Ok, I'm just starting the design of a ducted fan jet and I'm have problems with the wing tube. In my pencil sketches, the wing tube goes right through the ducted fan unit. I don't want to route the wing tube over or under the ducted fan unit because it puts the wing in the wrong location.
My first thought is to split the tube in half then construct some kind of plywood box with a big hole in the middle for the ducted fan unit and two wing tube holders on either side. The plywood box could also do double duty by serving as a mount for ducted fan unit and the main landing gear. But I'm still worried the wings will snap right off if I pull too many G's.
On Thu, 9 Feb 2006 21:52:44 -0600, "Jeff Stout" wrote in :
Roll the clock back and do a single wing instead of a wing tube?
If the wing is incorporated into the bottom half of the fuselage (and if the remaining fuselage structure is strong enough!), you might be able to meet your goals.
I do think you're asking for a wing fold if you're not carrying the tube all the way through the fuselage. Maybe if you bury the end of the tubes inside of a very rigid structure that would be tightly tied to the fuselage it would work. You could do testing to see how good your structure is.
Fighter pilots can only endure about 9G for short periods.
I think I've heard that some snap maneuvers with our models can produce around 20G.
If you can get your rig to hold 15G--and if you promise to fly nice--you'll probably do OK.
If I were you, I wouldn't want my testing to take place on the first flight. Do some on the ground where unhappy results don't cost you as much time or money.
There has to be a way of distributing the g loads caused by the wings on the fuselage. The box could hold the short wing tubes easily enough, but then when the model breaks up, you might find that the boxes are still secure...and the bottom of the fuselage split open because of the loads from the wings, into the tube box, and the box loads then on the rest of the fuselage. So you will have to make sure that the boxes are secure within the fuselage after making sure the tubes are secure in the boxes...and this gets heavier with each change. I would suggest you rethink the whole process of not having wing tubes and see where that goes. It might require a major redesign but it will produce a model that will fly like you want it...and stay in one piece on high-g maneuvers.
By "wing tube" do you mean you're stuck on a cylindrical spar?
What you want is a spar carrythrough, of course. How about using a spar with a square hole and plywood of appropriate thickness (how big is the model?) for the spar carry through:
This will have to be quite strong at the points where you transition from a straight stick to a ring, but the tops and bottoms can be quite thin (like making a deeper spar). If it were me I'd make some 'T' pieces out of carbon fiber sheet to reinforce the indicated areas. Plywood might do, but this is a high stress area so you'd have to use lots of it. Carbon fiber will be stronger, but it will want to delaminate and buckle, particularly on the top where it's under compression.
You'll have to use your judgment and lots of testing to determine just how thick a section you'll need -- I'd probably start at 1/4" plywood with carbon-fiber reinforcement for a 4 lb model, but I have no idea what I'd end up with once I was done breaking test articles.
If I were a better machinist I'd make the whole thing out of aluminum, with an 'I' beam section in the ring and stub-spars, but solid right where the stub spars cross the ring.
I actually considered a square spar or I-beam. But that still leaves the problem of how to integrate that structure from the wing into the fuse structure. If you make that structure an integrated unit, you are sort of removing the option of removing the wings for transport. It is not an option to be moving a plane around with these beams sticking out of either side. No, the sticks have to go with the wing and they have to be removeable.
With regards to the box structure, I was thinking about something like the following:
Hmm, interesting. I did a pic a couple of post down (Somebody asked about a tail wheel assembly). Hence I mentioned it. It did come through and the post was answered, so somebody must have been able to see the pic. I use MS Outlook Express, as my reader.
If you have enough room to the sides then you should be OK. Remember that the biggest thing you're battling is the moment on the wing, so with your idea the outboard web will be pulled upward and the inboard down (with positive G's). The closer together you make the webs the more that any play will be magnified, and the more pull will happen. I wouldn't want to try to do this with anything but a precision interface, and that's not only heavy, but it's getting to be too much like real work!
I wasn't advocating making the stub spars part of the wing, just making them integral to the fuselage and putting tubes in the wings to accept them. I was thinking along the lines of having stub spars that stick out maybe 15-20% of the size of the wing panel, so a 3' o/a wing would have maybe 3-4" on either side of the fuse. This would make stub span that's 8-12" wide for a fairly small plane; this could be a pain but I doubt that you'd have to make it wider than the stabilizer in most cases.
On Sat, 11 Feb 2006 11:52:54 -0600, "Jeff Stout" wrote in :
I carry around my Patty Wagstaff fuselage with the wing tube run through the middle--it's very handy.
You might thing of separating the removable part of the wing a few inches out from each side of the fuselage. That would give you more material for the wing tubes to slide in to and to be held by.
----- Original Message ----- From: "Martin X. Moleski, SJ" Newsgroups: rec.models.rc.air Sent: Saturday, February 11, 2006 10:23 PM Subject: Re: What to do with a wing tube
wrote in
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prototypes.
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I will, but I build things so slowly that it might take a while. Even my ARF jobs take two weeks to get into the air.
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