% climb gradient

[captain dad]

Could someone explain how to calculate % gradient. I think I got it but I want to check myself. Is it GS/60=%? Howdo you work it backwards from ft/NM?

Thanks

 

[FraxJockey]

Could someone explain how to calculate % gradient. I think I got it but I want to check myself. Is it GS/60=%? Howdo you work it backwards from ft/NM?

Thanks

Rise/Run=gradient 250ft/6080ft (1nm) = .04 or 4%

or the easy way and look at the chart on the jep plate at the 100 mark.

 

[h82land]

as far as the major numbers go, 200 ft/nm is about a 3.3% and 152 ft/nm is about a 2.5%. Hope that helps.

 

[Guitar Guy]

Add to that the vaunted 1.6% climb requirement is equivalent to 97 ft per NM.

 

[LAZYB]

Could someone explain how to calculate % gradient. I think I got it but I want to check myself. Is it GS/60=%? Howdo you work it backwards from ft/NM?

Thanks

When are you interviewing?

 

[Big Picture]

For a good approximation, divide ft/nm by 6000. For example, 300ft/nm equals a 5% gradient.

Your formula of GS/60 equals nm/min unless by GS, you mean glideslope.

Hope this helps.

 

[206amphib]

Just got back from simuflite...they have another little trick. This may not be what you're looking for, but maybe someone will use it. Just look at the little chart that jepp gives you on the departure procedure, go to the 100 knot column, and go down to your required fpm...then move the decimal. For example, 700 fpm = 7.0% percent climb required. Not that this is what you're looking for, but maybe it'll come in handy...

 

[C425Driver]

Ask NetJetWife. She's got an opinion on everything.

 

[Guitar rocker]

Dude, why did you post this in the majors too? Listen, you will never get the horse to breathe on this one....we have beat it to death.

 

[EdAtTheAirport]

Thanks for asking a technical question, because I was biting my lip trying not to respond to a particular narrow-minded poster who has her opinion plastered onto every thread on this board. Maybe we can be free of her here, since this actually involves aviating.

The simple answer: Percent gradient is "rise" divided by "run." This is easy when determining a runway gradient: just divide the difference in runway elevations by the length of the runway.

Climb gradients are rise/run also. A 4% gradient means that your climb rate is 4% of your groundspeed, but the numbers aren't the same. The problem is that you have climb measured in ft/min, and GS measured in nm/hr.

First, you need your "Sixty Number," "Magic Number," whatever. 60 kts = 1; 120 kts = 2; 150 kts = 2.5, etc. For a given airplane, you should only need one Magic Number. 120 kts is not an unreasonable GS for V2 @ SL, upwind. So for your airplane, just know the number "2." For Colorado with a little downwind, maybe "2 1/2" (representing a 150 kt groundspeed). For a two-engine calculation, or a turn to a strong downwind, maybe "3" (representing 180 kts GS).

Owing to the fact that God made the Earth the size that he did, man was able to define a nm as approx 6000 feet. Through the miracle of mathematics,we have an easy solution to this.

Climb required for a certain percent gradient:

FPM = % x 60 x Magic Number. (This is your answer).

If a DP requires a 4% gradient, then (at 120kt), you will require a 480 fpm climb rate. (4 X 60 X 2).

If a performance chart promises you a 6 1/2% climb gradient at a certain weight/temp/press alt, then it's saying your climb rate (if the chart assumes, say, 150 kts) will be 975 fpm (6 1/2 X 60 X 2.5).

Feet per NM:

DP charts usually specify a climb gradient in ft/nm, for example: "This departure requires a climb gradient of 520 ft/nm to 7000 ft." This is easier than % gradients. In this case, simply:

FPM = Grad X Magic Number.

So that DP would require 1040 fpm to comply with, at 120 kts GS. (520 X 2).

Notice that the only difference between the two is that number "60."

Gradients can also be expressed in degrees, such as ILS glideslopes. For that I suggest the following formula:

FPM = Appr mode armed + A/P On

By using this formula, your airplane will achieve the perfect descent rate at whatever GS you care to fly.

Hope this helps.