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
Pintle Geometry
If the correct pintle geometry is not used, it is not possible to have the wheels extended and tracking straight whilst lying at the correct angle (normally flat, parallel to bottom surface) in the wing, when retracted. This becomes more of a problem if doors are fitted. The pintle angle may be defined as the angle to the wing chord, in both the plan and side views, that the retract must pivot at to give the correct geometry.
The pintle angle is calculated as follows:
- Measure the rake in the down position (forward rake positive, rearwards rake negative).
- Measure the rake in the retracted position (forward rake negative, rearwards rake positive).
- Add these two figures (taking note of the signs, positive or negative).
- Divide by 2 (two) which gives the pintle angle.
The difference between the pintle angle and rake angles gives the angle that the leg has to be offset to the retract mechanism to give the correct geometry. Other factors can come into play and these can alter the calculated figure by up to 2 degrees. The main problem is finding accurate scale drawings to work to. I have measured from nine sets of Spitfire drawings and, even allowing for differences between early and later marks, every set showed differences!