By Willie Bodenstein

I have always been fascinated by the TMG concept and when Christophe Roelofse of PASASA invited me to spend a day at Potchefstroom Airport and to experience at first hand the thrill of Power Assisted Soaring (PAS) I jumped at the opportunity.

Photo by kind permission Jaco Mentz

Our aircraft for the day was a Scheibe Tandem Falke SF28A manufactured in 1978. Unlike most tandem aircraft, as with sailplanes, the Falke is flown from the front seat which to my surprise was to be my office for the day. The FAI Gliding Commission defines a TMG (Touring Motor Glider) as a fixed wing aircraft equipped with a means of propulsion capable of sustaining soaring flight without thrust from the means of propulsion. TMGs can take off and cruise like an airplane or soar with power off, like a glider.

Horsepower ratings in most TMGs leaves the aircraft totally under powered as is the this case of the 1700 cc 65hp Limbach engine that powers the Falke. One must remember in TMGs it is the wings that do the flying - not the engine. Un-powered gliders (Sailplanes) have one drawback; to take off they rely on a launch method, either aero tow launch or auto tow winch to get airborne and to gain sufficient speed and height to start a souring flight using natural lift such as thermals.

Attempts to overcome this have been made for almost as long as sailplanes have been in existence. Power plants were available in the 20s and 30s but they were just too heavy and bulky especially considering that the engine would only serve as an auxiliary means of propulsion for self-launch sailplanes ("sustainers"), a challenge even today.

The development of combining reliable heavier higher horsepower engines in airframes prone to better gliding characteristics resulted in the hybrid designs, we know today as TMG. The boxer air cooled engine that powered the Volkswagen Beetle in the 60s saw the birth of a large number of powered gliders that were able to take off under their own power and sustain flight even in the absence of thermals.

The large wingspan of TMG's provides glide ratios that might not be as efficient as sailplanes, though perhaps closer to the actual technical definition of a "glider" rather than a "sailplane." In the hands of a skilled pilot TMGs are able to travel reasonable distances engine off, or with very low power settings- called PAS (Power Assisted Soaring). Normal cruise with power settings of 55% or below is common, which makes them much more fuel efficient than conventional light aircraft. Consumption figures as little as 8 litres per hour are common in some models.

Sailplanes (commonly referred to as "gliders") and Touring Motor Gliders are two distinctively separate aircraft categories, in design, regulation definitions, pilot licence requirements and operations. South Africa was the first country to recognise the unique oversight requirements of TMGs, first published in the Government Gazette 2008 and finally introduced in the latest CAR's 2011 regulations as a separate category pilots licence.

After a comprehensive briefing during which Christophe explained to me the basics of power assisted soaring (PAS) and various cross country soaring techniques with thermals, we got ready to take off. Having flown with many skilled pilots in a myriad of different aircraft over many years, under various conditions the world over my flight with Christophe, a Grade A instructor with more than 1000 hours just on Scheibe types, was the first in a TMG.

Photo by kind permission Jaco Mentz

It was unfortunately not the perfect day for gliding but that is what makes TMG and PAS so practical, fly anytime in whatever mode is appropriate. With a few small scattered clouds about, I occupied the front seat with Christophe flying from the rear seat. My function would be cockpit management to monitor the Vario Meter that indicates lift and sink as well as to cut the engine and feather the propeller when we were ready to start the soaring phase of our flight.

Photo by kind permission Jaco Mentz

Take-off is deferent to a light aircraft, there is no rotation and the TMG simply floats off when the wing generates enough lift. The straight and level flight attitude feels distinctively nose down even when in cruise climb and similarly in thermal climbing. We soon located a small tight thermal and the Vario waved around 2 to 3 meters per second of straight line lift, and steadily improved to indicate 4 and 5 m meter per second as we centred and settled in for the spiral climb. Still under limited power (PAS) we used the lift from the thermal and climbed to 3500 feet AGL and dolphin off to the next promising lift. Then it became time to cut the engine, to no surprise a non-event!

The noise of the Limbach stopped and I feathered the prop and we were gliding, the only sound the wind rushing past. It was absolutely exhilarating! We entered the next thermal and gained some height for a while and then started to look around for another on our short cross country soaring quest. There was another cloud about five away to our northwest that looked promising but it was just too far away and time was not on our side.

PASASA member Nic Mourton in his Super Xhimango TMG ZS-GBC that was invited for the photo shoot contacted us on the radio. He was overhead Boskop dam and still in soaring mode we set out using what lift from scattered thermals we could find joined up with them flying a loose formation back to the field. A dead stick landing is not something that one would normally look forward to but I did. The Falke was in her element, doing what she was designed for and the landing a non-event. We had sufficient speed to taxi to the apron where we joined the Xhimango, a stunning example of a modern TMG. We had flown for just more than 40 minutes without any power relying on the lift of the occasional thermal.

The ever increasing price of aircraft maintenance and aviation fuel makes the TMG's a viable option. Older TMG's like the Scheibe, Faurnier and others can be bought for prices well below R200, 000.00. These oldies are back to basic sturdy simplistic aircraft, safe, reliable and great fun to fly. TMG's are ideal for hour building, recreational aviation and light commuting it is easy to see why TMG segment is showing so much interest as a very sensible option to conventional power flying.

Many thanks to Christophe Roelofse, Jaco Mentz , Nic Mourton, PASASA for sponsoring the shoot and Frank Smook who flew the camera ship during the photo shoot.

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