Know-It-All Q&A - Powered Parachute
Q. Why is the after-landing roll a critical phase of flying the powered parachute (PPC)?
A. The landing process must never be considered complete until the PPC has been brought to a complete stop, the engine shut down, and the wing collapsed and on the ground. Many accidents have occurred as a result of pilots abandoning their vigilance and positive control after getting the PPC on the ground. Some have damaged their parachute by failing to stop the engine before the wing falls into the moving propeller. Other incidents have occurred where the wind has caught a still-inflated wing and rolled the powered parachute over.
Q. What’s the stability of a powered parachute?
A. A stable aircraft is one that will routinely return to its original attitude after it has been disturbed from this condition. Usually this means returning to straight and level flight after encountering turbulence that disrupts a normal flight path. The more stable the aircraft, the easier it is to return to a straight and level position. The natural tendency of the pendulum—the powered parachute (PPC) cart hanging under the wing—is to return to its original centered position under the wing. The pendulum design gives the PPC airborne positive dynamic stability and positive static stability for roll and pitch because the weight of the pendulum wants to return the PPC to level stabilized flight. No matter what maneuver within the pilot’s operating handbook limitations the PPC is put through (regardless of whether it’s pilot induced or turbulence created), as soon as the disruptive force stops, the aircraft is designed to return to a stabilized flight condition, with virtually no pilot input.
Q. What makes the powered parachute unique compared to other aircraft?
A. The powered parachute is a category of aircraft that flies in a manner unique among light-sport aircraft. Three significant differences separate the PPC from other types of light-sport aircraft (LSA):
- The wing must be inflated and pressurized by ram air prior to each takeoff.
- The aircraft uses a pendulum configuration, where the cart hangs about 20 feet below the wing, connected via flexible suspension lines.
- The wing is at a relatively fixed angle with the suspension lines and flies at a relatively constant speed. Other aircraft categories allow pilots to change the speed of the aircraft, but the powered parachute airspeed remains within a very small range.
A powered parachute can be a single-place ultralight vehicle, a single-place light-sport aircraft, or
a multi-place light-sport aircraft. The common acronyms for this vehicle/aircraft are PPC (powered parachute), PPCL (powered parachute land), or PPCS (powered parachute sea).
Q. What is meant by a wing wall?
A. The term “wall” is simply defined as the canopy literally forming a wall-like appearance behind the PPC. The trailing edge of the canopy is still on the ground, while the leading edge of the canopy forms the top of the wall. The wall is the first canopy problem that might occur during the initial kiting of the wing.
Even though some pilots will try to “pop” the canopy out of the wall, the only safe solution is to immediately abort the takeoff and re-layout the canopy. By shutting down and restarting the takeoff preflight, pilots will save the expense of many line and propeller repairs. Lines will inevitably become damaged when a pilot tries to pop the canopy out of the wall via sharp throttle movements. When you fight the wall, you create an ideal situation for lines to get sucked into the propeller.
Q. Why does my powered parachute seem to have a longer ground run in a crosswind?
A. As the nose wheel is being raised off the runway, the steering control for the powered parachute is transferred fully to the wing flight controls. If a significant crosswind exists, it will take longer for the powered parachute to take off because the steering control adds drag to the wing. This may be naturally compensated for by the headwind component of the wind as well as the tendency for the deflected side of the wing to act as a flared wing.
As both main wheels leave the runway and ground friction no longer resists drifting, the powered parachute will be slowly carried sideways with the wind unless you maintain adequate drift correction. Therefore, it’s important to establish and maintain the proper amount of crosswind correction prior to liftoff by continuing to apply steering bar pressure.
Q. What traffic pattern should I fly at airports?
A. Different traffic patterns at the same airport may be established for heavy aircraft, GA aircraft, gliders, and light-sport aircraft (LSA) operations. The largest factor in determining the proper traffic pattern is airspeed. Slow aircraft do not mix well with fast aircraft. The powered parachute is at the slow end of the speed range of aircraft found around most airports. Regardless of the traffic pattern flown, you must be aware of your position relative to other aircraft in the traffic pattern and avoid the flow of fixed-wing aircraft. Helicopters fall under the same rule. This rule frequently affects the choice for a landing site.
With that in mind, you must understand the standard airport traffic pattern in use at the airport you are operating at and the traffic pattern you are flying to maintain separation from other aircraft traffic.
Q. Should my normal approach to landing be made power off or power on?
A. The objective of a good final approach is to descend at an angle that will permit the powered parachute to reach the desired touchdown point. Since on a normal approach the power setting isn’t fixed as in a power-off approach, adjust the power as necessary to control the descent angle or to attain the desired altitudes along the approach path. This is one reason for performing approaches with partial power; if the approach is too high, merely reduce the power. When the approach is too low, add power.
Q. Why do pilots pull their parachute lines down after they land?
A. When landing in a crosswind, there is a concern that the wing will blow downwind during the after-landing roll. This is due to the fact that the wing is flexibly attached to the cart.
Any time a powered parachute is rolling on the ground in a crosswind condition, the upwind side of the parachute is receiving a force that wants to push it downwind.
If no correction is applied, it is possible that the upwind side of the parachute will rise sufficiently to cause the downwind side of the parachute to strike the ground. If the wind and/or forward motion of the powered parachute is great enough, a rollover may result. It is important for a pilot to remember that the parachute should be flown or pulled to the ground right after landing the cart. The cart and the parachute’s movements should be controlled together on the ground.
Q. What are the steering bars?
A. The steering bars are located just aft of the nose wheel and mounted on each side of the aircraft; they move forward and aft when the pilot applies foot pressure. The steering lines from the trailing edge of the wing are attached to the outer ends of the steering bars. (Some manufacturers have developed a steering pedal system on their airframes, although the steering lines function in the same manner.) Main steering lines divide into various smaller lines, which attach to multiple points on the trailing edge of the wing. Pushing on either one of the steering bars causes the steering lines to pull down the corresponding surface of the trailing edge on the wing, creating drag. This in turn slows that side of the wing and banks the powered parachute into a turn.
Pushing both steering bars simultaneously causes the steering lines to pull down equally on the trailing edge, which causes two things to happen:It decreases the powered parachute’s forward speed by increasing the drag and; it changes the shape of the wing, increasing angle of attack which increases lift. This procedure, called “flaring” or “braking the wing,” allows the pilot to touch down at a slower rate of speed and descent, thus creating a smoother landing, which results in less wear and tear on the aircraft as a whole.
Q. How does propeller torque affect a powered parachute (PPC)?
A. Torque is a reaction to the mass of the turning propeller. If the propeller is turning to the right, the reaction is for the cart to want to turn to the left. Therefore, a right turn is sometimes designed into the PPC system to counteract the torque. PPC manufacturers compensate for this with various designs:
- Dual (counter-spinning) propellers. This is an ideal way to counter prop torque, but counter-rotating gearboxes are complicated, more expensive, and weigh more.
- Different riser lengths. On a clockwise-turning propeller, the left riser is longer than the right.
- Swivel the wing attachment on a tilt bar above the cart.
- Adjust the PPC frame (longer on the left, shorter on the right) to compensate for the engine torque (for a clockwise-spinning prop).
Additionally, P-factor can be an issue, producing a left turn if the nose of the cart is too high through improper center of gravity (CG) balance of the PPC. Rotating propeller gyroscopic action can also produce turning tendencies if a force is applied which would deflect the propeller from its existing plane of rotation.
There’s no corkscrew effect of the slipstream on a PPC because it doesn’t have a tail in the propeller prop blast.
Q: Can a powered parachute (PPC) wing exceed the critical angle of attack and stall?
A: The critical angle of attack is the angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight. Unlike a fixed-wing aircraft that takes constant awareness of angle of attack to prevent a stall, the PPC wing is designed by the manufacturers to maintain a specified range of angle of attack and airspeeds. It’s resistant to stalls because for all practical purposes it’s designed to fly at a constant normal operating range. This range is maintained if the operator flies within the operating limitations specified in the pilot’s operating handbook (POH). Flying the PPC within the limitations specified in the POH and avoiding turbulence means you shouldn’t exceed the critical angle of attack and stall the wing.
However, situations that could contribute to a stall are:
- a large increase in wing drag (full flare) – which the PPC pilot controls by pulling the wing back, thus increasing the angle of attack (AOA). (Note: A full flare is normally used and recommended only for landings.)
- a quick full rpm throttle input, creating a climbing dynamic pendulum effect loading the wing.
- a quick reduction of throttle during a high pitch angle climb. This quickly turns a high pitch climb into a high AOA. The wing is initially pitched high, climbing the inclined plane under full power, then quickly changes to a gliding flight path when the throttle is reduced, just like an airplane.
- a wind gust from flying in turbulent air. To prevent a stall, don’t go to full throttle while holding a full flare, or as specified in the POH.
Q. How can I minimize the chances of wing lockout?
A. Improper canopy layout, wind conditions, or inappropriate throttle movements during the initial building of the wing during your takeoff roll may cause the wing to “lock out” or stall behind the cart at a 30- to 45-degree angle on its rise. To correct the lockout, reduce power and push both steering controls simultaneously out in a flaring motion until the wing is pulled back to where the tail is almost touching the ground. Then rapidly release the flare so the wing “sling-shots” up and overhead of the cart. Note: This method isn’t recommended with elliptical-shaped wings, as these wings, with their reduced drag, may overfly the cart and land ahead of the rolling cart.
Q. Why do I lose altitude whenever I make a turn?
A. You need more thrust to overcome the increased drag. Try adding a little throttle in the turn. Both primary controls are used in close coordination when making level turns. Their functions are as follows.
- The steering bars bank the wings and so determine the rate of turn.
- The throttle determines vertical speed and must be increased during a turn for the powered parachute to remain level. The greater the degree of turn, the greater the throttle/thrust required to remain level; this is similar to an airplane and weight-shift-control aircraft.
Q. What is the typical service life of a powered parachute canopy?
A. The canopy should always be stored out of direct sunlight and in an area free from moisture and mildew when not in use. Prolonged exposure of the canopy to sunlight will weaken the fabric and shorten the life span of the canopy.
Canopies are made of very lightweight ripstop nylon material typically treated with silicone coatings to prevent air from leaking through the fabric. This fabric is degraded by exposure to sunlight, water, and dirt as well as a wide variety of chemicals that may be found anywhere the canopy is flown or stored. Fabric degradation often occurs very subtly over a period of time and may not result in obvious blemishes or tears. A regular inspection of the parachute fabric is necessary to ensure the fabric remains in good repair, retains an acceptable level of impermeability to air leakage, and remains airworthy. Periodically, canopies should be sent back to the manufacturer for complete factory inspection.
Q. Why am I having problems with my wing oscillating during the kite-up phase of takeoff?
A. Wing oscillations occur for several reasons. There may not have been enough power added initially to kite the wing, or the pilot may have waited too long to correct for a wing that was flying to one side. Some light oscillation is okay and will merely lift one side of the powered parachute into the air before the other. On the other hand, large oscillations will actually change the lift from a straight upward vector to an upward and side-pulling force. An oscillating wing forced into takeoff will most likely roll the airframe.
Oscillations are easier to prevent with good inflation techniques than they are to correct. However, if a wing is oscillating, it’s possible to correct by steering the wing opposite to the side that the wing is drifting toward. In other words, manage the wing, steer it straight. The wrong inputs can make the problem worse. If the oscillations become too severe, it’s best to abort the takeoff and set up again.
Q. I’m thinking about flying a powered parachute (PPC). Should I be worried about the wing blowing over after touchdown?
A. When landing in a crosswind, there’s a concern that the wing will blow downwind during the after-landing roll. This is due to the fact that the wing is flexibly attached to the cart. Anytime a PPC is rolling on the ground in a crosswind condition, the upwind side of the parachute is receiving a force that wants to push it downwind.
During the course of your flight training, your certificated flight instructor will teach you the proper procedure to prevent the wing from blowing over.
If no correction is applied, it’s possible that the upwind side of the parachute will rise sufficiently to cause the downwind side of the parachute to strike the ground. If the wind and/or the forward motion of the PPC is great enough, a rollover may result. It’s important for a pilot to remember that the parachute should be flown or pulled to the ground right after landing the cart. The cart and the parachute’s movements should be controlled together on the ground.
Q. I’m having troubles with initial takeoff canopy cell inflation. What can I do?
A. During the pre-takeoff roll when building and verifying your wing before takeoff, particularly if operating on a soft field, you may find it useful to press the pedals multiple times and hold them about half a second after the wing comes overhead. This has two beneficial uses. First, it assists with opening the outside cells by temporarily increasing internal wing pressure, pushing the air forward and transferring the pressure out to the tips. Second, it helps confirm the steering lines are clear of any impediments, ensuring they aren’t caught on or wrapped around any outrigger tubing or obstructions.
Q. Someone told me to watch out for a line-over. What does that mean?
A. A line-over is one of the most dangerous things that can happen to the powered parachute wing. Line-overs are exactly what they sound like. Instead of the wing line going straight from the wing to the riser system, it takes a trip over the top of the wing first. This means that when the wing inflates, the suspension line that’s over the top of the wing will pinch the wing together and prevent the proper inflation of the wing to produce the airfoil necessary to achieve flight.
If a line is over the top surface of the wing, the pilot risks serious injury or death if takeoff is attempted. To recognize a line-over before you take off, look for a line that is twisted with other lines on one or both sides of the wing. If you see that, your next step should be to inspect the leading edge and top of the wing closely. If you see a line wrapped over the top, you have found your problem.
Sometimes using the stacked method of laying out the wing during the final wing staging before flight versus the inverted method can inadvertently produce a line-over on the top side of the wing as it inflates. Also, stuffing the wing into the wing bag versus methodically folding the wing for storage can cause a line to become wrapped around the top of the wing mistakenly. To correct a line-over, pull the fabric of the wing through the loop made by the line-over. To know which side to pull the noncompliant suspension line toward, trace the line to its home line group (left or right riser) before you start pulling things around. Sometimes the side will be easy to determine because the line-over is either close to the left or right edge of the wing. When it’s not, tracing it is the best way to save time and to determine the correct way to pull the wing fabric.
Q. How do you flare a powered parachute (PPC) to lower the descent rate?
A. For landings, the amount of flare needed is directly related to the descent rate. The steeper and faster the descent, the more flare input is required for a smooth landing. Keep in mind the flare is converting forward momentum into lift. So, if the pilot is landing with a very slow descent rate, then the pilot would only need to apply partial flare during the landing. Use full flare during an engine-out descent, which is the steepest descent of a PPC, for landing.
The measured input of the flare is directly related to the leg extension of the pilot. For one-third flare, simultaneously push the steering controls out approximately one-third of your leg length. During a full flare, you would be fully extending your legs to apply input to the steering controls; one-half flare, you would be pushing the controls out half of your full leg extension, and so on.
A flare should be applied in a single 1-2-3 motion. Apply the flare smoothly, in a rhythmic, even, 1-2-3 motion.
Q. Why is wing trim important?
A. The powered parachute is designed so there is no pressure needed on the flight steering controls, thus, no pulling on the trailing edge when the powered parachute (PPC) is flying along normally. If properly trimmed, the PPC will fly straight with no pilot input except for slight variations due to left-turning tendencies. If the PPC is flying out of this basic balanced condition, one of the steering controls can be pulled down and slight pressure applied on the side to reduce the speed of the faster side wing with a trim lock to temporarily relieve the pilot of constant steering input. This trim lock is a mechanical device the pilot can set on the ground or in flight. It holds the pressure on the side that needs it so the pilot doesn’t have to continually apply pressure.
Due to the inefficiency of increased drag, the constant use of trim locks shouldn’t be a replacement for a well-setup and properly trimmed wing. Most PPCs are currently not equipped with trim locks, but this will depend on the specific manufacturer and make/model. An improperly trimmed PPC can quickly produce pilot tension and fatigue, requiring constant pressure on one of the steering bars.
Q. How do you make adjustments to the center of gravity (CG)?
A. Each manufacturer has specific procedures in the pilot’s operating handbook (POH) to adjust the CG of the cart so that the cart is hanging at the proper nose-high position. It is critical to adjust the CG properly to adjust for variations in occupant weight, which affect the CG location of the cart.
There are typically two types of wing attachment systems: CG adjustment tubes or a bracket with a number of fore and aft attachment points. Each of these systems performs the same task. Either system adjusts the wing attachment position relative to the cart CG. The CG adjustment is typically based upon the weight of the occupant in the front seat, usually the pilot. The rear seat occupant’s weight does not typically come into consideration when determining the CG position, as the rear seat is usually positioned very near the cart CG. To maintain the best overall performance, the aircraft needs to fly with a slight nose-up attitude as specified by the manufacturer in the POH.
Q. I am having problems over controlling and maintaining a smooth flight path during landing. Any suggestions?
A. Chances are you might be porpoising with varying pitch oscillations most noticeably during a landing. These erratic pilot-induced movements are a result of rapid throttle movements. This is a common, correctable error pilots need to be aware of. There is a delay between throttle changes and pitch changes. Porpoising will result if you overcontrol the throttle during a landing attempt, causing pitch oscillations. The overcorrecting throttle movements will cause the powered parachute (PPC) to enter into ever-increasing forward/rearward sing oscillations. If this happens, immediately abort the landing and climb back to pattern altitude. On the next turn to final, relax and use a slow, smooth throttle action.
Q. What makes powered parachutes a unique aircraft?
A. The powered parachute is made up of a cart and a wing. The wing must be inflated and pressurized by ram air prior to each takeoff. The wing is attached to the cart, and the cart hangs by pendulum effect under the wing by suspension lines. The wing is not in position to fly until the cart is in motion and the wing inflates by ram-air effect. The wing is at a fixed angle with the suspension lines connecting the cart to the wing, and flies at a relatively constant 30 mph.
The wing retains its rigid shape during flight due to air pressurization, just as an airplane’s wing is rigid due to internal structure. Both aircraft’s wings have a top skin, a bottom skin, a leading edge, and a trailing edge. Both have curved upper surfaces and relatively flat lower surfaces. The only difference is the fabric construction and the cell openings in the leading edge. The chute is made of zero porosity material that prevents air from escaping. Once air flows in, it has no means of escape except back through the leading edge. In flight, outside air cannot enter the pressurized wing and is forced to flow around the leading edge. This prevents air from escaping from the wing and ensures formation of an aerodynamically correct wing.