Capt. Ken's comments

By Ken Armstrong

The Diamond Xtremes can be found with two types of propeller feathering systems. The latest version has a hydraulic accumulator that feathers and unfeathers the prop in the snap of one’s fingers. A very desirable and reliable method, as it would require an air leak to render it unserviceable. The other format is an electrical stepping motor that moves the propeller between flat and feathered pitch in 70 seconds. This slower system requires the pilot to plan the operation a little more in advance and would be rendered unserviceable if the battery was run down in soaring flight. This seems like a significant shortcoming or risk until one realizes the 18-amp-hour battery is good for four hours of soaring flight at zero centigrade. (My larger 25 ah battery easily outlasts my bladder capacity) There is an added benefit to the electrically feathering propeller as it can be stopped at any pitch angle by turning the power off at that point in the feathering cycle.
Why stop anywhere less than feathered? Well, the drag on a half-feathered propeller isn’t significantly more than on a fully feathered prop so gliding performance isn’t affected. Moreover, if one soars long enough to drain the battery, perhaps at really cold altitudes, the aircraft can be dived to turn over the propeller and the engine started accordingly. I’ve done this twice and noted it requires an altitude loss of 1,400 feet in flat pitch and 1,000 feet partially feathered to accomplish a start. (The nose down attitude is not for the timid as it requires reaching close to the never-exceed speed of 141 knots to turn over the geared engine.) On the other hand, the hydraulically feathering prop is either in fine pitch or feathered and of course could not be dive started if it could not be unfeathered (ex. after a hydraulic failure).

CROSS-COUNTRY CONVENIENCE
Gliders are wonderful and the epitome of free flight on the earth’s generous energy. Every year records are set and medals obtained when gliders make lengthy cross-country flights. Nonetheless, something must launch them. The exception is a few men carrying, foot-lanched machines, but they have limited practicality. This reliance on a means of launching is the bane of gliders. Moreover, they are hopelessly impractical as a means of getting from A to B unless the most unlikely weather circumstances just happen to line up a series of convective clouds between departure and destination points. Enter the motorglider. While power purists and glider geeks may poobah “self launching gliders” (to quote Transport Canada’s definition), after flying 350 plus types, I see the motorglider as the ultimate compromise. I could go on at length as to my reasoning, but that will have to provide motivation for a future article, perhaps.

COME SOAR WITH ME
My motorglider begins with a Diamond Katana cockpit/fuselage, including the tailfeathers and then adds a completely different wing planform and advanced airfoil and lots more wing span. The result is the best of both worlds as the Xtreme wing’s extra lift can heft more weight off a shorter strip and then outclimb the Katana, big time. Specifically, the legal JAR certification limits restrict the maximum take off weight to 1,698 pounds (1,609 for the Katana) due to the need to climb through a 15 meter high obstacle “window” in a short distance. (This is similar to the clearing a 50-foot obstacle in North America.) Due to the Xtremes’ large wing and higher basic weight this allows a useful load of approximately 450 pounds. With the “long range” tanks filled with 20.1 U.S. gallons of go juice and a maximum of 26 pounds of baggage in the aft area we can carry about 300 pounds of occupants. Alternatively, for a soaring mission, one could carry two hours of fuel, 10 pounds of accoutrements and two 200 pounders. The bird will break ground in 600 feet and climb at 807 fpm on a standard day at S.L. (However, I can typically find some thermal lift on the climb out and average 1,000 fpm at an average climb speed of 70 knots. While the best L/D is 57 knots, I usually climb faster for improved engine cooling and visibility and so I don’t look like I’m hovering on the airport radar screens.
The exceptional visibility, light controls and semi reclined comfort make the climb out delightful and one finds the aircraft has reached altitude in little time. We chose a course after takeoff based on the most likely area that will surrender free lift and on this we depend on our growing knowledge of lift generation. However, our accuracy after a few weeks of soaring is about equivalent to the meteorological forecasters record for the area and we are more often wrong than right. Unfortunately, we cannot hedge our poor judgement or lack of knowledge by covering our tracks with terms such as “risk,” “chance off” or “occasionally.” However, like the weatherman, we can change direction in mid stream when some unexpected weather phenomenon dictates a diversion. Wheeling around, checking out probable areas of lift is a major part of the fun. Failure simply motivates one to continue and even sink is encountered with a positive attitude as descending air is always balanced by ascending air, somewhere. On encountering lift, the cranking and banking begins as one pursues the elusive upward air with best guesses as to the likely course of the invisible warm rising current.
While a good landing can provide a great measure of pleasure after hours of flying in most aircraft, each successive area of lift provides at least as much thrill. Continuous lift over the period of hours is impossible to describe as the glider betrays the laws we power pilots have learned over thousands of hours. Namely, let the engine quit and a pleasurable flight ends! With a glider (self-launching or otherwise), one never knows how long one can stay up, or how far one can go. That’s the question. That’s the bliss.

LIMITATIONS OR OPPORTUNITIES?
All aircraft are compromises. While the Xtreme is good, efficient cross-country transportation as well as a soaring/gliding platform, it has some limitations which might handcuff some aviators. Firstly, it is a day, VFR aircraft only and the amount of ancillary equipment is kept to a minimum to maximize useful load and soaring. A full panel of gyros, avionics and ancillary gauges are out of the question. These items are heavy, absorb electrical energy and the panel isn’t really big enough for any IFR gizmos.
The physical size of the aircraft also precludes it from living in most hangars. Although it is only 25 feet long, it is more than twice as wide. (Mind you, a trolley system could move it sideways into a long hangar) And you have to be careful that the airports you use don’t have objects in the “clearways” that could meet up with your wings during landing or taxiing.
My aircraft is the taildragger version and while it looks sexier, it also requires a considerable amount of area for manoeuvering on the ground as the tail wheel steering only allows a castor angle of 40 degrees. This is similar to taxiing an airliner on a crowded ramp at times. For pushing it into tight tie down areas, it generally takes two people to park. (But, I guess we all knew that from our younger days) The trike turns much quicker as it easily pivots around the main gear.
I’m finding you need to have a flexible schedule to own these soaring aircraft. In other words, you will want to drop what you’re doing when conditions are providing free flying. It’s getting so I don’t want to be tied down to anything lest the clouds call.
I have admired the gorgeous lines of motorgliders for years, but never once thought they were my dream machine. Now that I own an aircraft that answers all my needs (except aerobatics), it begs the question “how did I live without an Xtreme?”
If you are leaning the same way, contact Jeff Owen at Diamond Aircraft Industries for further information at Tel.: 519-457-4000 or write 1560 Crumlin Sideroad, London, Ont., N5V 1S2.

GENERAL PERFORMANCE AND SPECIFICATIONS
The following performance data is either provided by the factory and in most cases by the author who has confirmed this data through 100 hours on type. Data is for his normally aspirated tail dragger version.
AIRCRAFT TYPE Diamond Katana Xtreme HK36
BASIC PRICE $110,000 (US)
ENGINE Rotax 912 (or 914 Turbo)
POWER 81 hp (115 hp)
PROPELLER C/S Fully Feathering
BASIC EMPTY WEIGHT 1,189 pounds (mine is 1,254 pounds)
GROSS WEIGHT 1,698 pounds
LENGTH 23 ft 6 in
HEIGHT 5 ft 9 in
WING SPAN 54 ft 6 in
WING AREA 165 sq.ft.
WING LOADING 10.3 lbs/sq.ft.
CROSS WIND COMPONENT 15 knots
RANGE (with 45 minute reserve) 537 nm
RATE OF CLIMB 807 fpm
CRUISE SPEED 111 KIAS
STALL SPEED 42 KIAS
BEST L/D SPEED 57 KIAS
MAXIMUM L/D RATIO 28/1
MINIMUM SINK SPEED 51 KIAS
MINIMUM SINK RATE 225 fpm
SERVICE CEILING at least 17,000 feet

Ken Armstrong has enjoyed 14,500 flight hours on more than 350 fixed and rotary wing aircraft. He provides aviation consulting/training services and flies his Diamond Extreme motor glider out of a grass strip near Victoria, B.C.