Re: Medium bomber design - school exam question

On Jul 13, 8:41 pm, Gernot Hassenpflug <ger...@xxxxxxxxxxxxx> wrote:
guy <guyswetten...@xxxxxxxxxxxxxx> writes:
On 13 July, 10:16, Peter Twydell <pe...@xxxxxxxxxxxxxxxxxx> wrote:
You are a WW2 designer and are building a twin-engined medium bomber.

Do you have a large nose and slim fuselage and group the crew together
in the cosy Luftwaffe manner such as in the Ju 88 family, or build a
bigger fuselage and spread the crew about as in the B-25 and B-26?

State the reasons for your choice and write on only one side of the
paper at a time.
--
Peter

Ying tong iddle-i po!

It depends on the defensive armament required, if you want tail guns
and/or power operated turrets you need a B-25/B-26 style layout, if
not then everyone can be up front. However, being British I would
spend an eternity developing the Buckingham and then scrap the medium
bomber concept completely!

At least, being British, it's already decided that the crew can't be
together, not with all those class differences floating around. LOL

I'd go for a B-25/26 style layout, with plenty of forward firepower and
dispersed crew manning defensive machine guns. I'd want the most
powerful engines I could get, radial, and lots of armour...

Here's my design.

The year is 1940. I am working at North American Aviation. The folks
down the hall are working on a fighter concept, and the Blitzkrieg has
just been unleashed in Western Europe. With the fall of France, and
the Battle of Britain looming, I am tasked with designing a medium
bomber design to submit to the Army Air Corps and to other potential
customers in the Free World.

I go for a radial engine, because that is more reliable. I want the
biggest available, so I go with the Pratt and Whitney R-2000-8 Double
Wasp, which will also go on to power the Vought Corsair project.

http://www.warbirdalley.com/f4u.htm

I go with twin engines in conventional wing-mounted layout.

As I work at North American, I cheat a bit and steal some notes on the
work being done on a laminar flow wing down the hall. I base the wing
of the bomber on that, with laminar flow and with plenty of self
sealing fuel tank capacity.

The wing will be mounted in a high wing configuration. This will clear
the bomb bay for maximum capacity as well as raise the massive props
of the Double Wasp engines for more ground clearance. Perhaps a little
dihedral will also be added if it helps wind tunel readings. The
nacelles will have room for long main landing gear, and the rear
portions will be made of light wood if it can be comparable in weight
to aluminum. The nose gear will fold up between the bombardier's
position and the radio/bomb bay areas.

This brings us to the fuselage. The layout will be less in the Dornier
style, and more like the traditional American layout. It will be a
tapered, cigar shape at both ends, to help with streamlining. In the
middle, it will remain cigar like on top, while it flares out into a
more rectangular cross section at the sides and bottom. This will be
done in similar fashion to the B-24 Liberator, to maximise bomb bay
space and bomb load. Forward of the bomb bays, two slight triangular
fairings will smooth back into the fuselage just under and maybe a bit
in front of the cockpit, before the bombardier's position. They may be
engineered to help generate additional lift. They may also have an
additional purpose which I will get to later.

Weapons would also be similar to the B-25 and B-26, as Gernot was
saying. A glass nose for the bombardier is doable, with a single .50
caliber machine gun on flexible mount. (It can also be clamped
straight ahead if desired.) Standard two place cockpit. I am guessing
a standard twin .50 caliber turret in dorsal position, just behind the
cockpit. Remote controlled guns would be iffy, so I go with the new
twin turret here. Tail gunner's positon has a plexiglass top bubble
that can be jettisoned by pulling a pair of levers if they have to
bail out. Most likely twin .50 caliber machine guns would be the
armament although a 20mm cannon or two being there is a possibility.
The waist position would have a .50 caliber gun on either side,
mounted on storage brackets with a pneumatic or hydraulic cylinder.
When a cord is pulled, the cylinder aids the gunner in swinging out
the guns into fighting positions. A ventral ball turret is possible,
if there is enough ground clearance even with the high wing design.

The radio man usually had a gun, so I'd probably have a .30 caliber
or .50 caliber gun for them slightly aft of the dorsal ball turret.

The triangular "blending fairings" where the bomb bay fuselage blends
back into the cigar pattern at the front could also be used for
mounting guns. This is where I get a little different. I consider
mounting two 37mm cannon here, one on each side. Ammunition can be fed
by spring loaded magazines wrapping up the sides of the fuselage on
either side. I am thinking maybe 60 rounds per gun. They are an
option, and other weapons can be placed there or none at all. This
feature gives the aircraft unique forward firepower, especially for
1940. First flight is anticipated for late 1941 or early 1942,
although the fighter project down the hall is getting most of the
company's attention.

Aircraft: North American XB-27 Noreaster
Classification: Medium Bomber
Builder: North American Aviation
Powerplant: Two Pratt & Whitney R-2800 Double Wasp Radial Engines
2000 Horsepower each
Crew: Six (Seven with optional ball turret and gunner.)
Armament: Seven .50 caliber machine guns (Nine with ventral ball
turret) plus one .30 or .50 caliber gun for the radio operator, plus
two Oldsmobile 37mm cannon firing forward, plus bomb load projected
between 3500 and 4000 pounds.

What do you know... the P&W motors were the same as used on the B-26!

http://www.warbirdalley.com/b26.htm

It looks like the guys who built the B-25, the B-26, and the later
A-26 Invader got things down pretty well.

Another idea would be to use a turret with two remote controlled guns
in the "ball turret" position, controlled by the radio man. This could
put the gunner in the fuselage and allow for a more streamlined turret
with less ground clearance concerns. In 1940 that is pretty far off,
but hey it's worth a shot, though the Army Air Corps needs the bomber
design ASAP. Maybe I could consider it as an option and have some
people work on it as a possible option on a side team. (I doubt Boeing
has the idea in design phase for the B-29 yet, or if they did that
they'd let me hang out and take notes.)
.

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