Society of Allied Weight Engineers

Certified.  I am a Certified Mass Properties Engineer.  I have taken the test and I passed.

Why?  After all, I am retired, nearly a septuagenarian, unlikely to be employed again, particularly as a mass properties engineer.  Right now, you can count the number of Certified Mass Properties Engineers on the fingers of one hand.  We few are the vanguard, the first of many to come.  We set the example, and that example will bring an understanding by both those certified and those who desire informed mass properties engineers that there is a basic knowledge required to be an effective mass properties engineer.

My professional journey began in the 1970’s, a time of stagflation, disco and polyester, and general malaise.  I had a technical degree (Physics) and a desire to be in aerospace.  I interviewed at several companies in Wichita, got multiple offers, and chose a company that offered subsidized flight training, as I always wanted to fly.  I started in the Weight Control group, and began calculating weight, CG, and MOI of parts, which then got integrated into a database that modeled a new aircraft.  Mathematically, the work was interesting.  As I showed ability, I was given more complicated tasks, including running plots of CG vs fuel burn, landing gear kinematics, and control surface mass properties.  I was also taking flying lessons.

My instructor, Jim, was a big man, pushing 300 pounds.  When he sat in the plane, he took all of his seat and part of mine.  Calculations showed that with full fuel, the aircraft we flew was overweight.  Nevertheless, up we went on flight after flight.  Then came the big day, my first solo, three times around the pattern, three take-offs, three landings.  Jim got out, I taxied to the end of the runway, pushed the throttle in, and I was suddenly in control of something unfamiliar.  Acceleration was, well – not brisk, but peppier than I was used to.  Climbing out, I saw climb rates much higher than I’d seen in all the times I’d flown this plane, reaching pattern altitude before reaching downwind.  And the descent to landing was shallower, to the point that I landed much farther down the runway than I had intended.  The next two circuits were similar, except I anticipated the descent rate better.

It was a revelation – what I was doing for my job was not some mathematical exercise – there were real-world consequences tied to mass properties.  I began paying attention to physical objects, subconsciously calibrating the mass properties of my world.  Length times width times height times density equals weight.  Where’s the CG of that car, vertically and front to back?  What does it weigh?  Conversely, I started the long process of seeing how a design evolves, how the different pieces fit together and what drives design decisions.  For example, the horizontal tail of an aircraft in level flight provides a downforce sufficient to equal the moment that the CG has driving the nose down about the center of lift.  How much structure is required so that this downforce tilts the aircraft without bending it?  That, plus margins drive the weight of that structure.  Over time, that became wondering how to minimize the weight without compromising some other aspect.

I changed companies and went to work in the space world – rockets and spacecraft.  Now there was another aspect added – POI.  The three-dimensional placement of individual components became important.  I learned to visualize the consequences of component placement on axis misalignment.  My second spinning spacecraft drove me to improve on the process I’d been taught.  That process utilized a program that required multiple computer runs to adjust positions, check the resulting POI’s, calculate the misalignments which then could be compared to the requirement.  I created a spreadsheet that combined all the calculations and would instantly give me the result from any change.  This had two unexpected consequences.  One, since it was fairly early in the proposal phase, I was free to experiment with component placement.  My first run of the spreadsheet, with the parts where the designers had placed them was well outside the pointing requirement.  I visualized what I was seeing spinning about and realized that if I moved a couple of components that the majority of the misalignment would go away.  I presented this concept to the team, and the chief scientist came up to me and said this solved one of his most perplexing problems.  With this as the new baseline, then it became a matter of small adjustments of other components to meet the pointing requirement.  Then came the second surprise – when we turned the proposal in to the customer, the customer was so impressed with my automated solution they requested it be given to them.

I continued my career.  People I’d worked with on one program I ran across on other programs.  I had one program director tell me “The aerospace community is small.  You can move around and meet almost everyone, or you can stay at one company and they’ll come by and meet you.”  I stayed at one company, and quite a few of those I’d worked with became leads, managers, people in high places.  And they knew me and asked for me when there were tough mass properties problems.  And this was because I had the knowledge and experience, and the people in charge knew that I had the knowledge and experience.

Today, things are different in one key aspect – there is much more turmoil in the workplace.  Fewer and fewer mass properties engineers spend their career at one company.  Those that have done so are nearing retirement or have retired.  Today’s mass properties engineer probably don’t have the luxury of long association with people in high places that have first-hand knowledge of a mass properties engineer’s experience.  Nor do they have a way to determine if their engineers actually have the knowledge to do their job.

That is until now.  The SAWE has instituted a Certified Mass Properties Engineer program.  The first few adventurous engineers have successfully passed the certification exam.  The exam itself tests an applicant’s knowledge and understanding of mass properties.  Now we have a means to objectively show management and customers that an engineer has the required knowledge to perform in a mass properties role.  This should bring confidence to customers, employers, and employees alike, that engineers know what they are doing.

Right now there is no requirement that a mass properties engineer be certified, no requirement from a customer that a company’s engineering staff include certified engineers.  But that could and should change as more engineers get certified, and the supervisors, employers and customers gain confidence in knowing that there is a standard to which their engineers strive to meet.

Circling back to the beginning – why should anyone get certified?  Two reasons immediately spring to mind, depending on where you are in your career.  If you are new or relatively new, certification will bolster your confidence and bolster your employers’ confidence in you.  And that bodes well for you career.  If you are an experienced engineer, certification also bolsters your confidence and your employer’s confidence, but it also places you on the path to mentorship.  Mentoring others not only helps the mentee, but also boosts the mentor both mentally and within the eyes of your employer.  And for someone like me, past the employment stage, it is that certification institutionalizes the mentoring relationships that I may have.

Picture this scenario – an internal or external customer contacts a team, possibly through a Request for Proposal (RFP) or as an exercise. The customer knows that your team makes a certain product, and the customer desires to have a similar product. However, the original product is either too big or too small for the desired application. What generally happens?

A small team of engineers, along with a support team of management, financial, and business experts, convenes to define a solution that meets the customer’s desires. Since a similar product already exists, that product becomes a starting point for engineering, cost, and schedule studies. Usually, the preferred outcome is a product like the existing one but with more – more range, more seats, or more payload capacity. Occasionally the preference is for less – less range, less payload, or more likely, smaller external dimensions. The first course of action the team comes to is to take the current product and scale it to fit the new product’s specifications.

The problem then becomes how to do the scaling in a credible manner. I first realized this phenomenon when I was 6 years old, sitting in the rear seat of a four-passenger Piper Comanche. We had stopped overnight in Little Rock, Arkansas, and were sitting on the ramp with the engine idling when a North American P51D Mustang went by on a taxiway. I stared at the Mustang, my mind boggled by its sheer size. Up until that time, I had seen pictures of the legendary World War II fighter, and even had a model of one. But in my six-year old mind, I had made a basic scaling error – I took what I knew, the size of a four place single engine aircraft, and had scaled down that size for my internal picture of how big a Mustang ought to be, for it only had one seat, not four. And so, looking out the window from my vantage of a four place aircraft, and watching this behemoth roll by, caused a definite case of cognitive dissonance.

I had let one parameter guide my understanding of how big a Mustang is. A more thorough investigation would have uncovered some more pertinent parameters, such as engine horsepower (Mustang: 1490, Comanche: 250, or about 6 times the power), cruise speed (435 mph vs 180), and max gross weight (12,100 pounds vs 2900). Then I might have realized my mistake and understood that the Mustang was 50% longer and twice as tall as the Comanche, even with a similar wingspan.

Therein lies the fallacy of scaling – the scaling parameters must be categorized and prioritized, and for that you need knowledgeable experts. These are people who understand the interactions of different parameters, which ones to deprecate, and the ones that should dominate. And most importantly, what parameters really matter. If you are taking a four place aircraft and turning it into a six-place aircraft, there are lots of changes besides adding two seats. Most likely the fuselage length grows, and this upsets the balance of where the center of lift is for multiple reasons. Not only are you adding aluminum (or additional composites), but cable lengths (both electrical and mechanical) change. The outer mold line of the fuselage necessarily changes, the question becomes whether a “plug” is installed or the whole fuselage changes. These decisions have aerodynamic consequences. Think of the difference between the Beechcraft Debonair straight-tail Bonanza (four seats) and Bonanza 36 series (six seats) vs the Grumman American AA1 (two seats) and AA5 series aircraft (four seats). Both initial aircraft added two seats. The Bonanza took the route of blending the fuselage across the new length whereas the AA1 vs AA5 has a constant-width plug. Consequently, the AA5 has control problems in certain flight regimes, where the slab sides result in aerodynamic blanking of one or more tail surfaces. The Beechcraft solution was undoubtedly more expensive, but the 36 series of Bonanzas has endured in the marketplace whereas the AA series is a footnote.

So, what can you as a mass properties engineer do when faced with this very familiar scenario? We are in an irreplaceable position on any program because mass properties engineers have visibility across the breadth of a program. Use that to your advantage. Put on your systems engineering hat and look at how the various parts of your total system come together and how they interact. This is where mass properties engineers shine. We are among the few who have insight into every aspect of the product from where components are placed to how these components operate. And, because mass properties engineers have this insight, we are able to influence design and design changes, including functional and aesthetic aspects of a proposed design. Unlike most other engineering disciplines, we are not “pigeon-holed” into affecting one of a design’s parameters. We can interplay multiple factors and guide the program’s management towards arriving at a better solution than one by multiple engineers, each looking only at a subset of the available options. This is the true Unique Selling Point of Mass Properties Engineering, one that has immense value to a company employing mass properties engineers and it is one of the major reasons engineers choose to stay in mass properties.

Finally, what is the SAWE’s role in enabling an individual mass properties engineer to perform this powerful position? Look no further than the SAWE’s Mission Statement: The Society of Allied Weight Engineers is an international, professional, nonprofit organization dedicated to the promotion, practice, and innovation of the field of mass properties engineering. The SAWE executes its mission via a variety of initiatives encompassing peer reviewed papers, conferences, industry leading training, mentoring by experienced mass properties engineers, and establishing industry specific Standards and Practices. The SAWE has enabled countless mass properties engineers to better serve their companies through all the above methods of knowledge transfer, in the process creating the next generation of mass properties experts. Tying this all together, the engineers who become tomorrow’s experts will lead the innovations that power tomorrow’s products.