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Rocket recovery

A recovery system is used to return aothers. At the same time, the longer it
rocket to the ground without damage totakes to get down, the further it will
the rocket or objects on the ground. Thedrift in the wind on the way down.
typical recovery mechanism is aIn most cases you're aiming at a 20 fps
parachute. The components of oneor slower vertical terminal velocity. If
rocket's recovery system are shownyou fly to 1000' in a 5 mph wind and
below.have a 20 fps descent rate, you can
Rocket with Recovery Systemexpect 367' of horizontal drift. You'll
This rocket uses an altimeter to splitget about 734' with a 10 fps descent
the rocket at about the midpoint atrate. The longer it takes, the further
apogee. A small (drogue) parachute isit drifts.
used to stabilize the rocket's descent,Featherweight recovery: The rocket is
but not to significantly slow thelight enough (less than an ounce
rocket. Causing the rocket airframe totypically) that it won't do damage when
fall horizontally to the groundit hits (Estes Quark is an example). Or
maximizes drag, slowing the rocket. At athe rocket could have enough drag that
low altitude like 300' or 600' theit's terminal velocity is very low
altimeter causes the main parachute to(Estes Snitch). Often times the motor is
be deployed from the top section of theejected to make the rocket unstable too.
rocket. The ejection charge for the mainEjecting motors is not allowed in NAR
parachute is located above the altimetercontests unless a streamer or parachute
bay and cannot be seen.is attached to the ejected motor.
The main parachute is stuffed into aBreak-Apart recovery: Simply breaking
Nomex cloth deployment bag. The bagthe rocket in the middle and attaching
protects the parachute from the ejectionthe two sections by a shock cord will
charge.work for many small rockets. They won't
Single Stage Recoverycome in streamlined. It would be
Some rockets use only a single (main)possible to make large rockets, with
parachute, which is deployed at apogee.very large surface area and relatively
An ejection charge activated by thelow weight that would be safe to recover
motor, or an electronic device like anthis way.
altimeter or timer may be used to deployStreamer Recovery: The streamer adds
the parachute.drag and slows the rocket. The bigger
Two Stage Recoverythe streamer, the better. Anything over
Two stage recovery uses a drogue10 oz will not really benefit much from
parachute deployed at apogee and thea streamer. NAR requires 10 square cm of
main parachute deployed at a lowstreamer area per gram of mass in
altitude like 300' or 600'. This is donecontest models. Conversion to American
to minimize the distance a rocketunits is left as an exercise to the
drifts. This technique uses anreader. Streamers run afoul of the
electronic device like an altimeter orprinciple of diminishing returns when
timer to deploy the main parachute, andthey are enlarged. Eventually, adding a
it also usually deploys the droguebigger streamer will only add a small
parachute. Sometimes a streamer is usedbit more drag.
instead of a drogue parachute.Parachute Recovery: Using a parachute or
If a drogue parachute is deployed atparasheet for drag. Because of the
apogee and the rocket is suspended fromefficiency of parachutes, this is the
the parachute rather than fallingmost popular way. You get more drag with
horizontally, a larger drogue parachuteless cloth than in any other way. NAR
will be needed than if the airframerequires 5 square cm per gram of mass.
falls horizontally, which adds weight. ABecause of this efficiency they are used
horizontally falling airframe hasfor virtually all high power projects.
maximum drag, which helps slow theHelicopter Recovery: Using rigid blades
rocket. Therefore a smaller, andand auto-rotation to slow terminal
lighter, drogue chute can be used.velocity. Usually the whole rocket must
Parachute Deployment Bagbe designed around this recovery method.
Typical deployment bag arrangementThis is usually limited to small rockets
Deployment Bagas the stresses of a rapidly spinning
A deployment bag is literally a bag intorocket touching down are enormous. I've
which a parachute is packed. A bag canseen and heard of only 1 J800 powered
have one or more purposes, dependinghelicopter recovery rocket. Very
upon how the recovery system works. Thespectacular and it sustained damage when
two common purposes in a high powerit touched down.
rocket is to protect the parachute fromGliding Recovery: Using lifting
hot ejection charge gases and particles,aerodynamic surfaces to control the
and for orderly deployment. A commonterminal velocity. Since the aerodynamic
material for deployment bags is Nomexrequirements of vertical flight and
cloth, which is fire resistant.gliding flight are usually mutually
Orderly deployment means that theexclusive, there needs to be some sort
parachute's suspension lines are fullyof mass shift to allow transition
extended, and the harness is tightbetween vertical flight and gliding
before the parachute inflates. Thisflight. In addition, since the a glider
reduces the opening shock forces. Aand a rocket are optimized in mutually
large parachute opening force can tear aexclusive ways, all gliding rockets
rocket or recovery system apart.represent a compromise between these two
A pilot parachute (a small parachute)competing requirements. Even very large
may be used to pull the deployment bagrockets can be glided down. Many folks
off the parachute. Some deployment bagsuse radio control to fly their gliding
are designed to serve as its own pilotrecovery rockets.
chute.And this is not necessarily all. You
In all cases the aim of the recoverycould deploy a lighter than air balloon
system is to slow the rocket down. Allthat slows the rocket's descent. You
recovery systems decrease the terminalcould have huge air-brakes deploy from
velocity in some way, either through thethe rocket body. It depends on what you
properties of aerodynamic drag orwant.
aerodynamic lift. It might be possibleWhich one is best? It all depends on the
to use buoyancy as well, but I've neverrocket and what you're trying to do with
seen it done.it. For anything over a few ounces,
Two things to consider. You need tothough, parachute recovery is pretty
bring the rocket down slow enough thatmuch the baseline. They are the most
it presents no danger to itself orefficient for their weight and bulk.



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