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P-38 Lightning


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Charts from CC Jordan's excellent site: 

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I thought P-51's or 7th AF ran in 1945 though at higher power settings than that, 80" or something on 115/145 gas. I don't know if P-38L's did higher or not. That would be I think the main contemporary use of the two types, 1945 against Japan.

 

It's like I said before, I think one approach in evaluation emphasizes technical comparison, sort of in a vacuum as if say restored warbirds now, and another operational results. It's true operational results always have "unfair" aspects for one plane or another, so can be unsatisfying ("but what it really equal opposition", etc). But technical charts can be argued over a lot, plus again depends on whether they are tied back to which actual versions fought alongside one another at really the same time.

 

Continuing operational comparison of before, the P-38 was a superior plane for SWPA in 1943, no Merlin P-51's, and P-47C/D's which operated alongside in 5th AF while about equally successful v. the Japanese fighter opposition were definitely shorter legged; and how far you could project land fighter power for a landing, without asking for scarce Navy carrier help (scarce altogether at first, busy in central Pacific later on) was a big deal.

 

Then take say mid 1944. This was P-38J's I guess mostly or all pre-boost J's against P-51/B/C/D in 15th AF. It seems fairly clear the P-51 stood up better against the LW types at that time, claims aside you don't see the type of heavy losses P-38 groups sometimes still suffered among the P-51's. Around same time, P-38 v. P-47 as fighter bombers in 9th AF, again seems anecdotally the P-38's would get tagged for serious losses noticeably more often when jumped by LW fighters than P-47's though Germans had some success against both types, but OTOH not enough success against either to upset 9th's operations very much. And for ground small arms auto weapons fire seems any type big enough to have 2 engines was substantially easier to hit to point of probably negating the survivability of the second enging. And this sort of anecdotal is backed statistically again by the distinctly higher loss rate of the P-38, and since the USAAF got bigger and bigger all such stats are weighted fairly much away from the beginning of the war, though average P-38 loss would be earlier than the average P-47 or P-51 loss, the full difference in loss rate is "unfair" to the P-38. But the anecdotal evidence seems to be more or less in line for times when they operated together.

 

Against the Japanese in 1945 where it really was P-38L and P-51D, there's not an obvious operational result difference*. OTOH back on technical side you had P-47N operational near end and P51H on the way though not operational, another step ahead for those two types, while L end of the line for P-38.

 

Again taking whole careers of each, and cases where they did operate alongside, I think it's hard to say the P-38 was the best USAAF fighter. It wasn't the most successful for sure. So best would mean either correcting for circumstances of lesser success to say "best", or comparing a particularly favorable paper comparison (L v. P-51D running at 67" WEP). I'm not saying P-38 was a clearly worse plane than two main stablemates, but I don't think best of the three if forced to choose, nor necessarily any clear best among them considering all versions and times, with emphasis on operational results.

 

*somebody mentioned the Hellcat, outclassed on paper by later USAAF types, the Japanese thought it the most formidable opponent, probably a proxy for their general opinion that the USN fighter force was superior to the USAAF, which statement by the Japanese I've seen more than once, not necessarily constantly, but I've never seen the opposite.

 

Joe

Edited by JOE BRENNAN
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The problem with ignoring the technical (and measurable) performance aspects is that large organizations like the WWII USAAC could, and apparently did, have a greatly variable standard of training & experience. While it is edifying to look at what was achieved, discussions of relative platform effectiveness is not complete without analysis of the raw airframe performance against known baselines. The P-51 is popularly known as the "only" fighter with the range and performance to escort B-17s to Berlin and back. Yet PTO squadrons were getting much more range out of their aircraft than the 8th AF. Dealing with known flight test data removes much of the data nebulosity in attempting system comparisons because procedures have long been established for correcting data to a standardized condition. Therefore, we can easily make comparisons between Japanese and German fighter's potential performance, even though the aircraft did not go head-to-head in any theater of the war and without trying to come up with fuzzy metrics of whose training and tactics programs were "better."

 

Anecdotally, it isn't hard to find tales of F-86 pilots beating up on F8U drivers, but I think we all recognize that this is a case of poor/savvy tactics (depending on which side of the furball you are on), rather than a case of F-86 superiority. GregShaw has done some excellent work providing comparative data for the V1650 and V1710, baselined to similar conditions. From what I recall of his tables, the plotted data for the P-51D and P-38J is relatively accurate and, from a brief search (very cursory) on the Internet, the aircraft models compared on the charts are roughly contemporary. The P-38J entering significant service in the ETO in December 1943, the P-51D in March 1944. I didn't look too hard for P-38L service dates, but, based on the serial number blocks, I don't believe that it was much further behind the P-51D than the D-model Mustang was behind the P-38J.

 

Douglas

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The problem with ignoring the technical (and measurable) performance aspects is that large organizations like the WWII USAAC could, and apparently did, have a greatly variable standard of training & experience.  While it is edifying to look at what was achieved, discussions of relative platform effectiveness is not complete without analysis of the raw airframe performance against known baselines.

 

Anecdotally, it isn't hard to find tales of F-86 pilots beating up on F8U drivers, but I think we all recognize that this is a case of poor/savvy tactics (depending on which side of the furball you are on), rather than a case of F-86 superiority. 

 

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I wouldn't ignore them, just wouldn't make definite comparative statements based on them alone. Or to think of another way, IMO the true reality is combat results (real ones not claims). But it includes factors beyond the plane and we're talking planes, so there is an issue how to extract plane from the other factors. But I doubt it's entirely possible to scientifically separate them, doubt graphs represent that.

 

It's often hard to find complete agreement on what are objective numbers. Like here, those are certainly useful graphs but one might question the P-51 rating for the main period in question where the two types operated alongside (IIRC L's served little if at all in Europe, not common til late 1944 in PTO, so P-51D v. P38L operationally was mainly PTO 1945, and P-51B and D differed little in aerodynamic performance at the rating given, B slightly faster because of the razorback, so that level of Mustang performance does go all the way back to late 1943, common throughout 1944). And this is just USAAF; when you get to foreign types the threads I've read on sites with people who know alot on the topic (and Greg is certainly one of those) that have fascinated me as well as made my head spin, make me doubt the possibility of absolute objective comparison. For example it's common for figures long presented as "flight test" to turn out to have been calculations (for example Ki-84 v. the US types).

 

Anecdotally I'm speaking units of a type, not individual pilots. When reading one sided accounts the general proxy for success is losses, since you can generally assume those are real. Reading through chronology type books like Rust's on the numbered AF's, P-38 seemed generally to be liable to higher air combat losses same time as P-47 and P-51 units. Claims aren't reality but for a given AF at a given time one might reasonably assume claim accuracy was similar among types of plane; but again say 1944 15th AF, signifcant P-38/51 cooperation, 51 claim rate, ace production rate, etc. seem higher. On tactics, on a whole type or unit basis, it could be true one type needs to have them more finely tuned to the situation to succeed, but I think that's a negative reflection on the type, at least partly if just to succeed equally*.

 

*an example here is the F4F. It's often said F4F's used boom and zoom tactics and Thach weave; but when you read actual combat accounts of 1942 that's somewhat doubtful on both counts; sure they tried to gain altitude advantage in many missions defending Guadalcanal, WWII fighters always did, but seldom could do that in the carrier battles. Thach first used his Weave at Midway but it took time to filter back and through the training system, wasn't common up to end of 1942. One reason the F4F in 1942 did better against the A6M (real A6M's not "zeroes" like Ki-27's the AVG faced) than P-39/40, or even than Spit V's in 1943, was they could somewhat dogfight A6M's and not always be defeated, the F4F was not *that* much less maneurable than the A6M (though was generally slower and dove no faster, higher roll rate was its high speed advantage), it didn't demand specialized tactics stuck to as uniformly. That can be an advantage in itself. Turning in combat is very natural and to at least some degree required in order to shoot down opposing planes.

 

Joe

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Charts from CC Jordan's excellent site [snip]

 

I'm a bit suspicious about the tailing off of the P-51D at 25000ft, given that the TAS chart shows its FS full throttle height to be around 20,000ft. With that low a rate of climb at only 25000ft, how on earth did they manage to get TAS speed measurements from above 40000ft?

 

Joe Baugher indicates that a P-51D-25-NA model achieved 20000ft in 7.3 minutes, whereas the chart shows 20000ft in about 8:40.

 

There are some figures here: http://www.spitfireperformance.com/mustang/mustangtest.html

 

See for example the Mustang III, which at normal engine power manages 1500fpm at 3000 feet.

 

Which suggests that there might be something amiss with the blue line.

 

David

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My all time favorite airplane!  :D Couple of things I've been wondering about ...

 

Many sites on the net provide the following data on the weights of the various 38 variants:

 

38J

weight, empty: 12,780 lbs

weight, loaded: 17,500 lbs

weight, max: 21,600 lbs

 

38L

weight, empty: 14,100 lbs

weight, loaded: 17,500 lbs

weight, max: 22,000 lbs

 

Okay, so an empty L weighs roughly 1,320 lbs more than an empty J. Fine. But how come a normally loaded L doesn't weigh any more than a loaded J??? Did they just give her less fuel or what? Or is this just another case of people getting the different models messed up, and the L's loaded weight is actually higher (or the J's lower) than that?

Without knowing which J subtype there isn't enough information to make any conclusions. A J-25 was heavier than a J-1, how much heavier I don't have a clue without doing more research. The J-25 had dive flaps, new windscreen, more armor, hydraulic boost, leading edge tanks and probably lots more small changes I can't recall. The L-5 would have been even slightly heavier, tail radar, rocket pylons, slightly heavier Allison engines, etc...

 

I would take loaded and max loaded weights with caution as well. Without knowing the basic weight it is tough to come up with anything more than an average value. I usually just use 17,500 as average loaded weight, and 16,500 for combat weight. That works out to almost exactly 60% internal fuel, and since 16,500 is 1/2 of 33,000 it makes figuring climb rates really easy.

Also, does anyone know how the climb rates of the J and L models compare to each other? I know that the J was slightly faster than the L (420 mph vs 414 mph, at 25 kft respectively). Did it climb a little (noticeably) better than the L, too?

I have already covered the speed issues. The L-5 would be a better climber than the J, more power for the same weight more or less. If you use the 16,500 lb combat weight it is trivial to calculate the difference in climb rate. Every additional hp gives 2 fpm to the climb rate; 33,000 / 16,500 = 2, remember what hp is, 550 ft lbs/sec or 33,000 ft lbs/min. Then you have to take P% into account, the P-38 works out to almost exactly 80%.

 

So a 100 hp difference at mil power, 1425 x 2 vice 1475 x 2, times 80% gives about 160 fpm edge to the P-38L. Probably not quite that much since the P-38L is a bit draggier, call it an even 150 fpm.

 

For 1725 hp WEP vs 1600 hp WEP it works out to: 250 * 2 * .8 = 400 fpm. IF WEP is actually closer to 1825 hp @ 65 in Hg & 3200 rpm then climb increase would be: 450 * 2 * .8 = 720 fpm.

 

From tests we know that the P-38J climbed right at 4000 fpm on 1600 hp and approx 16,000 lbs. At 16,500 lbs that would drop to about 3875 fpm @ 1600 hp, 4275 fpm @ 1725 hp, 4575 fpm @ 1825 hp, 3475 fpm @ 1475 hp mi and 3315 fpm @ 1425 hp.

 

This is all a good theoretical exercise, in reality it looks like the J's may have been flying around at 65 in Hg, 3000 rpm & 1725 hp on 104/150 octane fuel by spring/summer of '44 as well. That is part of the "fun" about this, the more you learn the more you realize that the accepted reference figures are not necessarily representative of what real world performance was. Sometimes real world performance is better than book values, sometimes it is worse.

Oh, and lastly, I *think* I once heard someone claim that 2 engines capable of 1,600 hp will give you more forward acceleration than 1 engine capable of 3,200 hp. Is this true, and if so, why?

 

As for your question about 2 props being better than one, it is probably true. But only because it is a lot easier to get a prop to absorb 1600 hp while keeping P% up over a wide range of speeds than it is to do the same for 3200 hp. We could get into a long discussion on propellor efficiency, but that always gives me headaches, so I try to avoid it. Simply put, to absorb twice the power you could increase the prop speed, but that runs into problems when the prop tips go supersonic. Increase the prop area by increasing span, again once tips go supersonic efficiency plummets. Increase chord, great but that lowers the aspect ratio and increases induced drag, again efficiency suffers. Increase number of blades, efficiency goes down because blades are hitting disturbed air from the previous blade. You can use all those in combination and get good P%, but it would be easier to to it with 2 props each absorbing 1/2 the total power.

 

Greg Shaw

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Without knowing which J subtype there isn't enough information to make any conclusions. A J-25 was heavier than a J-1, how much heavier I don't have a clue without doing more research. The J-25 had dive flaps, new windscreen, more armor, hydraulic boost, leading edge tanks and probably lots more small changes I can't recall. The L-5 would have been even slightly heavier, tail radar, rocket pylons, slightly heavier Allison engines, etc...

 

I would take loaded and max loaded weights with caution as well. Without knowing the basic weight it is tough to come up with anything more than an average value. I usually just use 17,500 as average loaded weight, and 16,500 for combat weight. That works out to almost exactly 60% internal fuel, and since 16,500 is 1/2 of 33,000 it makes figuring climb rates really easy.

 

I have already covered the speed issues. The L-5 would be a better climber than the J, more power for the same weight more or less. If you use the 16,500 lb combat weight it is trivial to calculate the difference in climb rate. Every additional hp gives 2 fpm to the climb rate; 33,000 / 16,500 = 2, remember what hp is, 550 ft lbs/sec or 33,000 ft lbs/min. Then you have to take P% into account, the P-38 works out to almost exactly 80%.

 

So a 100 hp difference at mil power, 1425 x 2 vice 1475 x 2, times 80% gives about 160 fpm edge to the P-38L. Probably not quite that much since the P-38L is a bit draggier, call it an even 150 fpm.

 

For 1725 hp WEP vs 1600 hp WEP it works out to: 250 * 2 * .8 = 400 fpm. IF WEP is actually closer to 1825 hp @ 65 in Hg & 3200 rpm then climb increase would be: 450 * 2 * .8 = 720 fpm.

 

From tests we know that the P-38J climbed right at 4000 fpm on 1600 hp and approx 16,000 lbs. At 16,500 lbs that would drop to about 3875 fpm @ 1600 hp, 4275 fpm @ 1725 hp, 4575 fpm @ 1825 hp, 3475 fpm @ 1475 hp mi and 3315 fpm @ 1425 hp.

 

This is all a good theoretical exercise, in reality it looks like the J's may have been flying around at 65 in Hg, 3000 rpm & 1725 hp on 104/150 octane fuel by spring/summer of '44 as well. That is part of the "fun" about this, the more you learn the more you realize that the accepted reference figures are not necessarily representative of what real world performance was. Sometimes real world performance is better than book values, sometimes it is worse.

As for your question about 2 props being better than one, it is probably true. But only because it is a lot easier to get a prop to absorb 1600 hp while keeping P% up over a wide range of speeds than it is to do the same for 3200 hp. We could get into a long discussion on propellor efficiency, but that always gives me headaches, so I try to avoid it. Simply put, to absorb twice the power you could increase the prop speed, but that runs into problems when the prop tips go supersonic. Increase the prop area by increasing span, again once tips go supersonic efficiency plummets. Increase chord, great but that lowers the aspect ratio and increases induced drag, again efficiency suffers. Increase number of blades, efficiency goes down because blades are hitting disturbed air from the previous blade. You can use all those in combination and get good P%, but it would be easier to to it with 2 props each absorbing 1/2 the total power.

 

Greg Shaw

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How would contra-rotating props figure into this? how much extra weight?

 

btw, I'm using a rendering of the XF5U as my desktop :) Another plane I love. What would you estimate it might have achieved in performance? Teh low speed end seems to have been very impressive, at least in terms of takeoff and such...

 

Fast enough? Manueverable enough? I can't imagine that 6x 20mm cannons would not be enough firepower...

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How would contra-rotating props figure into this? how much extra weight?

Contra-props would have all the same problems. The only advantage that contra-props had was a reduction in torque and probably P force as well. I haven't ever looked into contra-prop issues enough to know for sure what other effects they would have. I doubt that a contra-prop gearbox would add much more than about 100 lbs to the weight.

btw, I'm using a rendering of the XF5U as my desktop :) Another plane I love. What would you estimate it might have achieved in performance? Teh low speed end seems to have been very impressive, at least in terms of takeoff and such...

 

Fast enough?  Manueverable enough? I can't imagine that 6x 20mm cannons would not be enough firepower...

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Unfortunately I don't have enough good data to make a model for the XF5U. And what I can find on the internet doesn't make a lot of sense. Example, most internet sources say that it had R-2800-7 of 1350 hp, and list about 425 mph @ SL. Others say 1600 hp but only 388 mph @ 20,000 ft. Neither of those make any sense on their own, much less when compared to each other.

 

My guess is that the R-2800-7 was essentially the same core engine as the R-2800-8 in the F4U and the R-2800-10 in the F6F. That should be good for 2000 hp TO and military at SL in neutral blower. And about 1600 hp in neutral blower normal power. I have no idea where 1350 hp came from, maybe a cruise setting. I don't know enough about the R-2800-7's other characteristics to make any sort of judgement; two-stage/two-speed like the -8/-10, or single-stage/two-speed like the -43 in the B-26 or the -22 in the F7F and F8F?

 

My feeling is that it would have abused any late war piston fighter, and probably gave 1st generation jets a run for their money. IF it was successfully developed, and that is a big IF. There were a lot of unconventional piston planes being developed at the end of the war, would have been interesting to see if any of them would have been workable.

 

Greg Shaw

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Contra-props would have all the same problems. The only advantage that contra-props had was a reduction in torque and probably P force as well. I haven't ever looked into contra-prop issues enough to know for sure what other effects they would have. I doubt that a contra-prop gearbox would add much more than about 100 lbs to the weight.

Greg Shaw

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I'm thinking the same. Almost all propeller driven aircraft during that era had gearboxes, so I should think that to have the propeller turn in the opposite direction would merely require a gearbox with one additional gear. More complicated of course would be to build the entire motor and gearbox as a mirror image of the other.

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  • 1 year later...

Besby Frank Holmes -- decorated WW II ace fighter pilot

 

John Koopman, Chronicle Staff Writer

 

Thursday, July 27, 2006

 

Besby Frank Holmes helped kill the Japanese admiral who p...

 

* Printable Version

* Email This Article

 

Besby Frank Holmes, a decorated combat ace who helped kill the Japanese admiral who planned and coordinated the attack on Pearl Harbor, died Sunday at Marin General Hospital. He was 88.

 

Mr. Holmes died of a stroke, said his son-in-law, Jeffrey Roehm of Fairfax, Va. He had lived in San Rafael since retiring from the Air Force in 1968.

 

Mr. Holmes was an avid flier and career officer, but the high point in his career came in 1943 when he was a 25-year-old pilot flying P-38 Lightnings from an airfield on the island of Guadalcanal.

 

The Army and Marines were battling the Japanese for control of the South Pacific. U.S. forces intercepted a message indicating that Adm. Isoruko Yamamoto would be flying to Bougainville island for an inspection tour of forward Japanese combat units.

 

Yamamoto was the commander of Japan's Pacific fleet, had studied in the United States and once said famously that he feared Japan had "awakened a sleeping giant" by attacking Pearl Harbor. He was considered one of the most brilliant military leaders of his time and a great threat to the American war machine in the Pacific.

 

The intercepted message indicated that Yamamoto would be within 400 miles of Guadalcanal, too far for any U.S. fighter aircraft at the time. But the newly arrived P-38s had a long range that could be extended by jury-rigging external fuel tanks. The men who planned the raid figured their chances at 1,000 to 1, because they would have to fly low and arrive at exactly the right time -- while Yamamoto's plane was still in the air but near its destination.

 

Mr. Holmes and 17 other pilots took off the morning of April 18. Two planes turned back because of mechanical problems. The other 16 flew just over the water, through Japanese-held territory, until they reached their destination. The gamble paid off, and they ran into six Japanese fighters and two bombers, one of which was carrying Yamamoto. In a short, furious dogfight, the bombers were shot down, and Yamamoto was killed.

 

The raid was a considerable morale booster for U.S. forces, even though the details had to remain secret so the Japanese would not know their code had been broken.

 

Mr. Holmes and the other pilots in the action were awarded the Navy Cross, the nation's second-highest award for valor.

 

Mr. Holmes finished the war as an ace -- an ace is a pilot with five kills or more. Mr. Holmes had 5 1/2.

 

He stayed in the military after the end of World War II, when the Army Air Forces officially became the Air Force. He flew in Korea and served in Vietnam, retiring as a lieutenant colonel.

 

Mr. Holmes was born Aug. 5, 1917, in San Francisco. He graduated from Balboa High School and San Francisco City College before joining the Army as a pilot candidate in March 1941.

 

He was sent to Hawaii and was at Pearl Harbor for gunnery school on Dec. 7. Roehm said Mr. Holmes had been attending Catholic Mass when waves of Japanese fighters and bombers swarmed the harbor and destroyed much of the U.S. Pacific Fleet.

 

Mr. Holmes ran out of the church during the attack and dashed to his airfield, his son-in-law said. He took off in an attempt to fight the attackers, but had to return to the airfield because every soldier, sailor and Marine on the ground was shooting at his plane, thinking it was a Japanese Zero.

 

"He said he stood on the airfield when a Japanese plane flew past, and he emptied his .45-caliber pistol at him," Roehm said.

 

In 2003, Mr. Holmes was inducted into the Commemorative Air Force's American Combat Airman Hall of Fame.

 

He is survived by his wife, Lavina; daughters Katherine Roehm of Fairfax, Va., and Diana Movey of Fresno; sons Frank Holmes of Petaluma and Robert Holmes of St. Petersburg, Fla.; a twin brother, Robert Holmes of San Diego County; 10 grandchildren; and six great-grandchildren. A brother, Richard Holmes, died in an accident shortly after returning home from World War II.

 

A rosary is to be held at 7 p.m. today at Keaton's Mortuary in San Rafael. A funeral Mass is to be said at 9:30 a.m. Friday at St. Raphael's Catholic Church in San Rafael. Mr. Holmes will be buried at the Golden Gate National Cemetery in San Bruno.

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I do not have the time to thoroughly read, nor respond to this fascinating thread. Only two specific points: I think I will start a non-profit foundation dedicated to educating people that the altitude problem was not the Allison's fault. Rather the absence of a a good Turbo-supercharger, EXCEPT as installed on the P-38.

 

Second, I noticed someone in the thread above used 104/150 in reference to fuel. The highest octane one can use in the first number is "100", and the second number is a comparative figure. I think the readily available airplane fuel was 100/130. Though I suppose 100/150 is possible.

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There was nothing wrong with the GE turbocharger. The problem was with part of the control mechanism that froze and caused overboosting.

 

When one sees 100/130 fuel it is the rich/lean mixture rating of the fuel. Note it could be lean/rich mixture - can't remember which.

 

Not only possible but used. The Brits and American used 100/150 fuel in 1944-45. It was used in British Merlins using 25lb boost and in P-51s of the 8th AF. Between Feb 44 and March 45 the Brits produced almost 115 million gallons of 100/150 fuel.

 

The Americans were producing 115/145 fuel.

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The P-38 was never hugely popular in northern Europe (operating out of England) because the Allison engines were prone to reliability problems in the cold and damp of the autumn/winter months and very poor cockpit heaters. Operations were often kept to 18,000 ft or less to keep them in warmer air. Also, replacement airframes were few and far between for this theater which meant many units operated understrength for much of the time, limiting what they could accomplish.

 

By March 1945 it had been almost completely replaced by the P-47, which 9th AF commanders prefered for its durability.

 

Strangely, they were very popular in the cold and wet Aleutian theater and remained deployed there from mid-1942 to the end of the war. Twin engines and long range were key factors here.

 

In the South Pacific the P-38 was first issued and saw action in November 1942 primarily to units converting from the P-39. They were immediately successful and remained so throughout the war. P-38's were preferred over the P-51 in the PTO as being more robust and suited to operations from rough, forward air strips. Only with the requirement to escort B-29 raids over Japan did the P-51 start to make an impact there.

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Second, I noticed someone in the thread above used 104/150 in reference to fuel.  The highest octane one can use in the first number is "100", and the second number is a comparative figure. I think the readily available airplane fuel was 100/130.  Though I suppose 100/150 is possible.

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Um, not quite correct. Those are lean and rich ratings, and they are performance numbers not octane ratings. Octane ratings mean a fuel has the detonation resistance equal to a reference fuel made up of x% iso-octane and the remainder normal heptane. So you can't have an octance rating greater than 100. Performance numbers are more useful as they are a direct comparison relative to 100% iso-octane. IE 104/150 means it has 4% more detonation resistance than iso-octane at lean ratings, and 50% higher at rich rating.

 

Western avgas started the war at 87 octane (PN of about 68), 91 octane (PN 76), 96 octane (PN 87) or for the USAAC 100 octane but without separate lean and rich ratings. By the BoB it had more or less standardized on 100 octane, with 100/125 lean/rich ratings being standardized in '41 or '42. 100/130 becoming the standard sometime in '42 or '43 and remaining as such through the end of the war. The RAF created 104/150 (sometimes seen as 100/150) and along with the USAAF used it in some quantity '44 and '45, but it had problems and never supplanted the 100/130. The US developed 115/145 and appears to have used it in the PTO in the last months of the war, and apparently standardized it as the postwar avgas standard.

 

Greg Shaw

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The P-38 was never hugely popular in northern Europe (operating out of England) because the Allison engines were prone to reliability problems in the cold and damp of the autumn/winter months and very poor cockpit heaters.  Operations were often kept to 18,000 ft or less to keep them in warmer air.  Also, replacement airframes were few and far between for this theater which meant many units operated understrength for much of the time, limiting what they could accomplish.

 

By March 1945 it had been almost completely replaced by the P-47, which 9th AF commanders prefered for its durability. 

 

Strangely, they were very popular in the cold and wet Aleutian theater and remained deployed there from mid-1942 to the end of the war.  Twin engines and long range were key factors here. 

 

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I wonder if this wasn't a case of ground crews and pilots in Alaska simply have more experience working and maintaining equipment in the cold. In various accounts of fighting in WWII, it seems as though mechanics and rear area types developed a huge number of techniques for making their equipment work in the cold.

 

Pat

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The P-38 was never hugely popular in northern Europe (operating out of England) because the Allison engines were prone to reliability problems in the cold and damp of the autumn/winter months and very poor cockpit heaters.

Did the Allison powered Mustangs have the same reliability problem?

 

The Allison was more reliable than the Merlin, fact. It was easier to keep tuned and easier to work on.

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I'm thinking the same.  Almost all propeller driven aircraft during that era had gearboxes, so I should think that to have the propeller turn in the opposite direction would merely require a gearbox with one additional gear.  More complicated of course would be to build the entire motor and gearbox as a mirror image of the other.

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Very easy to turn an engine in the opposite direction - all you need is different camshaft and prop assy (and maybe magneto drives)

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Um, not quite correct. Those are lean and rich ratings, and they are performance numbers not octane ratings. Octane ratings mean a fuel has the detonation resistance equal to a reference fuel made up of x% iso-octane and the remainder normal heptane. So you can't have an octance rating greater than 100. Performance numbers are more useful as they are a direct comparison relative to  100% iso-octane. IE 104/150 means it has 4% more detonation resistance than iso-octane at lean ratings, and 50% higher at rich rating.

 

Western avgas started the war at 87 octane (PN of about 68), 91 octane (PN 76), 96 octane (PN 87) or for the USAAC 100 octane but without separate lean and rich ratings. By the BoB it had more or less standardized on 100 octane, with 100/125 lean/rich ratings being standardized in '41 or '42. 100/130 becoming the standard sometime in '42 or '43 and remaining as such through the end of the war. The RAF created 104/150 (sometimes seen as 100/150) and along with the USAAF used it in some quantity '44 and '45, but it had problems and never supplanted the 100/130. The US developed 115/145 and appears to have used it in the PTO in the last months of the war, and apparently standardized it as the postwar avgas standard.

 

Greg Shaw

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Sounds like a good explanation, though contrary to my A&P education :unsure: Time to dig back into source material....

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Much easier, and simplier, to add a gear to the gear box.

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Not necessarily - gearboxes for 1500hp drives are quite complicated, and 'adding a gear' would probably change the configuration and mounting. A camshaft ground for opposite rotation still fits the basic engine configuration, and you'd need the reverse prop assy in either case.

 

Sort of a useless debate here; the designers went with a reverse rotation engine, and I'm sure they had more credentials than you or I

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There is more than just a different camshaft required for opposite engine rotation.

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It can't be that hard to run one in the opposite direction - seems a V-1710 varient was produced that could be run in reverse simply by throwing a lever -

 

From ‘Wikepedia’:

 

Another feature of the V-1710 design was its ability to turn the propeller either clockwise or counter-clockwise by assembling the engine with the crankshaft turned end-for-end, installing an idler gear in the drive train to the supercharger and accessories and installing a starter turning the proper direction. The ignition wiring and firing order were re-arranged to accommodate the direction of rotation.

 

From ‘Miss U.S.’ Page:

 

Both the Navy and U.S.A.A.C. were now interested in the V-1710, the Navy placing the anticipated order for reversible airship engines designated V-1710-B and the U.S.A.A.C. designated V-1710-C. The Navy engine eliminated the supercharger (rotary induction blower) in favor of two carburetors placed in the Vee of the engine. The engine was designed to reverse from full power one direction to full power the opposite direction in less than 8 seconds, while driving a remote mounted propellers mounted on outriggers equipped with swiveling heads which allowed thrust to be directed vertically or horizontally

 

From ‘Allied Aircraft Piston Engines of World War II’:

 

“Considerable development time was spent designing-in the new requirements, particularly the reversing feature, which involved a shifting mechanism for the camshafts, magneto, and distributor finger. Full reversing could be achieved in 8 seconds.”

 

My 'V-1710' book is in storage; maybe I'll dig it out to find more details

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First, I stand corrected on changing the camshaft to enable reverse rotation; I based that on the conversion of automotive engines for marine use where reverse rotation is desired of one engine in twin-engine installations.

 

It seems as though the V-1710 reversal was accomplished simply by re-arranging the parts, but I have to believe this was a 'designed-in' feature.

 

From "Vee's For Victory! The Story of the Allison V-1710 Aircraft Engine 1929-1948" by Daniel D. Whitney ISBN: 0-7643-0561-1, page 360 -

 

“The original design of the V-1710-F2R/L only required reassembly of the parts already in the engine, plus the use of a properly handed starter dog and R/L turning starter. The procedure to convert a V-1710-27(F2R) to engine to a V-1710-29(F2L) engine was as follows:

 

1. Turn the crankshaft end for end, retaining the connecting rods in their usual positions. This results in the forked rods being installed in the right bank and the blade rods in the left bank. Remount the damper hub and reduction gear coupling so that they remain in their usual front/rear locations.

 

2. Rewire the distributor heads to provide for the different firing order:

 

Right Hand Rotation 1L-2R-5L-4R-3L-1R-6L-5R-2L-3R-4L-6R

Left Hand Rotation 1L-6R-5L-2R-3L-4R-6L-1R-2L-5R-4L-3R

 

The firing order of each cylinder block is the same in either case, namely 1-5-3-6-4-2, however the phase relationship between the banks has been changed as a result of the reverse rotation of the crankshaft. By this expedient, there is no change in the valve mechanism (since the accessories continue to rotate in the same direction) or intake manifolding.

 

3. Reassembly of the Accessories Housing

 

a. Turn the starter shaft oil pump bevel drive gear end-for-end. This reverses the direction of rotation of the oil pump relative to the crankshaft, but since the crankshaft rotation has been reversed, rotation is the same relative to the housing.

 

b. Turn the generator and pump drive shaft gear end-for-end. This engages the generator and pump drive shaft directly with the gear off the end of the crankshaft instead of through an idler gear. The idler gear is moved to an upper ‘dummy’ shaft as described below for the supercharger drive. Reverse rotation of this shaft in combination with reverse rotation of the crankshaft retains the direction of rotation of all accessories driven from this shaft, including the vacuum pump, fuel pump and generator.

 

c. Install the left hand rotation starter dog.

 

d. The same direction of the rotation of the supercharger impeller is obtained with the reverse rotation of the crankshaft by incorporation of an additional gear in the supercharger gear train. The supercharger drive idler gear is turned end-for-end. The accessory drive idler gear is moved up from the lower dummy shaft to an upper dummy shaft and is thereby imposed as an additional idler in the supercharger drive train. When the accessory drive idler gear is installed on the lower dummy shaft (right-hand engine) it drives the generator and pump drives. In the left-hand engine the generator and pump drives are driven directly from the end of the crankshaft.

 

4. The Reduction Gear Assembly

 

a. The oil nozzle which provides a jet of oil to the reduction gears is reversed from one side of the gears to the other to account for the reversal of rotation

 

b. The scavenge oil pump in the reduction gear is also reassembled by changing the positioning of one casting in the pump to enable suitable operation when reversed."

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I know for a fact that a Continental W-670 will run in reverse simply by changing the timing and leaning on the prop when it's hot. :unsure:

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OUCH!! I hope any injuries were minor.......

 

I've only had one instance of a 'hot mag' - a bad mag switch and I was doing a 'pull through' on the prop during a pre-flight. Luckily I was taught to treat all props as 'hot', so all I got was a BIG surprise..

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