Speed Over Ground (SOG)
The actual speed the GPS unit is moving over the ground. This may differ from airspeed or nautical speed due to such things as head winds or sea conditions. For example, a plane that is going 120 knots into a 10-knot head wind will have a SOG of 110 knots.

source Garmin

Like I said in the other thread, PBL you never answer questions! I didn't ask if I could look at your profile.

Haha ya right! That's the biggest lie ever. First of all, if they're your colleagues I'm pretty sure you would know if they did or not, "apparently" wouldn't be used in that case. Second, the second sentence is perfect lawyer speak for making sure you can squirm your way out with an excuse. If they didn't "turn the screws personally" then what the heck does building it have to do with?! Also, if they did actually have a part in it then saying something like they developed the software, or they did the testing for it would help make things add up, especially since they were your "colleagues" and you couldn't say what they did. And last point, garmin and RC are two different companies, with two different products stated in my case. Again, if you were telling the truth, something a little more specific would help! Ya I got a bit of psychology and investigative background and you, PBL, are the equivalent to an imposter!

Regarding your last paragraph, are you seriously threatening me?!... A completely anonymous person on the Internet?! I thought that kind of ignorance only happened on YouTube.

Italia458--I agree most of these computations and definitions are from the ground and are therefore useless to aviation:}

Some people realise the importance of proper definitions, and how to make them. These people should include all scientists and engineers, or there'd be trouble.

Other people do not understand how important it is to know exactly what you are talking about. These may be fine using the equipment designed by the engineers based on the knowledge from the scientists, but they should be kept well away from science and engineering or there will be trouble.

And italia, noone is threatening you. You got a very friendly bit of equally sound advice, that's all. Take it to heart.

Yawn. Now let us get back to the topic at hand. No more troll feeding in this zoo until Tuesday next week, sorry if you missed it! :p

Exactly, that's why I use the definition used in aviation by EVERYONE

Yes, so except for about three people here on this thread, who are engineers and one who is also a scientist...the should stop pretending they are because they are NOT!!!..


no more here:* 83 posts of ridiculous and wrong conventions and 'definitions' through serious misinterpretation of technical works:yuk:

the fake 'mensa club' is ground based...go stop that oil gusher:rolleyes:

...all the self proclaimed geniuses...you don't need to hand wave your genius if you are a genius it is recognized subtly by all.... and not forced down people's throats

:=


the work done here is given by the following equation:

work = ∫axdx between the bounds{s,0}:E

just in case there's interest, as I don't like muddling in obscurity

here's the solution:as I have given in JB:}

in order 'integrate' a function of the form [ax^n] one applies the following formula:

∫ax^n dx =ax^n+1/(n+1) so ∫ax dx = ax^2/2 and ∫ax^5 dx = ax^6/6 ...and so on....

for a definite integral between two bounds for example between 2 and 0 and where 2 = b and 0 =a you have to replace those X's with the numbers always subtracting the [b-a]

so for this integral equation ∫axdx =AS^2/2 - [A0^2/2=0]

and since S^2 =S*S we can say that ∫axdx between the bounds{s,0}

= 1/2 ASS http://images.ibsrv.net/ibsrv/res/sr...s/badteeth.gif

And its STILL the speed of the aircraft relative to the ground!! It is not necessary to add anything more than plus or minus wind speed. Simples.

Finally Reason!!!:ok:

just to add nav fix displacement is important only in the planning stage the mileage is given on the charts, or using a plotter so that fuel can be determined...local winds vary anyway so the planning device flight computer, dispatch,..and so on is always trumped by actual conditions...i.e what the GPS or your clock and eyes, if done by DR, tells you, it is as referenced from over the ground...so you don't run out of fuel and crash....I just wanted that part clear.... as looking at this thread I now see that such a statement is open to serious interpretation:rolleyes:...Elmer Sperry must by gyrating:eek:

Rate of change of position!

Methinks Italia will eventually get around to reading some of PBL's other contributions to discussions on this site and begin to feel just a little embarrassed..

Me thinks not so!

We have had private messages discussing this and I believe our quibble should be resolved now.

How did this thread get to 5 pages ?
 

Two observers on the ground (ie dirt, either geoid, ellipsoid or prolate spheroid), measured distance apart. Aircraft flies directly over the two of them. From observer zenith (straight-up) to observer zenith measure the time taken. A bit of arithmetic and hey presto ground speed ! If aviation has managed to come up with an alternative definition I'll be unsuitably impressed (ps for PA this is the non-relativistic version).

How did this thread get to 5 pages

.. the joys of PPRuNe .. often the journey is more interesting than the destination.

Mr Optimistic asks:
Because there are at least two coherent possible definitions out there, and people are voting one by one for their favorite. Mostly without giving coherent reasons for so doing, unfortunately.

Lots of people have said this. One must ask "what do you mean by that?", because there are at least two coherent interpretations, as we have seen.

Looks like he votes for Kayton.

Then there is
Rate of change of position with respect to what? With respect to the fixed stars?

Best to illustrate with the questioner hisself:
So he votes against Kayton.

I guess he has not yet checked for himself.

And so it goes on!

PBL

Coherence ?
 

I've seen one coherent definition (in which ground speed = ground speed), and something else which is hard to describe. Some even believe that it is necessary to hold the nose up a bit to get the necessary lift for level flight. Given that the earth is not flat, it is clearly necessary in fact to maintain a continuous descent to maintain a constant height above ground, with a bit of a bank to the left to counter coriolis when flying north in the northern hemisphere. That's why INS systems are so expensive as they take this drudgery away.

Oh, terrific! Now we can get cracking on defining a descent, as there will clearly be some differing opinions on that one. :D

As for ground speed, define zenith as "above as defined by a plumb line" and I'll drink to the ground speed being the distance covered between being in zenith above point A and being in zenith above point B divided by the time taken to cover the same ground. Now, the question is... what distance?

(Above paragraph edited to avoid GS always being unity due to a brain fart in the denominator)

If you define instantaneous ground speed in the only sensible way, i e as the ground speed acquired when the distance between A and B approaches zero, we end up with it having to be the distance along the geoid. Otherwise, you'd end up with a difference between the distance A to B and the distance acquired when integrating the instantaneous ground speed over time.

And for those still suggesting that this complicating things unnecessarily, I suggest looking at the original post stating that this is for flight test purposes. What's good enough for plodding along from airfield to airfield is frequently no longer good enough in that scenario. Methinks this thread would have unfolded rather differently in the flight testing forum, without a lot of the "why on earth bother" posts.

Mr O raises some interesting points which go a long way to explaining why IRS systems need Profile Rate and Schuler Loops, and the Coriolis effect is actually covered (in 737s) by the built-in 'crab' you can see when they taxy, which derives from an offset vertical stabiliser setting.

The 'constant descent' requirement has, of course, become much easier to achieve with the growing use of GPS with altitude determination.

what about WGS84..aren't GPS waypoints all referenced to a standard datum?

and I guess we can just ignore the wind as it does not seem important for GS determination

I think that the position solution is the difficulty with modern navigation..No?

PA,
the GPS waypoints are in reference to the WGS84 ellipsoid, which is a gross simplification of the shape of the earth. For most practical purposes, you need to use the geoid which defines MSL. The geoid is a lot bumpier.

In practise, this means many things (as we have seen). One of them is that the distance between 45N 37E and 45N 38E, as travelled at sea level, may not be the same as the distance between 45N 40E and 45N 41E.

There are many difficulties with modern navigation, and I'd say sevaral are more intricate than the position solution. Position accuracy and positioning availability would be two tricky ones off the top of my head in the modern day of GNSS.

Everything in engineering is an inexact solution...everything!
the position solution is probably given an error analysis algorithm

WIND;)

PS the calibration for the ASI i.e flight testing methods were detailed in the report provided by Genghis:hmm:

:sad: