Hi guys, I do not own jacks for my aircraft and the method the shop has been using for jacking has been to place the jacks outboard of the main gear and use thick foam padding to protect the wing. Is this an acceptable alternative or is it likely to cause structural damage. I have noticed some hairline cracks in the gelcoat on close inspection.

Gerard,

 

If your 320/360 was built according to the plans, there are phenolic jack pads placed at the intersection of the aft edge of the main spar and the inboard edge of the cockpit closeout rib.  This places the pad under the glass continuation on the belly floor of the load transfer structure that securely attaches the fuselage to the main spar.  From the outside, the general location of the central part of the jack pad is 1" to 1.5" inboard of the inboard gear door hinge and a bit (1" or less) aft of the forward edge (corner) of the door opening.  This is a very strong area and it is this location of a jack lift point that requires 120 to 150 pounds applied to the tail (tail tie down ring) to lift the nose off the ground.  It is expected that the tail would also be supported for safety's sake.

 

You don't say exactly where the shop is applying lift pressure.  If the lift is applied from about 1 inch inboard and 1 inch outboard of the wing/stub-wing split and behind the main spar, the pressure is being applied to the stub wing rib and the inboard wing rib and these ribs extend to the outer skin.  While this is a strong area , any deformation could mean the rib has been deformed - this is a structural no-no.  If the pressure was applied under the main spar - just outside the outboard door opening, but not beyond the split, perhaps only the paint is damaged but since this is forward of the designed lift point, I don't know whether weight is required on the tail or the tail has to be supported (it should be supported in any case),  If the pressure is outside the split it would have to be forward of the main spar to be under the wing spar - this is not a very good balance point even if the wings are holding up the whole plane in flight.