Originally Posted by PilotDAR
Irish Stu, Though I will suggest caution when slipping fully flapped 172's, to my knowledge (the older ones for sure), doing this is something to "Avoid", it is not prohibited. This stems simply from non ideal handling in pitch at certain speeds. Similarly, a door off on a 172 can induce this at about 65kts, and it just feels a bit spongey in the elevators. It certainly won't hurt you.
During flight test, all of this era of planes had to meet this requirement:
3.118 Directional and lateral stability
(a) Three-control airplanes.
(1) The static directional stability, as shown by the tendency to recover from a skid with rudder free, shall be positive for all flap positions and symmetrical power conditions for all speeds from 1.2 Vs1 up to the maximum permissible speed.
(2) The static lateral stability, as shown by the tendency to raise the low wing in a side-slip, for all flap positions and symmetrical power conditions, shall:
(i) Be positive at the maximum permissible speed.
(ii) Not be negative at a speed equal to 1.2 Vs1.
(3) In straight steady sideslips (unaccelerated forward slips) the aileron and rudder control movements and forces shall increase steadily, but not necessarily in constant proportion, as the angle of sideslip is increased; the rate of increase of the movements and forces shall lie between satisfactory limits up to sideslip angles considered appropriate to the operation of the type. At greater angles, up to that at which the full rudder control is employed or a rudder pedal force of 150 pounds is obtained, the rudder pedal forces shall not reverse and an increased rudder deflection shall produce increased angles of sideslip. Sufficient bank shall accompany sideslipping to indicate adequately any departure from a steady unyawed flight.
(4) Any short period oscillation occurring between stalling speed and maximum permissible speed shall be heavily damped with the primary controls (i) free and (ii) in a fixed position.
The 172 does meet the requirement, but is marginal.
I shall quote William Thompson, former Cessna test pilot, who writes in "Cessna, Wings for the World"...
...and C-172 we encountered a nose down pitch in forward slips with the wing flaps deflected. In some cases, it was severe enough to lift the pilot against his seat belt if he was slow in checking the motion. For this reason a caution note was placed in most of the owner's manuals under "Landings" reading "Slips should be avoided with flap settings greater than 30 degrees due to a downward pitch encountered under certain combinations of airspeed, sideslip angle, and center of gravity loadings".
I very highly recommend that any Cessna pilot read that book, it is facinating!
Use caution, discuss with your instructor, and learn. Do not do "prohibited" things in planes. "Avoid" or "Use caution" are just that. Don't worry about flap tracks, just fly well maintained planes, and do walk around inspections as if you're about to hang in the air from the plane.
Be careful, but go and learn, that's what you're up there for.