High Energy Sports

Powered Parachutes - Articles - Micro-meteorology for the PPC Pilot
by Betty Pfeiffer with Bob Hawk

The performance window of a PPC is very narrow when it comes to safe flight. Beyond the abilities of the pilot and the mechanical condition of the aircraft, wind is the single most important factor in safely flying a PPC. This means that PPC pilots must be in tune with the current wind conditions and learn to identify the changing conditions. The purpose of this article is to introduce some practical approaches for identifying flight conditions.

Much of this information came from years of flying hang gliders. Some comes from the scientific approach of meteorologist and PPC pilot Bob Hawk. This information is far from complete but we hope it opens doors for better understanding of the air in which you fly.

PPC pilots must be able to evaluate the weather conditions to determine if they are suitable for safe flight. There are several ways pilots can evaluate the weather. Since most flights are less than 2-2 ½ hours, current conditions and short-range forecasts are of prime interest.

Look around you. Look at flags, smoke stacks, your favorite tree top, pond or lake surface, and a variety of other things that you have in your locale.

Check local radio and TV. Tune into the local conditions and forecast report on your radio station or television. The Weather Channel provides a local zone forecast several times per hour. The local forecast they provide is issued for your general geographical area by the National Weather Service. You should learn what area your zone forecast covers and know how you fit within this area.

Internet weather sources. There are many weather resources on the Internet. You need to find a source that is understandable to you and provides valid and appropriate weather information that you can use. It is important to become aware of the sites within your area that take hourly weather observations and have weather forecasts issued for them. You can then check out this information.

In viewing this site remember, the direction of the wind is the direction that the wind barb is pointing. North is straight up, South is straight down, East is to the right and West is to the left. For example, if the wind barb is touching the 9 o’clock position of the small circle that represents the recording station, then the wind is from the west.

The little flags on the side of the wind barb indicates the wind speed. A short flag indicates 5 mph, a long flag indicates 10 mph. A short and a long flag indicates 15 mph.

What to look for: Watch for indications of fronts moving in or changes in wind conditions. Look for areas of high and low pressure relative to your location. High-pressure systems are associated with stable, cooler good weather while low-pressure systems are associated with less stable bad weather. Air will move clockwise around a high-pressure system and counter-clockwise around a low-pressure system.

By viewing your local weather station model you can easily see the velocity and direction of surface winds and the temperature. The diagram below explains how to read the model:

Be sure to scan over the whole area and look for changes in wind direction, temperature or velocity.

Remember: weather can sometimes move faster or slower than expected. If you suspect a front will move in during the evening and you are flying in the afternoon, keep and eye out for pre-frontal conditions in the distance.

The real way to tell what conditions are like right now is to take a look outside. Do you feel a breeze? Is it consistent or gusty? Take a look at the following common wind indicators keeping in mind any obvious obstructions that may be affecting the wind direction.

Common wind indicators	Comments
Windsock	Learn to recognize wind velocity on your local windsocks by correlating wind speed with the angle of the windsock. Not all windsocks will angle at the same velocity.
Flags	If you can sight several flags, note if any are blowing in a different direction from the rest. Do not assume all flags will wave the same amount in the same wind velocity.
Smoke	The more the smoke leans, the stronger the wind. If the smoke flattens out at a certain altitude you can suspect an inversion or wind shear.
Tree tops	Good indicator of what the wind is doing at tree height. Sometimes you can feel no wind on the ground but see the trees shaking violently. Do not be fooled by rotors (mechanical turbulence caused by obstacles). When looking at trees always consider what might be behind the trees. A solitary tree is a better wind direction indicator than the trees on the edge of a forest.
Tall grass or other vegetation	Indicates wind at ground level
Dirt or sand	Watch for blowing dirt and dust devils
Birds	Pay special attention to their wing position, flight path, and altitude gain or loss. The faster they are climbing, the stronger the lift. The larger the circle they are flying without flapping, the bigger the thermal. If they are soaring in a straight line (no altitude loss) without flapping you can expect lifting air under their flight path. If they are soaring with wings tucked in you can expect strong wind. Once you become familiar with your local soaring birds you can correlate their presence with your safe flight conditions. One PPC pilot notes that when the vultures are soaring it is time for him to land. Special Warning…never trust a Raven. They are known for circling in sink and making it appear like lift just to lure over unsuspecting hang glider and sail plane pilots.
Clouds	Upper level clouds: Very simplistically if the upper level clouds are filtering out the sunlight you would expect less thermal activity and better PPC flying conditions. Medium and low level clouds Look at the shape of the clouds. If they are cumulous clouds and the edges are well defined and the bottom is flat or even a bit concave, there is lift. If the edges are ragged and the undersurface becoming fuzzy, there is sink. The magnitude of the turbulence is related to conditions such as air stability (low pressure versus high-pressure systems), lapse rate (air temperature changes as you increase your altitude), and the heat source feeding the cloud.
Haze lines	Polarized sunglasses make it easier to distinguish haze lines. The haze can be an indicator of a front coming through (especially if you see small clouds forming at the leading edge of the haze), or of an inversion where you have increasing warmth with altitude.
Smog	This works much like a haze line. Generally speaking the fumes near the top of the smog are the most toxic,
Fog	Watch for fog banks rolling in. Visibility can quickly get close to zero even at ground level. Do not be fooled by holes in the fog. These can close very quickly.
Lakes or Ponds	Watch for ripples on the surface, anything more than ripples or anything that creates waves is probably telling you that it is time to be on the ground. Note the direction and velocity the wind is blowing to produce waves. Before you draw any conclusions note the area around the water. Is the water surrounded by tall trees or brush thus shadowing the wind or is clear space all around the pond making the water a good wind indicator?

As Pilot in command you must constantly be aware of the changing conditions. This means you must remember to keep watching the wind indicators and make mental note of any changes and take appropriate actions. Watch the close wind indicators but scan the horizon for additional information.

Gust Fronts	A wall of dust or wind moving across the terrain. If there is moisture associated with the front, you may notice low level clouds moving in.
Sea Gulls flying inland	A storm is brewing at sea
Convergence	You start to smell moist air even though you took off in very dry air or vice-versa.
Birds thermalling	There are more birds starting to make circle tighter circles, and gaining altitude rapidly.
Spiders, Trash bags or other debris in the air with you	Thermal activity strong enough to launch the debris. Note, grocery bags have been known to fly an extraordinary number of miles on various air currents.
Temperature differences at altitude	Lapse rate refers to the change of temperature with height. The greater the change in temperature from ground level to altitude, the faster you would expect air to go up.

The better you "know your PPC" and piloting skills, the better you can utilize local weather information. Since wind is the primary factor restricting your airtime, if you know the predicted winds aloft, and know the time and temperature at which thermal activity is expected to begin, you can pretty much determine your safe flight window ahead of time.

Some important information that will help you determine the weather conditions for the day can be calculated with an Adiabatic Chart used by sailplane pilots to chart out the height and strength of thermals. If you are lucky enough to have a weather station close by that can provide you with a soaring report, you will want to pay attention to the thermal trigger time, altitude, strength and trigger temperatures.

If you know surface winds, winds aloft, temperature and altitude you can know when to expect thermal activity. With this information you can adjust your safe flying time accordingly.

All air sports share the need to accurately read and predict the weather. The more we learn about micrometeorology, the safer we are as PPC pilots. It is our hope that this article has stimulated some thoughts and provided direction for PPC pilots to learn more about the air in which they fly.