|Jun 24, 2006, 07:24 AM|
Mini build thread - DS Bat
This is going to be a mini build thread of a Windrider bat, which is being modified along the lines of the Predator Super Freak, but I'm adding a couple of extra items to beef it up a little, partly to compensate for my very poor DSing skills (ie I crash a lot). I thought it'd be a good idea to once again (among a recent rash of uber-complex builds) to visit a simple, but very versatile foamie that those with less skills, time and spare cash can put together and get, IMO, a very high performance foamy for their efforts.
OK, enough of the blab - on to the build.
First to assemble all the relevant bits:
- 1 off Windrider Bat. Keep the foam cores, corro hatches, strapping tape and packing tape, put the carbon rod in your useful parts bin, and bin the rest.
- 4 off 3mm fibreglass rods, 5' long for the main spars - IMO more suitable than CF ribbon(shields up!).
- 2 off 10mm X 0.5mm CF ribbon spars for the sub-trailing edge.
- 2 off 4-40 threaded rod for pushrods, with matching metal clevises, and heavy duty control horns.
- 2 off pushrod covers (I like the long ones from Hobby Lobby).
- 2 off servos - I'm using full size, cheap, Karbonite geared HS-322s
- RX and battery, I'm using a 4 cell 800mAHr.
- 1 off CF 4mm rod about 10" long for the tail boom.
- 1 off small 3mm corro sheet for tail and tail boom mount.
- 1 off 4" servo extension, for the 'switch'.
- 1 off balsa aileron stock, heavy duty to replace the EPP molded foam ones in the kit.
|Jun 24, 2006, 07:30 AM|
The first major mod is to make a straight trailing edge. This is helpful to move the CoG back (less nose weight needed to balance = lighter) and allows the use of the strength from the CF ribbon sub-TE.
- Get a square (or anything that can mark a right angle to a surface. Line it up against the TE of wing, and mark a line to meet up with the point of the nose. Do the same for the other core.
- Very quietly sneak into your kitchen and 'borrow' the biggest sharpest straight-bladed knife. I find that this is the best tool to achieve a clean cut on EPP. Cut the previously marked lines as shown in the photo below. Be careful toward the leading edge, which can flex, making an uneven cut.
- The last photos show the new roots placed together to give a nice, straight trailing edge.
|Jun 24, 2006, 07:32 AM|
Next, join the roots
- Mask of the surrounding area with the tape of your choice. I used packing tape, then wrapped on old towel around the rest of the wing.
- Spray the roots with some 3M Super 77, wait a few minutes for it to become tacky, then align and tack-tape the roots together. Leave to dry.
This sets up the cores for the next major steps. Nighty night.
|Jun 24, 2006, 08:04 AM|
Now onto the spar system.
I have used CF ribbon for a single curved spar in previous bats (Predator method). It makes the wing nice and rigid, but I have broken the spar on several occasions through rough (and some not so rough) crashes. It might be that my 10mm X 0.5mm local CF just isn't up to the job. Nonetheless, for this build, I'm using 3mm fibreglass rod. In my experience (glo-powered combat plane foam wings) the fibreglass is quite strong, and flexes just a little more than CF, which might provide improved durability.
In this case, I'm putting two spars in each surface - one full span curved spar along the thickest part of the wing, and another straight spar between the first spar and the sub-trailing edge.
- Find a cutting tool to carve a trench for the spars. I used a Dremel with a Perma-grit cutting wheel, which is about 2.5mm thick - this gives the slot a good grip on the 3mm FG rod.
- Mark and cut the spar trenches. They should be deep enough to just submerge the spar below the surface, which ensures that the profile of the wing is preserved, but gives maximum rigidity.
- Rough up the surface of the spars with sandpaper before inserting them, to give the CA more 'grip' on the spar.
- Put all the spars in, then triple-check the wing for warps and twisting before drizzling all the spars with thin CA, and allowing the wing a good hour to cure.
|Jun 24, 2006, 08:10 AM|
Now it's time to install the sub trailing edge:
I'm using two CF ribbon spars. The 10mm height of the locally sourced stuff exactly matches the thickness of the airfoil at the sub trailing edge. Unfortunately they are not long enough for the full span, so I have to use two, which are overlapped in the centre. Here goes:
- First, carefully cut the elevons off using the trusty sharp kitchen knife. Throw them in the 'spare EPP bits' bin.
- Next, cut off the centre trailing edge and the tip trailing edges. Angle of the cut to align the existing sub-trailing edge to make one, long continuous sub-TE. Try to do each with a single cut. Keep the fixed trailing edges that you just cut off - they'll be re-attached later.
- Cut each CF ribbon spar to overlap by about 4" in the centre, and to stop about 2" short of the tips - we want to retain some flexibility of the EPP at the tips.
- Medium CA the CF spars to the sub TE and allow to dry. Done.
|Jun 24, 2006, 09:51 AM|
Joined Apr 2004
A little history lesson
Originially before the freak was known with the straight t.e I made one known as the "batpipe" with a slightly swept te , it was one of my favourite bat-mods.. predator took this and created the superfreak from the idea .. from what i can see from your progress here , you are making one bad mother superfreak, that will suck up the ozone layer to zero hour....one word from a fellow bat modder , if you can afford it use some ultracote , othewise tape the bottom of your wing verticial , and the top horizontal , as there is less chances of tearing your covering , here is a photo of the originial ..
man those were the days....
|Jun 24, 2006, 06:28 PM|
There is one thing that you forgot to add to your list, enough lead to fill up the battery compartment. And seeing as you have added weight to the back of the wing (drag spar), you may need more.
My Bat is a standard build and I had to fill the battery area with lead to get the CG right
|Jun 25, 2006, 08:44 AM|
Next, install the servos and receiver, pretty standard stuff:
- Locate the servo so that the horn is at mid-span of the elevon, to ensure maximum control (least possible flex). Make sure that there is enough servo lead to reach the root of the wing where the RX will be.
Draw a close outline on the EPP, then carefully cut right through the full thickness of the wing in the shape marked. Press the bock out.
- Test fit the servo in the hole, then trim a sliver off the underside of the block to fill under the servo, maintaining the wing thickness. Push the rest of the block into the molded servo opening (to the gooped in later).
- Pot the servo using epoxy.
|Jun 25, 2006, 08:53 AM|
Time to install the battery and corro covers.
- The battery bay is smaller now due to cutting the roots out. Enlarge it as necessary to fit your battery of choice.
- Grab the roots that you cut out. Place them together and mark the corro cover to cut out so that the cover will fit the new shape of the battery recess.
- Fill in all of the remaining voids around the battery with EPP. Goop in the lot, then fit the corro covers.
|Jun 25, 2006, 09:04 AM|
Next, finish off the cores, ready for strapping tape:
- Submerge the servo wires to the RX location - nothing new here.
- Cut out a suitable RX hole for a snug fit.
- Submerge the RX antennae. Take a photo of its path, just in case you need to dig it out at some time in the future with minimum damage to the covering.
- Make a corro cover for the RX bay, cut a recess for the cover like the existing molded ones.
- Double check that everything is in place. Double check the RX setup and servos. Ready to start taping.
|Jun 25, 2006, 09:12 AM|
I used the stock Windrider supplied tape. The spars provide sufficient spanwise stiffness, to I will lay the tape at 45 degrees - two layers offset. Thinned-Goop the molded EPP first, lay the tape within 1 hour of gooping. Thinned-goop between layers. I butted mine edge to engde to prevent ridges. Not much to show here, pretty standard stuff.
This is a pretty slow part of the build as you need to wait between taping for the next coat of goop to dry sufficiently. But the results are worth the patience - the wing will be smooth (careful taping), strong (multiple spars), and stable (minimum twist through the shear layer) ... or so the theory goes.
|Jun 25, 2006, 05:39 PM|
Oh yeah ...
The bit that I forgot to add earlier is re-attaching the fixed trailing edges - important enough to make a note about:
- We carefully cut off these parts earlier and saved them.
- We now want to shave off a small amount of the base of these parts to remove the reflex. The difficult part is to take the same amount off each of these three parts so that when they are re-attached, the true trailing endge is straight. I gooped mine on - as its the strapping tape that provides the mose strength to hold them in place.
|Jun 26, 2006, 07:28 AM|
Now for the elevons:
- Measure and cut your balsa elevons to length and width. I bought a box of 24 sets of medium weight 60mm width elevon stock a few years ago, from which I have been able to cut to size for whatever plane projects come up. Cut a bevel in the leading edge - make sure that the leading edge is perfectly straight, to match the sub trailing edge of the wing.
- Lightly spray with 3M Super 77, allow 20 mins plus to become tacky, then cover in something white. I am cheap (and have zero covering skills), so I used packing tape.
- Prepare 20 pieces of (strapping) 'step hinge tape': Cut a length in half, then mate 5mm of the sticky sides together. This will make 10 'hinge points' (pairs), five for each elevon.
- Tack tape the elevon to the wing with some 'droop', measure a mark symmetrical spacings along each elevon for each hinge point, then carefully apply. The technique is simple to do, but complex to describe, so just focus on making each hinge point tight, and keep the elevon pressed firmly against the wing when applying the tape.
- Holding the 'droop' position for the elevons, apply 4 additional pieces of strapping tape across the top of the elevon (between each hinge-point) to complete the hinge.
This will make an extremely solid but near resistance-free hinge. I reckon the stepped hinge technique is by far the strongest, bestest technique out there for a foamie.
Pics hopefully show up the hinges
|Jun 26, 2006, 12:01 PM|
Sweet Job Kahnx-
Excellent eye for detail. I think you'll have a MONSTER there. It was VERY wise to do the Super freak straight TE. With all the other mods, many adding tail weight, ie. lots of tape, GOOP, servos a tad futher back. . . It will help immensely!
I think you would have needed a SOLID lead nose to get it to balance if it was a straight up bat build! As it is, I believe you will need a considerable amount of nose weight to balance but, MAN will that make it fast and stable.
I started off moving the servos out board too but, I found that the Balsa elevons are so thick and Beefy they did not twist either way at speed into the 100 MPHs range.
One thing I have learned after exploding ALL kinds of wings DSing. There comes a time when adding more armor has a point of diminishing returns. The weight of the armor actually makes the wing carry so much more inertia that it is actually more prone to damage despite the copious armor. A fine balance . I also use a lighter smaller battery in tha aft side of the Battery bay just so I can add lead (2X HEAVIER THAN BATTERY/volume) in the fore section of the bay to MAX leverage with minimal weight. Over all it becomes a lighter set up.
Either way, I think you will have a winner, just be EXTRA careful if you come out heavy (over 28 OZS) since it'll be SCREAMING and carrying lots of inertia NEAR THE GROUND !
The good news, a heavy weight tracks GREAT even through some NASTY shear! Give and take as usual . Let us know how it goes!
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