1936 to mid-42: fast 1-engined bombers instead of slow types?

[Wild_Bill_Kelso]

With the sole exception of the D4Y we haven't found a succesful operational single used as a bomber. It isn't that it can't be done, it's that it is not a logical use of resources. Two engines get you a far better bomber, and if you want a tactical aircraft you can use a current or slightly older fighter. Tactical aircraft don't need the range. Range and bombload involve trade-offs for a single which leave you in Battle, Ki-30, Ki-32 territory. Where singles had to be used, at sea, even the bigger engines didn't give the TBM or SB2C the kind of speed that beat a pursuing fighter.


Things I've found looking around at what could be done;

Ki-30 and Ki-32, with their fixed gear, were just as fast, or do I mean slow, as the Battle.

The proposed Ju187 with it's Jumo 213 was no faster than Ju87D. And every Jumo could have powered a 190D or half a Ju88G

Once jabos came in the idea of single-engine specialist bombers disappeared except for tactical aircraft and carrier-borne types. And the F-105.

Well, there is the A-36, though of course it's basically a fighter modified into a bomber (with dive brakes). In terms of those pre-war Japanese pre-war planes there is also the Ki-15, which (according to Wiki) made 300 mph with a ~640 hp engine and fixed landing gear. It's a recon plane but could carry a 550 lb bomb which is plenty.

Mitsubishi Ki-15 - Wikipedia

en.wikipedia.org

The D4Y probably would have done better if it had more fighter escort by the time it appeared. The B6N made 300 mph as well, but again came out too late. Both aircraft were delayed by getting the engines sorted out. If you put something like a Merlin engine in an airframe like that in the late 30s you could have had a good fast bomber, conceivably. The B7N was even faster at 350 mph and certainly could have been an effective naval bomber if it had come out earlier.

There is also the Su-2 which managed (again, allegedly) 300 mph when they put a Sh-82 engine on it.

And there are all those successful single-engined fighter bombers, which we know could go quite fast compared to most bombers (not, obviously while carrying bombs). I think those stand as proof that you could make a single-engined fast bomber.

We know nobody really pulled this off, with the possible exception of the A-36, no truly effective fast bomber showed up in time to make even a small difference in the war. The question here is I think, could it have been done.

 

[Shortround6]

In terms of those pre-war Japanese pre-war planes there is also the Ki-15, which (according to Wiki) made 300 mph with a ~640 hp engine and fixed landing gear. It's a recon plane but could carry a 550 lb bomb which is plenty.

The B7N was even faster at 350 mph and certainly could have been an effective naval bomber if it had come out earlier.

First, if something looks too good on Wiki, it probably is.
The Ki-15 was an amazing design, it also used a 640hp engine for take off that gave 750hp at 4,000 meters,
However most of the planes used 900hp Mitsubishi 14 cylinder radials. It was noted that the Low powered Ki-15s lost speed in prolonged wide turns and take-off and landing runs were disappointing.
The 551 bombload is probably what they used in 1945 when they were used for Kamikaze duty.

As far as the B7N goes, The Avenger would have been a great naval bomber if they had stuck an R-3350 engine in it in 1943.

All kinds of airplanes would have great if they had managed to stick 1944-45 engines in them in 1940-42.

 

[Wild_Bill_Kelso]

If you don't use the best engines you have got you are already screwed.
Bomber with best engines vs smaller fighter with 2nd best engine????
Bomber with 2nd best engine vs fighter with best engine?????

You misunderstood my point - I don't think you can lobby to get some bleeding edge engine that the front line fighters don't have. I think you'll have what they have, basically. Not the newer experimental types. No early Griffin for example, I don't think you could count on that.

The A-36 was great airplane, but it does point to a few problems.
1, it arguably one of the most streamlined planes around and maybe the most streamline. A bomber with enclosed bomb stowage has little chance of being as good.
2, the A-36 used a 1325hp engine for take-off which it puts 20-30% more powerful than any V-12 engine in 1939-40, let alone before. It is 15% more powerful than the Allisons used in the P-40D & E or even the Mustang Is.

Arguable. V-1710-73 was producing 1325hp for takeoff, the only difference from the -39 on the P-40D&E was the boost rating used, and in fact many P-40Es were refitted with -73s in certain Theaters.

More importantly, P-40K, F, L, M, N which were more widely used than the D or E and were contemporaneous with the A-36 had the same available horsepower.

3, and that brings us to one of my hobby horses, Field Length. The A-36 with its 1325hp engine needed 3150ft at 10,000lbs (full internal fuel and two 500lb bombs) to clear 50ft .
And that is at 0 degrees C or 32 degrees F Add 20% more length for 20 degrees C or 72 degrees F. This is on a hard runway.
You can operate a Halifax or Lancaster out of the same size airstrip.
4. now figure out the operational radius. with 180 US gallons. And any other plane you can make without a trunk load of NA drawings/documents won't have the same range.
How close you come is subject to question.

I agree field length - and field surface, as well as training, are all potential issues in deploying a relatively high wing-loading, small winged fast bomber. Maybe ask the American Seabees to make some airfields for you.

Ok, lets start doing the math. If we want 120,000lb of bombs on target (area) we need 20 big bombers and so we are going to loose 1 bomber for every mission.
If we use the 1000lb load bomber we need 120 planes and we are going to loose 2.4 bombers per mission. Adjust for imagined crew size.

Yes on a pure accounting level, this makes sense. This is the accountant's logic. The devil is in the details though.

When we look at the operational history, it doesn't seem to be so cut and dry. In Theaters where they had bombers with much heavier loads available, after hard won lessons, they relied on fast two-engined bombers and fighter bombers. A-20s and Baltimore's, Hurricanes and P-40s were the favored bombers in the Western Desert and Med for the British, even though they had Wellingtons which carried a much larger bomb load. Problem being that the Wellingtons were way too slow to evade flak and fighters, and couldn't effectively bomb Tactical targets at low altitude.

In the Pacific, the USAAF had B-17s and B-24s, (and the British / Commonwealth had some Wellingtons), but except in the rare cases where they did some (risky) low level bombing, B-17s and B-24s almost never hit their targets, and did far less damage and were far less useful than the smaller, faster A-20s, Beaufighters, P-40s, and later on, Corsairs. Heavy bombers were useful for armed recon, ASW, and harassment, but all those extra tons of bombs they carried tended to land harmlessly in the sea or the jungle.

The only advantage is the increase accuracy of the small bomber. How much of that is training?

I don't think that is the only advantage. Many heavy bomber crews were extremely well trained, and still didn't hit their targets. A huge number (almost 50% for Bomber Command) lost their lives. It turns out poor accuracy is an artifact of bombing at high altitude (or medium altitude, but at night) and it by no means guarantees survival. This does of course depend on the target. You can drop bombs on a city. Maybe a real large rail yard. If you are trying to hit a bridge, or a supply convoy, or a ship, or a dock, or a particular factory, or a column of tanks, it turns out bombing from 25,000 is pretty pointless no matter how much training you have.

Meanwhile I think the Mosquito had a much lower loss rate than the Lancaster, right? Wiki says 0.7% compared to 2.2% for heavy bombers.

Fairly untrained (at least for bombing) fighter pilots learned in the field how to hit bridges and barges and artillery positions and supply convoys and did so effectively enough to impact the outcome of battles. The difference here is potential. The huge delivery van of a bomber can only fly so fast, or with so much agility. The fighter bomber or relatively agile light bomber could swoop down and release bombs close to the target, and then fly away at very high speed and / or with the potential to maneuver and (in the case of fighter bombers) fight off interceptors if necessary. The heavies just lumber in and lumber out, counting on their luck to see them through.

This speaks to the other big advantage of a small, fast bomber (or fighter bomber) - increased survival rate. If you sent 50 x Wellingtons with max bomb load to strike tactical or operational targets during El Alamein, say, you would start with a very impressive 225,000 bomb load. You could send 50 x A20s and the load is a comparatively dismal 55,000 lbs. Send 50 x P-40s can carry the same. But all the Wellingtons will be shot down, missing, or too damaged to fly after 3 missions. Most of the A-20s and P-40s will still be available, and even the badly damaged ones often come back with pilots and crew. So you dropped 675,000 lbs with your Wellingtons in the 3 missions before they were all gone along with their crews. Meanwhile you got 20 missions out of your A20s and P-40s, so A-20s drop closer to 1,000,000 lbs. In both cases more accurately than the Wellingtons were likely to do. Which type is better? The heavy bomb truck or the small, fast bomber?

Now you may be able (with increased losses and smaller bomb load) attack targets further away with the big bomber.
You can't attack targets much further away with the small bomber at all.

I definitely don't think you get increased losses with smaller planes.

A lot depends on the theater of operations.

That's true, and the target type.

 

[Wild_Bill_Kelso]

First, if something looks too good on Wiki, it probably is.
The Ki-15 was an amazing design, it also used a 640hp engine for take off that gave 750hp at 4,000 meters,
However most of the planes used 900hp Mitsubishi 14 cylinder radials. It was noted that the Low powered Ki-15s lost speed in prolonged wide turns and take-off and landing runs were disappointing.
The 551 bombload is probably what they used in 1945 when they were used for Kamikaze duty.

Fair enough, but if that airframe could manage anywhere close to 300 mph with a 650-750 hp engine, I think you would have a candidate for a good fast bomber if you put retractable landing gear and a 1,000 hp engine in it.

As far as the B7N goes, The Avenger would have been a great naval bomber if they had stuck an R-3350 engine in it in 1943.

TBF was a great and very useful plane, but it was not known for agility, speed or grace and I don't think it could compare with the B7 in any way on the design level. Which is fair enough as it's a much earlier design. It's also much bigger and considerably heavier.

But the TBF did in fact have a comparable engine in the R-2600 which could produce between 1,600 and 1,900 hp, compared to 1,825 hp for takeoff and 1,560 at 21,000 ft for the Homare 12 in the B7. So I'm not sure the engine is really the major factor, except in the sense that the Japanese had nothing anywhere near as good as an R-2600 in 1942 when the TBF came out.

-------------------- TBF ---------------- B7A
Gross Weight, lbs- 15,400 --------------12,400
Wingspan ------- 54' ----------------- 47'
Wing area ------- 490' --------------- 381 sq ft
Length ----------- 40' ----------------- 37'
Height ----------- 16.5' --------------- 13' 4"
Speed ------------ 270 mph ---------- 352 mph
Range ------------ 905 ---------------- 1,888 miles
Initial climb ----- 1075 fpm ---------- 1,900 fpm
Wing loading --- 31 lb / sq ft -------- 32.5 lb / sq ft
Power/mass ----- 0.11 hp / lb -------- 0.147 hp / lb

The B7 is just a smaller, sleeker, faster airframe. The TBF is a bus but well designed enough to have good landing characteristics etc. (per the low wing loading with the massive wings).

All kinds of airplanes would have great if they had managed to stick 1944-45 engines in them in 1940-42.

See above - don't think the issue was the engine so much. I'd say the TBFs big advantage was that it was put together quite quickly and was pretty good for when it came out. The B7 was just 3 years too late to matter.

However on the design level it's still worth looking at.

 

[GrauGeist]

The Vultee A-31 was powered by an R-2600 and xould carry two 500 pound bombs internally.

 

[Wild_Bill_Kelso]

yeah the Vengeance is another interesting example, and another dive bomber. I'm not sure if it was quite fast enough to qualify as a fast bomber, but it's close, - 275 mph isn't too bad. The US military admin disdained them but the Australians seemed to like them and put store by their efficacy.

What if you made a slightly smaller aircraft. Similar to the Vengeance, but say 20% smaller? maybe only room for one bomb internally, or just a fast bomber not a dive bomber. But with the R-2600. Could that be done?

 

[Wild_Bill_Kelso]

There were several slow to moderately fast, single engined dive bombers around in the early part of the war. Skua, D3A, SBD, A-31, Su-2 etc. None of them seemed to be able to withstand the forces of dive bombing as well as a Stuka, or to be very survivable without fairly heavy fighter escort, but they had their moment. Some of those types were close to being a fast bomber, especially if you removed some of the extra dive bombing gear, and maybe gave them a bit better engine.

 

[nuuumannn]

Not having self-sealing tanks does matter.

this 'fast single engined bomber' only achieved the 'fast' by deleting basics like self sealing tanks and armour, that made it a flying torch that lit up with a single strike.

Ugh, here we go again with this self-sealing tanks and Japanese aircraft, ad nauseum...

A couple of things, the D4Y first flew in 1940, it was designed at a time when no one was putting self-sealing tanks in their aircraft. The SBD for example was not built with self-sealing tanks until the -3 model as standard and that first entered service in March 1941, the previous SBD-2 was retrofitted with them, but was not built with them. The earliest Ju 87 variants were not built with self-sealing tanks, nor were the Battle, Skua and plenty other similar type aircraft of the time.

On entry into service in 1942, D4Y pilots complained about the lack of self-sealing tanks, because other Japanese aircraft in service had them!

 

[Shortround6]

Arguable. V-1710-73 was producing 1325hp for takeoff, the only difference from the -39 on the P-40D&E was the boost rating used, and in fact many P-40Es were refitted with -73s in certain Theaters.

More importantly, P-40K, F, L, M, N which were more widely used than the D or E and were contemporaneous with the A-36 had the same available horsepower.

Not quite right. The A-36 used the -87 engine with 7.48 supercharger gears. and we are getting well into 1943 and later. The -87 engine made 1325hp at a lower boost pressure and a was allowed to make 1100hp at 2600rpm (max continuous) instead of 1000hp that the higher supercharger gears were limited to. The -87 was also allowed to use 1325hp for Military power while the -73 was still limited to 1150hp. Now the -87 was only good for about 5-6000ft doing this. This limits have got nothing to do with WER. This is what the designers and manual writers were looking at. One practical difference, even after the over boosting and WER showed up was that use of Military power, even if done several times in one flight, required no notes in the log book and no extra maintenance procedures.

Yes on a pure accounting level, this makes sense. This is the accountant's logic. The devil is in the details though.

When we look at the operational history, it doesn't seem to be so cut and dry. In Theaters where they had bombers with much heavier loads available, after hard won lessons, they relied on fast two-engined bombers and fighter bombers. A-20s and Baltimore's, Hurricanes and P-40s were the favored bombers in the Western Desert and Med for the British, even though they had Wellingtons which carried a much larger bomb load. Problem being that the Wellingtons were way too slow to evade flak and fighters, and couldn't effectively bomb Tactical targets at low altitude.

Yes the devil is in the details.
In the Desert range was not a big consideration for tactical use. While it was 630 miles form Tobruk to Tripoli you could usually find something to bomb/strafe much closer to the front line airfields. In Europe or the Pacific with several hundred miles of water between the home bases and the enemy bases short ranged fighters were not much good. And in 1936-42 the single engine bombers were sometimes considered to be more than tactical bombers or were intended to be in the first 4 years or so of the period. A-20s were not popular in parts of the Pacific because they didn't have the desired range.

Meanwhile I think the Mosquito had a much lower loss rate than the Lancaster, right? Wiki says 0.7% compared to 2.2% for heavy bombers.

Try looking at the loss rates for low altitude daylight bombing for the Mosquito.

 

[Shortround6]

Fair enough, but if that airframe could manage anywhere close to 300 mph with a 650-750 hp engine, I think you would have a candidate for a good fast bomber if you put retractable landing gear and a 1,000 hp engine in it.

A fast recon plane using a small engine is not a good basis for a bomber, They are among the lightest constructed aircraft. By they time you beef them up some of the performance goes away. The Ki-15 looks big in the pictures. It's wing was just over 2 ft longer than wing on a Ki-27 fighter and just about 10% bigger in area. (10 sq ft smaller than a Ki-43) and with the 9 cylinder radial engine in was about 10% heavier than the Ki-27.

TBF was a great and very useful plane, but it was not known for agility, speed or grace and I don't think it could compare with the B7 in any way on the design level. Which is fair enough as it's a much earlier design. It's also much bigger and considerably heavier.

TBF was bigger and heavier. it also carried a bit bigger payload, it's deck performance may have stricter (shorter deck and/or less speed?) and it's range capability was not the huge gap that Wiki claims. Normal range for the B7A was much closer to 1000 miles rather than 1800 miles. Fill the TBF full of fuel (inside the bomb bay and or under wing) and see how far it can fly.

There were several slow to moderately fast, single engined dive bombers around in the early part of the war. Skua, D3A, SBD, A-31, Su-2 etc. None of them seemed to be able to withstand the forces of dive bombing as well as a Stuka, or to be very survivable without fairly heavy fighter escort, but they had their moment. Some of those types were close to being a fast bomber, especially if you removed some of the extra dive bombing gear, and maybe gave them a bit better engine.

You might get some argument about the sturdiness of the Sku and SBD and A-31,
The problem with dive bombers was that they were several hundred pounds heavier than a light level bomber (or shallow diver) to keep them from breaking when pulling out of dives. There was some cross over. Battles were noted as being tough but they really didn't perform hundreds of practice dives in training. They did some. Battles were also over built as the engineers were sort of feeling their way with early monoplane structures.
Now in 1936-38 with 700-900hp engines that was a problem. 1939-40 with 1000-1100hp engines it got a little bit easier, in 1941-42 with 1200-1400hp engines things got bit easier again and in 1944 with 1900-2000 hp engines the designers jobs were a lot easier. A TBF-3 had more power than Blenheim or early SB-2. That was the progress of 6-8 years.
A 1930s single engine bomber does not have the power to go fast, get out of small fields, carry more than 500-550lbs worth of bombs and have the full capacity to fly very far.
They tried to make up for the lack of speed with the rear guns.

 

[yulzari]

The issue of landing field length is relevant to the initial war procurement. We know that vast efforts and expenditures were made in the war from 1939 to lengthen fields and put in hard runways. But when touting your wonder light bomber pre war, the buyers are not going to be happy with being told that they cannot actually carry any bombs and fuel into the air as the grass fields are too short. Nor to plan to have them standing around until a war starts a longer runway programme. The AASF in France were grateful that their aeroplanes were designed to drag themselves off short grass fields because that is what the French gave them. The thread putative light bombers would have had to stay at home no matter how wonderful they might be once they got into the air fully equipped.

Is it worth reminding ourselves that, for the heavy bombers of mid war onwards, the bulk operated from Britain and the task of providing them all with all weather long hard runways (and associated buildings etc.) was the largest civil engineering project Britain has ever seen. Dwarfing motorways etc. and done within just a very few years.

No, our thread single engined light bomber for the first three years of the war will have been designed pre war to operate out of pre war short grass fields. Literally fields in France in 1939/40.

The Japanese and Italians, together with the Commonwealth abroad, relied principally upon locally recruited pick and shovel labour to make better and longer open fields which were far from being hard surfaced all weather sites. In NW Europe after OverLord hard ex Luftwaffe airfields were prized. Especially when the autumn wet weather arrived. The shortage of all weather hard runways reduced tactical operations to being made from England or cancelled when grass airfields closer to the operational areas were waterlogged.

 

[Dimlee]

With the sole exception of the D4Y we haven't found a succesful operational single used as a bomber.

Aichi B7A?

 

[Wild_Bill_Kelso]

Not quite right. The A-36 used the -87 engine with 7.48 supercharger gears. and we are getting well into 1943 and later. The -87 engine made 1325hp at a lower boost pressure and a was allowed to make 1100hp at 2600rpm (max continuous) instead of 1000hp that the higher supercharger gears were limited to. The -87 was also allowed to use 1325hp for Military power while the -73 was still limited to 1150hp. Now the -87 was only good for about 5-6000ft doing this. This limits have got nothing to do with WER. This is what the designers and manual writers were looking at. One practical difference, even after the over boosting and WER showed up was that use of Military power, even if done several times in one flight, required no notes in the log book and no extra maintenance procedures.

I think you are laying out a questionable narrative here. There is very little difference in the V-1710 variant used by the A-36 and contemporaneous versions of the P-40 which were also used as fighter-bombers. Basically it was just what they were rated for and the supercharger gear ratio. The V-1710-73 was a lower altitude variant officially rated for 1,325 hp at 51" Hg for takeoff and 1550 hp at 60" for War Emergency rating (which it could make at up to 6,000 ft). The -87 had a supercharger gear ratio intended for slightly higher altitude, but was actually very similar to the V-1710-81 used on the P-40M and early P-40N series which were operated as a fighter bomber in the same Theaters and at the same time as the A-36, (unlike the earlier P-40E & D variants which you mentioned). The -81 engine was rated for up to 1480 hp at 57" Hg which it could maintain in level flight up to 9200 ft.

During fighter bomber missions neither aircraft type typically flew at high altitude, and both would use a cruise or fast-cruise power setting to get to and from the target. Higher boost settings ('military', 'takeoff' or 'war emergency' power, or overboosting which was also done with both types), were used when evading flak and / or enemy fighters.

Bottom line, there was no significant difference in the engine power between the A-36 and the P-40 fighter bomber variants used contemporaneously. The only difference is in how they were rated. The A-36 was fast because of it's excellent streamlining.

Yes the devil is in the details.
In the Desert range was not a big consideration for tactical use. While it was 630 miles form Tobruk to Tripoli you could usually find something to bomb/strafe much closer to the front line airfields. In Europe or the Pacific with several hundred miles of water between the home bases and the enemy bases short ranged fighters were not much good. And in 1936-42 the single engine bombers were sometimes considered to be more than tactical bombers or were intended to be in the first 4 years or so of the period. A-20s were not popular in parts of the Pacific because they didn't have the desired range.

Again, wrong and demonstrating either a lack of understanding of, or disinterest in the tactical realities both in the Pacific and China. US made fighter bombers and light and medium bombers were in heavy use in multiple land and naval engagements, during many of which range limitations were not significant. The P-40 and a host of light and medium bomber types including A-20 were in heavy use all around the large island of Papua / New Guinea for example, as well as in the Solomons, and the A-20 remained one of the most critical offensive weapons in the arsenal of Kenney's 5th Air Force. Similarly in China and Burma fighter bombers and light and medium bomber types, including the Vultee A-31 in Australian use, played a decisive role both as tactical and operational weapons.

There were some battles in the Pacific where range did become a more crucial factor which is where the longer -legged types became more useful, but there were no battles I can think of where heavy bombers were carrying the day or where a large bomb load turned out to be more important than accuracy or speed. The smaller faster aircraft were the main offensive weapons that actually did the damage to the enemy.

B-17 was still useful esp. for recon because it was high flying enough and did have so many guns that it could fend off Japanese fighters, but almost the only times it really had an impact on the fighting directly (i.e. from dropping bombs) was in a handful of low-level attacks. The vast majority of bombs dropped by heavy bombers killed little more than fish. B-24 (and naval varaint) ended up being quite useful in the ASW role.

But the operational history tells us that fast and agile mattered far more than heavy bomb load in those Theaters.

Try looking at the loss rates for low altitude daylight bombing for the Mosquito.

I am familiar with it, and it varied quite a bit. In some raids against very dangerous, highly defended targets such as in urban areas and so on, which no other aircraft type could have been used to even attempt an attack, Mosquitos took heavy losses. In other raids it was notable that they took far fewer than all other types, such as for example the famous Eindhoven raid.

 

[Wild_Bill_Kelso]

Ugh, here we go again with this self-sealing tanks and Japanese aircraft, ad nauseum...

A couple of things, the D4Y first flew in 1940, it was designed at a time when no one was putting self-sealing tanks in their aircraft. The SBD for example was not built with self-sealing tanks until the -3 model as standard and that first entered service in March 1941, the previous SBD-2 was retrofitted with them, but was not built with them. The earliest Ju 87 variants were not built with self-sealing tanks, nor were the Battle, Skua and plenty other similar type aircraft of the time.

On entry into service in 1942, D4Y pilots complained about the lack of self-sealing tanks, because other Japanese aircraft in service had them!

The other factor is that if you look at the operational history, for example Pacific Air War series which goes day by day, you'll see many, many cases where Japanese fighters and bombers such as 1942-43 vintage A6M, Ki-43, G4M, D3A and so on, with little or no protection for fuel tanks, were attacked and damaged and yet, did not blow up or catch fire. Or in some cases they did catch fire and the fire went out.

Self sealing fuel tanks were important but the propensity for aircraft to blow up like the Hindenburg with a single bullet strike is clearly quite exaggerated.

 

[Wild_Bill_Kelso]

A fast recon plane using a small engine is not a good basis for a bomber, They are among the lightest constructed aircraft. By they time you beef them up some of the performance goes away. The Ki-15 looks big in the pictures. It's wing was just over 2 ft longer than wing on a Ki-27 fighter and just about 10% bigger in area. (10 sq ft smaller than a Ki-43) and with the 9 cylinder radial engine in was about 10% heavier than the Ki-27.

Yes and my point is, lightly constructed or not, if your goal (per the OP) was to make a fast bomber, and you decided to make one which was not a dive bomber, you could probably do it in the late 1930s. If the Japanese could make an aircraft with fixed undercarriage and a radial engine of less than <800 hp go anywhere near 300 mph, then I think the British or Americans could make one with a 900 1,000 hp engine (and maybe in-line), and retractable landing gear which could carry a small bomb, and a small bomb is all you need to start with. You can carry more and heavier bombs as bigger and better engines become available.

TBF was bigger and heavier. it also carried a bit bigger payload, it's deck performance may have stricter (shorter deck and/or less speed?) and it's range capability was not the huge gap that Wiki claims. Normal range for the B7A was much closer to 1000 miles rather than 1800 miles. Fill the TBF full of fuel (inside the bomb bay and or under wing) and see how far it can fly.

I don't know what to tell you padnuh, you claimed that the difference in performance was due to "putting a 1944 engine in it vs a 1942 engine" but the TBF had basically just as powerful of an engine in 1942 as the B7A had in 1944. The US got powerful engines working fairly reliably much earlier. The difference in performance was due to size, weight, streamlining and overall design.

As for bomb load, so what? The B7A could carry a torpedo, and it could even dive bomb. I don't think it would be any less lethal against a ship and probably better against land targets simply due to being less vulnerable to AAA (faster and smaller) and far less vulnerable to enemy fighters (much faster and more maneuverable and also heavily armed. Some reports claim it could outmaneuver a zero and it did have armor).

You might get some argument about the sturdiness of the Sku and SBD and A-31,
The problem with dive bombers was that they were several hundred pounds heavier than a light level bomber (or shallow diver) to keep them from breaking when pulling out of dives. There was some cross over. Battles were noted as being tough but they really didn't perform hundreds of practice dives in training. They did some. Battles were also over built as the engineers were sort of feeling their way with early monoplane structures.

I agree about dive bombers being heavier and also in many cases, much more draggy. If you remove the bomb cradle made to carry the bomb past the propeller hub, and remove any external dive brakes (those mounted as flaps inside the wings are probably ok) then you may have a much faster bomber.

I think the efficacy of fighter bombers in the Tactical and Operational bombing role, which is basically what led to the end of the use of dive bombers by Allied air forces (though they lingered in the Navy role) proves that assuming a fairly high performance aircraft, you could have an effective low level bomber that wasn't a dive bomber. Dive bombers were more accurate, but so long as you were dropping your bomb at below 3,000 ft instead of 25,000 ft or higher, (or at night) you could actually hit targets with a tactically significant frequency. Enough to make a difference in battles and campaigns.

Now in 1936-38 with 700-900hp engines that was a problem. 1939-40 with 1000-1100hp engines it got a little bit easier, in 1941-42 with 1200-1400hp engines things got bit easier again and in 1944 with 1900-2000 hp engines the designers jobs were a lot easier. A TBF-3 had more power than Blenheim or early SB-2. That was the progress of 6-8 years.
A 1930s single engine bomber does not have the power to go fast, get out of small fields, carry more than 500-550lbs worth of bombs and have the full capacity to fly very far.
They tried to make up for the lack of speed with the rear guns.

As we have already established, the US already had at least 1,600 hp engines in 1942. By 1943 they had up to 1,900 hp.

 

[tomo pauk]

As we have already established, the US already had at least 1,600 hp engines in 1942. By 1943 they had up to 1,900 hp

Even beter - USA has 1850 HP engines (R-2800s) in production in 1941, and 2000 HP R-2800s in production from January 1942.

 

[Wild_Bill_Kelso]

Ki-15 also had a 39' / 12m wing span. Not tiny but much smaller than on most 'light' bombers. That is probably a major reason why it was so fast.

I also, by the way, checked and the 550 lb bomb load was not a kamikazi load out. It was apparently used with success as a bomber in China in the late 1930s.

Later versions of this plane got the Ha-26-1 engine of 900 hp, so no doubt the speed went up. History of war says speed of the -II was 317 mph. An experimental version designed in 1939 with an Ha-102 (1080 hp) got up to 329 mph, which is getting close to as fast as you can go with fixed undercarriage.

Obviously if you increased the weight on that airframe by say 1,000 lbs with a little armor armor, maybe another gun, and who knows? a bomb bay? you aren't going to get 1500 mile range or a 37,000 ceiling any more, but you would still have a viable light bomber, already.

Ki-15 just shows that it was possible.

Do something similar with a 1,000 hp engine, retractable gear etc. and you could have an actually pretty good bomber.

Interestingly Ki-15 was noted for a long takeoff run. They had to work around it with all those short fields in the 1930s.

A hypthothetical "late 1930s fast bomber" made by the Anglo-Americans, the French, the Russians, or say, the Germans, would have probably needed to be relatively small, with a fairly small wingspan like the Ki-15 (rather than something with the size and wingspan of a TBF or say, a Battle), and this would have meant a relatively high wing loading and therefore a long takeoff run would be necessary. This would be a problem, and an operational limitation. But I think they could have worked around it with relatively small numbers of aircraft, and it would have been a problem which diminished over time.

The reason they ended up using twin engined light bombers in early war designs was partly due to wanting to make them into dive bombers (like the Ju-88 and the Pe 2) which added too much weight to be fast with the engines available, and partly due to the safety / survival factor in the redundancy of the second engine.

The history of fighter bombers proves that a fast single engined bomber may well have had a role though.

 

[Wild_Bill_Kelso]

Even beter - USA has 1850 HP engines (R-2800s) in production in 1941, and 2000 HP R-2800s in production from January 1942.

Right but when were aircraft with these engines deployed in the field? I think 1943 right?

 

[tomo pauk]

Right but when were aircraft with these engines deployed in the field? I think 1943 right?

For example, four B-26s attacked the Japanese fleet at Midway in mid-1942.

 

[Wild_Bill_Kelso]

For example, four B-26s attacked the Japanese fleet at Midway in mid-1942.

Good point, I stand corrected. They had some B-26s in the New Guinea area for a while too also in 1942 IIRC