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Use of 7075-T-6 for wing attach fittings?

 
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careywf(at)sbcglobal.net
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PostPosted: Fri May 23, 2008 1:33 pm    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Hi,
New to the site. Building in basement in Beavercreek, Ohio, just outside of Dayton. Both wings, control surfaces and flaps complete. Yes, I can get them out of the basement. Fuselage 50 % complete, held together by Clecoes. Once complete, will disassemble and move to garage where fuselage will be aligned again and riveted together. Not new to aviation or aircraft maintenance, especially sheet metal work.

Question: Has anyone used, or thought about using 7075 T-6 Alclad .063 aluminum as a backing plate on the rear center spar running thru the fuselage, and as attachment plates between the rear center spar and the wing rear spar? 7075 T-6 is a high strength aluminum designed for use in high stress areas. I would like to do this as I am in agreement with several readers who have suggested that recent wing failures COULD have been the result of the failure of the rear spar attach plates. My thought is that until the NTSB comes up with a reason and a fix, why not add extra strength in that area. The added weight is minimal.

Any comments?

Walt
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Jim.Machin(at)uav.com
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PostPosted: Fri May 23, 2008 2:29 pm    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Walt,

7075 material, in general, is very susceptible to stress corrosion cracking and is prohibited from being used on any military programs. On our aircraft (I design UAV aircraft, Predator series) for the Air Force, we have had to substitute 7050 for all the parts that were originally 7075 as we had seen some premature corrosion problems on some very well corrosion-protected parts (anodized and painted). The corrosion process is accelerated when the material is continually stressed as in landing gear while the aircraft is sitting on the ground (which is where we saw problems). While being much stronger than 2024 or 6061, 7075 really is not a good choice of material. If the higher material properties are required, 7050 can be used but it is very expensive.

Jim
Quickbuild 601XL, 0-200



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Mitch Hodges



Joined: 10 Jan 2006
Posts: 45
Location: Powder Springs, GA

PostPosted: Fri May 23, 2008 2:45 pm    Post subject: Re: Use of 7075-T-6 for wing attach fittings? Reply with quote

[quote="careywf(at)sbcglobal.net"][b]Hi,
Yes, I can get them out of the basement.
Quote:


Had to smile at that! I'm also building mine in the basement, with basically the same plan. My response is "Well, I'll either get it out, or end up with a really cool bar in the new rec room!"

DO NOT ARCHIVE


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Larry Hursh



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PostPosted: Fri May 23, 2008 3:31 pm    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Quote:

Yes, I can get them out of the basement.

Had to smile at that! I'm also building mine in the basement, with basically the same plan. My response is "Well, I'll either get it out, or end up with a really cool bar in the new rec room!"

.....There's only one word that comes to my mind:

Sawsall....LOL





Larry Hursh
CH601XL (Building from Kits - Rudder, tail sections done, working on wings)
(N601LL Reserved)

Edwardsburg, Michigan

Keep your eyes skyward - always!
Do Not Archive


[quote][b]


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carlossa52(at)gmail.com
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PostPosted: Fri May 23, 2008 3:37 pm    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

..then we are at least three in this situation...

Cheers

Carlos
CH601-HD, plans

2008/5/23 Mitch Hodges <n601mh(at)hodges.info (n601mh(at)hodges.info)>:
[quote]--> Zenith601-List message posted by: "Mitch Hodges" <n601mh(at)hodges.info (n601mh(at)hodges.info)>

[quote="careywf(at)sbcglobal.net"][b]Hi,
Yes, I can get them out of the basement.

>


Had to smile at that! I'm also building mine in the basement, with basically the same plan. My response is "Well, I'll either get it out, or end up with a really cool bar in the new rec room!"

DO NOT ARCHIVE

--------
Mitch Hodges
N601MH (Zenith 601HDS)
Builder Log at http://www.hodges.aero
Wings Under Perpetual Construction


[b]


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stepinwolf



Joined: 21 Jan 2008
Posts: 133
Location: Canada

PostPosted: Fri May 23, 2008 5:21 pm    Post subject: Re: Use of 7075-T-6 for wing attach fittings? Reply with quote

Carlos,

You might want to make that four, since I too am building in the basement. The reason is because it's cool in the Summer, and warm during the cold Canadian Winters.

I can get everything out, except for the fuselage, which will be disassembled, and rebuilt in the garage.

Bob the 701 scratch
Three Rivers ,
Quebec

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PostPosted: Sat May 24, 2008 3:53 am    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Hi Larry,

Really like the idea of the cool bar in the basement. Walt in Ohio.

Larry Hursh <skyridersbn(at)yahoo.com> wrote:
[quote]
Quote:

Yes, I can get them out of the basement.

Had to smile at that! I'm also building mine in the basement, with basically the same plan. My response is "Well, I'll either get it out, or end up with a really cool bar in the new rec room!"

.....There's only one word that comes to my mind:

Sawsall....LOL




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careywf(at)sbcglobal.net
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PostPosted: Sat May 24, 2008 4:08 am    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Thanks for the info Jim. Maybe I'll just double up on the backing plate for the rear center spar and the wing attachment plates using .063 6061 T-6 aluminum. Retired from the AF in 1979 as CMSgt and 1998 as GM-14. In the AF, worked five years in electronics, five years as B-52 gunner, two years in field maintenance, and 10 years in OSI. As civilian, worked another 18 years on OSI. Any thoughts on the suspected wing failures? Walt.

Jim Machin <Jim.Machin(at)uav.com> wrote: [quote] Walt,

7075 material, in general, is very susceptible to stress corrosion cracking and is prohibited from being used on any military programs. On our aircraft (I design UAV aircraft, Predator series) for the Air Force, we have had to substitute 7050 for all the parts that were originally 7075 as we had seen some premature corrosion problems on some very well corrosion-protected parts (anodized and painted). The corrosion process is accelerated when the material is continually stressed as in landing gear while the aircraft is sitting on the ground (which is where we saw problems). While being much stronger than 2024 or 6061, 7075 really is not a good choice of material. If the higher material properties are required, 7050 can be used but it is very expensive.

Jim
Quickbuild 601XL, 0-200



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PostPosted: Sat May 24, 2008 4:49 am    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

just remember that 7075T6 is also very much more susceptible to corrosion that the others and is also quite notch sensitive - for instance the scratches across the thickness of the part from inserting the bolts are stress risers that are usually ignored in other alloys/tempers but need to be considered in 7075.

Walter Carey <careywf(at)sbcglobal.net> wrote:[quote] Hi,
New to the site. Building in basement in Beavercreek, Ohio, just outside of Dayton. Both wings, control surfaces and flaps complete. Yes, I can get them out of the basement. Fuselage 50 % complete, held together by Clecoes. Once complete, will disassemble and move to garage where fuselage will be aligned again and riveted together. Not new to aviation or aircraft maintenance, especially sheet metal work.

[quote][b]


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PostPosted: Sat May 24, 2008 4:49 pm    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Thanks for the info Dave. Reconsidering use of 7075. Will probably double up on the 6061 T-6. Thanks again. Walt.

David Downey <planecrazydld(at)yahoo.com> wrote: [quote]just remember that 7075T6 is also very much more susceptible to corrosion that the others and is also quite notch sensitive - for instance the scratches across the thickness of the part from inserting the bolts are stress risers that are usually ignored in other alloys/tempers but need to be considered in 7075.

Walter Carey <careywf(at)sbcglobal.net> wrote: [quote] Hi,
New to the site. Building in basement in Beavercreek, Ohio, just outside of Dayton. Both wings, control surfaces and flaps complete. Yes, I can get [quote][b]


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PatrickW



Joined: 27 Oct 2006
Posts: 380
Location: Fort Worth, Texas

PostPosted: Sun May 25, 2008 3:41 pm    Post subject: Re: Use of 7075-T-6 for wing attach fittings? Reply with quote

The rear spar is already doubled up for the first 270mm outboard from the root by part number 6W7-2 (.063 thick), according to the plans I have, dated 3/15/2006.

Take a look at the area of 6W7-2 on photograph number 19 of the Yuba City case.

Can anyone with a better monitor see if the doubler was there, or not...? The rear spar at the root is clearly torn out in this photograph, but I can't see if the doubler is present or not.

Also - does anybody have a copy of any older plans prior to 3/06 where this doubler is NOT present...? Is the doubler something new, or has it been there all along?


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PostPosted: Sun May 25, 2008 5:36 pm    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Hi Patrick,

Thanks for the feedback. My plans are dated Apr 04 and they show the .063 doubler at the end of the rear spar attached with 20 A-5 rivets. I checked my completed wings and I have them per plans. I was talking about doubling up the thickness of the center spar which runs thru the fuselage, plus doubling up the attachment plates which come out the side of the fuselage and connect the center spar to the rear spar of the wings.

By the way, where can I find the site you guys keep talking about where there are photos of the Yuba City accident? I have a 20 inch LCD computer screen and maybe I can see if there is a doubler riveted to the rear spar. Walt

PatrickW <pwhoyt(at)yahoo.com> wrote:
[quote]--> Zenith601-List message [quote][b]


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PostPosted: Sun May 25, 2008 6:54 pm    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

My plans are 08/05 and part 6W-7-2 is .063
Lee

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PostPosted: Mon May 26, 2008 12:07 pm    Post subject: Re: Use of 7075-T-6 for wing attach fittings? Reply with quote

careywf(at)sbcglobal.net wrote:
By the way, where can I find the site you guys keep talking about where there are photos of the Yuba City accident?

Here is the thread with that link:

http://forums.matronics.com/viewtopic.php?t=42585&highlight=link


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PostPosted: Tue May 27, 2008 10:59 am    Post subject: Use of 7075-T-6 for wing attach fittings? Reply with quote

Hi Walt,

As none of us here have all the facts, my opinions on the wing failures are just that – opinions. That being said, my thoughts are that statically, the wing is strong enough to meet the design requirements. It is very straight forward to calculate the wing lift capability and entirely acceptable to then test the wing to meet the requirements just as Zenith has done multiple times. There seems to have been more than one failure mode (with failures both in the positive and negative direction) so there is probably not just one explanation. Flutter is always a possibility especially with different rigging techniques resulting in different cable tension being a variable. I do know for a fact that a more balanced system would up the flutter speed (my aircraft does not have the trim system in the aileron) and I am considering additional balancing. Since there must have been a failure do to over control in the negative direction, putting in the control stop as recommended by Zenith seems prudent. The elevator is sensitive and it has occurred to me that with the reclined seating position, hitting a gust in the negative direction might cause the pilot to rotate about the lap belt and thus moving the shoulder forward (especially if the shoulder harness is loose) which could result in an unintended down elevator control input if the body tensed involuntarily thus exacerbating the negative G loading and possibly overstressing the wing.

My plan going forward is to build the wing as designed, make sure all the control cables have the right tension, install the control limit on the elevator, fly with a tight shoulder harness and always fly the aircraft within the design envelope.

Jim

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