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Acro Wot build advice

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Neil Collett28/03/2018 18:00:01
25 forum posts
55 photos

Hi All,

Brand new member here and have been RC flying for about a year. I went straight in and built a Seagull Challenger Balsa kit, and took it to my nearest RC club, and met a great guy taught me over 3 months to fly it properly, its still alive and in the garage so he must have done something right

I'm now building an Acro Wot kit with laminated foam wings, and I'm almost at the point of joining the wings, and need a little help. The instructions do not say to glue the wings together before using cloth and epoxy over the centre? just wanted to check this is right. Since there is no centre rod going through the wing this would seem a weak point to me....

Any help much appreciated.

Newbie.

Bob Cotsford28/03/2018 20:50:48
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7498 forum posts
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I glue the wing panels together using epoxy before applying the glass bandage. I don't really see a way of doing the job any other way. I imagine it would be very difficult to just hold the panels together and in alignment while applying the bandage. The strength in the joint comes from the glass cloth bonded to the veneers carrying the load across the join, there's little strength in the joint between the foam panels alone.

Jonathan M28/03/2018 21:02:25
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489 forum posts
257 photos

Neil

Photos are of a Chris Foss Middle Phase I'm just completing, which utilise exactly the same sort of foam-cored veneered wings.

First photo below shows wings just joined with epoxy, masking take used to both pull joint together and also keep it perfectly aligned until the epoxy cured:

dsc_0487.jpg

Second photo shows wing-bandage just before I started sealing it down with the first of half a dozen coats of Poly-C (an alternative to epoxy):

dsc_0502.jpg

Hope this helps.

Jon laugh

PS well done for diving straight in with both your first and second builds, and with getting yourself what sounds like excellent training!

Edited By Jonathan M on 28/03/2018 21:04:39

Percy Verance28/03/2018 21:02:50
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7051 forum posts
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Sound advice from Bob and Jonathan there. It's purely my personal take on things, but I'd use a bandage slightly wider than the fuselage itself, because this will add strength at the wing seat for very little weight penalty. My preference would be to use Aliphatic glue to apply the bandage rather than fibreglass resin, which stinks and is very messy. If you go with Aliphatic, it may need two or three coats to fill the weave of the cloth. A nice bonus is the fact that film or tex covering sticks nicely to the dried Aliphatic......

And yes, Poly C is also an excellent alternative to fibreglass resin. Brushes wash out under the tap when finished yes    

Poly C available from RC World.......

Jonathan

I've never been a foam wing fan, but on the ones I joined I used a big diamond shaped bit of cloth cut from a sheet rather than a strip. I then layed it on with the long pointy parts of the diamond going span-wise on both sides of the wing. This takes the flight stresses down the wing evenly rather than just coming to a stop where the tape ends.

Neil

Get those wing roots lined up as accurately as you can when you join them!  F3a flyers would of course shudder at this idea, but hey, it's an Acrowot we're talking about here, and Mr Foss's wings are usually good enough.......

 

 

 

 

Edited By Percy Verance on 28/03/2018 21:19:06

Andy Blackburn28/03/2018 21:23:15
448 forum posts
483 photos
1 articles

All good advice. The only thing(s) I'd add are:

  1. There's no strength in the joint itself (see Bob's post above) so I usually just use a small amount of fast-drying PVA (Speed Bond or similar) around the edges of the root joints (i.e. near the veneer), held together with masking tape overnight.
  2. It's best to eyeball the tip incidences and if it looks as though there's a warp (sometimes but not always the case) then some or most of it can be taken out by angling one of the roots; it's more important that the tips are straight than the root, otherwise you'll need aileron trim for straight and level flight. Not usually a problem with Chris Foss wings though.

 

Edited By Andy Blackburn on 28/03/2018 21:26:12

Percy Verance28/03/2018 21:34:31
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7051 forum posts
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Hence my reference to F3a flyers/models earlier Andy. They'd probably use two incidence meters, one on each tip, and lose any inaccuracy at the root where it won't have such a detrimental effect on the trim. These days I'd imagine they use lazers to do the job. That's lazers, not Lasers........

Percy Verance28/03/2018 21:46:37
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7051 forum posts
140 photos

Neil

I just had a further thought before you join those wings. Are you going with a single centrally placed aileron servo, or are you going the more modern route with a servo in each wing panel? A servo in each wing is the default choice these days, as it maybe gives you some control redundancy in the event of servo problems. It also gives you far more control and trimming options than a single servo. It'll be slightly more dificult - but not impossible - to get the servo wires down the wings once they're joined.......

Edited By Percy Verance on 28/03/2018 21:47:20

Neil Collett29/03/2018 07:16:04
25 forum posts
55 photos

Wow thank you all for the helpful advice, really appreciated.

I bought a load of finishing z-poxy which I was going to use on the bandage, but like the idea of Aliphatic glue and will most likely go down that route.

Jonathan thanks for the tip on using a diamond shape for the cloth and also making it larger then the fuselage, that all sounds like a good idea to me. Also I'm going with dual servos for the ailerons, I plan to mount them sideways and make a cover to keep the wing as clean as possible.

And yes Andy will be making braces at each wing tip to hopefully keep the incidences as close as possible. (I'm also not a fan of foam wings, the challenger kit had all balsa ply wings and actually really enjoyed the wing build process.

I couldn't resist adding a pic of my challenger build I did last year, it was a great experience to build and when it flew for the first time, there was such a sense of accomplishment, which I will never forget.

2017-04-12 22.51.39.jpg

Thanks again for the helpful advice.

Neil

Tim Flyer29/03/2018 09:14:44
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823 forum posts
132 photos

Nice looking challenger! Great advice above , as Percy says two aileron servos are best plus avoid fiddling around installing control rods etc . I also like a wide wing bandage as it also provides des a strong surface for the the rear wing bolts and spreads loads.

extra slim29/03/2018 09:55:55
419 forum posts
47 photos

Hi Neil, super looking challenger... the sense of achievement is priceless as you say. I have seen grown men weep when their creation takes to the sky and comes down in one piece. Good luck with your new one, and glad you enjoying all aspects of a great hobby.

Geoff Sleath29/03/2018 16:42:32
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2914 forum posts
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Posted by Percy Verance on 28/03/2018 21:02:50:

Sound advice from Bob and Jonathan there. It's purely my personal take on things, but I'd use a bandage slightly wider than the fuselage itself, because this will add strength at the wing seat for very little weight penalty. My preference would be to use Aliphatic glue to apply the bandage rather than fibreglass resin, which stinks and is very messy. If you go with Aliphatic, it may need two or three coats to fill the weave of the cloth. A nice bonus is the fact that film or tex covering sticks nicely to the dried Aliphatic......

And yes, Poly C is also an excellent alternative to fibreglass resin. Brushes wash out under the tap when finished yes

Poly C available from RC World.......

Jonathan

I've never been a foam wing fan, but on the ones I joined I used a big diamond shaped bit of cloth cut from a sheet rather than a strip. I then layed it on with the long pointy parts of the diamond going span-wise on both sides of the wing. This takes the flight stresses down the wing evenly rather than just coming to a stop where the tape ends.

Neil

Get those wing roots lined up as accurately as you can when you join them! F3a flyers would of course shudder at this idea, but hey, it's an Acrowot we're talking about here, and Mr Foss's wings are usually good enough.

All good advice. My only adverse comment is that epoxy resin is relatively odourless. It's the cheap polyester stuff you buy in car spares places to patch up bodywork that smells. With foam wings epoxy is the essential resin to use if you go that route (and I usually do). Smelly polyester resin will eat the foam.

When I joined my last pair of foam wings I slotted them and added 3mm birch ply dihedral braces rather than use bandage, except for a little at the root to join the skins. That's probably going too far for an Acrowot but mine was (is) a quarter scale Mew Gull.

Excellent Challenger build btw. You should be proud of that.

Geoff

Percy Verance29/03/2018 16:49:33
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7051 forum posts
140 photos

Absoltely agree Geoff. I've not used smelly fibreglass resin for years, and rather detest the stuff these days. I've been a Poly C convert for quite some years now, after seeing it at one of the shows way back when.

I've seen your ply brace/foam wing method used in a commercial kit Geoff. It was a Fine Flight Models Big T trainer which I covered for a new flyer about 25 years ago. It was one of the nicest trainers I've ever flown/seen. A great pity it's no longer made.

I joined several foam wings way back in the midst of time using fibreglass resin Geoff. There wasn't any thin epoxy resin around then. You did need to carefully ensure the whole wing root area had no holes or gaps to allow the resin to seep in of course. I remember the time I spent tidying up the hardened resin with a file so that the film covering would stick to it (it didn't). 

 

 

Edited By Percy Verance on 29/03/2018 17:04:48

Capt Kremen29/03/2018 17:37:40
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229 forum posts
63 photos

Shortly, I will be joining a set of foam wings and therefore have been following this thread with interest for the (very) latest techniques. In the past I've used resin on glass fibre bandage (urgh so messy), also Aliphatic glue having epoxied the wing halves together usually with a ply joining brace too ... tempted to try Poly-C ... However ...

Within the RC-World web site 'Poly-C' FAQ it says, quote:

"Q - Can I use it to join my wings together instead of glass resin? A - No although Poly C is strong it's not strong enough to trust on your wings"

Further thoughts from Poly-C users?

Bob Cotsford29/03/2018 18:00:28
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7498 forum posts
426 photos

I'd be wary of using PolyC for wing joining. I've used it for glass cloth covering and it takes a lot of coats to fill the weave on just the light cloth used for that, I dread to think how many coats would be needed for the heavier glass used in wing joining. Much like nylon and dope, glass and PolyC can be peeled away from a balsa surface, you won't do that with resin, aliphatic or PVA.  I don't think the PolyC has the same penetration or bond strength .

Edited By Bob Cotsford on 29/03/2018 18:03:27

Ace29/03/2018 18:16:48
233 forum posts
14 photos

My interpretation of the above Q & A would be it's referring to a butt joint ie. root to root with no reinforcing. So yes a BIG NO NO.

However if adding glass cloth either bandage or diamond pattern (my preference) then Poly C, Water based Polyurethane Varnish or Aliphatic would be strong enough.

On my Acro Wot I used a larger and then smaller diamond pattern of 50g & 25g GF cloth with WBPV, which after getting a 90' crosswind practice landing all wrong, the following cartwheel failed to inflict any damage to the wing. Tail was not so lucky sad

As previously mentioned Polyester resin eats foam.

NC - Nice job on the Challenger thumbs up

Percy Verance29/03/2018 18:40:30
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7051 forum posts
140 photos

I've never used Poly C to actually apply a wing bandage, as I prefer aliphatic. It fills the weave of the bandage far better than would Poly C. I joined the wings of my artf Wot 4 with aliphatic glue rather than epoxy, and it was still ok six years later when I sold it on.....

As you've stated Bob, I also get the impression that Poly C sits on top of the wood like a thin skin, rather than penetrating to any depth. Regarding aliphatic, I did read an article some years back about various modelling adhesives being tested and compared. And whoever wrote the article ( I can't remember) claimed that aliphatic penetrated the wood to a greater depth than did the usual types of pva woodworking glue. It was also claimed the aliphatic bond was several times stronger than pva. If the tests were to be believed, epoxy is something of a loser for most model building uses as it doesn't penetrate into the wood, but simply sits on the surface. It's also extremely heavy. As we're all aware cyano has it's uses for us, but the joints made with it can be rather brittle. That said, with the the types of structure it's usually used on - lazer cut ply - it isn't that much of a disadvantage, because if such a structure receives any appreaciable shock, then it shatters anyway......

And while we're talking crashes. I've often found that open structures - Super/Junior 60 type - seem to survive crashes rather better than extensively sheeted structures, which can split open in a bad crash. Maybe superior energy dissipation going on here?

 

 

Edited By Percy Verance on 29/03/2018 18:56:19

Edited By Percy Verance on 29/03/2018 19:00:17

Edited By Percy Verance on 29/03/2018 19:03:47

Neil Collett03/04/2018 17:17:03
25 forum posts
55 photos

So not sure if I should add build photos here, but thought I would share, let me know if this should go elsewhere.

I decided to seat the servos sideways in the wing, but didn't want to glue in, but have access to replace if needed, so has taken all days to knock up a containing box which houses the servo, and brackets within to hold in place (I really need a table saw!).

img_20180403_171017.jpg

img_20180403_171122.jpg

Percy Verance03/04/2018 20:32:35
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7051 forum posts
140 photos

Build photos are fine Neil, and positively encouraged. They can be helpful to lots of people. yes

It's never a good idea to glue servos in Neil. Glue then in, and at some point you can be sure you'll need to get 'em out......

Here's what I do with the wing servos in Multiplex foamies......that bit of wood is a cut down lollypop stick. To get it out I just slide a blade through the glue at each end of the stick.........

wing-servo-1.jpg

 

 

Edited By Percy Verance on 03/04/2018 20:41:26

Geoff Sleath03/04/2018 21:47:13
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2914 forum posts
241 photos

... or you can wrap the servo in masking tape before glueing then they can be removed fairly easily with a scalpel. Good quality paper masking sticks like the proverbial if left for a while so there's no chance of the servo coming loose until you cut it out to replace or reuse elsewhere.

Geoff

Jonathan M04/04/2018 07:59:38
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489 forum posts
257 photos

Neat job Neil, and this is the perfect place to continue to post your Acro Wot build stuff.

Jon

PS Guys, the servos aren't glued in.

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