Fast bomber for USAAC: how would've you done it?

[tomo pauk]

Let's see.

Kurt Tank added a plug and changed engines to the Fw 190 and created the Ta-152.

More a case of a new wing, than just adding a plug, for the Ta-152.

They added length to create the Spitfire 21.

No great shakes re. result achived - maybe better handling?

They changed engines from the B-29 to the B-50 or KB-50. They added a plug to so many airliners I can't count them ... and changed engines and props. The DH 7 turned into the DH 8. They changed the tail on the B-17. They stretched the Do-17 into the Do-217. They added a second fuselage to the P-51 and made the P-82, and the Germans made a twin Bf 109 and a twin He-111. They added plugs to the C-141 and Boeing 747, DC-9, DC-8, and the Piper Cherokee to create the Cherokee Six. They added plugs to the U-2 or create the TR-2. They turned the Manchester into the Lancaster with plugs and extra engines.

I'll reiterate: the A-20 was already a big brother of the DB-7, that received a beefed-up structure U/C, enlarged fin, new much heavier powerplant, ever incresing fuel tankage, the tanks themselves receiveing protection, increased the number and size of guns, eventually receiving the turret.
The B-50 also endured installation of bigger tail, longer nacelles, plus internal strengthening that 3-wievs don't talk about. The B-17 never went in service use with engines other than Cyclones - no much need for substantial changes. The Do-217 was a completely new A/C, not a variant of the Do-17. The P-82 was not two Mustangs mated together, the fuselage was different. Twin 109 is something else than a 109 with wing and fuselage extensions, new engines, new fin, new U/C, like you propose for the A-20. The twin He-111 served a different purpose than usual He-111.

Many airliners have different engines and the same airframe.

The list is LONG and distinguished ... and you say they could NOT do it with the A-20?

Covered above - A-20 was already a redesign of existing A/C.

What the heck are you thinking? And why?

Make your case. I say it was EASILY possible and quite probable that the goals could have been met.

Greg, don't loose any sleep over my disagreement with you. I've made my case, two times now.

 

[wuzak]

Hi Wuzak,

People are telling me it can't be done.

Bullshit.

It CAN be done. You are all just trying VERY hard to find reasons why it it was impossible. It WAS possible, and not with more effort than designing an entirely new aircraft. Try thinking of how it CAN be done rather than why it can't.

You naysayers just piss me off and I would fire the lot of you rather than miss a contract for an improved aircraft. The goal is to DO it, not find reasons why you can't. In real history it wasn't done, but that doesn't stop you from postulating all sorts of "what ifs" that are WAY more unlikely than creating a fast bomber from the A-20 via modifications to a plane that was a 340 mph plane to START with.

Geez.

I'd fire you if I were the commander. Tell me how it CAN be done, not why it can't. In real life, they went with the A-26, but it certainly COULD have been done differently.

I fully realize it wasn't. If we want to talk reality only, why are there so many alternate timeline and alternate history threads?

Greg, I'm not saying it can't be done, just asking if it is preferred to doing a new aircraft, and why.

If I understand your premise correctly, you are choosing to upgrade the A-20 with bigger, more powerful engines. R-2800s, presumabl

The increased span I understand is to allow greater take-off loads, and thus more equipment/more armour/bigger bomb loads. And hold more fuel.

I don't understand the need for a longer fuselage. Is it to hold a bigger or second bomb bay? Or is it a counter-weight to the heavier engines?

I think you also mentioned using turbos. Could these be positioned to counter-act the heavier engines, or is that part of the weight equation that requires the fuselage extension?

I take it the whole idea here is to upgrade the A-20 in quick time?

 

[Shortround6]

When both A-20 and A-26 were carrying 4000 lbs of bombs, the A-26 carried 900 US gallons of internal fuel, vs. 400 gals in the A-20. The A-26 also carried twice the number of machine guns, even before additional ones were installed under the wings or within them.

A few minor corrections if I may, A-20 carried 2000lb inside and 2000lb outside under the wings in later versions. A-26 carried 4000lb inside and 2000lb outside under the wings, for 6000lb total.

A-26 was also designed to carry a 75mm cannon in the nose although few were built with it. It is featured rather prominently in the early pilots manual though.

A-26 helped handle the greater landing weight not only with the larger wing, 540 sq ft instead of 465 sq ft, but by using a different flap system. I don't know if the flap system or the new airfoil or simply greater weight (or a combination) called for the change to the two spar wing structure.

I would also note that the A-26 was being designed and built in prototype form well before the A-20 was ever given .50cal mg in any positions and well before the A-20 got the under wing racks that boosted the short range bomb load to 4000lbs. A-26 was also designed to hold TWO torpedoes although the capability was never used.

 

[Shortround6]

A few figures for late war A-20, B-26, B-25 and A-26.


...........................................A-20G...............B-26B..................B-26J....................A-26B

Combat max gross..................27,000lb............36,500lb...............35,000lbs..............35,000lb
Normal internal fuel..................725 gal..............962gal..................974gal..................925gal
normal bomb load...................2000lb................3000lb..................3000lb..................4000lb
max internal bomb load............2000lb................4000lb..................4000lb..................4000lb

Max continuous power at max combat gross weight at 12,000ft

True air speed........................314mph..............287mph.................275mph................334mph
range SM..............................690 miles............550miles.................750miles...............780miles
Fuel burn GPH........................290....................398.......................319.....................386

Normal power at overload max gross weight at 12,000ft (includes warm up and climb)

True air speed........................264mph..............238mph.................245mph................296mph
range SM..............................1050 miles...........810miles................1120miles.............1365miles
Fuel burn GPH........................140....................240.......................205.....................209

Max range at overload max gross weight at 12,000ft (includes warm up and climb)*


True air speed........................233mph..............210mph.................215mph................255mph
range SM..............................1410miles........... 1090miles..............1510miles.............1710miles
Fuel burn GPH........................110....................149.......................135.....................139

* some planes numbers are not at 12,000ft but at 9,000 or 10,000ft as they were available.

Figures are from the Crowood book on the A-20 by Scott Thompson.

 

[tomo pauk]

Have yourself a bacon, it was way overdue Trying to make a formatted post on the forum is a b!tch, many thanks for that.

 

[Shortround6]

Thank you Tomo. I was rather struck by the advancement in speed/range of the A-26 compared to the other 3 aircraft. Due, I believe, almost entirely to the advancement of aeronautics (air foil, wing size/flaps and drag reduction) in just the few years between the planes, the first 3 being from 1938/39.

 

[tomo pauk]

Could you please check out the range and fuel burn rate for the B-26B, seems way more fuel hungry than B-26J? Was the B-26B from the table outfitted with bigger or smaller wing? What were the engines installed and power settings used?

The A-26 also have had a wing that was not just more advanced, but of smaller size than of either of the B-26s. Cuts plenty of drag - improves mileage?

 

[Shortround6]

Just getting the numbers from the table in the book. The B-26B was in production from May of 1942 until Feb of 1944 and the different production block numbers cover quite a number of changes (bigger wing was introduced on the B series with the -10-ma block, after it was introduced on the C series), different engines and different gross weights.

This chart from Zeno's http://zenoswarbirdvideos.com/Images/B-26/B-26FOIC.pdf

shows a fuel burn of 330gph at 10,000ft for 271mph and 368gph at 15,000ft for 285mph but this is for a B-1 with small wing, no cheek guns. The Manual shows speeds as low as 278mph at 15,000ft for the same 368gph in the 36,000-39,000lb weight range to a high of 300mph at same height and fuel burn but at a weight of 23400-27,000lbs.

Perhaps the 398 gallons an hour is a typo and should be 368 (number flipped?) but the Martin B-26 still gets the worst fuel mileage. The 238mph for 240gph is within a couple of MPH and Gallons per hour of the manual for the weight class.

 

[tomo pauk]

Here is the chart for the early B-26s (small wing, R-2800-5 engines). Manual can be downloaded at Willaim's site; scroll down: link.

I'm sure that B-26 will get the worst fuel mileage, just the numbers for the B-26B seem in too big a disadvantage vs. B-26J

 

[Koopernic]

A few figures for late war A-20, B-26, B-25 and A-26.


...........................................A-20G...............B-26B..................B-26J....................A-26B

Combat max gross..................27,000lb............36,500lb...............35,000lbs..............35,000lb
Normal internal fuel..................725 gal..............962gal..................974gal..................925gal
normal bomb load...................2000lb................3000lb..................3000lb..................4000lb
max internal bomb load............2000lb................4000lb..................4000lb..................4000lb

Max continuous power at max combat gross weight at 12,000ft

True air speed........................314mph..............287mph.................275mph................334mph
range SM..............................690 miles............550miles.................750miles...............780miles
Fuel burn GPH........................290....................398.......................319.....................386

Normal power at overload max gross weight at 12,000ft (includes warm up and climb)

True air speed........................264mph..............238mph.................245mph................296mph
range SM..............................1050 miles...........810miles................1120miles.............1365miles
Fuel burn GPH........................140....................240.......................205.....................209

Max range at overload max gross weight at 12,000ft (includes warm up and climb)*


True air speed........................233mph..............210mph.................215mph................255mph
range SM..............................1410miles........... 1090miles..............1510miles.............1710miles
Fuel burn GPH........................110....................149.......................135.....................139

* some planes numbers are not at 12,000ft but at 9,000 or 10,000ft as they were available.

Figures are from the Crowood book on the A-20 by Scott Thompson.

Thanks for that data. I recall that a "Wings" magazine edition had an article on the B-26 development in which it was stated that the B-26 when powered by a turbo supercharged R-2600 was expected to sustain a speed of 400mph. The development of this engine "fell through the roof".

Now consider replacing the single stage two speed R-2800 on the B-26 with a turbo charged variant. The Turbo R-2800 can maintain full power to 25,000ft whereas I expect a R-2800 would start falling of at 12000 feet with a rapid decline from 20,000ft. (I have no data on this latter engine Im taking an educated guess).

At 12000ft air pressure is down to 0.66 atmospheres (with the R-2800 gear driven version already loosing power)
At 25000ft air pressure is down to 0.30 atmospheres

Hence an turbo R-2800 equipped B-26 at 25000ft, with 2000hp, would experience considerably less than half the parasitic drag at 250000ft tahn at 12000ft but have 5%-10% more power. I reckon that should equate to a 25% increase in speed using a cube root law which for the early 305mph version of the Marauder would take it to 380mph. At 25000ft it would have been able to outrun most fighters of the day. As PW R-28000 Gains in power would increase speed.

The B-26 could carry the same load as the B-17 but for less distance and less altitude. A turbo charged B-26 could've carried the same load as the B-17, at the same altitude but at speed so high interception was unlikely, and remember this is still and armed bomber. I suggest a pair of 150 gallon drop tanks would allow such a B-26 to penetrate all the way to Berlin at a sustained high speed.

It has to be remembered that when the Mosquito entered service that it was actually slower than contemporaneous Me 109G1/G2 or even Me 110G1. What made the Mosquito effective was the two stage two speed Merlin which boosted the speed of both the Spitfire IX and Mosquito to slightly beyond that of the standard German fighters at high altitude. That's for the pathfinder and PRU versions. The low altitude Fighter Bombers received single stage supercharged engines with supercharger impellers and gearing tailored to low altitude work (at the expense of high altitude work).

A US 'fast bomber' would require similar tailoring: a specialized high altitude engine, which the US was the world leader in. It should also be recognized that some of the Mosquito's speed was a result of the use of WEP (War Emergency Power) which was highly developed in the Merlin engine and such WEP systems would also need to be developed for US aircraft.

The Germans had some very advanced high altitude work but they were faced with dealing with insufficient high octane fuel (their C3 fuel) and dealing with an incredible range of scenarios both in the West and East that limited their ability to handle all situations well.

 

[m37b1]

Thanks for that data. I recall that a "Wings" magazine edition had an article on the B-26 development in which it was stated that the B-26 when powered by a turbo supercharged R-2600 was expected to sustain a speed of 400mph. The development of this engine "fell through the roof".

Now consider replacing the single stage two speed R-2800 on the B-26 with a turbo charged variant. The Turbo R-2800 can maintain full power to 25,000ft whereas I expect a R-2800 would start falling of at 12000 feet with a rapid decline from 20,000ft. (I have no data on this latter engine Im taking an educated guess).

At 12000ft air pressure is down to 0.66 atmospheres (with the R-2800 gear driven version already loosing power)
At 25000ft air pressure is down to 0.30 atmospheres

Hence an turbo R-2800 equipped B-26 at 25000ft, with 2000hp, would experience considerably less than half the parasitic drag at 250000ft tahn at 12000ft but have 5%-10% more power. I reckon that should equate to a 25% increase in speed using a cube root law which for the early 305mph version of the Marauder would take it to 380mph. At 25000ft it would have been able to outrun most fighters of the day. As PW R-28000 Gains in power would increase speed.

The B-26 could carry the same load as the B-17 but for less distance and less altitude. A turbo charged B-26 could've carried the same load as the B-17, at the same altitude but at speed so high interception was unlikely, and remember this is still and armed bomber. I suggest a pair of 150 gallon drop tanks would allow such a B-26 to penetrate all the way to Berlin at a sustained high speed.

It has to be remembered that when the Mosquito entered service that it was actually slower than contemporaneous Me 109G1/G2 or even Me 110G1. What made the Mosquito effective was the two stage two speed Merlin which boosted the speed of both the Spitfire IX and Mosquito to slightly beyond that of the standard German fighters at high altitude. That's for the pathfinder and PRU versions. The low altitude Fighter Bombers received single stage supercharged engines with supercharger impellers and gearing tailored to low altitude work (at the expense of high altitude work).

A US 'fast bomber' would require similar tailoring: a specialized high altitude engine, which the US was the world leader in. It should also be recognized that some of the Mosquito's speed was a result of the use of WEP (War Emergency Power) which was highly developed in the Merlin engine and such WEP systems would also need to be developed for US aircraft.

The Germans had some very advanced high altitude work but they were faced with dealing with insufficient high octane fuel (their C3 fuel) and dealing with an incredible range of scenarios both in the West and East that limited their ability to handle all situations well.

DING!!!

 

[mhuxt]

It has to be remembered that when the Mosquito entered service that it was actually slower than contemporaneous Me 109G1/G2 or even Me 110G1.

How fast did the Me 110G1 go?

 

[GrauGeist]

Thanks for that data. I recall that a "Wings" magazine edition had an article on the B-26 development in which it was stated that the B-26 when powered by a turbo supercharged R-2600 was expected to sustain a speed of 400mph. The development of this engine "fell through the roof".

Now consider replacing the single stage two speed R-2800 on the B-26 with a turbo charged variant. The Turbo R-2800 can maintain full power to 25,000ft whereas I expect a R-2800 would start falling of at 12000 feet with a rapid decline from 20,000ft. (I have no data on this latter engine Im taking an educated guess).

At 12000ft air pressure is down to 0.66 atmospheres (with the R-2800 gear driven version already loosing power)
At 25000ft air pressure is down to 0.30 atmospheres

Hence an turbo R-2800 equipped B-26 at 25000ft, with 2000hp, would experience considerably less than half the parasitic drag at 250000ft tahn at 12000ft but have 5%-10% more power. I reckon that should equate to a 25% increase in speed using a cube root law which for the early 305mph version of the Marauder would take it to 380mph. At 25000ft it would have been able to outrun most fighters of the day. As PW R-28000 Gains in power would increase speed.

The B-26 could carry the same load as the B-17 but for less distance and less altitude. A turbo charged B-26 could've carried the same load as the B-17, at the same altitude but at speed so high interception was unlikely, and remember this is still and armed bomber. I suggest a pair of 150 gallon drop tanks would allow such a B-26 to penetrate all the way to Berlin at a sustained high speed.

It has to be remembered that when the Mosquito entered service that it was actually slower than contemporaneous Me 109G1/G2 or even Me 110G1. What made the Mosquito effective was the two stage two speed Merlin which boosted the speed of both the Spitfire IX and Mosquito to slightly beyond that of the standard German fighters at high altitude. That's for the pathfinder and PRU versions. The low altitude Fighter Bombers received single stage supercharged engines with supercharger impellers and gearing tailored to low altitude work (at the expense of high altitude work).

A US 'fast bomber' would require similar tailoring: a specialized high altitude engine, which the US was the world leader in. It should also be recognized that some of the Mosquito's speed was a result of the use of WEP (War Emergency Power) which was highly developed in the Merlin engine and such WEP systems would also need to be developed for US aircraft.

The Germans had some very advanced high altitude work but they were faced with dealing with insufficient high octane fuel (their C3 fuel) and dealing with an incredible range of scenarios both in the West and East that limited their ability to handle all situations well.

After all that reworking and rebuilding on the B-26 and when would it have been available?

The XB-28 would have been production ready before the B-26 and it was faster than the B-26, flew higher than the B-26 and could carry the same max. load as the B-26 with a range of nearly 900 miles further than the B-26.

With it's pressurized cabin, the XB-28 had a service ceiling of 34,800 feet compared to the B-26's 21,000 feet.

The XB-28's top speed of 370mph (nearly 90mph faster than the B-26) at 25,000 feet might not have been as impressive as a Mosquito, but was one of the fastest fully armed, turreted, twin-engined bombers available.

 

[Koopernic]

"On the Fw 190D and Ta 152 series it was to restore CoG."
The tail plug ( few inches, only 8 inches, ahead of the empenage) was as you say to help restore C of G as well as aerodynamic center given the longer (but lighter) Jumo 213 or DB603 engine.
The additional fuselage 'plugs' on the Ta 152 allowed a larger wider chord wing to be fitted as well as a massive increase in fuel and other liquids (MW50, GM-1) nevetheless the Ta 152 and Fw 190 shared a great many parts and metal work profiles to the extent that the larger Ta 152 tails started appearing on Fw 190. There are big gains in reusing parts in this way, even 70% reuse is of benefit in both design and production)

Spitfire never received a plug, the only fuselage mod was the heightened pointy tail, it was so stable to begin with. Counter weighting and parts redistribution was used to balance C of G. For Focke-Wulf the change from radial to liquid cooled was probably more radical than the addition of the two stage Merlin and then Griffon to the Spitfire IX and XIV respectively.

 

[Koopernic]

How fast did the Me 110G1 go?

In the G series the DB601E engine was replaced by the slightly modified (it was a new engine but you could say it was bored out since piston centers were the same) DB605A with a few other minor refinements. An armed Me 110G1 could manage 370mph which I believe was almost the same speed as an unarmed Mosquito with the single stage Merlin. A PRU Mosquito could manage 386mph while a bomber version (unarmed) 382mph. Take the guns and armour of the Me 110 and put guns on the Mosquito the speed advantage would reverse. An armed Me 109G1 could manage 400.5 mph with that same engine but fell over the year due to weight and drag increases to 386mph before climbing again in late 43 to 1944 to 440mph as improved engines came in. They entered service in the first few months of 1942. The Mosquito entered service with the single stage Merlin, it soon received more capable engines. Rolls Royce produced many different variants of the Merlin optimized for different missions, at the specific altitude they were optimized for they were unbeatable. Think of it this way, the Luftwaffe might have a fighter in the area where Mosquito were operating but they might need Fw 190 to have half a chance at intercepting a low altitude bombing run and a GM-1 equiped 109 for a high altitude attack. A Luftwaffe fighter equipped with radar was simply too slow.

The Me 110 by this time was turning into a pure night fighter (actually one of its initial design missions) but was much slower when equipped with radar. The Me 110 could haul a very heavy bomb load, 4400lbs, but it lacked a bomb bay to keep speed up unless a very light load and was short ranged though it could carry rather large drop tanks, (the Me 210/410 did have a bomb bay, which is why they were developed).

The Germans to a degree simply got caught out on high altitude engines. After the two stage Merlin's came in their only hope was GM-1 equipped Me 109.

Of course it doesn't take much of a speed advantage to cut interception chances.

 

[wuzak]

A production Mosquito F.II was tested at Boscombe Down at 358mph with a matt black finish and 366mph with a smooth black finish.It was fitted with the standard armament of 4 x 0.303" and 4 x 20mm.

The exhaust fitted was one of the early types - not the later ejector exhaust system.

 

[mhuxt]

Thanks, had never heard of a 110 G-1 before.

I suppose there's also the issue of which is faster at which other's rated altitude, and who sees whom first.

 

[fastmongrel]

The development of this engine "fell through the roof".

What happened did it fall off the plane.

 

[tomo pauk]

"On the Fw 190D and Ta 152 series it was to restore CoG."
The tail plug ( few inches, only 8 inches, ahead of the empenage) was as you say to help restore C of G as well as aerodynamic center given the longer (but lighter) Jumo 213 or DB603 engine.
The additional fuselage 'plugs' on the Ta 152 allowed a larger wider chord wing to be fitted as well as a massive increase in fuel and other liquids (MW50, GM-1) nevetheless the Ta 152 and Fw 190 shared a great many parts and metal work profiles to the extent that the larger Ta 152 tails started appearing on Fw 190. There are big gains in reusing parts in this way, even 70% reuse is of benefit in both design and production)

The incerese of the fuel tankage was due to installing the new tanks between the wing spars. The wing fuel tanks were also specified for some versions of later Fw-190Ds. Main benefit (intended?) of the increased volume between firewall and engine was the capability to have a powerful central battery installed, as it was the case for the Ta-152C - three cannons (and their ammo, of course) in fuselage.

Spitfire never received a plug, the only fuselage mod was the heightened pointy tail, it was so stable to begin with. Counter weighting and parts redistribution was used to balance C of G. For Focke-Wulf the change from radial to liquid cooled was probably more radical than the addition of the two stage Merlin and then Griffon to the Spitfire IX and XIV respectively.

When V-12s were installed on the 'basic' Fw-190 fuselage, they added also the cooling systems at the extreme front. In Spitfire, a good deal of the increased engine weight was counter-balanced by installation of bigger heavier radiators behind the CoG.

 

[tomo pauk]

Helo, Koopernic,

...
Now consider replacing the single stage two speed R-2800 on the B-26 with a turbo charged variant. The Turbo R-2800 can maintain full power to 25,000ft whereas I expect a R-2800 would start falling of at 12000 feet with a rapid decline from 20,000ft. (I have no data on this latter engine Im taking an educated guess).

At 12000ft air pressure is down to 0.66 atmospheres (with the R-2800 gear driven version already loosing power)
At 25000ft air pressure is down to 0.30 atmospheres

I too do feel that the B-26 would do better with greater power. The 2 turbos per A/C would add quite a bit of weight, however - around 2 x 800 lbs, judging by weight distribution of the P-47. The B-26 was already at the limits of the weight loading. Some weight should be cut by reducing armament and crew, but not all 1600 lbs?
The 2-stage R-2800 should offer better performance than turbo up to 20000 ft, and comparable between 20-25000 ft? Much smaller weight penalty, circa 2 x 300 to 2 x 400 lbs - easier to balance out with reduction of guns and crew.

Hence an turbo R-2800 equipped B-26 at 25000ft, with 2000hp, would experience considerably less than half the parasitic drag at 250000ft tahn at 12000ft but have 5%-10% more power. I reckon that should equate to a 25% increase in speed using a cube root law which for the early 305mph version of the Marauder would take it to 380mph. At 25000ft it would have been able to outrun most fighters of the day. As PW R-28000 Gains in power would increase speed.

The early B-26s were good for 325 mph, admittedly at not max weights?

The B-26 could carry the same load as the B-17 but for less distance and less altitude. A turbo charged B-26 could've carried the same load as the B-17, at the same altitude but at speed so high interception was unlikely, and remember this is still and armed bomber. I suggest a pair of 150 gallon drop tanks would allow such a B-26 to penetrate all the way to Berlin at a sustained high speed.

Maybe install some fuel tanks in the aft bomb bay, or use some space where the navigator and radioman were?

It has to be remembered that when the Mosquito entered service that it was actually slower than contemporaneous Me 109G1/G2 or even Me 110G1. What made the Mosquito effective was the two stage two speed Merlin which boosted the speed of both the Spitfire IX and Mosquito to slightly beyond that of the standard German fighters at high altitude. That's for the pathfinder and PRU versions. The low altitude Fighter Bombers received single stage supercharged engines with supercharger impellers and gearing tailored to low altitude work (at the expense of high altitude work).

The single stage engines in the Mossie were not specially tailored for low altitude. The Merlins XX, 21, 23, 31 and 32 were 'normal' Merlins, that gave better power at altitude than single stage V-1710s. The WER (over boosting due to ever better fuel) was only available at altitudes 'under' the FTH, though.

A US 'fast bomber' would require similar tailoring: a specialized high altitude engine, which the US was the world leader in. It should also be recognized that some of the Mosquito's speed was a result of the use of WEP (War Emergency Power) which was highly developed in the Merlin engine and such WEP systems would also need to be developed for US aircraft.

Interestingly enough, the single stage R-2800 did not received water-alcohol injection (ADI) until the 'C' series of engines, ie. too late for ww2. The turbo and 2-stagers were equipped with ADI from late 1943/early 1944. No ADI = no WER for US radials.
The V-1710s were allowed for WER without ADI (= WER dry), officially from mid 1942 on. Depending on version, altitude and time, the WER was between 1400 and 1600 HP.

The Germans had some very advanced high altitude work but they were faced with dealing with insufficient high octane fuel (their C3 fuel) and dealing with an incredible range of scenarios both in the West and East that limited their ability to handle all situations well.

Seems like the Germans embarked into the 2-stage bandwagon too late. Big engines, decent RPM, intercoolers and MW-50 should enable good high altitude performance even on the B4 fuel.