Flight planning: paper vs foreflight

[cavmedic]

I have entered the xc stages of my training and have a question on something I have noticed while planning my trips .


When I plan my trip using my instructors flight plan form, for giggles I plan the same flight using foreflight for comparison, and come up with some differences.

Difference 1 ,is foreflight will always show about a 10-15 degree difference on my CH than what I figure out.
Now understanding to my knowledge , there is no place in foreflight under aircraft data for compass variation , but that is not a factor in the plane I fly as there is no variation card, therefor no variation is figured.

Difference 2 , when I get the brief from foreflight, the winds aloft always seem to be different than what I get from the live briefer.

Difference 3, fuel burn and time is always off on foreflight from what I calculated.

What are some possibilities ( other than MY planning being off , but kinda debunked as instructor checks and verifies)

 

[jaybee]

Why no compass card is the first thing I'd like to know ?

edit - while it is not a 91.205 required item, i find it odd.

are you using True Virgins Make Dull Companions?

 

[cavmedic]

I do not know, no variation possibly ?

 

[jaybee]

Ok, lets start at beginning and use proper terminology - you may be confusing yourself.

Variation is the angular difference between True and Magnetic North - this is derived from your map via the agonic/isogonic line.

Deviation is the error caused in a compass by electrical interference either via the Earth's magnetic field and/or the airframe/electronics of the aircraft - which is why you would want a compass deviation card in the aircraft.

True Course is the the line you plot on your map. This is corrected to magnetic by using the variation found on the map. Then the magnetic course is corrected to magnetic heading read on the face of your compass with deviation.

Are you applying the corrections properly ?

edit - forgot last part = you may have heard "west is best"

that means you add if agonic line is W and subtract if isogonic line is E variation.

 

[MBDiagMan]

Foreflight calculates MH, plugging in the winds and variation for you. You must download latest weather so that it calculates the MH for you.

 

[TedR3]

Foreflight does not include increased fuel burn for climb or startup/taxi which you probably include in your flight planning.

It also does not have a decreased airspeed on your climb out, which you probably also include in your planning.

I don't like that Foreflight doesn't actually state the wind speed/direction, just the the headwind component. I guess you could reverse engineer it from the air speed, ground speed and wind correction angle.

 

[MBDiagMan]

Foreflight does not include increased fuel burn for climb or startup/taxi which you probably include in your flight planning.

It also does not have a decreased airspeed on your climb out, which you probably also include in your planning.

I don't like that Foreflight doesn't actually state the wind speed/direction, just the the headwind component. I guess you could reverse engineer it from the air speed, ground speed and wind correction angle.

Ted is correct in these critiques. That said, I think the Foreflight information is adequate in a practical sense for a lot of cross country work. For working out a detailed flight data sheet as you would do for your training, one needs to do it the old fashioned way in order to gain a thorough understanding.

I'm a firm believer that a student needs to learn all aspects in cross country flight planning using a chart, a plotter, etc. THEN after they have a good understanding of the elements involved, the modern technology makes more sense plus they can always go back to a chart with their finger on the next checkpoint in a pinch. I've never seen the battery go dead on a chart, a plotter or a manual E6B.

BTW, the wind details can easily be determined in several different ways in FF. You can go to the airport and it will give complete wind direction and velocity. On the specific airport, winds aloft info is available. On the Map a choice is winds. There are several ways to get such information in FF.

My $0.02,

 

[denverpilot]

Difference 1 ,is foreflight will always show about a 10-15 degree difference on my CH than what I figure out.
Now understanding to my knowledge , there is no place in foreflight under aircraft data for compass variation , but that is not a factor in the plane I fly as there is no variation card, therefor no variation is figured.

Difference 2 , when I get the brief from foreflight, the winds aloft always seem to be different than what I get from the live briefer.

Difference 3, fuel burn and time is always off on foreflight from what I calculated.

What are some possibilities ( other than MY planning being off , but kinda debunked as instructor checks and verifies)

Difference 1 and 2 may be related, since FF will calculate headings and times with winds aloft included.

Difference 3 is surprising, I haven't found mine to be that far off. Are you doing separate taxi fuel, higher fuel flow for takeoff and climb, and different segments? FF doesn't do that... it's pretty basic, it just multiply time by fuel flow for the stored aircraft.

(That's also a good point... make sure the aircraft you're choosing is stored correctly or that you're typing in the fuel flow directly.)

Not sure... interesting observations, though. I may have to play with it some more.

If there's errors, they don't seem to be a large percentage off, just looking at numbers FF has come up with, they usually pass the "smell test" and I haven't been heavily re-calculating them other than when I was first testing the software accuracy quite a number of flights ago...

 

[cavmedic]

Difference 1 and 2 may be related, since FF will calculate headings and times with winds aloft included.

Difference 3 is surprising, I haven't found mine to be that far off. Are you doing separate taxi fuel, higher fuel flow for takeoff and climb, and different segments? FF doesn't do that... it's pretty basic, it just multiply time by fuel flow for the stored aircraft.

(That's also a good point... make sure the aircraft you're choosing is stored correctly or that you're typing in the fuel flow directly.)

Not sure... interesting observations, though. I may have to play with it some more.

If there's errors, they don't seem to be a large percentage off, just looking at numbers FF has come up with, they usually pass the "smell test" and I haven't been heavily re-calculating them other than when I was first testing the software accuracy quite a number of flights ago...

( on paper) My first checkpoint is my top of climb. Included into that data is my startup/taxi consumption, based on the POH. I also calculate my climb speed @ 65 knots and then use the ground winds for WCA until desired altitude , then base the rest off winds aloft. I found trying to really figure out that waypoint on FF is a PITA.

When I get home tonight, I will do a paper plan , then do another FF plan , upload the images and see where the error is occurring.

 

[cavmedic]

Ok, lets start at beginning and use proper terminology - you may be confusing yourself.

Variation is the angular difference between True and Magnetic North - this is derived from your map via the agonic/isogonic line.

Deviation is the error caused in a compass by electrical interference either via the Earth's magnetic field and/or the airframe/electronics of the aircraft - which is why you would want a compass deviation card in the aircraft.

True Course is the the line you plot on your map. This is corrected to magnetic by using the variation found on the map. Then the magnetic course is corrected to magnetic heading read on the face of your compass with deviation.

Are you applying the corrections properly ?

edit - forgot last part = you may have heard "west is best"

that means you add if agonic line is W and subtract if isogonic line is E variation.

I'm tracking you here. I meant deviation card for compass ....

 

[cavmedic]

Ted is correct in these critiques. That said, I think the Foreflight information is adequate in a practical sense for a lot of cross country work. For working out a detailed flight data sheet as you would do for your training, one needs to do it the old fashioned way in order to gain a thorough understanding.

I'm a firm believer that a student needs to learn all aspects in cross country flight planning using a chart, a plotter, etc. THEN after they have a good understanding of the elements involved, the modern technology makes more sense plus they can always go back to a chart with their finger on the next checkpoint in a pinch. I've never seen the battery go dead on a chart, a plotter or a manual E6B.

BTW, the wind details can easily be determined in several different ways in FF. You can go to the airport and it will give complete wind direction and velocity. On the specific airport, winds aloft info is available. On the Map a choice is winds. There are several ways to get such information in FF.

My $0.02,

I do not disagree with learning the basics , i just can't stand using the wiz wheel . ( all the tic marks run together, its like waiting for the hidden image to appear but it never does) I have a cx2 i'd love to use in its place, but i probably shouldn't.

 

[MBDiagMan]

Difference 1 and 2 may be related, since FF will calculate headings and times with winds aloft included.

Difference 3 is surprising, I haven't found mine to be that far off. Are you doing separate taxi fuel, higher fuel flow for takeoff and climb, and different segments? FF doesn't do that... it's pretty basic, it just multiply time by fuel flow for the stored aircraft.

(That's also a good point... make sure the aircraft you're choosing is stored correctly or that you're typing in the fuel flow directly.)

Not sure... interesting observations, though. I may have to play with it some more.

If there's errors, they don't seem to be a large percentage off, just looking at numbers FF has come up with, they usually pass the "smell test" and I haven't been heavily re-calculating them other than when I was first testing the software accuracy quite a number of flights ago...

Yes, it does indeed calculate based on your entered altitude and winds aloft.

 

[denverpilot]

I'm sure your accuracy vs. FF's more general assumptions are probably where the errors are being introduced.

An old old flying salt once joked with me that the best way to get your flight planning nailed was to go out and try over multiple flights to get a few flight plans in a row to within one minute of arrival time. He then also joked, "and then it won't matter... the point of the exercise is to build your confidence in your ability to put all the numbers together to get good numbers, once you know what good numbers are, arriving within a few minutes of those numbers is usually good enough."

I've seen a few "races" and air rallies for us bugsmashers that you do your flight planning and turn in a copy to the "race" folks before-hand... and whoever hits their times the most accurately wins one of the prizes. That's fun practice. Right now, I'm out of practice on that... I wouldn't win the prize.

 

[cavmedic]

As for downloading the weather. It is connected to the web and for the airports ,it shows xx minutes old etc. Is that where it is getting its weather info from or is it pulling it from the data from DUATS when I get the briefing .

 

[MBDiagMan]

I do not disagree with learning the basics , i just can't stand using the wiz wheel . ( all the tic marks run together, its like waiting for the hidden image to appear but it never does) I have a cx2 i'd love to use in its place, but i probably shouldn't.

I'm old enough that I went through College, Electrical Engineering, with a slide rule, so the E6B is really no problem for me. I did all my student work with a Whiz Wheel because I was comfortable with it. I would fully expect that the CX2 or electronic E6B would be fine in today's training environment.

 

[MBDiagMan]

As for downloading the weather. It is connected to the web and for the airports ,it shows xx minutes old etc. Is that where it is getting its weather info from or is it pulling it from the data from DUATS when I get the briefing .

Yes, it gets the weather from the airport information. I have my CSC Duats account set up, but I don't think that is where the weather used for calculations comes from because I used FF a good while before setting up DUATS.

 

[cavmedic]

I flew to from KRDG to KTHV on Saturday and I arrived at all checkpoints within 30 seconds to a minute of calculated times.

I can agree with a few degrees here and there based on how thick my line drawn was , and where exactly my start point and end point were drawn on the sectional , but these weren't one or two degree differences.

 

[cavmedic]

I'm old enough that I went through College, Electrical Engineering, with a slide rule, so the E6B is really no problem for me. I did all my student work with a Whiz Wheel because I was comfortable with it. I would fully expect that the CX2 or electronic E6B would be fine in today's training environment.

When I went through electronics school and also commo school in the Army , all of our algebra was done on sci calculators. So you can see my comfort level there.

 

[jaybee]

I'm tracking you here. I meant deviation card for compass ....

Cool, seems as though the problem is not on your end then.

Tracking ? former Army?

In any event you can take the E6B into the written test with along with whatever information the manufacturer prints on it so that is one good reason to learn it. Also, doing the wind and ground speed deals on the back, once you get it - takes seconds ! Lastly, if you go into Instruments it can be very valuable for determining hold clearance and entries. Also can be useful for determining relative position from VOR's. Quite handy once you get the hang of it.

 

[cavmedic]

Cool, seems as though the problem is not on your end then.

Tracking ? former Army?

In any event you can take the E6B into the written test with along with whatever information the manufacturer prints on it so that is one good reason to learn it. Also, doing the wind and ground speed deals on the back, once you get it - takes seconds ! Lastly, if you go into Instruments it can be very valuable for determining hold clearance and entries. Also can be useful for determining relative position from VOR's. Quite handy once you get the hang of it.

Yes , medically retired Army @ 15 years. 8 Years of commo and 7 as a medic. ( and I sucked at land nav then also )

I can do the WCA on the back of the E6B no problem , its all the crap on the front and remembering when to decimal shift that gets me. Kinda like using a digital VOM for a long time with auto rang, then having to use an anolog one ... ewwwww

 

[denverpilot]

As for downloading the weather. It is connected to the web and for the airports ,it shows xx minutes old etc. Is that where it is getting its weather info from or is it pulling it from the data from DUATS when I get the briefing .

The xx minutes old variety... probably pulling the raw winds aloft data behind the scenes and choosing what it thinks is the closest altitude and closest stations along the route.

Unfortunately, it isn't verbose about saying what it's using, so it's a little tough to check it 100%.

One way to see if at least the flight plan distance/time itself is "sane" is to kill its ability to get data before launching it, so it'll do a "no wind" flightplan first... then turn on the data again and re-do it.

That was one of the only ways I could find to "beta test" it for my purposes.

 

[cavmedic]

Im doing a mock up one now . See how much it is off and will post results.

 

[MBDiagMan]

About a month ago I downloaded the Pilot's Guide to Foreflight Mobile from the blog.foreflight.com website. I can't find my copy right now. It might answer your questions without the experiment.

Good luck,

 

[cavmedic]

Ill have to download that . I don't mind doing the plan anyway. I like ( need) the practice.

 

[AggieMike88]

About a month ago I downloaded the Pilot's Guide to Foreflight Mobile from the blog.foreflight.com website. I can't find my copy right now. It might answer your questions without the experiment.

Good luck,

http://www.foreflight.com/ipad/guide

@Doc... when is you gonna zip down here and lets me buy you lunch?

 

[cavmedic]

Ok , here is the paper version that I just did with current data from FSS as of 0000z .

 

[cavmedic]

Here is what foreflight shows WITHOUT any wind data

 

[denverpilot]

Have you thought about e-mailing your results to FF? They're quite responsive.

Maybe it'd turn into better documentation of the assumptions the software makes...

 

[cavmedic]

I was awaiting some more feedback as to maybe someone catching an error I made prior to emailing them

It is interesting now , all night, none of the weather is updating on FF....

I ran a test on "naviator" on my droid and it also states that it is 248*

So I once again , laid out the sectionals and checked with my plotter and my 237 is damn close. + or - a degree.

My next step is to try it on AOPA's flight planner and see what numbers it shows. It could possibly be that maybe , just maybe my plotter is a bit off. Ill have to try another one.

 

[denverpilot]

Hmm. Can't look at your numbers on iPhone here easily until I get home, but 238 to 240-something makes me think Magnetic vs True is involved in the problem here somehow...

 

[cavmedic]

Ok , this HAS to be something I am doing wrong ...........

 

[midlifeflyer]

Foreflight does not include increased fuel burn for climb or startup/taxi which you probably include in your flight planning.

It also does not have a decreased airspeed on your climb out, which you probably also include in your planning.

Actually, I've never used either in my manual planning (other than as a learning/teaching experience).

 

[denverpilot]

Actually, I've never used either in my manual planning (other than as a learning/teaching experience).

I don't typically worry about it too much in a normally-aspirated 182. In the Turbo, the fuel flow is significantly higher for takeoff and climb until you lean it out, so to be conservative I like to make sure I have at least one leg at the higher fuel flow.

 

[cavmedic]

I don't typically worry about it too much in a normally-aspirated 182. In the Turbo, the fuel flow is significantly higher for takeoff and climb until you lean it out, so to be conservative I like to make sure I have at least one leg at the higher fuel flow.

But that only would show a difference in my fuel burn , understandable. But still trying to figure out where or what is getting screwed up on the course headings.

I have a night flight tonight , have my screenshot from last night and also the paper plan I did. Gonna run it past my instructor to double check my numbers are correct.

This really kinda sucks now , because it has me second guessing. Especially when three software options show the same and mine is different.......

 

[midlifeflyer]

I don't typically worry about it too much in a normally-aspirated 182. In the Turbo, the fuel flow is significantly higher for takeoff and climb until you lean it out, so to be conservative I like to make sure I have at least one leg at the higher fuel flow.

I haven't seen it as a significant issue even in a turbo.

In part it's something that I learned from my CFI as a student pilot. It's kind of based on averages - what you lose in the climb you'll mostly get back in descent, both in terms of speed and fuel burn. For timing, all we did was add 1 minute for each 1000' of climb. It was amazing how close those numbers turned out. Even used the 1 minute rule in a spreadsheet calculator and it worked well.

Another part is that those planning fuel burn numbers may not pan out in flight anyway. With rare exceptions, I plan all my flight to end with 1 hour of fuel based on the worst numbers in the POH. So I'm rarely concerned if we're going to make it.

 

[flyingcheesehead]

This really kinda sucks now , because it has me second guessing. Especially when three software options show the same and mine is different.......

Okay, looking through what you've got to try and see where you may have erred in the paper calculations... I also punched your route into ForeFlight, including the waypoints as close as I could get them, and the 90 knots/4.1 gph figures from your flight plan sheet, so I've got ForeFlight showing pretty much what your screen shot had.

First of all, what winds aloft are you using for the first (climb) leg? The only winds I see on your sheet are the ones at 4500, 260 at 39 knots. On your course of 249, that'll be slightly from your right, but your wind correction angle is listed as 5 degrees left. I would suggest that for the climb you use the winds aloft at 3000 feet interpolated between the AVP and EMI forecasts. Later in the flight, you'll be much closer to EMI, so for the last legs at 4500, the EMI winds interpolated between 3000 and 6000 might make more sense. Either way, IMO you should put the winds aloft that you're using for each leg on that leg's line, that's why all those spaces are there. You may have calculated the first leg correctly if you're using different winds than you are for the rest of the flight, but without knowing what those are, it's difficult to tell.

Second - Your total distance is a bit longer (51.4) than ForeFlight says (50). Check to be sure you're not rounding up on all your legs or something.

Third - On the first leg, there's something wrong. You've got it listed as 54 knots GS, 5.4nm, and 8 minutes. 54 knots for 5.4nm is 6 minutes; Or if you're using 8 minutes as your time to climb, 8 minutes at 54 knots would be 7.2 nm.

Fourth - On the third and fourth legs, you've got 12nm and 10nm as the distances, respectively, but 13 minutes for the time on both of them.

Now, on any of the electronic flight planners that didn't have you enter different speeds/fuel burns for climb, cruise and descent (such as ForeFlight) you may end up with a slightly higher fuel burn and total time on paper because you're taking into account the slower, thirstier climb while they may not be. Also, I believe ForeFlight has a system that results in a "gridded" winds aloft scheme that, while based on the forecasts you're using, is doing a much more complex interpolation so if the winds aloft forecast stations surrounding your flight are showing winds that differ from each other significantly, and you're only using one of them, the calculations will be different.

Hope this helps, let us know what you discover!

 

[MBDiagMan]

ASCII,

It's very nice of you to spend this much time and effort to help the OP understand the differences.

Although I had Foreflight on my IPhone while I was doing my student cross countries and other flight planning, I just hammered it all out by hand. I tried to correlate it with FF, and that's when I realized that FF was plugging in the winds and magnetic variation.

This forum has some really helpful members!

 

[kimberlyanne546]

In addition to sending them an email, maybe send them a link to this thread. They seem to want to improve their product and the customers on here could be providing useful feedback.

 

[dbman5]

Another possibility I haven't seen mentioned (and very few seem to be aware of) is that many on-line planners use the VOR to establish magnet north and that can easily be off by up to 6 degrees (FAA tries to reset them when they get that far off) and I've seen as much as 10 degrees.

I don't know whether ForeFlight uses that method or not but some do. Or at least they used to - I haven't checked in a couple years. (Most PPL training manuals also tell you to use VORs to determine magnetic north but don't tell you there is essentially a built-in inaccuracy. However, you should be able to figure that out for yourself since you should know that the magnetic variation changes constantly but the VOR radials don't.)

The 360 degree radial on the VOR only matched magnetic north when the VOR was installed or last reset.

My guess is that most people who see a difference in what they actually fly and what the on-line planner tells them to fly attribute the whole difference to changes in the actual wind direction. And, in many cases, the wind probably is the majority of the difference - just not all of it. By the way, 6 degrees is 1 mile off course for every 10 flown.

 

[NaviatorMike]

Naviator uses something called the World Magnetic Model to determine the magnetic declination for lat/lon coordinates. I assume foreflight and online flight planners are using the same model.

You can look up the the magnetic declination for a coordinate using this tool:
http://ngdc.noaa.gov/geomagmodels/IGRFWMM.jsp?defaultModel=WMM

I'm not sure if this is related to your particular problem or not, but I thought I'd mention it.

Cheers,
Mike