Posted Saturday, February 5, 2011 @ 01:26 AM  

Noticed that the trailing link on the main gear had finally passed the 90 degree point, so installed a new set of struts (gas filled shocks) that I purchased from E.I.S. several years ago. The struts were easy to change. It's quite a difference to see the gear at full extension. Will have to be careful the first few flights as there will be a much different sight picture over the nose. With the aircraft more strongly raked, it might reduce the ground roll. Would have been nice to measure before & after -- but I wasn't planning on replacing them.

My com has never transmitted well. Shortly after I bought the glider in '06, I had complaints from a couple of towers that they couldn't hear me well. A local radio shop diagnosed it as a bad antenna & replaced it. But the replacement has never been all that good either. During an electronics upgrade, I installed a new Garmin SL-40 (along with a GTX-327) -- and it didn't seem to be much better. In reading up on antennas, it seems that the ground plane should be at right angles to the antenna and should as big as the antenna is tall. My antenna slopes backward at 30 degrees and the ground plane is both smaller than it should be and curved due to the narrow fuselage.

I got a new antenna from Advanced Aircraft (www.advancedaircraft.com). It seems to be a thin fiberglass tape with a foil antenna inside. The key for me is that it doesn't need a ground plane and can be installed inside a wood or composite aircraft. I found that I can mount it nicely just behind the rear seat, inside the fuselage. Before I installed it, I wanted to see if I could tell if it made any improvement.

Our airport has an automatic wind announcement. Click your mic 3 times and get the current conditions. While inside my metal hangar, I can click the mic with the old antenna and the transmission is not strong enough to trigger the weather response from the airport. With the new antenna (even in a poor position for testing), it worked every time. 4 clicks allows for a radio check and my voice came through loud and clear. So, this antenna has been an excellent addition. (I guess I'll have to work on my communication skills now that people can hear me....)

After I use the new antenna long enough to be convinced there aren't any problems, will probably remove the old external antenna. I might save it to be used with a handheld. But at the moment, I'm thinking that I'd prefer to clean up the outside of the aircraft and just remove it.

Posted Saturday, February 5, 2011 @ 01:08 PM  

I have to confess that I have some old skepticism regarding dipole antennas ever since my Hangglider career. We didn't have a ground plane either, so at one period we used dipole antennas in the harness. They gave great performance at close range, but when you were low and might have to land in a remote, desolated valley in the Italian Alps you obviously wanted to communicate your position before you plunged into that valley with radio shadow and often there was no phones to be found (this was pre-cellphones...), if not else to ensure retrieval. You often found yourself trying to communicate while frantically curving in a weak thermal. Due to the dipole antennas directional transmission, your message would fade out twice every full circle, which made for very confusing and imprecise position reports to say the least....

In other words, make sure you put your dipole antenna vertical, not horisontal as we had to do in our hangglider harnesses. I think Eugenio claims all RF 5 b's had an antenna in the tail originally, and this is the case with SE-UDI too.

May the 4's be with you/ Jörgen

Posted Saturday, February 5, 2011 @ 02:29 PM  

The antenna is about 42" in length. The fuselage just behind the rear seat is about 31" tall.

According to Advanced Aircraft:

The basic orientation for a com antenna should be vertical -- same plane as the propeller -- for best radiation/propagation.

1. You can install the antenna at up to 45 degrees off vertical and still have it work ok. When I did my test, it was probably about 35 degrees -- and still worked better than the original antenna.

2. Another option is to mount as much of it as you can vertically, then let the ends curl over making something of a letter "C". I called the company and explained my situation. The tech recommended a letter C for best performance. The tech said that the ends of the antenna are "fairly quiet." That the main amount of the wave comes more from the center. He said that the 5" or so that are bent at each end would have a negligible impact on performance. (...much less than having a straight antenna at a slope)

You can go through a lot to make custom supports for the antenna out of wood or fiberglass. Yet, I found that if I centered it on a 28" strip of wood, I could mount it just behind the rear seat and the natural spring quality of the fiberglass strip of the antenna pushed it nicely against top and bottom of the fuselage. No flapping. Kept the whole thing as vertical as the fuselage would allow. Later if I see the ends curling at all, I can add a dab of RTV, etc., to help bond it....or even glue on a couple of small blocks that can create a slot that the ends would slide into. But for now, it is good as it is.

Simple. Inexpensive. Seems to take a thorn out of my paw that's been bothering me since '06. Right now....I'm pretty dang happy with it.

If something happens to cool my enthusiasm -- I'll include in a future post. But for now, all seems positive.