Olympic II Wing Mount Options - RC Groups
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Nov 06, 2017, 06:23 AM
Registered User

Olympic II Wing Mount Options

Building an original Oly II kit (third one over the course of 25 years). I'm building this one a little stouter using tapered carbon on the spars and hate the rubber band holddowns. I have some ideas for bolt on wings but I'm open to any ideas others may have used one these types of kits.
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Nov 06, 2017, 09:17 AM
Sagitta Fanboy
If I was doing a bolt-on wing, I'd look at what was done on the Sig Riser 100 for essentially the same conversion.

The Riser's bolt-on conversion uses a section of 1/4" ply (Sized so it sits in front of the spar) at the front of the wing compartment and 2 hardwood blocks at each of the rear corners as hold-downs. Epoxied in for strength, and up against the formers.

At the front end, the centre ribs were cut down forward of the spar so the 1/4" ply touches both the equivalent of the W1 and inner W1a ribs (rib numbers are from the Oly plans), with a section of hard 1/4" balsa glued between the ribs, spar and leading edge so it's flat to the ply (which would need to be cut into as well on the Oly, the Riser is an E205 wing, so the leading edge rides higher). The top sheeting gets a relieved hole, so the hold-down bolt rests on the 1/4" balsa (I impregnated the 1/4" balsa with thin CA for robustness). On the Riser, the hatch extends over the wing and covers the front bolt-down holes, I'd probably dublicate that with the Oly, as it's cleaner aerodynamically even with the rubber-band wing.

At the trailing edge, 1/16" ply reinforcements are added to the trailing edge stock, and the bolts go through the reinforced trailing edge into the hardwood blocks.

Bolts are 10-32 nylon, and the stock solution is to tap the ply & hardwood sections, although T-nuts on the underside are always a good option.
Nov 06, 2017, 10:23 AM
B for Bruce
BMatthews's Avatar
I prefer that style of bolts near the main spar too. The other "classic" method of some hook or a bolt at the leading edge and another at the trailing edge puts all the spar loads into the center line rib. Now that's fine if you used a good strong center rib. Not so fine if you built it as per the rubber band option. So for an "11th hour" conversion fitting the bolts into the wing through blocks of hard end grain balsa glued directly to the spar is a nice way to do this. It does mean cutting away a slice of the bottom sheeting though to give access for gluing on these blocks to aid with taking the strain. And ideally the head of the screw should be over the spar so there's some direct support as well as the block to hold the rest of the screw head.

At the trailing edge I'd opt for a second or third bolt to go with the main spar bolt(s). But this one should be a small size like a 6-32 nylon screw. That would have the advantage of being quite easily sheared in a bad landing that catches a wing tip and hopefully save the fuselage from whip damage. Other than that I really like what mawz posted and this reply is intended as an add on and support.
Nov 06, 2017, 11:24 AM
Registered User
Thanks for the replies so far, that is certainly the most common option or way of doing it. I was looking to see if there were other ideas for mounting the wings. I still have a little time before I move forward with the wings to make modifications before I commit to an idea though so I'm still open to suggestions or photos.
Nov 06, 2017, 01:56 PM
Registered User
You could make a 3/8" thick, separate rib in the middle, sort of a very short center panel, and put the nylon bolts in that. A big one in the middle and a small one at the t.e. 1/4" hard balsa in the middle, with a hardwood inserts for the bolts and 1/16" thick hardwood or ply on either side. Brass tubing for the wing rod and pin. This is just speculation, it may be you could make it a lot lighter. Wings themselves can stay totally stock.
Nov 06, 2017, 02:02 PM
Registered User
P.S. the nice thing about a central pivot is that, in a cartwheel, the wing can twist a long way before it breaks anything but the small rear bolt. I'm not sure if I'd make a nylon center bolt 1/4" or #10, but I'm guessing the rear one could be #8 in nylon. Anything but the 1/4 center bolt should be replaced now and then.

The Electro Junior name has been transferred to another design, but I used to have a wing for one that was retained with two 5mm bolts, one near the spar in each wing half. Seemed adequate, but I replaced them often. I think that wing was 93 inches, or was it 83?
Nov 06, 2017, 04:05 PM
B for Bruce
BMatthews's Avatar
If you do not already have the wing done then you still have some options.

I'm not a big fan of wing bolts on gliders being near the trailing edge simply because due to the end of the rear boom sheeting and the usual beginning of the opening under the wing this is often a weaker point on the model.

The other "issue" with an Oly II is that it does not have a raised forward cockpit such as models like an Aquila. So that means that any forward peg needs to be located under the wing. And that means odd building requirements. In light of this I'm thinking that one option to the single larger center bolt would be two bolts. One about an inch in front of the main spar and the other a couple of inches behind. The root rib for this would be done in 3/16 sheet with doublers of 1/16" plywood on each side. Holes for 10-32 nylon bolts are then drilled through at the locations mentioned and into cross beams.

As mentioned that's ONE option. It does have the disadvantage that you need TWO major cross beams. And those can get in the way of servos and such unless the final locations are all planned to fit such things.

All in all I think I prefer the idea of two bolts located close to the spar and spaced so they extend down very close to the inside surfaces of the fuselage sides. The screws then thread into two side blocks of suitable size that they form very good glue joints to the internal doublers and can easily take all the flying and launch loads. At the wing trailing edge you use either a nylon 6-32 screw as a locator or use a smaller size dowel that can shear off in a bad impact.

To form a good set of "scissors" to shear off the main hold down bolts in such an "arrival" you want the threaded blocks to be up very close to the wing's lower surface. Also the holes for the bolts on the lower side should have a decent sized insert of 1/16 plywood to act as the other jaw of the "scissors" to cut the nylon during an impact.

With any luck at all you'll never need any of this sort of feature. But it's sure nice to know it's there if you mess up at some point or the conditions over power you at the last second.
Nov 07, 2017, 02:46 AM
Registered User
I've had a couple of gliders with wings retained by one bolt, plus friction. Generally, it worked very well, but in one case I ended up flying around with 30 degrees or so of sweep forward on one side and aft on the other. It was still pretty easy to fly, but I recommend something like rubber to increase the friction. One disadvantage of doing it this way is that you have to eyeball the angle of the wing.
Nov 07, 2017, 12:19 PM
B for Bruce
BMatthews's Avatar
Originally Posted by lincoln
I've had a couple of gliders with wings retained by one bolt, plus friction. Generally, it worked very well, but in one case I ended up flying around with 30 degrees or so of sweep forward on one side and aft on the other. It was still pretty easy to fly, but I recommend something like rubber to increase the friction. One disadvantage of doing it this way is that you have to eyeball the angle of the wing.
A fair number of my own models rely on simple friction. To aid with setting and double checking alignment I put witness marks on the wing and fuselage. Or in some cases if trim extends from the wing to the fuselage the trim becomes the witness mark.

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