Almost an Epic Journey - Part 4

The day was getting active and time for a little PAS flying. Eric continued to be amazed at the steadiness of the plane. He is now flying it “outside the cockpit” and much more sensitive to the events around him, with great results. Steam gauges – at best lag 3 seconds.  It is definitely not twitchy, especially if you have a clear understanding of the rudder. (Ailerons should not pick up wings!) Fortunately he is use to flying light sport aircraft and comfortable with the rudder. Though the large wing area provides ample excitement when approaching a thermal, he soon learned that all you need to do is to ride it (dolphin). Unlike in power planes where you veer between thermals – here you actually deliberately feel your way into it, slight direction change, usually with rudder input (keeping wings level), as the lift build you pull back on the stick according to the thermal strength, sometimes past stall speeds. As the lift weakens – nose down recovery and re-direction action is taken. Instruments lag on average 3 seconds – hence you need to acquire an almost intuitive anticipation for identifying or recognising lift. Special awareness should be tuned - of out landing space, wind directions, cloud formations, etc.

The mountains before Gariep provided some excellent exercise, for scaling mountains, for what is to come on the last leg of this day - to Beaufort West.  We were doing well and ahead of schedule though a headwind was starting to slow us up. We arrived R10 – and rolled up to the main apron, 1,7 hrs. From November to end of January each year Gariep is transformed into a glider buzz and the home of serious (international) gliding. Now it looks like a desolate Texas outpost. We made a quick call and a dude in an Isuzu with a 7 year-old fuel attendant arrived. Hooked up a fuel trailer and all were done in no time. We took a 30 min break, replenished water, with a short discussion on the route ahead. Strapped the plane on, and got going. Taking off a SF 25 is always a handful, since it has one centre main wheel – it has all the tricks of a tail dragger and the complication of roll whilst still on the ground, having to fly the plane – wings level, as it starts to move. She does not rotate – you drive her into a flying attitude (with a pronounced nose forward / down stance) on the ground – and she will take off when it suits her, with no clear recognition of the transition into flight! But the soonest she is airborne – you can turn her out in a 360 with the wing on a sixpence pivot, with 60 plus degrees bank and she will simply sit there with little input, no effort or g-stress. The most satisfying is of course a reasonable cross wind take-off with wings absolute level, not a twitch (which is obviously a glider pilot skill requirement – if you are being aero-towed, with 22 meter wings 2 feet of the ground).

FAHV -2- FABW. If the previous run was thought for consideration, the last leg for the day, was the real challenge, forward to Beaufort West. Technically on the fuel endurance limit (with no reserve), distance 399km, head wind, some scary terrain, especially the last 100km. Thus according to calculated risk – we should exceed 4 hrs flying (headwind etc) and out of fuel – and short of the strip. What to do? PAS of course! Clouds have been building steady and started converging both right and left as we head out almost due west. Steadily climbing - hopping a few thermals. About 50 km outbound we encountered heavy clouds, and the odd raindrop, which made for some good cloud base powered gliding, unfortunately the thunderstorm itself (was just too far off to the south east to be really utilized, concept power pilots shivers at). Here we ran ground speeds of up to 150 to 160 km p/h. It was now pumping and keeping a tin plane course is a challenge, but Eric exceeded at this. Ideally the thing to do is to fly the cloud (lift) streets, but, since there is no time to waste (figures looks a little critical), we only make use of thermals directly on our path. The aim was 15:00B for Beaufort West (primarily due to foreseen wind conditions).

Thermalling is not flying in a circle. It starts off (as the initial phase of a dolphin move), but then - typically pulling up high, sharp and pronounced, near stall (actually min required inertia), while turning in towards the core and bank at least 45 degrees plus. The actions can be quite dramatic, almost violent as you reduce speed in the climb, to gain altitude, maintaining a tight turn not to pass the outside thermal boundary. Thermal boundaries can well defined, a sharp edge – if you miss it and slip into the sink in this unusual attitude. When it she falls away under you suddenly without warning, and the change in wind rush - it makes for a good wake-up call. Student pilots usually scare a bit and tend to level off and get there wits about them first, before the next attempt. With experience – simply pitch nose up a bit, slight less bank, pull back into it. In this case we were actively flying 3 to 5 turns, (gaining 500 to 1500 ft) and then apply the common exit technique. It is basically a very tight turn, through the core whilst climbing and levelling out on direction, near the stall – as the lift dissipates, put the nose down and run. Then simply increase the speed through the follow-on sink, steadily converting the excess altitude into additional speed, through sink.

This is the defining deference between PAS and power flying. In power flying speed is decreased through sink, in practice: Back on the yoke, nose up attitude, (usually increase power) - technically: Change of angle of attack – better to the downward air movement, to create more lift – with the primary objective to maintain altitude, (visa versa in lift). Whist in PAS quite the opposite methodology is practised – angle is decreased (nose is pitched down), speed is increased (think - speed v lift equation) to run through the sink optimized – to maintain a relative / acceptable “sink rate” and in lift to fly at “best glide speed”. (For the novice – as a rough gage, typically with an engine setting less than 55% power is OK). The skilled PAS pilot - practical engine setting – is usually near enough, at the correct minimum setting for level flight (set-up according to the average lift M/S, as he would encounter (and noted), at his preferred of optimal / minimum altitude) - in the particular circumstance. Resulting in the optimized power setting - versus maximum glide speed (equation) - at zero lift incidences. The BASIC method in practice (for advanced PAS soaring): Fly in identified thermal strength – straight and level (for attitude, - example 3 M/S, etc) – work the back to the minimum RPM required to maintain (“optimal RPM setting” – example 2200), whilst in the lift. If in sink – fly down, increase speed to maintain or just exceed the identified RMP (example 2200RPM), when in lift climb to maintain or just below the identified RPM setting. In zero lift, I prefer to fly the identified RPM setting. This set-up should produce the most efficient engine setting / best glide speed equation (for the particular circumstance). Thus the engine (RPM) is a constant. Remember best glide speed means – the shortest time for the maximum distance.  This basic method - provides a good platform form which to work to optimize your PAS performance – and for your TMG specific, with aspects such as better glide ratios – or - with variables such as feathering propellers.  Typical questions - Is it better to feather the prop on a long run, and have the engine at idle – or completely turned off? What about fuel evaporation, or excess consumption on restart?

Auther ~ Christophe Roelofse~

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