Project

Many hours of fun for little money?  Yes it is possible.

It is unbelievable how much fun and excitement a piece of foam can provide.  The same foam developed to provide head protection in safety helmets and more.

This foam commonly known as EPP is used in the automotive industry for bumpers and seat squabs, packaging industries, sports equipment and now recently another use, remote control flying objects.

It is extremely resilient and after compression will try to spring back into shape.

Why are we discussing it here?  Well, many times at the slopes, walkers and children ask the flyers what they are - Are they remote control? How much are they to buy?  Where from?   How do they stay in up in the air?  Are they hard to fly? And so forth.  Well for the purpose of this article we will skirt the laws of gravity, aeronautical dynamics, wing patterns and "rocket science" too.  We are going to assemble one.

Build a Combat Wing

Tools required - Small amount of epoxy resin.  A little piece of fine grade sandpaper.  A very sharp craft knife and spare blades.  A small pozidrive or Phillips screwdriver.

Electrical Bits - A cheap Transmitter (TX) (35Mhz) £39. TX Xtal £6.99. 1 small receiver (full range, 4ch) £14 & Xtal £6.99, 2 standard servos (eg; Futaba S3003), £20.  1 x 4.8v Flat Battery Pack. 1 battery pack extension lead.  1 Servo mixer £9.99 (This may not be required if you have a transmitter with delta mix or elevon mixing built in. ie; DX7, Futaba EX 6ch, JR)

Optionals - 2 inch fibre crossweave tape.  More rolls of coloured tape.

This project is based on the Irvine X-IT wing.  This is a little more expensive than many others but the kits do come with tape, etc.  Other popular alternatives are the JP Zagi Si.

I may deviate from the instruction manual a little but the outcome will be the same  - a strong combat wing.

Getting Started

In the box we need to verify first, the parts required:

• 2 wing sections left and right
• 1 carbon rod
• 2 Ailerons (Elevons)
• 2 Correx wingtips (Fins)
• 1 roll of fibre tape
• 2 Rolls of coloured tape
• 2 Pieces of pre-cut Velcro
• 2 Control Rods with Clevises
• 4 Correx cut-outs
• 2 control horns & base plates

 

 

Wing Assembly

Take the carbon rod and mark the middle with a felt tip pen or similar.  Now insert the rod carefully into the hole about a third back from the back edge.  When the rod "bottoms out" or goes no further the line you made should have just disapeared.  Now do the same with the other wing section.  If again the line just disappears we can proceed to the next step.   Push the rod into one wing and then slide the other wing on to it - push them together.  Does the leading edge line up?  Does the trailing edge (back edge) line up?  If they do we can move on to the next step.

Using the sandpaper roughen the shiny surface of the carbon rod.  This will help the epoxy resin to key into the rod.  Now mix an inch of 4 minute epoxy resin.  Using a stick push a little down the holes in the wing sections. Slide the rod carefully into one of the wings until your line disappears.  Now push the other wing down on to the rod until your about 2 inches from the gap closing.  Using the rest of your resin smear it on to one of the wing joint surfaces.  Now push the wings together, allowing excess adhesive to squeeze out. Wipe off the excess carefully.  Place the wing on a flat surface add ensuring that the leading edge is aligned, cut two pieces  of fibre tape ( I use 2 inch tape) and place one on the joint on the top surface and do the same with underside.  Trim with knife the excess tape. Ensure tape is laid flat with no wrinkles.  If so lift and redo.   Check again that the leading edges align - This is critical to having a stable, easily trimmed wing.  Put the kettle on for a cup of coffee.  Have to wait a while now while the epoxy cures enough to continue.  In warm conditions allow at least two hours or more.  If you can leave overnight all the better.

Here is where I deviate somewhat from the instructions, my personal choice and it has rarely let down.  We have to attach the elevons to the wing.  In the Irvine X-IT these are made from hard balsa with a tapered profile.  The thickest edge goes up against the wing's top trailing edge with the chamfer facing downwards.  In the instructions they say to use the coloured covering material to make a hinge line.  But I prefer to make "proper hinges" from my 2 inch tape.  You could just make two for each side but I have always used 3 hinges - hopefully in collisions if one gets ripped out there are another two to get you back to the ground safely.

With the elevon up against the wing's trailing edge mark a line to follow the angle at the wing tip.  Copy the same angle to the other end.  Cut angles these off.  The tip of the elevon now follows the line of the wing tip!  Do the same for the other elevon.  Ensure they are exactly the same length otherwise trimming for flight will be made more difficult.  See photos below.

Cut six lengths of fibre tape 3 inches (75mm) long.  Now, working on a flat surface push the elevon gently up against the wing edge check that the end is just inside the wing tip (no overlap) and apply at 90 degrees to wing edge, two of the tapes about 2 inches in from each end with the tape fully across the elevon and just lightly touch down on the wing.  Now lift the wing and ensure that the elevon can move up and down easily over 45 degrees.  If not, lift tape off wing and move elevon out by a very, very tiny amount.  When this is successful press down the tapes fully.  Between these two hinge tapes apply the third tape.  Check for binding or stiffness.  Do exactly the same for the other wing.

Now turn over the wing so underside is uppermost.  Cut another six lengths of tape same as before.  Put the wing nose downwards and fold gently back the elevon. In line with the tapes on the other side apply these taps following the contour of the folded back edge.  You now have an extremely strong  hinge!  Copy the same procedure to other wing.  Ensure at each application of a tape that the elevon still pivots easily with little effort!

I've used this method of hinging for sometime now and I have survived impacts with fences, bushes and other wings so I am sticking with it.

* Ensure the elevons are free to move in either direction easily.  If they are stiff or cannot move over at least 45 degrees up and down this will cause unnecessary strain on the servo gears and motor.

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Continued...

 

Taping Up Wing

The application of tape across the surfaces helps stiffen the wing and gives much more strength to absorb impacts and collisions.

Apply adeqate lengths of fibre tape, either the 1 inch supplied or 2 inch purchased from one side to the other of the wing with tape width spacing.  I prefer to cover completely overlapping each run across the previous run a little,  preferably starting from the back and move forward.  When the wing is fully covered and you have ensured all the tape runs are wrinkle free and stuck down properly then apply two diagonal runs from centre line just behind receiver bay to furthest wing tip.  Finally apply tape to edges of  leading and trailing but NOT to the wing tips.  You should now have shiny, smooth wing surfaces.

Using your knife carefully trim around the empty servo, radio and battery bay recesses just in line with rebates, but take care - do not press to hard and cut deeply into the foam.  Also the two slots on the uppermost wing surface, these are where your servo arms will protrude.  Time for another cup of coffee I think!

Install Electrics and Controls

We now have to install the battery pack, receiver and two servos.

First the servos - Select a long arm, some come with four arms on one hub and each is numbered.  Cut off three of the arms only keeping one, eg no1.  Do the same for the arm.  We now need to centre the servo positions.  Connect the servos to aileron (Ch1) and the other servo to elevator (Ch2).  Switch on transmitter.  Plug battery lead into any other port on the receiver.  You should hear the servos start up and centre.  Move your control stick around to make sure the servos are moving - don't worry about direction yet!.  With sticks in neutral/centre position place the arms on to the spindles at 90 degrees to the servo body.  Gently insert securing screw.  You can now unplug the battery and receiver for now.

Push the servos into the servo bays with the arms protruding through the slots.  They should just appear above the wing top surface with at least one hole clear of surface by 5 - 10 mm.  If the arms don't then you will need to purchase longer arms from the model shop.

If the arms clear okay then the servos can stay where they are as long as they are a firm fit.  If they are not a firm fit then gently push them out and put a few drops of superglue in the recesses and firmly press the servos into place.

A 4.8 volt flat (AA) battery pack is just a little bigger than the front bay on the Irvine so you may have to cut a little out all round, about 1 -2 mm.  Just enough for the battery to slide in neatly. Battery in?  Now to install the receiver. Plug in your servos, one lead in the aileron port and one in elevator port.

Note: If using a servo delta mixer - See addenum at end of article now.

Plug in your battery extension lead into battery port of any other spare channel.  Be aware of polarity!  Place your receiver in the bay and gently coil the leads over it.  You may also want to cut some small slots or grooves between the bays to allow the leads to pass bay to bay without coming proud of the wing surface.  Switch on TX.  Plug in the battery to extension lead and check servos still working.  If all okay proceed to next step.

Selecting your precut  hatches trim and locate them into their respective bays and securely tape down with fibre tape.  The battery hatch and receiver hatch - put a little nick in the edges to allow for the battery lead and extension lead to hang out a little.  This will enable powering up and charging.  You could fit a charge switch in the receiver bay with the push button protruding through on the top wing surface.  In the model featured I did. (See photo 2) The switch was placed in front of receiver and held in place with double sided tape.  With the receiver and leads packed into the bay it's unlikely to move.

If all is fine time to go on to next step.

With bay hatches as flush as they can be it's time to customise it with a colour scheme.  Remember, you have to be able to see it clearly and recognise your own wing amongst many others in the sky.  Let imagination go wild.  In the basic kit you only get white and one other colour.  Your local model shop should have more colurs to chose from.

Starting with the  elevons I favour covering the underside first and roll the excess edge over on to the top side.  For the top surface of the elevons  apply the tape starting from elevon trailing edge and cover hinge line/gap and continue on over the rest of the model wing.  Then go back and very carefully using the craft knife cut along the hinge gap but very careful as you pass over the hinge tapes.  Press edges down into the gap with back of blade or small flat screwdriver.  A nice neat hinge line!

* I recommend starting from trailing edge and work forward overlapping each strip  just a little.  This ensures that the none of the edges of the tape are facing into the wind in case they want to lift!

Check the photos!

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Continued....

 

Final Stages

You should now have a brightly coloured easily recogniseable covered wing!

Now to fit the control rods and the winglets.

Mark a point with a pen 2 inches or 50 mm from the inner edge of elevons.  Fit the control horns at an angle and screw down through elevons - don't forget base plate otherwisde screws could tear through! The angle should be about 30 degrees. Another way to get angle right is take one of the rods and lin eit up with the servo arm to control horn - this wil denote the correct angle.  Ensure the vertical holes of the horn are directly above the hinge line.

I have say at this point that Irvine in their wisdom seem to have supplied the control rods too short by about 20 mm.  The rod is not 2mm but some wierd size like 2.2 mm.  Which means that you could not use the supplied clevises on bog standard 2 mm rods from the model shop.  So in this case I fitted Du-Bro metal spring clevises on to new 2 mm rod.  At the other end we need to make a z bend similar to the original rod pattern.  To do this place the wing on a flat surface. Ensure the clevis has the rod threaded through it and some 3 mm proud inside the clevis (allows for lots of adjustment). Switch on your transmitter and plug in your battery to power up.  You should see the servo arm centreing.

Line up the clevis pivot pin with the vertical holes and mark where the rod passes by the hole in the servo arm.  This is the first 90 deg bend.  Do the same for the other rod too.  Now power down your wing and turn off transmitter.  Using a long nose plier or similar bend the rod at the line 90 degrees. Allow 5mm and make another 90 degree bend the other way.

You may have enlarge the hole in the servo arm to 2mm.  Use a 2mm drill bit and just wind it through with a pair of pliers. We need a good fit but not too loose!  Now push the rod through from the outer side and just lay the clevis on the horn.  The next job varies a little from model to model.  With the Irvine X-IT the neutral point for the elevons is 3mm up.  In other words in theory if you just threw it into the wind it would fly level.

Placing the model on a flat surface, power up again ensuring righthand joystick (mode 2 tx )are in neutral/central positions.  Using whatever method you wish wind the the clevises in or out so that when the clevis is connected to the top hole of the horn the elevon trailing edge behind the hinge is 3mm up.  Get the elevons as equal as you can because errors will require lots of trimming to fly straight and level.

Now when you wiggle the stick the elevons move up and down.  We now need to set servo direction and mixing.  On some TX's the elevons mixing is called just that (eg;  Futaba) on others it's called Delta wing.  In either case this needs to be selected.

Don't want pull back the stick and the wing goes into a dive do we? So we now need to check servo direction.   Using your transmitter servo reversing facility, when you pull back and push forward on the right stick both elevons should lift up and down  together.  If not reverse the servo on the channel, 1 or 2 to put this right.  Moving the stick left to right - left stick is left elevon up and right down equally.  Opposite scenario of course when right stick is used.  In delta wing mode the mis is automatic.  However in elevon mixing you need to set the mix for both channels to 50%.

Your control surfaces, elevons should work in elevator mode and aileron mode in equal movements of travel.

For initial/maiden flights it is best to set the movements of the control surfaces to small amounts.  A starting point is elevator 8mm up & down.  Aileron about 10 mm.  Too much travel could result in stalling, too steep a climb angle and wild turns!  With higher winds and speed the slightest movement of the control surfaces will make a lot of change of direction.

The Winglets or Fins

In most cases these winglets are made and cut out from a material called "Correx".  Used extensively in the packaging industry but now more recently in making sign boards too, take a look a estate agents boards.  Correx is very light but extremely strong.  It will bend fairly well along the line of the profile but is highly resiient across the profile.

In the wing kits these are usually cut from 3mm Correx and can vary in style.  I have previously used 5 mm but found no case to warrant this.  In the Irvine X-IT case they are an angular 3mm shark fin.

Before sticking the Velcro on to the wing and wingtip we will cut some slots in the fins for extra security and rigitidy.  They are identical is shape and size and they are not "handed" at the moment.  With the wing on a flat surface position one of the winglets against the wing tip, the forward point in line with the wings leading edge.  Using a pen or felt tip mark a line on the winglets inside face following the wing surface contour.

We now have a fin with a slightly curved line.  Mark two points about 35mm in from each end.  Then from these two points mark another two points 25mm further inwards.  We are going to cut out a slot between the two 25mm points.  These slots will enable us to pass some 25mm fibre tape through to doubly secure the fins and ensure they stand upright or perpendicular to the wing surface.

Optional and I favour this method.  Lay the marked fin exactly on top of the other fin.  You apply some tape to the edges to hold  them secure.  Now, using a 3mm drill, drill through both fins together at the 25mm points.  This method stops the plastic from further tearing and acts as a stop point for the craft knife.  Now taking each fin separately cut a slot of two lines between the 25mm holes.  Push out the cut out bits.  You should now have two fins with two neat slots in identical positions.

Pull apart your Velcro pieces and attach the prickly piece to the wing tip.  Trim if necesssary!  Apply the soft side of the Velcro to the winglet, the front edge of the velcro in line with front edge of winglet.  now push the winglet on to the wingtip.  Cut four lengths of 25mm fibre tape about 100mm.  Pass each one through each of the slots so ther eis an equal amount either side.  Ensuring winglet is perpendicular stick the tapes down firmly.  The winglets should now feel fairly rigid!  Done!

Pour yourself a drink.  You have earned it.  Two/three  hours work in total.  A finished masterpiece just iching to be launched of a steep hillside.

Don't know how to fly it?  Join Wimborne Model aero Club and enthusiasts and experts will show you how.  Maybe ask for a trial lesson.  Contact the Training Administrator.

The wing built and pictured in the article maidened on 28th November 2009 at the Gourds slope. The wind speed was not high only about 15 mph but the wing needed a two clicks of  left trim and five clicks of up trim and with "hands off" flew straight and level.

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Addenum:  If you do not have Delta or Elevon mix available in your TX then you wil need a channel mixer for this purpose.  The mixer will come with installation instructions but basically it equally mixes signals from the aileron and elevator outputs of the receiver before relaying the signal on to the relevant servo.

 

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