COMPLETELY DIY ultralight instruments

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Two lane aviator

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anyone know how to homebuild an airspeed indicator, turn and bank indicator, altimeter, and maybe an attitude gyro app for an android smartphone?

NOTE: only COMPLETELY do it yourself items please, almost everything available there in the us is either not available or stupid costly here in the Philippines
 

spaschke

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Denver, CO
I found an article from electronicdesign.com for making an air speed indicator. here is their link Linear pitot-tube air-speed indicator | Test & Measurement content from Electronic Design
[h=1]Linear pitot-tube air-speed indicator[/h]Jun 9, 1997W. Stephen Woodward | Electronic Design


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Among the many methods used for measuring air speed, one approach excels in applications related to aerodynamics and wind power: the Pitot-tube impact-pressure air-speed indicator. The so-called “impact” or “stagnation” pressure exerted by airflow striking a surface is given by P = (D × V2)/2, where D = air density and V is air speed. Pitot tube anemometry uses this relationship to produce: V = √—2P/D.
Although it might seem that this dependence of the air-speed estimate upon density is an undesirable complication, it’s actually advantageous in those applications to which Pitot-tube anemometers are uniquely suited. This is true because, in these applications, the forces of primary interest (e.g., lift from an airplane’s wing or propulsion from a boat’s sail) are themselves related directly to impact pressure and therefore to air density. The air speed measured by a Pitot tube is automatically compensated for variations in air density caused by changes in temperature, barometric pressure, or altitude. It’s therefore exactly the air-speed information most wanted by the pilot or sailor.
The heart of the Pitot tube airspeed indicator is piezoresistive differential pressure sensor G1. Op amp A1, in combination with VR1 and R1, R2, and R3 controls Q1 and Q2 to generate constant-current-bridge bias I1 = 500 µA. In response, G1 produces a differential voltage (V1 − V2) equal, after zero compensation via R4, R5, R6, and R7 to approximately 8 mV/psig of impact pressure. The A2, A3 differential pair controls Q3 so as to convert (V1 − V2) to impact-pressure-proportional current I2 ≈ 160 µA/psig.
Calculating √—I2 works as follows: Due to the logarithmic behavior of silicon transistors, base-emitter voltages Vbe2 = Alog(I1/2) + B, and Vbe3 = Alog(I2) + B, where A and B are constants common to all five transistors in the LM3046 array. Because addition of logs is equivalent to multiplication, (Vbe2 + Vbe3) = (Alog(I1 × I2/2) + 2B). Series/parallel connection makes (Vbe2 + Vbe3) = (Vbe4 + Vbe5) and, because of the implicit matching between transistors in a monolithic array, Vbe4 = Vbe5. Therefore, Vbe4 = Vbe5 = (Alog(I1I2/2)/2 + B). Division of logs is equivalent to inverse exponentiation. Hence, Vbe5 = log(√—I1× I2/2) + B.
This makes log(I3) = log(√—I1 × I2/2). I1/2 = 250 µA, so substitution and exponentiation yields I3 = √—I2 × 250mA.
With the components and circuit values shown, I3 ≈ 1 µA/knot. With suitable adjustment of R8, a wide range of full-scale air speeds can be calibrated for. If R8 ≈ 10k, for example, Vout = 10 mV/knot for a 1-V fullscale output at 100 knots. This is just about right for duty as a primary airspeed indicator in an ultralight aircraft. Of course, suitable adjustment of R8 can accommodate different preferences in air-speed measurement units, such as meters per second or statute miles per hour.
Supply-voltage regulation for this circuit isn’t critical and power demand is modest, easily allowing battery operation. The simple power supply shown will provide more than 100 hours of operation from a 9-V alkaline battery.
See associated figureasi.gif




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Floydr92

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Android would be complicating things a bit i think. The simplest way would be a manometer, but since we're talking electronics here, why not use an arduino or raspberry pi? (the Pi has the advantage of a HDMI output which you can connect straight to a nice big lcd on your dashboard). for airspeed indicator you would just connect a Piezo electric crystal or other pressure sensor of your choice to 5v, GND, and A0 (or any other analogue in). Then the 'sketch' (for arduino) would be very simple, something a bit like this:

...............................................................................................................................................

void setup()

// This will start a serial link with a computer or in your case, possibly an android device to view the output
{
Serial.begin(9600);
}

void loop()
{
int sensorValue = analogRead(A0);

float
voltage = sensorValue * (5.0 / 1023.0);

// Calibration info would go here, so that it would convert the analogue reading into the related pressure, and then the related speed before printing to your computer.

Serial.println(voltage);

delay(100);

// the above section will read the sensor output via pin A0, print the value to your serial port, wait for 100 milliseconds, and repeat. You could increase or decrease the 'refresh rate' as you like.
}

// from here, you would have the airspeed represented on your screen in a scrolling list of numbers. you could either connect this to android via an app (get some kind of bluetooth shield, and send the serial output straight to your phone to be used with your app?) or much easier: make a simple program, and output to a small LCD on your dash. You could also add a GPS for groundspeed, gyros for pitch, roll and yaw, loads and loads of possibilities here. (you could even connect servo motors to your trim wheels and you have an autopilot ;p )

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Topaz

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Android would be complicating things a bit i think. The simplest way would be a manometer, but since we're talking electronics here, why not use an arduino or raspberry pi? (the Pi has the advantage of a HDMI output which you can connect straight to a nice big lcd on your dashboard). for airspeed indicator you would just connect a Piezo electric crystal or other pressure sensor of your choice to 5v, GND, and A0 (or any other analogue in). Then the 'sketch' (for arduino) would be very simple, something a bit like this:...
Oh yes. Much simpler. :speechles
 

cluttonfred

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Guys, you are reminding of the apocryphal engineering story of someone who designed a complex screw extraction machine because nobody told him that it helps to turn the screw. ;-) There are plenty of simple "analog" DIY instruments that can be made for an ultralight. For example....

1) This airspeed indicator is actually from a certified DH Tiger Moth, but it's pretty self-explanatory. Piano wire, sheet metal or plywood, this and that, then calibrate by holding out the window at the end of a broom handle while driving down the highway.

09TigerMothAirspeedIndicator.jpg

2) See the PDF attachment for a DIY inclinometer as a slip/skid indicator.

3) It would be possible to rig up some sort of liquid-type barometer which would function as a rough altimeter, but I can't really see the point. You get an altimeter watch for about $50 and/or use a cheap GPS.

4) I have never seen a true ultralight that had any need for any kind of gyro instrument. By definition an ultralight is a fair weather day VFR machine...look outside!

5) The old FLYING AND GLIDER MANUAL reprints from EAA have some additional ideas for DIY instruments here and there as well, IIRC.

Cheers,

Matthew
 

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Victor Bravo

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KWHP, Los Angeles CA, USA
I'm not sure whether you would consider this DIY, but a "wind meter" is often used for an airspeed indicator. If you cannot find one in a camping or outdoor store, you can easily make one out of a plastic tube and a cork, with lines drawn on the tube to correspond the "wind" velocity to speed. Of course the homebuilt "paddle" type as shown in the photo is every bit as good for an ultralight as a certified and factory built unit. And you can build one of these out of sheet plastic, wood, metal, or cardboard along with a piece of coat hanger wire from the waste basket. The bendability of the coat hanger becomes your "calibration" adjustment :)

If you wish to have an electronic one, you can put a small plastic propeller on an electric motor or generator, and calibrate the voltage output to read out as airspeed. This was actually a product offered years ago I remember seeing in the Aircraft Spruce catalog, but the truth is you can make one from toy store materials today.

Like any glider pilot, I can guarantee you that the highest quality and most accurate slip-skid indicator is a 4 inch long piece of yarn taped to your windshield, or tied to a piece of wire in front of you.
 

clanon

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Jun 6, 2007
Messages
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What are the pros and cons of using a sensible (small and light)fan manometer for Air Speed?
Previously adjusted by other means...
 
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