Is your parachute airworthy???
Inspection guidelines for your parachute.
By Bill Gargano and Betty Pfeiffer
Powered parachutes offer great fun and enjoyment especially when the pilot has confidence in the structural integrity of his/her wing. As the parachute is exposed to a variety of environmental conditions, the flight behavior and structural integrity can change. The purpose of this article is to aid you in performing your own airworthiness inspections. Your inspection is not a substitute for periodically sending your wing to the manufacturer for a professional evaluation. It is our hope that these guidelines will help you determine the urgency of a professional inspection.
If you determine that you need a new canopy, do not fear. You will soon be able to purchase replacement parachutes designed for your personal wing loading, prevalent weather conditions and flight needs. You will have the option of flying with the appropriate wing for the day. These wings will be compatible with any conventional powered parachute vehicle.
Beginning at the beginning.
Inspections should be preformed on a regular basis. Preflight should include any "suspect" areas of damage you have spotted. The following chart offers initial guidelines for your inspection.
Before you begin:
Loosen the suspension lines so the parachute can be opened unrestricted. Do NOT remove them from the connector links!
Hold the parachute up from the trailing edge and shake the dirt progressively out of each cell. This should be done after each flying day before you put your parachute away.
Spread out parachute and begin your inspection
Begin at the tail of the stabilizer (either side)
Follow the lower seam of the pressurized stabilizer towards the leading edge, checking for damage both inside and out. Pay special attention to damage at the corners.
Check the leading edges of the upper surface, the lower surface, and each rib for signs of abrasion or strain.
Pay attention to the sewing at the load rib/surface junctions. Inspect all leading edges until you work your way to the opposite stabilizer.
Inspect the opposite stabilizer followed by the trailing edge.
Inspect inside each cell looking at the ribs, cross-ports and line attachments.
Inspect the material and seams on the upper surface followed by the lower surface.
Lay the parachute on it's side and fold it like an accordion.
Straighten and secure connector links.
Inspect each suspension line for signs of damage.
If your parachute has lines inserted into the seam be sure to follow the line to the very end. This will require that you inspect inside each load cell.
If your parachute has line loops be sure to also look at how the line loop attachments are secured.
Pay special attention to line cascade junctions for signs of wear.
Compare line lengths from each side of the parachute for symmetry. This will require that you apply equal tension to lines from both sides of your parachute. Please note: your flying cables or risers may not be symmetrical. Most vehicle manufacturers use different length left and right flying cables or risers to offset the engine torque. You will need to compensate for this difference in order to compare suspension line symmetry.
Inspect the connector links and the order in which the lines are attached to each connector link (suspension line continuity).
The following chart is to be used as a guide to determine the severity of the damage you may find. If you find damage not described here consult the manufacturer.
|Inspection item||Possible cause of damage||remedy||comments|
|Holes||Abrasion from gravel, twigs, pavement, people walking on the parachute while it is deflated, etc.||If only one ripstop square is
affected, leave it alone. If four or more are affected, temporarily cover with sticky back
rip stop tape.
If you have 4 or more holes within a 12" square, your parachute needs immediate attention.
|There is a large difference between a hole and a tear. Tears need immediate attention. A hole can develop into a tear, so be sure to keep an eye on all holes.|
||Small cuts from sharp objects catching on the material, razor grass, barbed wire, getting caught on your vehicle, or people walking on the parachute while it is deflated.||Patch the tear using conventional parachute patching guidelines. For greater detail consult The Parachute Manual by Daniel Poynter.||Tears are subject to ripping
dependant on the current strength of the material. Faded or worn material will rip more
easily than new material.
All tears are cause for grounding. Tears can rip and you cannot do anything about it once you are in the air.
|Snags in the
|Dragging the parachute on sharp
objects such as prickers, razor grass, gravel or rough cement.
Material contacting Velcro hook or zippers.
|If three or more fibers are pulled from the weave of the material a patch will be required. If you have 4 or more snags within a 12" square of material, patch immediately.||If the snags are minor you can sometimes work the fibers back into place by tensioning the area with your fingers and working the material using an up and down movement. Another possibility is using a pencil eraser to help work the fibers back into place.|
|Faded material||Ultraviolet degradation.||Have a professional evaluate the existing strength of the material.||Most current fabric manufacturers use effective UV inhibitors. Older powered parachutes may show more weakness due to the materials used.|
to outside substances
||Oil, grease, plant secretions, spills, squashed bugs.||Determine if the substance was alkaline or acidic and wash accordingly.||Use a mild soap, rub gently and rinse well. Only wash the affected area since some materials are adversely affected by water.|
|Pinched or severely wrinkled material||Fabric caught in prop, pulleys, engine or landing gear. This is a strong indicator that further inspection is necessary.||Hold the affected area up to the light and inspect for damage such as broken fibers and threads. Gently pull the affected area, or use the riggers thumb test, to see if it easily tears. If it shows any sign of weakness, have it professionally repaired. Try to determine where or how the material became wrinkled so you can make a special effort not to let it happen again.||If the material was tightly
stretched i.e. had become tangled in a rotating prop or axle, it was likely damaged beyond
safe use and needs to be inspected by a professional.
If you have not been properly trained to do a thumb test you could further damage the material.
|Hard or stiff areas||Fabric melted due to contact with extreme heat (220 degrees or more). This is most likely due to fabric dragging across the engine.||Determine the extent of the damage using a riggers thumb test and patch as necessary. If you have not been properly trained to do a thumb test you could further damage the material.||It does not take long for heat to damage small portions of your parachute beyond safe use. Thoroughly inspect any portion of your parachute or lines that may have come into contact with anything hot.|
|Loose Threads||Poor tension during manufacture.||If you can pull the seam apart 1/32" or more at the loose stitching the area must be re-sewn.||If you see an area with many loose threads, check to make sure there is stitching connecting them.|
|One continuous thread running along the seam||Sewing machine operator ran out of bobbin, sewing machine is skipping stitches.||Re-sew seam immediately.||Sometimes a seam can look like it is correct from the top but it is actually held together by one thread wedged in and out of the material. This can hold together for a period of time then pull apart. Inspect both sides of each seam.|
||Abrasion, poor stitch tension, poor thread quality, razor grass, alfalfa stubble.||If 3" or more of one row of
stitching is broken in a double stitched seam, reinforce immediately. If one seam has 2 or
more effected areas, reinforce immediately. If one parachute has 3 or more seams with
broken stitching, reinforce immediately.
Any one seam with 6" or more of missing stitches ground immediately.
|Any structural area of your parachute that is missing stitches should be grounded immediately.|
|Nicks extending over 1/4 the width of the tape||Abrasion or getting caught on sharp objects.||Send your canopy to the manufacturer for repair.||Tapes are usually located at the leading edges of each cell, on the load ribs, around the stabilizers and at the trailing edge. Sometimes they are exposed and sometimes they are rolled inside the material.|
|Nicks extending less than 1/4 the width of the tape||Abrasion or getting caught on sharp objects.||Preflight that area after each flights to be sure the situation is not getting worse. Have it repaired at your earliest convenience.||Do NOT cover the affected area. It is important that you can easily monitor the damage.|
|Broken tapes||Over loading the tape, environmental factors and sharp objects.||Do not fly! Send to manufacturer for repairs immediately|
|Line attachment points|
|Loose stitching||Sewing machine tension off or unusual strains placed on the line due to snags or other restrictions.||Re-sew immediately.|
|Torn or worn webbing loops||Over loading the parachute.||Replace immediately.|
|Straight line stitching overlapping 4 or more times||Manufacture or improper repair.||Consult manufacturer.||An area with too much stitching may actually weaken the material. Failure of certain line attachments can prove to make controlling your flight extremely difficult.|
|Stitching has overlapped the tape and gone into the material. This is more likely to happen on line attachments sewn with a single sew line||Sewing machine operator sewed too far.||Consult Manufacturer.||When the parachute is under load this over sew can cause undo strain on the fabric. The strain can cause a hole that can then become a tear. (Pointloading)|
|Broken lines||Abrasion caused by rubbing, or environmental factors, mufflers, cylinder heads.||Replace immediately with factory lines or do a proper field splice. Make sure there are no knots. The end result must be a line that is the proper length when compared to its matching line on the opposite side of the parachute. Note: Be sure to pull both lines with 15 pounds tension when comparing line symmetry.||DO NOT tie broken lines together in an attempt to fly. Tying any line or lines together is extremely dangerous.|
|Snags in lines||Getting caught on a variety of objects.||More than 3 snags within a 12" distance, replace the whole line.|
|Hard spot in line||Friction or heat damage.||Replace immediately. If your Steering line is affected, do not fly!|
|Line sheathing is worn||Rubbing.||Replace line immediately.||Once the sheathing wears through your line may stretch and cause problems in flight.|
|Abrasion caused by the steering line guide system.||Replace the line. Although the material used on many lower steer lines will retain much of its strength even though the sheathing is worn through, you can still experience stretching that will change the performance and "feel" of your parachute in flight.||Fixed pulleys and rings are prone
to cause severe abrasion when the pull angle is not lined up exactly right.
Articulated pulleys (freely moving from any direction) are less susceptible to contributing to this kind of damage.
|Cross line, E line or F line damage||Replace soon.||While your Parachute will still fly full performance has been changed and possibly compromised.|
|Stabilizer or A line damage||You are grounded. Replace immediately.||Do not fly Very dangerous if it should happen to break in flight!|
|Lines "out-of-trim"||Extended use, excessive loading, repeated high force maneuvers at high wing loading.||A qualified technician should verify the relationship of all lines to the design baseline. If "out-of-trim", all the lines should be replaced.||Parachutes that are "out-of trim" will not perform as when new. If your wing is no longer flying like it once did, and the wing has 200 hours or more flight time, your lines should be checked.|
|Lines you suspect have been stretched||Tangled with propeller, tangled in landing gear, became wrapped around axle.||Check the line for symmetry with corresponding line. If you have a difference of 2.0" or more replace the line immediately.||If this is an A line, do not fly. If it is up to 3 other lines, replace as soon as possible and understand that flight performance has been changed and possibly compromised.|
|Flying Cables, Flying Risers and Connector links (Maillion Rapide)|
does not open or close smoothly
||Rust, corrosion, dirt, not fully tightened before first flight.||Replace your link with the appropriately sized stainless steel Maillion Rapide Link from your vehicle or parachute manufacturer.||If you are not sure if your quick link is stainless steel do a magnet test. A magnet will not affect a stainless steel fitting.|
|Flying Cables twisted||Parachute twisted through itself when handled, or improper assembly.||Untwist the parachute or re-rig
the Flying cables, connector links, and steering so there are no twists.
Note: Do not remove the lines from the links.
|Twisted flying cables inhibit your ability to steer if the twist causes the lower steering line to go around the cable.|
|Flying cables or flying risers shows signs of nicks, wear or fading||UV exposure, rubbing or other abrasion.||Replace||The potential for a single point failure is not worth the risk of flying with damaged cables, risers or links.|
|Stuff Bags, Line sleeves and Connector Links|
|Velcro Hook and zipper on Stuff Bag||Inspect carefully for
threads or other signs of parachute or line fibers. If present try to locate the damaged
area and proceed accordingly.
When stuffing parachute into a bag, roll the Velcro hook to the outside of the bag before inserting canopy and lines.
|Velcro hook or zipper on line sleeve||Inspect carefully for
signs of line or parachute damage.
Adjust your line sleeve placement technique to insure no contact with Velcro or Zipper.
|Inflating your parachute before you fly|
|Listen to your wing||As your parachute pressurizes listen to how it sounds. If you hear anything strange stop, turn off your engine and inspect your wing. If you have had some damage to your wing listen for ripping sounds.|
|Listen to your wing||Become familiar with all the sounds you hear in normal flight so you can identify anything that may be new or strange.|
Over the past 15 years, the materials available to build better powered parachutes systems have improved dramatically. The following chart displays materials commonly used, the strengths and weaknesses of that material for powered parachute applications, and the maximum number of hours of airtime appropriate for each material. Obviously these hours can vary depending on humidity factors, temperatures, and harsh UV conditions. For the purposes of this article we will assume that the pilot carefully stores the parachute in a clean dry dark area in between each flight.
|Surface Panel Material Type||Performance strong points||Performance weaknesses||Recommended airtime limit and comments|
|1.9 ounce Nylon rip stop with polyurethane
coating. (This was used in a
very limited number of parachutes in the mid and late 1980s.)
Note: the actual fabric weight is 2.1 to 2.3 ounces per square yard.
|Readily available, tear strength of 8 to 10 pounds||Parachute weight was excessive, making it difficult to handle, inflate, and fly. Flight performance is also affected by the excessive fabric weight. Poor quality UV inhibitors allow for the early demise of a wing made from this fabric||150 hours flight time|
|1.1 ounce (F111, Exacta Chute, MIL-C-44378)
nylon parachute cloth. Silicone treated.
Note: the actual fabric weight is 1.2 to 1.3 ounces per square yard.
|Low permeability when new (0-5 cfm), readily available, light- weight, tear strength when new of 4 6 lbs.||Absorbs water and deforms shape when flown
wet. Permeability increases rapidly after 20 hours flight time.
Parachute fabric has less resistance to stretch than stabilized fabrics.
|200 to 300 hours flight time or less if you experience inflation difficulties or increased stall tendency.|
|¾ ounce nylon spinnaker cloth, or equivalent
urethane impregnated nylon cloth.
Note: the actual fabric weight is 1.2 to 1.3 ounces per square yard.
|Low stretch characteristics, zero air permeability. This is a stabilized cloth. It holds the designed shape better than traditional parachute cloth.||Tear strength of 1.5- 3 lbs. Creased areas become weakened over time.||150 hours flight time
Note that many of todays parachutes use spinnaker cloth for the vertical ribs of the wing. In this location, and properly reinforced, the spinnaker cloth will last an expected 750 hours of flight time.
|Soar-Coat / PN4 / Blue or equivalent 1.1 ounce
silicone impregnated, nylon cloth.
Note: the actual fabric weight is 1.2 to 1.3 ounces per square yard.
|High tear strength of 10 lbs. in both warp and fill direction. Zero porosity even after multiple washings, improved UV inhibitors, silicon coating improves snag resistance||Colors fade quickly (noticeable within 50
hours of flight time) and the fabric weakens due to UV exposure.
More difficult to inflate than a stabilized cloth. May require stiffer ribs or other design considerations to improve inflation and pressurized shape.
|750 hours flight time assuming no structural damage.|
|MO Powered Parachute cloth
1.0 ounce urethane impregnated, stabilized, zero porosity, nylon cloth
Note: the actual fabric weight is 1.2 to 1.3 ounces per square yard.
|Stabilized weave, high tear strength (5 lbs.),
constant zero porosity, exceptional UV resistance lasting up to 4 times longer than
traditional parachute fabrics.
Easier to inflate. Tends to hold designed shape in flight, which improves airflow and performance.
|Color fade becomes noticeable in about 200 hours of flight time due to UV exposure.||We expect 2000 hours flight time. This fabric will soon be available on select powered parachute canopies.|
Powered parachute lines have gone through a similar evolution as far as performance characteristics best suited to powered parachutes.
|Material Type||Performance strong points||Performance weaknesses||Recommended airtime limit and comments|
|Nylon parachute line, sheathed or coreless, treated or untreated.||Readily available in a variety of strengths and sizes.||Excessive elongation in load bearing areas up to 27%.||Do Not use. Will cause unpredictable turn and stall problems.|
|Dacron (Polyester) usually coreless and treated.||Readily available in a variety of strengths
Bitter ends can be inserted back into the line, providing a clean, strong junction.
|Up to 11% elongation. Will go "out-of-trim" over a period of time.||Parachute "trim" should be checked every 25 hours. Lines will likely need replacement around 250 hours.|
|Kevlar, usually coreless and treated.||Approximately 2% elongation, small diameter for strength.||Quickly degrades in dirt and UV. Snags easily.||100 hours flight time|
|Spectra 1000, usually coreless and treated.||Approximately 1.5% elongation, small diameter for strength.||Low melting point. Dangerous to handle in high winds (it will cut you).||750 hours flight time|
Dacron sheathed, Spectra core, braided line.
|Approximately 1.5% elongation, small diameter
Available in multiple colors, allowing suspension line location color-coding.
Easy handling. Easy to identify damage. Difficult to tangle. Low drag profile.
|Cannot be inserted into itself and therefore requires long zigzag stitching at each end.||Ultimate unknown at this time but we expect 1000 hours flight time.|
Damaged or "out-of-trim" line sets can be replaced when your parachute is still airworthy. A damaged line set may also be "out-of-trim". Therefore, your parachute may perform differently (more like new) once you replace the line set.
All field repairs require monitoring for further damage. If some repairs are done wrong they can stress adjacent areas. Below are a few tips to help you perform safe field repairs:
|Patches using sticky back rip stop nylon tape||Cut your patch to extend not less than
½" past the damaged area.
Round off all corners to minimize them being peeled up during use.
Patch both sides of the affected cloth.
Keep all patches away from dirt.
If patched area will not be repaired for 3 months or longer, machine stitch the perimeter 1/8" in from the edge.
|Sticky back patches are notorious for
collecting dirt at the edges. This dirt can cause abrasion damage to the material and you
can end up with a hole the same size as your patch.
All sticky backed patches should be replaced with a conventional patch within 1 year of application.
Sticky backed patched parachutes stored in warm areas are prone to having the patches slip and leave the original area gummy.
|Patches using Duct Tape||Use the same precautions as discussed above||Some duct tapes are excessively rigid others are excessively "gummy". Many work quite well in a pinch, but should be replaced with a proper patch.|
|Line replacements||Always replace your line with a line of the same material as the damaged line. Always compare line symmetry with 15 lbs. pressure on both the new and old line. If the line length difference is greater than 2" return the line to the factory for the correct size.||Different line materials may stretch differently. NEVER use dissimilar materials for line replacements.|
|Line splicing||This should only be accomplished by a trained person using the same material as the original.||Only coreless braided lines with appropriate weaves can be properly spliced in the field.|
|Tying lines together
||NEVER DO THIS UNDER ANY CIRCUMSTANCES||When you tie a knot in a line you automatically weaken that joint by 45 to 60%, depending on the knot that you use. If you tie both ends of one line together you have also automatically changed the line length and thereby the performance and function of your parachute. Do not tie lines together!|
Grounding your wing
As George Worthington once said "Id rather be on the ground wishing I was in the air than in the air wishing I was on the ground".
Briefly we would like to go over some general reasons to ground your wing. This list is far from complete since it pertains only to your parachute and not the hardware, engine or cart.
Holes in your parachute: Although you can still fly with a hole even as large as your fist, when that hole becomes ½ the size of the opening at the mouth of a cell, that cell will not pressurize as needed for proper performance. Your parachute will not fly as designed and may be dangerous
Tears: Remember, it does not take much for holes to become tears and tears to start to rip. Any torn parachute should be grounded. You cannot stop a tear once you are in the air!
"Out-of-trim" lines: This one that creeps up on you. While wings rigged with Dacron (polyester) lines are more likely to go out-of-trim, all wings should be monitored for changes in performance. You know how your wing flew when it was new, remember this and make it your personal performance baseline. Notice if your wing is reacting differently during inflation or during a maneuver that you perform regularly. Notice how your wing performs with extra weight (higher wing loading). Recognize when performance changes or appears to change, and inspect your wing. If it appears "out-of-trim", dont fly it.
Broken Lines Tied together: There is no way to predict how your parachute will react to even one tied line. There are too many variables to predict its performance. It is simply too dangerous to fly a parachute with any tied lines. Dont do it!
Damaged Lower Steering Line: Most powered parachute wings today have safety steering lines. These lines provide a reference for the lower steering line tie-off, and will keep all the upper steering lines in position, should the lower steering line break. However, If you tied your lower steering lines "tight" i.e. pulled in 6 to 10 inches extra for a better climb rate, and one steering line breaks, Your wing will go into a constant turn that you will not be able to control. Therefore, set your lower steering using the safety line and NEVER FLY WITH DAMAGED LOWER STEERING LINES.
Damaged Connector Links
Your Powered Parachute inspection requires you to touch, feel, look and listen to your parachute. There is nothing mystical or magical about your parachute. The more you learn about how and why it works the way it does, the better you can evaluate the airworthiness of your wing.
This article is not to be used as a replacement for having regular inspections as recommended by the manufacturer. It is meant to be a guide for you to evaluate the necessity of repairs in-between normal inspection cycles.
It is our hope that you will continue to learn all you can and enjoy many years of safe flight.
Bill Gargano and Betty Pfeiffer
About the authors:
Bill Gargano has been designing and building powered parachutes since 1983. He is considered one of the leading parachute designers as is evidenced in his current involvement with NASAs X-38 project. In that project he is one of two parachute designers responsible for the parafoil that, in an emergency, will hopefully fly the X-38 and its passengers from the space station safely back to earth.
Betty Pfeiffer has been building emergency reserve parachutes for hang gliding and paragliding since the early 80s. She has authored numerous articles on parachutes and regularly gives parachute safely clinics around the country. In 1997 she received the USHGA Commedation award for her work in promoting safety through education and product improvements.