Hang Glider Maintenance

Go to Hang Glider Maintenance by Mark Dale and Angus Pinkerton

I have been reading the accident report in the February issue of Hang Gliding and it is horrifying to find that approximately 20% of fatalities last year could have been avoided by a little thought before takeoff.

I am referring of course to accidents which occurred as a direct result of (a) not checking the glider before takeoff and (b) not checking the harness before takeoff. Let us start with the first cause - that of not checking the glider.  The reason that this check is carried out is to determine if the glider has been assembled properly and if it is damaged in any way.  The sort of things that we are looking for are: torn sail, worn sail attachment straps, dents or gouges in tubes, bent tubes, kinked wires, thimbles wrapped round tangs, sail pinching on saddles, bolts loose, safety pins missing, incorrect wire tensions, battens not correctly in sail, etc.   Take care to ensure that all bolts show threads past the nut and that ny-lock nuts are not recycled.

It is recommended, indeed mandatory, that you have another pilot check your glider before takeoff. I suggest that it is best to set up a routine for pre-flight checks similar to that described below in order to try and ensure that no stupid mistakes are made:

1. Start at the nose of the glider and run your hand down one leading edge to the cross tube, checking for: dents, scratches and tears in the sail and batten pockets.
2. Check leading edge bolts, tangs, wires and ensure sail is clear of saddles
3. Run hand along leading edge to wingtip, checking as before and then ensure the sail attachment is OK
4. Run hand along trailing edge to keel, checking for loose threads, proper fixing of battens and tension of the sail
5. Check rear of keel sail attachment, center batten, tangs,  wires and bolts.
6. Carry out the same procedure running along the other trailing edge and up the leading edge to arrive again at the nose.
7. Check nose plate bolts, tangs, wires and sail attachment.
8. Sight along keel and check reflex.
9. Visually inspect the kingpost and ensure the wires are clear.
10. Move to the crossbar and run your hands along its complete length, checking for damage. Yes- even if this means climbing inside the sail if you suspect damage (do the leading edge while you are in there).
11. Check that wire tensions are even on both sides (on level ground) Deflexors as well if yours has them.
12. Move to the "A" frame and check the heart bolts and top  A frame bolts.  Inspect both down tubes for damage and for "work hardened" metal from restraightened tubes.
13. Check both bolts at the bottom of the A frame and ensure the wires are securely attached and not tangled.
14. Run handkerchief along flying wires to test for any kinks or broken strands.
15. If there is anything you are not happy about, make sure the pilot knows about it.
16. Inspect the Harness straps for wear and tear and that the knots are tight and secure.
17. Check the Parachute Bridle for wear and then ensure the chute is securely contained and that the safety pins are in place.
18. Inspect the Hang straps for wear and the height the pilot hangs off the bar.
19. 19) Ensure their legs are inside the leg straps and that the harness lines are not tangled.
20. Tell the pilot your conclusion

As for the frequency that these checks should be carried out, the answer is:

1. After first rigging up.
2. After any hard landings, crashes, alterations or even laying the glider on the ground.
3. Always before a soaring flight because that is of greater duration (usually) than gliding

Now then, having completed that, having a sound glider with you does nothing if you forget to hook up.  There are several things you may not be aware of:

1. It's difficult to hold onto an A frame if taken by surprise
2. A glider dives at about 45o if you fly hanging from the A frame.
3. If you don't pull yourself into the A frame within 30 seconds, you never will.
4. You can't hang by your hands for more than about 1.5 minutes anyway.

So lets get another routine going which you as pilot always go through before takeoff:

1. Move the glider to the takeoff site.
2. Hook up and lie in your harness (if prone) and ask your nose launcher to see if all lines and straps are clear and check the carabiner is properly locked shut.
3. Check your helmet
4. Stand up and look left and right - just a quick visual check of the glider.
5. Ask your launcher to ascertain and tell you what other gliders are around and what they are doing - nothing is worse than to takeoff in the path of another glider.
6. Confirm with your nose launcher what your takeoff procedure will be - ascertain which way he intends to duck, tell him what you are going to say - and be explicit - "Ready, Go:" or "One two three, go" but TELL HIM.  The nose launcher is doing you a favor, he has no glider to stop him falling down the cliff - its only fair to keep him in the picture - TELL HIM.  And when you say Go!, Go for heavens sake.  Don't wait around for winter to fall.  If you don't need a wire launch  you don't need one from the start.

As a last point, don't forget to check out the launch site thoroughly and (hopefully) you will also know something of the landing area.

After all, we hope to minimized danger.  Everybody respects the safety conscious pilot - that should be you. And don't forget, if it doesn't feel right, don't fly, there'll be other times.

(Once you have rigged and inspected your own glider seek out someone else in the same position. This way two gliders can have their second pre-flight check at the same time - an added advantage is that the pilot doesn't stamp around impatiently waiting for you to finish.

With some of the more sophisticated supergliders it would pay to have someone familiar with the machine to do the second pre-flight check.  Otherwise the would be checker suffers form visual overkill inspecting all the wires, tubes, tangs, bolts, etc. which festoon these machines. Inspection efficiency is reduced and some vital fault could be missed.

Hang Glider Maintenance

Thanks are due to Mark Dale and Angus Pinkerton for their help in the preparation of this article.

Hang gliders are very simple machines. So simple, easy to rig, and fly that sometimes we lose sight of the fact they fly on the same principles as much larger and more complicated aircraft and that the failure of any of their many parts will result in a frightening experience ending in a reserve ride or at the worst extreme, death.

Two of the important tools for glider maintenance are not spanners or screwdrivers but pieces of paper, or to be more precise the manufacturers handbook or instruction manual and the batten profile. It is vital to have these in your possession, as many of the queries you may have about your glider can be answered by referring to these documents. Follow the instructions and stick to the placarded limits for your glider detailed in them.

Some of the maintenance that a lot of pilots overlook is maintenance of a preventative nature. < For example, most of the wear on a hang glider takes place not when it is being flown, but being transported. Using two very thin roof bars to which the glider is very tightly strapped means all the weight is being taken by two very small areas, and this will result in wear on the sail in a very small area and even dents in the main tubes if the glider is "dumped" onto the roof rack too hard. Using a ladder or similar to transport the glider on a roof rack will spread the load and avoid the risk of sail damage. Overloading the roof rack results in damage to rack, car roof and the risk of the roof rack coming off the car resulting in serious damage to the glider. An incident several years ago led to three cars being damaged and four gliders being trashed.

Glider storage is another issue that not too many pilots seem worried about. Leaving a glider out in the rain means that the sail will eventually start to develop mildew, with the discolouration and damage to sail fabric that will inevitably shorten a glider's life. Far worse though with aluminium alloy is the risk of unseen corrosion to the insides of the tubes, as the glider in its bag experiences first the extreme damp and cold of an English winter, then the humidity as the water trapped in the bag when it last rained evaporates but can't escape from the bag. Add to this the fact that the glider was landed on a beach and the salt and sand allowed to get inside the sail and you can see how a glider can be reduced to unsafe and valueless quite quickly.

Rigging wires are very easy to kink whilst packing away, and doing so will reduce their life quite considerably as well as risk in flight failure. Some gliders do not have a very good fitting where the side wire leaves the bottom of the upright, and rigging gliders with this type of side wire on the keel like pilots do on the continent will kink them within a few flights.

Battens, especially those made of softer alloy will flatten quite quickly. This has two consequences generally, the flattened aerofoil section does not have as good a minimum sink as the higher cambered original section, and the pitch stability of the flatter section is often worse. Additionally, if the battens have been flattened differently on each side, the glider will develop a turn. This, along with a leading edge bent in a careless landing is probably the most common cause of turns in gliders. Check your batten profile often, both the safety and performance of your glider are at stake!

So, we've discussed glider maintenance, and the word strip down hasn't yet been used. Treating your glider gently, packing it away carefully (both sail and wires), and finding a dry place to store it can do a lot towards delaying the inevitable aging process.

The pre-flight check is the next stage of preventative maintenance ,any gradual changes in the glider may be monitored over a period of time. If you find anything you're not sure about, ask! In one fatal accident, a glider that had been ground looped was flown subsequently without a serious check. The keel failed in flight and the glider folded up. Any thing that's bent in the tube department should be replaced, straightening tubes is very foolhardy. All nuts and bolts should be checked, recently a pilot had an upright fall off a glider whilst preparing it for flight. The bolt that held the upright in place had dropped out, because the nut that retained it had gone missing!

However gliders, like all other aircraft need periodic maintenance. Most of it is of a check nature. Despite the simple nature of a hang glider, after all they're easy to take apart and reassemble, there are a number of pitfalls for the unwary. Accidents and incidents have occurred due to incorrect assembly after a DIY stripdown. One glider had the string used in the early stages of tensioning the pull back bridle attached to the wrong part of the bridle. The force used to tension the bridle was incorrectly applied to the stitching, peeling the seams apart and resulting in failure of the bridle!

Over tightening bolts is a very common mistake. Any parts left over at the end of a rebuild point to a serious error on your part. Manufacturers don't fit parts that aren't necessary, and if you can't see what it does, don't make the mistake of thinking you can do without it!! Certain components will wear and stretch.

One of the most fundamental things to hang glider safety is pitch stability, an area not many pilots understand or have enough respect for. One of the main components of pitch stability is the luff lines. So you need to check your luff lines haven't stretched, and the lengths are still correct? WRONG!! Luff lines are not specified in terms of length, but of luff heights above a fixed datum. Sail stretch means that as a glider ages, if the sail stretches, the luff line lengths will need to be shortened to retain the correct luff line heights. This is definitely a job for the manufacturer. One pilot who had his glider checked found the luff heights at best on the very bottom end of the safety envelope. In fact of the six critical measurements on the glider four were below the acceptable safety standard. Luff lines only work at radical pitch angles, so having them longer will not make a glider go faster. A slight change in height will radically affect a gliders pitch stability.

Leading edges will also acquire a slight set, which is a gradual bend over their complete length. Clouting the leading edge results in a sharp but very small bend. Again, how much set is acceptable in a tube? Without knowing the proper tolerances on these components it is not possible to make an informed decision as to whether to replace them or not. For this reason gliders are best sent back to the manufacturers at the interval specified in the manual for a strip down. All bolts will then be replaced again with aircraft quality ones to the original specification and all wires and tubes checked.

A word of warning for the purchaser of the cheap glider: a glider that is more than five years old with no documented maintenance history may be expensive to make safe. The Germans have a mandatory glider "MOT" at five years and every two years after that. This does protect the second hand market and second glider values in Germany are much higher than the rest of Europe. Most manufacturers run a strip down service during the winter when the weather is bad and glider manufacture enters a natural doldrum. It's a very good idea to take advantage of this to get your glider serviced. The cost is nominal to cover labour unless any parts require replacement, in which case they will have to paid for at standard retail prices. Components like wing wires will need to be replaced very two years or 100 hours, the precise details will be found in your manual. Side wires are not expensive, but if one fails the results will be catastrophic. You may not get much time to consider whether the $323.50 would have been a good investment as you plummet earthwards.

Think about it now, with both feet on the ground!