RONGOTAI HANGAR

Evening Post, Volume CXXIII, Issue 17, 21 January 1937, Page 10

RONGOTAI HANGAR

TENDERS CALLED

MODERN IN EVERT WAY

WINGS AND ROOFS

The plans for the modern hangar-to be built at Rongotai were given their last lines this week and tenders are now being called. The building will be in accord with the latest in hangar construction and will be large enough to take several of the largest transport machines likely to run to Wellington for some time to come.

The door opening will be 131 feet long and 20 feet high. The main hangar floor will be 80 feet deep and behind that will be a workshop 20 feet deep, running the full length of the building. Th'e roof will be carried on four main columns, two main girders, and ten roof trusses, all in steel.

There will be no roof lighting, but there will be a great total area of glass in the walls and door, roughly about one-half. There are several standard types of hangar doors, but because of the limitation imposed at Rongotai the hanging types have been decided against, and the twelve doors, each 11 feet wide and 20 feet high, will slide to either end on six sets of closely-spaced rails, so that any section of the opening may be used, whereas with several of the door methods for instance, it is not possible to open an end section without throwing open a full half section. When the hangar is open the door sections will be enclosed in the end pylons. The roof construction is such that heavy lifts will be possible from the girders over the full length and this facility will enable heavy repairs to be made Without difficulty or for machines to be raised for work on undercarriages, tyre changing, etc. LOW PRESSURE TRICKS. Roof construction for a large hangar is a problem of design in itself, for strains and stresses not imposed upon any other type of building have to be provided against. The Rongotai hangar will face directly south, and strong winds must be met. The strains which will be imposed will be a good deal more than the mere lift from the pressure of the wind in the wide-open door, for there is a secondary and considerable effect when wind blows overs a long building of this side elevation. It is the same effect as that above an aeroplane wing, much of the lift obtained when the aeroplanes rushes through the air is from the low pressure above the wing, tending to lift the wing, and aiding the upward thrust from the high pressure below. The same thing exactly occurs when a strong wind blows over a large hangar roof. This fact has not been long recognised, and several cases of roof collapse unaccountable at the time, are now explained. The designers made ample provision for one set of stresses, but were caught out by unsuspected stresses. Aeronautical investigations have done a lot for roof design.

The trussing at Rongotai has been designed to stand up to a gale of 100 miles an hour, far above the heaviest gales so far recorded, and the roof covering to stand a wind loading as high as that of the wing loading oi an aeroplane. A double continuous ventilating break in the roof and a considerable area of louvring will give an escape to air piled up when a heavy southerly blows in the open doors. The high pressure-low pressure effect can play various tricks on hangars, as has been demonstrated already in New Zealand. For instance, if a strong wind blows on the back of the hangar a low pressure is induced about the front and inside the hangar itself. Air pours from the highpressure area . t the back through every craclt and opening, and rain comes through with it. At one New Zealand hangar this caused a lot of trouble until remedied by the cementing up of every space, and particularly the flutings of the vertical sheetings of the walls, through which wind and water were drawn. TO AVOID CORROSION. In the big Union Airways hangars a special form of steel covering has been used and has been \ found very satisfactory. Each sheet of steel, which may be in one or several sections, is completely sealed in a thick covering of bitumen and asbestos compound, edges and ends as well as surfaces. The sheets are ordered to actual finished measurement and go up without any break of the edge and end sealing. Probably something of the same sort will be Used at Rongotai, where, because of the salt and flying sand, special care has to be taken to prevent corrosion. The hangar will be built between the present iron hangar and the administrative building, and will, in fact, straddle the present shed. As the Wellington-Auckland air service is expected to commence by the middle of the year, there is no time to spare.