Merlin engined P40

special ed said:

The P-38, P-39 and P-40 were initially all interceptors as any attack on the U.S. would be coming in the air. No need for strafing ground troops. As with all fighters, as the type ages, they are assigned more to close support of our troops as newer fighters do the air to air fighting. Brother Martin has fiction and opinion in with his facts. I have most of his books, including his works of fiction.

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All his books should be considered as fiction.

MiTasol said:

Either the XP-38 or a YP-38 is at Planes of Fame at Chino. GregP will know for certain which one. He may be able to identify which turbos are fitted though from memory the plate is not visible when installed

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Neither the XP-38 or any of the YP-38's exist. Planes of Fame has a P-38J.

MIflyer said:

The 9th started out with F-4's (P-38E) and even had one engine that seemed to have been a V-1710C with a F series gearcase.

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MIflyer said:

Well, the engine in question had a completely different coolant attachment from all the others.

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That makes far more sense. C series cylinder banks will fit the E/F crankcase but have less coolant flow to the rear part of the cylinder head as we can see below.


Note the extra coolant connection to the cylinder head on the E/F cylinder bank inside the circle which shows up better in the schematic of the coolant system.

Well, the 9th had E's converted to F-4's and then moved on to the later models. But the only C series in the CBI would have been the Tomahawks of the AVG and the 9th would have had no reason to come in contact with them.

Why that particular F-4 had one odd engine, I guess we will never know. It ended up being something of a hangar queen and at one point was modified with guns to try to intercept a Dinah that was irritating the Allies by not only flying over but also issuing taunting radio messages. A stripped down P-40 finally got the Dinah.

I read where after the 14th AF got later P-40's that someone decided to take some of the older models and fly them to North Africa where they could be shipped to the USA for use in bond drives. But I don't think any of those airplanes survived the trip to the boat.

CD Baumann said:

And

And I've just scoured three books and several websites. It was designed to stay at low altitude. None mention the high altitude requirement that the P38 was designed too. They all say unequivocally that the P40 was bought because it could get brought into production quickly.
There is this thing called strafing too you know? I believe that's qualifies as ground attack.

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Do any of those sources mention how the term "interceptor" as versus "persuit" came about and how the requirements and specifications differed?

MiTasol said:

Either the XP-38 or a YP-38 is at Planes of Fame at Chino. GregP will know for certain which one. He may be able to identify which turbos are fitted though from memory the plate is not visible when installed

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The sole XP-38 was destroyed landing at Mitchel Field in Hempstead New York in Feb 1939, and was scrapped.

GreenKnight121 said:

The sole XP-38 was destroyed landing at Mitchel Field in Hempstead New York in Feb 1939, and was scrapped.

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You are correct. The Planes of Fame P-38 is a later model. They had a couple of parts off one of the YPs when they were at Buena Park.

I have mentioned on the forum somewhere about a WW2 pilot who spent his time in the US as an instructor. They had a very few P-38s and one of them was a YP-38. He hated to fly it because the cockpit was non standard with many toggle switches and knobs the others didn't use.

I asked Copilot the following: "What were the goals of circular proposal x-609?"

The answer is as follows:

Circular Proposal X-609, issued in 1937 by the United States Army Air Corps, aimed to develop a new high-altitude interceptor aircraft. The primary goals were:

1. Interception and Attack: The aircraft was intended to intercept and attack hostile aircraft at high altitudes [1].
2. High Performance: It needed to achieve a level airspeed of at least 360 mph (580 km/h) and climb to 20,000 feet (6,100 meters) within six minutes [1].
3. Heavy Armament: The aircraft was required to carry at least 1,000 pounds of heavy armament, including a cannon [1].
4. Advanced Features: Specifications included a liquid-cooled Allison engine with a General Electric turbo-supercharger and tricycle landing gear [1].

The Bell P-39 Airacobra was one of the aircraft developed in response to this proposal [2].

Is there anything specific you'd like to know more about regarding this proposal or the aircraft developed from it?

[1] warbirdsresourcegroup.org
[2] warhistoryonline.com
[3] warbirdsresourcegroup.org

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The follow up question: "What were the designs submitted?"

Several designs were submitted in response to Circular Proposal X-609. Here are a few notable ones:

1. Bell P-39 Airacobra: This design featured an innovative mid-engine configuration with the Allison V-12 engine mounted behind the cockpit. The propeller was driven by a shaft passing beneath the pilot's feet. This setup allowed for a streamlined nose and the incorporation of a 37 mm cannon firing through the propeller hub [1].
2. Curtiss XP-46: This was another design that aimed to meet the high-altitude interceptor requirements. It featured a more conventional layout compared to the P-39 but ultimately did not progress as far in development [1].
3. Seversky XP-41: This design was an evolution of the P-35, incorporating a turbo-supercharged engine to meet the high-altitude performance criteria [1].

These designs were part of the effort to push the boundaries of aircraft performance and armament during that era. The Bell P-39 Airacobra, in particular, stood out due to its unique configuration and heavy armament.

Is there a specific design or aspect you're more interested in?

[1] warbirdsresourcegroup.org

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"What was the original design goal for the XP-40?"

The original design goal for the XP-40 was to create a high-performance, single-seat fighter aircraft that could serve as an effective interceptor and ground-attack plane. Here are some key objectives:

1. Improved Performance: The XP-40 aimed to enhance the performance of its predecessor, the P-36 Hawk, by incorporating a more powerful Allison V-1710 engine [1].
2. Streamlined Design: The design included a streamlined fuselage and a low-wing monoplane configuration to reduce drag and improve speed [1].
3. Heavy Armament: The aircraft was equipped with a combination of machine guns and cannons to provide substantial firepower [1].
4. Versatility: It was designed to be versatile, capable of performing both air-to-air combat and ground-attack missions [1].

These goals were part of Curtiss-Wright Corporation's efforts to produce a modern and competitive fighter aircraft during the late 1930s and early 1940s.


[1] militaryhistoria.com
[2] arcforums.com
[3] militaryfactory.com
[4] cs.finescale.com
[5] tvd.im

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For what it is worth.

Unfortunately a lot things do not line up.

wuzak said:

I asked Copilot the following: "What were the goals of circular proposal x-609?"

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The X-609 proposal applied to the XP-39 and ????
The X-608 proposal applied to the P-38, a lot of things were the same but the desired endurance was double that of the X-609 and the extra fuel load required a larger engine which didn't exist and thus required two engines to meet the speed and climb requirements with the desired fuel. Advocates of 1937-39 singe seat escort fighter should think about that.
While heavy armament was required/desired the exact armaments was still undecided. Some people were pushing for a 25mm cannon, some for the 37mm (there were two different ones under development in the US at the time), Madison was pushing a 23mm and the 20mm may have been an outsider. This was both the P-38 and the P-39 at this point in time.
The change on the XP-39 from the 25mm gun to the 37mm gun was in Dec 1938(?).

wuzak said:

The follow up question: "What were the designs submitted?"

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Not sure if there was a typo or some other problem.
The XP-46 was several years behind the P-39 in development and was never a "high altitude fighter".
"Circular Proposal (CP 39-13) based on Berlin's proposal. The Army ordered two prototypes from Curtiss under CP 39-13 on September 29, 1939"
This is 23 months after the order for the XP-39. It used a single stage, single speed Allison engine and would not fly until Feb 15th 1941.
At the Jan 1939 trials there were two Planes with two stage P&W R-1830 radial engines. One was a Hawk 75 and the other was a Seversky. Seversky also had a turbo equipped plane that was about 95% identical and photos of the two planes are often swapped. But neither of these (or the YP-37 and XP-40) had cannon of any size/type/location.

wuzak said:

"What was the original design goal for the XP-40?"

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This gets real confusing.
The XP-40 had been ordered in June 1937 to be built on the 10th P-36 airframe, it was pretty much a firewall forward conversion It was ordered just about the same time as the XP-37 with turbo was delivered to the Army but 6 months before the Army orders 13 YP-37s. But the Army orders the 524 P-40s about 1-2 months before the first YP-37 is delivered. They trickle in slowly and confirm the army wisdom in NOT ordering more YP-37s at this time. Now as to the success of the design goals for the XP-40......

1. Improved Performance: The XP-40 aimed to enhance the performance of its predecessor, the P-36 Hawk, by incorporating a more powerful Allison V-1710 engine [1]. Check
2. Streamlined Design: The design included a streamlined fuselage and a low-wing monoplane configuration to reduce drag and improve speed [1]. Check
3. Heavy Armament: The aircraft was equipped with a combination of machine guns and cannons to provide substantial firepower [1]. FAIL
4. Versatility: It was designed to be versatile, capable of performing both air-to-air combat and ground-attack missions [1]. FAIL

The FAILs.
The plane was NOT equipped with cannon and not until the D model would cannon even be a provision (never utilized ?) . The P-40 NL (No Letter) was ordered with either two .50s with 200rpg or two 50s with 200rpg and two .30s with 500rpg (Army did not admit that the wing guns were there for quite some time leading to a lot of confusion). This was NOT substantial firepower for the time which was a reason for the XP-46 design in the Fall of 1939 with initial war experience from France. Now with the experience from France The P-40Bs got extra .50 cal ammo (not the best idea due to weight) and one extra .30 cal in each wing with 500rpg which put them on a par with the British eight gun fighters, assuming the cowl .50 cal guns actually worked, which they did not for British for a number of months. This in now the Spring of 1941 which is around 2 to 2 1/2 years after the the original design goals for the XP-40.
The Versatility goal. Whatever the capability of the early P-40s were in air-to-air combat (and it did well in NA against the Italians and in the hands of the AVG, it's ability do ground-attack missions was little better than Hawk 75s or Hurricane Is. It was pretty much machine guns only just like the other two and bombs, should they be available, would not have exceeded six 20lbs bombs.
The use of Tomahawks and Kittyhawks to operate as 'bombers' was close to 3 years after the "original" design goals. With the six .50s installed in the P-40E/Kittyhawk ground attack was pretty good even without bombs but the design work for them was in the spring of 1940, not the fall of 1938. And the extra weight of the guns/ammo with not much extra power hurt air-to-air combat.

Since this thread is about the Merlin P-40, one should point out that there were a few other issues not mentioned thus far.
First of all, the P-40E and P-40F can be considered as fairly similar other than the engine installation. The same can be said for the P-40K and P-40L. There is one very notable exception. Just about all the Merlin P-40s were the long tail variety while the Allison aircraft were short tails with the E and a mix with the Ks. This was important because the long tail aircraft were more capable of handling engine torque especially at take-off.
Another factor that hasn't been mentioned is that these early Allison P-40E/K with the smaller superchargers had no altitude performance but were screamers at low altitude. The Allison was capable of up to 1700 HP if over boosted but would run out of supercharger above 2000 feet.
As for speed, it wasn't that the Allison P-40 could not make 360 MPH, it just could not do it at 18,000 - 20,000 Feet like the Merlin could.
It was making its best speed at about 10,000 - 12,000 Feet like most contemporary Allisons.
One other factor that hasn't been mentioned is that the Merlin is a considerably heavier engine than the Allison. This caused some interesting problems. The P-40 typically has three fuel tanks: From the rear, these would be a Fuselage tank behind the cockpit, a Main tank under the cockpit and a smaller Forward (my term) tank ahead of the Main tank.
On Allison P-40s, the Forward tank typically served as the Reserve tank with the Fuselage tank being expended first. On a Merlin aircraft, the Forward tank had to be burned first and the Fuselage tank was burned off last to avoid CoG problems as long as possible.
The fact that the Merlin aircraft were so heavy wasn't unnoticed. Some quite brilliant folks had a great solution with the early L models.
The Forward fuel tank was deleted, two wing guns were deleted, brass coolers were replaced with aluminum and standard equipment was sometimes substituted with lighter, less durable versions. These were known as "Gypsy Rose Lee" stripper versions. Units unlucky enough to receive them usually tried to restore them as close as possible to standard configuration.

Ivan1GFP said:

The fact that the Merlin aircraft were so heavy wasn't unnoticed. Some quite brilliant folks had a great solution with the early L models.
The Forward fuel tank was deleted, two wing guns were deleted, brass coolers were replaced with aluminum and standard equipment was sometimes substituted with lighter, less durable versions. These were known as "Gypsy Rose Lee" stripper versions. Units unlucky enough to receive them usually tried to restore them as close as possible to standard configuration.

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Hi

Rather similar in some respects to the modifications made to Kittyhawks to carry a bigger bomb load during 1943:


(Source: Page 63 of 'Close Call, Volume II - Sicily to Victory in Italy 1943-1945' by Vic Flintham, Hikoki 2022)

Mike

I will call bull on the steel wheels. The P-40 landing gear was almost completely identical to the P-36 landing gear with over 90% of the parts being interchangeable, including the wheels and brakes. The P-36 had Hayes alloy wheels and as far as I know so did all P-40s. The P-40 interchangeability list only lists one wheel for all models before the N model which supports this though it would not include deleted parts.

What is more likely is they replaced the 30" wheels with 27" wheels, like was done on the N model aircraft. Pre-N wheels they were possibly T-6 wheels which would have been struggling to handle that much increased load. The A-36 wheel was also a Hayes 27" so may have fitted and had the braking capacity but the P-51 may not as I do not know if the Bendix disc brakes will fit the P-40 axle plate. T-6 wheels would also have had reduced braking as the T-6 brakes are not as wide as the brakes fitted to the N wheels. The 27" wheel was also used on many other aircraft. There were actually four different 27" Hayes wheels fitted to the N model so this suggests that they had to keep upping the strength of the wheels on the N models to support that increasing weight.

As the author notes they may just have been discussing N models anyway though the N battery is forward of the firewall, not behind the seat.

MiTasol said:

I will call bull on the steel wheels. The P-40 landing gear was almost completely identical to the P-36 landing gear with over 90% of the parts being interchangeable, including the wheels and brakes. The P-36 had Hayes alloy wheels and as far as I know so did all P-40s. The P-40 interchangeability list only lists one wheel for all models before the N model which supports this though it would not include deleted parts.

What is more likely is they replaced the 30" wheels with 27" wheels, like was done on the N model aircraft. Pre-N wheels they were possibly T-6 wheels which would have been struggling to handle that much increased load. The A-36 wheel was also a Hayes 27" so may have fitted and had the braking capacity but the P-51 may not as I do not know if the Bendix disc brakes will fit the P-40 axle plate. T-6 wheels would also have had reduced braking as the T-6 brakes are not as wide as the brakes fitted to the N wheels. The 27" wheel was also used on many other aircraft. There were actually four different 27" Hayes wheels fitted to the N model so this suggests that they had to keep upping the strength of the wheels on the N models to support that increasing weight.

As the author notes they may just have been discussing N models anyway though the N battery is forward of the firewall, not behind the seat.

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Hi
I don't know if the steel wheels mention is 'bull' or not, although Flintham was quoting from Bert Horden's book 'Shark Squadron Pilot' (No. 112 Sqn. Horden was flying in the squadron from 1942-1944 undertaking 130 operations, the book is quoted as being based on his flying log books and diary), pages from his book below:

The above is from page 127, it maybe that although he was there he was not aware of the technical details? and made assumptions? Horden implies that the weight reduction was started when they were in North Africa. He makes mention of the Kittyhawk IV (P-40N) just before he finishes his tour in April 1944, on page 163:

The 'steel wheel' mention may be a warning to historians that what people "who were there" say may not be totally true?

As an aside, according to Green and Swanborough in 'US Army Air Force Fighters Part 1' pages 58-59:
"First ordered early in 1943, the P-40N introduced a new light-weight structure and was subjected to a rigid component survey placing emphasis on weight saving. Aluminium oil coolers and radiators were incorporated, as well as lighter wheels and, as in the P-40L-5, he forward wing tank and two wing guns were omitted, with the ammunition capacity for the remaining guns reduced." Although it is also mentioned that the full six gun armament was reintroduced on the P-40N-5.

Mike

112 used the following P-40 variants from July 1941.

Tomahawk IIB Jul-Dec 1941
Kittyhawk I/IA Dec 1941 - Oct 1942 (NA campaign ended May 1943)
Kittyhawk III Oct 1942 - April 1944 (probably virtually all P-40K. Very few P-40M went to the Med)
Kittyhawk IV April-June 1944

At that point it moved on to Mustang III which it flew until May 1945. These were augmented by Mustang IV from Feb 1945 which it used until disbanded in Dec 1946.

Joe Baugher posted the differences between the various P-40N blocks.

MikeMeech said:

Hi

The 'steel wheel' mention may be a warning to historians that what people "who were there" say may not be totally true?

"First ordered early in 1943, the P-40N introduced a new light-weight structure and was subjected to a rigid component survey placing emphasis on weight saving. Aluminium oil coolers and radiators were incorporated, as well as lighter wheels and, as in the P-40L-5, he forward wing tank and two wing guns were omitted, with the ammunition capacity for the remaining guns reduced." Although it is also mentioned that the full six gun armament was reintroduced on the P-40N-5.

Mike

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The reduction of wheel and tyre diameter by almost 10% would have provided a roughly 10% weight saving. Both my 27" wheels weigh 10.4 kg (22.8lb) bare but I do not have any 30" wheels to compare them with. The weight saving would be in the region of 3kg 23lb for the pair of wheels and about the same again for the lighter tyres and a bit more for the smaller diameter brakes.
That is about the same as the saving in oil cooler and radiator weights.

EDIT According to TO 00-25-10 the weight saving on the brake unit is 2lbs per unit and the weight of the 30 inch wheel is "approximately 34lbs" meaning about 15.5kg each. The casings weigh 24lb vs 35lb each so the saving, not counting inner tube, are about 50lb. A lot of the wheel weight saving would be in the steel brake drums which I had forgotten are much thinner as well as smaller on the P-40 27" wheels.