Thrust, Drag and Lift Flashcards
(30 cards)
Thrust on low by-pass ratio engines reduces initially because of … and then increases slightly but steadily above … with improved …
intake momentum drag
M0.4
mass flow
what is intake momentum drag?
The air entering the intake is slowed down and loses momentum before it is again accelerated
decreases the overall thrust of the engine and it increases with increasing Mach No
Jet thrust … generally with increasing altitude due to …
decreases
reduced density
Jet thrust limited by one of two things, which are?
TGT limit
RPM limit
On hot days … limit is reached before … limit
TGT
RPM
when the TGT is limiting, a reduction in OAT allows an …
increase in RPM and a subsequent increase in thrust
As long as max thrust is regulated by the RPM limit, it will be almost … and independent of …
constant
temperature
at high temps thrust varies with … but at low temps, usually below about …, the thrust is constant and the engine is said to be …
temp
ISA+15
flat rated
As the mass of air entering the engine changes the FCU will adjust the fuel flow to maintain the optimum air to fuel ratio of around …
An increase in density will … fuel flow and vice versa
15:1
increase
jet power is rate of application of …, defined as …
thrust
thrust x speed
If we assume that jet thrust is relatively constant then power … as speed increases
increases
jet power also … with increasing altitude for the same speed because …
It will also decrease with … temperature
decreases
the amount of thrust decreases with altitude
increasing
propeller thrust produced depends on the … of the blade, which in turn depends on the …
angle of attack
airspeed and induced airflow through the propeller
At low airspeeds the AOA through the propeller will be …, and thrust will be ….
As forward speed builds the angle of attack … and thrust …
large, near to the stall
maximum
decreases
reduces
maximum thrust of a propeller driven aircraft is … at zero forward speed and … with increasing forward speed
maximum
reduces
Shape of drag curve different for propeller and jet aircraft because they are designed to fly at different speeds, Vmd on a jet is …
higher
what is the speed unstable regime?
at speeds less than Vmd, a reduction in speed leads to an increase in drag, which in turn reduces speed further and increases drag more and so on
wha is the speed stable regime?
Above Vmd an increase in airspeed also increases drag but this tends to restore the original airspeed
when flaps are deployed, because lift delivered is unchanged, the lift induced drag is hardly changed. Selection of the flaps does increase profile drag, which in turn reduces … and …
Vmd
Vs
If induced drag increases Vmd occurs at a … speed, if profile drag increases Vmd occurs at a … speed
higher
lower
Effect of mass on induced drag can be estimated coarsely. The induced drag is proportional to …
the square of the aircraft weight
(if weight increases by 10% or a factor of 1.1 then the induced drag will increase by 1.1squared or 1.21)
Can also roughly estimate the increase or decrease of Vmd with an increase or decrease in weight. Vmd varies by …
the square root of the weight change
Effect of speed changes on drag can also be coarsely estimated. At a constant weight:
profile drag is protortional to …
induced drag is proportional to …
(both are speeds)
V squared
1 / V squared (inversley proportional)
Max forward speed in level flight is achieved where the thrust available intersects the … curve, which is where …
total drag
max thrust equals drag
