Helicopter Flight Time

In teams of 4/5

Experiment with the design of a helicopter to result in maximum flight time

Money is only available for only10 prototype helicopters

What changes will you test to determine the best design?

Time 60 Minutes

Helicopter Design

Target: Maximise flight time

Y (seconds)

Changes allowed: (Design Parameters)

X’s (below)

X1: Wing length 90mm 115mm

X2: Wing Chord 55mm 65mm

X3: Weight 1 clip 2 clips

X4: Stiffness card paper

X5: Body length 85mm 100mm

X6: Body width 35mm 45mm

X7: Wing joint tape no yes

110 or 130 mm

35 or 45 mm

85 o

r 10

0 m

m

35 m

m

90 o

r 11

5 m

m

Paper clip

Standard Maximum

Wing Joint Tape

Helicopter

Proto Paper No. Taped Body Body Wing Wing FlightType Type Clips Wing Width Length Chord Length Test

Result

Strategy and Results

1

2

3

4

5

6

7

8Confirm

You have 60 minutes

You only have 10 attempts

How do you choose which experiments to run?

Go !

Who had the best time ?

Did The winner only use 10 prototype helicopters?

How do they do this in the real world?– The helicopters cost real money to build– They cost real time to build– You can’t just keep building new helicopters to find the best one

“One Factor at a Time”

Set baseline combination of conditions

Change one factor

If better, keep the change and try next factor

If results not improved, revert and try next factor

“One Factor at a Time” Strategy

ExperimentPapertype

No. Clips Tape

Bodywidth

BodyLength

WingChord

WingLength

1. Standard – – – – – – –

2. Paper Trial + – – – – – –

3. Clip Trial – + – – – – –

4. Taped Wing Trial – – + – – – –

5. Wide Body Trial – – – + – – –

6. long Body Trial – – – – + – –

7. Wide Chord Trial – – – – – + –

8. Long Wing Trial – – – – – – +

“Stick With a Winner” Strategy

Experiment Result

1. Standard – – – – – – – 2.0

2. Paper Trial + – – – – – – 2.4

3. Clip Trial + + – – – – – 2.2

4. Taped Wing Trial + – + – – – – 2.2

5. Wide Body Trial + – – + – – – 2.4

6. Long Body Trial + – – + + – – 2.6

7. Wide Chord Trial + – – + + + – 2.7

8. Long Wing Trial + – – + + – + 3.0

Papertype

No. Clips Tape

BodyWidth

BodyLength

WingChord

WingLength

“One Factor at a Time”

The results from changing one factor at a time could be plotted as the changes in the output Y against the change in a particular factor X

The “One Factor at a Time” approach can help to find the best design

But do the settings of the other Xs affect the amount of change in Y due to change in the selected factor?

Y

Paper typeX1

Y

Wing ChordX3

Y

Body lengthX2

Y

Wing SpanX4

Will these approaches always work?

Interactions between factors can and often exist.

Indeed, interactions can have a greater effect on the output than changes in individual factors

One factor at a time experiments cannot identify interactions between the Xs

If the optimum performance depends on interactions one factor at a time experiments will not find the optimum

Results can depend on the order of the experiments!

So “One Factor at a Time” or “Stick with a Winner” do not always work !

How do you find the best design ?

“One Factor at a Time” and “Stick with a Winner” approaches are good

They can reduce the number of experiments you need to perform

ie reduces cost

However they do not always work

If the factors are inter-related

Result can depend no the order you carry out the tests

“Test them All”

The best approach may be to test all possible combinations

How many prototypes would this need for our helicopter?

If you assume that each factor can only take on 2 values ie Body width 35mm or 45mm (not 40mm)

We need 128 prototypes to test every combination

That is way too many – way to expensive

How do you find the best design?

How do you find the best design?

every time?

With minimum number of prototypes?

Lowest cost?

Look up “Design of Experiments” on the web

– you might find a way