On Mar 4, 2018, at 11:03 PM, Ben Brockert <wikkit@xxxxxxxxx> wrote:
That's fun. Could have the primary load path between the second and
third stage be a plate at some load bearing circle inside the third
stage nozzle, likely near the throat, with a ball joint at the center
of the plate. A post extends up from the second stage front closeout
and loads into that ball joint. Two small BLDC linear actuators near
the OML, 90 degrees apart provide the gimbal actuation.
A sheet metal split ring could hold the two parts parallel during
atmospheric parts of the flight, then spring off when it's time to
hula.
Frangible bolts hold the linear actuator at the clevis on the bottom
of the 3rd stage. Or just make the linear actuator so that if it is
run past its nominal stop, it unscrews itself. I've seen that down
accidentally before. Chamber pressure when the third stage is lit
ejects the gimbal closeout plate.
Cold gas and possibly yoyo despin in the interstage attached to the
first stage. Maybe a small cold gas roll thruster on the second stage
if it turns out to be necessary.
(With spinning solids can make orbit without gimbals or LITVC, but
it's a fun thought experiment anyway.)
Ben
On Sun, Mar 4, 2018 at 9:46 PM, rebel without a job
<rebelwithoutajob@xxxxxxxxxxx> wrote:
Gimballing the motor tends to have one goal: steer the rocket by moving the
thrust line relative to the CG. The relatively small, light, and distal
nature of the object being gimballed relative to the rest of the rocket
means that deflecting the engine in one direction causes a relatively small
deflection of the rest of the rocket in the other direction.
The BPS system appears to have two effects.
Since the pivot between the motor and the rocket is so far up and the entire
motor is being moved, not only is the thrust displaced relative to the CG,
the body of the rocket moves non-trivially opposite the movement of the
motor assembly, causing some aerodynamic effects.
Which leads me to an idle daydream about multi-stage solids:
The first (atmospheric) would be fin-stabilized as per standard hobbyist /
hpr design. It pushes the stack out to thin air.
The second stage is connected to the third stage by a movable interstage
coupler (covered by a fairing). Once the stack is out of the atmosphere, the
fairing is separated, and the stack is controlled by swiveling the joint
between the second and third stages, wiggling the mass of the third stage
relative to the thrust from the second stage for steering.
A similar joint would be placed between the third stage and the payload, or
any subsequent stages. Significant despin would likely be necessary to make
this work.
This would allow solids to be used without the inconvenience of a gimballed
nozzle that has to seal and pivot in the middle of the hot section.
On Mar 3, 2018, at 9:16 PM, DH Barr <dhbarr@xxxxxxxxx> wrote:
For commercial high end hobby solids it's probably more useful to think
about it as wiggling the nose rather than gimballing the motor. I'm not
aware of any write-ups in this regard.
On Mar 3, 2018 8:43 PM, "Charlie Garcia" <dragonrider.hhcc@xxxxxxxxx> wrote:
Robert,
Joe is building low power rockets for a reason. The design doesn't scale
and Joe will tell you the same. It actually has nothing to do with speed
though. You won't hit Mach 3 if you have a motor less than 1/3 of your
airframe diameter.
Any University using solids in a rocket like you propose would have a wide
set of engineering solutions to choose for control. A BPS style gimbal would
not be one of them. Since you're so inclined to call University groups and
hobbyists green, perhaps you'd regale us with tales of your launches.
Charlie Garcia
On Sat, Mar 3, 2018, 8:35 PM Robert Clark <rgregoryclark@xxxxxxxxx> wrote:
What I was wondering is if the methods used by BPS.Space would still
work when the rocket is traveling at supersonic speeds. They are rather
green:
https://www.youtube.com/watch?v=u-86tsFJ7lE
About the gimbled nozzles, university teams trying to produce one would
have the advantage of knowing what was already done and trying to reproduce
what has already worked.
Bob Clark
On Saturday, March 3, 2018, Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Sat, 3 Mar 2018, Robert Clark wrote:
The method likely could be modified to gimbal a movable nozzle only as
is
done with large solids.
Not easily or cheaply. The hot-gas seals used in the nozzle gimbals for
the big solids were a considerable technological achievement, and took
quite
a while to develop, which is why a bunch of other vectoring methods were
used in the early days of big solids.
A big question though is whether the method would
work for rockets at supersonic speeds.
Since it's been used for ICBMs and orbital launchers for many years,
there is little doubt of that.
Henry
