[NSRCA-discussion] RF Interference

Tue Nov 7 14:26:03 AKST 2006

Two questions:

How old was the switch? I had a bad swich put in an Ultimate bipe and my Prophecy. Took an oscilloscope to prove that vibration was causing it cut in and out.

You want another Javelin? I'm selling mine.
  ----- Original Message ----- 
  From: george w. kennie 
  To: NSRCA Mailing List 
  Sent: Tuesday, November 07, 2006 2:29
  Subject: [NSRCA-discussion] RF Interference

  Hey Guys,
  Looking for some input here regarding RF interference. 
  I lost Javelin number 3 this morning which I had been having glitching problems with for over a month. 
  Originally I had been flying the plane with an OS-70 surpass II , but when the motor lost performance I decided to go for a little more oomph and installed a Saito 91 which was actually 2 oz. lighter. The Saito drove me nuts 'til I finally figured out the Low speed needle and then I became very satisfied with the extra performance. The next performance improvement I decided on was to replace the wing mounted gear which was prone to bending even on greasy landings, so I picked up a set of carbon-fiber gear (one piece) and bolted the unit to the bottom of the fuse just ahead of the wing which solved all the ground handling problems and also gave extra prop clearance. Now these two mods were executed about the same time and subsequently I started to experience glitching problems. When it first manifested itself it was in the nature of the throttle servo pulsing intermettently on the ground during warm-up and then it would smooth out and I would take off and fly and it would seem O.K.  Feeling uncomfortable with this condition I decided that I must have some metal to metal contact somewhere. Due to the fact that the 91 shaft was longer than the 70 I was forced to push the engine back all the way in the engine mount and I thought the carb might be contacting one of the bolt heads holding the mount to the firewall. Well, I corrected that problem only to find at my next outing that I still had Intermittent throttle pulsing. Back to the drawing board, I next decided that the receiver was suspect as it had been through a previous incident, so I installed a different receiver. Next time out the plane flew like a charm and I had about 4 outings with  no glitches and then on my 5th outing I got a resumption of the throttle pulsing ( actually, all servos were jittering, but the throttle audibly let you know it). I actually flew some flights like this and would experience serious glitches on the same maneuver in the same position within the maneuver repeatedly. It also seemed to be vibration related as I found that when I shut off the motor in flight the glitching would cease. Then I decided that the wiper on the throttle servo might be bouncing on the surface of the resistive element and giving me spurious signals within the system, so I decided to change out the throttle servo. In the process of disconnecting the throttle servo from the receiver I had inadvertently left  the receiver ON and when I lifted the receiver things started jittering,.......aha, pulling on the antenna wire was giving me spastics !   O.K., got ya, ya buggar! Spun out to the LHS and picked up a new antenna and figure VOILA home free ( with a little knawing feeling of wonder about why did the first receiver do the same thing? Do I have two receivers with broken antennas, after all I have strain reliefs on these things hmmmmm ???) 
  Well I show up at the field today with the new throttle servo and new antenna and start the engine which purrs like a kitten with no pulsing. GOTCHA !  Taxi out to the center of the runway, switch to low rates and feed it the oysters. Beautiful long low gradual climb out to 5 ft wherupon the right wing goes to KE position (L to R take-off), I slam in full left aileron and left rudder and it didn't budge as the nose came down and the right wing made contact with terra firma Pogoing the thing to oblivion.
  I had to go get petrol, and as I'm driving I'm doing the Sherlock thing, thinking, the only thing I changed is the motor and then It hit me! Holy Smoke, I put carbon fiber gear on that buggar.Could I be getting some kind of reflections from that thing to the antenna?? After all, The symptoms are identical to the symptoms that occurred when the antenna was broken.
  So you can see what my question is here. Has anyone experienced any kind of interference caused by using carbon fiber gear? I remember some of the guys with carbon reinforced fuses talked about how they had to run the antenna outside of the fuse. Also the Javelin has that chrome monokote under the transparent blue and I've heard about that causing potential interference, but I have had two previous Javelins with the antenna run the same way ( on the outside of the bottom of the fuse) With no interference problems and many many flights.
  What ch'all think?  Ed Alt?  Any of you electronic gurus?
  Georgie 

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