Acro Wot build advice

[Neil Collett]

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 Cotsford]

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 M]

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:

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):

Hope this helps.

Jon

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

[Former Member]

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[Andy Blackburn]

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

[Former Member]

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[Former Member]

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[Neil Collett]

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.

Thanks again for the helpful advice.

Neil

[Tim Flyer]

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 slim]

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 S]

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

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

[Former Member]

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[Capt Kremen]

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 Cotsford]

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

[Ace]

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

As previously mentioned Polyester resin eats foam.

NC - Nice job on the Challenger

[Former Member]

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[Neil Collett]

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!).

[Former Member]

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[Geoff S]

... 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 M]

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.

[Tim Flyer]

Regarding epoxy , I find it penetrates wood very well . It just depends which epoxy you use. Regular thick epoxy “glue” as we are all familiar with does not penetrate far . However “covering epoxy “ (Deluxe” make this and its available at RC World ) does penetrate just as deeply as Aliphatic. I use West Systems epoxy for covering which is also thin and designed to be painted . It certainly penetrates balsa and ply very well. The downside with epoxy covering is that it needs painting and plenty of disposable gloves and brushes  but it is super strong and water plus fuel proof . Laminating is very useful in modelling and you can apply extra small strips of cloth in vulnerable areas such as where Wing bolts go through wings. With glass cloth this is neat and easy and it’s much tougher than film.

Edited By Timothy Harris 1 on 04/04/2018 10:18:17

[Geoff S]

Plus one (or more!) for West epoxy. I first came across it for wooden sailing dinghy building and repairs and bought from a local sailmaker and (sailing) club-mate. When I took up aeromodelling I've continued to use it.

Geoff

[Martyn K]

You can use Gorilla Foaming PU glue to join the two halves together. However. Take when aligning. You must align so that the wing tip sections are parallel - this doe not always mean that you will get a perfect join at the root.

I think the wing is joined flat inverted. Put identical thickness packing under the TE under each wing tip and weigh the panel down. Then measure the height of the LE from the board at the tip. It should be the same for both wing halves.

Does that make sense?

Martyn

[Nigel R]

What Martyn said regards joining.

Personally, I use PVA and several layers of glass tissue, one wide (about 10" on a 40 size model) and one half that width (so about 5" ). The thinner glass needs less (or none) sanding and/or filler to finish it.

It's all variations on a theme. The strength in the join comes from the cloth being bonded securely to the veneer and from the joins in the veneer (at the centre) being unable to level themselves apart.

 

Edited By Nigel R on 04/04/2018 16:11:34

[Neil Collett]

Hi All,

So have finished most of the wings, and moving onto the dreaded task of joining in the centre. I am going to make a bracket for each wing tip to sit at the right height, which should make it easier to sand the edges to sit flush against each other. Still have to the hinge the ailerons, but waiting on delivery of some nylon pinned ones to arrive.

On a side note, by beloved Challenger (my first build last year) crashed last weekend!! Just seem to lose radio signal, dive bombed into the ground and snapped in half, very gutting as all the radio gear is new from last year, and never had a problem before. It really is gut wrenching, but I guess its part and parcel of the hobby. Decided I'm going to buy another Challenger kit and will build straight after the Acro Wot 

Cheers all

Edited By Neil Collett on 09/04/2018 16:51:28