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  #1  
Old 08-09-2011, 01:23 AM
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audioflyer audioflyer is offline
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Default Blind screws on firewall

This is from the Cozy project I bought. The two small rectangular pieces of the firewall, which have the three blind screws in them, are shown below. The screws are in the same triangular pattern, they just seem to be shifted.

The previous builder did not know why the pieces did not match the template, but said that the bulkheads were all made using the CAD template files.

Does anyone know a reason why these screws would need to be in the position shown in the picture as opposed to the M-drawing?

Thanks,
Ryan
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  #2  
Old 08-09-2011, 01:44 AM
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Default Re: Blind screws on firewall

he was one of a few builders that got them right.
the highter up the better the angal from the wing root for the pully .
the pully will need to be flatend a bit so the cable going down will be in line.
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  #3  
Old 08-09-2011, 08:20 AM
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Default Re: Blind screws on firewall

When you go to install your pulley brackets you will have to drill them to match whatever your blind screw arrangement is. No big deal. Steve build on
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Old 08-09-2011, 11:28 AM
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Default Re: Blind screws on firewall

There was a plans change to raise the height of the pulleys a bit. If you need to review the past changes, they are here
http://www.cozybuilders.org/ref_info/

BTW, the plans use of screws leaves something to be desired. Occasionally the screw head breaks loose in the flox and turns. There are several different ideas for that. One simple way is to notch the end of the screw with a dremel wheel and hold it with a small screwdriver as you tighten the nut. If you want other ideas, search the cozy archives or canard-aviators group for "firewall screws".
http://www.maddyhome.com/cozysrch/
http://groups.yahoo.com/group/canard-aviators/?tab=s
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  #5  
Old 08-09-2011, 12:00 PM
Marc Oppelt Marc Oppelt is offline
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Default Re: Blind screws on firewall

Why not use these behind the firewall: (I got some from McMaster, but then I saw them at Ace Hardware)
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  #6  
Old 08-09-2011, 12:34 PM
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Default Re: Blind screws on firewall

Quote:
Why not use these behind the firewall: (I got some from McMaster, but then I saw them at Ace Hardware)
Non-aircraft grade, not to plans, will get loose unlike AN nuts, and probably doesn't come in 1/4-28thread.
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Old 08-09-2011, 12:54 PM
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Default Re: Blind screws on firewall

Doing it all over again knowing what I know now, I would use AN525 screws with the washer head on the inside. It would take two people to install the brackets though. I did not like the plans method to stop twist, do not like the countersink as it creates a weak point for the screw to pull through, and the layups on the firewall side become uneven around the protruding screw studs. I would today install the pulley brackets after the firewall is installed. Pilot drill the brackets 3/32", locate them on the firewall, pilot drill through the firewall, then match drill #12 drill for the screws.
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Old 08-09-2011, 12:55 PM
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Default Re: Blind screws on firewall

..... yeah, best stick with the anchor nuts. They have a click-bond version of an anchor nut as well.
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  #9  
Old 08-09-2011, 01:19 PM
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Default Re: Blind screws on firewall

Quote:
Originally Posted by neverquit View Post
Non-aircraft grade, not to plans, will get loose unlike AN nuts, and probably doesn't come in 1/4-28thread.
Yes, non aircraft grade and not to plans (and of course we all follow the plans to a T).

These nuts are available in SS and are available in various threads and sizes (including 1/4-28), of course the bolts in question are 10-32 (also available). They are available in self-locking (mcmaster-carr), although safety wire/and/or locktite would be fine.

Following the plans, with these screws, has "screwed up" many a builder'.

If you use these, make sure that you insert them before glassing the cockpit side of the firewall or you won't be able to hammer them to place (the tynes will bend)
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Old 08-09-2011, 01:56 PM
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Default Re: Blind screws on firewall

Quote:
Following the plans, with these screws, has "screwed up" many a builder'.
Not sure where you're "many a builder" comes from but I and three others I am building with had no problems. I'm sure if you hunt the correct aviation grade or near-aviation grade hardware down it will take no time and effort at all not to mention more expense. Deviating from the plans is a much better idea. I can't count how many hours I spent inventing a "better idea" that just made it different, not better. How long did it take you to re-design that FHC again?
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  #11  
Old 08-09-2011, 02:50 PM
argoldman argoldman is offline
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Default Re: Blind screws on firewall

Quote:
Originally Posted by neverquit View Post
Not sure where you're "many a builder" comes from but I and three others I am building with had no problems. I'm sure if you hunt the correct aviation grade or near-aviation grade hardware down it will take no time and effort at all not to mention more expense. Deviating from the plans is a much better idea. I can't count how many hours I spent inventing a "better idea" that just made it different, not better. How long did it take you to re-design that FHC again?
Nev,
History is a wonderful thing, especially when one chooses to ignore it, or when one is unaware of it.

There have been many posts in this and other sheets about the rotational breaking loose of the through firewall bolts with solutions ranging from completely other approaches to welding some little arms to the heads of the bolts as an anti-torque mechanism.

I am happy for you that your following the plans, with all of your aircraft was successful for you, and many others. Apparently you didn't have the problems that others have had.

by your post, perhaps it is reading this, after a busy morning,I am not sure about what you are saying. although it seems like a little sarcasm. I would really appreciate it if you could clarify that for me.

My canopy mechanism, I admit took about a year to develop and perfect. My intention is not to get my plane into the air in the shortest time possible. I enjoy building and creating as much as the flying.

If my goal was to get into the air quickly, purchasing an aircraft would certainly satisfy that goal better than building.

Although many of the things that we try don't make things better, only different, if we extrapolate that thought, and follow it, we would still be flying machines covered in cotton, sitting outside with the propellers in the back and the elevators in the front....Oh well, two out of four aint bad
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  #12  
Old 08-09-2011, 11:32 PM
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Default Re: Blind screws on firewall

KJAshton,

Thanks for pointing me back to the plans changes. I found the following in the FIRST edition plans changes:

"Page 3, Step 5, 2nd para: Add, "Locate the two groups of three MS24694-S54 blind screws 2.0 in. higher than shown on M-7 and M-8 and detail D-D to provide more clearance between the rudder cable and the aileron push rods."

Now, maybe I misunderstood, but I thought that since I had third edition plans, I only needed to incorporate the third edition plans changes, that all of the previous ones would be included into the third edition. Is this not the case? If it's not, I'm going to have to go back through the changes for the first two editions as well...
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  #13  
Old 08-10-2011, 10:32 AM
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Default Re: Blind screws on firewall

How about using a drilled-head bolt--twist a bit of safetywire in the head and embed in flox. It would probably resist turning very well.

Not sure what plans changes got incorporated in later editions. Zeitlin would know.
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  #14  
Old 08-14-2011, 12:22 PM
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Default Re: Blind screws on firewall

I welded a piece of welding rod onto the head of the bolts and then routed the plywood for a nice tight fit. Seems to be working so far I have not spun a bolt. I did it per plans on my Longez and spun all the bolts I had to grind a slot on the end of the screw and used a small screw driver to put the nuts on. Steve build on
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  #15  
Old 08-14-2011, 01:19 PM
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Default Re: Blind screws on firewall

The real problem isn't the bolt head, it's the threads.
You install the bolts in chapter 4. The part then floats around the shop for a year or two until you get to the bit where you install the bulkhead, then you work with epoxy all around it until, finally, you're ready to install the control surface hardware. By that time the threads have accumulated two years worth of cured epoxy and dirt, and the nuts get stuck. Protect the threads with some shrink insulation for all that time or clean the threads before trying to install the nuts, and the problem will go away. I did neither, and my bolts turned
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