One of our PA28 is a '74 PA28-180 Archer. It's got the longer fuselage and extensions to the slab wing and stabilator. It wants to pitch up with flap extension, just like later PA28s such as our Warrior 2.
Now we also had for a while a slightly earlier PA28-180 with the longer fuselage but the original 'Hershey Bar' wing and stab. The first time I flew it, I was slightly taken by surprise when it pitched DOWN with flap selection.
So, you can have either reaction with apparently small changes to the airframe. Here's the takeaway:
We teach our students to trim for the cruise, 100kt, observe the attitude out of the window. An early exercise, having previously explored the handling at 75 kt and flap zero with a very nose-high attitude we then learn how to extend flap and set up for the approach. With carb heat hot, reduce power whilst maintaining pitch attitude. In a PA28, this invariably means accepting an out-of-trim load requiring back pressure on the yoke. Glance in and note reduced speed, when in the white arc, extend one stage of flap WHILST MAINTAINING THE PITCH ATTITUDE. Expect a change in amount/direction of force required on the yoke, but maintain attitude. Select second stage of flap, set new attitude to maintain 75kt, adjust power to maintain. As aircraft settles to new attitude, note force required on yoke and re trim. DO NOT trim during all these changes. You will probably find that the net trim change with the re configured aircraft is very small or zero. With this technique, there shouldn't be surprises and the speed should remain above the minimum safe speed.
TOO