As some of you may know by now, one of my focus areas is program cost – especially on composite aircraft programs. We see many programs and while many aspects and details are project specific, there are some universal rules. This is one – this is my wording but I am sure that the sentiment has been expressed before, mainly because it is bloody obvious:
Effective cost control includes all aspects of development and manufacture and all systems employed within the organization.
These costs are incontrovertibly affected by choices made early in the program. If the wrong choices are made early in the program, control over the cost of the program is lost. This may not be realized for months or years later.
A common issue is the rush to develop hard tooling early in the development cycle. It is attractive to look at the amortization of high-quality hard tooling over a hundred or more airframes. That advantage, on paper, makes the use of soft tooling for the first few aircraft, look unattractive. Choosing ‘hard’ tooling when you are prototyping is a decision that is often regretted.
You lock in critical OML and configuration features early in the design cycle. Unless you are very lucky these will change. You are then faced with a choice – do we potentially scrap millions of dollars worth of tooling or live with the sub-optimal design that was locked in too early?
We have seen amazing results with soft tooling and MDF fixturing. If I could give names and details I would. We have seen very tight surface tolerances, sub-assy and aircraft tolerances held with seemingly low quality and very cost effective tooling. This tooling is not suitable for volume production, but for the first few aircraft, those tools give sterling service – and they grant you the flexibility to make changes and when prototyping changes are inevitable.
Material choice is another area where seemingly good decisions can be financially ruinous. The cost of the material ends up being the least important factor. The factors, (assuming that strength and durability requirements have been met) with the greatest effect on the overall development and manufacturing cost are:
Type of composite materials
As much as wet laminate and infusion offer flexibility and (on paper) cheaper materials, passing responsibility for resin quality and control over resin content to a reputable pre-preg supplier provides a relief to your in-house quality systems that is hard to quantify – but it is significant. Wet laminate can work for low-performance aircraft and infusion, when targeted at specific applications, does bring some benefits. Boring old pre-preg is still the best overall choice for almost any aircraft product.
The Quality of the material is paramount. Pick your suppliers based on recommendations from multiple sources. Make sure that they have a good reputation in rectifying quality problems. If the material fails your incoming inspection or testing, will they replace or refund? Check the data that the material supplier provides. We have found that some suppliers use inflated strength and stiffness marketing values to get you to make a commitment, only to find out later that the real data is significantly lower than you had planned. If the supplier provides official AGATE or NCAMP data then rejoice (but it has to be NIAR published). These are the gold standards for consistent comparative data that you can rely on.
Does the material you have chosen (whether pre-preg, dry cloth, resin or adhesive) have a similar alternative material that can be swapped with zero or minimal effect on your in-house processes, tooling, design, and certification? The ply thickness of a product (dry cloth or pre-preg) ends up being the single most important factor in sourcing an alternative or substitute material. A small difference in ply thickness can have a disproportionate effect on bending stiffness, buckling performance, bond gaps, and tooling.
Using a unique new material could be a great idea – but…….
- You increase the risk of discovering a new negative strength, durability or processing aspect.
- The existing skilled workforce will require some retraining and time to become familiar with the key working characteristics of the new material.
- Finding manufacturing subcontractors to help you cope with manufacturing pinch points in your program is more difficult or impossible.
- The certification authority will require an expansion of your compliance activities. Compliance cost is the single greatest schedule and financial burden a development program will face. Management of compliance risk is potentially the single most important component of an aircraft development program.
There are other factors that should be considered – shelf life, processability, toxicology, sensitivity to the environment and finally material cost.
The raw material cost of composites is such a small component that it is swamped by the other more critical risk factors.
The lower performance your aircraft is, the lower your selling price will be, the lower your overall materials cost will have to be.
Risk is cost. Least risk is least cost. Converting the previous statement:
Effective risk control includes all aspects of development and manufacture and all systems employed within the organization.
Every engineering decision you make should consider the headline cost figure, but every strategic decision that you have input into should give risk a much greater weighting than the headline cost. Failure to acknowledge this critical aspect of aircraft product development is all but guaranteed to be the cause of your eventual failure.
And on that happy note……
This article first appeared in the May 2017 edition of our free newsletter, to subscribe click here