Deviating from Best Rate and Best Angle of Climb

[theamazingkent]

Hi all,

I got the following question from a past BAK exam asking "climbing at a slower IAS than that recommended for best rate of climb will result in - ".

Now the two answers that I wanted to pick were: 'a decreased rate AND angle of climb' and 'a decreased rate and an increased angle of climb'.

I'm sure that rate of climb decreases as you fly slower or faster than Vy, but the angle confuses me.

What confuses me more is that the answer for the exam is a decreased rate and increase angle, while my GFPT textbook says regardless of flying faster or slower than recommended, BOTH rate and angle decrease.

So what is the correct answer?

[Rithalic]

Decreased rate of climb and increased angle of climb.

[keith williams]

Vx give you best angle of climb so;

If your speed change takes you closer to Vx your angle will increase.
If your speed change takes further away from Vx your angle will decrease.

The same goes for rate of climb.

Vy give best rate of climb so;

If your speed change takes you closer to Vy your rate of climb will increase.
If your speed change takes further away from Vy your rate of climb will decrease.

Vy is greater than vx so sketch the two on a speed line

Low speed..............Vx......................................V y............High speed

Now draw a cross on this line to represent your starting speed, then move the cross in the direction of your speed change.

If you start at Vy then decelerate you will get


Low speed.............Final speed X............Initial speed X............High speed
Low speed.....Vx........................................Vy...... ..............High speed

You have moved away from Vy but towards Vx. So your rate of climb will decrease and your angle of climb will increase.

[Tinstaafl]

It's a poorly constructed question. You have to presume that only a small change in speed is being referred to in order to derive the 'correct' answer. The problem is that an alternative option is also correct if a large reduction in speed occurs ie to some speed slower than Vx.

The question also doesn't take into consideration flight at absolute ceiling where Vx=Vy, rate of climb = 0'/min and any reduction in speed will result in a descent ie a negative ROC. A -ve number is less than zero in our maths sytem.