Bomber escort logistics?

[drgondog]

http://www.wwiiaircraftperformance.org/p-47/p-47-differences.jpg

Note - the P-47D-30 which never went to Berlin has a tactical combat radius of 600 miles with 370 gallons internal fuel, 330 gallons external fuel. The P-47D-5 could go 225miles combat radius with 305 gallons internal fuel

Greg - one more time.

Why do you think the Hellcat with just over half the fuel with standard 150 gallons external fuel (410gallons) can go to Berlin and back with reasonable expectation of getting them back to England? Even at best cruise conditions of 12,000 feet and 200 mph?

Repeat - assuming you carried 3000 gallons of external fuel (a joke), made it to East Berlin with all 250 gallons of internal fuel remaining, fought for 20 minutes at 360+ gallons per hour to reduce your internal fuel to 160 gallons and had to return in a straight line with no reserve the 580 miles back.

Good luck when you consider a P-47D-30 can't do it when it starts with 370 internal, loses 90 gallons in the same scenario down to 280 gallons - or 75% more than your F6F-5

 

[Shortround6]

Precisely. What a lot of people don't get is that the combat range depends on how much fuel is left after external tanks are dropped (and CoG affecting rear tanks emptied) and you have combat and an escape. Fairly reasonable to assume you return basically unaffected (if you want) at a high altitude at most economical cruise.
For shorter missions, and you haven't shot off all your ammo, then you can shoot up things on the way home too.

In my LR Spit calcs I assumed 15 mins combat at max power, then economical cruise for return home after that and got to Berlin easily with a rear tank (plus a reserve). The same is for true any other plane.

A problem is that you cannot use "economical cruise for return home" from many targets in Germany. If you get "bounced" by German fighters while flying at economical cruise it takes way to long to accelerate up to a combat speed. Return speeds need to be at or close to max lean cruise.

For instance (and just because it is the first data sheet I ran across) a Spitfire MK XIV has a top speed of 448mph at 26,000, an economical cruise of 245mph at 20,000ft and a maximum weak mixture cruise of 362mph at 20,000ft. Now the return might not be made at 362mph but flying at 245mph over Germany is like flying towing a big kick me sign.

As for that 15 mins, that is a lot of combat time at full power. Even in combat full power (and maximum consumption) was used only sparingly. Thus the actual combat time could have been longer, with much of it at more reduced power settings. Basically you would have ran out of ammo fairly quickly as well.

In a lot of fights the planes lost altitude fairly quickly and could wind up with the fighters thousands of feet, if not over 10,000ft below the desired altitude. Do the fighters break off and return home or with ammo remaining try to climb back up to the bombers height or above? It depends on where they are ( how close to the next fighter rendezvous), fuel remaining, ammo remaining and how far below/behind the bombers they wind up.

 

[Neil Stirling]

Figures in nautical miles, kts and imperial gallons.

Neil.

 

[drgondog]

Thank you Neil.. once again RN and RAF a little more thorough in laying out great detail regarding performance than USN published documents that I have been able to find.

 

[Milosh]

Am I reading the graphic correctly in that the combat radius is 237nm (272mi)? If so, that would not get the F6F even half way to Berlin.

 

[bob44]

This is off topic but I am curious.

The talk of the Hellcats being used in Europe has made me wonder.

If the war for some reason ended in the Pacific quickly do to pure brilliance on the part of the allies and incompetence of Japan or I guess the Japanese see the writing on the wall and come to terms. What happens to all this naval airpower?

You have the pilots and planes. Do you have more carriers than are needed for Europe with the Pacific war complete? Do some of the Naval assets become land based? Clearly from what I have read they are not going to do the long range escort but there might be plenty of jobs they could do?

If the Pacific war ended early, I would think the US Navy aircraft would stay in the Pacific as part of an occupation. However, this would free up industry and manpower for the war in Europe.

 

[Shortround6]

Basically the F6F had less internal fuel than a P-47, more drag and a less efficient engine at altitude. If the P-47 was lacking in radius then unless you repeal the laws of physics the F6F will have even less combat radius.
Combat radius being defined by the amount of fuel after the tanks are dropped unless " thinking outside the box" means fighting with a fuel tank still attached.

 

[Neil Stirling]

Milosh you are

Neil.

 

[GregP]

Here's one back at you: http://www.wwiiaircraftperformance.org/f6f/hellcat-II-ads-a.jpg

You might note this is courtesy of Neil Sterling ...

Note that in column 3, about 2/3 or the way down the page on the left side, with only 333 gallons carried the Hellcat has a range of 1,430 miles (statute miles). I would remind you that Berlin is only 580 air miles (statute miles) from London and is thus WELL within range, unless m y math is wrong, carrying about half of the fuel it CAN carry, so you are coming off as quite disingenuous by continuing to insist the Hellcat couldn't perform escort duties.

I never said it would be optimum or even a good idea ... I said it could be done, and it can, unless you want to refuse to believe the facts. It seems that is exactly what you want to to do, so go ahead. Makes no difference, but you seem to be arguing for the position you took initially without looking at what is possible, which was my "what-if."

It IS possible and could easily be done, using factory specs ... not that they did or even SHOULD have. It was just a damned "what-if" that turns out to be possible.

 

[Jabberwocky]

I'd say that part of the problem is the extra conditions that the FAA/RN had when determining combat radius of the Hellcat, and how that differed from the RAF and USAAF's processes.

If you look at the figures, the Hellcat's radius is given as only about 20-25% of max endurance range. Not only are there the standard allowances for warm-up, climb to altitude and combat, but there is also a 20 minute allowance loitering around waiting to land on a carrier and 15% allowance for wind, formation flying ect, ect.

On land, these range penalties would not be as severe. The RAF estimated that the low altitude combat radius of the Tempest II/V and P-47 was about 40% of still air cruising range. Allowances were 5 min at take-off power, climb power for 2 minutes, combat power for 5 minutes, fast cruise for 15 minutes, balance at best economy and then subtract a 20% safety margin.

If we apply the RAF's range calculations (~40% of still air range) to the F6F, we get a combat radius of up to 470 miles, but for low altitude only.

I think that's overgenerous.

Here's my reasoning:

You're going to need another 10 minutes or so at higher power levels to get to 25,000 ft. The RAF has only a 5 minute allowance at combat power, rather than the 15 minutes for the RN/FAA. Thus, we might cut the land-based combat radius calculation back to 33-35%.

This would give you a practical radius of about 405-415 miles. That's better than anything the RAF had and much better than the early P-47s.

It's still not enough to get you to Berlin though.

Even if we assume a best-case range of 1430 miles and the (generous) 40% range allowance, then Hellcat's best combat radius will be 570 miles. With the same calculations, the RAF reckoned that the 'Thunderbolt II' could go to a 795 mile combat radius with 2 x 138 gal external tanks, and the Mustang III was good for 725 miles with 2 x 75 gal external tanks. Thus, the Mustang and late P-47Ds have a clear range advantage over the Hellcat.

 

[drgondog]

Here's one back at you: http://www.wwiiaircraftperformance.org/f6f/hellcat-II-ads-a.jpg

You might note this is courtesy of Neil Sterling ...

Note that in column 3, about 2/3 or the way down the page on the left side, with only 333 gallons carried the Hellcat has a range of 1,430 miles (statute miles). I would remind you that Berlin is only 580 air miles (statute miles) from London and is thus WELL within range, unless m y math is wrong, carrying about half of the fuel it CAN carry, so you are coming off as quite disingenuous by continuing to insist the Hellcat couldn't perform escort duties.

Greg - a.) you simply do not comprehend the difference between RANGE and Combat RADIUS, and b.) that Range in a straight line divided by 2 is NOT Combat Radius, and c.) that the speeds and altitudes for Combat Radius are NOT the speeds for Range, and d.) that Combat Radius for a Hellcat at 25,000 feet is even LESS than at 20,000 feet for the Hellcat II figures that RN developed quite well.

I never said it would be optimum or even a good idea ... I said it could be done, and it can, unless you want to refuse to believe the facts. It seems that is exactly what you want to to do, so go ahead. Makes no difference, but you seem to be arguing for the position you took initially without looking at what is possible, which was my "what-if."

Greg - DO THE MATH. The Math is Not Divide the Range at 200mph TAS at 15000 feet divided by Two.

It IS possible and could easily be done, using factory specs ... not that they did or even SHOULD have. It was just a damned "what-if" that turns out to be possible.

LOL. No.

Go find the SFC for the following for the R-2800-10 or -18.

1. Take Off Power for 2 minutes and then rich for about 25 minutes while 52 other Hellcats take off in pairs (4 spares) and assemble into formation.
2. Climb to 25000 Feet, level off and throttle up to approximately 330 mph true (you have to be able to catch the Bombers somewhere around Dummer Lake with a 150 gallon tank (extra drag thingy) or if you propose more find the SFC for the equivalent throttle position (increased to overcome the extra drag) to still maintain 330.
3. At RV point Ess at no less than 300mph while flying over a bomber stream at 200mph TAS between Dummer Lake and Berlin.
4. Engage with LW at Gardlingen or Celle east of Dummer Lake, drop tanks. Explain how much internal fuel you have at this moment.
5. Fight for 20 minutes at Military and War Power
6. Rejoin bombers from Steinhuder Lake to Berlin assume 330 will still catch up at 25000 feet
7. Return to Dummer Lake where P-47s can RV with you
8. Return to England at least 300mph TAS
OOPs, can't make it past Osnabruck.

Answer the following questions:
How much internal fuel is used, if at all, while warming up, taxiing, taking off and climbing? What were the SOP for the use of internal versus siphon from tanks for safety reasons. That will impact your already dicey situation when you punch tanks and go Internal fuel of 250 less whatever may have been used during warm up and takeoff.

What was the SFC for Take Off and Climb for a three tank configuration if you propose Ferry Tank configuration for combat escort in ETO.

Greg - you look like a fish flopping in a mud puddle when you keep going back to handbook range tables. Apply the same approach to the P-47D series with 150 gallon tanks in 1943 and ask, if Range divided by two is greater than Berlin radius, then why couldn't it go past Dummer Lake.

Go look up the same info that USAAF provided for Combat Radius for P-40, P-51, P-38 and P-47. They all lay out Lab assumptions based on warm up, take off, climb, cruise, combat, return, 30 minute reserve.

You may miss a couple of really important details regarding USN mission profiles vs ETO/MTO. A couple that come to mind is that Hellcat optimum cruise speed and altitude is around the same figure for SBD/TBF and you rarely ever see them Essing above the navy bombers. Simply because the chances of being intercepted until the target was rare. The courses were straight line, unlike ETO wher huge flak concentrations broke up most routes to target AND the planners were always ziging and sagging on the way to the target to make the LW guess and make mistakes regarding interception.

You keep whining that SR and I are 'not thinking out of the box', that we are bullheaded and refuse to see the crystal clarity of your intellect when you claim 'it CAN be done' but you simply don't know how to prove your thesis. You only resort to published tables for Range when you clearly do not understand the assumptions made for even those figures, nor do you seem to comprehend what must change in your assumptions and calculations to get to a logical fact based argument.

So PROVE your thesis with realistic flight/operations characteristics of an R-2800-10/-18 engine Hellcat as far as Fuel consumption based on climb, high speed cruise at 25000 feet, combat for 30 minutes, high speed cruise back with only the fuel remaining internally from engagement in combat, let down over the Channel, fish around for 30 minutes looking for home because of bad weather.

I've done it, Hop has done it for you in the past as two examples for Mustang and Spitfire. You could at least use the same assumptions for the F6F profile.

Go for it. Quit complaining that we don't get it.



'

 

[Shortround6]

I would be happy to see even 10 minutes at combat power or 5 minutes WEP and 5 minutes military and 300mph (or 297mph at 20,000ft) to the Dutch/Belgian coast. He can drop 15,000ft crossing the Channel while flying 200mph at that point. Still won't make it.

 

[drgondog]

I'd say that part of the problem is the extra conditions that the FAA/RN had when determining combat radius of the Hellcat, and how that differed from the RAF and USAAF's processes.

If you look at the figures, the Hellcat's radius is given as only about 20-25% of max endurance range. Not only are there the standard allowances for warm-up, climb to altitude and combat, but there is also a 20 minute allowance loitering around waiting to land on a carrier and 15% allowance for wind, formation flying ect, etc.

On land, these range penalties would not be as severe. The RAF estimated that the low altitude combat radius of the Tempest II/V and P-47 was about 40% of still air cruising range. Allowances were 5 min at take-off power, climb power for 2 minutes, combat power for 5 minutes, fast cruise for 15 minutes, balance at best economy and then subtract a 20% safety margin.

If we apply the RAF's range calculations (~40% of still air range) to the F6F, we get a combat radius of up to 470 miles, but for low altitude only.

I think that's overgenerous.

Here's my reasoning:

You're going to need another 10 minutes or so at higher power levels to get to 25,000 ft. The RAF has only a 5 minute allowance at combat power, rather than the 15 minutes for the RN/FAA. Thus, we might cut the land-based combat radius calculation back to 33-35%.

This would give you a practical radius of about 405-415 miles. That's better than anything the RAF had and much better than the early P-47s.

It's still not enough to get you to Berlin though.

Even if we assume a best-case range of 1430 miles and the (generous) 40% range allowance, then Hellcat's best combat radius will be 570 miles. With the same calculations, the RAF reckoned that the 'Thunderbolt II' could go to a 795 mile combat radius with 2 x 138 gal external tanks, and the Mustang III was good for 725 miles with 2 x 75 gal external tanks. Thus, the Mustang and late P-47Ds have a clear range advantage over the Hellcat.

There is another complication to the profile as you have presented it. In the ETO the take off and assembly for a Group sized force took approximately 30 minutes from Start Engine time, through warm up, taxi, military power take off in pairs for 24 to 26 pairs, assembly as each pair joins up, climb out to 25000 feet with max gross weight for another 15 plus minutes, then throttle back to fast cruise. The typical escort cruise was 300 to 330mph TAS at 26000 to 30000 feet or about 3000 to 5000 feet above the bombers for the high escort. Returning to base was dictated by fuel but typically it was the same until let down over the Channel. The 30 minute reserve to land was not conservative for all 48-52 aircraft in good weather and optimistic for bad weather.

The key is how much fuel does your aircraft burn at max boost/rpm for 15 to 20 minutes and how much of your internal tank drain before turning back for home from the air battle location of Berlin (in these discussions). The Hellcat burned a lot more (as P-47) than the Spitfire/Mustang. I have seen data ranging from 400 gallons per hour for the R-2800 at Military Power and 240 gph for the Merlin 1650-7.

Neither the RN nor the USN subscribed to USAAF bomber/escort Procedures for large, fast and high flying bombers.

Comparing Range and Combat Radius always begs the assumptions made to each step in the profile. When you peruse through Mike and Neil's website you will notice how much more detailed test plans at USAAF and RAF/RN test facilities map out differences in cruise speed settings, miles per gallon at different fuel weights and ordnance loads at different altitudes and the affect on power to maintain different cruise speeds based on external loads.

The USN does not seem to have spent as much time. For escort I assume that the range of a Hellcat with 150 gallon external tank is much the same as a SBD/TBF carrying 1000 pound or more of ordnance and were Ok with same cruise speed as the a/c they were escorting in a straight line - which is far different for ETO escort fighter ops.

Your points are well made.

 

[syscom3]

Even if the Hellcat could fly to Berlin, its just dogmeat on a platter. It wont hold up to repeated attacks from -109's and -190's. Not to mention flak batteries that will be in its way from having to fly straight lines.

Now if we were talking about Corsairs, this might be a more logical debate.

 

[Shortround6]

Using the cube law as a rough estimate it takes nearly twice the power to fly at 297mph as it does to fly at 237mph. Assuming a near identical specific fuel consumption that changes the miles per gallon to about 5/8ths what the 237mph will give you.

The F6F also has a situation with the supercharger. at 20,000ft is possible to get a bit over 800hp from the engine in low blower lean mixture and no ram? but that drops to 625-650hp at 25,000ft. Kicking the supercharger into high gear can give over 900hp max lean at 25,000ft at 34in and a lower rpm but you do need to figure in the extra power/fuel (change is spc) needed to drive the supercharger.

There is no doubt that a Hell cat could fly with enough drop tank fuel from England to Berlin and back in calm air. But fighting and making it back at a reasonable speed( NOT a speed that it might take two minutes to accelerate to full speed from) on reaming internal fuel is another story.

Using the USAAC radius conditions the extra 65 gallons of fuel in the later P-47DS was worth about 175 miles of radius on a drop tank equipped P-47. (two 150 gallon drop tanks in both cases) 425 miles compared to 600 miles for the bigger internal tank. Now cut the P-47 to just 250 gallons internal instead of 305. Anybody want to guess what the radius might be? 250-275 miles even with the drop tanks?
Remember the drop tanks ONLY work going in NOT getting out.

 

[drgondog]

Mike Williams has an abundance of performance/fuel consumption, miles per gallon data for P-47.
The extract below is for a P47C-1 with R-2800-18 which is close in SFC to both the -10 and -18 for the F6F-3 and -5
For 305 gallons and standard performance calc - namely warm up, Take off at Military Power, climb to altitudes (10, 15, 20, 25 and 30K), level off and cruise at MAXIMIM cruise range settings (2280 rpm/31.5 "Hg) with provision for 20 minutes Combat at Military Power (2700 rpm /52" Hg) then return at Maximum Cruise distance settings of 2280/31.5 and land with 15 gallon reserve. Start with 305 Gallons.

http://www.wwiiaircraftperformance.org/p-47/p-47c-tactical-inc2.jpg

Greg - take note that this table with the above set of assumptions yields the following:
170 miles Combat Radius at 25 K with 305 at take off. Clean, no external tanks for extra drag, no formation take off and assembly for extra 25 minutes of Normal Rated Power orbit. No provision for throttle jockeying for every body flying formation except Group CO. Everything you see below has the the P-47C and F6F-5 using same fuel consumption as the P-47N in the Williams presented tests. It follows pretty well with the P-47C-1 range as I run the numbers below.

Bring your own data and show how SR and I are complete Naysayers who can't think out of the box.

Note - when you dig further, you will see that Maximum Cruise settings of 1700/33" for P-47N yields a speed of 185 IAS which, at 25K is 260mph TAS which is at least 40-50mph too slow for ETO escort. If you can't catch 'em you can't cover 'em.

1. The typical profile would be to fast cruise at 2400/36.0" which would yield 230 IAS/335 TAS. That fuel consumption is about 115gph for the P-47N tables.

2. Combat fuel consumption = Military Power at 2700rpm (Not WEP) at 52" hg = 290 gph. 20 Minutes of MP = 1/3 od 290 = 97 gallons

3. Warm up, take off, assembly = assume 30 minutes at Rated Power = 162 gallons per hour = 81 gallons

4. Climb to 25K at Rated Power = 18 minutes for a P-47C/Hellcat = .30 x 162 = 19 gallons. Travel approximately (conservative) @160mph x .3 hr at 45 degrees = 48.6 gallons to get to 25,000 feet at rated powerNOTE -at 18 minutes to climb 25000 feet the actual climb angle is about 1:10 so the P-47C/F6F travels about 45 miles toward Zwolle

5. Set course for Zwolle Hooland ~ 200 miles away, to RV, at 115 gph. 200/335 = .6 hrs at 115 gph = 68 gallons

At this point 380 miles from Berlin the P-37C-1/Hellcat is essing over the bombers travelling 205-210 mph. The bombers will reach Berlin 380/210 in 1.8 hours. Fuel = 1.8 x 115gph = 208 gallons.

Pause for a moment. Assume a 250 gallon external tank, not one drop of the 250 gallon internal tank was used to warm up, take off and climb - all external. 97 plus 81 plus 67 means that the F6F/P-47C with 150 gallon tank ran out between the English Coast and Zwolle Holland. Between Dutch coast and Zwolle the P-47C and F6F dropped external 150 gallon tank and by the time they reached Osnabruck they have consumed 70+ gallons of their internal fuel (250-70 for Hellcat, 305-70 for P-47C).

So - at Osnabruck in weast Germany the Hellcat/P-47C with similar R-2800 engines have 180 and 235 gallons remaining assuming they used 150 gallon external tanks at 25000 feet. The F6F and P-37C used 220 gallons each to get to Osnabruck.

At this point if the Hellcat turns for home it might make it by leaning all the way back to 2280/31.5", but the B-17s will be unescorted fro the next 280 and back.

I did this pretty fast and welcome corrections to the math, but Greg

IF you want to take shots go get the facts on sfc for the Power Ratings at each stage.

 

[OldSkeptic]

Figures in nautical miles, kts and imperial gallons.

Neil.

Thanks Niel, backs up the reasonableness of my LR Spit calcs, ie allowance for takeoff, climb and 15 mins combat.

As for SR comments, well even at economical cruise a LR Spit (VIII variant) could easily catch the bombers again and climb back up again. You are probably talking about a 1-1.5 hour escort phase (after rendezvous), of which a 15 mins combat allowance is a lot...

As for return to base at MEC, the calc I used was at 20,000ft, ideally you'd climb to that (or even a bit above) then lean out and slow down for the return. Pretty immune, plus the Luftwaffe (correctly) is focusing on the bombers and is not going to waste planes and time climbing up to do an intercept with a bunch of fighters. At that altitude, even if getting a bit short on fuel, all they have to do is go into a shallow dive to pick up speed and leave the intercepting fighters behind (which have their own fuel issues). Plus you have a 100 mile reserve allowance for just this sort of eventuality and can, for a short time, crank up the speed if necessary. So, for example, a shallow dive and move to fastest economical cruise for say 5-10 mins, until you have left them behind and can slow down again.

Don't forget, another bunch of fighters have now taken over the escort position, which the defending fighters also have to deal with.

Now my calcs show that Berlin was about the limit for a Spit VIII LR variant (unless you maybe drop the 0.303s and add more fuel there* and/or have a slightly bigger rear tank and leave about 10-15 gals in it as a reserve, CoG would still be ok at that, I conservatively assumed all rear tank fuel being used), but still doable with careful planning and training, tight though. But for shorter missions (which were by far the majority, say around the 400-450 mile radius) it could be done easily with a much larger reserve for all those eventualities.

* If you delete the 0.303's and add even just 7 gals in each wing in that space (less room there) then the reserve fuel goes to 29 gals, or 198 miles at MEC. Add 10 gals left in the rear and it is now 39 gals or 268 miles at MEC. All gals UK ones of course.

 

[Shortround6]

Please note that it takes the P-47 25 gallons of fuel and 7 minutes to climb from 15,000ft to 25,000ft using 2550rpm and 42" map.( max continuous 1625hp=210 gal an hour) Granted that is at 12,500lbs. Climbing slower actually burns more fuel because it takes longer to get to altitude ( see fuel used in "ferry" climb). Time will be quicker using military power but fuel burn increases by about 1 gallon per minute.
A P-47D (early) could take about 5 minutes to climb from 15,000ft to 25,000ft using 2700rpm and 52-50in map burning 275 gallons an hour or 4.58 gallons a minute.

A fighter can use a fair amount of fuel just getting back into position or back into the fight without actually engaging in constant combat for 15-20 minutes.

Again, thanks to Zeno's for the chart.

 

[OldSkeptic]

Yep, which an issue in combat for the P-47, especially close to its max range. One dive and you are out basically..

 

[GregP]

Hi Drgondog,

I already did. It's in the posts.

You seem to forget that Naval ranges are VERY conservative. The carrier moves around, often without the knowledge of the WWII aviator. So the Navy has a requirement for a LOT of reserve fuel. The fighter must fly the misson, come back, look around for 30 - 45 minutes and then spend 15 - 45 or more minutes in the pattern to land while the other guys recover.

It is trite to say, but land bases don't move around much and the reserves are therefore much less.

The specs SAY it, the Hellcat CAN fly a 1,200 mile trip with adequate reserves if flown from a gound base, and I won't revisit this again. It absolutely CAN be done.

Your analysis is very flawed ... ask any Hellcat pilot. I have.