Fast bombers alternatives for 1939-40

[Art Medcalf]

Jug man,
But the V-1710 was rated 1425 T/O AND 1425 @ 24, 900' (WE 1600 @ 27,000'). What were the R-2600 ratings at those altitudes, which were possibly close to actual combat altitudes?
ArtieBob

 

[wuzak]

V-1710-91/R-1820/R-2600B
TO/ mil power
1425, 1200, 1700
Normal rated
1100, 1000, 1500
Max lean cruise
795, 750, 1125

Above 23'000ft or so the B-17 had to cruise in auto-rich in order to produce enough power to maintain a suboptimal cruise profile. The V-1710 doesn't offer enough improvement to change this fact.
The negative effects of climb on range is another consideration. Like all the other ETO heavies, the B-17 doesn't have enough power to climb straight to altitude at the higher take-off weights efficiently. Proper step-climb and/or cruise-climb procedures can alleviate this to some extent but it's obviously not that viable when most of your flying is over enemy territory.

A 10% increase in rated power is definitely helpful. But once again the R-2600 offers a 50% boost.

For a long range bomber cruising speed is very important. Not only does it reduce total exposure time, it increases the the area in which the bomber can be at any given moment. The V-1710 doesn't give any meaningful advantage over the R-1820. The R-2600 does.

The V-1710 offers weight savings and drag reduction compared to the R-2600.

The V-1710 was paired with the B-series turbo in the P-38, as was the R-1820 in the B-17.

Could an R-2600 use the B-series turbo, or would it need an upgrade to the larger C-series (as was paired with the R-2800 in the P-47)?

Without the turbo, the R-2600-13 or -29 in a B-25 had the following ratings:

T/O: 1,700hp @ 2,600rpm.
Military (2,600rpm): 1,700hp @ 4,500ft
1,450hp @ 12,000ft
Normal (2,400rpm): 1,500hp @ 6,700ft
1,350hp @ 13,000ft

https://www.wwiiaircraftperformance.org/B-25/B-25J_Characteristics_Summary.pdf

Below 4,500ft the R-2600 has up to 275hp advantage over the V-1710, between 4,500ft and 12,000ft the R-2600's advantage is ~25hp..

From an altitude just above 12,000ft the R-2600 is at the disadvantage.

Possibly the biggest detriment to cruising speed was the need for formation flying. With fewer guns, and the aim of high speed bombing, such formations would not be used.

 

[wuzak]

Perhaps another type that could have been pushed into a high speed bomber role is the Martin B-26.

Its speed dropped with the increase in wing area and change in wing incidence angle, plus weight from additional equipment.

Lose some weight (fewer guns/crew) and keep the smaller wing. Change to turbocharged R-2800 for medium/high altitude operation, stay with non-turbo if intended for low altitude operation.

 

[Steamed_Banana]

The A-20A made 350 mph in 1941. That is pretty fast.

 

[Shortround6]

The A-20A made 350 mph in 1941. That is pretty fast.

Quite true.
The problem in 19340 was extending the range or expanding the bomb load. Or indeed getting a plane of such performance into squadron service in 1940 and not prototypes.
The A-20 used the same engines right up until the last planes built in 1944 and they did add to the fuel load significantly. They did add to bomb load but they did it by using underwing bombs which hurt speed. Perhaps they could have juggled the bomb bay fuel tanks for more internal storage and used drop tanks or fuel in the outer wings?

 

[Steamed_Banana]

Quite true.
The problem in 19340 was extending the range or expanding the bomb load. Or indeed getting a plane of such performance into squadron service in 1940 and not prototypes.
The A-20 used the same engines right up until the last planes built in 1944 and they did add to the fuel load significantly. They did add to bomb load but they did it by using underwing bombs which hurt speed. Perhaps they could have juggled the bomb bay fuel tanks for more internal storage and used drop tanks or fuel in the outer wings?

The ultimate version of the A-20 was a different plane, the A-26, also pretty fast. That gives you the bomb load, extra range, a second pilot, armor and ss fuel tanks, and heavy defensive armament.

But prior to that they did develop A-20 variants which were only a little slower than the A-20A, had reasonable fuel and range, and still handled really well. Bomb load was never huge especially internally, but I'm always an advocate of precision over simple weight of ordinance. Fast and agile seemed to translate to fairly accurate in the case of this one. It wasn't a dive bomber but it could do low-level attacks, and also worked pretty well as a strafer.

The 1940 version was apparently flying just barely in time for the last few days of the Battle of France, got 70 of them to North Africa which then flew across the Med to France, and seem to have flown about one sortie each. But that variant (DB-7 B-3) had smaller engines (R-1830s) and a lot less fuel. Probably still pretty useful, I think it would be hard for German fighters to shoot down.

 

[Shortround6]

The ultimate version of the A-20 was a different plane, the A-26, also pretty fast. That gives you the bomb load, extra range, a second pilot, armor and ss fuel tanks, and heavy defensive armament.

But prior to that they did develop A-20 variants which were only a little slower than the A-20A, had reasonable fuel and range, and still handled really well. Bomb load was never huge especially internally, but I'm always an advocate of precision over simple weight of ordinance. Fast and agile seemed to translate to fairly accurate in the case of this one. It wasn't a dive bomber but it could do low-level attacks, and also worked pretty well as a strafer.

The 1940 version was apparently flying just barely in time for the last few days of the Battle of France, got 70 of them to North Africa which then flew across the Med to France, and seem to have flown about one sortie each. But that variant (DB-7 B-3) had smaller engines (R-1830s) and a lot less fuel. Probably still pretty useful, I think it would be hard for German fighters to shoot down.

The early A-20/DB-7 story is rather confusing. The Prototype, which crashed with a French observer aboard, was powered with P&W R-1830s and that is what the French ordered (different nose and canopy). Without cracking a book I can't remember if the French placed a 2nd order before anybody else got involved. I believe the British placed an order in the fall of 1939 (?) with R-1830 engines. The US took a 2nd look, they had not ordered any in the first months after the attack plane trials. Then they ordered the A-20 with the R-2600s and a beefed up wing, not larger, just stronger to handle the extra weight. At some point the Dutch got involved (Just before Holland failed) and sorting out the different models gets hard as a lot of them didn't go to the countries that ordered them.
The R-1830 versions were good for around 310mph give or take. There were several different versions of R-1830s used and the first ones the French got had single speed superchargers. Later ones (and British ) got 2 speed but since the British got some of the French left overs the British engine situation was a bit confused. The smaller engines didn't require as much fuel and the area of operations (France or cross channel) short range was not a big problem.
The US with the bigger, thirsty engines faced a problem.
The Douglas airplane was designed to use integral fuel tanks. The wing skin top and bottom was part of the fuel tank with other wing parts like ribs forming some of the other surfaces.
This style of fuel tank construction was all the rage in US design circles. Right up until somebody pointed out it wasn't a good idea for planes that got shot at.
The Original French aircraft held about 325-327 US gallons in two tanks. As did the early British planes. The American A-20s started with 4 tanks by adding an 87 gal tank to each wing for a total of 500 US gallons. BUT, only 16(?) were delivered that way. The rest got self sealing fuel cells placed in the area of the original fuel tanks but that dropped the fuel capacity to 400 US gallons. And that pretty much started the path to put more fuel in the upper bomb bay. Which was helped, in large part, by the size of the bomb bay because the US, in the 1930s was a big advocate for it's attack planes of not using precision bombing attacks. They were advocates of dropping large amounts (huge at times) of small 30lb bombs over a wide area while spraying with machine guns. One the French, British and finally the Americans decided they needed around four large bombs (250-500lb each) there was all this empty space in the top of the bomb bay they could fill with fuel tanks.
Keep note of this for "What Ifs" By the time the A-20 gets to the "G" series it is carrying 725 US gallons of fuel in internal tanks. It might have been a little faster with a skinner fuselage, less depth, if designed to hold four medium bombs at the start but then fitting the larger fuel tanks gets very hard. An A-20 bomb bay was only 28in wide at the top and 32in wide at the bottom but it was 62.5 in high. The bomb bay had been designed to load the small fragmentation bombs in tubes from the top of the aircraft.

The panel to the rear of the raised hatch/cover also hinges to the right. As time went on they filled the space with radio gear.
The US planes were also designed to hold two 600lb bombs or one 1100lb or in overload sixteen 100lb bombs.
Another case of the plane not being used as designed

 

[Steamed_Banana]

The predictive aspect of military aircraft design is really pretty... aspirational. And even more so for bombers and attack aircraft, arguably.

The issue with bomb-bays that were designed for ridiculously small bombs was almost universal in early war designs.

But the actual DB-7 / A-20s used in wartime were carrying a reasonable number of reasonably sized (250, 300 or 500 lbs etc.) bombs and hitting targets fairly often by WW2 standards, so it's good, especially considering that it could hit targets and survive to get back to base fairly often. So you could use the same plane tomorrow and the next day and the next, which improves the odds of destroying your target.

In both the Med and the South Pacific I believe they had a lower loss rate than the B-24s for example, even though well into 1943, they were flying these things with (mostly or completely) unprotected fuel tanks, barely any armor, and more or less token defensive guns. And only one pilot so if he was hit, the other two crew are SOL.

Speed kills, they say, but it also saves lives and airframes, it seems.

That's a great shot of that A-20... A-20A?

 

[Shortround6]

That's a great shot of that A-20... A-20A?

Not sure. I don't know what that exhaust stack is next to the air intake.
It does the extra cooling slots in the cowl that were used by many of the A-20s even without the turbo.
One book claims it was the 3rd airframe (?) but I have no idea of what the single digit number really means. Most other photos do not have it and one that does is supposed to be an A-20B as it rolls out of the Long Beech factory door.
You can find the slotted cowlings on a number of planes which does not help. One is a Boston III.
I have found a color photo of that plane with the crew in a slightly different positions.
caption says it is s/n 39-728, an A-20A and another photo shows no turbo.
That 'stack' might be some short of heat duct for de-icing?

 

[Shortround6]

The British, on their order, wanted a bit longer bomb bay to fit the long British 250lb bombs and the USAAC went along with it. Came in handy when the USAAC decided to go with four 500lbs. US bombs were a little fatter, with less taper and with shorter fins.

The US for some reason, didn't like 250lbs. That is to say they tended not use them once the supply of 300lb bombs were gone. They tended to jump right from 100lb to 500lbs.
The British hung plenty of 250lbs off not only their own fighters but the Tomahawks and Kittyhawks as well.

 

[Steamed_Banana]

Not sure. I don't know what that exhaust stack is next to the air intake.
It does the extra cooling slots in the cowl that were used by many of the A-20s even without the turbo.
One book claims it was the 3rd airframe (?) but I have no idea of what the single digit number really means. Most other photos do not have it and one that does is supposed to be an A-20B as it rolls out of the Long Beech factory door.
You can find the slotted cowlings on a number of planes which does not help. One is a Boston III.
I have found a color photo of that plane with the crew in a slightly different positions.
caption says it is s/n 39-728, an A-20A and another photo shows no turbo.
That 'stack' might be some short of heat duct for de-icing?

What happened to your previous post!?

 

[Steamed_Banana]

The British, on their order, wanted a bit longer bomb bay to fit the long British 250lb bombs and the USAAC went along with it. Came in handy when the USAAC decided to go with four 500lbs. US bombs were a little fatter, with less taper and with shorter fins.

The US for some reason, didn't like 250lbs. That is to say they tended not use them once the supply of 300lb bombs were gone. They tended to jump right from 100lb to 500lbs.
The British hung plenty of 250lbs off not only their own fighters but the Tomahawks and Kittyhawks as well.

Did Tomahawks actually carry bombs? i was trying to figure that out earlier and failed

 

[Howard Gibson]

Perhaps another type that could have been pushed into a high speed bomber role is the Martin B-26.

Its speed dropped with the increase in wing area and change in wing incidence angle, plus weight from additional equipment.

Lose some weight (fewer guns/crew) and keep the smaller wing. Change to turbocharged R-2800 for medium/high altitude operation, stay with non-turbo if intended for low altitude operation.

I proposed this on another thread. Behold the M26 Maraudaskito!

• 

Without gunners, the aircraft gets smaller, and quite a bit faster. The crew is two or three. Maybe there is a flexiable gun at the rear of the cockpit. I don't know much engineering it taker to get P47 style turbochargers on this thing, but de Havilland Mosquitos did lots of stuff at low altitudes.

 

[Shortround6]

Did Tomahawks actually carry bombs? i was trying to figure that out earlier and failed

I don't know. It is hard to even find a Tomahawk with the drop tank. I haven't seen a picture of one with bomb. Not saying they don't exist, just not in a quick google search.

 

[Steamed_Banana]

The problem with the B-26 was that it was so wide, it was designed for ten (!!!) crew. The Martin 187 Baltimore, made by the same company but sold to the French (abortively) and British, was much thinner and therefore also faster (over 300 mph) with (I think?) the same engines.

 

[Shortround6]

I proposed this on another thread. Behold the M26 Maraudaskito!

Might work in 1943
Maybe you can try an even smaller plane using the engines/turbos from a P-43?

 

[tomo pauk]

Might work in 1943
Maybe you can try an even smaller plane using the engines/turbos from a P-43?

The DB-7/A-20 sized & styled bomber, powered by turboed R-1830s/V-1710s should've been fast.

 

[Shortround6]

The problem with the B-26 was that it was so wide, it was designed for ten (!!!) crew. The Martin 187 Baltimore, made by the same company but sold to the French (abortively) and British, was much thinner and therefore also faster (over 300 mph) with (I think?) the same engines.

It was not designed for a crew of 10.
Maybe 6? Maybe 8 1/2?
The US was playing games with the crew size and weights but so were some other countries.

There are 10 crew positions listed in the manual for the early B-26s but then they lie and claim the normal gross weight for the B-26 and B-26A, is only 28,706 lbs and that includes the torpedo direct and wrench. Crew weigh is listed as 950lbs and the weights are listed for each crewman 3 men at 200lbs each, one at 180lbs and one at 170lbs (the gunner, position not given). Max load is 33,326lbs but a lot of that is the extra 997 gallons of fuel and the extra oil. Bomb load is four 500lb bombs.
Now how they were expecting the operate the aircraft with 5 men seems to have slipped through the cracks. There are 4 gun stations so either some are unmanned or you have crewmen, except for the pilot, running around like madmen trying to do their normal duties and get back the guns in time.
Now at this low weight the early B-26s was supposed to hit 323-326mph at 14,250ft. Trouble is you have 400 gallons at that weight (about 2000lbs less than gross or 400 gal and no bombs) and each engine sucks down 155 gallon an hour at that speed, granted nobody flies at that speed for very long.
Adding the "extra" crewmen cuts into the fuel and/or bombs or extra ammo.
So........
you want a bomb aimer/front gunner and leave the co-pilot in his seat? + 200lbs.
you want a radio operator and a top gunner at the same time? +200lbs
You want a dedicated tunnel gunner? +170lbs ?

So what did they think they were going to use for a crew?

 

[Steamed_Banana]

Interesting the speed for the early B-26 was that fast, that maybe explains why it seems to have done Ok in the South Pacific. The speed I always see for the (I guess later, wider winged) B-26 was more like 280 mph

 

[Shortround6]

Interesting the speed for the early B-26 was that fast, that maybe explains why it seems to have done Ok in the South Pacific. The speed I always see for the (I guess later, wider winged) B-26 was more like 280 mph

Yes, it was for the short, none tilted wing (That tilt hurt speed as much or more than the increased span did).
The performance figures are also done at an absurdly light weight.
Already pointed out the crew mismatch.
The planes could hold 962 gallons of fuel in the wing tanks. 100% is way to high but using 42% of fuel load to figure speed with?
Upper guns are weighed in at 200rpg. You could add in 120lbs (400 rounds ) as optional load. There was a single .50 cal in the tail with 200 round.
The Bow gun was a .30 cal as was the tunnel gun.
Now do you count the bomb weights in or out when figuring performance?
The normal gross counts 2000lbs of bombs which is 1/2 of max load Eight 500lbs or four 1000lb or 2 2000lbs bombs.
One reason the B-26 was "fat" is that it used the same width bomb bay as the B-17, just not quite as tall, only 3 500lbs in each stack in the forward bay.

Now the performance figures are for a weight at which either all bombs are gone and the plane is running for it's life with 400 gallons of fuel or it is carry a 2000lb load on the way in with about 67 gallons of fuel on board for two very thirsty engines = suicide run.

A lot of bomber performance specs are equally weird.