Grob SPn – Plastic Fantastic! Aerospace cutaways – it's what I do.

https://thecutawaycompany.com

After several hours of travelling by air, train and taxi, deeper and deeper into the Bavarian countryside, I found myself standing alone in the fog. It was the winter of 2007 and while I instantly felt comfortable in my location (it was an airfield after all), I have to admit that as I watched the taxi disappear from view, leaving me in absolute silence, I was increasingly concerned by the thought that I had somehow made a mistake with my travel plans and was in fact on the wrong side of Germany, miles from any form of transportation. I surveyed my frosty surroundings for a moment before walking towards the warm glow of a small gatehouse, where my fears were laid to rest thanks to an old sun-bleached photo of a Grob trainer hanging on the wall behind the receptionist. 

Within the hour I was in sitting in a toasty engineering department, drinking fresh coffee and totally immersed in a technical briefing on the Grob’s new SPn, which to the uninitiated looked conventional enough, but this was not your run-of-the-mill twin-engined business jet. The aesthetically pleasing SPn was a very interesting aircraft indeed with some unusual features, not least of which was it’s rough field capabilities. And, if the concept of building what was in effect a flying pick-up truck or SUV with wings was not unique enough, Grob had built the whole airframe with composites materials. 

Having worked with most of the "big" manufacturers, I have to say that it was a pleasure to spend the week working with such a small and dedicated design team, who possessed a wealth of aerospace and composite experience that belied their rural location. What probably amazed me most about the company, other than its quite production line (no rivet guns!) was the speed that components and complete aircraft could be design and prototyped, thanks to the nature of the cold lay-up composite structure.

While these materials and construction processes were extremely interesting due to their simplistic and integral nature, it was these very attributes that threatened to render my SPn cutaway very empty indeed! Faced with a wholly monocoque fuselage I was forced to totally rethink how to depict such large amounts of composite structures. While the inclusion of typical "Tupperware" skin sections or honeycomb floor panels could make an airliner more interesting by adding colours and textures to its aluminium airframe, such additions typically populated an already full or dense cutaway due to the nature of aluminium structures. This would not be the case with the SPn, as the majority of the fuselage was devoid of internal structure, other than the composite forward and aft pressure bulkheads. What’s more, the fuselage which was comprised of brown composite fabric and honeycomb filling (no confectionary pun intended!) possessed the perfect ingredients to produce a chocolate egg coloured cutaway, straight from Willy Wonka’s drawing board!!

Back in my office I had to work out how to balance the whole project and after much deliberation and numerous test illustrations, my solution was somewhat retrospective in nature. I determined that in order to make the cutaway work, I had to eliminate all attempts to section or cut through the skin panels, as I would normally illustrate an aluminium airframe and approach it as an old fashioned "ghosted" or "glass-airplane” style cutaway. This decision was followed by a very steep learning curve on the colour, depth, orientation and scale of textures. Once again, much experimentation and numerous test prints followed, as it became rapidly obvious that what appeared “perfect” on screen would simply fill-in or moiré when finally printed, even at high-resolution. 

The main issue with such textures is one of scale. Had I shown an accurate composite fabric at a size relative to the airframe, the cutaway would have ended up as a dark, blotchy mess. Conversely, if I showed the composite fabric at a larger and reproducible scale, it looked wrong! In the end I chose to show a composite style texture on the inner fuselage skin faces, which looked correct in scale and also reproduced in print. A complimentary flat colour was also used on equipment shelves and wing ribs, etc., to differentiate between assemblies and add depth. Interestingly, I revisited this same texture issue when I worked on the Boeing (Insitu) ScanEagle UAV cutaway in 2009. On that cutaway though it made perfect sense to show an accurate full-sized composite fabric sample due to the small scale of the vehicle – horses for course.

The SPn cutaway was published in May 2008 and well received by Grob, who invited me to do several signing events at trade airshows through the year. Unfortunately the program was short lived and terminated later in 2008 due to the economic downturn and the subsequent insolvency of Grob Aerospace. Interestingly, Pilatus have subsequently re-identified the flying pick-up sector with their stunning and robust PC-24, which is crying out for a cutaway…. 

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