×
##### PPL Video Lectures (10 Jul 2020)

PPL Video Lectures covering Aerodynamics, General Knowledge, Performance, Meteorology And Navigation are now available through our website see front page for details.

× Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

## Minimum climb rate

• Posts: 9

### JamesScot created the topic: Minimum climb rate

I suppose this is a rounding error issue - not sure
Refer to Echo performance and loading system in the CASA RPL, PPL, CPL workbook.
Given DH = 3000 ft, headwind = 15 KT, take-off weight = 2620 KG.
If the initial climb is at TOSS, what is the minimum rate of climb to achieve a 6.0% climb gradient?

I used Echo and got a 92 KT TOSS.
Less the 15 HW, giving a 77 KT GS.

Based on this: (77/60)*6076*0.06 = 467.9 feet/min
If I use 1nm = 6000 feet
(77/60)*6000*0.06 = 462 feet/min

Here are the options presented:
a) 620 feet/min
b) 580 feet/min
c) 290 feet/min
d) 490 feet/min
e) 460 feet/min

I want to answer 460 feet/min as the difference of 2 or 8 feet per minute is negligible. BUT, the question about the minimum, is that 460 feet/min is actually less than 6.0%.

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 555

### John.Heddles replied the topic: Minimum climb rate

This sort of question revolves on the specific wording.

Presumably you have related the question from somewhere else ? Can you confirm that you have not paraphrased at all or, better still, can you take a happy snap of the original and post the graphic to the thread ?

Side notes -

(a) while we are thinking about stuff, what units are the speed from the P-chart ? Are these the units in which you should be working ?

(b) the internationally accepted conversion from NM has, for many years now, been 1852 m = 1 NM, from which we obtain 6076 ft. 6000 ft has nothing to do with anything so I suggest you bin that part of your calculation.

Engineering specialist in aircraft performance and weight control.

• Posts: 1

### Santiago replied the topic: Minimum climb rate

Hi James,

I did two different calculations I must be confused as well.

First calculation.

I went to the chart page19 FIG 12.

Then I Went to 2620Kg and straight across to VTOSS & I got 92Kt.

I then got my flight computer E6B put in zero° under 3000 (DH) then I read 94 TAS.

I then did 94 - 15Kt HW which gave me 79KT GS.

Then did 6 × 79 = 474fpm.

Second calculation.

VTOSS from chart 92Kt then - 15HW = 77KT

6 × 77 = 462fpm.

Climb Gradient as a Percentage formula is ROC/GS.

ROC Required formula GS × Gradient 6.

My first calculation was because DH was given and a wind component. If it was not given I would of just got VTOSS from the chart and assumed at low level it is close enough to TAS and - HW as per my second calculation.

Would love to hear back where I went wrong thank you.

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 555

### John.Heddles replied the topic: Minimum climb rate

I then got my flight computer E6B put in zero° under 3000 (DH) then I read 94 TAS.

It might be useful were you to review the use of your navigation computer ? Indeed, there is a general observation that folks really should do a lot more study and practice with their whizz wheels ...

For both of you (and, I guess, lots of other students) it is important to keep in mind that the 6% thing is a WAT limit and WAT limits, being just lines in the sand, are for nil wind. Hence my earlier comment that the question revolves around just what the words in the question might say. Lots of confusion with WAT limits at PPL/CPL level as they are more relevant to heavy aircraft.

There might be some value in folks' reviewing these gradient calculations generally, methinks.

Engineering specialist in aircraft performance and weight control.

• Posts: 9

### dswire10 replied the topic: Minimum climb rate

Two questions from one who is endeavouring to become au fait with this new to me pilot material.

First, I do not see where zero degrees is related to 3000 ft density height ?

Second, WAT limit is a new term to me. Can you explain what it is, please ?

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 555

### John.Heddles replied the topic: Minimum climb rate

I do not see where zero degrees is related to 3000 ft density height ?

The whizz wheel calculation is made simple with the incompressible equations. You just go to the DH window, set 3000 ft, and then read off TAS on the outer C/D scale against IAS (strictly should be EAS or, for lighties, CAS is OK) on the inner C/D scale. There is an associated height/temperature cutout which is what figures out the DH for you. Here you just set the pressure height against the ISA standard temperature. For the example, you would set 3000 ft PH against (15-3x2 =) 9 on the OAT scale - same as just setting the DH in the DH cutout. Probably, the zero was just a miscalculated number ?

WAT limit is a new term to me. Can you explain what it is, please ?

WAT stands for (maximum) Weight for Altitude and Temperature. What this does is provide an absolute minimum climb gradient for specified conditions. 6% was a light aircraft certification requirement which, unfortunately, was a peculiarly Australian requirement in CAO 101.22 (now defunct). The operational rule in CAO 20.7 copied across the airworthiness certification rules from CAO 101 and, now, with the 101 stuff binned post-Yates Report, we have a mismatch between 20.7 and what the usual imported aircraft flight manual might be based on. A real dog's breakfast which probably won't be sorted out until we have an unpleasant court case which looks into it after a significant and relevant fatal accident. Basically, the pilot needs to check climb capability in the POH for the relevant configuration and adjust weights, where necessary, to meet the 20.7 requirement.

WAT limits get a little more complex for heavy aircraft but that is a bit beyond the needs of the student pilot.

Engineering specialist in aircraft performance and weight control.

• Posts: 9

### dswire10 replied the topic: Minimum climb rate

Thank you regarding the computer answer.

Regarding the WAT answer, you are indicating that the now defunct Australian rules were different to other foreign rules. May I request some further details on this aspect of the history, please ?

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 555

### John.Heddles replied the topic: Minimum climb rate

May I request some further details on this aspect of the history, please ?

I'm not sure how long you want to be bored by the history - it could go on and on for some considerable time - so I will give you a synopsis.

If we go back quite some years, the local system had its own airworthiness requirements. At about the time I came into the Industry these were in a set of inscrutable ANOs (the precedent documents to CAOs). Around the 60s, these were re-codified into the ANO (subsequently CAO) 101 series. Basically, the local rules called up foreign rules but then imposed local requirements as either variations or additions.

For light aircraft, such as you train in, the relevant CAO was 101.22. The operators, though, didn't routinely have access to the airworthiness rules under our system so we found them recast in the (operational) words of CAO 20.7.

Some of the differences to the foreign rules were advantageous to Australian operators. For example, the cruise WAT limits were based on a different premise to, say, the US requirements and there were some aircraft which took advantage of this difference to achieve a higher MTOW than would be permitted in the US (eg, Aero Commander 500A and 500S). Other requirements were more a distraction (eg the requirement for a specific AFM stowage location.

Eventually, Industry annoyance led to a review conducted by Ron Yates some years ago. Ron was a lovely chap but was Qantas through and through so, not surprisingly, the report was influenced somewhat by that background. Qantas, and many others in the Industry, took the view that we would be far better off scrapping the local rule variations and just running with the foreign rules appropriate to the aircraft's country of manufacture. This was all fine but did lead to a number of unfortunate outcomes where the local rules, by virtue of their being scrapped, then meant that the Industry lost the previous benefits. However, that is another story and just causes me to shake my head when I reflect upon some of the silly things which went on.

With the light aircraft TOW WAT limit discussed earlier, the old local rule, again, is different to the foreign rules. Now we have the situation where we have lost CAO 101 but still have CAO 20.7. Aircraft are imported solely on the basis of the foreign rules. So, Australian pilots now have the problem that some aspects of CAO 20.7 may disagree with what the aircraft AFM/POH documentation is based on.

How do you address that problem ? Ah, that is the \$64 question and can present some difficulties depending on what information is available in the POH.

Engineering specialist in aircraft performance and weight control.