Welcome the to the UNB Aerospace Society Wiki! Here, we document the accumulations of lessons and wisdom the team has accumulated over multiple years.
About High-Power Electronics
Altimeters also record altitude
●They don’t record apogee, but also track and preserve large amounts of in-flight data, including flight acceleration and the timing of in-flight events (e.g, apogee, Mach, burnout rate, etc)
●2 types of altimeters: pressure altimeters and accelerometers
●Pressure altimeters operate on the principle that atmospheric pressure decreases with elevation
●Contain aneroid wafers, thin metal canisters sealed with a known pressure reference inside
●A static or outside air source is connected to the altimeter, exposing the wafers to outside atmospheric pressure.
●As the rocket climbs or descends, the wafers expand or contract
●The altimeter translates these changes into measurements of altitude in feet
●Accelerometer altimeters analyze changes in the velocity or acceleration of the rocket
●The G-switch must be placed in the rocket in the proper position and orientation to monitor launch and acceleration
●Altimeters offer written instructions, such as “this ends up” “nose end” or “sky” to help with mounting. Usually stamped on the face of the altimeter
●Barometric-pressure altimeters must be vented to outside air to work properly.
Failure to properly vent the altimeter bay can result in false altimeter readings and even early deployment.
●They are also susceptible to pressure fluctuations if the rocket’s speed exceeds Mach 1.
●Leads to early deployment at high speeds.
●Accelerometers may not be as accurate in measuring altitude as barometric pressure altimeters.
●This is because an accelerometer measures altitude as a function of acceleration and time.
●The distance traveled will be equal to altitude if the rocket flies in a perfectly vertical trajectory.
●Don’t be afraid to ask the manufacturer questions.
●Consider how many charges you will need before buying your altimeter.
●Some altimeters report altitude with a series of beeps that are emitted after the rocket has been recovered.
●Most altimeters allow the rocketeer to fine-tune the altitude at which the main charge will fire.
●Many altimeters can be connected to laptop computers so that flight data can be viewed after flight.
●Buy more than one altimeter.
●Large or complex HPR should always carry more than 1 on-board altimeter.
●This is called redundancy.
●Because altimeters fail from time to time for a variety of reasons, such as low battery power, improper use, wires coming loose, or a host of other causes.
●Always read the instructions.
●Always use a new battery on launch day.
●If you are not sure of battery strength, do not launch.
●A static port allows the barometric function of the altimeter to work properly and provides for rapid pressure equalization between the outside air and the air inside the bay during flight. It must be located on the altimeter bay.
●It should be placed as to minimize any air turbulence caused by obstructions forward of the vent.
●Screws, ornamental objects, camera parts, and other items that protrude on the outside of the rocket should not be placed immediately forward of the static part.
●These objects may cause air turbulence that will interfere with the altimeter. Keep the static port as far away from the nosecone as possible.
●If you place electronics in the hatch-access bays between the fins on the rocket, consider the effect of turbulence around the fin area and how it might affect the altimeter.
●In big rockets, use several large vent holes. Alternatively, build a smaller, self-contained altimeter bay that simply slides into the large bay of the big rocket.
●The sizing of the static port can be determined by calculating the total volume of the electronics bay.
●A static port is used in an altimeter bay.
●A vent hole is used in an ordinary payload bay.
●The ejection charges is usually in the payload bay.
About Ejection Charges
●High power rockets use the same basic method of parachute deployment as model rockets
●At preset time after motor burnout, the ejection charge ignites, filling the body of the rocket with hot gas
●This gas over pressurizes the inside of the rocket body, which forces the rocket apart-usually at the nosecone and leads to the release of the parachute
●Ejection charges may be activated by on-board electronics
●Nosecone is connected internally by airframe by a cord or tether
●May be referred to as a recovery harness
●Also contains an ejection charge
●A container of black powder located somewhere in the rocket
●The gas escapes the rocket by taking the path of least resistance
●As the body and cone travel apart, the recovery harness is pulled out of the rocket, deploying the parachute
●The airframe and the nosecone remain connected to each other by the recovery harness as the rocket descends
●he nosecone and airframe may have separate parachutes and they descend independently of one another
Two methods:
1. Motor-based ejection charges
2. Electronic-activated charges
(may use both methods)
●Black rifle powder is made with potassium nitrate
●It is easy to ignite and burns quickly
●Can be purchased in gun stores
●Typically solid in one-pound cans
●Cost less than $20
●Should last a lot of flights
●The type most often used in HPR is designated FFFF-> also called 4F
●Should be handled with care (as it is explosive)
●Store in a cool, dry place and away from excessive heat or open flame
●The delay grain is located between the main propellant and the black-powder charge
●The delay grain burns at a much slower rate than the propellant
UNB Aerospace Society
UNB Saint John
100 Tucker Park Rd, Saint John,
New Brunswick E2L 4L5, CA