1941/42: fighter with single stage R-2800, a missed opportunity?

[tomo pauk]

An invitation for the discussion: how well would the Allied air forces fared with a fighter made around the single stage R-2800, production starting in second half of 1941 (1733 engines delivered in 1941, per table posted at the AEHS)?

 

[davebender]

What was the average life expectancy of a R-2800 engine during 1941?

 

[Shortround6]

The vast majority of those engines were the "A" series and the most common model is the -5.

1850hp at take-off 2600rpm and 49in of boost. Military ratings of 1850hp/2,600rpm/2,700ft and 1,500hp/2,600rpm/14,000ft. "normal" (max continuous) 1500hp/2400rpm/7,500ft and 1450hp/2400rpm/13,000ft.

weight 2270-2300lbs and a frontal area of 14.8sq ft.

it might have 1280hp at 20,000ft no RAM.

Compare to your favorite engine of the second half of 1941?

 

[ShVAK]

What's the point? USAAF needed a good high altitude fighter in the ETO, I don't think anything with a single stage engine would've cut it. If the fighter is big enough for a two-stage R-2800 and all its accompanying hardware all you have is a redundant competitor to the P-47, and in the meantime it would've probably shared the fate of the P-40--durable and good for low to medium altitude and ground attack, not much else.

 

[tomo pauk]

What was the average life expectancy of a R-2800 engine during 1941?

As good as of other US produced engines?

The vast majority of those engines were the "A" series and the most common model is the -5.

1850hp at take-off 2600rpm and 49in of boost. Military ratings of 1850hp/2,600rpm/2,700ft and 1,500hp/2,600rpm/14,000ft. "normal" (max continuous) 1500hp/2400rpm/7,500ft and 1450hp/2400rpm/13,000ft.

weight 2270-2300lbs and a frontal area of 14.8sq ft.

it might have 1280hp at 20,000ft no RAM.

Compare to your favorite engine of the second half of 1941?

Many thanks.
Seem like it was better the BMW-801C (1300 HP @ 14840), and the B series being better than the 801D, even if the BMW is not restricted.

What's the point? USAAF needed a good high altitude fighter in the ETO, I don't think anything with a single stage engine would've cut it. If the fighter is big enough for a two-stage R-2800 and all its accompanying hardware all you have is a redundant competitor to the P-47, and in the meantime it would've probably shared the fate of the P-40--durable and good for low to medium altitude and ground attack, not much else.

USAAF in 1941-mid 1943 did not wanted an high altitude fighter in the ETO, and the one they had was a problematic one. Single stage R-2800 has 20% more power than the single stage, 2 speed Merlin (I admit, more weight drag); it's more powerful than the BMW 801. Further, it's not necessary to build an 6 ton fighter to support the 2800. Look at the late war Japanese fighters, for example.
The fighter with 1-stage R-2800 was pretty much feasible in 1941, doubt it was the case for the turbo R-2800 (corrections welcomed).

 

[wuzak]

USAAF in 1941-mid 1943 did not wanted an high altitude fighter in the ETO, and the one they had was a problematic one. Single stage R-2800 has 20% more power than the single stage, 2 speed Merlin (I admit, more weight drag)

Which 2 speed single stage Merlin? The XX had 1430hp @ 11,000ft and weighed approximately 900lbs less. Take away some for the rad and you are still looking at 500-600lbs difference.

What about single stage Griffons? The Griffon II has less power down low, 1735hp @ 1000ft, but similar at altitude - 1495hp @ 14,500ft. Still lighter (1790lb) than the R-2800 with less frontal area.

 

[tomo pauk]

The 1st issue is availability. In the time USA starts producing the A series R-2800s, the single stage Merlin is more a year away from the production by Packard. By the time the V-1650-1 is in production, the R-2800 B series is being produced.
Second issue, power: we are looking at 1300 HP at 20000 ft, vs. 1050 of the Merlin XX, or almost 25% more. (yes, I'm a proponent of the Merlin XX on Spits Mustangs ) On military rating, it's 1550 HP @ 11000 ft vs. 1280 HP (all figures for B series vs the XX)?

Griffon is as good as unavailable for the US produced planes, even for the British built airframes prior 1943. So we can have an equivalent of the Spit XII a full year earlier?

If I may return at the post by SHvak:

What's the point? USAAF needed a good high altitude fighter in the ETO, I don't think anything with a single stage engine would've cut it.

The thread is about allied usage of a plane, not only USAAFS's. Costumers include the RAF/CW, VVS etc.
Then, the USAAF in 1941-43 (and beyond, of course) needed a plane that would threat IJA/IJN opposition, and a Hayate-sized plane with R-2800 would've fit there just fine. Second area of interest is the MTO, not much of high flying duties there prior 1943, but plenty of under-20000 ft action. Just for such a fighter.

 

[Vincenzo]

R-2800 is large engine (imho too large only US can afford the price to build a fighter with it) i don't think that a hayate sized plane is enough

 

[tomo pauk]

The single stage R-2800 was needing less space, weighted less and was of lower price than the 2-stage R-2800; the turbo R-2800 was of course the king in weight, volume used cost. So the planes built around that version are bound to cost less than historical F4U (even of we make allowance for the wing folding other CV stuff), and far less than the P-47.
On the other hand, I'd venture to say that the other big radials, either US or other, were of similar price (BMW-801, ASh-82, plethora of Japanese engines, Hercules?), or at least coming until 90% of the R-2800 price. Ditto for the big inlines (Jumo 213, Griffon, Sabre), let alone the coupled engines. The plane with R-2800 can carry a decent bomb load, too, unlike some other 'erzatz' bombers that were proudly carrying a single 250 kg bomb.

 

[davebender]

Ju-87D routinely carried 1,000 kg. Powered by 1,340 hp Jumo 211 V12 engine.

 

[Shortround6]

.
Then, the USAAF in 1941-43 (and beyond, of course) needed a plane that would threat IJA/IJN opposition, and a Hayate-sized plane with R-2800 would've fit there just fine. Second area of interest is the MTO, not much of high flying duties there prior 1943, but plenty of under-20000 ft action. Just for such a fighter.

Good call on the Griffon.

You are not going to get a R-2800 into a Hayate sized airplane. The Homare engine was 2190 cu in (Wiki is wrong, figure the displacement yourself using the bore and stroke) but the engine was compact, about 6in smaller in diameter (smaller than an R-1830) with a frontal area of 11.8ft. even more importantly it was about 400lbs lighter than an R-2800-5. The R-2800 is about 21% heavier than the Homare.
You also have the US armament problem. A Hayate carried about 291KG worth of guns and ammo (gun accessories, ammo boxes and links not counted) A P-40E carried about 332 kg and a P-51D carried 385kg. Unless you use the R-2800 to carry just four guns you wind up with 30-90kg more in gun/ammo weight depending on length of firing time desired.
You need 12-20 more square feet of wing just for the dry weight of the engine and guns/ammo to keep the same wing loading of the Hayate let alone any additional structure needed for the larger, heavier engine and armament.

Hayate carried 697 liters (?) 184 US gallons of internal fuel. All but 217 liters in the wings. Bigger fuselage of the R-2800 plane may house fuel ( and no fuselage guns) displaced from wings by US wing gun installation.

Did the Japanese build to the same 12 "G" limit as the Americans?

The Grumman F8F-1 went 9,600lbs with 185 gallons of fuel, I don't think you are going to get much lighter than that. An R-2800 single stage can suck down 60-63 gallons of furl per hour at 1650-1700rpm and 33in MAP at 0-5000ft cruise. Max continuous can be as high 198GPH at 2400rpm and 42in MAP at 5000ft.

 

[Shortround6]

Ju-87D routinely carried 1,000 kg. Powered by 1,340 hp Jumo 211 V12 engine.

Ju-87Ds made P***-Poor fighters.

 

[davebender]

My point is you don't need an R-2800 engine to carry a heavy bomb load or to provide an aircraft with significant armor protection.

 

[Shortround6]

You do (or an engine in it's class) if you also expect the same plane to engage in air to air combat.

Title of thread is "1941/42: fighter with single stage R-2800, a missed opportunity?

NOT

"1941/42: CAS aircraft with single stage R-2800, a missed opportunity?"

 

[wuzak]

Did the USAAF know what they needed in 1941?

They were pushing the P-38 pretty hard - that was a high altitude fighter.
They had wanted the P-39 to be turbocharged.
The X/YP-37s were turbocharged.
They took the P-40 because it could be produced in numbers quickly.

I suppose the argument would be that a single stage R-2800 powered fighter could be converted to a 2 stage R-2800 powered fighter relatively easily?

 

[Shortround6]

Or not so easily depending on initial design. you need 15-20 cubic feet of space for the inter-coolers and ducts and such. 20 cubic ft is a space the entire diameter of the engine and about 15 in deep. You can't cram everything into such a space as you need gentile bends in teh ducts to get them to flow properly and even if you need closer to 15 cu ft than 20 that is a lot of space fairly close to the engine. And no, you can't use the space for fuel on a non-two stage engine

Inter coolers and ducts are full of air and while bulky don't weigh that much.

You either design a bigger than needed ( and poorer performing) fuselage/airframe to take the two stage installation later or you design a smaller tighter better performing aircraft for the single stage engine

 

[tomo pauk]

...
You are not going to get a R-2800 into a Hayate sized airplane. The Homare engine was 2190 cu in (Wiki is wrong, figure the displacement yourself using the bore and stroke) but the engine was compact, about 6in smaller in diameter (smaller than an R-1830) with a frontal area of 11.8ft. even more importantly it was about 400lbs lighter than an R-2800-5. The R-2800 is about 21% heavier than the Homare.
You also have the US armament problem. A Hayate carried about 291KG worth of guns and ammo (gun accessories, ammo boxes and links not counted) A P-40E carried about 332 kg and a P-51D carried 385kg. Unless you use the R-2800 to carry just four guns you wind up with 30-90kg more in gun/ammo weight depending on length of firing time desired.
You need 12-20 more square feet of wing just for the dry weight of the engine and guns/ammo to keep the same wing loading of the Hayate let alone any additional structure needed for the larger, heavier engine and armament.

Hmm, what's your take about the P-51 sized plane that has 1-stage R-2800, compared with, say, historical P-51D? Maybe the wing area of some 250 sq ft? 6 guns, 350 rpg? I'm not trying to have a plane doing 430 mph, but 400 seem within reach?

Hayate carried 697 liters (?) 184 US gallons of internal fuel. All but 217 liters in the wings. Bigger fuselage of the R-2800 plane may house fuel ( and no fuselage guns) displaced from wings by US wing gun installation.

250 gals internal should be fine for the 'Fat-51?', plus drop tanks? Again, I'm not trying to escort any bombers in Germany proper in 1941/42.

Did the Japanese build to the same 12 "G" limit as the Americans?

Don't think so.

The Grumman F8F-1 went 9,600lbs with 185 gallons of fuel, I don't think you are going to get much lighter than that. An R-2800 single stage can suck down 60-63 gallons of furl per hour at 1650-1700rpm and 33in MAP at 0-5000ft cruise. Max continuous can be as high 198GPH at 2400rpm and 42in MAP at 5000ft.

Thanks (time and again) for the figures.

 

[wuzak]

Hmm, what's your take about the P-51 sized plane that has 1-stage R-2800, compared with, say, historical P-51D? Maybe the wing area of some 250 sq ft? 6 guns, 350 rpg? I'm not trying to have a plane doing 430 mph, but 400 seem within reach?

So, you're looking for an aircraft with similar performance and size to the P-51A but with a single stage R-2800?

 

[tomo pauk]

Something like that; the resulting plane is to be as fast on military power (15 min rating) as it was the P-51A on WEP (5 min rating), some 2 years earlier. Or, it's performance should be somewhere between FW-190s with BMW-801Cs/restricted 801Ds and un-restricted 801Ds (restriction removed in Autumn 1942). Or, similar to the Spit XII, but 18 months earlier.

 

[wuzak]

Surely "2 years earlier than P-51A" is quite a bit earlier than "18 months earlier than the Spit XII"? If it is the latter then the performance will be at about the same time as the P-51A?

Of course, if they don't particularly want the P-51A at the time, would they want the R-2800 equivalent?