This discussion will be a long one so bear with me. I will ramble from time to time so just keep reading and you'll get to an interesting part sooner or later.Return to Main Page
I will organize this section by component, ie, the rudder, the stab, the fuel system, so there may be some overlapping but I'll try to remember where I'm at and what has been mentioned. But first, I will go through the original AD's as developed by Quicksilver. Realize that they are many years old and newer thinking may actually supercede a 'fix' that was thought to be OK back then.
The seat mount assembly has had two revisions. It started as two separate pieces that bolted to each side of the seat support tube. The front ends attached normally. Hard landings caused the tubes to rotate and wear the seat, bend the bars and not carry the seat loads into the frame very well. These bars were replaced by an aluminum seat mount, u shaped and all one piece. This piece also failed to carry the loads imposed by bad landings and was replaced by a steel frame, u shaped, similar to that supplied today. I have seen the aluminum frame break and create a life threatening situation for the pilot. Any newly purchased MX should be checked for the correct steel frame. This may be done easily by inspecting the thickness of the mounting ears at the rear. The aluminum frame used 1/8 inch material and the steel part used only .090 inch material, which is noticeably thinner.
Early MXs had no cable to prevent the push-pull tube from getting up into the propellor. Every plane should have such a restraint cable. I have had one instance where a plane was taxied across a curb and the resultant bounce rattled the tube into the prop.
A large area of concern is the push button pins that were used for attaching the rudder, the elevato and many airframe components. these pins are strong enbough but often, a small grain of sand would enter the end of the pin and prevent the ball from coming out properly, thereby allowing the pin the fall out. Another likelihood is that wear in the joint will allow the small ball and the pin to exit the hole. I had a customer lose a rudder pip pin and have his hands full steering back to the airport. The rudder fell over onto the elevator and reduced the up travel at his flare too. I also have seen channels worn enough that the ball pins will slide in and out in the locked state. Check any new purchase and replace the 1/4 pins with AN 4-16a bolts and nuts, and the 3/16 pins with either pins and safety rings or AN3-5a bolts and nuts.
One area that also has caused problems is the drive line. Specifically the root tube. The channels at the rear of the root tube are attached using rather short bolts. The head of the bolt is inside the tube and not accessible. Hard landings and vibration have worked together to crack the tube aronund the head of the bolt. As this crack propagates, it can be seen outside the tube. It typically wraps around the tube at a 45 degree spiral as it grows. The crack may appear to be only a grease spot. This is actually aluminum oxide seeping out the crack. teh fix is to install an AN 5 Large Area Washer under the head of the bolt. This will require a total diassembly of the aft end of the root tube starting with loosening the kingpost and unbolting the trailing edges. While this is an important AD, and difficult to correct, the effort to correct it may offset a lot of money in the long run. The latter root tubes were assembled with this washer and a simple inspection will show the washers presence. Check the number of threads showing beyond the nut inside the channels at the trailing edge attach points. The extra washer will reduce the number of threads to about 2 to 2 1/5. If the washer is not installed inside, the threads exposed beyond the nut will be more like 3 or 3 1/32.
Teleflex cables have had their share of problems, mostly from abuse. But one thing that keeps them more trouble free is extra nuts installed on each threaded end. This extra nut should be run all the way to the end of the threads, thereby keeping the threaded portion of the sliding rod from entering the sleeve. The threads can catch on the end of the sleeve if they enter and prevent the teleflex from functioning. Another area is the teleflex guard kit installation. Putting ones feet down to stop the plane often bends the small rods extending from the teleflex. This reduces or stops the motion of the inner parts due to binding. The fix is a new cable but the guard kit will protect the teleflex from future abuse.
Rudders have been known to change their trim setting and require different amounts of left and right rudder to steer in a straight line.
Two updates have been made to stabilize the front balance strut to the plane of the rear portion of the rudder. The newer planes have small triangular plates which further restrain the flatness of the rudder. I offer even larger plates which extend several inches onto the balance strut and the rear compression strut. These plates are much better than the small tri plates used by the factory. Another small problem is the front balance strut may be low enough to catch on upper tail wires. The newer balance strut is bent at the front to provide more clearance.
The coupler on the rear of the engine originally was manufactured with a 1 1/2 inch outside diameter. This coupling failed at the end of the taper on the engine due to the bending of the shaft and the restraint of the rear bearing. The later couplers had the OD increased to 1 3/4 and this solved the problem. The final solution is to install the flex coupler which eliminates the small coupler either way.
Wing ribs may seem pretty uncomplicated but keeping them in the pocket was a real problem. When they ease back out, the center ones create a potential prop strike target. The end ones just cause people to wonder about the plane, and the owner,,? There have been several methods of retaining them but none work any better or are any easier than a short tiewrap placed around the rib and through a small hole melted in the sail. There have been other thoughts such as turning the tips over, installing them from the bottom, and slicing new slits for them to enter into the wing pocket.
The pivot bolt for the control stick was increased in size to 5/16 from 1/4 inch. This change was primarily for the MXII since the bolt carried the load into the stick attach tube, and then out to the side of the plane to the push/pull tube. The MX p/p tube attached directly to the stick so this load was never developed. The newer planes have the stick attach tube carrying the p/p loads and need the 5/16 bolt also. Any MX with the two piece stick conversion should make sure the bolt size is increased.
The shackles which attach the four upper and the four lower wires to the kingpost or tri-bar also had a revision. The early shackles were a marine part and while they looked OK, they weren't made of a high enough grade of material. The newer replacements are made from plate stock, with flat sides, machined to a dog bone shape and bent into a U. The older marine part was forged and the corners are all rounded much as the smaller AN shackles are formed. These parts come in two widths, 1 inch and 1 1/8 inch. The small one is for the kingpost and the larger goes at the tri-bar crosstube. It is important to replace these with the newer part on any of the older planes.
Wires also have had several changes along the way. The first wires were made with white vinyl coating. They were pretty but often had several shades of 'white' which clashed a bit. The switch to the present black made after a serious mistake was made making 1/8 inch wires. A 5/32 inch swager was used rather than the correct 1/8 swager. This crimped the nico too tight to pull apart by hand but loose enough that flying loads failed several wires. The black wires began a major change in philosophy which mandated the best Quality Assurance program the ultralight industry would ever see.
Some specific problems with wires was the lower nose wire upper thimbe. The first design had a 'Y wire' , a continuous wire up one side and down the other. This wire placed a double load on the single thimble at the top. Stretching this thimble changes the geometry of the tri-bar and the whole plane became loose as a result. The newer wires are separate with each wire having its own thimble and the addition of a Neverkink. This small piece of hard rubber keeps the thimble round and maintains the length of the wire properly.
This same thimble elongation problem occurred throughout the plane, the upper flying wires, the outer lower flying wire, the upper tail wire, etc. Newer wires have Neverkinks and offer an extremely strong and rigid airframe. Wires often were considered loose when they sagged with the plane at rest. While this looks possibly unsafe, it usually means that either the wires are stretched or the airframe components are distorted, producing the loose, sagging wire situation.
Trouble shooting wire looseness is difficult without an understanding of the way the wires hold the plane together. There are three sets of 'wires' acting on the typical MX model Quicksilver. The first is the upper nosewire, the upper tail wires, the lower tail wires/tubes and the cage assembly with the kin post. This is a continuous load path and screwing the king post up will tighten the wires and load the tubing. The second is similar consisting of the outboard upper and lower wires, the tri-bar crosstube and again, the king post. The third set is the inboard wires with the king post and tri-bar assembly.
In theory, tightening the king post will tighten all three of these load paths at the same time, evenly, and with the same tension in the wires. This will not be the case if for instance, the tri-bar crosstube is widened due to the abuse of many hard landings. I have seen this bar at least a 1/2 inch wider than the correct dimension. This will not pull the inner end of the lower wires to properly tension them. The outboard wires being flatter and more in-line with the tri-bar, are more likely to be loose due to this distortion. Other parts that create similar problems are the axle, the tail mount rear wire bolts, the root tube, landing gear downtubes, and general play in the numerous holes and bolts that assemble the plane.
One item that really needs attention is the thimbles at the ends of every wire. The thimble has a specific function to allow the small strands of wire that make up the cables to be on the 'outside' of the turn for an equal amount of time. If the wire was not twisted and was formed around a thimble, the small strand of wire on the outside of the wrapped wire, would take a larger diameter and as a result, carry all the load. That is until it broke and the next small wire carried the load. The thimble contour is important for this reason. Thimbles can be pulled hard enough to flatten the sides. They sometimes look more like a 'paper clip' with its flat sides than a rounded thimble. The sharp bend they have at the end will force the wire to also take a sharp bend and not allow the internal loads of the wire to distribute evenly. When starnds break, you can (carefully) feel the ends inside the shackle or tang. These wires should be replaced immediately.
Rarely do wires stretch from poor landings. The actual length of a wire is more dependent on the condition of the ends of the wire rather than stretch in the length of the cable. This is not always true following a major crash. A crash can impose high loads, stretch the wire and not actually break any strands of wire. The continued use of the wire would lead to strand breakage as the thimble distortion allowed the load to be caried by a reduced number of strands. The installation of Neverkinks has helped the thimbles but allowed wires to be stretched and still look OK from a thimble standpoint. Wire lengths should be checked following any major crash or if tightening the kingpost does not produce an even wire tension.