Design Evolution of the Kasperwing
The Kasperwing Ultralight is a collaborative design between Polish sailplane pilot and aerodynamicist Witold Kasprzyk (pronounced Vee-told Kasper) and American hang glider designer / entrepreneur Steve Grossruck. Kasper had won Poland's national sailplane championship on four occasions before World War II and had been working for several decades on a way to increase airplane safety and performance by developing a flying wing (tail-less) platform that utilized a type of high energy span-wise vortex to increase lift; in conjunction with a control system that functioned independent of forward airspeed (see patent #’s 3,438,597 and 3,831,885). The purpose of these improvements was to reduce drag, enable an ultra-slow landing speed and at the same time avoid some of the classical “stall-spin” problems of conventional tailed aircraft.
The great distinction between the Kasper platform and other tail-less aircraft is in the way the control system functions. Kasper had analyzed the advantages and shortcomings of the earlier flying wings of the time, such as those developed by the Horton brothers or John Northrop, and decided improvements could be made in the areas of stability and control. To do this he utilized a reflex airfoil, low twist constant chord wing and employed adjustable upswept horizontal stabilizers at the wingtips for pitch damping and to prevent tip stalling. The vertical winglet surfaces are a two- piece system consisting of a moveable rudder with forward balance tab/spoiler and fixed vertical stabilizer. The combination is canted outboard and toed inward to provide exceptional yaw and roll stability. Due to the canted geometry, the rudder acts like an aileron, rudder and spoiler when deployed and automatically coordinates turns. The winglet provides additional lift by increasing the effective aspect ratio, cuts drag by reducing the wingtip vortices and gives control that does not depend on the aircraft’s forward speed in order to function, unlike conventional aircraft control systems. The pilot could raise the nose of the wing, gently pass below the normal stall speed and settle into a near vertical descent or “Mush” and still maintain complete yaw and roll control. Kasper felt the system more closely resembled the way birds control their flight and noted “birds rarely stall and crash”. An airplane with this type of control system would perform better and be safer as a bonus.
MUSH MODE
Steve Grossruck, an avid hang-glider, sailplane pilot and engineering student had been designing and building hang-gliders since 1974 and was in the process of modifying the Manta Products Fledgling (see Pterodactyl Fledgling in NASM collection) to increase its soaring performance. The Ultralight design began in spring 1977 when he and Kasper were introduced by a mutual pilot friend, and an agreement was formed to integrate Kasper’s Aerodynamic principles into the fledgling airframe in small incremental changes. The Fledgling hang-glider structure was a good choice for experiments because it was strong, easily modified and could be readily transported and set-up for flight. Grossruck began the modification by changing the airfoil, reducing dihedral, replacing the Fledge’s tip drag rudders with canted Kasper winglets and de-sweeping the wing 5 degrees. No fewer than ten rudder-stabilizer combinations were tested in order to get the proper balance ratio and positioning of the rudder relative to the wing and fixed vertical stabilizer.
Next step: wing area was increased from approximately 160 to 180 square feet and the horizontal stabilizers were added. Significant performance gains in sink rate, glide ratio and, particularly, handling were realized beyond the original Fledge layout, and this wing became the prototype platform for the Kasperwing Ultralight. As a hang-glider the Kasperwing had magnificent performance for its time: sink rate 160 ft/min with a 14/1 glide ratio. Grossruck flew in a “supine” harness beneath the wing and shifted his weight fore-aft for pitch control. Yaw and roll were controlled by individual control sticks for each rudder. He used this wing to participate in several local hang-glider competitions and repeatedly demonstrated the ability to make near vertical descents into small landing fields while under complete control. He also performed mild aerobatics including wing-over's, intentional spins and 360 degree turns and reversals while in the vertical descent mode.
By 1978 many hang-glider pilots were tired of driving up and down mountains to gain “air time” and a few, like John Moody, were attaching go-cart and chain saw engines to their wings to get airborne. A bolt-on “Soarmaster Power-pack” based on a 7-hp Westbend industrial engine and fiberglass prop were attached to the Kasperwing, along with a 2-wheel undercarriage and a snow ski for a forward skid. The basic supine harness was retained along with the dual control sticks. The Soarmaster only provided about 70 pounds of thrust and the Kasperwing was dismally underpowered, yet still managed to climb about 200-300 ft per minute. The first of about 30 powered flights were made with this unit until its go-cart clutch and chain drive transmission self-destructed. Next came a 10-hp Yamaha go- cart engine with 3.5/1 V-belt reduction drive and wood prop. The front skid was replaced with a steerable nose wheel, and the dual control sticks were changed to an articulated “butterfly” shaped steering yoke that could deploy one or both rudders simultaneously. This configuration worked well and the Kasperwing could climb to altitude at about 500-feet per minute but was still light enough to allow the engine to be shut down for soaring as a glider. The Yamaha cart engine could only run about 10 hours before a total rebuild was required and was later replaced by a fan-cooled 250cc, 25-hp Yamaha snowmobile engine. This gave the Kasperwing an 800 ft/min climb rate and the prototype was flown for a couple hundred hours, garnering much attention from the local gliding community.
By 1980 the Ultralight movement was beginning to blossom and Grossruck decided there was enough interest in the Kasperwing to risk a business venture. He quit his full time job as a foreign car mechanic, and to save money moved into a hanger on the Skyport Airfield in Issaquah, Washington. Cascade Ultralites was formed on a shoestring budget with just a few Kasperwing's on order, but a trip to the Experimental Aircraft Association (EAA) convention in Oshkosh, Wisconsin in August 1980 changed all that.
Grossruck was allowed to demonstrate the wing’s performance, including the controlled, vertical descent maneuver, which earned him the EAA’s prestigious “Outstanding New Design” award and put the Kasperwing on the map of innovative kit-plane designs. He returned to Issaquah, flush with purchase agreements and began to tool up for higher production. At first deliveries were slow
By 1982 Cascade Ultralights could produce about 10 planes per week. The prototype 250cc Yamaha Engine was replaced with a 23-hp Kanematsu Zenoah engine and V-belt reduction unit and most Kasperwings built from 1980-1982 were delivered with this engine. Later units were powered by Rotax 277, 377 and 503 power-plants between 28 and 52 horsepower with gearbox prop drive, and a 2-place version used the 65-hp Rotax 532. There were three basic versions produced, all utilizing the 180- square foot prototype wing but with different control arrangements and options. Most were “180A” or “180B” models with the weight- shift harness, 2-axis control system and rigid landing gear, which still had the ability to soar with the engine shut down. Later, demand for a 3-axis version resulted in the heavier C-model which had a conventional stick and rudder pedal arrangement. The pilot sat in a fixed seat that was adjustable for trim. Hinged ribs operated by torque tubes served as “elevons” for pitch control. Roll was controlled through spoilerons on the upper surface of the wing but could also be accomplished by deploying the individual rudders through foot-operated pedals. Both spoilers and rudders could be controlled independently or together for a faster roll rate and were used together for glide slope control or to enter the vertical descent mode. The C-model also came with a sophisticated landing gear shock system (available as an option on the B-models) and had a castoring nose wheel, steerable through toe brakes attached to the rudder pedals.
Grossruck gave his customers a choice of several configurations: standard tricycle landing gear; twin plastic floats for water take-offs and landings; and a streamlined, Plexiglas pod to enclose the pilot and reduce the effects of wind and temperature. Grossruck's company, Cascade Ultralites, required a week to fabricate each kit, and the average buyer spent another 40 hours assembling the Kasperwing. Altogether, 333 Kasperwing's were delivered between the fall of 1980 and summer of 1988 when production was discontinued.
On a final note; to demonstrate the wings amazing low speed control, tight turning radius and promote the Boeing Flight Museum’s yearly in-door airplane contest, Grossruck flew the Kasperwing inside Seattle’s fully enclosed “Kingdome” stadium on three different occasions in May 1981.
Here is a video link:
http://www.youtube.com/user/flyboypa34