122 MODEL AVIATION
QUICKIE 500 RECORD: It’s great to be able to trumpet an up-andcoming
young Pylon flier’s accomplishments. In this case it’s Tanner
Pacini’s; he set a Junior record in Quickie 500 (AMA event 428), or Q-
500, at the annual Winterfest two-day meet hosted by the Speedworld
R/C Flyers at their field near Phoenix, Arizona.
I received the accompanying photo and the following note from
Tanner’s parents Tony and Donna Pacini, who are proprietors of the
Valley Hobby Shop in Prescott Valley, Arizona.
“Our 12-year-old Tanner Pacini is now the current national Q-500
record holder in his age group (Junior). He broke the existing record
(1:11) twice this weekend at Winterfest, first with a 1:10, then again
with a 1:09. Fast time for the contest was a 1:06 (Randy Bridge). For
reference, the current Senior record is 1:05 and the current Open record
is 1:03.
“Also note that this was Tanner’s first Q-500 contest. We have high
hopes for him at the JR Gold Cup Quarter 40 race next month.”
As a follow-up, I did see the Pacini family at the Gold Cup, and
Tanner and his dad were tough in that event. Congratulations!
Correction: A typo in a previous column gave the wrong telephone
number for Pete Reed, who is the current Pylon Racing Contest Board
chairman and the man to see for a high-quality, handcrafted National
Balsa Intimidator Q-500 aircraft at $200. The correct number is (603)
532-8975.
RCPRO Web Site: Speaking of sources and methods (the CIA can’t,
but we can), there’s been a great deal of activity and many upgrades at
the RCPRO Web site—www.rcpro.org/html/—which Don Stegall
(Monroe NC) maintains. The site now includes viewable and
downloadable video footage of racing action, building tips, and other
good stuff, and it has links to other sites.
It’s a challenge for newcomers to find the latest and greatest racing
gear, since much of it comes from small-scale “garage shop”
operations. It’s also a challenge to convey the thrill of racing in mere
words and photos. All too often we have to fall back on the old
“You’ve just gotta come out with me sometime and see it for
yourself!”—which sounds sort of lame and isn’t very efficient. RCPRO
takes a big step toward solving both of those problems.
RCPRO is not, nor does it aim to be, the AMA-recognized SIG for
RC Pylon. The National Miniature Pylon Racing Association
(NMPRA) fills that role, and it is accessible through its Web site:
www.nmpra.org/.
Engine Break-In: Spring is here, and with it comes the perennial
question: “What do I have to do to ‘hop up’ my engine so I can race
with you guys?”
Somehow the notion persists that an engine is no good for racing
unless it has been brutally attacked with a hand grinder, dismembered,
and remanufactured according to an ancient family recipe available
only to senior Freemasons and the chefs who prepare that “secret”
hamburger sauce. In fact, Henry Nelson and Dub Jett put an end to that
nonsense, beginning at least 20 years ago, by offering racing engines of
championship quality right out of the box.
Even the lower-cost engines used in introductory racing events such
as Sport Quickie (AMA event 424) are far more consistent these days.
Today, a $75 Thunder Tiger Pro .40 is as clean and strong as a $300
hand-built “Terry Tigre” was in 1980. Nowadays, the most significant
difference between a winner and a dog is whether or not the engine has
had a careful break-in.
Duane Gall, 1267 S. Beeler Ct., Denver CO 80231; E-mail: [email protected]
RADIO CONTROL PYLON RACING
Tanner Pacini (center) ran with the big dogs at Winterfest in
January and set a Junior Q-500 record. Tony Pacini photo.
Safe bench-running setup. Handheld remote needle at left.
Fiberglass-filled nylon meets polycarbonate. Don’t try this at
home. The author promotes wearing safety gear!
07sig4.QXD 4/23/04 12:43 pm Page 122
124 MODEL AVIATION
There are as many theories about break-in
as there are pilots, but following are a few
ground rules on which pretty much everyone
agrees.
1) New engines have tight fits between the
moving parts, and occasionally small burrs or
sharp edges inside need to be worn away to
reduce internal friction.
2) The process of wearing away tight
places and sharp edges produces “particles of
wear”—microscopic chips of metal that can
hang around inside the engine as it runs and
roughen up the places that need to stay
smooth, such as the piston/cylinder interface
(“piston seal”), ball bearings, and bushings in
the ends of the connecting rod.
3) Excess fuel, containing oil, flushes out
the particles of wear as they develop. The
way to get surplus fuel into the engine is to
run it rich, which also cools it off.
4) Heat is necessary to loosen the piston
fit at the top of the stroke on tapered-sleeve
engines such as the Nelson, Jett, and Thunder
Tiger. The way to increase heat is to run the
engine leaner, which also reduces the amount
of excess fuel.
The upshot of all this is that the engine
should be run fast, rich, and alternately warm
and cool on a small propeller for a substantial
period of time, on a test bench.
Why a test bench? Why not just mount the
engine on the airplane and tie it down—or
even better, fly it?
There are two reasons. First, you’ll be
varying the fuel/air mixture greatly. Unless
you have a radio-controlled needle-valve
setup and a good ear, you just can’t do that
while flying. Second, the test bench absorbs
vibration that would otherwise prematurely
age your airplane and radio system.
A test bench needn’t be elaborate. The
accompanying photo shows one I made from
a folding stool and a Tatone cast-aluminum
engine stand. Jett sells a beautiful test bench
that is machined from aluminum.
But whatever type you use, make sure the
engine stand is securely mounted to the bench
and that the bolts holding it down—and the
bolts holding the engine to the stand—are
tight and stay tight. Check them between
runs. Also, use a cord and anchor stake to
secure the bench.
Other safety gear includes high-impact
polycarbonate sunglasses or safety goggles
(more about this later), earplugs, and a remote
needle valve. I made mine from an O.S. Max
needle valve assembly (part number
21181902 or 22281903), a nylon control
horn, and a 4-inch section of broomstick.
Adjust the length of the fuel lines so you can
hang the needle assembly over the back edge
of the bench while starting the engine.
Now for that small propeller. On the
Nelson or Jett .40s, and anything else with a
tuned muffler, use either a hard maple 10 x 6
sport propeller (a Zinger will do), cut down to
6 inches in diameter and carefully balanced,
or the black carbon-fiber APC 7.4 x 8 Quarter
40 racing propeller (part LP 07480C), cut
down to 6.5 inches in diameter and carefully
balanced. Do not use anything else!
On a .46 or smaller engine that does not
have a tuned muffler, you can use an APC
gray Q-500 racing propeller with the extrathick
“D-1” hub, cut down to 5 inches in
diameter. Be sure that it is carefully balanced.
There is a widely used break-in recipe that
has worked well for me. In the following
sequence, “cool” means to shut the engine off
for at least three minutes so that the internal
parts can return to somewhere near ambient
temperature and approximately their original
dimensions. “Four-cycle” means the engine is
set so rich that on approximately every other
turn of the crankshaft, the fuel/air mixture
fails to ignite and simply squirts out the
exhaust port.
On each start, use low throttle or turn the
needle valve out (rich, that is,
counterclockwise) an extra turn, and then
move around well behind the engine before
throttling up or leaning out the needle. Use an
electric starter. Hand-starting is dangerous
because the small bench propeller has little
mass, and the engine will kick it over smartly.
1) Start up extremely rich (needle valve
out at least five turns). Run two minutes in
“four-cycle” mode, so rich that the engine
will quit without the glow battery attached.
2) Allow the engine to cool.
3) Run two minutes just lean enough that
the engine will run without the glow battery
attached.
4) Allow the engine to cool.
5) Run two minutes slightly leaner.
07sig4.QXD 4/23/04 12:44 pm Page 124
July 2004 125
6) Allow the engine to cool.
7) Run two minutes lean enough to
periodically break into “two-cycle” mode.
8) Allow the engine to cool.
9) Run two minutes in steady two-cycle,
pinching the line or needling up to clean out
for a few seconds at a time.
10) Allow the engine to cool.
11) Repeat the previous step, cleaning out
a bit more aggressively.
12) Allow the engine to cool.
13) Repeat the previous step, needling up
nearly to peak for five seconds at a time.
14) Allow the engine to cool.
15) Repeat the previous step (with fivesecond
peaks) twice more, including
cooldown periods.
Now you are ready to mount the engine on
the airplane, switch to a normal-sized flying
propeller, and fly it rich—at least 1,000 rpm
down from peak if you have a tachometer or
with an audible “burble” in the exhaust note
and a visible smoke trail in the air if you’re
not using a tachometer. Make at least three
flights this way, slightly leaner each time. If
you’re not in a hurry, make a dozen flights
this way.
At this point you are ready to race. When
race day comes, remember that it is better to
be slightly rich than slightly lean. In the
fuel/air mixture, fuel makes power; too much
air just makes heat!
Blah, blah, safety, blah, blah. In
aeromodeling, especially racing, we enjoy
pushing the limits. We’ve become
accustomed to technology and power that
were not even dreamed of just a few years
ago.
The typical .40 cu. in. racing engine
develops nearly five times the energy it did
when RC Pylon was young. Today’s carbonfiber
wings can weigh a few ounces and be
only an inch thick at the root, yet hold up
under the forces inflicted by a 4-pound
airplane turning hard at 180 mph, time after
time.
How did we get here? By trial and
error, mostly. The beauty of racing is that
it rewards results; anything that will get
you to the finish line ahead of the other
guy—safely and reliably—is by definition
good. If it doesn’t, it’s not.
While assembling material for this
column, I used good old trial and error to find
a few limitations you should be aware of, one
of which is the hub strength of fiberglassfilled
nylon sport propellers.
You might think that if you start with a
large, stout-looking propeller and cut off half
the blades, the hub is twice as strong as it
needs to be. Therefore, you can safely run the
propeller at twice the speed for which it was
designed, right? Wrong!
Kinetic energy increases by the square of
the velocity, so doubling the speed quadruples
the load. If the propeller was designed with a
100% safety margin, you’ve just exceeded it
by a factor of two. Even a flywheel with no
blades will explode if you spin it fast enough.
Another limitation is the notion that if it’s
working, it will keep working. Unlike wood,
chopped-fiber materials fatigue quickly,
especially under vibration.
There is also the ancient wisdom that if a
propeller fails, the pieces will go straight out
or forward, ahead of the propeller arc. This
doesn’t account for the fact that a piece of
propeller blade is like a wing without a tail to
stabilize it. And a wing without a tail will
“tuck” downward. In relation to the propeller
arc, this means it can actually travel backward
a little way.
In this case I was using a remote needle
but standing only a few inches behind the
propeller arc. It wasn’t enough.
Last, I’ve determined once and for all that
wearing safety gear does not make you a
sissy. Or if it does, I’d rather be a live sissy
than a dead anything else. I wish I had a
nickel for every time I’ve heard someone say,
“Oh, that little bit of protection won’t make
any difference” or “Come on, what are the
chances of that happening?”
A pair of polycarbonate wraparound
sunglasses from Performance Bike Shop
saved me from a combination of once-in-amillion
bad luck and my own poor judgment.
I hope you’ll clip out the accompanying photo
and hang it on your workshop wall. And
never be anywhere near a running engine—
yours or anyone else’s—without eye
protection.
See ya on the starting line! MA
RADIO SOUTH INC.
Pro-Driver MKIII "Platinum Edition"
Our new Pro-Driver unit is pocket-sized! It even comes with its
own charger!
• A bright yellow easy-to-see case. • Glow-Clip mount built in.
• Glow-Clip cord mount built in. • Push button timed start (like
the MKII). • Uses a 4-cell 1100 mAh NiMH battery pack.
• Interchangable top-quality glow clips. • AC charger
included, using 2.1mm barrel connector. • Can be easily
fast-charged. • Pocket-sized for easy carrying to the flight
line. • Limited 2-year warranty. Retail Price: $109.99
SALE PRICE: $74.95 3702 N Pace, Pensacola, FL 32505
Toll Free Order Line (Orders Only Please) 800-962-7802
Repair and Information . . . . . . . . . . . . . . . . . . . 850-434-0909 or visit our website at http://www.radiosouthrc.com
If not available at your local hobby shop, order
direct. DEALER INQUIRIES INVITED.
SCALE FLIGHT MODEL CO.
Repro Rubber Power Kits, Comet, Megow, Burd,
Scientific, Jasco, also available - Campbell,
Diels, Dumas, Florio Flyer, Guillow’s,
Golden Age Repro, Herr, Micro-X, Peck, Sig.
Send $2.00 for Model Airplane Catalog
Penn Valley Hobby Center
837-A W. Main St., Lansdale, PA 19446
www.pennvalleyhobbycenter.com
07sig4.QXD 4/23/04 12:44 pm Page 125
Edition: Model Aviation - 2004/07
Page Numbers: 122,124,125
Edition: Model Aviation - 2004/07
Page Numbers: 122,124,125
122 MODEL AVIATION
QUICKIE 500 RECORD: It’s great to be able to trumpet an up-andcoming
young Pylon flier’s accomplishments. In this case it’s Tanner
Pacini’s; he set a Junior record in Quickie 500 (AMA event 428), or Q-
500, at the annual Winterfest two-day meet hosted by the Speedworld
R/C Flyers at their field near Phoenix, Arizona.
I received the accompanying photo and the following note from
Tanner’s parents Tony and Donna Pacini, who are proprietors of the
Valley Hobby Shop in Prescott Valley, Arizona.
“Our 12-year-old Tanner Pacini is now the current national Q-500
record holder in his age group (Junior). He broke the existing record
(1:11) twice this weekend at Winterfest, first with a 1:10, then again
with a 1:09. Fast time for the contest was a 1:06 (Randy Bridge). For
reference, the current Senior record is 1:05 and the current Open record
is 1:03.
“Also note that this was Tanner’s first Q-500 contest. We have high
hopes for him at the JR Gold Cup Quarter 40 race next month.”
As a follow-up, I did see the Pacini family at the Gold Cup, and
Tanner and his dad were tough in that event. Congratulations!
Correction: A typo in a previous column gave the wrong telephone
number for Pete Reed, who is the current Pylon Racing Contest Board
chairman and the man to see for a high-quality, handcrafted National
Balsa Intimidator Q-500 aircraft at $200. The correct number is (603)
532-8975.
RCPRO Web Site: Speaking of sources and methods (the CIA can’t,
but we can), there’s been a great deal of activity and many upgrades at
the RCPRO Web site—www.rcpro.org/html/—which Don Stegall
(Monroe NC) maintains. The site now includes viewable and
downloadable video footage of racing action, building tips, and other
good stuff, and it has links to other sites.
It’s a challenge for newcomers to find the latest and greatest racing
gear, since much of it comes from small-scale “garage shop”
operations. It’s also a challenge to convey the thrill of racing in mere
words and photos. All too often we have to fall back on the old
“You’ve just gotta come out with me sometime and see it for
yourself!”—which sounds sort of lame and isn’t very efficient. RCPRO
takes a big step toward solving both of those problems.
RCPRO is not, nor does it aim to be, the AMA-recognized SIG for
RC Pylon. The National Miniature Pylon Racing Association
(NMPRA) fills that role, and it is accessible through its Web site:
www.nmpra.org/.
Engine Break-In: Spring is here, and with it comes the perennial
question: “What do I have to do to ‘hop up’ my engine so I can race
with you guys?”
Somehow the notion persists that an engine is no good for racing
unless it has been brutally attacked with a hand grinder, dismembered,
and remanufactured according to an ancient family recipe available
only to senior Freemasons and the chefs who prepare that “secret”
hamburger sauce. In fact, Henry Nelson and Dub Jett put an end to that
nonsense, beginning at least 20 years ago, by offering racing engines of
championship quality right out of the box.
Even the lower-cost engines used in introductory racing events such
as Sport Quickie (AMA event 424) are far more consistent these days.
Today, a $75 Thunder Tiger Pro .40 is as clean and strong as a $300
hand-built “Terry Tigre” was in 1980. Nowadays, the most significant
difference between a winner and a dog is whether or not the engine has
had a careful break-in.
Duane Gall, 1267 S. Beeler Ct., Denver CO 80231; E-mail: [email protected]
RADIO CONTROL PYLON RACING
Tanner Pacini (center) ran with the big dogs at Winterfest in
January and set a Junior Q-500 record. Tony Pacini photo.
Safe bench-running setup. Handheld remote needle at left.
Fiberglass-filled nylon meets polycarbonate. Don’t try this at
home. The author promotes wearing safety gear!
07sig4.QXD 4/23/04 12:43 pm Page 122
124 MODEL AVIATION
There are as many theories about break-in
as there are pilots, but following are a few
ground rules on which pretty much everyone
agrees.
1) New engines have tight fits between the
moving parts, and occasionally small burrs or
sharp edges inside need to be worn away to
reduce internal friction.
2) The process of wearing away tight
places and sharp edges produces “particles of
wear”—microscopic chips of metal that can
hang around inside the engine as it runs and
roughen up the places that need to stay
smooth, such as the piston/cylinder interface
(“piston seal”), ball bearings, and bushings in
the ends of the connecting rod.
3) Excess fuel, containing oil, flushes out
the particles of wear as they develop. The
way to get surplus fuel into the engine is to
run it rich, which also cools it off.
4) Heat is necessary to loosen the piston
fit at the top of the stroke on tapered-sleeve
engines such as the Nelson, Jett, and Thunder
Tiger. The way to increase heat is to run the
engine leaner, which also reduces the amount
of excess fuel.
The upshot of all this is that the engine
should be run fast, rich, and alternately warm
and cool on a small propeller for a substantial
period of time, on a test bench.
Why a test bench? Why not just mount the
engine on the airplane and tie it down—or
even better, fly it?
There are two reasons. First, you’ll be
varying the fuel/air mixture greatly. Unless
you have a radio-controlled needle-valve
setup and a good ear, you just can’t do that
while flying. Second, the test bench absorbs
vibration that would otherwise prematurely
age your airplane and radio system.
A test bench needn’t be elaborate. The
accompanying photo shows one I made from
a folding stool and a Tatone cast-aluminum
engine stand. Jett sells a beautiful test bench
that is machined from aluminum.
But whatever type you use, make sure the
engine stand is securely mounted to the bench
and that the bolts holding it down—and the
bolts holding the engine to the stand—are
tight and stay tight. Check them between
runs. Also, use a cord and anchor stake to
secure the bench.
Other safety gear includes high-impact
polycarbonate sunglasses or safety goggles
(more about this later), earplugs, and a remote
needle valve. I made mine from an O.S. Max
needle valve assembly (part number
21181902 or 22281903), a nylon control
horn, and a 4-inch section of broomstick.
Adjust the length of the fuel lines so you can
hang the needle assembly over the back edge
of the bench while starting the engine.
Now for that small propeller. On the
Nelson or Jett .40s, and anything else with a
tuned muffler, use either a hard maple 10 x 6
sport propeller (a Zinger will do), cut down to
6 inches in diameter and carefully balanced,
or the black carbon-fiber APC 7.4 x 8 Quarter
40 racing propeller (part LP 07480C), cut
down to 6.5 inches in diameter and carefully
balanced. Do not use anything else!
On a .46 or smaller engine that does not
have a tuned muffler, you can use an APC
gray Q-500 racing propeller with the extrathick
“D-1” hub, cut down to 5 inches in
diameter. Be sure that it is carefully balanced.
There is a widely used break-in recipe that
has worked well for me. In the following
sequence, “cool” means to shut the engine off
for at least three minutes so that the internal
parts can return to somewhere near ambient
temperature and approximately their original
dimensions. “Four-cycle” means the engine is
set so rich that on approximately every other
turn of the crankshaft, the fuel/air mixture
fails to ignite and simply squirts out the
exhaust port.
On each start, use low throttle or turn the
needle valve out (rich, that is,
counterclockwise) an extra turn, and then
move around well behind the engine before
throttling up or leaning out the needle. Use an
electric starter. Hand-starting is dangerous
because the small bench propeller has little
mass, and the engine will kick it over smartly.
1) Start up extremely rich (needle valve
out at least five turns). Run two minutes in
“four-cycle” mode, so rich that the engine
will quit without the glow battery attached.
2) Allow the engine to cool.
3) Run two minutes just lean enough that
the engine will run without the glow battery
attached.
4) Allow the engine to cool.
5) Run two minutes slightly leaner.
07sig4.QXD 4/23/04 12:44 pm Page 124
July 2004 125
6) Allow the engine to cool.
7) Run two minutes lean enough to
periodically break into “two-cycle” mode.
8) Allow the engine to cool.
9) Run two minutes in steady two-cycle,
pinching the line or needling up to clean out
for a few seconds at a time.
10) Allow the engine to cool.
11) Repeat the previous step, cleaning out
a bit more aggressively.
12) Allow the engine to cool.
13) Repeat the previous step, needling up
nearly to peak for five seconds at a time.
14) Allow the engine to cool.
15) Repeat the previous step (with fivesecond
peaks) twice more, including
cooldown periods.
Now you are ready to mount the engine on
the airplane, switch to a normal-sized flying
propeller, and fly it rich—at least 1,000 rpm
down from peak if you have a tachometer or
with an audible “burble” in the exhaust note
and a visible smoke trail in the air if you’re
not using a tachometer. Make at least three
flights this way, slightly leaner each time. If
you’re not in a hurry, make a dozen flights
this way.
At this point you are ready to race. When
race day comes, remember that it is better to
be slightly rich than slightly lean. In the
fuel/air mixture, fuel makes power; too much
air just makes heat!
Blah, blah, safety, blah, blah. In
aeromodeling, especially racing, we enjoy
pushing the limits. We’ve become
accustomed to technology and power that
were not even dreamed of just a few years
ago.
The typical .40 cu. in. racing engine
develops nearly five times the energy it did
when RC Pylon was young. Today’s carbonfiber
wings can weigh a few ounces and be
only an inch thick at the root, yet hold up
under the forces inflicted by a 4-pound
airplane turning hard at 180 mph, time after
time.
How did we get here? By trial and
error, mostly. The beauty of racing is that
it rewards results; anything that will get
you to the finish line ahead of the other
guy—safely and reliably—is by definition
good. If it doesn’t, it’s not.
While assembling material for this
column, I used good old trial and error to find
a few limitations you should be aware of, one
of which is the hub strength of fiberglassfilled
nylon sport propellers.
You might think that if you start with a
large, stout-looking propeller and cut off half
the blades, the hub is twice as strong as it
needs to be. Therefore, you can safely run the
propeller at twice the speed for which it was
designed, right? Wrong!
Kinetic energy increases by the square of
the velocity, so doubling the speed quadruples
the load. If the propeller was designed with a
100% safety margin, you’ve just exceeded it
by a factor of two. Even a flywheel with no
blades will explode if you spin it fast enough.
Another limitation is the notion that if it’s
working, it will keep working. Unlike wood,
chopped-fiber materials fatigue quickly,
especially under vibration.
There is also the ancient wisdom that if a
propeller fails, the pieces will go straight out
or forward, ahead of the propeller arc. This
doesn’t account for the fact that a piece of
propeller blade is like a wing without a tail to
stabilize it. And a wing without a tail will
“tuck” downward. In relation to the propeller
arc, this means it can actually travel backward
a little way.
In this case I was using a remote needle
but standing only a few inches behind the
propeller arc. It wasn’t enough.
Last, I’ve determined once and for all that
wearing safety gear does not make you a
sissy. Or if it does, I’d rather be a live sissy
than a dead anything else. I wish I had a
nickel for every time I’ve heard someone say,
“Oh, that little bit of protection won’t make
any difference” or “Come on, what are the
chances of that happening?”
A pair of polycarbonate wraparound
sunglasses from Performance Bike Shop
saved me from a combination of once-in-amillion
bad luck and my own poor judgment.
I hope you’ll clip out the accompanying photo
and hang it on your workshop wall. And
never be anywhere near a running engine—
yours or anyone else’s—without eye
protection.
See ya on the starting line! MA
RADIO SOUTH INC.
Pro-Driver MKIII "Platinum Edition"
Our new Pro-Driver unit is pocket-sized! It even comes with its
own charger!
• A bright yellow easy-to-see case. • Glow-Clip mount built in.
• Glow-Clip cord mount built in. • Push button timed start (like
the MKII). • Uses a 4-cell 1100 mAh NiMH battery pack.
• Interchangable top-quality glow clips. • AC charger
included, using 2.1mm barrel connector. • Can be easily
fast-charged. • Pocket-sized for easy carrying to the flight
line. • Limited 2-year warranty. Retail Price: $109.99
SALE PRICE: $74.95 3702 N Pace, Pensacola, FL 32505
Toll Free Order Line (Orders Only Please) 800-962-7802
Repair and Information . . . . . . . . . . . . . . . . . . . 850-434-0909 or visit our website at http://www.radiosouthrc.com
If not available at your local hobby shop, order
direct. DEALER INQUIRIES INVITED.
SCALE FLIGHT MODEL CO.
Repro Rubber Power Kits, Comet, Megow, Burd,
Scientific, Jasco, also available - Campbell,
Diels, Dumas, Florio Flyer, Guillow’s,
Golden Age Repro, Herr, Micro-X, Peck, Sig.
Send $2.00 for Model Airplane Catalog
Penn Valley Hobby Center
837-A W. Main St., Lansdale, PA 19446
www.pennvalleyhobbycenter.com
07sig4.QXD 4/23/04 12:44 pm Page 125
Edition: Model Aviation - 2004/07
Page Numbers: 122,124,125
122 MODEL AVIATION
QUICKIE 500 RECORD: It’s great to be able to trumpet an up-andcoming
young Pylon flier’s accomplishments. In this case it’s Tanner
Pacini’s; he set a Junior record in Quickie 500 (AMA event 428), or Q-
500, at the annual Winterfest two-day meet hosted by the Speedworld
R/C Flyers at their field near Phoenix, Arizona.
I received the accompanying photo and the following note from
Tanner’s parents Tony and Donna Pacini, who are proprietors of the
Valley Hobby Shop in Prescott Valley, Arizona.
“Our 12-year-old Tanner Pacini is now the current national Q-500
record holder in his age group (Junior). He broke the existing record
(1:11) twice this weekend at Winterfest, first with a 1:10, then again
with a 1:09. Fast time for the contest was a 1:06 (Randy Bridge). For
reference, the current Senior record is 1:05 and the current Open record
is 1:03.
“Also note that this was Tanner’s first Q-500 contest. We have high
hopes for him at the JR Gold Cup Quarter 40 race next month.”
As a follow-up, I did see the Pacini family at the Gold Cup, and
Tanner and his dad were tough in that event. Congratulations!
Correction: A typo in a previous column gave the wrong telephone
number for Pete Reed, who is the current Pylon Racing Contest Board
chairman and the man to see for a high-quality, handcrafted National
Balsa Intimidator Q-500 aircraft at $200. The correct number is (603)
532-8975.
RCPRO Web Site: Speaking of sources and methods (the CIA can’t,
but we can), there’s been a great deal of activity and many upgrades at
the RCPRO Web site—www.rcpro.org/html/—which Don Stegall
(Monroe NC) maintains. The site now includes viewable and
downloadable video footage of racing action, building tips, and other
good stuff, and it has links to other sites.
It’s a challenge for newcomers to find the latest and greatest racing
gear, since much of it comes from small-scale “garage shop”
operations. It’s also a challenge to convey the thrill of racing in mere
words and photos. All too often we have to fall back on the old
“You’ve just gotta come out with me sometime and see it for
yourself!”—which sounds sort of lame and isn’t very efficient. RCPRO
takes a big step toward solving both of those problems.
RCPRO is not, nor does it aim to be, the AMA-recognized SIG for
RC Pylon. The National Miniature Pylon Racing Association
(NMPRA) fills that role, and it is accessible through its Web site:
www.nmpra.org/.
Engine Break-In: Spring is here, and with it comes the perennial
question: “What do I have to do to ‘hop up’ my engine so I can race
with you guys?”
Somehow the notion persists that an engine is no good for racing
unless it has been brutally attacked with a hand grinder, dismembered,
and remanufactured according to an ancient family recipe available
only to senior Freemasons and the chefs who prepare that “secret”
hamburger sauce. In fact, Henry Nelson and Dub Jett put an end to that
nonsense, beginning at least 20 years ago, by offering racing engines of
championship quality right out of the box.
Even the lower-cost engines used in introductory racing events such
as Sport Quickie (AMA event 424) are far more consistent these days.
Today, a $75 Thunder Tiger Pro .40 is as clean and strong as a $300
hand-built “Terry Tigre” was in 1980. Nowadays, the most significant
difference between a winner and a dog is whether or not the engine has
had a careful break-in.
Duane Gall, 1267 S. Beeler Ct., Denver CO 80231; E-mail: [email protected]
RADIO CONTROL PYLON RACING
Tanner Pacini (center) ran with the big dogs at Winterfest in
January and set a Junior Q-500 record. Tony Pacini photo.
Safe bench-running setup. Handheld remote needle at left.
Fiberglass-filled nylon meets polycarbonate. Don’t try this at
home. The author promotes wearing safety gear!
07sig4.QXD 4/23/04 12:43 pm Page 122
124 MODEL AVIATION
There are as many theories about break-in
as there are pilots, but following are a few
ground rules on which pretty much everyone
agrees.
1) New engines have tight fits between the
moving parts, and occasionally small burrs or
sharp edges inside need to be worn away to
reduce internal friction.
2) The process of wearing away tight
places and sharp edges produces “particles of
wear”—microscopic chips of metal that can
hang around inside the engine as it runs and
roughen up the places that need to stay
smooth, such as the piston/cylinder interface
(“piston seal”), ball bearings, and bushings in
the ends of the connecting rod.
3) Excess fuel, containing oil, flushes out
the particles of wear as they develop. The
way to get surplus fuel into the engine is to
run it rich, which also cools it off.
4) Heat is necessary to loosen the piston
fit at the top of the stroke on tapered-sleeve
engines such as the Nelson, Jett, and Thunder
Tiger. The way to increase heat is to run the
engine leaner, which also reduces the amount
of excess fuel.
The upshot of all this is that the engine
should be run fast, rich, and alternately warm
and cool on a small propeller for a substantial
period of time, on a test bench.
Why a test bench? Why not just mount the
engine on the airplane and tie it down—or
even better, fly it?
There are two reasons. First, you’ll be
varying the fuel/air mixture greatly. Unless
you have a radio-controlled needle-valve
setup and a good ear, you just can’t do that
while flying. Second, the test bench absorbs
vibration that would otherwise prematurely
age your airplane and radio system.
A test bench needn’t be elaborate. The
accompanying photo shows one I made from
a folding stool and a Tatone cast-aluminum
engine stand. Jett sells a beautiful test bench
that is machined from aluminum.
But whatever type you use, make sure the
engine stand is securely mounted to the bench
and that the bolts holding it down—and the
bolts holding the engine to the stand—are
tight and stay tight. Check them between
runs. Also, use a cord and anchor stake to
secure the bench.
Other safety gear includes high-impact
polycarbonate sunglasses or safety goggles
(more about this later), earplugs, and a remote
needle valve. I made mine from an O.S. Max
needle valve assembly (part number
21181902 or 22281903), a nylon control
horn, and a 4-inch section of broomstick.
Adjust the length of the fuel lines so you can
hang the needle assembly over the back edge
of the bench while starting the engine.
Now for that small propeller. On the
Nelson or Jett .40s, and anything else with a
tuned muffler, use either a hard maple 10 x 6
sport propeller (a Zinger will do), cut down to
6 inches in diameter and carefully balanced,
or the black carbon-fiber APC 7.4 x 8 Quarter
40 racing propeller (part LP 07480C), cut
down to 6.5 inches in diameter and carefully
balanced. Do not use anything else!
On a .46 or smaller engine that does not
have a tuned muffler, you can use an APC
gray Q-500 racing propeller with the extrathick
“D-1” hub, cut down to 5 inches in
diameter. Be sure that it is carefully balanced.
There is a widely used break-in recipe that
has worked well for me. In the following
sequence, “cool” means to shut the engine off
for at least three minutes so that the internal
parts can return to somewhere near ambient
temperature and approximately their original
dimensions. “Four-cycle” means the engine is
set so rich that on approximately every other
turn of the crankshaft, the fuel/air mixture
fails to ignite and simply squirts out the
exhaust port.
On each start, use low throttle or turn the
needle valve out (rich, that is,
counterclockwise) an extra turn, and then
move around well behind the engine before
throttling up or leaning out the needle. Use an
electric starter. Hand-starting is dangerous
because the small bench propeller has little
mass, and the engine will kick it over smartly.
1) Start up extremely rich (needle valve
out at least five turns). Run two minutes in
“four-cycle” mode, so rich that the engine
will quit without the glow battery attached.
2) Allow the engine to cool.
3) Run two minutes just lean enough that
the engine will run without the glow battery
attached.
4) Allow the engine to cool.
5) Run two minutes slightly leaner.
07sig4.QXD 4/23/04 12:44 pm Page 124
July 2004 125
6) Allow the engine to cool.
7) Run two minutes lean enough to
periodically break into “two-cycle” mode.
8) Allow the engine to cool.
9) Run two minutes in steady two-cycle,
pinching the line or needling up to clean out
for a few seconds at a time.
10) Allow the engine to cool.
11) Repeat the previous step, cleaning out
a bit more aggressively.
12) Allow the engine to cool.
13) Repeat the previous step, needling up
nearly to peak for five seconds at a time.
14) Allow the engine to cool.
15) Repeat the previous step (with fivesecond
peaks) twice more, including
cooldown periods.
Now you are ready to mount the engine on
the airplane, switch to a normal-sized flying
propeller, and fly it rich—at least 1,000 rpm
down from peak if you have a tachometer or
with an audible “burble” in the exhaust note
and a visible smoke trail in the air if you’re
not using a tachometer. Make at least three
flights this way, slightly leaner each time. If
you’re not in a hurry, make a dozen flights
this way.
At this point you are ready to race. When
race day comes, remember that it is better to
be slightly rich than slightly lean. In the
fuel/air mixture, fuel makes power; too much
air just makes heat!
Blah, blah, safety, blah, blah. In
aeromodeling, especially racing, we enjoy
pushing the limits. We’ve become
accustomed to technology and power that
were not even dreamed of just a few years
ago.
The typical .40 cu. in. racing engine
develops nearly five times the energy it did
when RC Pylon was young. Today’s carbonfiber
wings can weigh a few ounces and be
only an inch thick at the root, yet hold up
under the forces inflicted by a 4-pound
airplane turning hard at 180 mph, time after
time.
How did we get here? By trial and
error, mostly. The beauty of racing is that
it rewards results; anything that will get
you to the finish line ahead of the other
guy—safely and reliably—is by definition
good. If it doesn’t, it’s not.
While assembling material for this
column, I used good old trial and error to find
a few limitations you should be aware of, one
of which is the hub strength of fiberglassfilled
nylon sport propellers.
You might think that if you start with a
large, stout-looking propeller and cut off half
the blades, the hub is twice as strong as it
needs to be. Therefore, you can safely run the
propeller at twice the speed for which it was
designed, right? Wrong!
Kinetic energy increases by the square of
the velocity, so doubling the speed quadruples
the load. If the propeller was designed with a
100% safety margin, you’ve just exceeded it
by a factor of two. Even a flywheel with no
blades will explode if you spin it fast enough.
Another limitation is the notion that if it’s
working, it will keep working. Unlike wood,
chopped-fiber materials fatigue quickly,
especially under vibration.
There is also the ancient wisdom that if a
propeller fails, the pieces will go straight out
or forward, ahead of the propeller arc. This
doesn’t account for the fact that a piece of
propeller blade is like a wing without a tail to
stabilize it. And a wing without a tail will
“tuck” downward. In relation to the propeller
arc, this means it can actually travel backward
a little way.
In this case I was using a remote needle
but standing only a few inches behind the
propeller arc. It wasn’t enough.
Last, I’ve determined once and for all that
wearing safety gear does not make you a
sissy. Or if it does, I’d rather be a live sissy
than a dead anything else. I wish I had a
nickel for every time I’ve heard someone say,
“Oh, that little bit of protection won’t make
any difference” or “Come on, what are the
chances of that happening?”
A pair of polycarbonate wraparound
sunglasses from Performance Bike Shop
saved me from a combination of once-in-amillion
bad luck and my own poor judgment.
I hope you’ll clip out the accompanying photo
and hang it on your workshop wall. And
never be anywhere near a running engine—
yours or anyone else’s—without eye
protection.
See ya on the starting line! MA
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