#27 Model Airplane Building Clinic >> Mimi DLG 1 meter polyhedral<<

[aeroknot]

Sand to the line - will do - thanks.

Some wing panel details - I looked at Frans' many build photos on his web site which help tremendously - any miscues such as not sanding to the line are me learning.

Gusset - custom cutting photo.
wingtip - balsa - slightly buried ply - balsa

[aeroknot]

some of my wing panel weights

weight (grams)

weight listing order:
panel - left outer - right outer - left inner - right inner
raw wood - 19.2 - 18.5 - 24.8 - 24.1 - total 86.6

glued unshaped
wing - - - - 21.3 - 19.2 - 25.2 - 24.6 - total 90.3

I accidentally posted some higher kilobyte photos - I've 'dumbed' these photos down to a smaller size, maybe a little too low resolution this time.

[aeroknot]

sanding templates update

I switched to better 2mm ply and sanded a little closer to the line.

These are better but still need some touch-up.

[aeroknot]

preparing to sand -
I stacked the two inner panels and two outer panels and sanded to the same size where the wing panel joins will be.

I made some long sanding bars with 1/16 inch aluminum L pieces, and double stick carpet tape - it's the about 1/16 inch tape that it used to put down carpet.

The sanding part of the bars are 17 inches, two 8.5 inch strips cut to width.
The join between the two edges were fortunately not a problem, and nothing came apart from the tape.

[aeroknot]

This is the right inner panel - sanded weight is 16.2 g.
Pre-sanded weight was 24.1 grams

[aeroknot]

Oh yeah, I attached the sanding templates with spray adhesive sprayed to the template.

I set the bottom of the template about 1mm up from the bottom of the wing panel (photo). The template was removed with a #11 blade.

[aeroknot]

Improved on sanding the sanding templates to the line.

I improved sanding the wing panels to the sanding template as I progressed through the panels.

The plane was used for the initial balsa removal on the tip panels.

[aeroknot]

Sanding the polyhedral angles - the sanding block is vertical on the left in the fourth photo. I did the two left panels - both the same angle and then the two right panels.

When making the wind tip panel blocks, cut the outer edge straight, round off later. I filled in the circled area with balsa and sanded straight, curved off wingtip later.

Only sand the sides shown (red line on photo) for the polyhedral angles.

[aeroknot]

Front wing peg - According to the plans, I should have angled the front of the peg down a little bit, but it should be ok.

I started the groove with a metal hacksaw blade, did not have a round file so gouged out a groove with drill bits by hand. With a drill bit in the middle, I slid the second panel back and forth to mark the groove for the second panel.

[aeroknot]

I've figured out that with a four panel polyhedral wing with three glue joins, the best order of gluing is the two center panels, then one of the outside panels, and then the last outside panel is the critical one - test fit so that the left wing tip is the same height as the right one. For this wing, all the sanded side angles should be the same.

So, I've glued 3 of 4 panels together. Sometime soon, I'll test fit the last one and make sure the wing tip heights match, and then glue the last panel on.

[aeroknot]

For gluing the side panels together, I used 30 minute epoxy and microballoons - 30% epoxy, 30% hardener and about 40% microballoons, or maybe 1/3, 1/3, 1/3. The microballoons shorten the epoxy hardening time a little.

The microballoons make the epoxy white and a little lighter, both nice features if building with white Depron. (And the little lighter is nice for this build.)

[aeroknot]

Another thing I learned (when using epoxy building foamies) is to not try to use less than about 1.5cc of epoxy and the same amount of hardener even if I plan to use just a tiny bit of the mixture.

When trying to mix just a little bit, it was too difficult to guess the identical amount of hardener for the amount of epoxy. A little too much or too little hardener, and the mixture would never cure properly. (the glue ended up sticky even after 3-4 days.)

So, I'd rather mix up 3 cc of epoxy, hardener 1:1 ratio and waste 2.5cc and have properly cured epoxy.

[Frans Bal]

Hello knot,

I am not sure mixing in micro balloons is a good idea.
The weight advantage isn't that big and on the other hand micro balloons lowers the strength of the bond.
Better is to sand the joints precisely to get a (almost) perfect fit with no gap.



Prick some holes



Tape the bottom side



Ad epoxy liberally



Hinge back and wipe of any access epoxy.

This method uses a small amount of epoxy(weight) and is very strong.

Frans

[stuart]

this is an enjoyable build ya have going here aeroknot . frans, i never really thought of using tape on a wing seam like that to join halfs. very nice.. aeroknot,your also doing a nice job with the camera,it's a lot of fun to to see your progress.

[aeroknot]

Thanks for the note and photos, Frans. I sanded as best as I could although my sanding skills are improving. I have a wee gap here and there. I've already glued three of the panels together, the two center ones and I think the left wing (I'm right handed so that's the throwing blade wing!) I'm confident the epoxy-microballoon glue joint will be strong enough, particularly with the short CF reinforcement on the plans. (But you're absolutely right that there is minimal weight savings.)

I wish I had made little pin holes in the facing parts when gluing the ribs and the wing panel blocks since I used the Titebond II - I did that with the epoxy and wing panel joints.

Thanks for the good words, stuart. I like lots of photos - beats lots of words!

These are the only photos of the glued panels I've taken so far. Building will slow down over the next 2-3 weeks. I have made the throwing blade and am working a little on the elevator and rudder. I'll post a few photos over the next few days, so photos will lag my progress a little.

I have some thin 5mm wide carbon tow which I can hopefully use instead of the kevlar roving for the fuselage, but that's a few weeks away.

[aeroknot]

To verify that the outside wing panels were at the same angle, I used two methods.

1. Direct looks about right measurements (Photos against the wall.)
2. Placed the glued panel down and put the supporting blocks under each side, then placed the to be glued joint down, checked and glued.

[aeroknot]

Maybe I'll use a worse camera....that way some of my building blemishes would not be so outstanding

Here are some the wing panel joint detail photos. Wing panel weight tomorrow after the last glued joint hardens.

[aeroknot]

I'll fix the left bottom later on.

edit -
Also, I think I placed the sanding templates on the right outer panel more aft, so that there is a mismatch in the larger front and trailing pieces compared to the center panel.

Still learning.

The overall wingform is preserved and I'm sure my built mimi will fly well despite the learning curve

[aeroknot]

Here's a photo of the unsanded wing panel blanks.

[aeroknot]

Some early sanding on the horizontal stabilizer and elevator.

[Frans Bal]

Looking at the pictures of the jig you used to glue the panels I think the angle of the tip panels is to big.
The total center angle is 12 degrees and the total angle of each tip is 6 degrees.



Lifting each side 26 mm gives a total angle of 12 degrees





Here you used the same jig. You should have removed the left block to get a 6 degree angle on the tip.






Frans

[aeroknot]

Good eye, Frans! That sure is disappointing. Sigh. I'm glad you caught that and it sure is awesome that your helping me out

Well, the weight of the wing fully glued with too much angle was good at 59.9g. Looking at the tip panels on the current photo, the angle looks maybe even worse, a little greater. I think the center panel measures about 10 degrees and the outer ones 11 to 12.

I think I sanded the correct angles, but brain dead used the same gluing jig on the left wing panel as the center which is why the bottom of the left joint was wide. Then a couple of days later, I matched the right wing panel angle to the left side.

I think I'll continue with the fuselage, etc. It would be better to rebuild the wing rather than to hack correct this one. I'll be able to build the wing better the second time, now that I have some experience.

Won't get too much done the next few days, working.

So, the plan is to continue with everything else, and then build a second proper wing at the end. I'll probably end up using both wings - I have plenty of 1.5mil laminate - wish it was 1.2mil.

[stuart]

seems a fresh razor blade with careful slicing would separate the wingtips and a new angle could be fashioned. remember,a little extra length on the wings [or less] wouldn't effect your flight . far less work than building a new wing for sure. i tend to stick with what ever part i'm building before moving on to other parts,but it's not a bad idea to build the fuse and come back to the wing when less frustrated. i'v spent many hr's in the workshop and good or bad ,it's always rewarding and fun in the end.

one thing i love about building is figuring out how to rectify errors and still have a good build. from what i can see....you'v got a real nice build going on here. wonder what this bird would look like with a 118"ws. a "bird of time".

[aeroknot]

Thanks, stuart - I've been working non-stop at the job, just made it back to wattflyer. I'm going to order some kelar roving and unidirectional CF and proceed with everything else. I think I have enough decent balsa to build a second wing and since I now have a little more experience, building the second wing really won't take very long. Time available for building is highly variable.

[Frans Bal]

A builder here in Holland also put in to much angle in the tip.
Model flew just as good.
Launch is a bit lower, thats all.

Frans