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Old 02-25-2014, 03:37 PM
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Quote:
Originally Posted by Pistolera View Post
If the cores are lightened (hotwire honeycombed) is less vacuum recommended?
Yes. Definitely as there's less foam to withstand the load.
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Old 02-25-2014, 06:46 PM
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IMAC FANATIC
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Clamps... someone said clamps... the total combined weight of my clamps is my secret and my burden .

Hey jerry, how bout some pics. Where you at ?
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Old 02-25-2014, 07:33 PM
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Brian I'm done with the fuse and I'm ready to start sheeting the wings. No pictures this time, or at least not yet.

Been too busy at work to get the plane done.
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Old 02-25-2014, 08:05 PM
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Ditto on the too busy also, preparing to move at end of month and work is in full swing here does not leave much time for fun.
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Old 02-26-2014, 04:46 AM
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Quote:
Originally Posted by Flynbulldog View Post
The proper unit of measure for vacuum is "inchs Hg" which imparts about 70psi per 1 inch Hg.

(Edit: sorry if this came across as terse. I was informed tonight that I need to lighten up - I will do my best to do so)
?? Whoa...terse? Yes, I think so.

And, you might want to check your conversion from "inches Hg", "inHg", or " "Hg". 1 "inch Hg" = 0.491psi. That's 29.92 inHG = 14.696psi std atmosphere. I don't think I made any reference to "inches Hg" in my statement you quoted anyway.

Why would someone inform you to lighten up?
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Old 02-26-2014, 04:59 AM
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The density of the foam in my kit averages at 0.87pcf, based on my measurements and weight measured on a postal scale.
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Old 02-26-2014, 06:22 AM
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Quote:
Originally Posted by Pistolera View Post
If the cores are lightened (hotwire honeycombed) is less vacuum recommended?
Quote:
Originally Posted by Pappy View Post
Yes. Definitely as there's less foam to withstand the load.
And... the balsa sheeting can only span so far across a void without failing under pressure, so it depends on the size of the voids. Another reason for keeping the vacuum to a minimum, to just form the balsa to the core.

I am wondering why there is such a tendency to crank up the vacuum? Are there areas out at the extremities from the tap that is not getting the full indicated vacuum? Do the vacuum manufacturers not have recommendations? Or, is it just a guy thing? Crank it up! More must be better!

OK, Ok. I will have to admit to one thing, and DirtDoctor alluded to it.

The samples I tested are unconfined. They are free to bulge at the sides.

Whereas, a wing is relatively flat, with the free side-face very small. A 2" x 2" section within the wing would be somewhat confined by other foam around it. That is, until you get out to the free edges. I suspect that you can take the vacuum up to about 4 to 5psi (8 to 10 inHg), before starting to get permanent deformation. I believe my testing is still good information at the lower ranges of pressure though.

I may try to confine a 5psi and 10psi sample by wrapping some strapping tape around them. Had thought about doing this if I saw much bulging, but I didn't see bulging of the sides until the 5psi and 10psi samples. I still think I would want to keep the pressure down to a minimum though.
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Old 02-26-2014, 08:12 AM
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Wingwall,

Don't take this wrong, Its meant to be humorous, One thing I learned in college and the aerospace industry. There is no such thing as an engineer under engineering anything. Honestly I have not read much of you findings and I am sure you have lots of great information and it looks like you have put a lot of work into it.

A couple of things:

1) what did you actually discover in layman terms. ( please keep you answer fairly short)
Over a normal 40% wing how much weight would you ( personally use per your findings )use for sheeting. What factor does the sheeting thickness or bonding agent play? The kit uses 1/16" sheeting.

2) You have put a tremendous amount of thought and work into these findings!! I'll bet you could have had all your sheeting done by now LOL

By the way we use .85 lb foam and when we vacuum bag we use about 5 hg

Al
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Old 02-26-2014, 12:45 PM
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Approaching critical AoA...
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I am by no means an expert, but there must be something to using higher pressures for bonding. In my limited capacity thinking, a higher pressure would cause the glue to penetrate further into the cells of both the wood and foam, increasing the bond. I remember Will or Dean did some bond tests on their Carden core scraps, to see how the glues penetrated. I dont remember pressures being discussed in those threads though.

But don't plywood manufacturers use tremendous pressure? And I think manufacturers making carbon fiber parts (like car body panels) use both heat and pressure to get a solid bond. But perhaps those principles dont apply to our materials here.

Pete

And Mike - you're too polite! I didn't think you were terse at all! (At least you wouldn't offend the true rednecks in the crowd...)

Pete
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Old 02-26-2014, 01:52 PM
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I have been known to pulversize a wing panel or two into powder when vaccum bagging some pylon wings... :-)

Al, Kevin,

You're so good at framing these bad boys up, Im sure you could just whip one up for me to be picked up at Nall!!! ;-)
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Old 02-26-2014, 02:18 PM
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5 inHg is about 2.5psi.
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Old 02-26-2014, 02:59 PM
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Quote:
Originally Posted by TheTank View Post
I have been known to pulversize a wing panel or two into powder when vaccum bagging some pylon wings... :-)

Al, Kevin,

You're so good at framing these bad boys up, Im sure you could just whip one up for me to be picked up at Nall!!! ;-)

Yeah... There's a thin line between good pressure and a flat wing!
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Old 02-26-2014, 03:16 PM
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Quote:
Originally Posted by MattyMatt View Post
Yeah... There's a thin line between good pressure and a flat wing!
Nothing like turning a full symmetrical airfoil into a Bannana'd Clark-Y!!!!!!!!!
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Old 02-26-2014, 03:42 PM
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Quote:
Originally Posted by TheTank View Post
I have been known to pulversize a wing panel or two into powder when vaccum bagging some pylon wings... :-)

Al, Kevin,

You're so good at framing these bad boys up, Im sure you could just whip one up for me to be picked up at Nall!!! ;-)

call
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Old 02-26-2014, 07:00 PM
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Quote:
Originally Posted by jtec/radiowave View Post
Wingwall,
Quote:
Originally Posted by jtec/radiowave View Post
Don't take this wrong, Its meant to be humorous, One thing I learned in college and the aerospace industry. There is no such thing as an engineer under engineering anything. Honestly I have not read much of you findings and I am sure you have lots of great information and it looks like you have put a lot of work into it.
A couple of things:
1) what did you actually discover in layman terms. ( please keep you answer fairly short )
Over a normal 40% wing how much weight would you ( personally use per your findings )use for sheeting. What factor does the sheeting thickness or bonding agent play? The kit uses 1/16" sheeting.

First, it would appear that 0.75psi to 1.0psi (8.6 to 11.5" of concrete blocks/bricks, or 1.5 to 2 inHG) is about minimum to keep the expansion of the glue (Garilla brand polyurethane) in check, and force the glue (or epoxy) into the pores of the balsa and foam.

Second, and on the maximum side, I would say not to put any more than about 3psi (6 inHg) on the panel, if you want it to rebound back to the desired wing thickness. Although, 4psi and 5psi may not be a big deal, as the load tests indicate a permanent strain of about 1% for 4psi, and about 2% strain for 5psi. That's 1/32" loss in a 3" thick panel for 4psi, and 1/16" loss in a 3" panel for 5psi. After that the loss goes up rapidly.

As for the sheeting, I believe the grain of the balsa should be running pretty close to parallel to the leading edge of the wing panel, particularly for the rudder.

2) You have put a tremendous amount of thought and work into these findings!! I'll bet you could have had all your sheeting done by now LOL

Yeh, that's probably true.

By the way we use .85 lb foam and when we vacuum bag we use about 5 hg
Al
Al, you may want to measure and weigh some of your foam as a check. I did that to all the panels in my kit, and they were pretty consistent at 0.87 pcf. I noted that at the top of Figs. A and C.
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Last edited by wingwall; 02-26-2014 at 07:09 PM.
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