Re: teeny vertical fins

Date:         01 Mar 97 02:44:59 
From: (Mary Shafer)
Organization: NASA Dryden Flight Research Center, Edwards CA
References:   1 2 3
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On 19 Feb 97 02:46:22 , (Scott Miloro) said:

S> Speaking to the cases
S> of B747-200 and 757, I have only seen the dorsal blade antennae - I
S> will have a look at pics to see for myself (too lazy to go out to
S> Logan.)  Any guess as to possible advantages/disadvantages to the
S> ventral placement of blade antennae?  I think that on smaller a/c
S> designers might worry about some lummox tweaking one, but who
S> knows.

It's possible that either the dorsal or ventral antennae might be
blocked by the maneuvering of the plane.  Turning away from the
receiver means that the fuselage and, possibly, the wing will blank
the signal, for example.  Having them in each location ensures
continued contact.  Having two in different locations reduces
interference and ensures redundancy, too.

We install radio and TM antennae, both blade type, both dorsally and
ventrally on our aircraft and radiate from both.  Radar beacons, which
have tiny little button antennae, get mounted ventrally, quite far
forward, where the wing won't blank them.  (We use tracking radar, not
scanning radar like ATC does.)

Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA                               DoD #362 KotFR
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