Need your opinion on mechanical variometer - RC Groups
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Mar 15, 2012, 03:10 PM
Euphoric flights
GreenAce92_v2's Avatar

Need your opinion on mechanical variometer

This was an idea to make a mechanical variometer based on the AC location of a glider and a small pivot.

This variometer could be made out of a paper clip if it could work which is where you guys come in.


A seesaw mechanism with electrical contacts is placed on an airplane. The fulcrum is located precisely on the Aerodynamic Center of the aircraft. Any change in height (impulse) would cause the see saw to pivot. The seesaw is quite sensitive and when the contacts meet, an LED circuit is completed and glows.

This variometer is intended for FPV use

Do you think that this idea would work?
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Mar 15, 2012, 03:48 PM
Registered User

A couple of things to ponder -

1. Your device depends on acceleration. What about constant-rate climbs, when acceleration is zero?
2. What about when the airplane rotates? The contacts will close and you will get a false reading.
3. When the airplane does rotate (and it will), it will rotate about the center of gravity. That will result in a sensed accelertion at the aerodynamic center, and a false reading.

Originally, variometers were based on a closed chamber. As the airplane climbed, air moved out, and moved a pellet in a tapered tube. As the airplane descended, the air moved back in, and the movement elevated a pellet in another tube. The pellet indicating climb was usually green. The descent pellet was usually red.

Good luck.

Yours, Greg
Mar 15, 2012, 03:51 PM
Euphoric flights
GreenAce92_v2's Avatar
See this is why I needed to post this.

Thanks Greg, as always

What is the simplest vario you can think of that can be visually used by FPV?

The last one down is a bit pricey for my taste though I did come across this "pellet" Variometer you speak off on hang gliding forums.

Also a guy mentioned moire effect on one of the home made variometers.

I did find a full schematic layout of a home made vario but it seemed pretty complicated for a noob at circuit making.
Mar 15, 2012, 03:57 PM
Registered User
R.M. Gellart's Avatar
Doesn't the Aerodynamic Center of the AC change with speed, AOA, etc? That is why they can fly nice but tuck under certain circumstances.

Mar 15, 2012, 09:29 PM
Will fly for food
davidjensen's Avatar
How would this unit work in blustery turbulent air?
Mar 15, 2012, 09:41 PM
LSF303-AMA Fellow
tkallev's Avatar
I built some free flight models in the 60's that used a pendulum to move the elevator and rudder ... models kind of staggered across the field until you got the range of motion right.

Bought a radio and never looked back
Mar 16, 2012, 09:20 AM
Registered User

A variometer for RC use, that can also transmit a signal, will probably set you back $300. Sorry about that.

A basic variometer is actually quite simple, but bulky. It requires a vacuum bottle and a thermistor. It's the vacuum bottle that is bulky. Check out "variometer" on wikipedia.

There is no reason you couldn't use a GPS receiver in your model. The actual receiver in a cell phone is a chip about the size of a fingernail (the bulk in your cell phone is battery, screen, keyboard and speaker). If you started with a Radian, for example, you could use a whole cell phone.

Yours, Greg
Mar 16, 2012, 11:57 PM
Registered User
rrcdoug's Avatar

GPS variometer woes

I used a GPS based variometer last summer. It worked OK as long as the lift was gentle. The GPS usually has a "filter" to keep height data "reasonable", ie you are in a ground based vehicle or walking. The vario typically sensed lift for 30 seconds after winch launch as it caught up with the sudden gain in altitude. I am working on a pressure sensor driven system that will insert pressure altitude into the GPS NMEA stream so my software (SkyNavigator) will still read it.

The sturdiest and most compact varios we used for hang gliding were differentiated pressure altimeters. An analog electronic pressure sensor was sensed through a capacitor and some Op amps.The resulting signal was proportional to the rate of change of the pressure. This is pretty obsolete now with digital pressure sensors and microprocessors that can count feet (or meters). A lot of the RC varios are talking now!

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