Wire Hanger Retracts

This idea resulted from a question/challenge from a commenter on another article I wrote about "Wire Hanger Landing Gear".  Baronbernie said "Now if you can just make it movable".  At first I dismissed the idea but the more I thought about it the more doable I thought the concept was.  I played with it a little and came up with something that works pretty well.  So, here you go...

The basis of the design is to mount the gear on a set of pivots and provide a lug that can be operated by a servo and push rod.  The landing gear is basically the same as my "Wire Hanger Landing Gear" but with the bends eliminated where the rubber bands go.  There is one striaght piece running across with a set of bends in the middle to make a lug.  The straight parts are held in place with small pieces of gift card material cut into triangles and drilled for the hanger wire to pass through.  The card material is hot glued into slots or onto the sides of the swappable to secure the pivot. A push rod is attached to the lug and to a servo mounted from the inside of the pod with the pivot and arm sticking out below.  For tail draggers there is just one set.  For tricycle gear there is a double servo arm and movable gear front and back operated by one servo.  The thumbnail for this article shows the trike gear retracted.  

Retracted is somewhat of a misnomer.  It is really just folded for a lower profile.  It does not go "in" anywhere but should provide less wind resistance since the wires are not hanging out crossways to the air stream.  It will also look retracted in the air.

This is what they look like:

Here is how you do it:

Tools and materials:

You should have a wire hanger (2 or 3 extra for do-overs), a tape measure and either needle nose or side cutter pliars or both that measure 3/8" wide.

Take a standard wire hanger and cut off the hook end on both sides as close to the twist as possible.  Straighten it carefully and cut in half.  You should have two pieces about 17 3/4" each.

Mark the center on each.

Now, be aware that the lugs we make will make not be in the center.  Each will be offset to one side because of the opposing servo arms.

For the main gear start by placing one side of the needle nose or side cutting pliers on the center line.  This will make one leg about 1/2" longer.  Bend both legs 90 degrees in the same direction.

Like so:

Then take the pliers around each side of the bend holding it tight in the corner and bend each leg back in the original direction.  If you do it right they should end up exactly opposite each other.

Like so:

Play with the bends till it will lay flat on the table with both legs touching their entire lengthes no matter how you roll it.  You can also sight it from each end. Except for the offsets it should look like one continuous piece of wire.

Take your time and work with it till it is straight.

Then take the shorter side and place your pliers right against the last bend.  This is a little tricky because the lug and landing gear legs are at different angles about 45 degrees apart.  You will start with the lug straight toward you and then rotate it down about 45 degrees.  Then grip hard and bend the shorter leg straight toward you at 45 degrees.  You could use a 45 degree gage or draw 45 degrees on your work table but I usually just eyeball it.

Like this:

Next we have to gage the position of the next bend based on the width of the swappablew core.  Hold the piece against the swappable with about 1/8" of the straight part hanging over the side.  Mark 1/8" past the other side on the remaining unbent long piece.  This will be the piosition of the second side bend. Or you can just measure 2 1/4" from bend to bend (cores are 2" wide). The bend will be in the same direction as the last 45 degree bend but on the opposite side.

It should look like this:

The picture below shows the completed part.  To get there measure 6" along each leg and make a mark.  Then bend each part out at a 45 degree angle. Sight between the two and adjust till they are exactly in line.  You should be able to roll the piece on a table with the shortpieces touching for their full lengths throughout the roll.  In the picture the piece is laying flat with the lug at 45 degrees away from us. You can grab the corners of the lug with pliers and adjust the angles of the legs forward or backward if needed.

This was the easy one.

Next we are going to make the anchor tabs.  They need to be installed on the nose gear before the last few bends are made,

Take an old gift card and lay it out in 6 equal squares,  They should be 1 1/8" square each.  Cut them out with scissors.  Take three of the 6 pieces (one card will make two sets of retracts) and cut them diagonally into two equal triangles.  Take two of those and cut them each into two equal triangles again (half as big)  You should end up with (4) 45 degree triangles 1 1/8" per side and (4) about 3/4" per side.  Stack each size up with the 90 degree corners lined up and drill a 3/32" hole through all 4 leaving at least 1/8" from both edges.  After drilling the smaller ones measure 3/16 from the drilled hole and cut the excess off the long side (about 1/8").  These will have to embed in a slot right up to the hole so they do not want to be too big. Nip about 1/8" off all 3 corners of the bigger ones and just the corner with the hole on the smaller ones. 

They should look like:

Now we can make the hard one:

Hold the pliers with the side of the pliers 1" to the left of the center mark or measure 10" from the end of the wire to the side of the pliers.  Bend both sides 90 degrees like before.  Move one width of the pliars and make the second bend same as before.   Go one width of the pliers toward the longer  side and pivot the lug bends down only about 30 degrees this time (because the front gear tilts forward 15 degrees) and make a 90 degee bend straight toward you.  Use the swappable core to gage or measure 2 1/4' again and bend the second side the same direction as the first. One side will be about 3" longer than the other and it should be. 

At this point you have to put the 4 anchor tabs on because the next step closes the loop and they will not go on after that.  Trust me, I have one without tabs sitting on my bench.  It doesn't matter where they are just so you have two small ones in the middle and the two larger ones on the outsides,  Just slip them on and forget them for now.

It should look like this:

Then we make the remaining bends.  We will be bringing the two wires together and reinventing the twist that we just cut off along with the hook in pepreparing the materials.  

Start by holding the pliers tight to the last bend on each side and bending in about 45 degrees straight toward the wire on the other side.  The goal is to have them cross exactly in the center with a measurement of 2 3/4" from the last 90 degree bend we made on each side.  It is worth the time to check and adjust this as exactly as you can.  It determines whether your nose wheel is centered or not.

It should look like this:

Check your measurements again and then hold the pliers as shown with a strong grip.  Hand twist the two wire ends for two full turns till it looks like:

This:

 Still holding the grip take the longer leg and bend it straight.  Take the shorter one and bend it 90 degrees to the twisted wires.  Then take the shorter wire and wrap it arouind the longer one two full turns.  It should wrap very tight right around by hand.  Use a second set of pliers if needed.  After wrapping cut the short wire as short as possible and then use the pliers to roll the cut in as tight as possible,

Like this:

After all this twisting there will be some straightening to do. You will probably have to bend the twist and long straight wire a little to straighten.  Everything should lay flat and look centered.

Then take a grip below the twist.  Hold that straight and bend the wire below that to one side about 45 degrees move your pliers down to just after that bend and then bend the remaining wire back 45 degrees.  

 Then measure 5 5/8 " from the other end and mark the straight piece.  Bend it 90 degrees parallel with the pivot wire on the other end.

 It should look like this and be about 5/8" longer than the main gear (because of the forward slope).

 It doesn't matter which direction the last 3 bends go, right or left.  The wheel will just go on the open side.  

Next we are ready to install the landing gear on a swappable pod.  These will be permanently installed instead of rubber banded so they will be harder to replace if they get banged up.  Make up your mind which way you want to go.  I will always have a rubber band back-up close at hand. 

First you have to establish the locations that you need for the model you have.  Mine are mostly flying wings so I want the nose gear well out front.  With a nose prop you need to be careful of the nose gear angle.  You may need the main gear tilted back and the nose gear more vertical.  In that case you would have to make the main gear longer and the nose gear shorter.  For a tail dragger you will need just the main gear and a single servo arm.  This set is for a pusher flying wing with main gear at 90 degrees and the nose gear at 15 degrees forward.  Lengths and angles can be adjusted to your needs.  The nose should be level or slightly down.  Rotation will bring the nose up as you take off.

CLARIFICATION /CORRECTION 2-24-14:

In these pictures I am placing the main gear very near the back of the swappable pod.  This might be true for a conventoinal platform with a fairly long fuselage but may not be the case for a flying wing.  The main gear of a tricycle set should be just aft of the CG enough to provide ground stability.

Here is one I reworked to the proper position for the third design in my "One Sheet / Two Sheet No Waste Flying Wings" series (see separate article below).  The core also appears below before the relocatoin illustrating the alternate design (not requiring stop wedges):  

This is the one with generous sweep but no motor area cut out at the rear so the swappable is shortened but still fairly long.  The main gear position is about 3/4" or 6% of the center wing / fuselage length behind the CG point.  With this location you can tip the plane over backwards by lifting the nose about 20 degrees.  I think that is about right.  For increased stability the gear can be bent a little backwards, for easier rotation a little forward.   (end of clarification)...

So, let's begin installing:

I like to position the anchoring tabs so that a rubber band set of gear could still be used if the retracts fail (you can always take a pair of nippers and remove them in a couple of minutes).  So, avoid the standard gear dowel positions if possible.  This works well for the flying wings since the gear wants to be as close to the ends as possible anyway (see correction above).  Establish and mark the desired positions:

I have inserted the dowels for the fixed gear, established the tab location and squared the marks across using a drafting triangle.

Then set the gear in place over the marks making sure to overhang evenly on both sides and having the lug toward the end of the swappable.  Make small knife cuts each side of the center lug.

This cut is not real tight to the bend but just a little gap because of the radius of the bend.  Mark both sides.

Extend the cuts both sides of the layout longer than half of the length of the small anchor tabs using the triangle as a giude.  I use a cheap plastic mechanical pencil (lead retracted) to open the slots.

 Then dry fit.

A little squeeze here between where the small tabs are placed helps the lug stay centered where it belongs.  

You can either remove the tabs, glue and reinsert or just squeeze the glue into the ends of the slots.  I have done both ways and removing does not allow much time for reinserting before the glue dries.  Considering that you have two larger tabs to do the bulk of the work I would leave them in.  Make sure you are in your marks and down tight as the glue sets.

Then glue the side tabs on.

Just apply a moderate amount on the back side and slide into place.  Hold for a few seconds and do the other side.   If you have a little squeezing out in a spot or two you have about the right amount.  I added a little around the edges of the small tabs but not the large ones.

Pretty much the same procedure on the other end.

 Position the gear where you want it and mark.  Square it across with a triangle.

Cut and open the slots.

Install the front gear  the same way as the main.

Be careful to stay on the marks as you glue the small tabs.  Double check and then glue the side tabs.

The completed installation.

Open: 

Closed:

Both sets should be very firm in position and swing through the entire arc with almost no resistance.  If you did not line the pivot wires up carefully you will tell it here with resistance somewhere in the motion.

You are now ready to install the servo, linkages and stop blocks.  The servo arm should be double and you will probably use the last or next to last hole.  I would suggest stepping up one size from 9g. as this will have some touque requirements.

CLARIFICATION 2-24-14:

I stripped this servo while working on the set-up.  I am now ordering all metal gear servos and recommend using them exclusively for this application. The torque values are just too high for plastic.  They are still not too expensive at $5 - $6 from HK.

(end of clarification) 

Here are a couple of pictures of one I completed earlier.  

The servo position works well under the nose gear twists.

The retracted position shows the stop blocks clearly.  These are 1/8 lite ply which I had some scraps of lying around.  They could be any hard material.  They just have to keep the lug from over rotating.  They should be installed after you have all the adjustments made on linkages.  Once they are in the extended gear position will be set.  ( I have to play with linkages on this on this one to get the nose gear to close more fully.) 

It looks sloppy enlarged but I used extra glue around the wood block and as stops either side of the push rod.

The push rods are tricky to get this tight.  I formed an eye around a pair of needle nose and then spread it sideways enough to slip over the gear wire.  I then had to tighten it both sideways and in the loop till everything was snug.  There was a little !*#!*!! involved but if you are patient it is doable. I used the 3/8" wide side cutters and just kept squeezing this way and that till I got it where I wanted.  Some other connection device could be used but it would have to be installed on the nose gear as it is made and on the main as it is installed.

This is the stop block in the extended position.  It is directly behind one side of the wire lug so it bears the full length.

The servo in the open position.  It is installed from the inside to minimize the projection and nose wheel clearance in the retracted position.  I kept it roughly centered so both push rods are fairly short.

I do not think it makes any difference which way the pushrod loops (under or over).  The one below is probably easier to tighten and lets it run closer to the model. 

Bottom views of the wood blocks and linkage connections (above).

Alternate design:

This uses a more complicated set of bends in place of the stop blocks.

I have only done one of these and it works pretty well but the bending is more demanding and it is less adjustable after made.  I may do a how-to on it later if anyone is interested.

A couple of points not covered above:

I recommend flag wire for the push rods due to it's stiffness.

I used gift cards for the anchor tabs but any suitable strong flat thin material would do.

Your gear length and angles may be different because of your airpalne design requiremants.  Just adjust the lengths and positions as needed.

When bending wire it is always best to hold the pliers on the part that is finished and bend the unfinished part so you are not distorting the finished part.  Sometimes you have to reverse due to working on a short length but whenever possible...

Your experience will probably improve upon what I have done so don't be afraid of experimenting and sharing your results.

Well that is about it ...

Good luck and let me know how you make out.

UPDATE - 2-19-14

I have worked out the geometry and have built a solution to the problem mentioned by the first two commenters.  They were concerned that the servo may not hold up to the pressure of the front gear.  My solution uses a second pivot system that relays the servo force to the landing gear.  When fully deployed the two part linkage between the two is straight which braces the gear with no pressure on the servo.  My test build is too rough to show but stay tuned.  I will post a cleaned up version in a day or two (have to scrounge up some more hangers, having used up all that were in the house). 

Rough sketch of the geometry:

 (Yes.  I do know what it means.)

Update 2-22-14:

Here is a better drawing of the geometry and a couple of photos of the prototype:

Thie design uses a piece of plastic hanger to make a link between the front wheel strut and a separate cam that transfers the force from the sevo linkage to the wheel strut.  In doing so it moves into a slightly past straight position and the pressure of the strut is transferred through the link and cam to their attachments to the body.  All pressure is relieved on the servo linkage.  However it is still in the proper position to retract the gear with light pressure.  

I originally intended the zip tie attachment just to test the geometry but Iit seems to work pretty well when all the gaps are filled with hot glue. It is also much easier to install than the gift card tab version.  I am giong to make a fully functional installation with this attachment method to verify.

I am going to do a separate how-to article on this new design since there are a lot of new methods.  I hope to have it up this week-end.

Keep an eye open for it if you are interested. 

Retract Video: