Douglas A-20 & Defensive Armament

[KJ_Lesnick]

From what I remember the A-20 had a turbocharger initially (though it was removed due to cooling issues) and was designed with the ability to fly fast enough and high enough to evade interception on it's own.  

That being said: Why did it need defensive armament if it was supposed to be so fast?

[Go4fun]

Wilipedia
" In March 1937, a design team headed by Donald Douglas, Jack Northrop and Ed Heinemann produced a proposal for a light bomber powered by a pair of 450 hp (336 kW) Pratt & Whitney R-985 Wasp Junior radial engines mounted on a high-mounted wing. It was estimated that it could carry a 1,000 lb (454 kg) bomb load at 250 mph (400 km/h). Reports of aircraft performance from the Spanish Civil War indicated that this design would be seriously underpowered, and it was subsequently cancelled.

In the autumn of the same year, the United States Army Air Corps issued its own specification for an attack aircraft. The Douglas team, now headed by Heinemann, took the Model 7A design, upgraded with 1,100 hp (820 kW) Pratt & Whitney R-1830 Twin Wasp engines, and submitted the design as the Model 7B.Original American indifference to the Model 7B was overcome by the improvements made for the French and British, and the Unites States Army Air Corps ordered two models, the A-20 for high-altitude bombing and the A-20A for low and medium altitude combat. Both were similar to the DB-7B. The A-20 was to be fitted with turbosupercharged Wright R-2600-7 engines, but these were bulky and the prototype suffered cooling problems, so the remainder were completed with the two-stage supercharged R-2600-11, 59 as P-70 fighters and 3 as F-3 reconnaissance aircraft. One A-20 was evaluated by the U.S. Navy as the BD-1, while the U.S. Marine Corps flew eight as the BD-2".

Can you ever have too many guns to cover your back? They were probably designed into the original "seriously underpowered" model and just kept later.

[rickshaw]

Obviously the Mosquito did without any...

[KJ_Lesnick]

rickshaw

My point exactly -- if the A-26 was built without any defensive armament and designed from the outset with just two crew members (pilot & nav/bombardier) it would have been probably an even better performer than it was.

Defensive armament requires gun-positions and/or turrets and ammo to go with it which generally require people to operate them; should the turrets be remote controlled and sighted by periscope, you'd probably require an extra person to operate them (admittedly the volumetric works better because the person controlling the guns is in the cockpit) and even with the smaller turrets, it still takes up volume inside the aircraft; furthermore the turrets add additionally drag -- should they be retractable the drag will only be present when extended, but volume will be needed to tuck them into the plane.

If you remove the turret and the gunner that goes with it you free up volume inside the aircraft which either allows
1: The aircraft to be made smaller while carrying the same fuel load: This results in a superior fuel fraction (same fuel/less weight) which furthers range.  Power to weight ratio increases as well which in turn allows superior climb performance, acceleration, turn-performance, and top-speed
2: The aircraft to remain the same size while carrying a greater fuel load: OEW would be lighter not needing the turrets, and while power-to-weight ratio would be the same at takeoff, the aircraft would perform better as fuel burns off due to the lighter OEW.

Turrets add drag when extended into the airstream, removing them reduces drag as well.  This in turn produces superior acceleration and higher top-speed.

[Go4fun]

Obviously the Mosquito did without any...

Simple answer? Havoc: American Design. Mosquito: British Design.

[rickshaw]

Obviously the Mosquito did without any...

Simple answer? Havoc: American Design. Mosquito: British Design.

Yes.  Different philosophies backed each design.  Even so, the Mosquito faced considerable resistance within the Air Ministry initially when it was proposed.  Even the Luftwaffe was opposed to an unarmed bomber, forcing guns on the He 119 when it was proposed as a Schnellbomber.  So, it was a common idea that bombers needed guns to protect themselves.

[Dizzyfugu]

Obviously the Mosquito did without any...

And IIRC, it took the design team a long time to talk the ministry out fo the idea of adding defensive armament - with a defensive turret, the plane would have certainly needed it, and without it was able to avoid trouble.

[wuzak]

Obviously the Mosquito did without any...

And IIRC, it took the design team a long time to talk the ministry out fo the idea of adding defensive armament - with a defensive turret, the plane would have certainly needed it, and without it was able to avoid trouble.

There was a Mosquito prototype built with a turret - W4053. This was the turret fighter prototype. The turret impinged on the bomb bay, so no useful bomb load could be carried.

There is a story that John de Havilland went up for a flight manning the turret, with Geoffry Jnr piloting and an engineer. At rest the turret pointed forward with its 4 guns over the cockpit. JdH rotated the turret to the rear comfortably, but when he tried to rotate the turret forward it would not go, due to the slipstream. That caused a problem because the entry hatch for the turret could not be accessed without the turret pointing guns forward. After a couple more flights riding in the turret was banned.

The original prototype, W4050, at some stages during development sported a dummy turret, which had dummy guns which could be positioned (on the ground) in different orientations. This was to see what effect the turret had on performance and stability.

The turret was only ever intended for the fighter version.

There were various proposals for some form of defensive armament. One was a fixed "stinger" gun in the tail. There may have been aimable weapons too.

[wuzak]

Wilipedia
" In March 1937, a design team headed by Donald Douglas, Jack Northrop and Ed Heinemann produced a proposal for a light bomber powered by a pair of 450 hp (336 kW) Pratt & Whitney R-985 Wasp Junior radial engines mounted on a high-mounted wing. It was estimated that it could carry a 1,000 lb (454 kg) bomb load at 250 mph (400 km/h). Reports of aircraft performance from the Spanish Civil War indicated that this design would be seriously underpowered, and it was subsequently cancelled.

In the autumn of the same year, the United States Army Air Corps issued its own specification for an attack aircraft. The Douglas team, now headed by Heinemann, took the Model 7A design, upgraded with 1,100 hp (820 kW) Pratt & Whitney R-1830 Twin Wasp engines, and submitted the design as the Model 7B.Original American indifference to the Model 7B was overcome by the improvements made for the French and British, and the Unites States Army Air Corps ordered two models, the A-20 for high-altitude bombing and the A-20A for low and medium altitude combat. Both were similar to the DB-7B. The A-20 was to be fitted with turbosupercharged Wright R-2600-7 engines, but these were bulky and the prototype suffered cooling problems, so the remainder were completed with the two-stage supercharged R-2600-11, 59 as P-70 fighters and 3 as F-3 reconnaissance aircraft. One A-20 was evaluated by the U.S. Navy as the BD-1, while the U.S. Marine Corps flew eight as the BD-2".

Can you ever have too many guns to cover your back? They were probably designed into the original "seriously underpowered" model and just kept later.

I know not of a turbocharged A-20/DB-7. Production A-20s did not, however, have two stage R-2600s. I don't think such a beast existed, at least not in production.

The R-2600 used was a single stage two speed supercharged engine.

[wuzak]

My point exactly -- if the A-26 was built without any defensive armament and designed from the outset with just two crew members (pilot & nav/bombardier) it would have been probably an even better performer than it was.

Would probably have needed a 2 stage R-2800 as well.

Having said that, the P-61 wasn't much faster (even without its turret), though it was probably a lot better at altitude. The A-26's service ceiling was 22,000ft, the P-61's 33,000ft.

[KJ_Lesnick]

There were various proposals for some form of defensive armament. One was a fixed "stinger" gun in the tail. There may have been aimable weapons too.

How much difficulty would have been needed to have put a remote controlled stinger turret in the design?

[rickshaw]

There were various proposals for some form of defensive armament. One was a fixed "stinger" gun in the tail. There may have been aimable weapons too.

How much difficulty would have been needed to have put a remote controlled stinger turret in the design?

It would have been very difficult and it would have cost a lot in performance.  The Mosquito's key was that it was a lightweight, aerodynamically slippery design with powerful engines.  Any added weight simply took performance away and anything that increased drag decreased speed.  QED.

You really must stop trying to compare apples and oranges, Kendra.  It doesn't work.  Aircraft may fulfill a broadly similar role in different air forces but there is a lot of dogma/doctrine/philosophy which backs why they are designed the way they were.   There is also a difference in time period usually.  No two designs start at exactly the same time, so the technologies backing them are slightly different as well.

[KJ_Lesnick]

It would have been very difficult

What difficulties would appear in terms of the complexity of the system either for the Mosquito, or a fictitious 1942 era design.

it would have cost a lot in performance.

How so... a gun in the tail looks like it wouldn't add much drag.  Weight could be an issue, but there's little drag penalty and if the gun was remote controlled it could be operated by the bombardier (say you have the bombardier sit to the side of or behind the pilot with a bombsight to look through, and a periscopic system for the gun) and you'd keep the crew complement the same.

The Mosquito's key was that it was a lightweight, aerodynamically slippery design with powerful engines.

I understand that -- and I agree with it actually.  I was thinking of a whiffie "mosquitofied A-26" that would be designed only with a single tail-cone turret instead of upper and lower and using maneuverability instead.  Being that the US didn't believe in having no defenses, you'd have minimal to be accepted while keeping a streamlined shape.  The A-26 had more defensive armament than the early A-20's.

Any added weight simply took performance away and anything that increased drag decreased speed.  QED.

Understood, contra-rotating props could add some performance back to fight the weight-gain...

You really must stop trying to compare apples and oranges, Kendra.  It doesn't work.

Good point. 

Aircraft may fulfill a broadly similar role in different air forces but there is a lot of dogma/doctrine/philosophy which backs why they are designed the way they were.

True, but this would be a kick-donkey design and I have some line-drawing ideas which I can bring up on the CGI section

There is also a difference in time period usually.

Well the A-26 first flew in June (?) 1942 and the Mosquito first flew November 25, 1940 and was first seen by the US in April 1941

No two designs start at exactly the same time, so the technologies backing them are slightly different as well.

I can't argue with you there

[pyro-manic]

Any added weight simply took performance away and anything that increased drag decreased speed.  QED.

Understood, contra-rotating props could add some performance back to fight the weight-gain...

No. Contra-props are to eliminate torque issues, and/or to reduce overall prop diameter. They don't magically increase power.


Adding tailguns to the Mossie would have been enormously difficult. It would have required the entire tail section to be redesigned and re-engineered to be larger, which would have been much heavier and would have had a detrimental effect on weight, balance, drag and therefore performance.

And you can't directly compare the A-26 to the Mosquito. The A-26 empty was heavier than the Mosquito was fully loaded.

[rickshaw]

As Pyro suggested, Kendra.  Exactly what sort of "remote control" set up do you want?  One that moves in elevation and traverse or one that is fixed (as many German bombers carried as "scare guns")?  If its the former, then you're looking at a massive weight and drag penalty for all the machinery.  If it's the latter, why bother?  They weren't particularly successful and just added weight to the aircraft's tail.

As for contra-props they both can eliminate torque and can be used to transmit extra power, Pyro.  It allows an aircraft to utilise smaller diameter propellers as well, which can be important in smaller aircraft.