USING TRIZ TO IMPROVE AN AIRCRAFT COMPONENT

Frank Gornall, BAE Systems, demonstrates how an air force requirement for the cooling duct that supplies
 low pressure / low temperature air installed within an equipment crate is improved using
TRIZ tools of contradictions and 40 principles.

SRES* DUCTING DESIGN 

PROBLEM CONTEXT

An air force has a requirement for the SRES* to all aircraft.

(*note:  SRES  is a fictitious acronym to preserve identity of restricted information)

The SRES system consists of various units and antennae along with associated wiring and cooling provisions where necessary.  However, for the sake of this TRIZ exercise/demonstration, we are only looking at the cooling duct that supplies low pressure/low temperature air to the SRES and PS (Power Supply) units installed within an equipment crate. This new duct 'taps' cooling air from the existing plenum chamber** attached to the rear of the crate (via a newly introduced cut-out).

Earlier development activities and ECS (Environmental Control system) testing have previously been carried out to arrive at the development solution shown below (Figures 1 & 2) from which the Design department have been tasked with creating a ‘production’ solution.


BAE SRES fig2

BAE SRES fig2

It has to be noted that the retro modification is split into two stages:

  • Stage 1
    At Stage 1 (Provisioning) the SRES and PS units are not fitted – however, it is still necessary to fit a small section of the duct to the rear of the crate. The reason for this ‘stub duct’ is to maintain space provision for the continued use of existing systems whilst simultaneously negating the later removal of the equipment crate and subsequent refit/retests when SRES is finally installed. The Stub Duct requires sealing off at this stage in readiness for Stage 2.
  • Stage 2
    At Stage 2 (Installation), the existing units/racks and the Stub Duct blanking are removed to allow installation of the Manifold Duct part, new rack and SRES/PS units.    

 **depending upon aircraft build Block standard, this existing plenum-type chamber is manufactured from either SPF (super plastic formed) aluminium alloy or GRP (glass reinforced plastic) with slightly different profiles. Hence two versions of Stub Duct were designed at the development stage. For cost and kitting considerations, it has been envisaged that only one type of ducting shall be designed for production.

DISCUSSION OF PROBLEM

Problem Statement

The problems identified with the current development solution are:

  1. The duct parts comprise of many fabricated aluminium alloy parts welded together, with the welding is dressed out at critical locations. Clearly, this is a very labour intensive and costly method of manufacture that would also require a lot of tooling.
  2. Both duct parts are rigid. Furthermore the Stub Duct is riveted to the equipment crate plenum chamber and the Manifold Duct is bolted to the SRES/PS rack assembly. Consequently, it is imperative that these duct parts are perfectly aligned (notably in X & Z) in order to prevent a build up of stresses when assembled. Due to aircraft build differences, design would need to impose controls such as close manufacturing tolerances on the duct parts, use of packing/shim and possibly further (costly) tooling for use at the installation stage.
  3. At Stage 1, failure of the clamping force exerted by the Clamp Ring may lead to loss of the Sealing Cap and consequent loss of cooling air to vital aircraft equipment including the main computer. The development solution is reliant only upon the friction between mating surfaces to withstand the air pressure being applied from within the crate plenum chamber.
  4. Disassembly/assembly of the Clamp Ring (bolt and nut) would be awkward at Stage 2 due to limited access as the Zone 12 crate would be fitted in the aircraft. Risk of FOD (foreign object damage). 


Design Constraints

  1. Extensive ECS testing has previously been performed at the development stage in order to determine duct internal geometry and restrictor plate requirements so as to provide suitable ‘balanced’ cooling airflow to all required electrical units. To avoid further testing, Design are unable deviate too far from the duct internal geometry offered by the development solution. 
  2. The ECS department have specified that air loss from any of the duct interfaces/joints is not acceptable.
  3. There is very little clearance between the back of the equipment crate and the aircraft frame structure.   

TACKLING THE PROBLEM

TRIZ provides various tools to help solve problems including:

  1. Thinking in Time and Space 
  2. Eight Trends of Technical Evolution 
  3. Uncovering and Solving Contradictions 
  4. Using the 40 Principles 
  5. Standard Solutions for Problem Solving 
  6. Smart Resources to Find the Right Systems and Overcome Constraints 
  7. Understanding What We Want 
  8. System Modelling and Analysis 
  9. Accessing and Using the World’s Knowledge Bases 
  10. Getting to Solutions and Minimising Risks 
However, only a few of the more useful tools (in the author’s opinion) are demonstrated in this report. Further information on each can be found on the TRIZ website.

System Modelling and analysis

Shown below is the functional analysis model of the SRES ducting arrangement for the development solution. It shows clearly how parts of the system interact with each other and more importantly whether the actions between them are useful or harmful.

Where there are both useful and harmful actions between two subjects or objects, we therefore have some kind of contradiction. In this case, the Ring Clamp is securing and sealing the two duct parts but it is also inducing stresses as a result (i.e. if, due to aircraft build differences or build up of manufacturing tolerances, they are not correctly aligned). 

In TRIZ language, this is a 'technical contradiction' because by improving the engineering parameter 'Loss of Substance' we have inadvertently worsened the 'Strength' and 'Stress' parameters. See explanation of contradictions below.


BAE SRES fig 3

Uncovering and Solving Contradictions

This is a three step process:

Step 1: Identifying the contradictions

Note that there are two types of contradiction in TRIZ:

  • Technical Contradiction (TC) – for example we wish to make a chair stronger but when we do it becomes too heavy. The technical contradiction here is Strength versus Weight; these are the engineering parameters that we need to consider when using the Contradiction Matrix (in Step 2).
  • Physical Contradiction (PC) – for example we need an umbrella to be both large (when raining) but small/portable when the weather is fine.


Step 2: Solve the Contradictions

Technical contradictions are solved by using the Contradiction Matrix (Appendix ‘A’). Using the chair as a basic example we can cross reference the ‘Improving Feature’ of Strength (14) against the ‘Worsening Feature’ of Weight of a stationary object (2) to give us four generic Inventive Principles to look at that have been used in the past to solve similar problems. These are:

(1) Segmentation (split chair into 2 parts maybe?)

(26) Copying (?)

(27) Cheap Short-Living Objects (have many light weight disposable chairs?) 

(40) Composite Materials (Use mixture of materials – steel frame/plastic seat)

Further information regarding the Inventive Principles can be found here.

Physical Contradictions cannot be solved using the Contradiction Matrix. Instead, they are solved using Separation Principles of which there are four types:

  1. Space: were we require certain properties in one place but different properties somewhere else (e.g. coffee cup – hot on inside but cold on outside to prevent burns to hand). 
  2. Time: were we require opposite benefits at different times (e.g. telescopic board pointer – long to point but short to fit in a pocket).
  3. Condition: we need something IF one condition applies, but something ELSE if a different condition applies. (e.g. kitchen sieve stops spaghetti but does not stop water).
  4. Alternative Ways


Step 3: Generate possible Solutions

Interpret and apply the resulting Inventive Principles (Appendix ‘A) based on the current problem in order to generate possible solutions. In the case of the chair, we can reduce its weight by splitting it into two parts (Segmentation); make many cheap disposable chairs (Cheap Short-Living Objects) that can be thrown away when broken; or we can use a mixture of materials such as steel frame and plastic seat (Composite Materials).


THE SOLUTIONS

For ease of reference during the SRES ducting investigation, it was decided to code each contradiction/solution as below:

BAE SRES fig 4

PC1

With reference to the problem list and design constraints list generated earlier, the following contradiction was discovered: 

The duct parts need to be rigid to maintain the correct airflow through the duct – i.e. the internal duct geometry must not be compromised. However, the duct also needs to be flexible to allow for aircraft build differences when joining the duct parts. Thus we have a physical contradiction.

As we need the majority of the duct to be rigid (maintaining its shape) but the duct joint area to be flexible to allow for any duct misalignment, the Separation Principle "Space" is used to solve this ‘physical contradiction’. This suggests that we look closely at the following Inventive Principles for solution ideas:

(1) Segmentation
(2) Taking Out
(3) Local Quality
(4) Asymmetry
(7) Nested Doll
(14) Spheroidality/Curvature
(17) Another Dimension
(24) Intermediary
(26) Copying
(30) Flexible Membranes & Thin Films

Solution PC1A – (3)(30)

Fasten (e.g. rivet) a flexible rubber sleeve to the open end of the Stub Duct. The Sealing Cap/SRES Manifold Duct can slide into the sleeve and be secured using some kind of clamp, tie-wrap, Jubilee clip, etc.

BAE SRES fig 5

solution PC1b – (7)(30)

Have Sealing Cap/Manifold Duct slide into the Stub Duct and use a wiper type seal to take up any duct misalignment.

BAE SRES fig 6

Solution PC1c – (30)

Thin membranous flaps bonded on inside of Stub Duct. The intention is that the airflow through the duct will lift the flaps outwards to seal against the inside of the SRES Manifold Duct. 

BAE SRES fig 7

Note: TRIZ encourages us to look for all resources available to us and make use of them when possible; in this case, we are making use of the ‘air-flow’ resource.

Solution PC1d – (24)(30)

Fit an intermediary rubber-type bellows type sleeve to fit between duct flanges.

BAE SRES fig 8

Solution PC1e – (30)

Seal duct joint using standard adhesive ‘duct-tape’ wrapped around the joint area.

BAE SRES fig 9

TC1

The Function Analysis of the SRES ducting has highlighted that the Clamp Ring used to seal the two duct parts together could also induce stress into the parts during assembly.

Looking through the list of 39 engineering parameters (or Features) we can select ‘Loss of Substance’ (i.e. the Clamp Ring is sealing to prevent air loss) as an improving feature and 'Strength' or 'Stress' as the worsening feature.

By cross referencing ‘Loss of Substance’ against ‘Strength’ on the Contradiction Matrix, it is suggested that we look at the following Inventive Principles:

(35) Parameter Change
(28) Replace Mechanical System
(31) Porous Materials
(40) Composite Materials

Note: see TC2 below for ‘Loss of Substance’ versus ‘Stress’.

Solution TC1a – (35)(28)

Elasticated sleeve fitted over joint area rather than a stiff Clamp Ring.

BAE SRES fig 10

Solution TC1b – (31)(28)

Omit the Clamp Ring and compress a porous rubber section into the joint area of the ducts that seal on assembly. Any duct mis-alignment would still allow air to pass through with minimal loss.

BAE SRES fig 11

Solution TC1c – (40)(28)

Replace the Clamp Ring for a neoprene impregnated nylon moulded sleeve that can be secured to each duct end by means of tie-wraps or Jubilee clips.

BAE SRES fig 12

TC2

By cross referencing ‘Loss of Substance’ against ‘Stress’ on the Contradiction Matrix, it is suggested that we look at the following Inventive Principles:

(3) Local Quality 
(36) Phase Transition
(37) Thermal Expansion
(10) Prior Action

Solution TC2a – (3)

Investigate additive layer manufacture (ALM) hard plastic duct body blending into flexible rubber sleeve in joint area. Secure with tie-wrap or Jubilee clip.



Solution TC2b – (37)

Heat-shrink sleeve fitted over joint area. [See TC1a].

BAE SRES fig 13

Solution TC2c – (10)

Introduce use of packers, laminated shim, floating anchor nuts (at interface of SRES Manifold Duct with Rack Assembly) to eliminate any mismatch in duct alignment (and thus stress).

BAE SRES fig 1 TC2c

Solution TC2d – (10)

Ensure SRES Stub Duct and Manifold Ducts are positioned accurately during fitment to the crate by making use of tooling fixtures. 

BAE SRES fig 15 TC2d

TC3

The Function Analysis also shows inherent technical contradictions within the SRES Manifold and SRES Stub Duct parts. Although both are doing there intended function of containing the airflow, they are very difficult to manufacture and therefore costly (i.e. the ducting is of a complex shape and is made up of many intricately shaped/folded sheet metal components welded together).

Extracting the first technical contradiction of ‘Shape’ versus ‘Ease of Manufacture’ we are guided into looking at the following Inventive Principles:

(17) Another Dimension 
(32) Colour Change
 
(1) Segmentation
(28) Replace Mechanical System

Solution TC3a – (1)

Manufacture the duct part in layers using glass-fibre or carbon fibre rather than by fabrication. 

BAE SRES fig TC3a

TC4

Following on from TC3, the other technical contradiction we can explore is 'Shape' versus 'Productivity'. 

Note: the ‘'Productivity' parameter is the closest we can find that captures the 'cost' element we are interested in. The Contradiction Matrix reveals the following Inventive Principles:

(17) Another Dimension
(26) Copying 
(34) Discarding and Recovering
(10) Prior Action

Solution TC4a – (10)(34)

Manufacture duct parts using a 'lost-wax' casting process.

BAE SRES fig TC4a

Standard Solutions for Problem Solving

Originally, '76 Standard Solutions' of TRIZ were compiled by G.S. Altshuller that offered innovative solutions to inventive problems. However, due to many people finding the method difficult and tedious to use, a simplified version has been developed by Oxford Creativity that groups the Standard Solutions into five main categories:

  1. How to do something we want.
  2. Dealing with harm (prevent, transform or block)
  3. How to improve something (or action) we already have. 
  4. Detecting or measuring something.
  5. Simplifying and making cheaper.
For further information on each group, see 'TRIZ Standard Solutions' course booklet.

The solutions derived from using the 'Standard Solutions' method are coded thus:

BAE SRES standard solutions

DEALING WITH HARM

TRIZ recommends that any 'harms' are dealt with first – i.e. getting rid of unwanted features in order to move towards an ideal solution:

BAE SRES fig 18 Ideality

The Standard Solutions offer four groups associated with eliminating harm of which there are a number of methods available that allow us to deal with them:

2.1 Six ways to stop a harmful action being harmful.
2.2 Seven ways to eliminate a harmful action (TRIMMING).
2.3 Three ways to correct the results of a harmful action.
2.4 Three ways to turn harm into good.

SS-2.2.3-A 

With reference to the Function Analysis diagram, there is a problem with the clamp ring inducing stresses into the duct parts. Standard Solution ‘2.2.3’ states “If the Subject’s useful action cannot be eliminated, obtain it from some other source and eliminate the Subject”. Expanding on this statement, the Ring Clamp’s useful actions (sealing and securing) are still required but we can obtain these actions from the duct parts themselves by incorporating a flexible seal and securing device within them; thus, we can ‘trim-out’ the Clamp Ring component and hence its associated harmful effect.


BAE SRES fig 19

SS-2.1.1-a

Standard Solution ‘2.1.1’ states “Insulate the Object from the Harmful Action”; we could improve the design of the Ring Clamp by adding a soft rubber sponge-like layer onto its inner surface that will seal the joint and take into account duct misalignment without inducing any high stresses.

BAE SRES fig 20

How to improve something (or action) we already have

The current design of the Sealing Cap (SRES Stage 1) relies upon the frictional clamping force of the Ring Clamp only to hold it in place. Loss of the Sealing Cap in flight would unbalance the ECS system and could possibly lead to important equipment overheating. TRIZ provides the following groups of Standard Solutions to help deal with Insufficient Action:

1.1   Find and use a better/different action.
1.2   Add another action to intensify/supplement the effect/action.
1.3   Change the Subject or Object to increase the effectiveness of the action on the Object.

SS-3.3.1.1-a

Standard Solution ‘3.3.1.1’ states “Add something permanent or temporary inside the Subject or Object”; for example, a ‘quick-release’ pin to mechanically lock the Sealing Cap onto the Stub Duct. 

BAE SRES fig 21

SS-3.3.1.3-a

Standard Solution ‘3.3.1.3’ states “Add something between the Subject and Object”; for example, bond the Sealing Cap onto the Stub Duct using PRC. 

BAE SRES fig 22

SS-3.3.1.2-a

Standard Solution ‘3.3.1.2’ states “Add something external (permanent or temporary) inside the Subject or Object”; for example discard the Ring Clamp and add locking tabs onto the Stub Duct and Sealing Cap that allow the components to be bolted together.

BAE SRES fig 23

THE FINAL SOLUTION

Combining the benefits of a selection of solution ideas, we arrive at the following final solution:

BAE SRES fig 24 solution

BAE SRES fig 25 solution


BAE SRES fig 26 solution
BAE SRES fig 27 solution

SUMMARY & CONCLUSIONS

As the SRES project was started prior to attending the TRIZ course, it must be noted that many solutions were already created prior to applying the TRIZ theories. As a result, the earlier solutions were in fact ‘matched’ to a specific Contradiction type for the sake of this study.

Ideally, it would be beneficial to apply the TRIZ methodologies on a regular basis for the user to become fully proficient. However, due to the nature of the business the user may only feel the necessity to use the tool occasionally.

Nevertheless, TRIZ does provide some very useful tools to help focus on the problems at hand and arrive at solutions far quicker and easier than the more traditional methods such as brainstorming.

During the SRES case study, the Functional Analysis map was found to be extremely useful in providing a clear overview of the system whilst at the same time highlighting any problem areas from which to identify and solve any Contradictions via the matrix.

The ‘Standard Solutions’ method was found to be more tedious to use but offered a different perspective of looking at the problem.

Another tool, 'Thinking in Time and Space', was not demonstrated in this case study but it can also be a very useful tool for mapping out a problem in a time-versus-scale context.

It must be noted that nearly all the solutions generated had advantages and disadvantages; thus (in time) we could probably carry out further work using the TRIZ tools in order to reduce and eliminate the disadvantages.


Benefits of TRIZ

The main benefits that can be realised as a result of using TRIZ are:

  • Improves the initial definition of problems – thus allowing for better solutions.
  • The generation of creative, innovative solutions in a very efficient manner.
  • It reveals how product design and technologies will evolve in time.
  • TRIZ can be used to improve on current designs.
  • Help create a culture of innovative thinking – enhancing current practices.
  • Gives awareness of access to knowledge bases (i.e. patent databases).
  • Improves quality, reliability and safety (e.g. by getting it ‘right-first-time’).
  • Greater customer satisfaction.
  • Time saving.
  • Cost savings. 

Report prepared by:

Frank Gornall
BAE Systems

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