CALCULATION OF SPORTS CLASS HANDICAPS

by Graham Brown
AG Jan 1993

The currently used handicaps for sports class competitions in Australia are based on the work of Peter Rigby (A.G. Oct 1981).These handicaps have worked well over the years and are based on cross country speeds calculated from the polar curves.In order to advance the science of hanicapping gliders it is now more appropriate to model glider performance using a computer.The following describes a simple computer model which I have implemented on a PC which is not too different from the Rigby calculations but automates the process and takes into account additional factors such as wind, weight, and start and finish heights. A comparison of the computer calculated handicaps is made to the existing handicaps and the effects of some of the previously unmodelled factors noted.Handicaps for some of the newer aircraft that are not yet flying in sports class are also calculated.

In addition to Sports Class handicaps the computer allows any aircraft to be the standard rather than just the Pilatus.(The Pilatus is the current standard aircraft for handicaps in Australia) This is probably of interest to people running regattas wishing to handicap a fleet of ballasted gliders to their chosen standard.

THE COMPUTER MODEL:
The computer model works as follows:
The computer model assumes gliders gain height in thermals of a nominated average strength and then glide to the next thermal at a cruise speed.This cruise speed is calculated from the polar and is your block speed or the speed indicated by your Macready ring or flight director.The computer program calculates two cruise speeds, one from a ring setting that you chose and one for a ring setting equal to the climb rate. The latter is used in calculations of handicaps.
The climb rate is calculated by subtracting 1.2 times the minimum sink rate of the glider from the thermal air mass vertical speed.The factor 1.2 is to reflect the greater sink rate of the glider while turning in the thermals. An achieved speed is then calculated by determining the time to climb then glide a unit of distance. This achieved speed is then adjusted due to the fact the glider does not have to climb a height equivalent to the start height minus the finish height over the total length of the course.
Given a course to be flown, the wind strength and direction and the above achieved speed through the air ,simple vector arithmetic gives the speed ,direction and time to fly each leg. The speed over the entire course is the total course distance divided by the sum of the times taken to fly each leg.

In order to make the above calculations the minimum sink rate of the aircraft must be known and the cruise speeds for any rate of climb.These are obtained from the polar curve which is entered and stored in a file on the computer.It is imperative that the wing loading at which the polar was measured is known and is also entered.If calculations are required at different wing loadings the polar curve is translated by the square root of the ratio of the wing loadings.
The handicap for any given flight is calculated by determining the speed of the standard aircraft over the course and dividing it by the speed of the selected aircraft.
The computer output is illustrated below:

Cross Country Flight
Aircraft type = pik20b wingloading = 31.2 kg/m2
thermal strength = 5.5 knts climb rate in thermals= 3.9 knts
wind = 17 knts 300 degs
leg = 1 44.9 kms 52 degs 25.6 mins 105.4 kph
leg = 2 79.7 kms 344 degs 67.7 mins 70.7.kph
leg = 3 107.1 kms 209 degs 76.4 mins 84.1 kph
total distance = 231.7 kms
ring setting = 3 cruise speed = 72.1 kts opt cruise speed = 77.1 kts
strat height = 5000 ft finish height = 600ft
total time for course = 2 hrs 50 mins
speed for course = 81.9 kph opt speed for course = 82.5 kph
handicap = 0.83
handicap std = pilatus handicap speed for course = 67.9 kph

EFFECT OF THERMAL STRENGTH
Computer runs at thermal air mass strengths of 3, 6 and 12 knots demonstrate the effect of thermal stength on handicaps.
3 Knts 6 Knts 12 Knts
Ka6e .95 .98 .99
Std Libelle .89 .91 .89
PIK 20B .86 .84 .84
Nimbus 2 .66 .76 .78

For example the Ka6e does a lot better than the Pilatus in light conditions but then is constantly handicaped in medimum and strong conditions.The Libelle is fairly constantly handicapped in all conditions as is the PIK.The Nimbus does extremely well in light conditions then is relatively constantly handicaped.

EFFECT OF WIND
Computer runs at wind strengths of 0, 10, 20 and 25 knots across a course demonstrates the effect of wind on handicaps.
Wind (knts) 0 10 20 25
Arrow 1.14 1.15 1.20 1.25
Ka6e .99 .98 .98 .98
Std Libelle .91 .90 .88 .86
PIK 20B .84 .84 .81 .78
Nimbus 2 .77 .76 .72 .69

Lower performance aircraft to the Pilatus progressively do worse as the wind strength increases.Conversely higher performance aircraft to the Pilatus progressively do better.

EFFECT OF WEATHER

Because the handicaps move around a bit depending on thermal strengths and wind it is only fair to average the handicaps calculated over a number of flights with the weather conditions expected in the region at that time of year.I have chosen in my calculations to average 10 days representing the expected 10 days of a competition. Bill Tugnett and myself pooled our records of sports class competition flights in the Temora Leeton area for January in the last 5 years and came up with the following distribution:
Wind (knts) 0-10 11-20 22+
28% 61% 11%
thermals(knts) 1.5-4.5 4.6-6.5 6.6+
33% 47% 20%
task dist (Km) 100-200 201-300 300+
46% 40% 14%

This distribution led to the selection of the following 10 standard flights over which the handicaps would be averaged.
Day 1 2 3 4 5 6 7 8 9 10
wind 5 15 12 20 17 13 25 10 15 10
thermals 3.5 4.5 4.5 5.5 5.5 6.5 6.5 6.5 8.5 9.5
distance 126 198 181 171 233 267 283 297 328 390

EFFECT OF BALLAST

Computer runs at ballast weights of 80, 95 and 110 Kg from the empty weight of the glider demonstrate negligble effects on handicaps as long as all the gliders have the same ballast.Differential ballasts however do change the handicaps as shown below.

  • Standard = pilatus at 80 kg ballast.
  • Ka6e at 80 kg = .99 at 110 kg = .95
  • std libelle at 80 kg = .90 at 110 kg = .87
  • PIK20 B at 80 kg = .83 at 110 kg = .81
  • nimbus 2 at 80 kg = .75 at 110 kg = .73

    (Calculations were done using the conditions of day 6) The above example shows that a glider carring 30 kg over the nominated ballast has an avantage of 2 to 4 points.

    COMPARISON TO EXISTING HANDICAPS

    For the following calculations I have chosen a ballast of 95 kg which represents the weight of the pilot plus chute plus a bit for miscellaneous items. This ballast is added to the empty weight of the glider and divided by the wing area to get the appropriate wing loading. Results show handicaps close to the ones currently used.
    eg

    HANDICAPS FOR NEW AIRCRAFT

    As can be seen in the table of handicaps newer aircraft such as the DG 600 ,Ventus,DISCUS,and even the ASW 22 and NIMBUS 3 have handicaps which reasonably reflect their performance. Handicaps for new gliders can be calculated on the spot and all that is required is the polar with its corresponding wing loading, the empty weight and the wing area.

    HANDICAPPING DISTANCES

    The computer model does not take into account the cycle of heating over the day. It assumes the average thermals keep on going as long as they are needed.This is of course absurd and is the reason why handicap competitions should also handicap the distance gliders must fly.The scratch distance must be set for the standard glider and all other gliders must fly a distance equal to the scratch distance divided by the handicap.This will mean all gliders will spend about the same time in the air and hence experience the same average thermal strength. If the gliders have to fly different distances then it is an opportunity to introduce an extra dimention into the competition by letting the pilots chose the course and hopfully bias their average thermal strength. This was the reasoning behind the introduction of POT tasking practiced at the national sports class competitions .

    ERRORS

    The largest errors in computing handicaps come from the polar data that is entered.Bill Tugnett and myself have tried to use Johnson data or DFVLR data where possible but sometimes all that is available is manufactures data.If we can obtain better polar data the computer will be able to calculate better handicaps. The computer calculations are undoubtly only one input to the sports class hanicapping committee but for new aircraft it will be the only one until some history is accumulated for that aircraft.

    CONCLUSIONS

    The computer model allows handicaps to be easily calculated which should facilitate handicapping gliders which have not previously competed in sports class.It also calculates the effects of ballast which has been controversial over the years and we are now in the position to consider the topic quantatively. The computer model provides for different aircraft to be the standard and for the aircraft to be handicaped at different weights.This will give more flexibility to change the scope of sports class competitions in the future and hopefully it will be tried in regattas in the mean time.

    E Mail Graham Brown gbrown@zeta.org.au
    Last Updated Monday November 21, 1997 - 9:06:00 PM