Whats a Thermal sniffer?

[shaneyee]

I read about a 'thermal sniffer' in Joe Wurt's account of his Cross Country record run....

What's a thermal sniffer and how does it work?

Thanks

Shane

[GeeW]

Hi
A thermal sniffer is the guy who launches before you to check out whether the thermals have started yet and he has either;
1. A very short flight with a pig of a retrieve from the bottom of the hill
2. The best flight of the day as he launched at the perfect time to catch the first thermal!

I can normally manage the first......have managed the second a couple of times.

Regards
Gordon

[Masterpiece]

Somebody with a bad cold ;) .

Ha ha, anyway joking aside my best guess would be like a "picolario" unit. But I have heard of free flight enthusiasts using such devices many many years before the "Picolario" unit was made available.

Sorry I am just as curious as you are now.

Cheers
G

[Ollie]

It is the trade name of a variometer with a telemetry link back to the pilot. It is no longer in production but other companies make more modern and sophisticated units such as the Picolario. The original product was very sensitive and. It telemetered a tone whose pitch rose in proportion to the strength of lift and descended in proportion to the strength of sink to the point where the tone became sub audible. The more modern products even have synthetic voice out put of results.

[shaneyee]

What's a variometer? Does it measure altitude, vertical velocity ( by barometric changes ) or vertical acceleration ( by means of a gyro? )? Now I'm really interested...hmmm.... a telemetric link could also feedback altitude, velocity, even direction and position if you wanted!

Shane

[Ollie]

The Thermic Sniffler consisted of a chamber of air with a small exit tube. There were two thermistors in line, one behind the other in the tube. The thermistors were part of a bridge type audio oscillator whose frequency was determined by the balance of the bridge. When air flowed into the reservoir the first thermistor was cooled more than the thermistor in its wake and the audio oscillator tone decreased. When the air flowed out of the reservoir in the opposite direrction the cooling of the thermistors was reversed and the audio oscillator frequency increased. Therefore, the audio tone changed with the rate of change of barametric pressure. The unit was sensitive enough to indicate a rate of change in altitude of less than one foot per second. The output of the audio oscillator modulated a low power radio frequency transmitter. The electronics were mounted on a single printed wiring board located within the air reservoir unit. The low power transmitter operated in a different radio frequency band than the R/C system. The pilot typically carried a small receiver in his pocket that was tuned to the variometer's radio frequency with an ear phone that allowed the pilot to monitor the audio tone.

Some people connected an external venturi type device to the vent tube that converted the variometer response to one that depended on the rate of change of the total energy (potential energy plus the kenetic energy). This modification to a total energy variometer made the unit unresponsive to "stick thermals" caused by pilot elevator input that traded kenetic and potential energy. With this total energy response, a porposing sailplane that was rising in a thermal would transmit a more or less constant tone rather than a tone that warbled in response to the porposing.

There was a feature article in Sailplane and Electric Modeler magazine a few years ago that explained how to make the total energy modification.

The original unit was developed by Dr. Walt Good and manufactured by Don Clark beginning in the late 1960's. Sometime in the 1980's the business was sold to ACE who produced units in a rectangular box reservoir configuration rather than the original cylindrical configuration. Sometime in the 1990's Ace sold the business and production stopped.

[thelocust]

If we had LiftZone forum awards, I'd vote for Ollie as MVP :)

[shaneyee]

I'd second that!

Ollie,
Thank you again. Its a very clever design I think.... I had all sorts of ideas but everyone of them would have weighed many times more and might not have been anywhere as sensitive.

Shane

[J_R]

The Thermic Sniffter never had a large following. It worked fine, but, it was mostly used in sanctioned contests, where a CD has to enforce the rules. The use of a device transmitting back to the ground requires a ham license and since most guys don't bother with a ham license, it never caught on. It seemed that the guys that did use them were so intrigued with the technology, they forgot to compete in the contest and were far more intersted in the device :)

When your trying to set records, like Joel is, it's worthwhile to get the license.

[Ollie]

As I recall, the units made by Don Clark were all on the six meter amateur band and required an amateur license to operate. Later ACE used the 49 Mhz licence free band.

The most frequent applications were for cross country work where good results require flying at altitudes well above 1000 feet or so. At the higher altitudes and when flying directly overhead, it is very hard to tell lift from sink by visual indications alone. Therefore, variometers are frequently used. In thermal duration contests, where target times are usually under 15 minutes, it is seldom necessary to fly above 1500 feet or so. At the lower altitudes, visual indications of lift work well enough that few people find the distraction of a tone in their ear to be an advantage.

The new variometers from Germany have periodic voice reports that are less distracting.
See:
http://www.mail-archive.com/soaring@airage.com/msg81867.html
http://www.picolario-usa.com/
http://www.tek-variometer.de/englisch/