| The lightweight Knight Twister, N-11RU, built by Robert Uebel, before the first test flight and subsequent landing gear change. (Photo by C. D. Fairbanks) |
By Robert M. Uebel (EAA 44423)
1345 Washington Circle
It all started in September of 1968, while discussing my idea of rebuilding a "Champion" or "Cub" with Don Fairbanks, owner and operator of Cardinal Air training, also a good friend.
Don had just started building an airplane he had long dreamed of -- the Knight Twister. Don had purchased a Twister 40 percent complete and, since he had decided to build his plane to race, he had a complete grouping of material for the wings that he wouldn't be able to use. The original wing area was less than required for racing.
I said: "Don, I want to rebuild an airplane in order to learn; maybe later I would have enough knowledge to build from scratch." Don's reply was: "Bob, you know as much about building an airplane as I do." Well now, here is the man who introduced me to flying, taught me to fly, and also gave me my check-ride for my license, and he says that I know as much as he does about building airplanes! This just can't be! Finally I said: "Don, what is a Knight Twister?" Up to this point, not wanting to show my ignorance, I had skillfully avoided the fact that I didn't even know what a Knight Twister looked like. Don gave me a shocked look and then produced some photos of Twisters. Don waited, finally asking: "Isn't it the most beautiful airplane you've ever seen?" Now, I was a little shocked, for here was my own "god" image flight examiner saying he really likes the weirdest biplane I've ever seen. I mean, after all, not a wire on it, and it doesn't look low and slow; it just looks fast. Finally I answered, "absolutely beautiful." After all, here I am with one rating with 50 hours, and Don with every rating in the book and 16,000 hours. Surely my tastes have not yet developed, so I agree to build a Knight Twister.
Now with this decision made, I faced a rather precarious situation -- my wife.
Of course, as soon as I pulled in the drive she wanted to know what all that lumber was that I'm unloading into the basement. She said: "Oh, Bob, you're finally going to build the shelves for the children's room as you promised." Well, thank the good Lord for the superman traits inborn in all pilots, for I came back instantly with the perfect answer: "Honey, we are going into the wing building business; a great demand -- we'll make a fortune." I must have really impressed and overcome her with this answer; she couldn't even answer me. She just started mumbling, kind of shook her head, and quietly walked away.
That crisis solved I started reading everything I could find on Knight Twisters. Clyde Parsons' account of a sharp roll on take-off, Gus Limbach's saying 500 hours of mostly "Swift" and Luscombe time was mandatory, and a few more -- even more -- encouraging reports. Within ten seconds I traversed the five miles to the airport and asked Don: "What have you gotten me into?" Don smiled -- no, he laughed -- and then added: "You didn't read far enough -- good stall characteristics, relatively slow landing speed, stressed for 9G's positive and negative, very responsive to control pressure down to the stall." Then he added: "Don't worry, we'll get you some conventional time and you won't have a bit of trouble."
Confidence reinstilled, I went to work for the next 24 months. Working over 1000 hours a year plus spending over $1000.00 per year leaves little time or money for flying, therefore I only built up a total of 115 hours when finally I got the airplane to the airport. As the time to fly neared, doubts began to enter my mind. Also, what may be a major problem had evolved. The landing gear seemed to be too light for the final aircraft weight. Alas, after taxiing for a couple of hours in the grass, confidence is built up again and I decided that the time had come. Don was on his way to Reno to participate in the races with his newly finished Knight Twister "Imperial", N-5DF. I decided to go ahead with the test flight, thereby having a surprise for him when he returned.
| LEFT: The Knight Twister looks as sharp as the lance portrayed on its side. The narrow wing chord is quite evident, as is the fold-down cockpit-access door. RIGHT: The landing gear was modified considerably and simplified in the same process, rectifying a too-springy condition of the first gear. |
So that eventful morning started with me out on the pavement lined up to go. Within the next two minutes I performed a fascinating feat -- a precision 180 around a blade of grass, commonly known as a ground loop. While taxiing back I began to think, just maybe, some of the things they say about the Knight Twister are true. Naturally, being a good pilot type I had the springy landing gear to blame for a scratched wing tip and bruised pride.
After another month's work building a new landing gear, I decided to ask Don to test hop my plane. Don agreed and on October 23, 1970 the airplane wanted to fly but, using a 65x64 propeller with a 65-hp Continental, the engine failed to develop more than 1800 rpm. This incident had caused a decision to delay the test hop and return the airplane to the shop. We then decided that more rpm would be mandatory for the test flight. This time I installed a 69x48 propeller which ran 2150 rpm static. Finally, the airplane flew on October 26, 1970 but alas, more problems! The airplane had a strong roll to the left; also, the engine had developed an oil leak. With these problems evident, the FAA asked to see one more flight. On November 3, 1970 the airplane flew well and was signed off.
Now began my fight to overcome the "Knight Twister Syndrome" of which I was showing symptoms. Most of my taxi work was performed in the worst possible speed range, that is, to a point when the tail was ready to come up, and then back off on power. The reason for working in this range was quite sound -- stark terror! The ground loop had taken its toll! Finally, after two hours' taxi work on the hard surface, I developed enough courage to push the tail up. In doing this I reduced my control problems by 80 percent. When the tail comes up the first problem you solve is visibility. Forward visibility in a three-point attitude is non-existant in my Knight Twister. Next, you suddenly aren't quite so busy on the rudder pedals and, believe me, you are busy when the tail is on the ground.
Okay, now I had 50 percent of the problem licked. The next phase was to fly the airplane. Well now, this shouldn't be a problem, because, after all, how much different can one airplane be from another in flight? Don had cautioned me on overcontrol, emphasizing sensitivity of control. Just how sensitive is "very sensitive", though?
So, on Tuesday, November 17, 1970 I went out to try it once more. I started the take-off roll with no problem, and at about 40 mph indicated I lifted the tail. The airplane flew off very nicely at 70 mph, but I pushed forward on the stick for negative angle of attack and built air speed to 90 mph. Now, the reason for this should be quite evident by now -- I'm chicken! I came back gently on the elevator and she rotated very nicely, then as I climbed out of ground effect things began to happen. Suddenly the left wing dropped. Well, now! This is no problem, is it? Simply get on right rudder and a little right aileron to pick that wing up. Not in a Knight Twister, for just as fast as I corrected I was in a 90 degree bank diving at the ground with 30 ft. of altitude and 100 mph indicated. I knew from Don's flights that the airplane stalled at 60 mph indicated, so I used some of that excess air speed to gain altitude. Gently, a little back pressure, left rudder, left aileron - gently now, don't lose your cool! Whoops, too much again. Now we were standing on the tail making a tight left turn. But now I'm learning just how sensitive "very sensitive" is, also that this airplane is not a rudder airplane. Bring the nose up very gently. I pushed it down rather rapidly, otherwise my "cool" was threatening to abandon ship. Just a hint of right aileron was added and now things started to shape up. A nice gentle climb out to the practice area to decide - bail out, or attempt to land this devil? Really not much of a choice, since I hadn't worn a chute.
Well, after 40 minutes with the outside air temperature at 30 degrees, I was about numb enough to figure that perhaps I could land this airplane. I decided to make a long flat approach in order to have plenty of time to get lined up, stabilize my approach speed which would be 90 mph, and perhaps say a few quick prayers. I came into the pattern on a left base, turned final, pulled up the nose, and slowed to 90 mph. Now, not just the runway but the entire airport was obliterated by the long nose of the airplane. Now again my superman pilot instincts, which it seemed I had overtaxed of late, told me instantly that this wasn't going to work. Therefore, I went around the patch for a steeper descent. This time, power was backed to 1300 rpm, and 90 mph gave good visibility. Down, down, down, across the threshold at 15 ft., gently applying back pressure and slowing to 75 mph. Whoops, too much again! I leveled off and I knew this airplane sinks like a rock, so I was sure I wouldn't have enough elevator for a flare. I sank down to three feet, drew back on the stick and -- what do you know! -- there is something left. The airplane responded nicely and came into a three-point attitude -- gently back on power and she settled to the runway with only a quiet squeak.
Now by this time my legs were shaking so bad I was doing an automatic tap dance on the rudder pedals. I felt sure that it was the cold. Getting on those brakes, I slowed it down to a crawl -- a slow crawl -- and back to the hangar.
| Robert Uebel and his Knight Twister. |
Don was all smiles and his first comment was, "want to sell it?" Of course, I jokingly replied, "where's the interested party?"
Later, over a hot cup of coffee, Don and I discussed the problem of roll on take-off. After much discussion we decided that Don, weighing 175 lbs., puts the CG on the extreme aft side of the envelope. Myself, weighing 150 lbs., puts the CG on the extreme forward side of the envelope. These two conditions, in turn, create different center-of-pressure points on the airfoil. This indicated that my past solution to the roll problem only corrected it for Don's given weight/CG condition. Since the Knight Twister wing is full cantilever, of torsion box construction which is extremely strong, this makes a minor rigging problem such as this a major repair problem.
Vernon Payne, the designer of the airplane, had been very helpful in the solving of this problem and others that came up during construction.
My Knight Twister is called the "Light-Weight Knight Twister", which is not the way it turned out. The airplane weighs 650 lbs. empty. It has a 15 ft. top wing, and a 13 ft. bottom wing, giving it a total wing area of 55 sq. ft. It is 14 ft. 10 in. in length, and is powered by a Continental A-65-8 engine using a McCauley 1A101 69x48 propeller. This combination gives 100 mph indicated at 2000 rpm and 125 mph indicated at 2600 rpm. This combination does not give the airplane a good climb, showing only 600 or 700 fpm. It also requires about 1500 ft. of runway for take-off and landing. I plan to have my other propeller, a 65x64 McCauley 1A100, repitched to 65x60, and also thinned and raked, which should improve performance. Perhaps at a later date I will install a larger engine, but for now I'm helping a very talented designer and a good friend, Vernon Payne, prove his point. A Knight Twister will fly with much less than 85 hp, and a low time pilot can handle it.
I will say that a low time pilot should prepare himself better than I. I had only two hours of tailwheel time before flying my airplane, but I also had other advantages that another pilot might not have. I won't pretend to tell you how you should prepare yourself to fly a Knight Twister or any other homebuilt, for I'm not qualified to do so. Besides, only you are the best judge of your abilities, if you're honest with yourself.
Now, what have I tried to say by writing this story? It proves that, with the help of the good Lord, your local EAA Chapter, good friends, and an understanding wife, you too can build your own airplane and fly it successfully, even if it does have a reputation of being very "hot." Only two ingredients are necessary - desire and fortitude.
Right now the sun is shining, the sky is clear, the wind is calm and, if you'll excuse me, this 100 hour pilot is going to go fly his Knight Twister.
| The fuselage of the Knight Twister is seen here covered and ready for the cowlings and final paint. The original landing gear was fashioned from a double leaf crossbar with each leg inserted between the leaves. (Photo by Robert M. Uebel) |