A naval version for Warhawk?

[kool kitty89]

Having only 4 MGs (2x.30/2x.50) brings to mind the shortcomings of the Italian aircraft. Wonderful machines but nearly harmless to an adversary.

Remember the Italian .50s and .30s were MUCH less powerful and somewhat slower firing than American .50s.

That and 2 .50 M2s in the wings and 2 M1919s in the nose would be putting out almost as much metal than the P-40B (mass, not actually dealing with energy, but given the similar ballistics, it'd be close too):
2x M1919s at 1000 RPM (synch) with 10.5g rounds + 2x .50 M2s at 800 RPM (wings -adverage of 750-850 RPM) at 43.3g = 90.28 kg/min
(94.6 kg/min at 850 RPM for the .50s)
vs
P-40B with 2x .50s at 500 RPM (worst case) and 4x .30s at 1200 rpm =
93.7 kg/min (maybe 98-100 kg best case)

6x .30s (2x 1000 rpm, 4x 1200 rpm) =
71.4 kg/min

For comparison purposes, let's look at the Re.2002's armament:
2x 12.7 mm Breda-SAFAT (700 RPM ... but synchronized so perhaps 600 rpm?) 34.2 g + 2x 7.7 mm Breda-SAFAT (900 RPM best case) 10.6g =
60.12 kg/min

BUT, also remember the muzzle velocity is much lower on those guns (in the 750 m/s range vs 880 for the brownings) so any chemical filler aside (just AP/ball ammo considered) you've got roughly 85% the muzzle velocity and 85% the kinetic energy weight for weight. That turns the 60.12 kg/min into an effective 51~52 kg/min by .30-06/.50 BMG standards.

That said, the P-40C wing was not configured for .50 gun mounts, so that above scenario isn't valid ... though would be for the F2A. (2 .50s in the wings, 2 .30s in the nose -easily save over 250 lbs loaded given the F2A's 500 RPG)
Note the F2A-3's standard 4x .50 armament (assuming 2x 800 RPM + 2x 500 RPM) would =
112.58 kg/min
(perhaps 120 kg/min on a good day)

Switching to .30s in the nose of the F2A would result in 75-80% of the raw kinetic firepower of the standard F2A-3, though a higher hit-rate due to the sheer number of .30s in the fray (double the RoF of the synched .50s). With incendiary ammo, that'd favor the .30 arrangement more. (and over 126% the kinetic firepower of 6x .30s on a P-36)

You also don't save much more weight if you swap the 2x .50s in the wings for 4x .30s, even using only 500 RPG for the .30s, so that's not really worth it. (unless you think 4x1200 RPM .30s is more potent than 2x 800 RPM .50s against average early-war Japanese opponents) And again, this is for the F2A-3, not the P-40/P-36.

By the time you get the P-40D wing, just drop the nose guns and go for 4x .50s with 300 RPG like the F4F-3.

Another possibility would be to strengthen the P-36 and do a serious streamlining program to increase speed. The only issue would be the engine. I don't know if the R-2600 would have been possible, but I'm sort of doubting it. Perhaps an earlier R-2000? Or a new R-2300 or thereabouts ... a new engine would be fraught with delays. An earlier R-2000 maybe not ...

R-2600 would be a bad fit, yes. 2-stage R-1830 + (late) XP-42 cowling would be good for a speed boost for later models (unlike the F4F-4) but that's about it for existing engines. R-2000 is a bit late and didn't get 2-stage versions. The R-2180 would have been interesting had it continued development with the 2800, but it didn't.

For hypotheticals, I'd say an 18 cylinder R-1535 might be best, and a potential alternative to R-2000 develoment as well. An R-1973, if you will. Almost the volume of the R-2000, but with smaller cylinders meaning better cooling, higher potential RPM, and the nice small diameter of the Wasp Jr line. (perhaps 45-46 inches) Couple that with a 2-stage supercharger, and you've got a really nice engine for the P-36/P-40 airframe, especially with the cooling fan technology included, or just cooling cuffs mated to a conventional cowling + spinner. Honestly, if that engine was a success, it could/should have replaced the R-1830 entirely. (unlike the R-2000 which, aside from added cost and weight, was bulkier -lighter, 1200 HP class R-1973s might displace the older R-1830s from the market, or indeed, if the 18 cylinder engine had started well pre-war it could have hit the 1000+ hp range by the time the R-1535 hit 800 hp and be a good fit for the earlier P-36)

I doubt that a navalized P-40 would have been considered. The navy seemed to have a very strong prejudice against water cooled engines. Maybe one if the experimental radial engine upgrades to the P-40 Curtiss kept coming up with throughout the was?

One of the P-36 airframes was used as a testbed for the F4F-3's 2-stage engine and cowling, and I believe it managed 380~390 mph at 21,000 ft. Of course, this was a light airplane with the somewhat lighter P-36 structure and no military equipment. (I'd expect something in the 350~360 MPH range fully loaded a la P-40B/C, but that's significantly faster than the F4F-3 or the P-40B/C/D/E/K at that altitude -without overrevving the V-1710)

 

[Shortround6]

One of the P-36 airframes was used as a testbed for the F4F-3's 2-stage engine and cowling, and I believe it managed 380~390 mph at 21,000 ft. Of course, this was a light airplane with the somewhat lighter P-36 structure and no military equipment. (I'd expect something in the 350~360 MPH range fully loaded a la P-40B/C, but that's significantly faster than the F4F-3 or the P-40B/C/D/E/K at that altitude -without overrevving the V-1710)

I don't believe any P-36 was used a test bed for the F4F-3 engine installation.

There were two different Curtiss hawks fitted with two stage R-1830s though.
There was a Hawk 75 fitted with a two stage supercharger at the 1939 fighter trials. It went nowhere near 380mph.
P&W was given an early production P-40 airframe as a test bed for a later version of the 2 stage engine. That is the one that did 380-390mph but it did in in the late summer/early fall of 1942 which is a bit late. It used what was essentially the -86 engine though. And rather different cowl and exhaust set up than any F4F

 

[kool kitty89]

P&W was given an early production P-40 airframe as a test bed for a later version of the 2 stage engine. That is the one that did 380-390mph but it did in in the late summer/early fall of 1942 which is a bit late. It used what was essentially the -86 engine though. And rather different cowl and exhaust set up than any F4F

Thanks, that would be the one I was thinking of. The photograph in the article depicting that aircraft had a cowling that at least superficially resembled the F4F-3's but perhaps more so the F6F-3's, and it was not using a spinner to cover the hub. I'd have to dig around and find it again to see. (I'm confident you're right about the mechanical differences, I just mean I'd like to see if my memory was correct on the similarities to Grumman cowlings)

Given it was using more or less 1940 technology already in use in production F4F-3s and P-40s, it's still relevant to the discussion here.(with the possible exception of the cowling and exhaust refinements used)

To actually be competitive, Curtiss would have needed to be working on a competitor to the F2A-3 and XF4F-3 at the same time as the XP-40 and having access to properly functioning R-1830-86 class 2-stage engines as Grumman did.

 

[Shortround6]

Ok, I will save you the trouble

and BTW the F4F-3s used R-1830-76 engines at least the early ones, I am not sure what the difference/s were, except that P&W lists the -86 with front mounted magnetos, chrome moly cylinder bores and is about 4in shorter.

That is one honking big scoop on the top of the Hawk cowling.

 

[GrauGeist]

That's a Hawk 81A2 - P-40B (or may be a C)

The XP-42 was a reworked P-36 airframe that was powered by a P&W R-1830-31 and had two different cowl configurations.

Shown here is the "short cowl" version.

 

[Shortround6]

Yes but the XP-42 didn't use a two stage supercharger. And actually the XP-42 went through about dozen or more cowl configurations.

http://alternathistory.org.ua/files/users/user4907/XP-42-25.jpg

http://alternathistory.org.ua/files/users/user4907/XP-42-21.jpg

 

[GrauGeist]

The cowl configurations were broke down to two groups:
"Short cowl" which was the more conventional lay out
"Long cowl" which was an attempt to be more aerodynamic (think "pointy")

But it was the P-40 airframe that bore the brunt of the countless experiments, upfits and new type attempts.

The P-36, to the best of my knowledge, had just the one type that was experimented with, the XP-42 which was actually the 4th production P-36A off the assembly line. With the XP-42, they tested a couple engines, many cowl/spinner configurations and various armament layouts (including a Hispano 20mm config at one point).

* I should have added that the photo of the XP-42 I posted had a date of 1942 on it, however, the XP-42 project started in 1938, but the arrival of the P-40 and it's better performance pretty much shut down the XP-42 program, except for later equipment testing.

 

[kool kitty89]

Ok, I will save you the trouble

and BTW the F4F-3s used R-1830-76 engines at least the early ones, I am not sure what the difference/s were, except that P&W lists the -86 with front mounted magnetos, chrome moly cylinder bores and is about 4in shorter.

That is one honking big scoop on the top of the Hawk cowling.

Thanks!

So it only looks superficially similar to the F4F and F6F cowlings. The cowl seems to curve and taper inward to a tighter radial opening around the hub than any of the Grumman cowls and that certainly is a huge (carb?) air intake on top. (I wonder what sort of ram performance that thing got) The lack of cooling cuffs is interesting, I'd have thought the tighter cowling would merit those more but it could be a very well designed cowling that doesn't need any forced air beyond limited prop wash and ram air. (unless that big intake is partially for supplemental cooling air ducted around some sort of radial/ring duct -that intake is much deeper into the prop's airflow path than the hub region, so it seems possible) That also seems like it might save weight over using a large spinner to deflect air into a wider diameter cowl opening.

If that arrangement worked as well or better than Curtiss's own fan cooling set-ups (the functional ones), I'd think the lower weight and mechanical simplicity of P&W's cowl would be preferable all around especially on a naval fighter where weight is more critical. (I wonder if that experiment might have benefited the R-2800 powered fighters, the F6F was in development at the time, but the F4U and P-47 obviously had older cowl designs that might benefit from modifications related to P&W's research)


In any case, back in 1939, a R-1830-76 powered Hawk 81 based prototype likely would have adopted the more conventional P-36 cowl maybe with some modest improvements, and anything like fan cooling or that neat P&W cowl wouldn't likely appear until 1942 unless research was more aggressively pursued.

The P-36, to the best of my knowledge, had just the one type that was experimented with, the XP-42 which was actually the 4th production P-36A off the assembly line. With the XP-42, they tested a couple engines, many cowl/spinner configurations and various armament layouts (including a Hispano 20mm config at one point).

* I should have added that the photo of the XP-42 I posted had a date of 1942 on it, however, the XP-42 project started in 1938, but the arrival of the P-40 and it's better performance pretty much shut down the XP-42 program, except for later equipment testing.

Curtiss was using the XP-42 also as a general testbed for optimizing radial engine cooling and streamlining in general, and applying their newer ongoing projects (mostly R-2800 stuff).

This 1945 picture of the XP-42 (or what's cited as such) appears to be using a cowl more like the one the P&W Hawk 81 testbed used, but features a large, rounded spinner (not so large as the pointed one on the 1942 XP-42).

https://commons.wikimedia.org/wiki/File:Curtiss_XP-42_in_flight_1945.jpg

The camera angle doesn't really show off the upper air intake or show if there's any obvious cooling fan, so it's hard to tell if it might not actually be that Hawk 81 with a spinner added. From what I can see, it seems to more likely be the same cowling as that 1942 image, but using a different propeller and spinner without those prominent cooling cuffs.

 

[GrauGeist]

That's certainly the XP-42 in one of it's many configurations. To get a better idea of the changes, look at the links SR provided.

The XP-42 was the 4th P-36 off the assembly line, serial number 38-004, carried the IOMD on the vert. stab and upper/lower mainwing, plus had an arrowhead insignia on the fuselage.

If you look at the photo I posted of the XP-42, you'll note the early national insignia, so the date on the photo may be for archival purposes.

 

[Shortround6]

In the picture of the F4F the scoops at 4 o'clock and 8 o'clock are the intakes for the cooling air for the intercoolers. The carb intake is at 12 o'clock and there is an oil cooler under each wing. On the P W Hawk 81 ALL three functions are handled by the top and bottom scoops, Much like all three functions/needs were meet by the partitioned scoop under the R-2800 on the F6F.

They were also learning how to use the exhaust pipes/gases not for just thrust but by exhausting the gases at the right point in a suitably designed cowl, it would draw air from the cowl in front of the pipes and resulting low pressure would draw air in the front of the cowl. Very few planes had trouble cooling the engine at high speed. Ground running and long slow climbs where the main problem times for overheating the engine/s. Some designers were trying for a Meredith effect. Getting the cooling air to leave the cowling at a higher velocity than when it entered. I don't know if any succeeded but the closer they got to matching velocities the less drag the installation had.

 

[kool kitty89]

They were also learning how to use the exhaust pipes/gases not for just thrust but by exhausting the gases at the right point in a suitably designed cowl, it would draw air from the cowl in front of the pipes and resulting low pressure would draw air in the front of the cowl.

Yeah, similar to (or a literal example of) the venturi effect. It's the same way those thrust augmenter ducts work (hot exhaust gas passes through a ring-shaped airfoil, the high speed flow draws in more cool air and blends to form a higher volume, lower velocity stream with more working mass and higher net thrust -at least at lower speeds). Using stub exhausts that eject inside the engine cowl should have a similar effect, making the entire cowl into one big thrust augmentor duct. As you say, it still might not produce more thrust than drag, but it's going to be better and lighter than longer ejector exhaust pipes extending outside the cowl and certainly better than large exhaust collector manifolds extending well beyond the cowl (possibly around the wing, depending on the aircraft) adding more weight, drag and little thrust.

Having the hot exhaust exit inside the cowl would be tricky though as it would need to maintain enough cooling airflow to avoid overheating the cowl or airframe with the exhaust jets. A well designed cowl with plenty of forced airflow from prop wash or a fan and effective cowl flaps should be able to avoid that though.