HP Aircraft HP-18
Designer Richard E. Shreder’s HP (for high-performance) 18 is a 15-meter Standard Class sailplane racer, which made its first flight in 1975; it is designed for sale in kit form for homebuilt construction and assembly, and about 170 had been built or were under construction by early 1979.
It is constructed with machined aluminium spars for the cantilever shoulder wing and precut hard foam wing ribs spaced at 10cm intervals; the HP-18A differs in having carbon-fibre spars but has similar wing rib construction. The HP-18 uses the Wortmann 67-150 airfoil. Camber-changing flaps and ailerons occupy the entire trailing edge deflecting 90 degrees, and up to 200lb of water ballast can be carried inside the wing box spar.
The design also incorporates certain improvements over the Standard Class RS-15 to which it is generally similar, such as new wing tips, a removable tailwheel, better gap seals and improved streamlining.
The HP-18 has a slightly longer fuselage than the RS-15 , with a circular instead of oval section, and this is supplied as a pre-formed Kevlar pod, aluminium rear fuselage and the V-tail; the pilot sits under a two-piece flush canopy. The control stick is side-mounted with attached brake handle and trim tab although modifications using a conventional stick have been made. A retractable Tost monowheel with a mechanically-expanding brake is supplemented by a steerable tailwheel.
One HP-18, C-GOIY, has been modified by its Canadian builders Don Band and Peter Masak to have winglets of glassfibre and balsa and Wortmann FX-60-126 section at the wing tips.
One belongs to the National Soaring Museum.
Span: 15m / 49 ft 2.5 in
Length: 23 ft 6 in
Height: 4 ft 0 in
Wing area: 10.5sq.m / 114.7 sq ft
Aspect ratio: 21.4
Airfoil: Wortmann FX 67-150
Empty Weight: 213kg / 470lb
Gross Weight: 440kg / 970lb
Wing Load: 41.9kg/sq.m / 8.58lb/sq.ft
Water Ballast: 90kg / 200lb
Max speed (smooth air): 150 mph
Top speed (rough air): 120 mph
Max aero-tow speed: 120 mph
Stall clean: 40 mph
Stall flaps: 35 mph
Min sinking speed: 0.55 m/s / 1.8 fps / 1.07 kt at 45 mph
Min. sink, 656 lb: 1.8 fps @ 50 mph
Best glide ratio: 40:1