climb gradient

[Hakeem]

Hello all,

I got this question,

You are doing an instrument approach with 3 deg GS and 150 kts Ground speed which gives you 450 ft/min (150*3)...

If you are doing a SID and climb gradient is 6% and climbing GS is 150 kts what should be your ROC????

Please clear this doubt...

Thanks in advance...

[rudderrudderrat]

Hi Hakeem,
You are mixing different units together.
450 ft/min (150*3) which gives you 7.85 knots rate of descent.
(7.85 * 6080/60) = about 800 feet per minute.

Edit. Thanks torob, I miss read 6% as 6 degs.
You are correct.

[torob]

150KTS = 2.5NM/min

Conversion NM to feet: 2.5NM/min x 6080 = 15200 ft/min

6% x 15200ft/min = 920ft/min (or just GS x 6 = 900ft/min)


Rule of thumb: GS x 5 = ROC/ROD for a 3° path (3° = 5%)

For a 4° path just calculate for a 3° path, (GS x 5), devide by 3 and multiply with 4

In your instrument approach example it should be 750ft/min instead of 450 ft/min for a 3° glidepath at 150KTS (GS x 5)

Minimum climb gradient on SID charts are shown in %. Just multiply this number with your groundspeed and you have your min. ROC

[Hakeem]

Oh thank you so much both you!!! Got your points yeah!!!

Thanks a ton again!!!

[Microburst2002]

The rule for approach (3º or 5% approx) is:

divide GS by 2 an multiply by 100..

GS 150, so it will be 750 fpm

GS 200, 1000 fpm

GS 130, 650 fpm

...

It is extremely useful to hand fly an ILS, no matter how the wind component, configuration and other factors affect the approach, if you have GS you instantly have a V/S target to keep the G/S.

[Hakeem]

Thanks microburst!!!:ok::ok:

[keith williams]

Not wishing to be pedantic but shouldn't

divide GS by 2 an multiply by 100

be

divide GS by 2 and multiply by 10.


using divide GS by 2 and multiply by 100 gives

GS 150, so it will be 650 / 2 x 100 = 7500 fpm

GS 200, 10000 fpm

GS 130, 6500 fpm

But the method is far better than many that I have seen.

[thermostat]

This is the scientific version :
Sine of the angle X 6076 = Gradient (feet up or down per N.M.)
The sin of the angle is also the % gradient.

With the gradient in hand :
Altitude divided by Gradient = Distance
Altitude divided by Distance = Gradient
Gradient X Distance = Altitude.
Note: Altitude is above runway threshold elevation, (not sea level).

In the front of the Jepp approach chart book is a chart "Gradient to Rate Table".

E.g. Take the popular 3 degree angle for the ILS,
The Grad is 318 ft per NM. 5.2 % Grad. (The sin of 3 deg is 0.052335)
Sine is used as it represents slant range DME distances. (Hypotenuse).
This formula can be used to set the FPA on Airbus for constant descent angles on approach.

Here is a very helpful exercise. If you want to capture the Glide Slope from above, you need to double the GS angle of 3 degrees. So 6 degrees is needed to capture the slope from above. The quick way to determine the rate of descent to set up is to determine the Ground Speed, add 10 then add a zero.
EG: GS 170 + 10 = 180 + a zero = 1800. This is the rate of descent for
6 degrees at 170 kts GS. (1800 FPM).
So 140 = 1500 fpm, 150 = 1600 fpm etc, etc.
CAUTION : never exceed 2,000 fpm rate of descent.

Have fun flying.

[keith williams]

The sin of the angle is also the % gradient.

Strictly speaking % gradient = 100% x the tangent of the angle

You can see this if you look at your other comments


Altitude divided by Gradient = Distance

Altitude divided by Distance = Gradient

Gradient X Distance = Altitude.



In each case you are talking about the tangent of the angle not the sine.

But for small angles the tangent and the sine are almost the same, so in terms of getting the right answer it really doesn't matter much which you use.

[Microburst2002]

no time to be so scientific


Here is how it goes:

divide GS by 2 and multiply by 100

for instance, GS 140, 70 times 100 = 7,000 fpm

aim for 700 fpm because 7000 will kill you

next time, multiply by ten.

this is the empirical method.;)

[nitpicker330]

Why so complicated?

GS x 5 = ROD

easy, only 1 step to remember, not divide by this multiply by that malarky!

[thermostat]

As you say, for small angles it doesn't matter. However as I explained,
I use the sin because of the slant range DME info that pilots use, therefore it is a wee bit more accurate in that respect. Use the TAN if you prefer (which relates to the adjacent side or ground distance).
Thanks.

[Capn Bloggs]

Why so complicated?

GS x 5 = ROD

easy, only 1 step to remember, not divide by this multiply by that malarky!
I find it less complicated to divide by 2 than multiply by 5 (if you can't work out the zeros, then you shouldn't be in the seat).

[aterpster]

Is this the type of math stuff you guys do on a dark and stormy night?

If so, I am truly impressed.

[Microburst2002]

yesterday I performed a visual approach, which I haven't for a year or so.

the captain switched off both ILS indications, to make it "real". I was already on slope, two red, two white, so it was very easy. GS was about 185 knots, so immediately I aimed for a 900 fpm (half the GS plus one zero, really easy). As I configured (flaps 2, 3, full) the GS decreased to about 100 knots (I had about 30 knots headwind). So I reduced the rate accordingly, halving the GS and adding one zero until I had 500 fpm. The papi was still on slope, and the atmosphere was relatively stable, so with few inputs I was able to keep desired rate. The captain "cheated" from time to time an showed me the G/S and LOC indication and I was very accurately on the ILS. Wind component decreased sharply, GS mini did its job and I had to increase the rate to about 700 fpm as the GS was then about 130 kt. I flared at the aiming point.

I like to fly by the numbers and supported by the seat of the pants, or by the seat of the pants supported by the numbers.

I really think it is a good exercise to carry out an ILS without the ILS, conditions permitting, purely visually (with or without papi) to enhance "seat of the pants" experience and also to practice raw data ILS approaches, to enhance "flying by the numbers" experience and then combine both. Then, you have that experience and knowledge the day you have to land in the middle of nowhere, with no ILS or papi.

[Capn Bloggs]

GS was about 185 knots, so immediately I aimed for a 900 fpm (half the GS plus one zero, really easy).
As aterpster frantically calls for a calculator! :p

[Microburst2002]

what's the problem with my maths?