Composite Allegro

[ericTheHalf]

There either isn't a lot of information about building a composite Allegro, or whenever I search for "Allegro" all of the Allegro Lite information gets returned and I can't sort out what I need.

From what information I can find, it looks like the preferred spar is something more like the Aegea, or Allegro Lite, than what is on the plan. What have others done for joiners when building the Aegea like spar? Both between the root- and mid-panels, and the mid- and tip-panels?

-eric

[rdwoebke]

On an Aegea wing (or a Supra wing) you get pre-epoxy cured carbon spars. They are tapered in thickness (and towards the tips, you taper in width) and then pre-build the spar by either using balsa wood for the spar core or foam from the foam cores (I used balsa). Then you bag the spars with a bias wrap of glass cloth.

The rest is fairly typical. You slice the cores and glue in the spars, then bag the wing.

I think the Allegro Composite was designed before these nice thikness tapered carbon strips were on the market, hence it is a bit different.

Ryan

[ericTheHalf]

My question is more about the joiners.

If I was going to follow the Allegro lite joiners, the mid- to root-panel joiner has a carbon rod permanently epoxied into the spar of the mid-panel. Can I do the same on the composite build and just bag the wing with the carbon rod already in place?

[jirvin_4505]

My question is more about the joiners.

If I was going to follow the Allegro lite joiners, the mid- to root-panel joiner has a carbon rod permanently epoxied into the spar of the mid-panel. Can I do the same on the composite build and just bag the wing with the carbon rod already in place?

Hi Eric 1/2

Info in Electric forums plus here on the Aegea 2m similar build to the allegro - defferent airfoil etc.

Recently viktor has done a great build log on the aegea 3m - lots of details

Plus there is the Supra the slow way thread of John stevens heaps of drela style building - my way of saying the info is here:)

maybe post on viktor thread may yield some joiner insights:-
http://www.rcgroups.com/forums/showthread.php?t=723896

Ryan (above) has a done the build also - I think he has a thread on the aegea wing.


On the allegro light yahoo groups site -= link from allegro page on Charles river has posts by richard hallet on his allegro composite build plus photos.

cheers jeff

[rdwoebke]

My question is more about the joiners.

If I was going to follow the Allegro lite joiners, the mid- to root-panel joiner has a carbon rod permanently epoxied into the spar of the mid-panel. Can I do the same on the composite build and just bag the wing with the carbon rod already in place?

Yes, you can bag the wing with the joiners in place in the tips (this is how I did my Aegeea). I think you pretty much have to do it that way, if you use a joiner Allegro/Aegea style where the joiner is a round joiner that is sanded to give more angle.

Making the joiner boxes, the vertical grain basswood method with a drill press works well. I did this on my Aegea.

Ryan

[ericTheHalf]

Thanks for the replys. I've been studying the other threads and getting some ideas. This is my first composite build so I'm feeling pretty unsure about everything I do and am going very slowly.

[ericTheHalf]

I just bagged a tip panel today. (still waiting to take it out of the bag) Would it have been better to bag the tip- and mid-panel together then cut them apart once finished.

-eric

[ericTheHalf]

My first ever panel out of the bag. I thought it was going to be a mess, but I'm pretty happy with it. Plan calls for 14 grams and this came out at 13. I hope that doesn't mean I left out something important.

-eric

[ericTheHalf]

Having seen Phil's video I was prepared to see some of this from internal stresses in the foam, but I wasn't expecting this much. Is this going to cause me problems as I proceed? Or will I be fine as long as I use enough weight to flatten it out?

I practiced with Foamular 250, this is 600 and it really needs a lot more weight to get it to co-operate.

[jirvin_4505]

Eric - push on
>fine as long as I use enough weight to flatten it out?
exactly

cheers jeff

[ericTheHalf]

I finally got the spar slots cut out of my cores and ran into a little problem. I thought I might run into this trying to use the Allegro Lite spar with the composite build since it is a thinner airfoil. Up until now I hoped that the power of positive thinking would get me through, but once I could see the spar next to the joiner tube I knew I had to deal with it.

The tube plus the spar caps is just about as thick as the wing. Add in a few wraps of fiber glass and kevlar and it might work if I put the tube in straight, but NOT if I put it in with the angle for dihedral. (well maybe a little dihedral, but not what the plan calls for)

Any ideas what to do here? Build it with as much dihedral as I can? Maybe some sort of a bent joiner instead of the straight rod, like the Composite Allegro plan calls for? (which looks pretty complicated when compared to the tube and rod approach).

[rdwoebke]

Any ideas what to do here? Build it with as much dihedral as I can? Maybe some sort of a bent joiner instead of the straight rod, like the Composite Allegro plan calls for? (which looks pretty complicated when compared to the tube and rod approach).

Are you going to do the deal where you sand the carbon rod and have it perminantly mounted in the tip sections like on the Allegro? If so then you don't have to worry about the thickness of the rod.

Ryan

[jirvin_4505]

... snip...

Any ideas what to do here? Build it with as much dihedral as I can? Maybe some sort of a bent joiner instead of the straight rod, like the Composite Allegro plan calls for? (which looks pretty complicated when compared to the tube and rod approach).

Hi Eric 1/2

Bent joiners are certainly possible - bent aluminium like phil Barnes uses.

Smaller joiner with steel joiner rod - have used 6mm tool steel to join outer panels on 3m winch launch models. 5mm carbon rod used on my 2.5mm flyQ/omega electric model (5mm solid carbon rod joiner strong enough for centre of 1.8m electric eg flyQ/omega)

I have made bent carbon rounds by pulling carbon through bent joiner tube (used on 3m winch launch models).

Lightest option is probably the original spec as per mark Drela.

Good to see you back at the project.

One other option... 1 piece wing with joiner similar to SG11 .. playininthepark recent 2m aegea had 1 piece wing using sg11 style joiners.. more than strong enough for electric.

cheers jeff

[ericTheHalf]

Are you going to do the deal where you sand the carbon rod and have it perminantly mounted in the tip sections like on the Allegro? If so then you don't have to worry about the thickness of the rod.

Ryan

That was the plan. The panel into which the rod is permanently mounted is less of a problem than the root panel that will contain the tube.

Perhaps I mount the tube with as much angle as I can get, then adjust the angle at which the rod is permanently attached to make up the difference. I should sketch that up to see how different it would have to be.

-eric

[rdwoebke]

I think you can pretty much put the rod staight in the center section then you can probably sand it well enough to get at least a few degrees that way. You might make the difference up in the outer pannels.

Ryan

[ericTheHalf]

I went round and round with how I was going to cut the spars; bandsaw, hot wire, etc... I finally came up with something that worked well for me and I thought I'd post pix so if someone else is looking for ideas this might help.

For the first cut on the leading edge to the spar I made a sled to attach the core to, and a guide to slide it along. The guide is a piece of 1/8" x 1" aluminum bar that I carpet taped to the bandsaw table. I made a notch so that the edge of the bar would align with the edge of the blade. The sled is some 1/4" plexiglass. I sprayed a light mist of 3M to the plex, then with the core upside down attached the plex to it. This way made it easy for me to get the edge of the plexiglass exactly where I wanted it on the core and I knew that the edge of the plex would be exactly where the edge cut would be. When attaching the core to the plex I pressed down enough the flatten out the camber and I did this for every cut so that they would be parallel to each other.

For the second cut I C-clamped some 90 degree aluminum to the table to use as a fence. This time I just held the core flat to the table and fed it through.

I did try freehand cutting a scrap core I had but did a really bad job of it so I thought I would try this. It worked well, except I managed to account for the saw blade's kerf on the wrong side of the cut. I seem to always mess something up no matter how careful I try to be.

-eric

[ericTheHalf]

I bagged a second set of tip spars today since I have decided the first tip panels didn't cut it. You can see in the photo that there is a little bump down the length of the front and back. This is where the bag came off the spar. I used peel ply and paper towels to remove as much excess epoxy as possible, so where you see the bump is where the fiber glass in not contacting the spar at all. This happened on the first set of spars as well. Is that going to be a problem?

I'm inclined not to worry about it since this is the tip spar, but for the other panel's spars I would be more concerned, is there are way to avoid this?

-eric

[jirvin_4505]

Not sure if I can answer the - is it OK question - I would be worried if glass wasn't tight against the shearweb.

Can we have more details of the system and procedure you used - maybe recreate the process and show us a picture in the bag - Since it has happened twice must be a proceedual thing we can help you fix?

cheers Jeff

[ericTheHalf]

That's what they say, but I don't know about these pictures being worth that much. This is a reenactment of the actual process. Maybe too many layers of stuff in there?

The fiber glass is not contacting the shearweb in the "bump". I was thinking I could wet out the sides and bag the spar again but rotate it so the bag comes off the top and bottom this time.

-eric

[jirvin_4505]

OK - when I vacum long thin things I spirally wrap the object with the peel ply. It looks like you are getting puckering where the peel ply meets - wrapping avoids this.

I also then wrap on the loo paper - this way when the vac bag meets and puckers there is breather to handle this.

cheers jeff

[ericTheHalf]

I bagged the tip spars again, this time rotated 90 degrees to see it I could get the fiber glass to attach to the foam. Not completely, but better than it was. I'm starting to wonder if I should back off on the vacuum. Not sure if you can see in the photo but the foam has compressed slightly so that now the spar core is just a bit narrower than the carbon caps. The vacuum was about 20 inches, which is just where it was and not a conscious setting on my part. I'm tempted to go with it as is since, as you can see, it is just the tip of the wing.

[ericTheHalf]

I'm trying to imagine working through the rest of the process to finish this thing, and am having concerns. Having that rod epoxied in place seems like it cause some difficulties.

First, it just seems likes having that thing sticking out is going to make something awkward when bagging.

And second, how do I sand the root rib to get a nice fit with the root panel? Without the rod in place, I could just get out a nice big sanding block. With it in place I'd have to sand in front of it, then behind it which would make keeping it straight more difficult, plus I'd probably end nicking the rod with the sanding block. I might be better of trying to sand everything before the rod is in place, but until the rod is epoxied in place I just have a bunch of parts that I would have to assemble very carefully.

Maybe I'm over thinking this. Maybe I just get it close and when I put it together to fly it I just tape over an un-perfect fit. (that is if I ever get this thing done.)

-eric