Tuesday, September 26, 2017
Home » How To's » Bending Perfect Pushrods

Bending Perfect Pushrods

The light, clean pushrod installation detailed on these pages is perfect for models of all sizes from park flyers such as this Aero Craft Ltd. Small Stik up to 60-size models and beyond.

If you have ever tried to set up solid aileron pushrods with Z-bend linkages, you know the frustration of trying to get the second bend in just the right place, or adjusting a V-bend in the middle of your pushrod. It turns out that there is an easier way. Here is how I bend aileron pushrods for most models with wing-mounted aileron servos. In this case, I was setting up the new Small Stik from Aero Craft Ltd. The same technique can be used on models up to 60 size and beyond, depending on the pushrod wire size.

To make a snake bend, simply grip the last 1/8 to 3/16 inch or so of the wire, and make a 90-degree bend over the edge of the pliers jaws. Now reposition the wire so that you are grabbing the next 1/8 inch or so, and bend the wire again. Thats it; youve made your first snake bend. The advantage of snake bends is that you can form them with any pliers, and you can twist the pushrod with a pair of needle-nose pliers and insert it into the control horn after everything has been assembled.
 

Step one: ditch the Z-bend. I know you can buy nifty tools that will make a Z-bend in a second or two, but Ive never been much of a fan. The number one reason I dont like Z-bends is that you need to remove the servo arm to install or remove the pushrod. Thats one more chance to lose those little servo-arm screws, and often, thats the only chance I need. Instead, I use a modified Z-bend Ive heard referred to as a snake bend. The snake bend is almost identical to the Z-bend, but instead of having all three segments of the bend co-planar, the tail of a snake bend is perpendicular to the other two. Because of this, you can also make both 90-degree bends with any normal set of pliers in just a few seconds. Grab a scrap of music wire or even straighten out a paper clip and give it a couple of quick bends as shown to see what I mean.

To install the pushrod, thread the U-bend through the servo arm, and then grip the snake bend with your needle-nose pliers.

Twist it enough to get the leg into the control horn, and then release it. It should snap right into place, but if it doesnt, some gentle persuasion with the pliers will seat it easily.


Insert the snake bend into your control horn, and extend the wire forward alongside the servo arm. Make one last check to confirm that the servo is at neutral and the servo arm is centered, and then tape the aileron to the wing panel to keep it centered. Now mark the wire next to the servo-arm hole with a Sharpie marker. At this point, I cut off the wire about 1 inch or so past the mark. I use the small music/piano-wire cutters from Stevens AeroModel for cutting all my music-wire pushrods.

Use a pair of round-nose pliers or a Harry Higley Zee Bender to put a radiused, 90-degree bend in the servo end of the pushrod. Re-insert the snake bend into the control horn, and thread the other end of the pushrod into the servo arm to check the length. It will quickly be apparent if this bend is a little too long or too short. Fortunately, you can still adjust it quite a bit to get it perfect. If it is too short, reposition the wire in the pliers or bender, straighten out the pushrod side of the bend a little, and tighten the 90-degree bend on the short-leg side. I try to make the first bend just slightly too long, as it is easier to roll the bend a little farther into the pushrod side than to straighten it neatly.

Once you have done it once or twice, you should be able to find just the right length with only a test or two. Now regrip the wire and finish the bend to a 180-degree U-shape by bending the outer leg, and then trim it to length, again with the Stevens cutters.

Compare this clean, simple pushrod with the example on the right with typical double Z-bends and the V-bend for adjustments. Not only does it look better, but the straight run also gives you more positive control and lighter weight.

All three segments of a traditional Z-bend lay flat on your bench. Snake bend tails should be bent so they stand 90 degrees to your bench. Note that you can bend both left and right handed snake bends.

CONCLUSION

Ive found this a quick and clean way to make aileron pushrods without fussing with extra hardware and little screws or trying to make or adjust a V-bend. If your test flights reveal a need to adjust the length a little, you can roll the U-bend back and forth with your roundnose pliers or Harry Higley bender.

Links

Aero Craft Ltd., www.aerocraftrc.com , (631) 369-9319

Harry B. Higley & Sons, Inc., www.harryhigley.com

Stevens AeroModel, www.stevensaero.com , (719) 393-0830