Questions and Answers 2/center>
This section will continue discussing problems and their fixes.
Welded and Formed Parts
Q.................My tribar crosstube measures a bit wide. Can I bend it back ?
A..................My first instinct is to recommend buying a new one, but that is the easy way out for me, and an expensive one for you.
I suggest taking the a frame totally apart and giving the tribar a good look, especially at the welded brackets that attach the seat mount. This is the area that gets highly stressed when the bar is first bent and then bent back.
I then install the uprights into the tribar. The upper ends should align without forcing them, be about the correct spacing for the saddles and the 1.8 inch spacer, plu, the upper ends shoul be the same height. Any other fitup of the verticals and the tribar needs some bending. Typically, the original bvends are opened a bit, making the verticals further apart. If the sides are not opened the same, the verticals will not align at all, but some thought will show which side to bend and about how much.
The rebending almost has to be done with a mandrel bender to keep from flattening the tube diameter.
I make replacement bars using the next larger diameter of crosstube. This makes for a much stronger bar that is much less likely to open up. It is a direct replacement for the original.
Q.................. My front tire is rubbing the sides of the front fork. I think the steering is factory. What gives ?
A...................The newer tires are a bit flatter profile and a bit wider, less diameter. This makes for likely rubbing. The fix is to find one of the older tires that is narrower and doesn't rub, or order a new fork. I make front forks I call 'wide forks' that are 5 1/4 inches inside. This fork will clear the stock wide tire and also accept a larger diameter too. I typically use a 4 by 6 wheel barrow style tire with them.
The 'extra wide' fork is 5 3/4 inside, taking a 5 by 6 tire nicely.
Q...................My elevator control horn has the push pull hole walloed out quite a bit. Replacing it is expensive. I there a better option?
A....................Yes, there is. I offer a small kit that allows the re use of the worn elevator horn. The kit contains a rod end, a short piece of tubing and some bolts. The hole in the horn is drilled on out to 5/16 and the rod end bolted on, the fitting threads on the rod end, and inserts in the pushpull or use the tube and it goes inside the two piece rear push pull tube. It is a good fix and the horn will never wear any more.
Q....................I replaced several tubes after a crash, but my rudder cables are still loose. Any help ?
A....................Yep, happened to me too during the rebuild of a customers plane. The cables have a small amount of adjustment at the front full threaded eyebolt, but that isn't intended to adjust for broken or bent parts.
My case had a bent rudder horn. During the crash, the pilots feet pushed on the pedals, the cables pulled really hard on the horns and bent one of them forward. It was hard to see, but once noticed wa sfairly obviou. The horn being bent forward, moved the attach point forward making the cable loose.
The fix was to replace the horn as it had some stress cracking of the anodizing, and this fixed the cable tension.
I did come up with a small fix to help prevent this happening again. I drilled a forth hole above the rear bolt, and added another bolt. I used a 1 inch spacer so the bolt could be tightend. This actually improved the performance of the rudder a bit.
Q....................I've seen planes with sleeved compression struts. Are they required ?
A.....................Sleeved compression struts and also sleeved diagonals were introduced following a structural failure of an MX while doinf aerobatics. The outer tube is 1 1/8 and slides over the existing tubes. This can be easliy done, still use the same end fittings and will upgrade the strength of the plane quite a bit.
Since this combination became alost twice the weight, the newer design is a larger diameter tube with machined end fittings. Changing to this design will lghten the plane by several pounds, but the new tubes and fittings will be over two hundred dollars.
The same changes were made with the diagonals, in that they were first sleeved, and then upgraded for less weight to the 1 1/4 dimater tubing. The end channels and length were also changed, but the parts are fully interchangeable with the original single wall or sleeved diagonals.
What Fits What
One problem that many newcomers to the world of the quicksilver run into is that they need to know what fits what. T help, I have several questions following an overall discussion of what fits what.
In general, If a part looks like a part on a different model, it is likely interchangeable with that part. For example, the nose strut on a single place MX looks just like the one on a new Sport, and they are exactly the same part. One major difference is that the MX part has a shiny brite blue finish, and the Sport, well, it could have the same shiny finish, or be the newer dull matte dark blue.
Another example, the landing gear downtubes on all the planes are the similar. The small differences still allow them to interchange but with some definite concerns. The early LGDTs were a heavy wall tube inside a slightly shorter sleeve. the tube was standard for a couple years, on both single and two place planes. The coming of 103 called for a lighter version, and this is a single heavy wall tube used on the later MXs and the Sport and Sprints. It is the weakest and lightest of all the LGDTs. The original is still the mainstay and recommeneded for all replacements.
I do make a couple variations,,,,,,,one is similar to the LGDT on the MX Super where the sleeve goes all the way to the upper end and requires the AN5-50a bolt. Another extra HD variation has another sleeve, three feet long or so, and is used when shoulder harnesses are installed for extra support during a possible crash.
Axle struts come in several different variations too. The early weight shifts and the MX series all have the same tube, with the WS version having an extra hole for the nose strut channel. The MX II had a slightly shorter axle strut since it mounts onto a much thicker tube, the tribar DT, so the strut was shortened about a 1/2 inch. The newer top mounts use a much longer axle strut due to pushing the nose out further.
Wing spars are a constant concern for safety. They get damaged sometimes, and what might swap with what is a constant concern. I don't recommend trying to swap themfor a couple reasons. The two place tubes are a larger diameter, and they require a longer sail to go around them properly. While the bolt holes on the spars are in similar locations, they will bolt up and so on, the sail will not fit right at all. two place spars are quite heavy and the extra strength is surely not required on a single place. For that reason, never swap single place spars onto a two place.
Now, what may be done, is to use an MX spar to make a sport spar, or an MXL spar, all single place planes. Some holes may require redrilling but if done in a profession manner, should be OK. There are some sleeves and such at the end which should be retained when the spars are shortened or reworked.
Tail parts are all the same, except for the tapered and rectangular stabs.
Lower tail tubes are different and some discussion of them is required. The early MX with lower tail wires, had a fairly high tail location. The elevation of the tail is set by the place it attaches to the trailing edge spar. Using the root tube as a reference point, the high dihedral of the MX places the tail boom channels quite high. This height actually goes up should the high performance tail/prop be installed. The attach point goes down should the dihedral be reduced either from a wire change or on the stock MXL. As this attach point raises and lowers, the lower tail tube lengths must change to match.
For example, the stock MX with the high dihedral, requires the longest lower tail tube. The MXL with less dihedral, uses about an inch shorter lower tail tube. The upper tail wires are also different, the MX being the shortest, the MXL being somewhat longer. A typical plane should have a consistent set of lower tail tubes and upper tail wires so the airframe tightens properly. Mismatching these parts/wires will result in all manner of problems.
Since there are not numerous sets of tubes and wires to properly align all the possible combinations of dihedral and tail attach distances, the stabilizer needs to be shimmed at the front to achieve proper flight trim.
Q..................I am installing the tapered stab and want to save some money. Do I need to buy a new stab trailing edge ?
A...................No you don't. The only difference between the rect stab TE and the tapered stab TE are two holes 1 inch from the end for the attaching of the curved lE stab tube. If you can drill these two holes reasonbly square, you can use the existing tube. The savings are doubled since shipping on this long tube will be quite high too.
Q...................The ruder brace wires attach to the upper end of the vertical tube in the rudder. I like to install them but I'm not sure the tube is the same. Help?
A.................... The rudder vertical tubes are all the same, the more recnet ones have the rudder brace wire hole already drilled even though the rudder brace wires haven't been sold ina kit for almost twenty years. The kit instructions will give a dimension for the hole.
Q................... My instructors two place has a steel kingpost. Is it stronger and recommended ?
A.................... It is only a single wall tube compared to the typical MX KP, so the strength isn't much different. Since the tube usually fails in bending/buckling, the larger diameter of the sleeved aluminum one may have a very slight advantage but I have no way of testing this theory. The steel one is about 40 percent heavier though and not as pretty so I can't recommend changing to it.
Q.....................Speaking of kingposts, my friends sport has two kingposts. My MX might be stronger with two, Not sure ?
A..................... The parts and wires sets of the MX and the sprint/sport are not interchangeable. They could be swapped completely since all the attach holes are the same though, ie, you could take the complete kingpost/s and wires, and swap the whole package from plane to plane.
But before you run out and buy some sport wires and such for your MX, there are some other things to consider.
There is a lot of small hardware parts to get it all together such as all the channels for the KPs, the end fittings and such, and the sport double KP is too short to allow the use of upper tail wires. Bummer, since these wires tighten the whole tail assembly during flight and ground handling. Also, since the tail is only attached at the wing and the axle, the tubes are much larger in diameter as they must take much higher loads without the upper tail wires.
I like the upper tail wires as they greatly stiffen the plane during severe manuevers, and turbulence. The lack of top wires means the trike portion is on its own too and this is in itself a problem.
The double kingposts push at the front and rear of the root tube. The a-frame comes up and pushes up just behind the gas tank. This mismatch tends to bend the root tube. Most sprint/sport crashes will likely break or bend the root tube due to the misaligned loads from the KP and a-frame.
The single KP pushes down right above the single a-frame, and few bent or broken root tube sare seen on the MX planes, just the sprints and sports.
Another problem, is that when the wing wires are tightend, the KPs and the aframes tend to bow the root tube. This loosens the lower nose wire and the rear trike wires, allowing the whole undercarriage to single fore and aft as the lower tail tubes push and pull. I don't like this loose feeling at all. Most of my custom planes have top tail wires, and none have misaligned KPs and lower aframes.
Note that during the redesign of the two place for the top mount engine, this probelm of misaligned loads was fixed by adding another a-frame under the root tube. This design is a REALLY stiff one, and likely strong as well. The flexure during flight is almost non-existent compared to a stock sprint/sport.