PAS is indeed an independent category and the doctrine for flying a touring sailplane is unique, different from a sailplane and in practice certainly from a power aircraft. It is a combination of (a) soaring (including techniques such as thermalling and straight-line dolphin) and (b) power flying (including techniques – such as engine management, navigation, etc). Correct power settings for thermalling is crucial, though the common thought is to merely conserve fuel, you need to compensate for thermal strength and shock ascending cooling, etc. The wrong power setting will result in continuous adjusting throttle (less attentive stick and trim), exactly the opposite of the PAS theology. Similar to control surface inputs – every throttle adjustment, is in principal a waste, inevitably directly of indirectly culminating in additional energy / fuel consumption. It is no use burning fuel going up, in a slow rate thermal; when the energy could have been spend on covering distance, and visa versa. Unlike the common practice of powered flight – where straight and level is the objective, and the throttle (thrust) is the tool for going up or down, a Touring Sailplane is all about flying the wing. Since the engine is usually too weak to really feature significantly. The fastest route between 2 points – is usually not a straight line, since there are various elements (conditions) to be considered. Acceptable standards: Direction within 15 degrees, and average navigation course within 30 minutes of ETA, altitude: Also within 50 feet …? - Ideally within a band of 50 feet underneath clouds base, … actually - wherever the lift takes you!
In a glider competition – the equation is: Speed over Distance – the quickest shortest time, over the total length of the course (from point to point – irrespective of the actual route), is the winner (essentially the best energy manager - latent / potential, etc). Power aircraft racing is similar, the fastest plane wins – in a straight line from A to B, primarily dependent on the conversion of fuel (stored energy) to thrust, etc. The fuel in the TMG tank is also energy – that should be factored into the equation. Hence the major difference to – the general power flying competitions. PAS is NOT about minimum fuel burn for maximum flight time (fuel efficiency) – as commonly misbelieved - but in essence about “total energy efficiency” (over distance?). It should be described as: The practice of the continuous and conscientious exploring of the total (potential, etc) energy index of the aircraft. Thus total energy versus speed (time) / distance. The equation is simple: Distance ÷ time elapsed ÷ fuel consumed = to provide an efficiency index. To cover a set distance – though one can use no fuel when engine is shut down, time elapsed could be considerably more (thermalling gaining altitude, etc), whist the shortest time (flying straight and level) will result in more fuel consumption, etc. It is about the optimal balance. Yes, different, indeed a skill, even perhaps an art (and to some a religion), but certainly - to its own!
TMG events try to emulate the practical reality of typical TMG flying, (based on flying these aircraft to the full application / envelope) - such as to artificially include limitations: Low cloud base, airspace restrictions, time restrictions, etc. Example: In the National PAS2007 event, the winning TMG (this very same ZS-GVL) - used just a little over 5 litres over a course of 208 km, including a required low level leg of 30 km (no thermalling possible – under 1500ft restriction), and a 70 km leg with a altitude limit of 10500ft (not utilise top thermal strength or long runs) in 2h34m! The aircraft – a 30 year old SF 25 C 1700 cc, taking the no1 spot on the EI (efficiency index), with glide ratio of only 1:22 at beast. Make no mistake, there are some of the modern Touring Motor Glider machines with cruise speeds of 280 km/h, burning 12 litres p/h, with glide ratios exceeding 1:50 - and endurance in some types of 8hrs is not uncommon. The world is going green – in practical general and recreational aviation, the concept of - total efficiency, is lead by Touring Motor Glider technology.
This particular model – GVL, SF 25 C – has the “full” compliment of instruments suite: Airspeed (in km/h), altimeter (surprisingly in feet, with 1013 setting), variometer (in M/S), a VW ref counter, oil temperature - a master switch lever (on a chain), 1 fuse (alternator), and a very basic radio. The fuel gauge is a vertical pipe in the rear of the cockpit, behind the baggage compartment. There is none of the typical power aircraft stuff to be concerned or confused about – such as dual magneto’s etc. It has a maximum cruise speed of 120 km/h, with our weight configuration – probably no more than 110 km p/h. The 1700 cc Limbach (basically a VW Engine) – at best produces 60 odd horsepower. No need to say she was loaded to the brim. With maximum usable weight at 180kg – it does not leave much for 2 guys, gizmos and baggage. (The baggage compartment, behind the shoulders, is restricted to 10kg). With a predicted ground speed of 110 km/h, we are looking at 13, 5 hrs for the trip, Springs to Worchester. Fuel is max 40L (useful 37L odd) and at a safe calculation of 10 L p/h distances exceeding 300 km should be sensibly considered (especially where no real soaring) is involved and a 25km headwind constitutes 25% reduction of distance. Typical stopover airfields for your Cessna are either too far (or too close) and creative planning is a must. Simple considerations such as: Mogas in Richmond
2 days prior – weather, arrangements such as fuel, was confirmed. Good-2-Go. Eric was in charge of navigation (this man has it down to an art that puts to shame most professional navigators). His basic planning (printed paper back-up) covers an entire A4 flip folder, everything calculated to decimals! Every single map, including alternatives, 2 x GPS, sun panels, the works. NASA – come learn. (He does not appreciate the notion of an “out landing”). Though we glider pilots have a different approach to these things (PDA’s, running Win Pilot, etc), there are good things to say for tin pilots (especially in navigation division). To glider pilots: Knots - is a thing you get in ropes, miles - is something you grandfather used to describe some unsure far off destination. Gliding is almost exclusively in metric, speeds (km), attitude (meters), - and who cares about QNH – QFE is important (it is not the sea – but the ground that will kill you), etc. (Though of course when you are in tin territory – you have to be on par with power flying environment, and I advocate NO less!)
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