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  #16  
Old 06-27-2007, 10:45 PM
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by Steve parkins View Post
i used a staple gun once, but the next day i needed the gun back, so i had to cut the big bump and retreve it. it was no good anymore.
next time i'll try a staple.
D@MN!!!!!! I wish you would have posted that sooner!
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  #17  
Old 06-27-2007, 11:41 PM
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Lightbulb Re: N200LZ: Chapter 21 - Strakes

I'm afraid your 3M #77 is just a little short, try #78, it's the Cat's Aaaa....meow.
It was made fer extruded polystyrene and such.
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  #18  
Old 06-27-2007, 11:54 PM
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by Clutch Cargo View Post
I'm afraid your 3M #77 is just a little short, try #78, it's the Cat's Aaaa....meow.
It was made fer extruded polystyrene and such.
perfect timing - i'll get it
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  #19  
Old 06-28-2007, 10:34 AM
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Default Re: N200LZ: Chapter 21 - Strakes

3M #78 seems to be exactly what I need. I should be able to hotwire through it easily (with no ill effects.)
I was trying a test piece with the #77 and yes, it does do some damage to the foam. I loaded up an area (which is more than you ordinarily use) and you could see it was dissolving the foam to some degree.

While this foam will not be used as a structural element, I do want to be sure that I don't have to do a bunch of filling etc. to have a good mold.

Because I am using the Infinity retracts and the internal baffles and ribs will be positioned differently (per the Infinity install plans) I can identify their locations on my foal mold. That way, after my skins are created, I can slice the mold up at the rib locations for a perfect profile shape for the ribs.
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  #20  
Old 06-28-2007, 10:38 AM
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by TMann View Post
I can slice the mold up at the rib locations for a perfect profile shape for the ribs.
Don't you just love aiming for perfection, i never get there but i aim a lot
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  #21  
Old 06-28-2007, 11:56 AM
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Default Re: N200LZ: Chapter 21 - Strakes

I've long been considering this same approach, for the same reasons.

Have you considered how to do a "Steve Parkins" strakes (curved front) using hotwired foam molds?
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  #22  
Old 06-28-2007, 12:15 PM
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Default Re: N200LZ: Chapter 21 - Strakes

I considered having the strake nose curve as one continuous form but after thinking it over I decided I really did not want to have my fuel that close to a leading edge. It might not be an issue but I don’t want to find out it is.
What I plan to do is shape the skin such that there will be a slight flange where the top and bottom skins meet. That will allow me to have an area to put some clamps when I join the two halves. The strake nose foam will be slotted to accept that flange.

I threw together a quick sketch.
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  #23  
Old 06-28-2007, 01:44 PM
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Default Re: N200LZ: Chapter 21 - Strakes

The strake kits that featherlite sells (sold). Its perhaps 3/8 (maybe 1/2) foam and it curves all the way around.

More photos at:

http://www.iflyez.com/LongEZ_Constru...s_Strake.shtml

Waiter
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  #24  
Old 06-28-2007, 01:48 PM
Marc Zeitlin Marc Zeitlin is offline
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by TMann View Post
I considered having the strake nose curve as one continuous form but after thinking it over I decided I really did not want to have my fuel that close to a leading edge. It might not be an issue but I don’t want to find out it is.
The Aerocad premolded strakes have a lap joint right at the LE, and extra fuel capacity partially due to that extra room. Anything that hits hard enough to damage the tank is not going to be stopped by 2 BID and some urethane/polystyrene foam.

Quote:
Originally Posted by TMann View Post
What I plan to do is shape the skin such that there will be a slight flange where the top and bottom skins meet. That will allow me to have an area to put some clamps when I join the two halves. The strake nose foam will be slotted to accept that flange.
Good from a MFG standpoint and sealing standpoint - not good from a structural standpoint. Anytime you modify what the plans call for, you should be thinking about whether or not you're going to be putting a joint in peel, rather than shear, tension, or compression.

Your joint is in peel on the inside surface of the tank. Not good. That's why AC uses a lap joint on their pre-molded strakes, and why the plans calls for a bulkhead at the LE of the strake with tapes connecting it to the top and bottom skins.

Yes, the joints of the top skin to the top of the ribs is just flox, but there's less chance of a peel developing there (it's essentially tension), and removing what was a shear joint and substituting a peel joint in a proven structure is not a good idea.
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  #25  
Old 06-28-2007, 01:59 PM
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Default Re: N200LZ: Chapter 21 - Strakes

Quote:
I'm planning on making my strake molds this weekend.
Yes, I know this isn't per plans but I'm planning on laying up my skins such that they are curved from the start vs. trying to curve them after the fact.
So, your method for madness is to make a one (or two split) piece of pre-formed fiberglass strake then add bulkheads? I'm visioning you laying the bid on the mold (or buck) then laying foam over it, then then the outer layer?
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  #26  
Old 06-28-2007, 02:03 PM
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Default Re: N200LZ: Chapter 21 - Strakes

Quote:
The Aerocad premolded strakes have a lap joint right at the LE, and extra fuel capacity partially due to that extra room. Anything that hits hard enough to damage the tank is not going to be stopped by 2 BID and some urethane/polystyrene foam.
May not be good enough for trees or powerlines but might be Burt's plan was to keep them safe from hangar rash, lawn chairs, birds? Better little dents than pin hole leaks on a cross country.
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  #27  
Old 06-28-2007, 02:06 PM
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by Marc Zeitlin View Post

Your joint is in peel on the inside surface of the tank. Not good. That's why AC uses a lap joint on their pre-molded strakes, and why the plans calls for a bulkhead at the LE of the strake with tapes connecting it to the top and bottom skins.

Yes, the joints of the top skin to the top of the ribs is just flox, but there's less chance of a peel developing there (it's essentially tension), and removing what was a shear joint and substituting a peel joint in a proven structure is not a good idea.
So Marc, how about this (see pic). At least this way I could do both the flange type joint for the flox plus the overlap plies to provide the joint that would be in shear as you mentioned.
(sorry about the graphic. I'm using that new high tech graphics package from Microsoft - Visual Paint .NET)

I have never manufactured a strake so everyone really has an advantage here ........ but, would you think it possible to actually fabricate the entire strake seperate from the aircraft and then bond it to the center section spar and fuselage as 1 piece?
It seems to me that if that was at all possible, any leaks you discovered could be addressed more efficiently.
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  #28  
Old 06-28-2007, 02:24 PM
Marc Zeitlin Marc Zeitlin is offline
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by TMann View Post
So Marc, how about this (see pic).
Bingo. That fixes the problem.

Quote:
Originally Posted by TMann View Post
........ but, would you think it possible to actually fabricate the entire strake seperate from the aircraft and then bond it to the center section spar and fuselage as 1 piece?
You'd want to use the fuselage/spar/wing as a jig (if you haven't built wings/center spar yet, you shouldn't be building strakes), and it would weigh more, because in the stock config the center spar is used as the rear of the tank - you'd have to add another rear surface for the tank, so you'd lose some capacity and add some weight, but yes, it would be possible.


Quote:
Originally Posted by TMann View Post
It seems to me that if that was at all possible, any leaks you discovered could be addressed more efficiently.
Maybe so, at the cost of some weight and capacity loss.


Quote:
Originally Posted by neverquit
May not be good enough for trees or powerlines but might be Burt's plan was to keep them safe from hangar rash, lawn chairs, birds? Better little dents than pin hole leaks on a cross country.
The AC strakes have approximately 10 layers of BID/UNI and 0.030" of flox at the leading edge. You'd have to whack on it with a lawn chair for 1/2 hour to beat your way through it. Leading edges of wings and canards have stood up to bird strikes, and they have less material in them.
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  #29  
Old 06-28-2007, 02:41 PM
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by neverquit View Post
So, your method for madness is to make a one (or two split) piece of pre-formed fiberglass strake then add bulkheads? I'm visioning you laying the bid on the mold (or buck) then laying foam over it, then then the outer layer?
Cut the strake shape as 1 piece.
put thin poly over it followed by peel ply , glass/epoxy, peel ply, perf ply, batting and into the vacuum bag, then the whole works goes between the waste pieces of foame just to give it a nice warm cozy place to be for a few hours.
Pull it all out, flip it and do the other side. In considering what Marc said about the joint being in shear, I could sand out a small depession towards the top of the leading edge to make a flush fitting lap joint which shoul not be that hard to do.

Anyway, once I have the top and bottom skins made, I can slice up the mold on the vertical axis to get the perfect pofile of the ribs. By laying the large waste pieces in the skins as I go, I should be able to mark the skins as to where the ribs will go to insure perfect alignment.

Waiter - The pics on your site are great! I need to get my build documented to that level of detail! (i.e. You are setting the standard!)
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  #30  
Old 06-29-2007, 09:58 AM
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Default Re: N200LZ: Chapter 21 - Strakes

Picked up my foam last night at Home Depot. I keep hoping my neighbor from 2 doors down (he built a Q-2000) to stop by. Figure I'll yank his chain: "Yeah ... all that foam from Wicks is so expensive when compared to what I can get at home depot. )
I don’t need to rename my build as “the Pink Flamingo” on account of all the foam being removed from the end product. So that’s what I’ll be up to while I’m waiting for parts to cure!
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