A 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.
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 - see instruction below). 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
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
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 with care.
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
8. Do not operate motor unless it is securely attached to model or test stand.
9. Do not used damaged propeller. Never use metal propeller.
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.
11. 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
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:
1. Supplied 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
Speed, rpm: 2500, +-500
Maximum mass of motor and propeller, ounces: 1. 06
Propeller rotation, front view: counter-clockwise
Motor dimensions, inches: Length: 5.4; height: 4.0;
width: 1. 0
##3. COMPLETE MOTOR SET:
Please note that Russian illustrations show packaging which is different from
that used in "Junior 451."
##4. SAFETY PRECAUTIQNS:
Please refer to page 1 and page 4 of this manual for listing of safety precautions.
13. Piston 14. Connecting rod 15. Crankshaft
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.
Also 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 test again.
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 storage.
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.
With 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 be used.
Parts for recharger are shown in Fig. 5 under section 6.
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
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
To remove exhausted CO2 cartridge from recharger, carefully adhere to following
1. Relieve remaining gas per Fig. 6 using supplied fitting. (Fitting is found
in spare parts container)
2. Carefully 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.
Problems 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 foreign latter.
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. Bushing 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.
##7. CHARGING FUEL SYSTEM AND STARTING MOTOR:
Before 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.
Charge system 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.
Operating Problems and Suggested Actions:
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
Always keep motor as clean as possible.
##9. CRANKSHAFT MODIFICATION AND/OR REPAIR
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 run.
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.
Install repaired 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'.
Posted September 6, 2007
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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,