Unitracts International
Unit 5, Ebbsfleet Industrial Estate, Stonebridge Road, Northfleet, Kent, DA11 9DZ, U.K.
t.: +44 (0) 1474 359990 f.: +44 (0) 1474 359994
Retraction Angle
Once a particular project/model is decided upon, the modeller needs to study scale drawings (which are not necessarily correct) and photographs or the full size aeroplane if accurate retraction geometry is to be determined. The following notes give a guide to calculating the required angles.
Special Gauge
On the face of it, the retraction angle is that measured when viewing the front (or side in the case of twist and turn mechanisms) of the aeroplane from the extended position to the retracted position in the dihedral of the wing (not in relation to the ground datum). Whilst this is satisfactory if the wheel moves in an arc perpendicular to the fuselage/wing datum, it is not the case if the wheel scribes an arc at an angle to these datum’s, for example if the oleo leg is angled forward when down but rearwards when retracted. This angle is not easy to calculate and we use a special gauge.
By way of example the Spitfire has a retraction angle of 93½º as measured from the front but requires an angle of 96º for accurate geometry. In other cases the oleo leg does not lie in line with the wing datum’s when retracted and this has to be compensated for (for example the T28 and Dauntless).