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Shortround6
Major General
Lets not forget the Halifax.
Oops, I somehow misread it that he meant the first to be designed with the Merlin, in which case it was the Battle. And the Lancaster, although if you count it as the Manchester Mk.III, then its still a Manchester. Also the Lincoln, although again, it could be read as the Lancaster Mk.IV...
- Thread starter
- #25
The USAF almost got their hands on a rather fast bomber with the A-20 (no suffix). It featured a turboed R-2600, and speed was estimated at 388 mph at 20000 ft. From Joe Baugher (in italics):
Only one aircraft was destined to be completed as an A-20. This was the first aircraft on the A-20 order (39-735). It was fitted with the turbosupercharged R-2600-7 engine which offered a power of 1700 hp at 20,000 feet.
However:
Unfortunately, the turbosupercharger installation was large and bulky, and the engines developed serious cooling problems.
Too bad the turbo installation was not sorted out, but then again the 'A' designation meant it was all about the low level performance.
The usual A-20s with single stage R-2600 were also good performers, 340+ mph for early versions.
With the wing strong enough to carry the heavy R-2600 and turbo (and wing bombs later), it is maybe too bad the non-turbo R-2800 was not installed. It would give much more power, especially above 13-14000 ft.
Only one aircraft was destined to be completed as an A-20. This was the first aircraft on the A-20 order (39-735). It was fitted with the turbosupercharged R-2600-7 engine which offered a power of 1700 hp at 20,000 feet.
However:
Unfortunately, the turbosupercharger installation was large and bulky, and the engines developed serious cooling problems.
Too bad the turbo installation was not sorted out, but then again the 'A' designation meant it was all about the low level performance.
The usual A-20s with single stage R-2600 were also good performers, 340+ mph for early versions.
With the wing strong enough to carry the heavy R-2600 and turbo (and wing bombs later), it is maybe too bad the non-turbo R-2800 was not installed. It would give much more power, especially above 13-14000 ft.
When Handley Page was allowed to change it's design to four engines (what would become the Halifax) the intended engine was the Merlin.
Avro was not permitted to develop a four engine design at the time and so persevered with the ill fated two engine Manchester-Vulture combination. Chadwick did continue with limited 'paper' development of a four engine version of the Manchester, but not at Air Ministry expense.
Cheers
Steve
Shortround6
Major General
You keep forgetting that high altitude power came with a cost.
This plane was about 5000lbs heavier empty than a B-25C/D yet had a max gross only about 3000lbs more.
Extra weight/bulk and drag of intercooler meant the plane will be slower at low altitudes. Bomb load wasn't any better. US also figured out that high altitude bombing wasn't all that it was cracked up to be real quick. Accuracy was much worse than medium altitude bombing. Needing more missions/sorties to get the same amount of bombs on target is going to require careful balancing to get the bombs on target per plane lost ratio the same or better than using the slower more vulnerable planes.
edit:
Going by the cube law it takes 3.375 times more fuel to travel at 300mph as it does 200mph. Since you are going 50% faster it does mean you are using 2.25 times the fuel per mile traveled. This is assuming planes of identical drag and engines that burn the same amount of fuel per hp per hr.
Going at 250mph vs 200mph you need to make 95% more power and will burn 56% more fuel per mile traveled.
By pulling turrets and guns you can reduce weight and drag and you can make the plane smaller but at some point you need a certain sized plane to hold the fuel and the Bomb load. The last part gets a bit tricky as you have to decide what kind of bomb load. 1 or 2 big (heavy) bombs? 4-10 medium bombs? lots of little bombs? Incendiaries that have a lot of bulk but not a lot of weight? that affects the size of the bomb bay.
Fast high up means either a bigger bomb load or more planes to make up for the poor accuracy. It also means a bigger plane to hold the high altitude supercharger set up/s.
Fast low down means more safety from AA but does mean the enemy has a better chance of using speed from diving to catch you. Navigation is a little ( or a lot) harder too.
Going fast for a 400 mile round trip (200mile radius) may not be hard at all, going fast for a 1200 mile round trip (600mile radius) is a lot harder.
How fast do you need to go in order to out run the enemy fighters (or at least make it very difficult for them) you may be able to get by being 10% slower or 15% but once you are considerably slower, say 30% or so does it matter much if you are 35% or 40% slower?
This plane was about 5000lbs heavier empty than a B-25C/D yet had a max gross only about 3000lbs more.
Extra weight/bulk and drag of intercooler meant the plane will be slower at low altitudes. Bomb load wasn't any better. US also figured out that high altitude bombing wasn't all that it was cracked up to be real quick. Accuracy was much worse than medium altitude bombing. Needing more missions/sorties to get the same amount of bombs on target is going to require careful balancing to get the bombs on target per plane lost ratio the same or better than using the slower more vulnerable planes.
edit:
Going by the cube law it takes 3.375 times more fuel to travel at 300mph as it does 200mph. Since you are going 50% faster it does mean you are using 2.25 times the fuel per mile traveled. This is assuming planes of identical drag and engines that burn the same amount of fuel per hp per hr.
Going at 250mph vs 200mph you need to make 95% more power and will burn 56% more fuel per mile traveled.
By pulling turrets and guns you can reduce weight and drag and you can make the plane smaller but at some point you need a certain sized plane to hold the fuel and the Bomb load. The last part gets a bit tricky as you have to decide what kind of bomb load. 1 or 2 big (heavy) bombs? 4-10 medium bombs? lots of little bombs? Incendiaries that have a lot of bulk but not a lot of weight? that affects the size of the bomb bay.
Fast high up means either a bigger bomb load or more planes to make up for the poor accuracy. It also means a bigger plane to hold the high altitude supercharger set up/s.
Fast low down means more safety from AA but does mean the enemy has a better chance of using speed from diving to catch you. Navigation is a little ( or a lot) harder too.
Going fast for a 400 mile round trip (200mile radius) may not be hard at all, going fast for a 1200 mile round trip (600mile radius) is a lot harder.
How fast do you need to go in order to out run the enemy fighters (or at least make it very difficult for them) you may be able to get by being 10% slower or 15% but once you are considerably slower, say 30% or so does it matter much if you are 35% or 40% slower?
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- Thread starter
- #28
A bomber with two-stage R-2800 would involve a far smaller weight penalty than it was the case with turbo R-2800. At medium altitudes it will provide more power than the 1-stage R-2800, 1800 HP up to 15500 ft vs. 1600 HP up to 13500 ft. I am not that sure that intercooler drag will be greater than sticking a pair of 2 'cheek' HMGs.
Granted, to take a full advantage of the 2-stage engine, something lighter more streamlined than B-26 should be an airframe.
Granted, to take a full advantage of the 2-stage engine, something lighter more streamlined than B-26 should be an airframe.
Shortround6
Major General
Tomo, it is not the size of the airscoops or bulges of the intercoolers.
model picture
It is the thousands of cubic feet of air per minute that have to flow through them and the matrix inside.
AS far as the B-26 goes, there were a LOT of changes made that slowed it down.
Spinners came off, Air intakes got bigger (to house sand filters), Wing changed size (before being tilted) Big wing was worth 7mph, and a larger fin and rudder were fitted. Blaming the Cheek guns for a major change in speed is giving them way to much credit (or blame?).
Later model B-26s picked up over 2000lbs empty weight over earlier ones. Operating weights went up by 5-8,000lbs.
model picture
It is the thousands of cubic feet of air per minute that have to flow through them and the matrix inside.
AS far as the B-26 goes, there were a LOT of changes made that slowed it down.
Spinners came off, Air intakes got bigger (to house sand filters), Wing changed size (before being tilted) Big wing was worth 7mph, and a larger fin and rudder were fitted. Blaming the Cheek guns for a major change in speed is giving them way to much credit (or blame?).
Later model B-26s picked up over 2000lbs empty weight over earlier ones. Operating weights went up by 5-8,000lbs.
- Thread starter
- #30
I'm not trying to blame the cheek guns. Both costumer and designer were trying to have a bomber that would came close to the 4-engined bombers in almost all categories, while using two (more powerful) engines. Accommodating 7 crew members in an un-cramped manner means a big fuselage = heavy fuselage etc. - I've covered this before.
Intercoolers are draggier than no intercoolers, but they contribute to engine power. A trade-off that is worth it.
Intercoolers are draggier than no intercoolers, but they contribute to engine power. A trade-off that is worth it.
Shortround6
Major General
They are not worth it if the plane is to operate at low altitudes. (and cheek guns are pretty useless at anything but on the deck). The B-26 was NOT designed for a 7 man crew, it was designed for a 5 man crew. I would note that a number of "fast" German bombers used 4 man crews and only one man was primarily a 'gunner' and the Germans were not using co-pilots. There was quite variety of shared crew tasks.
Designers were NOT trying to come close to a 4 engine bomber.
"In July of 1939, Boeing revised the design still further to produce the Model 334A. It eliminated the buried engine installation and the twin fin-and-rudder assembly of the Model 334 and replaced them with four conventionally-mounted Wright R-3350 radials and a single vertical tail. A high aspect ratio wing of 135 feet span was to be used. The Boeing proposal had finally begun to take the recognizable shape of what was eventually to emerge as the Superfortress"
"In January of 1940, the Army issued requirements for a "superbomber" with a speed of 400 mph, a range of 5333 miles, and a bomb load of 2000 pounds delivered at the halfway-point at that range. The official specification was revised in April to incorporate the lessons learned in early European wartime experience, and now included more defensive armament, armor, and self-sealing tanks. This became the basis for Request for Data R-40B and Specification XC-218. On January 29, 1940, the War Department formally issued Data R-40B and circulated it to Boeing, Consolidated, Douglas, and Lockheed."
It takes more time to design 4 engine bombers of over 100,000lbs than it does to design 2 engine bombers of 30-35,000lbs, especially if the 4 engine bombers are to be pressurized and have remote control gun turrets.
The B-24 was started a number of months before the B-25 and B-26 and was a response to a 1938 Army suggestion that Consolidated get ready to build B-17s under licence.
Shortround6
Major General
Fuselage cross section was more often determined by the size of the bomb bay.
B-26 could hold in the forward bomb bay.
2.........2000lb bombs
4.........1000lb bombs
6..........500lb bombs
10........300lb bombs
20........100lb bombs
the aft bombay could hold
2.......500lb bombs
6.......300lb bombs
10.....100lb bombs
When you start stacking bombs vertically you need to room to hoist them and then work around them to check latches/shackles, wire safeties and so on.
Picture of B-29 bomb bay'
B-26 bomb bay
late B-26s often operated with rear bay sealed and extra fuel tanks in place.
Mosquitoes carried 500lb bombs side by side with fuel tanks in the wing above the bomb bay.
BTW the B-26 manual says the cheek guns were worth 2% on range.
US 2000lb bomb was just of 23 in diameter (fins were bigger) and the B-26 used a rack system a bit like the B-17. Beams went up from the floor/walkway to the top of the fuselage with a passage way between them.
Some interior pictures of B-26 here: Inside a Martin B-26 Marauder.
Crew of B-26 could go to eight men.
Bombardier in nose.
Pilot and co-pilot in cockpit.
Radio operator and navigator in compartment behind cockpit and ahead of bomb bay.
3 gunners behind bomb bay, one manning the turret, one in the tail and one manning the lower/waist guns.
B-26 could hold in the forward bomb bay.
2.........2000lb bombs
4.........1000lb bombs
6..........500lb bombs
10........300lb bombs
20........100lb bombs
the aft bombay could hold
2.......500lb bombs
6.......300lb bombs
10.....100lb bombs
When you start stacking bombs vertically you need to room to hoist them and then work around them to check latches/shackles, wire safeties and so on.
Picture of B-29 bomb bay'
B-26 bomb bay
late B-26s often operated with rear bay sealed and extra fuel tanks in place.
Mosquitoes carried 500lb bombs side by side with fuel tanks in the wing above the bomb bay.
BTW the B-26 manual says the cheek guns were worth 2% on range.
US 2000lb bomb was just of 23 in diameter (fins were bigger) and the B-26 used a rack system a bit like the B-17. Beams went up from the floor/walkway to the top of the fuselage with a passage way between them.
Some interior pictures of B-26 here: Inside a Martin B-26 Marauder.
Crew of B-26 could go to eight men.
Bombardier in nose.
Pilot and co-pilot in cockpit.
Radio operator and navigator in compartment behind cockpit and ahead of bomb bay.
3 gunners behind bomb bay, one manning the turret, one in the tail and one manning the lower/waist guns.
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- Thread starter
- #34
The initial requirement was for the service ceiling to exceed 20000 ft. The front-firing guns were also useful for thwarting the head-on fighter attack.
It have had no problems accommodating the crew of 7, meaning that fuselage was a sizable one from get-go. The radioman's compartment was about as big as second bombs bay, or pilot's co-pilots compartment.
The B-17 was conceived to carry 1 ton (2000 lbs?) of bombs over 2000 miles. The same costumer wanted an aircraft with about same initial engine power (total) to beat that by 50%, ie. 3000 lbs over 2000 miles.
Shortround6
Major General
And here you run up against what different air forces thought what was needed for a crew. Was a copilot needed (British didn't use them on 4 engine bombers), was a dedicated navigator needed? was a dedicated radio operator? unless you can convince the USAAF that the answer is no the US is never going to fly a 2 seat bomber. (A-20 used a navigator-bombardier, a Pilot and the rear gunner was also the radio operator. Rear gunner also had emergency flight controls for a good part of production.
True but then the initial B-17 requirement was from In May of 1934, almost 5 years earlier than the B-26 requirement. First flight of the Model 299 took place on July 28, 1935. almost 5 1/2 years before first flight of the B-26 and as for power. " Four Pratt Whitney R-1690E S1EG Hornet radials rated at 750 hp at 2250 rpm at 7000 feet". The 299 only weighed 21,657 pounds empty, 32,432 pounds normal loaded and had 1420 sq ft of wing.
By 1937 they were delivering the Y1B-17s with Four Wright R-1820-39 Cyclone radials rated at 930 hp for takeoff, 850 hp at 5000 feet, 775 hp at 14,000 feet. and bombload/range had gone to "Range with 4000 pounds of bombs was 2400 miles and 3320 miles with no bombs".
By the summer of 1939 B-17s (just 3-4 months after the requirement for the B-26 is issued) are flying with 1200hp engines
trying to compare the requirement for the first "B-17" to the B-26 is like trying to compare the requirement for the P-35 with the requirement for the P-47B.
- Thread starter
- #36
Since the initial requirement includes the 2000 miles range, guess it would be quite a task convincing the USAF that future B-26 should not have such a numerous crew (even without gunners). The crew and range, at least when going by USAF's request, is where it came close to the in-service B-17s. A bit less on bomb load, but with much greater speed.
The P-47B was to have twice th engine power of what the P-35 had, so USAF's hopes for a world-beater were far more realistic in this case.
The P-47B was to have twice th engine power of what the P-35 had, so USAF's hopes for a world-beater were far more realistic in this case.
Shortround6
Major General
They learned a lot about aerodynamics and structure between 1934/5 and 1939/40.
However back to the idea of the fast bomber. A B-26 could burn 339gph at about 293-4mph at 14,000ft standard temp and pressure at max continuous power at 26,000lbs weight. You can slow down or somehow cut a lot of drag if you want to go further (and a B-26 at 26,000lbs is not carrying much in the way of fuel (let alone bombs). backing off to 75% power can cut the fuel burn to about 262gph and the speed is about 280mph. cutting the speed to about 265 gets the fuel burn down to about 210gph.
As a check on what was the very best case an F7F-3N Tiger cat could go about 1000 miles at 300mph at 15,000ft on 375 gal internal and a single 150gal drop tank (525US gal total) , no bombs. Increasing speed to 325mph cut the range to about 800 miles.
I really doubt you are going to get a twin R-2800 bomber to have less drag than the Tigercat even if it is the two seat night fighter version. You are going to have find someplace to put even a pair of 1000lb bombs after all. The Tiger cat is using R-2800-34W engines ("C" Series) and can pull 1700hp military power at 15,000ft and 1500hp max continuous.
However back to the idea of the fast bomber. A B-26 could burn 339gph at about 293-4mph at 14,000ft standard temp and pressure at max continuous power at 26,000lbs weight. You can slow down or somehow cut a lot of drag if you want to go further (and a B-26 at 26,000lbs is not carrying much in the way of fuel (let alone bombs). backing off to 75% power can cut the fuel burn to about 262gph and the speed is about 280mph. cutting the speed to about 265 gets the fuel burn down to about 210gph.
As a check on what was the very best case an F7F-3N Tiger cat could go about 1000 miles at 300mph at 15,000ft on 375 gal internal and a single 150gal drop tank (525US gal total) , no bombs. Increasing speed to 325mph cut the range to about 800 miles.
I really doubt you are going to get a twin R-2800 bomber to have less drag than the Tigercat even if it is the two seat night fighter version. You are going to have find someplace to put even a pair of 1000lb bombs after all. The Tiger cat is using R-2800-34W engines ("C" Series) and can pull 1700hp military power at 15,000ft and 1500hp max continuous.
That's the gist of it really, isn't it. Different philosophies enabled different requirements to flourish in different countries' armed forces. The Americans saw that the Mosquito certainly had merit; Hap Arnold was a big supporter of the concept, but not as a bomber, writing in much correspondence about its superiority as a photo recon platform over the F-5 (P-38 ). I guess stripping armament and extra crew positions from the B-26 is going to produce a faster aircraft, but would it have made a big difference in the role it was being used? It might have made a difference being faster, running into the target, then getting away quickly, but if it gets attacked by enemy interceptors, it has no defensive armament. Would its speed advantage be enough to evade enemy attackers? Interesting thought. Reconfiguring the interior is going to take time and is it done on the production line or in service? More questions...
- Thread starter
- #39
I'm not a great fan of the idea that B-26 would be a good base for a fast bomber. Rather to conceive it from ground-up.
With that said, the B-26 might be faster if the wing (both size and incidence) remain as on early models, have only the twin MGs in tail position, while installing a two stage R-2800. It might produce up to 350 mph; the 1st B-26 were good for 315 mph with early R-2800 (1850 HP for take off).
Of course. The 3000 lbs over 2000 miles would still require an aircraft carrying maybe 1500 gals of fuel, rather than 900 gals. 3000 lbs of bombs, 9000 lbs of fuel require a big airplane, and 2000 miles require a sizable crew that pushes the size of airplane further; it needs to go faster than 300 mph. Going with two R-2800 means that some of the requirements will not be fulfilled, whether it is range, speed or bomb load (as historically).
As before - the B-26 will not make it as a very good fast bomber. Better to go from ground-up.
Tigercat will never be better than the bomber with a proper bomb bay, a problem shared with P-38. Plus, with one drop tank it still has 200 US gals less fuel than late dash numbers of A-20G. 525 gals is less than what the P-47N had of just internal fuel. The late P-38 could carry more(?), 710 gals + 1000 lbs bomb vs. Ploiesti.
'Bomber' means it regularly carries bombs. The Tigercat carried them outboard - meaning it is one draggy bomber - shades of P-38 as a bomber, or Ju-88 with outboard bombs. The USN almost got the (X)TSF built, a sibling of the F7F that was to have a bomb bay for up to 4000 lbs of ordnance.
The single stage C series will have less power than two-stage B series R-2800 above 7-8000 ft, from winter of 1943/44 can also use water injection, to keep up with newer fighters.
The A-20G-20 will do 1570 miles with 725 gals and 2000 lbs of bombs, that is with reserves. So something like the 'A-20 plus', with pilot co-pilot side-to-side, bombardier in nose, tail gun position, up to 800 gals of fuel and up to 4500-5000 lbs of bombs, with the currently best R-2800 available.
With that said, the B-26 might be faster if the wing (both size and incidence) remain as on early models, have only the twin MGs in tail position, while installing a two stage R-2800. It might produce up to 350 mph; the 1st B-26 were good for 315 mph with early R-2800 (1850 HP for take off).
Of course. The 3000 lbs over 2000 miles would still require an aircraft carrying maybe 1500 gals of fuel, rather than 900 gals. 3000 lbs of bombs, 9000 lbs of fuel require a big airplane, and 2000 miles require a sizable crew that pushes the size of airplane further; it needs to go faster than 300 mph. Going with two R-2800 means that some of the requirements will not be fulfilled, whether it is range, speed or bomb load (as historically).
As before - the B-26 will not make it as a very good fast bomber. Better to go from ground-up.
Tigercat will never be better than the bomber with a proper bomb bay, a problem shared with P-38. Plus, with one drop tank it still has 200 US gals less fuel than late dash numbers of A-20G. 525 gals is less than what the P-47N had of just internal fuel. The late P-38 could carry more(?), 710 gals + 1000 lbs bomb vs. Ploiesti.
'Bomber' means it regularly carries bombs. The Tigercat carried them outboard - meaning it is one draggy bomber - shades of P-38 as a bomber, or Ju-88 with outboard bombs. The USN almost got the (X)TSF built, a sibling of the F7F that was to have a bomb bay for up to 4000 lbs of ordnance.
The single stage C series will have less power than two-stage B series R-2800 above 7-8000 ft, from winter of 1943/44 can also use water injection, to keep up with newer fighters.
The A-20G-20 will do 1570 miles with 725 gals and 2000 lbs of bombs, that is with reserves. So something like the 'A-20 plus', with pilot co-pilot side-to-side, bombardier in nose, tail gun position, up to 800 gals of fuel and up to 4500-5000 lbs of bombs, with the currently best R-2800 available.
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Shortround6
Major General
The Problem is for the 'fast, unarmed bomber" to actually work it has to cruise fast. Peak speed is pretty much useless if the plane has to cruise at low speed in order to reach the target. It could take a MK V Spitfire around 2 minutes to go from the low 200mph range to full speed. This is why they had to cruise at high speeds and why the US escorts flew at 300mph + and weaved above the bombers.
Unarmed bombers or bombers with sketchy armament are going to have to cruise fast. They cannot cruise slow and hope to accelerate and run when when bounced. The R-2800 was pretty economical at low power settings. It got real thirsty when pushed.
Sorry for the misunderstanding, I really wasn't suggesting the Tigercat as a bomber. It was the smallest twin R-2800 powered plane I could think of and if it couldn't fly the distances wanted at the speeds needed than any larger plane is going to have real trouble.
I believe the 4000 lbs of ordnance the (X)TSF carried was four 1000lb AP bombs which are smaller than 1000lb GP bombs. The 1000lb AP bombs were 12in in diameter, the 1000lb SAP bomb was 15in in diameter and the 1000lb GP bomb was 18.8in in diameter.
found a listing for the (X)TSF. Bay could hold one Mk 13-3 torpedo, one 2000lb bomb, two 1600lb AP bombs, four 1000lb AP bombs, two 1000lb bombs or four 500lb bombs.
This goes back to what size bomb bay do you want/need. Carrying 1000lb GP bombs side by side means a fuselage about 1ft wider than carrying 1000lb AP bombs.
The US 1600lb AP was only 14 in diameter which is why it was beloved by people writing specification charts. US 500lb GP bomb was 14.2in in diameter. 250lb bomb was 10.9in and the 100lb bomb was about 8.2 in.
The 2000lb GP bomb was 23.3in in diameter. Fins are a bit bigger.
So basically if you wanted to stack 250lb bombs one over the other 2 are going to take up the room (height) of a 2000lb bomb.
Just saying the plane will hold 4,000lb isn't good enough as obviously eight 500lb GP bombs will take up much more volume than four 1000lb GP bombs.
Sounds a lot like an A-26
An early A-20 could do 1210 miles on 580 gals of fuel (54 used for warm up and take-off out of 634) no reserve but was flying at 151 mph IAS (around 174mph true) at 12,000ft, 2.08 mpg. This rather obviously won't work for survivability.
Bringing the plane up to 253mph true at 12,000ft cut the range to 850 miles, burning 147 gal and hour instead of 72, 1.46mpg. You could run the plane at max continuous power and get 305mph out it at 12,000ft but you sucked down 308 gal an hour (just over 1 gal per mile) and range dropped to an estimated 555 miles.
How fast does the unarmed/lightly armed bomber have to fly to get a reasonable measure of safety?
Granted you do not have to fly all of the mission at high cruise speeds, just the parts over enemy territory.
Unarmed bombers or bombers with sketchy armament are going to have to cruise fast. They cannot cruise slow and hope to accelerate and run when when bounced. The R-2800 was pretty economical at low power settings. It got real thirsty when pushed.
Sorry for the misunderstanding, I really wasn't suggesting the Tigercat as a bomber. It was the smallest twin R-2800 powered plane I could think of and if it couldn't fly the distances wanted at the speeds needed than any larger plane is going to have real trouble.
I believe the 4000 lbs of ordnance the (X)TSF carried was four 1000lb AP bombs which are smaller than 1000lb GP bombs. The 1000lb AP bombs were 12in in diameter, the 1000lb SAP bomb was 15in in diameter and the 1000lb GP bomb was 18.8in in diameter.
found a listing for the (X)TSF. Bay could hold one Mk 13-3 torpedo, one 2000lb bomb, two 1600lb AP bombs, four 1000lb AP bombs, two 1000lb bombs or four 500lb bombs.
This goes back to what size bomb bay do you want/need. Carrying 1000lb GP bombs side by side means a fuselage about 1ft wider than carrying 1000lb AP bombs.
The US 1600lb AP was only 14 in diameter which is why it was beloved by people writing specification charts. US 500lb GP bomb was 14.2in in diameter. 250lb bomb was 10.9in and the 100lb bomb was about 8.2 in.
The 2000lb GP bomb was 23.3in in diameter. Fins are a bit bigger.
So basically if you wanted to stack 250lb bombs one over the other 2 are going to take up the room (height) of a 2000lb bomb.
Just saying the plane will hold 4,000lb isn't good enough as obviously eight 500lb GP bombs will take up much more volume than four 1000lb GP bombs.
Sounds a lot like an A-26
An early A-20 could do 1210 miles on 580 gals of fuel (54 used for warm up and take-off out of 634) no reserve but was flying at 151 mph IAS (around 174mph true) at 12,000ft, 2.08 mpg. This rather obviously won't work for survivability.
Bringing the plane up to 253mph true at 12,000ft cut the range to 850 miles, burning 147 gal and hour instead of 72, 1.46mpg. You could run the plane at max continuous power and get 305mph out it at 12,000ft but you sucked down 308 gal an hour (just over 1 gal per mile) and range dropped to an estimated 555 miles.
How fast does the unarmed/lightly armed bomber have to fly to get a reasonable measure of safety?
Granted you do not have to fly all of the mission at high cruise speeds, just the parts over enemy territory.
