The MX and the MXL were delivered with lower tail wires. The wires are plenty strong but they allowed the tail to raise and lower depending on the position of the elevator.

This raising and lowering of the elevator is noticed by having to move the stick farther than would be necessary. As the elevator moves down for instance, the tail is raised up. As the tail raises up, the distance the push-pull tube must move is increased therefore making the stick move farther. Most MX's require forward stick as the speed increases and the required down elevator for level flight requires extra reach on the part of the pilot.

Lower tail tube conversions reduce the distance the stick must move to effectively fly the plane. Most people will like the stiffer feeling or more secure control that lower tail tubes provide.

Lower tail tubes come in two different lengths depending on the dihedral of the plane. This may not make sense so I'll try to explain it so the differences are understood.

The entire tail attaches to the wing about 27 inches from the root tube. As the dihedral changes between an MX and the MXL, the attach point point lowers as the dihedral is reduced . This would alter the incidence of the tail since the upper tail wires and the tail tubes (or lower tail wires) establish a fixed point at the rear of the stabilizer. Moving the wing attach point of the tail boom tubes moves the front of the stabilizer about 1/3 of the wing elevation change.

This variation can be offset by changing the number of shims at the front of the stabilizer. For example, when I install a big prop kit on an MX II, I remove all the spacers from the front of the stabilizer. Let's follow the math on this one .

As the attach point for the tail booms moves out the wing, the effect of the dihedral raises the attach point about 1 1/2 inches. If this point goes up this much then the front of the stabilizer goes up 1/3 as much or 1/2 inch. This equates to two shims!!

Therefore removing the two shims gives about the same incidence change as the movement of the tail booms along the wing trailing edges. While this ratio and theory is not exact, it provides a plane with better incidence for the first flight whereupon the proper incidence changes can be evaluated better.

Shims should never be removed from the rear bolt of the stabilizer. The proper stack-up is a 1/4 inch saddle, one or two 1/4 inch spacers and another 1/4 inch saddle. Less than 3/4 inch between the tubes will reduce the travel of the elevator in the down position and possibly affect the control of the plane. The MX has one spacer as standard and the MXL and later models all have two 1/4 inch shims (all are plus two 1/4 inch saddles.).

The original attachment of the tailbrace tubes to the tailskid was a rather weak design. It was easy to assemble and disassemble and that was the order of the day. Nowadays, few disassemble their planes with any regularity and a new attachment has been developed which makes a much stiffer and stronger attachment.

The photo shows the new method. It consists of through bolts with back to back saddles. The tail brace tubes are 7/8 inch and have 7/8 saddles against their inner sides. The other saddles are the 1/8 by 1 standard saddle against the tailskid and the lower tail tubes.

Since the original tail brace tubes are straight, they must be bent to align with the upper through bolt. The upper bolt is an AN 4-36a and the lower one, an AN 4-40a.

The second sketch shows the attachment of the tailbrace tubes at the forward end of the upper tail boom tubes. This also requires 7/8 saddles and 1/8 by 1 saddles back to back. The bolts are AN 4-25a.

I will bend the tailbrace tubes for free but this requires shipping them to me. They will be returned with the lower tail tubes.

This next sketch shows the changes at the axle. Note that the tang for the wing-to-axle wire goes behind the 1 inch channel.

Also purchased with the lower tail tubes should be a lower tail tube installation kit. This kit would be rather expensive if all the pieces were purchased separately. By coincidence, the tail brace tube hardware ( the original stuff ) can be reused for the lower tail kit. To best do this, I recommend that the tail brace tubes be removed with ALL the attaching hardware and the tubes and hardware be shipped back to us. We will repackage the hardware where reusable and provide separately marked bags for the tail brace tube installation and the lower tail tube installation. Also, the tail skid needs to be drilled 1 1/4 inches down from the tail brace tube hole for the lower tail tubes. Give the tail skid a good inspection prior to drilling. Cracks, excessive wear or bending indicate a new tube is required.

The combination of bolting the tail brace tubes directly to the tail booms and the tail skid plus the new lower tail tubes will greatly stiffen up the tail of the plane. These changes will be greatly complimented by the addition of a rudder brace kit.

One last word about a problem. CPS once suggested that the addition of lower tail tubes would allow the removal of the upper tail wires from an MX . This is not safe !!!

It is true that upper tail wires are absent from the later Sprint and Sport models but the tail tubes, tail mount and the tail boom tubes are much larger and therefore stronger.

Do not remove the upper tail wires!! Having the upper tail wires even on the Sprint or Sport is a significant benefit. The wires pull the tail up and preload the lower tail tubes thereby reducing the wear considerably. After the above conversions, see if the tail on your MX is stiffer than the Sport. Check his tail tubes at the axle for wear and elongated holes. A rough field will greatly affect the unsupported tail of the later model planes lacking the preload of the upper tail wires.

We offer an overhead wire guard when we sell the large prop kit allowing the upper tail wires to remain in place.