Newsletter July 1997 Volume 17, Number 7 Chapter 724, Experimental Aircraft Association Merritt Island, Florida Mailing address: P. O. Box 320923, Cocoa Beach, FL 32931 Internet Web Site: http://www.BeginAt.com/EAA724 Officers Technical Counselors President: John Murphy 783-1515 Ted Yon 783-7966 Vice President: Eric Kennard 631-3264 John Murphy 783-1515 Secretary/Treasurer: John Soukup 783-7128 Young Eagle Coordinator Newsletter Editor: Fred Mahan 452-5797 Tony Yacono 459-0080 The next meeting will be the second Wednesday of July July 9, 1997, 7:30 P. M. Big Merritt Island Air Service Hangar, South Side of Runway Second Floor, Southwest Corner Meeting Room ______________________________________________________________________________ EAA Chapter 724 P. O. Box 320923 Cocoa Beach, FL 32931 Calendar of Events Jul 5-6 Homestead General Airport, UL Chapter 103 Air Fair, 305-460-3356, cduenas@aol.com. Jul 12 Crystal River Airport, 1997 Annual Bomb Drop & Spot Landing Contest, 352-795-6868. Jul 30 - Aug 5 Oshkosh, WI, 45th EAA Annual Fly- In, 414-426-4800, http://www.eaa.org/ Oct 11-12 Plant City, EAA Chapter 1178 Annual Strawberry Aircraft & Auto Show, 1-800-760-2315. Apr 19-25, 1998 Sun 'n Fun. Regularly Scheduled EAA Fly-Ins Across Florida Every First Saturday, Cannon Creek Airpark, Lake City, Fly-In Breakfast, 904-755-4760 Every Second Saturday, Charlotte County Airport, Punta Gorda, EAA Chapter 565 Pancake Breakfast, 813-627-6461. Every Third Saturday, Sebring Airport, EAA Chapter 803 Pancake Breakfast, 941-465-6996. Every First Sunday, Ft. Myers Airport, Chapter 66 Pancake Breakfast, 941-945-7000. Every Second Sunday, Naples Airport, EAA Chapter 1067 Fly-In Breakfast, 941-261-5701. Every Third Sunday, Kissimmee Municipal Airport, west side of the field, 9 am on. Every Fourth Sunday, Bob Lee Airport, De Land, EAA Chapter 635 Fly-In Picnic, 904-734-1032. Every Last Sunday, Quincy, FL, EAA Chapter 445 Pancake Breakfast, 904-421-4335. __________________________________________ June Chapter Meeting At the chapter meeting on June 11, __________________________________________ Valkaria Airport Don't forget the County commission meeting on Valkaria's runway 09-27. Be there and be heard. For information, call Mark Cannon at the Valkaria Aviation Association at 407-724-8671, or contact the Valkaria Aviation Association by e-mail at airport@iu.net, for the latest developments. _________________________________________ _________________________________________ Chapter Internet Site Did you know that Chapter 724 has an Internet Web Site, set up by chapter member and on-line impresario Ron Cadby? And an E-mail address (which forwards your note to your newsletter editor -- me)? And that your newsletter editor got it wrong last month? The site has an archive of past Chapter 724 newsletters going back to January 1996. It also has free classified ad posting for chapter members. The address for the Chapter 724 Web Site is: http://www.BeginAt.com/EAA724 Go have a look. Suggestions for other information to post on the site are welcome. You can contact Ron at his E-mail address at: rcadby@BeginAt.com _________________________________________ Alternator Whine By Cy Galley, Bellanca-Champion Newsletter You mean that there is still a whine in your ear phones even when the strobes are off? If that is the case, it might well be alternator-induced radio noise. Here's how to identify alternator and regulator noise, what causes it, and how to get rid of it. If the radio noise is a high pitched whine whose pitch and intensity increases and decreases with changes in engine speed, then it could be your alternator. If you have an alternator master switch, turning it off will also turn off the whine in the radio. On the other hand, solid state regulators that use a pulse-width-modulated field control system might also create a whine in the radios. Regulator caused whine can be distinguished from the alternator-caused whine in that the intensity and pitch of regulator-induced noise changes with changing current load at a constant engine speed. Thus, if turning on the landing lights increases the whine, then it is the regulator, not the alternator. Current generated in a generator or alternator is alternating current. In a generator, the brushes mechanically convert it into DC, but diodes in an alternator convert it from AC to DC. Six diodes are required to rectify the 3-phase output. Each of the three stator windings is connected to a pair of diodes. Three diodes are connected to the positive output terminal of the alternator, and the other three are connected to the negative (ground) terminal. This produces a DC voltage with a slight amount of AC ripple voltage. Normally, there is not enough ripple voltage to cause radio noise. But, there are two conditions that can cause an increase in ripple voltage sufficient to create radio noise. These are diode failure and increased circuit impedance. When an alternator diode fails, the amount of ripple voltage increases markedly. Therefore, alternator whine can be a symptom of one or more bad alternator diodes. Almost any automotive alternator tester can be used. You can also use an oscilloscope to check the alternator output for excessive voltage ripple or rectifier spikes caused by a bad diode. Once you know that there is a bad diode, you can find it by disassembly by using a VOM set to measure ohms. Check to see that each diode conducts in only one direction. You will need to isolate each diode by unsoldering the stator leads from each diode. Each bank of three diodes should have a small resistance of about 6 to 20 ohms resistance in one direction but infinite resistance in the other direction. Since one is the positive bank and the other negative, each will be opposite of the other bank. When you find a diode that has low resistance in both directions it is shorted and needs replacement. On the other hand, if you find infinite resistance in both directions, it is burned out and likewise needs replacement. Alternator whine can also be caused by poor electrical connections, especially at the battery. Normally, the low impedance of the battery keeps the aircraft's electrical circuits at a DC potential. (Impedence is simply resistance to an AC current.) Any AC ripple voltage in the aircraft bus is absorbed by the battery. Thus, the aircraft battery asts as a big ripple absorber. If the battery provided zero impedance (i.e., a short-circuit for AC current), alternator noise could not occur. In the real world, there will always be some impedance. But the lower it is, the less ripple voltage there will be. Let's assume that the battery positive terminal is corroded. Although DC resistance as measured with an ohmmeter may still be low, the high-frequency resistance (i.e., impedence) may be very high. The higher this impedence, the greater ripple voltage on the bus and the more whine you hear in your radios. Circuit impedence can be lowered by making sure the battery posts are clean and making good contact. DC resistance should be less than 0.01 ohm … virtually zero. Also check the alternator ground connections, including the engine grounding strap. DC resistance between the alternator and the negative post of the battery terminal should be as low as possible. This will also make it easier to start your engine. Flat braided ground straps are ideal for grounding the airframe _________________________________________ For Sale New King KX-155 Navcomm with KI-209 head. 760 channel com, 200 channel nav with glideslope, built in audio amplifier and intercom, 14 volts. Meets latest specifications. 10-watt signal output. In original box, unopened. Complete kit lists for $4750. Sell for $3300. Call 407-267-5683. Telex PC-2 portable 2-place high-tech intercom. Used 1 month. Lists new for $265, sell for only $200. Call 407-267-5683. King KR-86 ADF with tray, with KA-42B antenna. Both just checked and yellow-tagged by Sebastian Communication. $1200. Call Fred at 407-452-5797 or e-mail at: mahan@digital.net Items from Jerry Rooks's "Contact" Sporty's A300 hand held radio, $150; new ACK ELT, $150, 914-473-9502 (NY). Banty ultralight project, never completed, includes Rotax 277 and most items necessary to finish, $1200, 813-856-6123 (FL) Home on Little River Airport runway, north central Florida, 3BR, 2 BA, 40 X 40 hangar. 904-963-1110 __________________________________________ 2 3