Van's Air Force
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SB 14-01-31; RV-6, 7, 8
- Thread starter RV7A Flyer
- Start date
Walt
Well Known Member
What is a double margin threaded drill bit?Not familiar. Thanks.
http://www.panamericantool.com/double-margin-drills/double-margin-drill-information.html
I am relieved to report that inspected today and found no cracks
My data
440+ hrs.
Nicely rounded notches per plans
Plans from 2008
IO,360 180hp, hartzell cs
Only pavement operation
Push/pull via prop and tow bar
I have taken pictures with the IPHONE and though not as good as some folks but for a reference.
HS4 by bavafa1, on Flickr
HS3 by bavafa1, on Flickr
Will continue Bi-annual inspection.
My data
440+ hrs.
Nicely rounded notches per plans
Plans from 2008
IO,360 180hp, hartzell cs
Only pavement operation
Push/pull via prop and tow bar
I have taken pictures with the IPHONE and though not as good as some folks but for a reference.
HS4 by bavafa1, on Flickr
HS3 by bavafa1, on Flickr
Will continue Bi-annual inspection.
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I was thinking the same thing. My spar web looks the same as in the picture above. No notches per MY plans (dated Feb 28/01). Instructions say to "trim to fit"
Bevan
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Jim Lewellyn
Well Known Member
SB
1998 RV6
670 Hours
O-320
FP Sensenich
Occasional Rolls
Mostly Hard Surface
No Notches
No Cracks
1998 RV6
670 Hours
O-320
FP Sensenich
Occasional Rolls
Mostly Hard Surface
No Notches
No Cracks
brad walton
Well Known Member
MELCTL and BEVAN
My plans indicate the web across the center section should be 3 and 7/16 high and no mention of notching. My plans were dated 96 (I think) and had revisions nos. 1 and 2.
My plans indicate the web across the center section should be 3 and 7/16 high and no mention of notching. My plans were dated 96 (I think) and had revisions nos. 1 and 2.
Approaching 2000 hours AirFrame
Pulled the fairing and at first look thought I was home free. One piqued my interest a little though so more cleaning and buffing and macro photography and the lower right relief had a crack about 3/16th of an inch. But, it's a crack.
In the really blown up photo you can see the relief was no smoothed and polished as well as it could have been. The other three were smooth and no cracks.
I'll fly some and when the parts are available I'll comply with the SB. The safety of the air frame is not in question as it stands right now.
1900 hours, lot's of acro, some grass.
205HP, CS.
Really hard to see any crack here but as I looked really close I could see a tine hair line running across the relief notch, which didn't look rough until I really macro'd and blew it up. see below
Here is a really zoomed in clear shot of the crack... a lot of work over a little crack..
Yes, I see that the bottom rivet is not set correctly, but thanks in advance for pointing that out..
I at least have not lost my sense of humor over this
Pulled the fairing and at first look thought I was home free. One piqued my interest a little though so more cleaning and buffing and macro photography and the lower right relief had a crack about 3/16th of an inch. But, it's a crack.
In the really blown up photo you can see the relief was no smoothed and polished as well as it could have been. The other three were smooth and no cracks.
I'll fly some and when the parts are available I'll comply with the SB. The safety of the air frame is not in question as it stands right now.
1900 hours, lot's of acro, some grass.
205HP, CS.
Really hard to see any crack here but as I looked really close I could see a tine hair line running across the relief notch, which didn't look rough until I really macro'd and blew it up. see below
Here is a really zoomed in clear shot of the crack... a lot of work over a little crack..
Yes, I see that the bottom rivet is not set correctly, but thanks in advance for pointing that out..
I at least have not lost my sense of humor over this
LettersFromFlyoverCountry
Well Known Member
Decided to let it ride and not fix something that's not broken. Went out to hangar today (-7.at sunrise,) and spent a couple hours putting the elevators back on (all new hardware of course) I sure love squeezing in all those washers aside rod end bearings. Yeehah.
I'll put the VS on tomorrow and then make the rudder bottom fairing change to get rid of the snap bushing for the tail light and widen out a slot. Found too much chafing on the wiring.
In the meantime, it all gave me an opportunity to go over the the rudder, VS, and elevator with a fine inspection to get the progressive annual underway, I've been meaning to move it to too-cold-to-fly season anyway.
I'll plan on buying some HS parts from time to time over the years and slowly build a second HS. If the cracks appear, I'll just swap it out. the longeron attach point redrill isn't an issue. The shim makes a good drill guide .If I sell the plane, it'll be a relatively inexpensive A&P bill for the next owner.
I'll put the VS on tomorrow and then make the rudder bottom fairing change to get rid of the snap bushing for the tail light and widen out a slot. Found too much chafing on the wiring.
In the meantime, it all gave me an opportunity to go over the the rudder, VS, and elevator with a fine inspection to get the progressive annual underway, I've been meaning to move it to too-cold-to-fly season anyway.
I'll plan on buying some HS parts from time to time over the years and slowly build a second HS. If the cracks appear, I'll just swap it out. the longeron attach point redrill isn't an issue. The shim makes a good drill guide .If I sell the plane, it'll be a relatively inexpensive A&P bill for the next owner.
One Crack! Top left side
Did the inspection this afternoon. One crack in the top left corner. Bummer!
RV-7A
635 hours
A little acro
A good bit of formation flying
180 HP Constant Speed Prop (Whirlwind composite)
Notches per the plans
Fewer than 10 grass landings
Did the inspection this afternoon. One crack in the top left corner. Bummer!
RV-7A
635 hours
A little acro
A good bit of formation flying
180 HP Constant Speed Prop (Whirlwind composite)
Notches per the plans
Fewer than 10 grass landings
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We are doing the inspection on Tuesday.
No cracks found......
No cracks found......
BillL
Well Known Member
My count is 8 with Danny King being the first -8. I am making a list with hours to make a failure probability plot.
2-6's
4-7's
2-8
Considering 5000 planes flying this number is extremely low, not to mention the crack is a soft failure, and no incidents are known in the fleet. One would have thought the 6's would have more hours and be higher in the reporting, but not yet. The population reporting here must be quite limited. Surely it will unfold with time.
posts go too fast to update the count!!
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DougJ
Well Known Member
I concur! As I said in my post regarding my inspection results, I didn't like the look of that notch in the example photo in the SB. It appears to focus any stress into a smaller section, and the slightest roughness in that area would obviously make that significantly worse.
No cracks
No notches
RV-8, 0360, CS
Light Acro
Occasional grass
170 hours
No notches
RV-8, 0360, CS
Light Acro
Occasional grass
170 hours
Kahuna
Moderatoring
FWIW, 30% of our team aircraft found cracks.
Thats 3 of 10 RV-8's. We have an RV-4 that is of course not impacted by this.
We don't see much rhyme or reason or correlation other than time.
My fat, fast, heavy, 2k hour Super 8 did not show cracks. So high time, speed, weight, and long hours of edge of the envelop flying well beyond the design recommendations is not a direct correlation.
The 3 we found were all over 1k hour planes. We found none in the sub 1k hour planes. We have other planes nearing 2k hours and no sign. So again no direct correlation. We also inspected non team aircraft(we access and fly other RV's as well) and found cracks in a couple of those. Also over 1k hour planes. We are not going to be following or adding to this this thread much unless or until something more scientific and manageable takes place somewhere. Too hard to filter out the noise on these posts. So thats about all you will hear from us. We fly them hard, fast, often. PM me if you have any questions.
Thats 3 of 10 RV-8's. We have an RV-4 that is of course not impacted by this.
We don't see much rhyme or reason or correlation other than time.
My fat, fast, heavy, 2k hour Super 8 did not show cracks. So high time, speed, weight, and long hours of edge of the envelop flying well beyond the design recommendations is not a direct correlation.
The 3 we found were all over 1k hour planes. We found none in the sub 1k hour planes. We have other planes nearing 2k hours and no sign. So again no direct correlation. We also inspected non team aircraft(we access and fly other RV's as well) and found cracks in a couple of those. Also over 1k hour planes. We are not going to be following or adding to this this thread much unless or until something more scientific and manageable takes place somewhere. Too hard to filter out the noise on these posts. So thats about all you will hear from us. We fly them hard, fast, often. PM me if you have any questions.
Dan, I was thinking the same thing. Except this isn't about statistics. It's about increased stress in the spar member where it has a reduced area, due to these reliefs.
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Smilin' Jack
Well Known Member
I noticed in a lot of the photo's that where cracks exist even the slightest roughness or bend in the relief seems to be. I have zoomed in on most of the photos even including the one in the SB and you can see the roughness. Am I seeing something that is not there.
I would be interested if Vans comes up with a revision to this service bulletin down the road and offers a different fix.
The comments made about drilling out all the rivets and elongating the holes could make the repair worse than the fix.
I have no cracks, but will pull off the fiberglass fairing every oil change and take a look. I will order the kit and be prepared for a week or so of down time while doing the SB... I will use a very small drill bit on the rivet and work up to a larger size and try to only dislodge the head and punch out the body. I think that is the best option for not damaging holes.
Anyone else given any thought to their procedure? I think technique will matter in this repair and any suggestions could prove invaluable.
Jack
I would be interested if Vans comes up with a revision to this service bulletin down the road and offers a different fix.
The comments made about drilling out all the rivets and elongating the holes could make the repair worse than the fix.
I have no cracks, but will pull off the fiberglass fairing every oil change and take a look. I will order the kit and be prepared for a week or so of down time while doing the SB... I will use a very small drill bit on the rivet and work up to a larger size and try to only dislodge the head and punch out the body. I think that is the best option for not damaging holes.
Anyone else given any thought to their procedure? I think technique will matter in this repair and any suggestions could prove invaluable.
Jack
Walt
Well Known Member
Drilling out rivets when you can use a regular hand drill and have a straight shot at them is relative "childs play" compared to trying to drill out rivets at an odd angle, in an enclosed area, with a 90 deg drill. The latter is much more difficult to perform without messing up.
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LifeofReiley
Well Known Member
Jack, I think what you are seeing is real. I hope Van's also will also consider coming up with a revised SB as this seems to be extreme overkill for the issue. Or, supply the Build Numbers with a revised updated redesigned HS kit.
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curtis
Well Known Member
In these pictures the flange of the spar does not set flush with the skin and the skin looks pulled up just a bit. I wonder if this condition is putting a possible load on the flange exist on the other aircraft that have found cracks?
Pulled the fairing and at first look thought I was home free. One piqued my interest a little though so more cleaning and buffing and macro photography and the lower right relief had a crack about 3/16th of an inch. But, it's a crack.
In the really blown up photo you can see the relief was no smoothed and polished as well as it could have been. The other three were smooth and no cracks.
I'll fly some and when the parts are available I'll comply with the SB. The safety of the air frame is not in question as it stands right now.
1900 hours, lot's of acro, some grass.
205HP, CS.
Really hard to see any crack here but as I looked really close I could see a tine hair line running across the relief notch, which didn't look rough until I really macro'd and blew it up. see below
Here is a really zoomed in clear shot of the crack... a lot of work over a little crack..
Yes, I see that the bottom rivet is not set correctly, but thanks in advance for pointing that out..
I at least have not lost my sense of humor over this
flyboy1963
Well Known Member
one last time....any 9 issues?
Okay, now that the superbowl is over is there anything on the 9 worth looking at?...or is the structure so different, that it's moot!?
The -9 drivers have been absent from the discussion, so just want to put that to bed to save others unneeded concern.
Okay, now that the superbowl is over
is there anything on the 9 worth looking at?...or is the structure so different, that it's moot!?The -9 drivers have been absent from the discussion, so just want to put that to bed to save others unneeded concern.
kjowen
Well Known Member
Being a buyer and not the bulder of my -8....
... I assume (?) I can do the inspection and log book entries myself, although it would probably be prudent to get someone who has built an -8 to assist me, or am I mistaken? Since I'm not the builder, I understand I can't do annuals. So with that said, can I or can I not do a SB? I've read all the posts thus far and feel pretty confident in what I should be looking for, but I wouldn't mind an experienced set of eyes taking a look as well either way.
Additionally,
(Not to hijack the thread) but since I can not do my own annual since I'm not the builder, I know I'm going to have to find someone to perform my annual in July, and would appreciate any additional recommendations from the group ( I've gotten a few already). I would prefer someone with -8 or similar firsthand experience. A PM would be great!
Finally, what credentials are necessary for the individual who would be inspecting my -8? Do they have to be an IA, or just another -8 builder? If I do need an IA, wouldn't it be best to find one that also has -8 knowledge? Just wondering.... Would I self qualify to do my -8 annual once I complete my -14(sometime in the next ten years)?
Thanks for the help.
I'm going to take a look at mine sometime this week. I'll report results.
... I assume (?) I can do the inspection and log book entries myself, although it would probably be prudent to get someone who has built an -8 to assist me, or am I mistaken? Since I'm not the builder, I understand I can't do annuals. So with that said, can I or can I not do a SB? I've read all the posts thus far and feel pretty confident in what I should be looking for, but I wouldn't mind an experienced set of eyes taking a look as well either way.
Additionally,
(Not to hijack the thread) but since I can not do my own annual since I'm not the builder, I know I'm going to have to find someone to perform my annual in July, and would appreciate any additional recommendations from the group ( I've gotten a few already). I would prefer someone with -8 or similar firsthand experience. A PM would be great!
Finally, what credentials are necessary for the individual who would be inspecting my -8? Do they have to be an IA, or just another -8 builder? If I do need an IA, wouldn't it be best to find one that also has -8 knowledge? Just wondering.... Would I self qualify to do my -8 annual once I complete my -14(sometime in the next ten years)?
Thanks for the help.
I'm going to take a look at mine sometime this week. I'll report results.
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az_gila
Well Known Member
I was just going to post the same thing.
It may not be a cause - see Paul Dye's Valkyrie - but it must be creating a little extra stress when riveted.
It appears that the spar caps (the angle stock) on the outer portion, or the forward rib heights, are slightly higher than the flanged portion of the spar web - the area that did not get cut away.
Not being familiar with the later pre-punched kits, could this misalignment be more exaggerated with the pre-punched kits?
The original RV6 instructions even had a sketch to help keep this transition smooth.
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N363RV
Well Known Member
Were good.
Amanda refused to go out to the hangar with me. It was ~34 F. I got the fairing off pretty quick and began looking in the corners of the forward HS spar. I must admit that I have never looked here before. With my best flashlight I took a look. Thankfully we don't have any cracks. Whew! Regardless if we mod this or not, it is now on our perpetual inspection list.
6A
275 hours
O-360 A1A
Hartzel blended airfoil, 7497
We have the original tail (vertical). Some folks have the larger 7 tail on their sixes.
We have the relief radius.
We use only improved runways, with maybe the exception being 52F...
No aerobatics, but an occasional 3 g pull in some tight turns for fun.
Amanda refused to go out to the hangar with me. It was ~34 F. I got the fairing off pretty quick and began looking in the corners of the forward HS spar. I must admit that I have never looked here before. With my best flashlight I took a look. Thankfully we don't have any cracks. Whew! Regardless if we mod this or not, it is now on our perpetual inspection list.
6A
275 hours
O-360 A1A
Hartzel blended airfoil, 7497
We have the original tail (vertical). Some folks have the larger 7 tail on their sixes.
We have the relief radius.
We use only improved runways, with maybe the exception being 52F...
No aerobatics, but an occasional 3 g pull in some tight turns for fun.
Frank Smidler
Well Known Member
Testing data
Without a doubt I am sure that Van's did extensive finite element analyis and testing to determine root cause and validate the corrective action before issuing the SB. I remember touring thier old R&D shop in North Plains when they were developing the RV-8/7 machined flange main spars and they were in the process of load testing one that was fully instrumented with strain gages even back then (1994?). This is not coming from a one car garage company with a want-a-be Engineer. They have a very good professional staff of Engineers that I have a lot of confidence in. I just hope that they will volunteer to share a little more data from thier testing so that the "why" speculation can come to a close.
They are also a very concervative company in regards to the design of aircraft. If they had any serious concern about the short term affect of the crack thier response would have been elevated to a more critical level.
I have done plenty of strain gage testing on aluminum structures to determine caused of fatigue cracking and I can not see any obvious cause just by looking at the pictures. With out close inspection of many examples and test data any speculation is not of much value.
FYI, I can not get throught he snow to my hanger to inspect my plane yet. Maybe later int he week.
Without a doubt I am sure that Van's did extensive finite element analyis and testing to determine root cause and validate the corrective action before issuing the SB. I remember touring thier old R&D shop in North Plains when they were developing the RV-8/7 machined flange main spars and they were in the process of load testing one that was fully instrumented with strain gages even back then (1994?). This is not coming from a one car garage company with a want-a-be Engineer. They have a very good professional staff of Engineers that I have a lot of confidence in. I just hope that they will volunteer to share a little more data from thier testing so that the "why" speculation can come to a close.
They are also a very concervative company in regards to the design of aircraft. If they had any serious concern about the short term affect of the crack thier response would have been elevated to a more critical level.
I have done plenty of strain gage testing on aluminum structures to determine caused of fatigue cracking and I can not see any obvious cause just by looking at the pictures. With out close inspection of many examples and test data any speculation is not of much value.
FYI, I can not get throught he snow to my hanger to inspect my plane yet. Maybe later int he week.
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jthocker
Well Known Member
Redline will fix this!
Jerry has volunteered to be the guinea pig for us at Redline to fix this as per the service bulletin. We intend to document it this week, and come up with a plan to offer it as a service.
Pulled the fairing and at first look thought I was home free. One piqued my interest a little though so more cleaning and buffing and macro photography and the lower right relief had a crack about 3/16th of an inch. But, it's a crack.
In the really blown up photo you can see the relief was no smoothed and polished as well as it could have been. The other three were smooth and no cracks.
I'll fly some and when the parts are available I'll comply with the SB. The safety of the air frame is not in question as it stands right now.
1900 hours, lot's of acro, some grass.
205HP, CS.
Really hard to see any crack here but as I looked really close I could see a tine hair line running across the relief notch, which didn't look rough until I really macro'd and blew it up. see below
Here is a really zoomed in clear shot of the crack... a lot of work over a little crack..
Yes, I see that the bottom rivet is not set correctly, but thanks in advance for pointing that out..
I at least have not lost my sense of humor over this
Jerry has volunteered to be the guinea pig for us at Redline to fix this as per the service bulletin. We intend to document it this week, and come up with a plan to offer it as a service.
I don't hear any serious questioning of Van's Aircraft. As for the speculation, conjecture, and discussion - well, this is an Internet discussion board!
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You can do it yourself and log it. Fly over here and I'll look with you.
You can assist with the annual, said assistance being at the discretion of your A&P.
You can perform the SB modifications, but it will be a lot harder to do right than your RV-14 structure.
Just more data-I don't hear any serious questioning of Van's Aircraft. As for the speculation, conjecture, and discussion - well, this is an Internet discussion board!
RV7 tipup
300 hrs
Mild aero
Some grass
O-360 ECI
No cracks
Two more data points:
My RV-6:
Built 1996
~650 hours
O-320 150HP
Sensenich fixed pitch metal prop
Light aerobatics since I bought it at ~500 hours - Nothing over 4G
No notches, just a rounded corner
No cracks.
Another owner's RV-8 on the field:
Don't know hours
Completion ~2010
O-360
Hartzell constant speed
No notches
No cracks
We were talking about this and wonder if the correlation is the notches... Maybe one of the Team Aerodynamix guys can comment whether the forward spars on their airframes that didn't pass had notches or not?
My hangar-mate has another RV-6 that has been used for a lot of RV transition training, it's likely been abused more than any in our area... He hasn't checked his yet but when he does i'll either get him to post the results or i'll do it for him.
Looking forward to seeing the stats. Hopefully we'll see a spreadsheet with the data at some point?
My RV-6:
Built 1996
~650 hours
O-320 150HP
Sensenich fixed pitch metal prop
Light aerobatics since I bought it at ~500 hours - Nothing over 4G
No notches, just a rounded corner
No cracks.
Another owner's RV-8 on the field:
Don't know hours
Completion ~2010
O-360
Hartzell constant speed
No notches
No cracks
We were talking about this and wonder if the correlation is the notches... Maybe one of the Team Aerodynamix guys can comment whether the forward spars on their airframes that didn't pass had notches or not?
My hangar-mate has another RV-6 that has been used for a lot of RV transition training, it's likely been abused more than any in our area... He hasn't checked his yet but when he does i'll either get him to post the results or i'll do it for him.
Looking forward to seeing the stats. Hopefully we'll see a spreadsheet with the data at some point?
8 inspected today
Just FYI, without going into a lot of detail, our group in Central Ark and North LA inspected 8 RVs today. Including Mark Burns RV7a noted in the early posts. We have 1 (his) with cracks and 7 without.
Marks would be the high time model, and the rest would have 200-600 hours each.
Just an update today
Inspected 9 RVs total
8 were fine
1 crack in 7a
1 out of 8 for an 11% Crack rate
Just FYI, without going into a lot of detail, our group in Central Ark and North LA inspected 8 RVs today. Including Mark Burns RV7a noted in the early posts. We have 1 (his) with cracks and 7 without.
Marks would be the high time model, and the rest would have 200-600 hours each.
Just an update today
Inspected 9 RVs total
8 were fine
1 crack in 7a
1 out of 8 for an 11% Crack rate
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RVG8tor
Well Known Member
No Cracks
I inspected yesterday, not an old plane but 176 hour Tach time, 193 Hobbs
RV-8A
Hard Surface Only (so far!)
Fly often and upside down at least once each flight or nearly so
I never need to pull more than 3g unless I try, once it a while I pull more.
I do have the relief notch mine done almost identical to the SB, oddly enough.
I still have to remove the paint, the Jet Glo would not budge even with MEK.
Flew today and did several loops and other over the top stuff, felt very safe. Serious good day for cloud surfing!
Cheers
I inspected yesterday, not an old plane but 176 hour Tach time, 193 Hobbs
RV-8A
Hard Surface Only (so far!)
Fly often and upside down at least once each flight or nearly so
I never need to pull more than 3g unless I try, once it a while I pull more.
I do have the relief notch mine done almost identical to the SB, oddly enough.
I still have to remove the paint, the Jet Glo would not budge even with MEK.
Flew today and did several loops and other over the top stuff, felt very safe. Serious good day for cloud surfing!
Cheers
Captain Avgas
Well Known Member
Inadequate deburring
This is the second post that has raised this question ie. might the notches themselves be adding to the problem.
However I am inclined to believe that the problem is not with the relief notches per se. Logic would suggest that they should distribute stresses rather than concentrating them.
The big problem is that notches are much more difficult and time consuming to consistently deburr than straight edges due to difficulty of access.
Therefore what we may be discovering here is that many notches may be poorly deburred and thus worse than no notch at all.
Take a good look at the photo on the Vans SB. The straight edges all look deburred....but not the notches. And that's probably very common.
This is the second post that has raised this question ie. might the notches themselves be adding to the problem.
However I am inclined to believe that the problem is not with the relief notches per se. Logic would suggest that they should distribute stresses rather than concentrating them.
The big problem is that notches are much more difficult and time consuming to consistently deburr than straight edges due to difficulty of access.
Therefore what we may be discovering here is that many notches may be poorly deburred and thus worse than no notch at all.
Take a good look at the photo on the Vans SB. The straight edges all look deburred....but not the notches. And that's probably very common.
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Sheldon
Well Known Member
Inspected mine yesterday.. Dye Penetrate test..No cracks!
707 hrs RV6A 180 hp no acro no grass strips.
Smooth edge dressing to keep from having stress risers probably is the key. Even samples with relief notches, (done correctly or otherwise) have cracks..
I'll keep inspecting.. But there has to be an easier fix...??
707 hrs RV6A 180 hp no acro no grass strips.
Smooth edge dressing to keep from having stress risers probably is the key. Even samples with relief notches, (done correctly or otherwise) have cracks..
I'll keep inspecting.. But there has to be an easier fix...??
Tom Martin
Well Known Member
One thing that has not been discussed in this thread is the "grain" of the sheet metal. When I started my RV4 thirty years ago a very experienced airframe mechanic informed me about the grain of aluminium. When possible it would be better to form the radius of a bend across the grain of the sheet. Although a larger radius bend negates the necessity for this consideration the grain is still something to be concerned with. You can see the grain on the sheet as the very fine almost invisible lines on the surface. These are a function of the manufacture of the sheet. Try bending a tight radius with and against the grain and you will find that it cracks much easier when the grain is "with" or parallel to the bend.
The problem with making bends like this is that it is not practical to make all the bends 90 degrees to the grain as you would rapidly run out of useable parts of the sheet metal. Now to the parts in question.
In post 191, you can seen the grain in the bottom picture, and yes the crack follows the grain. I have not examined all the pictures but as this particular part is fairly long, probably over 48", the typical sheet width, then I suspect that all these spars are bent with the grain.
I am not a professionally trained sheet metal person but after 10 airplanes I certainly have a feel for metal and I wonder if "grain" could be a factor in these spar cracks.
The problem with making bends like this is that it is not practical to make all the bends 90 degrees to the grain as you would rapidly run out of useable parts of the sheet metal. Now to the parts in question.
In post 191, you can seen the grain in the bottom picture, and yes the crack follows the grain. I have not examined all the pictures but as this particular part is fairly long, probably over 48", the typical sheet width, then I suspect that all these spars are bent with the grain.
I am not a professionally trained sheet metal person but after 10 airplanes I certainly have a feel for metal and I wonder if "grain" could be a factor in these spar cracks.
