Wing panel joining

[Tim Mackey]

Although an ARTF, I have done some modifications to my fairly large ( 1.8mtr, 12lb AUW ) Seagull PC9 to facilitate fitting the beasty in my car.

I wonder could I just get a couple of opinions from builders as to the integrity of my wing joining system.

The original design was for the two outer panels to be simply inserted over the main alumimium spar, and alignment was completed by a small wooden dowel toward the trailing edge. The main spar / wing tube is a nice fit into a strong cardboard tube which runs a long way into the wing sections. The panels were to be glued at the wing root ribs. I have done one panel as per design, but made the other one removable. This involves two 1/8th ply straps permanently fixed to the main centre section root rib, and secured to the outer panel after sliding the wing over the tube, by a 6mm nylon wing bolt. I would just like some re-assurance that the main forces will indeed be through the main tube/spar, and that these straps of mine will suffice to merely keep the panel from sliding off the spar IYSWIM.

I have gliders which use a similar method ( some even rely on pure friction alone on the spar to keep it all together! ) so I presume my proposal will be fine.

Here's a link to photos of the system on page 5 I think

Edited By Tim Mackey - Administrator on 14/02/2011 13:14:19

[Biggles' Elder Brother - Moderator]

It looks good to me Tim. I too have seen and used this technique.

 

One thing that might be worth thnking about is just easing the screw holes in the ply strap a little bit. The reason for this is that, as you say, the function of the plate is only to stop the wings from separating - it is not there to support the bending load - the metal tube does that. But if you fix the strap very tight it will not have the freedom to move a little - then it will start to contribute to supporting the bending load and might break in flexure (bending). You really want the loading on it to be purely tensile (pull) with no bending. Making the hole for the nylon screw just a tiny bit oversize (oval in a spanwise direction) will just allow it that bit of room to slide when the wing flexes under load.

 

BEB

Edited By Biggles' Elder Brother - Moderator on 14/02/2011 14:18:10

[001]

Hello Tim I think I can understand the system from the description and photos.

 

Looks well thought out. The main difference between the glider wing and a low wing model with main u/c in the wings is the impact loads when taxiing across rough ground and on landing. I would assume that in any more than a graceful arrival the U/C legs would give up first. Which is obvious, although it might be an idea to elongate the holes in the plywood strap slightly to allow a little 'give' otherwise you might find that the screws get bent over time and become difficult to remove.

 

There again all your landings are, I know immaculate.

 

As an aside, but relevant remark. I have the Seagull PC 6 Turbo Porter. In the instruction book the wings have a long aluminium tube spar. The retainers are two 6mm nylon bolts behind the spar and it has bolt-on struts. The U/C is, of course attached to the fuselage. (mostly ).............

 

BUT the model actually has a second shorter smaller dia. aluminium spar in front of the main spar, as if Seagull had second thoughts about the installation - after the instruction manual was produced. I wonder, did they do anything similar with the P.C. 9.!?

[001]

Yes , BEB had the same idea, posted whilst I was composing mine!

[Tim Mackey]

Thanks gents...that makes sense - Ill get me round file out then Means Ill have to enlarge the recesses for the plate too - or simply make the plate a little shorter on the panel end. I was so careful measuring and cutting to get a perfect snug fit too

Incidentally, the undercarriage track is narrow, and all the relevant forces of it will be confined to the fixed centre section.

 

She's all finished and awaiting a maiden flight or two - dont think I will risk this one in the back garden

Edited By Tim Mackey - Administrator on 14/02/2011 15:59:29