A Rotax Falke for Faulkes?

Mike Woollard, Managing Director of The Faulkes Flying Foundation Ltd explains why he is considering buying one of the new SF25C Rotax Falke motorglider/tugs for this recently formed youth organisation The Faulkes Flying Foundation Ltd is a new venture to provide adventure training for youngsters in gliding to inspire them to consider a career in aviation or aeronautical engineering, or to develop a love of gliding. The Foundation buys launches and accommodation from gliding clubs as required. Eventually, we plan to have a definite base at a BGA site, with regional centres. Our hardware is currently based on Blaniks, ideally suited to training young people as well as capable of being parked out of doors in all weathers. Our operations focus on aerotowing to give quality flying time, with motorgliders for navigation exercises. Because of this and our perceived need for our own launch capability, we decided to look at the new breed of aerotowing motorgliders; and, in particular, at the SF25C Rotax Falke. For many years, I had a share in one of the original Falkes, at Nympsfield. I learned to value its many admirable qualities for training and pure fun. However, with a small three-bladed prop, a 1500cc Stamo engine and a 60kt cruise this was no performance machine. Careful application was required at take-off to clear the trees at the end of the field without scaring the wits out of the nesting birds. As you cleared the airfield boundary you did become acutely aware of the whites of their upturned eyes.

I was considerably surprised when I test flew an SF25C Rotax Falke at Lasham to evaluate its suitability for the Foundation. The short (90m) take-off run meant we seemed airborne almost immediately; my instinctive reaction to keep the nose down so the airspeed could rise resulted in red-lining the engine and a protest from the P1.

We climbed at an attitude I would have considered impossible for a Falke, more than 5m/s at 50kts (compared to a figure of 3.2m/s for the previous Limbach-powered Falke 2000). In the cruise, 80kts in level flight was easily achieved despite the fixed-pitch prop

The comfortable, functional cockpit has more space than I remember. The redesigned panel is more sophisticated, and a removable cowling gives better access to instruments and wiring

Getting over my surprise, I began to suspect that the engine responsible must inevitably have compromised something. But to my delight, all the attributes I appreciate about the Falke; its glider-like handling, docile stall characteristics, and light controls, have all been retained. Furthermore, the noise from the non turbo-charged 100hp Rotax 912S seemed more acceptable both inside and outside the cockpit than earlier variants.

The salesman explained the concept behind the new SF25C Rotax Falke: to produce a simple, cost-effective motorglider which can also aerotow. The non turbo-charged Rotax 912S had therefore been selected, ideally used with a fixed-pitch propeller to avoid the extra cost, weight and complexity of a turbocharger and variable pitch mechanism (I gather a variable-pitch propeller is available, giving a higher cruise speed of about 97kts, albeit with impact on cost, complexity and cockpit loads).

High power:weight ratio
The engine achieves its relatively high power: weight ratio from the higher engine speeds (up to 5,800rpm) which the use of a reduction gearbox allows. This means an engine weighing much the same as earlier VW variants can achieve many more horses. Water-cooled heads quieten the unit down while reducing cylinder head cracking problems.

As a tug, the SF25C Rotax Falke seems to perform very well, climbing with heavy two-seaters at 400ft/min. This is marginally slower than, say, a Robin DR400, but this Falke uses only half as much fuel and the noise pollution is much less. In Germany, official analysis of comparative tug noise estimates a single tow in a Robin DR400 type tug equates to 4.8 tows in a SF25C Rotax Falke. Glider-tug speed compatibility, similar wing loadings and aspect ratios, and reduced wake turbulence, mean the motorglider aerotowing option offers significant safety features.

The manufacturer's fuel consumption figures are 16-18 litres (c 3.5 gallons) an hour, hardly thirsty for tugs. Taking into account all the costs of operating the Falke, including an engine rebuild every 2,000 hours, insurance, fuel and maintenance costs, a Falke is estimated by its makers to tow at about 60 per cent of the cost of today's conventional tugs.

The Falke we need has the fixed-pitch propeller and an undercarriage with a lockable castering tailwheel and two main wheels. This version weighs 650kg (compared to 610kg for the Limbach-powered version). Cockpit limits are 190kg (425lbs), ideal for us.

In my opinion, this new Falke retains all the functionality of before, with welcome added performance which allows for safe aerotowing. I love the simple functionality of this motorglider, its robust construction is so suitable for operation at typical BGA clubs and it can be easily derigged for trailer transport. It is ideal for the work of the Foundation and I can't wait until circumstances enable us to have one.

Mike Woollard April 2000