Need information on altitude values among several Typhoon H's on the same CCC script

[slw74]

OK, I need some expert help. I have 3 Typhoon H's and two ST-16 controllers. All three of the drones work great and all have been calibrated in the last couple of days (accelerometer, gimbal and compass). I run a CCC as a flyover of a new construction site in preparation for ground breaking and subsequent construction at the request of the owners. There are a number of fairly tall trees around the perimeter of the property and in order to clear those trees, I have set the overall altitude of the CCC at 32 meters. All three of the drones fly the course just fine, but they all do it a different altitude based on my visual estimates. They all leave the ground from the same location and all indicate the same altitude on either of the ST16 controllers, but clearly they are flying at different altitudes. I realize that barometric pressure conditions can affect the altitude, but all of the flights have been on very nice days with clear weather. What am I missing that makes this situation so confounding? Solutions?
Thanks,
Stephen

 

[NorWiscPilot]

OK, I need some expert help. I have 3 Typhoon H's and two ST-16 controllers. All three of the drones work great and all have been calibrated in the last couple of days (accelerometer, gimbal and compass). I run a CCC as a flyover of a new construction site in preparation for ground breaking and subsequent construction at the request of the owners. There are a number of fairly tall trees around the perimeter of the property and in order to clear those trees, I have set the overall altitude of the CCC at 32 meters. All three of the drones fly the course just fine, but they all do it a different altitude based on my visual estimates. They all leave the ground from the same location and all indicate the same altitude on either of the ST16 controllers, but clearly they are flying at different altitudes. I realize that barometric pressure conditions can affect the altitude, but all of the flights have been on very nice days with clear weather. What am I missing that makes this situation so confounding? Solutions?
Thanks,
Stephen

Good question posed here. I am confident a few will chime in with their theories, probably similar to mine.

First, do you have any estimates to share, as to how much in variation you are perceiving as to altitudes of each of your H480s?

If only a few meters, you have likely already answered your own question. The altitude calculations are not very precise, but usable in most situations. Comparatively, I am not surprised you are not getting exactly the same routes (altitudes).

I will be curious to read if your perception of the altitude differences are much greater, say 20 or 30 meters difference, or more.

Good luck with this conversation and investigation. Will be watching to see what others offer as to explanations.

Jeff

 

[MM1992]

While the altitude is fairly approximate, I've found that I get good results on days with a bit of wind. A light breeze seems to help the H maintain a consistent reading, and when I land it might only be off my 4 feet or so vs 20-30 feet I've seen on calm days. The other one is where I take off from. If there is any wind and I take off in a sheltered area, the altimeter will be significantly off. I once used a section of a patio with a short wall around it as a landing spot, and while the ST-16 showed an altitude that was supposed to clear a building by 100', the H was nearly on the rooftop.

 

[Eagle's Eye Video]

Agreed... there is a known variability of 3 to 6 meters both when comparing the route flown to program CCC vs. the actual route flown when running CCC... as well as the same degree of variance when running a saved route on different flights. That variability also needs an additional cushion in terms of greater altitude to not have the route come too close to the ground or obstructions.

It depends on your usage, but the newly released Steady Drive may be a useful alternative.

 

[PatR]

Primary cause is likely temperature. Temperature inside the body of the Typhoon H. Temperature affects pressure, pressure establishes altitude.

Toss in lack of precision for component design and manufacturing, and inability to adjust for changes in sea level barometric pressure (calibration) and altitude can be all over the place.

 

[PatR]

Just a PSA, sea level pressure is predicated on a “standard day”. A standard day sea level altitude consists of a pressure of 29.92”hg, a temperature of 59*F, and 0% humidity to establish 0’ of altitude at sea level. A temperature higher or lower would provide an altitude reading at sea level of higher or lower than 0’. As altitude increases temperature and pressure usually, but not always, decrease at what’s called a standard rate. Inversion layers and rising terrain complicate that.

So if you built your CCC flight plan on a day that had a location pressure of 29.87”hg at 70*F and went back to fly it on a day with a pressure 29.97”hg at 55*F the flight would happen lower than when you first flew it. A lot lower.

If we could adjust our altimeters to reflect actual pressure conditions we could correct for that and have a fairly repeatable flight plan altitude, but we can’t.

Toss in variable temperatures inside the aircraft and the situation becomes even more wonky as the altimeter uses pressure at start up to define zero and calculates changes in pressure with altitude gain to generate height above the ground. Heat alters air density. If air pressure is reduced because density was artificially reduced by electrical component heat generation the height will be quite inaccurate.

 

[slw74]

The variation that I am experiencing is all within the several meters as many have indicated. I believe it's typically 3 to 5 meters for me. Information about CCC use does indicate that you need to have a sufficient altitude in order to be safe. I just want to miss the trees! Thanks to everyone for the advice and information.