Quit Stalling) f (Prepared for SPORT AVIATION by Safe Flight Instrument Corp. of White Plains, N.Y.)

Ihis pilot depended upon the "seat of pants" to guard against accidental N THE EARLY days of flying, a

spins and stalls. Unfortunately, this was not always very reliable, and as the number of airplane owners increased the number of stall and spin accidents multiplied. Of course, some airplanes possess adequate natural stall-warning characteristics, but the majority do not. It could cost a prohibitive amount of time and money for a manufacturer to build such features into a specific airplane and, in the end, the airplane's performance capabilities might be reduced. To circumvent this expensive problem, most aircraft manufacturers around the world now include Safe Flight's Pre-Stall Warning System as standard equipment on their various models. Since first introduced in 1948, when 15.27 percent of all accidents resulted from stalls and spins, about 80,000 systems have been installed on light airplanes. Not surprisingly, the percentage of accidents directly attributable to stalls and spins declined. A more sophisticated system may be found on many of today's turbo-prop and jet airliners and military aircraft. Basically, the system consists of two components: (1) a horn and light warning unit in the instrument panel which is actuated by (2) a small metal tab protruding from the

Fig. 2

Horn and light warning unit

leading edge of the wing. The tab is connected to a lift detector enclosed inside the wing, Fig. 1. When the plane slows to within five to ten miles per hour of stalling, the metal tab actuates the warning unit in the instrument panel, Fig. 2, thus providing plenty of warning of the ap-

Fig. 4

Air-flow over and under wing

type of maneuver being performed. Its operation is based on the aerodynamic fact that a wing cuts through the air so that some of the air passes above the wing and some passes below. In passing over the leading edge of the wing, the air flow actuates the tab or vanes of the wing unit. Fig. 4A shows the wing in normal flight. The enlarged area illustrates how the air flow depresses the vane, thus keeping open the electric circuit to the horn and light warning unit. Fig. 4B shows how the separation point of air passing above and below the

Fig. 3

Control column or stick-shaker

The red light and

the pilot ample warning to increase

raucous horn are very effective, and their warning cannot be ignored in

preaching stall.

The Safe Flight Indicator warns

his airspeed, to lower the nose, or both. Thus set, the system will operate with the same margin of warning in steep turns, landing approaches, climbs after take-off, or from any other attitude of the airplane. Fig. 5 illustrates that the system

of an impending stall regardless of

is designed to operate on a 6, 12 or

the attitude of the airplane or the

(Continued on bottom of next page)

a closed cabin. For airplanes with open cockpits, a control-column or

stick shaker is substituted for the horn and light. Fig. 1

Lift detector

wing moves downward

when the airplane approaches a stall. The air flow then pushes the tab or vane forward as a stall approaches. This action closes the electric circuit and actuates the warning device. The installation of the vane can be adjusted so that the warning of an impending stall occurs at a point between five to ten mph above the critical speed at which the plane will stall or spin. This margin gives

SPORT AVIATION

33

AUTOBIOGRAPHY OF A JODEL . . .

(Continued from page 32)

well for it in the fuselage bottom is really a snap. Four

bolts! That's all. The original gear design on the Jodel is a rather difficult piece of construction composed of a streamlined

piece of steel, requiring considerable machining and rather critical welding. Moreover, the gear is quite narrow, about five and one half ft., which was felt to be too narrow. So, it was decided to change it and to rig on a Cessna 140 gear. This we did by constructing a clamp-on arrangement around the spar about eight in. wide to distribute the landing loads. After several hours of running it over my own rough strip on taxi runs, slow and fast, and lift-offs, it is still holding fast, and is one of the softest gears I've ever flown. By the way, as one can observe in the photos, the spread on the gear is now 9 ft., 3 in., giving the ship terrific longitudinal stability on the ground on landing roll out. One other change in the basic ship was made, namely changing the rocking central stick control. I didn't like this arrangement, so a dual wheel type control was substituted. The arrangement clears up the floor space well and makes for easier getting in and out of the ship. To cut a long story short, the weight and balance data brought the empty weight center of gravity right to the posterior limit which worked out fine. It allowed me io put on a metal prop, generator, and battery, and later the installation of a good radio. Like all other amateur builders, I plan to make some improvements of course: things like a cowling over the stabilizer, wheel fairings, and two

QUIT STALLING . . .

small wing tanks for extra range when the 50 hour test period is over. The final inspection was accomplished on November 20 and the airworthiness certificate issued. The necessary registration and flight test area designation already had become an accomplished fact about two weeks prior. I want to get in a plug for the FAA men in the RaleighDurham area, and in particular Alien Roth who made repeated trips out to my place to go over the ship with me during its construction stages, and who helped me expedite the paper work with amazing promptness. He had many excellent suggestions along the way which were heartily appreciated. He was one fellow I never had to wait on, and I know how busy a guy he is. The first flight went off on a beautiful Sunday afternoon, November 24, 1963 at 3 p.m. After Tri-Pacers and Aeroncas, this ship felt like it went up like a skyrocket, actually lifting off in about 300 ft. and climbing out at close to 1,000 fpm. It was soon discovered that the airspeed indicator was out of whack and the first flights that day were strictly by the seat of the pants! The stall however, is soft, with excellent control all through it, and on through the landing roll. The rudder needs a fixed tab, however, to counteract the torque at cruising speed. Visibility in the Jodel is really panoramic with the full canopy of plexiglas. All in all I stayed up 45 min. that first day and shot several landings. Such is the brief autobiography of a Jodel D-ll. It has been a rewarding and tremendously educating experience and I am looking forward to many an hour of fun in flying the ship. %

PANEL UNIT WING UNIT

(Continued from preceding page)

24-volt electrical system. The installation of the lift detector on the leading edge of the wing requires a hole only 1 x IVa in.

This hole is

covered by a plate through which the vane protrudes. The FAA-approved installation is quite simple and should take no more than two to four hours. Flight-testing is normally completed after two short flights. Not only is the system an aid during all normal flying conditions, but it helps to prevent accidents caused by performing reckless maneuvers. Take the case of the show-off who thinks more of impressing his girl friend than of his own hide. He flies over her house at a low altitude, and then with an eye on a tree or a water tower, or both, he pulls the airplane around in a tight turn. By using too much rudder or stick pressure, he is simply hastening the approach of a stall. The system

might not discourage the culprit from

trying such a dangerous maneuver,

but the red light and the sound of 34

MAY 1965

MOMENTARY DISCONNECT . .

SWITCH (OPTIONAL)

5 AMP. FUSE • T

!_' _L 'J

T

MASTER SWITCH

T STORAGE BATTERY OR 6V. DRY CELL LANTERN BAT.(S)

Fig. 5

Wiring Diagram

the warning horn or the vibration

of

a stick-shaker might save him

from a stall and the inevitable crash. In taking off in gusty air, or if you have a tendency to pull the plane off sharply, the stall-warning indicator on the panel, like the lighthouse that juts out of a treacherous

stretch of sea, stands ready to provide its friendly warning. Since the system with a horn and light warning unit costs only S64.50 (slightly higher with the controlshaker), you really can't afford to fly without it, even if you are a good pilot! *