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 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 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 propeller.
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 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:
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 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.
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 5. Filter 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)
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. 8.
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 is exhausted.
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'.
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,