Flight Experience/Test course 2008

Due to the large number of students it is necessary to run the course between April and September.

This will enable all students to staying the club house on the airfield

Flight test accommodation

Because a some of your cohort will take the course in September the report cannot be assessed in ME201

The report must be submitted by during Semester 1 academic year 08/09 and will form part of the assessment of 16351 Flight and Spaceflight 2

Report

Exams

If there is a class test while you are on course the class test will be held on site.

However, I will need to know in advance to enable me to arrange exam papers etc. with the registrar

Courses last approximately two and a half days starting on either Monday morning at 9am – Wednesday 12 pm or Wednesday 1pm – Friday 5 pm

By Car

Portmoak Airfield is to the East of Kinross. From Glasgow take the M8 towards Edinburgh. Across the Forth Road Bridge and then right at Junction 5 on the M90 turn right. The airfield is signposted from this point

Please complete the contact form so that I know how you intend to travel to the airfield and can arrange transport from Lochgelly station if required,

TRAVEL

Portmoak is not the easiest place to get to

By train

Morning start Lunch time start

Dep. Glasgow Queen 07:15 Arr. Edinburgh Haymarket 08:01 Dep. Edinburgh Haymarket 08:17Arr. Lochgelly 08:59

Dep. Glasgow Queen 11:00 Arr. Edinburgh Haymarket 11:45Dep. Edinburgh Haymarket 11:54 Arr. Lochgelly 12:36

this will get you into Lochgelly station where I will arrange transport to the airfield.

Safety

You will be staying and working on an active airfield. Whilst every effort is made to ensure that the airfield is a safe environment, your safety depends entirely upon you working and behaving in a responsible manner.At the start of each course a safety briefing will be given to you. If you miss this briefing you will not be allowed onto the active side of the airfield.

RiskThere is an inherent risk of injury in any activity and, whilst every effort is made to reduce this risk, you must be aware that it exists. The aircraft will, at all times, be under the command of the instructor in the back seat known as the “pilot in command” or P1. The safety of the flight will be P1s responsibility. P1 will be a BGA qualified instructor with many hours of flying experience.

Insurance You will be covered by the Scottish Gliding Centre’s £2m second seat liability insurance. You will not be covered by university insurance on the course.

The course is not compulsory and any concerns you have regarding your participation should be discussed with Dr Stickland

Accommodation

All courses this year will be staying in the club house accommodation.

The rooms will be two bed twin rooms with linen and towels supplied.

There is a canteen on site which provides good food all day with a breakfast that you will struggle to finish for about £3.50.

Do not eat a big breakfast upon arrival as the experience of flying in a glider can occasionally produce motion sickness. Make sure you are not affected before experiencing the delights of a full breakfast followed by steep stalls.

If you know that motion sickness can be a problem let me know.

Main meals in the evening cost about £5.

There is a bar on site

Entertainment in the evening is fairly limited.

There is a TV in the bar in the club house

In the bar old pilots swap stories about their latest 750k flight in wave up to 36,000 feet and the instructors say how Bloggs (pilot under instruction) in the front seat nearly killed them.

Also, between flights there will be a lot of sitting around so bring along revision, course work, reading material, Nintendo DS etc. to while away the hours.

Entertainment

Clothing

Airfields suffer extremes of temperature.

They are either baking hot or extremely cold

Bring along suitable clothing for both.

If there has been rain the wet long grass on the airfield will rapidly make trainers sodden so bring water resistant shoes or boots.

If it is sunny their will be lots of glare whilst flying so bring sunglasses (a chance to put those Ray Ban Aviators to their proper use)

A hat for sunburn protection as well as warmth in the cockpit. The hat should not have a peak (lookout is impaired by peaks) - baseball caps may be worn reversed

Flying Programme

Programme will consist of 4 flights

Flight 1 - Aircraft controls

Flight 2 - The Stall

Flight 3 - Aircraft Performance

Flight 4 - Dynamic Stability

Flight 1- Aircraft Controls

Rudder, Elevator, Ailerons,Airbrake,Trimmer

The effect of the flying controls will be demonstrated

Coordinated Turns

When they ailerons are deflected the up going wing generates more lift and hence more induced drag

This causes the aircraft to yaw towards the up going wing out of the direction of turn.

To counter this the rudder is used to generate a moment to counter the adverse yaw.

When the aircraft turns without sideslipping it is referred to as a coordinated turn.

To help coordinate turns use the string!

Trimmer Used to reduce control forces - tab or Spring

The aerodynamic trim tab reduces stick forces by moving the centre of pressure nearer the hinge

The spring trimmer applies a mechanical force to reduce the stick load

The K21 has a spring trimmer

Airbrake

The airbrake is deployed to increase the rate of decent of the aircraft.

It does this by reducing the lift generated and increasing the form drag. They may reduce the induced drag as they modify the wing’s lift distribution.

They are not usually used to slow the aircraft down.

Flight Instruments

The operation of the following flight instruments will be shown;

Air speed IndicatorAltimeterVertical Speed IndicatorTurn and slipg meter

Lift increases almost linearly as the angle of incidence is increased

Angle of attack (degrees)

Lift

Coe

ffici

ent

-4 0 4 8 12 16 20

0.2

0.4

0.6

0.8

1.0

1.2

0.0

ordinary angles of fl ight

What happens if we increase the angle of attack above 10o

Flight 2 - The stall

Angle of attack (degrees)

Lift

Coe

ffici

ent

-4 0 4 8 12 16 20

0.2

0.4

0.6

0.8

1.0

1.2

0.0

stal

l an

gle

ordinary angles of fl ight

If the angle of the aerofoil relative to the wind exceeds a certain value the flow separates and the lift decreases and the drag increases - the stall

To maintain constant altitude as airspeed is reduced the angle of attack must be increased.

If the angle of attack is increased sufficiently then the wing will stall.

The angle of attack at which a wing stalls is constant but the IAS for the stall depends upon a/c weight and load factor.

As the stall is approached there are several indications to the pilot that stall is near

• change in noise level• change in control responsivenes• buffet.• change in attitude.

These will be demonstrated during the flight

Calculations;

You are required to calculate;

straight and level stall speedbank angle for a 2g turnstall speed in a banked 2g turn

You will require

mass of aircraft (inc. pilots, parachutes etc)Cl vs plots for the aerofoilWing area

max21

Lstall SC

mgV

2g turn

Load factor, n=2

n

1cos 1

1kt = 0.514m/s

Pre Flight

During Flight

Record the straight and level stall speed

Record the stall speed during the banked turn

Record the g indicated if not 2

Post Flight

Calculate stall speed for indicated g

Calculate the bank angle for the indicated g

Flight 3 - Performance

The aim of this flight is to compare the performance characteristics of the aircraft;

• Calculated theoretically

• Given in the manufacturers handbook

• Measured in flight test

Lif t

DragThrust

Weight

You need to calculate Cdo and k

The drag coefficient is given by;

2LDD kCCC

o

Drag (CD)

Form Trim Base Wave Profi le Cooling I nterference Skin f riction

I nduced (AC )2L

Parasite (C )Do

Flight test data

During your flight record

• Indicated airspeed• Time to descend 100’• Control column position

For two different Flight Speeds

For 50kts brakes full

Check the VSI reading at your estimated min sink speed

Check that this is the speed for minimum sink

Post Flight Calculation

For data point one, calculate;

Lift Coefficient

SV

WC

eo

L 221

Drag Coefficient

Glide angleV

v

SV

WC

eo

D 221

sin

Hence have two equations of the form 2kBCA

oD

Where A and B are known. Solve for CDo and K

Carry out the same analysis from the data in the published polar.

Measurement of Neutral point by flight test

The aircraft is flown in trim at several different airspeeds.

The stick position is measured for each speed

trim is determined from the

calibration shown.

The lift coefficient, CL, being

generated is calculated.

The centre of gravity location is determined.

From these series of flight tests a series of curves of CL against

elevator angle to trim may be plotted for each flight.

Stick poition -vs- Elevator angle

= -1.7296x + 43.803

-20

-15

-10

-5

0

5

10

15

20

25

30

10 15 20 25 30 35

Stick Position (cm)

Ele

va

tor

An

gle

(d

eg

)

flight 1

flight 2

trim

CL

GL

trimn haV

dC

dh

T 2

See notes for the proof that

For each flight plot variation of elevator angle to trim against lift coefficient

hG1 hG2h

n hG

dCL

d

Each student will have flown with the cg at different locations so the above graph can be plotted

Extrapolation of the line created gives the location of the neutral point

h=h then 0=Cd

dnG

L

Flight 4 – Dynamic Stability

The aim of this flight is to assess the dynamic stability of the K21.

Demonstration of the phugoid

Demonstration of spiral divergence

Demonstration of weathercock stability

Dynamic stability is concerned with the subsequent motion of a body which possess static stability.

The motion usually consists of oscillations about the equilibrium position and again there are three possibilities;

•A body is dynamically stable if the oscillations eventually damp out.

•A body is dynamically unstable if the oscillations are undamped or divergent, increasing in amplitude.

•A body is dynamically neutrally stable if the oscillations are undamped and of constant amplitude.

Flight 4 – Dynamic Stability

0 10 20 30 40 5018

20

22

24

26

28

30

32

ui

ti

Dynamically stable

0 5 10 15 20 25 306

8

10

12

1412.212

6.607

ui

256.25 103 t

i

Neutrally stable

t solution 0

0 5 10 15 20 25 304

6

8

10

12

14

16

ui

ti

Dynamically unstable

the vertical fin provides stability in yaw.

The fin is placed well behind the centre of gravity and tends to turn the aircraft towards the relative airflow. - hence “weathercock” stability.

Note that excessive yaw stability can be problematic as the fin will turn the aircraft towards any side gust experienced by the aircraft.

Also the centre of pressure of the fin is above the cg of the aircraft and will cause a rolling moment as well as a yawing moment – see this near stall.

Weathercock stability

Lif t

sideforce from fin

weight

normal component of weight

sideways component of weight

relative direction of airflow

When an aircraft is banked the resultant forces tend to produce a sideslip towards the lower wing.

The sideforce generated by the fin then causes the aircraft to yaw towards the lower wing.

This is an unstable case and would, if not compensated for by rudder deflection by the pilot, result in a spiral divergence.

To impart stability in roll to counter this it is usual to give the wings dihedral.

Lateral Stability

The figure left shows an aircraft with dihedral.

If the wings were canted down this would be referred to as anhedral.

Consider an aircraft that is sideslipping.

The relative airflow is from the front quarter.

It can be seen that the near wing creates a higher angle of attack than the far wing.

The near wing, at a higher angle of attack, will therefore produce more lift than the far wing and the aircraft will roll back to the horizontal

Dihedral

High Wing

If a high winged aircraft is sideslipping the fuselage will deflect the flow up on the lower wing and down on the upper wing

With the increased angle of attack on the lower wing the lower wing will generate more lift than the upper wing.

The aircraft will roll the back to level flight.

Phugoid

Consider an aircraft in trimmed level flight.

The aircraft is now put into a dive by the pilot and the stick released.

The downward component of the aircraft weight will cause the speed of the aircraft to increase.

The lift increases due to the increase in speed.

The flight path levels out due to the increase in lift.

Now have greater lift than weight for level flight so the aircraft will climb.

Speed deceases.

Lift decreases.

Aircraft levels out.

Less lift than weight so aircraft descends and process is repeated.

0 5 10 15 20 25 306

8

10

12

1412.212

6.607

ui

256.25 103 t

i

If there were no losses the motion would be un-damped and neutrally stable.

However, as the speed increases the drag of the aircraft also increases and when the aircraft slows down the drag reduces.

The drag variation therefore works to oppose the motion and creates damping in the oscillation.

For most aircraft the change in drag is small and the motion is only lightly damped.

The period of the phugoid is normally long, about a minute, and usually instinctively damped by the pilot through control input.

The stability of the phugoid depends upon the aircraft remaining in trim and is thus dependent upon cg location.

Spiral Divergence

If an aircraft is disturbed in yaw then a side flow across the wing, fuselage and fin will result.

The sideslip will create a yawing motion through the change in the angle of attack on the fin.

As the aircraft yaws the advancing wing creates more lift than the retreating wing

This creates a rolling moment and the aircraft rolls.

Weight is now not acting vertically through the centerline of the aircraft but towards one side. This generates a sideslip.

The lift will be less than the weight and the aircraft will start to descend and accelerate. The sideslip will create an increase in the yawing moment which will cause the aircraft to roll.

The aircraft now enters a descending, spiral motion.

If the aircraft has dihedral, the restoring moment created by the dihedral can be greater than the unstable rolling moment created by the fin.

However, the motion is usually quite slow and easily damped out by the pilot.

Increase dihedral to damp out the oscillation automatically is not always possible as it can lead to an oscillatory lateral motion – Dutch roll.

Data recorded during flight:

Period of the phugoid from =10o and pitch =30o (10o above horizon) at 60kts trimmed airspeed stick fixed and stick free

Min airspeed during phugoidMax airspeed during phugoid

Period to =45o (estimated roll) during spiral divergence from 60 kts trimmed flight =2o (initial roll)

Time to 80kts indicated during divergence.