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climb gradient vs flight path angle

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climb gradient vs flight path angle

Old 6th Mar 2014, 21:34
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Question climb gradient vs flight path angle

" The climb gradient is defined as the ratio of The increase of altitude to horizontal air distance expressed as a percentage " therfore a still air distance.
When relating the "climb gradient" to ground distance the correct term to be used is Flight Path Angle

where can i find a good solid reference for this, have a bit of a debate with colleagues
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Old 6th Mar 2014, 23:12
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Highfly33,

I don't think you'll find a 'good solid reference for this'. Both can be relative to air or relative to earth, depending on the context. Gradient is usually expressed in percent and FPA in degrees.
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Old 7th Mar 2014, 00:26
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In common usage, "gradient" is represented in percent, while "angle" is represented in degrees. Take your pick as to which one you want to use, because they're essentially interchangeable.
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Old 7th Mar 2014, 08:05
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In performance, the required climb gradient s are still wind .. n'est Pas ???
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Old 7th Mar 2014, 09:18
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Apart from the obstacle clearance ones!
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Old 7th Mar 2014, 11:30
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Obviously, but that's related to the flight path.. the achieved still air gradient does not change right ??
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Old 7th Mar 2014, 12:33
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here is my higly respected Grund Instructors take on the selfsame issue:

CS25 111 and 115 specify the climb gradient requirements for certification.
These are still air gradients of climb. If they weren't then the gradient of climb would continually change with the prevailing wind. So its common sense that its a still air gradient!

The CLTOM graph is based upon still air. There is no wind input!
Clearly the wind effective gradient is different and it is this that gives the flight path angle.

Wind effective gradient = still air gradient x TAS/GS
We would use the wind effective gradient for obstacle clearance calculations.

this is matching my understanding and aided me in the EASA ATPL examinations for Performance,

however there STILL seem to be lot of confusion on this specific subject, even among line flying and military pilots ...

i find performance rather tricky, but take it as important bread and butter stuff, therfore my hunt for the truth... (its out there somewhere)

next step will be an email to Scully and Moulder
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Old 7th Mar 2014, 13:51
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Originally Posted by HIGHFLY33 View Post
When relating the "climb gradient" to ground distance the correct term to be used is Flight Path Angle
As HazelNuts39 and Intruder have said, a gradient is a ratio, usually expressed in percent. Therefore, it would be wrong to call a climb gradient which is based on ground distance a flight path angle. The fact you can calculate a flight path angle from still air climb gradient and wind data is another story, but still a gradient is a gradient and an angle is an angle.

Originally Posted by HIGHFLY33 View Post
Clearly the wind effective gradient is different and it is this that gives the flight path angle.
Yes, it 'gives' the flight path angle, i.e. the flight path angle can be calculated from the wind effective gradient.

As far as you ask for references, I could offer the following two definitions, but I'm afraid they contradict your assumption 'flight path angle' was a better term for a ground based climb gradient.
For every point of the aircraft’s flight path, the angle of climb γ is the angle between the airspeed vector and the horizontal plane (Torenbeek/Wittenberg, Flight Physics, Springer 2009, p 279)

The climb gradient is the ratio between the height increment dh and the horizontal distance travelled ds during a small time interval dh (loc. cit., p 280)

Last edited by hvogt; 7th Mar 2014 at 13:57. Reason: text formatting
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Old 7th Mar 2014, 16:35
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Not sure why people are bringing wind into this?
Angle and gradient are interchangeable.
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Old 7th Mar 2014, 17:19
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HIGHFLY33,

The minimum gradients required in 25.111, 25.119 and 25.121 are still air gradients because 25.101(a) specifies:

(a) Unless otherwise prescribed, aeroplanes must meet the applicable performance requirements of this Subpart for ambient atmospheric conditions and still air.

The gradients specified in 25.115(b) are not still air because 25.1587(b) specifies:

(b) Each aeroplane Flight Manual must contain the performance information computed under the applicable provisions of this CS–25 (including CS 25.115, 25.123 and 25.125 for the weights, altitudes, temperatures, wind components, and runway gradients, as applicable) within the operational limits of the aeroplane, and (...)
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Old 7th Mar 2014, 20:54
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Thank you, Nuts.

I will guarantee you that I can get higher at the end of the runway with a head wind and basic climb procedures.

Sheesh.

The plane is climbing in the air mass, and if the air mass is moving "backwards" compared to the runway heading, then I'll get higher than with no wind, or worse, a tail wind.

Those that have not flown a HUD with an inertial flight path vector ( not angle, but actual vector based on the Earth) would see this.

Every carrier pilot sees this when they have "wind over the deck" and lurch over the end of the boat.
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Old 7th Mar 2014, 21:37
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Intruder:

In common usage, "gradient" is represented in percent, while "angle" is represented in degrees. Take your pick as to which one you want to use, because they're essentially interchangeable.
In FAA-speak "gradient" is used for higher-than-standard climb gradients and is expressed in feet per mile. "Angle" is used for descent on approach procedures; the final approach segment.

Unlike PANS-OPs, TERPs does not use percentages to express required climb gradients.
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Old 8th Mar 2014, 01:45
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Question

Guys are we talking about different application of definitions between FAA & EASA. ??

I fully understand the effect on wind on your flight path.
I am still talking about the performance required climb gradient to be achieved.

According CS25. This is a still air gradient.. ie required performance to be achieved...

I also understand that this required gradient does not give you obstacle clearance.

For obstacle clearance wind is considered to give your flight path angle,

pleas keep your view s coming... I want clarification..

Please give reference s if you have any. Thanks in advance
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Old 8th Mar 2014, 01:55
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Gums , still not clear..

Your rate of climb and time is unaffected.... right??.
Therefore you are achieving the same level change for a given still air distance??
( your flight path is obviously affected as you describe)


If you check your WAT climb limited graph, there is no corrections for head or tailwind
Needless to day this chart will not ensure obstacle clearance.. for this we refer to different charts..





Wish I could get 1 clear definite answer
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Old 8th Mar 2014, 02:00
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Hi nuts,

Thank you for your contribution, To me, this is in line with what I have been though t at ground school..(EASA ATPLtheory)
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Old 8th Mar 2014, 02:07
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Gradients and angles are "iron rails" in the sky. Ground speed is what is needed to make them work, because they are a fixed path over the ground (disregarding the curvature of the earth, please.)

So, to those who don't understand, what does it take to get an airplane to fly ground speed?
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Old 8th Mar 2014, 08:02
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terpster, I sence a bit of irony in your post..

GS is irrelevant when considering your requirements.. surely
IE.. for a given TAS you will get a given value of Lift assuming all other factors remain constant. ( Your V speeds are surely not derived from GS)

For the certification the demonstrated gradient to be achieved on climb out is a still air gradient..

Hence the climb gradient in your WAT CLIMB limited graph is also a still air gradient..

In order to achieve obstacle clearance and calculate your flight path over the ground, wind is obviously a factor.


It Am I falling of the Iron Rails in the sky, as you describe them ??
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Old 8th Mar 2014, 08:51
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Hi Hifly

Applying some PPRuNe logic to this

FACT: You are having a debate with your colleagues
SPECULATION: It was in the pub
RESULT: You are happy in your work which probably puts you in the top 10% of Forum members

Other than that.... Isn't one you plan for,the other you actually do? Sorry i can't be more help...unless you are in the pub and then il BS all night with you
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Old 8th Mar 2014, 11:14
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Highfly33,

for the purpose of the discussion you started in your first post above I suggest you should leave the WAT-limits out of it. The purpose of those requirements is to define a weight limitation, which is part of the limitations of the airworthiness certificate of the airplane. The pilot is supposed to respect the weight limit, and has no business with the gradient on which it is based.

The flight path gradient is subject to wind and the AFM performance information usually presents it as as a percentage.

Flight path angle is usually expressed in degrees. The FPA presented on the PFD of a modern airplane is relative to ground, i.e. includes the effect of wind. However, in the well-known expression
"pitch angle = FPA + AoA" it is relative to the airmass.

Last edited by HazelNuts39; 8th Mar 2014 at 11:31.
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Old 8th Mar 2014, 15:31
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highfly:

GS is irrelevant when considering your requirements.. surely
Ground speed is what determines climb gradient; i.e. "This departure requires a climb gradient of 425 feet per mile. Those miles are ground miles, not air miles.


IE.. for a given TAS you will get a given value of Lift assuming all other factors remain constant. ( Your V speeds are surely not derived from GS)
V speeds are performance values, which are expressed as indicated airspeed, not true airspeed and not ground speed.
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