Antenna?

Does anyone know if it is possible to mount a standard antenna in the wingtip? I want to hide my antennas if possible but I do not want to use the tip antennas that are made of the flat material as I have heard bad things about them.

Will it hurt to mount an antenna sideways on the end rib? Will the length of wire to get to the antenna be a factor?

Is there an issue with the transponder antenna not having a large metal surface above it?

Thanks for any input and Doug, thanks for this website.

I don't think a regular antenna mounted in the wingtip will perfrom much differently than the flat wing tip antennas. As I understand it, the problem with the wing tip antennas (if there is one; some think they are fine) is that they are horizontally polarized while the stations to whom they are most often communicating are vertically polarized. The cross-polarization results in signal loss. A regular antenna in the wing tip would still be horizontally polarized.

Com antennas need to vertical. VOR ant. need to be horizontal. ELT ant. need to be vertical. Transponder and DME ant. need to be vertical. Transponder needs to point "down" because all interagations come from ground based radar. The ground plane for transponder ant. should be at least 6-8" diameter.
Mel...DAR

Say again. Say again, over?

ww2planes said:

Does anyone know if it is possible to mount a standard antenna in the wingtip? I want to hide my antennas if possible but I do not want to use the tip antennas that are made of the flat material as I have heard bad things about them. (THINGS will NOT GET BETTER WITH A "STANDARD" ANTENNA MOUNTED INSIDE THE WING TIP.)

Will it hurt to mount an antenna sideways on the end rib? Will the length of wire to get to the antenna be a factor? (BAD IDEA)

Is there an issue with the transponder antenna not having a large metal surface above it? (YES, It needs a GROUND PLANE)

Thanks for any input and Doug, thanks for this website.

Click to expand...

Why? A single bent whip com antenna mounted on the outside of a RV going 200 MPH is going to cost you may be 1/4 to 1/3 MPH (max if you do it right). The ability to communicate is kind of key to safe aviation. No wing tip antenna, "flat" as you call it or "standard" laying semi sideways in the tip of a metal plane will have the omni-directional and long range characteristics of a typical installation. When some one says "mine works great". Great might mean they can talking to a control tower 5 miles directly ahead, not to a flight service station or ATC 120 NM away.

I am all for experimenting but when you look at the "hidden installation" trade offs in performance, not to mention installation issues, long heavy coax runs, this is not something that is as a clear choice at\s with fiberglass planes. Consider putting your antenna on the out side the fuselage, vertically, for uncompromising communication. You'll be annoyed with spotty short range COMM of the hidden wing tip antenna.

The transponder needs a ground plane. Again the extra drag might be 1/10 MPH penalty (max) at 200 mph, at most. Good luck. Consider mounting the antenna on the belly. It will not ruin the beauty or performance of your plane, but you will actually have a COM radio you can use. A good COM is really a critical safety item for so many reasons.


George


PS that is about 0.50 hp to drag the antenna, not 5 hp, see calcs below.

Here's another piece of interesting but useless information. It takes approx 5 hp to drag a round comm antenna thru the air at 200 mph. Jim Ayers who lurks on this list has done all the math.
Tom

tin man said:

Here's another piece of interesting but useless information. It takes approx 5 hp to drag a round comm antenna thru the air at 200 mph. Jim Ayers who lurks on this list has done all the math.
Tom

Click to expand...

Jeeze............

Between three antennas, three sets of wheel pants, three gear legs, two exaust pipes, two little canopy lift handles, plus handle on the top, and two steps.....................I might never get off the ground!

Speed?

Who said anything about speed? This topic is strictly about position and in this case I just don't want to look at them. I want to try and go for a smooth exterior. Just want to know if they will work if I put'em out there.

I've talked to a couple of people that have tried to hide their antennas in the wing tip and ended up putting a bent antenna on the belly. Both have told me that they could spit on the people they were trying to talk to before they could communicate with them. I really don't know anything about horspower to pull one through the air or how much one slows an RV down. But I feel they are kind of like brakes on a car. If you don't have any it doesn't matter how well the engine runs. If you can't talk to the people on the ground a reasonable distant away then why have a radio.

I've been in a couple of situations in which I've lost radio communication. It sure changes the atmosphere in the cockpit. Next thing you are trying to do is locate an airport that isn't tower controled and has a radio repair station. Good luck. Besides that, I don't remember all of the light signals. And, I've always thought that even if I did, how do you get close enough to a tower controled airport to read them without being in a lot of trouble with the authorities.

Nothing like having good communications anyway you can get it. In fact it makes me wonder about the cell phone patch cord I've seen advertised. I guess if all else fails you could call the tower with your cell phone .

Vertical and ground plane are what matters

ww2planes said:

Does anyone know if it is possible to mount a standard antenna in the wingtip? I want to hide my antennas if possible but I do not want to use the tip antennas that are made of the flat material as I have heard bad things about them.

Click to expand...

As long as you can install it vertically, don't change the antenna's length, and have a big enough ground plane (couple of feet in diamter), you can install it in a wingtip. I don't know how to accomplish that, though.

That is way off my friend

tin man said:

Here's another piece of interesting but useless information. It takes approx 5 hp to drag a round comm antenna thru the air at 200 mph. Jim Ayers who lurks on this list has done all the math.
Tom

Click to expand...

Jim Ayers is math impaired I am sorry to say.

5 HP Really. That is off by a factor 20. I guess if you
had 10 antennas the airplane fall out the sky? Silliness

Here are some numbers (conservative)

Fluid Dynamic Drag, by Hoerner, assume a drag coefficient (Cd)
of approximately 0.5 for a whip antenna
(test data in figure 13 on page 3-9).

Drag is equal to the dynamic pressure times frontal area times the Cd.

Dynamic pressure (lb per square foot) at sea level equals the speed
in mph squared, divided by 391 (from Hoerner, eqn. 16 on page 1-10).

Frontal area of the antenna in square inches, we get:
20 inches long, diameter of 3/16 inch, frontal area of 20 * 0.1875 = 3.75
square inches. (actual area really 2.88 in sq, bent whip including base)

drag = speed squared times frontal area times Cd divided by 56,304
(drag in pounds, speed in mph, frontal area in square inches)

At 200 mph the drag would be: 200 x 200 x 3.75 x 0.5 / 56,304 = 1.3 lb.


Power required = speed x force.
200 mph x 5280 ft/mile x 3600 sec/hour = 293 ft/sec.


So, the power in ft-lb/sec = 293 x 1.3 = 381.


One hp = 550 ft-lb/sec, so it takes 381/550 = 0.69 hp.

Prop efficiency assumed as 0.8,
that means we need 0.69/0.8 = 0.87 engine horse power
to drag that antenna.


Assume it takes 160 hp to go 201 mph (RV-6)
Speed loss, 1/3^(159.31/160)*201=200.71

So it takes .29 MPH.

The above is conservative. It is closer to 0.50hp /.25 mph.


Jim sells a Comm antenna fairing that goes on the top of the vert stab.
Jim was on another list with this claim that one comm antenna was
worth 1/3 the drag of the wing! He got it down to 5 hp, which is still
too high of a number. Like Jim, but he tends to exaggerate or get the
math wrong. At least he tries. Now all we have to do is get him to
admit MT props are slower than Hartzell and Sensenich props.

George

As long as you go with one Comm, one Transponder and a VOR antenna
the drag of antennas is small about, 0.81 mph total! that's it, about 2.1hp.
I can see hiding the VOR antenna since it is like two comms, but still
its not a big loss. However wing tip VOR's work better than comms, but
if you want to fly long range IFR NAV with a VOR I would go with an
external VOR antenna. Any antenna jammed inside a metal plane is
compromised. When I raced I took my tail VOR antenna off in about 2
minutes (to get that 1/3 mph). Picture below, click.

VANS canopy mounted antenna?

Is there any experience of using the antenna that VANS sells that sticks on the inside of the canopy?

I find the $7 cost more appealing than the .25mph, but perhaps most of all the aesthetics and less to get knocked off. Still, its no use if it does not work.

Thanks, Steve.

George, would it make sense to come up with a better antenna rod cross section (ie, airfoils shapped)? It would seem that the drag could be significantly reduced...of course in the bigger scheme of things, we're splitting hairs here.

Deene.

Ya sure you betcha!

deene said:

George, would it make sense to come up with a better
antenna rod cross section (ie, airfoils shapped)? It would seem that the drag
could be significantly reduced...of course in the bigger scheme of things,
we're splitting hairs here.

Deene.

Click to expand...

Well first the whips are tapered down to the tip, but
assumed that it was 3/16 all the way. But to answer your question the idea
was already figured out. Most high speed "Jet" antennas are blade or airfoil
shaped. Since they are made for 400-600 mph the bases tend to be large.
You could make your own "blade" airfoil with a small base suited for 220mph.

Here is a do it yourself antenna from RST engineering's Jim Weir
http://www.rst-engr.com/kitplanes/KP9911/KP9911.htm

The other down side of "Jet" antennas is they cost $300.

There is a trade off in cost and appearance for little planes. I personally don't
like the looks of a jet antenna on a small plane, but aerodynamically it makes
sense. One caveat is the airflow going around a piston plane with tractor engine is not stright. It is a bit of a corkscrew. So putting a a blade antenna on "aerodynamically" crooked could cause more drag. A whip is pretty tolerant of being put on crooked.

However you point is valid. The differnce may save 0.10 mph? Who knows.
I look at the big picture. Cost, installation, (radio) performance and drag. The drag is so small it is not critical. Radio performance is a tie. Cost differnce for off the shelf is significant. Installation about the same. As far as drag, it goes up exponentially with speed. So if you are going 250kt or faster it may be well worth it. Over 300-350kts you should use a blade antenna.

George

Foil antenna

Steve Sampson said:

Is there any experience of using the antenna that VANS sells that sticks on the inside of the canopy?

I find the $7 cost more appealing than the .25mph, but perhaps most of all the aesthetics and less to get knocked off. Still, its no use if it does not work.

Thanks, Steve.

Click to expand...

I'll give the punch line first. I know just enough about antennas to be
dangerous. I am not totally against the foil windscreen antenna. To be
honest I have not used them. To be fair they "work" but when compared
in parallel with an external antenna the reception signal was weaker and
ATC could not hear sometimes, I was told. Its a fair guess it will have
"directional lobes".


Copper foil or tape antennas in the windscreen work, but again it is not an all
around primary antenna. "Work" means differnet things to different people.
Visually they are not attractive. On the upside they are cheap and no drag.
When compared to the wing tip at least the coax run is short and guess it
might have a little range advantage in the direction it is best in, ahead.

You can make your own with some cheap foil tape and coax. Solder the
center connector to the tape, and ground the shield with a crimp lug screwed
to the metal glare shield. Foil about 21.5" ro 23" long and at least 1/2" wide.
The wider the better, which gives a wider freq band, really that is the way it
works. There is all kind of tricks to tune it. People use toroids or Balun on the
coax (also called chokes and ferrites beads). These are "magnetic donuts"
along the coax, that help reduce the SWR, standing wave ratio. I don't think
you need them. If attempting this get an antenna tuner to read SWR. Too
much SWR can damage the radio.


Some would not care for the lack of visual appeal, however from a technical
stand point it is a decent radiator at least forward. The down side it is good
for mostly straight ahead of you, and that may be fine for local around the
airport, but cross country, no so good. I feel the COM radio is such a
important piece of safety equipment that you should not compromise. Even
local when you call in the blind, you want people to hear you, even if they
are behind you.

The foil antenna is a good secondary antenna or back up but here is a clever
solution say for a backup antenna for a hand held. Say the main radio goes.
Most put their COM antenna in the floor off set to the left or right, forward of
the main spar. You have access to the BNC and could just reach down and
disconnect the coax and put a short coax to the handheld if needed. Here is
another clever idea from RST using a phone jack for a backup handheld
antenna jack: http://www.rst-engr.com/kitplanes/KP0203/KP0203.htm

Bottom line a foil antenna in the windscreen is a compromise. It will not have
the "gain" or "omni-directional" qualities of an external radiator.

George

PS, there is some concern about 7 watts of power going out a few feet from your head.
Remember the cel phone brain tumor scare, that was milli-watts. Something to think about.
Whatever you do do not mount the transponder near your head or other body parts you
don't want 200 watts of RF radiation on.