Performance help

[Chintito]

Can anyone give me a few pointers on the easiest way to remember the TAS/Mach/IAS relationships and how they function in relation to one another during climb/descent etc.

I remember using some diagrams but i forgot them.

much appreciated

[Penworth]

For their relationship depending on altitude, I just remember ERTM, for EAS, RAS, TAS, Mach. Draw a vertical line for the one which is constant with altitude, then draw angled lines from the same base point upwards to represent the other ones in the sequence E R T M. For example, if TAS is constant, then the Mach number will be increasing with altitude, positive gradient line, whereas EAS and RAS will be decreasing with altitude, negative gradient lines.

That's the way I was taught, and its dead simple despite the complicated explanation above (a simple diagram would help!)

cheers

PW

[pugzi]

For those of you whom I had the pleasure of teaching, Chiken Tikka Masala worked pretty well.

i C T M
i i i i
i i i i
i i i i
i i i i
i i i i
i i i i
i i i i hmm, this picture has gone pear shaped, sorry
i i i i
i i i i
i i i i
i i i i
i i i i
i i i i
i i i i
i i
---------------------------------------------->
speed

If you climb or descend at a constant TAS (the line is straight up) then you can see what happens to CAS and or MACH.
If you climb at a constant CAS then make the C line straight up and you the other two lines will slope forwards.

Hope it helps

Steve Francis

[Keith.Williams.]

FOR ISA CONDITIONS BELOW THE TROPOPAUSE
Draw a horizontal line to represent values of seed, increasing from left to right. Now draw a vertical line starting at the left end of the speed line. This second line represents altitude, high at the top and low at the bottom. Now draw four straight lines fanning out from a single point as they move up from the horizontal speed line.

Starting from the left, label these lines E (for EAS), C (for CAS or R for RAS if you prefer), T (for TAS) and M for Mach number). These lines show how the relative values of these speeds vary with altitude. As you climb they move apart and as you descend they converge. A line sloping up to the right means an increasing value and a line sloping up to the left means a decreasing value.

Now to model for example a constant CAS climb redraw the lines, but this time with the CAS line vertical. You should still have them in the order E, C, T, M, but the C is vertical. Moving up the page shows that at constant CAS the EAS decreases (line moving left) and the TAS and Mach both increase (lines moving right). For a constant CAS descent just move down the lines. This will show EAS increasing and TAS and Mach decreasing.

For constant EAS, TAS or Mach simply redraw the lines, with the line representing whatever is canstant vertical. Provided you do not alter the order of the lines they will show how the speeds vary with changes in altitude.


FOR AN ISOTHERMAL (INCLUDING THE STRATOSPHERE)
Draw similar lines but this time use only three, with the one at the right representing both TAS and Mach. This is required because constant temperature means a constant TAS to Mach ratio.


FOR AN INVERSION
Simply redraw the original four lines, but reverse the order of the TAS and Mach lines. You should now have them in the order E, C M, T from left to right.

For all of these methods simply draw the line representing your constant speed vertical, and the others will show how the other speed vary with changing altitude.

PUGZI
Does your Chicken tikka masal method involve four fingers stretched over the mouth while chucking up the curry???

[pugzi]

It most certainly does if it's from the local curry house round here. Have you tried looking right towards me as well? L R T M
Lss, RAS, TAS MACH

[no sponsor]

Everybody Runs Towards the Mach can be the rhyme to remember the order.

(of course not for an inversion). Nothing to add to the graph method already mentioned.

[Ray_DK]

Code:

         Climb                               Descent
CAS  TAS   MACH  LSS            CAS  TAS   MACH  LSS

---   ^     ^     `´            ---   `´    `´    ^
`´   ---    ^     `´             ^   ---    `´    ^
`´   `´    ---    `´             ^    ^    ---    ^

--- constant    `´ Decrease   ^ increase

Just had a go at it.