Its not for an R/C plane, I’m a pilot and working on a number of sensors (including airspeed, altitude, etc), the problem with using a barometric altitude sensor for this is that small changes in pressure can cause a 5-10’ error. Right now the altitude sensor calibrates when the sensor pack is turned on to 0’ AGL, but a couple hours of flying or flying to a different location can throw that off.
So I was wondering if there was a sensor out there that can be used like that. The laser sensors don’t seem to be a good fit, and ultrasonics seem to only go to about 25’.
Any links to laser? This is mostly for VFR, which means good weather (sunny days), and the beam would have to reflect off of non-reflective surfaces such as grass and tarmac, so if you have any links to lasers that fall into that category please let me know.
Its not for an R/C plane, I’m a pilot and working on a number of sensors (including airspeed, altitude, etc), the problem with using a barometric altitude sensor for this is that small changes in pressure can cause a 5-10’ error. Right now the altitude sensor calibrates when the sensor pack is turned on to 0’ AGL, but a couple hours of flying or flying to a different location can throw that off.
So I was wondering if there was a sensor out there that can be used like that. The laser sensors don’t seem to be a good fit, and ultrasonics seem to only go to about 25’.
I have experience in this field... and can offer no suggestions on something practical, except...
very bright IR LED on airplane. Sending digital ID code pulse stream (microprocessor of your design).
TV camera(s) on ground. Feeding IP or analog video to PC/laptop. Software looks in the digitized video raster for the pulse train - maybe doing an FFT/DCT to search the bit rate in the frequency domain. Solve for X, Y, Z using photogrammetry based on knowledge of the lens focal length, pointing angles, etc. Or calibrate each camera emprically with IR diode in a known place.
Not sure that applies to what I’m talking about. I’m wanting a system that I can place on the airplane (alone) and measure distance to the ground as I’m landing at various airports giving me an audio cue as I land. Pretty sure the FAA wouldn’t be too happy with me installing IR camera’s around airports
If the laser is a non visible eye safe class II you might get away with it. Other than that, you may find yourself breaking big rocks into little ones and getting 3 free meals a day.
There are certainly lasers that fall into this catagory. Happen to be using a custom one at work. But the optics and electronics needed to put it together is pretty much out of the reach of the average person.
How about the altitude system they used on the damm busting airplanes in WW2. Bright lights on each wing tip focused downward. When the two spots were on top of each other you were at the right altitude. You could simply have two bright beams and a camera to look at the seperation distance of them. A bit of trig and you get altitude.
Its an interesting idea, but not sure I can make that work, would like to avoid shining lights. I know a lot of “can’t do that” but when working with things that fly over peoples houses and land on things controlled by the FAA, its bound to happen
I guess I have to put more thought into this. I was really looking for a long-range ultrasonic since they are low power (its a battery device) and would not need to be permanently attached (permanent attachment requires an FAA approval, note in the log book, and test flights, and I rent the aircraft).
I’ll have to look at somehow synchronizing the barometric altimeter with local readings through the monitoring interface (right now a cell phone), maybe I can get accurate enough readings to be within 5-10’…
Ultrasonics work via a sound wave moving through air. The air stream on your airplane will greatly distort that wave. It would also likely need to be angled forward so as to account for the motion of the airplane. That complicates the measurement of altitude. I think this explains why aircraft either rely on baro or radar altimiters. IR, ultrasound, or lasers all have serious deficiencies.
