Transponder antenna - blade vs stub monopole

Any aerodynamic thoughts on the two available choices?

My ASH-26E came with the stub mounted just behind the wheel. Every
now and then it catches on the trailer, so I just straighten it, no
big deal.

An ASW-24B in our club is about to get a transponder and the factory
recommends the installation to be part way up around the fuselage
above the rear gear door hinge - looks like just behind the oxygen
bottle.

The blade looks cool, but is it really any better aerodynamically than
a $20 (http://www.aircraftspruce.com/catalog/avpages/
ted_transponder.php) stub?

-Tom

Hi Tom,

I prefer the "shark fin" blade, and not just because I sell them and they
are more expensive.

I'm not an expert, but I do remember my Fluid Dynamics classes at Purdue
University in which they stated that 2 of the worst shapes in regard to drag
are the sphere and the round rod - which is exactly what the rod style
antennas are. However, the shark fin antenna has a lot more surface area -
so it is not clear that the shark fine is dramatically better - but it is
probably a little better.

I also think the shark fin antennas look cool (as you mentioned below).

I imagine the shark fin antennas are more robust and would handle trailer
bangs better, but I wonder whether they would chip or be damaged by a hit to
the trailer.

I'm amazed by the low price you found below from Aircraft Spruce on the rod
style antenna. I wonder why the Comant brand I buy is so much more
expensive? The Comant antennas are very nice but they have gone up in price
dramatically over the last year or so - much more than the drop in the US
dollar would account for. I wonder if the low cost units that "meet the
same specifications" are approved for use in certificated aircraft. If they
are then I should sell them. So far, I've been very hesitant to sell what I
would consider "low cost copies" of aircraft parts. I would never want a
customer to come back to me and tell me I'm selling items that should not be
used in certificated aircraft.

Good Soaring,

Paul Remde
Cumulus Soaring, Inc.
http://www.cumulus-soaring.com


"5Z" wrote in message
...
Any aerodynamic thoughts on the two available choices?

My ASH-26E came with the stub mounted just behind the wheel. Every
now and then it catches on the trailer, so I just straighten it, no
big deal.

An ASW-24B in our club is about to get a transponder and the factory
recommends the installation to be part way up around the fuselage
above the rear gear door hinge - looks like just behind the oxygen
bottle.

The blade looks cool, but is it really any better aerodynamically than
a $20 (http://www.aircraftspruce.com/catalo...ransponder.php)
stub?

-Tom

At 17:50 13 June 2008, Paul Remde wrote:
I prefer the "shark fin" blade,
"5Z" wrote in message
My ASH-26E came with the stub mounted just behind the wheel. Every

What about the "transflex" antenna?

http://www.lxavionics.co.uk/transponders.htm

This seems to have the least drag.

Rory

What about the transflex antenna?

http://www.lxavionics.co.uk/transponders.htm

Rory

Is there a downside to mounting on a ground plane inside the fuselage
of a non-carbon glass glider?

Hi,

I was thinking the same thing. I believe that a ground plane would be
useless inside a carbon fiber glider. However, the same is true for any
other type of transponder antenna. They all should have a good ground
plane.

Paul Remde

"brianDG303" wrote in message
...
Is there a downside to mounting on a ground plane inside the fuselage
of a non-carbon glass glider?

I strongly suggest you DO NOT but the blade antenna's!....
ever if there were some small aerodynamic advantage (I doubt it could be
measured at any glider speeds anyway) but these are very expensive and they
are easily damaged....
I offer blade antennas, the "preferred" simple and cheap stub antenna's and
the composite dipole antenna's..I've had several buyers of the blade
antenna's break them (they aren't typically very happy when this happens).it
doesn't take much effort to damage the composite blade antennas since they
are essentially a tiny wire on a thin metal plate with small (6/32) screws
in a very nice looking shark fin that is mostly filler (putty) with a thin
composite shell..
best regards
Tim
Please visit the Wings & Wheels website at www.wingsandwheels.com

"5Z" wrote in message
...
Any aerodynamic thoughts on the two available choices?

My ASH-26E came with the stub mounted just behind the wheel. Every
now and then it catches on the trailer, so I just straighten it, no
big deal.

An ASW-24B in our club is about to get a transponder and the factory
recommends the installation to be part way up around the fuselage
above the rear gear door hinge - looks like just behind the oxygen
bottle.

The blade looks cool, but is it really any better aerodynamically than
a $20 (http://www.aircraftspruce.com/catalog/avpages/
ted_transponder.php) stub?

-Tom

Not all transponder antennas need a ground plane, only monopoles do. I
use the L-2 dipole antenna on this page: http://www.advancedaircraft.com/
inside my fiberglass ASW-19 tail cone. It works great with my Becker
ATC 4401-175 and was very easy to install.

-John

Paul Remde wrote:
Hi,

I was thinking the same thing. I believe that a ground plane would be
useless inside a carbon fiber glider. However, the same is true for any
other type of transponder antenna. They all should have a good ground
plane.

Paul Remde

"brianDG303" wrote in message
...
Is there a downside to mounting on a ground plane inside the fuselage
of a non-carbon glass glider?

On Jun 13, 1:08*pm, "Paul Remde" wrote:
Hi,

I was thinking the same thing. *I believe that a ground plane would be
useless inside a carbon fiber glider. *However, the same is true for any
other type of transponder antenna. *They all should have a good ground
plane.

Paul Remde

"brianDG303" wrote in message

...

Is there a downside to mounting on a ground plane inside the fuselage
of a non-carbon glass glider?

Antenna vendors or glider manufactuers will often want you to back the
carbon fiber fuselage where the antenna is mounted with an adhesive
aluminum foil or thin plate - mostly for purposes of good contact with
the outer (ground) parts of the antenna. Follow the glider
manufacturer and antenna vendors instructions. Schleicher certainly
show such a plate used on the ASH-26E. They also specify a rod
transponder antenna. No idea why. Maybe easier to physically mount (no
concerns about surface curvature, etc.). Personally I'll eat my hat if
anybody could ever measure the drag difference between a rod and
streamlined antenna.

Darryl

Darryl


Darryl

In article brianDG303 writes:
Is there a downside to mounting on a ground plane inside the fuselage
of a non-carbon glass glider?

Since the ground plane should extend at least 23 inches in each
direction around the antenna, it is probably hard to get that inside
the glider.

One that extends front and back but is more limited to the sides
(perhaps wrapping around inside) probably would work, but would be
a bit reduced from a full ground plane.

Alan