Art Hobby Wings

[GBR2]

I've looked at the building instruction for a lot of the Art Hobby gliders and wonder why there is no wing joiner in the structure between the wings. I know that there are spars in there but why don't they get joined together with some sort of joiner as every other ARF wing I've ever built. I'm sure the fiberglass cloth is fine and makes the wing center section fairly strong but intuitively it just rubs me the wrong way. Everytime I think about ordering a kit I just can convince myself that the structure is strong enough. Guess I really need to look elsewhere.

[fly1milehi]

You know despite all the stuff that has been written in these posts on R/C groups I have not seen one post claiming a folded wing from regular flight or launching of an Art Hobby product. Several threads have reports of flutter in the tails because of either the thin light wood or suspect hinges.

The thing to realize about the center section joint is this.
Each side of the joint is faced with epoxy and glass (that you glue on, atleast so the instructions said on my thermik) so the foam and wing skin CAN NOT compress downward or inward. (its similar to the wing bolt rib on the bubble dancer design) Then the expoxy and glass that is wrapped around the outside of the center joint only has to keep the two panels from pulling apart at the bottom edge of the joint. Which it will do very easily because thats a tension joint that would have to pull the fibers of the glass apart to fail, or delaminate from the wing skin.. both are highly unlikely
The wing joiner is really a "left over" from our stick and tissue days of building or merely for the convenience of transporting long skinny wings in a reasonably small car.
Greg

[GBR2]

OK, that makes sense. Guess my mind is just stuck back in earlier days.

[Wiker]

The Sierra have a plywood wing joiner. Velvia also seems to have one.

[Prawnik]

Fly1MileHigh: I had considered using kevlar cloth for joining the wing on my next AH project, but I take it that this is not necessary?

[fly1milehi]

Kevlar wont hurt anything but as I recall from reading on here somewere, Kevlar has poor compression strength which is why you dont see model fuselages made of 100% kevlar, they would buckle along the sides at somepoint. Same goes for Whitewater kayaks, which is why you pretty much only see 100% Kevlar used on flat water racing kayaks..
Use it but put some regular fiberglass over it as well.. In my opinion
Greg

[Gemarl]

I've looked at the building instruction for a lot of the Art Hobby gliders and wonder why there is no wing joiner in the structure between the wings. I know that there are spars in there but why don't they get joined together with some sort of joiner as every other ARF wing I've ever built. I'm sure the fiberglass cloth is fine and makes the wing center section fairly strong but intuitively it just rubs me the wrong way. Everytime I think about ordering a kit I just can convince myself that the structure is strong enough. Guess I really need to look elsewhere.


I bought a Velvia. It does come with a piece of strong plywood that has the outline of the wing joiner drawn on it. Wing joiner is about 10-15 cm. There actually about 70 cm of space in the spar for a wing joiner. You are correct, the instruction make no mention of a when or how to install the wing joiner.
So, I made a 60 cm spruce wing joiner with Carbon fiber 1mm thick CF strips on the top and bottom. It adds about .5 oz of weigh but I don't trust the wing without a joiner. I hope it works out. I'm still building it.

[slopemeno]

FWIW, I had an ArtHobby "WhipIt" and dove that thing straight down from the limits of my vision, crashed it into trees, cartwheeled it on landing, and the center section and dihedral joints never complained. The center was 2 layers of .75 ox fiberglass and the outer dihedral breaks was only on layer. In fact I just dug it out of the "projects" pile and it's going to be a light-lift 55" sloper next.
If you want to make it a two piece wing it would be really easy to build in a box/tube/rod setup.

[DACeller]

'Where' exactly are these building instructions for Art Hobby planes? I would like to see them beforehand as well. I just assumed there was a joiner, so this is surprising. I typically glass the bottom of all the cheap gliders I've built and the wing never breaks, there..

Thanks.

[rwmson]

'Where' exactly are these building instructions for Art Hobby planes? I would like to see them beforehand as well. I just assumed there was a joiner, so this is surprising. I typically glass the bottom of all the cheap gliders I've built and the wing never breaks, there..

Thanks.

I don't think that Art Hobby makes their instruction manuals available online. There are a few Art Hobby build threads on RCGroups - perhaps they would address your concerns.

Roger