Has anyone gotten a stormscope to
work properly in a lancair? We are just now flying and the wx 500 sold to me and
installed by lancair avionics is not cutting it. Any suggestions or lessons
learned? Thx. Stan.
Stan,
I have this task
still ahead of me but I have inquired.
My belief is:
-yes it has been made to work.
-The location
believed to work is far back on the under side of the
fuselage.
-an alternate
suggested location is at the wingtip (although seems incompatible with
strobes)
-if you don't
skin map and place accordingly, it won't work. every plane is
different
- ground planes
are an issue. I include a post from Bob Simon from June
2005
Colyn
Bob Simon's post
Several different techniques are being used on composite aircraft to
produce the antenna ground plane required by a 'spherics (Stormscope) and a
TCAS-type traffic alert. I started an investigation into the use of a
metallized graphite scrim that could be easily applied. At this point that
application is questionable because the Ryan TAS operating frequency is 1 GHz
and the wavelength is so short that the open spaces in the scrim might become
re-transmitting antennae. Jury's still out on that one.
However the engineers at Ryan like Bob Schofield have been helpful beyond
measure, and here is what I have gleaned from them so far:
The
ground plane must be VERY conductive. The resistance from center antenna
attach point to aircraft ground must be less than 10 milliOhm - 0.01 Ohm.
Don't try to measure that with the VOM that you bought at NAPA. The plane
must be symmetrical along 2 axis fore-aft and port-starbord. Curved to
match the fuselage shape is OK.
A ground plane of solid metal
foil seems to work best. Conductive paints based on Ni or Ag plated copper
will NOT work over time. Tests on composite helicopters have shown that
the painted plane is effective initially but after one year begins to
degrade. The engineers theorize that the paint becomes brittle with age
and begins to crack. That leaves slots that re-transmit and isolated
islands that are not grounded. The situation would be worse with a
pressurized aircraft where the skin walls flex out and back with every flight,
so a definite no-no for the Lancair IV-P and ES-P.
One
material recommended is a thin Al foil available from McMaster-Carr, p/n
9060K16. It is dead soft, 0.005" thick, and comes in rolls 36" wide by 100
feet long. The full rolls cost $145 - hopefully your avionics shop will
sell you smaller quantities. Typical installations require two pieces
about 3 ft by 3 ft each. The material is soft enough to conform to curves
and bumps on the cabin deck and overhead, and could be adhered with a contact
spray like 3M 7700. The ground plane must be connected to the aircraft
ground with at least two 12 to 14 ga. wires - do not rely on the coax cable
shield to ground the plane.
The external antenna should be mounted
over a thin Al sheet cut the exact same footprint as the antenna. That
sheet should be affixed to the fuselage with two 6/32 countersunk machine screws
that go through the Al sheet, then the fuselage and then the internal Al ground
plane where the screws are fastened with two self-locking nuts. The
external antenna is then attached with its six screws to the fuselage, trapping
the Al plate beneath, and the external sandwich edge is sealed with RTV.
The coax cable to use is 50 Ohm RG-400 cut 16 feet long. Not
about "15 feet" - cut it 16 feet long. The extra could be looped into a
large coil at least 2 feet in diameter. You will need 4 of the leads, they
each must be 16 feet long, and they should measure 2.5 dB to 3.5dB at 1
GHz.
More details when and if I get 'em.
Robert M. Simon, GlaStar N161GS and Lancair ES-P(xl)
N301ES.