Grob Strato 2C
The Grob G 850 Strato 2C was a high-altitude research aircraft, which built the Grob Aircraft AG on behalf of DLR with funds of the BMFT to explore the stratosphere. It is the largest purely made in CFRP aircraft in the world.
History
The Strato 2C or Grob G 850 was the successor of the Grob G 520 EGRETT or Strato 1, which had also been financed by funds of the BMFT and had the same use. These were in addition to the communication monitoring, mainly geophysical research and monitoring of pollution and weather patterns. The aircraft should be stationed at the airfield of the DLR in Oberpfaffenhofen since 1995.
Technology
First, the plane was designed for a pilot. Due to security issues, a second pilot was added and the emergency facilities have been revised. For Notabstiege from great heights, the use of a brake in the rear screen was considered, which would have a sink rate of 35.56 m / s ( 7000 ft / min) allows.
The aircraft is largely made of carbon fiber reinforced plastic. After flight performance calculations pusher propeller were favored because in this configuration, an undisturbed flow to the wings is guaranteed and available more space for the large propeller. When two charged engines Teledyne Continental motors should be used.
The choice fell on gasoline engines, as compared to those with diesel engines and jet engines have the lowest specific air consumption. In contrast to diesel and jet engines consume gasoline engines with their combustion air ratio λ (lambda ) is equal to 1 the total oxygen supplied, while diesel and turbine engines operate with excess air, with turbine engines typically about 70% of the oxygen supplied can not use because the turbine blades not stand high temperatures. Because of the higher air requirement ( λ ≈ 1.4 ) were the compressor of the supercharger and the intercooler must be designed significantly greater for a diesel engine with a comparable level performance. In addition, the design weight caused by diesel engines. A turbine drive for the configured altitude should have been heavily throttled at lower altitudes, which would have the use of oversized engines and loss of efficiency.
To ensure the air supply to the motors in the great commitment of up to 24 kilometers, the air was compressed with both turbochargers as well, each with a low and medium pressure compressor of a Pratt & Whitney PW127 turboprop engine. These compressors with own drive turbine used in the turboprop engines as gas generators for the free-running power turbine, which is not incorporated in the Strato 2C, because the gas generated electricity is derived and applied to the compressor of the turbocharger, which act as a third loader stage (high pressure compressor). The power turbine of the low - and intermediate-pressure compressor is driven by the exhaust gases of piston engines, which is conducted after passing through the turbocharger into the turbine section of the PW127. The compressor capacity is regulated by means of a bypass valve. The exhaust gas is then passed through an exhaust pipe from the engine nacelle, which put an extra boost of 12 % of the propeller thrust can be generated by expansion within 24 km altitude. Because of the low air density at the maximum operating altitude and because of the high compression ratio of the charge air by up to 1 | | 45 bulky heat exchanger for water, oil and charge air cooling are housed in the large engine nacelles except the drive and compressor components. All these measures should allow full pressure altitude of 24 km and a service ceiling of 26 km.
With a wingspan of 56.5 meters and a wing of high aspect ratio to date is the largest purely made in CFRP aircraft. Although the machine was able to meet the required performance in soil as well as flight tests, but also the development costs increased rapidly, which is why the federal government finally getting out of funding and coarse put the project on hold.