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a.s.elliott(at)cox.net
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 Posted: Sun Aug 26, 2007 1:19 pm Post subject: 601XL Rear Spar Reinforcement Idea |
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Gang:
There has been some concern about the unexpected in-flight failures of
various 601XL's. As an experienced (Ph.D. + 25 years) aerospace engineer,
I am tempted to brush these off as "cause unknowable" due [1]to the large
number of unknown variables in construction, maintenance and operation of the
accident aircraft, and [2] the lack of available data about the accidents
themselves. That is my "official" opinion.
A few people have asked me about this, however, so I took a good look at the
1/2 built wings in my garage. Knowing that the wings have passed static proof
tests, I looked mainly for what you might call "less than optimal" design
features, including places in the design where a reasonable error in
construction might lead to a more serious condition.
The only thing I found was that the clearance hole for the aileron pushrod is
rather large and is located rather close to the rear spar lower flange. It would
be easy during construction to make this hole closer to, or even touch the flange.
Since the top and bottom of the spar carry the large part of the wing bending
load, this *could* weaken the spar.
NOTE: This is an analytical discussion, not support by experimental evidence.
In engineering one often lacks complete data, and in those cases you look for
ways to mitigate risk. If the cost of mitigating the risk is large,
you may decide to do more extensive analysis or experimental testing.
If the cost of mitigating the risk is small, however, you might just decide
to go ahead and do the fix regardless. That is what I chose to do.
So I cut a piece of .025 standard angle to a length will cover the three
A5 rivet holes in the bottom flange on both sides of the aileron pushrod hole.
I bent the piece to match the angle of the spar flange, then trimmed it to fit
flush with the flange and also to clear the exit hole. Finally, I match drilled
it to the spar, deburred and primed.
Complete details and pictures of this "fix" are available on line at:
http://members.cox.net/n601ge/drawings/rearspar.html
This small doubler strap reinforces the flange in that section of the spar, and
thereby helps transfer wing bending loads across the hole. It has many good
characteristics:
* It takes about an hour to make and install.
* Installed, it is invisible.
* It does not interfere with aileron operation.
* It weighs approximately nothing.
* It costs approximately nothing.
* It can be easily retrofit to completed wings.
and no bad ones that I know of, and therefore fits the requirements
for risk mitigation, IMHO. So I'm putting them on my plane. If you think
differently, please do not put them on your plane. If you think my analysis
is flawed, please correspond with me off-group.
All standard disclaimers apply, etc. FWIW,
Andy Elliott, Mesa, AZ
N601GE (reserved)
601XL/TD/QB, Corvair, building...
[quote][b]
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Jaybannist(at)cs.com
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| Posted: Sun Aug 26, 2007 2:33 pm Post subject: 601XL Rear Spar Reinforcement Idea |
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Andy,
Your reinforcing looks reasonable. Just don't forget that, on the inboard part of this reinforced area, the flap hinge will go between the bottom skin and the bottom flange of the rear spar. And that hinge won't be riveted until much later.
On my particular airplane, the drawings called for a 38mm hole, 20mm from the bottom of the bottom flange. That leaves less than 1mm between the hole and the flange. The hole was later changed to a 32mm dia., leaving about a 4mm clearance; which I suspect is what you have. I might measure the clearance between the flange and the control rod end to see if I can partially cover the hole with the reinforcing angle.
Instead of trimming the vertical leg fo the doubler angle, I think I would only notch it (at the hole) and put some A4 rivets into the web of the spar to help resist buckling of the doubler angle.
Just my 2 cents worth.
Jay
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malcolmhunt(at)mha1.fsbus
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| Posted: Wed Aug 29, 2007 11:02 am Post subject: 601XL Rear Spar Reinforcement Idea |
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Hi Jay
Where did you get the information on the 32mm dia hole from? I have looked
up the revisions to the drawings and cannot see it.
Has anyone on the list made the spar cap angles (6W3-6&7) in two pieces to
bend them on a 8' brake? I have e-mailed Zenair technical people asking
their veiws without a reply. I wonder if they are still considering the
implication for the load test of the wing as noted in this months
newsletter?
Best regards
Malcolm Hunt
CH601XL Plans Builder in England
---
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Jaybannist(at)cs.com
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| Posted: Wed Aug 29, 2007 12:11 pm Post subject: 601XL Rear Spar Reinforcement Idea |
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Malcolm,
There is a section of the Zenith web site for builders. You must log in with a user name and password (which are available from Zenith) In that section there is an option to choose Zodiac XL and then select "For the lateset Drawings updates". This change can be found under "updates 2006" in the 3rd edition 3rd revision. I didn't locate this information until I had already drilled the 38mm hole.
| Quote: | From their we site, I surmise that they have already done the re-testing, but just have not compiled and published the results.
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Jay in Dallas
"Malcolm Hunt" <malcolmhunt(at)mha1.fsbusiness.co.uk> wrote:
| Quote: |
Hi Jay
Where did you get the information on the 32mm dia hole from? I have looked
up the revisions to the drawings and cannot see it.
Has anyone on the list made the spar cap angles (6W3-6&7) in two pieces to
bend them on a 8' brake? I have e-mailed Zenair technical people asking
their veiws without a reply. I wonder if they are still considering the
implication for the load test of the wing as noted in this months
newsletter?
Best regards
Malcolm Hunt
CH601XL Plans Builder in England
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malcolmhunt(at)mha1.fsbus
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| Posted: Wed Aug 29, 2007 1:11 pm Post subject: 601XL Rear Spar Reinforcement Idea |
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Thank Jay will have a look
Do not archive
Malcolm
---
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dfmoeller
Joined: 19 Jun 2006
Posts: 60
Location: Austin, TX
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| Posted: Wed Aug 29, 2007 3:22 pm Post subject: Re: 601XL Rear Spar Reinforcement Idea |
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Not to be contrarian here, but I believe that change is actually the developed length of the hinge doubler, not the aileron rod hole. I have both the original issue drawings from 2001 and the 3/06 drawing set. The size of the hole is 38 mm (or 1 1/2") on both. The only difference is that in the original set, the distance from the flange was several mm more. That change was done very early though. Your 38 mm holes are still the correct size.
I agree that adding a doubler or some sort of reinforcement, around that hole is extremely cheap insurance and I am adding it!
Doug
| Jaybannist(at)cs.com wrote: | Malcolm,
There is a section of the Zenith web site for builders. You must log in with a user name and password (which are available from Zenith) In that section there is an option to choose Zodiac XL and then select "For the lateset Drawings updates". This change can be found under "updates 2006" in the 3rd edition 3rd revision. I didn't locate this information until I had already drilled the 38mm hole.
| Quote: | From their we site, I surmise that they have already done the re-testing, but just have not compiled and published the results.
|
Jay in Dallas
"Malcolm Hunt" <malcolmhunt> wrote:
| Quote: |
Hi Jay
Where did you get the information on the 32mm dia hole from? I have looked
up the revisions to the drawings and cannot see it.
Has anyone on the list made the spar cap angles (6W3-6&7) in two pieces to
bend them on a 8' brake? I have e-mailed Zenair technical people asking
their veiws without a reply. I wonder if they are still considering the
implication for the load test of the wing as noted in this months
newsletter?
Best regards
Malcolm Hunt
CH601XL Plans Builder in England
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Scotsman
Joined: 27 Aug 2007
Posts: 89
Location: Johannesburg, South Africa
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| Posted: Thu Aug 30, 2007 7:00 am Post subject: Re: 601XL Rear Spar Reinforcement Idea |
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Andy et al.
Just browsing through the accident reports I was wondering, as I haven't received my ordered kit, if you noted any potential design "problems" around about the 6 feet inboard mark as I noted that NTSB did specify additional damage in this area?
"The leading edge wing skins for both wings had separated from the wing spars and ribs about 6 feet from the wing tip inboard"
Is there any possibility that the wing baggage locker space set could interfere with the structure stability of the wing under a torsional load?
j
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psm(at)ATT.NET
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| Posted: Thu Aug 30, 2007 7:46 am Post subject: 601XL Rear Spar Reinforcement Idea |
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I suspect the area mentioned is around the end of the fuel tank in
the nose of the wing. I personally didn't worry too much about that
part of the report.
Of course, I'm no expert -- just another builder.
Paul
XL fuselage
do not archive
At 08:00 AM 8/30/2007, you wrote:
| Quote: |
<james.roberts(at)computershare.co.za>
Andy et al.
Just browsing through the accident reports I was wondering, as I
haven't received my ordered kit, if you noted any potential design
"problems" around about the 6 feet inboard mark as I noted that NTSB
did specify additional damage in this area?
"The leading edge wing skins for both wings had separated from the
wing spars and ribs about 6 feet from the wing tip inboard"
Is there any possibility that the wing baggage locker space set
could interfere with the structure stability of the wing under a
torsional load?
j
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=131798#131798
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pchapman(at)ionsys.com
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| Posted: Thu Aug 30, 2007 8:33 am Post subject: 601XL Rear Spar Reinforcement Idea |
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At 11:00 30-08-07, you wrote some stuff that was pretty suspicious
about 601 structural integrity:
| Quote: |
<james.roberts(at)computershare.co.za>
"The leading edge wing skins for both wings had separated from the
wing spars and ribs about 6 feet from the wing tip inboard"
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This is re: the 601 XL in report LAX06LA105.
Considering that the aircraft spun in with both wings folded, and the
spars were extensively bent from the inflight failure and crash, the
simple fact that leading edge skins had separated is of no real concern to me.
| Quote: | Is there any possibility that the wing baggage locker space set
could interfere with the structure stability of the wing under a
torsional load?
|
Of course it reduces it but the design analysis used on homebuilts is
not like airliners where more is taken into account. I'll guess that
all anticipated torsional loads can be handled by the main and rear
spar and ribs alone. Or perhaps the leading edge box was taken into
account too for the torsional strength it can give. Any skin
stiffness is then bonus.
From another post:
| Quote: | Makes you wonder what was reduced/removed to facilitate this? j
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If that refers to the UL being lighter weight than the HD, you've got
it turned around. They didn't take stuff out of the HD to make the
UL; the UL came first and later was beefed up into the HD.
Peter Chapman
Toronto, ON
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