Accuracy/Consistency of CHT Download data

[cbretana]

How accurate is the Cylinder Head Temperature readings output by the Skyview system? I have Lycoming O-320 E2D, with Dynon HDX, and all Dynon engine sensors installed. The CHT sensors are in the Lycoming standard CHT Sensor ports on the Intake manifold. I had a possible CHT over-temp the other day, where I saw temps on two cylinders over 500F for a short time. On my HDX display CHT widget, I saw numbers up in 550-560F range... So I downloaded the User Log file to a flash drive, loaded it into Excel, and generated a Graph (converting the Centigrade output values to Fahrenheit). The graph looks like this:

But on this graph, the highest temp cylinder only got to 535F, which is inconsistent with the numbers I saw inflight on the widget.
It is possible that I misread the numbers on the screen. or am misremembering what I saw, but I thought I'd ask here if the file export output is accurately representing the actual measured values.
The formula I used to convert the Centigrade output to Fahrenheit is:

F = (C * 9 / 5) + 32

Thanks in advance!

 

[kurtfly]

So, you are seeing 279 C (535 F) for cyl temps? If so, that is way too high. You have a problem if this is real. The 350 F looks nominal for cruise. 400 F for climb. The DYNON system is normally very accurate. Your engine will not last long if those are real. Need to see more time to and know what was going on at this time. Climb or cruise? Momentary one time or periodically spikes. Could be radio interference If it happens when you key mic?

 

[cbretana]

Oh, sorry, not enough information... This happened in my Long EZ because I was distracted and took off with speed brake extended. This blocked the airflow into the NACA inlet on the pusher engine and caused the high CHTs. The graph display is for the first 5 minutes after takeoff, at max power. When I first noticed the high CHTs, (around 16:24), I reduced power and enrichened the mixture. Then when I realized the speed brake was extended, (right around 16:26, at the kink in the graph), I raised the Speed brake and the CHTs immediately went down.

I am posting this only because the widget showed 560F, but the output of the export file had a maximum of around 535F, and I want to know how reliable these values are. I am having the engine inspected to determine what damage might have occurred in the short time the CHTs were so high, but it would be useful to know exactly how hot it got.

 

[kurtfly]

I suspect you may have the logging periodicity set to slow, and the temperature spike was in between samples at a very short duration. You can set this in the skyview setup menu.

"SkyView can record data as frequently as 16 times per second or as infrequently as once every 10 seconds. Recording more frequently trades off the amount of time that the data log covers. At once every 10 seconds, SkyView’s User Data Log can store up to about 150 hours of data. At 16 times per second, the log stores about 2 hours of data. When the data log fills up, the oldest data is automatically discarded to make room for new data.
Navigate to SETUP MENU > SYSTEM SETUP > DATA LOG SETUP > RECORD RATE to choose the frequency that data is recorded to the internal User Data Log."

You may want to take advantage of the SkyView Discrete inputs and wire one to the speed brakes so you have an indication on the screen when deployed. Similar to the open door status.

 

[Dynon]

How accurate is the Cylinder Head Temperature readings output by the Skyview system?

The short answer is very, although I don't have a number at hand. CHTs are type J thermocouples, and EGTs type K thermocouples (with the exception of the Rotax CHT/coolant temps, which are the sensors on the engine). Thermocouples are essentially voltage differential measurements turned into a temperature readings. The measuring equipment (SkyView) is able to measure these extremely accurately. In short, the sensors error accuracy itself is going to be the main driver of the end accuracy on these sensors.

 

[cbretana]

Kurt,

I am already planning on adding a Speed brake Open input to the Skyview system.. But thanks for suggestion....

And I am getting 240 readings per minute, or 4/sec, so I guess I am already at a high enough sampling rate. The values change only gradually, and are consistent with each other.

I am thinking that the speed brake was open for about three minutes, and almost every reading during that time is more or less consistent with gradually increasing CHT values, so that is probably not an issue.

Which means that the numbers are probably an accurate reflection of the actual temperature.

 

[DBRV10]

Set them to 1 per second for best diagnostic value.

A CHT that went over 500 for any length of time would be a real concern to me, luckily this was not for very long. I would replace the spark plugs in that cylinder if nothing else and have a good look with a borescope.

 

[cbretana]

Yes, I am having a borescope & compression check done this morning. Changing the oil this afternoon. Hadn't thought about spark plugs... I will make sure they are inspected at minimum. A comment in Lycoming service bulletin om this issue said to examine exterior appearance of cylinders for paint discoloration as that can be an exterior sign of heat damage. waiting for borescope and compression check results, but exterior paint on my engine appears unaffected, so I am hopeful all is well....

 

[Michael Jackson]

How accurate is the Cylinder Head Temperature readings output by the Skyview system? I have Lycoming O-320 E2D, with Dynon HDX, and all Dynon engine sensors installed. The CHT sensors are in the Lycoming standard CHT Sensor ports on the Intake manifold. I had a possible CHT over-temp the other day, where I saw temps on two cylinders over 500F for a short time. On my HDX display CHT widget, I saw numbers up in 550-560F range... So I downloaded the User Log file to a flash drive, loaded it into Excel, and generated a Graph (converting the Centigrade output values to Fahrenheit). The graph looks like this:
View attachment 4198
But on this graph, the highest temp cylinder only got to 535F, which is inconsistent with the numbers I saw inflight on the widget.
It is possible that I misread the numbers on the screen. or am misremembering what I saw, but I thought I'd ask here if the file export output is accurately representing the actual measured values.
The formula I used to convert the Centigrade output to Fahrenheit is:

F = (C * 9 / 5) + 32

Thanks in advance!

Hi,

I have a few customers using the 'Flight Data Viewer' with the Dynon SkyView. They haven't reported any accuracy issues with the CHT or EGT readings.

Check out the 'Flight Data Viewer'. It's an easy way to extract and store all of your flight data. For example you can select a range of data and instantly see the minimum, maximum, average, mean and standard deviation of your CHT and EGT readings. It also has tools that allow you to calculate takeoff distance, climb rate, etc. You can also see your flights in Google Earth. And, of course, it does all the unit conversions automatically. (F/C, MPH/Knots/KPH, Feet/Meters, Miles/KM, etc)

Flight Data Viewer

-- Michael