Bottle Rocket Tips

Bottle Rocket Tips For

Students In Science Olympiad

Robert

Youens

I am not an official representative of Science Olympiad and rules clarifications need to be addressed to the official Science Olympiad web-site.

The following is a copy of the hand out I provided to students and coaches who attended my Bottle Rocket Sessions at the Science Olympiad National Coaches Clinic held in Hammond, Indiana (10-4-02).

1. Stiff fins are the best fins. Flexibility decreases the effectiveness of a fin.

2. To trace the bottle's shape on the fin material, place the bottle directly under a light source.

3. Place the grain of the fin perpendicular to the bottle. This will make the fin stiffer and stronger.

4. Do not sand the bottle prior to gluing. It will get you disqualified and is not necessary.

5. Best glues for fins: PL Premium - available at Home Depot or Lowes, Goop - available at most hardware stores, Shoe Gu - available at shoe stores and sporting good stores, 100% GE Silicone Glue - available everywhere. All hold well, PL Premium is the stiffest, probably the most toxic, Shoe Gu and Goop are both fairly stiff, GE Silicone is less toxic, but more flexible. Contact Cement or Rubber Cement can be used to glue on paper fins. You should be in a well-ventilated area and wear latex gloves when using PL Premium, Shoe Gu, and Goop. It will usually take fins about 2 hours to cure enough to put on another fin and about 2 days before launching.

6. "Swing Testing" is a quick way to determine if a rocket has reasonable stability. This test is done by tying a string around the rocket at its CG and swinging the rocket around.

7. Fins cause very little drag and do not weigh very much. A non-stable rocket that is flying sideways is creating a lot of drag. Non stable rockets have a lot of problems with pre-deployment of their parachute.

8. The cost of non-vertical flight is tremendous. A flight that is 5 degrees off vertical can loose 10% of its potential altitude.

9. Parachutes are more efficient with more shroud lines. Shroud lines hold the shape of the parachute and keep air from burping from the chute.

10. Parachutes should be as large as possible while still meeting overall length requirements and efficiency standards.

11. Parachute efficiency is improved by using the correct shroud length. Shroud lengths should be between 1.2 to 1.5 times the parachute diameter.

12. The best parachute material that I have found is dry cleaner bags. If you request the bags used by commercial cleaner for drapes or wedding dresses you may find one large enough for your parachute.

13. The best material for shroud line is nylon upholstery thread.

14. How much water? 1/3 of the capacity of the bottle will get you close. Use simulator listed on page 4.

15. When humidity is low and there is no chance of rain, you can use talc to keep the chute from having static cling.

16. The best folding technique for passive deployment is to zig zag fold the cute, starting from the top to bottom. When you fold the chute to the shroud lines, gently make a couple of wraps with the lines. You want to use as few wraps as possible so that the chute will deploy quickly.

17. The parachute should be attached securely to the rocket. It can be glue or tied. If glued, you should reinforce the bond with fiberglass reinforced packing tape. This also applies to the cord that attaches the cone to the bottle.

18. Deployment at apogee and a quick opening parachute are essential to increasing hang time.

19. If the rocket arches through apogee and does not slow down, wind drag will not allow the cone and body to separate even with active deployment.

20. Make sure that your cone sits securely on the rocket. I have seen numerous rockets disqualified due to cones shifting during pressurization or by being blown off by the wind.

21. The rules no longer allow for a wind block to be used by a competitor to shield the rocket from wind gusts during launch.

22. Beware, bottles expand under pressure. The expansion can upset a cone if the rocket is not designed to deal with this problem.

23. You can design a cone that fits loosely on the bottle. It will need to be supported by a ring or pegs. Both pegs and rings (butter tub seal) can be glued to the rocket with PL Premium.

24. Many competitors use poster board paper or banner paper to make their cone. See: http://txsnapper.eezway.org/powerdeployment, for procedure to make a simple cone.

25. If you use pegs to sit the cone on, make sure to use Bass Wood (not balsa) and turn the grain so that the G-forces of take off will not cause the cone to cut through the peg.

26. Another simple method of controlling expansion and creating a ledge for the cone to sit on is to wrap fiberglass reinforced packing tape around the top of the bottle until it has created a ledge.

27. Practice many times in all conditions including rain.

28. Have a written procedure and follow it every time. The teams I coach follow step by step through their checklist every time even though they know it by heart. Airline pilots and surgeons both use checklists, shouldn't you? Laminate your checklist!

29. How heavy should my rocket be? That is a good question. The weight that would give the rocket the best loft may not allow it to reach the highest altitude. Go for stability first, loft second, altitude third. Try to reach a good compromise.

30. How much air pressure do I use? Easy question, all that is allowed. The more stored energy, the higher you go.

31. Use this flight simulator to determine the best amount of water. http://homes.managesoft.com.au/~cjh/rockets/simulation/

32. Check the opening of your bottle, a standard piece of 1/2 inch, Schedule 40 PVC pipe through the nozzle of your rocket. If it will pass through the opening, it will launch from any standard launcher.

33. With rocket designs where a tall cone sits loosely on the bottle, the cone mass can do little to correct an initial flight stability issue. Why? Because when the fins attempt to correct the instability, the rocket can bend in the middle where the cone sits on the bottle. If you notice that you are getting a lot of pre-deployments, you may attempt to move some of your cone mass toward the base of the cone or you may choose to shorten your cone.

34. Make sure that you have a waterproof box to store your rocket and supplies. Also make sure you have an umbrella to cover the rocket while staging and before launch. Bring rain gear for yourself. The last 2 years at nationals we have had intense rain and many rockets were damaged.

35. Try not to use paper, cardboard or wood components in the rocket. If you do, attempt to waterproof them.

36. Bring too much clothing. You don't have to wear it, may want to. When cold or wet it is hard to concentrate.

37. Know the launcher that will be used at the event you are going to attend. This is a particular concern for rockets that have fins that are swept below the flange on the bottleneck. Many launchers including the typical "Bent Fork Launchers" and the NERDS launcher will not launch rockets with swept fins. If you plan to use a swept fin rocket, I recommend that you contact the event supervisor or event director to determine what type of launcher will be used. In the past at nationals a launcher that is capable of launching all typical rocket fin configurations has been used, but it still doesn't hurt to check.

38. I recommend a fin jig be used for installing fins with precision. A fin jig is a necessity when using slow set glues. You can see my fin jig at my rocket web site: http://txsnapper.eezway.org/powerdeployment

39. To measure your water, build you own custom measuring device from a 1 Liter Bottle. Mark it for just the right amount of water for your rocket. This will help eliminate measuring mistakes.

40. Mark your rocket with the correct water level as a double check.

41. If you are going to be launching off a launcher where you will have to tip your rocket, rather than the launcher tipping for loading, always put in a little too much water. As you tip your rocket you will always lose a little water. You can lift up on your rocket gently to let out a little water while on the pad. (Don't get too bent out of shape if you don't have exactly the correct amount of water, a few ml of water will not make that much difference)

Bottle Rocket Resources

(Bottle Rocket Are Commonly Referred To As Water Rockets)

Recovery:

Vertical, Horizontal Systems http://txsnapper.eezway.org/powerdeployment

& Passive

Dave Johnson Air Flap http://dogrocket.home.mindspring.com/WaterRockets/

Gary Ensmenger - Balloon http://www.h2orocket.com/topic/balloon/balloon.html

Nerds Recovery Systems http://tc.unl.edu/rbonnstetter/rockets/recovery.html

Paul Grosse http://ourworld.compuserve.com/homepages/pagrosse/h2orrecsys1.htm

Ulrich Hornstein http://home.t-online.de/home/u.hornstein/wr.htm

Aaron Allen - VDEN Aaronswaterrockets.html

Division C Backslider Recovery: