Curtiss P-36 with the Wright R-2600 Twin Cyclone (hypothetically)

_PabloSniper_ · Saturday at 10:24 PM

Hello everyone!
I believe everyone here should know the history of the P-36.
What if Curtiss had insisted a little more on its development?
When I think of the development of the P-36, I imagine this.
A P-40N with an R-2600 radial. (Same as the XF6F-1 Hellcat prototype, the B-25 and the TBF Avenger)

The R-2600 is about 600 pounds heavier than a V-1710, but I think with the right tuning it could have extended the life of the Curtiss fighters.
And since the P-40N had a larger tail than the P-36, perhaps it would be possible to balance the weight.
I'm not sure how much the V-1710's liquid cooling system weighs, but since it would be unnecessary, it would probably save about 200 pounds.
In short, we are talking about something around 400 pounds more weight, and 450 to 500 more Hp.

tomo pauk · 2024-10-13T03:30:51-0400

_PabloSniper_ said:
When I think of the development of the P-36, I imagine this.
A P-40N with an R-2600 radial. (Same as the XF6F-1 Hellcat prototype, the B-25 and the TBF Avenger)
The R-2600 is about 600 pounds heavier than a V-1710, but I think with the right tuning it could have extended the life of the Curtiss fighters.

Not the 1st time such a contraption was suggested. On this forum several times (once by yours truly, too), eg. here, and there was also Curtiss' own thinkering (see here). The end result would've been very dependent on the engine version installed.
If the so-called 1700 HP version is in the nose, as indeed powered the B-25s and Avengers, we'd probably gotten a fighter than is great at low altitudes, still useful at medium altitudes, and bad at high altitudes, due to the inadequate supercharger of that engine.
The engine that powered the XF6F-1 was with the 2-stage supercharger (more or less the auxiliary S/C was added to the basic 1700 HP engine), that much improved the altitude performance. If that engine is used, with the assumption that it works as advertised and that there is a ready supply of them, we'd get a fighter that is no worse than the Fw 190, and probably better than it above 20000 ft - IOW, an excellent fighter.

Shortcoming of the R-2600 was the bulk, that meant the drag is increased vs. the V12 installation. It also took a while for the USA to implement the good layout of the exhaust stacks for the increased thrust and thus better speed. Another shortcoming is that fuel mileage will go down due to the heavier, bulkier and more thirsty engine, so the brave new fighter will be even more shorter ranged than the P-40.

FWIW, the early A-20 was still good for 350 mph with 1600 HP R-2600s, despite the bulky engines, the portly fuselage of a bomber, and despite the thick (18% at root) and big wing.

_PabloSniper_ said:
I'm not sure how much the V-1710's liquid cooling system weighs, but since it would be unnecessary, it would probably save about 200 pounds.
In short, we are talking about something around 400 pounds more weight, and 450 to 500 more Hp.

P-40's cooling system was at just under 300 lbs for the V-1710 engines. The R-2600 will have the heavier oil system (extra 50 lbs?), a bigger & heavier prop (another 50 lbs?), heavier engine bearers.
If the 2-stage engine is used, another 200 lbs weight vs. the 1-stage R-2600?

Engine power at 12000 ft is 1450 Hp (196 gal/hr fuel used) for the R-2600 as installed on the B-25, while in the same time the V-1710-39 from the P-40D/E was making 1150 HP there (130-140 gal/hr). Cruise fuel consumption was more modest, the R-2600 still using at least 50% more fuel per hour.

_PabloSniper_ · 2024-10-13T05:27:05-0400

I confess that I was happy to see Curtiss' drawing.

It's a sign that I'm not crazy.

Shortround6 · 2024-10-13T11:39:06-0400

Tomo has given a very good rundown on the problem/s.
The drawing is interesting as it shows the cockpit near where the YP-37 cockpit was which may indicate trying to get the CG in balance.

Many engines got 2 speed superchargers with little increase in bulk or weight (20-50lbs?) but two stage superchargers and especially turbos added bulk and weight.
Fitting a two stage supercharger with intercoolers intended for an F6F into a P-40 airframe is going to require a heavy high steel alloy shoehorn with a 3 meter handle.
As Tomo says the 2 stage engine was almost 200lbs heavier and that does not include the inter coolers and ducts.

C-W may have had problems with high altitude cooling. While the air is colder at 22,000ft you have 1/2 the mass airflow (weight of air) at the same speed that you do at sea level.

_PabloSniper_ · 2024-10-13T14:32:34-0400

tomo pauk said:
Not the 1st time such a contraption was suggested. On this forum several times (once by yours truly, too), eg. here, and there was also Curtiss' own thinkering (see here). The end result would've been very dependent on the engine version installed.
If the so-called 1700 HP version is in the nose, as indeed powered the B-25s and Avengers, we'd probably gotten a fighter than is great at low altitudes, still useful at medium altitudes, and bad at high altitudes, due to the inadequate supercharger of that engine.
The engine that powered the XF6F-1 was with the 2-stage supercharger (more or less the auxiliary S/C was added to the basic 1700 HP engine), that much improved the altitude performance. If that engine is used, with the assumption that it works as advertised and that there is a ready supply of them, we'd get a fighter that is no worse than the Fw 190, and probably better than it above 20000 ft - IOW, an excellent fighter.

Shortcoming of the R-2600 was the bulk, that meant the drag is increased vs. the V12 installation. It also took a while for the USA to implement the good layout of the exhaust stacks for the increased thrust and thus better speed. Another shortcoming is that fuel mileage will go down due to the heavier, bulkier and more thirsty engine, so the brave new fighter will be even more shorter ranged than the P-40.

FWIW, the early A-20 was still good for 350 mph with 1600 HP R-2600s, despite the bulky engines, the portly fuselage of a bomber, and despite the thick (18% at root) and big wing.

P-40's cooling system was at just under 300 lbs for the V-1710 engines. The R-2600 will have the heavier oil system (extra 50 lbs?), a bigger & heavier prop (another 50 lbs?), heavier engine bearers.
If the 2-stage engine is used, another 200 lbs weight vs. the 1-stage R-2600?

Engine power at 12000 ft is 1450 Hp (196 gal/hr fuel used) for the R-2600 as installed on the B-25, while in the same time the V-1710-39 from the P-40D/E was making 1150 HP there (130-140 gal/hr). Cruise fuel consumption was more modest, the R-2600 still using at least 50% more fuel per hour.

tomo pauk

Have more modest options been considered for the XP-42, such as the R-2000?

tomo pauk · 2024-10-13T14:47:35-0400

_PabloSniper_ said:
tomo pauk
Have more modest options been considered for the XP-42, such as the R-2000?

Good catch wrt. the XP-42 with the much improved exhausts. Unfortunately, it took inexplicably long time before that improvement 'percolated' into the mainstream.
By the time R-2000 was around - the monthly production went into triple digits as late as early 1943 - USAAF was fully commited towards the V-1710 (both turboed and non-turboed), R-2800 (turbo mostly, but also 1- and 2-stage S/C), as well as towards the Packard Merlin. R-2000 was not offering anything over these engines (it was the other way around), and it will require the turbo to satisfy the altitude requirements. All of these engines were being manufactured in hundreds per month already by 1942; eg. the R-2800 was made in some 12000 copies in 1942, with new factories making the R-2800 entering the stage in 1943.
Some 7200+ of the Packard Merlins was made in 1942.

By that time, USAAF saw the P-40 as the fighter behind the curve, too.

Shortround6 · 2024-10-13T15:10:21-0400

the R-2000 didn't offer the improvement at altitude that the take-off figures suggest.

Engine.....................................take-off...................Mil power low....................Mil power high
R-1830-61...........................1200hp........................1200hp/4900ft.....................1050hp/13,100ft
R-2000-3..............................1350hp........................1350hp/2000ft....................not listed
R-2000-9..............................1450hp........................1450hp/1000ft.....................1100hp/16,000ft

It does not appear that they sized the supercharger to flow enough air at high altitudes.
They were interested in high take-off power for transports.

_PabloSniper_ · 2024-10-13T15:22:15-0400

I was looking for information about the XP-42, and found this version. Did it have a larger engine than the R-1830?

Shortround6 · 2024-10-13T15:55:37-0400

No.
They did test something like 14 different nose cowls on the XP-42 but it was much more of an aerodynamic test bed than anything else. They used a few different engines with different length prop-shafts but the basic engine didn't change much, if at all.

_PabloSniper_ · 2024-10-13T16:02:26-0400

Shortround6 said:
No.
They did test something like 14 different nose cowls on the XP-42 but it was much more of an aerodynamic test bed than anything else. They used a few different engines with different length prop-shafts but the basic engine didn't change much, if at all.

Continuing the search for an aircraft that could accommodate the R-2600, I found the XP-44 Rocket.
Which was planned for the R-2180, but is already much closer to the R-2600 than the R-1830.

Shortround6 · 2024-10-13T16:08:49-0400

The R-2180 use 14 cylinders that were the same size as the cylinders used in the R-2800 and the engines were the same diameter.
P&W cancelled development of the R-2180.
The R-2800 was smaller in diameter than the R-2600, it was only about 200-250lbs heavier, it made more power. It pretty much killed the R-2600 as a fighter engine.
They did leap frog each other a bit. Each went through about 3 power levels.

_PabloSniper_ · 2024-10-13T17:59:53-0400

Shortround6 said:
The R-2180 use 14 cylinders that were the same size as the cylinders used in the R-2800 and the engines were the same diameter.
P&W cancelled development of the R-2180.
The R-2800 was smaller in diameter than the R-2600, it was only about 200-250lbs heavier, it made more power. It pretty much killed the R-2600 as a fighter engine.
They did leap frog each other a bit. Each went through about 3 power levels.

I completely agree with your statement.
My point is that we will not have R-2800s fully ready for use until 1943.
A fighter using the R-2600 in 1941 could have allocated more investment to optimize the R-2600.
Remember that the Hellcat prototype used a modified R-2600 to maintain good high-altitude performance.

tomo pauk · 2024-10-13T18:06:31-0400

_PabloSniper_ said:
My point is that we will not have R-2800s fully ready for use until 1943.

Care to elaborate?

_PabloSniper_ said:
A fighter using the R-2600 in 1941 could have allocated more investment to optimize the R-2600.

FWIW and IMO, just using a bigger supercharger, with the perhaps 12 to 13 in impeller (the 11 in impeller was used on the S/C of the R-2600s) would've netted a very useful high altitude performance.
Wright was one of rare Western radial engines' makers that stuck with 'good' impellers between the late 1930s and the mid ww2, rest of the radial engines' makers used impellers with straight blades instead of these with curved/parabolic frontal section.

_PabloSniper_ · 2024-10-13T18:10:29-0400

tomo pauk said:
Care to elaborate?

I meant that the R-2800 was ready well after the R-2600.

Shortround6 · 2024-10-13T19:24:58-0400

_PabloSniper_ said:
I meant that the R-2800 was ready well after the R-2600.

Yes and no,
The 1600hp R-2600 was ready well before the 1850hp R-2800.
But the 1700hp R-2600 didn't show up until 3-4 months before the 2000hp R-2800s, at least in numbers more than a few dozen a month.
The 1900hp R-2600 didn't show up until late summer of 1943. The 2100hp R-2800s showed up in the spring/summer of 1944.
These are for either single speed single stage or two speed single stage. Production two stage superchargers took a while longer, either turbo or mechanical except....
Wright never had a production two stage supercharged R-2600, ever, of either type.

_PabloSniper_ · 2024-10-13T20:31:47-0400

Shortround6 said:
Yes and no,
The 1600hp R-2600 was ready well before the 1850hp R-2800.
But the 1700hp R-2600 didn't show up until 3-4 months before the 2000hp R-2800s, at least in numbers more than a few dozen a month.
The 1900hp R-2600 didn't show up until late summer of 1943. The 2100hp R-2800s showed up in the spring/summer of 1944.
These are for either single speed single stage or two speed single stage. Production two stage superchargers took a while longer, either turbo or mechanical except....
Wright never had a production two stage supercharged R-2600, ever, of either type.

I found this page with the respective speeds of the R-2600 and R-2800.

Shortround6 · 2024-10-13T21:05:30-0400

What is interesting is the difference in climb.

Without knowing the altitudes the max speeds were at the information not really that helpful.
The Zero did not climb at 4500fpm. It's climb was deceptive. It best climb speed was slower than many other fighters so it climbed at a steeper angle.

tomo pauk · 2024-10-14T12:09:29-0400

_PabloSniper_ said:
I meant that the R-2800 was ready well after the R-2600.

As noted above, that really depends on the version.
The erstwhile 1500 and 1600 HP types were with the low-altitude S/C, meaning that their suitability for the USAAC fighters was simply not there (at least not without the support by turbo system).
The 2-speed supercharged R-2600s, as installed on the A-20s, were the 1600 HP versions (giving also 1400 HP at 10800 ft). These were indeed made already in 1940, with 1925 pcs manufactured in 1940. So a scenario where the 1st versions of the P-36/-37/-40 are 1st flying in 1938/39, and are in series production might provide the AAc with a workable fighter of the era, with the some shortcomings (need to reinforce the wings and fuselage even more than what was the case historically; small radius of action).
The 1700 HP version, that was much better at altitude, was being series produced from mid-1941, and was made in 443 pcs in 1941. More or less a drop-in upgrade vs. the 1600 HP version, with much better altitude performance.
It will be 1942 until the 2-stage supercharged R-2600 is being made, and in a handful of engines.

The R-2800 was manufactured in about 1720 pcs in 1941, and it made even better power than the 1700 HP R-2600s. The 1st 2-stage supercharged R-2800 powered the XF4U-1 from late May of 1940, ie. some 2 years before the XF6F-1 took flight, powered by the 2-stage R-2600.

Curtiss P-36 with the Wright R-2600 Twin Cyclone (hypothetically)

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