Avteк 400. What is it?

Vocabulary: pitch-axis control, pusher propeller, tractor propeller, supple, turbulent, proof of concept prototype (РОС), exhaust, gap, wake, pitch-axis trim, stalling speed, strake, pinion tank, nose-up moment.

Exercises:

1. Read the text and point out the main idea of each paragraph.

2. Answer the questions:

1. What advantages has the Avtek 400 over its predecessors?

2. What is the fundamental feature of this aircraft?

3. What are the main aerodynamic problems resulting from the aircraft configuration?

4. Where is the OG located?

5. How is the fuel carried?

6. Why were the engines P & WC РТ6А-28’s chosen for this type of an aircraft?

7. How is the take-off of the Avtek 400 performed?

3. Make a summary in English:

What the Avtek 400 offers is a quantum leap¹ in turboprop performance, at least as great as is being made by the Lear fan and the Cheyenne 400 LS, plus an even lower fuel consumption giving hitherto² unattainable economy. None of the three aircraft beats³ any of the jets in sheer speed, except the Citation I in the 20,000ft to 25,000ft height band. But they far outperform³ existing turboprops. The Avtek 400 offers jet-like climb performance and 37,000ft cruising altitude, with the very important result that is behaves like a jet on the airways.

The fundamental feature of the Avtek 400 configuration is the tandem-wing lay-out which has the well-known effect of produoing pitch-axis control by modulating lift at the front end rather than lift-defeating down-pressure on a conventional⁴ tailplane. Most of the rest of the configuration stems from⁵ that. It is the light weight of the modern powerplant which makes it fully practical to use the pusher propeller. The benefit of drawing air over the wing, as distinct from the usual blowing from tractor propellers, is complicated by the relatively turbulent conditions in which the propellers have to operate, particularly if flaps are lowered ahead of them. Technology, in the form of the supple composite propeller, solves the problem. While the proof of concept prototype (РОС) has metal Q-tip propellers, the production aircraft will have the new Hartzell Kevlar blades, still with Q-tips for noise suppression. These also have a lower diameter, at 64-in, easing the problem of propeller ground clearance. Happily, the hot exhaust from the turbine provides free propeller de-icing. The propellers run at a rather high 2,100 rev/min.

A critical aerodynamic problem is to area-rule the gap between engine nacelle and fuselage to form a channel of constant cross-section. Avtek chose a fore-plane to main wing lift distribution of 24:76 and gave the fore plane dihedral to try to lift its wake clear of the-main wing and propeller arcs. All pitch-axis control is vested in⁶ the elevator surfaces on the foreplane.

Pitch-axis trim is vested in the two tabs just inboard of the ailerons on the main wing, controlled by a conventional trim switch. These could be seen fully deflected upwards in pictures taken during early flights and Avtek admits that this was because the canard was at too small an incidence. The unusual incidence re­quirement had been detected in flight trials with 20 per cent scale radio-controlled models before the РОС flew. Omac apparently made the same mistake in the Omac-1. The incidence of the РОС canard has now been adjusted. These scale-model dynamic flight trials have aroused interest with NASA, which is developing techniques and instrumentation for more extensive research.

With its present wing-loadings, the POC requires no high-lift devices to achieve a low stalling speed and good landing performance. The centre of gravity locates itself at or ahead of the leading edge of the main wing, which makes it desirable to 1ocate fuel ahead of the wing in order to avoid loading problems and large in-flight CG movements. The РОС was designed to carry 200USG in the wing box and 40USG in the canard, but it actually carries two composite boxes of fuel inside the cabin between the centre windows, well ahead of the wing. By the same token⁷, the main function of the large strakes of the Omac-1 is to house the fuel around the CG. That strake has apparently now been replaced by what is called pinion tanks on a strakeless wing.

The lifting surface areas of the POC are 38ft² for the canard and 110ft² for the main wing, plus soot front-end lift, or nose-up moment produced by the fuselage. For the gross weight, this gives an overall wing loading of 371b/ft², which is a little low for the most efficient high-altitude cruising performance. The engines in the РОС are P & WC РТ6A-28s, which conserve⁸ their 680HP sea level take-off rating up to an unusually high altitude, and were selected specifically for their high-altitude cruising performance. Were their full power to be used at sea level, they would produce a staggering power loading of 4 lb/HP, worthy of a highly aerobatic aircraft. In fact, take-offs have normally been made at about 60 per cent torque, but the power is very useful for climbing promptly to the 37,000ft cruising altitude. The tremendous excess power also makes it possible, for once, to optimise the propellers for cruising performance rather than take-off.

3700 знаков

Notes:

1. quantum leap - (зд.) значительный скачок

2. hitherto - до сих пор

3. to beat - to outerperform – превосходить

4. conventional - standard

5. to stem from - происходить от

6. to vest in - помещать в

7. by the same token - к тому же

8. to conserve - сохранять

4. Make a written translation:

The impressive feature of the Avtek 400 structure is that the company has produced apparently effective answers to all the classic queries about composite structures. The Nomex/Kevlar has been shown to resist 0.22in bullets and to survive 0.357 Magnum impacts. Avtek has adopted the Lightning Technologies technique of laying-up a thin, aluminium-coated glass-fibre mesh in the, outer skin to provide overall lightning resistance, plus bonding of adjacent components with metal straps. Ultra-violet light resistance is provided by a Bostik paint on the outside and a resin paint containing carbon black on the inside. A new resin is used to go with a glass having a lower transition temperature, which reduces moisture absorption, though at the cost of slightly poorer microcracking characteristic in the resin. It is easy to blend graphite with Kevlar when using these lower-temperature materials. The composite has been shown to recover its characteristics when dried after soaking at high humidity end low temperature.

900 знаков

5. Make a report on the topic “Avtek 400” in English.

UNIT 21