couple years ago I purchased a set of three "Junior 451" airplane
kits off of eBay. The Junior 451 is an all-Styrofoam free-flight
model that comes with a "DP-03" CO2 motor. I only bought them for
the motors. Two of the models were re-sold shortly thereafter and
I netted enough to pay for the motor I kept and even pocketed a
couple extra bucks.
The Junior 451 was a high-wing, Cessna-like
model imported by Sig manufacturing in the early 1990s from a Russian
company. It had a wingspan of 27.5", and weighed a little under
3 oz. ready to fly.
Run time per charge for the DP-03 motor
is specified at 55 seconds on a full charge under ideal conditions
(temperature, altitude). A supplied 7x7.8, 2-bladed propeller permitted
the motor to turn at around 2,500 rpm. Weight for motor and propeller
is 1.1 oz.
CO2 engines run off a cylinder of compressed carbon
dioxide gas. A metal tube feeds the top of the cylinder where a
metal ball under pressure from the gas seals off the cylinder until
the piston pushes up on it. Doing so forces the piston down to where
the gas is ejected at the exhaust port. Momentum from the propeller
mass swings the piston back to the top of the cylinder where it
once again opens the ball valve to start the cycle all over again.
Carlson Engine Imports used to sell this
DP-03 motor for $35, but they no longer do.
Here is the user's manual that was scanned and then OCR'ed
to allow for searchable text (it was a lot of work). Note that in
many places there are references to a drawing of the motor, but
my manual did not include the drawing.
##SAFETY COMES FIRST!
Operator assumes all risks in operation of this model, motor, and
all related support equipment. Under no circumstances ,ill the purchaser
be entitled to consequential or incidental damages. Charging device
lust be handled with care, used only in accordance with following
safety precautions and written instructions. Be extremely careful
to keep clear of propeller at all tiles. Safety considerations must
come first at all tiles. Please refer to 'SAFETY PRECAUTIONS' listed
below and on page 1.
1. CO2 cartridges (not supplied) are a high-pressure
device which lust be handled with care.
2. While our
newly-redesigned charger (machined aluminum top differentiates current
charger from older unit which was prone to leakage of CO2 gas) is
an excellent piece of equipment, it lust be kept clean and used
3. At end of each flying session, relieve
pressure of CO2 cartridge and airborne (model-mounted) CO2 tank
per 'DP-03' Service Manual. Do not store charger with CO2 cartridge
installed do not store model with airborne tank charged.
4. Always handle charger with care. Never look in outlet hole
of charger. Do not point charger at yourself or other people.
Due to high pressure of CO2 cartridge, charger lust be handled
and treated with caution at all tiles.
5. Be aware that
motor is capable of running in either direction equally well. Always
start motor with a start flick of the propeller and ensure rotation
is correct before launching model.
6. Before starting motor
make sure it is securely fastened to model and propeller is securely
attached to motor shaft.
7. Do not place your fingers or
any other parts of your body into the area surrounding propeller.
8. Do not operate motor unless it is securely attached to model
or test stand.
9. Do not used damaged propeller. Never use
10. Do not take CO2 cartridge out of recharger
until all remaining gas has been relieved from cartridge. Perform
this operation per Section 6 and Fig. 6.
Do not store charger with CO2 cartridge installed. Always relieve
pressure per instructions on page 6 of this Service Manual and then
remove cartridge from charger.
12. Be careful not to get
your hands or any portion of your body into gas let cooling from
CO2 cartridge gas can be as cold as minus 95 degrees F.
13. When finished running the motor, Always relieve remaining gas
in system by flipping the propeller until it rotates freely and
without any gas exhaust.
##1. IMPORTANT NOTES:
CO2 motor is factory set. While vast majority are properly set,
a few may need adjustment. Please refer to Section **5 and Section
**7 of this Service Manual for instructions on operation of motor
and tips for increasing flight times via adjustments which effect
power output and run time of motor.
2. CO2 cartridges
are available from hobby dealer. Cartridges for BB guns, etc. are
too long and cannot to be used.
3. Graphic instructions
furnished with this motor are adequate for successful operation.
However, these English language instructions are provided to ensure
easy and pleasant operation of your new motor.
4. The "Junior
451" motor is designed for use by twelve-year-old and older modelers.
Those under the age of 12 are encouraged to seek adult assistance.
5. This motor lay also be installed on flying model aircraft with
maximum total weight of 130 grams/4.5 ounces and a wing loading
no greater than 5 ounces per square foot, Please refer to page 8
for suggested built-up balsa models.
6. The 'Junior
451' motor is a highly precise device which should always be handled
with care and in compliance with this Service Manual. When using
motor and support equipment always obey all safety precautions.
##2. MOTOR SPECIFICATIONS:
Working medium . . . . . . . . .
. . . . . . . . Carbon Dioxide, CO2 Minimum/maximum run
time per charge, seconds . . . . 15/55 Propeller diameter/pitch,
inches . . . . . . . . . . . . . . 7.0/7.87
Source of carbon dioxide . . . . . . . . . . . . . . . .
CO2 cartridges Air temperature at which motor operates,
not lower than . . . . . . . . . . . . . . . .
. . . . . . . . 40 degrees F
13. Piston 14. Connecting rod
15. Crankshaft 16. Plug
Your "Junior 451" motor is a piston-type motor operating
on compressed carbon dioxide (CO2). Principle of operation is shown
in Fig. 4. Upon rotation of propeller, connecting rod pushes piston
up. Piston then lifts valve ball, letting compressed gas flow into
chamber. Expanding, this gas pushes piston down and propeller begins
rotating. As piston reaches Bottom Dead Center (BDCI, exhaust holes
open and used gas is exhausted. Continuing movement of piston to
Top Dead Center (TDC) takes place due to inertia of rotating propeller.
This cycle is then repeated until all gas in system has been consumed.
Please note that above principles apply whether motor is operating
clockwise or counter-clockwise. As propeller only ,arks effectively
when spinning counter-clockwise (as viewed from front of model it
is important that in first starting motor propeller be given a smart
flip in proper direction and that proper rotation be confirmed prior
to launching model.
Once the principles are understood it
is easy to see how readily power output and run time characteristics
of this motor lay be adjusted by loosening collar at base of cylinder
and turning cylinder "in" or "out" of crankcase, effectively raising
or lowering cylinder in relation to crankcase. All adjustments should
be lade no more than 1/16 turn at a time and with motor at rest.
It is much too dangerous to lake this adjustment with motor running.
By lowering cylinder a maximum of 1/16 turn, piston will raise ball
a little higher off seat, allowing more CO2 gas into motor, delivering
more power but also consuming more &as with each cycle thus
reducing run tile. The opposite is also true, raising cylinder has
the effect of letting less CO2 gas into motor, reducing power while
increasing run tile.
The exact 'best' setting for your motor
,ill vary depending upon leather conditions. If there is much wind
blowing you may wish to have a little more power which helps model
penetrate into the wind and recover from any wind-induced changes
to flight of model. For calm conditions the longest flights are
generally achieved by setting your motor to develop just enough
power for 1 nice climb while depending upon the longer run time
to achieve maximum altitude. As a general rule, maximum power is
not effective in obtaining longest-possible flights.
please note that you must use this feature with care. While it is
obvious when cylinder is too high (motor does not run), one
can also go too far in trying to obtain maximum power if cylinder
is lowered so far that piston tries to push ball through head of
motor. If there is any question in your mind after making an adjustment,
first bleed CO2 gas from airborne tank and then slowly rotate motor
through one complete revolution with propeller held firmly in one
hand in case there is any residual gas in system. If there is resistance
as piston reaches TDC, adjust cylinder by raising it 1/16 turn and
While your CO2 motor and its "fuel" typically
operate at a relatively low temperature, it should be understood
that, as opposed to a compressed-air motor which develops power
strictly from air pressure, a CO2 motor generates little power from
compressed gas alone. The majority of the power comes from expansion
of CO2 gas as it is released to ambient conditions, in our case
as it is delivered to the motor. This explains why performance of
your motor will be seen to suffer when operated at low outside temperatures
with 40 degree F, generally being too low for satisfying flights.
These same low operating temperatures indicate that when
tuning for maximum performance an oil designed for low-temperature
operation will result in increased performance. Your best source
for oil which is better than sewing machine oil is suggested to
be a good gun shop which will offer several different types designed
specifically for low-temperature applications and minimum friction.
These oils are also excellent for treating motor prior to long-term
During first 2 or 3 seconds from starting, especially
if model has very recently been flown, motor may slow due to over-cooling
and then regain full power. For this reason we suggest you allow
motor to run 2 seconds before launching model. And remembering that
motor will run in either direction, this time should be used to
make certain propeller is turning in proper direction.
airborne tank fully charged per Section 6 and 7, motor is started
by quickly and positively flicking propeller in counter-clockwise
(as viewed from front of model direction. with motor running, model
is smoothly launched directly into any wind at a positive angle
of attack which only needs to be about 5 to 15 degrees 'up' in relation
to the ground. A properly adjusted model will smoothly take off
in straight or spiraling line of flight.
##6. PREPARING RECHARGING DEVICE:
Recharger is used to charge fuel system
with CO2. Recharger is a fixture for holding and puncturing CO2
cartridges. These are are available from your hobby dealer. Large
cartridges for BB guns, etc. are too large for charger and cannot
Parts for recharger are shown in Fig. 5 under section
1. Charger body
3. Rubber bushing
7. Charger cap 2. CO2 cartridge
4. Puncturing needle 6. Valve ball
When charging obey all rules of SAFETY PRECAUTIONS.
Order of Charging:
1. Place CO2 cartridge into charger body.
Application of small amount of saliva or light oil to bushing in
charger cap will result in better sealing and longer bushing life.
2. Being sure to leave vent hole in charger body clear of
obstructions, turn cap into body until faint noise of cartridge
being punctured is heard. This sound confirms CO2 cartridge has
been punctured with needle. Continue to tighten cap approximately
one (1) more turn or less. Recharger is now ready for charging fuel
system. It is possible to charge motor fuel system from one CO2
cartridge about three to five times.
To remove exhausted
CO2 cartridge from recharger, carefully adhere to following steps:
1. Relieve remaining gas per Fig. 6 using supplied fitting.
(Fitting is found in spare parts container)
remove charger cap from charger body in a manner which assumes CO2
cartridge has pressure remaining.
3. Carefully and gently
rocking CO2 cartridge, remove from bushing. Depending upon type
of cartridge used, it lay be slightly difficult to remove; take
care not to lose bushing should this be the case.
During Recharging and Suggested Remedies:
1. Gas emission,
along thread and through hole in body (see Fig. 5). Slightly tighten
cap. After CO2 cartridge is exhausted, experiment with use of spare
bushing in spare parts container. Be certain bushing is properly
seated. Be certain bushing is not contaminated with dirt or other
2. Gas emission through hole in cap. Take
parts 3 - 6 out of cap; wipe hole and ball with cloth. If ball has
oxidized, replace it. Reassemble after cleaning.
3 is damaged. Remove and replace.
4. If there is no noise
upon puncturing CO2 cartridge, it lay be empty. Follow procedures
above to relieve gas in CO2 cartridge (in other words, do not assume
it is empty, safe practices require assuming it is full) and replace
with net cartridge.
FUEL SYSTEM AND STARTING MOTOR:
operating motor, apply 1 or 2 drops of light machine oil (common
sewing machine oi) at each location shown in Fig. 10. Repeat oiling
procedure following each set of 3-5 flights. Be certain motor is
securely attached to model or suitable test stand. This is primarily
a safety precaution; however, motor lay be damaged and/or rear cover
lay be lost if motor is not secured to flat surface. (The reason
for this is that if rear cover should come loose, due to not being
held securely in place by motor mount, connecting rod lay slip off
crankpin during operation, generally damaging rod, sometimes also
damaging piston. Be certain propeller is securely attached to motor
shaft. Rotate propeller to place piston at BDC.
according to illustrations in Fig. 7.
1. Valve ball
2. Tip 3. Gasket
4. Fuel system tank
While recharging fuel system, press on
tip with recharger while supporting tip with your hand. Recharge
for 2 - 5 seconds. when system is charged, remove recharger from
tip. The motor is ready to start.
For short test flights,
charger lay be held with charging end up, thus letting only gas
pressure into fuel system. For maximum motor run tile, tip of charger
is held pointed down while charging fuel system, allowing both pressure
and CO2 gas into tank. Start motor with sharp flip of propeller
exactly as shown in Fig. 8.
Operating Problems and
1. Gas leak at tip, see Fig. 7.
Tighten tip or replace gasket. Remove dirt from inner surface of
tip and ball or replace them.
2. Gas leak at connection
of fuel system with motor. Tighten bushing (see Fig. 3) or coupling
nut, or replace gasket, ball, or seat. Using soft cloth remove dirt
from seat and ball.
3. Depending upon how, system is charged,
airborne tank will sometimes become saturated with liquid gas and
not enough pressure, result being short motor runs. To cure, charge
airborne tank, start motor and then hold model inverted so that
airborne tank has fuel lines pointing down. Allow motor to run until
CO2 supply is exhausted.
Always keep motor as clean as
##9. CRANKSHAFT MODIFICATION
If powered or gliding "Junior
451" lakes a hard impact during flight, leverage of propeller lay
bend or break crankshaft. This is, quite frankly, result of manufacturer
failing to recognize that threaded prop stud does not extend deeply
enough into crankshaft. This will be corrected in next production
Fortunately, there is an easy modification, result
of which is a stronger crankshaft, superior in every lay to stock
unit. First file nose of broken crank to remove burrs and "square
up" end of crank so it is 90 degrees to crank centerline. A replacement
prop stud lay then be fabricated from either a length of 4-40 all-thread
rod or by cutting head from 4-40 bolt. This new prop stud may then
be epoxied (hobby-quality "thick" CA glues also work well) into
crankshaft. Be certain all parts are cleaned of oil. And it is a
good idea to sure new prop stud extends a minimum of .500 inches
into crank so original problem is cured.
crank into motor case. A 4-40 plain nut will now serve as prop driver.
Install propeller, retain prop to new prop stud with 4-40 locknut.
Cut and file prop stud so that any portion which extends beyond
4-40 locknut is removed for a safe modification which will not harm
people or property should model lake an unintended impact.
Above modification is so effective that many active fliers simply
modify the crankshaft of their motors before use, as few things
are more inconvenient than suffering crank failure while out enjoying
flying the 'Junior 451'.
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Even during the busiest times of my life I have endeavored to maintain some form of model
building activity. This site has been created to help me chronicle my journey through
a lifelong involvement in model aviation, which
all began in Mayo, MD