Escort Fighter Performance Comparison

[Shortround6]

Great minds think alike (and with the benefit of hindsight)!

Some basic problems with the idea are
1. the US (Packard) only made about 42 Merlin engines in all of 1941. and 2/3rds of them are for the British.
2. Those engines are the equivalent of the Merin XX (as used in Hurricane IIs), and if stuffed into a P-51 Airframe it may give you a better airplane than a P-40F (in the summer of 1942), but it won't give you an airplane that can escort B-17s and B-24s.

 

[drgondog]

He's another idea, lets forget the escorting in 1942-43, just send Spit V's and P47's out as far as they can go, say 200 miles and let MkIX's go as far as they can go which will be over 400 miles, instead of escorting per say lets make them fighter sweeps so they can fly at their best altitude an speed, the Luftwaffe are going to engage if there is a bomber mission going on so the fighters can engage independently of they are doing.

LW basically ignored 8th AF Fighter Sweeps in 1943. Only the bombers drew their undivded attention. P-47s didn't make a straight line penetration of 200 miles until 4th, 78th and 56th first tried draggy 200 gal Ferry Tank.

Internal fuel is THE Boundary condition for max combat range.

When you compare (or fantasize) about LR escort role for Spitfire, compare your visionary Spit internal fuel to even Mustang I with 170 gal internally or P-51B/C w/269gal. It took the 85 gal fuse tank inst'l for P-51B and upgrade on P-38J to add 2x55gal LE tanks to get either one operational over Berlin.

 

[33k in the air]

Some basic problems with the idea are
1. the US (Packard) only made about 42 Merlin engines in all of 1941. and 2/3rds of them are for the British.
2. Those engines are the equivalent of the Merin XX (as used in Hurricane IIs), and if stuffed into a P-51 Airframe it may give you a better airplane than a P-40F (in the summer of 1942), but it won't give you an airplane that can escort B-17s and B-24s.

Perhaps not, but it does demonstrate the promise of the combination, and that might provide an earlier impetus to more aggressively develop the combination.

 

[tomo pauk]

2. Those engines are the equivalent of the Merin XX (as used in Hurricane IIs), and if stuffed into a P-51 Airframe it may give you a better airplane than a P-40F (in the summer of 1942), but it won't give you an airplane that can escort B-17s and B-24s.

(my bold)
The P-51/Merlin XX combo will certainly produce a far better airplane than it was the P-40F.
Why it will not be able to escort the B-17s and B-24s?

 

[Shortround6]

Perhaps not, but it does demonstrate the promise of the combination, and that might provide an earlier impetus to more aggressively develop the combination.

The two stage Merlin didn't show up in production until the spring of 1942 (in England), there were about 4 squadrons of MK IX Spits at Dieppe in Aug of 1942 and RR was already working on drawings to fit the engine into the Mustang in England and NA was working on their version in the US in Aug (didn't fly until oct/nov?)

So there was no "combination" in early 1941. You might have been able to work on the engine mounts but you didn't know how big the radiator was going to be, you didn't know how big the oil cooler was going to be, and you didn't know how big the intercooler on the engine (the Merlin XX didn't have an intercooler) or how big the intercooler in the radiator duct/s was going to be.
You didn't know were everything was going to be under the cowling or how big the ducts were going to be and you didn't know how far in front of the firewall the engine was going to be or how much the engine weighed or were the center of gravity was going to be (making final design of the engine mounts (more than just laying out the bolt holes) a bit difficult.)
The bare and dry (no fluids) 2 stage engine weight just 200lbs more than the bare and dry 2 speed engine. The extra cooling arrangements (radiator and fluid, oil system without oil and intercooler ) added over 300lbs to the Merlin XX installation. And you needed a bigger propeller.

The early 2 stage engine offered around the same power as the 2 speed engine did but it offered it at 27-29,000ft instead of 18,500ft.

That is what made the possibility of a Merlin powered escort fighter for US turbo charged bombers become attractive.
A two speed supercharged plane was never going to operated at the altitudes necessary to provide top cover to the bombers. Flying several thousand feet below the bombers was not going to work.

Stuffing a 2 speed Merlin into a Mustang I airframe could have been done, but it wasn't going to give you an escort fighter for the US and the whole engine installation is going to have to be redone anyway for the 2 stage engine/s.

 

[Shortround6]

(my bold)
The P-51/Merlin XX combo will certainly produce a far better airplane than it was the P-40F.
Why it will not be able to escort the B-17s and B-24s?

Because the engine hits it's FTH between 18,500ft and 20,000ft, by the time you get to 25,000ft you have lost at least 10% of you power.
The Turbo B-17s and B-24s can maintain sea level power to 25,000 (roughly).

Now in the summer of 1942 nobody knew exactly what altitudes the bombers would be operating at. It took quite a while to figure that out (also what cruising speeds).

However, with hindsight, we can see that a P-51B could reach 30,000ft in just under 10 minutes and being climbing at 2175fpm. The engine was making 1075hp and could make 51.6in of boost.

Our P-40F needed 21 minutes to reach 30,000ft and in fact it needed just over 10 minutes to get from 20,000ft to 30,000ft.
Granted it was running at 2850 rpm and not 3000rpm.
But the engine was only making 680hp and the plane was climbing at 530fpm. In fact the plane was only climbing at 1000ftm at 25,000ft.
That was about the minimum for combat maneuvers.
Other charts show some improvement. like 1070fpm at 28,000ft.



The Mustang airframe is going to allow the plane to go faster, it isn't going to do as much for climb, better than the P40F but not the same difference that the speed shows. And climb shows you how well the plane can maintain speed in turn or other maneuvers.

An early P-47 (tooth pick prop and no water injection) will outclimb the 2 speed Merlin Mustang by several thousand feet (be several thousand feet higher at any given climb rate).
The Early P-47 was making about 1600hp at 30,000ft or over double what the Merlin XX engine could give you and your early Merlin Mustang was going to weigh at around 2/3rds not 1/2.

You can fly at 25,000ft and up, but you are not going to be able to fight well.
Just showing up isn't going to be the solution. You are going to have to fighter above where the bombers are in order to keep the Germans from booming and zooming the bombers.

 

[drgondog]

(my bold)
The P-51/Merlin XX combo will certainly produce a far better airplane than it was the P-40F.
Why it will not be able to escort the B-17s and B-24s?

First, NAA tried to strike relationship with Rolls in 1941, was shut down by General Motors parent company (on behalf of subsidiary Allison). Second the AAC/AAF didn't want the Mustang with any engine combo in 1941. Third, the deal betwen Packard and R-R was 50-50 production split and the P-40F/L consumed all of FY 42 Priority and funding for the Merlin XX (1650-1). Those are the practical reasons that prohibited the 'early bird'.

Most Important Reason? The first Mustang to be delivered with plumbing and external rack was NA-97 delivered at the same time as the last of NA-91 Mustang IA - and that only because NAA was allowed to propose to NAA specification - not Materiel Command after a hard poiltical fight or the A-36.

Other important reasons:
Arnold prioritized external fuel tanks for extended Range use in Jan 1942, but MC moved like molasses on the execution of the prioity and had to be kicked in the ass in April, and still did't deliver a tested prototype for 60gal ad 75 gal combat tank until summer.
NONE of the US fighters had a tank pressurization feature for fighters delivered in 1942 and deep into 1943 with P-38J and P-51B.
Despite intense pressure by Gen Barney Giles on Materiel Command and NAA/Republic/Lockheed/Bell/GM (XP-75) work on prototype schemes to increase inernal fuel the prototypes (NAA and Lockheed) first flew in July 1943 and kits were not designed, fabricated and shipped to Depots until Oct 1943.

Conclusions:
Even if 8th AF changed doctrine of tactical deployment of high altitude B-17/B-24 which had excellent speed at 22-25K, down to say 18K, the Merlin XX equipped airframe could not go to Berlin until the actual P-51B/P-38J.
Wheteher XX or 1650-3 The Mustang design changes for engine and radiator changes, the bomb rack/internal plumbing, the aft fuselage fuel tank - all needed to be in production six months to field One Fighter Group for mid altitude operations in ETO. Better than P-40F? Yes but it needed the above range features and 8th AF doctrine change for lower altitude to be considered over the P-38G/H with 300gal and external 300 gal tanks - for Stuttgart/Hamburg range targets.

But, to make the question "why not" into an early 1943 P-51B reality with Merlin XX? No sooner than Merlin 60 series save a little less time sorting out the radiator/rumble due to lower heat loads.

To extrapolate earlier mandates necessary for mid 1943 Merlin XX operations:
prescience on part of B-17 Hq Acolytes that disaster was looming in 1943;
full knowledge of the future is 'bright' for NAA by Oliver Echols in Feb 1940, throwing his energy into introducing NAA as a better choice for Britain and France than a two year re-tooling nightmare for P-40 -in Jan 1940;
willingness to re-commit Merlin XX from Curtiss to NAA - when R-R Packard cut their deal;
immediate vision that internal fuel needed priority increase based on 'unheard of' 2200 mi ferry range;
approval by GM Board to abandon sales of Allisons to NAA fighter production; Incremental funding from MC 'with no strings attached', leaving NAA to develop 'best solution' vs 'XP-75, XP-46, P-60 solutions' driven by MC.

 

[Shortround6]

the deal betwen Packard and R-R was 50-50 production split and the P-40F/L consumed all of FY 42 Priority and funding for the Merlin XX (1650-1).

I don't know what the deal started out as but it wound up as an initial contract for 9000 engines, 1/3 for the US and 2/3rds for the UK with peak production at 800 engines per month.
aside from that I have no argument with anything in you post.


Follow up contracts and changes to contracts get short shrift in most common accounts.
It took Packard until March of 1943 to complete the original contract but I don't know when the follow up contracts were signed or what the details were.
We do know that Packard built almost exactly 800 engines a month for the last 6 months of 1942.
The US may not have taken delivery of the full 3000 engines from the first contract.
Packard did build over 26,750 two speed engines by the end of 1944 and just under 18,600 two stage engines by the end of 1944.

By the summer of 1944 Packard was building over 2000 engines a month.

That is from the historical production perspective. Changing the numbers of engines built in 1942 requires more factory space, more machine tools and more employees.
In some cases expanding Packard production may mean something else may not get built, tank engines? Landing craft engines? a different aircraft engine?


perhaps somebody could have beaten some sense into a few officers in material command to allow drop tanks and the needed plumbing and pumps sooner.

What you can't make somebody do is make a significant change in the rate of climb of a well over 8000lb airplane that was using the single stage Merlin engine at the higher altitudes (over 20,000ft). That is more physics.
Once you specify a certain amount of weight for guns and ammo, and the desired fuel and protection and the structural strength and so one, you are going to wind up with a over 8,000lb airplane for US service. And if your available engine only offers 1100hp at the crank at 18,500ft in climb you don't have lot of options to change the climb performance.

see. http://www.wwiiaircraftperformance.org/mustang/Power_required_available_P-51A_P-51B_P-47B.pdf

Yes this report was from late 1943 but engineers could have done (and probably did ) similar studies earlier. In fact teh P-47Ds were in production when this report was issued.
Please note that the power curves are for thrust HP and figure in the efficacy of the propellers.
Similar curves could have been done for higher altitudes.

The power you have to climb is the surplus power you have between the required power to actually fly at the desired speed and the max power of the engine.
In the case of the 3 planes shown the P-51A at 180mph needs about 250hp to fly and has 800hp available so it has 550hp thrust to climb with.
The P-51B needs 275hp to fly but has1150hp available so it has 875 hp thrust with.
The P-47B needs 435hp to fly ( a lot more drag and weight) but has 1600hp available and has 1375 hp thrust to climb with, however that horsepower needs to deal with almost 50% more weight.

engineers and engineering officers could make charts and predictions on performance based on charts/formulas like these.
A Merlin V-1650-1 is going to fall in between the P-51A and the P-51B in both needed power (only a small change) and the available power.
The problem for this question is that the available power at 20-25,000ft is not going to be enough to give the plane the performance it needs. And they could figure that out without actually building the plane.
Now as used in 1943-44 the B-17s and B-24s often did not fly at 25,000ft but flew 2-5,000ft lower but they didn't know that in 1941-42, they were planning on 25,000ft (or close) altitudes and in the US only the P-38 and P-47 offered the desired performance at altitude, until The two stage Merlin showed up.

 

[PAT303]

Here's a better idea: put a Merlin into a P-51 airframe in early 1941 instead of late 1942.

You may be better off using your time machine for better purposes.

 

[PAT303]

The Germans had had almost 2 years of experience in avoiding fighter sweeps and trying to bounce small pockets of bombers (used as bait) and small pockets of fighters (disconnected from the main groups).

Why don't we use the fighter sweeps to orbit fighter bases which is what the 2 TAF actually did so the German fighters can't get off the ground, support the bombers that way, we don't have P51's, lets use the planes and tactics that we do have.

 

[33k in the air]

You may be better off using your time machine for better purposes.

(1) My comment was mostly tongue-in-cheek (though it did spur good comments from Shortound6 and drgondog).

(2) As has been pointed out, the Spitfire was not developed into a long-range escort fighter, so claiming it could have been one would also involve a time machine.

There was no pressure on the RAF to develop a long-range escort because Bomber Command had long before switched to nighttime bombing. The USAAF was only forced to develop a long-range escort because it was firmly committed to daytime bombing and unescorted daylight raids had proved too costly no matter how good the formations and heavily armed the bombers.

I'm not sure how you convince the RAF to develop something that its own tactics say its doesn't need.

 

[PAT303]

I'm not sure how you convince the RAF to develop something that its own tactics say its doesn't need.

The Spit needed range regardless of what theater it flew in, the lack of it was it's biggest drawback.

 

[Thumpalumpacus]

Why don't we use the fighter sweeps to orbit fighter bases which is what the 2 TAF actually did so the German fighters can't get off the ground, support the bombers that way, we don't have P51's, lets use the planes and tactics that we do have.

Well, the obvious answer is that you can't keep fighters over a German base forever. They're going to run low on fuel. So you want to cab-rank them then? Great. Let's see how many Tiffies y'all can produce, and pilots, and fuel, and repair facilities, and so on.

Good luck doing that in 1941-42.

No, the bombers were the bait that drew up the fighters, and I'm pretty sure German radar could tell the difference between 50 bombers escorted by 100 fighters, and 500 bombers escorted by 250 or so fighters.

During the height of Pointblank, German fighters flew to attack bombers, day and night. It was only when Doolittle had 1) a fighter that could do long-range escort in the Mustang and 2) had so many bombers that the LW fighters had to come up and play that he could actually set fighters loose ahead of bomber formations.

Until then, Eaker had to husband his fighters. But once Doolittle took over, fighter numbers were such that they could operate in relays, and be loosened from the bombers:

Available evidence demonstrates that Doolittle had a direct influence on changing fighter tactics in the Eighth Air Force. In his memoirs, he claimed responsibility for changing the fighter tactics, which he considered "the most important and far-reaching military decision I made during the war."21 Minutes from a 21 January commanders meeting show that Doolittle "emphasized that the fighter role of protecting the bombardment formation should not be minimized, but our fighter aircraft should be encouraged to meet the enemy and destroy him rather than be content to keep him away."22 Moreover, in a postwar interview, Gen Pat Partridge confirmed that the offensive fighter posture was Doolittle's idea.23 The decision to "let the fighters loose" marked an innovation in fighter tactics. The prevailing AAF doctrine discouraged escort fighters from pursuing enemy aircraft. AAF Field Manual 1-15, Tactics and Technique of Air Fighting, dated 10 April 1942, stated the mission of close escorts "precludes their seeking to impose combat on other forces except as necessary to carry out their defensive role." The Eighth Air Force under Eaker's command had TACTICAL AND TECHNICAL INNOVATION 62 closely followed this guidance. To conserve his bomber force, Eaker prohibited his fighters from pursuing the Luftwaffe.24 Discussion held during an Eighth Air Force commanders meeting in September 1943 illustrates this bomber-centric philosophy. The commanders agreed that the fighters' priority was escorting the bombers, not destroying German fighters.25 The defensive policy frustrated fighter pilots. It ceded the initiative to German fighter pilots and wasted the escorts' offensive potential.26 For example, on 3 November 1943, P-38s achieved their first aerial victories in the European theater with no losses. However, the number of kills was limited to three because strict rules of engagement prevented the fighters from pursing enemy aircraft.27 Doolittle's pursuit policy changed the Eighth's fighter philosophy and "stood official doctrine on its head."28 Fighter escorts were transformed from passive defenders to aggressive attackers. The offensive tactics also optimized the use of fighter escorts. Fighters performing close escort had previously rendezvoused with bomber formations and followed them to the target or to the limits of their range. Because fighters cruised at a higher speed than bombers, the "little friends" weaved to stay in position. These maneuvers wasted fuel and reduced the fighter's escort range. Shortly after Doolittle arrived, the Eighth implemented a relay escort system. Under the new policy, a fighter group rendezvoused with bomber formations and escorted them for 150–200 miles until they transferred escort responsibilities to another group. The new tactic optimized the use of the three different types of fighters in the Eighth Air Force: P-47s escorted the formations during the shallow-penetration portions of the mission, P-38s during the medium-penetration, and the P-51s assumed escort duties for the deepest portion of the route.29 The new tactic also enabled a new role for fighter aircraft—strafing ground targets. Returning fighters, free from their escort duties, began to drop to low altitude in search of targets of opportunity.

This was certainly not the case in 1942. You didn't have the numbers of fighters, they didn't have the fuel to do much free-ranging, and an aggressive strategy like that requires the ability to take losses that frankly couldn't be absorbed in 1942.

Rodeos over France got shot up. Put up 400 bombers, yeah, they will need to come up and play, but 40 Havocs or what-have-you? The LW can pick and choose the fight, and they certainly did.

 

[PAT303]

Okay I give up, the Spit is stuck with it's 85G of fuel.

 

[Thumpalumpacus]

Okay I give up, the Spit is stuck with it's 85G of fuel.

Brits were and are clever. If they could've have had it doing Rodeos over the Rhine, don't you think they would have? Whatcha got? Why'd they pass up what appears to be a golden opportunity in you eyes? What are you seeing that they missed?

 

[Shortround6]

The Spit evolved in certain ways for real reasons.
Sometimes the reason may not what we think of as good looking back but the reasons were at least valid at the time.

Both the Spit and Hurricane were literally shacked with the the wooden propellers, They made the planes have long take offs and slow climbs and that was with small fuel tanks.
The two pitch props were better but the constant speed prop cut several minutes off the climb to 20,000ft and improved the climb at all altitudes.

Unfortunately by the time they short out the propeller problem it is the summer of 1940 and they are trying to get Castle Bromwich to actually produce Spitfires and a not piles of parts.
Supermarine can introduce modifications in short order but Castle Bromwich needs everything standardized with few changes as they mass produce things. the fastest production they can manage is the the order during the BoB and not too many experiments with long range fighters which aren't really needed in the summer and early fall of 1940. The Raids on South Hampton at the end of Sept also totally screw things up. It takes a number of months to get production up and running in the dispersal scheme. Supermarine is introducing the MK IIB (with cannon) and the Mk V over the winter. The MK Vb makes it appearance. These improve the hitting power of the Spitfire and improve the performance as the Germans start to introduce the 109F. RR is allowing higher boost limits but for carry increased loads needs the changes in climb settings and in max cruise settings.

Unfortunately the Spitfire took several hits to performance during 1940-41. The IFF, crucial to the battle, added a bit of weight and added two antennas for more drag, the 20mm guns added drag with the big gun barrels and the blisters on the wing to hide the cannon drums. Depending on canopy the external BP glass cost about 6mph of speed. The Spit was more capable but if you want to start adding fuel the increase in performance gets even smaller. In June of 1941 the Spit VB was being tested using 9lbs of boost. By Jan 1942 they were rating the engine at 15lbs for combat. So sometime in 1941 they could have decided they had the performance to handle a bigger fuel load. Of course during 1941 the 109F came into wider use and in June of 1941 the F-4 started to show up with it's improved engine.

So when do you want start adding the fuel tanks to the Spitfire in 1941?

In Jan of 1942 two stage Merlin had passed it's type test but they weren't expecting production until the summer.

RR had tried to improve altitude performance with the Merlin 46 engine. While this increased altitude performance by several thousand feet it also cost 100hp or more at lower altitudes. This was the engine used in the Darwin Spits and the idea of adding 300lbs or more to Spitfires powered by these engines flying over the France and low countries?
In 1941 the only way to justify making the Hurricane was to stuff the Merlin XX engine into it so the Spitfire got the 2nd choice engine.

The British had ideas, but they were limited by trying to keep numbers up by keeping changes to a minimum.


As far as trying to orbit German fighter fields?
The bombers often flew dog leg courses to throw of German plotters and to both cause the Germans to take-off and burn fuel as the bombers turned away or cause mad scrambles as the bombers changed course and crossed behind what appeared to be a bypassed group of fighter fields. Dog legs were also used to avoid Flak guns. The exit routes were also planned to be a good distance sideways from the entry routes to keep the German guessing.

How long before the Germans start figuring out that visits from orbiting fighters means they will soon be within striking distance of an allied bomber group? Germans can start plotting the bomber group's course by plotting which German airfields are getting attention from the Allied fighters.
How long before the Germans start bring up fighters from other airfields to clear the Allied fighters off and allow the fighters on the ground to take off with full fuel to go after the bombers?

This is not 1944-45. The Germans have a lot more distance/time to set things up than the Germans had when Allied fighters were based in France and the low countries.

 

[Shortround6]

I would also note that the engine in the Spitfire IX was about 200lbs heavier than the engine in the Spitfire V and the propeller was heavier which makes sticking a fuel tank behind the seat a whole lot easier from a CG standpoint.

 

[33k in the air]

The Spit needed range regardless of what theater it flew in, the lack of it was it's biggest drawback.

Range for what? Unless it's accompanying bombers to a distant target, where is the pressing need for range?

 

[Milosh]

Range for what? Unless it's accompanying bombers to a distant target, where is the pressing need for range?

Range equals time in the air.

 

[PAT303]

Brits were and are clever. If they could've have had it doing Rodeos over the Rhine, don't you think they would have? Whatcha got? Why'd they pass up what appears to be a golden opportunity in you eyes? What are you seeing that they missed?

They did do rodeo's out to 300 miles with just a 90G drop tank in 1944, why couldn't they do it in '43?.