Frequently Asked Questions about Rockets
WARNING AND DISCLAIMER: If you are underage, then consult with your parents or guardians before attempting any of this. You are on your own - I'm not responsible for your actions or harm you may bring to others because of your actions. Making the items described below can result in injury or death to you or people in your vicinity. Some things mentioned here may be illegal to make in your city, county, state, or country so check the laws that apply to you before you attempt anything described here. These notes are not complete on purpose. If you are reading them and new to pyrotechnics, then you are making a mistake. Stop now - this page is not for you. Get a beginning book on fireworks (see Skylighter or American Fireworks News (very quick shipping) for a start) and read up. You can't make any of this work without more information so read up or join a club or ask someone to help you.
The following are some frequently asked questions about rockets and rocket fuels.
Q: Is it safe to ram RP? (ramming is putting the compound into the rocket tube and pounding it into a single grain with a hammer)
A: RP generally has aluminum in it. Aluminum doesn't spark and bright (not dark or blackhead) aluminum in a BP base doesn't make a sensitive compound. While you will get differing opinions on this (search the archives on rec.pyro and see what I mean), bright Al in BP isn't a problem with ramming. Nearly all other metals (including dark aluminums) are! If you make RP with titanium, iron, ferro-titanium, etc, then do not ram it.
I ram and press aluminum based RP all the time.
Q: Should you add boric acid to the BP Al mix?
A: Another argumentative area. Shimizu made a mixture of 1/2 nitrate and 1/2 fine aluminum - wet it to a dough and waited. It got hot (started to run away) but he did not say it combusted. He added 1% boric acid and the reaction stopped. Many have interpreted that as reason to never make a BP and Al mixture without adding the acid. The fact is, up to 10% of Al can be added to BP and it doesn't change anything. However, if you are going to store it for a long time, I recommend adding 1% boric acid if for no other reason than to protect the aluminum from long-term deterioration. Also add it if you are going to keep the compound wet for a long time - the aluminum reacts to water and will turn to oxide - which will not give proper results when ignited. It is a minor step that might make you feel better.
Q: Is it safe to ram Benzolift (or whistle)?
A: Absolutely not! Benzolift is just modified whistle and while it is less sensitive than whistle, it is still a very hot mixture. Treat it with great respect. Whistle and flash will explode if rammed.
Q: Generally, what is safe to ram?
A: BP and BP like compounds without metal (see first question for an exception). Do not ram anything with chlorates or perchlorates in it. Do not ram anything with dark aluminum or other metals. I only ram BP and sugar fuels.
Q: What are the alternatives to ramming?
A: There are two alternatives. One is casting - such as wetting the composition with acetone and pressing it by hand into the tube and letting it dry. This is a pain to do and almost no one does it this way. The more popular alternative is to press it with either an arbor or hydraulic press. For small rockets (5/8" and below), you can use an arbor press - get a 1 ton model or, if you can find a used one, a 2 ton model. For larger rockets, you will have to go to a shop press - a 10 ton model is best if you are shopping. See presses.html for more about pressing.
Q: What kind of paper tubes should I use?
A: You can roll your own, buy recycled paper tubes from one of the hobby vendors, or go together with other hobbyists and buy New England Paper Tube (NEPT) virgin kraft tubes (actually, they may have about 10% recycled paper in them). In any case, use convolute instead of spiral wound tubes. A toilet paper tube is spiral wound. A convolute tube has one seam that runs horizontally. The NEPT tubes are very strong but are also expensive.
If you roll your own, consult Weingart or other text on the technique. Generally, start rolling smaller tubes first. Gummed packing tape can be used for tubes to 3/8" or 1/2" I.D. For a 3/8" motor, use a 3/8" rod as a mandrel. The rod can be almost any material. Wax it, wrap 12" of moist packing tape on it (moisten with a damp sponge - don't over wet it). The best bet for keeping the tape taut is to clamp one end and roll it on by hand. Slide the tube off, and dry on a screen (not on a flat surface else it will warp). Repeat until you get really good at the process. Make the walls 3/16" for a 3/8" rocket, up to 1/4" for bigger rockets.
You will have to reinforce the tubes with a pressing sleeve if you press them in a hydraulic press. See extras.html for information on reinforcing tubes.
Q: What kind of paste should I use for rolling larger tubes?
A: Nearly any wallpaper paste, flour paste, carpenter's glue or water based paste will work. You can make your own or buy it. Dilute carpenter's paste by a little (up to 1/2) if it is too thick. Put a liberal amount on the first layer so it slides off the mandrel easily.
Q: What about strobe and whistle mixes - what are the precautions to use with them?
A: Whistle mixes are sensitive mixtures that will self-confine if larger piles of them are ignited. Keep your work area clean and do not leave open working containers of either mix. That is, take a measure of the mix from the working container and then close the container. Add the mix to the motor and press it. Repeat until done. Do not ram whistle or strobe and do not keep quantities of either mix on-hand. Make only what you will use.
Strobe mix is the most sensitive to shock and will easily explode if you use a 'hammer' test. That is, take a pinch of it and put it outside on a sidewalk. Hit it with a hammer. It will likely explode every time. Add to the sensitivity the poisonous nature of the ingredients, the non-compatibility of the oxidizer with many other chemicals, and the sensitivity to moisture and you have a special case that needs careful attention. Be very careful when using strobe mixes.
Consult with experts before making your first whistle or strobe rockets. Passfire is a good place to find experts.
Q: Why do strobe rockets fail so much?
A: Most strobe CATOs are due to the incorrect amount of whistle boost and not the strobe mix. Most flop-overs (a strobe just keeps pulsing right into the ground) are due to untested strobe mix and a poor guess on how to make the motor.
Before you attempt making strobe rockets, seek advice from a known successful maker of strobes. Do not accept hearsay from web discussion groups or knowledge fakers (those who post answers but really haven't been there). Whenever someone advises you, it is ok to ask about his or her experience.
Strobe mixes burn with a pulsating throb that is controlled by the ratios and quality of the ingredients. The barium sulfate and the mesh size of the magnalium are critical to the success of the mixture. Until you work out a successful mix, you should not try to fly a strobe rocket. Ground test it instead.