lowNslow wrote:doug8082a wrote:Also placarded on the flap handle. "Avoid slips with full flaps" as I recall.
B model IPC Fig. 68 item 72, page 113, p/n 0510188
This placard was installed by Cessna but is not required per Type Cert. so some airplanes my not have it.
The CAA (FAA) Approved Flight Manual (AFM) is required equipment to be onboard the aircraft and it's limitations must be observed. The AFM, Notes, Item 6 states, "Avoid sideslips with full flap (40') extension."
All flaps provide additional lift at a point near the aft portion of the wing's chord. The airplane has a CG forward of the Center of Lift (CL). The tail provides a
downward lift which, like a lever/fulcrum, uses the fuselage to leverage the forward CG about the CL fulcrum. This keeps the nose from falling.
The flaps, when deployed, also create a down-wash of air immediately forward of the horizontal tail. This has the effect of increasing the angle-of-attack (AOA) of the tail (which is producing downward-lift) and brings that tail closer to a stall. (And is the reason the B-model has larger, balanced elevators.)
A sideslip will blank off the relative wind on the downwind-side-of-the-slipped fuselage... thereby blanking off that portion of the horizontal tail. In other words... in a B-model the increased-area-and-effectiveness of those large flaps will destroy the effectiveness of one-half of the tail due to a blanking effect. The remaining side will be much nearer to a tailplane stall due to the increased AOA caused by the flap downwash.
A sudden downward pitching moment may be inescapable and uncontrollable.
It is not a disadvantage of a B-model. It is merely a difference. The B-models larger and more effective flaps are nice and they increase aircraft performance. But they have handling differences that must be understood by the pilot and accounted for.
Either use the full flaps..... or slip it.... but not both. (And a B-model...in comparison with and in the same scenario as other 170's... does not need to be slipped with full flaps to accomplish steep descents. It will exceed the capability of earlier models because of it's larger, slotted, Fowler's ... and will equal or exceed earlier model's performance in slips as well, when slipped with only 20 or 30 flaps. Just don't exceed 30-degrees of flaps if you intend to slip it.