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Predator Pilot Update (2005)

Dear Predator Pilot,

The Predator design is now ten years old. There are about one hundred Predators in the field. Most are 142s and only about ten are 158s.

I have flown the 142 Predator exclusively as my personal glider for the past ten years. Joe Spinney has also gained a great deal of experience on his 142 over the past 5 years. Additionally we receive reports from Predator pilots on an on-going basis. Because of these facts, we have acquired understanding of the pros and cons of the design. I wish to share this information with all Predator pilots and with those who are considering buying a new or used Predator.

It turns out that the 158 Predator is a big man's glider. For those of you who remember the TRXs, the 160 TRX (same size as the 158 Predator) came first followed by the 140. The TRX was a fairly twisty wing; consequently, a lighter pilot could get away with flying the big one without much trouble with handling.

The Predator has a very different configuration in the outboard area of the wing. The span efficiency is much greater than that of the TRX. The 158 works well in the range of 250 - 330 pounds (hook-in). Even carrying more than 300 pounds the 158 displays excellent sink rate, climb, speed range and landing characteristics. Pilots who hook in at much less than 250 generally find the handling to be stiff. Conclusion: It takes a heavy pilot to be happy with the 158. The 142 works well between 160 and 220 (hook-in). I know of three pilots who hook in around 230 pounds on the 142 and do very well.

Haul-Back cable retro-fit

There is a problem with the original configuration of the top front-rear/haul-back cable assembly. Originally there was no plastic tube covering the two cables that run forward from the “key-hole tang” to the haul-back rope thimble. In some fold-down situations one of the cables would lag and kink at the key-hole tang, weakening the cable. Now this cable assembly is manufactured with a plastic tube covering the two cables in this area (about 32 inches).

If neither of your cables has kinked (or bent at all) at the key-hole tang, there is a retro-fit of shrink tube that will solve the potential problem. See "Predator Haul-Back Safety Advisory" at upgliders.com for more information. If one of your cables is bent or kinked, the entire top front-rear/haul-back cable assembly must be replaced. This recall was first announced in 1998.

Pulling the king post down before folding the wings in during fold-down is what causes this problem. The leading edges should be folded in first. Read more here.

Important note

Predator pilots should be aware that any rope, string, or strap tied or otherwise fastened around the keel at any point between the keel pocket and the nose can interfere with the free operation of the glider’s fold-down system. For example: a simple string tied around the keel to attach a tow release can restrict the keel cables and damage them during fold-down.
Always remove any auxiliary equipment you attach to the keel before fold-down.

Cross spar restraint safety

I have had one report that the "rue ring" safety on the cross spar restraint cable was snagged, damaged, and pulled out in flight ostensibly by the hang strap. Those concerned about this can replace the stock rue ring pin with a normal “ring” safety.

Carbon fiber spars

There have been two cases of in-flight failure of carbon fiber spars. Both involved aerobatics. Both were, I believe caused by prior damage to the spars.

The first was on an early prototype which I believe had prior damage to the front (inboard) leading edge spar where it failed during a loop. Some of the fibers held together allowing the pilot to fly down and land without injury. This happened about 1995.

The second happened in 2004. The pilot was doing aerobatics on a high airtime Predator 142 that was a factory conversion from his old TRX. Though it is impossible to tell once complete failure has occurred, I believe that prior damage was the cause of this accident. Tragically, the pilot was killed. There are those who wonder if carbon fiber composites lose strength as they age. Composite experts say no. There are carbon fiber parts on military aircraft built in the early days of composites and still flying today that show no evidence of strength loss.

There is one thing that definitely affects the strength of carbon fiber spars. That is undetected prior damage. It is important to keep your wing out of harm’s way, and inspect it annually or after a hard landing or crash.

The carbon fiber spars are no more damageable than aluminum spars. Experiments have convinced some that carbon fiber spars are less susceptible to damage than aluminum. The fact remains that any glider can have a damaged spar concealed by the sail. It is up to the pilot to be attentive and know his wing before flight.

A good way to verify the structural integrity of your frame just before flight is to flex the tip upward (about a foot) while a helper holds down at the leading edge/cross spar junction. I have never tried this on an aluminum glider.

King post hang strap

The tangs that attach the hang strap to the king post can cut through the strap after hundreds of hours of flight. Some of these tangs were sewn into hang straps without proper deburring, causing damage to the strap much earlier than expected.

The king post “boot” should be detached from the sail and slid up to allow inspection of the hang strap during your annual. Also, slide the spreader tube to inspect the area of the strap that lives inside the spreader for possible damage by the rivets. You should always adjust the spreader so the rivets are on the top before flight to prevent this damage.

There have been no reports of pitch stability problems on a Predator. No reports of tucks or tumbles. Be sure to monitor your reflex bridle height annually by the in-flight method of using the shadows of the bridle lines on the sail to check for looseness. It is well known that all reflex bridles lower with time. It is due to sail shrink/stretch rather than stretch of the lines themselves.

In full-tight VG (while flying at trim speed) shake the control bar and look for excessive looseness of the inboard and outboard pairs. If you suspect they are too loose, stack washers between the ring safety and sail grommet until they are just tight, then remove a washer(s) until they are just loose. This procedure takes several test-flights of course. See manual for static method of bridle height checking.

Internal Wing-shape Definition System

The internal system that maintains and adjusts the shape of the wing through a series of lacing strings must be adjusted properly. If the strings are too tight, the glider will not fly like a Predator. Handling and pitch feel will be affected.

I have found several Predators with their lacing strings too tight. I believe the 205 cord used in the lacing system shrinks with time. REMEMBER TO CHECK THE TENSION ONLY WHEN THE VG IS TIGHT. Check your Predator flight manual for the correct adjustment procedure. In the original manual I forgot to indicate that the VG must be tight while making this adjustment.

Reprinted from the manual (with correction)

The purpose of the lacing device inside the front of the wing is to maintain tangency between the flatness of the bottom surface and the curve of the leading edge area. The system is divided into two sections - inboard and outboard. The lacing strings from the outboard section of each wing are connected together at the root of the wing, and the strings from the two inboard sections are connected together.


Set the glider up completely. SET THE VG AT FULL TIGHT. If you attempt to adjust the lacing strings in loose VG mode, they will be much too tight when the VG is pulled tight.

Untie the string for the rear section. With one hand on the string, watch the leading edge stiffener where it meets the bottom surface at mid-span. Gently pull the string through the loop and then relax it several times as you get a feel for the tension that just makes the bottom surface tangent with the curve of the leading edge. Tie the string off with several half-hitches. Repeat this procedure with the front section.

NOTE: Over tightening the system will defeat the purpose and will pull wrinkles in the top of the leading edge. Handling and pitch feel will also be adversely affected.

Upward wishes,
John Heiney

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