RONGOTAI MODEL

Evening Post, Volume CXX, Issue 9, 10 July 1935, Page 12

RONGOTAI MODEL

IN RUNNING ORDER NOW

HILL OBSERVATIONS

DOWN TO FINE .WOEK

Members of the airport committee of the City Council and of the special .committee of the Wellington Chamber of Commerce today inspected the wind tunnel model of the Rongotai aerodrome and found the hour or so particularly interesting. The model is now well into working order, but the making of observations still has a long way to go, for it is extremely detailed work if it is carried out properly. From the comparison of general results of the effect of winds of a given direction at the aerodrome itself and over the modelled hills and valleys of the model a common basis has been arrived at and the observers are working down to finer observations, which include calculations of model wind velocities. This is a tricky business, for the results given by the usual outdoor gauges, and anemometers in one form or another, are not sufficiently accurate, and the placing of any standard gauge introduces eddy complications, so the "hot-wire" system of measuring the air current is being tried out. The application of this system is very technical and calls for exact observation, but the principle is that the resistance of a given length of wire changes as the temperature is decreased by the cooling effect of an air current; from these factors, and an- exact measurement of the current which passes through the wire, -the air velocity can ,be calculated. . . MOA POINT EXCAVATIONS. The general observations have reached an interesting stage in that the Moa Point section of the model is being experimented with. Above Moa Point is a fairly high hill, which causes considerable turbulence under either northerly or southerly conditions. It is generally agreed that some part of this hill, or all of it, will have to be cut away, with a double end in view: of getting rid of the turbulence and of obtaining spoil for the filling to extend the landing ground seawards, but the difficulty is to know how much to take away. This section has been built to be removable so that trial shapes can- be replaced, and already some surprising results have been obtained, suggesting that a complete removal of the hill is not the solution, as turbulence may be created elsewhere, and indicating also the probable most efficient and economical slopes to which the faces should be cut. Certain of the observations, moreover, appear to indicate that the best approach may be over a saddle over the point, rather than over the fully excavated point, but this work has not been by any means completed. So far the model has been tested only for northerly winds (which represent about 60 per cent, of all winds), and southerly tests will need to be equally thorough. A neat estimating trick is worked as various cuts and faces of the Moa Point- hill are tried. The removable section has been weighed and its cubic content carefully worked out as representing so many hundreds of thousands of'yards. The suggested cut is made with a saw and the portion removed is weighed and found to be such and such a fraction of the whole, and therefore an excavation to that extent on the hill would be of so many thousand yards, at so much per yard of excavation. The resulting estimate may* be accurate to within 10 or 15 per cent. If the model demonstrates —as it gives every promise of doing—that a partial excavation of the hill will be as equally effective as a full excavation its cost will have been saved many times over.