Post by thevon on Sept 6, 2007 21:46:15 GMT 10
I’ve been so impressed with Sean’s modified Bat - it flies absolutely incredibly. Plus, it seems to DS really well for a foamie. OK, I know its aerobatic pizazz is largely a function of Sean’s flying skills, but it was tempting to get one – particularly as the price is good ($70US including delivery) so I ordered one and it arrived within a week. After the initial excitement it’s always a shock opening a foamie kit – all those dollars for a couple of bits of foam …
Sean initially built it standard, then modified it to have a straight trailing edge like a “Superfreak Bat”. He’s now rebuilding it again (!) so I had the ideal adviser on tap!
My thoughts initially were to build it (shapewise) exactly like Sean’s but he wondered if it would be better to do a stock build, or at least leave some of the forward sweep in the wings. I decided to leave about ¼ of the sweep, so it’s going to be close to Sean’s but probably a bit heavier and a bit more stable and less trim sensitive.
The Bat has spar holes moulded into each wing and with a standard build, you slide each wing halfway onto the spar. As you can see, the stock spar doesn’t go full span.
But you can’t use a central spar in those holes when you change the sweep, obviously. I decided to extend the existing spar holes to the wingtips so that I could have a full length spar in each wing. Fortunately the spar holes go further than you’d expect so I only had to bore them about 10cm longer. I had another looser-fitting spar at home and I shaped the tip so I could use it to bore the holes bit by bit, spinning it in my hands like an Indian making a fire! Here's my borer-spar just poking through.
I set the wings up with my desired sweep, marked the overlap at the TE, then remarked half of that on each wing. Drew the lines then using a flexible steel ruler as a guide, cut the wedges out of the wing roots taking great care to keep the wing flat and the cuts vertical.
Also at this point, I used the ruler to cut off the floppy EPP elevons. I bought some perfect-sized balsa aileron stock for $4.50 from Hobbyrama. I also continued the trailing edge line to cut the “fixed” elevons off too. They’re no good because 1) they’re EPP and too flexy, and 2) their inbuilt reflex is no good, and they’d have to be cut off and reset with nil reflex anyway, so it’s better to do that with balsa of the same size as the elevons.
I got a couple of matching spars at Briskites, smeared them with PU glue and jammed them in. I then glued the wing halves together with 5 min epoxy. I do it in 2 stages – the back half first, then when it’s set, the front half. I like the 5 min because you hardly need any of it and it gives you time to lovingly massage the 2 wings into perfect alignment and hold them there while it sets. Also since it sets hard, you can always find the centre line by pushing with a pen or fingernail to find the hard line … even when it’s covered in layers of tape and glue.
Once the wings were together I sanded it to remove all the bumps from the mould. The open weave sanding cloth on a Gyprock padded sanding tool works amazingly well.
I had to fill in the holes that are moulded for the standard servo position, and also the battery bay hole, using EPP from old wing beds, and PU glue.
I really wanted servos with no slop, and fine resolution and I wanted to put them out further in the wing. I worked out that standard sized ones would (just) fit, so if I’d had a pair of good standard Hitec ones I’d have been happy with them but I had to buy some. The Hitec HS-475’s with Karbonite gear train have a great rep, about $30 each, but when I found that the same thing was available in digital (HS-5475’s) for about $50 each I leapt at the chance! I also got some Sanyo Eneloop batteries - $25 for 4 AA’s. I don’t think there’s any choice; they’re the only battery to buy. They must expect these servos to work hard – they come with thick cables and huge servo arms!
I got some fine multistrand power cable from Jaycar and stripped it to get an aerial. For $2.50 this amount will last a while …
I took a knife to a male and a female servo connector and pulled out the 3 individual little metal male and female connectors. I borrowed an Rx from another plane and fitted the connectors to the Rx and to each aerial, so I can swap the Rx around easily. These MZK Berg receivers are tiny!
I glued 2 pairs of batteries using Shoe Goo. Then soldered the wiring onto the batteries and soldered the wiring to a $1.50 switch plug. I put on a new LMA (lost model alarm) which I’d just got from Glenn (Zipper); $20 each including postage is not bad, and they’re good. Then turned it on and bench tested the radio gear, chose some servo arms and screwed them on straight while the gear was switched on.
Then I set up the radio gear in the middle of the plane. Then carefully cut the holes for the new servos and fitted them. The standard size will fit in front of the spar, but only just, so care is needed to position them where they won’t protrude (not too forward, and not too far out along the wing as it tapers thinner.This is the underside. The lines are to show the position of the main spars, so I know to avoid them.
I've covered over the tops of the servos with EPP wafers, but they're flush on the bottom. Now I'm waiting for some ribbon spar to arrive, which I'll use to make drag spars on the TE's, and also to lay onto top and bottom of each wing - a bit of an experiment which I think will make it really very stiff. I'll sand shallow channels for them and lay them flat flush with the wing surface. I'd like to run them full span, but unfortunately they're only available in 1 metre lengths so they won't run to the tips.
Sean initially built it standard, then modified it to have a straight trailing edge like a “Superfreak Bat”. He’s now rebuilding it again (!) so I had the ideal adviser on tap!
My thoughts initially were to build it (shapewise) exactly like Sean’s but he wondered if it would be better to do a stock build, or at least leave some of the forward sweep in the wings. I decided to leave about ¼ of the sweep, so it’s going to be close to Sean’s but probably a bit heavier and a bit more stable and less trim sensitive.
The Bat has spar holes moulded into each wing and with a standard build, you slide each wing halfway onto the spar. As you can see, the stock spar doesn’t go full span.
But you can’t use a central spar in those holes when you change the sweep, obviously. I decided to extend the existing spar holes to the wingtips so that I could have a full length spar in each wing. Fortunately the spar holes go further than you’d expect so I only had to bore them about 10cm longer. I had another looser-fitting spar at home and I shaped the tip so I could use it to bore the holes bit by bit, spinning it in my hands like an Indian making a fire! Here's my borer-spar just poking through.
I set the wings up with my desired sweep, marked the overlap at the TE, then remarked half of that on each wing. Drew the lines then using a flexible steel ruler as a guide, cut the wedges out of the wing roots taking great care to keep the wing flat and the cuts vertical.
Also at this point, I used the ruler to cut off the floppy EPP elevons. I bought some perfect-sized balsa aileron stock for $4.50 from Hobbyrama. I also continued the trailing edge line to cut the “fixed” elevons off too. They’re no good because 1) they’re EPP and too flexy, and 2) their inbuilt reflex is no good, and they’d have to be cut off and reset with nil reflex anyway, so it’s better to do that with balsa of the same size as the elevons.
I got a couple of matching spars at Briskites, smeared them with PU glue and jammed them in. I then glued the wing halves together with 5 min epoxy. I do it in 2 stages – the back half first, then when it’s set, the front half. I like the 5 min because you hardly need any of it and it gives you time to lovingly massage the 2 wings into perfect alignment and hold them there while it sets. Also since it sets hard, you can always find the centre line by pushing with a pen or fingernail to find the hard line … even when it’s covered in layers of tape and glue.
Once the wings were together I sanded it to remove all the bumps from the mould. The open weave sanding cloth on a Gyprock padded sanding tool works amazingly well.
I had to fill in the holes that are moulded for the standard servo position, and also the battery bay hole, using EPP from old wing beds, and PU glue.
I really wanted servos with no slop, and fine resolution and I wanted to put them out further in the wing. I worked out that standard sized ones would (just) fit, so if I’d had a pair of good standard Hitec ones I’d have been happy with them but I had to buy some. The Hitec HS-475’s with Karbonite gear train have a great rep, about $30 each, but when I found that the same thing was available in digital (HS-5475’s) for about $50 each I leapt at the chance! I also got some Sanyo Eneloop batteries - $25 for 4 AA’s. I don’t think there’s any choice; they’re the only battery to buy. They must expect these servos to work hard – they come with thick cables and huge servo arms!
I got some fine multistrand power cable from Jaycar and stripped it to get an aerial. For $2.50 this amount will last a while …
I took a knife to a male and a female servo connector and pulled out the 3 individual little metal male and female connectors. I borrowed an Rx from another plane and fitted the connectors to the Rx and to each aerial, so I can swap the Rx around easily. These MZK Berg receivers are tiny!
I glued 2 pairs of batteries using Shoe Goo. Then soldered the wiring onto the batteries and soldered the wiring to a $1.50 switch plug. I put on a new LMA (lost model alarm) which I’d just got from Glenn (Zipper); $20 each including postage is not bad, and they’re good. Then turned it on and bench tested the radio gear, chose some servo arms and screwed them on straight while the gear was switched on.
Then I set up the radio gear in the middle of the plane. Then carefully cut the holes for the new servos and fitted them. The standard size will fit in front of the spar, but only just, so care is needed to position them where they won’t protrude (not too forward, and not too far out along the wing as it tapers thinner.This is the underside. The lines are to show the position of the main spars, so I know to avoid them.
I've covered over the tops of the servos with EPP wafers, but they're flush on the bottom. Now I'm waiting for some ribbon spar to arrive, which I'll use to make drag spars on the TE's, and also to lay onto top and bottom of each wing - a bit of an experiment which I think will make it really very stiff. I'll sand shallow channels for them and lay them flat flush with the wing surface. I'd like to run them full span, but unfortunately they're only available in 1 metre lengths so they won't run to the tips.