aircraft antenna mounting

[Higgler]

Has anyone out there added antennas to jet aircraft.
I'd like to find out what hoops one has to jump thru to add antennas to high speed aircraft (military or commercial)? this will probably be a large (36"x36") thin (0.5") antenna added to the belly and top surfaces.
And what are the challenges to adding large antennas directly applied to the surface (I realize that aircraft skin expansion as aircraft heat up is a biggie).
Just a reference would help.
Thanks,
kch

 

[rb1957]

i was thinking either Al or graphite as a substrate. if the antenna is very flexible, it'll need support. you also want it to strain like (or be as stiff as) the surrounding structure. there is a reasonable amount of spanwise strain in a wing, but this should be manageable. the areodynamic pressures will be significant, but they'll be +ve on the lower surface of the wing (most of the time!) ... aero-suction on the upper surface. these pressures can be very large. by putting in discrete fasteners you are introducing fatigue sites which will need to be considered. i'd have thought localised doublers (internal?) would be sufficient (ie, not a whole bunch of structure).

you could ask 3M what adhesives they might recommend, if this is meant to be reasonably permanent. they may have suggestions if the antenna needs to be removed as well.

i'd have thought a bigger concerns on the wing would be adding something 1/2" thick, and making sure the antenna didn't deform under the applied pressures (so if it is flexible, it'll need some suppport).

good luck

 

[Higgler]

Thanks rb1957,
I'll take your info and pretend I know a little while writing the proposal.
Can you suggest a good book to order on the subjects we've discussed?

kchiggins.

 

[berkshire]

I do not know at which stage of design you are at. Have you considered incorporating your antenna into an electricaly transparent section of primary structure i.e a molded composite panel of equal strength to the surrounding structure and leaving the outside contours of the aircraft alone? Or is this an existing aircraft?
Berkshire.

 

[Higgler]

berkshire,
This is an existing aircraft in US military inventory.
kchiggins.

Question for All:
When someone says "conformal/low profile antenna", does anyone have thoughts for thickness on commercial or military high speed aircraft. I suppose it depends where you mount the antenna. Let's say fuselage top or bottom in the center of the aircraft. I would think conformal is 0.5 to 1.0 inches? or is this too thick

 

[rb1957]

higgler,

i think it matters more where you're putting the antenna. fuselage mounting is much less sensitive (to aerodynamic effects)than wing mounting. in a fuselage mounted context, to me the distinction is between low profile (which a 1" thick antenna is) and blade (self explainatory?).

as the plane is grey and very fast, i'd be a little careful about interactions with any of the aerodynamic surfaces, a 1" thick "lump" make get some appreciable load from the Cp raise associated with these.

to reply to an earlier comment of yours, the appearance of knowledge is a pale imitation of the real thing ... careful or some "grey beard" or "silver back" will pick you apart like a chicken wing !

 

[Higgler]

rb1957,
thanks for the warning. I wouldn't try to say problem solved, just that I'm problem aware. I'm smart enough to know that real experts/consultants would be necessary in a phase II program for this antenna.

If you listed the worst locations, I think
tail is the worst,
wings next (maybe equal to the tail, and more sensitive to shape causing problems, i.e. losing lift)
fuselage fore or aft,
then fuselage center area is the friendliest.
kchiggins.

 

[rb1957]

sorry, about 180 degrees ... visualise the pressure peaks (and the mach shocks) around the lifting surfaces ...

fuse over the wing and near the pilot's canopy are the most sensitive areas (highest Cp), then fuse near the trailing edge of the wing and the fin leading edge; everywhere else shouldn't be much of a problem