commgrp@silver.bacs.indiana.edu (BACS Data Communications Group) (09/09/89)
to sci.electronics, rec.aviation, rec.models.rc I need references and construction details for electronic vertical- speed indicators (called variometers by sailplane pilots). I'm told that plans have been published in magazines of soaring and remote- control aviation. The device is basically a hot-wire anemometer. Some designs use bare filaments of flashlight bulbs in a bridge circuit. The cooling effect of wind on two of the filaments changes their resistance in proportion to velocity; the other two filaments are shielded from wind and used as a reference. The variometer has an accumulator tank connected to outside air through a small orifice in which is mounted the hot-wire sensor. Air from the tank flows outward when an aircraft climbs, inward when it descends, i.e., the instrument is a differential barometer/altimeter. I don't know how the hot-wire circuit senses direction of air flow. Some of these devices are intended for manned sailplanes and ultralight aircraft, others are used for telemetry from radio- controlled model sailplanes. I am especially interested in the latter type. I intend to use it for studies of barometric wind in caves. Will pay reproduction and mailing costs. Thanks in advance, Frank Reid W9MKV @ K9IU C,I,SEL NSS 9086F P.O. Box 5283 Bloomington IN 47407
tswift@well.UUCP (Theodore John Swift) (09/16/89)
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>I need references and construction details for electronic vertical-
>speed indicators (called variometers by sailplane pilots). I'm told
>that plans have been published in magazines of soaring and remote-
>control aviation.
Frank;
Yes, there was a variometer construction article in the March 1969
"Flying Models" magazine by Maynard Hill and R. Ben Givens. They used
tiny (~.005" dia.) bead thermistors placed across the center of a 1/16"
diameter tube. One bead is immediately "downstream" from the other, almost
touching, so air blowing either way will create an imbalance in the bridge
circuit, giving you magnitude and direction of flow. Maynard Hill and
a bunch of his friends keep popping up in the literature with things like
this, and with electrostatic autopilots for RC aircraft; they all work(ed)
for Johns Hopkins Applied Physics Lab and got *paid* to develop these things!
If you're also interested in the electrostatic goodies, write to
Aeroprobe Technology Corp.
2001 Norvale Road
Silver Spring, MD 20906
Mr. Hill & Co. have developed an autopilot "kit"
There's a "Solid State Barometer" construction article in the June 1984
issue of Radio Electronics, p. 41, which uses a SenSym pressure transducer.
You may get some ideas from this, but medium- and long-term drifts may be
a problem.
There's an article on the fine points of thermistors: "Practical Design
Techniques Tame Thermistor Nonlinearities" in ._Electronic Design
News_ (EDN),
20 Jan 1983. Copies of these articles are in the mail.
For your cave measurements, you probably don't need the radio downlink, or
you could take the bridge output and use it to drive a voltage-to-frequency
(V/F) conve.rter for longer c
able runs. An LM 555 would
work;
various other
specialized chips, such as the LM 566 VCO would also work.
How do you plan to measure the flow in and out of the cave? Seems to me
you'd have to block off the entrance and insert your flow sensor through
the barrier.
--
Ted Swift "Mortui vivos docent"
{hplabs,lll-crg/lcc, pacbell} The dead teach the living.
!well!tswiftwaynea@cadnetix.COM (Wayne Angevine) (09/19/89)
Ace R/C markets the Thermic Sniffler (undoubtedly TM) which is
what you are looking for. It is used by R/C glider pilots.
It sends out a continuous tone (I believe on 50-some MHz) which
varies in frequency according to the vertical speed. I believe
that the cost is around $150 with receiver. The package weighs
a couple of ounces.
Wayne Angevine Internet: waynea@cadnetix.com
Daisy/Cadnetix Corp. UUCP: cadnetix!waynea
5775 Flatiron Pkwy. {uunet,boulder,nbires}!cadnetix!waynea
Boulder, CO 80301steve@eos.UUCP (Steve Philipson) (09/21/89)
In article <9542@cadnetix.COM> waynea@cadnetix.COM (Wayne Angevine) writes: >Ace R/C markets the Thermic Sniffler (undoubtedly TM) which is >what you are looking for. It is used by R/C glider pilots. >It sends out a continuous tone (I believe on 50-some MHz) which >varies in frequency according to the vertical speed. I believe >that the cost is around $150 with receiver. The package weighs >a couple of ounces. I've have and use this device. I've been pretty happy with it, as it works well and adds another dimension to my model aircraft flying. I've also taken it up in a full scale glider to use as a poor-man's audio variometer. It does have its limitations in this application, although with a little engineering work, it could be improved significantly. The device has been around for many years and has been refined over time. You might want to pick one up and use it as the basis for your project -- it could save you some time and effort. -- Steve (the certified flying fanatic) steve@eos.arc.nasa.gov