Air Data Computer - Pressure Sensor

Hey,

I'm attempting to build an Air Data Computer which obviously requires pressure sensors (one for static and one for pitot). I've done some maths and I know I want them to be operable between around 0.7 to 4 bar (about 10-60 PSI) as this is roughly the pressure at 10000ft and the max pressure at sea level based on the max speed of the aircraft I will use.

I can't seem to find any suitable sensors, or ones that are easily compatable with the Female-Male wires (Male for connecting to my Uno board). Does anyone know any that are good, or would work for my project or has someone done a similar project before.

Any help would be greatly appreciated <3
Maple :slight_smile:

Most pressure sensors that include connectors have several options available, including bare wires.

If bare wires are not an option, either buy a matching connector and make your own adapter cable, or cut off the existing connector and replace it with anything you like.

On an aircraft subject to vibrations and other forces, you MUST use secure connectors or soldered leads. An Arduino board with female headers is not on that list.

Are you sure about those pressures ? Seem rather high .

Pitot

Hi,
For static sensor:

ft m mbar psi mmHg inHg
-5000 -1524.0 1210.23 17.553 907.75 35.738
-4000 -1219.2 1168.55 16.948 876.48 34.507
-3000 -914.40 1128.03 16.361 846.09 33.311
-2000 -609.60 1088.66 15.790 816.56 32.148
-1000 -304.80 1050.41 15.235 787.87 31.018
-900 -274.32 1046.64 15.180 785.05 30.907
-800 -243.84 1042.89 15.126 782.23 30.796
-700 -213.36 1039.15 15.072 779.42 30.686
-600 -182.88 1035.41 15.017 776.62 30.576
-500 -152.40 1031.69 14.963 773.83 30.466
-400 -121.92 1027.98 14.910 771.05 30.356
-300 -91.440 1024.28 14.856 768.28 30.247
-200 -60.960 1020.59 14.802 765.51 30.138
-100 -30.480 1016.92 14.749 762.75 30.030
-50 -15.240 1015.08 14.723 761.37 29.975
0 0 1013.25 14.696 760.00 29.921
50 15.240 1011.42 14.669 758.63 29.867
100 30.480 1009.59 14.643 757.26 29.813
200 60.960 1005.95 14.590 754.52 29.706
300 91.440 1002.31 14.537 751.80 29.598
400 121.92 998.689 14.485 749.08 29.491
500 152.40 995.075 14.432 746.37 29.385
600 182.88 991.472 14.380 743.67 29.278
700 213.36 987.880 14.328 740.97 29.172
800 243.84 984.298 14.276 738.28 29.066
900 274.32 980.727 14.224 735.61 28.961
1000 304.80 977.166 14.173 732.93 28.856
2000 609.60 942.129 13.664 706.65 27.821
3000 914.40 908.117 13.171 681.14 26.817
4000 1219.2 875.105 12.692 656.38 25.842
5000 1524.0 843.073 12.228 632.36 24.896
6000 1828.8 811.996 11.777 609.05 23.978
7000 2133.6 781.854 11.340 586.44 23.088
8000 2438.4 752.624 10.916 564.51 22.225
9000 2743.2 724.285 10.505 543.26 21.388
10000 3048.0 696.817 10.106 522.66 20.577
15000 4572.0 571.820 8.2935 428.90 16.886
20000 6096.0 465.633 6.7534 349.25 13.750
25000 7620.0 376.009 5.4536 282.03 11.104
30000 9144.0 300.896 4.3641 225.69 8.8855
35000 10668 238.423 3.4580 178.83 7.0406
40000 12192 187.54 2.7200 140.67 5.5381
45000 13716 147.48 2.1390 110.62 4.3550
50000 15240 115.97 1.6821 86.987 3.4247
55000 16764 91.199 1.3227 68.405 2.6931
60000 18288 71.717 1.0402 53.792 2.1178
65000 19812 56.397 0.8180 42.301 1.6654
70000 21336 44.377 0.6436 33.286 1.3105
75000 22860 34.978 0.5073 26.236 1.0329
80000 24384 27.615 0.4005 20.713 0.8155
85000 25908 21.837 0.3167 16.379 0.6448
90000 27432 17.296 0.2509 12.973 0.5107
95000 28956 13.721 0.1990 10.291 0.4052
100000 30480 10.902 0.1581 8.1769 0.3219

Now what air speed and what pitot tube diameter are you calculating for?

Tom.... :smiley: :+1: :coffee: :australia:

Yeah, I'm aware, luckily my aircraft has no engine so there are far fewer vibrations. I'm just looking to make something rudimentary more as a proof of concept :smiley:

I took my minimum pressure as the approximate pressure at 10000ft ~700mbar.

I took the maximum pressure as: 0.5 x rho x 61^2 (~120knots which is the max speed of my aircraft) which was around 4000mbar

Do I need to adjust these for tubing diameters?

Hi,

Don't you know?
It looks like you had better research pitot tube dynamics before looking at pressure sensor types.

120knots = 222 kph, what is your unpowered projectile?

Tom... :smiley: :+1: :coffee: :australia:

I had used 120knots = approx 61.7 m/s
Projectile is the incorrect word :wink:
I fly gliders :smiley: (albeit there may be vibrations upon launch and if this is the case I'll solder everything together).

I was using something similar to this for my calculations:

Hi,
Thanks for that; Good old Bernoulli..

So dPressure = ( V * V * density ) / 2

V = 61.7 m/s
density at STP = 1.225 kg/m^3

difference in Pressure == dP = (61.7 * 61.7 * 1.225) / 2 = 2,331.7 kg/m^2

dP = 228.6 mBar

I may have done something wrong, correct me if I have.
Its been 40 years since I did any of this. :open_mouth:

Also this is at STP, at altitude density will be lower so dP will be lower.

Tom... :smiley: :+1: :coffee: :australia:

Hey Tom, sorry for the delay.

ahh ok, that makes sense
The value found with STP is the highest dP as it decreases with altitude?

Thank you,
Maple :grinning:

4 bar?? That's the stagnation pressure at Mach 2. What on earth are you building??

Ah, I see, you didn't use the correct units for you calculation.

stagnation pressure = 0.5 x density x velocity^2
All in SI units. Always work throughout in SI units!!!

You got the 61 right as metres/second.
No idea what value you used for rho, but 1.2kg/m^3 is the one to use.
However the SI unit of pressure is the pascal, Pa, not bar or millibar. 1 bar = 100,000Pa. Thus your calculation should give 2233Pa, or about 22mbar

Lol, yeah, that makes 4bar seem ridiculous! I'm definitely not planning on flying at mach 2!!

I guess it shows the importance of using SI units.

Thank you for reworking the calculation for me. Hopefully I can now find a pressure sensor with this more sensible range

Maple :grinning_face_with_smiling_eyes: