ATPL performance and loading Qs

[Hailstop3]

Hi

I'm in the process of self studying my Australian ATPLs and have my performance and loading exam on the 13th. I think ive got a grip on it all except for one thing that is really bugging me. My current study notes don't seem to cover turboprop aircraft too well which is half the problem.

Here are 2 questions.

A turboprop aircraft's max L/D speed (best lift drag ratio speed) is at Y. At what speed do you need to fly to achieve max rate of climb?

A turbojet aircraft's max L/D speed is at Y. At what speed do you need to fly to achieve max angle of climb?

Both questions have the options Y, less than Y, greater than Y.

My problem is that the correct answer for both is Y.

I understand that obviously there is a difference in relation to best angle and rate of climb from the power required/power available curves, and drag curves, that is due to their propulsion methods, but could someone please explain it all relating to the 2 aircraft as i can't seem to nut it out.

Thanks in advance.

[TINTIN25]

Are you doing your distance learning through AFT in maroochydore? If you are just email/call Nathan Higgins. You get free course support if you are on the AFT distance learning program for ATPL subjects.

[Hailstop3]

if i was i would have done that. But unfortunately i have not got the huge amounts of money he asks for his courses. Sure they are very good, but since i have already sat in a classroom b4 at uni doing almost the same subjects, i dont see the point again. If i was doing it all ab initio it would be a different story.

[redsnail]

You might find the answer in the "tech log" forum. Chances are it's been asked before. :D

Failing that, the D&G forum may be able to help.

[Keith.Williams.]

Sine Angle of climb = (Thrust -Drag)/Weight

The sine of an angle increases with increasing angle up to 1 at 90 degrees.

This means that for maximum angle we require maximum sine.

This in turn means that we require maximum (Thrust-Drag)

For jets the thrust is almost constant as speed increases, so max (Thrust - Drag) is achieved at the minimum drag speed Vmd.

This is also the speed (Y in your question) at which Lift to Drag ratio is greatest

So for jets max climb angle is Vmd (or speed Y)

Rate of climb is equal to Power available - Power required) / Weight.

So best rate of climb is achieved at the speed at which (power available -
Power required) is maximum.

Power available is Thrust x TAS

For fixed pitch props the thrust falls off rapidly with increasing airspeed, so maximum power available is at a fairly low speed, slightly greater than the minimum power required speed Vmp.

But for variable pitch props (which turboprops have) the rate of fall-off of thrust is much less.

This means that high levels of thrust and power available can be maintaned up to speeds closer to Vmd.

This in turn means that the speed for maximum rate of climb in a turboprop is much closer to Vmd.

It is a bit of an over simplification to say the best rate of climb speed in a turboprop is always exactly Vmd, but your examiner appears to be assuming that it is.