The 1968 C-177 Owners Manual says, "Slips are prohibited in full flap approaches because of a downward pitch encountered under certain combinations of airspeed, sideslip angle and center of gravity loadings."
The
current TCDS, though, has somewhat less restrictive language. On the original Model 177 a placard on the flap control must read, "Avoid slips with flaps extended." No such placard is required for the Models 177A and 177B.
The C-177 was originally designed to have a max 40° flap deflection. Cessna engineer and test pilot Bill Thompson wrote,
With the large, powerful flaps giving more than enough drag for a steep power-off descent, we had envisioned no need for forward slips for proper descents. Crosswind landing approaches in sideslips were typically performed with only one-half flaps for better rudder control. However, we were disturbed with control in a sideslip [...].
A nose-down pitch was encountered during sideslips with 40° flaps, which as a result of tuft studies was attributed to stall of about 40% of the stabilator semi-span on the pro-slip (wing-low) side, and some loss of lift due to reduction of angle of attack on the wing-high side of the stabilator. Thompson quoted from an SAE report on the flight tests:
"The nose-down pitch characteristic was eliminated with 25° or lesser flap settings. It was considered mild with 30° flaps and, at this flap setting, it is felt in the controls as a heavy buffet at extreme sideslip angles and is easily controllable.
"In addition to this characteristic, the advantages of only 30° flaps (instead of 40°) were considered to:
"1. Improve the handling characteristics because of excessively high sink rates with full flaps as discussed previously.
"2. Provide easier flare-out capability.
"3. Improve the rate-of-climb in the balked landing go-around."
For all of these reasons, the maximum flap setting was established as 30-degrees for initial production.
[...]
Occasionally, an airplane in Mort Brown's production flight test activity would exhibit the previously-described pitch-down motion in flaps-down sideslips. Some of our customers would experience this in a crosswind landing flare where the pitch-down would bang the nosewheel hard enough to deform the firewall. We were unable to duplicate this fault on the prototype.
Ultimately the factory decided to incorporate slots in the leading edge of the stabilator so it could "tolerate a steeper downflow of air without stalling the under-surface of the stabilator." All Cardinals already in the field were retrofitted with the slots, at no cost to the customers. Pending the modification, a service bulletin called for a temporary physical limitation of flap travel to 15°.
OK new thread started on this.
