Model rocketry tips and techniques?
Leslie Houk
to get a thread started. Do you have a tip or idea for your fellow
model rocketeers? If so, post it, and let's see if we can make RMR
useful again.
To start off, here's an idea I haven't seen elsewhere. The narrowest
roll of masking tape I've seen is 3/4 inch, but sometimes you need it
to be thinner. For example, to make a thrust ring on a 13mm engine,
or to secure an engine hook to a 24mm reload engine. In those
situations, I use floral tape -- the green tape that florists use to
make flower arrangements. It's cheap, available in any craft or
floral store, and comes in 1/2 inch widths.
Anyone have any other tips?
Leslie
DJ Delorie
Use slow-setting epoxy for larger body tubes - yellow glue grabs too
quickly, risking an incomplete connection between parts if it grabs
before you're done inserting the BT.
Leslie Houk
tubes, you have to make sure your guide lines are drawn straight along
the length of the tube. My favorite way to do this is by using angle
irons -- "L"-shaped lengths of metal -- as a guide when drawing the
lines.
My local Ace Hardware store sells 1/2" x 1/2", 3/4" x 3/4" and 1" x 1"
aluminum angle irons in 4' lengths. If you don't have a local
hardware store that carries them, one online source is http://www.onlinemetals.com,
which sells 6063-T52 aluminum angle irons in various widths and
lengths. (I'm sure there are other sources, but that's the first one
I found while searching online).
Leslie Houk
power and larger rockets, you need to use epoxy. When I use it, I
tend to repeatedly mix small amounts -- for example, mix a little up
and make fin tang fillets inside the body tube, wait for them to dry,
rotate the rocket 90 degrees, and repeat three more times. I've found
it handy to keep a box of toothpicks and a box of kitchen wax paper in
my workshop. When I need some epoxy, I tear off enough wax paper to
give me a mixing surface, and use a toothpick to mix it.
The toothpick is also good for applying the mixed epoxy to accessible
areas, but for applying it to recessed areas in a body tube I use
shish kebab skewers. You can get a bag of 100 ten-inch skewers at
most grocery stores for a couple of dollars.
Bob
> White glue is great for model rockets, but when you start building mid-
> power and larger rockets, you need to use epoxy.
A common fallacy.
While I'd use yellow glue instead of white glue for my models, yellow
glue works fine on any size rocket as long as the materials being
bonded are wood and paper. In fact, any good yellow glue is going to
make a stronger bond between wood and paper than 5 minute, 30 minute,
and even the aircraft/boat building epoxies like West and System3. The
mass market epoxies just won't hold up to motor mount heat, even on a
rocket as small as a Mosquito.
I tested this to the extreme over a decade ago, building a THOY Hornet
(same size as a Graduator or Initiator, 29mm MMT, I added a baffle
system to the MMT) with nothing but Titebond. To date it's flown on
everything from a D to an H238, which is the limit of what will fit in
the motor mount.
A rocket like a LOC Magnum, a popular L2 kit, would have no problem
flying on a J or more even built with Titebond.
Of course regardless of glue, you need to use proper building
techniques everywhere, such as fillets and reinforcing where needed.
When you switch to materials like G10, fiberglass, and the like, then
you do need to use epoxy. But not until then.
Leslie Houk
> On Nov 12, 11:23 am, Leslie Houk <lh...@ghg.net> wrote:
>
> > White glue is great for model rockets, but when you start building mid-
> > power and larger rockets, you need to use epoxy.
>
> A common fallacy.
> When you switch to materials like G10, fiberglass, and the like, then
> you do need to use epoxy. But not until then.
I stand corrected. Thanks for the tip!
§
One of my favorite tips is to use Future floor wax for the clear coat.
After the flying season is over I use Windex to remove the clear coat
and redo the process for the next flying season.
Ted Novak
TRA#5512
Peter Fairbrother
Not a tip as such, but - has anyone tried dimpling a rocket, like a
golf-ball?
It's been tried with cars, and they do go faster ...
-- Peter Fairbrother
ke...@askforaddress.com
They work great for grabbing things inside those small diameter airframes.
Kevin
Leslie Houk
>
> Not a tip as such, but - has anyone tried dimpling a rocket, like a
> golf-ball?
>
> It's been tried with cars, and they do go faster ...
>
> -- Peter Fairbrother
No one else has replied yet? I haven't heard of anyone trying this.
My off-the-cuff thought is that any gain in a rocket's aerodynamics
would be offset by the additional weight of the rocket coating, but
that's just a guess. This sounds like a possible NARAM R&D project.
Build a couple of rockets, one with dimpling and one without, and see
if one performs better.
Alan Jones
wrote:
One of my favorite rockets was a Big Bertha painted white and covered
with metal flake blue punched paper computer tape (an old altitude
prediction program). It was purely cosmetic, but it may also qualify
as a dimpled surface.
In your research, be sure to learn about separated flows, and how the
type of boundary layer affects separation. If you find a rocket
design that may benefit from inducing boundary layer transition, you
can research more effective ways of tripping the boundary layer on the
rocket than dimpling. You might also discover that using vortex
generators can be even more effective.
Dimpling etc. will not improve a typical well designed rocket,
although you may find an exception. In general you just want a well
built and finished model with a rubbed/waxed finish.
Alan Jones
Leslie Houk
favorite method, and I know that someone will chime in with "but it's
really simple to..." But I just get discouraged when I take the time
to carefully sand my balsa fins into an airfoil shape, then spray
Krylon Sandable Primer onto them, only to watch the air bubbles form
due to all the air in the grain.
So what do I do? Replace the balsa fins with basswood ones. Basswood
sheets are available in most hobby stores, and basswood has a much
finer grain than balsa. A single light coat of Krylon Sandable Primer
is usually quite sufficient to give me a smooth finish.
Bob
Back in the day I brushed on coat after coat of sanding sealer, balsa
fillercoat,
and Aerogloss dope until I got mirror like finishes. Then I did the
same with an
airbrush. PITA!
The best method I've used lately is to fill the grain with Elmers Fill
& Finish (or
whatever they call the product today), then prime & paint. For the
fins, use a
plastic squeegee or an old credit card to spread it around. For the
tube spirals,
a glue bottle will deposit a fine line along the spiral better than a
brush.
One technique I learned from former Estes employees but never did
myself is to
coat the balsa surfaces with a thin layer of finishing epoxy, then
sandwich between
glass sprayed with Pam or some other release agent and weigh down with
phone
books. The epoxy hardens to a glass smooth surface that is easy to
prime and
paint. They used this for many of the catalog photo models.
Alan Jones
wrote:
Well, it is clear by the lack of replies, that there is no interest in
doing R&D, not even for a NARAM entry. Even though I view with
disdain those awful R&D projects where the "researcher" simply flys
two rockets with some difference between then, "observes" that A went
higher than B, and concludes that the difference was effective.
Nevertheless, I encourage R&D. At least the "researcher" benefits
from going through the motions of writing an R&D report. I was
prepared to offer some additional key words, and other help.
I would also like to suggest the opposite approach. Instead of
dimpling to hasten boundary layer flow from laminar to turbulent,
consider using riblets to try and stabilize the flow and extend the
laminar region or lessen turbulence. Riblets are fine surface ridges
parallel to the airflow. They are typically W ridges, similar to old
phonograph records. I think the idea originated with shark skin, yet
the technique is much more recent than the dimpled golf ball. I think
3M makes riblet tape that can be easily applied.
Alan Jones
Leslie Houk
my name, email address and NAR member number on them. I put one on
all of my model rockets, so that if someone comes across a rocket I
lost, they can get in touch with me.
David Erbas-White
As long as the email address doesn't point to a CompuServe or GeoCities
acoount... <G>
David Erbas-White