Originally Posted by
megan
Never ever experienced or heard of the "jump", never ever used the coolie hat other than to set a ROD, flew the 76 and 412 coupled en route and reverted to trim off when hand flying, VFR operation, cough, cough.
Here's a proper description of stick jump from Eric Fitzpatricks book on flight test in the chapter about flight control characteristics:
Where a force trim release button is fitted the sudden release of the force will oftencause the control to ‘jump’ as the pilot changes the amount of force he is applying. In the case of the cyclic this is known as stick jump. To the pilot this can become irritating, as it is not possible to make small changes to the datum trim position. To test control jump, the control is displaced from the trim position, the release operated and the reaction of the control noted. The amount of displacement used for this test is a realistic amount that an operational pilot might employ before operating the release. After ground tests, an airborne assessment is made to determine if any control oscillations cause an undesirable aircraft response.
The Bell 412s I flew needed a microscopic amount of cyclic displacement before the dreaded stick jump. A109E not much better