I am a Mechanical engineering student and i am completely new to arduino and need some advice. i have a project to measure the maximum deflection in a sailplane wing (up to 9 meters)

  1. How do i measure distance using ultrasonic or light sensors to a non perpendicular surface

  2. what hardware would measure such a large distance as ultrasonic have a max range of 4 meters

ANY HELP would be greatly appreciated

the attached

Diagram of mounted wing, the Ymeasurement is what i need to measure

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    $\begingroup$ I would use a Time-of-flight laser sensor $\endgroup$
    – chrisl
    Commented Mar 14, 2021 at 17:27
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    $\begingroup$ I suspect this is better suited to the Engineering SE, as it is only moderately associated with an Arduino, while selecting methodology and sensors are certainly engineering. $\endgroup$
    – fred_dot_u
    Commented Mar 14, 2021 at 17:40
  • $\begingroup$ Your question reads as though the wing will deflect up to 9 m which is unlikely. Can you edit to clearly state the wing length and maximum deflection to be measured and the required accuracy. Are we allowed to attach a vertical scale to the wingtip? $\endgroup$
    – Transistor
    Commented Mar 15, 2021 at 13:12
  • $\begingroup$ you just need a steady camera. then you can see what row/column of pixels the wings extend to, and that tell you the position. I used to have a golf rangfinder that was simply a bar scale overlay that expected a 6 foot hole pin; by confining the top and bottom of the pin to the visible slope, you could tell how far away that 6' pole was... $\endgroup$
    – dandavis
    Commented Mar 15, 2021 at 23:06

2 Answers 2


Please draw a diagram of the measuring scheme you're envisioning, edit your question, and add it to your question.

It sounds to me like you're planning on putting a distance sensor on the top of a sailplane's canopy, aimed out to the sides and slightly downwards to point directly at the wing tips. You then correlate the distance to the wingtip deflection. Under higher Gs the wing tips will flex up more.

Since this will likely need to take measurements during flight, even if ultrasonic sensors had sufficient range, the wind noise would likely render them useless, in addition to the fact that you're literally flying away from the sound waves as they occur, causing them to not return as well, and drastically affecting the return time if the sound waves travel with or against the wind at all. If that were the case, you'd have to take airspeed into account to adjust the ultrasonic return time. Plus, the near zero angle is far from the ideal 90 deg angle to the wing tips, making the ultrasonic return very very weak, if it returns at all.

I suggest you buy a laser rangefinder which you can hook up to an Arduino to log measurements. If it doesn't work well due to the shallow reflection angle, then a better plan may be to mount strain gauges to the bottom (and maybe top too) of the wing at a fixed point along the wing (ex: 2/3 of the way from the root to the tip). Then, you can put the sailplane in a test setup on the ground to experimentally flex the wings and correlate strain gauge readings to wing tip deflections.

Another option is to place a large fiducial sticker on the top of the wing tip. Have a high resolution camera on the canopy aimed at the wing tip. Use computer vision and photogrammetry to correlate the angled view of the fiducial to wing tip deflection. The greater the upwards deflection, the more perpendicular the fiducial will be to the camera.

Note: if using the strain gauge sensor approach, calibrating strain gauge readings to wing tip deflection in a ground bench test setup would be best done with a laser range finder aiming straight up at the wing tip during the test, close to perpendicular, from the ground, during forced wing tip deflection. It would be the source of truth for wing tip deflection, allowing you to determine wing tip deflection as a function of strain gauge readings.

See also my comments below.

  • $\begingroup$ Be careful that putting stickers etc on aerodynamic surfaces can be a serious issue if they trip the boundary layer at a different place, which can seriously ruin your day after an unexpected stall or spin. During WWII the RAF banned squadrons from painting their own logos etc on aircraft wings, after nothing more than an extra layer of paint caused several crashes! $\endgroup$
    – alephzero
    Commented Mar 15, 2021 at 13:13
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    $\begingroup$ Hi i added a picture of what i meant. sorry that my question was not clear. this is tto measure the deflection of the wing while the wing is in a test bench. the wing is bent upwards and i need to measure the distance from the ground to the wing at any point along the wing. What sensors will work for this purpose as the wing is a massive curved surface and the sesor wont be tangent to the surface $\endgroup$ Commented Apr 5, 2021 at 11:20
  • $\begingroup$ I'd go with a laser range-finder. I suspect it will work well-enough even at non-perpendicular angles. Some are called "laser profilometers" and have extremely high precision and resolution. I recommend you find a laser rangefinder or laser profilometer, or make one, which suits your needs. I suspect they will do the job very well. Note that diffusely-reflecting (ex: matte) paint will reflect better than specular (ex: shiny) paint when at a non-perpendicular angle. $\endgroup$ Commented Apr 6, 2021 at 3:41
  • $\begingroup$ To aid in reflection, you can also consider using retro-reflectors, including retro-reflective tape or paint. (This is the material used on roads, road paint lines, and road signs and reflective clothing. It reflects light back in the direction from which it came, with a very high signal strength, and shows up extremely bright to laser-based sensors such as profilometers, range-finders, and lidar). $\endgroup$ Commented Apr 6, 2021 at 3:46

I would definitely just use a camera with a rule or other scale or something in the screen if possible to scale rather than designing an entire electronic measurement system if you're not an EE. It should be easier, faster, and more intuitive to set up. You have other project concerns to worry about anyways.


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