CONTROL LINE RACING - 2003/10

144 MODEL AVIATION
AS I WRITE this I am frantically getting ready for the 2003
Nationals, but all of the action will be finished when you read this.
I guess that is the way the magazine business is.
This past winter I made several trips to Texas, where I stopped by
John McCollum’s to test new Quickie Rat engines. During my
visits we tested new sleeves and made new rings for some of the
liners.
One of the big questions I get from people is, “How do I make
rings?” There are a couple of options. You can buy them from a
few different sources, which I will list at the end of the column, or
you can make them yourself if you have a lathe.
A couple of things you need to determine first are whether or
not the liner is round and its size. Without this information, even
buying a ring is a hit-or-miss proposition. If you do not have a
proper bore gauge, send the liner to someone to be measured, and
honed if required. Assuming that your liner is round and that you
know its size, purchasing a ring is easy; just provide the size of the
liner to .0001.
Many people think that making a ring is a black art, but it is
simple if you have seen one manufactured. John and I used
schedule 40 ductile iron for the rings we made. Other materials
may be available, but I get the best speed and results using the
iron. I have observed that rings made from other materials seem to
be slower, and I believe that is because of their metallurgical
composition.
Another thing to think about is the size of the slitting saw to put
the gap in the ring. I use a .010 saw, and I know that others use
smaller, and others even break their rings to create a ring gap.
The next step is to make a fixture to hold the ring while putting
the gap in it. This is just a piece of aluminum plate that the ring
rests on and a second piece of aluminum or steel that sits in the
land area of the ring and is bolted to the first plate. This prevents
the ring from springing open during the slitting operation.
The last task required is to make a fixture that will sit inside the
ring and allow you to lap the bottom of the ring. The lapping
procedure is probably one of the most important and probably the
most overlooked. You will get better results by lapping the ring,
providing that the land in the piston is in good shape. If it is not,
the piston should be thrown away or repaired.
Now that all of the fixtures are made—they are simple to make,
and it should take approximately an hour for all of them—it is time
to cut a ring. To determine its size, I use the following formula
(remember that I use a .010 saw): .010/3.1416 = X. X + bore is the
ring’s outside diameter.
Some experts will tell you that you are not actually producing a
round ring, and that is correct, but it is within .0002 of being
round. The sleeve will not be any better than that, especially after
it is run once. If you think .0002 is a large variable for a ringed
engine, adjust a set of micrometers to .0002, or even .0003, and see
if you observe a gap between the anvils.
Now that you know the ring’s outside diameter and you have
your material in the lathe, make the ring from the inside out. Bore
the inside diameter, then turn what is actually the top of the land
area. After that is done, turn the outside diameter to the required
size, then cut the ring off to the desired thickness. Keep in mind
that the land area is of the greatest importance; if it’s too small, it
will affect the performance as much as if the ring is too tight.
While the ring is a solid—meaning that there is no gap—I lap it
to get the land to the exact thickness I want. The lapping will
remove any burrs from the turning operations.
Now you are
ready to slit the ring
using the slitting
saw. After doing
this, you need to
just touch the
bottom lap area
because under
microscopic
inspection you will
see that the saw has
actually put a small burr on the ring.
If your calculations were correct, you will have a ring that
provides a snug fit at the top portion of the sleeve. As long as you
can move the ring to the Top Dead Center position, it will run in
with minimal effort. I run liners with no chrome, and after roughly
a minute of running, this fit provides a ring with a gap of
approximately .001.
If you are running a chromed liner, a new ring should be a tad
looser because the ring will not wear in as quickly and you do not
want it to be too tight; that would distort the ring or damage the
piston.
Before installing the piston, check its diameter and make sure
that it is not too tight in the liner. I suggest approximately .002
smaller piston than bore because the aluminum piston will grow at
a greater rate than the liner. Anything less than .002 could cause
piston drag and some galling of the piston in the liner.
With this finished, it is time to put your new ring on the piston
CONTROL LINE RACING
Dave McDonald, Box 384, Daleville IN 47334; E-mail: [email protected]
Aluminum Nelson .15 Rat pan is extremely lightweight.
This is overkill on ring fixture; top covers entire ring. But fixture
is important—must be used before slitting ring.
Excellent small hinge is made from brass
shim stock and stainless-steel wire.
October 2003 145
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and break in your new setup. Some light oil
is recommended before you start the
engine. Break it in slow, running it rich and
bringing it up to temperature, then backing
off. Following these steps should provide
you with a ring that will give you very
good results.
Henry Nelson has produced some
wonderful half pans for the .15 Rat event.
Although these pans were developed for
.15 Rat, they would make great half pans
for .21 Sport Speed or any category for the
.15- to .21-size engine.
Each of Henry’s pans is 8 inches long,
weighs 11⁄2 ounces, and is made from
aluminum. It features six hold-downs: two
in front of the engine, two behind, and two
at the back of the pan. The pan’s wall
thickness is approximately .045 inch. They
are also designed to give maximum area to
accommodate a fuel system.
Anything that Henry makes is first
class. I strongly suggest that you give him
a call and get your pans before the supply
is gone.
The debate is still going on regarding
the front-intake versus the rear-intake
engines. As you can see from one of the
pictures, I have decided on the front-intake
version. The minipipe is also a Nelson
product and should provide an extra benefit
in engine performance.
Sometime ago Stoo Willoughby sent me a
nice little hinge that is compact and stable.
The material is shim brass bent over
stainless-steel wire and soldered on itself.
As you can see in the photo, the brass has
been drilled with small holes to allow glue
to completely encapsulate it, providing a
stable joint.
The trick to the hinge is the small bends
in the stainless wire; these help prevent the
wire from pulling out of the wood, which
will cause hinge failures. The stainless wire
can be purchased from Small Parts in
Florida. Sizes for the wire and brass shim
stock depend on the size of airplane it is
being used on, so individuality for your
application may be required.
As always, your comments are solicited
and appreciated. MA
Rings:
John McCollum
300 VanZandt County Rd. 4717
Ben Wheeler TX 75754
Vic Garner
832 Jefferson Ave.
Livermore CA 94550
Frank Bowman
1211 N. Allen
Farmington NM 87401
.15 Rat pans:
Henry Nelson
121 Pebble Creek Ln.
Zelienople PA 16063
“$TOP PAYING TOO MUCH FOR BATTERIE$”
VISIT OUR WEB SITE! http://www.rc-aero.com/biz/bandt
GOLD PEAK 3300 NIMH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $5.50 Ea
SANYO 2600 NIMH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $4.75 Ea
SANYO RC-2400 SCR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $5.50 Ea
SANYO CP-2400 SCR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $4.50 Ea
SANYO CP-1700 SCR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $4.00 Ea
SANYO CP-1300 SCR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $3.75 Ea
SANYO KR-1400 AE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $3.50 Ea
SANYO HR4U-270 NIMH AAA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . $2.50 Ea
SANYO KR-600 AE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $2.50 Ea
SANYO N-700 AA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $1.50 Ea
SANYO 1700 NIMH AA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $2.50 Ea
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