(From Sport Aviation, 06/1971, Page 16)
By C.D. ‘Don’ Fairbanks
Photography by R.W. Fyan, Jr.
THE KNIGHT TWISTER “IMPERIAL” was born at the 1968 EAA Fly-In at Rockford. Two months before, I had purchased some “beginnings” for a basic Twister (including the wing ribs, basic fuselage, landing gear, and partially completed tail section) from a homebuilder in Michigan, and I went to Rockford with the hope of seeing a couple of Twisters “in the flesh.”
Fortunately, Bill Nagle and Tony Sablar both attended the Fly-In, so I got my chance to check the details on their Knight Twisters and talk over construction techniques. One day, while looking around Tony’s airplane, I was talking to a fine old gentleman who seemed very knowledgeable. When I asked if he were familiar with the Twister design, Tony stepped in, laughed, and said: “Don, meet the Knight Twister’s designer, Vern Payne.”
I spent most of the next two days talking with Vern about finishing my Knight Twister. We began thinking about making a Knight Twister Sport-Biplane-Class racer, since I was interested in trying the racing circuit and was at a good point to effect any change in my airplane. Vern agreed to work up a design for the wings so that they would meet racing requirements for the class. He came up with the NACA 21 airfoil to replace the standard M-6 used on earlier Knight Twisters.
The wing area was increased to 75 sq. ft. from the normal 55 sq. ft. This was accomplished by lengthening the top wing to 17-1/2 ft. from 15 ft., and the lower to 15-1/2 ft. from 13 ft. Also, the chord was increased approximately six inches. We also decided to use a new, longer stabilizer/elevator design that would dampen porpoising at high speed. To make the airplane more stable, Vern suggested lengthening the fuselage, and this was accomplished by inserting a nine-inch section just forward of the cockpit. The name Imperial came from Vern after we were finished making all the modifications to the basic Knight Twister design for a racer. Throughout the entire construction effort, he was a tremendous help and nothing was done without his approval.
For power we decided to install a Lycoming O-290-D2 engine that would develop 135 hp at 2700 rpm. Since we had moved the pilot rearward, we had to place the engine farther forward to maintain the proper CG. This made the aircraft about two feet longer than the original Twister design. We also decided not to install flying wires as both wings are full-cantilever and the design was stressed for 7G’s without wires and 9G’s with.
The turtledeck was made of hardware cloth covered with fiberglas and was made to include the fin. It was also made removable for aft fuselage inspection. The fuselage, wings, and tail were finished using the Stits Poly-Fiber process. The wings and stabilizer were skinned with mahogany plywood prior to covering.
The Knight Twister Imperial, N-5DF, with builder C.D. Fairbanks at the controls.
The underside of the upper wing is seen prior to covering. The airfoil was changed from the standard M-6 used on the type.
The Knight Twister has its upper wing mounted here, and the fuselage nearly ready for covering. The deep firewall is faired to the tail and, along with the longer cabane struts, appears to have “lowered” the airplane rather than raised the wing.
The Knight Twister fuselage displays the darkened areas on the longerons aft of the landing gear where a nine-inch section was added to the fuselage length.
The Knight Twister “Imperial” appears to have a lot of “broadside” to it because if squats low to the ground. The “Twin Commanche” type of nose adds to its “stretched” appearance in the air.
Since it was being built to race, and since races are scattered all over the country, we decided to give the airplane a decent range. To do this, we installed two fuel tanks: the main tank of 22.5 gals. was installed on top of the fuselage cross members between the firewall and the instrument panel, an auxiliary tank of 12.4 gals. was installed aft of the firewall below the main tank and forward of the rudder pedals — one of the extras we gained by lengthening the fuselage.
Since we had to use a longer engine mount, we were afraid of fuel starvation during acceleration or nose-high attitudes and so we installed a gear-driven fuel pump to give us the needed fuel flow. The nose bowl design was modeled after the Twin Comanche and was laid up using fiberglas.
After assembling all parts and pieces, the airplane, now carrying registration number N-5DF, was ready for first flight on June 19, 1970. During the initial test hop, the Twister was extremely tail heavy, and my first thought was that we had miscalculated the CG due to our fuselage modification. Immediately after landing, I called Vern Payne in California to see if he had any suggestions. He asked what the angle of incidence was on the stabilizer, and there was our problem. I had installed it with zero degrees, and it should have been angled at three degrees. After adjustment, the problem disappeared and the plane flew very well, meeting or exceeding all our expectations. It was very nimble and positive, used very little control movement, and was very comfortable.
My first chance to check both the range of the Twister and myself was by flying to the Fly-In at Oshkosh non-stop in both directions. The flight up from my home in Cincinnati — about 480 air miles — took 3:15 hours and left nearly an hour’s fuel reserve. Coming home took a few minutes longer due to some rain showers we went around, but the little airplane still made a good showing in the range department. My longest trip to date was to Salt Lake City, Utah in one day with 11:15 hours in the air with three stops. The aircraft will true 150 mph at 5500 ft. and 75-percent power, which isn’t bad for a biplane.
Building my Knight Twister was the realization of a boyhood dream that began back before World War II. Now we hope to be active in the race circuit in 1971, so wish Sport Biplane No. 50 lots of luck!