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  #16  
Old 03-24-2016, 12:00 AM
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lutorm lutorm is offline
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Default Re: Front seatbac longeron cutout edge glassing

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Originally Posted by Marc Zeitlin View Post
Angles are important for load transfer and stress requirements - if it says 45, make it as close to 45 as you can.
This is actually one of the things where I think the plans are the most deficient (Long-EZ, I don't have any Cozy plans so I don't know about them): The almost complete lack of specified tolerances.

In engineering, if a dimension is critical, it should be given with a tolerance. In this example, how do I know what is acceptable? "As close as I can" by eyeball? Protractor? Laser measurement system? I *can* get it pretty darn close to 45 if I have to, but the build will take years.

I think it would eliminate a whole lot of anxiety of things were given with tolerances. BID must be at 45deg plus/minus 5. Bid tapes need to be 2" wide plus/minus 0.5. Ply overlap should be 1" +-0.25. Maximum allowed joggle in fibers 1/8", etc. But there's almost none of that.
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  #17  
Old 03-24-2016, 12:09 AM
Marc Zeitlin Marc Zeitlin is offline
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Default Re: Front seatbac longeron cutout edge glassing

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This is actually one of the things where I think the plans are the most deficient (Long-EZ, I don't have any Cozy plans so I don't know about them): The almost complete lack of specified tolerances.
That's something that we've discussed many times over the years on the COZY mailing list. And I agree with you 100% - as an engineer, it drives me nuts not to know what the tolerances are. Over time, I've developed an understanding of what they PROBABLY are, given what works and what I've seen, but it is a PITA that they're not specified.

I don't know if the lack of tols causes folks to try harder and do better, or to throw up their hands and say "whatever". Probably some of both, from what I see and hear.
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  #18  
Old 03-24-2016, 12:11 AM
Marc Oppelt Marc Oppelt is offline
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Default Re: Front seatbac longeron cutout edge glassing

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Originally Posted by lutorm View Post
This is actually one of the things where I think the plans are the most deficient (Long-EZ, I don't have any Cozy plans so I don't know about them): The almost complete lack of specified tolerances.

In engineering, if a dimension is critical, it should be given with a tolerance. In this example, how do I know what is acceptable? "As close as I can" by eyeball? Protractor? Laser measurement system? I *can* get it pretty darn close to 45 if I have to, but the build will take years.

I think it would eliminate a whole lot of anxiety of things were given with tolerances. BID must be at 45deg plus/minus 5. Bid tapes need to be 2" wide plus/minus 0.5. Ply overlap should be 1" +-0.25. Maximum allowed joggle in fibers 1/8", etc. But there's almost none of that.
Overthinkage.

It's just to get some plans, foam, glass & glue and get to it. Crack a beer...and for gawd sake RTFD. This ain't rocket science, as evidenced by the 2000ish planes that have been built and flown.
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  #19  
Old 03-24-2016, 04:06 AM
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Default Re: Front seatbac longeron cutout edge glassing

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Overthinkage.

It's just to get some plans, foam, glass & glue and get to it. Crack a beer...and for gawd sake RTFD. This ain't rocket science, as evidenced by the 2000ish planes that have been built and flown.
Perhaps. But Burt also said "Your best is barely good enough!" in regards to workmanship. Certainly out of those 2000ish planes there have been cases where shoddy workmanship led to structural failure, so it's not impossible to f**k it up.

I'm not particularly risk-averse, but I like to know what I'm getting into and a ~1/2000 chance of dying is a lot worse than many other hobbies that come to mind. It's probably up there with dragging knees on public roads, and I don't do that either.
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  #20  
Old 03-24-2016, 11:17 AM
argoldman argoldman is offline
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Default Re: Front seatbac longeron cutout edge glassing

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Turbo is the 4th builder I have heard of that is not happy with the seatback. I don't think it is a good bit to start the build on, ...clip


When I attempted the seatback I was surprised how much harder it was than the previous, the flox corners and large area seemed to soak up time and gallons of epoxy compared to F-22/28. I felt the urge to heat-gun it majorly to squeegee the epoxy out, but restrained myself as I was happy with the result I had with the smaller parts. Result was lovely!
Some disagreement here (as usual)
Although I wasn't there at the plans drawing, doing the setback first is a great teaching method on the various types of layup/corners etc. The type of foam used in this part is more demanding to micro and epoxy than many of the "smoother" types that are used later (such as in F22, F28 (in my recollection) that you will be later doing for more structurally important things. Perhaps it's order was was specified as first to allow you to try/fail/try etc until you got the techniques right before moving on to other tasks.

With the seatback you do flox corners, layup schedules, rounded edges, large layups etc, all of which you will use later, many on more expensive parts.

Doing this part gives you the opportunity, on a large, rough surfaced piece to create and then evaluate many of the flaws that you may laterl introduce on smaller more vital parts. Getting over this hump probably will help you do the rest of the layups more easily and accurately.

I think that the plans were developed for the first time builder, ones who had no experience with glass/epoxy.

Of course, there is nothing to say that you have to do the construction in the order in which it was presented in the plans. The result is the important thing, not the order. However for a Newbie, which many builders are, this hand holding can be of great benefit.

Indeed the post that started this thread is a great example of the learning process to which I speak. None of us wants to redo parts, but the learning experience, unfortunately at some cost, is a cheap investment and invaluable (IMNSHO).
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  #21  
Old 03-24-2016, 11:20 AM
argoldman argoldman is offline
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Default Re: Front seatbac longeron cutout edge glassing

Quote:
Originally Posted by Spodman View Post
Turbo is the 4th builder I have heard of that is not happy with the seatback. I don't think it is a good bit to start the build on, ...clip


When I attempted the seatback I was surprised how much harder it was than the previous, the flox corners and large area seemed to soak up time and gallons of epoxy compared to F-22/28. I felt the urge to heat-gun it majorly to squeegee the epoxy out, but restrained myself as I was happy with the result I had with the smaller parts. Result was lovely!
Some disagreement here (as usual)
Although I wasn't there at the plans drawing, doing the seatback first is a great teaching method on the various types of layup/corners etc. The type of foam used in this part is more demanding to micro and epoxy than many of the "smoother" types that are used later (such as in F22, F28 (in my recollection) that you will be later doing for more structurally important things. Perhaps it's order was was specified as first to allow you to try/fail/try etc until you got the techniques right before moving on to other tasks.

With the seatback you do flox corners, layup schedules, rounded edges, large layups etc, all of which you will use later, many on more expensive parts.

Doing this part gives you the opportunity, on a large, rough surfaced piece to create and then evaluate many of the flaws that you may laterl introduce on smaller more vital parts. Getting over this hump probably will help you do the rest of the layups more easily and accurately.

I think that the plans were developed for the first time builder, ones who had no experience with glass/epoxy.

Of course, there is nothing to say that you have to do the construction in the order in which it was presented in the plans. The result is the important thing, not the order. However for a Newbie, which many builders are, this hand holding can be of great benefit.

Indeed the post that started this thread is a great example of the learning process to which I speak. None of us wants to redo parts, but the learning experience, unfortunately at some cost, is a cheap investment and invaluable (IMNSHO).
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  #22  
Old 03-24-2016, 11:20 AM
argoldman argoldman is offline
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Default Re: Front seatbac longeron cutout edge glassing

sorry for the double post!!!
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