- 20.2 Electronic Altimeters
- Only commercially available altimeters approved by the NAR Contest Board and publicly announced as approved at least 30 days before any contest where they are used may be used in competition. These altimeters may not be altered or modified in any manner, including use of power sources that are outside the voltage range published by the altimeter manufacturer. To be approved by the Contest Board an altimeter must meet the following requirements:
- Uses barometric measurement techniques to record flight apogee altitude above launch pad altitude based on the formula for conversion of pressure to altitude in the International Civil Aviation Organization or US Standard Atmospheres.
- Uses a digital integrated pressure sensor with at least 16 bits of resolution in its digital conversion of pressure measurement.
- Recalculates launch pad pressure altitude by sampling local pressure at least once per minute after activation and before launch.
- Has resolution of 1 meter or better in readout.
- Has accuracy of 1 percent of recorded altitude or 2 meters, whichever is greater, across an operating range of no less than 4000 meters in flight altitude above sea level, 0 to 50 degrees Celsius in launch site temperature, and 750 to 1050 millibars in launch site ambient pressure.
- Has a sampling rate of 10 per second or greater.
- Employs processing functions to reject false short-duration launch or apogee altitude transients that may be created by wind gusts or the pressure transients of ejection events.
- Provides a readout of apogee from the most recent flight.
- Is capable of being placed in a preflight state of readiness to record new flight data and report this new data post-flight. This state must be audibly or visibly verifiable.
The altimeter must be fully enclosed within the rocket body through apogee. Any attempt to deliberately produce excessively high altitude readings, by use of devices such as venturis is prohibited.
- 20.2.1 Approved Altimeter List
- The Contest Board approves altimeters for use in NAR competition. Approved altimeters are listed in Appendix E – Altimeters Approved for Contest Use.
- 20.2.2 Check-In Procedure
- The model of the altimeter will be noted on the competitor’s flight card. The safety check officer may request the “owner’s manual“ for the altimeter if any questions arise concerning its operation or post flight readout.
- 20.2.3 Temperature Compensation
- The ambient temperature at the launch site shall be recorded on the competitor’s flight card in degrees centigrade rounded to the nearest whole number. This temperature shall be recorded prior to each flight.
A competitor’s recorded altitude must be corrected for the effect of ambient air temperature by multiplying the uncorrected altimeter reading by a factor of (273.15 + T)/288.15 where T is the ambient temperature in degrees Celsius.
- 20.2.4 Returns Procedure
- The altimeter must be returned for data verification. The Returns official and competitor should agree on the altimeter raw data. If the Returns official and the competitor cannot agree of the raw data, an additional official shall be called upon to resolve the disputed data. The altimeter’s raw data shall be recorded on the flight card. Any other specific event rules may also apply. If the altimeter cannot be returned or fails to report an altitude, the flight will not be considered an official flight unless the flight is disqualified on other grounds. Alternately, at the option of the competitor, he/she may choose to consider the flight as an official flight with an altitude of zero; in which case the flight cannot place but is eligible for flight points at NARAM; except in an event where the score is composed of several factors, in which case the flight must be scored as having an altitude of zero.
- 20.2.5 Performance Records with Altimeters
- Altitude records may only be set using a recording altimeter. After the flight, if a record is suspected the altimeter data will be downloaded by the competitor and reviewed by a contest official. If the data reveals that the peak altitude is attributable to an ejection event or other flight anomaly, that peak or anomaly will not be used to determine the recorded altitude. The maximum altitude excluding the anomalous peaks will be reported.
If the maximum altitude occurs more than five seconds after the ejection event (due to thermals or other anomaly), only the peak altitude prior to ejection (excluding sudden peaks or anomalies as described above) will be reported.
If the altimeter data is, in the opinion of the contest official, significantly inconsistent with the observed flight, the altimeter data will be disallowed. The decision by the contest official on the interpretation of the altimeter data is final.