Density Altitude and Flight Times

[GregD]

I recently received a personal weather station that will display density altitude. I am curious if anyone logs weather data when they fly.

While studying for the Part 107 exam density altitude and aircraft performance was covered. It got me to wondering if differences in density altitude would have much affect on the flight time of our drones.

Have any of you logged any of this data to find out? I plan on logging the data to see what shows up.

Thanks

 

[sdold]

I've wondered the same thing, I've had mine as high as 7000' MSL on a hot day, so the D/A was probably around 8-9000 feet, and the flight time didn't seem too far off of what it would have been at sea level. I think people here have had them much higher. I'm curious about the lifting ability since I will be doing this carrying small payloads with radio equipment. If you do any logging, it might be interesting to compare the motor RPMs at different density altitudes.

 

[GregD]

I've wondered the same thing, I've had mine as high as 7000' MSL on a hot day, so the D/A was probably around 8-9000 feet, and the flight time didn't seem too far off of what it would have been at sea level. I think people here have had them much higher. I'm curious about the lifting ability since I will be doing this carrying small payloads with radio equipment. If you do any logging, it might be interesting to compare the motor RPMs at different density altitudes.

I plan to track several data points. What kind of radio equipment will you be carrying?

 

[sdold]

It's a little Arduino-controlled receiver that measures the amount of RF energy coming from radio transmitters, and plots the signal strength and GPS position for making antenna pattern measurements of tower top transmitting antennas for two-way public safety, broadcast, etc. It weighs about 0.7 pounds (300 grams). The Mavic Pro carries it pretty well but I have only tried it up at around 3000 feet MSL so far. It would be great to see your data if you don't mind posting it.

 

[GregD]

It's a little Arduino-controlled receiver that measures the amount of RF energy coming from radio transmitters, and plots the signal strength and GPS position for making antenna pattern measurements of tower top transmitting antennas for two-way public safety, broadcast, etc. It weighs about 0.7 pounds (300 grams). The Mavic Pro carries it pretty well but I have only tried it up at around 3000 feet MSL so far. It would be great to see your data if you don't mind posting it.

Once I have some data I will post it. As a ham radio operator I am interested in hearing more about the Arduino-controlled receiver. Do you have a link you can share?

Thanks,
Greg - AF8GD

 

[sdold]

It's this one:
RF Explorer - Internet of Things Modules

It needs a 3.3v Arduino, so I'm controlling it with a Due and also have an SD card shield and an Adafruit GPS module.

 

[GregD]

It's this one:
RF Explorer - Internet of Things Modules

It needs a 3.3v Arduino, so I'm controlling it with a Due and also have an SD card shield and an Adafruit GPS module.

Looks pretty nice. I have a few RPi's, so I might give it a go.

 

[sdold]

If you do, let me know if you get stuck or need source code (although the Arduino stuff might not be compatible). I was barely able to get it doing what I wanted, but am happy to share what I have.

 

[GregD]

If you do, let me know if you get stuck or need source code (although the Arduino stuff might not be compatible). I was barely able to get it doing what I wanted, but am happy to share what I have.

Thank you. I may go with the Due as coding is not my thing. I can do bash scripts, but things like Python & Perl take me a while. With the SD card hat and GPS module what are using using for power?

 

[sdold]

I used the Adafruit data logger as the SD card reader/writer, not sure of the model but you can see it in the pic below and compare it to the ones on her web site. The GPS module is her "Ultimate GPS breakout" version 3. Here's a picture. Oh, everything runs on a single 9v battery, and it lasts about 4 hours.

 

[GregD]

I used the Adafruit data logger as the SD card reader/writer, not sure of the model but you can see it in the pic below and compare it to the ones on her web site. The GPS module is her "Ultimate GPS breakout" version 3. Here's a picture. Oh, everything runs on a single 9v battery, and it lasts about 4 hours.
View attachment 59144View attachment 59147

That is a sweet little package. What format is your data stored in?

 

[sdold]

Thanks! Every second it writes a line of comma-delimited text to the SD card that has the latitude, longitude, received signal level in dBm, and the frequency it received. The frequency is there so that I can weed out bad data from other frequencies by putting it into an excel spreadsheet. I can than plot the data in Google Earth. When the drone flies, I use the "Point of Interest" mode to fly a circle around the antenna, and then plot the data in Google Earth. That way I can enter the numbers into an excel spreadsheet and make a pattern plot. I haven't figured out a way to have excel draw the plot from the data yet. That might be harder than I'm capable of! But doing it manually still beats any other method, especially when the antenna is on a tower on a mountain peak.

 

[GregD]

Thanks, that output makes sense.

 

[GregD]

Thanks! Every second it writes a line of comma-delimited text to the SD card that has the latitude, longitude, received signal level in dBm, and the frequency it received. The frequency is there so that I can weed out bad data from other frequencies by putting it into an excel spreadsheet. I can than plot the data in Google Earth. When the drone flies, I use the "Point of Interest" mode to fly a circle around the antenna, and then plot the data in Google Earth. That way I can enter the numbers into an excel spreadsheet and make a pattern plot. I haven't figured out a way to have excel draw the plot from the data yet. That might be harder than I'm capable of! But doing it manually still beats any other method, especially when the antenna is on a tower on a mountain peak.

I have never had much luck getting excel to draw graphs from my data.

Did you receive my private message?

 

[747P4]

I recently received a personal weather station that will display density altitude. I am curious if anyone logs weather data when they fly.

While studying for the Part 107 exam density altitude and aircraft performance was covered. It got me to wondering if differences in density altitude would have much affect on the flight time of our drones.

Have any of you logged any of this data to find out? I plan on logging the data to see what shows up.

Thanks

DA will be directly proportional to the lift the propeller produces and many other factors come into play such as power output which is also related to real engines be it jet or prop.
TAS (true airspeed) and GS (ground speed) are also factors in DA calculations. As an example, look at high DA airports and the runway lengths compared to sea level airports.

 

[Weaponized]

DA has more of an effect on fuel burning engines. More dense equals more power available but also more drag. The way its presented in 107 materials is misleading in that I believe it states that an decrease in DA (higher pressure) decreases performance. What they fail to differentiate is "engine" performance. Aircraft performance actually increases as DA increases (lower pressure). There's a reason aircraft fly at altitude... Faster, farther, lower fuel consumption. For a drone its probably a wash in that the engines are electric. Climb time, maneuvers, and wind are likely the biggest influence on battery life. You can't escape low DA with a drone because of operating limitations.

 

[747P4]

DA has more of an effect on fuel burning engines. More dense equals more power available but also more drag. The way its presented in 107 materials is misleading in that I believe it states that an decrease in DA (higher pressure) decreases performance. What they fail to differentiate is "engine" performance. Aircraft performance actually increases as DA increases (lower pressure). There's a reason aircraft fly at altitude... Faster, farther, lower fuel consumption. For a drone its probably a wash in that the engines are electric. Climb time, maneuvers, and wind are likely the biggest influence on battery life. You can't escape low DA with a drone because of operating limitations.

A number of factors (altitude/pressure, temperature and humidity) influence air density. A higher altitude, low pressure area, higher temperature and high humidity all have one result: they lower the density of the air. And as a result of that: a reduction in aircraft and engine performance.

When air density decreses, aircraft performance decreses.

Effects of Pressure & Density Altitude on Aircraft Performance

Hope this helps.

 

[Weaponized]

A number of factors (altitude/pressure, temperature and humidity) influence air density. A higher altitude, low pressure area, higher temperature and high humidity all have one result: they lower the density of the air. And as a result of that: a reduction in aircraft and engine performance.

When air density decreses, aircraft performance decreses.

Effects of Pressure & Density Altitude on Aircraft Performance

Hope this helps.

Yes. Point being...its out of your control given the altitudes a drone operates at. With the exception of seasonable environmental changes, drones operate in very narrow environmental range. An aircraft can take off in 90 degree heat, and climb to -20 degrees at FL300

 

[jeplane]

Because it is physics, density altitude will influence how the drone behave. ( mostly the aerodynamics on the props, affecting rate of climb or descent, acceleration and deceleration)

However, because it is being flown in a narrow band of altitude, it is negligible and you don‘t have to think or worry about it. You can’t see the difference with the naked eye...

 

[747P4]

Yes. Point being...its out of your control given the altitudes a drone operates at. With the exception of seasonable environmental changes, drones operate in very narrow environmental range. An aircraft can take off in 90 degree heat, and climb to -20 degrees at FL300

You bring up an interesting point about the operation of drones at altitude. Would love to know if DJI tested these drones at altitude or they used other methods in determing max altitude and operating temperatures

At FL300 a lot depends on where the tropopause is, which will also affect temperature at altitude.
-20F is -28.89C which isn't a normal OAT or TAT for this altitude (-47C = -52.6F)

AWC - Winds/Temps Data


https://aviationweather.gov/data/iffdp/2302.gif