Jul 09

Choosing Your First Rocket

Congratulations on participating in the 4-H Rocketry project. In this blog post I want to provide you with some tips on picking out a rocket for the county fair. These tips apply to most counties in Kansas but possibly not all.  These tips will also help you if you are eligible to take your rocket to the Kansas State Fair.

If the rules for rocketry seem really really long you are right they are.  The rocketry project is really complex. After all it is rocket  science. 🙂 Luckily in this post and the ones to follow I will try to break it down so you can get started building really cool rockets for the county fair.

The first thing we have to figure out is where should we go to purchase a rocket. There are several choices. I recommend you try one of of the following.

  1. A local hobby store or science center. These will have the best selection and will be the most knowledge about rocketry.
  2. A hobby chain store, like Hobby Lobby. These will have a good selection of rockets you can choose from. Big box stores don’t typically carry a good selection of rockets so you may want to skip them.
  3. Online. There are many hobby stores online that have rockets you can order. It can be hard to get a good idea of what the rocket looks like.
SwingTest

Now that you know where to buy your rocket lets think about what type of rocket you might want to build. You probably know there are all sorts of rockets to choose from, from rockets that are 6 feet tall to rockets that are shorter than 4 inches. Which is the best rocket for your first or second year at the fair?

First thing we want is a rocket that has cardboard or balsa wood fins. DO NOT get one that has plastic fins, even if they snap together. Most counties and the state fair do not allow plastic fins of any sort. The reason for this is the judges want to see your ability to construct a rocket not the company that makes it. That said there are a lot of good rockets to choose from that have balsa wood or cardboard fins.

It’s ok if you want to build one with plastic fins, just don’t bring it to the fair unless you know your county allows them.

Now that we have the fins taken care of what other things should you look for when choosing a rocket?

The next thing you want to check is if the rocket is a “scale model” or not. What’s a scale model? In simple terms its any full sized rocket you’ve seen before. For example the space shuttle, AMRAM missiles, Atlas missiles, the Star Trek Enterprise, etc. What the Enterprise isn’t a real rocket? Your right, but the TV series defined the dimensions of the full sized ship so it counts as a scale model. At this point you’re probably wondering if there is an easy way to figure out if a rocket is a scale model. In most cases there is. If you look at the package it will say something like “1:25 Scale” or “Replica” or “Scale Model.”

If its a scale model I recommend avoiding that model for your first year. The reason for this is judges are more picky on these rockets especially with how they are painted. There is a rule in most fair books that says “scale models” are to be painted like the real thing. That means if the rocket has red paint on the fins and the rest of the rocket is white the judges will expect it to have red fins and a white body.  So skip the “scale models” for your first year.

RocketLaunchIt’s my personal preference to get an Estes model rocket your first year. The reason for this is that most of the time their instructions are very complete and they are really good if something was damaged when you open up the model kit to start constructing it.

So which model to choose? Pick something fairly simple. 3 or 4 fins that’s about a foot long. I know you want something that has a lot of fins and looks really cool. The best way to impress the judges your first few years in the project is build a high quality simple model. To judges that is more cool than a complex rocket. As a rocketry judge I have seen simple rockets that have received a purple and an average looking complex rockets that got a Red.  It’s not about how cool a rocket looks, it’s about how well you construct it.

So go and pick a rocket with balsa wood or cardboard  fins that’s not a “scale model.” Then get ready to blast off!

In my next post I’ll cover picking up the supplies you will need to build your rocket.

Cheers,

Tony

May 22

National Association of Rocketry High Power Rocket Safety Code (Aug 2012)

This is a copy of the NAR High Power Rocket Safety Code and is only listed here for referance. The original document can be found at http://www.nar.org/safety-information/high-power-rocket-safety-code/ Please refer to this link for the most up to date version of the High Power Rocket Safety Code.

High Power Rocket Safety Code
Effective August 2012

  1. Certification. I will only fly high power rockets or possess high power rocket motors that are within the scope of my user certification and required licensing.
  2. Materials. I will use only lightweight materials such as paper, wood, rubber, plastic, fiberglass, or when necessary ductile metal, for the construction of my rocket.
  3. Motors. I will use only certified, commercially made rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer. I will not allow smoking, open flames, nor heat sources within 25 feet of these motors.
  4. Ignition System. I will launch my rockets with an electrical launch system, and with electrical motor igniters that are installed in the motor only after my rocket is at the launch pad or in a designated prepping area. My launch system will have a safety interlock that is in series with the launch switch that is not installed until my rocket is ready for launch, and will use a launch switch that returns to the “off” position when released. The function of onboard energetics and firing circuits will be inhibited except when my rocket is in the launching position.
  5. Misfires. If my rocket does not launch when I press the button of my electrical launch system, I will remove the launcher’s safety interlock or disconnect its battery, and will wait 60 seconds after the last launch attempt before allowing anyone to approach the rocket.
  6. Launch Safety. I will use a 5-second countdown before launch. I will ensure that a means is available to warn participants and spectators in the event of a problem. I will ensure that no person is closer to the launch pad than allowed by the accompanying Minimum Distance Table. When arming onboard energetics and firing circuits I will ensure that no person is at the pad except safety personnel and those required for arming and disarming operations. I will check the stability of my rocket before flight and will not fly it if it cannot be determined to be stable. When conducting a simultaneous launch of more than one high power rocket I will observe the additional requirements of NFPA 1127.
  7. Launcher. I will launch my rocket from a stable device that provides rigid guidance until the rocket has attained a speed that ensures a stable flight, and that is pointed to within 20 degrees of vertical. If the wind speed exceeds 5 miles per hour I will use a launcher length that permits the rocket to attain a safe velocity before separation from the launcher. I will use a blast deflector to prevent the motor’s exhaust from hitting the ground. I will ensure that dry grass is cleared around each launch pad in accordance with the accompanying Minimum Distance table, and will increase this distance by a factor of 1.5 and clear that area of all combustible material if the rocket motor being launched uses titanium sponge in the propellant.
  8. Size. My rocket will not contain any combination of motors that total more than 40,960 N-sec (9208 pound-seconds) of total impulse. My rocket will not weigh more at liftoff than one-third of the certified average thrust of the high power rocket motor(s) intended to be ignited at launch.
  9. Flight Safety. I will not launch my rocket at targets, into clouds, near airplanes, nor on trajectories that take it directly over the heads of spectators or beyond the boundaries of the launch site, and will not put any flammable or explosive payload in my rocket. I will not launch my rockets if wind speeds exceed 20 miles per hour. I will comply with Federal Aviation Administration airspace regulations when flying, and will ensure that my rocket will not exceed any applicable altitude limit in effect at that launch site.
  10. Launch Site. I will launch my rocket outdoors, in an open area where trees, power lines, occupied buildings, and persons not involved in the launch do not present a hazard, and that is at least as large on its smallest dimension as one-half of the maximum altitude to which rockets are allowed to be flown at that site or 1500 feet, whichever is greater, or 1000 feet for rockets with a combined total impulse of less than 160 N-sec, a total liftoff weight of less than 1500 grams, and a maximum expected altitude of less than 610 meters (2000 feet).
  11. Launcher Location. My launcher will be 1500 feet from any occupied building or from any public highway on which traffic flow exceeds 10 vehicles per hour, not including traffic flow related to the launch. It will also be no closer than the appropriate Minimum Personnel Distance from the accompanying table from any boundary of the launch site.
  12. Recovery System. I will use a recovery system such as a parachute in my rocket so that all parts of my rocket return safely and undamaged and can be flown again, and I will use only flame-resistant or fireproof recovery system wadding in my rocket.
  13. Recovery Safety. I will not attempt to recover my rocket from power lines, tall trees, or other dangerous places, fly it under conditions where it is likely to recover in spectator areas or outside the launch site, nor attempt to catch it as it approaches the ground.

 

MINIMUM DISTANCE TABLE
Installed Total Impulse (Newton-Seconds) Equivalent High Power Motor Type Minimum Diameter of Cleared Area (ft.) Minimum Personnel Distance (ft.) Minimum Personnel Distance (Complex Rocket) (ft.)
0 — 320.00 H or smaller 50 100 200
320.01 — 640.00 I 50 100 200
640.01 — 1,280.00 J 50 100 200
1,280.01 — 2,560.00 K 75 200 300
2,560.01 — 5,120.00 L 100 300 500
5,120.01 — 10,240.00 M 125 500 1000
10,240.01 — 20,480.00 N 125 1000 1500
20,480.01 — 40,960.00 O 125 1500 2000

Note: A Complex rocket is one that is multi-staged or that is propelled by two or more rocket motors

Revision of July 2008

May 22

National Association of Rocketry Model Rocketry Safety Code (Aug 2012)

This is a copy of the NAR Model Rocket Safety Code and is only listed here for referance. The original document can be found at http://www.nar.org/safety-information/model-rocket-safety-code/ Please refer to this link for the most up to date version of the Model Rocket Safety Code.

Model Rocket Safety Code
Effective August 2012

  1. Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.
  2. Motors. I will use only certified, commercially-made model rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer.
  3. Ignition System. I will launch my rockets with an electrical launch system and electrical motor igniters. My launch system will have a safety interlock in series with the launch switch, and will use a launch switch that returns to the “off” position when released.
  4. Misfires. If my rocket does not launch when I press the button of my electrical launch system, I will remove the launcher’s safety interlock or disconnect its battery, and will wait 60 seconds after the last launch attempt before allowing anyone to approach the rocket.
  5. Launch Safety. I will use a countdown before launch, and will ensure that everyone is paying attention and is a safe distance of at least 15 feet away when I launch rockets with D motors or smaller, and 30 feet when I launch larger rockets. If I am uncertain about the safety or stability of an untested rocket, I will check the stability before flight and will fly it only after warning spectators and clearing them away to a safe distance. When conducting a simultaneous launch of more than ten rockets I will observe a safe distance of 1.5 times the maximum expected altitude of any launched rocket.
  6. Launcher. I will launch my rocket from a launch rod, tower, or rail that is pointed to within 30 degrees of the vertical to ensure that the rocket flies nearly straight up, and I will use a blast deflector to prevent the motor’s exhaust from hitting the ground. To prevent accidental eye injury, I will place launchers so that the end of the launch rod is above eye level or will cap the end of the rod when it is not in use.
  7. Size. My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse.
  8. Flight Safety. I will not launch my rocket at targets, into clouds, or near airplanes, and will not put any flammable or explosive payload in my rocket.
  9. Launch Site. I will launch my rocket outdoors, in an open area at least as large as shown in the accompanying table, and in safe weather conditions with wind speeds no greater than 20 miles per hour. I will ensure that there is no dry grass close to the launch pad, and that the launch site does not present risk of grass fires.
  10. Recovery System. I will use a recovery system such as a streamer or parachute in my rocket so that it returns safely and undamaged and can be flown again, and I will use only flame-resistant or fireproof recovery system wadding in my rocket.
  11. Recovery Safety. I will not attempt to recover my rocket from power lines, tall trees, or other dangerous places.
LAUNCH SITE DIMENSIONS
Installed Total Impulse (N-sec) Equivalent Motor Type Minimum Site Dimensions (ft.)
0.00–1.25 1/4A, 1/2A 50
1.26–2.50 A 100
2.51–5.00 B 200
5.01–10.00 C 400
10.01–20.00 D 500
20.01–40.00 E 1,000
40.01–80.00 F 1,000
80.01–160.00 G 1,000
160.01–320.00 Two Gs 1,500

Revision of August, 2012

May 22

Rocketry Crib Sheet (Finding height & other math)

This is a quick crib sheet to help you as you build model rockets. There is much more to be found on the Internet. If you find a helpful link please share it in the comments section below.

To Convert Inches (in) to Centimeters (cm):       (in) * 2.54 = (cm’s)

Example: 5 in * 2.54 = 12.7 cm

 

To Convert Feet (ft) to Meters (m):                     (ft) / 3.281 = (m)

Example: 7 ft / 3.281 = 2.1335 m

 

To Convert Meters (m) to Feet (ft):                     (m) * 3.281 = (ft)

Example: 30 m * 3.281 = 98.43 ft

 

Updated 7-20-16, some of the links below have changed the content and no longer include the simple altitude calculation so we have added it below.

To calculate the height of a right triangle:         tan(angle) * distance = height
(yes, use a calculator to find the tangent)

Example: tan(59°) * 100 feet = 166.43 feet

Example: Sandy is launching her rocket. Her cousin, Tim, is standing 300 feet away with a protractor when Sandy launches her rocket. The protractor angle reads 127° when the rocket reaches its highest point, known as apogee. Tim knows he needs to subtract 90° from the angle on the protractor to get the correct angle. How high did the rocket go?

tan(127° – 90°) * 300 feet = height Rocket Height
Simplify
tan(37°) * 300 feet = height
Simplify
~0.75355 * 300 feet = height
Simplify
~226.07 feet = height

Sandy’s rocket flew about 226.07 feet in the air. (We round off the extra digits after .07)

 

Finding a side in a right-angled triangle

https://www.mathsisfun.com/algebra/trig-finding-side-right-triangle.html

 

How to measure model rocket altitude

http://www.hobbizine.com/rocketaltitude.html

 

Rocket Center of pressure calculator

http://physics.gallaudet.edu/tools/rocketcop.html

 

Rocket Altitude Calculator

http://www.unm.edu/~tbeach/flashstuff/RocketAltitudeFixedSize.html

 

Determine Maximum Altitude

http://exploration.grc.nasa.gov/education/rocket/rkthowhi.html

 

OpenRocket Model Rocket Simulator – Freeware

http://openrocket.sourceforge.net/

 

Altitude Tracking

http://quest.arc.nasa.gov/space/teachers/rockets/act9.html

 

Flight Simulator Programs (List of different software)

http://www.thrustcurve.org/simulators.shtml