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Rate Of Climb

  • jukzizy
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jukzizy created the topic: Rate Of Climb

Today I sat performance and didn't make it, got 67%..

I got one question that asks about ROC.

Use the Echo work book figure 12..

If the density height is 3000ft, what will be the ROC required for the air craft to archive 3.2% climbing gradient with 20kts head wind when the MTOW is 2800KG?

Please bob, stuart and john need some help with this question..
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SJM replied the topic: Rate Of Climb

Rate of Climb = Requred gradient x speed.

Required gradient is 3.2

Speed: use all the information available to get best answer. For the exam, in terms of accuracy, ground speed is best, followed by TAS, followed by IAS. You can see during take off in the cockpit IAS is the easiest to use (though TAS and GS maybe available via GPS etc and more accurate)


In this question, you can work out the IAS at 2800kg, convert this to TAS at 3000ft Density Height and finally calculate ground speed, in this case by subtracting 20kts for the headwind.

Plug this into the equation about and you will get the answer suitable for an exam.
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jukzizy replied the topic: Rate Of Climb

How would I work out the answer when there is no Tas or IAS?
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SJM replied the topic: Rate Of Climb

jukzizy wrote: How would I work out the answer when there is no Tas or IAS?


If this is for Echo, the VFR booklet has a take off performance chart. You'll notice there's a Take Off Safety Speed chart that varies by weight (2800kg) and wind (20kt headwind). With this information you can extract the required IAS and complete the question.
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John.Heddles replied the topic: Rate Of Climb

If this is for Echo, the VFR booklet has a take off performance chart. You'll notice there's a Take Off Safety Speed chart that varies by weight (2800kg) and wind (20kt headwind). With this information you can extract the required IAS and complete the question.


I don't think so. The takeoff chart has absolutely nil relevance to the question. Were the intention to be to use it that would represent quite negative training, apart from being quite silly.

If the question be reported correctly, it is flawed as it requires some further information.

Engineering specialist in aircraft performance and weight control.
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Carello replied the topic: Rate Of Climb

Hi John

Perhaps I've been out of the game for too long; to my mind, the question seems to be perfectly valid.

First Off, CAO 20.7.4 says:



Note: The gradient of 6% is an air gradient @ TOSS, not a ground gradient.

Referring to the Echo Chart - Fig 12 below, the TOSS at 2800 kg is 95.5 kts-IAS (give or take)



For a DH of 3000' the TAS = 100 kts @ TOSS
Correcting for wind (20 kt HW), the G/S = 80 kts @ TOSS

To achieve a 3.2% ground gradient:
ROC = 3.2 x 80 = 256 fpm.

To achieve a 3.2% air gradient
ROC = 3.2 x 100 = 320 fpm

To achieve a 6% air gradient (the certification standard)
ROC = 6 x 100 = 600 fpm

In reality, you would climb out at Vx or Vy or faster, not TOSS.

I would have to say that SJM is correct on this one.

Have I missed the point that you were trying to make?
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jukzizy replied the topic: Rate Of Climb

Thank you very much..That's makesens.
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John.Heddles replied the topic: Rate Of Climb

Have I missed the point that you were trying to make?

Probably. However, that would follow from my having a certification background in addition to an operational history

the question seems to be perfectly valid.

.. except for its attempt to relate certification data to a certification-irrelevant consideration. Had the question simply said to use this speed or that, or had provided, for example, a climb performance chart from which the candidate were to extract relevant data, all would have been fine. Tying the question into a very particular certification set of data creates a problem, however.

First Off, CAO 20.7.4 says:

One needs to be a little circumspect with the 20.7 operational Orders. The P-chart is one of the old DCA Civil Mk II (if my memory cells serve me correctly - you, I have no doubt, would remember having played with many of these in your younger days) charts. While I haven't bothered, as yet, to see if I can identify the origin of the Echo, the P-charts for the Echo, without any doubt, would have been lifted from a convenient Industry flight manual by the then examiner in the same way that the Alpha loading system (originally designed by Norm Overmeyer and then modified a tad by Bruce Clissold at the examiner's request) was lifted (almost certainly) from a Turbo Lance Civil Mk I flight manual - its design predates the general introduction of the GAMA Spec 1 POH format manuals which came into vogue, as I recall, in the early 80s (can't have been much earlier as the original GAMA document only dates to 1975).

The light aircraft P-charts were produced to satisfy the requirements of ANO (then CAO) 101.22, which was the relevant certification document. The 20.7 operational series were, in respect of certification requirements, an (often, but not always, correct) recasting/copying of the certification requirement. However, the cited Order paragraph is from the 101.22 words. As an aside, I often wonder how the 20.7.4 requirements are imposed these days, given rubber stamp certification of foreign NAA POH documents

Note: The gradient of 6% is an air gradient @ TOSS, not a ground gradient.

All certification WAT limits are for nil wind. The operational requirements then impose whatever pilot-related stuff needs to be applied.

Referring to the Echo Chart - Fig 12 below, the TOSS at 2800 kg is 95.5 kts-IAS (give or take)

I have no problem using whatever speed, only tying a certification-irrelevant question to a certification-specific set of data when, to do so, sets the new chums up for significant negative learning. The question should have nominated whatever speed by alternative means.

To achieve a 3.2% ground gradient:

Does it not give you any concern that to achieve the cited gradient would require the takeoff power to be reduced by a significant margin ? This is the basis of my concern as the certification standards proscribe any reduction in power setting by the pilot during the takeoff manoeuvre. To have such a question sets the new chum up for negative learning.

In reality, you would climb out at Vx or Vy or faster, not TOSS.

If one has an interest in achieving the POH/AFM distance data, then it is appropriate to use Vtoss only. To adopt a higher speed involves a significant distance penalty. Vx/Vy are speeds which might be appropriate following the initial takeoff phase of the operation. This point is an extremely important factor for the new chums to get into their thinking very clearly (notwithstanding that more experienced pilots, who have the technical skills to run appropriate sums on the fly, might do something a little different in appropriate circumstances).

I would have to say that SJM is correct on this one.

If the point is that the calculation is fine, I'm comfortable. However, not with the purported linking of a certification dataset with a calculation that has absolutely naught to do with the certification manoeuvre.

Should my words not convince you then we shall have to continue to disagree.

Engineering specialist in aircraft performance and weight control.
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Carello replied the topic: Rate Of Climb

G'day John

I don't disagree with anything that you have said, but I think you are reading too much into the question - an occupational hazard for an engineer.

Yes, it is a silly question; it has no nexus to the real world. Who in their right mind would reduce power on take-off to achieve a 3.2% ground gradient; the premise is absurd.

That being said, I can only guess that the question was designed to test the student's knowledge of a very useful rule of thumb, in an unusual context.

Rule of Thumb:
ROC(ROD) = Grad x Speed
(Using TAS for Air Gradient and G/S for Ground Gradient)

The more useful version of the rule being:
Grad = ROC(ROD)/Speed
(Using TAS for Air Gradient and G/S for Ground Gradient)

All certification WAT limits are for nil wind
Nil wind gradients are air gradients

How are you coping with the Covid lockdown? Life is a little easier here in the sunshine state.

Cheers
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John.Heddles replied the topic: Rate Of Climb

Yes, it is a silly question; it has no nexus to the real world. Who in their right mind would reduce power on take-off to achieve a 3.2% ground gradient; the premise is absurd.

It would appear that we have common ground. My concern is not with the question - that's a case of whatever the examiner comes up with. However, the potential for negative training is a major concern. The question should have been posed without any reference to the takeoff chart and the speed derived from some other source. (Postcript - On the other hand, the question would have been fine had it asked something along the lines of "what ROC would you require to achieve the minimum certification takeoff AEO climb gradient, but allowing for wind ?").

I can only guess that the question was designed to test the student's knowledge of a very useful rule of thumb, in an unusual context.

Not quite a rule of thumb. The calculation derives directly from the trig and represents an approximation which only loses a negligible practical degree of accuracy in the real world - for the typical triangle in a climb (or descent) situation -

gradient = tan (a) (strictly we should be considering sine for airspeed but, for small angles, the two ratios are near enough the same)

= ROC/speed

and, as a percentage -

= ROC/speed x 100

converting from the mixed units to a non-dimensional ratio -

= ROC ft/min /speed nm/hr x 100 x 1/6080 nm/ft x 60 min/hr

= ROC/speed x 6000/6080

= 0.987 x ROC/speed when the numbers are tidied up a bit.

That is, the ROC/speed pilot calculation over estimates the gradient (as a percentage) by about 1 %. In the overall scheme of things, not a major concern to the pilot.

All certification WAT limits are for nil wind
Nil wind gradients are air gradients


Indeed.

How are you coping with the Covid lockdown? Life is a little easier here in the sunshine state.

We are getting a little sunshine down in Gippsland at the moment - quite a novelty. Do take care with the dreadful bug

Engineering specialist in aircraft performance and weight control.
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