Ch 07.qxd 8/25/04 11:20 AM Page 7-2 ¥P enetration Ski— The wheel extends down par- tially below the ski, allowing the skiplane to operate from both snow and non-snow surfaces. This type of ski gives poor ground clearance on non-snow surfaces and causes extra drag when on snow. [Figure 7-3] The condition of the limiting cables and their fasten- ings is important to safety in flight. Be sure there is no fraying, kinking, rusting, or other defective condition before each flight. In the air, skiplane flight characteristics are similar to those of airplanes with standard landing gear, except for a slight reduction in cruising speed and range. Leaving the skis in the extended position in flight pro- duces no adverse effect on trim, but may cause a slight loss of speed. Consult the operator’s manual for skiplane performance data, and weight and center of gravity considerations. The AFM/POH skiplane supplement may provide lim- itations including limiting airspeeds for operation with skis in flight and for other wheel/ski configurations. These speeds may be different from the wheel-type landing gear configuration, depending on the type of ski and the tension of the springs or bungees holding the fronts of the skis up. Understand both the limitations and advantages of the ski equipment. Compared to the standard wheel equipped airplane that incorporates individual brakes for steering, skis are clumsy and the airplane is less maneuverable while on the ground. Like a floatplane, a skiplane has a tendency to weathervane with the wind and needs considerable space to maneuver. Maneuvering on the ground and parking require spe- cial techniques which are acquired only through practice. The plastic polyethylene sheathing on the bottoms of the skis may be punctured by sharp objects, including ice. It also may shatter from impacts in extremely cold temperatures. Replacing the bonded type sheathing is very difficult in the field. If the sheathing is riveted, machine screws may be used to secure loose sheathing, but the screw holes must provide for expansion and contraction. Follow the manufacturer’s recommen- dations for patching limited sheathing damage. If damage is extensive, the entire ski bottom may need new covering. Shock cord bungees used in ski rigging deteriorate rapidly when left under tension. When parking the skiplane overnight, detach the bungees at the lower fitting and allow them to hang free. Reattaching the bungees normally requires two or more people. Hydraulic ski retracting mechanisms usually function well in cold environments, but the small, abrupt change of ski attitude occurring at touchdown imposes a severe load on the external hydraulic lines leading to the skis. These lines are a more prevalent source of trouble than the internal parts. Use low temperature oils and greases to lubricate fric- tion points. For lubrication requirements, see the AFM/POH or the ski manufacturer’s manual. 7-2 ¥ Clear Ice— Ice that forms smoothly over a sur- face and has a transparent appearance. ¥G lare Ice— A smooth sheet of ice that is exceed- ingly slippery with no deformities, cracks, or other irregularities in the surface. This ice lacks any kind of traction, with a coefficient of friction near zero. ¥G laze Ice— Snow that has been packed down and frozen to a solid ice pack, or frozen snow. ¥G ranular Snow— Wet snow that has had a temperature drop causing the snow to ball up and/or crust. ¥W et Snow— Contains high moisture and is associated with warmer temperatures near the freezing point. ¥P o wder Snow— Dry snow in which the water content and ambient temperature are low. TYPES OF SNOW TYPES OF ICE OPERATIONAL CONSIDERATIONS Figure 7-3. Penetration ski.