Altitude Data

« Altitude Competition
20.1 Scope
All entries in a given event, other than non-competition record attempts, are to be tracked using the same method. The electronic sanction submitted by the Contest Director must, for each altitude event, designate whether altimeters or theodolites will be used for altitude tracking. In the case of Record Trials, the Contest Director may designate either or both types of tracking. Contest Director must ensure that all announcements and publications for the sanctioned meet inform prospective entrants of the tracking method for each altitude event.
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, and the entry is not disqualified for any other safety or event rule violation, then that flight can be considered “No Data” per Rule 20.3.3 – Untracked Flights.

If the altimeter fails to report an altitude, and the flight has not been disqualified for any safety or event rule reason, then that flight can be considered “No Data” per Rule 20.3.3 – Untracked Flights.

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.

20.3 Theodolite Tracking
All entries in any event for which an achieved altitude figure is scored may be tracked in flight by theodolites of a design approved by the NAR Contest Board. Any tracking theodolite that:

  • Is equipped with both azimuth and elevation axes at right angles to each other
  • Can be leveled or adjusted to an otherwise proper plane before use
  • Has an accuracy of 0.5 degrees in both azimuth and elevation
  • Uses a pair of open sights mounted at least twenty centimeters apart or a rifle-sight or equivalent optical sight with or without lenses
  • Uses crosshairs in the open or optical sight
  • Is mounted on a sturdy tripod or other solid base in a manner that does not permit the tracking head to wobble or otherwise lose its zero-reference under normal use
  • Has a provision for securely holding the sights firmly in any desired position, so that the operator may accurately record the tracking data associated with a flight
  • Is capable of tracking to an azimuth of +/- 180 degrees and an elevation from 0 degrees to 90 degrees
  • The Contest Board must approve theodolites that do not meet all of the above requirements before they may be used in a sanctioned activity
20.3.1 Baseline
Two or more tracking theodolites must be used on appropriate baselines. The baseline should be between 50% and 400% of the expected altitudes to be tracked. Therefore, a 300 meter baseline would be appropriate for 75-600 meter flights. While very low power events may require a baseline less than 300 meters, proper care and judgment should be used before this is done. Longer baselines are strongly encouraged for high-powered or high-performance entries. Proper baselines must be used to track any record setting flight.
20.3.2 Tracking
Entries must be tracked to apogee if practical. When apogee tracking is used, one person must be designated to give a mark to the theodolite operators at precisely the instant the entry appears to reach apogee, and the theodolites must be locked at the mark. At the discretion of the Contest Director, entries may be tracked to ejection instead of apogee. When ejection tracking is used, it is recommended that the entries to be tracked contain colored tracking powder to create a visible cloud at ejection, and that the theodolite operators lock their theodolites at the appearance of the tracking powder cloud. It is further recommended that all entries that are to be tracked be painted in colors or patterns that will aid tracking. All entries in an event must be tracked using the same tracking method (either apogee or ejection).
20.3.3 Untracked Flights
At the option of the competitor, Track Lost or Track Not Closed may be considered an official flight if it is not disqualified for any other reason. In this case the flight cannot place but must receive flight points; except in an event where the score is the sum of several factors, in which case the flight must be scored as having an altitude of zero.
20.3.4 Communication System
A reliable voice communication system must be used to link both trackers and the launch control area, for the purpose of calling marks and for the transmission of tracking data.
20.3.5 Data Reduction
Angular data obtained from theodolite tracking must be reduced to an achieved altitude figure by means of a standard system of equations approved by the NAR Contest Board. All data must be recorded for all altitude events and flights, including those flights that may be disqualified; this permits the altitude data to be available in case the disqualification ruling is later reversed.
20.3.6 Error Check
The error figure as computed by the approved equations must be less than or equal to 10% to be considered valid and acceptable for competition and record flights. Flights whose reduced altitudes do not satisfy this constraint shall be scored as Track Not Closed. Flights, whose data is incomplete, preventing calculation of their altitude, must be scored as Track Lost. All altitudes must be rounded off to the nearest meter per Rule 1.5 – Rounding. The rounded altitude shall be the official scored altitude. When tracking with theodolites, an altimeter reading reported by a competitor will NOT be officially considered and will NOT apply per Rule 20.3.3 – Untracked Flights.
20.3.7 Multiple Stations
When more than two trackers are used, altitude and closure percentage shall be calculated for each combination of trackers. The official altitude score is the average of all closed tracks, rounded per Rule 1.5 – Rounding. It is only necessary for one pair of trackers to close.
20.4 Novel Methods
The NAR Contest Board must approve novel altitude determination methods before the results are accepted for competition.