Altitude Data

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14.1 Theodolites

All entries in any event for which an achieved altitude figure is scored shall 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 rifle-sight or equivalent optical sight with or without lenses, or uses a pair of open sight mounted at least twenty centimeters apart
  • Uses crosshairs in the optical or open 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 shall be acceptable for NAR contest use.

The Contest Board must approve theodolites that do not meet all of the above requirements before they may be used in a sanctioned activity.

14.2 Baseline

Two or more tracking theodolites shall be used on appropriate baselines. The baseline should be between 50% and 400% of the expected altitudes to be tracked. Thus a 300-meter baseline would be appropriate for 75-600 meter flights. While very low power events may require a baseline under 300 meters, proper care and judgment should be used before this is done. Longer baselines are strongly encouraged for high-powered or high-performance models. Proper baselines must be used to track any record setting flight.

14.3 Tracking

Models shall be tracked to apogee if practical. When apogee tracking is used, one person shall be designated to give a mark to the theodolite operators at precisely the instant the entry appears to reach apogee, and the theodolites shall be locked at the mark. At the discretion of the Contest Director, models may be tracked to ejection instead of apogee. When ejection tracking is used, it is recommended that the models 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 shall be tracked using the same tracking method (either apogee or ejection).

14.4 Communication System

A reliable voice communication system shall be used to link both trackers and the launch control area, for the purpose of calling marks and for the transmission of tracking data.

14.5 Data Reduction

Angular data obtained from theodolite tracking shall be reduced to an achieved altitude figure by means of a standard system of equations approved by the NAR Contest Board. Samples are included in Appendix E. All data shall 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.

14.6 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, shall be scored as Track Lost. All altitudes shall be rounded off to the nearest meter. Fractions of a meter less than 0.5 must be rounded to the next lower meter; fractions 0.5 or above must be rounded to the next higher meter. The rounded altitude shall be the official scored altitude. Any altimeter reading reporting by an entry that was optically tracked using theodolites will NOT be officially considered and Rule 14.9 will NOT apply.

14.7 Multiple Stations

When multiple-station or parallel systems are used, it is only necessary that one pair of trackers (one at each station) close. In the case that more than one pair of trackers close, the official altitude shall be computed by averaging all closed tracks, and then rounding them as above. The averaged rounded altitude shall be the official scored altitude.

14.8 Novel Methods

The NAR Contest Board must approve novel altitude determination methods before the results are accepted for competition.

14.9 Untracked Flights

Track Lost or Track Not Closed, if it is not disqualified for any other reason, is considered an unofficial flight. In this case the contestant is entitled to an additional flight, to be made during the period allocated for tracked flights. At the option of the contestant, 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 shall receive flight points; except in an event where the score is the sum of several factors, in which case the flight shall be scored as having an altitude of zero.

14.10 Electronic Altimeters

Approved electronic altimeters may also be used for altitude determination. All entries in a given event, other than non-competition record attempts, are to be tracked using the same method. The sanction request form submitted by the contest director shall, for each altitude event, designate under “Special Provisions” whether “Theodolites (14.1)” or “Altimeters (14.10)” for altitude tracking.

In the case of record trials, the contest director may designate either or both types of tracking. The contest director shall ensure that all official announcements and publications for the sanctioned meet inform prospective entrants of the tracking method for each altitude event.

Only commercially available altimeters approved by the NAR Contest Board and publicly announced as approved at least 60 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 which are outside the voltage range published by the altimeter manufacturer. Appendix G lists currently approved altimeters.

An altimeter must meet the following requirements to be approved by the Contest Board:

  • 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 audio or visual readout of apogee from the most recent flight directly from the altimeter.
  • 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. The part of the rocket containing the altimeter must be vented to the outside air by multiple small vent holes that are placed at locations behind the curved forward surface of the rocket’s nose. Any attempt to deliberately produce excessively high altitude readings by use of devices such as venturis is prohibited.

14.10.1 Safety Check-In Procedure

The flight ready entry with the altimeter removed must be presented to the safety check official for inspection to verify the altimeter is unaltered and has been properly powered. The safety check officer may request the “owner’s manual” for the altimeter if any questions arise concerning its operation or post flight readout. The make and model of the altimeter will be noted on the contestant’s flight card under the “remarks”section. The altimeter’s power source will be turned on in the presence of the safety check official, and readiness to record new flight data will be verified after boot-up. Alternately, the altimeter may be installed immediately after power-on and readiness verified after installation, provided the safety check official is satisfied the altimeter can be heard or seen for readiness verification per Appendix G. Installation of the altimeter in the rocket must be observed by the safety check official.

14.10.2 Returns Procedure

The model and altimeter must be returned as recovered, unopened. If necessary (as in the case of visual readout), the contestant shall open the altimeter compartment in the presence of the returns official to read the altimeter. The returns official and contestant both will concur on the reported altitude. Any other specific event rules may also apply.

If the altimeter can NOT be returned, and the model is not DQ’d for any other safety or event rule violations, then that flight can be considered “Track Lost” and Rule 14.9 can be applied. If the altimeter fails to report an altitude, and the flight has not been DQ’d for any safety or event rule reason, then that flight can be considered “Track Lost” and Rule 14.9 can be applied.

14.10.3 Performance Records with Altimeters

The altitude reported for performance records with altimeters is subject to additional requirements and review. An altitude record may be set only using a recording altimeter. Altitude records may not be set using a reporting-only altimeter. After the flight, the altimeter data will be downloaded by the contestant and reviewed by a contest official (RSO, CD, or member of the contest jury). If it is shown that a sudden peak in altitude is attributable to the ejection event or a flight anomaly, that peak 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 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.

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