|Dec 02, 2012, 08:45 AM|
Polaris Aileron Pushrods
I have always used the standard wire pushrod setup as shown in the kit manual. It works well and is easy to do if you approach it correctly. The keys are using the correct wire, stiff enough but with flexibility, and getting the plastic tube guides correctly positioned and angled through the fuselage sides so the pushrod has a straight run and doesn't bind.
To get a sense of how the whole setup works, go to my earlier blog on control setups for the XL. I first install the servo the with suitable output arm and use Dubro Mini EZ Connectors to provide for adjustment and make it easy to remove the pushrod if necessary later.
I install the usual plywood control horns in the ailerons and make sure the hinges work freely. I generally use Blenderm Surgical Tape for the hinges.
I run a straightedge from the connector on the servo arm to the control horn and use it to draw a line across the bottom edge of the fuselage side to get the position and angle right. It takes a bit of eye-balling to do this but it isn't terribly hard. Then I establish the correct vertical position on the fuselage side to give a straight line from the connector to the hole in the horn. I do this by measuring from the wing underside to the wire attachment at the servo and at the control horn and then using an appropriate intermediate value (about half).
Now I make the two right angle bends on the end of the wire to go into the horn (it isn't a z-bend -- see photo in earlier blog). I cut the wire to the correct length to reach the servo, plus 1 cm or so to allow for adjustments.
I use the previously established marks to identify where the push rod should go through the fuselage side and the appropriate angles, then poke the push rod through and attach it at the servo and control horn. This verifies that I got things about right and that the pushrod isn't going to have a bend in it.
Because I'm only making a small hole, it's easy to make adjustments. I remove the pushrod and poke a rattail file through the fuselage side at that point, using it to make a suitable size hole for the pushrod tube. I use the combination of plastic tube and heat shrink shown in the kit manual.
I slide the tube over the pushrod insert the push rod in the connector and the horn and check that the push rod moves the control surface without binding, etc.
Same on both sides. Get everything working and test the operation of the servo and ailerons.
Finally, I mix up some epoxy and microballoons and glue the push rod tubes into the fuselage sides.
The resulting linkage is smooth operating and reliable. The wire has just the right amount of flex to allow for the slight sideways movement due to servo rotation.
By the way, you should set up the transmitter so you don't have more than about 30-35 degrees on the servo arm at full throw, high rate (this usually corresponds to about 100% throw). If you use more than this, the longitudinal motion becomes excessively non-linear and the sideways motion introduces binding. On the other hand, you don't want to use very small amounts of angular travel, as that way you lose resolution and get into problems of linkage slop. So arrange the linkage to give approximately full control surface throw (see manual) with 100% throw (travel) and 100% rate (D/R).
Be sure to measure the aileron throw before closing things up. The amounts shown in the manual are maximums and are what you should get on high rate. Somewhat less will be ample -- don't go more!
For initial flights and normal flying you should use much less -- I generally recommend 70% for low rate, assuming high rate is 100%.
Note that once you've got the aileron setup adjusted correctly for throw and centering, there's normally no reason to do anything other than adjust trim at the transmitter. So you can glue the bottom on. If ever you need access, just cut a hatch in the bottom, angling the cuts slightly to the piece you remove can go back in easily.
|Jan 03, 2013, 08:36 PM|
I rigged my ailerons similar to your description. I chose to put the Z bend on the control horn on the servo. I then put the adjustable piece on the control horn of the aileron. I can adjust it without having to get into the bottom of the fuselage.
I inserted the control rods (.055 or .047) into the short tubes and into the bottom of the fuse. I then used a Z bender to bend the ends of the wire in the bottom of the fuse. I then inserted both wires into the control horn and turned it upwards 90 degrees. Both wires are then in the control horn. The adjustable clevis is installed on the aileron and is adjustable at any time.
I did the same on the rudder.
I know there are many ways to do things. This is just my preference.
I attached a photo to illustrate what I did. You'll also notice the small hole in the tail in this photo. I drilled the hole and glued in about 1" of a drinking straw. I use it to store the Polaris by hanging it inverted on a headless nail on the wall in my shop.
I appreciate your assistance to the Polaris list.
(working on Polaris #3)
|Jun 17, 2013, 02:57 PM|
If you use it, be sure to iron it on for good adhesion (but keep the iron temp low enough to avoid excess shrinkage).
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