problem with upper longerons

[f16falcon6]

Ok so I purchased a partially built cozy. I am working on chapter six and am at the point where I need to install F-28 to the upper longerons. The problem I have is that the previous builder cut the small block attached to the upper longeron to short by an inch or so. So the F-28 will not fit in the proper location without lengthening it. I am wonder if I should cut out the block completely and install a new one or should I do some kind of splice joint and try to lengthen it. I hope my written description helps, if not I am about to go down and take some pictures to help people visualize my predicament.

 

Craig

[f16falcon6]

Here are some pics to explain my predicament.

[argoldman]

My inclination is to replace that block of wood and it's supporting glass. It is in that block of wood that you bury a pin which locates the trailing edge of the canard.

 

The above would probably be simpler than trying to scarf an additional piece to it.

[f16falcon6]

can I use poplar instead of spruce

[Kent Ashton]

I would just insert a piece of wood--anything-- and glass over it with a couple of layers of BID. The pins that go in there later are not highly loaded. They just set the preliminary canard incidence. The canard incidence is really set when you clamp the lift tabs to the F-22 with some wet BID in between, later. I don't think my pins even go into that extra piece of wood. I imagine Burt/Nat called for it to give a little more area for inserting the pins. You probably don't even need the extra wood if your pins go into the longerons.

-Kent

[Marc Zeitlin]

... the previous builder cut the small block attached to the upper longeron to short by an inch or so. So the F-28 will not fit in the proper location without lengthening it.

By "it", you mean the lower doubler, not F-28, right?

 

Chapter 12 shows that F28 should be positioned 5.9" aft of F-22. However, if you've read through the FAQ at:

 

http://www.cozybuilders.org/mail_list/

 

you'll have noted that many people install it at 6.25" aft of F-22 to facilitate canard installation later. You don't state precisely where the front of the doubler is - "an inch or so" doesn't really say much.

 

While Kent is correct that the alignment pins do not take substantial loads, they do take SOME of the canard load - any loads induced by elevator deflection and hinge moments, as well as moment coefficients will be taken by the alignment pins, as the lift tabs are just that - LIFT tabs, and only take vertical loads. They cannot take any moments, which must be reacted by the alignment pins. For this reason, I would not be cavalier about eliminating the strength of the doubler holding the pins.

 

I would flox in a wooden block of spruce (or another specie that's at least as strong - many folks use douglas fir, IIRC) and then reproduce the fuselage side layups over it, lapping 1" onto the existing longeron and doubler (you should read the chapters in the plans on repairs - 3 and 25). This will add negligible weight, minimize repair time, and ensure structural integrity for the pins.

 

You can then install F-28 at the 6.25" position.

 

If you're not already a member, I'd recommend joining the COZY email mailing list.

[f16falcon6]

Ok the front of the Doubler is located at 6.75, sorry about being so vague. As far as you saying just flox another piece in, should I do a scarf joint or just butt the other piece up to it and then flox it into place?

[Marc Zeitlin]

Ok the front of the Doubler is located at 6.75, sorry about being so vague. As far as you saying just flox another piece in, should I do a scarf joint or just butt the other piece up to it and then flox it into place?

Just scarf the existing glass plies on the longeron/doubler; butt the 1/2" piece of wood needed in place with flox, then add the extra/replacement plies over the small piece of wood. Done.

 

Flox is at least as strong as the wood - there's no need to scarf the wood. It's just heavier.

[mfryer]

IMHO...I would carefully cut out and replace the doubler, then glass over both the doubler and the longeron with a couple plies of bid. A Fein tool would probably make that job easy. I just think that would leave a cleaner result than scarfing something in.

 

Probably not a big deal though if you scarf something in to fill the gap.

 

I hear that a good tight grained, knot free piece of fir would substitute if you cannot find aircraft grade spruce.

[f16falcon6]

Ok the next question I have is this. So I compared the doubler that is currently installed to the dimensions stated in the plans and the doubler was cut to the proper size. If I were to carefully remove the doubler by cutting it away from the longeron and the fuselage side, would I be able to reattach it the proper location without any structural consequences? Also If I were to leave the Doubler in place and add an additional piece of spruce to increase its length, would the extra length of the doubler interfere with any other areas of the build being that the doubler is now approximately 1" closer to the instrument panel? Thanks

 

Craig

[Phil Kriley]

Do what Marc said.