Spar parts

[wbpace]

I am fortunate in that I live only an hour's drive away from Aircraft Spruce West, so I intend to buy most of my raw material from there. A couple weeks ago at their yearly Super Sale, I bought three sheets of .025 sheet to start the ribs. I have some final honey-do's before I can officially start to build, but in the meantime, I am working on the foreplay, er, setup and material acquisition.

But I digress, to the point of this post:

I was thinking about bending my own spar channels and ailerons (for cost reasons), but I think the difficulty (read risk of screwing it up) may be greater than the cost of buying them premade from GPAS. Has anyone bent their own, and how well did it come out? Did it take multiple attempts?

Similarly, as I cost out the spar cap material, it seems that GPAS (at $329) is actually cheaper than buying raw 20204T4 bar from AS (at $5.50/ft or $517 total). For reference, the AS prices can be found here: www.aircraftspruce.com/catalog/mepages/alumbar.php and the GPAS kit here: www.greatplainsas.com/scspar.html .

What am I missing? Is my math wrong? If not, then the cost of the GPAS vs AS materials is a wash, making it easy to choose the GPAS parts.

Also, from the pictures on their web site, the GPAS spar caps appear to be tapered. I know from my RV6A days that its spar caps can and should be tapered to save weight. So am I interpreting the GPAS picture correctly? If the GPAS caps are indeed tapered, then they win hands down.

Regardless of what my lying eyes may be seeing, does anyone taper their spar caps to save weight? Before anyone accuses me of heresy of even thinking of this, keep in mind that the loads on the caps decreases the further out you go along the wing. That's why the RV can do this, and besides, they are only tapered the last quarter or so of each strip (if I recall correctly). I see no reason why this would not be the same for the Sonerai, but I'm not dumb enough to try it before asking :-).

Any insight would be appreciated.

Bill

[hans]

Bill,

those links are not working for me.

Hans

[o2koold]

Hi Bill,
GPAS offers a great deal on the cap strips. I priced out the caps from ACS and Wicks, and GPAS's price could not be beat. You are getting just enough from them. I made a cutting mistake and had to order from Wicks to make my spar. As for the taper, if you are talking about in thickness, yes it it tapered. But they stay 1 1/8" in height until they end after the 8th rib. Build it to the plans and you will not go wrong.
If you really want a deal form GPAS, wait a few more weeks and check out their annual Beatle Flyer sale promotion just in time for Christmas. Most years they offer a discount on the channel, cap-strips and ailerons all shipped in one box. This was how I purchased mine.
If you are still intent on bending your own, I think it was Gary Green (http://glgreen232.freehostia.com/WebPage/index.html) attempted to bend his channels, but this was on a homemade bending break. Those channels ended up as floor panels.
I hope this helps.
Scott R

oops on the 1 1/8", you are right it is 1 1/4. I have not looked at that for a long while now

[wbpace]

Hans - I modified my original post to fix the links. Thanks for pointing this out.

Scott - The taper I am talking about is on the wide side (or height, as you call it) where it decreases from 1-1/4" down to something less. I am not talking about the 1/8" side. Apparently my eyes aren't lying to me after all.

I just looked up the site you mentioned by Gary. You are right, he abandoned his home bent spars.

The sale is good news, thanks for the tip. I'll keep my eye out for it. I'm not intent on bending my own spars, just saving money! The less I spend, the happier the wife is. ;-)

Bill

[Tom H]

Bill, I wanted to bend my wing spars, too. A number of years ago, but seems that the cost of .040 2024-T3 was quite a bit less expensive than the cost of finished spars.

My first try was to make a bending brake from some steel rectangular tubing. I was able to make good test bends on small sections, but when you try to bend 8 - 10 feet of this stuff it is a different story. Takes more force than I could get together. So, I gave up on that idea and contacted an industrial sheet metal shop that we used at work.

They were more than happy to make the bends. Simple deal for them in their 12' hydraulic press brake. I drew up a sketch of the cross-section that I needed, with emphasis on the correct bend radius. I talked to the foreman and he understood what I wanted. Several times I stressed that the bend radius was crucial; a tighter bend would crack the material. Of course, he knew all about that. Problem was, they usually worked in galvanized ducting or stainless sheet; bend radius not at critical. And, what did I know about bending metal - I wasn't the pro.

Of course, the parts were made, and the bends cracked. They were real sorry about it, and suggested they would get it right the next time. I had just enough material left so I let them try again, worse that could happen was they would fail again and I would purchase the material. They got the bend radius correct this time, but the depth of the spar was not consistent along the length. Maybe 1/16" error, which I was able to shim and use the spars.

If I could have used the equipment, I probably could have gotten it correct the first time. If I was to do it again and had the choice of letting a commercial shop do it (it was free, have to consider that) or purchasing the parts from Great Planes, I think I would purchase from GP.

But hey, you can't put a price on the learning experience, can you?

Tom Hubbuch
S2LS

[schines]

I find myself in the same position as Bill. As previously noted, 1/8" 1-1/4" 2024-T4 bar is still $3.95-$5.50/ft, but Wicks has 1/8" 1-1/2"x1-1/2" 2024-T3 angle for $1.33/ft. As I understand it, the difference in 2024-T3 and -T4 is just age. My question for the group is this- could I just buy the -T3 angle and cut it down to 1-1/4 strips? Less than half the price!
Scott

[schrome]

Scott,

You should compare the strength of each one, which you can find by Google (try "2024-T3 mechanical properties"), or maybe Wicks already publishes those figures. But even if that comparison is favorable for the angle, you really ought to mill, file and/or sand the saw-cut edges to remove the stress risers, which sounds like a lot of work to me. Did you try Dillsburg? Their phone number is 717-432-4589.

Good luck,
Ed

[wbpace]

Scott,

I'm waiting for GPAS to publish their Beetle Flyer, which they told me by email should be around Dec 10. I encouraged them to put these parts on sale, but they replied that the would not know until then.

So keep an eye on your email and the GPAS site in about a week. We may get lucky.

Bill

[splischke]

Dec 2, 2011 12:25:37 GMT -5 schrome said:

Did you try Dillsburg? Their phone number is 717-432-4589.

Just an FYI... Dillsburg closed their doors after 65 years in business. I believe Wicks purchased most of their inventory.

www.eaa.org/news/2011/2011-06-16_dillsburg.asp

[schrome]

"Dillsburg closed their doors..."

They're in my own back yard and I didn't even know that! Thanks, Scott.

It was quite an operation. If you drove past the place in winter it looked just like any other farm - a house and a couple of barns. But in the summer when they had the doors open you would be amazed at how much steel and aluminum was packed into those barns, a testament to old fashioned barn construction. They didn't practice anything like marketing but it was a nice, or at least for me convenient, place to do business.

Ed

[schines]

Thanks guys. I guess I will wait a bit and see what GPASC does.
Scott

[wbpace]

Great Plains published the Beetle Flyer and their sale items this evening. (See their home page).

The bad news is no Sonerai specific parts were put on sale this year. Oh, well. I guess I'll have to buy the wife that jewelry, instead of a Christmas present for myself.

Bill

[mayday]

Nooo! I've been waiting for a few months for this to buy my spar's.

[hans]

This time it is more a newsletter than a catalog of special offers....


Hans