08/31/2010. Remarks by Bill Wolfe: "I knew George G. Spratt (1904-1998) as a personal friend for 29 years. He was a visionary aeronautical engineer, inventor and a true gentleman, and perpetuated the work on the Controlwing principle, started by his father, Dr. George A. Spratt (1870-1934). Dr. Spratt and his son George built, in all, some twenty different gliders, sea and land planes, each one incorporating a Controlwing in some fashion.
George (junior) built the Model 106 all composite Controlwing flying boat in 1962, it was powered by a modified 60 hp Mercury outboard marine engine. Registered N910Z it accumulated several hundred hours of safe flight time in the Chesapeake Bay area where George often demonstrated it during the mid 1960s to mid 1970s. He operated it from his personal aircraft carrier, a homebuilt 55 ft (16.8 m) arc welded steel diesel powered utility vessel while conveniently anchored over a shallow sandbar in the middle of Chesapeake Bay.
The sole Model 106 was soloed by over 100 pilots who only had to ask, and I first saw and had the opportunity to fly it in 1969. I immediately fell in love with it and decided this was the only aircraft I would ever care to own. In the mean time George had designed a more advanced prototype, and the Model 107 was built with the help of Elliott Daland. Registered N2236 it was powered by a modified 80 hp Mercury 800 outboard marine engine, and first flew in 1967.
After dreaming about it a long time I finally built my Model 107 in the late 1990s, using George's 1973 plans and 84-page construction manual (these can be found on speleotrove.com) with many of my personal changes incorporated and marked on the plans. Registered N107GW it was only the third plans-built aircraft to be completed and flown up to now as far as George and I knew. All three were built primarily of wood rather than the all composite construction of the Model 106. Of the other two, both using VW engines, one was lost in a water collision and the other one may be deteriorating in Florida.
N107GW is the only Controlwing aircraft in the current FAA registry. I used an 85 hp Mercury 850, modified per George's instructions. Wooden construction was used throughout, not the all composite construction of the early prototype N910Z which weighed only 500 lb (227 kg). Mine and one of two other known all wood plans-built aircraft flown weighed from 250 to 275 lb (113 to 125 kg) more.
I taxied my Controlwing flying boat a lot but flew it only on very brief test hops as the FAA flight test plan got underway. Testing dragged out a very long time as numerous bugs such as engine installation, carburetors, V-belt tension adjustment, exhaust system, cooling system, control linkage revisions and wing panel balance were ironed out including my lack of experience and with no other knowledgeable technical assistance available.
There were no defining instructions from George regarding control rigging, wing panel balance and the desired pilot pitch control inputs. This important information was gained only from experience. The FAA Experimental Aircraft license is primarily for the builder's education and recreation. I got a lot of the educational part but very little of the recreational part as my medical expired just as flight testing started. With no other experienced Controlwing pilot available to continue the flight test program, development of the Controlwing technology has stalled.
Almost five years of labor and test time went into this project, my first attempt at building an aircraft. I was a Senior Aerospace Design Engineer for thirty six years but that helped very little with this project requiring woodworking, metalwork, glass fiber, machining, welding, engine and instrument installation plus a bit of flight testing. My last brief test flight on October 4, 2000 is seen in a video showing the takeoff at 50 mph (80 kmh) to about 75 ft (23 m) before outdistancing the chase boat. There were not enough brief liftoffs to record any meaningful data during our frequent trips to Beaver Lake, mostly to tinker with engine operation or V-belt tension.
Spratt Controlwing Flying Boat Operations
In flight, both hinged parasol wing panels collectively and aerodynamically maintain a relatively constant angle of attack to the relative wind with a variable angle of incidence in reference to the hull. The NACA 23112 reflex airfoil was selected due to its favorable aerodynamic pitch response and small excursion of the lift vector. The wing panels are moved differentially to provide a very gentle bank and turn. The wide fixed V-shaped tail has no movable surfaces. It only guides the aircraft like feathers on an arrow and provides tail lift at high power settings.
Flight controls consisted of a throttle, steering wheel and an auxiliary pitch stick. Since the inherently stable Controlwing flying boat has no ailerons, rudder or elevator; the usual pilot control coordination is not required. Conventional aircraft which can stall, spin and dive use those movable surfaces to direct an aircraft in pitch, roll, yaw and maneuvers about the CG.
The steering wheel of a Controlwing only controls the differential angle between wing panels to provide a gentle bank and turn in the air and move the very effective kick-up water rudder. There is no feedback or cross talk between the pilot's pitch and roll inputs or outputs with this very simplistic control system. The auxiliary pitch stick is only used when the pilot desires to shorten a takeoff, move above or below an existing stable flight path or glide path, or to flare for a smoother landing.
The throttle, conveniently attached to the auxiliary pitch stick which is mounted low like a helicopter, is the primary vertical flight control. Hands-off takeoffs and landings may be made solely by increasing or decreasing power. With high power settings the flying boat hull will assume a relatively level attitude for takeoff and cruise flight. When power is reduced to idle, tail lift is reduced and the hull will assume a slightly nose high attitude essential for a safe water landing and the angle of incidence of the wing panels will automatically be reduced by aerodynamic forces to accommodate the stable glide path.
No air rudder is needed for the flying boat since the very small angular difference between the wing panels does not create adverse yaw. Fast, sharp turns can be made on the water due to the low center of gravity, wide hull and the lack of wing tip floats to trip over. A Controlwing flying boat can bank into the turns like any motorboat and can pivot about a wingtip touching the water and is very crosswind tolerant.
With a minimum of flight training, a novice could easily and safely fly a Controlwing flying boat and almost any pilot could receive adequate flight instructions by telephone. These kinder, gentler and safer aircraft have no inherent spin or dive characteristics and when the stick remains unrestrained during flight through turbulence, the occupants will sense only about one quarter of the normal gust loads. The Controlwing flying boat is the safest, simplest, easiest to fly and most comfortable aircraft ever developed. Fly one yourself and you will believe it!