Antenna Install in a Metal Glider

[Markus Graeber]

Happy Easter everyone! We have a IS-28B2 Twin Lark which we use quite a bit for instruction, it is good for spinning and intro into flying complex gliders (flaps & retractable gear). It is due for a complete overhaul which will include a new radio with a repeater control unit in the back for the instructor.

Since we´ll then be re-working the whole radio install anyway I have been considering doing something about the dragmaster factory radio antenna that looks more like a car antenna installed ontop of the fuselage tail boom. For you experts out there what would be your recommendation for an interior radio antenna install (or a low drag exterior install) in an all metal glider like the Twin Lark?

Many thanks in advance,

Markus Graeber
Aeroclub de Colombia

[Evan Ludeman[_4_]]

On Apr 8, 9:12*am, Markus Graeber > wrote:
> Happy Easter everyone! We have a IS-28B2 Twin Lark which we use quite a bit for instruction, it is good for spinning and intro into flying complex gliders (flaps & retractable gear). It is due for a complete overhaul which will include a new radio with a repeater control unit in the back for the instructor.
>
> Since we´ll then be re-working the whole radio install anyway I have been considering doing something about the dragmaster factory radio antenna that looks more like a car antenna installed ontop of the fuselage tail boom.. For you experts out there what would be your recommendation for an interior radio antenna install (or a low drag exterior install) in an all metal glider like the Twin Lark?
>
> Many thanks in advance,
>
> Markus Graeber
> Aeroclub de Colombia

Partial solution: 90 deg bent whip http://store.wagaero.com/product_info.php?products_id=459

Depending on the material your current antenna is made from, you might
try a tubing bender.

The radiated power from a whip antenna comes disproportionately from
the "bottom" quarter, which is why this works. It's still ugly, but
the drag is much lower.

T8

[Markus Graeber]

I probably should mention for those that are not familiar with the Twin Lark that it is all metal but does have a fiberglass turtle deck and a fiberglass nose and tail cone.

Markus

[Paul Remde]

Hi Markus,

I recommend this one.
http://www.cumulus-soaring.com/rami.htm#AV-534

I had one of them on my Schweizer 1-35C. It worked great. I had it mounted
on the fuselage behind the turtle deck. The fuselage acted as a nice ground
plane.

For a metal sailplane there is no way to mount a radio antenna internally
and get good performance. And there aren't any available low drag radio
antennas that I'm aware of.

Best Regards,

Paul Remde
Cumulus Soaring, Inc.
_____________________
"Markus Graeber" > wrote in message
news:28640239.2914.1333890736652.JavaMail.geo-discussion-forums@ynmc17...
Happy Easter everyone! We have a IS-28B2 Twin Lark which we use quite a bit
for instruction, it is good for spinning and intro into flying complex
gliders (flaps & retractable gear). It is due for a complete overhaul which
will include a new radio with a repeater control unit in the back for the
instructor.

Since we´ll then be re-working the whole radio install anyway I have been
considering doing something about the dragmaster factory radio antenna that
looks more like a car antenna installed ontop of the fuselage tail boom. For
you experts out there what would be your recommendation for an interior
radio antenna install (or a low drag exterior install) in an all metal
glider like the Twin Lark?

Many thanks in advance,

Markus Graeber
Aeroclub de Colombia

[Bob Kuykendall]

Once upon a time, I tried many different com antennas on an HP-18, an
all-metal sailplane with fiberglass nose and turtledeck. The most
effective antenna was a bent 1/4-wave whip mounted over the aft
fuselage.

For the HP-24, I install a 1/4-wave dipole inside the rudder, but that
is not a realistic possibility for the Lark.

Thanks, Bob K.

[Markus Graeber]

On Sunday, April 8, 2012 11:04:13 PM UTC+2, Bob Kuykendall wrote:
> Once upon a time, I tried many different com antennas on an HP-18, an
> all-metal sailplane with fiberglass nose and turtledeck. The most
> effective antenna was a bent 1/4-wave whip mounted over the aft
> fuselage.
>
> For the HP-24, I install a 1/4-wave dipole inside the rudder, but that
> is not a realistic possibility for the Lark.
>
> Thanks, Bob K.

Thanks Bob, I was actually thinking about the possibility of installing the antenna in the rudder since it has fabric cover. The other more extreme option could be to replace the vertical stabilizer leading edge aluminum panels with fiber glass but that might have some structural side effects and I am not sure how much aluminum ribbing will affect an 1/4 wave antenna install.

Certification wise it's not a problem since gliders are treated here similar to experimentals in the US...

Markus

[Wayne Paul]

Markus,

The antenna recommended by Paul Remde, or similar antenna, mounted on the
top of the fuselage aft of the cockpit will provide excellent radio
communication.

I really think that you overly concerned about the minimal drag produced by
an externally mounted antenna on your Lark. Granted the antenna produces
drag; however, on a gliders with similar polars to the Lark the performance
differences is undetectable. The only reason to hide your antenna is that
the Lark looks sleeker without it mounted on the top of the fuselage.

Wayne


"Markus Graeber" wrote in message
news:15119856.896.1333962866197.JavaMail.geo-discussion-forums@yncd8...

On Sunday, April 8, 2012 11:04:13 PM UTC+2, Bob Kuykendall wrote:
> Once upon a time, I tried many different com antennas on an HP-18, an
> all-metal sailplane with fiberglass nose and turtledeck. The most
> effective antenna was a bent 1/4-wave whip mounted over the aft
> fuselage.
>
> For the HP-24, I install a 1/4-wave dipole inside the rudder, but that
> is not a realistic possibility for the Lark.
>
> Thanks, Bob K.

Thanks Bob, I was actually thinking about the possibility of installing the
antenna in the rudder since it has fabric cover. The other more extreme
option could be to replace the vertical stabilizer leading edge aluminum
panels with fiber glass but that might have some structural side effects and
I am not sure how much aluminum ribbing will affect an 1/4 wave antenna
install.

Certification wise it's not a problem since gliders are treated here similar
to experimentals in the US...

Markus

[bumper[_4_]]

On Apr 9, 6:41*am, "Wayne Paul" > wrote:
> Markus,
>
> The antenna recommended by Paul Remde, or similar antenna, mounted on the
> top of the fuselage aft of the cockpit will provide excellent radio
> communication.
>
> I really think that you overly concerned about the minimal drag produced by
> an externally mounted antenna on your Lark. *Granted the antenna produces
> drag; however, on a gliders with similar polars to the Lark the performance
> differences is undetectable. *The only reason to hide your antenna is that
> the Lark looks sleeker without it mounted on the top of the fuselage.
>
> Wayne
>
> "Markus Graeber" *wrote in message
>
> news:15119856.896.1333962866197.JavaMail.geo-discussion-forums@yncd8...
>
> On Sunday, April 8, 2012 11:04:13 PM UTC+2, Bob Kuykendall wrote:
> > Once upon a time, I tried many different com antennas on an HP-18, an
> > all-metal sailplane with fiberglass nose and turtledeck. The most
> > effective antenna was a bent 1/4-wave whip mounted over the aft
> > fuselage.
>
> > For the HP-24, I install a 1/4-wave dipole inside the rudder, but that
> > is not a realistic possibility for the Lark.
>
> > Thanks, Bob K.
>
> Thanks Bob, I was actually thinking about the possibility of installing the
> antenna in the rudder since it has fabric cover. The other more extreme
> option could be to replace the vertical stabilizer leading edge aluminum
> panels with fiber glass but that might have some structural side effects and
> I am not sure how much aluminum ribbing will affect an 1/4 wave antenna
> install.
>
> Certification wise it's not a problem since gliders are treated here similar
> to experimentals in the US...
>
> Markus

Markus,

The antenna will only work well in the rudder if the rudder frame is
non-metalic. More modern ships often put the comm antenna in the
fiberglass rudder as close to the trailing edge as practicable in
order to keep it away from other conductive things. This is a
reasonable compromise, though often with a narrow null or "radio free
zone" directly ahead of the aircraft.

bumper
zz
MKIV and QV

[Papa3[_2_]]

My club made a habit of converting Larks to scrap aluminum (3/5 of the way to black ace), so we got to see a number of different radio installations. IIRC, all of them used a pretty crude antenna installation similar to what you describe.

FWIW, have you considered a fiberglass encased 1/4 wave antennal like what you see on many metal GA aircraft? Comant is a major manufacturer.

http://www.cobham.com/about-cobham/aerospace-and-security/about-us/antenna-systems/fullerton/products/vhf-comm.aspx

On Sunday, April 8, 2012 9:12:16 AM UTC-4, Markus Graeber wrote:
> Happy Easter everyone! We have a IS-28B2 Twin Lark which we use quite a bit for instruction, it is good for spinning and intro into flying complex gliders (flaps & retractable gear). It is due for a complete overhaul which will include a new radio with a repeater control unit in the back for the instructor.
>
> Since we´ll then be re-working the whole radio install anyway I have been considering doing something about the dragmaster factory radio antenna that looks more like a car antenna installed ontop of the fuselage tail boom.. For you experts out there what would be your recommendation for an interior radio antenna install (or a low drag exterior install) in an all metal glider like the Twin Lark?
>
> Many thanks in advance,
>
> Markus Graeber
> Aeroclub de Colombia

[Markus Graeber]

Thanks all for the feedback. I know that the difference in drag will not be quantifiable but, as pointed out, it would look a lot sleeker. Just trying to take advantage of the complete overhaul we'll be doing and hoping to turn the Twin Lark into more of an eye candy, a sleeker looking machine. It currently does have to compete (often unsuccessfully) with our G103 for attention so first impressions do help.

The polar sucks especially on the high speed end (even the flaps won't get it near the G103 polar, the Germans give it a close to 10% better handicap....) but at least you'd be coming down faster in a nice looking glider that does allow students to get a good handle of spins, flaps and retractable gears :-)

Markus

[Bob Kuykendall]

On Apr 9, 2:14*am, Markus Graeber > wrote:

> Thanks Bob, I was actually thinking about the possibility
> of installing the antenna in the rudder since it has fabric
> cover...

As others have said, that probably will not work very well. The metal
frame of the rudder will interfere with the antenna's radiation
pattern, and it will probably have an unacceptably high SWR (standing
wave ratio).

> The other more extreme option could be to replace the
> vertical stabilizer leading edge aluminum panels with fiber
> glass but that might have some structural side effects
> and I am not sure how much aluminum ribbing will affect
> an 1/4 wave antenna install.

I think that will not work very well either. It would require a non-
trivial structural analysis to make sure that there is adequate
torsional and bending stiffness in the absence of the metal skin of
the modified areas.

I suppose that you could develop a composite (fiberglass or aramid,
but not carbon) rudder for the Lark and put the antenna inside of
that. But in the overall scheme of things, the effort is great and the
payoff is rather modest. You are probably a lot better off just
installing the bent 1/4-wave whip antenna and investing your time and
money on more productive endeavors.

Thanks, Bob K.


>
> Certification wise it's not a problem since gliders are treated here similar to experimentals in the US...
>
> Markus

[Tony[_5_]]

>
> I suppose that you could develop a composite (fiberglass or aramid,
> but not carbon) rudder for the Lark and put the antenna inside of
> that. But in the overall scheme of things, the effort is great and the
> payoff is rather modest. You are probably a lot better off just
> installing the bent 1/4-wave whip antenna and investing your time and
> money on more productive endeavors.
>
> Thanks, Bob K.
>


wait isn't the rudder on the IS28-B2 fabric covered?

[Bob Kuykendall]

On Apr 9, 7:50*pm, Tony > wrote:

> wait isn't the rudder on the IS28-B2 fabric covered?

Yes, I believe it is fabric on an aluminum frame. If that is so, the
metal frame will disrupt any sort of internal antenna, an antenna
placed between the fabric and the fabric cover, and even an antenna
glued to the outside of the fabric.

Thanks, Bob K.

[Bill D]

On Apr 9, 10:19*pm, Bob Kuykendall > wrote:
> On Apr 9, 7:50*pm, Tony > wrote:
>
> > wait isn't the rudder on the IS28-B2 fabric covered?
>
> Yes, I believe it is fabric on an aluminum frame. If that is so, the
> metal frame will disrupt any sort of internal antenna, an antenna
> placed between the fabric and the fabric cover, and even an antenna
> glued to the outside of the fabric.
>
> Thanks, Bob K.

How about a retractable 1/4 wave antenna? I seem to recall some HP's
with them back in the '60's.

Alternatively, a rubber ducky from a handheld mouonted under the
fiberglass fairing over the wing root just might work well enough for
1 - 5 mile local talk. Sparkies will have to explain if that would
work.

[Wayne Paul]

Here is a link to the retractable antenna/TE probe Bill mentioned.
http://www.soaridaho.com/Schreder/Construction/T_E_PROBE_ANTENNA.html

Wayne


"Bill D" wrote in message
...

On Apr 9, 10:19 pm, Bob Kuykendall > wrote:
> On Apr 9, 7:50 pm, Tony > wrote:
>
> > wait isn't the rudder on the IS28-B2 fabric covered?
>
> Yes, I believe it is fabric on an aluminum frame. If that is so, the
> metal frame will disrupt any sort of internal antenna, an antenna
> placed between the fabric and the fabric cover, and even an antenna
> glued to the outside of the fabric.
>
> Thanks, Bob K.

How about a retractable 1/4 wave antenna? I seem to recall some HP's
with them back in the '60's.

Alternatively, a rubber ducky from a handheld mouonted under the
fiberglass fairing over the wing root just might work well enough for
1 - 5 mile local talk. Sparkies will have to explain if that would
work.

[Vaughn]

On 4/10/2012 12:32 PM, Wayne Paul wrote:
>Alternatively, a rubber ducky from a handheld mouonted under the
> fiberglass fairing over the wing root just might work well enough for
> 1 - 5 mile local talk. Sparkies will have to explain if that would
> work.

First, It must be said that a rubber ducky is inferior to a properly
installed 1/4 wave antenna. Exactly how inferior depends on the
construction of the individual ducky (since they come in various heights)

That said, most of the communicating I have done from gliders has been
with hand-helds with rubber ducky antennas. For local communications,
they've always worked great for me. It's my opinion that a nicely
installed rubber ducky on a proper ground plane will do better than that
same rubber ducky tacked to the top of a portable radio. In lots of
gliders, there are places where you could mount a rubber ducky under the
canopy and have a short transmission line (to help mitigate some of the
loss) and zero drag penalty.

Vaughn