Piper Cub Vs F-15

Cub Driver wrote:

On Wed, 30 Jun 2004 19:48:28 +0100, Alan Dicey
wrote:

I think this is also the kind of system the original poster was thinking
of, where the aircraft is kept from departing from controlled flight by
the flight control computer overriding the pilot inputs and keeping the
aircraft right on the edge of its flight envelope.

And would crash without the computer? As I understand it, a human
pilot can't control the B-2 unaided. Is that correct, and would that
be a fair definition of fly-by-wire?


That is my understanding of it. Some modern aircraft are designed to be
aerodynamically unstable (center of pressure in front of center of
gravity) in part or all of the flight envelope, for reasons associated
with stealth, variable geometry or vectored thrust.

Here's a couple of links with some basic descriptions of the B-2 FCS:

http://www.edwards.af.mil/articles98...er/page_5.html

http://www.globalsecurity.org/wmd/sy...-2-history.htm

recompose them to one line if they break in your newsreader.

Here's another discussion of flight control systems in general, with a
definition of fly-by-wire that seems to agree with mine in that it
specifies computer signal processing;

http://www.aero.polimi.it/~l050263/b...6-FligCont.pdf


From what I can find, it looks as if the B-2 is designed for
fly-by-wire control, probably to keep it stealthy as much as anything.
The flying wing shape by itself does not demand FBW, as the XB-35 and
YB-49 designs of the 40's were controllable without computer assistance.

From what I can find, it looks as if the B-2 is designed for
fly-by-wire control, probably to keep it stealthy as much as anything.
The flying wing shape by itself does not demand FBW, as the XB-35 and
YB-49 designs of the 40's were controllable without computer assistance.


The B-2 has FBW controls and a 6000 psi hydraulic system to move the control
surfaces for a number of reasons, mainly stability and weight reduction. I
have several friends who have flown it and they generally describe it's flying
qualities as F-111-like. The B-35 and B-49 designs were unsuitable as bombers
because of lack of directional stability expecially on a bomb run. If you
notice, the competition (B-36) has a large vertical fin.

Steve

The flying wing shape by itself does not demand FBW, as the XB-35 and
YB-49 designs of the 40's were controllable without computer assistance.

Not really. The 35 had those great engine pods, and the 49 had a bunch
of vertical fins, so in fact neither one was a true flying wing.
Nobody ever managed to fly the 35 enough to determine its utility (the
long shafts were the main problem), and the 49 was so afflicted by
dutch roll that the bombardier got sicksick. Plus there was the
question whether it (and a British flying wing design) wasn't prone to
spin around its lateral axis. The latter is disputed. For opposing
views see www.warbirdforum.com/cardenas.htm and
www.warbirdforum.com/tucker.htm

The Germans may have had more success with their nurflugels. It's hard
to tell; the most famous Horten design killed its test pilot in
disputed circumstances. I once corresponded with a Horten associate
who claimed that the problem with the Northrop designs had to do with
center of gravity, but I'm not enough of an engineer to follow these
arguments.


all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! weblog www.vivabush.org

Cub Driver wrote:

Plus there was the question whether it (and a British flying wing
design) wasn't prone to spin around its lateral axis.

Having built and flown experimental flying wings since 1996 I can
attest that if you find yourself in a spin around the lateral axis
(i.e: a "tumble") better hope you have jam in your pockets cos'
your ass is toast...

http://www.motolotnie.rsi.pl/mpg/film1s.mpg

Cub Driver wrote:
Not really. The 35 had those great engine pods, and the 49 had a
bunch of vertical fins, so in fact neither one was a true flying
wing. Nobody ever managed to fly the 35 enough to determine its
utility (the long shafts were the main problem), and the 49 was so
afflicted by dutch roll that the bombardier got sicksick. Plus there
was the question whether it (and a British flying wing design)
wasn't prone to spin around its lateral axis. The latter is disputed.
For opposing views see www.warbirdforum.com/cardenas.htm and
www.warbirdforum.com/tucker.htm


I read that the YB-35 managed to do without vertical surfaces due to the
props providing enough longtitudinal stability; although I'm not
entirely clear as to how that would work. In any case, when it came to
the YB-49 it was found that the turbines did not provide the same effect
and the vertical fins had to be added.

The British design would be the Armstrong-Whitworth AW52. Barrie Hygate
in British Experimental Jet Aircraft relates that it had severe probelms
of pitch sensitivity leading to oscillations, at least partly due to the
short control arm provided by the modestly swept back wing. One
prototype was lost in 1949 after entering divergent pitch oscillations,
the pilot making the first British use of a Martin-Baker seat for real.

All three aircraft needed at some stability augmentation system to be
safe and usable platforms. The AW52 was only ever intended as an
experimental type, to test laminar flow.

From: Alan Dicey
Date: 7/4/2004 5:27 AM Central Daylight Time
Message-id:

Cub Driver wrote:
Not really. The 35 had those great engine pods, and the 49 had a
bunch of vertical fins, so in fact neither one was a true flying
wing. Nobody ever managed to fly the 35 enough to determine its
utility (the long shafts were the main problem),

The main reason the 35 flopped was the contraprop gearing system was unreliable
so they went with the single props which radically affected performance.

snip

I read that the YB-35 managed to do without vertical surfaces due to the
props providing enough longtitudinal stability; although I'm not
entirely clear as to how that would work.

It wasn't the props as much as the drive shaft fairings.

snip

Dan, U.S. Air Force, retired

I read that the YB-35 managed to do without vertical surfaces due to the
props providing enough longtitudinal stability; although I'm not
entirely clear as to how that would work.

It wasn't the props as much as the drive shaft fairings.

Right, the fairings were long and (by the time they reached the prop)
high above the trailing edge of the wing, rather like the wing of a
paper dart. They would have acted very much like a vertical
stabilizer. (And created, as was posted, no end of problems with the
XB-35's propeller shafts, which vibrated.)

The fairings (and later the vertical fins on the YB-49) also served as
air dams, perhaps inadvertently solving a problem with swept-wing
designs, where the airstream tends to move laterally toward the
wingtips rather than straight back in the line of flight.


all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! weblog www.vivabush.org