climb gradient vs flight path angle

[HIGHFLY33]

" 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

[HazelNuts39]

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.

[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.

[HIGHFLY33]

In performance, the required climb gradient s are still wind .. n'est Pas ???

[BizJetJock]

Apart from the obstacle clearance ones!

[HIGHFLY33]

Obviously, but that's related to the flight path.. the achieved still air gradient does not change right ??

[HIGHFLY33]

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 :uhoh:...

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 :confused:

[hvogt]

When relating the "climb gradient" to ground distance the correct term to be used is Flight Path AngleAs 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.

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)

[FE Hoppy]

Not sure why people are bringing wind into this?
Angle and gradient are interchangeable.

[HazelNuts39]

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 (...)

[gums]

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.

[aterpster]

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.

[HIGHFLY33]

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

[HIGHFLY33]

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..



:ugh:

Wish I could get 1 clear definite answer

[HIGHFLY33]

Hi nuts,

Thank you for your contribution, To me, this is in line with what I have been though t at ground school..:ok:(EASA ATPLtheory)

[aterpster]

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?:)

[HIGHFLY33]

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 ??

[Global Warrior]

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 :ok:

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 :)

[HazelNuts39]

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.

[aterpster]

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.

[gums]

Thank you ater

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.

I would add RoC in the airmass, which normally is moving WRT to the ground.

If you have a headwind on takeoff of extreme velocity, you have a greatly reduced takeoff roll and using basic climb schedule can easily have a "true" climb angle very high. Not pitch attitude, not AoA plus pitch, but a velocity vector referenced to Mother Earth. Hell, if the headwind was strong enough you could have 30, 40 or 50 degrees of actual climb compared to the runway.

The "gradient" WRT to the ground was what I was always concerned about. How many feet to get above the ground for available runway and obstacles at the other end. On one mission at heavy weight, I had the wind shift halfway down the rwy and simply stopped getting more CAS. Too fast to abort, and skimmed over the palm trees on the edge of the max AoA once up, barely. So I know what the "gradient" is. On that ride we had about 80% of available runway "computed" for takeoff considering our weight and the "predicted" wind down the runway. Then two check speeds at various rwy markers. Not something a commercial jet would go with, but it was a wartime scenario, O.K.?

[flyer101flyer]

Don't forget that a wind gradient (increasing headwind w/ alt) improves climb rate... can be rather significant... and also increases the sink rate...

[Intruder]

Rate is unchanged from 0-wind case. Angle changes.

[HazelNuts39]

Intruder,

think again!

[awblain]

Gums and aterpster have good points:

Whether and how you fly depends on your airspeed, but where the mountains and palm trees are depends on your ground speed.

Whether you have the right terminology is perhaps less important than whether you are confident that you're going to keep flying and avoid them based on using the right measures for the right problem.

[HIGHFLY33]

Thank you all for great feedback,

The situation and questions arise from a lesson in performance.
Talking about the different required gradient for certification for the 4 stages.

For this I assume still wind,

As for day to day operation and obstacle clearance it is evident that wind does affect our flight path and Is taken into consideration...

I initially reacted to a simple statement ..

Headwind increases your climb gradient

Well yes if speaking about obstacle clearance.. (ground referenced gradient)but NOT when considering your climb gradient of whatever depending on number of engines

I still maintain that without specifying what the gradient gradient is referenced to. The aforementioned statement is incorrect..

What I have learned sofar, is. Perspectives from either side of the pond as well between mil & civil pilots differ..

We all achieve the same outcome , but our verbiage to describe what we are doing seems to be different.. perhaps it is a context issue too..

I am adamant to get to the bottom of this simple conundrum, so please continue to give feedback

[HIGHFLY33]

Flyer 101,

Are you sure ??

Roc is fpm, and you don't get to fl 100 any faster in a headwind..
Time to climb is also unaffected right ?

You are though correct that you will get to your level over a shorter Ground Distance.

[aterpster]

highlfy:

Climb gradient is always over the ground. It does not have a conditional definition.

[aterpster]

From the FAA's AIM:

3. Pilots must preplan to determine if the aircraft can meet the climb gradient (expressed in feet per nautical mile) required by the departure procedure, and be aware that flying at a higher than anticipated ground speed increases the climb rate requirement in feet per minute. Higher than standard climb gradients are specified by a note on the departure procedure chart for graphic DPs, or in the Take-Off Minimums and (Obstacle) Departure Procedures section of the U.S. Terminal Procedures booklet for textual ODPs. The required climb gradient, or higher, must be maintained to the specified altitude or fix, then the standard climb gradient of 200 ft/NM can be resumed. A table for the conversion of climb gradient (feet per nautical mile) to climb rate (feet per minute), at a given ground speed, is included on the inside of the back cover of the U.S. Terminal Procedures booklets.

[FE Hoppy]

HYGHFLY33


You are overcomplicating things.

The gradient required, whether it be climb or obstacle related doesn't change with wind.

It's just geometry in the case of obstacles and rules in a book for segmented take off flight path.

The gradient you will achieve when flying at a fixed IAS will vary with head or tail wind.

Therefore we calculate the gradient we can achieve in the actual wind (not really) conditions and confirm it is greater than that required.

[gums]

Thank you, Hoppy and Ater.

Sheesh.

There must be fifty ways to define gradient ( cheap reference to Paul Simon's song).

The big thing is not to contact Mother Earth. THAT is where the "gradient" comes into play.

RoC is normally a constant for power, gross weight and AoA and such. That's in the air mass. Over Mother Earth, it's a different story.

You are making this more complicated than the original question, Highfly.

If the chart says you must achieve "x" feet, "x" miles from the runway, then I would look at my plane's performance and the appropriate charts for my plane.

This thread is getting old, and I am not sure we are satisfying the questions that Highfly started with. Many of us here have thousands of hours, and I flew many right at the limits of the aircraft performance. If one can not trust us to provide an decent answer, then who else can?

[flyer101flyer]

Re question #27: I wasn't trying to say you always climb faster in a headwind. I was talking about a wind gradient. (Yet another use of the the term "gradient"!)

I agree that I'm adding another "twist" that wasn't stated in the original question, but a headwind gradient (increasing headwind with altitude) absolutely does boost the climb rate. So does a reverse tailwind gradient (decreasing tailwind with altitude) but this is much less common. We climb through some amount of headwind gradient on nearly every takeoff.

The same headwind gradient that helps the climb rate, also increases our sink rate as we descend down through it. This is a very real effect that demands some extra airspeed for a safe landing approach when the gradient is strong. So that we have enough energy to flare, ie. arrest the high sink rate.

Descending through a tailwind gradient, on the other hand, will reduce the sink rate. This can add to your woes if you are accidentally landing downwind, in which case there are two different factors tending to carry you far down the runway-- higher groundspeed than you may be used to, and also a lower sink rate.

These effects are real enough to be easily detectable in light plane flying. Near the ground is where the largest gradients usually exist. Are there real-world cases where you could measure a significant change in climb rate due to these effects when testing over intervals of 1000 feet or more, starting at least that high over the ground? I'm not sure...

[aterpster]

flyer:

I agree that I'm adding another "twist" that wasn't stated in the original question, but a headwind gradient (increasing headwind with altitude) absolutely does boost the climb rate. So does a reverse tailwind gradient (decreasing tailwind with altitude) but this is much less common. We climb through some amount of headwind gradient on nearly every takeoff.

Wind gradient? How about wind component?

Here is what my PC's Webster dictionary has to say about the word gradient:

gradient

gra·di·ent [gráydee ?nt] noun (plural gra·di·ents)

1.slope: an upward or downward slope, for example, in a road or railroad

2.steepness: the rate at which the steepness of a slope increases

3.PHYSICS measure of change: a measure of change in a physical quantity such as temperature or pressure over a specified distance

4.BIOLOGY rate of growth: any of a series of changes in the rate of growth or metabolism of an organism, cell, or organ

5.MATHEMATICS slope on a curve: the slope of a line or a tangent at any point on a curve

adjective

sloping: sloping evenly and uniformly

Encarta® World English Dictionary © & (P) 1999,2000 Microsoft Corporation. All rights reserved. Developed for Microsoft by Bloomsbury Publishing Plc.

[FE Hoppy]

Wind gradient is a very common term. I'm surprised a terpster isn't familiar with it.

[aterpster]

FE Hoppy:

Wind gradient is a very common term. I'm surprised a terpster isn't familiar with it.

Only in terms of rapid velocity changes in climb or descent in a jet. :)

In my performance experience related to departure procedures it simply means feet per mile (nautical ground mile).

[flyer101flyer]

Wind component means something different than wind gradient. Ask the albatross.

Every pilot should understand the effects of a wind gradient.

Surely we can do better in "the very best in technical discussion" than looking things up in various non-aviation dictionaries? ;)

PS definition #3 fits exactly.

[aterpster]

flyer101flyer:

Wind component means something different than wind gradient. Ask the albatross.

Every pilot should understand the effects of a wind gradient.

Surely we can do better in "the very best in technical discussion" than looking things up in various non-aviation dictionaries?

PS definition #3 fits exactly.

I did a phrase and word search in Aerodynamics for Naval Aviators.

Lots of "gradients" and lots of "wind," but no "wind gradient."

[john_tullamarine]

"wind gradient" generally is used to refer to change of wind component with height. This is quite measurable at low level (ie boundary layer) especially over featureless terrain (eg oceanic). Important to the larger birds such as albatross.

[aterpster]

J.T.:

"wind gradient" generally is used to refer to change of wind component with height. This is quite measurable at low level (ie boundary layer) especially over featureless terrain (eg oceanic). Important to the larger birds such as albatross.

Sort of what I said in Post #35:

Only in terms of rapid velocity changes in climb or descent in a jet.

[safetypee]

Wind Gradient is used in AC 25-7 in relation to determining engine-out climb performance; page 71

[john_tullamarine]

Doesn't necessarily need to be a massive gradient to be significant.

Operationally important for assessment of when and if one ought to take the higher cruise level ...

[FE Hoppy]

AB use the term in here :
http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-APPR-SEQ01.pdf

[aterpster]

j.t.:


Doesn't necessarily need to be a massive gradient to be significant.

Operationally important for assessment of when and if one ought to take the higher cruise level ...

I admit total defeat. :)

All those years I flew the line the company spoon-fed me optimum routes and altitudes based on winds aloft.

[john_tullamarine]

They gave us lotsastuff .. which was all very good ... but, with forecasting which left a bit to be desired and in the GAFA navigational wilderness, we ended up having to make up most of what we did on the fly, as it were ....

I never flew the Diesel 9 but I gather that the boys on that were always interested in fuel remaining and paid much attention to wind gradients and just what level they ought to be re the latter to maximise the former.

[deefer dog]

High Fly 33.

It seems to me that gradients are used for climb and FPA (degrees) is used mostly in respect of descent. They are two methods of arriving at the same answer. One is rise over run, and the other is opposite over adjacent.

Wind is a red herring, but you understand that part of it anyway. Wind gradient, which of course is an unknown value that aint included in the ATIS, is splitting hairs!

[aterpster]

j.t.

I never flew the Diesel 9 but I gather that the boys on that were always interested in fuel remaining and paid much attention to wind gradients and just what level they ought to be re the latter to maximise the former.

I flew the DC-9-10 as my first PIC airplane. The longest leg was probably 1:30 or so, so winds aloft were far less important than Boston to Los Angeles on a 1011.

Winds aloft were a big deal; wind gradients were in the dust of the details.

[flyer101flyer]

It's often very easy to notice the effects of wind gradient during the last 50 to 100' of descent in a light plane, sailplane, or ultralight aircraft. The sink rate increases quite dramatically due to the strong wind gradient often found near the ground. It's a very real thing. It's also not unusual to notice a higher-than-normal climb rate immediately after takeoff, for the same reason. Physics are no different in fast jets but you might need a stronger wind to get a noticable effect. On the other hand in a steep fast climb you are obviously moving up through the wind gradient a lot faster than you would in a light plane.

The effects of wind gradient on glide angle, as opposed to sink rate, may be a little more subtle. Still, if you have an autopilot controlling the glide path w/ elevator and airspeed w/ autothrottle, it seems that more power will be applied whenever the a/c is descending through a strong wind headwind gradient, no?

[deefer dog]

Yes, I'm sure all of us here understand the nature and effect of wind gradients, but in the context of obstacle clearance flight planning or descent profiles it is miniature you can ignore. It has nought to do with the OP's question.

[flyer101flyer]

It seems not "all" understood-- read the posts -- but perhaps they do now! Or are motivated to learn more.

I have had more than one working "professional pilot" tell me wrong things about the wind, so I say it's fair game for discussion. Yes it was not the original question.

[elcol]

From Boeings Jet Transport Performance Methods: Chapter 22
EASA regulations
The European Aviation Safety Agency, in its Certification Specifications for Large Aeroplanes CS-25, Book 1 Subpart B, contains precisely the same climb requirements as the FAR25 requirements quoted above. CS 25.121 corresponds to FAR Part 25 Section 25.121.quoted above. Thus the requirements to both FAA and EASA/JAA operators are identical.


wind corrections to required gradients
We said earlier that the gradient requirements quoted above are unrelated to the requirements for obstacle clearance; instead, they’re a means of mandating a minimum acceptable level of surplus energy during a takeoff. Because of this fact, the gradients specified are zero-wind gradients – they are not corrected for the wind expected during the takeoff. The airplane’s surplus energy state is not a function of the wind encountered during the takeoff.


Obviously, however, when we’re concerned with obstacle clearance we must consider the wind since the wind affects the airplane’s path over the ground and hence its ability to clear any obstacles.

[HIGHFLY33]

Greetings Elcol, Thank you for a solid reference , this is precisely what I was looking for;much appreciated,

I appreciate all contributions to this thread, I have been taken by surprise over how many differences of opinions thoughts and so forth there is on this subject matter.. It is indeed a interesting discussion,

"clear as mud" is a term that comes to mind when speaking about aircraft performance, hopefully by-gaining a deeper understanding , the sediment will settle and clarity will yet again prevail,

Best Regards
HIGHFLY33

[elcol]

Just to clear up a previous post that dismissed the CLTOM/WAT limit as an irrelevance. The purpose of this graph is to ensure that the aircraft complies with the most severe gradient requirement (normally segment 2) of the NTOFP as specified in CS25. There is no wind input into the graph because they are still air gradients.