Capt. Ken's comments - September

	Cruising at 135 knots at 11,500 feet proves the worth of turbocharging.
	Ken’s normally aspirated tail dragger at Nelson, B.C., during a refuelling stop and lunch. Photos courtesy Ken Armstrong

RADICAL HOOT DUDES

A summer trip to hot sultry London introduced me to an aircraft that would figure prominently in my future. If I had sensed what I was in for, I would have woken up with my ears joined by my lips.

My mission at Diamond was to fly the new 125 hp Continental powered Katana but the aircraft was still undergoing a developmental flight test program. So, the company offered a few hours in the motor glider to cut my losses.

It wasn’t love at first sight with that 54.5-foot wing span greedily gobbling up the tarmac - what a set of obstacle catchers those could be. (Incidentally, they will fold to yield a nine-foot 10-inch width for storage with the optional wing fold gear.) I love composites with their low drag, rivetless construction, corrosion resistance and sound dampening ability and since I hadn’t flown the turbocharged Rotax 914 yet it was worth the time to evaluate this new engine and motor glider.

Actually, the Xtreme has been a success for years in Europe and while it is still built in Austria, the potential demand in North America warranted its introduction here. Future North American orders are to be built in London.

I toured the production facility where the familiar Katana series are built and was very impressed by the advanced technology employed there and the exacting quality control procedures.

Many readers might argue that composite aircraft haven’t entirely proven themselves yet, in terms of their aversion to the sun and possible delamination after moisture penetration. Diamond doesn’t seem to have any doubt about the reliability of their construction as they stand behind their products with an impressive 10 year and 13,000 hour warranty.

My luck began to change when the company assigned high-time glider instructor Roger Lanier from Florida to watch over me. It was a good thing for them, as I might have been tempted to abscond with the plane by the end of the flight as the fuel tank was still nearly full after two hours of flight time. Roger has flown all the competition’s machines and was a veritable compendium of glider and motor glider information.

EXTREME KNOWLEDGE

The HK36TTC we flew was the tricycle geared turbocharged version of the Xtreme. Purchasers have their choice of tricycle or conventional gear as well as the normally aspirated 912 or the turbocharged 914 Rotax. This turbocharged 914F is a natural growth of the normally aspirated 912 engine that has established an enviable record in dozens of aircraft installations.

In the Xtreme, these horizontally opposed, four cylinder powerplants use a mixture of air and liquid cooling, dual CDI ignition, gear reduction drives and a composite, constant speed propeller system to provide efficient thrust, low fuel burns and light installed weights for four stroke engines. The normally aspirated version (912) has a 1,200 hour TBO and the turbocharged (914) 1,000 hours.

One flying school in Victoria was running their 912 powered fleet of Katanas on condition and logging well over 3,000 hours on each before overhaul, although the factory dislikes me pointing that out.

As many readers know, I purchased my own taildragger Xtreme after this evaluation and plan to fly for decades, on condition when the time comes.

During the walk around, Roger indicated this Austrian-registered prototype was fitted with the optional aileron gap seals to improve performance and the skin had built-in UV protection allowing it to be stored outside, indefinitely. The turbo Xtreme boasts modern day winglets that apparently increase stability during low speed, steep turns, i.e. soaring.

They should also reduce induced drag at low speed to make the wing more efficient for soaring. The aircraft is easy to pre-flight as there are either access doors or see through inspection panels for the important items.

One climbs over the sill to access the Xtreme and although the seating is side by side snug, it proved very comfortable, even in the heat, until we closed the canopy. (I have added home made scoops that insert into the sliding window slots that scoop huge volumes of air into my machine - they fit all Katanas.)

The adjustable rudder pedals “travel” to accommodate most pilot sizes and the firm seats are reasonably comfortable for hours of soaring. (I have added an Obus Forme support for my soaring flights which often exceed three hours.)

Other than the choke and constant speed pitch control with feathering, there was nothing unusual in the semi-reclined cockpit of this sleek trike. Still, I must admit a high degree of comfort and this cosy cockpit reminds me of my early days in the RCAF flying jets.

Something about the seating, visibility, joystick, speed brake and throttle all close at hand inspires the promise of titillation. Prospective purchasers with hairlines above six foot four inches should try the cockpit for size to avoid polishing the canopy with their pates.

The hat rack storage area with its cord security fence is limited to 12 kg of “carry alongs” and is best stuffed with soft-sided bags to maximize the curved space available.

The on/off fuel valve controlled 20.3 US gallons of fuel and the quoted empty weight of 1,189 permitted a pilot load of 381 pounds with full fuel and three quarts of oil.

Prospective purchasers will want to pay close attention to their Xtreme’s basic weight as the cockpit size and gross weight may preclude larger specimens of humanity.

COME SOAR WITH EAGLES

Start up is accomplished quickly (even in cold weather) with the choke and when coolant and oil temperatures enter the green, we check the carb heat at 1,500 rpm and cycle the prop pitch governor and dual CDI ignitions at 2,000 rpm.

With due attention to the taxi lights and signs owing to our 54-inch ground/wing tip clearance, we use differential brakes and a swivelling nose wheel to accurately taxi to Runway 33 where we would jostle with the fleet of Dash 8 commuters.

At the maximum gross weight of 1,698 pounds, Roger applies the full 115 hp with its 5.5 minute limit and holds the Xtreme on the runway for 850 feet in deference to the 10 mph crosswind.

I would suspect our climb angle exceeds any aircraft that flew out of London that day. Roger then proceeds to leave full power on for 14 minutes with the engine showing no tendency to overheat with an OAT of 23 C.

Subsequently he reduces the power from 40 inches MAP and 2,400 rpm to the 100 hp setting of 38 inches and 2,400 rpm. I then take control and climb at approximately 1,000 fpm in the choppy air while holding a smidgen of right rudder at 57 knots.

Although the company conservatively installed cowl flaps to help with anticipated heat rejection of the turbo installation, they can remain closed for pretty well all operations except the hottest days or during towing operations.

Since we’re almost climbing vertically into the headwind and really want to get out of the controlled airspace, I convert the climb to 90 knots and 500 fpm. The nose down attitude of the Xtreme is quite significant such that visibility is always excellent during the climb and for that matter throughout the entire flight envelope.

The control forces are moderate - matched by the response. The Xtreme is no sports car, but it is nicely balanced for inexpensive cross-country flights and loitering amongst the clouds or perhaps training ab initio pilots. A Cessna 152 pilot would have no difficulty converting to the Xtreme.

We level off in short order at 5,000 feet and the 75 per cent power setting of 33 inches and 2,400 rpm provides an indicated airspeed of 119 knots on 3.75 (US) gph (15 litres per hour). This would translate into a very respectable true airspeed of approximately 140 knots at altitude.

For the supplemental oxygen crowd, you could easily top 160 knots up where the turbo props cruise. Nonetheless, the recreational crowd will likely set 23 inches of MAP and 2,350 rpm for an indicated speed of 90 knots as they sip fuel at the rate of 3 (US) gph (12 l./hr) while leisurely searching for monster thermals.

Yep, there’s no life like it for a Type A personality who likes to escape the office hassles and relax by competing in an aerial ballet with Mother Nature. Whether you fight to conquer the vertical currents or lovingly massage the controls striving to learn her secrets you will be rewarded for your efforts and punished for your mistakes.

Taking up gliding - albeit with a self launching glider - will open a challenging realm that will continually hone your skills but still leave you short of perfection. While powered experience will eventually allow you to fly the perfect circuit from time to time, the greater challenges of gliding will always leave you feeling you could have done better.

“If I had only turned a little more steeply...or if my airspeed control had been better I could have...or I should have charged over to the Cu building over that freshly ploughed field....”

Roger figures our late afternoon flight is unlikely to attract any free lift and this turns out to be the only error he utters during the flight. Lanier has me retard the throttle to a neutral power setting of 20 inches MAP, turn off the ignition and then feather the propeller by bringing the pitch control fully aft. My grin widens as Roger points out the engine isn’t at risk for thermal shock thanks to the mass of its coolant.

The cessation of moderate amounts of noise and lack of trim change are a pleasant phenomena as I settle into a best L/D speed of 57 knots and work my way to the edge of a cloud a few miles distant. We are giving up approximately 250 fpm (min. sink rate 230 fpm) until nudging into a modicum of lift and by the time I pitch up to the 51 knot minimum sink rate and whirl left to stay in the lift, we are showing 300 fpm on the positive side of the variometer.

Smiles break out in the cockpit as this novice glider pilot coaxes free lift from the earth for 40 minutes and only surrenders 1,800 feet in the give and take of convective soaring.

I got very comfortable, very quickly, soaring the Xtreme and soon found I was “maxing” out aileron and rudder travel cranking around in the updrafts. I was surprised how easy it was to learn aggressive soaring with Roger’s prompting - especially considering I really haven’t done much soaring before.

Normally, a stop-cocked prop is reason for concern, not jubilation. If you haven’t soared, you’re missing an indescribable thrill that combines challenge and pleasure in a most satisfying blend. I could wax poetic about the thrill of soaring at great length; but, it’s the sort of satisfaction you need to savour yourself.

The Xtreme’s 27 to one glide ratio (28/1 on the tail dragger) puts it in the moderate gliding performance range between trainers in the lower 20s and high performance sailplanes beyond the mid-30s. For comparison, consider that a modern piston powered aircraft typically provides between 8-12/1 for a lift/drag ratio.

Obviously, the Xtreme will glide about three times farther than most factory aircraft. To put this into perspective, from a height of one mile, in still air, the Xtreme could glide far enough to land in an operating area of 2,291 square miles (assuming no free lift).Under the same conditions, a gliding Cessna 152 has the option of approximately 201 square miles.

If on comparison to other gliders you come to doubt this wing’s efficiency, you should know the 81 hp normally aspirated version of the Xtreme holds the motor glider altitude record of 17,000 feet. Obviously, the 115 hp turbo version will easily beat this record in with its boosted powerplant. I’m sure it could easily surpass 25,000 feet - without any mountain induced wave lift. I should point out that the Xtreme is only certified to 17,000 feet at this time; however, this envelope may be extended.

Important speeds for the glider pilot to keep in mind include the VNE of 141 knots and a turbulence penetration maximum of 113 KIAS. It might be common on actively convective days to reach both ends of the 42-113 knot spectrum while darting between areas of active lift.

Because the stick loads are insignificant in the Xtreme, pilots can undergo large speed changes without the pressing need to make any trim changes in the pitch axis. Of course, trimming the aircraft allows the pilot improved sensitivity feeling for the nibbles of lift; but the pitch trim loads are never heavy enough to cause problems - even for the weakest of aviators. Trim changes are immediate as one simply lifts a knob and moves it forward or aft - no delay.

Pilots who have only flown powered aircraft will note that while the nose seems to point down quite steeply in descent, the actual rate of descent and therefore glide angle is quite shallow. Roger added the 27/1 glide ratio is an honest measure of the Xtreme’s capability and that this Katana can outperform much of the competition that claims higher L/D ratios. I haven’t flown many motor gliders so I can’t confirm or deny his statements; however, I trust their veracity as Roger has been there and flown them all (and bought the T shirt).

At the low end of the speed spectrum the Xtreme gives a little nudge of warning and enters a rather tame stall at 40 knots indicated. Still, I must point out that I lived on the edge of buffeting quite often during this flight’s periods of lift and found the forgiving characteristics completely acceptable - and desirable.

Not once did the Xtreme drop a wing as I hovered and wheeled in the rising columns of air, even though I often touched the edges of the stall. After all, the minimum sink speed is only two knots above the zero “g” stall speed. Even a full power departure stall with a steep bank angle only produced a minor nose down pitch.

As you might imagine, the Xtreme, with its lengthy wings is not approved for any aerobatics, nor is it likely you would want to accomplish same with the moderate stick forces.

Eventually, the sun tires of heating the local earth and pangs of hunger implore us to start the engine for the ferry flight back to London International. To convert to powered flight, one simply cracks the throttle open, turns the fuel pump on and unfeathers the propeller by moving the lever forward triggering a blast from the pneumatic accumulator and then cranks the starter till the Rotax purrs.

From 2,300 feet AGL we would be able to select any landing spot within 11.75 statute miles - so an engine that refused to start would not be considered a significant emergency.

To put it another way, at the minimum sink rate, we had 10 minutes to get the engine on line. Roger points out that as long as one has altitude underneath, one can always dive the plane to crank the engine over - this is also the starting technique to use with a fully discharged battery. (Mind you, testing on my Xtreme shows it takes 1,000 feet and 120 knots indicated to turn over this geared engine.)

During soaring operations, the Xtreme is operated on a split battery system that eliminates the non-essential bus thereby saving battery power for cranking the engine to life. With the “soaring” master on, electrics such as the communications radio, transponder and gyros are kept powered - unless you turn them off. Incidentally, the battery’s endurance in the soaring mode is four hours at 0 C and two hours at -10 C.

Converting our extra altitude to airspeed, I apply cruise power and lower the nose to indicate 135 knots in the now smooth air. As expected the controls load up somewhat with the extra airflow such that it is unlikely one would be tempted or able to overstress those long wings with rapid control movements.

The Xtreme is a lot of fun in the circuit so Roger and I perform a series of widely varying approaches and landings on returning to YXU, all of which terminate in smooth arrivals. Of course, the long span, high aspect ratio wing allows the pilot a lengthy period to feel for the runway and there is no reason for a landing being any less than a greaser on anything but the shortest runways when full spoiler would be used to reduce the float period.

Dead stick landings, short field touchdowns and full spoiler approaches with flat propeller pitch showed the wide variation in glide path capabilities between very shallow and very steep for this easily flown motor glider.

Finals were typically flown at 57 KIAS with the throttle at idle and one hand on the Schamper-Hirth style spoilers to select one of two detents of flap or beyond the notches into the infinitely variable pull and the area of full aerodynamic braking.

The brakes extend vertically from the wing on a mechanical scissors assembly that provide a mechanical advantage to the pilot and allow full extension with little effort. (Springs hold them retracted to avoid inadvertent extension.) Their ability to give the pilot virtually any approach angle he might desire can bring any deviant approach back on the VASIS.

EVERY MAN’S AIRPLANE

Some aviators deem the Diamond offerings pricey. At $150,000 (US) including radios, this newly certified aircraft is price compatible with competitive offerings. Moreover, when you consider the quality and performance combined with the minimal operating expense, the Xtreme can be a good value. Katana operators I’ve spoken with claim maintenance costs are low - further adding to the value.

The self-launching Xtreme not only eliminates the need for a costly tow plane, but with the optional tail mounted release it can tow other gliders up to a MTOW of 1,156 pounds. Most two-place gliders would meet this weight limitation.

In a flight school, the Xtreme can take a student to his pilot’s licence and then provide oodles of challenge for years seeking and eking out the earth’s free convective energy.

It would appear the extra get up and go of the Turbo Xtreme could make it very popular with the gliding clubs as it is a very capable towing aircraft that could also double as a glider when the convective activity keeps all the gliders airborne.

Besides when you look at the prices for high performance gliders, the Xtreme is a bargain. Why? Because the factory makes so many Katana-like airframes, the economy of mass production allows considerably lower prices. The popularity of the Katana series has ensured the prices have remained reasonable in the marketplace.

Before I flew the HK36TTS, I thought the name Xtreme was massive hyperbole for a motor glider. How could a two-place airplane with 115 hp be outrageous? A month after my flight, it’s still hard to quantify why the flight was such a thrill. Was it the comfy cockpit with its fighter-like environment? Was it the sweet flying characteristics that allowed one’s every move to feel professional and rewarded? Was it the ability to climb high, glide long and command final approaches at virtually any glide angle one could desire? I think not.

Sure, those were all desirable factors; however, the challenge of seeking lift and maximizing powerless flight time are pure thrills for me. I’ve always been very competitive and matching machine and man against the invisible currents is a very rewarding pastime.

Not too many aircraft tweak my desire-to-own strings (but this one did). Hmmm, a self launched glider. Wonder if I could combine frontal, orographic and convective lift to make it across Canada with one load of gas. There isn’t a record to break nor an award for this, but wouldn’t it be the flight of a lifetime!

If you are as intrigued as I am about powered gliders and specifically the Xtreme selections, contact Diamond Aircraft at Tel., 1-800-268-4001 or write them at 1560 Crumlin Sideroad, London, Ont., N5V 1S2.

The following specifications were provided by the factory. I have included 100 hp Cessna 152 comparative data to show the relative performance to the 81 hp Rotax 912 powered Xtreme.

Ken is a COPA director who lives in Victoria and provides services internationally in advanced training, expert witness, flight test and aircraft sales. He has logged 15,000 hours on 375 types of fixed wing and rotary aircraft. Soaring his Diamond Xtreme is what he does for pleasure.