The German Government's unexpected withdrawal of funding could kill a unique high-altitude research aircraft.

Andrzej Jeziorski/MUNICH

AIRCRAFT EMISSIONS are just one, probably a relatively minor, contributor to anthropogenic environmental change. Yet, combined with all the other natural and man-made contributors, the prognosis for climatic change over the next half century is both worrying and insufficiently researched.

To date, nobody has had a research platform which can probe high enough, linger long enough and travel far enough at high altitude, to give a reliable picture of what is really happening to the upper atmosphere. Until such data have been gathered, nobody can tell just how much work and investment is needed to ensure that any polluting industry, including air transport, can keep developing in an ecologically acceptable way. Neither can anyone tell for sure whether efforts being made now are sufficient, inadequate or, perhaps, excessive.

It seems strange, then, that a high-altitude research aircraft which could provide the sort of firm evidence needed should now be threatened by apparent Government apathy in a country where both "green" issues and aerospace are high on the political agenda. Yet that is what is happening to the Grob Strato 2C.

The aircraft, built by German manufacturer Burkhart Grob Luft- und Raumfahrt, is intended to be operated with two pilots, two scientists and experimental equipment, at up to 72,100ft (22,000m) for up to 5h. Composites specialist Grob says that its creation could be flown non-stop nearly halfway around the world.

At a distance, the Strato, which has an empty weight of 7,600kg and a maximum take off weight of 13,500kg, could almost be mistaken for one of the sleek gliders with which Grob first made its name, but the impression is belied by its two large engines with pusher props mounted atop the wing.

Up close, the Strato's proportions are startling. On its own, the fuselage looks like that of a 30-seat regional turboprop. The high-aspect ratio, high-mounted wing gives the aircraft its sailplane silhouette, but with nearly the span of a Boeing 747. At 56.5m, this is the largest all-composite wing ever made. The variable pitch propellers, from MT-Propeller are great five bladed windmills 6m across, driven by a compound propulsion system developed by Ottobrunn-based scientific and technical services firm IABG, while the empennage is a tall T-tail, rising 7.8m above the ground when the aircraft is parked - as indeed the Strato has remained for some time now, because of the current wrangle over outstanding funds.


The programme's funding has been divided between the state - specifically the education, science, research and technology ministry - and the manufacturer. Development costs were first estimated at DM93.4 million ($63 million), of which the Government was to cover DM72 million, and the manufacturer the rest. This has been enough to complete the first phase of development, but the delay in the next tranche of funding has cost Grob millions more. The delay may now turn out to be permanent.

The programme started in April 1992, following a recommendation from the ministry and researchers to intensify stratospheric research in Germany. The German Aerospace Research Establishment (DLR) was commissioned to manage the project, and was to have been the end user.

The schedule anticipated a development programme lasting from 1992 to 1995, in parallel with the establishment of a ground-support infrastructure by the DLR at its Oberpfaffenhofen site in Bavaria. The preparation of the first missions was planned for the beginning of 1996, and the aircraft was scheduled to be operational from 1996 to 2000. One of the main areas targeted for research (among various climatic, chemical and technical investigations) was pollution caused by air traffic, and its influence on trace gases and the radiation field.

Grob was selected as the manufacturer because of its expertise in composite-aircraft construction: metals could not provide the strength and surface finish necessary for flight in thin air at extreme altitudes. The company also had experience in the high-altitude aircraft field from the Egrett programme - a joint venture with E-Systems of the USA to meet the German air force LAPAS 1 observation aircraft requirement, which was finally cancelled because of defence cutbacks.

Early proposals from Grob centred on a twin-boom design with tractor props. There was the turboprop Strato 2TP, with a 52,000ft ceiling, and the Strato 2R, again a turboprop, but with a controllable hybrid rocket motor mounted on the fuselage to boost the aircraft up to a maximum 65,500ft for short periods.

The "flagship" proposal, however, was the Strato 2C, intended for long operations at 78,700ft because of its compound engines.

The problem with turboprop and turbojet engines at high altitude is that their available power drops rapidly the higher they fly, while the aircraft power requirement to maintain speed and lift increases exponentially. Compound propulsion solves the problem by using a turbocharger to provide a piston engine with constant "breathing" conditions from take-off to its design altitude. The available engine power therefore remains constant.

To save time and money, it was decided to use as much existing hardware as possible, in the system rather than designing everything from scratch. The two main components of the Strato's propulsion system are the liquid-cooled Teledyne Continental TSIOL-550 9litre, flat-six engine, and a Pratt & Whitney Canada PW127 gas generator which provides the engine with about 12% jet thrust in addition to the propeller thrust.

The system can be thought of as two propulsion groups. The first consists of the engine, a standard Teledyne turbocharger, the ZF-designed reduction gearbox and the constant-speed propeller. This works as a standard piston-prop engine during take-off and landing. The second group comes into operation at higher altitudes and consists of the PW127-based low-pressure charger, with its own oil system and integrated charge air coolers. This feeds charged air to the engine at a pressure which allows it to maintain 300kW (400hp) power up to its design altitude, and also provides the jet thrust.


By June 1994, it was clear that the original funding, was not going to be enough to produce a certificated aircraft and Grob went to the DLR, asking for additional funds, promising that the initial funding would still be enough, to produce a proof-of-concept (PoC) prototype, which could later be improved.

Grob says that the extra funds were needed to cover certification costs and unexpected development cost increases. According to Grob vice-president and general manager Roland Rischer, the cost of avionics and testing had turned out to be higher than anticipated. The Honeywell auto-pilot, for example, was expected to cost DM3 million, but came to DM16 million.

Unfortunately, Grob's request for more money came during the run-up to Germany's October 1994 elections. The ministry's purse strings were pulled tight, and the programme funding was stopped DM10 million short of the DM72 million initially promised, leaving Grob to continue funding from its own coffers.

With the election over, money began to trickle into the programme again by early 1995, and the PoC aircraft had its maiden flight on 31 March. During its 29th flight, on 4 August, 1995, the Strato 2C set a world altitude record of 60,700ft for piston-engined aircraft, which Grob saw as a successful conclusion of the first development phase. Altitude chamber tests had already shown that the propulsion system was capable of being operated at 78,700ft, but weight optimisation of the airframe - particularly the fitting of a new, lighter wing - was needed, and the aircraft's aerodynamics and engines also needed to be refined to achieve acceptable mission performance.

Rischer says that the flight tests showed that the PoC aircraft was capable of flying for 1h at 65,600ft. A 1t weight saving could then boost performance up to 1h at 70,500ft, or 10min at 72,100ft. An achievable 15% performance optimisation of the engines could then allow 6h at 72,100ft, while drag reduction by the addition of extra fairings and modification to the tail section would allow 5h at 75,400ft. The original DLR performance specification was for 8h at 78,700ft, according to Grob.

Grob proposed that it could achieve preliminary type certification by the beginning of 1997 for an additional DM47 million. Full certification would cost an additional DM38 million.

The DLR still stood behind the project, even though it now seemed that the mission aircraft would fall short of the performance standards it had hoped for, and the PoC aircraft had not reached its expected 65,600ft. The parliamentary budget committee had stated on 10 May that if the PoC aircraft achieved an altitude between 59,000ft and 65,500ft, the project should continue to be funded, and it was on this understanding, says Grob, that the company decided not to try to push the aircraft higher, even though it felt it could have. Now everything was up the research ministry, under minister Jurgen Ruttgers.


On 11 September 1995, while still awaiting a decision, Grob put its Strato team - half the workforce - on short working hours, and drafted a redundancy plan. The company remained optimistic that job losses could be avoided because it seemed that the ministry would clear the necessary funds, provided Grob and the DLR agreed a new contract taking the reduced performance requirements into account. The contract was drafted, lowering performance specifications to a conservative 5h at 72,100ft, but still the ministry stalled.

By the end of December, when the costs of keeping on the workforce had pushed Grob's investment in the Strato 2C up to some DM30 million, the company could wait no longer. It sacked the 131 Strato employees. Even if the Government eventually clears the additional funding, says Grob, the expertise is being lost and this means additional time and cost.

On 17 January, R_ttgers recommended to the budget committee that the programme be stopped, and that the Government should try to claim its money back. Grob says that it will fight any attempt to retrieve the funding in court, but concedes it could lose up to DM11 million in guarantees, which the DLR is entitled to if the contract is not fulfilled. Grob says that if the decision goes against the programme, it will look abroad for partners, exporting technology which is for now exclusive to Germany and "five years ahead" of the competition.

The ministry and the DLR are saying nothing other than that they expect a response from the budget committee on 31 January. The prognosis for the future does not look good. It may turn out that the Strato 2C has already flown too close to the Sun.

Source: Flight International