Acerc, since you're working with an open ended tube I'd suggest that is why it works for you. You've got a relatively open end at the nose with the, presumably, fiberglass cowl and plywood firewall. And at the rear the sheathing is open ended with the wood rear section. So that's why you're not having an issue. Not to mention the open top of the cockpit and the opening on the belly for the lower wing. So you've got SOME aluminium but it's got more holes in it than a colander.....

It would quite possibly be a whole other story if the model in question were an aluminium foil sheathed B-52 model with the receiver in the middle of all that metal with no similar openings.