Chapter 3 - Climbing, Descending, Turning and Stalls Flashcards
What is rate of climb (RoC)?
An aircraft’s vertical speed - the rate of positive altitude change with respect to time or distance.
RoC = Excess Power/Weight = Pav - Preq/Weight
What determines an aircraft’s RoC?
The amount of additional power required to maintain the same airspeed as in level flight.
What is angle of climb?
The ratio between distance travelled over the ground and altitude gained.
What determines an aircraft’s angle of climb?
The amount of excess thrust left after opposing drag?
How should the aircraft be flown to achieve the maximum angle of climb?
At the speed which gives the maximum difference between thrust and drag.
How should the aircraft be flown to achieve the maximum rate of climb?
At the speed which gives the largest difference between power available and the power required (drag x airspeed, i.e. power needed to overcome drag)
What is Vy?
The best rate of climb speed
What is Vx?
The best angle of climb speed
What is Vmu?
Minimum Unstick Speed
The calibrated airspeed at and above which the aircraft can safely lift off the ground and continue the take off.
What is the best angle of climb speed, Vx, for a jet?
Vimd
What is the best angle of climb speed, Vx, for a piston aircraft?
Just above Vmu (minimum unstick speed)
What is ‘absolute ceiling’?
The altitude at which the maximum power available curve only just touches the power required curve and sustained RoC is no longer possible.
What is ‘service ceiling’?
The altitude at which the maximum sustained rate of climb falls to 500fpm (100fpm for a piston aircraft).
What affect does altitude have on climbing?
Thrust horsepower of an engine decreases.
Jet engines are more efficient, but power available is lowered.
Therefore, max angle of climb and best rate of climb will reduce?
What are the two types of descent?
Powered Descent
Glide Descent
How does power affect the descent of an aircraft?
It reduces the descent angle and increases the distance travelled over the ground, increasing the range from a given altitude.
How do we fly an aircraft for endurance gliding?
Minimum rate of sink.
For a given aircraft weight, at what speed is the rate of descent least?
The speed where the power required is least.
What is range gliding and how do we fly to achieve it?
Range gliding is going as far as possible over the ground during the glide. It is achieved by flying at the aircraft’s optimum lift/drag ratio, Vimd (+ approx. 4 degrees AoA).
How does altitude affect best gliding speed for a given weight?
It does not, the best gliding EAS is constant regardless of altitude. However, the rate of descent will decrease as lower altitudes are reached and the TAS reduces.
How does wind affect gliding descents?
Tailwind INCREASES gliding RANGE
Headwind DECREASES gliding RANGE
Wind does NOT affect gliding endurance
How does aircraft weight affect a glide descent?
Does not affect gliding angle
Range gliding is unchanged - higher rate of descent but travel further over that distance due to higher ground speed
Endurance gliding decreases with an increase in weight and vice versa
What controls the Rate of Descent?
Power
More power = lower RoD
Does banking affect the amount of lift produced?
No, but a component of the lift is angled in to the turn. Therefore, more lift needs to be produced to increase the vertical component of the lift. This is done by gently pulling back on the stick to increase AoA.
Higher AoA = More lift, therefore more LDD. Means a power increase is needed.
More bank = More lift needed = Larger increase in AoA = Larger increase in LDD = Larger increase in power required to maintain speed
I.e. additional thrust is proportional to the angle of bank.
How does weight affect angle of bank required to turn at a set rate?
It does not, angle of bank remains the same.
(More AoA needed though for a larger vertical lift force to oppose weight? - Check)
If the same TAS and AoB can be obtained, the radius of turn is basically independent of the weight of the aircraft (limited by g-loading and aircraft tolerances).
What is a minimum radius turn?
Achieving the turn in the smallest possible ground area.
How is a minimum radius turn achieved?
Wing loading as low as possible
Air as dense as possible
Max value of the product of CL and AoB (CLmax)
Higher TAS = Higher AoB possible = Smaller radius of turn
I.e. min radius at infinite speed
What is the equation for centripetal force (CPF)?
CPF = (W x V^2)/gr
V = TAS in mps g = Gravitational force r = Radius W = Weight
How does the EAS for a min radius turn (in reality, not theory) change with increasing altitude?
It remains the same, but the radius of turn achieved at this speed increases.
Due to a reduction in CLmax.
Thrust also reduced at altitude.
How is a max rate turn achieved?
Wing loading as low as possible.
Air must be as dense as possible.
Maximum value of the AoB, speed and CL value must be obtained.
Note - Both max rate and min radius turns are flown at full power with max lift
How does thrust affect max rate and min radius turns?
It contributes a vertical component into the turn, so reduces the lift needed from the wing or can help improve turn radius.
Reduction in thrust with increasing altitude causes a reduction in turning performance.
How does altitude affect max rate and min radius turns and why?
Increases both (worse performance)
Due to less thrust from the engine, the TAS/EAS relationship and the reduction in CLmax.
What is the approximate stalling AoA for aircraft like the Prefect?
15 degrees
Note - Look at 1-3-4 Stalling, note the Pressure distribution with AoA interactive diagram.
Check NOW!
What is the Centre of Pressure (CP) and how does it move with increasing AoA?
CP is the point where the lift force appears to be acting from.
It moves forward as AoA increases, its furthest point forward being when CLmax is achieved. When the aircraft then stalls, the CP generally moves back along the chord.
What is the boundary layer?
The layer of air extending from the surface to the point where no drag effect is discernible.
What does the boundary layer determine in flight?
Maximum lift coefficient
Stalling characteristics of a wing
Value of form drag
Certain high-speed characteristics of an aircraft
What is Vb?
Stalling speed
What is stalling speed?
The speed of an aircraft in flight at its maximum lift coefficient (CLmax).
What are the key factors that change stalling speed (Vb)?
Change in weight (heavier = higher stalling speed)
Manoeuvre (load factor, n)
Configuration (changes in CLmax)
Power and slipstream
Is the AoA at which an aircraft stalls affected by weight?
No
If weight increases the AoA required to maintain level flight is increased for a set speed, therefore the aircraft reached the crit AoA at a higher speed.
How does AoB affect load factor?
Increasing AoB in a turn increases the load factor.
What is the new stall speed in a turn?
Vb (normal stall speed) x Square root of g
E.g. in a 4g turn, New stall speed = Vb x 2
What is the ‘thrust-line’ affect of stalling?
Stalling speed will be SLIGHTLY reduced by the effect of power, due to some of the thrust being inclined upwards, contributing to lift.
Aided by the flow of the prop slipstream over the lifting surfaces.
