Altitude ,how it works

[Steve Carr]

his response was in angle mode the barometer and GPS is used to verify altitude ,in manual mode obviously the barometer is used so ,take it for what it’s worth.

I would suggest he has been misinformed or is making a guess. While his explanation might seem reasonable, it ignores the basic principle of inaccurate GPS altitude generation. It also ignores the fact that GPS is never really turned off. It continues to function normally. Turning it off is simply an instruction to the Flight Controller to disregard GPS for station keeping. The calculations for distance continue to be displayed. Whether it is on or off doesn't matter because it isn't used for altitude.

This would not be the first time a tech had the wrong information. I has happened many times and in some cases a tech will give horrendous advice to a caller. I suspect the training they get is meager. Again, I'm not critical of you. I simply have an aversion to incorrect technical information. It may seem like a trivial matter but it sets in motion more speculation which is also incorrect. Consider this: "I need a new GPS board because my altitude reading is wrong." "My H crashed into the ground because my GPS altitude forced it into a dive."

 

[Phaedrus]

FWIW here is the NTSB evaluation of aviation GPS.

http://www.nstb.tc.faa.gov/reports/PAN96_0117.pdf#page=22

Vertical resolution was around 15 meters at best and worse most of the time.

 

[Oscar Cymru]

If you were standing on 1000 foot tall building and you take off and fly 100 feet above, your telemetry will read 100 feet of elevation if you’re a maned aircraft pilot and you take off from the top of the building you need to set your altimeter to 1000 feet before you take off so your barometer will read 1100 feet . In GPS mode it is a triangulation between satellite or satellites ,controller and aircraft . In manual mode the barometer is always set at zero @take off just like an aircraft pilot of a maned aircraft would do and then from there on in manual mode your barometer will reflect the difference of height from takeoff.

Depends on whether you're flying on the QFE or QNH!

 

[Oscar Cymru]

Seems to me that the way to understand this problem is to carry out a couple of flight tests. I've got both a Typhoon H and also a 520 so will do this with both when I get decent weather.

Angle mode.
1. Fly from the mid point of my local hill recording take-off point altitude on both. This should read 0 ft altitude in both cases
2. Fly down and hover just above a fixed point. This should read a -ive altitude on both aircraft.
3. Fly to top of hill and hover above fixed point. This should give +ive altitude on both aircraft.

Re-fly with both aircraft in manual mode.

I''ll publish figures here ASAP. Any thing else I should include?

One thought... on the H520 there is terrain following mode, might put that into the figures to see what is produced.

The other thing to remember is that barometric pressure varies... Altimeter Pressure Settings - SKYbrary Aviation Safety. QFE is set when flying circuits (i.e. you set you altimeter to read 0ft at your local airport), QNH is set when you're flying away. QNH gives an area/region air pressure so all aircraft flying in that region report heights relative to each other and therefore to a fixed datum.

 

[Flying eyeball]

Seems to me that the way to understand this problem is to carry out a couple of flight tests. I've got both a Typhoon H and also a 520 so will do this with both when I get decent weather.

Angle mode.
1. Fly from the mid point of my local hill recording take-off point altitude on both. This should read 0 ft altitude in both cases
2. Fly down and hover just above a fixed point. This should read a -ive altitude on both aircraft.
3. Fly to top of hill and hover above fixed point. This should give +ive altitude on both aircraft.

Re-fly with both aircraft in manual mode.

I''ll publish figures here ASAP. Any thing else I should include?

One thought... on the H520 there is terrain following mode, might put that into the figures to see what is produced.

The other thing to remember is that barometric pressure varies... Altimeter Pressure Settings - SKYbrary Aviation Safety. QFE is set when flying circuits (i.e. you set you altimeter to read 0ft at your local airport), QNH is set when you're flying away. QNH gives an area/region air pressure so all aircraft flying in that region report heights relative to each other and therefore to a fixed datum.

That is awesome Oscar , A forum of the people by the people ,and through this freedom to exchange knowledge and ideas, the truth will be revealed in the best outcome ,this is what our country is lacking. Unfortunately we are left with only the rituals of democracy ,we all might as well just be doing a rain dance . I am truly very excited about this forum participation I am learning a lot . Let’s keep it going brothers and sisters !

 

[Phaedrus]

Still not sure what the discussion is about. The aircraft records your starting point as 0 altitude. It does not matter what the local terrain is doing since it is changes in barometric pressure relative to that zero altitude starting point that are being displayed. What "testing" needs to be done and what questions still remain?

 

[arruntus]

Still not sure what the discussion is about. The aircraft records your starting point as 0 altitude. It does not matter what the local terrain is doing since it is changes in barometric pressure relative to that zero altitude starting point that are being displayed. What "testing" needs to be done and what questions still remain?

It also matters partner, but I think we are already getting into a technical level that I think does not contribute anything to the 99.9% of colleagues present, me included. The elevation is also a determining value when the barometer makes the measurements.

In short, the barometer is in charge of giving the "real" height of the aircraft with respect to the take-off point

P.D.: Your summary is also very good

 

[PatR]

I think Yuneec Support must be wrong, both use barometer.
GPS receivers return altitude data, but this is inaccurate. The error margin depends on the satellite constellation geometry and whether or not you have both on.
A barometer is a much more accurate and fast device to extract altitude,

This is why our military does not accept GPS altitude as height referenced with drones. They insist on baro pressure altitude references. Far too many times GPS altitude reporting has been found to differ from pressure altitude reporting by hundreds of feet.

If you need accurate altitude from a multirotor it needs to have a magnetometer linked with the pressure sensor.

 

[DoomMeister]

If you need accurate altitude from a multirotor it needs to have a magnetometer linked with the pressure sensor.

OK, the magnetometer threw me off. Could you elucidate on that subject just a bit @PatR. I am in student mode at this point and I know you love teaching.

 

[AH-1G]

OK, the magnetometer threw me off. Could you elucidate on that subject just a bit @PatR. I am in student mode at this point and I know you love teaching.

Attitude & Heading Reference System (AHRS) | Magnetometer - Watson Industries
How Does It Work?
An AHRS integrates rate information from the gyroscopes to provide 3D orientation. Reference data – such as gravity (provided by the accelerometers) and the Earth’s magnetic field (provided by the magnetometer) – is used to compensate for the drift created by this integration. This makes the AHRS a much more cost-effective alternative to high-grade inertial measurement units (IMUs).

 

[arruntus]

Attitude & Heading Reference System (AHRS) | Magnetometer - Watson Industries
How Does It Work?
An AHRS integrates rate information from the gyroscopes to provide 3D orientation. Reference data – such as gravity (provided by the accelerometers) and the Earth’s magnetic field (provided by the magnetometer) – is used to compensate for the drift created by this integration. This makes the AHRS a much more cost-effective alternative to high-grade inertial measurement units (IMUs).

They are two different things, one is the orientation and the other is the altitude. Altitude barometer, orientation the IMU's (on almost all controller boards), which are formed by different sensors, gyroscopes, accelerometers, magnetometers and even takes information from GPS to know the location globally and make calculations.

Something similar has happened above, we should not join the devices used in manned aircraft with the devices used by drones. Obviously they're better, but what price would the drones have then?

 

[DoomMeister]

I understand aircraft attitude and positioning systems. It was just the reference to barometers and magnetometers alone that had me scratching my head.