Improve the P-47

[Reynolds]

First off, Bodhi, Nice to see that quote is still in SOMEONE's signature,

And I like the idea of cannons. With a good gunner, Id say it would be much more lethal. 'specially if they were '30s!

[Krusty]

Historically cannon were considered to have 50% to 200% the range of MGs. They got in close for MGs, but with cannon had the same hitting power much further out.

That is, at least on non-evading bombers. Nimble fighters present other problems.

[Widewing]

I'm afraid that AquaShrimp needs to bone up on his history...

When it came to performance, the P-47 ruled the roost at high altitude. Moreover, that's exactly where it was designed to fight. While the Merlin powered P-51Ds were on the back side of the power curve at 25,000 feet, the P-47 was just beginning to hit its stride. Nothing in the ETO was as fast as the P-47s above 30,000 feet. Up there, its excess power made it feel positively agile, and its acceleration and climb rate up that high was without peer. Seriously, the R2800-59 engine was making 2,300 hp at 31,000 feet! Compare that to any other in-service fighter and you'll see that this is about 1,000 hp better than any of them, and that's for a B series R2800. The C series engines generated 2,800 hp at 32,600 feet!! The fastest fighter in squadron service as of April 1945 was the P-47M, able to reach up to between 475 and 480 mph at 32,000 feet and 370 mph at sea level. Even the heavier, long-range P-47N could flirt with 470 mph.

As to a "low critical Mach", that is simply baloney. Max permitted dive speed was exactly the same as that for the P-51D, with its laminar flow wing; 500 mph IAS @ 1g. Jugs were able to exceed 600 mph TAS without damage. Indeed, one P-47D was dive tested post war over 200 times, with all dives exceeding Mach .77, and some reaching Mach .83 without problems or issues. I've posted some of the original flight test data on my website. IIRC, the P-47's critical Mach was actually higher than that of the P-51.

As others have noted, the P-47 was a stressed-skin design. The P-47N did get squared-off wing tips, which did improve its already excellent rate of roll, but only above 300 mph. I have seen data that attributes roll rates between 82 and 90 degrees/second for the various P-47s.

By 1944, all P-47s could carry three external drop tanks. In the Pacific, P-47s were frequently flown with 160 gallon P-38 drops tanks, and sometimes carried another 75 gallon tank under the belly. With the arrival of the P-47D-25-RE, the Jug had the range to reach Berlin. When the P-47N came into service, it was THE longest ranging single-seat fighter on the planet... Even better than the P-51D. Just on internal fuel, the P-47N had a range of 1,700 miles. Add another 395 gallons externally and it had the ability to fly nearly 2,600 miles. In 1944, Republic demonstrated the ability of the P-47N by flying one from Long Island to Eglin Field in Florida, where it then flew mock dogfights with another Army fighter. After this was concluded, it then flew back to New York, all without landing. How's that for range? That was a 1,930 mile flight, with 20 minutes at MIL power and 5 minutes in WEP included. When it finally landed, it had enough fuel remaining to fly up to Boston and still have a 30 minute reserve....

No one thought that eight .50 caliber Brownings were inadequate, because they were more than enough for its mission. Those 8 guns could put out 6,000 rounds per minute, a rate of fire on par with the M61 rotary cannon in service today.

Your statement that the P-47 was relegated to ground attack because of its "short-comings" is... well, simply uninformed.

P-47s were used for ground attack and close support because they were far more durable than the liquid-cooled P-51s. They could absorb much more damage and fly home. Of all USAAF single-engine fighters, the P-47 had the lowest loss to sortie ratio, and by a significant margin too.

Some rather well credentialed aviation historians have stated that while the P-38 was first to take the air war deep into Germany, and the P-51 finished off the already mauled and depleted Luftwaffe, it was the P-47 that broke its back. Jugs had already killed off a significant portion of the Luftwaffe's west-front experten before the P-51s arrived in any significant numbers.

P-47s continued to fly escort missions until the surrender. Flying with the 8th AF, the 56th FG simply refused the Mustang and produced the highest scoring aces in the ETO. 9th AF P-47s flew escort for B-26s right up through April of 1945, when most B-26s stood down for lack of targets.

The whole premise of your argument is that the P-47 was somehow inferior and needed to be redesigned. Clearly, that is false. Neither the USAF, RAF, Lufwaffe or the Japanese thought that the P-47 was inferior. They all recogized that it was the best high altitude fighter of the war, and it got better with each new update. Indeed, the ultimate derivative of the P-47 was the XP-72, powered by a 3,300 hp, 28 cylinder R-4360 engine. This Super-Jug, was able to attain 490 mph, running at reduced manifold pressure (and 415 mph at sea level). A production order was cancelled as being unneeded, and Republic received a contract for design and development of the XP-84 Thunderjet instead. Nonetheless, the P-72 was expected to be a true 500 mph fighter.

Now, to futher your education, I suggest that you read this 8 part article on the design, development and operations of the P-47.

My regards,

Widewing

[Knegel]

Great post Widewing!!

Only that the P47 was the best high alt fighter in WWII may not be true, cause speed isnt all in high alt!! There was other high alt fighters with a much better turn performence and a still very good speed and climb(Ta152H, SpitIXc Merlin67 extended wing for example), but for sure the P47 was very good and not that rare! The only disadvantage was its high fuel burn rate, probably the only real advantage of the P51 over the P47.

Greetings,

Knegel

[Charge]

"I completely disagree. The cannon may have heavier hitting power, but it has less range, and less "lead on target". "

Less range? Actually more effective range, especially if you had Minengeshoss ammo which hitting power was not dependent of range.

I think 8 .50 cals was perfect for ground work the Jug did. Lot of scattered damage and thus more hits because the firing times are short. Also the penetration is practically almost similar to 20mm AP.

-C+

[HoHun]

Hi Squire,

>As far as dive speed, @600mph TAS seems to be most oft quoted

Hm, I don't believe that's anywhere near realistic as that Mach 0.79 at sea level (and more higher up) - far in excess of the critical Mach number of the P-47. It might be that it's a "straight" conversion from an actual airspeed indicator reading, but these are not too accurate at very high speeds.

Mach 0.79 was the limit for the Me 109, and close to the limit for the P-51 and the Fw 190, but the P-47 couldn't even get near it.

>50 cal vs 20mm weight savings is about 3 percent of its loaded weight of @14000 lbs

It should be appreciated that in aircraft design, 3% of the loaded weight is a biggie.

I've got a weight and balance chart for the P-47 here that indicates 1830 lbs maximum internal fuel. You can increase fuel load and thus endurance by 25% by going to four cannon, and the impact on practical range is actually even greater than that.

Besides, four cannon were the "luxury" version of weight saving because they virtually doubled firepower. If you're going for a lean P-47, you might go for a 2-cannon-setup with the following characteristics:

2x Hispano II - 308 rpg - 252 kg - 94% firepower

For a neglegible drop in firepower, you'll save 310 kg weight, or 684 lbs.

>Overall I think Hispano Vs would have been a better choice (ala the Tempest), but its not what the USAAF was issued in WW2.

Certainly, 2 x Hispano V would actually yield more firepower than 8 x 0.50", but as the Hispano V was only used late in WW2, I thought the Hispano II was a more realistic comparison.

Regards,

Henning (HoHun)

[bozon]

A few remarks:

The biggest problem of the P47 was range. It was constantly increased with more and bigger DT and the addition of an AUX tank, bigger tanks and eventually wet wings in the P47N.

The way to improve the P47 and over come the weight problem was more power. The paddle blade prop contributed to the efficiency of transforming engine power to thrust adding about 500 FPM to climb rate. The hotrod P47-M was not such a great improvement over the 56th FG Jugs as they already had their engines over boosted reaching close to the M,N engine's output. And that was in lighter better stream lined razorback models way before the M was developed. Johnson repeatedly claimed that his P47 was boosted to 72".

If it would have been designed as a ground attack plane it would have used a gear charger and save a lot of weight and complications. However, what made it a superior high alt fighter (its real purpose) was its distinctive feature - the supercharger. The plane was literaly designed around it.

The crittical mach numer is not what matters, it's how you reach that number. The P-51 was a very fast diver but it's handeling was problematic. At certain speed the stick forces would reverse and if the pilot was not ready for it, it would slam the stick into his belly and risk breaking the plane. Other planes would buffet or suffer early degregation of control. The P47 handeled very well right up to the critical mach where the stick would freeze. Not to mention the superior dive acceleration meaning you cover more distance before reacing max speed.

Bozon

[Knegel]

Hi,

Hohun always forget that hitpower while a aircombat and specialy while escort missions often is less important than hitprobability.

The .50 cal was good enough vs Fighters, 8 x 13rps will have a better probability to hit than 2 x 11rps or 4 x 11rps, specialy with so far outside placed guns and so a smal range of convergence.   One time 104 rps fly toward the target, the other time 22rps or 44rps.  Also cannon shels are not always HE, the 20mm AP dont cause much more damages on a Fighter than the .50cal and the smaler armament need relative more tracer rounds.


While groundattacks it simply depends to the targets, vs groups of soldiers and unamned vehicles the 8 x .50 cal was  probably the better weapons, similar to cluster bombs, while vs light armored vehicles (halftracks etc) and groundobjects (AAA and Flak) the 20mm was better, vs Tanks both guns was rather uneffective.

Imho vs smal and or nimble targets the armament with smaler guns is good, while vs big or slow moving targets the bigger guns armament is better, despite the much smaler rate of fire.  

More guns also provide a better reliability(smaler probability to jam all guns) and was the P47 wing able to handle 4 x 20mm without to make it more tough(more weight)??

[Squire]

The P-47 easily "could have" had 2 x 20mm in each wing, just look at the Tempest, and, for that matter the Spitfire XIV, which had bays for 2 x 20s in each wing, although the second 20 wasnt mounted. It wasnt a case of couldnt.

[bkbandit]

M model. hmmmmmmm, say here that there were 130 built, i wonder if AH would do it, it say here that it was a moded d so it should be hard to do.

I dont know whats the big deal about the cannons. 8 50s, thats a strong gun package. i have snap shoted cons to death with the 4 of the p51b, now double it.

[Widewing]

Originally posted by HoHun
Hi Squire,

>As far as dive speed, @600mph TAS seems to be most oft quoted

Hm, I don't believe that's anywhere near realistic as that Mach 0.79 at sea level (and more higher up) - far in excess of the critical Mach number of the P-47. It might be that it's a "straight" conversion from an actual airspeed indicator reading, but these are not too accurate at very high speeds.

Mach 0.79 was the limit for the Me 109, and close to the limit for the P-51 and the Fw 190, but the P-47 couldn't even get near it.
 

This is incorrect. See below.



This was a fully instrumented aircraft (Mach meter and data probe, including calibrated strip chart recorder). It attained Mach .83 on several dives and it was not fitted with dive recovery flaps.

Typically, a P-47 diving at the allowed limit of 500 mph IAS at 12,000 feet is doing 601 mph TAS, or Mach .82, and this was the placarded limit. It was often exceeded in combat. Mach .82 is well into compressibility, but there's no doubt that the P-47 was capable of these speeds.

Bf 109s and Fw 190s were unable to escape from P-47s, even in prolonged dives.

My regards,

Widewing

[HoHun]

Hi Widewing,

>It attained Mach .83 on several dives and it was not fitted with dive recovery flaps.

Quite impressive! Especially if no dive recovery flaps were used. Makes me wonder why they were considered necessary at all, though.

Was the aircraft configuration in fact representative for a WW2 aircraft? I'm just asking because the chart seems to indicate a 1949 test date, and there would have been ample of time for the airframe to receive modifcations. On the other hand, there might not have been that much reason to modify the type once the war was won. What were the objectives of the tests, by the way?

>It was often exceeded in combat. Mach .82 is well into compressibility, but there's no doubt that the P-47 was capable of these speeds.

Hm, it would be interesting to have a look at the development history since I've seen a couple of texts that seem to suggest quite clearly that at least the early Jugs were troublesome. Here's what Eric Brown wrote:

"About the beginning of 1944 reports begang reaching the RAE of Thunderbolts diving out of control from high-altitude combat, and eventually in March of that year a P-47D was seconded to RAE Farnsborough from the US Eight Air Force for investigation, since it was suspected that the cause was compressibility induced, and the RAE was at that time heavily involved in researach in the transonic flight range.

[...]

Before the next flight, a Machmeter was fitted to the aircraft, and as instructed I climbed to 35,000  ft, carried out a 2 min level run at full power and trimmed the aircraft before pushing over into a 30 degree dive. At Mach=0.72, the aircraft begang to buffet slightly and pitch nose down, requiring a strong pull force to maintain the dive angle. At Mach=0,73 the buffetting increased severely and the nose-down pitch was so strong that it needed a full-blooded both-handed pull to keep the dive angle constant. I had to hang on grimly in this situation, unable to throttle back until Mach number decreased as altitude was lost. The pull-out was not effected until 8,000 ft. Analysis showed that a dive to M=0.74 would almost certainly be a 'graveyard dive'.

I have only subsequently experienced such severe compressiblity nose-down pitch effects in two other aircraft, the Messerschmitt 163B and the Gurmman F-8F [sic!] Bearcat."

(From "Testing for Combat".)

From Brown's tests, a recommendation to fit dive recovery flaps to provide a nose-up pitch moment resulted. Apparently, they were fitted to most P-47D aircraft as recommended.

>Bf 109s and Fw 190s were unable to escape from P-47s, even in prolonged dives.

If the P-47 could be dived to Mach 0.82, it certainly was faster than the Bf 109. I don't know about the exact absolute maximum speed of the Fw 190, but it's my impression that it was tested to Mach 0.80 at least.

Regards,

Henning (HoHun)

[HoHun]

Hi Squire,

>The P-47 easily "could have" had 2 x 20mm in each wing, just look at the Tempest, and, for that matter the Spitfire XIV

Absolutely! Just look the P-51 which was designed for four machine guns in each wing, and fitted with four Hispano cannon without much ado.

The Hispano II was a long-recoil weapon anyway that generated relatively low recoil forces, and as the 4 x Hispano II installation was in fact considerably light than the 8 x 0.50" installation, the P-47 could have been converted easily.

Regards,

Henning (HoHun)

[HoHun]

Hi Bozon,

>The biggest problem of the P47 was range. [...] The way to improve the P47 and over come the weight problem was more power.

Hm, the problem is that with the "1943" approach, we can't use the power that only became available gradually due to progress in engine and supercharger technology from the beginning.

Weight did indeed directly counteract range. The "Breguet" range equation does in fact feature the ratio of loaded weight to empty weight in an important role, and if you accept that any weight saving could be used to carry extra fuel, Aquashrimp's concern about weight is indeed a very valid one.

>If it would have been designed as a ground attack plane it would have used a gear charger and save a lot of weight and complications. However, what made it a superior high alt fighter (its real purpose) was its distinctive feature - the supercharger. The plane was literaly designed around it.

Hm, I'm not so sure that this would withstand a technical analysis. The important thing about the turbo-supercharger was the intercooler, and two-stage mechanically-driven superchargers were quite effective at high altitudes, too, if adequate intercooling was provided.

The turbo-supercharger in fact improved engine efficiency, but not necessarily peak output - while it had more shaft power, the extra exhaust thrust at high power settings might have more than compensated for that. (At least, DVL research reached this conclusion, of course in a generalized fasion.)

While the mechanically-driven two-stage supercharged P-47 would have been less efficient, it might have been able to use the rear fuselage location of the turbo-supercharger for an extra fuel tank to compensate for the poorer efficiency or maybe even surpass the turbo-supercharged version.

(I'm not saying it would - but I think one would have to run a very close analysis before one could tell for certain which version was longer-ranged. I suspect this was not actually done in WW2 since until the second Schweinfurth raid, fighter range was considered to be of secondary importance by the USAAF.)

>The P-51 was a very fast diver but it's handeling was problematic. At certain speed the stick forces would reverse and if the pilot was not ready for it, it would slam the stick into his belly and risk breaking the plane.

Hm, I believe you must be thinking of the turn behaviour with a full fuselage tank.  The symptom in dives was increasingly violent buffeting and a loss of control effectiveness.

If you look at Brown's description above, the P-47 suffered from that at lower speeds than the Mustang, and added a dangerous nose-down change of trim on top of that.

Regards,

Henning (HoHun)

[HoHun]

Hi Bodhi,

>The P-47 was relegated to ground attack due to it's survivability over the inline engined aircraft.  

Hm, according to what I have read about the USAAF's decision making progress, the thing that concerned the top brass was range, and the P-47 was in fact considered inferior to the P-51 in that respect, which seems to have been the primary motivation for the change-over of the 8th Air Force to Mustangs.

However, I have not seen a good account of that in the history books, with a timeline of reports and orders to document that decision, so I don't consider that a "verified opinion".

My impression is that the good points of the P-47 with regard to ground-attack capabilities were emphasized when the 9th Air Force received the Jugs in an act of good leadership.

I'm not sure that we can actually tell for certain that the P-47 was in fact superior to the P-51 as I'm not aware of any truly useful loss statistics. Not to say the P-51 was actually as good as the P-47, but you might have read the threads on the B-17 vs. B-24 and the Navy aircraft toughness discussion (in which the SBD emerged as the true champion) - my conclusion was that we should try to check the reliability of reputations whenever possible :-)

>I completely disagree.  The cannon may have heavier hitting power, but it has less range, and less "lead on target".

Hm, you don't want to hit the target, you want to knock it down. The actual killing power is determined by the product of the number of hits and the destructiveness of each round.

As the destructiveness of each round can be considered to be roughly equivalent to its total energy (kinetic and chemical), you can actually calculate the hitting power, and for a battery of a given weight, cannon generally come out superior because their larger shells can carry a greater amount of chemical energy.

>As for your statement regarding a truck, provide data.  Have you ever seen the effects of a .50 round impact????

Here is an interesting statement regarding the opinions at the time, quoted from "Flight Journal Special, Winter 2000" and referring to the Joint Fighter Conference:

"In Monroe's discussions, it became apparent that the British and the U.S. Navy were in the process of making a switch from .50-caliber guns to 20mm cannon. The principal reason was that although the 20mm cannon had a slower rate of fire, it put out more weight of metal than the .50-caliber gun in a given time, and it did not jam during a 20-second, full-load burst."

(The Army opposed this switch vehemently. It was a flame war even back then ;-)
 
The Army at that time favoured the .60" machine gun, an adaptation of the German MG151. Just for fun, here the comparison between two such batteries for the P-47:

6x MG 151 - 298 rpg - 578 kg - 116% firepower - firepower per weight: 113%
8x ,50 Browning M2 - 375 rpg - 562 kg - 100% firepower - firepower per weight: 100%

As you can see, the difference is rather small, so it's not suprising the .60" MG never replaced the proven .50" Browning.

Regards,

Henning (HoHun)