tips and tricks tips rr When inserting the nozzle in the closure sand a slight bevel onto the narrow end of the plastic nozzle to when it passes by the o-ring into the closure it does not damage it. If you must remove and replace an oring use a dentist's pick to get the o-ring out of the groove. When inserting delays into the delay well, use a "press" motion not a pounding or forcing motion. Use a 5/8" dowel so the entire face of the rubber is pressed all at once and it does not bind because a too narrow or too rounded tool is used. We include 5/8" dowels for free. We provide additional liners for free. We provide additional delay for free (all associated with need of course). While a very small amount of grease is neded on the threads to prevent gauling and on the very surface of o-rings to provide a wet seal, most other grease is optional. We find some customers (who like grease anyway) spread it on the outside surface of the liner to make removal easier. We provide an ejection dowel in closure sets for that. Also some customers use Vaseline (petroleum jelly) in lieu of high temperature automotive grease. Your preferance may vary but they all work. Many customers use baby wipes right after the firing for cleaning of closures and tubes. Many customers leave closures soaking in white vinegar overnight to clean off excess rubber and scum. Ejection charges can be retained with simple masking tape over the end, or around the end closure and pressed down over the top surface of the motor mount is loose enough. Some customers use paper discs and in those cases the surface has to be free of grease. Many kits come with a set delay such as a typical 8 second delay. Never switch the delay element to a different motor DIAMETER or propellant STYLE and expect the same delay time. Consult a custom delay length table for guidance as to what length delivers what delay in what motor diameter and propellant style. Delays can always be shortened by using a drill bit in your hand perhaps 3/16 - 1/4" in diameter and drilling into the CENTER of the delay end surface and removing 1/32" (0.03125") for each second of delay time you want to remove. best to only modify delays after you gain experience with a particular load so you can see if delays run a bit short or a bit long of what is advertised to begin with. It may be rocket science but it is not perfect. You can always run fewer grains in a longer case such as a 180 load in a 240 case. However you must use the full length liner for the case, in this example 240. The grains can be left totally loose inside, but many customers place an empty paper tube as a grain spacer nearer the nozzle to act as a plenum to improve combustion efficiency of the propellant. Igniters must always be inserted all the way into the motor and touching the top grain. if you have a large delay cavity without propellant due to very short delay or very high burning rate propellant, be sure the igniter is not in the delay well, but against the propellant. Igniters that have some duration to them are preferred so if a high temperature wick style (Thermalite) or a dipped igniter style is used, dip it deep or cut it long (1.5") to get best ignition. When holding the igniter in place simple masking tape of the wires to the end of the motor and then bending them to the side and taping outside of the thrust ring works. If the tape covers the entire nozzle, punch a hole in it with a pen to allow some airflow. If a particularly long motor is used or if the wires are not particularly stiff a 1/16" dowel the full length of the motor can be used. Tape the igniter to the stick every foot or so. Be sure the stick is a tiny fraction of the nozzle throat diameter and that it is only taped in sufficient to keep it from dislodging due to wind and pad conditions and simple igniter operation initially. Make sure there is a free path out. If the outside surface of a delay element is peeling, discard it, or dispose of it properly. Makes a great fireplace or BBQ starter. If a delay element is not a snug fit in the closure, apply a smooth layer of celophane tape (Scotch tape) so the fit is tight and the seal surface is smooth. Press the delay element all the way into the delay closure and against a grease wetted o-ring to double assure a good seal. One can know the seal was improper by the flight ejecting during the motor thrust phase. This can be harsh indeed on rockets. Please avoid it. It normally does not destroy the closure. Our nozzles are reuseable. Other brands are single use most of the time. When refiring a used nozzle scrape the slag (melted propellant metals) from the face of the convergent section (inside collection funnel) and away from any other areas. We usually run the specified drill bit through the nozzle by hand to clean it out, but that is not even necessary as the 500+ psi gasses from the next firing will clean it out just fine (smile). If a nozzle is expanding in diameter it need not be discarded. Just drill it out to the next larger useful size and keep using it on faster propellants in that diameter or in larger diameter motors. By the time you have some experience you will only be flying bigger and bigger motors. We like that! All of our nozzles use english inch 1/64" drill bit sizes as commonly available in most hardware stores. It is handy to bring a battery drill to the site if alot of last minute drillings are expected such as at group launches. Always print out and keep in your range box the "cheat sheets" for nozzle diameters and delay lengths for various diameters and propellants. The delays remain about the same independent of motor length or grain count within a given diameter and propellant. The throats are all different. When you start collecting spare nozzles, start ordering your propellant in bulk packs and only ask for as many nozzles, o-rings, liners, delays as you actually need. We are glad to help you save cost when you return the favor. If an o-ring has obvious visual damage replace it. Even a marginal o-ring works on our system. You're welcome. All of the o-rings are standard Buna N 70 in 1/16" thickness (or as obviously different for larger motors) and are avialable worldwide as stock items. We also give them free to customers. When using altimiter dual deployment set the secondary deployment at the lowest setting practical. We suggest 350 feet but no lower than 200 feet because that is about the resolution of most barometric sensors with parachute deployment time factored in. Most hardware we have seen has a lower limit of 500 feet. A drogue parachute should be about 16 inch for rockets 1-2 pounds with 15%-25% spillhole and preferably nylon chute or over the top construction. for 2-5 pounds a nylon chute of 16-24 inches with a 15-25% spillhole is good. For 6-15 pounds a 24-36 inch parachute with 15-25% spillhole is good. For 16-35 pounds 37-50 inch parachute with 25% spillhole is good. For 36-70 pounds 48-60 inch parachute with 25% spillhole is good. For primary recovery chute refer to online decelerator programs. Delays from AT, USR and other firms burn at 1/32" per second nominal and can be modified shorter by that amount for every second you want to remove from a delay. Due to the many variables of burn time, propellant style, throat size and other factors a "reference" delay time should be determined for each specific propellant, grain geometry, throat size and delay length in each individual case diameter. From THAT, delays can be lengthened and shortened, but ANY of the stated factors variance requires a new delay reference point be determined. No exceptions. Ejection charges of black powder should be about 1/2g for a model rocket, about 3/4-1g for a HPR rocket and monster rockets can be calculated using online calculators which overestimate required ejection so a stout ejerction should be assumed when designing a rocket. Small 1/8-1/4" holes are placed in the airframes of rockets with large air volumes (>30% volume is air) to offset air pressure changes vs altitude on relatively quick travel into lower atmospheric pressure regions on flights of 4000 feet or more.