Soaring Late in the Day
In these articles I have avoided reference to specific times of the day - because so much can depend on a particular day, how far east or west you are in your time zone, and what time of year it is. In this section of the article, I define “late in the day” as whatever period your achieved climbs are beginning to trend down in strength because of lower surface heating. As this occurs you have to make changes in strategy, in cruise speed, and sometimes jettison water ballast if you are carrying it. And, a big part of your decision-making turns on whether you are confident you will make it to your goal (so your emphasis is on maximizing speed) or you are doubtful about making the goal (so your emphasis is on maximizing distance).
Going for Speed
If it is getting late in the day but the thermals are still working, your object is to fly as efficiently as possible in the final hour or two and not waste energy or altitude. If there are good clouds ahead you can continue to be choosy about stopping to thermal and start your final glide a bit early (i.e. under the glide) using the clouds on the final leg to “bump” up to a true final glide. Resist the temptation to “milk” the last thermal up to final glide altitude. While it’s fun and relieving to hear or see your computer announce “task on final glide” it is really inefficient to accept 5 or 10 minutes of climbing in weak junk lift to accomplish that - followed by a final glide where you pass through 3 great thermals that you don’t need anymore. It’s better to start a little early, monitor your progress, and if you are not coming up into final glide take a good climb a little later.
If you are flying for a speed record or a contest finish make sure that you have your minimum finish altitude set into your glide computer independent of any safety reserve altitude (or set the safety reserve altitude to a very low value or zero). Most modern computers will “stack” your safety reserve altitude on top of your minimum task finish altitude which is pointless if your task minimum finish computation has you finishing high above the landing point anyway. Also - remember to check your leading edges for bugs and make appropriate adjustments for glide if you have very many.
Going for Distance
If the day is beginning to deteriorate and you are in serious jeopardy of not making it home, it’s time to dial back the cruise speed to the setting that corresponds to the climb rate you expect from the weak thermals in the rest of the flight. It is also time to seriously consider whether dumping the water ballast will help you climb better and faster, and to stay as close to the top of your height band as you can, even if it means accepting a reduced climb rate near the top of the thermal. If this sounds like the opposite of my earlier advice against “milking” a weak thermal to get to final glide - it is exactly that. Here we are dealing with a situation where we might not get back and we want every foot of climb available. Altitude and reduced speed give you increased range and a better chance at finding lift or reducing the retrieve distance if you can’t. Late in the day, you must resist the temptation to keep cruising fast or leave the thermal early - don’t worry, you won’t run out of daylight - nobody ever does. Moderate course deviations to fly under more promising clouds are helpful - but only if the clouds can be used to gain significant altitude. If the effect of the deviation is uncertain or gets you only a minimal climb it’s probably not worth it. If you are flying a crosswind course, an upwind track deviation makes more sense than one downwind. This part of your flying takes great patience, especially if you have been flying fast and aggressively earlier in that day.
A flight computer that monitors your progress and tells you how much altitude you need to climb to get to your goal is very helpful at times like this. If you are at or near-final glide altitude continue to monitor your airspeed and the altitude needed to make sure the glider is progressing as the computer predicts. Note that the computer prediction is based on the wind at your current altitude. If there is a wind gradient below you then expect that your computer will be overly optimistic heading downwind and overly pessimistic heading into the wind. This is because of the effect of the reduced headwind or tailwind at lower altitudes. Some computers allow you to make a manual wind entry and this is a time when that can be helpful.
Banner photo by Petr Kolmann
Roy Bourgeois is a well-known US and South African glider pilot who serves as the Chief Pilot for the Greater Boston Soaring Club. He has held several US national records, competed in many US and Canadian Nationals, and has flown over a quarter million XC kilometers in his 4200 hours of gliding. He can be reached at royb@bw.legal