Vintage Instructor THE
BY Steve Krog, CFI
Fearing (and Understanding) Crosswinds: Part 1 Mention the term “crosswind landing” to any group of hangar flying pilots and each will have a tale to tell. In candid one-on-one conversations, many pilots will tell you crosswind landings are the single most uncomfortable (feared) maneuver they have to perform in generalaviation (GA) pleasure flying. Ask them why and they will tell you they lack crosswind landing confidence, received minimal crosswind training, and rarely (if ever) practice crosswind landings. Unfortunately, the lack of crosswind training, lack of ongoing practice, and thus a lack of confidence deny many of us the opportunity to enjoy the pleasures of flight on beautiful, albeit breezy, visual flight rules (VFR) days. Be honest with yourself; how many times have you gone to the airport on a blue-sky day intending to fly to a pancake breakfast and then, after a thorough preflight, decided against the flight because the wind “seems to be picking up and I’ll have to make a crosswind landing at the breakfast destination”? Why is that? And what can we, as GA pilots, do to alleviate the fear of the crosswind? For discussion purposes, let’s define a crosswind as a wind that is 10 degrees or greater off the runway centerline on which the landing is intended and the wind velocity is measureable, usually 10 mph or greater. We need to determine the approximate crosswind component, which is the component of the wind vector that is trying to push the airplane sideways (see the Figure 1). In Figure A the 30-knot wind approximately 20
degrees from the left gives us a crosswind component of only 10 knots. In Figure B the 90-degree, 12-knot wind gives us a crosswind component of 12 knots. There are two methods for calculating the crosswind component: The first is the crosswind component chart. The crosswind component chart is simple and easy to use and takes but a minute or two to become familiar with.
FIGURE 2
FIGURE 1 34 JUNE 2010
This is an example of the standard Civil Air Patrol (CAP) Crosswind Chart. Using the example of a 30knot wind that is 30 degrees off the runway centerline, we can determine that we have a 15-knot crosswind component. First select the wind velocity on the vertical scale at left; then follow the 30-knot arc around to the point where it intersects the 30-degree diagonal line. At the point of intersection follow the vertical line down to the horizontal scale indicating the crosswind component, which is 15 knots.
For those of you who like to play on the computer, do a Google search for Crosswind Component Chart and you’ll find pages of charts. (If you’re a smart phone user, yeah, there’s an app for that.—HGF) If a crosswind component chart is not handy, there are some general rules of thumb that you might want to keep in mind: • If the crosswind is 20 degrees off the runway centerline, the crosswind component is 25 percent of the wind velocity. • If the wind is 40 degrees off the runway centerline, the crosswind component is 50 percent of the wind velocity. • If the wind is 60 degrees or more off the runway centerline, the crosswind component is 75 percent of the wind velocity. • If the wind is 90 degrees off the runway centerline, the crosswind component is 100 percent of the wind velocity. Now that we’ve determined how to calculate the crosswind component—either by computer, graph, or the crosswind general rules of thumb—we need to determine what the crosswind capabilities are of the aircraft being flown. Many airplanes that fall into the “vintage” category do not have a pilot operator’s handbook, nor do they have any published information about crosswind components. When many of these airplanes were designed, airports consisted of a quarter-section of turf, and everyone always landed into the wind. However, when runways replaced the turf fields, dealing with crosswinds became an issue. Due to a lack of published information from the various airplane manufacturers, the FAA developed standards for addressing crosswinds. Before an airplane is type certificated by the FAA, it must be demonstrated in flight to be satisfactorily controllable with no exceptional degree of pilot skill or alertness in 90-degree crosswinds up to a velocity equal to 0.2 VSO. This means a wind speed of twotenths of the airplane’s stalling speed with power off and landing gear/flaps down. Regulations require that the demonstrated crosswind velocity be included on a placard in airplanes certificated after May 3, 1962. Using an example of a 1929 Travel Air 4000 powered by a Continental 220-hp radial engine and a stall speed of approximately 55 mph, the crosswind component is 11 mph. For a Piper J-3 Cub with a 65-hp Continental and a stall speed of 38 mph, the crosswind component is about 8 mph. Having flown both of these airplanes, I know they will handle significantly more than this formula indicates. Remember, these are FAA standards, which are general in nature in order for the aircraft to be certificated. Surface winds at the airport of destination are oftentimes gusting. For example: surface winds 240 degrees at 10 mph and gusting to 20 mph. How does one understand and plan for dealing with gusts? Again, there is a general rule of thumb for handling gusty wind conditions; it recommends adding onehalf of the gust amount to the aircraft approach speed.
Using the J-3 Cub as an example, which recommends a 60-mph approach speed, based on the stated winds above, there is a 10-mph gust amount. Add 5 mph to the normal approach speed and fly the final approach at 65 mph. The added airspeed is insurance for sudden wind changes close to the ground by providing more responsive control authority while compensating for the wind variations. However, there is also a downside to the added airspeed, as it will result in a longer landing distance. Now that we’ve come to an understanding of crosswinds, how to interpret them, and what your airplane is generally capable of doing, the final part of the crosswind equation is you, the pilot: • What is your current skill and comfort level? • Do you get a pit in your stomach every time you have to deal with a crosswind? • How often have you denied yourself the opportunity to enjoy a great pleasure flight because “the wind seems a bit too strong”? • How often do you practice crosswind landings? In the next issue we’ll take a look at different methods for making crosswind landings, along with offering some tips to raise your comfort level and expand your personal flight envelope. There is an old saying that definitely applies to pilots: “Confidence comes from practice; caution comes from knowing your limits.”
VINTAGE AIRPLANE 35