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flybyme
2nd Nov 2009, 18:03
Hi! for a jet aircraft when do we practically use the option of Best Rate of climb and Best Angle of climb speeds?

CaptB737
2nd Nov 2009, 18:09
Best angle of climb speed -------> when to clear an obstacle (= shortest distance to reach a certain level).

Best rate of climb speed ---------> when to reach a level in the shortest time (= mostly a request by ATC to keep separation with other traffic).

Hope that answers your question ;)

framer
3rd Nov 2009, 00:30
In some parts of the world ATC routinely ask for best angle when they mean best rate. It is a shame because one day when they want best angle the pilot will give them best rate.

Capn Bloggs
3rd Nov 2009, 01:56
Best Rate: when ATC asks or to get up quick or when you can turn at an altitude. The quicker you get there, the quciker you turn.

Best Angle: when you're trying to get over a SID step.

Framer, I have never, in Australia, been asked for best angle of climb. Have you?

framer
3rd Nov 2009, 02:49
No I don't think so. Not that I can remember anyway.

welliewanger
3rd Nov 2009, 23:36
This is a question I've asked for when you get EGPWS warnings. The standard procedure is essentially a zoom climb, but after a few seconds you find yourself "behind the drag curve".

How do we find Vx and Vy for big aeroplanes?

Capn Bloggs
3rd Nov 2009, 23:42
My understanding is:

Max Angle is Max Climb: ie Vmin+5.

Max rate is allegedly CI 0 (although my hunch is that it is less than that). Max endurance is min drag, max excess power, which would better fit the bill for best rate of climb.

plugster
4th Nov 2009, 11:17
My understanding is:

Max Angle is Max Climb: ie Vmin+5.

Max rate is allegedly CI 0 (although my hunch is that it is less than that). Max endurance is min drag, max excess power, which would better fit the bill for best rate of climb.
Max endurance is min drag=min thrust on a jet, on a prop however it is min power which isn't necessarily the same.
Min drag on a jet is not the same speed for best rate

FE Hoppy
4th Nov 2009, 11:59
How do we find Vx and Vy for big aeroplanes?

Look in the AOM/AFM/FCTM/SOPM. It should be covered as part of your transition training.

On the E-jets Vx is aproximately Vfs and Vy is aproximately Vfs + 50 or .60M

Microburst2002
5th Nov 2009, 07:27
In Airbus, Vx is "green dot" speed (minimum drag speed).
Vy is CI=0 in some texts. In others they state that flying at rough air speed you are close to Vy.
Vy happens to be, according to the above, much much faster than Vy.

With the nowadays low cost indexes, ECON speed is not far from Vy.

Every time I am instructed to "expedite climb" I don't know if they want me to climb soon in time or in distance. When they say "Be level or pass FL XX by position ZZZ" then it is clearly Vy (min drag)."

Vx is also used after take off with, say, a north heading and your route is to the south. There is no point in flying miles north, so you climb as steep as possible until you reach the turning altitude or until ATC tells you to turn. This does not apply if the SID is just a sequence of geographical waypoints. In this case you cannot alter the total number of miles to be flown.
But in a "at 6,000 ft turn right to XXX" departure, climb at Vy, since every mile you fly in the non desired direction will be flown twice (one going and one coming).

Vy can be used to clear a cloud or turbulent layer, if it is not far from turbulent speed (which is not in the 320).

Old Smokey
5th Nov 2009, 08:37
If you don't have the information for Best Angle and Best Rate readily available, the following will be VERY close to the mark -

As Best Angle and Best Holding speed are both Best L/D speed or Vmd, use the published HOLDING speed for BEST ANGLE. Note that published Holding speed will not exactly be Vmd (for relationship with the declining Thrust available on the low side, and for improved speed stability on the high side of Vmd), but the difference in actual performance is negligible.

As CI=0 provides for a high climb rate, use the Climb Speed for CI=0 for BEST CLIMB RATE. CI=0 actually provides for a speed in excess of actual best rate, but, as before, for all practical purposes produces a negligible difference between actual and achievable best climb rate. If you examine Power Available Vs Power Required for a Jet aircraft at the best climb rate, the 2 curves are almost parallel at that point, and some small speed variation from optimum makes hardly any difference.

Regards,

Old Smokey

flybyme
7th Nov 2009, 08:26
Vy or Vx is always avlbl in the new FMC equipped a/c. If the ATC tells you that FL350 is avlbl if you can reach it by XXXXX waypoint, then what is more apt, to select Best angle or Best Rate?

Microburst2002
7th Nov 2009, 12:01
Best angle, of course.
In that case it is a geometrical question.

The problem is that reaching cruising level at minimum drag speed means you have then to accelerate to crusing speed. In some cases this can take minutes with the engines at maximum climb thrust, which is not economical. It might be better to fly initially to a lower level without an ATC constraint and wait to be cleared to a higher level later on.