USAAF Attack & Light Bombers: Needs & Desires

[Zipper730]

See aView attachment 491273

Okay, I did some looking in a book I recently got: "Convair Advanced Designs II: Secret Fighters, Attack Aircraft and Unique Concepts, 1929-1973", and the entry on the XA-41 basically lists an early armament consisting of the following

• Payload
  • Maximum Internal
    • 1,000 lbs (4 x 250)
  • Maximum External
    • 5,500 lbs
  • Maximum Total: 6400 lbs
  • Typical Load: 3200 lbs
    • Internal: 1,000 lbs
    • External: 2,200 lbs
• Armament
  • 2 x 37mm M-9
  • 4 x 0.50 caliber
• Performance
  • Range
    • 800 miles with 1,000 pounds
    • 3000 miles with external tanks (and possibly a bomb-bay filled with fuel)
  • Speed
    • Maximum: 363 mph @ 15,500 feet

The original design was based on an inverted gull-wing for weight reduction, and after this produced directional and lateral stability, it was replaced with a tapered wing with dihedral in the outer panels. It was evaluated on 4/29/43, and specifications were modified for low level ground attack rather than dive-bomber, which resulted in the removal of dive brakes, bomb-displacing gear, change to load-factor (no idea how much), and reduced load by 1,600 pounds.

If I read the cost figures right, it was $110,000 a plane.

The design was not really liked because it's speed and altitude didn't give it the ability to defend itself (I'm not sure how good the A-26 did in that department, though they were working on improvements with redesigned cowls and a jet engine in the back), which may or may not be pre-textual. On 10/22/43, they decided they would eliminate the requirement for single-engined, single-place ground attack planes: I'm not sure if the rationality of this was the performance or the fact that they just preferred twins.

 

[Zipper730]

Shortround6 and wuzak: Do you have any idea what the typical maximum gear-ratios were for variable speed superchargers?

 

[Shortround6]

Somewhere between 10.0 and 11.0 to 1.

Please remember that the actual physical speed limit is the tip speed of the impeller. Once the tip speed goes supersonic the resulting shock waves inside the supercharger disrupt the air flow. While due to the pressure/temperature inside the supercharger compared to free air the speed of sound it higher there is still a limit.

 

[Zipper730]

Deleted

 

[Zipper730]

Somewhere between 10.0 and 11.0 to 1

What's the maximum spread between minimum and maximum?

 

[Shortround6]

And the minimum gear-ratio is around 4-8 less right with a variable speed in theory right?

I believe the DB engines on the 109 had a low speed of just over 7 to 1.

The R-2800 in the F8F-2 had a minimum of 7.29 and max of 10.55

The R-2800 in the F4U-5 may have used a min of 6.70 and a max of 9.66.

 

[Zipper730]

I believe the DB engines on the 109 had a low speed of just over 7 to 1.

And the maximum was like 10.3?

 

[Zipper730]

I'm curious if it would have been possible to have developed any piston-powered, single-engined tactical bomber with the ability to do at least one of the following things?

1. Radius of action: 800 miles with 1,000 pounds of bombs
2. Radius of action: 575-775 with 2,000 pounds of bombs
3. Radius of action: 500-550 with 3,000 pounds of bombs
4. Maximum level speed of at least 395-405 mph at critical altitude, presumably between 15,000 - 25,000 feet

 

[Shortround6]

I'm curious if it would have been possible to have developed any piston-powered, single-engined tactical bomber with the ability to do any of the following things

• Radius of action: 800 miles with 1,000 pounds of bombs
• Radius of action: 575-775 with 2,000 pounds of bombs
• Radius of action: 500-550 with 3,000 pounds of bombs
• Maximum level speed of at least 395-405 mph at altitude: This altitude could be anywhere from 10,000 - 25,000 feet

When?
1943 or 1945 or 1949?

But I would say it would be pretty hard. An AU-1 Corsair can only do about 388mph clean (with empty pylons and rocket launchers) at 14,000ft with a post war R-2800 running on 115/145 fuel (engine making 2270hp at 11,000ft ).
Combat radius of 380 NM (437 statute miles) with a single 1000lb, six 500lb bombs and two 150 gal drop tanks. average cruising speed 190mph.

You left out desired cruise speed and cruise altitudes for your desired wish list. The AU-1 was cruising to target at 15,000ft and returning at 5,000ft.

 

[swampyankee]

I'm curious if it would have been possible to have developed any piston-powered, single-engined tactical bomber with the ability to do any of the following things

• Radius of action: 800 miles with 1,000 pounds of bombs
• Radius of action: 575-775 with 2,000 pounds of bombs
• Radius of action: 500-550 with 3,000 pounds of bombs
• Maximum level speed of at least 395-405 mph at altitude: This altitude could be anywhere from 10,000 - 25,000 feet

I suspect it's not possible with pistons. Probably, an internal bomb bay would also be needed.

 

[Zipper730]

When? 1943 or 1945 or 1949?

First flight around 1944 based on the XA-41's first flight.

But I would say it would be pretty hard.

I'm not sure if the top-speed figures for attack/bomber aircraft are based on them flying clean or with a bomb-load of some sort.

I actually know very little about the AU-1 other than it was an F4U variant, and had a different supercharger: I didn't know 388 could be achieved at only 14,000 feet but that sounds pretty impressive. Are the cruising speed figures indicated or true airspeed?

You left out desired cruise speed and cruise altitudes for your desired wish list.

As for cruising speed I'd say somewhere from 240-250 mph, as for cruise altitudes

From what I remember with altitudes

• The A-1 would cruise to target at 15,000 feet and return at 5,000 feet
• The P-47N would cruise to target at 10,000 feet and return around sea-level

I assume the A-1 would dive from 15,000 feet down as low as they dare, release the bombs; then climb back up to 5,000 feet on the ride back home right? I'm curious honestly as to the merits of cruising at 20,000-25,000 feet versus 10,000-15,000 and exiting at 10,000-15,000 feet versus 5,000 feet or sea-level? It seems like it would make for superior range and allow a higher cruise-in speed.

I suspect it's not possible with pistons.

I wouldn't be shocked.

Probably, an internal bomb bay would also be needed.

That kind of goes without saying. Using the XA-41 as a starting point, it's internal bay could carry 4 x 250 pound bombs. I'm curious if the dimensions would also allow 1 x 1600 AP as well. I figure the rest would be carried on external pylons with at least one hard-point on each wing plumbed for a drop-tank if need be.

 

[swampyankee]

Generally, best range is not strongly affected by altitude for piston-engined aircraft.

 

[Zipper730]

Generally, best range is not strongly affected by altitude for piston-engined aircraft.

I figured it would because the air gets thinner and it makes it easier to chop through the thinner air allowing higher speeds for the same amount of power, or less power for the same speed.

 

[Shortround6]

Actually range does go up with altitude for Piston powered planes. Otherwise there were be no market for Turbocharged/pressurized Cessna's and Beechcrafts

However it almost always involves more complicated engine set ups with higher maintenance regardless if you have a flat six or a radial 28 cylinder. Dag at 20,000ft is only a little of 1/2 the drag at sea level so if you can keep sea level power or close to it at 20,000ft you get much more range.

 

[swampyankee]

Actually range does go up with altitude for Piston powered planes. Otherwise there were be no market for Turbocharged/pressurized Cessna's and Beechcrafts

However it almost always involves more complicated engine set ups with higher maintenance regardless if you have a flat six or a radial 28 cylinder. Dag at 20,000ft is only a little of 1/2 the drag at sea level so if you can keep sea level power or close to it at 20,000ft you get much more range.

There are advantages to flying higher, one being that there tend to be fewer clouds stuffed with rocks at 20,000 ft than at 5,000. Another is that the ground speed for best range increases with altitude. I don't know how an air force chooses the airspeed / range combination, but I suspect that for aircraft which are not dominated by either maneuver or runway demands, the designer will try to get that airspeed as close to that for best productivity, which is VL/D.

 

[Zipper730]

Please be more specific.

F7F-1, R-2800-22W

However the F7F-1 & -2 used R-2800-22W engines , these were single stage "C" series engines and were good for 1600hp at 16,000ft in high gear, no ram. . . . Nobody picked up 8,000ft of altitude with RAM.

According to this source, which I have found to be highly reliable...

Images courtesy: WWII Aircraft Performance

... figures clearly show a critical altitude of 24,000 feet on normal power, and 23,400 on military power settings.

Addendum: It would appear that some of the charts on the F7F-1 indicate different critical altitudes, most of which match yours. It is my suspicion that they might very well have re-geared the supercharger for one reason or another. One possible reason could be to increase maximum speed at critical altitude, and sea-level. Oddly climb-rate was decreased on these.

 

[Zipper730]

While, this is a slight detour from topic, it still regards bomber and attack aircraft...

The XB-42 . . . was designed for the long range heavy bombardment mission, as a cheaper and faster alternative to the B-29

To avoid any ambiguity, was the XB-42 classified at any point as a medium-bomber, or was it always considered a light-bomber?

 

[Zipper730]

No, Baugher hasn't got it wrong - look at his bibliography - he's using Wagner....

Why the discrepancy in Wagner's figures and others?

 

[Zipper730]

C CORSNING S Shortround6 T ThomasP

I was thinking of something about a WWII-era design achieving a combination of high speed and good range with one engine and I was thinking about the power output of the R-4360 (3400 hp with WEP, 3000 hp with military rated power, and 2550-2700 hp with normal rated power).

That power output is about twice the output of some RR Merlin variants, and that got me thinking of the De Havilland Mosquito with the RR Merlins removed and an R-4360 put up front (and this is, of course, grossly over-simplified): While the Mosquito isn't capable of the normal-rated g-loads demanded by either the USAAF (8-9) or USN (7-8), I figure something with the strength of the Tempest scaled-up to the Mosquito's size with a R-4360 could probably deliver some remarkable performance in terms of both speed and range.

 

[Shortround6]

And fuel consumption.

• Empty weight: 13,519 lb (6,132 kg)
• Gross weight: 20,508 lb (9,302 kg)
• Max takeoff weight: 21,691 lb (9,839 kg)

Internal bomb bay was not as big as Mosquitos.