Problem on climb gradient

[aviator82]

Please some one help me this ques on climb gradient-

The second segment climb gradient requirement for a two engine aircraft is 2.4%
If the V2 speed is 150kts IAS the rate of climb at sea level ISA when operating at the WAT limit would approx be???

[Keith.Williams.]

For a very approximate answer just use ROC in fpm = % x TAS in kts

In this case 2.4 x 150 = 360 fpm

For a more accurate answer got to Section 3 MEP1 page 9 of your CAP698 and find the equation

Still Air % = (ROC / TAS) x (6000/6080)

This can be rearranged to give

ROC = (% x TAS x 6080) / 6000


In this case ROC = (2.4 x 150 x 6080) / 6000 = 364.8 fpm

[rsaf]

Many SID states the ,minimum required climb gradient. How do u knw that your aircraft performance is able to meet this climb requirement?

[RTN11]

Do the performance calculations before you take off?

[GTTIB]

Get a plane with big engines...?

[john_tullamarine]

Following on from Keith's answer -

(a) WAT (weight for [pressure] altitude and [ambient] temperature) limits relate to Design Standard requirements and impose a reasonable probability of an aeroplane's being able to achieve a modest climb performance.

The current words are at FAR 25.121(b)(1) (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=f912188e85fc6f4f541562734b1ef9a6&rgn=div8&view=text&node=14:1.0.1.3.11.2.155.18&idno=14).

(b) second segment WAT limit is 2.4% gross gradient for twins.

(c) at sea level ISA indicates that you may treat IAS=TAS which, for nil wind conditions (as the question infers), gives G/S=TAS.

(d) the error using the rule of thumb equation given is about 1.3 percent which is within normal tolerances for government work so it is fine for use flying on the line. The 6000 and 6080 cover unit conversion factors so that we can use mixed units in the sum.

(e) it is important to keep in mind that the WAT limit is a flight to flight limit which varies according to ambient conditions. Unless the runway is at low altitude, temperature is near standard, runway is longish for Type, and there are no significant obstacles .. you can plan on having to reduce weight to achieve a higher required gradient for a particular takeoff.

Hence, for the question How do u know that your aircraft performance is able to meet this climb requirement? it is a matter of adjusting RTOW to achieve the required gradient. This data usually is in the AFM. The ROT then gives the minimum target ROC for monitoring the gradient.

Keep in mind that you don't know what is limiting for the SID. On the basis that it MAY be obstacles, it is appropriate to add the 0.8% margin to the SID requirement to cover all bases. This matches the net gradient requirement to the SID. This requirement is at FAR 25.115(b)(1) (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=87a0750e05c3bfa31372cfd466667cef&rgn=div8&view=text&node=14:1.0.1.3.11.2.155.15&idno=14).

Mind you, this is a simplistic approach and you need to think about third segment considerations. Plenty of threads covering this subject in Tech Log if you wish to run a search or two.