Aircraft of the EAA Air Museum Collection Prototype
(From Sport Aviation, 05/1981, Page 22)
By Fred B. Kacena
Photography by Jack Cox
By Fred B. Kacena (EAA 22880), 206 W. Park Place, Newark, DE 19711
Next to his first great love, the famous P-51, was his Knight Twister, N3TL, “Chutzpah.”
The late Col. Thomas MacAdoo Love had a growing love affair with his Knight Twister. It first came into the Maryland Eastern Shore area in the fall of 1974. Tom called the GADO for an appointment to have the little bird recertified. This was the beginning of my association with Tom and “Chutzpah.”
From that day on a continuous program of improvement to the Twister was started. As a trained engineer, Texas A & M, and West Point and thirty years as a combat pilot, Tom approached each improvement with true scientific analysis and each modification was given a test pilot’s proof.
Directional stability on the ground was the first item. This aircraft was just plain squirrely, so a new Scott tail wheel was fitted and the angle of the tail wheel leaf spring was changed. This proved a help but more improvement was needed. So new landing gear wheels were fitted, the floating disc brake wheels were discarded and Cleveland wheels and brakes installed with careful alignment of the toe in and camber angles. After a series of test take-off’s and landings, a true roll out was achieved.
Another problem became apparent: cylinder head temperature. The fish gill air exits on the cowling were being deflected closed in flight by slipstream pressure. “Z” clip spacers were riveted in place to hold the “gills” open. The head and oil temperatures made a noticeable drop, but still remained on the high side.
On the next recertification inspection I pointed out to Tom that the cooling baffles were not making a tight seal against the engine cowling and no intercylinder baffles were installed on the engine. So Tom made and installed new baffles, but the high temperatures had done their damage and a top overhaul was in order. With this accomplished, the engine performed beautifully.
But Tom loved speed and he was not satisfied with “Chutzpah’s” get-up-and-go! He felt things could be done to improve its speed without major alterations.
A general eyeballing for obvious drag generators was made. A large flat plate area above the carburetor airscoop was filleted in with a sharp leading edge. This was formed of foam and fiber glass and faired into the bottom cowling. Flight testing showed a 7 mph jump in cruising speed.
A word about the speed tests. Tom had located two large navigation buoys in the Chesapeake Bay that were exactly three miles apart. Speed runs were made in both directions between the buoys. Incidentally, this speed course was located just five miles south of the speed course where Jimmie Doolittle won the Schneider Trophy in 1925.
Next, the ailerons had large trim tabs that were bent at nearly 90° to the line of flight. Something was obviously wrong here. The ailerons were rerigged with a minor improvement, but the lower wings needed the wash in and wash out changed. Shimming of the attachment bolts improved this and another increase in speed resulted.
As these improvements were going on, a few creature comforts were also added — padding and upholstering, a rebuilt instrument panel and additional instruments, also a Nav-Com radio and OBS.
During the course of flying, Tom remarked the Twister became increasingly nose heavy as the cruising speed moved up. I suggested that he change the angle of incidence on the stabilizer. He considered doing this, but it would have entailed considerable changes in stabilizer attachment fittings and the tail fairings. Tom also noticed that the slipstream over the cockpit caused his helmet to lift off his head with an annoying constant tug on the chin strap. Tom felt that the bubble shaped windshield was generating lift over the top of the fuselage, so a new windshield design was developed, using racing car shapes that split the airflow to either side rather than deflecting it upward. The new windshield shape relieved the lift situation and improved the vertical stability.
Now he went back to improving the speed performance. New wheel pants and landing gear fairings were installed, speed runs were made with wool tufts installed (the engineer’s approach). Adjustments were made in alignment to achieve a smooth airflow and minimum drag. Again speeds crept upward.
During these flights a turbulence was noticed in the lower wing root area, so Tom tufted the top surface of the lower wings. Airflow at the fuselage wing juncture was poor and at landing approach speeds the lower wings were stalling for two feet out from the fuselage. New wing-to-fuselage fillet fairings were developed. The original Delta fairings were removed and concave contoured fiber glass fillet fairings installed. After the final shape had been determined flight tests showed the unwanted stall pattern was eliminated giving, in effect, six to eight square feet more lifting wing area. Tom stated he could reduce the approach speeds by 10 mph with good, all around control and slower landing speed. Flying out of the Baybridge, Maryland Airport, with the Chesapeake Bay on the prevailing wind end of the runway, Tom said, “With the lower landing and take off speeds, I won’t worry so much about a bath in the bay.”
Summer was here so “Chutzpah’s” development work stopped while Tom was very busy teaching aerobatics. Home base for the tiny biplane was moved to Easton, Maryland and plans were formulated for further improvements.
I visited Tom’s hangar several times during the summer and winter and saw more things in the works for the Twister. Tom had checked the contour and pitch of the metal propeller. He was surprised to find the maximum thickness of the propeller airfoil was just 5 percent back of the leading edge. He reasoned that this could not be of maximum efficiency. So he went to work recontouring the airfoil of the blades, moving the maximum thickness back to 20 percent of the chord. The process of altering the contour of the propeller was a real challenge to Tom’s craftsmanship, largely in maintaining the proper shape and balance. In addition, the blade tips were formed into the Hoerner contour. I was concerned about the effect all this would have on the loading of the engine. Tom assured me that the static rpm of the engine made little change but the take off and climb performances were remarkable and the top indicated airspeed went up another 12 mph. “Chutzpah” could really move!
Tom felt that a more efficient engine cowling and exhaust system was in order, with an eye to smoother airflow around the fuselage where the cooling air left the engine cowling and better scavenging by the exhaust system.
Four days before his death Tom had told me when the cowling and exhaust systems were completed he was going to install fairings on all the wing struts and the tail wheel. These were never accomplished and “Chutzpah” resides in the EAA Museum, a monument to a man’s love of flying.
(Photo by Jack Cox) Chutzpah, a Knight Twister donated to the EAA Air Museum by the family of Colonel Thomas M. Love.