Another Foreflight question

[ahypnoz]

ForeFlight to set Heading Indicator

I have always used my old liquid compass to set my steam gauge heading indicator, even though my liquid compass has many known different errors depending on which direction I am pointed, if I was accelerating or decelerating, turning north or south etc?

Yesterday evening I was flying with a friend and I was using Foreflight with my Stratus 2S and I compared FF magnetic heading during the whole flight with his Garmin 1000 heading indicator. The heading indicator on the Foreflight (with the Stratus) was exactly the same as his heading indicator on his Garmin display. It did not matter if we were in level flight, climbing in decent, accelerating or decelerating, it was always exactly the same. We were shooting approches and doing holding patterns.

Is there any reason why I could not use the magnetic heading indicator in Foreflight to set my heading indicator in flight for better situational awareness? My heading indicator gets a lot of precession error whenever I do a lot of turns.

Note: I am not talking about the nav log in FF, which takes into account wind for the course, but the split screen view of the magnetic heading which is not using true north, but a magnetic course.

 

[Challenged]

I have a couple of devices that show me the current magnetic heading and I typically use those to set my DG, but if there isn't a lot going on I'll look at the compass too for fun. I usually verify the validity of the magnetic heading information given to me while I'm taxiing.

 

[luvflyin]

ForeFlight to set Heading Indicator

I have always used my old liquid compass to set my steam gauge heading indicator, even though my liquid compass has many known different errors depending on which direction I am pointed, if I was accelerating or decelerating, turning north or south etc?

Yesterday evening I was flying with a friend and I was using Foreflight with my Stratus 2S and I compared FF magnetic heading during the whole flight with his Garmin 1000 heading indicator. The heading indicator on the Foreflight (with the Stratus) was exactly the same as his heading indicator on his Garmin display. It did not matter if we were in level flight, climbing in decent, accelerating or decelerating, it was always exactly the same. We were shooting approches and doing holding patterns.

Is there any reason why I could not use the magnetic heading indicator in Foreflight to set my heading indicator in flight for better situational awareness? My heading indicator gets a lot of precession error whenever I do a lot of turns.

Note: I am not talking about the nav log in FF, which takes into account wind for the course, but the split screen view of the magnetic heading which is not using true north, but a magnetic course.

I haven’t seen ‘magnetic heading’ on FF. Where is that?

 

[ahypnoz]

I was told to always use my compass, because FF my not be accurate.

 

[ahypnoz]

When in actual flight while using the Stratus 2S, the heading indicator (split screen) will automatically switch from true north to magnetic north.

 

[Raymo]

The Stratus is using GPS heading. If it had a mag compass inside, it would be very problematic would have to be re-calibrated for every location and aircraft where it were used. That said, I don't see a problem using it for heading for VFR flights. GPS navigators rely on the same tech for their heading.

 

[luvflyin]

When in actual flight while using the Stratus 2S, the heading indicator (split screen) will automatically switch from true north to magnetic north.

From True to Magnetic what? I think you and @Ray Eaker may be confusing ‘Heading’ with ‘Track.’

 

[ahypnoz]

What I am saying is the magnetometer of the GPS 1000 AHRS gives a heading output and that number was exactly the same as the ForeFlight “magnetic heading number” which everyone uses as a heading indicator for the g1000.

Garmin is calling it a “heading indicator” not a track.

 

[luvflyin]

What I am saying is the magnetometer of the GPS 1000 AHRS gives a heading output and that number was exactly the same as the ForeFlight “magnetic heading number” which everyone uses as a heading indicator for the g1000.

Garmin is calling it a “heading indicator” not a track.

Where in ForeFlight is ‘magnetic heading number?’ I can’t find it. I haven’t done the last update, 10.1 I think. Is this something new?

 

[simtech]

I think he is talking about using the AHRS and at the bottom it has the HSI and gives a heading like 270M. Still think it is GPS track though.

 

[luvflyin]

I think he is talking about using the AHRS and at the bottom it has the HSI and gives a heading like 270M. Still think it is GPS track though.

I was thinking that. If it’s a GPS Track then that’s what it is though. Not ‘heading,’ unless the winds are very light or on the nose or tail. If there is an input from a device with a ‘magnetometer’ or something else like a flux valve in it that will detect ‘heading,’ and it is giving that input into ForeFlight, then I could see ‘heading’ being able to be displayed. I looked in the ForeFlight Manual and didn’t see anything about that. I went to settings and didn’t see anything that lets you toggle between ‘heading’ and ‘track.’ I think they are confusing heading with track

 

[simtech]

I think they are confusing heading with track

I fully agree with that. I think the "M" next to it might be confusing too.

 

[ahypnoz]

Look at number 4 on the Garmin screen shot (108 degrees), bottom picture compared to the top picture which is FF. Notice that Garmin uses “current heading” not current track. I think that FF is also giving a heading and not a track.

Note: I did not see heading in the FF manuel, but my observation was that they both tracked exactly the same for two hours.

So my question is, this seems like a better indicator for the heading indicator, then cross check it with the liquid compass.

Thoughts?

 

[Ryan F.]

Look at number 4 on the Garmin screen shot (108 degrees), bottom picture compared to the top picture which is FF. Notice that Garmin uses “current heading” not current track. I think that FF is also giving a heading and not a track.

Note: I did not see heading in the FF manuel, but my observation was that they both tracked exactly the same for two hours.

So my question is, this seems like a better indicator for the heading indicator, then cross check it with the liquid compass.

Thoughts?

Yeah, that's your track (which can certainly be displayed in "magnetic," of course), and not heading, regardless of whatever nomenclature you may be using. It must have been a light wind day on that particular outing for those two indications to match up, but in no way is your GPS track ever a suitable replacement for magnetic heading information. If your aircraft's source for that information is a magnetic compass, that is still the only way to set your DG's heading.

 

[denverpilot]

That is extremely misleading to label that “M” unless it’s coming from a real magnetic source.

 

[flyingcheesehead]

That is extremely misleading to label that “M” unless it’s coming from a real magnetic source.

Not if it's a Magnetic track...

@ahypnoz, go flying on a heavy-wind day and try your comparison again. You'll find that the GPS track that you get in ForeFlight will NOT match the heading on the G1000. If it does, you're flying either directly into or against the wind.

The G1000 has an indication for winds aloft (near the bottom of the airspeed tape) so you should be able to turn so that the winds aloft are a direct crosswind. Now compare the two.

Short answer: Use the compass. ForeFlight displays track, not heading.

 

[denverpilot]

Not if it's a Magnetic track...

That's not a normal number to see. Primacy. Label it "MT" or something sane. Differentiate it from "MH" which is commonly seen.

Students, most pilots, whatever... usually see "Track" but not "Magnetic Track" on most GPS devices. It's USUALLY in True...

BUT then again, Garmin and others hide the True/Magnetic thing down in a menu, and it has bit people in the butt before.

It's a dumb label. All it takes is a "T" to make it match what it's actually showing.

 

[ahypnoz]

I think you are correct, it was just really unusual how closely it matched and I was unsure if the Stratus had a magnetometer or not.

 

[denverpilot]

I think you are correct, it was just really unusual how closely it matched and I was unsure if the Stratus had a magnetometer or not.

Hahahahaha if they stuck one inside that thing it would swing wildly or be stuck pointing at the power supply inductor or something.

There’s a reason those things are mounted way out in the wing away from the noisemakers in the panel.

 

[arkvet]

WTH is magnetic track???

I mean track is the path you’re on. Heading is the direction you’re pointing. Heading can be magnetic or true.

The only way to get any number that should be labeled as “heading” is with a compass or magnetic input (magnetometer for most modern instruments)

Since the stratus 2 has zero capabilities of a magnetometer it should not be labeling anything as “heading” of any kind. For some this may be semantics but oh well.

If there is any cross wind component to your flight and the “numbers” are same between G1000 and FF then the G1000 is also showing ground track. I don’t care what the label says.

I anything above is incorrect please correct me. That’s just my understanding.

 

[ahypnoz]

Maybe since FF downloads the winds aloft data at different altitudes and FF has the current metar data live, maybe it is incorporateing and calculating all the raw data into the “magnetic heading/track” it would be a relatively simple calculation considering they have all the needed data. It could a proprietary number like their forecast MOS weather?

Doesn’t ATC have something similar?

 

[Sam D]

Maybe since FF downloads the winds aloft data at different altitudes and FF has the current metar data live, maybe it is incorporateing and calculating all the raw data into the “magnetic heading/track” it would be a relatively simple calculation considering they have all the needed data. It could a proprietary number like their forecast MOS weather?

Doesn’t ATC have something similar?

Are you sure FF has actual winds aloft info?

 

[ahypnoz]

They do not have actual winds aloft, but an approximation, which is probably good for the calculations.

How are winds aloft used in NavLog calculations?
Wind Aloft information is derived from the ForeFlight Global Winds engine. This allows us to provide winds aloft forecasts for any point on the planet up to 54,000′ (FL540). ForeFlight Mobile will compute the wind impact for any route of flight: flight plans using airways, SIDS, STARs, known airports, any waypoint pairs, and even a string of custom user waypoints or lat/long entries.

The ForeFlight Global Winds engine blends observed data from the National Weather Services and computer model data for the entire planet. The engine produces forecast grids of winds, temperatures, turbulence, and icing covering the entire world, making them applicable for planning any length of flight anywhere on the planet. Forecasts are updated four times each day by processing output from the National Weather Service’s Global Forecast System (GFS) numerical weather prediction model through a suite of custom algorithms to improve usability for aviation planning operations.

The GFS model itself is a state-of-the-science computational fluid dynamics (CFD) code that incorporates a plethora of global weather observations collected by a variety of surface, aircraft, and satellite-based platforms. Via advanced data assimilation techniques, these observations are used to create a three-dimensional gridded analysis of the state of the atmosphere. Then, a large supercomputing system advances the basic weather elements forward in time via a complex set of differential equations that describe momentum, heat, and moisture changes as a function of time, producing global grids of forecast data on a grid covering the entire world with 0.5-degree latitude/longitude spacing.

The raw data grids are received from the NWS and complex algorithms are applied to compute additional parameters such as turbulence and icing potential and converts the output from meteorological coordinates to flight levels used by aviators of all types.

In the NavLog, we take that interpolated wind data at the different positions and altitudes and calculate your projected groundspeed (and thus, time and fuel-burn) on different segments based on the climb & cruise performance numbers you enter. For example, if you're climbing to 9000' and the winds at 3000', 6000' and 9000' are dramatically different, we take that into account in the calculations for how long you'll be in the climb, cruise & descent phases.

 

[NordicDave]

Foreflight has access to iPad's internal magnetometer. It performs a calculation between true and magnetic north. The G1000 has a certified magnetometer away from electronic interference.

Foreflight is stunning, but it's accuracy is limited to internal consumer grade components of the iPad or Stratus 2. Even the AHRS in the GTX-345 is uncertified consumer grade components as stated by Garmin.

Surprising how many pilots rely on Foreflight for navigation and flight information, and don't realize their using GPS.

 

[John Collins]

That's not a normal number to see. Primacy. Label it "MT" or something sane. Differentiate it from "MH" which is commonly seen.

Students, most pilots, whatever... usually see "Track" but not "Magnetic Track" on most GPS devices. It's USUALLY in True...

BUT then again, Garmin and others hide the True/Magnetic thing down in a menu, and it has bit people in the butt before.

It's a dumb label. All it takes is a "T" to make it match what it's actually showing.

ForeFlight labels the HSI like instrument on the SV view as °T (Degrees True) or °M (Degrees Magnetic). It is a track, not a heading. All the GPS systems I have ever seen default to displaying track as magnetic (not USUALLY in True). I would also agree that most pilots would not know how to change the setting.

 

[ahypnoz]

The reason I even brought this up was my experience in comparing a certified g1000 to an uncertified FF product and how closely they correlated during a 10 to 15 knot, on the ground, flight while doing all the turns and altitude changes in several different approaches and holding patterns. FF M heading tracked his certified Garmin heading indicator almost perfectly for the whole flight.

Especially since I just turned on my Stratus and left it “in” my flight bag in the back seat during the flight and was really just using it to help spot traffic that had adsb out.

I was wondering since FF has most of the needed data to make a pretty accurate (non certified) source of a magnetic heading i.e the mathematical model of Earth's geomagnetic field that FF uses, Gps positioning to know current earth magnetic field variations as well as their own proprietary estimated winds aloft data) if they were making some mathematical corrections to their “magnetic heading/track” indicator to make it appear extremely accurate.

 

[flyingcheesehead]

WTH is magnetic track???

Track can be true or magnetic, just like Heading can be true or magnetic. One is your path relative to actual latitude and longitude, the other is your path relative to the earth's magnetic field.

The only way to get any number that should be labeled as “heading” is with a compass or magnetic input (magnetometer for most modern instruments)

Agreed.

Since the stratus 2 has zero capabilities of a magnetometer it should not be labeling anything as “heading” of any kind. For some this may be semantics but oh well.

It's not being labeled as heading. It is being used on the on-screen HSI, but ForeFlight is far from the only company doing that sort of thing. If you get the G5 AI without the magnetometer, you'll have track on it too, not heading!

If there is any cross wind component to your flight and the “numbers” are same between G1000 and FF then the G1000 is also showing ground track. I don’t care what the label says.

The G1000 shows heading on the HSI, and track up at the top of the screen in a data field. Anything on the iPad is showing track, unless it's being fed heading information from something in the panel (and a stratus is not "in" the panel).

Foreflight has access to iPad's internal magnetometer.

I don't think they're using it at all, though. It's quite unreliable. They're using GPS track.

 

[Raymo]

From True to Magnetic what? I think you and @Ray Eaker may be confusing ‘Heading’ with ‘Track.’

Simantics, I guess. My point was that the Stratus is using GPS for compass indications. Heading, if not compensating for winds, or track, if compensating.

 

[wayneda40]

Hahahahaha if they stuck one inside that thing it would swing wildly or be stuck pointing at the power supply inductor or something.

There’s a reason those things are mounted way out in the wing away from the noisemakers in the panel.

It appears that iPhones and iPads do have embedded (solid-state, I assume) magnetometers: http://www.byteworks.us/Byte_Works/...our_iPhone_or_iPad_into_a_Metal_Detector.html
"Starting with the iPhone 3GS, all iPhones have a built-in magnetometer. All iPads have one, but the iPod touch does not."

 

[denverpilot]

It appears that iPhones and iPads do have embedded (solid-state, I assume) magnetometers: http://www.byteworks.us/Byte_Works/...our_iPhone_or_iPad_into_a_Metal_Detector.html
"Starting with the iPhone 3GS, all iPhones have a built-in magnetometer. All iPads have one, but the iPod touch does not."

They do. They’re not that accurate and you have to “recalibrate” them by waving the phone in a figure eight pattern.

I’d use one to find cardinal headings, but definitely not to navigate by. Definitely not in a cockpit full of other electronics.

They’re used by the directional services in the phone in conjunction with the GPS to know when you turned your car to update a moving map, for example, but not typically used by themselves.

You can fire up the “compass” app from Apple to see how accurate or not accurate it is. Mostly mine wander around sloppily unless outdoors away from vehicles, and never accurate down to single degree digits.

But that’s neither here nor there, since that screen isn’t pulling its data from the magnetometer. You can prove it just by holding a magnet near the phone.

 

[Ryan F.]

Maybe since FF downloads the winds aloft data at different altitudes and FF has the current metar data live, maybe it is incorporateing and calculating all the raw data into the “magnetic heading/track” it would be a relatively simple calculation considering they have all the needed data. It could a proprietary number like their forecast MOS weather?

Doesn’t ATC have something similar?

With all due respect, let's put the brakes on this train of thought. This is the wrong path. I'm a little concerned because your statements seem to indicate a bit of confusion in this area and despite what has been stated in this thread, you're still looking for ways to plug a square peg into a round hole. The short answer is there's no way to "compute" an actual, accurate, reliable magnetic heading solely from derived GPS data. You can guess at one, but you can't compute one without a source for the information. That source isn't going to be your Stratus or iPad, or both hooked together. Period. And for that matter, FF doesn't have "all the needed data" to even make a guess... not even close. More on that in a bit.

You need to understand that magnetic heading comes only from a source such as a magnetometer or magnetic compass (among other possible common aviation sources for magnetic heading information.) An iPhone or iPad has a magnetometer, sure, but for one it's consumer grade and nowhere near accurate enough for aviation use; two, it's internal to the device so it's literally telling you the "heading" of the device, not the aircraft; three, it's subject to all kinds of interference in the cockpit so even if it was accurate, it wouldn't be usable in that location; and four, neither Foreflight nor the Stratus have an access to that data, nor would FF ever attempt to use it, I'm quite certain.

Further, it's actually a rather sophisticated function, at least as far as most legacy light piston GA aircraft are concerned, to compute air data, including winds. This requires an ADC (air data computer) to interface with an AHRS to determine not just indicated airspeed, but true airspeed, coordinated with outside air temperature and accurate heading data. Of course you are starting to see this is in some light aircraft now, but you're not going to get anything close to that from an iPad and a Stratus.

Finally, it's most important for users to fundamentally recognize what's going on here and why it's not advisable or safe to attempt to correlate that kind of information using portable devices like the ones you've described as a substitute for magnetic heading information. A good source for that data is one of the most important pieces of equipment in the aircraft. Even the most barebones rag and tube airplane dating back to the 30s has a whiskey compass, and for good reason. It's the only reliable way to know the actual heading of the aircraft. No matter how you slice it or dice it, because of the fact that a zero-wind day is as rare as hen's teeth, your GPS track and magnetic heading are almost always going to be two, constantly varying (relative to each other) figures.

Foreflight and a Stratus can provide you with all sorts of useful SA tools on the flight deck, but magnetic heading isn't one of them. End of story.