WHAT IF: Longer range P-47 from start

[gjs238]

That is very interesting.
So it would seem the engines with the aux blowers (2-stage supercharging), and the planes powered by them, would have had high altitude advantages over engines and planes without aux blowers (single-stage supercharging.) And perhaps have the potential to participate in high altitude operations in ETO.

AFAIK, V-1710 did not have an aux blower and Merlin only installed a 2nd stage later on, although I don't think R/R called it an aux blower.

 

[Shortround6]

So it would seem the engines with the aux blowers (2-stage supercharging), and the planes powered by them, would have had high altitude advantages over engines and planes without aux blowers (single-stage supercharging.) And perhaps have the potential to participate in high altitude operations in ETO.

In General the answer to the first part is yes. To the second part is a bit harder. The R-1830 2 stage was the first to fly (by several years) and had some problems. It apparently wasn't all that efficient. Not surprising considering the efficiency of single stage superchargers of the time (1938-39-40). Supercharger efficiency was, like many other technologies, constantly evolving during WWII. While some designs remained frozen for production reasons, other engines made jumps as new models were introduced. Comparing some late 1944/early 45 superchargers to 1939-40 superchargers are going to show some major changes in efficiency and pressure ratios.

AFAIK, V-1710 did not have an aux blower and Merlin only installed a 2nd stage later on, although I don't think R/R called it an aux blower.

The V-1710 used an aux blower in the P-63 and P-82 and a number of experimental aircraft. The Merlin began with the two stage supercharger in the '60' series which reached operations (in small numbers) in the summer of 1942. In the R-R set up both impellers were in the same case, both were on the same shaft, and both rotated at the same speed. There was a two speed drive to the supercharger.

 

[davparlr]

We know that the P-47 had about 3/4 the profile drag of a Corsair but we may not know the induced drag or parasitic drag.

The F4U seems to be more overall aerodynamically efficient. SL max speed for the P-47C running 2000 horses was about 335 mph whereas with the same power output, the F4U-1 hit about 350 mph. I am not sure if the F4U is just cleaner or if its power is being more efficiently applied. Now the F4U-1 is about 1000 lbs less, about 10%, than P-47, but that should have only lead to a few mph difference.

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

From the data I have, I could not discern top speed difference between the F4U-1D and the FG-1D. I do not think the drag difference would be of significance. The difference between the P-51B and the P-51D, which had a much larger cockpit footprint, was only a few mph at SL and top speed. Certainly, at altitude, form drag is less an impact to aircraft performance due to reduced air density.

Rear tanks were apparently tried and quickly dropped from consideration.

It would be interesting to know why, cg problems, like the P-51?

Asking for P-47N fuel capacity and range in 1940-42 was probably too much for the early 2000hp engines. Not only did engine power go up but runway lengths were getting longer all the time. Long range aircraft don't do any good if they can't get of the ground with a full load of fuel.

I agree with this. Raising the internal fuel to 370 gallons did not seem to be a big problem, though.

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.

Dean says the aft P-51 tank was "protected". I don't know what this means whether it just had CO2 or whether it was protected like the main tanks. Other references failed to shed light.


Now for the question of increasing the range of the P-47 for escort duty, I do think it would not have been a big deal to increase internal fuel tanks to 370 and provide adequate drop tanks. Using the P-47 Tactical Planning Characteristics and Performance Chart, I did a bit of analysis very similar to Shortround6 based on a P-47C with enlarged main tank of 270 gallons and a 100 gallon aux tank for a total of 370 gallons internal. In addition, external drop tanks were carried sufficient enough to allow 600 mile cruise, say 300 gallons at max continuous cruise power and 260 mph at 25k ft. Tanks are jettisoned approaching target and the P-47 has full internal fuel load. The question is how much combat fuel do I have and still make it home. Now, the chart shows that at max continuous cruise power at 25k and 260 mph, 281 gallons would be consumed, minus 65 gallons reserve and landing, leaving only 24 gallons for battle, not enough. However at 10k and 220 mph, only 220 gallons are consumed going home, leaving a healthy 85 gallons! It is interesting to note that the chart shows that the P-47 is more efficient at 25k than at 10k. So, the P-47 could return at 25k which would be comfortable. 220 mph True at 25k is slow Indicated, 150 mph, but should be well above stall. It should work fine

Now I think the F4U performance is similar to the P-47 but maybe a bit more efficient and lighter. While carrying less fuel, it should be in the same ball park as the above P-47 when operating in the same environment.

I am ignoring bullet holes, after all, one bullet hole through a P-51 cooling system does him in and we know it was an effective escort fighter.

Performance wise, both aircraft would be effective against 1943 – late 1944 German fighters at the altitudes required for bomber protection 20-25k ft. The P-47 had an advantage in that it controlled the altitude above the bombers, a big advantage for an escort I would think. The F4U could effectively take the fight down to the surface.

In comparison, the P-51, would use only 108 gallons to go home minus the 65 gallon reserve and landing and that would leave 96 gallons to fight, and 96 gallons in a Merlin powered P-51 is a whole lot more than 85 gallons in a R-2800 powered aircraft. And the P-51 could advantageously take the fight to the enemy from 30k to SL. It just wasn't around earlier, another error by the AAF?

I think that with a little up-front thought, the AAF could have fielded a reasonably capable escort fighter much earlier by providing extra internal fuel to the P-47 and provided a lot of help to those bomber crews. In any event, they could have expanded their umbrella coverage.

 

[Lighthunmust]

The F4U seems to be more overall aerodynamically efficient. SL max speed for the P-47C running 2000 horses was about 335 mph whereas with the same power output, the F4U-1 hit about 350 mph. I am not sure if the F4U is just cleaner or if its power is being more efficiently applied. Now the F4U-1 is about 1000 lbs less, about 10%, than P-47, but that should have only lead to a few mph difference.



From the data I have, I could not discern top speed difference between the F4U-1D and the FG-1D. I do not think the drag difference would be of significance. The difference between the P-51B and the P-51D, which had a much larger cockpit footprint, was only a few mph at SL and top speed. Certainly, at altitude, form drag is less an impact to aircraft performance due to reduced air density.


It would be interesting to know why, cg problems, like the P-51?


I agree with this. Raising the internal fuel to 370 gallons did not seem to be a big problem, though.




Dean says the aft P-51 tank was "protected". I don't know what this means whether it just had CO2 or whether it was protected like the main tanks. Other references failed to shed light.


Now for the question of increasing the range of the P-47 for escort duty, I do think it would not have been a big deal to increase internal fuel tanks to 370 and provide adequate drop tanks. Using the P-47 Tactical Planning Characteristics and Performance Chart, I did a bit of analysis very similar to Shortround6 based on a P-47C with enlarged main tank of 270 gallons and a 100 gallon aux tank for a total of 370 gallons internal. In addition, external drop tanks were carried sufficient enough to allow 600 mile cruise, say 300 gallons at max continuous cruise power and 260 mph at 25k ft. Tanks are jettisoned approaching target and the P-47 has full internal fuel load. The question is how much combat fuel do I have and still make it home. Now, the chart shows that at max continuous cruise power at 25k and 260 mph, 281 gallons would be consumed, minus 65 gallons reserve and landing, leaving only 24 gallons for battle, not enough. However at 10k and 220 mph, only 220 gallons are consumed going home, leaving a healthy 85 gallons! It is interesting to note that the chart shows that the P-47 is more efficient at 25k than at 10k. So, the P-47 could return at 25k which would be comfortable. 220 mph True at 25k is slow Indicated, 150 mph, but should be well above stall. It should work fine

Now I think the F4U performance is similar to the P-47 but maybe a bit more efficient and lighter. While carrying less fuel, it should be in the same ball park as the above P-47 when operating in the same environment.

I am ignoring bullet holes, after all, one bullet hole through a P-51 cooling system does him in and we know it was an effective escort fighter.

Performance wise, both aircraft would be effective against 1943 – late 1944 German fighters at the altitudes required for bomber protection 20-25k ft. The P-47 had an advantage in that it controlled the altitude above the bombers, a big advantage for an escort I would think. The F4U could effectively take the fight down to the surface.

In comparison, the P-51, would use only 108 gallons to go home minus the 65 gallon reserve and landing and that would leave 96 gallons to fight, and 96 gallons in a Merlin powered P-51 is a whole lot more than 85 gallons in a R-2800 powered aircraft. And the P-51 could advantageously take the fight to the enemy from 30k to SL. It just wasn't around earlier, another error by the AAF?

I think that with a little up-front thought, the AAF could have fielded a reasonably capable escort fighter much earlier by providing extra internal fuel to the P-47 and provided a lot of help to those bomber crews. In any event, they could have expanded their umbrella coverage.

I completely agree with you regarding the effectiveness of an early P-47 with extra fuel. My opinion on the escort mission that the better high altitude performance of the P-47 is more important than the medium and low altitude of the F4U.

I've been looking at Bodie's two books "Republics P-47 Thunderbolt" and "The Lockheed P-38 Lightning", Ludwig's "P-51 Mustang", Bowman's "Vought F4U Corsair", and Dean's "America's Hundred-Thousand". Even with the performance of the early P-47s the extra fuel weight needed would not have prevented them from being effect enough escorts. With soon to be available engine performance increases the lack of P-51B/C/Ds would not have made any difference.

The mere fact of having adequate P-47 escorts may have resulted in the development of the P-51 as an escort being derailed. I strongly believe if P-51Bs had been available at the beginning of the 8th AFs activation certainly a great many inexperienced american fighter pilots would have been killed because their aircraft did not protect them as well as the P-47. Most fighter pilots are more often targets than shooters. The majority of kills are made be a small group of experts, but those experts need time to develop their skills. Considering how much the experienced and expert pilots of the Luftwaffe mauled the inexperienced american fighter pilots it may have been a godsend that the P-51 was not available earlier. You could argue early P-51Bs may have saved more bombers, however I just think it would have encouraged earlier missions into deeper enemy territory with even greater loss.

 

[Shortround6]

I agree with this. Raising the internal fuel to 370 gallons did not seem to be a big problem, though.

By the time the 370gal internal fuel showed up they had the water injected engines and the paddle blade props. They had also been using drop tanks with 200 gallons for a 505 gal total fuel capacity in some configurations. I don't know when the 150 gal tanks showed up but the combat radius charts show both 305 and 370 internal combined with 300 gals external.

Now for the question of increasing the range of the P-47 for escort duty, I do think it would not have been a big deal to increase internal fuel tanks to 370 and provide adequate drop tanks.

I think that with a little up-front thought, the AAF could have fielded a reasonably capable escort fighter much earlier by providing extra internal fuel to the P-47 and provided a lot of help to those bomber crews. In any event, they could have expanded their umbrella coverage.

The lack of at least some sort of "combat" belly tank on the early P-47s does seem to be a rather glaring mistake. "Combat" as opposed to "ferry" tanks which often could not be used above certain altitudes or had other restrictions that prevented them from being used to full capacity even for initial climb out, formation and very early part of journey. The provision of of even a 75 gallon drop tank extended the radius to 340 miles (using different conditions than shown in the chart?) 10,000 75 gallon P-39 tanks were shipped in Aug, Sept 43 but they should have been there from the beginning. earlier provision for under wing tanks would have been a big help in 1943 too. Even if the early engine and short runways weren't up to twin 150 gal drop tanks even twin 75s might have bought a radius of 400miles while still being almost 1000lbs lighter than the big tanks. Once the later engines with water injection are cleared lifting the bigger heavier tanks shouldn't be a as much of a problem and with the "C" series R-2800s in prospect for even more power perhaps the "N" could haev been started a bit earlier but let us not forget that the "N"s sometimes used their 2800 WER horsepower to get off short, tropical runways with heavy loads. Asking the early 2000hp engines to do the same thing may not be reasonable.

 

[Shortround6]

renrich

I have found a couple of other descriptions/differences of "combat radius"

one is here for the F4F: http://www.wwiiaircraftperformance.org/f4f/f4f-4.pdf

It differs from the Air Force description in a number of details (as well it should considering the capabilities of the aircraft) but has an understandable 60 minute reserve built in, finding and landing on the carrier being a bit more difficult that finding and landing on an airfield (any airfield).

Another differences is that the Army planned on a P-47 using 45 gals to start, warm up, taxi, take-off and climb to 5,000ft.

The Navy allowed a Corsair 10 gals to start warm up and take-off but then counted the fuel burn to even 5,000ft together. As in 18 gallons for start, takeoff and climb to 5,000ft. Why a P-47 needs another 35 gals for warm up and take off I have no idea.

All I am pointing out here is that it is very difficult to compare ranges and radius unless we really know the conditions and trying to guesstimate combat radius from a yardstick figure is full of pitfalls if one or the other users mission requirements differs too much from the yardstick.

warm up and take off allowances are from the flight operation instruction charts available at Zeno's.

 

[Milosh]

Could it be that some of the 35 gal was used going from dispersal to the take off point? Then there would be waiting for the a/c in front to line up and take off also.

 

[renrich]

Again, according to Dean, these "yardstick" ranges are as follows:
P47D/late model/M----- 370 gallons of internal fuel---1020 statute miles
F4U1D---237 gallons internal fuel----1020 statute miles
Corsair at 5000 feet and most economical cruise and Jug at 10000 feet and most economical cruise. I know these are no good for gauging combat radius but they do give a useful comparison. If a Jug is at midpoint of his mission and is on internal fuel only he cannot go nearly as far as a Corsair with the same amount of internal fuel.
Page 508, Dean, the F4U1 is able to carry 361 gallons of internal fuel along with a drop tank of 175 gallons capacity.
An interesting point about combat radius was made somewhere in Lundstrom(the "First Team" I think.) He states that the A6M operating from a carrier had a CR of around 300 miles (twice that of an F4F) and a CR of 500 miles from a land base. I don't know if that was with a drop tank or not but it points out some rather strong differences between the two types of ops. One being of course, that it is nice to know if the base you left from will be in the same place when you get back.
I still think that it is an interesting exercise to speculate what would have been the result if the US had decided in 1941 to concentrate on only two fighter types, the F4U and P51. With all the fighter manufacturers developing and building those two designs, some good stuff may have happened.

 

[Lighthunmust]

If you want to see P-47s shooting down P-51s set your TiVo to TCM HD for Sunday 1:00AM MST.

 

[tomo pauk]

Here is what I've been able to find out re. additional hull tanks for P-47, from US 100K, pg. 292:
It was tried as a field/depot modification, a 42 gal tank under the pilot's seat, by FE AAF Service Command for the 5th Air force. The issue was that the experiment was carried out as late as Aug 1944, on the P-47s that were already carrying 370 gals internally, while being able to carry 220 gal in belly tank, plus 2 x 150 gals under wing (it was either belly tank or wing tanks in the same time). They were also trying a 'form fitting belly tank', 70 gals - that would be called 'conformal tank' today?
The experiments both with under-seat and form-fitting tanks were canceled because the plane was already overloaded (505 gals total was considered as safe maximum for their P-47D-25s, unless the heavy-ply tires are mounted); the CoG issues are not mentioned in the paragraph.

I've attached the map found somewhere on the 'net.
It was just too bad that 165 gals tanks (as the ones P-38s were carrying from 1942) weren't fitted in mid 1943, under belly. A P-47 with 305+150 gals was having an escort radius of 350 miles (London to Frankfurt is 400 miles), but that tank was available from Feb 1944 in ETO.

 

[Arossihman]

The Start of this thread was "What if the USAAC, recognizing the historically expeditionary nature of the US military, and the need to reach out to the enemy rather that wait for the enemy to come to you, had specified "P-51 like" ranges in fighters such as the P-40 and P-47?"
Now maybe I misinterpreted it But I took that to mean 'what if the USAAC had specified the longer range either at the beginning of the P-47 development or in the earliest stages of the P-40s development'. Changing specification too much in the middle of production leads to changes in tooling and lost production that many countries were hesitant to do.
I do not have the full specifications or requirements that the P-47 was designed to. These would include not only top speed, ceiling, desired climb rate or time to altitude, range and armament but things like landing speed and field length "G" loading strength and landing "G" load requirements among others. Some of this can be traded back and forth on paper while the plane is in the proposal stage before contracts are signed with performance guarantees. Curtiss lost over $14,000 in penalties on the XP-46 contract because the prototype would not perform up to contract specifications. The Army may relax some of these requirements once a plane is in service, like adding the rear fuselage tanks to the P-51, rather than call for a new design, but while a plane is still on paper or in prototype trials they are going to want it to meet the specifications (or mutually agreed modifications).
Adding hundreds of pounds of tanks and fuel, even if you can find room, will impact not only field length and climb, but those stress requirements.
If we are talking about specifying the extra range/fuel from the beginning, I am pointing out that the power plant (engine and propeller) available or planned was not capable of the performance not only of the real the P-47N engine and propeller of late 1944/45 but even of the field modified "D"s of the end of 1943.

Once again for an Idea of the performance "hit" the plane would take see this chart: http://www.zenoswarbirdvideos.com/Images/P-47/47TOCL.gif

Look at the climb rates for the different weights. Please look at the notes, like this is for O degrees Celsius and add 10% to climb times for each 10 degrees above O degrees. Also note that after 5 minutes at military power the engine is throttled back to "normal" power which is 1625hp instead of 2000hp so a lot of the climb figures are not true combat figures but you can still get an idea of the performance "hit" of the extra weight.
Drop tanks helped designers out because they could increase range while not hurting performance at short range like a bigger airframe/ heavier internal tanks would. But the planes "Combat radius" is limited to how far the plane can fly after dropping the tanks, engaging in combat and then flying home with enough reserves to handle weather conditions and minor navigation errors.
Please note that the later P-47Ds had 15-25% more power available than the "B" and "C" versions to handle not only the drop tanks but the change from 305 to 370 gals of internal fuel. P-47s sometimes used their water injection for take-off while carrying heavy loads from short airstrips in hot conditions.
When building fighter aircraft it helps if the "balance" is not tipped too far to one side or the other. A long range fighter for escort use is great, as long as it can actually fight once it gets there or can fight near it's own home base if the situation changes.

I have a p-47 spec and complete history book at home i will check to verify this statement but i believe it actually did not meet range requirements when first introduced...more tomorrow.