Tunnel Topics

Down the placid waters of broad Chesapeake Bay from Washington last week churned two boatloads of aviation experts, manufacturers and operators to the brick and grass coziness of Old Point Comfort, Va. to attend the twelfth annual Aircraft Engineering Research Conference of the National Advisory Committee for Aeronautics. Carefully watched by soldiers and with cameras forbidden, they were driven to Langley Field to be chaperoned physically by NACA's Secretary John Victory and mentally by NACA's Research Director Dr. George William Lewis through the world's greatest collection of wind tunnels, to see what the finest U. S. aviation research group had learned in the past year. High-spots:

P: High-speed tunnels, spinning tunnels, atmospheric tunnels, variable-density tunnels and propeller research tunnels are old stuff. This year two more were added to the list--a freeflight tunnel and a gust tunnel.

The freeflight tunnel is a cylinder which may be tilted at a normal airplane glide angle. On the bottom rests a small model of a commercial plane which is to be tested for such things as controllability. As the air rushes into the tunnel, the model takes off, flies completely free. Trailing from it is a thread-like copper wire through which the operator can control ailerons and rudders, see how the ship obeys them.

The gust tunnel is important because all airplanes experience their maximum loads when they encounter sudden gusts or "bumps." The gust tunnel faces upward and a small model is shot across 'its top at 50 m.p.h. Accelerometers and a fast camera record how it reacts. Gusts are also being measured by pocket-size gadgets called V-G recorders installed on many airline transports. The China Clipper has one, for example, which indicates that maximum gust velocity over the Pacific averages 30 ft. per sec. up & down.

P: Modern air engines have cowlings which both improve streamlining and help cool the engine by concentrating the air taken in at the front. Engines need cooling most when taking off, for then they are generally turning over at full power. But air-speed is slow then, so the stream of cooling air is not so effective as it is later when the plane is flying faster but when the engine needs less cooling because it is throttled down. To meet these shifting conditions the NACA has devised a shifting cowling with two nose slots. Air enters around the propeller hub, flows back over the cylinders, then is turned forward and issues from a small slot running the entire circuit of the cowling front. A gearshift makes this slot movable, so that air pressure on the engine can be controlled and adjusted to any cooling requirement.

P: As the struts and wires which characterized old planes have been removed, the wing has increased from one-third of total drag to about half. To reduce this the NACA experimented with the friction set up by rivets and lapped plates on the wing surface. A modern plane weighing 20,000 Ib. and having a wing area of 1,000 sq. ft. was found to require 182 less horsepower to reach 225 m.p.h. if its wings were smoothly polished than if it had normal overlapping plates and brazier rivets with a head-diameter of 3/12 in.

P:With airplane size now reaching vast proportions, most airports are becoming obsolete. The NACA has been experimenting with catapults to solve this problem, found that the forthcoming Douglas DC-4 will need a thrust of 15,000 Ib. to take off in 1,150 ft. This requires an engine of 3,250 h.p., which is too expensive. Probable solution will be a large flywheel which can store up this much energy. The catapult would presumably rise from an emplacement in the centre of the field. Passengers might need headrests, but would not be internally distressed by the sudden start.

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