Tips Page

Tools.

      You are most likely going to need some extra items in your rocketry tool kit when you start flying hybrid rocket motors. Here are some tools that you can't do without.

Snap ring pliers:

     You will avoid much frustration while working with the snap rings of Sky Ripper hybrids (and AMW / Ellis solids) if you acquire a good pair of snap ring pliers. Go to your local hardware store and find a pair of snap ring pliers. Take a good look at them. In most cases, this is what a good snap ring tool does not look like. Here is a list of  what you want to look for and avoid.

when selecting a good snap ring tool;

• Look for thick steel at the hinge point.
• Look for one piece fixed-tip construction
• Avoid 'gimmicks' like interchangeable tip styles.
• Avoid convertible/reversible pliers.

     The problems with cheap snap ring pliers is that they will flex under the stress of ring compression. When they flex, the ring isn't held in the tips squarely, and an un squarely held ring quickly becomes a eye piercing projectile.

Good Pliers	Not so good pliers

     You can get a good snap ring plier at Mc Master Carr online at www.mcmaster.com  This McMaster part number; 5449A92, will get you a solid plier for 38 and 54mm motors.  Part number 5449A91 is the same style, and will fit the rings in 29mm motors.

Adjustable wrench:

     Even if you choose not to own hybrid GSE, you will probably get into a situation in the field where you wish you had an adjustable wrench. If you are planning on getting GSE, you are going to want to have two adjustable wrenches since flying hybrids can be 20% plumbing.  I don't have any advice on adjustable wrench buying, other than if you buy two, select two different sizes.  One that opens to 2", and another than opens to 1"

Motor clean out rod:

     For any of the monotube hybrids, you'll need a piece of non-metallic rod to push the pieces out of your motor after firings.  A 1" diameter 3' long wooden dowel is a good choice, but  Sky Ripper recommends that you get a piece of 1" PVC pipe, and cut a 4' long piece to use as your clean out rod. This PVC push out rod is just the ticket for your 38mm hybrids.

Lubricants.

     You'll want to use Krytox® brand grease. It's totally Ox safe, and very nice to work with. It's also kind of expensive, but a little goes a long way. Bob Fortune at Aerocon Systems has the best price we've seen on Krytox® . Tell him SRS sent you.  If you think you might want to use another type of lubricant for your hybrid motor, don't.  It's really not worth it.  While it looks expensive, one 2oz tube of Krytox should last you for a couple of flying seasons.

Applying lubricants: 

     When lubricating O-rings for hybrids, remember the maxim 'less is more'.  The primary function of the lubrication is to allow the O-rings to easily move in the tube without binding.  The O-rings would seal fine without the lube at all, if we could get them into place.  Therefore, you want just enough lube on your O-rings to make them shine.

Dealing with vent tubes.

Lining up vent holes:

     Consider marking the very top of your vented closure with a dot, small arrow, or other feature in permanent marker right above the 1/8” vent hole.  If your fin can is one that isn’t sealed, you’ll be able to look down into the rocket, see your mark, and easily line it up with the vent hole on the airframe while installing your motor.

Easy vent tube installation

     Installing the vent tube from the outside of the rocket body into the motors vent hole can sometimes be the most challenging part of getting your hybrid rocket ready to fly. To make this task easier, try this helpful tip.

     Start by getting the motor installed in the rocket with the motor vent hole a few degrees one way or the other of being in line with the exit hole of the rocket. Take a piece of semi-rigid wire and feed it through the hole in the airframe, then into the vent hole on the forward closure of the motor.

     Once the wire is in place, feed the plastic vent tube over the wire, using the wire as an installation guide. Your vent tube will follow the wire right into the hole with minimal effort. The larger the diameter of wire, the easier this technique will be. Remember to remove the wire once you have finished.

Plumbing.

     This may be the most confusing aspect of hybrids as there are many different fittings with different names, and sometimes they all don't seem to add up.  Here are the most common fitting types found in hybrid rocketry.

At the supply bottle:

      Most likely, your nitrous bottle will terminate at one of two male threads. CGA326 or CGA660. CGA660 is what is commonly found on a NOS bottle intended for performance automotive applications, and CGA326 is a common medical/industrial size thread.

     CGA660 Pros and Cons:

• +With this fitting, you can get a refil at any speed shop that sells Nitrous Oxide.

• +There are thousands of speed shops that cary N20
• -Nitrous Oxide tends to be more expensive at these shops.
• -This fitting requires a nylon washer that is a loose piece, and is notorious for coming up missing.

     CGA236 Pros and Cons:

• +Designed not to need the silly nylon washer.
• +Can be filled easily by industrial gas suppliers.
• -Some industrail gas vendors will not fill bottles of this size or type.
• -Industrial gas vendors may require that your tanks are hydro-tested every year.
• +Can be adapted to a fitting that most speed shops can deal with.

Solenoids:

      Most automotive solenoids terminate at both ends with female 1/8" NPT threads. NPT stands for National Pipe Thread, and the nominal sizes (1/8, 1/4, 3/8) correlate to the nominal ID of the pipe. NPT threads are tapered, and the taper helps to form a tight seal.

Pressure gages:

     Because nitrous oxide is pressure sensitive when used with hybrid rocket motors, it's a good idea to have a pressure gage as part of your setup.   The pressure gage should be placed in-line after the tank valve and before the solenoids.  Most pressure gages will terminate with female NPT threads on both the inlet, and outlet.  Select a gage that reports pressure from the 400 to 1000 psi range.

Other fittings:

37 degree flare JIC (SAE J514):
These JIC (Joint Industrial Council) fittings work with standard straight threads that when fully engaged, seat off on the 37 degree angles to form a seal. The fitting sizes are derived from the nominal O. D. of the pipe, and are referd to by a number representing 1/16ths of an inch. For example, a 37 degree JIC fitting for 1/4" OD pipe, would be called a -4 (as 4*1/16" = 1/4") The actual thread sizes, however, do not correlate with the pipe O. D. Fun stuff, isn't it? Here is a reference chart: AN Tube OD Nut/Tube End Thread Size   -4  1/4 "  7/16"-20  <- Most common size for hybrid GSE -6  3/8 "  9/16"-18   -8  1/2 "  3/4"-16   Find these fittings at McMaster Carr, page 127.
37 degree flare JIC Swivel:
The female fittings for the above male fittings, they feature a swiveling nut that allows the fitting to spin while tightening, allowing whatever they are attached to to remain fixed. It is common to see these fittings at the end of a stainless steel braided teflon hose.  These fittings often will not be referred to by their pipe OD, but rather by the thread size.  For example; a -4AN JIC swivel fitting may be referred to as a 7/16"-20. Find these hose assemblies at McMaster Carr, page 204.
Quick disconnect (instant) tube fitting:
These are the fittings that the nylon fill tube from the motor gets attached to. The fitting works with a series of collapsing fingers that grab the tube to keep it from falling out, and an O-ring that wraps around the OD of the tube to seal it. Pressing in on the end of the fitting releases the fingers, and a sharp tug on the nylon hose will free it. These fittings come in many configurations. One end of the fitting is specified as the O. D. of the nylon tube we are using, and the other is normally a NPT thread. 1/8" and 1/4" NPT are common. Find these fittings at McMaster Carr.
Compression fittings:
These fittings can also be used  to connect the nylon fill tube to our GSE.  They are essentially the same fitting that is on the floating injector in your rocket motor.  They utilize a brass sleeve that is compressed around the nylon tube when a nut is tightened.  Some flyers prefer these to the quick disconnect fittings, as they provide a more positive seal, and are less prone to failure from prolonged use.  The only downside is that you have to replace a 10~20 cent brass sleeve each time you connect a fill hose to your equipment.  Compression fittings usually have 1/8" or 1/4" NPT threads.

Putting it all together:

     So, now that we know a little bit about the different fittings,  here are some McMaster part numbers that can be used to get the parts needed to build up a braided hose assembly for our GSE.  We'll assume that the fill solenoid terminates with female 1/8" NPT.

37 Degree JIC flare fitting;  male 1/8" NPT to male -4 JIC, steel.

    McMaster #50695K161

    This fitting will screw into the fill solenoid and allow for a connection point for the braided teflon hose.  If a dump solenoid is being used, a 'T' will have to be made up, with 1/8" male NPT on both ends and the -4 JIC fitting in the middle.  One 1/8" NPT will go into your fill solenoid, the other to the dump solenoid

Braided teflon hose; female JIC swivel, both ends, stainless steel.

     McMaster # 4552K431

     You can order this hose in several lengths.  It is advisable to keep the hose between 3 and 6 feet long.  This will allow you to keep the bottle away from the pad, without losing too much N20 in the 'pipeline' after the rocket is launched.

37 degree flare fitting; male -4 JIC  to 1/8" NPT female, steel

     McMaster #50695K171

     This piece accepts the quick disconnect fitting on the NPT end, and attaches to the braided hose on the other.  It is beneficial to make up several of these fitting assemblies (JIC fitting + quick disconnect fitting), one for each fill tube size you plan to use.  When changing fill tube sizes you'll only have to screw a new sub-assembly to the braided hose.  You will find that 37 degree JIC joints thread together much quicker and easier than NPT joints.

Ground Support Equipment:

Here are some tips for out at the pad:

• It does not take much force to tighten up a 37 degree fitting.  Resist over tightening, as it will damage the threads.  Tighten the nut by hand until you can no longer turn it. Next, put a wrench on each nut and slowly tighten with minimal force until you feel it stop.  Finally, give one extra 'nudge' with just a little bit of force.  The nut may turn less than 1/32" at this point.  This will seat the 37 degree angles, and ensure a long life for your fittings.
• Pushing the fill tube into a quick disconnect fitting may require more force than you think is needed. When you install a tube into the fitting, you are actually pushing it through an O-ring seal.  If you pay attention, you will feel the resistance of the O-ring as you hit and slip past it.
• The end of the fill tube that gets pushed into the quick disconnect fitting needs to be reasonably square with the tube in order for a seal to be made with the fitting.  If there is leaking from this area, remove the tube from the fitting and trim the end square.
• The common quick disconnect fittings are easily susceptible to damage.  It is a good idea to secure the end of your braided fill tube to the launch pad with a zip-tie, so that the fitting doesn't get damaged by being randomly blown around when the rocket launches.
• Removing the tube from quick disconnect fitting can be a pain, but there is a trick to make it a little easier.  If you have one that is stubborn take an adjustable wrench and adjust the opening so that it is just a little bigger than the fill tube size.  Slip it over the fill tube so it rests squarely against the plastic part of the quick disconnect fitting.  Holding the wrench in one hand, grab the fill tube in the other and give a tug.  The fitting will easily come off.

Cooling down the N20 on a hot day:

     When the temperatures climb above 80f, it's a good idea to have some way to keep your N20 supply bottle protected from the heat.  Here are some ways to ensure that your N20 stays at a constant temp.

     The simplest (and least effective) thing you can do, is to cover your bottle with a white sheet while it is in the field.  The white sheet will reflect the direct energy from the sun.  If you wrap a white sheet around the supply bottle and keep it wet with water, some actual cooling will be done as a result of the evaporation process.

    You will get better results if you put your supply bottle into a receptacle and fill this receptacle with an ice/water mixture.  A round drink cooler (you see them on the sidelines at sporting events) might be the best you could use as it is insulated and designed for holding icy liquids.  If you can't find one of them, a white plastic kitchen-sized trash bin makes a perfect bottle holder for a 20lb bottle. It wont take much water/ice to fill this up, and a gallon of water with one bag of ice will keep your bottle cool for a complete day of flying. Cover the complete setup with a white sheet or a solar blanket to keep the warming effects of the direct sunlight to a minimum. 

     Most importantly, always monitor the pressure of your N20.  Never fire a hybrid rocket motor if the N20 pressure is above 900psi

Keeping N20 warm on a cold day:

     Many things have been tried in regards to keeping N20 temps up in the flyable range when it gets cooler.  There are bottle warmers that are used to keep N20 tanks warm for racing applications, but the flaw is these warmers are intended to keep the bottle toward the high 90's (Ideal for racing, I guess), and tend to draw large amounts of 12v DC power.  The best advice that can be given at this point is to keep your supply bottle in a warm environment until you are ready to fly,  carry it out to the pad before the launch and return it afterwards.  Also, keeping a black wrap on the bottle will allow suns energy to provide some limited warmth.

 Monitoring N20 pressure without a pressure gage:

Scott Miller of SFSM industries gave us a good tip about monitoring your N20 pressure with out a gage.  Get one of these self adhesive fish tank thermometers from a pet store, and stick it to your nitrous bottle.  This will give you  temperature, which you can then derive a pressure from by using the chart below:

Adapting Hypertek GSE to work with Monotube hybrids:

    There is a lot of Hyperek GSE being used by clubs all over, and it is very easy to adapt it to fill and fire Monotue hybrid rocket motors. You will need to make up two items.

     1) An adapter to go from the Hypertek braided fill hose (blue fittings) to a quick fitting that matches the tube size for the hybrid you wish to launch.

     2) A set of igniter leads to plug into the Hypertek relay box.

     The tube adapter is just an assembly of one 37 degree flare fitting (male -4 JIC to 1/8" NPT female), and one 1/8" NPT quick disconnect tube fitting, sized to fit the fill tube of the monotube hybrid you'll be flying.  The igniter leads can be made from a 6 foot long two element extension  cord, with the female (receptacle) end cut off, and an alligator clip soldered to each lead.

Setup Procedure;

     1) Take the fill stem assembly off the rail/rod

     2) Remove the N20 fill hose from the fill stem assembly (Blue fittings)

     3) Place the fill stem in a place where it will be safe.

     4) Screw the tube adapter to the N20 fill hose.

     5) Unplug the High voltage ignition box from the relay box, and plug the igniter leads in.

     6) Unplug the GOX solenoid from the relay box.

     7) Put the launch vehicle on the rail/rod, arm the altimeter.

     8) Connect the fill tube to the tube adapter.

     9) Connect the igniter to the alligator clips.

   10) Fill and fire the rocket using the Hypertek control box just as you would a Hypertek rocket.