A WW2 fighter design for rugged areas

[Hood]

Would something like the Commonwealth Boomerang fit for this thread?

 

[blockhaj]

Well I guess the question remains how did they manage to achieve that? Developing the AN/M3 proved quite a challenge even with the scale of manufacturing the USA had to work with. And why didn't Springfield Armory or the others have any examples to take apart? I would be surprised if none of the guns ever found their way to the UK at some point. A lot of other stuff from Belgium did.

We can start a separate thread if u want, i have info up the ass on that gun.

As for the fire rate it simply came down to the barrel weight, later on Sweden installed barrel weights for peace time to lower the ROF to 800 rpm in an effort to increase barrel life. Barrel heat from high ROF could also detonate the high explosive shells when traveling through the barrel. Burst were thus limited to 2 seconds of fire if the barrel ran hot.

 

[blockhaj]

Like I said, 13.2mm Hotchkiss is more powerful than .50bmg, which will drive up the cyclic rate, and the barrels are going to be lighter even if the outer profile is the same as the AN/M2 .50cal due to larger chamber and bore. Those two combined would not surprise me to get +200rpm out of the gun, and the total is only +300rpm.

They have more or less the exact same case capacity and dimensions, u can reload 13,2 cases with 12,7 ammo and crimp the neck to fit 12,7 machine gun chambers (not recomended FYI).

FN reported a minimum fire rate of 600 rpm and a maximum of 1500 rpm, no clue what lube they used for the latter one. Prewar manuals and Romanian alike state 1080 rpm at traditional summer temp and pressure. Wartime manuals from Sweden and Finland both say 1100 rpm ditto.

 

[Pasoleati]

Like I said, 13.2mm Hotchkiss is more powerful than .50bmg, which will drive up the cyclic rate, and the barrels are going to be lighter even if the outer profile is the same as the AN/M2 .50cal due to larger chamber and bore. Those two combined would not surprise me to get +200rpm out of the gun, and the total is only +300rpm.

Scott, the LKk 42 fired the same 12.7 x 99 ammo as the M2.

 

[riggerrob]

Another question: is the fighter for 1939, for 1942 perhaps, or for 1945?

I got the impression that the original poster was aiming for 1939, to provide Finland with a better fighter for the Winter War.
Bonus points if the basic design has enough growth potential to remain effective up to mid-war.
For example, Grumman’s first XF4F-2 Wildcat/Martlet prototype was a dud, losing a competition to Brewster’s Buffalo. So Grumman engineers did an extensive re-design to produce the F4F-4 which proved the best WALLIED carrier fighter at the start of WW2.
During that re-design, Grumman made cowl cooling flaps much shallower, reducing a “dam” of air exiting the cowling. That “dam” slowed the XF4F-2 prototype.
F4F had tremendous growth potential with the original Wright R-1820 engine growing from 900 horsepower to 1500 hp. by the late 1940s.
Grumman also learned a lot about cowling design during WW2. Look at how the later F6F Hellcat and F8F Bearcat moved exhausts to the sides so that exhaust and cooling air both exited into the low pressure area over the wing roots (ala. FW.190). To see the full growth potential of F8F, look at the “Conquest 1” and “Rare Bear” race planes with bigger propellers, spinners, internal spinners (borrowed from Lockheed Constellation) tighter cowlings, water-injection, etc.

 

[riggerrob]

Would something like the Commonwealth Boomerang fit for this thread?

Sure!
Start by updating the cowling so that it more resembles an F8F Bearcat, perhaps even the post-war “Rare Bear” racer cowling.

 

[Foo Fighter]

What would the potential perfomrance be? Aproximately.

 

[Pasoleati]

What would the potential perfomrance be? Aproximately.

I would set around 320 mph at sea level as minimum. It should be comfortably (=even with a worn airframe) faster than medium bombers.

 

[blockhaj]

I would set around 320 mph at sea level as minimum. It should be comfortably (=even with a worn airframe) faster than medium bombers.

so 514 kph in common language..

 

[Pasoleati]

so 514 kph in common language..

Yep. Faster than the Bf 109G-6 as per Finnish service condition. Usually post-repair test runs gave 490 - 500 km/h with Steig- und Kampfleistung. The G-6 was an aerodynamic disaster.

 

[blockhaj]

Yep. Faster than the Bf 109G-6 as per Finnish service condition. Usually post-repair test runs gave 490 - 500 km/h with Steig- und Kampfleistung. The G-6 was an aerodynamic disaster.

Finnish 109s should defacto go 100 kph faster than that, or did they not get water injection or something?

 

[Nik]

Are you hunting military aircraft ? You need those steel rifle-calibre, or cannon. Are you strafing 'soft' vehicles and troops ? Rifle-calibre for the extra load-out...
Sounds like you need either a mix as-is, or arm the aircraft with integral aircraft-killer(s) plus under-wing pods with ample rifle-calibre for ground attack and riddling eg flimsy Condors...

 

[Pasoleati]

Finnish 109s should defacto go 100 kph faster than that, or did they not get water injection or something?

That's the sea level speed. In fact, even the factory figures for the 109G-6 weren't much higher even with Notleistung at sea level. It is 99 % certain that no wartime Finnish 109G used Notleistung in combat. Not even the official test report with the G-2 used Notleistung as it was banned.

 

[riggerrob]

Are you hunting military aircraft ? You need those steel rifle-calibre, or cannon. Are you strafing 'soft' vehicles and troops ? Rifle-calibre for the extra load-out...
Sounds like you need either a mix as-is, or arm the aircraft with integral aircraft-killer(s) plus under-wing pods with ample rifle-calibre for ground attack and riddling eg flimsy Condors...

Podded MGs hung under wings makes it look like the initial designer lost track of the primary mission.
This hypothetical fighter should be able to perform its primary mission with only internal fuel and weapons.
The only exception should be bombs hung below the wings or fuselage.

 

[Nik]

"The only exception should be bombs hung below the wings or fuselage."
Fair point.
My suggestion was to give best performance against 'combat' aircraft, plus options for other work. IIRC, the H-Guy exasperated his aircraft designers by insisting everything should double as a bomb-truck, despite structural complexities and dead-weight penalties. Perhaps fortunately, rocket-firing pods were not thought viable until too late to reverse-engineer...

 

[Pasoleati]

Strafing of troops would require too much armour to make it viable. I would emphasize attacking trains, vehicles, boats and enemy a/c on ground.

 

[Scott Kenny]

Strafing of troops would require too much armour to make it viable. I would emphasize attacking trains, vehicles, boats and enemy a/c on ground.

All of which requires heavier guns than rifle caliber.

Scott, the LKk 42 fired the same 12.7 x 99 ammo as the M2.

oh? Thought it was 13.2 Hotchkiss. My bad. Would have required lighter bolt and barrel than the classic AN/M-2, then,

 

[Pasoleati]

All of which requires heavier guns than rifle caliber.



oh? Thought it was 13.2 Hotchkiss. My bad. Would have required lighter bolt and barrel than the classic AN/M-2, then,

A comparison table: Tulinopeus=rate of fire.

 

[blockhaj]

Tbh the FFVS J 22, conceptualized in 1940 as the GP9 would in hindsight have been a very solid pick for this thread.

• Engine: Bristol Taurus (1200 hp), 680 kph
• Armament: 2x 8 mm Browning (1200 rpm) with 500 rpg, 2x 13,2 mm FN (1100 rpm) with 250 rpg
• Ordnance: drop tanks and lighter bombs most likely in the pipeline as per the J 21 (competing design)

 

[blockhaj]

All of which requires heavier guns than rifle caliber.

30 caliber AP can easily penetrate the boiler of a train. Armored trains is another story.

 

[Pasoleati]

30 caliber AP can easily penetrate the boiler of a train. Armored trains is another story.

The thing is that in practical conditions the heavy calibre MG is much better weapon for 99 % of cases.

 

[Scott Kenny]

The thing is that in practical conditions the heavy calibre MG is much better weapon for 99 % of cases.

And if your 12.7mm MGs are doing 900rpm...

See also what monstrous damage a P-47 did on a strafing run with 8x .50cals.

So, we're looking at 2x 20mm and 2x .50cals for our fighter? 20mms synchronized through the prop and .50cals in the wings?

 

[Scott Kenny]

A comparison table: Tulinopeus=rate of fire.

Ah, they loaded the cartridges significantly hotter for the LKk42!

If I'm parsing that correctly, the Browning .50 has a muzzle velocity of 770m/s while the LKk42 has an 805m/s muzzle velocity, with the same length barrels and same weight projectiles.

That will significantly drive up cyclic rate in a recoil-operated MG.

35m/s is a big bump for the .50bmg, that's already running close to the limits of metallurgy stock.

 

[blockhaj]

The thing is that in practical conditions the heavy calibre MG is much better weapon for 99 % of cases.

That is a myth. Heavy caliber machine guns are better against vehicles granted, especially protected such, both ground and air, but against soft targets its more economical and suitable with rifle caliber. Look at the Cessna A-37 Dragonfly and most COIN-aircraft for example.

 

[Pasoleati]

And if your 12.7mm MGs are doing 900rpm...

See also what monstrous damage a P-47 did on a strafing run with 8x .50cals.

So, we're looking at 2x 20mm and 2x .50cals for our fighter? 20mms synchronized through the prop and .50cals in the wings?

I would settle for 2 x 20 mm MG 151/20E. In fuselage.

 

[publiusr]

I imagine a lot of fire from aircraft are glancing blows—thus a need for cannon.

 

[Scott Kenny]

That is a myth. Heavy caliber machine guns are better against vehicles granted, especially protected such, both ground and air, but against soft targets its more economical and suitable with rifle caliber. Look at the Cessna A-37 Dragonfly and most COIN-aircraft for example.

Those COIN aircraft are not shooting vehicles. They're all assuming troops on foot so you need the ludicrous rate of fire of 7.62mm miniguns to cover a dense beaten zone.

An actual WW2 fighter or fighter-bomber is going to be dropping light bombs on leg infantry and strafing their transport trucks with the installed guns.

 

[Scott Kenny]

I imagine a lot of fire from aircraft are glancing blows—thus a need for cannon.

That's one of the reasons for discarding rifle-caliber MGs, yes. The bullets would just slide along the aluminum skin in most cases.

 

[Pasoleati]

Ah, they loaded the cartridges significantly hotter for the LKk42!

If I'm parsing that correctly, the Browning .50 has a muzzle velocity of 770m/s while the LKk42 has an 805m/s muzzle velocity, with the same length barrels and same weight projectiles.

That will significantly drive up cyclic rate in a recoil-operated MG.

35m/s is a big bump for the .50bmg, that's already running close to the limits of metallurgy stock.

Further information received. The ammo used for the data in the table was the same, the difference is simply variance with individual cartridges.

 

[tomo pauk]

ShVAKs were known to be unreliable and fired overall worse ammunition than western or axis equivelant.

Shvak's ammunition was certainly weaker thna what the Western 20mm cannons were firing.
OTOH, Shvak was the only belt-fed 20mm cannon in mass service before mid-1941, RoF was very good, and was able to fire synchronized, unlike the Hispano.
Care to post definitive source that can confirm that Shvaks were unreliable?

Well I guess the question remains how did they manage to achieve that? Developing the AN/M3 proved quite a challenge even with the scale of manufacturing the USA had to work with. And why didn't Springfield Armory or the others have any examples to take apart? I would be surprised if none of the guns ever found their way to the UK at some point. A lot of other stuff from Belgium did.

Belgian mechanical engineers working at FN Herstal were probably the cream of the crop in Belgium (similar with the best Czech and Swedish engineers, that worked at the gun-makers). Best American mechanical engineers probably worked in GE, P&W, Wright, Ford, Allison/GM - neither of whom were making automatic weapons, let alone the ones between 0.50 in and 57mm.

Passing of J.M.Browning left a void in the US design of heavy automatic weapons.

 

[tomo pauk]

For example, Grumman’s first XF4F-2 Wildcat/Martlet prototype was a dud, losing a competition to Brewster’s Buffalo. So Grumman engineers did an extensive re-design to produce the F4F-4 which proved the best WALLIED carrier fighter at the start of WW2.
During that re-design, Grumman made cowl cooling flaps much shallower, reducing a “dam” of air exiting the cowling. That “dam” slowed the XF4F-2 prototype.

Grumman installed a 2-stage supercharged R-1830 on the next version, that was the -3. Much better power above 15000 ft and some nip & tuck improved the performance of the F4F.
Unfortunately, any Wildcat we look at was one draggy aircraft, let alone with the R-1820 in the nose.

F4F had tremendous growth potential with the original Wright R-1820 engine growing from 900 horsepower to 1500 hp. by the late 1940s.

If there was the growth potential, it was d@mn well hidden. It never flew with the 900 HP R-1820, and with 1350 HP version it was still under 340 mph, despite loosing 1/3rd of it's firepower.

I would set around 320 mph at sea level as minimum. It should be comfortably (=even with a worn airframe) faster than medium bombers.

320 mph at SL is perhaps 30 mph faster than the Spitfire I at S/L? Or even faster than the Bf 109E. Works to perhaps 400 mph at ~15000 ft (depending on the engine)?
Not aiming low, I see

Tbh the FFVS J 22, conceptualized in 1940 as the GP9 would in hindsight have been a very solid pick for this thread.

• Engine: Bristol Taurus (1200 hp), 680 kph

680 km/h with the Taurus - please, do tell.

 

[HoHun]

Hi Pasoleati,

A fighter for rough conditions for low and medium altutudes

What's the upper altitude limit at which it's supposed to be competitive?

-R-1820 H-series with water injection (1475 hp)

What are the model designations of the H-series R-1820? I couldn't find anything to identify them in the lists at enginehistory.org.

When is the fighter supposed to be available? It seems that the R-1820-56 engines were among the most powerful variants, and they came relatively late in the war, it seems.

-Fowler flaps with a maneouver setting actuaed by a stick switch
[...]
-undercarriage suitable for fields
[...]
2. In Finnish service the availability rates of aircraft was much higher with air-cooled radials vs. liquid-cooled ones.
3. Ruggedness of general construction is of great importance. Especially that of the undercarriage.

I guess you're going to have a certain amount of conflict between these requirements.

Fowler flaps are mechanically complex, have many moving parts, and stick out far below the wing, which with a conventional tail-dragger, low-wing, tractor design is especially bad as not only the wheels, but the propeller slipstream as well will be able to throw sticks and stones at your fowler flaps.

It's not by accident that the very rugged Focke-Wulf Fw 190 had mechanically simple split flaps.

Regards,

Henning (HoHun)

 

[Pasoleati]

Regarding ŠVAK: According to Tony Williams's Autocannon there were problems with cartridge cases being broken in two when extracted (Williams says the gun has very fierce case extraction).

HoHun: Altitude range 0 - 6000 m. The history/variants of the R-1820 is surprisingly poorly covered in available sources. It doesn't help that the JAWA often uses civilian/factory designations in the tables.

Regarding Fowlers: Many Japanese aircraft used them while being taildraggers and the fields were definitely rough.

 

[Pasoleati]

HoHun: It seems that very few German aircraft had Fowler flaps and I don't recall a single one with double-slotted flaps.

 

[tomo pauk]

Regarding ŠVAK: According to Tony Williams's Autocannon there were problems with cartridge cases being broken in two when extracted (Williams says the gun has very fierce case extraction).

Do you have any data about when was that problem noticed, how long it took to cure it, how often it happened?

 

[Pasoleati]

Do you have any data about when was that problem noticed, how long it took to cure it, how often it happened?

No. Williams's book has less than one page on it (or basically single gun). Very far from Chinn's level of detail.

 

[tomo pauk]

No. Williams's book has less than one page on it (or basically single gun). Very far from Chinn's level of detail.

Thank you anyway.

 

[HoHun]

Hi Pasoleati,

HoHun: Altitude range 0 - 6000 m. The history/variants of the R-1820 is surprisingly poorly covered in available sources. It doesn't help that the JAWA often uses civilian/factory designations in the tables.

Well, if one assumes the R-1820-W of the Grumman (well, Eastern) FM-2 is an example of a fully-developed H-series engine, it's worth noting that the full-throttle height in high gear and with the aid of ram effect in high-speed flight is just 3300 m (10800 ft) at 2600 rpm, 52" Hg boost, water injection active (based on AN 01-0190FB-1 Pilot's Handbook of Flight Operating Instructions Navy Model FM-2 British Model Wildcat VI Airplanes).

Regarding Fowlers: Many Japanese aircraft used them while being taildraggers and the fields were definitely rough.

I'm afraid, I don't have any numeric data, but it's my impression that the Japanese were really struggling to keep their aircraft properly maintained under rough conditions. So I don't think their use of Fowler flaps implies that they were robust in the sense of your requirement.

HoHun: It seems that very few German aircraft had Fowler flaps and I don't recall a single one with double-slotted flaps.

Fowler flaps had their own set of draw-backs, and if you're not critically short in terms of runway length, they weren't all that great. Besides, Fowler flaps have only become sort of a generic term post-war as far as I can tell, there were quite a few variations on the theme of slotted/area increasing flaps, such as the British Youngman flaps or the German Arado Wanderflügel.

In any case, are you aware of double-slotted flaps in use in WW2 with anyone else than the Germans? I can't think of any, spontaneously, but of course I don't have all the details of every type memorized I seem to remember the Vought Kingfisher had quite a few high-lift devices integrated in its design - a bit ironic that it was supposed to operate from the open ocean, also known as "the longest runway in the world" :-D

Regards,

Henning (HoHun)

 

[riggerrob]

Enough about guns and wing-flaps … let’s shift the conversation down to the landing gear.
My first guess is a conventional, tail-wheel landing gear.
Do we ask for a ribbed tail-wheel (ala. Lancaster) to improve steering on soft surfaces?
Do we need to retract the tail-wheel on an airplane with a top speed of less than 400 knots?

Do we install a single, soft, large diameter tire on each main landing-gear leg?
… or do we install pairs of main-wheels in tandem (ala. C-130 Hercules)?
At what width do tires become too thick to retract into wings?

Yes, we know that modern STOL bush-planes (Cessna 208 Caravan, PAC 750XL and Quest Kodiak) all have large nose-wheels, but nose-wheel technology was still in its infancy during the 1930s.

 

[Pasoleati]

Hohun: A-26 Invader certainly double-slotted and I think the P-61 too.

The Pe-2 had very large flaps and I don't recall Finns had much damage on them despite very sandy fields.