Frank's Cobra Z build- by Pilot

[Frank v B]

Have started the Cobra Z by Pilot models.  Built it 20 years ago with a Norvel .061, then electrified it with a 150 watt out runner on 3 cells.  This plane is small at 24" span but it had unlimited vertical.  Just bought a snarly 2826 2200KV at the Milton swap meet this morning and uses a 5x5 prop at 300 plus watts.  See if I can make it balance otherwise I will use the original 2805 bell motor.

It has a straight wing and a box fuselage so the build should be fast.

Frank

[Andy Hoffer]

Hey @Frank v B ,

I love the push-pin morse code.  We should talk about whether it is even possible to save your soul.   

Happy building!

Andy

[bweaver]

@Andy Hoffer

Re: I love the push-pin morse code.

Yah, but did you notice he spelt it wrong... or did he intend to?   

What's up @Frank v B ?

[Frank v B]

More Morse code,

Coloured rubber bands to hold the trailing edge on while the glue was drying.
Black clamps to hold the shear webs while the glue was drying. 

Frank

[bweaver]

.... ._  .... ._ .... ._ .... ._

... _. ._ _ _ ._. _

  and the construction looks good too! What are you using for glue, or is the wood that warped that you need that many clamps to hold it in place? 

[Frank v B]

Bruce,

The glue I used was carpenters glue. You can see the glue drops on the wax paper in the top right hand corner of the picture.  I use round toothpicks to apply it to the wood.  The clamps were to solve a problem. The glue expands the wood and causes it to curl while it is curing.  Without the clamps on each end of the shear web the ends would curl away from the spar and weakens it.

Of course you use CA so you wouldn't know this.

Frank

[bweaver]

I don't like shear webs.  They are always breaking off.  Carpenters Glue...? We used that in Kindergarten.

CA works for me, so yes, I don't need to know this thank you.  Saves on having to buy so many clamps and pins, etc.

[Frank v B]

Bruce:

re:"I don't like shear webs. They are always breaking off."


I guess you need to use shearless webs.

Yep, carpenter's glue.  I can't use CA in my house or it would be the equivalent of a thousand Cha's being miffed at me.   If I use 5 minute epoxy I get lambasted on the Forum.  Welcome to my life.

Frank

[Andy Hoffer]

Bruce:

re:"I don't like shear webs. They are always breaking off."


I guess you need to use shearless webs.

Yep, carpenter's glue.  I can't use CA in my house or it would be the equivalent of a thousand Cha's being miffed at me.   If I use 5 minute epoxy I get lambasted on the Forum.  Welcome to my life.

OK @Frank v B .  I'm taking the bait.  What is a "Cha" (besides being half of a great Cuban dance)?

Andy
Frank

[Frank v B]

Andy,

re: "What is a "Cha" (besides being half of a great Cuban dance)?"

Sorry about the lack of info. 

"Cha" is (was) Bruce and Katie's 5 lb Chihuahua watch dog that fiercely protected the household.

Frank

[Frank v B]

Update:

Attached the leading edge sheeting.  Did both sides at the same time to minimize the wing curling.  Attached it with 15 minute epoxy.  Put in the pins and to hold the balsa in place.  Then rubber banded it to a piece of 1x6 poplar to keep it straight when it cured.  First photo

Attached the trailing edge sheeting top and bottom, pinned through all 3 layers of balsa and clamped it to the 1x6 to keep it straight while curing. (Second and third photos.)

Frank

[Frank v B]

Center sheeting completed both sides.

Next step: fuselage.

Frank

[Andy Hoffer]

I'll bet @Frank v B has some interesting stories to go with the bent pins sitting on the sidelines!! 

Andy

[piker]

Very true.  And have we talked before about that archaeological dig at the front of the bench?  There's a lot of history there I think.

I'm also curious about the unusual center section sheeting on the Cobra.

Robert

[Frank v B]

Piker,

re "I'm also curious about the unusual center section sheeting on the Cobra."

Unusual for two reasons:
- I have not decided which side of the wing is up.  That will be decided when I see if the wing is straight.  It is a symmetrical airfoil.
- there will be two aileron servos buried in the wing.  It needs one side to hold the servo and the other side for the output slot.  Once I decide I will trim the center sheeting properly.

"Don't make a decision until you have to" is my guiding principle.

Frank