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C Payload Altitude
For NARAM-50, the Payload event is for C engine
class.
Payload Altitude combines the challenge of flying a standard size
and weight payload while trying to fly to the highest possible altitude.
The payload needs to be completely enclosed in the model, and remain
inside the model from launch to return. Nothing can be permanently attached
(i.e. glued) to the payload.
Payload Altitude models can be staged, though this does not seem to be
beneficial for B class based on the current choice of engines.
Payload models MUST use a PARACHUTE for recovery. The chute needs only
to be large enough for a safe recovery.
For the full rules for this event, please see the Payload Altitude Rules
on the NAR web page.
Scoring - For Payload Altitude, the scoring is best SINGLE
qualified flight altitude of two flight allowed. The model must be returned
on each flight, in order to confirm the payload was not altered or lost any
mass.
Design considerations - Designing and building a low-drag model
that must hold a one ounce payload that is the same diameter as most body
tubes used for 18mm engines, to fly as high as possible
Payload specifications - To quote the Pink Book rules, from 25.2:
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"The standard NAR model rocket payload is a non-metallic cylinder
containing fine sand, with a mass of no less than 28.0 grams. This
cylinder shall be 19.1 +/- 0.5 millimeters in diameter, and 70.0 +/- 10.0
millimeters in length. The payload may be permanently sealed to prevent
the loss of the sand. No holes may be drilled into it, no changes made in
its shape, and no other material may be affixed to it."
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No need to grab any calipers, here's what this effectively means: The
payload diameter happens to be about the same external diameter as an Estes
BT-20 body tube. Payload models need to have a payload section that is
larger in diameter than the payload in order to house the BT-20 diameter
payload inside. The payload length can vary from 60mm (2.362") to 80mm
(3.15").
NARAM-50 Payload Official
Information:
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Payloads will be available for all contestants, and may be kept
afterwards as souvenirs. The provided payloads will be made from standard
BT-20 tubing, 2.75 inches (70 mm) long, and weigh 28.2 grams. Contestants
may use their own payloads if they choose.
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Scales will be available at
check-in for contestants to use to verify the mass of their payload, but
pre-flight weigh-ins are not required.
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ALL payloads will be weighed and
measured at returns.
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Building and flying this event - There are not many good plans
available for this event. Before July 1979, the NAR standard payload was a
very short (1/2" long by 19.1mm diameter) lead cylinder. This is why
earlier payload designs had short payload sections as they were designed to
loft 1/2" lead payloads. Payload is not flown as often today, so there
are not many published designs for the longer (sand-containing) payloads.
The list of plans is somewhat limited and some of the old lead payload
plans would need for the payload sections to be lengthened quite a bit.
Fortunately, ASP and QCR have
contest-quality payload rocket kits available, as listed
further down this page.
If the old Apogee B7 motors (13mm diameter) were still contest
certified, the optimal designs for this event would look much different
with the rear half of the models tapering down to 13mm tubing. As staging
13mm A's is not a good choice this narrows the practical options to a
single 18mm B engine.
A key to any altitude event is building the model to fly straight and
true. Work towards attaching all of the fins so they are straight and
parallel to the body. This should translate to a straight boost, with minimal
wobbling that would hurt the altitude. A good finish is important for
altitude models. Don't overdo it though, it helps to keep the model as
light as possible, even though it is carrying a one ounce payload. As
weight goes up, peak altitude goes down. Try to focus on light weight
designs and not build too heavy.
Sources for 20mm tubes and noses - If you want to build from a
plan, or design from scratch (instead of using the ASP or QCR kits), here
are sources for the body tubes that slip fit over BT-20 tubes and nose
cones to go with them:
- ASP (Aerospace Specialty Products) - Nose
Cone: #BNC20TT TT - 20 Wood Nose Cone
- ASP (Aerospace Specialty Products) - Tube:
#TT - 20 Telescoping Tube (.745" ID, .785" OD,
30" L, wt 22 gm)
- BMS (Balsa Machining Service) - Nose Cone: (order a custom
made parabolic nose cone to order to match the tube diameter)
- BMS (Balsa Machining Service) - Tube: #T20Q-34
.787x.748x.039x34 MPC/Quest T20 (this tube is a bit thick
and heavy)
- Apogee Components - Nose Cone:
#19091 Wood Nose Cone 19mm, .765" O.D.
- Totally Tubular - Tube: #T-20+
(slips-over T-20) 0.770 O.D. x 0.744 I.D (thinner & lighter
than BMS' tube)
- Quest - Tube: #T-20 This tube is
not sold separately from their kits, and it is hard to suggest buying
a kit just to cannibalize. However, the Quest "Sprint" kit
can be modified to be a payload model (see plan/kit list below). The Quest
T-20 plastic nose cones are somewhat heavy compared to other nose
cones..
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Tracking Powder - It is highly recommended to use tracking
powder in your model. This produces a small "cloud" at ejection
which the tracking crew looks for. Without tracking powder, it is not
likely your model will get tracked.
Dry Tempera paint, or a fine powdered Fluorescent Dye, are often used
for tracking powder. Some contestants used to rely on powdered chalk, but
it is clumpy and does not really produce much of a tracking cloud for the
volume/weight of the powder. Red is a good color choice for tracking
powder, though some like to use black if there is a high overcast or hazy
"white" sky. Fellow competitors are often willing to share
tracking powder.
Here's a good way to install tracking powder. After installing
wadding, pack the parachute and shock cord into the model, and push them
down into the tube to leave room for the tracking powder in the upper
part of the tube. Use a piece of wadding or plain paper to make up a long
narrow "cup" than will easily slide inside the body tube. Press
that cup into the tube, then pour in the tracking powder to fill the cup.
About 1" or so depth of powder is a good ballpark. Using tracking
powder can require greater forces to expel everything out of the body,
which sometimes results in the engine kicking out instead (however, the
cup method reduces this problem a bit compared to just dumping powder
into the tube). Make sure the engine is secured in the rocket
extra-tight. Some people like to attach the fins a bit above the bottom
of the body tube so they can apply a "collar" wrap of tape to
the bottom of the tube and the engine. This helps prevent the engine from
ejecting.
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click on thumbnail
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Above: Example of a tracking powder
cloud, having ejected from a model that was stuck in its launcher.
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Engine recommendations for C
Payload Altitude:
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C6-3 (abnormally heavy or
draggy model, like an Alpha with payload section added)
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or
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C6-5 (typical contest
payload models)
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or
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C6-7 (low drag light
contest payload models, pistoned models)
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