# Essay John Locke

Topics: Aerodynamics, Lift, Rate of climb Pages: 14 (2851 words) Published: March 9, 2013
When comparing Vx to Vy:

a) Vy will always be greater than or equal to Vx <-- Correct b) Vy will always be greater than Vx

Climb Performance

A headwind component increasing with altitude, as compared to zero wind condition (assuming IAS is constant):

a) has no effect on rate of climb <-- Correct
b) improves angle and rate of climb
c) does not have any effect on the angle of flight path during climb d) decreases angle and rate of climb

With increasing altitude, the rate of climb: "decreases because power available decreases and power required increases"

The rate of climb:

a) Is approximately climb gradient times true airspeed divided by 100 <-- Correct

The climb gradient is defined as the ratio of:

a) The increase of altitude to horizontal air distance expressed as a percentage <-- Correct b) The increase of altitude to distance over ground expressed as a percentage c) True airspeed to rate of climb

d) Rate of climb to true airspeed

Equations below expresses approximately the un-accelerated percentage climb gradient for small climb angles:

Climb Gradient = [(Thrust - Drag)/Weight] x 100

Assuming that the required lift exists, which forces determine an aeroplane's angle of climb? "Weight, drag and thrust"

For a given aircraft mass, the climb gradient: "decreases with increasing flap angle and increasing temperature"

In un-accelerated climb thrust equals drag plus the downhill component of the gross weight in the flight path direction.

What will happen to VX and VY if the landing gear is extended? "VX and VY decrease"

Increase in the profile drag will shift the drag curve to the left.

If the aircraft mass increases, how does the (i) rate of climb, and (ii) rate of climb speed change?

a) decrease; increase

Rate of Climb = (Power Available - Power Required) / Weight

Climb Performance

Other factors remaining constant, how does increasing altitude affect Vx and Vy: "Both will increase"

Compared to Vx and Vy in clean configuration, Vx and Vy in configuration with flaps extended will be: "Lower"

Profile drag due to flaps shift the drag curve towards left

For a piston engine aircraft the service ceiling corresponds to: "The altitude at which the aircraft is capable of a climb rate of 100 feet per minute"

The absolute ceiling: "is the altitude at which the maximum rate of climb is zero"

On a twin engined piston aircraft with variable pitch propellers, for a given mass and altitude, the minimum drag speed is 125 kt and the holding speed (minimum fuel burn per hour) is 95 kt. The best rate of climb speed will be obtained for a speed:

a) equal to 95 kts <-- Correct
b) < 95 kts
c) is between 95 and 125 kts
d) equal to 125 kts

The examiner is trying to tell you something by specifying a powerful aircraft with VP propellers. For this aircraft In the lower speed ranges you would expect the THP available to be a nearly flat line, although I admit a constant speed prop would give a flatter trace. If you draw THP available as constant over this range and superimpose the power required curve you will see that the maximum power surplus occurs at minimum power speed, Vimp. You have been given this as 95kt.

My whole argument relies on having THP available as roughly constant at these speeds, which is a special case. It would not necessarily apply in the real world or to a fixed pitch prop. The shape of the THP available curve (assuming constant EHP) depends on propeller efficiency versus TAS and on your ordinary bugsmasher rises rapidly from zero TAS and then falls off again

This speed is now your best rate of climb speed, Vy. Your best angle of climb speed, Vx, is where you have maximum excess thrust over drag and because props give maximum thrust at very low speed to find Vx you would fly as slowly as possible - minimum control speed is usually quoted

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