Hi all,

I'm looking for an airspeed measuring device that will transmit airspeed data to a receiving unit to show current airspeed (preferred), or something that can log airspeed over time for download to a laptop after landing. A turnkey system integrating a sensor and all electronics would be nice, otherwise a kit or plans/schematics.

I'd like to put such a system into a glider, probably just temporarily, as an aid to trim for a certain flying speed (lift coefficient), or to stay above Reynolds numbers where the polars start breaking down.

Any info, links, or words of wisdom appreciated.

robbe/futaba has such a device

mec

Check out this thread

http://www.rcuniverse.com/showthread...61&forumid=162]

Wildblueyawner,

We have such a device. It is for Giant Scale Racing and might be a bit much for you. You can download the manual in .pdf format at http://www.aerosport.org/edl414.pdf

If you have any questions, feel free to give me a call at the contact number on the website.

Shawn Everson
Electronics Engineer
Aero Sport

Go and get a garmin Etrek gps handheld. They are very small, and will record max speed. The unit would be totally self contained, attachable to the inside of the plane with velcro, and accurate to 1/10 mph. You could put one under the canopy, that would be an ideal place.

mec,
I contacted Robbe / Futaba - the airspeed indicator is no longer offered

PAINLESS,
Sounds like it'll be a nice (real-time indication) system once released. I inquired as to whether they might offer a unit in a lower speed range, e.g. 0-100 mph. Will be interesting to see the production version.

F1race11,
Yes, the functionality is more than I need. Can you offer a system stripped of everything but airspeed measurement? Approx. price? Need size/weight info also, although it might not be an issue as I'll be putting the system into a 17-foot span glider.

mtthomps,
YES! Your comment jogs my memory of this article I saw on performance testing an SB-XC glider with a handheld data-logging GPS http://www.xcsoaring.com/articles/articles.htm That just might be the way to go . I had completely forgotten about this approach. Thanks!

Check out:
www.emsjomar.com
under their data logging systems.

Jack

ground speed measurements by Garmin eMap (HotSpot):

You could convert an old Ace Thermic Sniffler variometer into a telemetered air speed indicator. Remove the case that acts as an air chamber. Get a small needle valve assembly. Connect the needle-valve assembly to the variometer vent with rubber tubing. Put the whole thing on a long pole that you can hang out the car window with the hole in the needle valve facing into the air stream. Use the needle valve to adjust the sensitivity to a convenient range. On a windless morning take the speed and tone data to plot a calibration curve of the tone's frequency versus the speedometer reading. Mount the needle valve on the model so that it is in minimally disturbed air. A standoff 3 or 4 inches long, aligned with the direction of flight, at the top of the fin might be a good place for the needle valve with a long piece of tubing connecting to the modified variometer located conveniently in the fuselage. The needle valve has to be oriented to the airstream of the model in the same way as it was to the air stream it was calibrated in. The length of tubing for the glider instalation should be the same as when the calibration was done.

vortex00
The EMS devices appear to be well-engineered and economical, unfortunately they only record min / max data. A workaround entails hooking into a spare rx channel, enabling 25 readings to be taken, however that's probably still not enough for accurate speed info. Thanks for the link - might try reverse-engineering the speed indicator or picking parts for a wireless widget.

mec,
Thanks for the photo as another GPS option.
As a simple method not requiring any special retrofitting, difficult mounting methods or adjustments, the GPS approach is attractive. Another major plus is the altimeter, a barometric one on the Garmin eTrex Vista (used in the SB-XC tests) which, as I've read, offers generally more accurate indication of elevation than GPS-based altimeters. Note that I didn't state "low cost" as an advantage - the Vista runs about $300-up. It has gotten some good reviews, however, and is touted as one of the most feature-laden units on the market.

Advertised accuracies of the Vista with WAAS (US only) refinement (I'm assuming these figures are plus/minus):
Position: 3-5 meters, 95% of the time
Altitude: 10 ft
Speed: .05 m/s

Given the stated positional accuracy, averaging ground speed over a certain period of time may effectively compensate for wind, given no radical change in wind conditions or flight behavior. Still, the ideal approach is a "real-time" airspeed indicator, so . . . .

Ollie,
Getting resourceful! I was considering a similar, albeit more brutish, approach based on a standard pitot-tube sensor, voltage-output differential pressure xdcr, voltage-to-frequency converter, and pulse-emitting transmitter or signal fed into the guts of one of those pocket-size walkie talkies. Ref calibration curve would be accomplished via car testbed as you state, the frequency determined with a scope or frequency counter. To simplify in practice, if only a target airspeed was needed, I envisage the receiving end outputting an audible tone and another device outputting a fixed tone set at the target frequency, then flight trimming until a resonance is heard.

Don't think I'll put effort into a radio-based system that can provide a direct digital readout as: a) others are already developing them, and b) although I'm an engr, I'm not the "wired" kind - I'd love to have time to learn about micro-P's, PIC chips and all, but as it is, I know just enough about electrons to be a danger to my community.

The only problem I have with the Thermic Sniffler is their scarcity - These things seem to be about as common as penguins in the Sahara. Heard they worked well though. Were they total-energy compensated? Any thoughts as to why they became extinct? If I had one, I'd probably just put it into an antique showcase rather than do anything practical with it.

A lot depends on what you want to spend and your ability to write computer programs. In my research planes, I use an onset data logger ($300) with a motorola pressure sensor hooked to a pilot tube in the wing. A relationship was established between the air pressure at a range of speeds and the corresponding digital values sensed by the data logger from the onboard A/D converter. A program was written to log the airspeed (along with other parameters like pressure based altitude estimates) several times per second. Airspeed could be logged several thousand times a second if you wanted. Add a handheld gps and you could record the position of the plane each second (writing the correct routine in your program of course).

Really, the sky is the limit using this approach.

Elson

rc bugman,

I've seen references to the Motorola sensor(s); seem to be very popular for these low-pressure applications, but I don't remember the p/n - Can you provide the p/n of the sensor?

Since your request is work related, I will have to wait until Monday to look up the part number. I will try to post it on Monday nite.

Elson

If you want to explore this today, use google.com to search for Digikey. Search the Digikey page for motorola sensors. Select the differential sensors.

I come up with a pN which looks right

PN MPX2010DP Differential pressure sensor range 0-1.45 psi $14.43 each.

You can also seardh the Onset computer page for the data logger I use. (under OEM I think)

Hope this helps

Elson

rc bugman,

Don't bother at work, the info you've provided will do, think I can take it from there, thanks.