Project

The Tempest is an EPP flying wing which could be deemed as large scale - at 1.8 mtrs this is one big wing.  Not primarily designed for combat as the more general wings of 1mtr and 1.3mtrs.  It makes for a big target too but woe betide smaller wings getting into it's path, especially with a flying weight of 1.2 - 1.3 kgs unballasted.

For the purpose of this article I will show you how it's put together, maybe some mods on the way and any problems that might occur because I haven't had one of these before either!

The big foamie kit comes in a big plastic bag, no pretty colourful box here.  There are a lot more parts than your normal zagi,  four part wing sections, 4 fibre glass ribs, 6 carbon rods, 2 steel rods, 2 control rods, 2 fins, some string, some strips of foam obviously from the cutouts, 2 epp elevons.

Unlike most other kits the receiver, servo and battery bays have not been cutout for you, albeit that
might be no big deal.  There is no fibre-reinforced tape supplied or coloured covering tape either.  For those dedicated foamie fans the latter shouldn't be a problem.  You can also cover with Profilm, Oracover or whathaveyou.

Now I know there are couple of giant wing wannabees out there who want to see how it goes together and ultimately flies using me as the "guinea-pig".   So, with that in mind let's get started.

 

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Central Wing Assembly

Because of the wings size and to aid transport the wing has been designed to break down into two sections.  Normally this would be rather unreliable I think but we will follow the instructions and see how rigid the joint is afterwards.

First job is to prepare the carbon wing joiner tubes.  Sand off the gloss of the four short tubes to give a bit of a key for the epoxy.  The instructions also suggest wrapping string around and glueing this on first with CA - the idea being to act as a gripper to assist the epoxy in the wing joiners - any weakness here could be near fatal.  Allow to set.  See photos.

Dig out the two steel rods from the kit.  They are a tight sliding fit into the four wing joiners but really need the cut ends beveling off , burrs etc, for ease of assembly.  I then put a light coating of vaseline on them, you will see why shortly. 

There are 2 pairs of fibre glass ribs precut and nicely finished with the joiner rod holes and cable passthro's already drilled - that is a good idea and very helpful.  Now place the wing joiners on a flat surface.  Slide the steel rods through the tubes and mate up surfaces - a dry run to check all is in alignment, etc.   Then pull rods out and epoxy the tubes into the bottom of their respective slots and epoxy the fibre ribs to the central wing pieces.  Watch out with the fibre-glass ribs, they are two pairs.

After allowing time to set, trim off any protruding tubing flush with fibre glass rib face.  Thats the two central wing joiners finished for now.

It's at this point problems start to appear.  Even though the steel rods are supposedly slippery I had great difficulty in getting them to slide through the tubes as before.  I even reamed the tubes out a little but still the tubes were a very hard push to slide.  At this point I have a suspicion that posslibly the CA glue may have distorted the tube oh so very slightly.

At this point the project stalled for a little time.  If I ream out the guide tubes more the rods will be a loose fit and this make the wings flap a little in use which will ultimately get worse over time.  So, I decided that this wing will be a one piece job.  I tapped the rods through one central wing piece until flush with main wing side rib.  Layed over the rods, the other wing joiner to see how much rod may need cutting off for a flush fit here also.  About 12mm over length.  No problem, marked up and then proceeded to hacksaw through rod.  Simple?  No!  After what seemed eternity I had just about scratched the surface.  What sort of steel is this?  Right - time for the big guns.  One angle grinder to be precise.  It cut it alright but took some perserverance.  Filed ends clean after cooling off.

Again tapped the rods throught one wing joiner till flush then aligned the other and very gently tapped this down too.  I don't think this join will pull apart easily if ever again so a couple of spots of epoxy for good measure.

Main Wing Fitting

Time to prepare and fit main wings - Push one of the main wing halves up to its central wing joiner, aligning the diagonal slot in both.  Using one of the pre-sanded long carbon rods push into the main wing slot and it's the associated wing joiner  getting the tube flush with wing root.  If everything lines up which it didn't in my case, I had to dremel out the hole in the fibre-glass rib to allow the tube to just sit pass through a little, about 5mm. When everything is set-up then re-assemble the rods and glue using 5 minute epoxy.  Do the same with the other half.  

At this point you should notice with the completed central joiner and the two long carbon rods sticking out either side the built in Anhedral.  Allow adequate time for epoxy to cure.

I then sild the wings up to their respective positions along the rods to check alignment and that their roots sit flat and tight up against the central joiner fibre rib.  In my case this was acceptable so time to fix the wings to the carbon rods and central joiner.

I used epoxy between the wing root and fibre rib - there is no flexing here so epoxy will be okay.  I then used two spots of 4 minute epoxy on each rod one at the wing root end and the other spot at the end of the rod.  This will effectively lock the wings in place after alignment - I used two inch fibre tape to hold leading and trailing edges in line till epoxy is set.

With the rods now held in place time to fill slot with adhesive and epp beading.in    STOP - This is the Czech instructions version but where are you going to place your servo leads and in my case with Futaba servos at least one extension too?  (Lead length - See cutting out bays)

I am going to utlise this slot to run the servo leads down.  If your planning Navigation Lights or similar ilk,  like I plan to do, dropping some bell wire into the slots wouldn't go amiss here at this point.  After you have decided your own personal preference then read on. 

To glue the epp beading I have selected a flexible but very strong instant grab adhesive because the wing will flex in turns and definitely need to flex on impact with the ground, fences, trees and other wings.  I opted for Evostick Nail & Seal.  This is an interior/exterior instant grab adhesive that is waterproof and flexible and bonds all materials well especially if one surface is porous. ie; EPP.  It is also solvent free so won't melt or destroy the expanded polypropolene (EPP).  It grabs well but is movable for some time but after 16 hours in reasonable temperatures it sets permanently and becomes waterproof.

This gives us plenty of time to verify the wing positions and although they are fixed by epoxy at the wing roots there is stilll the chance of final adjustments if necessary, up and down in the wing slots if needed.   Insert the supplied epp beading to fill the wing slot and then allow to set without disturbance.  Once the adhesive has cured fully we can trim off flush the epp fillers to complete the wing.

Note:  Earlier when there was  a perceived option to have the wing split in to sections, I could not see any reference in the instructions to keeping the wing joined together by the two steel rods.  There was two little 2 mm screws in the small parts bag and I assume that these may be for the joiner.  But for this idea to work the screws would need to be a lot bigger, ferrule guides to stop them tearing sideways into the foam and large washers too, to spread the pull-down load when you tighten them up.  With this problem in mind I am swaying toward making the wing a one piece job and use the tried and tested method of using fibre tape to keep it together.   Also one of the wings will be carrying the receiver and battery pack.  If we decide to make it a two piece jobby then we will also need 1 servo extension lead too!  Will have to consider this shortly before starting the covering and taping work!

As previously written in the project I was unable to to do this but I have left this paragraph in for review.  Any of you also comtempating the Tempest may find your joiners work okay in which case you may have that option.

We have got cut outs to make!

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Electronics Bays

Cutting out and installing servos, receiver and power pack.

Cutting of the servo bays and battery/receiver bays was achieved with a soldering iron with the tip removed.A piece of old control rod was duck-taped to the handle to act as depth gauge. This being a first attempt at cutting through foam with heat I was surprised how easy it is to make shapes etc. using a steel rule as the irons guide for depth and straight cutting.

All was going well and I now had the servos in place with arms attached to get an idea what to cut through for the arm movement. A couple of slots were made to allow movement fore and aft and to be able to connect linkages.

Standing back admiring my handiwork I then noticed a BIG boo boo. I had cut the servo bays from the wrong side, i.e.; cut from topside. Um! Also the servos leads are on the far side of the bay from the wing slot. Another Um!

If you read the instructions word for word they say that the bays should be cut through "full thickness" of wing. After considering this momentous statement I can see why they may say this. It will allow you to adjust height of servo by sliding up and down the slot. Referring back to previous Irvine Wing builds they cut the bays for you and they don’t go right through. When the servo bottoms out the arm should just protrude above the wing surface - the lower the better too, less likely to get snapped off in a collision.

After a cup of tea I decided that the bays will have to be cut through after all, and make sure I adjust the bays offsets for the servo arms, i.e.; the right way round. The cutting was done with the soldering iron again. The servos just slide through with a little push.

In my junk area I have some foam packaging very similar to EPP and when you squeeze it, it springs back to shape - If I remember correctly I found loads of this stuff in the skip after new computers were installed at work. Easy to cut with a nice sharp craft knife too so I set about cutting out some shapes to replicate the servo bays. Al I had to do now was alter the thickness to set the servo height. These were then glued in with Nail & Seal or I could have used Silicon sealer - flexible but hangs on to "near death" to virtually any surface. Advantage with the latter if you need to take out the servos you can just run a sharp knife round the servo and pull out. Afterwards you can then peel off the remaining silicon.

Fitting Servos

I found that the depth of the wing allowed for a 20mm deep servo, I am using Futaba S3003, 10mm of that packaging foam which left just 5mm for the Correx hatches (not supplied). Did a test fit and the fitting was reasonable considering all the previous problems.

Note: Before securing servos, switch on your TX and power them up through your selected receiver thus ensuring they are centralised.  Fit your servo arms so that they at 90 degrees to servo body.  You must do this now because you will be unable to fit the arms correctly  later after glueing!

Cutting as far forward as practicable, the battery and receiver bays were made identical sizes, about 5mm wider than the AA pack all round. This will allow a little room for servo extension leads to pass through too. The bays were cut 20 mm deep. I am using a AR500 RX which has top pin connections so a little more depth was required in one area to allow for the rx drop lower.Depending on your switch a little depth may be required for this to sit flush with wing surface.

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Fitting Elevons

With the servos now secure and covers cut out for the battery and receiver bay it was time to fit the elevons.  These are not planks like other wings but are tapered with the wider end to be outboard.  They are made from "blue foam" unlike the wing section.  Being quite large they were a bit "bendy" so to stiffen them up I used my favourite trick - Laid on a flat surface I fold 2 inch fibre tape over and along the leading and trailing edges.  This also helps keep the elevons keep better appearance.  The fibre tape also seemed to "take" to the blue foam better than the EPP wing.

THe instructions show three hinges made from 25mm fibretape.  Um!  Wouldn't last five minutes I think.  I used as in all my previous EPP wings three 2 inch fibre tape "hinges" per elevon.  Using three gives support at each end and in the middle which also reduces flexing.  Positioning the elevon up against the wing edge I used some thin card as spacers between the elevon and trailing edge. Three 150mm strips of tape where laid on to the elevon 50mm from each end and one in the middle.  Did the same for both elevons.

Turning the wing over I laid three more 150mm strips of tape on to the wing directly over the tapes on topside but this time laying the tape into the trailing edge contours of the wing.  You now have a double sided hinge.  Ensuring the elevon doesn't bind through at least 45 degrees of up and down.

With the elevons fitted time to make up the control rods and fit the control horns.  I have to say at this point that the horns supplied are a joke.  They are small with a small footprint and would probably tear through tthe elevon in no time at all.  The rods are pre-made up with a pre-formed stop at one end and the idea is to epoxy the plastic clevis on to the rod once the length has been ascertained.  Yuk!

I opted for a couple of Dubro horns with larger feet width (20mm) albiet a little taller but just have to use some of the holes futher down maybe.  I also discarded the supplied rod idea too.  Favouring my own made up 2mm ones - Z bend at one end for servo arm and spring metal clevises at the other for adjustment.  Using a ruler protracted an imaginary line from the servo arm to the elevon.  The line crossed the wing/elevon gap about a third up from the inside edge of elevon.  Mark the spot with a pen.  Did the same for the other elevon but this time verified that the point of crossing the gap is exactly the same as the other.  Any discrepancy here will have adverse affects on handling.

The pen spots mark the point where the pivot point of the horn will be.  Now I was able to drill through the elevons and fit backing plates.  With horns now fitted it was easy enough to judge roughly the length of rods required.  Powering up the TX and receiver the servos will now return to their neutral positions.  With elevons about 5mm up I wound on the clevises about halfway up the thread section and then aligning the clevis pin with the horn holes marked the point where the rod passed the hole in the servo arm.  This will be where the first "bend" will be.  I bent rod here with pliers to 90 degrees and then allowing a 5mm gap bent the rod the other way to create a "Z" bend.

Whilst power is still on, now seemed a practical time to fit the rods properly and watch their operation.  Some rough adjustment for length can made now.  Power off and make another cup of coffee.

Final Stages

At this point I removed the rods remembering with one is which and put them to one side for now.  Time to secure the bay hatches and cover the wing.

Now it's at this point I have became aware that the fibre tape doesn't seem to have the same hold as I have experienced with Irvine wings.  As I said previously the EPP seems to be of a coarser grain and I think this is the problem.  How to make the EPP more "sticky"?  Well, i don't have access to any 3M sealer but rummaging in the garage came across some foam carpet adhesive.  This stuff I used frequently when I used to fit carpets and it has some and bad tendencies.  It has a high content of petroleum products and is highly inflammable but it is very sticky!

I do know that this stuff will melt polystyrene but as EPP is expanded polypropylene I don't think it will affect the wing.  A small test on a discarded piece of EPP proved this to be the case.  It tends to soak in  little but seals the surface - Good.  However, the blue foam is'nt EPP.  A tiny test area was made and within a few seconds the foam was melting away.  Not so good!

The elevons are not a problem I think, as the tape seems to stick fairly well.  So, I lightly sprayed the entire wing surface with this carpet imapct adhesive and before it could dry completely wiped it into the wing surface.  After a short period of a minute or two the wing surface had a sealed feel.  Where the adhesive had gone landed on to the  2inch strips of fibretape crossing  the wing the tape had become very tacky but this was no bad thing except when laying down the coloured tape, once you pressed it down it was down!

Starting from the trailing edges and moving forward I laid strips of coloured tape from centre to wing tip.  I found this easier considering the width of the wing and the tacky surface.  This also means that the none of the tape's edges face directly windward.  The central ends covered by a strip of tape going from front to rear for cosmetic purposes.

With the wing now decorated it was time to refit the control rods, with power on and the wing on a flat surface to get the elevons set up identically.  With elevons set up mechanically all that is needed for final correction is trimming whilst in flight.

The winglets are the usual Correx tips.  In my case the correx was black unfortunately, because this would entail several layers of coloured tape to get a deep colour finish.

Using heavy duty Velcro (not supplied) I cut to shape the velcro to follow the wing tip profile and stuck the velcro on to the wing tip and winglet.  Another favoured trick of mine is to wrap 2 inch fibre tape along all the correx edges giving it a "finished" look and slightly more stiffness.  I then covered my winglets with colour tape.  Finally as in previous wing projects cut two slots through each winglet to allow for 25mm fibre tape to pass through to doubly secure to wing.

Done!  All that is needed now is some favourable wind for a "Maiden"  Hopefully soon I will post up some flight pics and possibly a video.

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See you on the Slopes!

Update:

It flew easily in a fair wind, not fast and turns were slowish.  Wings do flex a bit and the general purpose servos must be really struggling to move those big elvons.  If the smaller zagi/combat wings were fighters then this would the Lancaster bomber!  It's advantages were that the fighters turned too quick and missing the slow flying Tempest.  And what's more if they contacted it, it was them which fell out of control.

Conclusion:

• Glue wings together
• Use hi-torque servos
• Get an estate car/van for transport
• Easy flyer

Pros:

• Easy to fly
• Good for novice
• Very visible

Cons:

• Foam not of good quality
• Foam surface rough
• Large vehicle to transport

 

 

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