Spar web update

For anyone else who might be in the same predicament, the fine folks at Homebuilt Airplanes came up with a couple more sources. B&D International carries 5′ x 5′ sheets of Finnish birch aircraft plywood, and will cut and ship UPS. Boulter doesn’t carry as wide a variety, but might be good if you’re closer to the east coast than the west.

The price at B&D is higher than Aircraft Spruce. If you price it by the square foot, it’s not terribly higher. 13%, on the 1/8″ sheet I need. Not terrible.

Spar webs

The plans and BOM call for plywood spar webs, cross-cut, 60″ long. The webs are butt-spliced mid-wing, with what seem to me to be fairly narrow blocks of spruce on either side.

Problem is, you can’t buy 60″ wide sheets of aircraft plywood in the US. Aircraft Spruce has ONE size, and not a size I need. Everything else I’ve found is in 48″ wide sheets. And since the web needs to be crosscut, it’s not as simple as just buying a 4′ x 8′ sheet. I’ve contacted Fisher Flying Products as well as another supplier in Canada. Fisher’s tab will be roughly $340, the other place was pretty reasonable for the plywood but wanted over $500 for crating and shipping. To put that in perspective, ACS will sell me the plywood I need for about $100, delivered.

The question is, can I make 48″ long spar webs work in a way that is at least as good, or preferably stonger and better, than the original design? I am no engineer. Especially a mechanical engineer. I’m certainly not qualified to make such a call. Fortunately, I have someone local who is an engineer, and is qualified to help make that decision and recommend another way to do it — if there is one. I’ll be taking the wing plans to the February EAA chapter meeting to go over them with him and see what we can figure out.

If that doesn’t work out, Spruce does sell 5/32 ply in 61″ x 61″ sheets. The spar webs are specified as 1/8″ for the main spar, and 1/16″ for the rear spar. I could just make both webs 5/32 with a slight weight penalty. The plywood would weigh 3 to 5 pounds more, but I’d probably also need to trim 1/32 to 3/32 from the spruce stiffeners, so that might make up for some of it. Again, I’ll need to consult with a real engineer to see if that wold work or not. Ending up with a plane that’s a couple pounds heavier but significantly stronger is OK. Ending up with a plane that is in any way less strong or less safe is absolutely not. And if the ribs need to be modified a little to clear a beefier spar — I’m OK with that.

Tempus fugit

Another year draws quickly to a close, with what feels like not a lot of progress on this project. I have a tall stack of ribs, but really nothing else. I had hoped to have a good start on the tail surfaces by now, but haven’t even started on them. We’ll need the basement for a family Christmas party, so no laying a 4×8 sheet of MDF over the island down there to start laminating pine. No worries, though. I have located some nice clear pine boards at Menard’s that will rip down nicely into 10′ long lamination strips. I have an order of Finnish birch ply queued up on Aircraft Spruce’s web site, ready to place the order once I’m sure I have all the stuff on there that’s going to be expensive to ship. As soon as we’re finished with the post-party cleanup, I’ll have the basement available to work in through the rest of the winter since the garage will just be a bit too cold for epoxy.

I also got a great idea from one of the guys on the Biplane Forum. I’ve been pondering how to store the wing ribs. I think I’ll build short pieces of main and rear spars out of pine and non-certified plywood, just to assemble all the ribs and clamp them together. That way I can surface sand them all together, and maybe if I’m lucky use that assembly to run them through the table saw for trimming as well. Maybe.

Musing.

Haven’t done much in the past few days, mostly because I’ve had the workbench cleared off to fix a recalcitrant robot vacuum.  I did unroll some of the plans and take a good long look at the tail surface sheet.  Sixteen feet or so of paper, mind you…  not the easiest thing to manage on a 6′ countertop!  I wish that had been split into two sheets. 

It looks like I can build the entire fin and rudder out of pine and plywood, so that’s my next project, I think.  I’ll go look for a suitable 10′ length of pine at Menard’s that can be ripped down into decent quality lamination strips.  Once the saw is set up for that I’ll make as many as I can, since I’ll have a bunch of other laminations to do as well for the wingtips and fuelage.  Then I’ll look at what to do for the elevator and stabilizer spars. 

Minor milestone – the last full rib

Sitting in the rib jigs right now are the last aileron rib (#16 of 16), and the sixth false rib.  After the glue cures on these, I’ll modify the second jig to fit as many false ribs as possible.  I think I can fit three on it for sure, possibly four – but that’s doubtful.  I’d like to start cranking out four false ribs at a time.

So I guess it’s time to go start shopping for the best plank or two of white pine I can find to get started on the laminations for the tail surfaces.  Pretty sure Menard’s will be my source for those; the stuff I find at the other big box stores is more suited for a dog house or the pulp mill than anything else. 

Bending wood and building ribs

I got two false ribs glued up last night and pulled them from the forms today.  The new razor saw arrived yesterday afternoon, so that was nice to have.  I’m leaving all of the ends of the top and bottom capstrips a little long.  I am planning to just build a sled for the table saw out of MDF, with dowel pins or wood blocks to locate the ribs for the four cuts I’ll need, referenced to the main spar and rear spar.  That’s one cut for the nose, one for the trailing edge, and two for the tail ends of the false ribs.  That can wait until all of the ribs are finished, maybe later depending on how cold & crowded it is in the garage.  They really don’t NEED to be trimmed until I’m ready to assemble the wings, so that may be a while yet.

I figure I’ll get two, maybe three false ribs out of a pair of capstrips that would make one regular rib, so I’ll have plenty of opportunity to use whatever method I do finally end up using to pre-bend the wood.  Over the past couple of nights I’ve tried a couple of methods of bending capstrip.  The other night I ran a bucket of the hottest water I could get from the tap.  It was probably 140 F or so, coming from a bar sink just a few feet from the water heater.  I put half a dozen capstrip pieces in there, let them soak a couple of hours, and put them on the bending forms.  That seemed to work well, with no broken pieces.

Last night I added a gallon or so of hot water to the bucket, just to top it off some more.  The water would have been lukewarm at best.  I soaked another half dozen strips for 12 hours or so.  Of the six, one snapped as I was bending it in the form.  That’s about what happened the last time I tried soaking in cold water, so obviously that’s a waste of time and good spruce.  Won’t make that mistake again.

Ready for ribs

Well, the work bench is cleared off — well, at least enough to get both jigs on it.  I’ve got a couple dozen sticks of geodetic brace stock shaved down.  The epoxy syringes are filled.  All I need now is a razor saw and a steam setup.

Yes, I have a razor saw.  Somewhere.  I pulled it out during the kitchen remodel, and I remember seeing it in a box of tools we were using, but now I can’t find it.  It’s a Zona, good quality but inexpensive.  A new one is on the way.  Two, in fact; one medium and one fine tooth.  I also have a steam box that I built for the capstrips, but I’m unsure whether I’ll use it in the basement.  It takes  bench space (which I now don’t have down there), and drips water out the end by design.  I’m thinking about ways I can use it vertically.  I had looked at rigging up a piece of pipe or something with a heating element for hot water, but it looked like an awful lot of extra work considering I’m over halfway through the ribs.  I’ll probably need it for the tail and wingtip bows as well, but I’m not entirely sure yet how I’m going to steam 6 to 9 foot long strips of wood.  Tonight I tried soaking half a dozen capstrips in a bucket of hot water for an hour — we’ll see how well tat worked. 

Back at it…

Well, I thought it had been a lot longer since I did any construction, but I see it was only back in February.  I really wouldn’t have been surprised to find that I’d gone an entire year without building anything.  But, I’m getting ready for winter and more building.  To be honest, I’d had second thoughts recently about even continuing with this project.  Sometimes it seems like such a massive undertaking, especially when I see pictures of guys attaching the wings and getting flying wires made and rigging done…  only to tear it all apart again and then start covering.  Covering!!  How the hell an I ever going to cover this beast?  But then I decide that maybe I’ll keep at it after all.  Hey, it’s relatively cheap…  so far…  as hobbies go.  It keeps me occupied for as long as I care to work on it, and nothing bad happens if I let it sit idle for a while.  Even a long while. 

Over the past few days I’ve been working on getting my absolute pit of a basement workshop cleaned up at least enough to be able to move around and use the workbench.  A new water softener installation, a kitchen remodel and a few other household projects meant there was a lot of mess left over, and a whole lot lot of crap got just piled everywhere.  Most of it’s cleaned up.  Not enough, really, but at least enough for me to be able to take stock of where I am.  In hindsight, I suppose I could have, you know, looked at my blog posts, but where’s the fun in that?

I need 26 normal wing ribs, and they are all done.  I need 16 aileron ribs — the same as the normal ribs, but just missing a couple of cross pieces.  Of those, I have built ten, so there are six left to build.  Then there are 34 false ribs — just stubs from teh leading edge back to just behind the main spar.  I’ve built one of them, so 33 left to build.  Those should be quicker to build, since there are only about a quarter of the geodetic braces to cut and glue.  Unfortunately, each will still occupy a full rib jig — so two at a time is still the limit.  Unless…  maybe after the aileron ribs are done, I can tear down one of the rib jigs and rebuild it to do several false ribs at a time.  I think keeping one rib jig intact would be good, just in case I should ever need to build more ribs for a repair or whatever. 

I’ve got a bunch of geodetic brace stock sanded down to the correct thickness.  Enough for sure to do the rest of the aileron ribs and get a good start on the false ribs.  I’ll probably do half a dozen more, then put the oscillating sander away and maybe knock out a few ribs.  I’m starting to get a little fired up again. 

Slow progress

I’ve knocked out a few more aileron ribs, two at a time.  I’m about halfway through them and trying to speed things up a little, so I don’t die of old age with a half finished airplane.

Yesterday I decided to use up a piece of obviously bad capstrip Aircraft Spruce saw fit to ship me.  This piece has a large chunk missing out of one edge, part of a knothole or pitch pocket or something.  Part of it is in no way suitable for aircraft use or much else for that matter.  But – there’s enough good wood there to use it for false ribs, so I made one of those.  That went OK, but it’s apparent that I will need to soak the top capstrip in HOT water for the false ribs.

I’m looking forward to starting work on the tail surfaces.  I’m planning to get out to the garage and clear off the workbench this week, lay out the plans and see exactly what I will need to get started.  The wood called out is white pine, so I’ll start checking the local places for suitable pieces of white pine or Douglas fir…  a little heavier, but I know Menard’s sells some good boards from which I can cut suitable pieces for the laminations.

Plugging along on aileron ribs

Five down, eleven to go.  Cutting the geodetic braces individually is really not as much of a chore as I thought it would be.  I am finding that I’m going through the 6′ lengths of stock quickly, though — I figure I have enough shaved down for the next 3 ribs, maybe 4, then I’ll have to fire up the drum sander again and make some more.  Not that it’s stupidly tedious work or anything, mind you.

In hindsight, it would have been a whole lot less work and actually less expensive to have bought 3/8″ thick spruce spar stock and just ripped it down to 3/32 strips, losing half the board to saw kerf.  I am at a loss to explain why that little bit of math didn’t make itself obvious.  Of course, I thought at the time that shaving 1/32″ off those strips would be quick and easy.  Not so much.  So…  if you’re building a Celebrity from plans, you’d be better off doing that.