That is an idea that I've considered before, specifically regarding
pressure-fed rockets. Having a container full of an inert gas pressurized to
chamber pressure at the top of the rocket does sound very convenient for use as
a compressed air thruster. Venting that container in a few downward-facing
ports would provide some braking action. Since it's above CG, it has a degree
of passive stability (and also makes the control software much simpler).
Should the mass of pressurization gas not be sufficient, increasing the volume
of that gas involves merely enlarging an existing container.
Crush structures are relatively low mass, but they tend to be high volume.
Subject: [AR] Re: Flight Controller Features
From: george.herbert@xxxxxxxxx
Date: Sun, 10 Jan 2016 13:10:37 -0800
To: arocket@xxxxxxxxxxxxx
For the delta-V required from 10ish m/s on chute, a compressed gas / air
thruster would work without too much weight.
These aren't orbital mission mass constraints.
Also consider low cost crush structures. Land nose down with a meter of foam
in a thin aluminum shell, density tuned to absorb the on-parachute descent
energy entirely with margin.
George William HerbertSent from my iPhone
On Jan 10, 2016, at 12:34 PM, Ben Brockert <wikkit@xxxxxxxxx> wrote:
That's a fun idea that I've considered as well, though I see one possible
issue. Most of the places you can easily fly interesting experimental rockets
are in the desert, which tend to be covered in flammable brush. It would be a
pity to nail a retrorocket landing only to land in a fire you just started.
My scheme was to use a rear drogue or ballute and have the retro mounted in the
nose. That way it can be mounted on axis, the mass of the retrorocket
contributes to flight stability, and the drogue or streamer doesn't have to
overwhelm the fins.
I'm sure someone has done it at FAR at some point. There was a guy flying a
ramrocket there a few years ago, would have made a good topic of discussion.
Ben
On Sunday, January 10, 2016, David Summers <dvidsum@xxxxxxxxx> wrote:
If I were trying to stretch the current state of the art in amateur rocket
landings, I'd go for this:
1. At (or after) apogee, pop a streamer from the nose, keep the rocket
otherwise intact. This merely keeps the rocket nose up on the way down, and
makes it subsonic.
2. Make a really good altitude detection system, and 5 feet off the ground fire
a solid landing rocket that brings the rocket as close as possible to 1 foot
altitude, zero velocity.
That seems feasible, though difficult. Honestly from what I've seen I don't
think it would be that much worse than a parachute in reliability. We seem to
see a lot of parachute failures!
(I'm working on other things, but this is what I would build.)
Thanks!
-David Summers
On Sun, Jan 10, 2016 at 1:18 PM, rebel without a job
<rebelwithoutajob@xxxxxxxxxxx> wrote:
From an amateur perspective, parachutes seem to be the only cost-effective
solution. Active rocket landings imply a great number of technologies that are
outside the capabilities of all but the most well-heeled amateurs. The hardest
one would be a gimballed, restartable, deep-throttleable engine. Add to that
the control and lubrication of the gimbal system, and associated hydraulic
actuation and pumping, and I think we may be out of the amateur range
altogether.
At this point, building a flying biprop with some aerodynamic controls seems to
be the upper edge of the amateur capability.
A guided parachute seems wonderful. I’d prefer a choppy landing near me to a
choppy landing in a distant, unknown location. It also has the benefit of
being usable and testable by the large group of people flying high-power
solids, thus speeding development cycles.
For recovery of the motors, I think a few inflatable airbags may be optimal.
They would cushion the landing well enough to protect the tail end from the
initial impact. Depending on the lateral velocity, the airframe may be damaged
from a subsequent tip over. Reliable recovery of airframe and propulsion
system does seem difficult though.
On Jan 10, 2016, at 11:28 AM, Uwe Klein <uwe@xxxxxxxxxxxxxxxxxxx> wrote:
Parachutes provide for a rather choppy landing
that may not be over when you have touched down.
( And the payload tends to require carefull packing that comes at significant
cost in weight.)
Dragchutes should work well for energy management.
But for the actual landing something more sophisticated needs to be used.
You require point landing and very low speed final approach.
( Rocket engines are not designed or being dropped asswards on the ground)
We've seen that an active rocket landing works.
