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Old Jul 23, 2009, 09:29 AM
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Balsa USA has warning labels on their plans saying do not use insidence meters on the wings to determine incidence. The incidence is designed into the plans and uses the flat bottom of the wing, to produce the correct angles.
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Old Jul 23, 2009, 10:33 AM
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Quote:
Originally Posted by Mode One
Balsa USA has warning labels on their plans saying do not use insidence meters on the wings to determine incidence. The incidence is designed into the plans and uses the flat bottom of the wing, to produce the correct angles.
No such warnings here with this particular Sig kit. Sig got back quickly in answering my e-mail yesterday with:

"The wing and tail incidence are engineered into the design and if built correctly it comes out right. If it is not built right good luck trying to correct it."

EJWash
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Old Jul 23, 2009, 11:24 AM
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I think this might be another example of how we're dumbing down America. If they were to include the incidence and decalage angles, they would have added a couple words needing deciphering and understanding to the project. They made it easier, by simply stating "Do it like this"!
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Old Jul 23, 2009, 12:53 PM
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I agree! I can't see the harm in printing, "the ('X') amount of (+/-) wing incidence is built into the plan."

Sig goes through the trouble of warning about the horizontal stab "alignment" (incidence) but no warning nor mention of the wing incidence. Saving on ink I guess...

I've measured the plan and the model several times now and it appears that the wing incidence is zero. I still have to add cabin doublers over the cabin formers that are in place now. Maybe they'll make a difference.

I took out a few plan sets and it's hit and miss on listing incidence and engine thrust offset. The Great Plans 1/6 J-3 spells it all out on the plans though.

I ran into a website that listed a whole slew of model's specs and settings, but I can't find it now!

EJWash
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Old Jul 28, 2009, 08:33 PM
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Glued the horizontal stab and vertical stab dorsal platform into position. The horizontal stab platform will be planed down to match the contour of the fuselage later.

EJWash
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Old Jul 29, 2009, 01:29 AM
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Moved on to the main landing gear.

I was warned by one poster that the main gear was a weak-spot for his Sig Citabria, so I paid particular attention to it. I really appreciated the heads-up.

The 3/32” thick aluminum main landing gear legs are sandwiched between two pieces of 1/8” plywood. The main gear measures 1-1/2” front to rear, and the plywood mounts 3-3/8”. A piece of 3/32 balsa serves as a spacer to fill the gap between plywood mounts (see pics).

The 3/32” balsa spacer was the next area of concern. I can see where in the event of a hard landing that the balsa spacer can be the weak spot and first to fail. I replaced the balsa with plywood. The three pieces that make up the mount was laminated with West System epoxy.

The main landing gear mount is positioned between two fuselage formers. The formers are attached atop fuselage cross-braces. Another area of concern.

The fuselage formers are 1/8” thick balsa, and the fuselage cross braces are 1/4”. The plane shows the forward former mounted on the aft edge of the cross brace, and the aft former centered on it’s cross brace. This means that the landing gear platform does not come in contact with the forward cross-brace at all, and only 1/16” of the aft cross-brace. Instead of the 1/4” square cross braces, I used 1/4” X 1/2” cross braces here. More than enough “meat” for the gear platform to contact.

When attached to the fuselage, the plywood landing gear mount shaped to match the contour of the fuselage. Since all of the surrounding area of the mount is balsa, sanding and shaping dissimilar hardnesses of wood that are next to each other can be a challenge. I made a jig to place the mount in for sanding. The front and read vertical pieces that you see in the pic match the contour of the two fuselage formers that are fore and aft of the landing gear mount.

Thanks for following along!

EJWash
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Old Jul 29, 2009, 01:50 AM
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Shop weather report:

Just for kicks I picked up a combination thermometer and hygrometer at my local Ace Hardware. When I mounted it on "Festus", I noticed that the temperature card ONLY goes up to 100 degrees (f)!!! What a rip-off!!! Who sells such a thing in Arizona???!!

EJWash
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Old Jul 29, 2009, 02:25 AM View Post
Zor
A moderator felt this post violated the following rule: Trolling (Obnoxious behavior). Show it to me anyway.
Old Jul 29, 2009, 08:15 AM
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Old Jul 29, 2009, 09:12 AM
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That's like selling thermometers here in Northern Minnesota that only go down to -40 F.
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Old Jul 29, 2009, 09:44 AM
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I love your build log. I picked up so many tips for building. I am now building my 3rd plane (all from kits), it is a sig kobra. My first two kits were from greatplanes a pt40 and the 40 size corsair.

I am shamed to say that your build methods are 100 times better than mine. I am lucky just to build a straight wing/fuse. I have glue trails everywhere

so how many kit builds do you have under your belt? (asking all readers)


I see that zor got a slap on the wrist for trolling but I did not see what was said in time
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Old Jul 29, 2009, 09:55 AM
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Quote:
Originally Posted by mhuff

so how many kit builds do you have under your belt? (asking all readers)

Hi mhuff,

If we ask all readers the thread will take off in a new direction and stray from the build log it is... maybe you can start a new topic with that question, as it may be interesting!

Take care,

Chuck
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Old Jul 29, 2009, 10:18 AM
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I was looking for a simple answer to a simple question to the 4 or 5 guys in this thread that I like to read and respect their post.
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Old Jul 29, 2009, 11:03 AM
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Originally Posted by mhuff
I love your build log. I picked up so many tips for building. I am now building my 3rd plane (all from kits), it is a sig kobra. My first two kits were from greatplanes a pt40 and the 40 size corsair.
Thank you mhuff.

I'm having a good time with the build, and its fun to post the progress.

Are you building the King Kobra, or the 45" size? I built the Kougar as soon as my LHS got it in back in the 1970s. It was a blast!

As far as building, I have more an appreciation for joinery than I did when I was younger, so this slows me down a bit. I get a big kick when a piece of wood fits into place snugly.

Quote:
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I am shamed to say that your build methods are 100 times better than mine. I am lucky just to build a straight wing/fuse. I have glue trails everywhere
Trust me, I've built a few boomerangs...

As far as glue trails (and I’m referring to aliphatic glue from here forward). A really hard part of building to conquer is the amount of glue we use. We all want a strong ship, and its natural to think that more glue means more strength. It is also natural to take advantage of the glue manufacturers “used friendly” built-in applicator bottles.

I squeeze out small portions of glue from the bottle into a small mixing cup, and apply my glue using an artist’s paint brush. This gives me great control over how much glue I put on a piece and I can apply glue in smaller amounts in places where the glue bottle applicator would deliver a blob. It also allows me to draw a nice narrow bead of glue along the edge of sheet of wood (a fuselage former or the top of a wing rib, for example). How much glue is enough? Enough that when you press the glued piece of wood in place that a very small amount squeezes out of the joint in tiny beads. If a line of glue squeezes out instead of beads, too much glue was used. If no glue squeezes out, too little was used. Yep, this takes practice.

You see me use a lot of clamps, both in number and type. Clamping is where the strength of a joint is determined. Clamping pressure drives the glue into the wood fibers. We primarily use soft woods in our models for the advantage of weight. Care must be taken in clamping because too much pressure will cause the wood to break.

Just like with the belief that more glue creates a stringer joint, it is sometimes assumed that more clamping pressure is better. A “death grip” clamping crank-down will squeeze too much glue from a joint. You are not going to fully purge the joint of all traces of glue, but you will have a joint of less strength than one that was joined with the proper amount of glue and the proper amount of clamping pressure. How much clamping pressure is enough? Just enough to make the glue start to squeeze out of the joint in tiny beads.

After the glue dries (and do wait for it to dry) you can clean up the trails using a square-tip X-acto knife. The glue beads will just pop off.

If you go back to the building of the wing, you’ll see that I laid-out small glue fillets at the ribs and main spar junctions. The ribs slid over the spars and there was no way to apply any glueing pressure to the rib/spar joints, so these fillets will help stabilize the ribs. Aliphatic glue fillets should be used in conjunction with glue applied to the joint and not used by themselves. In the case of the wing ribs, the ribs were positioned and CA’d to the spar. The fillets come in only as a small insurance policy.

Quote:
Originally Posted by mhuff
so how many kit builds do you have under your belt? (asking all readers)
Fourteen (14) in my younger years, and this is my third since getting back into the hobby two years ago after a twenty-two year hiatus.

Mostly powered models, but there are a few gliders in there too.

Quote:
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I see that zor got a slap on the wrist for trolling but I did not see what was said in time


Thanks for following along!

EJWash
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Old Jul 29, 2009, 11:58 PM
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Forward fuselage doubler sheets glued into place. Also attached side stringers. These stringers are in place to hold the covering away from the fuselage sheeting to create a "tube and rag" effect that will simulate the full-size aircraft's cloth-covered steel tube frame. Being that they do not contribute to the structural strength of the fuselage, I bonded them in place with CA.

You'll see many square edges and ends of stock unevenly hanging over the ends of edges and what-not. I like to cut long and trim/sand flush. This makes it far easier to get all parts equal and square rather than cutting to fit, which usually does not happen.

Thanks for following along!

EJWash
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