What if the F-82 was based off the XP-51F/G instead of the P-51H?

[PStickney]

Actually, the NA-133 Proposal (not accepted) had only the tail hook and some wing changes - strengthened spar/main gear and slight crank to the inboard leading edge to accomadate wheel well changes for larger wheel. I have no idea why NAA even wasted time on the proposal - the USN would not (Could Not) buy a in-line engine for carrier ops - every gallon of coolant was a gallon less of AvGas.

Ethylene Glycol (Prestone) is flammable - That Navy really doesn't like having any more flammable liquids on a ship than they absolutely have to have.
Add in the need to be messing around with radiators, ducts hoses, and large quantities of liquid working on a hangar deck...
Let's just say that after the 1920s, the U.S. Navy was as likely to use a liquid cooled engine in an airplane as an air cooled engine in a submarine.

 

[PStickney]

Wonder of the Royal Navy would've been interested to have a longer ranged plane than a Seafire?

I'm really looking forward to the new book once it's completed, even if it doesn't have much on the F-82.

They had them. F6F Hellcats and F4U Corsairs. The Seafire, while once in the air, was a very good Point Defense Interceptor, was horrendous around the boat. Even in combat, most Seafire writeoffs were from landing accidents. Thing is, they had to give the Hellcats and Corsairs back at the end of the War (Lend-Lease), and could only build Sea Furies at a moderate rate, so there were Seafires serving postwar, but pretty much by default.

 

[tomo pauk]

Ethylene Glycol (Prestone) is flammable - That Navy really doesn't like having any more flammable liquids on a ship than they absolutely have to have.

A fighter with 2000 HP radial engine will require much more of inflammable liquid per air mile covered than a 1500 HP V12, yet USN had no problems in ordering the fighters powered by 2000 HP engines and stocking the inflammable liquid for these.
Wrt. future USN fighters of the day, problem with US V12s in very late 1930s was that they were not offering anything close to what R-2800 was offering. That was the killer.

Add in the need to be messing around with radiators, ducts hoses, and large quantities of liquid working on a hangar deck...

Radiators were pretty much fixed item, no need to mess with them that much? Large quantities of liquid - again, the big radials were the ones requiring it, the V12s less so. Even a R-1820- or R-1820-powered fighter will offer worse fuel mileage than a V-1710, but then again V-1710 was not available in the 1930s.
Problem with leakage might be present, since 100% pure Prestone was harsh on materials used in early 1930s.

 

[PStickney]

Fixed it.

Coolant was not really a consumable. The plane was expected to return with the same amount of coolant it left with (or nearly) unlike oil and fuel.

How much coolant did the Mustangs you flew use per flight?

The Navy was certainly using some fuel hog aircraft with those R-2800 engines.

Until you had to work on the cooling system, at which point you're draining the cooling system and probably disposing of it.
A cooling system hit on a carrier airplane was a certain loss - and, quite likely a lost crew. When there's nothing but water below for the whole mission...

And, pulling out the manuals, when dialed back for range cruise, both the P-51D and F4U-4 were drinking fuel at 40-45 U.S. gallons / hr. (Surprised me, too)

 

[ThomasP]

Apples to Apples

P-51C/D w/2x75 USgal DT = 330 USgal, - 33 USgal allowance for WUTO & climb to 20,000 ft = 297 USgal for range
best range cruise = 1700 miles at ~250 mph TAS = 44 USgal/hr
max weak mixture cruise range = 1050 miles at ~300 mph TAS = 85 USgal/hr

F4U-1/1A/1B w/1x170 USgal DT = 407 USgal, -75 USgal allowance for WUTO & climb to 20,000 ft = 332 USgal for range
best range cruise = 1290 miles at ~250 mph TAS = 64 USgal/hr
max weak mixture cruise range = 750 miles at ~300 mph TAS = 138 USgal/hr


Both aircraft have a V for best range of 180-185 mph IAS which is ~250 mph TAS at 20,000 ft.

Both aircraft can use significantly less fuel at lower altitudes and lower speeds.


P-51C/D as above but flight altitude is only 1,500 ft
best range cruise = ~1800 miles at ~182 mph TAS = 32 USgal/hr (10 USgal allowance for WUTO & climb to 1,500 ft)

F4U-1/1A/1B as above but flight altitude is only 1,500 ft
best range cruise = ~1500 miles at ~182 mph TAS = 42 USgal/hr (16 USgal for WUTO) & climb to 1,500 ft)

So at V for best range, at high altitudes the P-51 uses about 20 USgal/hr less (~30% less) fuel than the F4U-1, and at low altitudes about 10 USgal/hr less (~24% less), for the same ~speeds with the P-51 achieving significantly longer ranges.


If I did my math right.

NOTE that these numbers match up by both the US PFOI manuals and the UK Pilot's Notes to within a couple of %.

 

[BarnOwlLover]

Time to revive a 9 month old thread based on a random thought (and probably shows convergence and divergence of the P-51H and XP-82/P-82B). There was the NA-117, which was built in mock up form and was originally a XP-51F/G with changes (modified floor, raised seating position like the definitive H and the F-82, etc), and basically resembled a foot shorter P-51H. When the NA-117 evolved into the NA-126 (production P-51H), the fuselage was lengthened by over a foot, and the wing position was shifted back about 6 inches. Both of these were due to accounting for CG with a 50 gallon fuselage tank.

About the biggest thing that the NA-117 and the NA-120/123 had in common was the basic power plant and no use of a fuselage fuel tank (though the P-82B Betty Jo did have small fuselage tanks and one installed in the gun bay for its record flight).

 

[MIflyer]

Lindberg developed a procedure to cruise at high boost levels and at very low altitudes to save fuel, first used by F4U, P-38, and P-47 in the Pacific where you have very long distances with almost no chance of being shot at. This was also adopted by P-47 fighter bomber units in the ETO after airfields on the continent were established. I don't know if you could even do that with P-51's because the pilot had limited direct control over the supercharger. But the postwar P-51D manual says that you get longest range by climbing to high altitude and putting the supercharger into LOW manually. Normally you could not put the supercharger into HIGH at low altitude because the manual HIGH setting was spring loaded but some Mustangs in the Pacific had the switch modfied to allow it.

 

[Shortround6]

Lindberg developed a procedure to cruise at high boost levels and at very low altitudes to save fuel,

Something similar was done by the British in 1942 With Spitfire Vs, and many other aircraft. They posted signs in the crew areas and hangers.
Something like "Lower the revs and boost your boost, you will have enough fuel to get home to roost".
They did issue information sheets showing fuel burns at different speeds and altitudes for several combinations of rpm and boost for each speed and altitude.

Tony LeVier did a number of demonstrations in Britain to P-38 pilots to do the same thing.

Unfortunately it took people like Lindberg and Levier on the front lines to get around the instructions of the Army (and Navy) because those military officers knew more than the both the airframe makers and the engine makers on how to operate the planes.

 

[MIflyer]

"Lower the revs and boost your boost, you will have enough fuel to get home to roost".

I read of one RAF crew who were one of the first to do that, only to have them accused of not actually flying their complete missions because they were coming back with too much fuel.

Lindberg was sent to the Pacific as an employee of United Aircraft, which included P&W and Chance Vought to help with the F4U. He expanded his teachings into the P-47 and P-38 and while flying a P-38 actually shot down a Japanese aircraft.

I was surprised to read that P-47 units based in France climbed up to "nought feet" and used the same techniques enroute to targets in Germany , but that was possible only after there was no one in France shooting at them.

 

[Shortround6]

There may be two/three different things going on here.
Using the least amount of revs possible while getting the power needed by boost works an any altitude.
With two speed (or multi stage superchargers) using the least supercharger (lowest gear or stage) that works at the altitude you want for the rpm and pressure you want works.
With a P-47 (and others to a lesser extent) you can burn 70-90 US gallons just getting to 25,000ft (depends if you count take-off or not and how heavy the plane is.
Burn off some fuel on the way in at low altitude and you burn a bit less fuel climbing later on. Question here is that makes up for the higher fuel burn per mile at low altitude.

 

[MIflyer]

Thing is, though, it generally is assumed that the lower drag at high altitudes as well as the less fuel that burns with the less oxygen more than offsets the fuel needed to climb up high. The jet airliners climb up quite high even for pretty short trips.

I read that when they started flying Hudsons to Sweden they used the early models which had R-1820 with two speed superchargers. The later Hudsons were optimized for ASW and had R-1830 with single speed superchargers, but when they tried those for the Sweden trip things did not go so well.

When the P-51's flew from Iwo Jima to Japan what altitude did they use? They had to climb up to 25,000 ft to get close to the B-29's but they did not really need to do that until they got close to Japan.

 

[drgondog]

Thing is, though, it generally is assumed that the lower drag at high altitudes as well as the less fuel that burns with the less oxygen more than offsets the fuel needed to climb up high. The jet airliners climb up quite high even for pretty short trips.



When the P-51's flew from Iwo Jima to Japan what altitude did they use? They had to climb up to 25,000 ft to get close to the B-29's but they did not really need to do that until they got close to Japan.

Unfortuately, the escort was sheparded by the better B-29 navigators - so they made RV immediately and flew formation. Fortunately the P-51 cruise settings for formation with the much faster B-29s enaled them to fly straight line range setting.

 

[MIflyer]

Yep, they had B-29 lead ships, but they did not have to fly at 25,000 ft even so. I'd guess that oxygen quantity might have been an issue for flights that long, since the P-51's were not pressurized and apparently they had better heating systems than the "Ice Wagon" P-38 but it still could not have beent very comfortable.. I need to go back and look at the book "The Last Fighter Pilot" which has more detailed descriptions of P-51 escort missions to Japan than anywhere else I have seen.

 

[BarnOwlLover]

Maybe one advantage that the F-82 def. would've had. I've seen cutaways and photos of the XP-82 restoration and it had huge oxygen tanks, No fuselage tanks as standard and longer fuselages probably helped. That being said, P-51Hs were earmarked for PTO B-29 escorts, maybe even with a 100 gallon fuselage tank according to something I read at secretprojects. Also, the P-51H and P-47N were slated to use an autopilot system as well.

 

[PStickney]

Lindberg developed a procedure to cruise at high boost levels and at very low altitudes to save fuel, first used by F4U, P-38, and P-47 in the Pacific where you have very long distances with almost no chance of being shot at. This was also adopted by P-47 fighter bomber units in the ETO after airfields on the continent were established. I don't know if you could even do that with P-51's because the pilot had limited direct control over the supercharger. But the postwar P-51D manual says that you get longest range by climbing to high altitude and putting the supercharger into LOW manually. Normally you could not put the supercharger into HIGH at low altitude because the manual HIGH setting was spring loaded but some Mustangs in the Pacific had the switch modfied to allow it.

Uhm, Lindberg didn't invent the protocol; for getting the most efficient fuel burn - (Low RPM. High Manifold Pressure, Mixture to Auto Lean, if you had a multi-speed supercharger, then select the lowest blower gear that will give the required Manifold Pressure) had been known for years, and was in the manufacturer's Technical Information, and the Aircraft Flight Operating Instructions. Thing is, many pilots, particularly in the Pacific, where type transitions were done in the field, and were often very ad-hoc, and documentation didn't catch up.
This happened throughout the War - When C-46s started to replace C-47s in the Pacific, even information like the maximum cargo load, and distribution for CG location wasn't available, leading to an inordinate number of crashes when overloaded and out of trim C-46s lost an engine. It's been an Aviation Old Wive's Tale that running High Manifold Pressures at Low RPM is Bad. (And in the extreme, it is), but in the prescribed limits, and with proper engine handling - when increasing power, -it's Mixture to Auto Figh or Full RIch, Prop to Increased ROM, Throttle to required Manifold Pressure) you're not going to break the engine.
The context for the F-51 entry in the manual is this - when you're climbing out at climb power, the blower will automatically shift from low to high to maintain power (46" MAP, 2700 RPM) in the climb, somewhere between 20,000' and 25,000',. Once you reach you cruising altitude, and pull the power back to Cruise Settings - (Full Throttle and 2100 RPM) you'd have to manuallly switch the supercharger to Low Blower, since it was too high for the aeneroid in the Automatic Control to trip.

 

[PStickney]

Something similar was done by the British in 1942 With Spitfire Vs, and many other aircraft. They posted signs in the crew areas and hangers.
Something like "Lower the revs and boost your boost, you will have enough fuel to get home to roost".
They did issue information sheets showing fuel burns at different speeds and altitudes for several combinations of rpm and boost for each speed and altitude.

Tony LeVier did a number of demonstrations in Britain to P-38 pilots to do the same thing.

Unfortunately it took people like Lindberg and Levier on the front lines to get around the instructions of the Army (and Navy) because those military officers knew more than the both the airframe makers and the engine makers on how to operate the planes.

I don't think it was "Those Military Officers" so much as for units already deployed, particularly in the Pacific, transition to a new type often consisted of going to a Repair Depot and picking up a new airplane. If you were very lucky, a set of Flight Operating Instructions and Erection and Maintenance manuals came with it. But often they didn't. When all you've got to go by is the seat of your pants and the Instrument Markings, knowledge tends to be "I knew a guy who..."
This wasn't just with fighters. other types - like the B-26 Marauder and C-46 had horrendous operational loss levels due to a lack of real information when the aircraft were delivered.