Any acceleration in climb, with a constant power settings:

[Flion]

A. Improves the rate of climb if the airspeed is below Vy
B. Improves the climb gradient if the airspeed is below Vx
C. Decreases rate of climb and increases angle of climb
D. Decreases the rate of climb and the angle of climb

[Cirrussy]

I would say:

A is correct (up to Vy)
B is correct (up to Vx)
C is incorrect
D is correct (beyond Vy)

Although I did not open any books to reach these answers!

[500 above]

Acceleration in climb - ATP Forum (http://www.atpforum.eu/forum/technical-subjects/-032-performance-a/3743-acceleration-in-climb)

[RedBullGaveMeWings]

If I remember correctly the correct answer to this particular ATPL question is D. I passed Performance on Tuesday and I already quit the Question Bank mode:hmm:

[Flion]

The correct answer is D. However I can't get why the A. is wrong.
Btw, I'm doing a PPL. Is it also in ATPL question bank?

[lasseb]

I think the "logic" of the question is something like this:
If you need to accelerate in a climb without touching the power, the only thing you can do is pitch down..
So that would decrease ROC and angle of climb...

[Flion]

Correct. Therefore, assuming that I'm flying at speed lower than Vy, I will pitch down to increase ROC until I reach Vy which gives me the best ROC, isn't it?

[Reverserbucket]

Vy = Best Rate of Climb hence in principal if V < Vy acceleration towards Vy will improve RoC until V>Vy. I avoid spending too much time thinking about what's happening aerodynamically in terms of fixed throttle and adjustment of pitch for this type of problem.

[lasseb]

ahh, read it as speed above Vx/Vy in A,B..... My mistake...
Well no cant really explain it. A,B is correct. D only correct if above Vy.
Althoug you could argue that at the instant you lower the nose and start accelerating, the angle/ROC will decrease for a short while. But that is maybe kind of far fetched

[rudestuff]

... But that is what they are looking for. Lower the nose, lower the roc and aoc. Obviously, once you hit Vx / Vy and raise the nose to stop the acceleration, the aoc / roc will go up. But they're only asking what happens while accelerating.

[Rukovodilac]

Lowering the nose will not lower your ROC if you are flying below Vy speed. You will increase speed to Vy and therefore come to the best ROC speed. Even while accelerating the closer you are to the Vy the better ROC. I can't grasp this one. :ugh:

[ChimneySweep]

A and B are not correct because although it is true that once you reach and maintain Vy/Vx then the RoC/climb gradient would be greater, during the acceleration both will be lower.

[Flion]

I'm still not sure I grasped it completely but at least I discussed it and will stick to it. Thanks guys.

[keith williams]

This is a very old JAR ATPL question which has been around for about 15 years.

For max climb angle we need max excess thrust. For max roc we need max excess power. These conditions occur at vx and vy respectively.

During any acceleration we are using some of our thrust and power to accelerate, so this thrust and power is not available for climbing. So while we are actually accelerating our climb angle and roc will be reduced.

If you have difficulty with this idea just imagine that we have two identical aircraft, same weight, same altitude, same configuration, same power setting. One is flying at a steady speed at Vx. The other is accelerating through Vx. How will the angles of climb compare? Now repeat the test at Vy, how will the rates of climb compare. In both cases we would find that the climb performance of the accelerating aircraft would be less than that of the aircraft at steady speed. If we now repeat that test at any speed we will find the same result.

The question is not saying that continuous acceleration causes a continuous reduction in climb angle and roc. It is saying that at any moment during an acceleration our climb performance is less than it would have been if we had not been accelerating.

[KayPam]

I would say:

A is correct (up to Vy)
B is correct (up to Vx)
C is incorrect
D is correct (beyond Vy)

Although I did not open any books to reach these answers!

Two elements :
C is correct between Vx and Vy
D is correct if we consider the question to be about the transitory phase of the acceleration.

[keith williams]

KayPam, I think that you need to look at option c again.

Any increase in speed between vx and vy will take us closer to our max roc (vy) speed and further away from our max gradients speed (vx).

[KayPam]

Oh yes it looks like I confused acceleration and deceleration :o

[Vessbot]

There is confusion and ambiguity since the right answer changes depending on the assumed timescale. Would have been nice if they specified.

If the question is about the immediate response (the first few seconds) then you're pushing the nose down, which will of course lower both your climb rate and climb gradient (aka angle) no matter what, and the right answer is D.

If the question is about the new stabilized condition where the speed has settled at its new value, and the attitude is raised to whatever will hold that speed (say, 30+ seconds in the future) then A and B are both right.

For answering a standardized test of course you can't go up to the proctor and ask for more detail about the unstated background, all you can do is pick one of the 4 answers. Fortunately, in most testing formats, there can only be one right answer. That means it can't be both A and B, so I'd pick D.

More important is the actual flying application of this ambiguity. With any elevator input, you always have to think both about the short-term response, and the longer-term new energy state. Failing to do this gets every student in trouble when they find themselves a little low on short final, and don't have as much mental room to consider everything. They only think of the naive and simplistic response: to pull back on the elevator. This pulls the nose up, and shallows out the descent, but only for a few seconds. Then we're below best glide speed, with more total drag, and the plane starts descending even steeper.

Trouble is, that the response over the first few seconds, (a shallower flight path) reinforces the student's incorrect view of elevator control inputs (that the airplane goes where you point the nose), he sees that and thinks "job well done" and goes onto the 50 other tasks that are simultaneously overloading him. When he sees that the plane is coming down steeper, if he's bright, he'll do the right thing for his energy state and give it some power; if not, he'll pull the nose up even higher, slow the plane even more, thereby adding even more drag, and increasing the ultimate sink rate even more. If he's really bright, then on his next approach, he'll give it power instead of elevator the first time he sees himself getting low!

Or if he flies a plane with autothrottles he can forget about all this nerd junk and just fly the airplane around by pointing the nose like a video game. Then when there's a breakdown in some part of the total system, become the next Asiana 214 or Pinnacle 3701 because he doesn't understand how airplanes fly.

[lasseb]

Well the question does say "any accelleration...". This implies a transition phase and not the point where you are established with a new speed and all the vectors are steady.

[OhNoCB]

Stupid question I think which lures you into choosing 'A' if indeed 'D' is the correct answer.

If you read at as a hypothetical scenario whereby you are in an established climb at Vy-30 knots and then you gain an acceleration and are still in an ESTABLISHED climb having accelerated then any acceleration is initially going to take you closer to Vy and improve the rate.

If you read it more literally and imagine that you are established in the climb at Vy-330 knots and then you start your acceleration by pitching forward for example to accelerate in level flight, then obviously your rate reduces until you restablish in the climb at the new speed.