Status: company-owned experimental prototype
Type: tandem-wing STOL bush plane
Powerplant: 1 x 180 bhp 4-cylinder Avco Lycoming
First flight: 22 January 1982
The Model 72 Grizzly was an all-composite, tandem-wing proof-of-concept STOL bush plane/research prototype aircraft to be used to evaluate the feasibility of flaps on a canard aircraft and achieving STOL and amphibious capability with a canard/tandem-wing configuration. It was a four-seater with a large baggage area, powered by a 180 hp Lycoming IO-360B engine and a Hartzell CS propeller. The sliding canopy had bulging side windows, allowing straight-down visibility for the pilots. To enhance the go-anywhere, land-anywhere capability of the Grizzly, its cabin converted to sleep two, with 78 inch long beds in the back for go-anywhere, land-anywhere camping, hunting, fishing, etc. Folding the rear seat forward resulted in a level, 78- inch long bed.
Though an all-composite canard—as was expected from a Rutan design—everything else was “different.” Both the wing and canard were forward swept and had interconnects that doubled as torsional braces and fuel tanks. Fowler flaps were employed on all four flying surfaces, increasing wing area by 45 square feet. When deployed, they were intended to provide excellent STOL characteristics. The Grizzly’s airfoil and wing systems were the first to be developed by a RAF aerodynamic design computer.
The structure of the Grizzly was all composite, using fiberglass and carbon fiber facings/reinforcements with rigid foam sandwich cores. The Grizzly airframe was a test bed for evaluating and comparing several structural configurations. For example, the right wing was a hollow, sandwich-skin configuration and the left wing was the full-core construction technique pioneered on the VariEze. It's interesting to note that not only did the full core wing require far fewer man hours to build, it was also lighter and stiffer than the hollow wing.
Fuel was carried in the wing interconnects, keeping fuel away from the cabin while providing the torsional bracing required for the forward-swept wings. The four Fowler flaps averaged over 50 percent chord, adding over 45 square feet of wing area when deployed. The Grizzly airfoil and wing systems were the first to be developed by a new RAF aerodynamic design computer program which handled the complex interactions of tandem wings and high-lift devices.
By August of 1980, personnel of the Rutan Aircraft Factory were building the airplane in a shop, which was closed to the public. The Model 72 prototype was not intended for a specific market. RAF planned no certification/production of this model and it was considered too large for the homebuilt market. The Grizzly was strictly a research project, to study canard aerodynamics in the STOL category. RAF's previous canard aircraft had not been designed for short-field operation. Thus, many had concluded that tandem-wing aircraft may not be suited for STOL performance. Therefore RAF hoped to gather the necessary data during the Model 72 test program to considerably expand their technology base, expecting the knowledge gained by testing this proof-of-concept aircraft would be invaluable for future developments.
Burt was concerned the interesting airplane would be mistaken for a new homebuilt. For this reason, the Grizzly project was kept a secret, while the new sailplane, the Solitaire, basked in the Rutan spotlight. The 'Griz', as Scaled people affectionately called it, made its first flight on January 22, 1982, with Mike Melvill at the controls. It actually went so well that he was up for 2.6 hours. Progressing through his test flight schedule card, Melvill was able to go as far as to crank out full flaps – something not always possible on the first flight of conventional configurations, let alone the Grizzly.
In June of 1982, Burt Rutan worked with the FAA to get the Grizzly signed off as a tow plane so it could be used to tow the new Solitaire for its test flights. Rutan checked out as the tow plane pilot and sent the FAA into a bit of a whirl since they had never licensed an experimental plane to tow another experimental plane. The Grizzly towed the Solitaire for many flights, the first of which occurred on June 23, 1982.
Built strictly as a proof-of-concept research vehicle, the canard featured a Fowler-type flap system (a first for a tandem wing aircraft); rounded, double-wheel landing gear; bubble side windows for good downward visibility; and interconnects that doubled as torsion braces and fuel tanks. It was muzzled by a Hartzell F7666A-4Q prop and packed a 180 hp Lycoming IO-360B. Empty, the Grizzly weighed 1,473 pounds but had a maximum gross weight of 2,500.
The Grizzly was unique in being a Three-Surface Aircraft (or TSA) of the Active Control type (also referred to as close-coupled canard TSA). Simply put, this type of configuration adds canard surfaces to a conventional aft-mounted tail configuration. This design presents quite a few advantages: it provides additional lift in the nose region; it presents a simple high lift system and improved rotation behavior; it allows for shorter take-off and landing paths; it reduces the negative lift of horizontal tail plane; finally, it enables to carry larger payload at fixed wing size. The possible disadvantages of a typical TSA configuration are the additional skin friction, the possible higher aircraft weight, and especially the changed stability and aeroelastic characteristics. Rutan took all these into consideration when he introduced the Grizzly in 1982, the first practical TSA aircraft that paved the way for the later Grumman X-29 or Piaggio Avanti.
However, the Grizzly remained a unique design because instead of close-coupled canard surfaces, its forward wingplan was actually blended with the main wing. The Grizzly was noted for its excellent short takeoff and landing (STOL) capabilities. Just because it didn't go into production doesn't mean it was a failure. It even featured one of Burt Rutan's three original patents, this one for a wide-chord flap suspension system (US Patent Number 4614320).
The aircraft was tested in its bush configuration with four low-pressure tires on the main gear for soft or unprepared fields. It was supposed later to be fitted with a new type of amphibious float system to allow it to operate from either water or hard-surfaced runways. The goal of the new float system was to allow operation from land to lake and back without the requirement to raise or lower wheels or to operate a water rudder. Schedule for testing the amphibious system depended on the success of the flight test program with the bush configuration, but was never implemented. "Due to a higher priority on the Solitaire and to some consulting commitments we are not pursuing the Grizzly amphibious floats at this time", said Rutan early in 1982. "Grizzly has not been and will not be our highest priority"
Given the limited success of the 'Griz', the plant decided to focus on the Solitaire and Long-EZ designs. Part of the experience gained on the Grizzly was used in the development of the Model 133 ATTT demonstrator—which has also been mentioned as another 'Grizzly' by a former Scaled employee. The Model 72 prototype was donated to the EAA AirVenture Museum at Oshkosh, where it is usually displayed near the Main Admission Gate.
Burt Rutan reflected on the Grizzly program as follows: "We never kitted the Grizzly. We flew it. It wasn't a good idea because it wasn't a very good bush plane. A bush plane needs to have a high wing, not a low wing, and it can't have the flaps two or three feet off the ground dragging through the bush. For me, it was an experiment to show that I could achieve a high lift coefficient on a tandem-wing airplane and, yeah, it parked so that you had a sleeping bed level in it and whatever. I needed more power and it was pretty early that I understood that I should have gone up and spent more time in Alaska understanding what a bush plane really needs to be. I'd put that in that category."
After all test flights for the Grizzly and Solitaire were completed, Burt decided to donate his experiment. He donated the Grizzly to the EAA AirVenture Museum in 1997, where it resides in the honored company of other innovative Rutan designs.
Population: 1 [N80RA] (c/n 001)
Crew/passengers: 4 seats