Replace VOR/ILS antenna

[aaronk25]

So the avionic shop called and my coax cable is severed near the control stops in the tail and needs to be replaced.  They have to remove the ugly bath towel holder antenna in order to replace the coax.  As long as the antenna is off, I was considering replacing it with a blade or wire v style antenna.  My avionic shop typically likes to replace it with a belly mount V style antenna, but I don't see this used on Mooneys much, so I think I want to stay away from that, but the shop doesn't know which whip antenna would mount on top of the vertical stabilizer.  Any ideas?

 

The pricing on aircraft spruce for a "blade style" is in excess of $1,000 where the whip is around 280-350.   Thoughts?

Here is what I found

 http://www.aircraftspruce.com/menus/av/antenna_vornav.html

 

[N601RX]

On my F model there is a coax bulkhead connector at the hinge joint of the tail. They should be able to just replace it from there inward or outward depending on which side it is cut on.

[PTK]

It's not a simple antenna replacement with a blade. It requires doublers, skin work and paint. Any reason why not replace the coax? 

[aaronk25]

The severed cable is aft of the bulkhead connector and there isn't enough room in there to fix it so it has to come out though the top and have a new cable installed from the top side.  I think I'll take Allsmiles advice and leave it because of the necessary work involved with switching to the blades.  

[Alan Fox]

It is already set up for the v type antenna , I have the antenna , and the fairing if you are interested in removing the ugly towel bar....

[PTK]

Personally, I don't see much aesthetic difference between the towel bar and the blade. Also I'd be willing to bet the drag delta between the two is imperceptible.

[CoachTom]

I know it might sound simplistic, but why can't the wire at the bulkhead be soldered or spliced onto to a new length of coax and then just pulled up to through the existing track using the old cable as a snake or leader line?  Then you put two new BNC connections on and roll. 

[KSMooniac]

I've got the cat whiskers (V-style) on my '77 J and would love to have the blades as they look better and are much lower drag.  I am not willing to do the labor (or pay for it) yet to switch as it looks like a very difficult job with very limited access.  An alternative might be to mount the blades on the lower tailcone under the h-stab since there is more room to work.

[OR75]

I've got the cat whiskers (V-style) on my '77 J and would love to have the blades as they look better and are much lower drag.  I am not willing to do the labor (or pay for it) yet to switch as it looks like a very difficult job with very limited access.  An alternative might be to mount the blades on the lower tailcone under the h-stab since there is more room to work.

 

 

Need to make sure that nothing is obstructing the line of sight of the antenna on the plane to the emitting antenna on the ground (GS of ILS for example). There is a reason the VOR/ILS/GS antenna is mounted high on the tail. 

 

It is still puzzling why the price of the towel bar is so much higher than the whiskers. Is there a performance difference ?

[OR75]

The severed cable is aft of the bulkhead connector and there isn't enough room in there to fix it so it has to come out though the top and have a new cable installed from the top side.  I think I'll take Allsmiles advice and leave it because of the necessary work involved with switching to the blades.  

 

with the proper tool, crimping a new coax connector does not require a lot of room.

 

Don't think the VOR/ILS/GS are that sensitive to signal loss if two coax cables are used.

[N601RX]

The cat whiskers type have a VSWR of about 1/2 what the blade type and towel bar ones have.  Lower is better.

 

Then again the blades have less drag.   In reality your going to have line of sight and probably not going to see any noticeable RF advantage between the 3.

[KSMooniac]

Need to make sure that nothing is obstructing the line of sight of the antenna on the plane to the emitting antenna on the ground (GS of ILS for example). There is a reason the VOR/ILS/GS antenna is mounted high on the tail. 

 

It is still puzzling why the price of the towel bar is so much higher than the whiskers. Is there a performance difference ?

I would think that a position under the h-stab would be better than up high, performance wise, since the fuselage and wing wouldn't be in the way of a ground signal.  But, I'm a structures guy and not a sparky.  

[Bennett]

If you have the modern wingtips, the blade antennas can be mounted in them, which reduces drag.  I did this in my prior Mooney when I was on a "hide the antennas" quest.  They worked just fine from the wingtip locations. I currently have the towel bars, and I was going to replace them with blades on the vertical stabilizer, but two avionic shops told me that the thin towel bars had less drag than the blades.  Does anyone know if this is true?  

[KSMooniac]

At one time I found drag specs for all of these, but can't seem to find them anymore.  Here is a good discussion from the Beech folks:

 

http://www.csobeech.com/nav-blades.html

 

I know the towel bars are quite draggy.  

[bumper]

The towel bar antennas are quite draggy. But I've discovered they are far worse with towels on them.

 

bumper

[OR75]

I would think that a position under the h-stab would be better than up high, performance wise, since the fuselage and wing wouldn't be in the way of a ground signal.  But, I'm a structures guy and not a sparky.  

 

I don't think I would want my VOR/LOC/GS antenna under the h-stab on an ILS approach

[N201MKTurbo]

I had to replace my cat wisker antenna once because one of the wiskers decided to live in New Mexico. It was a real PITA....

[dcastor]

I would think that a position under the h-stab would be better than up high, performance wise, since the fuselage and wing wouldn't be in the way of a ground signal.  But, I'm a structures guy and not a sparky.  

 

People often think that the localizer used for approach is the one they fly over on short final.  Actually, unless you are flying a "reverse course" the localizer you are using is at the opposite end of the runway.  I imagine that with a nose low attitude, having antennas under the h stab would be at least partially obstructed by the wing and/or main gear. 

[Scott Aviation]

My whiskers coax was snipped by the guy who transported my plane to Canada by truck. Totally unnecessary as there was the bnc quick connect 4" away. That stunt forced me to pull the coax up through the tail, take them to an avionics shop and rebuild the coax length to the whiskers. Ps. I had them add an extra few inches in case it was damaged in the future. One thing to make sure is pull a rope or wire up through the tail with the coax if its removed or you will never get a new cable fished down the vertical stab.

Point being you would be best suited to pull the towel bar out get a new piece of coax for it and put it back together as is.

[tony]

  But, I'm a structures guy and not a sparky.  

 

The proper term is cone head.

[davidsguerra]

would you need an STC to put the VOR recievers in the wingtips? what about to get the blades?

[Bennett]

I believe my avionics shop used regular vertical stabilizer blades, but mounted them inside the wing tips. I seem to recall a lot of grumbling about pulling the coax cables through the wing. It was done at the same time that various antenna were mounted upside down in the fiberglass belly pan to get them out of the air stream. The only one (except the comm antenna) we did not move was the antenna for the stormscope, but that was fairly flat, and location was critical. The old Mod Works in Florida did the work and filed a 337 form.

[FlyWalt]

The towel bar antennas are quite draggy. But I've discovered they are far worse with towels on them.

 

bumper

 

Oh that is just TOO FUNNY !!!!!