Chap B: Basic Aerodynamics Flashcards
(43 cards)
mass flow rate equation
ρAV (kg/s)
ρ - density
A - cross-section area
V - Flow velocity
what is the maximum velocity for compressibility to be neglected?
100m/s (M = 0.3)
what happens when compressibility is accounted for?
density, ρ, changes
types of flow and its explanation
steady flow - no change in parameters at any given time
unsteady flow - parameters at point of consideration are constantly changing
streamline definition
imaginary line joining all particles moving along the same path, there is no flow across streamlines (no exchange)
what is a stream tube?
a bundle of streamlines for a stream tube (no exchange of particles)
how is velocity related to area in continuity equation?
as cross-section area decreases, flow velocity increases
Total energy equation
ET = P∀ + 1/2 mairV2 + mairgz
P - static pressure
∀ - volume of air
V - speed of air
z - height above reference datum
which factor is the same between reality view and wind tunnel view?
airspeed & Vrelative
magnitudes are the same just that airspeed for real. view is against drag whereas Vrelative in WT view is same direction as drag
what does Bernoulli’s equation neglect?
it assumes that there is no fluid friction (energy lost due to friction is ignored)
What is static pressure?
static pressure is pressure exerted by still air at a point (not moving)
what is dynamic pressure?
pressure exerted by moving air (1/2 ρV2
what is stagnation pressure?
flow is brought to rest (Pdyn = 0)
so Pstagnation = Ptotal = Pstatic
how to measure stagnation pressure?
stagnation tube or pitot tube
dynamic pressure formula using difference of pressure
1/2 ρV2 = Pstagnation - Pstatic
why would using difference of pressure to calculate velocity be inaccurate?
1) as it requires density, and it cannot be measured during flight. And using ISA table is not accurate it assumes SL density is 1.225kg/m3
2) compressibility effect
what does pitot tube and static tube measure?
and what does pitot-static tube measure?
pitot tube - total pressure
static tube - static pressure
pitot-static tube measures the differential pressure (ΔP) to calculate airspeed
what is indicated airspeed?
IAS -measured by pressure difference and flight altitude density
what is equivalent airspeed?
EAS - airspeed using SL density, using Pdyn at altitude and bring it down to SL to get speed at SL.
what is true airspeed?
TAS - obtained with accurate density at flight altitude, when flow is incompressible, TAS = IAS
what is calibrated airspeed?
CAS - airspeed obtained by SL pressure and temp. (P0 & T0)
approx speed only, as speed increases, it is less accurate
types of error in airspeed measurements
1) density error - EAS is using SL density to calculate airspeed (EAS always < TAS when flying at altitude other than SL)
2) compressibility error - density changes for speed > M0.3
3) instrument error - not calibrated properly
4) position error
types of position error in airspeed measurements
1) location & orientation of the pitot-static tube
2) pitot tube may not sense full stagnation pressure at high angle incline
3) static port will not sense correct pressure when landing gears/flaps are extended / covered in ice
what is VIAS equal to in pressure formula?
VIAS = V
V in 1/2 ρV2
