Good luck to everyone who's doing their January ATPL exams.

Now I have a question from Performance.

You descend at a constant mach, what is going to happen to your angle of pitch?

a) increase
B) decrease
c) remain the same
d) depends on temp.

Since you descend at M then I assume you'll have a TAS increase and that's why I went with the angle of pitch as increasing.

L=CL x speed x 1/2p

Since speed goes up, CL has to increase to remain constant but then I didn't factor in the density, so if P and S increase then there's more a reason for CL to decrease, am I nuts????

Maybe someone can help me see what I'm not seeing.

Keith,

Please could you explain the concept of the C-T-M sketches that you mentioned in your post?

I'm taking the JAR CPL exams a week on Monday including Principles of Flight and Performance and I'm wondering if I'm missing a trick here.

Wonder if anyone else is sitting the CPLs at Gatwick this month? I was on my own for some of the exams in November, and I think January may be even less popular.

QNH 1013, the CTM sketches are a quick way of remembering the relationship between speeds in a descent or climb.

In a Climb Cas Tas Mach

You might be asked, what happens if you maintain a constant Mach no during the climb? You look at C T M as above, and see that for a constant Mach, Tas would decrease. You can see this by noting that Tas is on the left hand side of Mach, the same with Cas.
For a constant Tas in a climb, Cas would decrease and Mach would increase (because Mach is on the right hand side) etc

For a descent the effects are reversed I believe.

With regard to the Jan exams (next week), I too will be taking Performance, and i'm also taking Principles of Flight. I'm not exactly looking forward to taking them, but i've worked damn hard over the last weeks, so hopefully the work will pay off.

According to the feedback I have regarding your question, the pitch angle would decrease. I would think that this is the case as your Tas is increasing, so you would want to raise the nose, decreasing the pitch.But as Keith rightly says, what is a decrease in pitch? Is it nose down or what?

QNH 1013,

I would have thought that your FTO would have made you aware of the CTM sketch. If not shown to you then that is quite scary, considering the exams are so close. Which FTO are you with?

Sounds like the one that we at Bristol know of as ERTM (Equivelent Rectified True Mach).

And yes this question has dubious choices and that's why I asked a fellow student first, his teacher told him that an increase in pitch angle relative to the horizontal. So if you are already pitching nose down then you'll have to increase pitch (Pitching down in his lang.).
If you are nose up you will have to decrease pitch.

I've seen this question 5 times in my feedback and I really don't like to see it again!


the CTM btw isn't hard to memorize since all you have to do is remember what happens when you are in ISA, Isothermal and Inversion.

ISA> CTM (If C constant in climb then TM increase, if T increase then C decrease and M increase)
Iso> C decrease in climb and MT same.

Inversion> CTM is now CMT!
SO if climbing at constant Cas then M and T go up

The sketches were taught in my school but you can simply use the THREE finger method to help out.

WARNING if a question comes up asking about you maintaining constant MACH and overall temp decreases then the CAS will stay the same. I cannot explain why this is so but the question pops up 10 times in my fback so it's one of the cases where CTM is invalid for this type of question. Otherwise CTM(ISA)/CMT(Inversion) works for climbs and descents.


Climb at constant C in ISA, T and M both increase
Climb at constant T in ISA, C decrease and M increases
Climb at constant M in ISA, C and T both decrease

*Climb at constant C in ISOTHERMAL, T+M increase (This is the *odd one)
*Climb at constant M in Iso, C would decrease and T would stay *the same. (again this is the odd one so be carefull with it)*


Inversion>
This one is where CTM becomes CMT (yes only T and M switch their positions)
Climb constant C in Inversion, T and M increase
Climb constant T in Inversion, C decrease and Mach DECREASE.
Climb constant M in inversion, T increase and C decrease.



It's very easy to use after a bit of practice and helps me to find out what I have to do with angle of attack if descending at constant mach and such. They might not ask you what happens with TAs, they are more likely to ask what happens with angle of attack or the dreaded PITCH angle. (In which case I just write down the L=Clx etc..)


Hope this helped a bit. :ok:

you made one mistake when making the answers.

in question 27. The correct answer is given as CG will not affect SFC, which is answer A).

I disagree with this since a forward CG will make it harder to pitch up and since it's harder you'll need more power and therefore SFC will increase.


So the correct answer should be> SFC will increase with forward CG movement and that's B)

Keith, Many thanks for the explanation. Saves me having to picture the lss in the atmosphere which is what I was doing before.

I'll work through the examples when I can keep my brain working long enough, and I'm not drugged up on Day-Nurse / Night-Nurse or whatever it is Mrs QNH keeps giving me; I'm suffering a stinking cold at present. At least I should be over it by exam day.

Good luck to all of you sitting this month.

Keith, thanks for posting the questions. Personally I have found those questions, very similar to the ones I have already worked through, in fact, a few are exactly word for word. I am finding that the more times I work through my feedback, my knowledge and understanding is increasing. 2 or 3 weeks ago, I would not have stood a chance in answering the questions above. However now I am able to go through them, and similar questions with few problems.

Thanks for your help.

Good luck to eveyone sitting exams.