MODIFIED BAT BUILD - STANDARD WING SHAPE

[thevon]

Well, I swore I'd never do another build thread. I got a new Bat kit recently and although the old Bat's still flying (very fast, actually) I started tinkering with the new one tonight.

And (sigh) started taking photos so I will kick off yet another long, boring, photo-infested build thread! I dont' know why we do these threads ... some sort of fiendish sense of pride in our creativity ... anyway, I'll post and you can sn-igger sarcastically, or totally ignore, whichever is your preference!

This one will be built with the standard wing plan, rather than cutting the root to give a straightish TE, like I did last time. I have no complaints about the "Old Bat" but various people have commented that the standard shape is more DS stable, plus it has the benefit that the standard internal spar holes line up! Not so if you change the angle!

I was going to use big fat golf club spars, like the Reaper and that would indeed be the strongest option. But I haven't succeeded in finding any at a good price. Plus, to install them I would need to cut a huge trench, threatening the integrity of the wing foil ... so would need to make a plaster mold to hold it in shape while spar fitting. All possible, but it looked too hard so I took an easier way out, which is simple but very effective!

More tomorrow, that was just to create the suspense ... next episode (and some pics) tomorrow!

Hey did you realize this software changes "sn-igger" to "sblack person" !

[chamm37]

sweet as....i like the little ending there at the end.....it made me laugh

More tomorrow, that was just to create the suspense ... next episode (and some pics) tomorrow!


Where did you pick up your Bat from Andrew

[thevon]

For interest, this is my previous Bat build thread: windsock.proboards76.com/index.cgi?board=general&action=display&thread=92&page=1

These pics show the shape of the stock cores, vs the shape of the Old Bat. As discussed in the previous thread, the shape was modified by cutting the wing roots at an angle to make the TE nearly straight.





The stock spar hole fits a 5.5 or 6mm round tube carbon spar, but the spar tunnel in the wing stops about 10cm short of the tip. It's best to run the spar right to the tip to protect the tips from scrunching in cartwheel crashes. So as for last time, I used a fairly loose fitting long spar, cut some notches in the tip of it, and used it to bore the tunnel to the tip. You need to be careful to lay the wing flat, topside up, and use a board and weight to press down on the back of the wing - the Bat has a complex wing shape and that's the only line that's naturally straight. If you try to press any other part of the wing down, you’ll put a bend in the wing.

But this time rather than doing it by hand I used a drill! Much easier. Just go slowly when you get near the tip. Best to drill back in from the tip, rather than letting it push out. I tore a bit from one tip, but easily fixed.



But I want to use a thicker spar. The best I have is a long 8mm carbon tube so I devised the ingenious plan of boring it through too, using the thinner spar as a guide. That worked really well. But be careful because the drill chuck will crush it, which can be prevented by putting a piece of the thinner spar inside it. It bored through successfully, but it was still a tight fit so I worked rods back and forth for a while, gradually pushing out EPP beads and widening the tunnel.

This shows the end of the thick spar:



Being slid over:



And this shows it in place.

Note: at this point push the wing halves together and check that they are well aligned. I didn’t – just assumed they would be, and regretted it later! You may have to butcher around the holes a bit to get a good alignment.



Then to glue it in I squirted some PU glue in the hole and worked that back and forth with a long thin rod. Did that from both ends until I was sure the entire length of the tunnel was coated with glue. This is very important, or you won’t get a good bond.





Then I smeared PU glue and some water over the 8mm spar. Plugged the hole in the end of the spar with a cone of masking tape so it didn't get full of glue. Then forced it through and left it to set (one side only at first).

This is a lot of words, but it only took 30 minutes or so. I'm wondering if it would be a good idea to glue the thinner spar inside the thick one, for more break-resistance.

More later!

[thevon]

The PU glue foamed up nicely and set overnight.



Had to trim some glue from the centre too. But if you're doing this, be careful not to score the spar at all, since it could help it to crack, since the centre cops the most flex forces.

I glued and slid the other wing half onto the spar (plug the end of the spar again) and wiped the excess PU clean. I had some puddles of 5 minute epoxy ready to mix, so that I could glue the wing halves together. When the 2 halves were pressed together you can see that they don’t line up perfectly. My last Bat was the same … I think the EPP molding is a bit inaccurate. The hole is where I've broken away the thin skin over the radio bay - I'll fill this, and the stock servo bays, with solid EPP later.



I mixed and smeared the epoxy just between the nose and around the spar. I always do this in 2 steps – front then back, because you end up with a better aligned wing. I forced the nose halves to keep them aligned while the glue set. Then mixed more epoxy for the back end, worked it in with a thin blade, and again forced the halves into alignment. There, done! All glued up.

[thevon]

I got some balsa elevons 50mm wide, 10mm thick to match the Bat TE. I’m going to cut a few mm off them so they’ll end up a bit narrower.

I’ve ordered a ballast tube from Zipper, but an important thing is to plan where it is going to go.

I knew the CG of the Old Bat was 136mm, but the New Bat’s CG of will be a different distance as I’m building it with a different (standard) wing plan. However, it will be very close to the same mean aerodynamic chord (MAC) which you can work out using a CG calculator which you can download from here: pagesperso-orange.fr/scherrer/matthieu/english/mce.html

Unfortunately the English one is in inches, but you can substitute mm for inches and it will work … or use the French one. I traced the outline of the Old Bat on my bench. and entered the measurements into the calculator. By trial and error entering different %MAC’s I worked out that the Old Bat’s CG was at 23%MAC. So I entered the measurements for the new Bat, and conservatively worked out that at 22% MAC (a tiny bit further forward) the CG would be 121mm, so I marked that on the wing.

I also marked the position of the main spar and the servo positions, similar to where they were on the old Bat. The control rods will be at 265mm from the centre, and aligned with the midline.



I also cut the EPP elevons away and extended the cut to the tips, as a carbon dragspar will go right along there from midline to tip (also ordered, from Kite Magic). Also the EPP fixed elevons (center and tip) will be replaced with balsa ones, and the reflex built in to the standard ones will be removed. Removing the reflex is a very important change to make a fast Bat.



Sand the square edge of the TE to make it really straight. You can see that the 2 lines don’t match perfectly due to that manufacturing mis-alignment. Probably not worth worrying about. Won’t make any difference.
Still muddling along. Cut some chunks of scrap EPP to fill the servo holes and battery/ lead bays.



Masking tape really helps to avoid a mess. Spray a light mist of water into the holes too. PU glue needs a bit of moisture to really “go off”.



Smear the holes and the plugs with PU, and push them in. It helps to put some paint tins or other medium weights on the plugs to hold them down. PU can lift things up.

[felix]

some handy tips there mate i'll definately use on my next model (especially the spar fitment!).
can't wait to see this one airborne.keep the pics coming

[thevon]

After letting the PU go off, there was foam oozing everywhere!





Then trimmed and sanded it flush.



I began to rip the gear out of the Old Bat. I had forgotten that I used Eneloops in this plane. These batteries are excellent. (See Sanyo Eneloop thread).



I think I can honestly say that every time I’ve checked the charge in this plane, it’s been full. Can’t say that about any other plane I have. Some of them have Sanyo 2700mah’s which cost MORE than the Eneloops, but they don’t perform as well. As they say, it’s a no-brainer.

It’s really useful to do a thorough post-mortem on a plane when you retire it! To have a good look at what worked, and what broke, etc. It helps you work out what’s worth doing next time.

I cut the hingelines to free the elevons – they were undamaged! This is the first time I haven’t had to repair elevons on the plane. I reckon that’s due to 3 things:
1) the fixed outer elevons taking the big hits and protecting the moving elevons.
2) the elevons are fully wrapped in strapping tape.
3) the thick carbon dragspar along the trailing edge. This was a bit of an experiment, but I think it’s very successful.

I hacked the thick carbon dragspars off the trailing edge to check them out. The glue had really bonded well – not easy to get off. And … they are undamaged! Amazing! I would expect dragspars on any plane subjected to this sort of abuse to have a crack somewhere.



Then I bent the wing and I couldn’t believe how floppy and flexy it was once the dragspars were taken off. Each wing has a single 5.5mm carbon tube spar in the centre, and there are LOTS OF paired ribbon spars embedded vertically, one above the other, to stiffen it. (see photos of all the spars in the thread windsock.proboards76.com/index.cgi?board=general&action=display&thread=92&page=3)



Once the dragspars were removed if bent the wing as shown in the above photo, it revealed 4 broken carbon ribbon spars, and under load, the wing buckled significantly at each break. (I wish I’d taken a “before” pic too to show how good the wing looked under similar load, before cutting off the dragspars). This shows that the carbon dragspar was very effective in resisting bending forces, making the wing much stiffer. It didn’t break, and it probably helped to preserve the ailerons and their hinges.

However after lots of previous raving about how good the thin flat carbon ribbon spars are, I can’t recommend them for planes that are going to take a beating. Doesn’t matter if you lay them flat or vertical, no matter what, they will break.

The Profilm was pretty hard to strip away from the Goop, but not impossible. The PU/ spackle underneath had remained really tough – no crumbling to be seen.

Back to the new wing now ... I sanded the little bumps off the surface – this plaster sander with mesh is great for sanding EPP flat.



I had left the central Rx bay open, then changed my mind and epoxied a cover on the top, then changed it again and filled the whole thing. Next morning the whole wing was glued to the bench! Beware – PU glue will force its way through tiny gaps and foam out and stick to everything. I should have put some plastic under it. This is the messed up wing as a result:



I removed the servos from the Old Bat– they were like new, no slop at all. They are Hitech HS5475’s, and are a truly awesome servo. Digital, Karbonite gears and at around $42 each they are not cheap, but for their performance and the fact that they’re going to last many times longer than a standard servo, they’re worth every cent. They have nice long, strong leads too.

To cut out the servo bays in the new wing, first carefully mark around the servo. You’ll need to use the piece you cut out, so mark an L or R inside the square and draw an arrow pointing forwards. Cut neat, full depth, full width cuts with a very sharp long knife, all around the square shape of the servo (ignore the gear shaft bit) keeping the knife very vertical. Sharpening your long blade on a sharpening stone just before slicing EPP really helps get a smooth cut. Push the EPP plug out. Sit the plug on the bench topside up next to your servo, and press the servo against it and mark a line all around the height of the servo, all around the plug.



Then carefully cut just below the line. Take it slowly to slice the wafer off the top.



Then in the wing cut a wedge to accommodate the servo arm, and make a tunnel up one corner for the servo wires. Sit the servo so the bottom is completely flush with the underside of the wing.





Put your wafer on top and if you got the cut perfect, it will sit flush. If you stuff it up, no worries, wait till the servo’s glued in then cut up another bit of scrap later.

I got some elevons but when they turned up they’re the wrong size – 8mm thick, not 10mm, so I will have to wait till I get some better ones.

[chamm37]

looks great but why did ya have to ruine the old bee

[thevon]

The stuff I ordered from Kite Magic turned up so I got ready to glue the 11 x 1.8mm carbon strip dragspars. This stuff is very thick. There’s a thinner strip (I think 12 x 1.2) available from Hobby Model Warehouse which I used on the Reaper. But this Bat doesn’t have golf club spars so I’m happy to use the thicker stuff for the extra strength and stiffness. I sanded along the TE to get the thickness fairly constant (these Bats are pretty irregular – bends and bumps everywhere!). Actually it's a good idea to sand anything you're going to glue, particularly with epoxy, as I've noticed that epoxy doesnt' bond well to the smooth molded skin of Windrider EPP but it's fine if it's cut or sanded.



The Bat wing has a bit of a banana bend in it, so you need to clamp the trailing edge flat before gluing the dragspar on. I lay the wing on a piece of flat formica board with a bit of laminating film in between to stop it sticking. Here you can see the strip ready to go on one side.




I zigzagged a thick line of medium CA on the strip, smeared it smooth with a gloved finger, and pressed it hard onto the TE. Then repeat for the other side, butting the strips neatly in the centre.
Note: before doing this, use a straightedge to check that the TE is really straight. I just did it by eye and after gluing the dragspar on, one side is a bit bowed out.
Then next morning I got a wood plane and planed the small amount of excess height on the dragspar so it was flush with the wing. This is really easy to do.



I am using fibreglass rods as “external stiffening spars”. The f/g seems like a graet idea to me because it’s so cheap (about 1/5 the price of carbon!) and it doesn’t snap like carbon. As an external spar we don’t need it to be stiff. When you bend EPP, one or both sides must stretch or compress so if you glue something which won’t stretch or compress onto both sides, it resists the stretching and compression of the skins, thus resisting bending.

I did the first pair of rods in a curve, which I think helps give some torsional rigidity as well as bracing the midline. I also put a straight pair across the centre. I used 3mm on the top, and 2.4mm on the bottom. Lay the first rod down and use strips of masking tape to hold it in the desired position, then mark closely either side with a pen. Cut the rod to length, plus another one the same length to use later on the other side of the wing.

Use a fine knife to cut a V between the lines. Tear the fillet out with a small flat screwdriver. Experiment with the width and angle of your knife cuts before you do too much, till you get it just so the rod sits flush or just below the surface. It helps to have a small offcut of your rod to use to test the depth, and to use to rip a few daggy bits out of the channel. Sounds tricky, but it’s surprisingly easy. Once you get the knack you can rip through it. Much faster and safer than dremelling it. It doesn’t matter if you cut a bit too deep since you’re filling the trench with CA anyway.





I used thin CA for this – man, that stuff grabs the f/g rods like crazy! Dribble CA along the channel, spread it back and forth quickly with a stick, put the rod in and rub over it in with a rag. It’s easier if you glue one half first, or it you mightn't be able to keep up with it going off!.

Use a sharp pointer, needle etc to push thru the wing to mark the rod positions on the reverse side. Repeat the process on that side. Remember, to get the maximum stiffening effect you want the 2 rods to be directly one above the other. As soon as you get a pair of top and bottom rods glued in, the wing feels enormously more rigid.

This process of gluing in fibreglass rods is so quick and easy to do! But wear gloves! And have lots of thin CA on hand!

I was on a roll so I taped 3mm rods to the leading edges, then cut the V channel for them too. But this is a shallower V, since we want the rod to protrude slightly so it forms the tip of the leading edge. I’ve wanted to try this, as I suspect it will make the Bat last longer by resisting impacts from ripping the LE.




Since the LE has 2 sections, I extended the long rod into the centre section EPP at the bend, by heating a small screwdriver with a lighter and poking it in to make the hole. I CA’d the long rods, then cut the shorter ones and made a nice bevel for them to butt up to the buried end of the long one. Confusing? You’ll understand if you try it! When these rods were glued in the LE felt very strong and smooth! The original Bat LE is pretty crappy and bumpy.

But don’t push too hard on the ends of the rods when the glue’s setting! I did, and bowed them slightly.

Not very clear in this photo, but here are all the rods in place.



I then cut a piece of EPP out from in front of the dragspar join, and cut a piece of scrap dragspar, bevelling it very shallow both ends, to make a bridge between them.



The whole area is Shoo-Goo’ed together, and left to set. This worked really well on the Bat and the Reaper. I filled some of the gap with some EPP to save weight. However it was a bit silly to make such a long bridge … I should have made a much shorter one. Don’t know why I did that! One plus is that it will give a stronger platform for the tail mount.



At this point the weight is 271gm, with no gear, ballast tube, ailerons or covering.

The elevons which I got are 50mm x 12mm, so they’re about 2mm thicker than the trailing edge.



So I had to cut them narrower to match. Sean will be happy as he was aghast that I was planning to use 50mm wide elevons! They are now about 43mm. (note: I’ll have to recalculate that CG!).

First I cut some sections 45mm wide to use as fixed elevons at the tips, and marked their positions. I’ve decided to have a fairly wide centre fixed section, 7cm either side of the midline, so I marked that too. Then cut each aileron a bit longer than the final length (which will be about 555mm), and marked them, eg “left top”.

Taking an offcut of the stock, bit by bit I cut some width off the thick side, till it was a neat flush fit to the TE at the centre end. This is because the TE is thinner at the tip. Then cut both elevons to that thickness. You need a long steel straight edge for this (cheap at Bunnings). It’s important that you have them the right way up to match the desired hingeing … I’m going for bottom hingeing on this one, so after they were trimmed to width I turned them over, laid the rule along the edge and cut the bevel in.





A bit of custom sanding was then required to get the elevons to flush match the TE all the way along.

[chamm37]

looking great andrew....cant wait untill it is done and see it fly ;D

[thevon]

Well, this is a long and boring story isn’t it! Tell me if you want me to stop! Sorry!

Had a few intermittent sessions getting a bit more done. I decide to mount all the gear from the bottom, to keep the top surface intact. Firstly worked out approximately how much area I would need for the nose lead, then marked battery positions. Carefully cut as deep as batteries + a few mm, and ripped out foam chunks till they could be well buried in their graves. Make sure you leave some slack in all wires, or they can rip off in a big prang/ bend. I used goop (Shoe Goo) to glue them in. As far as I’m concerned, the more goop the better in the nose area! These planes would be better if the entire nose was solid goop!



Then to make it really tight, clamped them in lightly overnight, using EPP offcuts underneath to protect it.



Next day, I cut some blocks to cover over them, gooped those, and clamped them for half a day too before trimming.

Then, taking into account where the ballast tube is going to go (a couple of mm in front of the planned CG) I cut a bay just deep enough for the receiver and wiring.



Then I punched a thin screwdriver thru to the other side in 2 spots to accommodate the model alarm and socket switch, which were hot glued into place from top and bottom.




I took off the old servo arms and found some new ones. My control rods are made from thin-ish stainless bike spokes which I happen to have around. I also use fairly strong nylon clevises which are a really tight fit on the spoke thread. I think the nylon clevises are very rigid, and I use them on the Reaper too. I actually like the fact that they’ll break or bend in a big crash, which may stop an elevon breaking, or a servo stripping. It’s very easy to replace a broken clevis!

To make the hole for the control rod, I cut a piece of the bike spoke and use it as a drill. It makes a really tight fit. I strongly recommend this! It’s a bit of an effort getting the rod thru it later (I use a Z-bender) but the fit stays very solid.




Then I hooked up the servos to the Rx and checked that it all worked, and that the servos worked the right way, etc. I am using my old Bat Tx memory program which saves some setup, but first you need to reset the centring of both servos to zero, and make sure you also set the trim switches to centre (I forgot). Then I trimmed the excess bits off the new servo arms and fitted them on so they are pointing slightly (about 10 degrees) towards the front. You may have to fiddle with programmed servo centring to do this. When you’re happy, don’t forget to screw the servo arms on! I’ve regularly forgotten and had to punch holes thru the wing to get the screws in later!

Then make sure you have a channel cut to keep the wire clear, and hot glue the servo in. I really like using hot glue for things that may need to be removed later, eg servos and socket switches (I can tell you the latter need replacing after being dunked in salt water!). But I’m not used to this new glue gun and its different glue stick so the first one was a bit of a panic when it set too quickly. My old gun got so hot it would melt the foam if you weren’t careful, but I got plenty of working time. I’ll try one of my old glue sticks next time.



I cut narrow channels for the servo wires and pushed them in and ran them to the Rx bay. Remember try to leave all wires a bit slack, and a bit of loose end in the servo area – very useful if you ever have to replace a servo. Then I stripped a couple of lengths of thin wire from this ribbon cable, to make an aerial.



For more details it’s on page 2 of the “Suppliers” thread windsock.proboards76.com/index.cgi?board=general&action=display&thread=5&page=2.

I used 2 wires – both are soldered at the RX end, and one runs along each wing and does an L bend about ¾ of the way along. The more aerial the better, I reckon. I made a hatch for the Rx bay using corflute. Here it is all in place.



Time to attach the fixed elevons. This is a serious job because it’s accepted that it’s very important to get the reflex just right. The standard Bat has a lot of reflex and it’s said that it stuffs up the handling, big time. They go much better with just a slight amount (2 or 3mm) of reflex. I pressed one wing TE very flat using weights, and shaped the face of this one till it was just right, then I used Shoe Goo to attach it. I like the Goo because these tip elevons get a battering, and the Goo has a bit of give.

LATER NOTE: At this point you should sit the elevons in place and make sure that the fixed elevons have equal reflex in relation to the moving elevons. I didn’t do this – I just did it relative to the underneath of the wing at the back. When I later hinged the elevons on I found that the inner fixed ones were reflexed more (sitting higher) than the outer ones, compared to the moving elevons.



After doing the tips I did the centre section but used 5-min epoxy here, mainly as it’s quicker. Again I weighted the wing down and did one side first, checking that glue set with the reflex just right. Then it’s an easier process to cut and glue the other side to match. If you try to do both together it’s really hard to keep it all schmikko.



By the way, you can buy 125mL twin bottles of 5min epoxy for about $40, and it’s such better value than the little tubes. I use it heaps. This is the result so far:



I then set about covering the elevons with laminating film, which is a fantastic simple and durable way to cover balsa bits. Very easy to do, very smooth, very strong. You wouldn’t believe how rigid these elevons feel – almost like composite ones. Only problem is it’s clear, and very hard to colour. I’m going to silicon-hinge these elevons. Silicon sticks really well to the film and I’m hoping it will stick well to the carbon dragspar. I used Ezza’s method of wrapping the film around from the front, and ironing it onto itself at the TE, making a thin “feather” at the TE. I had also knocked up a basic fin for it during the day, and I covered that with thinner film at the same time.



Now I just have to wait for the ballast tube to turn up from Glenn (Zipper – he makes beautiful ballast tubes!) then I can install it, then it will be filling/ gooping/ covering.

[felix]

keep the tutorial going mate! great information that'll i'll be using on the reno of my bees.cheers mate.....quick Q for you do you have a cheap supplier of carbon fibre?

[Vanders]

Yep I agree, always good to see some little tricks & ideas guys use during a build thread.

Keep up the good work mate!!!!

[thevon]

I got a carbon rod close to 6mm from Kite Magic, mixed up some long-cure epoxy, and glued the 6mm inside the 8mm, full span. Nice slidy fit. Should really help to prevent the thin walled 8mm tube from splitting in a Richter Force 9 impact.

I also smeared some of the excess epoxy over the face of the carbon dragspar, which I think is a good measure to help the silicon to stick to it when the ailerons are hinged.

The ballast tube arrived from Zipper – this is a lovely job. I have one in my Reaper which was in the Drongo before that. Slugs and tube really well made.



The tube empty weighs 51gms, and it holds 8 slugs which have a total weight of 567 gms (70gms per slug). The tube is 16.6mm outer diam, and the slugs are 15mm diam.

Marked the position of the tube at the predicted CG position, and cut all around and through it, and ripped out chunks of EPP. This just doesn’t feel right!



Due to the wing being thicker in the middle, the trench had to be quite deep in the centre to get the ends buried. When it was within a couple of mm of a close fit, I decided to make up a handle for it and hold it over the stove to heat up, then push it hard into the trench. This worked well … but don’t get it hot enough to melt the solder on the ends.



Next step was to put the slugs in and mask the opening. The sprayed the tube and trench with water, smeared PU glue all over the walls and floor of the trench, and over the tube. Pushed it in hard and then cut some “bridges” of EPP (all the same thickness) to sit on the tube to keep pressure on it. You have to allow some air to get to the PU. This shows the detail - I cut a V into them to make them a snugger fit.



Here are all the bridges in place –



Then put a piece of flat timber across the top and weight it down.



Here it is with the glue set and partly trimmed. I have put a bit more PU into the bigger holes, to fill them more before trimming.

[Pij]

Andrew, regarding the LE carbon rod: Some of my old free-flight forum friends have tried carbon on their leading edges, and found that in an impact, it would sproing off at one point or another. They found that something less rigid was better for LE protection. And the gliders they were building were generally between 5g to 50g, so there was only low momentum in the impacts. I hope you don't find the same result with yours.

You certainly have some stiffening in all that carbon you are using. I'm especially impressed with how rigid your hinge-lines are going to be in terms of NO wing TE flexing under load. But it looks terribly expensive.