AN INSTRUCTOR’S THOUGHTS ON FLYING THE

DG-1000S

by Dean Carswell

The DG-1000S is the exciting newcomer to DG’s stable of two-place sailplanes. Initial evaluation shows it to be a well harmonized, comfortable sailplane with very good cross-country potential. DG’s rationale for developing it reportedly began with an assessment of the Schleicher ASK-21, regarded by DG as the ideal glider for flight training, the Schempp-Hirth DuoDiscus as the most modern 2-place designed especially for cross-country flying, and its own 18/20m DG-505 Orion with good training capabilities, cross-country performance and aerobatic ability. DG considered that it could design and build a sailplane combining the best of all three is; the result is the DG-1000S. At the moment, it is offered only as a pure sailplane, but the DG-1000T with a 30-hp Wezel single-cylinder two-cycle sustainer engine is planned for 2004.

The 1000 is offered with an unflapped 17.2m span trapezoidal (think Discus-shaped) wing and a choice of tips giving 18m span for training and aerobatics, and 20m with winglets for best cross-country performance. It has been designed to conform to JAR 22 standards, and has an FAA Approved Type Certificate. Limited aerobatics are permitted with the 18m tips, with additional maneuvers allowed if the gross weight does not exceed 1,389 lb (‘g’ limits increase to +7/-5). The test sailplane, s/n 10, came with both span options and the long-stroke retractable sprung main gear (without nose wheel) located slightly ahead of the loaded CG. This adds to the initial impression of the 1000 as a large – the cockpits stand high off the ground, and graceful entry requires a tall pilot, fitness, or a footstool.

The tandem cockpits, with separate side-opening canopies, are roomy with very deep seat pans – a good safety feature. Entering the front seat requires a little care to prevent long pants becoming tangled with glider parts. A 6′ 2″, 265-lb pilot declared both cockpits to be comfortable. The rear cockpit is raised slightly above the level of the front to improve forward visibility for the rear pilot. The controls come easily to hand with airbrake and landing gear levers both situated against the left cockpit wall and duplicated in the rear cockpit. The airbrakes come equipped with a “Piggott Hook” which limits lever travel to a couple of inches if the airbrakes are inadvertently left unlocked – another good safety feature.

The elevator has a bias spring trim operated by a small trigger on the front of each control column. There are also trim quadrants on the left cockpit wall which give a visual indication of the trim setting. The front-seat rudder pedals are ground- and flight-adjustable; both the pedals and the seat back in the rear are fixed. The rear seat has an unusual feature: the seat pan pivots at its front edge, allowing for height adjustment with a webbing strap. This lets the eyeline of the rear pilot be raised to improve forward vision – the limiting factor is the need to maintain adequate headroom beneath the canopy. The lack of pedal/seatback adjustment did not seem to cause any problem for occupants with heights varying between 5′ 7″ and 6′ 2″.

Permitted cockpit weight is governed by JAR 22; the minimum front seat weight for solo flight is 148 lb. Water ballast up to 42.3 U.S. gallons (353 Ibs) can be carried in the wings to raise wing loading and permit optimum performance to be achieved at higher airspeed. There is a 1.6-gal tank in the tail to provide trim compensation when the wing ballast tanks are used.

The 1000 also has an unusual solid ballast system, consisting of 6 brass weights totaling 26,5 lb that can be placed in a compartment in the vertical fin to adjust the glider’s center of gravity – primarily to reduce tail plane trim drag, but also to enable spins to be demonstrated. I really liked this feature as it allows realistic spin training – lack of this ability in many 2-place sailplanes risks an important gap in a student’s training. The ballast compartment has a transparent cover to simplify visual checking. The same weights can be used in the cockpit should it be necessary to compensate for a lightweight front seat occupant. Needless to say, with the possible permutations and combinations of ballast, care needs to be taken to ensure the glider is operated within permitted CG limits. An electronic indicator in the front instrument panel helps by showing the number of fin weights installed. All of this should be a clear warning to apply with care a “CB SIFT BEC or other pre-takeoff checklist to ensure safe loading.

Empty weight of the test was 907 lb (11.5 lb less with the 18m tips); certified max. gross is 1,653 lb. The 20m tips give a wing area of 188.7 sqft and a maximum wing loading of 8.76 lb/sqft. Redline speed in both configurations is 146 kts and a yellow-triangle speed (recommended lowest approach speed at maximum weight without water ballast) is 54 kts. The maximum demonstrated crosswind component is 8 kts, but this is likely a low estimate of actual safe capability.

I made three flights in the – two in the front seat with rear seat occupants weighing up to 265 lb and one in the rear seat when the front seat occupant weighed about 150 lb, a weight similar to mine. Two flights were made with the 20m. tips and the third at 18m span. Trim weights were added to the fin to put the CG close to the aft limit so any adverse handling qualities would likely be more apparent.

Weather was 35′ F with broken clouds and a surface wind of 10-15 kts, more or less down the runway. Even so, there was a little weak scrappy thermal lift. Wing dihedral gives good tip clearance – a good safety feature, particularly in a glider used for training. The aero tow hook is fitted at the extreme front of the long nose. This appeared to have a good directional stabilizing effect while the DG-1000 accelerated on the take-off roll. As expected on a glider of this size, control sensitivity is moderate, with very little risk of over-controlling. The ailerons are responsive from very low speed, but feel a little heavy. Once airborne, the view ahead is excellent, even from the rear seat, where the ability to raise the pilot’s eyelevel is clearly a benefit. In general, the controls felt responsive on tow, although the relatively smooth conditions did not provide any real challenges.

Off tow, control harmonization was good. Raising the gear, which can be accomplished from either seat, felt a little heavy, but the gear lever is well positioned to give the pilot good leverage. Pilots would be well advised to delay raising the gear until after release from tow to avoid a potential risk while retracting the gear. With the 20m tips, adverse yaw is considerable, but at the yellow-triangle speed the large rudder can balance a roll with full aileron applied; slowing down to 48 kts there is not quite enough rudder authority to be fully coordinated. The spring trim is easy to use and effective – it can eliminate elevator forces all the way up to the bottom of the yellow arc (100 kts). Visibility, from either cockpit, is nothing short of remarkable – it is possible to see through almost the whole 360 degrees, only a few inches of the horizontal tail plane next to the fin is not visible. Ventilation is very good, both from the scoops on the canopy, and through a well-placed eyeball louvre set on the right side of each cockpit. The very low level of cockpit noise is worthy of comment: it’s achieved without a rubber gasket or other seal between canopy and frame, simply by very accurately profiled GRP surfaces mating together.

As I have already implied, handling is pleasant, and the 1000 sat steadily in the weak narrow thermals at 30 to 40 degrees of bank with little need for control inputs. While the conditions were more a test of the pilot than the glider, it thermals easily and comfortably, and should not be a big challenge even for a low-time pilot. Exploring the low-speed handling showed just a slight tail plane buffet a couple of knots above the stall – only a subtle warning, which might be missed by a distracted or inexperienced pilot. With the 20m tips, this occurred around 37 kts with a 320-lb cockpit load and about 3 kts higher with a 435-lb load. Airbrakes open raised the stall speed by 2-3 kts.

In each stall except a turning stall to the right, the glider dropped the left wing; recovery is swift as soon as the back pressure on the stick is relaxed. At close to aft CG, in 18m, configuration, there was little difficulty inducing a spin from a cross-controlled skidding turn, although substantial control deflections are needed. A little surprisingly, the nose nodded upward during the departure, but following the standard drill resulted in immediate recovery, with some height loss and the airspeed peaking around 80 kts.

As some surplus height remained after spinning, I attempted a loop and a stall turn which were easily and enjoyably accomplished. I was surprised at the fast rate of acceleration as the glider was dived down to get entry speed – a good sign for a sailplane designed, in part, for aerobatic training, when the pilot wants to minimize height loss while trading height for speed to get started. The double-segment top-surface Schempp-Hirth type airbrakes are effective, and operation results in little pitch change. The Piggott-Hook is bypassed by rotating the airbrake lever inboard during the first few inches of travel. If ever required, the 1000 can be slipped to materially increase the descent rate. In the process, rudder overbalance occurs at close to full deflection, meaning a firm push on the pedals is required when discontinuing the slip. Approach control is easy, again with excellent forward view of the field and runway. Touchdown is nicely cushioned by the sprung main gear. On rollout, directional control is good and, in the prevailing conditions, the ailerons remained effective until the glider had slowed to walking speed.

The Cleveland hydraulic disc brake, operated by the airbrake lever, is powerful and, carelessly applied, could easily result in the nose being pitched down with possible minor damage to the finish of the glider.

Conversion issues should be minimal with a qualified instructor or experienced DG-1000S pilot to accompany the pilot being checked out. As always, a careful and systematic approach to conversion will pay dividends and avoid surprises.

In conclusion, the DG~1000S is a delightful state-of-the-art two-place sailplane that can be used as a serious cross-country as well as a general-purpose and acrobatic trainer. It is an excellent platform for cross-country instruction. Its main wheel/tail wheel configuration and retractable gear should make it a good glider for converting low-time pilots to high-performance flapless gliders even if pitch and roll sensitivity is quite different from the typical 15m single-place sailplane.

While I hesitate to make comparisons between different make/models, especially when not compared side by side, DG seems to have designed a cross-country very comparable to the DuoDiscus while adding the possibility of training and aerobatics. I am bound to say that its size and cost probably make it less attractive as a general-purpose trainer – I would have just a few qualms sending a student on first solo in a glider which costs around $95,000, although logically there is nothing intrinsically wrong with doing so.

About the author:
Dean Carswell holds a Gold badge with two Diamonds, has been an active gliding instructor for over 35 years, and is presently the SSKs Chief Master Instructor. He normally flies from Texas Soaring Association’s glider port at Midlothian, TX, where he is the chief flight instructor.