Aerodynamics

Question 1

What occurs when you lose an engine? Why? How do you compensate?

Answer 1

1. Pitch down due to loss of slipstream over the horizontal stabilizer. Back pressure
2. Roll toward failed engine due to loss of slipstream over wing. Raise dead engine
3. Yaw toward dead engine due to loss of thrust on failed side. Rudder opposite

Question 2

How does size of rudder vs vertical stabilizer affect VMC characteristics?

Answer 2

chord line of deflected rudder trailing edge to vertical stabilizer leading edge creates a greater AOA to relative wind when the rudder is big and stabilizer is small. more AOA available when rudder is big means it’s possible for vertical stabilizer to stall

Question 3

What happens as VMC yaw begins to the left?

Answer 3

Yaw string moves left because relative wind is coming from the right. AOA of vertical stabilizer increases. It can increase beyond critical and actually stall, yawing violently to the left. left wing is blocked by windmilling prop and has bad airflow so it will stall, dropping the wing. right wing creating even more lift and banking left. you will spin!

Question 4

What’s a zero sideslip condition? What does it achieve?

Answer 4

Dead engine raised 2-5deg and ball “split” by the line. Minimizes drag by aligning fuselage with relative wind.

Question 5

When are Vyse and Vxse equal? When does the airplane reach this point?

Answer 5

at the Single Engine Absolute Ceiling. Plane drifts to this altitude when an engine fails.

Question 6

In a plane with conventional props, what factors cause the left engine to be critical?

Answer 6

P-factor
Accelerated slipstream (over the wing)
Spiraling slipstream ( pushes on side of tail)
Torque effect

Question 7

Why do multi-engine aircraft spin easily?

Answer 7

The weight of the engines and gas is distributed outward from the CG

Question 8

How much does losing an engine affect power and performance?

Answer 8

50% loss of power

70-80% loss of climb performance due to drag.(climb performance comes from EXCESS power available)

Question 9

Why not raise dead engine >5deg?

Answer 9

Results in sideslip towards operating engine (more drag degrades climb performance)
Large ball displacement
Vmc will be significantly higher
The more horizontal component of lift you create to fight the asymmetric thrust, the less vertical lift you have to maintain level flight or climb

Question 10

When an engine is out, why does it want to yaw more the slower you go? (2 reasons) Assume you’re not touching the throttle.

Answer 10

P-factor and because rudder less effective

Question 11

For a given rate of turn, drag ___

Answer 11

drag is the same. can test by making r and L turn. if you hold alt, AS drops the same. if you hold AS, alt loss will be same. Aerodynamically they are the same.

Question 12

What’s the load factor when you raise the dead engine? Why do we care?

Answer 12

There is no load factor caused by raising the dead engine. Load factor is affected by the additional bank that causes a turn.
It is dangerous to turn too fast because overbanking increases load factor and decreases performance.

Question 13

P-factor

Answer 13

Descending blade produces more thrust. On left engine, descending blade is closer to centerline. Arm from centerline is longer on the right engine descending blade.

Question 14

Accelerated Slipstream

Answer 14

P-factor (Air over wing causing more lift) causes center of lift that is closer to longitudinal axis on L engine and further on R, so stronger roll force produced by R engine.

Less tail-down force causes pitch down.

Question 15

Torque

Answer 15

When L engine lost, aircraft will roll to L, adding to torque factor. More aileron input required = more drag

Question 16

Vyse
Is it on airspeed indicator?
Does it change with weight? altitude?

Answer 16

Vy on single engine. blue line.
Vy is the greatest excess HP (available HP increases slowly with airspeed, less excess HP when higher/heavier.)
Vy Increases slightly with weight (higher AOA = more drag, HP required curve moves up and slightly right)
Vy TAS increases slowly with altitude (Vx can catch up). IAS actually decreases due to decreasing air density.

Question 17

Vxse

Does it change with weight? altitude?

Answer 17

Best angle of climb on single engine
Vx is the greatest excess thrust. At higher weight(AOA) and altitude, the total drag curve moves right. Vx increases because to lift more weight, induced drag must be reduced.
At higher altitude, available thrust decreases. Vx TAS increases quickly, IAS increases slowly. They both catch up to Vy at the absolute ceiling.

Question 18

What is Vmc?

Is it on airspeed indicator?

Answer 18

Min control speed with inop critical engine under specific set of circumstances (stop turn within 20deg original heading + fly straight <5deg bank). red radial line on airspeed indicator 14 CFR part 23 where plane certified. doesn’t mean you can climb, directional control only

Question 19

Published VMC predicated on what?

Answer 19

Critical engine failed and windmilling (max drag)
Operating engine at max t/o power
Max takeoff weight
Bank up to 5°
Aft CG (most unfavorable)
Takeoff configuration (least stability)
Standard day, 29.92” Hg, 15°C, sea level (max engine power)

Question 20

How does weight affect Vmc?

Answer 20

In a given bank (up to 5deg), heavier aircraft has greater horizontal component of lift - assisting rudder force and decreasing Vmc.

Question 21

How does CG affect Vmc?

Answer 21

As CG moves forward, moment arm between rudder and CG lengthened, increasing rudder leverage and effectiveness and lowering Vmc.

Question 22

How does density altitude affect Vmc?

Answer 22

Thinner air results in lower engine performance and prop efficiency, decreasing adverse yaw and Vmc.

Question 23

How does operating engine power affect Vmc?

Answer 23

Exceeding RATED power by removing manifold pressure limitation or turbine or turbosupercharged engine increases yaw and Vmc. Power reduction or an old engine decrease Vmc.

Question 24

How does feathering the prop affect Vmc?

Answer 24

A feathered prop decreases drag on dead engine side, requiring less rudder input and lowering Vmc.

Question 25

How do gear, flaps and trim affect Vmc?

Answer 25

The gear & gear doors have a stabilizing “keel” effect. The flaps also have a stabilizing effect due to symmetrical drag (and perhaps because throttle on good engine can be reduced?)

Question 26

How does raising the dead engine affect Vmc?

Answer 26

Introduces a horizontal component of lift that helps counteract the yaw, decreasing rudder input and Vmc

Question 27

How does ground affect affect Vmc?

Answer 27

The reduction in induced drag reduces the thrust required at low airspeeds. The extra thrust on the good engine will increase yaw and Vmc.

Question 28

What are the warning signs that Vmc is about to occur?

Answer 28

1. Loss of directional control - rudder pushed al lthe way down
2. Stall warning horn - single engine stall can result in a spin
3. Buffeting before the stall - same as above
4. Rapid decay of control effectiveness - could result in loss of control of the airplane

Question 29

Spiraling Slipstream

Answer 29

Spiraling slipstream from L engine hits vertical stabilizer from the left, counteracting yaw when R engine lost. Slipstream from R engine spirals away from tail and does nothing to help counteract yaw.

Question 30

How does HP affect VMC characteristics?

Answer 30

more HP means stronger yaw when you hit VMC and bigger AOA of vertical stabilizer, leading to stall and spin. (verify this)

Question 31

How does drag from certain configurations affect your climb performance?

Answer 31

Full flaps -400fpm
Windmilling prop -400fpm
Gear down -150fpm