WHAT IF: Longer range P-47 from start

[renrich]

In looking at a website posted by some member, thankfully, about a AAF bomb group, most of the missions in the early going in 1942-43, were flown at around 20000 feet. The F4U1 had very good performance at 20000 feet and was used extensively as the high cover on bombing raids in the Pacific along with the P38. It was only after the missions began to go deep into Germany that they began to be flown at altitudes above 20000 feet(24000-29000 feet) apparently because of the flak concentrations. If you look at the combat radius of the F4U1 versus the P47C on internal fuel, the Corsair was somewhat better in that respect and could have easily carried an additional 300 gallons in drop tanks and would not have needed a lot of runway to get off the ground contrary to the P47. The Corsair would not have been perfect as an escort fighter but the FW190, possibly the best LW fighter of that period was not all that adept above 20000 feet either.

 

[davebender]

At the altitude the F4U was designed to operate. If the mission requires bomber escort then that version of the F4U will be designed for high altitude performance.

 

[Shortround6]

At the altitude the F4U was designed to operate. If the mission requires bomber escort then that version of the F4U will be designed for high altitude performance.

And just how is it going to be designed for high altitude performance?
Or any higher than it was operating to begin with.

 

[Shortround6]

OK, maybe I am being really stupid about this or just pig headed. P-47s carried 305 gallons of internal fuel to begin with, later changed to 370. F4U carried 361 internal. 124 in unprotected wing tanks. 237 in protected tank/s
BOTH planes are going use similar amounts of fuel at about the same speed and altitude while cruising. They both use the same basic engine. The P-47 doesn't get exhaust thrust but then it isn't using several hundred HP to drive the first stage of it's supercharger either.
Combat radius is defined both by the total amount of fuel carried and by the amount of fuel carried after the tanks are dropped.

Somebody please explain how the Corsair gets back using 361 gallons of fuel after the tanks are dropped flying EXACTLY the same mission profile (speeds and altitudes) as the P-47 when the P-47 cannot get back using 370 gallons. The extra 65 gallon in the late P-47 was good for about 200 miles on at the cruising speeds used for mission planing. Without drop tanks that means an extra 100 miles of radius and with drop tanks it means an extra 200 miles of radius.
That is what the Corsair will get you BEFORE you add the weight (or subtract capacity) of protecting the wing tanks. And you still have a slower level speed, slower climbing plane over 20,000ft with 25% less firepower.

 

[gjs238]

I wonder if the P-38 with R-1820's or R-1830's would perform well at altitude to have performed the 8th AF escort mission well.
The aircraft would have less HP, but may have awesome reliability, as the engines were already successfully and reliably turbocharged in the B-17 B-24.

 

[renrich]

According to Dean, "America's Hundred Thousand," There are two tables published which give a fairly good comparison. Unfortunately they are not combat radius for both planes. However the combat radius table for AAF fighters gives the P47D with 305 gallons internal as 125 miles. The two tables for the two planes which is a close match gives the P47C-early D a yardstick range of 835 miles with 305 gallons at most economical cruise at 10000 feet. The same type of table for the F4U1 with 361 gallons at 5000 feet at most economical cruise is a range of 1596 miles. I don't believe the 5000 foot difference would make any significant difference. You don't need to protect the wing tanks because they had a C02 purge system and they would be used up first. I believe the 85 gallon aft tank of the P51 was unprotected and was always used first. With the F4U1 you get a plane that has at least 100 miles more combat radius, is more maneuverable, has more than adequate firepower, better climb rate at least to 20000 feet and is faster below 20000 feet. Not a huge difference between the two but that extra 100 miles or so could save some lives.

Of course you are right in that a mission profile has to include enough fuel to get back. However, both planes are going to have to, if they are carrying drop tanks, get into internal fuel before the mid point of the mission. The drop tanks on a max range mission are going to be used up early because of the increased drag and weight. In other words the mileage from a 150 gallon drop tank is not the same as 150 gallons of internal fuel. I have read it is about 50%. We have not factored in either the decreased weight of the Corsair because of no wing fold, no arresting gear, no marinisation weight and perhaps a little structural weight loss.

 

[Shortround6]

I have no figures for the R-1830 but you can find figures for both the P-38s and the B-17 either in the manuals on this website or Zeno's. The fuel burn per hp/hr seems pretty much the same. You loose a bit of weight (assuming you can redistribute everything to get the CG right) but you loose power all across the range. 750hp max lean cruise for the R-1820 vs 795hp for the late model Allisons. the R-1820s are barn doors as far as streamlining goes. They actually have slightly more frontal area than a R-3350. Which means not only less top speed (and climb) but a higher fuel burn to get the same cruising speed. Vision from the cockpit could get real interesting too
There is a reason they made the XP-50 the way they did, and there is no evidence it ever reached the speed figures estimated for it before the in-flight turbo explosion took out the aircraft.

All P-38 engine problems seemed to get lumped together when actually there were a succession of problems, some not the Allison's fault, some that were the result of the type of engine the Allison was, and perhaps a few that were the fault of Allison.
Problems in 1942, early 1943 were general turbo problems and plagued ALL US turbo equipped planes to some extent. As these got sorted out new problems cropped up. The change in the fuel blend for some batches of 100/130 fuel cause problems. Heavier compounds were allowed to be used ( or higher percentages of the heavier compounds) which affected the volatility of the fuel, it's ability to vaporise and stay vaporised at low temperatures. V-12 engines are more susceptible to fuel coming out of suspension in the fuel/air mix than radials because of the longer distance from the supercharger outlet to the cylinders than on a radial. This can lead to strange mixtures even while cruising, some cylinders getting richer or leaner mixture than the next cylinder over. It is made worse by bad piloting technique. Running low rpm and high boost will keep the intake charge warmer (and the fuel in better mix with the air) than running high rpm and low boost. Over the course of the summer/fall of 1943 the P-38 introduced new engines, new models of the turbos, new inter-coolers and new turbo controls but not all on the same model aircraft. Because of a shortage of engines or other parts ( I forget at the moment) P-38Hs and Js were being built side by side for a while. putting all these together made it hard to pinpoint the cause of the P-38s troubles in the fall of 1943 because a number of the problems overlapped/combined. Allison had also been working on a new intake manifold to cure some of the fuel pudding problem. These began to be fitted in the fall of 1943 and were shipped overseas to be RETRO-FITTED to ALL Allison engines, P-39, P-40, P-51 in addition to the P-38.
Because of the demands of fighter flying ( bombers seldom went to WER power after a few hours of cruising unless they had major problems, like loosing an engine) it is a little hard to compare the Allisons to the radials in some ways. Bomber engines in general would often go longer than fighter engines of the same type between overhauls.
The radials probably would have been more reliable than the Allisons but engine type is no protection against a mis-rigged turbo control. Because of the installations in the P-38 the turbo controls did follow the exact same path on each engine and in at least one squadron the engine on one side would fail much more often than the other.

 

[Shortround6]

According to Dean, "America's Hundred Thousand," There are two tables published which give a fairly good comparison. Unfortunately they are not combat radius for both planes. However the combat radius table for AAF fighters gives the P47D with 305 gallons internal as 125 miles. The two tables for the two planes which is a close match gives the P47C-early D a yardstick range of 835 miles with 305 gallons at most economical cruise at 10000 feet. The same type of table for the F4U1 with 361 gallons at 5000 feet at most economical cruise is a range of 1596 miles. I don't believe the 5000 foot difference would make any significant difference.

I think we have been around and around on this one before. The problem with this yardstick range is that the yardstick is severely bent and twisted for what we are trying to measure. the 5,000 ft difference actually brings in two differences in fuel consumption for the F4U. They are that at 5,000ft the engine has the 1st stage of the super charger not only clutched out and not driven (and taking no power) but movable doors in the intake system are routing the intake air straight from the wing root inlets to the carburetor for some "free" ram effect even at cruising speeds. As I have pointed out before this "yardstick" speed is at 178-180mph. The P-47 has got a convoluted intake system and a more restricted exhaust system. Yes the F4U is getting about 5.14 miles to the gallon as this rather useless speed ( for European conditions). The P-47 can burn 60gallons and hour at 6,000ft and cruise at 230mph for a mileage of 3.82 miles per gallon. Yep the F4U is winning hands down.
Now lets go to 25,000ft and try cruising at 300mph. the P-47 burns 95gallons an hour, we know that at 1200hp at the same altitude the P-47 burns 105gal/hr. what power do we need for 300mph? a bit under 1100?
F4U burns 82 gals at 26,000ft to make 950 hp speed unknown.
or:
F4U burns 121gals an hour at 21,500ft to do 334mph.
P-47 burns 145gals an hour at 25,000ft to do 337mph.
F4U is coming out ahead but by 20% not the 90% advantage given by the "yardstick"
And you do need to protect the wing tanks if you are doing deep penetration/escort.
Our P-47 goes in with 305 internal and 300 in drop tanks. it's "radius" is given as 425 miles. It hits the limit, drops tanks and engages the enemy. 5 minutes combat power and 15 minutes max continuous suck up about 75 gallons of the 305 (?) still on board leaving 230 gallons. take out 46 gallons for a 20 reserve and landing and you have 184 left for the flight home.
Say our F4U goes in with 363 aboard and 300 under and drops tanks engages at the same time. it uses about 85 gallons for 5 min combat and 15 min max continuous (thats what the charts say) for 278 left, looking good right? now lets say the F4U took a couple of 7.9mm rounds through one of the un-protected wing tanks, no fire but unless that was the tank in use when hit the plane could be down to 215 gallons for the trip home. With it's better mileage than the P-47 it should make it but you don't really want to extend the radius much further from base if you can't protect the wing tanks.

 

[renrich]

Page 105, "America's Hundred Thousand"-regarding the supercharging system in the F4F, F6F and F4U, "In this system, again with additional weight and complexity involved to keep power up at altitude, there were two blowers. The main blower was always speedup geared to the engine crankshaft and THUS RAN WHENEVER THE ENGINE TURNED OVER." MY caps! I interpret that to mean that the first stage is always running if the engine is running. Am I wrong? If not what does that do to your figures?

The wing tanks did not have to be protected as the Corsair used them first and then purged the tanks with CO2, just as the P51 did, I think.

I believe your figures are off a little but can't prove it. I do know that the Wildcat in carrier ops had a combat radius on internal fuel of around 150 miles. I do know that the Corsair exceeded that substantially. I do know that the combat radius of the P47C on internal fuel had a combat radius of 125 miles. Therefore I reason that the F4U1 had a combat radius greater than the P47C. Adding drop tanks to any or all of those should not change the disparity as long as the drop tanks were the same capacity.

The issue of how much weight or drag the Corsair lost because of being landbased only has not been addressed. I do know that the tailhooks were removed by Navy and Marine landbased squadrons and I also know that a number of Corsairs were produced by Goodyear with no wing fold. It makes sense to me that a Corsair, not marinised, with no arresting gear, with no wing fold and possibly some structural modifications would have less weight, less drag and thus be faster, climb faster and have more range. Do you disagree?

Strangely, I have never seen any published figures about the performance of Goodyear Corsairs with no wing fold and presumerably no arresting gear.

 

[gjs238]

We know the Brits initiated Merlinizing the P-51...
And we know the P-40 got Merlinized...
Did they try the same with the P-38?

 

[renrich]

SR, first let me say that I know you are a well informed poster as I have read many of your posts and always enjoyed and was impressed by how well thought out and persuasive they are. However, I feel that I am pretty firm ground here. I think a reasonable assumption early in the war is an escort mission with internal fuel only. The Corsair with 361 gallons of fuel internal will use the wing tanks first, just like they did in the Pacific and still have 237 gallons to complete the mission and go home. If a 150 gallon drop tank is carried, it is used first, then dropped and the Corsair still has the 361 gallons left and it uses the 120 or so in the wings and still has the 237.
With two 150s carried the drop tanks are used first and dropped and the Corsair has about 50% of it's fuel left. However, because the takeoff and climbout with the drop tanks uses a lot of fuel, the plane is nowhere near the midpoint of the mission, so the wing tanks are then used and if combat is begun and fire is feared if the wing tanks are hit the tanks can be purged with the CO2. My bet is that if that event occurs the pilot will keep using the wing tanks and count on not being hit so he will have more fuel. In any case, a lot less fuel is needed to go home since the plane is lighter and there is no long climb out and takeoff and it is all downhill.

 

[davparlr]

Strangely, I have never seen any published figures about the performance of Goodyear Corsairs with no wing fold and presumerably no arresting gear.

Dean shows the F4U-1D with an empty weight of 8971 and a gross weight of 11,962. Wagner shows the FG-1D with an empty weight of 8695 and a gross weight of 12,039. If one was inclined, the range difference could be calculated.

 

[renrich]

Dav, would not there be slight drag difference because of no tail hook and no gap where the wind fold was?

 

[Shortround6]

Page 105, "America's Hundred Thousand"-regarding the supercharging system in the F4F, F6F and F4U, "In this system, again with additional weight and complexity involved to keep power up at altitude, there were two blowers. The main blower was always speedup geared to the engine crankshaft and THUS RAN WHENEVER THE ENGINE TURNED OVER." MY caps! I interpret that to mean that the first stage is always running if the engine is running. Am I wrong? If not what does that do to your figures?

It depends on what you mean by "first stage". The impeller closest to the engine is the "main blower". the mixture from this leaves the supercharger and goes to the Cylinders. The auxiliary blower is the one further away. when it is in operation the air enters the auxiliary blower (what I call the first stage) is compresses goes out to the intercoolers where it is cooled, goes to the carburetor where the fuel is added. The carburetor is mounted on the inlet to the "main blower" where the air/fuel is further compressed and then to the cylinders. The "main blower" is the 2nd blower the air goes through. At low altitude the air is routed from the intakes straight to the carburetor and the "Main blower" bypassing the "auxiliary blower" and inter-coolers. Please note that this is for the Corsair only. F6Fs ran the air though the "auxiliary" (1st) stage at all altitudes and wither the "auxiliary" (1st) stage was turning or not.
I don't think it does anything to my figures. My figures are taken from either charts at "Zeno's" or from F4U Performance Trials

If somebody was to call the "Main" stage the 1st stage and the "auxiliary" stage the second stage I guess they can. It just seems simpler to describe the various 2 stage (including turbo) supercharger set ups by following the air flow.

The wing tanks did not have to be protected as the Corsair used them first and then purged the tanks with CO2, just as the P51 did, I think.

If the F4U used the wing tanks first then they are NOT AVAILABLE for the flight home after combat and the Corsairs "radius" is limited to the distance it can cover using the fuselage tank, 237gal?

Mustangs took off climbed out using the left main tank, then switched to the rear tank until a portion had been used up, depending on operation down to 25 gal (?) then alternated drop tanks to keep the plane in balance until they were empty then switched to the mains and repeated the alternating pattern. Use remaining rear fuselage fuel for landing.
This is from a post war manual, war time procedures may have differed but the Mustang was not rated for full combat maneuvers with the rear tank full.

I believe your figures are off a little but can't prove it. I do know that the Wildcat in carrier ops had a combat radius on internal fuel of around 150 miles. I do know that the Corsair exceeded that substantially. I do know that the combat radius of the P47C on internal fuel had a combat radius of 125 miles. Therefore I reason that the F4U1 had a combat radius greater than the P47C. Adding drop tanks to any or all of those should not change the disparity as long as the drop tanks were the same capacity.

A question on this is what were the Navy standards for "combat radius" vs the Army's standards. The Army included warm up, take-off, climb to 25,000ft (with NO allowance for distance) Cruise out at 25,000ft and 210ASI (315mph true?) 5min military power, 15minutes max continuous power, flight back at 25,000ft and 210ASI (315mph true?), reserve of 30min at minimum cruise power, no allowance for decreased fuel consumption in decent. No allowance for formation flying or evasion other than the combat allowance.

I have no idea what the navy standard was but the idea of a Wildcat having a 150mile radius under the Army conditions seems pretty unlikely even with 147 gallons of fuel. That 315mph true cruise at 25,000ft bit just might suck up all the wildcats fuel in about 1 hour giving you the 150mile radius but no take off, climb combat allowance or reserve. assuming the wildcat could do 315 at 25,000ft for more than a few minutes without trashing the engine.

The issue of how much weight or drag the Corsair lost because of being landbased only has not been addressed. I do know that the tailhooks were removed by Navy and Marine landbased squadrons and I also know that a number of Corsairs were produced by Goodyear with no wing fold. It makes sense to me that a Corsair, not marinised, with no arresting gear, with no wing fold and possibly some structural modifications would have less weight, less drag and thus be faster, climb faster and have more range. Do you disagree?

I do not disagree, the question is how much improvement you get. deleting a few gallons of anti-corrosion paint and the tail hook doesn't buy much for weight. the wing fold will gain a bit more but changing the weight by even 300-400lbs isn't going to change speed (top or cruise) by more than a couple miles an hour. The drag of the hook maybe worth more. The weight may make more difference in climb. See page 125 of "AHT".

Strangely, I have never seen any published figures about the performance of Goodyear Corsairs with no wing fold and presumerably no arresting gear.

This may tell you something. If it is only on the order of 2-4% it may not have been worth recording. The Goodyear Corsairs being a minimum conversion. No other structural lightening or other modifications.

 

[gjs238]

It depends on what you mean by "first stage". The impeller closest to the engine is the "main blower". the mixture from this leaves the supercharger and goes to the Cylinders. The auxiliary blower is the one further away. when it is in operation the air enters the auxiliary blower (what I call the first stage) is compresses goes out to the intercoolers where it is cooled, goes to the carburetor where the fuel is added. The carburetor is mounted on the inlet to the "main blower" where the air/fuel is further compressed and then to the cylinders. The "main blower" is the 2nd blower the air goes through. At low altitude the air is routed from the intakes straight to the carburetor and the "Main blower" bypassing the "auxiliary blower" and inter-coolers. Please note that this is for the Corsair only. F6Fs ran the air though the "auxiliary" (1st) stage at all altitudes and wither the "auxiliary" (1st) stage was turning or not.
I don't think it does anything to my figures. My figures are taken from either charts at "Zeno's" or from F4U Performance Trials

If somebody was to call the "Main" stage the 1st stage and the "auxiliary" stage the second stage I guess they can. It just seems simpler to describe the various 2 stage (including turbo) supercharger set ups by following the air flow..

How does this differ from the F4U-4?
It sounds like both the F4U-1 and the F6F always had one supercharger stage feeding another.

 

[Shortround6]

We know the Brits initiated Merlinizing the P-51...
And we know the P-40 got Merlinized...
Did they try the same with the P-38?

There were 3 paper studies (of varying effort or detail) of putting Merlins in P-38s over several years. They covered several different Merlin versions compared to the current Allisons of the time.
Some of them showed minor improvements in performance at certain altitudes or in rates of climb but they also usually showed a decrease in range. In one case under certain specified conditions (picked by Allison and Lockheed?) it was estimated the loss of range at 30%. This was by far the worst estimate.

 

[Shortround6]

SR, first let me say that I know you are a well informed poster as I have read many of your posts and always enjoyed and was impressed by how well thought out and persuasive they are.

I do thank you for the compliment.

However, I feel that I am pretty firm ground here. I think a reasonable assumption early in the war is an escort mission with internal fuel only.

I would go along with that. The P-47 and the F4U are very close in timing a lot of land marks of going into service seem to be within a few months of each other. The F4U has a definite advantage with with the 361/3 gallons of internal fuel. However even with that the radius seems too short for the Army mission. after subtracting the warm-up-take-off-climb out fuel, the combat allowance and about 40 gallons for reserve you are left with 200 gals for travel or about 100 gals each way. Even if you get 20% better mileage than the P-47D with the Big tank that gets you a radius of around 275miles. Much better and perhaps nipping at the heels of the P-51. This is what the figures are showing so far and I am surprised, I did not think they would be that good.

With two 150s carried the drop tanks are used first and dropped and the Corsair has about 50% of it's fuel left. However, because the takeoff and climbout with the drop tanks uses a lot of fuel, the plane is nowhere near the midpoint of the mission, so the wing tanks are then used and if combat is begun and fire is feared if the wing tanks are hit the tanks can be purged with the CO2. My bet is that if that event occurs the pilot will keep using the wing tanks and count on not being hit so he will have more fuel. In any case, a lot less fuel is needed to go home since the plane is lighter and there is no long climb out and takeoff and it is all downhill.

Using the figures from the charts the combat allowance is about 85 gallons and the reserve allowance for finding the field and landing is about 20-21 gallons. Now each combat is different but using this as a "yardstick" you need to subtract about 105 gallons from what ever fuel you have in the internal tanks at the point where combat is joined to figure the amount of fuel to get home. The Army did not count the decrease fuel consumption that came with the "downhill" descent. On any given day that could be used up and more by the prevailing winds from the west. The fuel left times the rate of consumption at the desired/required height/speed define the actual "safe radius". Too much fuel in drop tanks and not enough in the internal tanks means a plane could get in deeper than it could get out. I will also note that it appears the Corsairs either had the wing tanks and a single pylon tank or no wing tanks and two pylon tanks. At least on the F4U-1s. Max fuel about 536 gallons.

 

[Shortround6]

How does this differ from the F4U-4?
It sounds like both the F4U-1 and the F6F always had one supercharger stage feeding another.

1st question. there is no difference.
2nd question. when ever the auxiliary supercharger was engaged it feed the main supercharger. Just like the P-47 (and every other WWII turboed American Plane) always had the turbo feeding the main supercharger on the engine. Merlin 2 stage engines always had the rear/outer supercharger feeding the inner (main?) supercharger but there was no real cooling between stages, all cooling happened between the main stage and the engine itself. Merlins could also not declutch the outer (1st stage?) compressor at low altitude to save power and lower charge temperature like the Navy engines.
At low altitudes the navy engines could declutch the auxiliary supercharger and either bypass it (F4U) or just suck right through it passed the either stationary or windmilling impeller (F6F). I don't know if the impeller turned on it's own in the airflow or not. This can be seen in the extra "notch" in the power graphs for the Navy engines compared to a two stage Merlin.

 

[gjs238]

Did the other US radials have 2-stage superchargers (main blower and aux blower) as well?
R-1820, R-1830, R-2600, etc.
F4F?
If so, then I imagine when these engines were turbocharged, the turbocharger replaced the aux blower?

 

[Shortround6]

Only the R-1830 used the two stage mechanical system and then only in some F4Fs and perhaps some C-47s, aside from a few prototypes.
The Wright engines never used a two stage mechanical supercharger ( at least none that got out of the factory).