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Competence, Authority and how to get it wrong……

A version of this article first appeared in the October 2018 edition of our free newsletter, to subscribe click here

I would like to thank a trusted contact for asking me to review some paperwork as it provided a great teachable moment for myself and my class – and a good subject for the newsletter. I can’t mention them by name but you know who you are. Thanks.

As part of the course that I teach at UCCI we have just covered some engineering ‘disasters’. Events caused by insufficient understanding, inadequate assessment or generally bad engineering.

It is important for an engineer to understand that things do go wrong. Not often, but they do. Understanding the root cause of failure is the only way to consciously avoid the same situation.

Sometimes even the understanding and knowledge of what you should do cannot overcome the general sunny optimism that both bless and curse humans. The week that I was teaching this important element of engineering reality I was sent a perfect example of optimism overcoming common sense.

Over the years I have ended up with a large network of aircraft developers and operators. One of them called me because of a concern they had with an aircraft that was flown in to their facility to have some work done.

The small composite aircraft had a major change to one of the wing spars at the root (for those of you who are not in the know the spar is the element of the wing that carries the bending load created by the wing lift and the root of the spar – where it meets the fuselage- carries the highest bending load.)

This major modification (or repair, it was not clear what the reason for the change was) carried with it a one page qualification.

To put that in perspective, we are doing a small amount of work for a famous part 23 OEM – writing substantiation reports for equipment going into their flight test aircraft. The oxygen bottle installation report runs to 30 pages.

The one page qualification consisted of 3 paragraphs of prose and a diagram.

  • The first paragraph was a description of the level of competence of the author. He is a professor emeritus at a university, he has written textbooks, he is a lifetime member of an industry body (I never understood that, was he inducted as he passed out of the birth canal?). In his own words he is experienced, competent and respected by his peers.
  • The second paragraph was a verbal description of the change, it contained some vague terms but overall was ‘okay’ as far as it went.
  • There was a diagram of the change.
  • Then there came the all Important qualification: “I have done no analysis of this change but it is many times the strength of the original design. In my opinion this is adequate”. That was the start and the end of the substantive component of the qualification, and marked the end of the document apart from the signature of the author.

Even if it is your opinion that the change was adequate, you still do the analysis, even a simple one. You might even add some qualifications to your assessment. How about “assuming that good practice was followed with regard to material choice, material handling, surface preparation and curing during the implementation of change by the manufacturing team…….”.

There are several problems here:

  1. There is no numerical demonstration that the change is adequate and therefore there is no evidence that the aircraft is safe to fly
  2. The description of the change is inadequate, there is some geometric definition and some generic materials mentioned but nothing specific enough and it is incomplete.
  3. The engineer has used an argumentum ad verecundiam (an appeal to authority without evidence) in order to convince somebody else that the aircraft is safe to fly
  4. The engineer has exposed the occupants of the aircraft to unnecessary risk
  5. The language that the engineer has used demonstrates his own negligence and creates clear liability for the engineer.

Engineers have to be aware that not only are they responsible for the safety of others, but they also have a responsibility to give clear evidence that the appropriate level of safety has been achieved.

This is necessary to safeguard the public – even if the design appears to be strong enough, some level of analysis has to be done especially if the structure is one of the most critical components of the aircraft. The engineer has to be more than sure and has to prove to himself or herself (xerself?) that safety is proven.

It is also necessary to maintain your ethical standards as an engineer. Are you really that clever? Are you really that sure? Is your opinion so valuable that a quick calculation would somehow degrade your authority?

This is also necessary to achieve a level of personal protection against future claims of liability. You work hard for your money and your family. Do you really want to put all of that on the line because you can’t be bothered to spend an extra 15 minutes getting it right?

This was a particularly poor example and is similar in nature to the Hyatt Regency disaster of the mid 1980’s when over 100 people were killed because of a change in the design of a walkway that the engineer thought was strong enough and failed to do any analysis for.

The irony is, the engineering professor who wrote and signed the substantiation for the wing spar has probably used the Hyatt Regency incident as a subject in one of his classes.

It is also worth noting that on the sketchy substantiation of the wing spar, there was no checking signature. An engineer (or a good engineer) does not trust his own assessment without a second pair of qualified eyes to review, spot errors and validate the work.

Every step of the engineering has to be specific, accurate, comprehensive and clear. Failure to meet these minimum standards endangers people, your own well being and the well being of the organization you work for.

Do it right, do it once and get it checked.

Interview with Sam Bousfield, CEO of Samson Sky

A version of this article first appeared in the September 2018 edition of our free newsletter, to subscribe click here

At the end of August I spent a couple of hours with Sam Bousfield and Senior Engineer Dana Beebe at their Prineville hangar. We had a wide ranging technical conversation and I was impressed with the level of detail and attention to the engineering specifics of the technical challenge they are grappling with.

Sam was kind enough to agree to an interview.

Can you describe what makes the Samson sky different to other roadable aircraft of the past and the present?
The Switchblade was designed to answer the question: “What is the best layout for a driving/flying vehicle?”, rather than “How do you make a car fly?“. Answering that question is what I feel was the most important aspect of the design that sets us apart.

The second was our decision to have a design that was high performance in both modes, and not compromise on that premise. With the power to weight of a Corvette on the ground, and the ability to achieve 200 mph in flight with reasonable range, the Switchblade has a high performance pedigree. Okay, it looks pretty cool, too!

What was the moment when you knew you would go forward with this program?
When the marketing surveys came in, we realized that we had a potential winner. We found solid support at a price point where we could survive as a company, and that made the future bright for us.

In the process from concept to customer, what has been the greatest challenge you’ve faced?
Financing has been the biggest challenge by far. Technically there have been challenges, but they have been spotted and tackled mostly in advance. While we are gaining investment traction now, earlier it took some creative thinking and running a tight financial ship to survive and make progress.

Which aspects have been more difficult to deal with? The aircraft aspects or the automobile aspects?
There are probably more aircraft related engineering issues that we have dealt with than driving related issues. I think the level of performance in the air, and the added safety required of that, tend to make it more difficult than anything on the ground.

The truth about this question is that there are lots of ways to deal with individual aspects of flight or drive. But, to make solutions for one work out well for the other is a worthy goal, and one we have worked hard to achieve.

How have you reconciled the difference between catering for the driver and the pilot with a single control system?
With the wings located between the front and rear wheels under the belly of the vehicle, we knew the rear wheels would be too far aft to rotate as one would typically in a tri-gear.

That meant the front wheels could not be held up to bleed off airspeed on landing, and that the front wheel would drop almost immediately upon touchdown. So that told us that the front wheel would always have to be connected to the control wheel, and that the pilot would not have time to change from a flying control mechanism to a driving control mechanism at touchdown.

The aero engineers did not feel that having a front wheel ‘steering’ while in flight would be problematic other than increase tail efficiency requirement slightly. The change of front tire direction was not great in flight. We looked at joystick controls for driving and flying, as well as other less conventional means. The simplest, we felt, was to use a steering wheel/control wheel that could be used for either. People are used to driving with a wheel, and a wheel can be used for flight as well. Our control wheel is oblong rather than round, as we have certain control features built into it for flying that aren’t related to the ground and it was easier to accomplish this with an oblong control wheel. You can still hand-over-hand it for cornering or controlling a fishtail maneuver if needed on the ground.

What involvement has the FAA had and what was their reaction to the concept?
All of my contact with the FAA has been positive, and all I have heard is ‘How can we help?’.  I have many supporters in the FAA who would like to see us succeed.

Who would you like to thank and give a name check to?
Our lead engineer, Alexander Bondar, and his team have been very helpful. Composite Approach in Redmond, Oregon also has been very helpful in the carbon fiber realm. Kevin Risse of Risse Racing in Redmond has been awesome at delivering machined parts, as has ISCO of Bend, Oregon. Composite Universal Group of Warren, Oregon, has given us some really nice carbon parts. Willem Anemaat and the guys at DAR Corp for their aero design, plus Rob Bulaga at Trek Aerospace for the ducted fan design. We have a lot of really good consultants and suppliers that deserve mention, but I know you may be limited in space here.

How do I reserve my Samson sky?
A Switchblade can be reserved at the web site. Until we fly, reservations have no commitment and no finances required. After we fly, we will ask for a $2,000 deposit which will be mostly refundable (less $500 for administrative costs) until we are in production.

Once we are in production, we will ask that people make their deposit hard, so we know how many engines, transmissions, and propellers to make.

When will you start customer deliveries?
Samson will begin initial production within six months of first flight, but will be ramping up production for almost 22 months before we really get the production machine in high gear.

We have to have a building built, assembly line established, supply chain established, production molds made, and assembly jigs built. Not an overnight operation! We also figure that we will need to remain agile in our business, so are taking that into account in the equipment we choose, and the way we lay out our spaces. Technology changes very quickly, so it pays to maintain as much ability to change as possible, even in manufacturing.

Any final words?
At Samson, we feel that we can have a positive impact on transportation. Knowing that you are working towards a worthwhile goal, and can make money doing that, is a really exciting way to spend your time. I don’t think there are too many days that staff in our shop come to work thinking “gee, only two more days until Friday”. People here are pretty pumped up, as are our suppliers and consultants.

We are accomplishing something that has not been done before on Planet Earth, and everybody who helps is thanked for doing so. When we succeed, it will be because the group pushed hard to make it happen. I can point the way, but with the help of the whole team, we can actually make it happen. That will be our legacy, and I hope many people can benefit as a result and drive/fly their way into the future.

To find out more about Samson Sky:

Brexit, Big Fish and the UK Aircraft Industry

A version of this article first appeared in the July 2018 edition of our free newsletter, to subscribe click here
In the last couple of years there have been a number of new aircraft projects in the UK. I Have been involved with some of them and it has been interesting to see the progress and reactions.
The new startup companies complain that while there is public funding or other types of assistance available (innovation centers co funded by the larger corporations in the industry such as Rolls Royce Aero Engines and Airbus) there is a freezing out of startup companies in favor of internal projects within the two giants in the UK.

Of course you would expect this. Little Billy Startup has little to no political sway compared to the established players. So when it comes down to the final decision it does not matter how good your design or business plan is, you’re just not in with the in-crowd.

You can see this in the UK. Rolls Royce has come up with a VTOL urban mobility design concept. It looks like around 20 other VTOL design concepts and has the same likelihood of success.

Rolls Royce have never proposed an aircraft program before. They have not issued an aircraft concept. Why now? Why are they competing with a bunch of startups in a field with a low probability of eventual success?
Do they plan to be the first to market? Do they see themselves as the post brexit UK aerospace leader? Is this just a case of keeping up with everyone else? Or is it a route through to public money meant for innovative startups?

The public should be worried as traditionally the market monopoly position of companies is used as a boogeyman to justify blocking mergers and acquisitions. An equal problem, but one that is largely ignored is the monopoly over public money. The more new companies depend on public money to get off the ground and overcome the unavoidable statutory product and corporate costs the more critical this becomes.

Mergers and corporate consolidation create this problem, as public money that is meant to promote innovation and technical risk ends up covering the day to day expenses of inefficient industry giants.

One of the most egregious cases of this is Bombardier in Canada (although I am sure you all have your own favorite). No one is really sure how much public money that they have received at the federal and provincial level in the form of cash gifts, grants, loans and subsidies. But the ones that I have counted in recent years come to over $1bn per year. I am sure it is impossible to calculate the total amount but it is significantly over this number.

This keeps a lot of people employed – which is a good thing. But what is the opportunity cost?

For the same money you could give 1000 technology startups a grant of $1m each. Imagine the innovation you would be fostering if you did that? How many ‘Bombardiers’ could Canada create with that approach? Well, hopefully not ‘Bombardiers’ that need $1Bn per year just to get by – but you know what I mean
Right now Canada has one – and it is very expensive.

So the UK as a newly independent nation (Theresa May notwithstanding) has a choice to make with it’s public funds. It can follow the Canadian model, it can reward inefficiency and established corporations or it can actually help cover the downside risk of innovative start up companies.

From what I have seen from my contacts and clients in the UK, it looks like it is business as usual. Just the process of applying for funding from these pots of public money is so onerous that many companies do not even try.

A project run by a good friend of mine was all ready to get approval for a substantial government grant. They had got top marks from all of the adjudicators and had ticked every box. Two days before the formal announcement of the award they got a call that things weren’t actually so cut and dried and that they should not assume that the grant will be awarded.

Another project we are working with are looking at getting space in an innovation center funded by Government and large industry partners. But this is in doubt because they may be judged as competing with one of the giant industry partners involved in the funding.

In a society where taxes are high and success, in a large part, depends on getting some of those taxes back in the form of a government grant, the monopoly that we allow large companies over this process is just as negative as a monopoly over the market. Maybe more so, as the only way the market can be bought is by providing additional value to the actual customers. In order to monopolize government grants you just have to lean on your local or national politician – a much simpler and less expensive process.

So with the large players being a big fish in a much smaller post-brexit pond where does that leave the little fish?

Cayman Islands UAV Test Cell

A version of this article first appeared in the July 2018 edition of our free newsletter, to subscribe click here

We have been invited to participate in a working group in the Cayman Islands to examine using the airport at Cayman Brac as a unrestricted UAV test cell.

Over the last year, as we have had more involvement in UAV programs the need for a UAV test range with minimal restrictions has become more obvious and urgent. We have had reports of fees charged up to $10,000 per day and severe envelope limitations that make it impossible for developers to fully realize the potential of their products.

I am hoping we can get the policies and procedures in place over the next few months to make this a reality. If you are interested in bringing your UAV to the Cayman Islands let me know ( The more interest we generate the greater the enthusiasm will be from the island authorities and the quicker we can make this happen.

If you have a UAV to test why wouldn’t you test it in a tropical paradise, at a low price with next to no restrictions? Trust me – cocktails do actually taste better when you are sat on a white sand beach looking out over a turquoise ocean, palm fronds rustling gently in the breeze…….

Update: Initial discussions have begun with the Cayman Islands Civil Aviation Authority and in a few months we will be looking for industrial partners to join a consultation process to develop the standard operating procedures for UAV operators in the test cell.

Boeing and Embraer – The cost of doing business where you want to live

A version of this article first appeared in the July 2018 edition of our free newsletter, to subscribe click here

I was asked this question this month “Where would you certify an aircraft if you had a choice?”. My answer was instinctively “Brazil”.

We have done studies to determine what factors make aircraft programs successful. In order to do this you have to define your measure of success and then you have to go hunting for metrics that inform your method and reveal the truth.

We use project level profitability as a measure of success. I.e. does a project manage to payback all of the costs of development and all the ongoing costs of unit production – project break-even. Beyond break-even does the project generate a profit and how does that profit relate to the investment required to bring the product to market.

To the outsider this can all be dreadfully boring, but to those of us wrapped up in the industry it can reveal some intriguing insights why programs succeed or fail. This information then may then give us the knowledge to help significantly increase the chance of success of a program.

The success of a program affects thousands of people – everyone working on the program and all of their families. Supplier companies, their employees and their families. When a program gets it very wrong not only are the investors out of pocket but the lives of thousands of people can be negatively affected.

There is no malice in programs that fail, there is also usually no lack of technical competence but there is a lack of asking the right questions and recognizing the right answers

So – how does all this relate to the original question “Where would you certify an aircraft if you had a choice?”.

This is an example of a project asking exactly the right question.

We categorize risks into 3 categories – technological, certification and market. There are other risks, supply chain, liability, etc, but all of those can be managed. Technology, certification and the market are the areas of an aircraft program that can present intractable problems that may be impossible to solve.

Of these ‘Big Three’, certification and the market at the two risks outside of the companies direct control. By that, I mean that the company can choose a technological basis for their product and once chosen that technology will not stop working – the technology is going to work in the same manner that it worked when you selected and developed it. Physics is reliable.

The market is fickle. Designs and product features can fall in and out of fashion. Focus groups may not represent the wider market trends and the economy and the buying power of your potential customers is in constant flux.

Certification regulations are subject to change, they can become less onerous or more onerous. The people responsible for interpreting the regulations change, some are good and some are ‘less good’. This is out of the control of the company.

It is reasonable to say that a company has no control of the market or the economy. You just have to do your best, hedge your bets the best you can and appeal to the largest market possible.

What can the company do to influence and minimize the risks and costs of the certification process?

In our study we examined 25 ‘high end’ part 23 aircraft projects from the last 30 years. We found that when their development costs are normalized for inflation the yearly ‘burn rate’ in development and certification has a surprisingly small scatter.

There are some outliers – the Eclipse 500 program had an average yearly burn rate over 5 times the average burn rate and 4 times the standard deviation.

In 2018 US dollars the average yearly development and certification spending rate of these 25 programs was US$50M.

(when two outliers of the 25 projects examined are removed the average yearly spend drops to US$35M per year)

Ignoring outliers it is accurate to state that the yearly spend rate of a program does not affect the success of the program.

When you examine program duration the critical metric for success is clearer (although not universal).

The program duration for the 25 programs examined range from 4 to 16 years. Using the limited data I have quoted so far this reveals that the lower limit program cost in 2018 US Dollars is going to be around US$200M and the higher limit will be US$800M.

This factor 4 difference can be influenced by a number of factors – one of the factors that significantly influence program duration is certification. The program duration is also influenced by the certification interface and process management competence of the company. This specific competence of the company and the attitude of the certification authority can combine into a perfect storm of schedule extensions.

In a perfect world where the regulations are universal and harmonized across international boundaries it should not matter where you choose to certify your aircraft.

The world is not perfect and even within national borders there are large differences in how regional offices approach certification and this can significantly influence the success of a program.

Everyone has a comfort zone – including the staff at the FAA (and every other certification authority in the world). You create very high financial risk trying to certify a part 29 rotorcraft using a local ACO (Aircraft Certification Office) that has predominantly worked with fixed wing LSA aircraft.

When an FAA/EASA/CAA (fill in the blank…) employee is operating outside their personal/professional comfort zone are they more or less likely to make a finding of compliance for your project? You know the answer to that question.

From our study, based on our criteria and the assumptions we have made, there are four successful part 23 companies that produce high performance aircraft. Cessna, Cirrus, Embraer and Pilatus and for all of 25 projects reviewed only 4 were found to meet our criteria of success.

Note: We omitted some companies and projects from the study due to lack of data, among these omitted companies and projects were Beech and Diamond Aircraft.

These companies are successful because of a number of critical factors. They design and develop great aircraft and they work with their local certification representatives to minimize the duration of the certification program.

So within the US, for larger part 23 programs, considering only certification cost as a critical factor, you would select the Wichita or the Chicago ACO to work with.

Internationally you would consider Brazil or Switzerland.

As Embraer are the only company of all companies examined with two projects that display good success indices (the Phenom 100 and the Phenom 300), ignoring all other factors, Brazil would be our certification jurisdiction of choice.

Both of the Phenom jet projects took less than 3 years to complete, the shortest programs out of all the programs we studied. This is due to the high level of competence of the development program management and the relatively small additional burden imposed by local certification authority.

Most aircraft projects are located where the initial development team is located or where a region offers the most financial incentive to locate the manufacturing.

Our advice is to locate the organization in a jurisdiction where the certification authority has a track record of enabling a return on investment.

This brings us back around to the title of the article. Boeing and Embraer.

Boeing’s ‘partnership’ with Embraer may partly be one-upmanship on Airbus and Bombardier. It may be sensible consolidation and a way to protect the market share they have of the larger aircraft sizes. It may be to save on manufacturing cost by outsourcing to a supplier/partner with clearly demonstrated competence.

Or it just may be a path for Boeing to certify new aircraft programs through a different certification authority. A certification authority that have facilitated Embraers extraordinary growth while maintaining appropriate product safety levels.

What do you think? Will Boeing take the plunge and conduct a type certification program outside of the US?

On a related note. Many of the new Aerial Urban Mobility projects are based in California. The Los Angeles ACO do not have favorable history of assisting and supporting companies certify new types of civil aircraft. We would advise all of these projects to seek new locations and plan on working with FAA ACOs that will maximise their chance of success by minimizing program duration and therefore program cost.

Current View (June 2018) of the General Aviation Market

A version of this article first appeared in the June 2018 edition of our free newsletter, to subscribe click here

This month I have been doing some work on the manned aerospace market. For those of us with an involvement in the market it is interesting to go through the numbers. There is good data available on the North American market from GAMA and the FAA as well as other online sources.

The North American Market is not predicted to experience dramatic growth over the next two decades, however there will be significant end of life replacement in the existing private and commercial aircraft fleet.

In commercial aviation the North American (N.A.) commercial aircraft expenditure is expected to grow at a CAGR of 0.6%, the Asia Pacific region commercial aircraft expenditure is expected to grow at a CAGR of 6.6% – 11 times greater than N. A., Latin America and the Caribbean a CAGR of 7.3% – 12 times greater than N.A

Global MRO Expenditure Growth 2015-2025 (Doan, 2015)

The values are indicative of the overall growth of the economies.

2016 World Economic Growth (FAA-2017, 2017)

It is reasonable to assume that the general aviation sectors will grow in line with both the general economic growth and the growth in MRO aircraft expenditure.

Comparison of Other Countries to the United States

Registered GA Aircraft per Million Population, source data from (Hu, 2015)

General aircraft ownership per population is very high in the traditional developed economies. This is the result of multiple factors: Wealth, Culture, Level of Education, Available Infrastructure, Regulations. It is reasonable to assume that over time the level of general aviation aircraft ownership in developing nations will significantly increase.

Some individual countries/regions are examined below:


In India between 1990 and 2015 the number of business aircraft grew from 41 to 487, a tenfold increase. Of this growth 245 aircraft were helicopters and 100 aircraft were turbo props.  (Martin Consulting, 2016). In the same report several growth rates for the India business aviation market are given, the median case is 7% CAGR. This results in an additional 857 aircraft predicted to join the business aviation fleet in India by 2025


In 2016 China had 2185 registered general aviation aircraft, by 2020 China plans to have 5000 registered general aviation aircraft. (Brent & Yuan, 2017).

Fixed Wing Market

Historical Data

General Aviation Sales Figures 1995 to 2017 (GAMA-2017, 2017)

The Piston Aircraft and LSA Fixed Wing Market

It should be noted that the market for piston aircraft was significantly attenuated in the financial crisis of 2008 and the number of aircraft shipped has not recovered to pre 2008 numbers. However the US$ billing amount in the piston aircraft segment has recovered to 76% of the total billing amount.

Piston Aircraft Billings US$ 1994-2017 (GAMA-2017, 2017)

It should be noted that the average unit price for a piston engine aircraft has been rising at a near constant rate of $20,000 per year over the range of the available data – from around $250,000 per unit to $650,000 per unit between 1994 and 2017.

To take some individual data points, 2 US ‘recently’ (within the last 20 years) certified 4 seat piston aircraft:

Cirrus SR22 certified in 2000, initial price $276,600, Current price: $540,000

Based on the US Bureau of Labor Statistics the cumulative rate of inflation between 2001 and 2018 would result in a price increase from $276,600 to $395,780.

The price of a basic Cirrus SR22 has increased by $144,000 over the rate of inflation

Diamond DA40 certified in 2000, initial price $179,900, Current price: $459,800

Based on the US Bureau of Labor Statistics the cumulative rate of inflation between 2001 and 2018 would result in a price increase from $179,900 to $254,507.

The price of a basic Diamond DA40 has increased by $200,000 over the rate of inflation.

There are many reasons for the relatively large increase in real price of new general aviation aircraft over time:

  1.       The original price of the aircraft was underestimated and the initial production run for the original orders was done at little to negative profit. After the original orders were fulfilled the price was increased to create or increase profitability.
  2.       There was an increase in the cost of doing business (raw materials, labor, regulations) over and above the rate of inflation.
  3.       There was a large reduction in volume of sales and a price increase was necessary to cope with the loss of ‘economies of scale’, however the rate of price increase has remained relatively constant through the large reduction in market size in 2008.

Piston Aircraft Average Unit Price 1994-2017

Conclusion on the Piston Aircraft Market

  • The large used aircraft market, combined with higher prices for new aircraft, is largely responsible for the reduction in new piston aircraft sales.
  • The increase in the price of new piston aircraft is partially responsible for the interest in used aircraft.
  • To compete in the piston aircraft market the aircraft manufacturer must present a value proposition to the purchaser better than the current aircraft in the market.

The Turbo-Prop Aircraft General Aviation Fixed Wing Market

In contrast to the piston engine market the general aviation turboprop market was minimally affected by the 2008 financial crisis.

Turboprop Billings 1994-2017 (GAMA-2017, 2017)

And the overall billing value for the Turboprop market shows gradual ‘table’ growth over the period for which data exists.

The turboprop unit price shows a slight downward trend over time. The unit price is still between US$2,500,000 and US$3,000,000.

Turboprop Aircraft Average Unit Price 1994-2017 (GAMA-2017, 2017)

In comparison to the piston aircraft market, steady growth over time with a small downward trend in unit price is to be expected in a utilitarian product based on mature technology. It also shows that the original (pre 2008) pricing for turboprop aircraft was likely more realistic compared to piston aircraft.

Projected Data

The FAA predicts a reduction in the US general aviation fleet size. This does not mean that there is not a growing market for new aircraft. The average age of the general aviation fleet in the US is 46 years for single engine piston aircraft and 43 years for twin engine piston aircraft, for turboprop aircraft it is 28 years (GAMA-2017, 2017). Over the next 20 years a significant proportion of these aircraft will have to be replaced.

General Aviation Fleet Size Prediction 2007-2037 (FAA-2017, 2017)

Note that the value of the Light Sport Aviation (LSA) segment is projected to grow over the next 20 years as is the fixed wing turbine and rotorcraft segments.

From the available data the North American general aviation market appears to be saturated and sales are mostly from fleet replacement. In contrast the rest of the world (excluding Europe and Australia) are likely to experience a growth in general aviation at least in line with their predicted economic growth – and that could be very good news.

A Risk Review of Aerial Urban Mobility Vehicle Concepts

We have developed a tool for risk analysis for Aerial Urban Mobility Concepts and have ranked the Top 5 design concepts using this unique risk analysis method.

The spreadsheet tool and white paper are made freely available from our website here.

This is an extract from the white paper:

At the start of any technological or market revolution, there is an evolutionary explosion of ideas and concepts. This can be conceptualized similarly to the Cambrian Explosion of 541 million years ago. Over time the many genetic variations are naturally selected until only the variations that naturally suit their environment or are able to adapt to their environment survive.

This effect can be observed to a lesser or greater extent when any technological breakthrough is developed in a relatively free market.

Phase 1: Many organizations will evolve many different designs which will be tested in the market and regulatory environments. Over time different archetypes made by several manufacturers will survive the natural selection process.

Phase 2: In the long term, these organizations will grow their market share, reduce in number through consolidation and will stabilize as two or more large organizations.

These two phases can be characterized as ‘Conceptual Cull’ and ‘Corporate Consolidation’. This white paper is concerned with the ‘Conceptual Cull’ phase. This paper is not entirely scientific in nature. Where possible empirical assessments are made. These assessments are combined with the informed experience of the author and the reviewers in order to draw rational conclusions.

Technical Feasibility:

This white paper is not intended to be a criticism of any single concept or any single company. This paper is not concerned with technical feasibility and for the purpose of this study, it is assumed that all of the designs reviewed are technically feasible. 

Stratos Wing Test

This article first appeared in the December 2017 edition of our free newsletter, to subscribe click here


In December I flew to Redmond Oregon to spend some quality time with the Stratos Aircraft project. Nirav Shukla and I have worked on the production version of the wing for the Stratos 714 jet and the wing test article has been constructed over the last few months.

I can’t give specific figures but we reduced the weight of the wing by several hundred pounds compared to the prototype aircraft wing. This was, in part, relatively easy because there is never enough time in a prototype program to get the structure to the target weight – so there was some low hanging fruit. However, we were happy with the result and the test went very well and we are comfortable with the strength of the structure and Stratos is happy with the weight. All good!

Between the prototype and the production design, we upgraded the FE model of the wing – and the whole aircraft.

In the finite element model of the prototype, we modeled all of the cored composites with single laminate element cards. This creates large offsets relative to the element size:

Laminate elements can become unreliable as the offset approaches the element size, especially so for asymmetric layups.

We changed the finite element mesh to the following configuration:

The core is modeled with solid elements and the laminate elements have a much smaller offset relative to their element size. This means that we could increase the mesh density without compromising the veracity of the solution.

We could also model features such as core chamfers more accurately.

Wing Upper skin showing laminate Element Thicknesses


View on the underside of the upper skin showing modeled Core Features


Because of the increase in mesh density we have a greater trust in the buckling solution from the finite element model so we could move away from hand buckling checks that we knew to be very conservative to using the finite element solution for buckling.

In using the large assembly and global FE model for buckling we saw buckling results that we knew were likely to be ‘non-real’. These were compression buckling modes that were centered on the node at the bottom of the core chamfer and were very local to that region of the panel.


Typical compression buckle at core ramp down

We still made sure that these modes occurred above 150% of limit load. We were happy with a zero margin of safety for these buckling loads as we did not expect to see them on test and we did not see any sign of them on test.

If you have any experience of this behavior from this type of modeling we would love to hear from you to compare notes.

The wing attachment bracket regions were sized using typical hand methods available in our technical library.

Yours truly in front of the wing mounted in the test rig just before the test was done

The test went very well. Dieter Kohler was on hand to conduct the test. It is much better to have an independent expert conduct the test. As it is ‘our wing’ if I were conducting the test we would have stopped at every noise coming out of the wing box. Dieter ran the test up to limit and then from zero to limit and finally ultimate briskly, largely ignoring the few noises that came out of the wing box.

On post-test inspection the integrity of the wing box was not compromised. There were some minor hairline adhesive cracks at a couple of locations. These cracks may have been present before the test – the scrutiny that an assembly is subjected to post-test is much higher than the inspection before the test and the cracks were so small that they may be been missed by the pre-test inspection.

In the end, it should have come as no surprise that the wing passed the test – we are using strain limits that give very high residual strength for the undamaged structure.

After a series of other tests (static loading of the MLG in the wing, testing of the flap on the wing, internal pressure testing) we will be able to play with the wing – induce some damage and find out what the true residual strength of the wing is by testing to destruction. The fun stuff!

Note: the test documented in this article and the planned series of tests are internal company development tests and will not be used for certification of the aircraft.

Thanks to Stratos Aircraft for first of all including us in the development team for their fantastic aircraft and for allowing us to publish this article.

It’s all about the Money – Part 2

This article first appeared in the November 2017 edition of our free newsletter, to subscribe click here


In the last few years there has been a proliferation of unique electric vehicles and flying cars. Blue sky thinking and disruptive technology are the order of the day and I can see that there will be a number of disappointed investors ahead.

I talk to some of these projects and one I spoke to a few months ago told me something revealing. One of the principals on the project told me “It is too early in the program to start to talk to ‘aircraft’ people”.

Hmmmm – that might be a good attitude if you were not engaged in an aircraft development program. I have devised a series of assessments to judge what the likely chance of success of one of these ‘blue sky’ projects is.

  1. On the ‘About us’ part of a project’s website does the featured key team members include a CTO, a VP Engineering or a chief engineer? If a project dedicated to air vehicle engineering development does not include an engineer in the top echelons of their project they are likely not to succeed. With the best will in the world visionary leaders, CFOs and marketing experts are likely to go off the rails if left unchecked in an ivory tower at the head of a project.
  2. How many engines/rotors does the aircraft have? No civil aircraft has been certified with more than four engines (to my knowledge). No hovering civil rotorcraft has been certified with more than one lift rotor. In the wild, west of the new part 23 regulatory environment, the FAA will likely exercise more caution – as everybody generally does when faced with greater uncertainty. Trying to certify an exotic aircraft is likely to be made more difficult than it would have been in the old regulatory environment.
  3. Is the aircraft electric or liquid fuel powered? It is worth noting that no electric vehicle has been certified under part 23. I don’t think this is because electric aircraft are inherently less certifiable – there are advantages regarding reliability and maintenance. The drawback is that the energy density of batteries is just not comparable to oil derivatives.

If we do some simple math. We can rate the endurance of a powerplant and fuel system by the energy density of the fuel x the efficiency of the engine.

A gasoline powered piston engine:
The energy density of Kerosene = 42.8MJ/Kg, a good piston engine efficiency = 30% or 0.30.

The Abbott Aerospace power plant success index for a piston engine = 0.30 x 42.8 = 12.84

A gasoline powered turbine engine:
The energy density of Kerosene (as before) = 42.8MJ/Kg, a good turbine engine efficiency = 45% or 0.45.

The Abbott Aerospace power plant success index for a turbine engine = 0.45 x 42.8 = 19.26

A battery powered electric motor:
The energy density of rechargeable lithium metal batteries (in development, about twice the current Tesla battery energy density) = 1.8MJ/Kg, a good electric motor efficiency = 90% or 0.9.

The Abbott Aerospace power plant success index for an electric power system = 0.9 x 1.8 = 1.62

To summarize:

(Abbott Aerospace Power Plant Success Index)
Piston engine 12.84
Turbine engine 19.26
Electric motor 1.62

It is worth noting that as you burn liquid fuel the aircraft gets lighter and more efficient, a battery weighs the same whether it is charged or empty. This effect has not been quantified in this mini-study.

When an electric aircraft is certified will there be a market for it considering the endurance of the aircraft is likely to be an order of magnitude less than a traditional alternative?

I love electric power systems – they are safe, very cheap to maintain, quiet and efficient. Even the performance projection for the next generation of batteries still put them an order of magnitude out.

References and Sources

To get back to the original point. One of these 3 points is enough to constitute a high program risk factor. If a single program has all of these characteristics my assessment is that the likelihood of failure is so close to certain that it can be regarded as certain.

…..and by failure, I mean failure to repay the financial investment in the project. It is not a success to get through certification and realize that you are selling every aircraft at a loss and the market is a fraction of what was projected at the start of the program.

Investors are free to make whatever assessments they make and invest in whatever they choose. My concern is that the extent of private equity investments in very high-risk programs is causing a lack of investment in credible programs which have a greater chance of commercial success. The failure of the programs that do receive investment is likely to hurt the credible aerospace startups as the entire sector will get a bad reputation.

Marketing mockups and GCI animations of people getting into exotic looking vehicles in their driveways and being whisked off to futuristic commercial complexes to make important decisions are just figments of someone’s imagination.

You still have to deal with the laws of physics and governmental statute, regulation and policy and they do not care what you or anyone else think the future should look like.

I hope that investors start to rub the pixie dust from their eyes and observe proper due diligence and risk assessment exercises.

I know of many part 23 programs that are credible and low risk but cannot get funded, in part because of the rush to take part in the next ‘revolution’. I only hope the investment community start to take a more rational view of the risks and benefits of the projects they have to choose from.