ANALYTIC HIERARCHY PROCESS.docx

8/13/2019 ANALYTIC HIERARCHY PROCESS.docx

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ANALYTIC HIERARCHY PROCESS

Objective:

One of the major sources of drag for an aircraft in flight, results from the wing tip

vortices. Many efforts has been made to reduce this by employing devices such as tip fences,winglets, sails etc.. Ive taken tip sails as my area of project. So let us examine by AHP the order

of priority of sail parameters.

Criteria:

Though sails are used for drag reduction, some other criteria are also expected from them.

They are,

Induced drag reduction (Di-R) Increased L/D ratio (L/D) Vortex strength reduction (VS-R) Less structural Problems (LSP) Less zero lift drag (Do-R)

Alternatives (factors affecting criteria)

Not all criteria mentioned above can be achieved at one time. Factors such as sail

geometry, no. of sails favour some criteria while hindering the other. Such factors are

Sail Geometry (SG) No. of sails (No. S)

Sail span (SS) Tip Tanks (TT) Sail arrangement (SA)

Criteria Ranking:

The relative importance of one criterion over the other is expressed in the following

matrix. Here 1 represents equal importance whereas 9 represents extreme importance of one over

the other. The rankings are given from 1 to 9.

which can be written as


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[

]

The eigen vector is

The normalised eigen vector is

[

]

Priority of criteria (from most to least):

1. Induced drag reduction2. Increment in L/D ratio3. Reduction of vortex strength4. Reduction of zero lift drag5. Less structural problems

Factors ranking:

Now the effect of one factor over the other in terms of each criterion is analysed.

In terms of induced drag reduction

[

]


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Which is

The eigen vector is


In terms of L/D increment

which is

The eigen vector is



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In terms of vortex strength reduction,

[

]

which is

[

]

The eigen vector is

[

]


In terms of less structural problem,

Which is


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The eigen vector is


[

]

In terms of less zero lift drag,

[

]

which is,

The eigen vector is


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The final solution,

[

]

[

]

=

[

]

Factors in order of priority, (most to least)

1. Sail Arrangement2. No. of sails3. Sails geometry4. Tip tank5. Sail Span

Inferences:

This qualitative analysis gives an approximate priority ranking of factors affecting sail

performance. There is also some ambiguity between tip tank and sail span ranking, which may

have arised due to some error in the quantitative preference of one over other. More accurate

results (similar to the qualitative analysis) are expected when quantitative analysis is employed.

ANALYTIC HIERARCHY PROCESS.docx

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