Conceptual Rules for a New R/C Soaring Contest

Copyright © Blaine K. Beron-Rawdon
Envision Design
12/12/00 Revision 2/8/02

Electric Altitude Limit

This paper presents conceptual rules for a new type of contest for radio controlled thermal sailplanes.

All current radio controlled thermal soaring competitions are heavily influenced by the launch of the model. This places an emphasis on the aircraft structure and flight controls that is inconsistent with the soaring phase of the flight. It can be argued that powerful launches have perverted the fundamentally elegant and serene character of RC thermal soaring. Recent advances in the size and cost of sensors and transmitters presents the opportunity for an alternative contest that emphasizes the soaring phase of flight. 

An onboard altimeter with downlink can provide the means to limit competition launches to a equal height. Electric propulsion can provide a low-impact means of launching the model.


The contest pertains to radio controlled sailplanes launched with electric propulsion systems. 

Basic Concept

The contest is a man-on-man duration contest with a fixed maximum launch height. All of the models in a heat are launched within a two minute window. The motor must be turned off by the end of the launch window. Following motor shutoff, the pilot must remain below the maximum launch altitude for 10 seconds. When this is achieved, duration time starts. The models are then flown for a prescribed period of time or longer and landed within a large landing zone. The score is based on duration if the landing is made within the landing zone and time period, and on the scores of the other pilots in the heat.


Limitations to the size, propulsion system and control system of the models may be defined by the Contest Director (CD) in advance.

The sailplanes are equipped with downlinked altimeters. These are provided by the Contest Director and have been calibrated to insure consistent measurement.

Launch thrust will be provided by an electric motor driven propeller or fan. Energy for the motor will be provided by commercially available nickel cadmium batteries.


The models are flown in man-on-man heats. The pilot is judged and advised by a timer. A two minute launch window is announced. The model may be hand launched or may rise off ground. No other mechanized launching mechanism is permitted. At the end of the two minute launch window the motor must be shut of for the rest of the flight.

The maximum altitude of the start gate must be specified by the CD in advance of the contest. The highest typical altitude is 500 feet. (Higher altitudes are permissible, but the two minute launch window must be extended so that no more than a 250 ft/min rate of climb is required.) Lower limit altitudes may be used when excellent conditions are expected.

Following motor shutoff, the model must remain below the limit altitude for at least 10 seconds. This inhibits very high launches with zooms down to limit altitude and back up. Altitude is read by the timer from the altimeter instrument and is regularly reported to the pilot during the climb phase. 


The pilot attempts to remain airborne for the prescribed duration or longer. The prescribed duration (a max) should be long enough that it is impossible to achieve without thermal assistance, and long enough that it is challenging to achieve in good conditions. Furthermore, the CD should set the limit launch altitude according to conditions so that few pilots achieve a max in any heat.

During the climb phase the timer may report the time and altitude to the pilot according to the pilot's request. Note that it may possible to exceed the range of the altimeter downlink - it is the pilot's responsibility to remain within radio range during the critical 10 second launch gate. At other times this is not required.


The model is landed either in or out of a large landing zone. Landings outside the zone give a zero flight score. The landing may be made during any time within the maximum flight time, and up to 30 seconds beyond that time. This feature is intended to reduce the influence of landing on the score. The time stops when the model contacts a ground-based object. The model may be caught by the pilot.


Each pilot in a heat is scored based on his duration. This score is rationalized against the maximum score in the heat, with the highest score equalling 1000 points. Flights exceeding the maximum time, but less than 30 seconds greater than the maximum time, receive a maximum score.


Multiple rounds should be flown. The number of rounds should be announced by the CD in advance. Flight order in each round is determined by the CD.



The intention of the contest rules is to provide for a contest in which soaring capability is the key. It is also the intent to reduce the importance of the electric propulsion system by limiting the required rate of climb to a modest value. 


The onboard altimeter is the key to this contest. The current absence of the altimeter system is the only technical impediment to the realization of this contest concept.

The concept is that the altimeter-downlink would be in a small, streamlined blister pod that can be quickly taped to the underside of the wing or side of the fuselage. This permits rapid change-out from heat to heat. Ultimately, models would be designed to accept the altimeter in an internal receptacle to reduce the impact on drag.

I am unaware of any commercially available device of this description. Stuart Sechrist of AeroVironment Inc. tells me that such a device is technically feasible. Many key components are already available as highly integrated chips. Transmitters-on-a-chip are available in at least 8 nearby frequencies. Stuart says that a sensor-downlink-receiver-display package could cost less than $200 in modest production quantities. Amateur construction from plans is possible at even lower cost.

One variation on the concept of the altimeter system would be to intentionally limit the range of the device to a modest distance, say 300 meters. This would have the effect of forcing all pilots to start the duration phase nearby to each other - a sort of start gate as used in full scale soaring contests as well as in sailboat racing.

Propulsion System

In most electric sailplane contests, altitude is limited by the duration of the motor run. This places a great emphasis on high power and propeller efficiency. This in turn leads to expensive batteries, motors, gearboxes and propellers, so that the sailplane is again compromised by the launch phase.

In this contest, a modest rate of climb is required, and a rule to inhibit zooming to high altitude is proposed. The intent of this is to approximately equalize all varieties of propulsion systems and encourage the use of modest, low cost systems. It would appear that a small weight advantage can be obtained by using small, powerful and expensive motors. This might reduce the overall airplane weight by only a few percent, so the potential benefits are limited.

Commercially available nickel cadmium batteries are required in order to limit battery cost.


It is not clear what the optimum airplane for this contest is. Major variables include span, wing loading, control system and propulsion system. It may work out that big, complex models are best. In this case it may be desirable to break the contest into classes based on span or control system.

Limit Altitude

It is a key element of the contest concept to provide for man-on-man competition in which the soaring phase of flight is emphasized. To that end, the flight duration and launch altitude should be set so that few in each heat are able to max. 

I recommend that in early morning rounds before lift is present that the limit altitude / duration combination is set so that no pilot can reach the maximum duration. Later in the day, limit altitude can be lowered to make each heat challenging. This limit could be adjusted dynamically between each heat or round according to the percentage of pilots making their maximum times. 

Alternatively, a prescribed schedule of launch altitudes can be used. For example, instead of the typical duration contests 3 ,5 and 7 minute duration, this contest could use a uniform 10 minute duration with a 500 ft, 400 ft and 300 ft launch. I recognize that everybody is happy when they make their maxes, but the tendency to reduce duration so that more can make their maxes must be resisted in order to prevent the contest from becoming a landing contest.

Landing Points and Tiebreakers

Landing points are not awarded except as a qualification. It is required that the pilot make it back to the field in order to score duration points. This should inhibit desperate downwind flights that result in the loss of a model.

This contest format may lead to ties at the end of the prescribed rounds. A final flyoff round with a combination of low launch altitude and a long maximum time may be used to break ties. Alternatively, flyoff rounds may involve typical launch altitude and duration but can be decided by who has the greatest altitude at the end of the fight period. Limited altimeter radio range can then force the pilots to return their airplanes near to the field at the end of the flight period. This leads to tactical decisions regarding when to leave that downwind thermal!

Contest Management

Aside from providing calibrated altimeter sets, the duties of the CD are modest. Key preparations include devising the rules, setting up landing areas, making up the flight order, announcing the launch window, scoring and moderating the contest. Note that no launch equipment is required.

The timer's duties are a little more complex than usual, but they may be more fun too! The timer now has to watch the launch window, measure the 10 second glide before duration starts, and measure flight duration. He must also measure the landing score. The timer must also watch and report altitude to the pilot. Note that if the airplane is within range, the timer may report to the pilot his altitude - a human audio variometer. 

Altimeter Design Needed

The missing link required to make this contest concept real is an affordable downlinked altimeter. Perhaps you or someone you know is in the position to design the required equipment. This design could be manufactured, kitted, or simply published. I would be pleased to publish the plans on my site, or post a link to your site. Please let me know if I can be of assistance.

Copyright © Blaine K. Beron-Rawdon