February 2001 117
IT’S ANoTheR GReAT month for flying
RC (Radio Control) helicopters! It’s also a
good time for building and/or maintaining
for most “Northerners,” since it’s likely to
be unfriendly outside for flying.
Modelers are often asked if it’s
“possible” to fly during cooler weather—if
the helicopter can “take it” in temperatures
just above freezing. I tell people that the
only weak link with their helicopters in cold
weather is the pilot—it’s not possible to fly
well if your thumbs have lost all feeling!
If you are comfortable flying in the weather,
go ahead and fly. The lower temperature means
a lower “density altitude.”
Density altitude describes how much air
is in the air, to paraphrase from my pal Rick
Allison. The colder it is, the more dense the
air is at any given actual altitude.
Cold weather and the accompanying
denser air is good for engines and airfoils.
The engines gain three advantages:
they have cooler air blowing over them
for cooling, the air is denser, and there’s
more “air” in the air, meaning you need to
richen the needle as temperatures drop in
order to keep the fuel/oxygen ratio at the
optimum setting.
Think of it as a climatic supercharger,
allowing a denser fuel/air mix in the
chamber. This allows the engine to put
out more power than it will in warmer
and leaner times.
The blades benefit because they are
flying in denser air, giving them more “bite”
at any given angle of attack. I suspect there
is a point where you should be concerned
about fiberglass or carbon blades becoming
brittle in extreme cold, but I doubt you
would fly in such temperatures.
Qualified engineers can feel free to
write me, and let me know the scoop on
that situation.
There are other parts on your
helicopter besides engines and blades,
and some of them need attention if you
want to fly in cold weather.
When the mercury drops below
approximately 50°, pay close attention to
your gyro—especially the modern headinghold
variety. They come with instructions
that are quite clear about warning you to let
the gyro acclimate to the flying conditions.
If you take your helicopter out of your
warm house and transport it to the field in a
warm vehicle, you do need to let it sit
outside for 10-15 minutes so the gyro can
stabilize at the current temperature. Failure
to do so can—and will—cause you grief!
Battery packs also have no love for
cold weather. They will work, but watch
them even more closely than in warm
temperatures.
All batteries I know of lose capacity
as the thermometer drops. It’s not wise
to fly without checking your packs
anyway—even in warm weather. It is
foolish to make assumptions about
remaining capacity when it’s cold out.
If you watch the batteries, let the gyro
acclimate, and richen the needle on your
engine, you can enjoy your favorite sport at
freezing temperatures, or slightly below.
Just remember that you’re doing this for
fun, so don’t get yourself frostbit and don’t
try to fly if you can’t feel your thumbs!
Raytek® Retake: I wrote about the
Raytek® infrared thermometers in the
October 2000 column.
I have word that Horizon Hobby has
picked up the Raytek® line, so you or your
dealer now have at least two places to get
these nice engine-tuning tools. (Horizon and
HeliProz distribute the Raytek®
Eric Hawkinson, 319 Yellowstone Ave., Billings MT 59101; E-mail: [email protected]
RADIO CONTROL HELICOPTERS
Eric’s JR Ergo 60s with PPG Concept® paint jobs. Text has details.
Eric Hawkinson’s Ergos, showing cutouts for fuel-tank visibility, muffler clearance.
thermometers to dealers, and both have
retail sales divisions).
Great Planes announced that it
distributes a similar device. It’s a bit more
expensive than Raytek®, but it should be
easy to find at your local dealer with Great
Planes’ vast distribution network.
Whichever one of these devices you get,
you’ll have less guessing and more
consistency when tuning engines.
Painting canopies: This month I have a
couple pictures to share; the subjects are my
Ergo 60s. I don’t have any pictures to show
of the helicopters readers are building and
flying, but perhaps you can send me some!
These shots of my Ergos will have to
suffice for my discussion on painting
fiberglass canopies for a showstopping finish.
The first thing most of you will notice is
that these are not the stock molded canopies.
The stock canopy is very rugged, but
is also pretty heavy, and is made from a
special “decal-and-paint-repelling”
substance. So I bought some of the
molded fiberglass canopies and painted
them. (I’d rather work on that sort of
project than try to fly during a typical
Montana winter!)
My raw canopies came from a dealer
who had them made for his shop, and the
quality of the fiberglass work was very
poor; I put a lot of extra work into
finishing them.
Now you can get a fiberglass Ergo 60
canopy from your JR dealer; I’ll probably
paint some of those for next spring’s flying.
The fiberglass work on these Revolution
brand canopies is excellent. I’ve probably
had 50 of the Ergo and Vigor canopies, and
they have all been top quality. There are no
external seams, which eliminates one of the
most annoying parts of many fiberglass
finishing projects.
The Revolution Ergo canopies are very
light; even after painting them, I shaved a
couple ounces off compared to the molded
canopies. And there were very few pinholes
in the canopies I’ve painted. They are
worth the price tag.
Before priming the canopies, I made
the side cutouts for the mufflers and cut
out the side windows. I also like to make
cutouts in the lower “door” areas so I can
see the fuel tank, which is otherwise
hidden inside the canopy on the Ergo and
Vigor helicopters.
Make whatever arrangements you need
to for mounting your canopy. In general,
make it ready to mount and fly before you
start priming and painting.
Give the canopy a thorough bath with
warm (not hot) water and mild detergent.
Rinse it thoroughly, and let it dry.
Now give the canopy a careful
inspection. Any visible imperfection in the
fiberglass needs to be fixed. Fill moderate
pinholes and any flaws in seams with a
polyester patching compound. Let it dry
completely, sand it down, and look again.
You won’t see all the pinholes at this
stage, but don’t worry—you’ll see them
when you prime. Clean the canopy again
with paper towels and rubbing alcohol,
and let it dry.
Everyone has his or her own paint
preferences. I used to like Super Poxy,
but the new product is not the same as the
old and I haven’t been able to get
comfortable with it.
These days I do all my painting with
PPG’s Concept® acrylic urethane paints.
I use PPG’s catalyzed white K-36
primer because it dries fast, flows well,
and sands easily if you follow the
instructions. You’d do well to use this
primer even if you don’t use the PPG color
coats, because it is fuelproof.
The primer is a bright white; it can be
the primer and the base color if you are
going to spray a clear coat.
Whatever you use, wear the called-for
safety equipment. A simple paper mask
is not adequate. Ask your paint dealer
which type of respirator should be used
with your paint. While you’re at it, pick
up some cheap paper “overalls” and
some latex gloves.
Follow the instructions for mixing the
primer, activator, and thinner. With the
canopy free of oil and dust, spray on a tack
coat of primer, wait 5-10 minutes, and
follow with a fill coat.
When it’s dry, sand it with 240-grit,
then 320-grit open-coat paper. You’ll
probably see a few more pinholes. Use
the patching compound to fill those
pinholes. When that’s dry, sand the entire
canopy smooth.
Go on to color coats if there are no
imperfections, and you are going to spray
color over the entire canopy.
If there are any big patches or spots
where you sanded the primer unevenly,
spray another coat of primer. Keep priming
(lightly) and sanding until you have a
perfect surface to paint.
With PPG Concept®, mix the color
coats using more reducer (thinner) than the
instructions indicate. They presume you are
painting cars and trucks, where weight is
not an issue. You want a fairly thin mixture
that can be sprayed with the lowest possible
air pressure (without splotting).
I have used two types of equipment
on the canopies: an expensive HVLP
(high volume, low pressure) gun and a
Paasche double-action airbrush. On
small parts, such as helicopter canopies,
I prefer the airbrush for paint and the
gun for primer. Either will do a good
job, so use whatever you prefer or what
you already have.
After setting the pressure and the gun,
spray a very light tack coat of your base
color. You should see plenty of the
primer under this coat—do not
completely cover the canopy. This coat
provides adhesion for the next coat.
Let the tack coat flash off for
approximately five minutes, then go
back and spray a light fill coat. This coat
needs to go on “wet,” but stop spraying
as soon as you have coverage. Do not go
back and spray a third coat—you’ll just
add unnecessary weight.
Wait a day for the base coat to cure
before applying trim colors. Clean the
canopy with rubbing alcohol and paper
towels, then mask off the area for your first
trim color; the 3M™ blue or green trim
masking tape gives the best results.
Spray the trim the same way you did
the base coat. Wait 30 minutes, then very
carefully remove the masking tape—
without touching the fresh paint! (Pulling
the tape early lets the paint edges cure
more smoothly.)
Repeat the above steps for remaining
trim colors and you’re halfway there!
Now decide how nice of a finish you
want. You could just stick on the decals
and spray on a clear coat. It will certainly
look better than the plastic canopies.
For the best finish, wet-sand the edges
of the trim colors to smooth them down
after the paint is cured. Do so with paper no
coarser than 320 grit.
Sand the entire canopy with 600-grit
wet-or-dry paper, used very wet. The
sanding will kill the gloss, but don’t
worry—the clear coat will fix that.
You’re just sanding to remove all the
“dimples” in the paint.
The paint will have small dimples in it,
just like your car does if it has been painted
in the past several years. You don’t notice
them on your car, because they are
proportionally very small.
Clean the canopy well, then put on all of
the decals and any lettering or panel lines
you desire. One more cleaning, and you’re
ready to spray on that clear coat!
The clear coat is the hardest one to put
on, because it’s clear! Make sure you have
lighting that lets you see the “sheen” of the
paint as you spray it.
Spray a light tack coat then spray a
wet-fill coat, as with the colors. If you
miss a spot, go back and spray the whole
canopy with a very thin coat. This adds
weight, so be careful and get the entire
canopy painted in one coat.
When you’re satisfied, clean the gun
and go away for a day.
At this point, you should have a
beautiful canopy just waiting to go fly.
The clear coat will have the same small
dimples in it that the colors did. If that
doesn’t bother you, put the canopy on
your helicopter and coat it with a highquality
car wax. It should be a big hit at
the field.
If you want the “glassiest” finish possible,
hold off on waxing until you’ve spent some
more quality time with the very wet 600-grit
paper, followed by even more time with a
high-quality polishing compound.
If you go that route, you’ll be
rewarded with the most glossy, beautiful
paint job possible. (You’ll also be
extremely upset if/when you have an
accident with that helicopter!)
I’m out of space. Until next time, fly safely
and happy rotoring! MA
118 M ODEL AVIATION
