, and they were unfamiliar with two engine idiosyncrasies like, maybe, asymmetric thrust.

Overall, I think the P-38 had potential to be an effective fighter, it was certainly deadly in the PTO. However, I suspect it took some time for a pilot to learn how to handle the uniqueness of the aircraft. Also, two engines adds cost, reduces mission reliability and increases maintainability requirements. Faced with the simplicity, cost, ease of flying and performance of the P-51, it was difficult to justify.

I'm trying to remember something I read a long time ago, but it comes down to the USAAF not providing adequate twin-engine flight training to its P-38 pilots, especially in type, before putting them on operations. One of the dangers of twin-engined aircraft is that the few seconds after engine failure are very busy, with a lot of choices. Make the wrong choices, and you crash and die. In a single-engined aircraft you don't have many choices, and you just want to make the crash as comfortable as possible. You can still crash and die, but in the quiet after the only engine fails, it's much easier to concentrate. As a potentially interesting factoid, the insurance rates for light twins are (or at least were in the 1980s) higher than they are for comparable single-engined aircraft.

I think the other problem was that early models of the P-38, before hydraulically boosted ailerons were added, did not have rapid roll response, which made them feel unmaneuverable. Reportedly, P-38 pilots got an improved view of their aircraft after Tony LeVier gave some demonstrations.

 

[Aozora]

According to Der Gabelschwanz Teufel - Assessing the Lockheed P-38 Lightning there was a combination of problems:

Even with the arrival of the P-38J, engines and turbochargers continued to fail. The new intercooler/oil cooler design was actually too efficient and the enlarged radiators became a new problem. Fuel too, was a source of trouble, it is believed by many knowledgeable people that the majority of fuel used in Britain was improperly blended, the anti-knock lead compounds coming out of solution (separating) in the Allison's induction system at extreme low temperatures. This could lead to detonation and rapid engine failure, especially at the higher power settings demanded for combat.

Many of the P-38's assigned to escort missions were forced to abort and return to base. Most of the aborts were related to engines coming apart in flight. The intercoolers that chilled the fuel/air mixture too much. Radiators that could lower engine temps below normal operating minimums. Oil coolers that could congeal the oil to sludge. These problems could have been fixed at the squadron level. Yet, they were not. It took the P-38J-25-LO and L model to eliminate these headaches. Add sub-standard fuel, green pilots, poor tactics and the 8th had a serious problem in the making.

Re: the pilot training - there were some small but vital flight techniques that were needed to operate the turbo-chargers properly; much the same fundamentals still apply: - Flight Training

If you fly a turbocharged engine, you need to know how the system works and be aware of several important operating techniques. Because oil pressure closes the wastegate, you must allow time for the engine and oil to warm up completely before taking off. If the oil pressure is low or the oil is cold and sluggish, the wastegate may be slow to close, which means the engine won't develop its full, rated power during takeoff and climb.

Also, engine oil lubricates the turbocharger, which can spin at more than 30,000 rpm at takeoff power During normal operation, several gallons of oil flow through the turbocharger's bearings every minute. Cold oil doesn't flow properly. If you apply high power settings before the oil warms to the proper temperature, the oil may not lubricate the turbocharger sufficiently.

Power should be applied smoothly and relatively slowly. If the throttle is shoved rapidly to the firewall on takeoff, the turbocharger controlling mechanisms may not have time to function properly, causing the engine to surge and possibly overboost.

 

[Shortround6]

Unfortunately P-38 engines required 5 years to fix (1939 to 1944). By then the war was almost over..

Ah, no. The early P-38 engines weren't too bad. The crises was with the P-38J model. The early models with the leading edge inter-coolers could not over cool the intake mixture while cruising like the "J" could. The crises started in the fall/winter of 1943/44 with the introduction of the "J" model. It was made worse by a change in the fuel specification that allowed different blends of compounds to stretch the available fuel supply to provide more 100/130 fuel. The change was implemented in the winter/spring of 1943, Allison was working on a new intake manifold to help solve this problem during the summer/fall of 1943. The manifold was standardized in Nov 1943 but many P-38s had been shipped to England before that.

Kind of hard to "fix" a problem in 1939-42 for a fuel that doesn't exist yet.

One reason the the MTO had a lot fewer problems was that the first P-38Js went to England, the MTO and Pacific got the Fs, Gs and Hs. By the time the MTO got P-38Js the problem had already been fixed.

SO the P-38 didn't have severe problems for 5 years, It had severe problems for around 6 months.

Because turbo installations are more complicated they need more maintenance and/or more careful maintenance. Turbo control linkages were often improperly set. If the turbo controls are mis-rigged is that a design fault or a maintenance/erection fault?

 

[tomo pauk]

I was afraid that Greg will see the claim about the unreliable V-1710; fortunately, SR6 was close to the keyboard

 

[davebender]

Biggest problem when discussing P-38 reliability is that sources disagree. Some claim problems were fixed by 1943. Other sources claim problems were never completely fixed.

However it's a fact that U.S. 8th Air Force chose to replace P-38s with P-47s and P-51s when enough of those fighter types became available. Production cost can't be the issue as P-47 costs almost as much as a P-38. P-47 was also a fuel hog. P-47 and P-51 both had weapon packages inferior to P-38. So I've got to assume people operating P-38s at high altitude lacked confidence in the aircraft even during 1944. I have not personally flown the aircraft and can only defer to those that did historically under combat conditions.

 

[JtD]

Two engines is two times the risk for a single engine failure. Additionally, the P-38 compressibility problem made it an imperfect high altitude fighter.

On the other hand, if an engine gets shot up in a twin you still have one to bring you home, compressibility was nearly irrelevant down low and the P-38 could carry a more than impressive array of ground attack weapons, equivalent to unit cost. It's only logical that the P-38 was phased out of high altitude escort duty and used for other tasks.

 

[tomo pauk]

Some of the issues that reduced the need for the P-38 were due to it's construction, some were due to it's engines experiencing issues in the crucial time and place (exacerbated by out-of-book use), some were due to it's performance. Pointing out at the engines as main culprit, even indirectly, is definitely not a painting a whole picture. While the P-38 did have had central battery, it was maybe a single thing that it had over P-51. Climb and turn abilities were also good on P-38, but that was not on the top of the list of USAF needs in 1943-45.

-construction: 2 engined airplane will need more pilot training, it will not roll as good as the S/E plane (especially at lower speeds), it was much more expensive than P-51 to produce and operate. The wing was not that thin (16% TtC ratio at root), nor it was last word in aerodynamics for late ww2. Big plane is easier to spot than a smaller one - enemy pilot will act 1st. As-is, the P-38 offered many blind spots, too. It took Lockheed too much of time to fix cabin heating and to introduce the generator on second engine (AAF 'gulity' for this?), too. Here the P-51 was holding most of the cards, even the P-47 did.
-engines: covered by SR6
-performance: both P-51 and P-47 were faster, both in level flight and in dive. Even once the dive flaps were introduced on the P-38 (by then the P-47 got them, too).

Then we have the nuber of the planes built in last 2 years of ww2 - Allies having far more planes than trained pilots? Further, from June/July/Aug of 1943, USA was producing 3 P-47s/-51s for each P-38 produced.
With all this said, no wonder USAF decided it they will be better served with P-47/-51 only.

 

[drgondog]

Biggest problem when discussing P-38 reliability is that sources disagree. Some claim problems were fixed by 1943. Other sources claim problems were never completely fixed.

However it's a fact that U.S. 8th Air Force chose to replace P-38s with P-47s and P-51s when enough of those fighter types became available. Production cost can't be the issue as P-47 costs almost as much as a P-38. P-47 was also a fuel hog. P-47 and P-51 both had weapon packages inferior to P-38. So I've got to assume people operating P-38s at high altitude lacked confidence in the aircraft even during 1944. I have not personally flown the aircraft and can only defer to those that did historically under combat conditions.

Well, not so simple. The P-38 was in high demand in the PTO/MTO and had the P-51 not been available in theatre, the 8th AF would have continued with it. While the airframe cast was not too much above the P-47, the training, the operating costs were at least twice as much as a p47 and close to 2.5x over a Mustang.

I know a lot of pilots that flew both and liked both the P-51 and P-38. Robin Olds comes to mind in the forefront.

 

[davebender]

Many pilots disliked the P-47 (i.e. most numerous American fighter aircraft). Especially if they had experience flying other fighter types. So I'm not surprised some expressed a strong preference for the P-38 even if it had technical glitches.

 

[Aozora]

Many pilots disliked the P-47 (i.e. most numerous American fighter aircraft). Especially if they had experience flying other fighter types. So I'm not surprised some expressed a strong preference for the P-38 even if it had technical glitches.

It's a given that pilots will often/usually express a strong preference for one aircraft type over another, so of course there were pilots who disliked the P-47, particularly those who had flown the Spitfire. It could equally be said that many pilots preferred the P-47 over every other fighter, including the P-38.

 

[davebender]

2,309kg empty weight. Spitfire Vb (most common variant).
4,536kg empty weight. P-47D.

Easy to see why. Double the empty weight and comparison gets worse with loaded weight. Like telling a Formula One driver that next week he will be driving a beer truck.

 

[Jugman]

Thanks for the link. Both P-38s were flown without leading edge tanks, and we are left in dark why the P-38K was not faster under ~30000 ft on WEP - it did have 2x1725 HP, vs 2x1600, in the same time featuring a better prop.

Read the first sentence of the second paragraph. Speed at 1725 hp would have been about 2% better at all altitudes.

The weight of 30 gals of ADI liquid (water-methanol) in the P-47 was 124 lbs. Lockheed assumed that ADI system would've weighted 600 lbs, 400 lbs being the ADI liquid - seems they intended to replace the LE fuel tank with ADI tank - 400 lbs is almost 100 gals of water-methanol?

The weight of 30 US gallons ADI was about 224-248 lbs. (50-50 to 95-5 water-alcohol) Total system weight for the P-47 was less than 300 lbs. The P-38 system seems to be a 24x2 gallon system. This system was not where the leading edge tanks were but most likely located in the wheel wells and/or outboard of the nacelles behind the main spar. The fixed weight of the systems seems very high for the capacity.

 

[tomo pauk]

Read the first sentence of the second paragraph. Speed at 1725 hp would have been about 2% better at all altitudes.

Many thanks for pointing me at power setting used.
If I'm reading the report right, the RoC (all altitudes) and speed (at lest from 35000 up?) was only because a better prop was installed?

The weight of 30 US gallons ADI was about 224-248 lbs. (50-50 to 95-5 water-alcohol) Total system weight for the P-47 was less than 300 lbs.

Thanks again.
I've read the item 'Water' (124 lbs) on the table at pg. 285 of AHT book, and then there is another item named 'Water', on the same table but lower, and this item weights 248 lbs (or zero lbs for 'Design' mission profile). Anyone up to clear it to me why two items of same name are listed there - 248 lbs would indeed be the ADI liquid.

The P-38 system seems to be a 24x2 gallon system. This system was not where the leading edge tanks were but most likely located in the wheel wells and/or outboard of the nacelles behind the main spar. The fixed weight of the systems seems very high for the capacity.

I'd love to see a proper description of the system myself; the 2 x 24 gall system does make much more sense. BTW, if the ADI tank is located behind the main spar, it might cut into the inboard (main) fuel tank, or may dictate different construction/location of the dive flaps.
The paragraph 5 from the linked document says that Lockheed assessed that weight penalty will be 600 lbs for the ADI system, out of which 400 lbs is to be water(/methanol).

 

[Jugman]

Many thanks for pointing me at power setting used.
If I'm reading the report right, the RoC (all altitudes) and speed (at lest from 35000 up?) was only because a better prop was installed?

Yes.

Thanks again.
I've read the item 'Water' (124 lbs) on the table at pg. 285 of AHT book, and then there is another item named 'Water', on the same table but lower, and this item weights 248 lbs (or zero lbs for 'Design' mission profile). Anyone up to clear it to me why two items of same name are listed there - 248 lbs would indeed be the ADI liquid.

The top part of the table is for early models with the 15 gallon tank and the bottom is for later models with the 30 gallon tank.

I'd love to see a proper description of the system myself; the 2 x 24 gall system does make much more sense. BTW, if the ADI tank is located behind the main spar, it might cut into the inboard (main) fuel tank, or may dictate different construction/location of the dive flaps.
The paragraph 5 from the linked document says that Lockheed assessed that weight penalty will be 600 lbs for the ADI system, out of which 400 lbs is to be water(/methanol).

Nothing in the report suggests that the normal fuel capacity was reduced in any way. My best guess is the system had two 12 gallon tanks per engine located in side the main wheel wells just in front of the supercharger intakes.

 

[tomo pauk]

The top part of the table is for early models with the 15 gallon tank and the bottom is for later models with the 30 gallon tank.

Indeed, thanks.

Nothing in the report suggests that the normal fuel capacity was reduced in any way.

Reading the 1st post here, the (X)P-38K prototype was a modification of the P-38G, ie. no leading edge tanks present - 300 gals internal fuel.

My best guess is the system had two 12 gallon tanks per engine located in side the main wheel wells just in front of the supercharger intakes.

That would allow for maybe 7-8 min operation only (25 gals giving 15 min of operation in the P-63), but I guess the space would've been at premium.
Unfortunately, apart from mentioning the ADI sytem twice in the 'Vee's for victory', and 'more than 1875 bhp' by Bodie, is there any firm document about the P-38K ever using the ADI? The Vee's do not give more than 1600 HP at 3000 rpm, 60 in Hg MAP for the P-38K (= same as P-38J/L) , war emergency power.

 

[Jugman]

That would be 14-16 minutes per engine (remember it's 12X2=24 gallons per engine). The ADI flow rate for the P-38 would be lower because the P-38 had intercoolers. So more like 18-24 minutes.

 

[silence]

What's "ADI"?