efish

My Feedback: (5)

Hi, here's question that's probably little silly for the more experienced flyers.

I'm putting together an ARF that has a large diameter alumimium wing joiner tube housed in a cardboard tube. In looking around the web, it seems that such construction is reasonably common, especially in the older planes.

I've only just gone into the bigger planes where 2 piece wings are the norm and every other 2 piece wing plane I've put together has had this "housing" made out of fibreglass. So I was just wondering:-

1. Is this cardboard "housing" construction adequate? I'm guessing that this housing just acts like a guide for the actual wing joiner tube and the main stress is bourne by the tube and the plywood structure. The plane does seem to be decently put together otherwise and the cardboard sits very well in substantial plywood structures. and

2. Is there any special care/attention that I need to be aware of? Seems like spilling fuel/oil in the fuselage would do the cardboard permanent damage.

Thanks.

da Rock

Raw cardboard? If it is, then you've already spotted a fatal flaw that should be corrected. And it's easy to do. Treat the cardboard with something fuel proof. It'll also give it some additional compression strength.

BTW, spilling fuel in the fuselage is going to do more damage to your radio. And will do lots of damage to any raw wood etc. Lots of modelers who know they're going to have their model for years have learned to fuel proof the insides. ARF manufacturers don't bother because they figure most ARF buyers aren't going to have the suckers for very long, and just might not want them to as well.

What airplane?

ram3500-RCU

My Feedback: (221)

I agree with the last post in fuel proofing. A thin coating of epoxy that has been thinned with alcohal, and then brushed on, works fine. Structurally, the cardboard will hold, as the real strength comes from the aluminum, not the sleeve. Why I prefer fiberglass for these, is that the cardboard wil swell in the humidity and make sliding the tube in difficult.

efish

My Feedback: (5)

Thanks guys. It was a little worrying seeing the cardboard in there. Fuel proofing sounds like a great idea! Guess I should have have thought of it.

da rock - that's a good tip too on fuel prrofing the insides. Normally I stop around the fuel tank compartment. So far, I've only had one really bad spill that went beyond the former into the middle section of the fuselage. Getting the oil out took a couple of days! (cornstarch and a vacum cleaner). But with these bigger planes and ga engines, I'm putting the tank right in front of the joiner tube, so I guess a little thinned out epoxy would be good insurance. The plane is a 1.20 sized Extra 260. Think it's made by Will's Hobby or something like that.

ram3500 - thanks for helping out on this thread too. you're right about the card board swelling. Its pretty humid over here, and the aluminium tube is a really tight fit!

forestroke

i think it's okay not to fuel-proof it unless it's a place where fuel will likely go. i have a plane that has this, too but the wing connects inside the fuse so fuel will rarely ever get there. if the joint is out in the open and subject to fuel, only then i'd think about it. maybe then you should just epoxy the whole thing.

the main reason i say this is because the tube should already be reasonably tight. any additional fuel proofing may make the tube's inside diameter too small. why go through all the trouble of having to sand it or the bar to fit?

plus, should the cardboard fail, it is surrounded, supported by ribs.

just my two cents...

ram3500-RCU

My Feedback: (221)

When I say to fuel proof, I'm talking about the outside of the sheath that is in the fuselage, not the inside. The section of sheath in the wing should need no fuelproofing.

opjose

Good clarification, as applying almost anything on the inside of the cardboard tube may cause the wing tube not to fit in anymore!

Don't ask me how I know.