EAA SPONSORED BY •

AIRCRAFT SPRUCE & SPECIALTY and JOHN FLUKE MFC. CO., INC.

By WHEELER NORTH EAA 400623 2005 Morena Blvd. San Diego, CA 92110 This device was initially built to set and adjust the blade angle on my GSC ground adjustable propeller. I have since found that it works quite well for setting up just about any other wing or fuselage alignment parameters. It is a piece of wood carved to the necessary shape and dimensions, with a machinist's protractor screwed and glued onto it and two bubble tubes stolen from a cheap bullet level, glued onto the wood and to the protractor as diagrammed. The basic precept is that we don't really care what the value of the number generated is. But we do need a way to reference one part of the plane to another. So what is needed is a constant reference that won't change as we move to take the next measurement. The bubble gives us that constant reference to the approximate center of the earth and if used correctly can be accurate up to 1/3 or better of one degree depending on

how fancy you want to get with the level tubes. For example, in the Kitfox instructions they suggest that one set the first blade to an initial setting. Then they have you go through an elaborate process to set the other blades the same angle. With this device we can set the initial blade setting as described, on a flat surface with a

©

Blade attach resting points

wedge trimmed to the proper angle, inserted between the blade face and the flat surface, at the proper blade station. Next we mount the propeller on the plane and measure the same blade with the protractor. We don't care what the number is, all we care is that we get the other blades to the same number at the same blade station. Then the engine is tested for the correct static rpm and adjusted accordingly. It is very important that the protractor attaches to each blade in the same fashion. I found this was best done by a double hook that reached over the leading edge of the blade with a Vee that was slightly wider than the leading edge cross sectional profile and routed out in the center. It then projects down the face of the blade and touches the blade at one point by means of a raised point at about 2/3 to 3/4 across the blade face, the face is the side that would equal the bottom of a wing. The idea is to have a three point stance on the blade, i.e., the two outer edges of the wood at the Vee hooked on the leading edge and the one point on the face. The length of the protractor mount was made to equal the distance from the blade tip to the suggested blade SPORT AVIATION 83

station for quick reference as each new blade is rotated into position for measuring and adjustment. Although having each blade rotated to the same position for measurement did not turn out to be as critical as I thought it would be, I mounted the second bubble tube across the top, above the Vee hook, parallel to the blade axis, and found that I could position each blade exactly the same. In reading the level tube I have found that most often the bubble is slightly smaller than the two centering lines. By setting one side of the bubble on its respective line and then moving it to position the other side of the bubble on its line, I was approximating 1/3 of a degree of movement. When mounting the level tube

onto the protractor you want to get it as close to 90 degrees as possible but it is not too critical, because we don't care what the numbers actually read, we just care that they are the same, or as in other cases, such as wing washout, that the difference of the two numbers is appropriate. It is important when comparing one part to the next that the aircraft not be moved between measurements. If this occurs, needless to say, start over (where have we all heard that line before). In measuring wings I have found it to sometimes be very difficult to jig the protractor to the wing. Particularly if it calls for a measurement on the top surface of a high wing aircraft. Well, I found that the protractor works just as well upside

down as it does right side up. The most difficult part of using it is to make sure that you are keeping apples with apples between mea- surements. Think it out first. Don't forget, if you cross over the centerline of the scale or, as in the case of mine which has two opposite direction scales, don't switch scales halfway through the reading. You will wonder why your wing doesn't look upside down even though the protractor says it is. If the measurements are given in units of distance, dust off the old Trigonometry calculator, and try to work it out. Or the formula R2 Pi 360 degrees, where the R equals the wing chord or jig attach points, i.e., whatever is called out for as measuring points. This will give you 1 degree = X number of distance.

By SAM THRASHER EAA 82247

the circuit and powering the avionics bus. Power from the now energized avionics bus keeps the relay energized and the circuit closed as long as the master switch is on. When the master switch is turned off, the ground to the relay is broken and the relay returns to the open position. The theory here is that you are more likely to notice that none of your radios work when you need them than you are to notice they've been left on when you don't. The circuit includes a safety bypass in case the relay decides to fly just as you are transiting the Los Angeles TCA.

._. RELAY BYPASS SWITCH SPST ._.

AVIONICS BUS

RELAY&RADIO SHACK I 30 AMP 275-226 -^ PUSHBUTTON SWITCH, MOMENTARY TYPE SPST

5225 Pla Vada Dr. Bakersfield, CA 93306

This layout for an avionics master switch makes it all but impossible to leave the avionics master in the "on" position after shutting the airplane down. The relay (or relays, depending on the configuration used) are open in the nonenergized state, isolating the avionics bus from the aircraft power bus. After engine start, a momentary (PTT) type switch is closed, energizing the relay, closing

Readers are invited to submit entries for the Aircraft Spruce & Specialty Hints For Homebuilders and the John Fluke Mfg. Co., Inc. Electronic Hints columns. Send to EAA, Hints For Homebuilders, Att: Golda Cox, P. O. Box 3086, Oshkosh, Wl 54903-3086.

Entries will be reviewed by a panel of EAA judges. Readers whose hints are published in any EAA magazine will be awarded a $25 gift certificate plus a current catalog from Aircraft Spruce. The winner of the Fluke award will receive a Fluke Model 23-2 Multimeter with Holster. The contest will run from August through July of each year with a Grand Prize of a $250 gift certificate being awarded by Aircraft Spruce. A Grand Prize will also be awarded by the John Fluke Mfg. Co. These awards will be presented during the EAA Convention. We extend our thanks to Aircraft Spruce & Specialty and the John Fluke Mfg. Co. for providing these awards. 84 SEPTEMBER 1992