This event is about pure altitude! Who’s rocket can go the highest on a specified amount of total impulse?
The rocket may be single or multi-staged. It must have a recovery device. The model does not have to be returned unless there is a question from the Range Safety Officer (RSO) about whether it had a rules issue in its flight (ejected engine, etc.). If the event is flown with altimeter-based tracking, then the rocket must contain an altimeter and must be returned after flight for the altimeter to be read.
For the full rules for this event, please see the Altitude rules in the Model Rocket Sporting Code.
Score is the higher of the altitudes from the two allowed official flights. If the trackers cannot see the rocket and a “track lost” is recorded on a flight, that flight may be reflown.
by Trip Barber, NAR 4322
The keys to this event are minimum body size, minimum drag, proper motor selection, and optimum weight.
Minimum Body Size. Always use the smallest body diameter that will contain the motor or (if staged) motors that you use. Then use the minimum body length that will ensure a straight boost with good dynamic stability — generally about 10 times the body diameter. This will minimize the frontal area and wetted surface area of the rocket, minimizing its drag.
Minimum Drag. Put the best surface finish on rockets for this event that you know how to do. Use a nose cone that is parabolic in shape with a length-diameter ratio of 2 or 3 to 1. If the nose cone is balsa, user filler coat, sanding sealer, or Elmer’s wood-filling paste to completely fill the grain and polish it with at least 600 grit sandpaper to make the finish mirror-smooth. Pay close attention to the nose-body joint to ensure that it is smooth. Sand the surface of the body tube to ensure there are no ridges from any spiral winding. Use thin waferglass for the fins or, if you use balsa, use the same techniques as the nose to ensure a smooth surface finish and put a good symmetrical airfoil on the fins. Use a fin jig to put the fins on absolutely straight so the rocket does not spin during its upward flight. Make the shock cord mount internal so there are no protrusions on the surface of the body. Use a piston launcher or a tower launcher (or a piston inside a tower) to permit leaving off the draggy launch lug or rail buttons.
Motor Selection. The best motor selection for this event is one with low average thrust, the smallest possible diameter, the highest total impulse that fits within the power class being flown, and a long delay time. If you have a choice between a 13mm motor and an 18mm motor for this event, always use the 13mm motor. Staging is generally not advantageous unless it permits you to use a smaller body diameter than single-staging, without sacrificing total impulse (i.e. staging two 13mm diameter “A” motors vs single-staging one 18mm diameter B motor with the same total impulse as the two A’s together). The optimum thrust for maximum altitude is twice the weight of the rocket, i.e. very low; an F10 will go much higher than an F50 of equal total impulse because the rocket with the F10 will travel at a lower average velocity and drag goes up as the square of velocity so low velocity equals lower drag equals higher altitude for the same total impulse. Altitude models tend to need long coasting times after motor burnout in order to reach their maximum feasible altitude, so always use the longest available delay time for the motor type you choose. In some power classes, particularly “A”, the longest delay time currently available for the smallest-diameter available A, the Estes A3-4T, is far too short for maximum altitude but you don’t have any alternative choice.
Optimum Weight. Every rocket has a weight that leads to optimum altitude performance for that design. If the rocket is too light, it will not have enough momentum to coast as far as it could have after motor burnout, as it turns the velocity it achieved during motor burn into altitude. If the rocket is too heavy, it will not reach as high a burnout velocity as it might have done if lighter, and therefore will not coast as far. Flight simulation programs such as Rocksim or Open Rocket permit you to determine what this “optimum” liftoff weight is for your particular design and this is what your rocket should weigh, if possible. In general, this optimum weight is lower that it is possible to achieve for A power class and below altitude designs, while for C power class and above you may actually need to add weight (such as extra tracking powder) to the basic rocket in order to hit the optimum and achieve maximum altitude.
Other Considerations. For recovery, use a small aluminized mylar streamer, narrow and long. The mylar takes up little room, and it can reflect sunlight to make it easier to see coming down and after landing on the ground. If optical tracking is being used to determine altitude, use lots of tracking powder (keeping the optimum liftoff weight in mind) so that the people doing the tracking can see the point of ejection, which is what they track to. See the section on “tracking powder” elsewhere on this website. If altimeters are being used to determine altitude score, use the lightest available altimeter that is approved for contest use by the NAR Contest Board, particularly in C and below power classes where optimum weight is a concern.
–Gone I kit (1/4A through A) – Qualified Competition Rockets
PLANS AND ARTICLES
A Altitude, C Payload, and Flying Altitude Events by Dan Wolf
|Altitude & Payload Events (Wolf)||May 28, 2014, 5:24 am||3 MB|