ROBERT N. ROSSIER BETTER PILOT / STICK & RUDDER

Taming Turbulence Skills for the bumps

NOTHING IS AS TRANQUIL as flight through silky-smooth air. Sometimes we feel as if we’re hardly moving at all. But all that changes when the air around us begins to bubble and boil. Turbulence is a fact of life in the world of aviation, but with knowledge and skill, we can keep the ride as smooth and safe as possible.

CAUSE AND EFFECT

Turbulence arises from a variety of factors. Some of these are as obvious as a developing cumulus cloud, but other times, there’s little or no warning of turbulence ahead. The first type of

Source: FAA Pilot’s Guide to Aeronautical Knowledge

52 Sport Aviation June 2010

ILLUSTRATION BY ALAN LEPKOWSKI

turbulence is called convective turbulence, and it is caused by vertical currents of air created by uneven heating of the Earth’s surface. Unstable air combined with a lifting action is a surefire recipe for a rough ride, and usually signposts warn us of the rough ride ahead. Anytime we see clouds with vertical development, convective turbulence is a sure bet. Another form of turbulence is called mechanical turbulence, and this occurs when obstacles lie in the path of strong winds. The obstacles—either natural (mountains or otherwise uneven terrain, trees) or manmade (buildings or cities)— disturb the smooth flow of air, causing it to alter course abruptly.

to initiate turbulent conditions. Even smaller buildings on the windward side of an airport can cause the wind to become turbulent as it spills across the runways. If we can visualize what the wind might be doing as it encounters these obstacles, we can gain some insight as to where the worst turbulence may lie.

REROUTE YOUR FLIGHT

Depending on the situation, it may be appropriate to reroute your trip to avoid turbulence. Certainly if that turbulence comes in the form of a thunderstorm, a diversion to an alternate flight path is likely needed. Other times, all that might be required is a slight deviation or a change in

AIRCRAFT TOOL SUPPLY COMPANY Toll Free: 1-800-248-0638

AIRCRAFT ENGINE STAND KIT

Unstable air combined with a lifting action is a sure-fire recipe for a rough ride . . .

Our new engine stand requires ABSOLUTELY NO WELDING. We ship it to you in a compact 11”x11”x36” box (which makes shipping costs downright reasonable), with everything you need to get going. All you need to supply are a couple of 1/2” wrenches and a little elbow grease.

Mountain wave turbulence is a specific type of mechanical turbulence created by a special set of conditions. Anytime we have (1) mountaintop winds in excess of about 20 knots, with (2) the wind flowing roughly perpendicular to the mountain range, and (3) a layer of stable air at altitude, conditions may cause the formation of a mountain wave. On the windward side of the mountains, the air flows up the terrain. Beyond the mountaintops the air descends again, often establishing an up-and-down oscillation that extends for tens or even hundreds of miles before it dissipates. In some cases, the mountain wave “breaks” downstream of the mountain tops, resulting in a horizontally twisting wave called a “roll cloud” or “rotor.” This region of severe turbulence lies on the downwind side of the mountain, parallel to the range. Mountains aren’t the only obstacles that can cause “mountain waves.” High terrain, in the form of large city buildings, can create a sufficient lifting force

Works with all Continental and Lycoming engines.

*Shown how you will receive your Engine Stand Kit.

p/n 65530C

* Can ship via Air * Assembled dimensions: 24” high, 36” distance between legs * Includes a set of locking casters for easy mobility * Supports up to 1200 lbs (static tested to 2500 lbs * Includes Adapter for Continental and Lycoming engines * Radial engines may require an optional spline adapter (p/n W670985-20)

www.aircraft-tool.com www.eaa.org 53

ROBERT N. ROSSIER

altitude to avoid the worst of the bumps. Reports from other aircraft can often provide useful cues. Avoiding mountain wave turbulence is often simply a matter of flying a parallel course a greater distance from the mountains, or choosing to fly along the windward side of the mountain range, rather than on the lee side. When flying in mountainous terrain, one way to get a handle on the potential for turbulence is to keep track of the wind direction, and then imagine the wind as water flowing in a rocky streambed. The water rises up over obstacles, accelerates between high points, and then tumbles down the back sides. That tumbling water is where the turbulence lies. If we can avoid those areas, we may be able to find a smoother passage through the terrain. Turbulence along with updrafts and downdrafts can be particularly exciting during departures and landings. Here again, an extra measure of caution is required. The rule of thumb is to add half the gust speed to our approach speed to avoid inadvertent stalls. It might not be a bad idea to add a safety cushion to our climb speed as well. Wake turbulence avoidance begins with situational awareness. In areas where large jet aircraft may be taking off and landing, or climbing or descending, we must always maintain an awareness of our relative position and avoid beingin the areas where wake turbulence is likely. SPEED CHECK

Anytime an encounter with turbulence is expected, the first thing to do is check your speed. An encounter with turbulence while flying above maneuvering speed could spell trouble in the form of structural damage to the airframe. Remember that the published maneuvering speed for the aircraft is for its maximum gross weight, and any weight below that speed implies a lower maneuvering speed. A simple way to calculate maneuvering speed for a reduced aircraft weight is to find the percent by which the

54 Sport Aviation June 2010

weight has been reduced below gross weight. Then, reduce the published maneuvering speed by half that same percentage to determine the reduced value. For example: An aircraft with a gross weight of 3,000 pounds and a maneuvering speed of 120 knots is being flown at an actual weight of 2,700 pounds. Since the weight has been reduced by 10 percent ((300/3000) x 100), we reduce the maneuvering speed

An encounter with turbulence while flying above maneuvering speed could spell trouble in the form of structural damage to the airframe. by half that percent (5 percent). The maneuvering speed for the actual weight of 2,700 pounds is 114 knots ((120 – 0.05(120)). Once again, speed is an important consideration when flying an approach. When making an approach in windy, turbulent conditions, we should adjust our speed accordingly to compensate for the gusts and their effect on aircraft performance. SECURE THE AIRCRAFT

The next item of business in turbulent conditions is to make certain that any loose items are properly secured. This should have been accomplished before departure, but sometimes flight bags and sundry personal items are taken out during the flight. Have your passengers check around the cockpit, and pick up and stow loose items in a secure location. Then make certain that both you and your passengers are belted in securely. When you’re carrying passengers who are unaccustomed to small aircraft, remind them that turbulence in itself is usually not dangerous—just

Solid IFR...

uncomfortable. Explain that the aircraft can withstand much more turbulence than the passengers. RELAX

It really pays to try to relax when turbulent conditions are encountered. Pilots don’t have to wrestle an aircraft through the “bumps.” Instead, make certain the aircraft is properly trimmed, and relax your grip on the yoke. An old freight pilot’s trick for dealing with turbulence is to let your legs do the work by keeping the wings level with rudder input. When a wing begins to drop, pick it up by applying opposite rudder. While such maneuvering is not totally coordinated, this technique can make a difficult flight in turbulence a bit more bearable. REGAINING CONTROL

Sometimes turbulence gets the best of us, and the result can be an “unusual attitude.” If it’s been a while since you’ve practiced unusual attitude recovery techniques, a quick review might be in order. In general, if the airspeed is high and getting higher, reduce power, level the wings, and then pull back gently on the yoke to reestablish level flight. If the airspeed is low and getting lower, add full power while simultaneously rolling wings level and pushing the nose down. Then reestablish straight and level flight. For more hands-on unusual-attitude recovery training, contact a flight instructor or take an introductory aerobatics course. Turbulence is a fact of life that we all must deal with occasionally. By understanding the nature of turbulence, and following standard procedures, we can minimize the discomfort and complete our flight safely.

...with confidence. Its not just the crystal clear synthetic vision, the comprehensive autopilot coupling, vertical steering, flight director, or hundreds of other details that makes GRT Avionics the perfect choice for IFR flight. It is the confidence that comes from hundreds of thousands of hours of proven performance. Designed by experienced aerospace engineers. IFR proven. Expect nothing less from GRT. Primary Flight Display with synthetic vision Moving Map with shaded relief terrain Graphical Engine Monitor with EGT history Dual AHRS - Auto-cross check. No degradation with loss of an AHRS; no need to revert to partial panel backup. Synthetic Approach with highway-in-the-sky to any runway Extensive Lateral and Vertical autopilot coupling expands autopilot functionality. 8 serial ports in/out, 8/14 analog inputs/outputs, ARINC 429 for today and built-in growth for tomorrow. XM Weather, TIS Traffic, Stormscope, ADS-B, and much more...

Dual AHRS/Air Data Computer

Robert N. Rossier, EAA 472091, has been flying for more than 30 years and has worked as a flight instructor, commercial pilot, chief pilot, and FAA flight check airman.

AVIONICS

Grand Rapids Technologies, Inc.

616 245-7700 GRTAVIONICS.COM

www.eaa.org 55