Aviation – Random Projects

New Engine Monitoring for Old Aircraft – Part 1

Fig 1 – The original gauges. Thats a frightening charge rate.

I own a lovely Robin aircraft which was built in 1974 which makes it older than me. The Robin 200/100 series aircraft were not built in vast numbers and this point its rarer then the spitfire. Finding parts is difficult and many parts are completely unobtainable. So when I noticed on eBay an instrument cluster that probably only fits 20 serial numbers but was identical to mine I needed to buy it as a spare.

Fig 2

As soon as it arrived I checked to see if it was the same unit as in the actual aircraft and it is. There will never be another come up for sale, I can’t believe my luck. Obviously we should hook this up to 12V and see if it works. Its clearly not mass produced and you can see that the coloured bands are hand-painted. But its survived 50 years and for gauges in aircraft, which are notoriously unreliable this is amazing. The serial number between this one and mine is 13. We can guess that this any my aircraft were manufactured pretty closely together. I think it came from G-BICS which would be serial 104 approx. 50 later than mine.

How do these gauges work?

These are called “balanced magnetic indicators”. They are found in cars from all of the 20th Century and most aircraft such as Piper, Cessna, Robin etc.

The three Coils are arranged in two Branches, where Coil III in Branch 1 and and Coil II are oriented at a right angle to Coil I of Branch 2. Because of the differing orientation of the Coils, the effective magnetic fields of the two branches are in opposing directions and combine to give a resultant field which has a quotient relationship between the two fields. In other words: it works by creating two magnetic fields that oppose each other, and the gauge shows the difference. The idea is that as the system voltage changes the gauge should show a proportional reading over a range of voltages.

In Fig 2 above, I simulate the fuel sender with a variable resistor and use a system voltage of 12.5V. The fuel sender is a resistor to ground. In this way “senders” can earth through the vehicle chassis requiring only a signal wire. Wiring this up allows me to get any reading I like and fully exercise the meter.

This is where I realise how dodgy older gauges can be. I notice issues: its not linear, if you leave it on for 20 mins and let it soak (it generates a watt or so of heat) it drifts by 5% or so in the upward direction. Thats probably because the coil opposing the reading heats up, increasing its resistance and reducing the current and thus magnetic field. It changes by about 8% over 12V to 15V range for a fixed sender value. I always suspected that when the battery is low the fuel gauge reads a bit lower – it actually does. Finally, there is a bit of stiction in the movement; moving up to or down to the same value doesn’t always give you the same reading; but this doesn’t matter because the engine vibration sees to it that it doesn’t stick. For a 50 year old meter a value within 5% isn’t bad. I tested all the other gauges, they require different biases because the senders are all different but they all work work.

The ammeter is different. I thought it would be a current shunt with a moving coil meter but its not. Its a bar of brass (shunt) and the needle is a sprung loaded magnet. So the magnetic field, which is proportional to the current, tries to twist the needle against the spring which is linear – very simple. Of course if the current flows the other way, it twists the needle the other way and that allows the needle to show charge and discharge. The down side is that the needle bounces around with no damping and the readings are to be taken with a pinch of salt. Basically it tells you if you are charging or discharging. At +10A it was showing halfway to 20. at -10A it was showing closer to -15A but it doesn’t sit at zero either. You can adjust it, but best to leave it as its very fragile. High end gauges can be filled with mineral oil to add damping but it would only leak out – like it does on aviation compasses- which is a right pain.

Calibration

Next – does it agree with the actual aircraft meter? You cannot place the gauges in parallel, because the sender and the meter produce a potential divider, so putting two meters in parallel would halve its impedance and change the reading. Since my actual gauges may pack up at some point, its a good idea to see if they match now before that becomes an issue otherwise we’d be guessing. The answer is they agree within about 10%. So the fuel is reads 55 where as the plane reads 50, the others are in broad agreement. I didn’t check the ammeter because you can’t read either one sensibly – but you can check it on the bench and we already know its acceptable. We have used a calibrated thermocouple on the aircraft and the oil temp gauge is pretty close at 60C. For the fuel, when its showing about 60L and we brim the tank we get just under 60L of fuel in, and since the tank is 118L that shows its also reasonable.

If we ensure sufficiently high enough impedance input we can measure the voltages presented to the gauges at any indicated value we want and read off the voltage. This means we could build our own indicator which wouldn’t be susceptible to wear or temperature or voltage variation.

Measurements

Since the gauges are only within a few percent there is no point investing in high precision instrumentation amplifiers and 10 bit resolution will be fine. I have boxes of esp32 controllers with ample analogue inputs available and whilst the esp32 isn’t known for having a super linear ADC (analogue to digital converter) its only poor at the extremes and rather than try to model its response and that of a filter, we might as well build the actual circuit and use the ADC values straight off. – I mean, we’re not going for mass production, so the values only need to be repeatable on this specific device.

The signal was fed in to a potential divider because the esp32 must be within 0 – 1V or 0 – 3.3V depending on the attenuation setting. The potential divider chosen is a potentiometer of 100k Ohms, thats because we do not want to load up the gauge because we’ll affect the reading – not just what we measure but the actual displayed gauge reading. Then after the potential divider a capacitor is added to ground which then forms a low-pass filter which will help reject noise and interference. This means our input impedance is about 100k and since the resistance of the gauges is a few hundred ohms, we are taking 1/1000th of the current the meter is which is 0.1%. 1% probably would have been fine, 10% wouldn’t be.

The reading is non-linear but remember that the sender is in parallel with half of the meter coils so that is of the form you’d expect. Using Excel we can get the formula for an approximation line form the actual values which results in over-reading at the higher fuel readings and under reads at the low end. That is definitely the way you want a Gauge!

Now, can we use those figures to build our fuel gauge? The answer is no. Because the actual voltage (ADC reading) changes with system voltage. The mechanical gauge compensates for this because the current flowing through the coil is proportional to system voltage. But we need to compensate for it.
So we pick a middle reading and observe it across a sensible voltage range.

What we get is a linear relationship. That makes sense because basically the current in the meter scales with system voltage.

When plotting the values against various bus voltages we see that the readings are simply scaled and they cross the axis at zero.

Another thing to think about is the geometry of the fuel tank. Ours is like half a barrel on its side, that means that the volume isn’t linearly related to depth, the level drops faster as the volume decreases. If you look at the gauge to see that the manufacturer has squeezed the higher readings closer together but also the way these coils work also has the inverse effect which helps with linearity.

Here we can see the 14V values and then the transfer function. We then use the raw values through the inverse transfer function so cross-check our work and the values are reasonable, any deviation would be impossible to see on the actual gauge.

Aircraft Alternator Teardown

The aviation industry might make you think that aircraft alternators are made out of special materials, have been tested to impeccable standards and are manufactured on special production lines sprinkled with pixie dust. A normal engineer couldn’t hope to service one. The reality is that they are 1950’s or 1960’s American car (like Ford) alternators that wouldn’t stand up to the quality, power output or or rigours of a modern car alternator. Modern car alternators can produce a smooth output from 750 to 6000 rpm with little or no noise in the output because the tolerances and power electronics / frequency are far more advanced.

Mid overhaul, rotor shaft removed. The red ring is the laminated stator ring. The top casting has a simple sealed ball bearing and the rear casting contains a roller bearing. The through bolts contain 2mm holes cross-drilled at the end of the thread for lock wire. (actually the same alternator as first figure)

Basic Operation

The principle of operation is simple, a rotating magnet induces an alternating current in a stator winding (hence the name alternator) that is then rectified and delivered to the battery.

The figure above shows the schematic layout. The stator would work with a single coil but by arranging 3 at 120 degrees (equally around the circle) the sine waves from each phase sums to a smooth output. In theory it shouldn’t whine or produce large amounts of ripple or pulse. This 3-phase approach also doesn’t require a return path at the centre of all 3 connected coils because each phase works against the other two. The aux output (at the centre of the windings) isn’t required and can be left unconnected.

Stator windings. The bearing at the bottom. The stator is laminated steel which helps control eddy currents increasing efficiency. The round things are diodes of which there are 6 because its a 3-phase rectifier.

rectifier plate mounted at the end. The plate is the output of the positive end of the diodes which leave via the output terminal (left) the other 3 diodes go to ground which is the alternator casing (top two and bottom right). The white wire is tied to the centre of the 3 coils which leaves to the aux terminal which is isolated from the rectifier plate. One or two needle bearings are visible in the bearing (centre) and the black ring is an oil grease seal.

Regulation

We said that all we do is swing a magnet around in a coil to produce our output but obviously, there is more to it because that would overcharge the battery. If an alternator became detached from the battery, the output voltage may reach hundreds of volts.

Aircraft alternator regulators tend to be very simple on or off affairs and the electric regulators are in some cases mechanical. They are unreliable to the point that its typical to include an over voltage relay (OVR) which cuts off excitation completely if a preset output voltage is exceeded. For a 14V system this would typically be set to 16V. If the system reached 16V the relay will latch on turning the alternator off.

To regulate the alternator output we want a variable strength magnet in the rotor instead of a permanent magnet. In an alternator the rotor is an electromagnet and when the battery is low the strength of this magnet is high and when the battery is fully charged the magnet is its weakest and its the job of the regulator to control this. In a car this will be built into the alternator and it will use fast modulation of the rotor current in a closed control loop to produce an output that is always spot on. In an aircraft regulators tend to be separate units like they used to be in cars. In cars they stopped doing that because regulation control is poor, being affected by voltage drops, stray magnetic fields and radio interference as well as emitting radio interference all over the place. What normally happens when there is parasitic resistance is that the voltage will fluctuate, often oscillating, but even under the best situation its poor.

The rotor. The slip rings (copper coloured) connect a single winding axially wound around the centre former. The windings are visible.

An electromagnet is just a winding, and winding around an iron core concentrates the field. As such, the rotor is a single winding around an iron former. The two interlocking sets of fingers are opposing poles (each end) of the electromagnet which means that the rotor actually has alternating N-S-N-S… arrangement. As we can see in the picture, one finger is part of one end and the next finger is part of the other end. Just like the stator where there are multiple windings, there are multiple poles rotating in the stator which improves output power.

The problem of how to connect the windings is solved using slip rings where graphite brushes are pressed against the rings by springs to maintain contact. The graphite has good conduction, is hard wearing and also lubricating.

The external regulator is a sealed unit that essentially varies the current flowing through the rotor from terminal F to ground via the output transistor T3. If T3 is fully on, then F would be driven to ground providing full current, typically 2 – 4 Amps.

The heart of the regulator is a reference voltage. A zener diode has a fixed voltage drop across it which can be used to work out if our measured voltage is above or below a threshold.

When the system voltage connected to ‘I’ terminal reaches a value at which the Zener diode connected to the divider network conducts, current will flow from the ‘I’ terminal through Rl through Z1 causing Tl to conduct which diverts the base current of T2 flowing from ‘I’ terminal through R4 to ground, turning off T2 which turns off T3, de-energizing the rotor Winding. When the alternator output voltage falls to a value which permits Z1 to cease conduction, Tl will turn off which turns on T2 and T3, re-energizing the rotor winding. Filtering is provided by C1 which usually dries out and can’t be fixed.

This type of regulator is on or off but happens so quickly that the average current flowing through the rotor should be proportional to the charge current required and thus we can loosely refer to it as “regulating”.

Its fairly easy to bench test the regulator by using a variable bench supply, and a bulb in place of the field coil, if the voltage is below about 14 the bulb should be on and should go out as the voltage rises. You can vary the point slightly using a variable resistor (potentiometer) P1.

Self Preservation

Of course, the rotor windings are unlikely to always have perfect connection to the regulator due to the slip ring arrangement and because the rotor is a big inductor, the resulting field collapse when it becomes interrupted will induce large voltages which would rapidly result in the destruction of T3. To quench these spikes the designer has used a neon bulb L1. This is quite neat, a neon bulb will strike an arc at about 95V and will then clamp the voltage to about 60V. I would expect the bulb to have a hard time if the slip rings were dirty and I’m not sure how often they fail in practice.

In contrast a modern automotive alternator such as Bosch has solid state protection, diodes with larger breakdown breakdown voltages and much more robust transistors. This means regulator failure isn’t really a thing even if the output is shorted or reversed. The most common failure mode is bearing failure or salt water corrosion.

For aviation alternators regulator, wiring faults, poor earths, marginal batteries, diode and brush failure are all so common that if it were in a car it would fail every 50,000 miles or so – which is about what you’d expect from a 1950’s alternator.

Finally, although the output ought to be smooth because of the use of 3-phase the diodes do take some forward voltage to conduct so the current will suddenly kick-in when they become forward-biased, and this can caused a whine on the electrical system that may be heard on radios and amplifiers. So an output capacitor is typically fitted to the output terminal to ground usually around 2.2uF. These also dry out and should be replaced if a whine is heard and they can be doubled up to get 4.4uf if its still an issue. The suppressors supplied with Prestolite alternators are between 1 and 2.2uf but they have such a high ESR (effective series resistance) of 15+ Ohms that they might as well not have bothered.

Zaon Flight PCAS MRX Teardown

Zaon MRX – Approx 1.9 miles – 500ft above descending.

The Zaon PCAS portable collision avoidance system is a very simple box which is considered as carry on – therefore requires no certification. Aircraft carry transponders which are interrogated by ground based radar and respond with a signal which may include height information. This is used to plot the aircraft on an ATC screen.

The Zaon device listens to the responses from nearby aircraft and estimates their distance from you based on signal strength. If the aircraft is transmitting height it will also show you that and if it is climbing or descending.

It prioritises the received aircraft and gives you a warning. It does not tell you in which direction it is – but its enough to add a level of safety.

The main PCB is split into 3 distinct parts. On the left there is the power supply, its a buck-boost circuit which provides 3.3 from batteries that may below 3v. An external connector uses the same power supply and can operate up to 28V.

On the right there is a radio front end which operates on 1090Mhz, with basic decoding of mode C signals.

In the middle there is a microcontroller that does all of the processing and drives the display. My guess from the label P16F877 is that its probably a Microchip Pic 16F177 controller. I’m familiar with these from my past, they are a 40 pin controller with USB connectivity – you can see it does have 40 pins. These are still in production in 2022.

The only other point worthy of note is the display which is insanely bright. A broadcom device found here.

Sadly, Zaon no longer seems to exist but Garmin make an XRX version which gives quadrant directional information. But to be honest you can achieve the same today with a Raspberry PI and a software defined radio – which also allows you to decode ADSB.

3dD printed Cooler

Not one of my crazy projects – looks like this aircraft needed some extra cooling so the owner has taken to creating an air pump at the root of the propeller. Normally there isn’t much going on there so seems reasonable.

What could possibly go wrong?

The print layering is weakest between layers so you could find it separates. At a maximum of 3000rpm thats probably unlikely but I would be checking it carefully for cracks and would have liked to have seen a lamination with the layering going 90 degrees.

If the blade does become detached, it could find its way directly into the intake entirely blocking it. That would be enough to overheat that engine and bring down that aircraft.

Last Wright’s

I don’t really know why I find this so astonishing.

“I guess I ran the whole plane for a minute but I let the machine take care of itself,” Wright said of the experience. “I always said airplanes would fly themselves if you left them alone.”
Wright also pointed out that the Constellation’s 123-foot wingspan was longer than the distance of his first flight, which had travelled just 120 feet.

Orville died January 30th 1948 aged 76.

By wallycacsabre – mig1, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=59596165

I find it astonishing that he would have experienced the first powered flight and seen in his lifetime such dramatic developments. Prototypes like the MiG-15 and the B-47 flew in the month before his death.

Retro METAR Clock

Time and Weather

As an aviator its important to know what the weather is doing and in my case whether there is an point tuning up to the airfield.

I had been toying with the idea of making a retro LED clock for some time, but as I now have to use an ESP8266 connected device for everything because its cheap and east to use, I thought I could add value by displaying the current METAR. A METAR is an aviation text encoded weather observation that really belongs 100 years in the past, but is still useful. It tells us what the wind is doing, the pressure, cloud and visibility. These are all available online in JSON requests or via many free API’s. So all we need to do is make a web request.

The ESP8266 does not have a real time clock, but it is able to sync with NTP (Network Time Protocol) and keep time that way. So all we really need is the ESP8266 and the LED display.

Two 4 panel LED displays is too large for my 3D printer so its made it two halves. Simple affair, there is no back but it includes screw hangars and a notch for USB entry.

To join the two LED panels, I used 5 wire links between them.

CDS light cell / resistor tacked on to the board allows sensing of ambient light levels. Other than that its all driven directly from the ESP8266, the USB powers everything.

ArduinoOTA – allows for it to be updatable over the air, essential when its screwed to the wall.
Adafruit GFX Library – required for the LED panel.
MegunoLink – used to filter the light sensor data to stop the brightness hunting.
ArduinoJson@5.13.4 – specific version required to parse the JSON web request for the METAR data.
WifiManager – to create a hotspot to allow the device to be configured.
Max72xxPanel – the shift register driver for the matrix panel.

Refinements

I found that the string class, although very powerful, can lead to heap fragmentation on the ESP8266. The forums are not terribly helpful basically saying that people should learn to use char arrays and pointers instead and stop being lazy. Whilst that may be true especially on a tiny process with a few kb of RAM its not helpful when leveraging 3rd party libraries, particularly the JSON class – you could do this manually but its unwieldy.

The solution I went for is to restart the ESP every 24 hours instead to clear up the memory. The LED display will just retain whatever it was showing whilst the restart fires, and it only takes a few seconds. I may revisit this and refine it a bit later, but for now its perfectly workable.

Clones

As it happens by word of mouth I have made quite a few of these. Its ironic that the most expensive part is a nice USB cable! There’s one at Flightpath flying school at Wolverhampton Halfpenny Green.

TrafficLite Part 2

A battery management system needed to be added and this proved to be tricky. For convenience we want a rechargeable battery and, like any gadget, to be able to charge it from USB. The unit draws 170mA and I opted for a 1000 mAh lithium battery which includes battery protection from overcharge, short-circuit etc. This should see up to 5 or more hours use. I used a charge management chip and programmed the charge current to 300mA. This conservative charge rate means a very safe 3.5hr charge time and doesn’t demand too much from the battery.

Prototyping The Case

I wanted to make a device that was as small and lightweight as possible. After modelling the display PCB, all the other parts were modelled as accurately as possible. Finally we know the minimum size the case can be. Originally I designed it with screws, but then I realised I was still thinking like it would be made from milled metal – now I can 3D print a case I can make it snap together. Note the two tabs on the top part which snap in to the bottom part. The thinnest shell I was comfortable with was 2mm and this makes the case a feather weight and yet still surprisingly rigid.

For the switch I tried a few different things and again I was thinking along the wrong lines. Plastic allows you to make flexible parts. The switch can be made out of the body in one piece, which is quick cheap and simple. Just cut a slot so it can move. I added a raised area to make it easy to find and since the print direction is left to right, its optimal for the 3D print. It worked really well and I’ll definitely use this technique in future. I wanted a black case, but have lots of white PLA that I needed to use up so the prototype cases were white.

The software was updated to hook up the ADC input to monitor battery voltage. A housekeeping task runs once per second and this monitors the voltage and displays approx capacity rounded to the nearest 25% – for simplicity.

Next Steps

Go flying with it!
Battery percentage calibration
Printed Circuit Board design and manufacture

TrafficLite Part 1

In the previous project, we saw a traffic display involved a far bit of hacking of the Pilotware unit. The downside of this is that it makes it difficult to keep the Pilotaware unit up to date.

The Pilotaware unit provides traffic information via a Wifi hotspot. The system provides an interface on port 2000 which provides FLARM and NMEA GPS information.

What we need is something lightweight, cheap with wifi and a display. Until recently this would have been an expensive development, but today we have the internet of things. Esspressif systems have made this extremely easy with a system of a chip, which includes WiFi, can easily be programmed in C++ using arduino compatible libraries …..and all for the price of a McDonalds! It should be possible to create a unit about the size a fag packet that you can stick the dashboard for very low cost.

A complete computer (esp8266) for £5 and a £10 TFT colour display.

All that is required is to connect the esp8266 serial peripheral interface to the display. In this case I used a wimo d1 mini board.

Next we need to connect to the PAW which is only a couple of lines of code, then connect to port 2000 and handle the data stream. Once that’s done we install some SPI display libraries and we can draw whatever we want on the screen.

I chose to depart from the TCAS display symbols because I’m not used to them and I found a ‘spaceship’ pointing towards me far easier to interpret than squares moving sideways. Other than that the large number indicates the level and I can display the reg or whatever with it.

Next Steps

3D printed case
USB Rechargeable lithium battery – gives about 7 hours of use from a 1 hour charge.
Battery level monitor
If it can’t connect to PAW show a demo
A funky start up screen
Single button power on and off

Pilotaware Display

I had forgotten to post updates to the project. Progress was extremely slow because of family etc.

I really liked the Pilotaware system having known people personally to die in GA mid-air collisions. If you have a certified aircraft, you cannot change anything and it must be regarded as carry on. However, what you don’t want is a mass of cables and obstructed views.

The Pilotaware radar view is awesome as it is, but its a fiddle to connect to it on your phone and a distraction you don’t need. My idea was to create a purpose built display. I searched on eBay until I found a 1950’s ADF that would form a chassis that I could use. It was plenty big enough and had standard connectors already on it- someone already did all the hard work!

Then I realised that I’d be creating a system ideal to support the actual Pi. So I stuck the Pilotaware Pi in the back. One box, one set of connections.

Internally it is based on the following

Anker 5V 3A charger – recommended by Pilotaware as its very low noise and seems to cause the least issues. This is happy with anything between about 7V and 28V and provides a rock-solid 5.1V output.
A Pilotaware radio module, attached to a Raspberry Pi 2 Model B (that’s how it came)
Pi Zero with Bluetooth and Wifi – amazing that this is only a tenner.
Adafruit 2455 Pi TFT 2.4 Inch touch display – I very carefully cut the touch overlay off because it was too reflective and not required. Getting the display to work on the Pi Zero was a bit of a pig.
Vero Strip board – some mil-spec stock I acquired ages ago.

Software

Setting up the Pi Zero was a bit of a fiddle. I wrote a script to keep trying to connect to the Pilotaware system. Next, it starts the x windows environment and opens a windowless browser to the radar page. There is a script that checks that all is well and if it does loose connection it will sort itself out.

Hacking the Pilotaware

The radar app isn’t quite right. The lines are too thin and on a low resolution the screen its too difficult to see – so I needed to alter it. You cannot get access to the Pilotware system because they don’t give you the password. However that doesn’t offer much of a challenge. In the end I mounted the card under windows using some Paragon software.

I altered the CSS significantly and changed the javascript that draws on screen, to make everything using fully saturated colours and 3 pixel width line to make it really easy to see. I drew my own Compass Rose which is a PNG file. In the end it looks like a proper glass cockpit design. I wanted to keep mods to a minimum otherwise updating it is a pain. In the end I created a Radar2 folder such that updating the system leaves my hacked version intact. It sounds like I know what I’m doing with this; I didn’t it took ages – this project was on an off over 18 months. I created a debug environment and could locally test it using chrome with mobile device screen set up.

I wanted to see what it would look like on a real panel, from the pilots seat its lucky that this is a good angle for this screen.

Unfortunately, in sun light the screen reflections are a problem. I looked at anti-glare film and bonding the display to the screen like a smartphone but these are messy solutions.

What would be better is no glass. I 3D printed a prototype bezel. Shown here was an early prototype. The volume / power knob can now be added as there is no glass to worry about. I also added an LM386 audio amplifier connected to the Pi so you can hear the traffic alerts. Volume / Mute was a must. I scrapped the text and mention of TCAS because it isn’t TCAS, its a traffic aid.

Most connections are made remotely over a 2m cable with a Tesco USB hub. For some reason all sorts of expensive micro-hubs wouldn’t work but a 4 year old one from Tesco’s works perfectly. This allows easy placement of GPS and ADSB receiver at the back of the cockpit out of the way rather than trailing cables all over the place possibly jamming the controls!

I’ve worked hard to ensure that it produces as little radio frequency interference as possible. I have the old non 8khz navcom to play with on the bench and I also have a scope that shows the radio frequencies and strength being emitted so they can be addressed. The power inlet is RF filtered and the case forms a Faraday cage. Additional shielding was still necessary and grounding was a bit of a dark art. In the real aircraft, I realised I probably didn’t need to worry as the existing electrical noise was 3 orders of magnitude higher. There is a lot of electrical noise from the strobe and the alternator, its a wonder any radio navigation equipment works at all.

Final Thoughts

I think this project worked out quite nicely and I learned a lot doing it. It gives you an appreciation for the complexity and radio compatibility issues you can have with airborne systems. My end result with its black panel doesn’t look like its homemade and the performance is remarkable and I tested in the car at the airfield.

Unfortunately, you can’t fix something like this into a certified aircraft – though I’m sure many would. You can place it on the top of the dash although I hat anything obstructing the view – a non-moving dot hiding behind it is exactly what traffic on a collision course looks like.