On Sep 13, 8:00 am, Eunometic wrote:
On Sep 13, 1:55 am, "Ken S. Tucker" wrote:



On Sep 11, 4:08 pm, WaltBJ wrote:

I was attending the Air Defense Command's Interceptor Weapons School
back in 1963 and one of our lectures was "Future Developments' by a
team from Wright Pat Air Development Center. In the course of events
the 'suits' mentioned chaff rockets - folding-fin 70mm rockets fired
from a bomber that dispensed spaced bundles of chaff to mask the
bomber and draw off radar-homing missiles. The 'suits' complained that
they had tried firing them sideways out of a special turret mounted on
a B29 but the rockets insisted on going straight ahead. We looked at
each other incredulously and finally one of our group asked "Did you
ever consider that there was a 300 mile an hour wind blowing past the
rocket launch tube?" No, they hadn't . . .

Yeah rockets are designed to point into the wind,
that's why the fin's are at the back!

Indeed, prior to development of the R4M "Orkan" (Hurricane) folding
fin rocket (this was the grand daddy of all such rockets) German
researches put a great deal of effort into pure spin stabilized
rockets that could easily be fired from tubes and 'revolver' style
magazines eg RZ65 and RZ73. Although they worked their dispersion was
simply to great to make them particularly effective Air to Air or even
Air to Ground weapon that could engage point targets and as a result
the folding fin rocket was born. Admittedly the R4/M may just have
also had the advantage of a more powerful rocket motor to give it
speed.

Having said that the pure spin stabilized rocket would surely be far
superior and possible totally effective in lateral launches with
enormous cross winds, which on a B-29 would approximate 150ms.
Assuming a 100G acceleration to 500m/s over a 0.5s boost the bulk of
the acceleration is within the cross wind and one would expect the
rocket to expend most of its acceleration heading into the direction
of flight. In the 500G case things would be only a little better but
not that much. Fins will quickly orient the rocket in the direction
of airflow.

A flat plate has a Cd of about 1 so assuming a pair of fins on a 70mm
rocket has a total area A of 10cm x 10cm (0.01sqm) the force in
Newtons will be F = 0.5Cd x p x A v^2 where v = velocity in m/s and p
= air density in kg/cubic meter. Assume 330mph or 150m/s later launch
at about 5000ft where air density is about 1kg/cubic meter

F = 0.5 x 1.0 x 1.0 x 0.01 x 150^2 = 112N or about 12Kg.

A missile weighing a few kilograms will very quickly orient in the
direction of flow. A 2 kg mass at the tail will accelerate at 112/2 =
56m/s more than at the nose. In 0.1 sec during the boost phase
seconds it would move 27cm relative to the nose section of the rocket
which is enough to orient it about 45 degrees. If the burn was 0.5
seconds it would more or less end up flying with the bomber.

That's agreeable, however the initial correction
could impart enough yaw - via inertial moment -
into the missile to blast it into the cockpit!

Bullets obviously don't change direction and they don't have fins.
Only the relatively lighter weight of the tail would induce it to
accelerate faster than the warhead nose section.

Modern MEMS inertial guidence technology combined with finless thrust
vectoring nozzles would make it easy to accurately launch and guide
missiles from aircraft at almost any angle. Take a look at the
guidence system of the MBT LAWhttp://en.wikipedia.org/wiki/MBT_LAWhttp://www.army-technology.com/projects/mbt_law/

We launched a small experimental rocket in a 20-30
knot stiff breeze and decided to point the launcher
into the wind, that was a mistake. What we should
have done is pointed with the wind, because it get's
twisted at lift-off.
We wrote up a "sim" to confirm that.

I believe it is also known by bazooka launchers that the missile has
to be fired 'with the wind' rather than against it to compensate.

Interesting to know.
Ken