Four years ago, a visit to Grob Aerospace's factory and airstrip in the Bavarian village of Tussenhausen-Mattsies, one hour's drive west from Munich, would have been quick and relatively uneventful. The company - an offshoot from the Grob industrial machinery group - had made its name developing composite gliders and light trainer aircraft for the military market in the 1970s and 1980s, but was facing a post-Cold War collapse in orders and indifference towards its efforts to break into new markets with its composite technology. A backlog of 175 G115 motorgliders in 2003 had shrunk to just six half a year later, and the workforce to 50 people.

But in a corner of the factory and with scarcely anyone in the aviation world being aware, a prototype was being quietly developed that the company believed could transform its fortunes.

Composite First

That was the SPn - a six- to eight-seat, medium-range "utility" twinjet unveiled at the Paris air show in 2005 and the first business jet to be built entirely of composite material. For a new name in the sector, the $7.7 million aircraft has done well, notching up around 80 orders - half of them in North America where the Grob name was virtually unknown until a few years ago. The programme survived the crash of its second prototype in 2006, killing its chief test pilot and delaying the schedule by almost a year. European and US certification is now expected in the final quarter. For the past two years, the company has been majority owned by a holding company set up by Swiss-based ExecuJet chief executive Niall Olver and, although the two businesses are separate, ExecuJet acts as SPn distributor outside North America (Grob has set up its own US-based subsidiary).

Grob Aerospace
 © Grob Aerospace

Today, the factory is bustling as it gears up for series production, and Grob urgently needs more space and staff - although much of the sales operation for the SPn has transferred to Zurich. The fourth prototype is about to fly, while the third test aircraft will undergo ice trials later this year in northern Scandinavia having completed a series of tests in Granada, Spain. An area of the factory - hidden from visitors - has also been set aside for development work on the Bombardier Learjet 85 fuselage following a deal struck with the Canadian manufacturer at the end of last year. The first three composite prototypes of the new aircraft will be built at Tussenhausen-Mattsies.

Glider Roots

The genesis of the SPn can be traced back beyond Grob's own origins to Germany's burgeoning cottage industry of glider manufacturers after the Second World War. With restrictions on aircraft manufacturing, many experienced aerospace engineers turned to developing gliders for flying clubs and recreational use. As a sideline to the main family business manufacturing industrial machinery, Dr Burkhart Grob set up Grob Aerospace in 1971 to build glassfibre gliders and within a few years was producing eight a week. The first 200 were Cirrus gliders produced under licence, but Grob went on to develop its own Astir series. The robust, aerodynamic and roomy aircraft, keenly priced, put many of the "home build" manufacturers out of business as the market evolved from enthusiasts to professional flying schools to the military, who viewed gliders as an ideal way of introducing cadets to flying.

After virtually saturating that market with 2,000 aircraft, Grob moved on in the early 1980s to motor gliders with the G109. After doing much the same to that market with 600 sales, the next development was into powered, two-seat aerobatic aircraft with the G115 and G120. A four-seat version, the G140, was developed in 2002, this time with a turboprop as opposed to piston engine, although the project has been put on ice with just the prototype having flown. With every new model, Grob finessed its composite engineering skills building a reputation as a world leader in aerobatic training aircraft.

It also branched out into other experimental areas. Capable of flying at more than 55,000ft (18,300m), the G520 Strato 1 Egrett was developed in the late 1980s as a high-altitude spyplane, and is still today the largest certificated all-composite manned aircraft. It was followed in the 1990s by the even bigger Strato 2C high-altitude research aircraft, developed with government funds. With two Teledyne TSIOL-550 pusher engines, a 56.5m wingspan and designed to fly for 50h and at almost 79,000ft, the aircraft never made it to certification, but the prototype still sits proudly at the Tussenhausen-Mattsies factory.

With the trainer market drying up and a lack of government funding for its more adventurous projects, Grob in the early 2000s was being kept afloat largely by the largesse of its owner. With the G140 on hold, the company looked to the growing business aviation market and developed the six-seat G160 single-turboprop Ranger as a competitor to the Socata TBM 700, unveiling the prototype at the Paris air show in 2003 and completing 150h of flight testing.

Marketing Support

It was at this time that Grob approached ExecuJet for marketing support. The business aviation services company and its chief executive, Olver, were not interested in taking on an aircraft smaller than the Pilatus PC-12, but, during the course of the conversations with Burkhart Grob, the two came up with the concept of a no-nonsense, composite light twinjet able to operate in rugged conditions in the bush. Olver - a native South African - believed there was no jet alternative to these workhorses that offered short-field capability, a comfortable cabin, sufficient range and a high payload, without a significant hike in price. "We wanted the pluses of a jet with none of the compromise on the ability of a turboprop," says Grob joint managing director Andreas Strohmayer.

A full mock-up of the eight-seat, Williams FJ44-3A-powered SPn was introduced to a surprised aviation press at the 2005 Paris air show as a joint venture between ExecuJet as distributor and Grob Aerospace. The aircraft appeared to straddle categories, with an eight-seat cabin just smaller in size than a Cessna Citation Excel, but pitched in terms of price against smaller light jets and larger turboprops. Its other selling points included a large, 84cm (33in)-wide door, making the aircraft suitable for cargo or medevac, and the capability to take off and land at under-1,000m runways.

Grob SPn
 © Grob Aerospace

The aircraft first flew in July 2005 and over the next two years the cabin design concept evolved. Initially the SPn had been pitched as a utility 4x4, but, after customer feedback, the cabin and the marketing changed following a deal in 2006 with interior specialist Porsche Design Studio. "Originally the market interpreted it as a pick-up truck," says Olver, who went on to buy his majority stake in Grob Aerospace in 2006. "We dropped the word utility, while still pushing its attributes as a single-pilot, rough field-capable aircraft."

Manufacturing Process

In Tussenhausen-Mattsies, the fourth SPn taking shape in the final assembly hall may not look radically different to other light jets, but closer inspection reveals just how different the manufacturing process behind an all-composite aircraft is. It all starts in the hall next door, where resin and hardener is applied to rolls of dry, black carbonfibre cloth and layered over honeycomb plates to create what will become the aircraft's skin. Meanwhile, a full-scale representation of the aircraft is effectively "sliced" down the middle like a chocolate egg to create two carbonfibre shells or moulds, each representing half the airframe.

Similar pairs of moulds are created for the upper and lower part of each wing and the horizontal tailplane. The carbonfibre resin mixture is then cut into shape and "laid up" in the moulds. Frames, floor panels, webs and control rods are glued into in the right-hand shell, before each half is put into the oven overnight under vacuum pressure in a large heating chamber at 60°C (140°F) - no autoclave is involved. The next day the two moulds are glued together and cured again. The structure is then trimmed, with windows and other holes cut out. More small parts are attached before the structure is given a final curing at 80°C ready for the tailplane and wings - with Liebherr landing gear attached - to be mated and wiring and systems installed.

grob manufacturing
 © Grob Aerospace

Rock Cakes Recipe

If the whole process sounds scarcely more complex than a recipe for rock cakes, do not be fooled. "The mind-boggling beauty of the technology is its simplicity," says Strohmayer. "But it's only very simple because we have been doing it for 35 years. It's a simple approach, but knowing how to do it properly is not simple." Although when we visited, the factory was only just gearing up for series production, Tussenhausen-Mattsies sounds unlike most aircraft factories, in that there is very little sound to speak of: little drilling, no welding, no heavy fuselage sections being winched into place. "Guys from a metal manufacturing background have been known to say: 'Where do you produce the aircraft?" says Strohmayer.

The aircraft, naturally, does contain some metal components, most of them manufactured in-house. For lightning protection, aluminium filaments are woven into the outer layer of carbonfibre skin. The wings also have an aluminium leading edge while the wing is joined to the fuselage with four titanium bolts. When it came to designing an all-composite aircraft of this scale, there was not really a rule book, says Strohmayer. "You have to invent every bit of it. You can't put aluminium to carbonfibre just like that. You have to know how to separate them."

The main systems suppliers on the SPn, aside from Williams, are Liebherr (landing gear) and Honeywell (Primus Apex avionics). Grob produces many smaller components such as piping, electrical and cable harnesses and reservoirs in-house and others - such as fuel tanks and spars - are integral to the airframe. "Typically we do not give a system to a supplier. We mix - sometimes we buy in, sometimes we manufacture ourselves," says Strohmayer, who admits such levels of vertical integration are "an outdated concept, but it works for us". Control of every aspect of the product is key to Grob, he says: "The driver for us is quality and scheduling. The biggest nonsense you can do is get rid of all your levers in these areas." He adds: "A lot of things we do you might ask: 'Is that cost effective?'. The answer is partly no, but because we are a carbonfibre company, it makes sense."

Apex Flightdeck

The Primus Apex integrated flightdeck - with optional enhanced vision system - further puts paid to the image of the SPn as a rugged workhorse. "We decided that the Apex architecture offered the most growth options and was poised to go beyond 2010," says Strohmayer. "Coming up with one of the first clean sheet designs of the 21st century, we did not think that we could do without this level of avionics." Similarly, the aircraft's optional Honeywell RE100 auxiliary power unit - the only Part 23 light jet to offer this - was cited as a key factor in the decision of two Middle Eastern operators, Falcon Aviation and Prestige Jet, to order the SPn. In fact, half of all SPns have been ordered with APUs. "There is no other aircraft with an APU at less than $12 million," says Strohmayer. "In many countries it's a must have."

The choice of the FJ44-3 - used on the Cessna CJ2 and CJ3 as well as the PiperJet - was also an easy one, says Strohmayer. Williams International had to keep the selection secret for a year before the SPn emerged at Paris. The engine came with full control digital engine control and, with 2,000 engines in service and 2 million flight hours, had a proven track record powering virtually all the light and many of the very light jets on the market at the time. According to Strohmayer the two companies were also similar in the way they ran their businesses: "We enjoyed working with them. They had a similar culture and line of command to us."

Grob's experience in designing experimental high-altitude aircraft in the 1980s and 1990s helped it make the leap from aerobatic trainers to business jets. Although designing a pressurised cabin was new, says Strohmayer, the Strato 2C had been pressurised to 80,000ft. "We could draw on the company brain," he says. As with lightning protection, Grob could adapt its proven system designed for the high-altitude aircraft. While the composite technology was "a given", according to Strohmayer, incorporating the necessary metal elements - such as the metal leading edge for ice protection - was probably the biggest technical challenge. Coming up with an integrated cockpit was also a major hurdle, but "this is not something unique to composite aircraft", he says.

Grob SPn General Arrangement

Staff Challenge

Like all aerospace companies, one of the greatest challenges Grob faces is finding skilled staff. Although the area immediately surrounding Tussenhausen-Mattsies is more famous for farms and genteel spa resorts than high-tech industry, travel a bit further afield and the wider region around Munich is one of Germany's prime aerospace hubs. It is home to Eurocopter, EADS defence businesses, Liebherr Aerospace and formerly to Fairchild Dornier, many of whose ex-employees have come to work for Grob, says Strohmayer.

"When Dornier collapsed in 2002, 4,000 engineers their jobs. Some went abroad, but didn't want to move their families. Others went into the automotive sector but weren't happy. We had some that went to work in Hamburg or Bremen and ended up designing toilet piping for Airbus. The great advantage of working here is that we are a growing company and those who work for us can actually see the aircraft taking shape. This sort of motivation is an important factor," he says.

Growing Recruitment

There are currently 380 staff working at Tussenhausen-Mattsies - more than treble the number of three years ago - and this will go beyond 500 next year, including about 150 working on the Learjet 85. Employees outside Germany will rise from around 30 today to 130 by 2009 (this takes into account Grob's US sales and support subsidiary, but not ExecuJet staff responsible for sales outside North America). Grob is recruiting around 10 employees a month ahead of full-rate production at the start of 2009. "We decided last summer to go for this number to make sure they were trained in the Grob way of doing things," says Strohmayer.

For production staff, the region's automotive industry has proved fertile recruiting ground. Others are former military technicians. The difficulty has been finding specialists. "If we are looking for a particular expertise, there might only be five or 10 of them in Europe, and getting them to move to Grob is a challenge." However, having aircraft in flight test and a healthy orderbook helps. "When people thought of us as just another start-up that might never survive, it was always going to be difficult to persuade engineers to bale out of EADS for Grob. But now that we are at this stage in the jet programme, it is easier," says Strohmayer.

The Tussenhausen-Mattsies factory is slowly turning from a development centre into a production line. The first two series aircraft are in the early stages of manufacture and these will join the three prototypes in the flight-test programme in the third quarter. With the first prototype having completed over 350h of flying and P3 another 150h, the SPn will have 1,000h under its belt by certification, says joint managing director Ulrich Gehling, recently recruited from Pilatus because of his experience in aircraft certification. Some 28,000h of testing is also under way on the fatigue test rig.

By the time the first aircraft is delivered there will be about eight aircraft in various stages of manufacture (the third series aircraft will be the first to go to a customer. The first two will remain as demonstrators - one in Europe and one in the USA). Aircraft will then be delivered at the rate of one every two weeks for six months, increasing to one every 10 days for the following year. After 18 months, the factory will reach its capacity of 45 aircraft a year.

Of the 80 or so orders, almost half are from North America, a much higher percentage than Grob originally envisaged. Another quarter are from Europe, with the Middle East making up much of the remainder. The customer profile has also changed. "In the beginning, we were targeting mainly owner pilots," says commercial director Cedric Migeon. "Now we are seeing many more charter companies coming on board." One of the most significant deals, for 25 aircraft, has been with US fractional scheme PlaneSense, until now a Pilatus PC-12 fleet managed by New Hampshire-based Alpha Flying.

Stretched Version

Down the line, a stretched version of the SPn could be on the cards. Grob has always said it would develop a family of jets around the SPn concept, but no decision will be taken until well after certification, says Strohmayer. Special mission variants of the light jet, however, are already being touted.

As well as stressing its use as a medevac, freight or maritime patrol aircraft, Grob has also unveiled a high-altitude surveillance concept based on the SPn airframe. The G600 draws on the company's heritage in designing high-altitude aircraft in the 1980s and 1990s, with a fuselage extended to 18.65m and a wingspan of 35.6m, allowing it to fly at up to 60,000ft for 18.6h.

Grob Aerospace may have joined the business aviation mainstream with the SPn, but the German manufacturer has not lost its experimental edge.

Grob SPn
 © Tim Hall/Guiseppe Picarella

Global Network Prepares to Play its Part

Grob faced several challenges in setting up a global sales and support network robust enough to compete with Cessna, Hawker Beechcraft and Pilatus. Before the SPn, the manufacturer had a small team used to dealing with military customers of its aerobatic trainers, mostly in Europe. Its brand had little traction in the world's biggest business aviation market.

With partner ExecuJet also largely unknown in North America, despite its strong presence elsewhere, Grob opened, in September last year, its own US arm in Portsmouth, New Hampshire, backed by regional sales offices and one independent sales company, Sunwest Aviation in western Canada.

Three partners were enlisted for service, spares and warranty support: Aero Air in Hillsboro, Oregon Landmark Aviation (now Standard Aero) in Houston, Los Angeles and Springfield, Illinois and Stevens Aviation in Denver and Greenville, South Carolina. Grob plans to add more.

Training these centres to repair composite structures presents another challenge, but, says Grob director of customer and product support Hans Doll, the US MRO sector is not completely without experience in fixing non-traditional materials. "A lot of secondary parts, radomes for example, tend to be composite so there has always been some expertise there," he notes. "Also, we are not too different to metal aircraft in that if there is damage to the primary structure, the manufacturer has to provide the repair."

The rest of the world is handled by ExecuJet's operations in Copenhagen, Dubai, Johannesburg, Sydney and Zurich, with Manchester's Ocean Sky Jet Centre responsible for customer support in the UK.

After holding an inaugural meeting of all its service representatives in Tussenhausen-Mattsies in December, Grob will shortly convene the group again. Within a year, the centres could be getting hands-on experience of the world's first composite business jet.

Conservative Customers Opt for Comfort

Following the decision to enlist Porsche Design Studio to design what it calls its "high-end German sports utility vehicle" inspired six-seat cabin, Grob now offers two standard interiors for the SPn.

However, only one in 10 customers have opted for the original six-seat "utility" layout designed to appeal to operators who wanted to be able to remove seats quickly and reconfigure the cabin for cargo or medevac.

It is perhaps a case of the customer knowing better than the manufacturer when it comes to cabin comfort, as the SPn had at first been pitched almost exclusively at a market for whom amenities played second fiddle to no-nonsense rugged versatility.

The Porsche cabin - announced in 2006 and unveiled at last year's EBACE in Geneva - comes with a small lavatory at the front and an even smaller refreshment centre.

The aircraft has a full, 1m (3ft)-wide forward galley and rear lavatory with washbasin and vanity cabinet. Such considerations matter to US business executives and Arab dignitaries - among the typical passengers likely to travel on the first SPns in service.

"We introduced the SPn as a utility aircraft with the eight-seat layout, but we found the market was more conservative," says commercial director Cedric Migeon.

In fact, Grob sales staff have found themselves talking as much to potential customers of smaller Cessna Citations as operators of the likes of Beechcraft King Airs interested in trading up to a jet, he says.

Grob claims the SPn has the largest interior cabin volume of any light jet, at 11.5m3 (405ft3), with the carbonfibre construction helping to create a floor to ceiling cross-section of 164cm (64.5in). The 12 windows are 39 x 31cm.

The aircraft, says Grob, can also be quickly configured to carry patients, with room for two stretchers and three seats.

Grob will carry out cabin completions itself on the first 10 aircraft or so. "We want to be sure these first aircraft are close to our engineers, so we can be reactive to any issues that come up," says Migeon. The company is keeping its cards to its chest on any link with a completions specialist after that.

Source: Flight International