Today's Message Index:
----------------------
1. 04:21 AM - Re: Mass Balanced Ailerons (hansriet)
2. 06:41 AM - Re: Main gear flex (Leroy Wheeler)
3. 07:03 AM - Thoughts regarding Flutter ()
4. 07:05 AM - Re: Main gear flex (pavel569)
5. 08:17 AM - Re: Main gear flex (Jay Maynard)
6. 08:19 AM - Re: Thoughts regarding Flutter (Bill Budgell)
7. 09:12 AM - Re: Thoughts regarding Flutter (Gig Giacona)
8. 10:09 AM - Re: Thoughts regarding Flutter (n85ae)
9. 11:39 AM - Re: Thoughts regarding Flutter (Jeyoung65@aol.com)
10. 05:06 PM - Canopy install (AZFlyer)
11. 05:14 PM - Re: Thoughts Regarding Flutter (Larry Hursh)
12. 06:06 PM - Re: Re: Thoughts Regarding Flutter (Bryan Martin)
13. 06:12 PM - Re: Canopy install (jaybannist@cs.com)
14. 07:25 PM - Re: Re: Thoughts Regarding Flutter (Larry Hursh)
15. 08:58 PM - Re: Re: Re: Thoughts Regarding Flutter (Bryan Martin)
16. 09:32 PM - Re: Thoughts regarding Flutter (T. Graziano)
Message 1
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| Subject: | Re: Mass Balanced Ailerons |
All the mass of the Zodiac aileron is located behind the hinge, so an arm is necessary
to balance it.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=239675#239675
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Your best bet is to look at Larry McFarland's website. He's flying the same
configuration and has hundreds of hours on his HDS. I'm using the same
pipes and hoses he is and I've had good success with weight & balance so
far. I'm using the VW Diesel Rabbit Radiator (it's slightly larger),
Larry's scoop and an aluminum heater core. The water temp has never gone
over 180 degrees even at full static RPM. I think if you're going to
counterbalance the weight of the engine you might as well make the weight
useful.
Leroy Wheeler
N601LH About to certify
-----Original Message-----
From: owner-zenith601-list-server@matronics.com
[mailto:owner-zenith601-list-server@matronics.com] On Behalf Of pavel569
Sent: Thursday, April 16, 2009 4:07 PM
Subject: Zenith601-List: Main gear flex
One building question in this "grounding" war time.
Placement of my radiator. To have Stratus Subaru as my powerplant, I'm
trying to shift the water radiator as aft as possible to balance this
heavier engine. I have a set of Alu pipes for using with air intake from
Larry McFarland. They are 32" long and I'd like to keep the length as is. It
will move the radiator way back so it will be partially under the main gear.
Does anybody know how much the landing gear center section flexes down when
land hard? I can move the radiator up or down by fabricating its side
brackets.
Generally, is it a good idea or is it better to keep it forward, in front of
the gear channel?
--------
Pavel
CA
Zodiac XL N581PL (Reserved)
Stratus Subaru EA-81
Tail, flaps, ailerons, wings done, fuselage is on the table ....
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=239591#239591
Checked by AVG.
7:08 AM
Checked by AVG.
7:08 AM
Message 3
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| Subject: | Thoughts regarding Flutter |
I believe the problems that we are experiencing with the 601XL are not
the result of flutter or any other single issue but instead the result
of 4 specific and simultaneous factors that have caused the wing
failures of our aircraft.
First, why not flutter? Because in the instances that have been reported
to be flutter, the time that was required to identify the vibration and
to escape from its destructiveness has been too long (more than a few
seconds). My opinion is that we are seeing a simple harmonic vibration
of the ailerons that, depending on the tension in the cables, can be
considered as scary enough to cause real concern.
My first theory is that the problem we are seeing with the ailerons is
harmonic vibration, not flutter, and is dependent on the tension of the
cables. In my flight, the cables had loosened to the point that I could
feel a 1-2 inch movement of the stick without any corresponding movement
of the ailerons. As I went over the Valley River Mountains near Andrews,
NC, I could see the ailerons start to vibrate, so I decreased the
throttle and the vibration stopped. In another case locally, the pilot
had loose cables and, during flights above Va, experienced severe
vibration. He tested this by purposely flying into that portion of the
envelope repeatedly (observing the same type of vibration each time) and
then to test it again after tightening his cables. In his case, the
vibration stopped above Va. I believe that depending on the combination
of engine, aerodynamics and cable tension, the vibration of the ailerons
could be seen as mild or severe... but not flutter. Another possible
instance of severe vibration was a 601 in Georgia that experienced
vibration after flying over a power plant and which required a dive to
eliminate the vibration. It is known that to reduce flutter, you need to
reduce airpseed and pray. But in this case the means of reducing the
aileron vibration was to dive at speeds that were close to Vne. Not the
usual way to stop flutter and in any case, the resulting actions took
considerably longer than required to avoid desctruction from flutter. In
two of the three cases mentioned, the vibration was severe enough to
apparently cause movement of the wing, as stated by the pilots.
So, if the problem is just vibration how does that cause destruction of
the wings? My second theory is that the wings of every aircraft that has
failed to date was structurally compromised at some point in the history
of the aircraft. Recently, I was talking to a gentleman here in
Andrews, NC that was in the Lakeland bound 601 just a week or so before
it lost its wings and was destroyed. He stated that while flying with
the pilot over the mountains near here, they experienced what he
described as severe turbulance. He mentioned to the pilot how really bad
the turbulance was and the pilot stated that "this was nothing compared
to a week earlier". Apparently the turbulance was so bad that the pilot
called the experience "bone crushing". As for the Yuba City 601, the
owner of that aircraft had stated that there was an indication of
"smoking rivets" on the bottom of the wings. This condition usually is
the result of rivets becoming loose and creating a condition that
results in a decrease in structural integrity. The Yuba City aircraft
also (I believe) was flying near or in mountainess areas during its
history.
The third condition that must be met is looseness of the aileron cables.
I believe that vibration will not occur while the cables are tight.
And the fourth criteria for these wing failures is flying above Va
(maneuvering speed).
So to summarize, if these 4 conditions are met, the probability is high
for the aircraft to be lost even in mild turbulance.
Once again, they are:
1. Aileron Vibrations
2. Previous structural damage to the wings.
3. Loose Aileron Cables
4. Speeds above Va
I had originally thought that the only way we could explain the loss of
wings on the 601XL was from flutter, however, since 98% of the fleet has
not lost its wings and yet reports continue to surface of severe
vibration, loose cables, etc., it seems to me that there must be a
combination of problems that occur simultaneously that result in
destruction of the wings.
Anyone who has experienced severe turbulance should carefully look over
their wing roots for damage and avoid flight, especially if they also
have loose cables!
Scott Thatcher, N601EL
601XL with WW Corvair, 25 Hours
Just finishing first Condition Inspection
Message 4
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| Subject: | Re: Main gear flex |
Leroy,
I'm using the pipes and scoop and radiator louvers from Larry too. The only, but
important, difference is that I'm building 601XL not HDS with solid one piece
landing gear across the fuselage. However it may become an option in case they'll
limit speed of XL to 97 kts or so, I'll probably switch to HDS instead.
flyboy3847(at)onecommail. wrote:
> Your best bet is to look at Larry McFarland's website. He's flying the same
> configuration and has hundreds of hours on his HDS. I'm using the same
> pipes and hoses he is and I've had good success with weight & balance so
> far. I'm using the VW Diesel Rabbit Radiator (it's slightly larger),
> Larry's scoop and an aluminum heater core. The water temp has never gone
> over 180 degrees even at full static RPM. I think if you're going to
> counterbalance the weight of the engine you might as well make the weight
> useful.
>
> Leroy Wheeler
> N601LH About to certify
>
> --
--------
Pavel
CA
Zodiac XL N581PL (Reserved)
Stratus Subaru EA-81
Tail, flaps, ailerons, wings done, fuselage is on the table ....
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=239691#239691
Message 5
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| Subject: | Re: Main gear flex |
On Fri, Apr 17, 2009 at 09:41:16AM -0400, Leroy Wheeler wrote:
> Your best bet is to look at Larry McFarland's website. He's flying the same
> configuration and has hundreds of hours on his HDS.
This won't help. The original poster is building an XL, and he wants to know
if he can put the radiator beneath the gear center section - and the XL gear
is entirely different from the HD/HDS main gear.
--
Jay Maynard, K5ZC, PP-ASEL, AGI http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (KFRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC http://www.tronguy.net/N55ZC.shtml
Message 6
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| Subject: | Re: Thoughts regarding Flutter |
you should not assume anything at this time.- Assumptions in aircraft acc
idents are usually wrong'.
--- On Fri, 4/17/09, s_thatcher@bellsouth.net <s_thatcher@bellsouth.net> wr
ote:
From: s_thatcher@bellsouth.net <s_thatcher@bellsouth.net>
Subject: Zenith601-List: Thoughts regarding Flutter
onics.com, ZBAG@yahoogroups.com
Received: Friday, April 17, 2009, 9:55 AM
I believe the problems that we are experiencing with the 601XL are not the
result of flutter or any other single issue but instead the result of 4 spe
cific and simultaneous factors that have caused the wing failures of our ai
rcraft.
-
First, why not flutter? Because in the instances that have been reported to
be flutter, the time that was required to identify the vibration and to es
cape from its destructiveness has been too long (more than a few seconds).
- My opinion is that we are seeing a simple harmonic vibration of the ail
erons that, depending on the tension in the cables, can be considered as sc
ary enough to cause real concern.
-
My first theory is that the problem we are seeing with the ailerons is harm
onic vibration, not flutter, and is dependent on the tension of the cables.
In my flight, the cables had loosened to the point that I could feel a 1-2
inch movement of the stick without any corresponding movement of the ailer
ons. As I went over the Valley River Mountains near Andrews, NC, I could se
e the ailerons start to vibrate, so I decreased the throttle and the vibrat
ion stopped.- In another case locally, the pilot had loose cables-and,
during flights above Va, experienced severe vibration.-He tested this by
purposely flying into that portion of the envelope repeatedly (observing th
e same type of vibration each time) and then to test it again after tighten
ing his cables. In his case,-the vibration stopped above Va.-I believe
that depending on the combination of engine, aerodynamics and cable tension
, the vibration of the ailerons could be seen as mild or severe... but
not flutter.- Another possible instance of severe vibration was-a 601
in-Georgia that experienced-vibration after flying over a power plant a
nd which required a dive to eliminate the vibration. It is known that to re
duce flutter, you need to reduce airpseed and pray. But in this case the me
ans of reducing the aileron vibration was to dive at speeds that were close
to Vne. Not the usual way to stop flutter and in any case, the resulting a
ctions took considerably longer than required to avoid desctruction from fl
utter. In two of the three cases mentioned, the vibration was severe enough
to apparently cause movement of the wing, as stated by the pilots.
-
So, if the problem is just vibration how does that cause destruction of the
wings? My second theory is that the wings of every aircraft that has faile
d to date was structurally compromised at some point in the history of the
aircraft.- Recently, I was talking to a gentleman here in Andrews, NC tha
t was in the Lakeland bound 601 just a week or so before it lost its wings
and was destroyed. He stated that while flying with the pilot over the moun
tains near here, they experienced what he described as severe turbulance.
-He mentioned to the pilot how really bad the turbulance was and the pilo
t stated that "this was nothing compared to a week earlier". Apparently the
turbulance was so bad that the pilot called the experience-"bone crushin
g".- As for the Yuba City 601, the owner of that aircraft had stated that
there was an indication of "smoking rivets" on the bottom of the wings. Th
is condition usually is the result of rivets becoming loose and creating a
condition that results in a decrease in structural integrity. The Yuba Cit
y aircraft also (I believe) was flying near or in mountainess areas during
its history.
-
The third condition that must be met is looseness of the aileron cables.-
I believe that vibration will not occur while the cables are tight.
-
And the fourth criteria for these wing failures is flying above Va (maneuve
ring speed).
-
So to summarize, if these 4 conditions are met, the probability is high for
the aircraft to be lost even in mild turbulance.
-
Once again, they are:
1. Aileron Vibrations
2. Previous structural damage to the wings.
3. Loose Aileron Cables
4. Speeds above Va
-
I had originally thought that the only way we could explain the loss of win
gs on the 601XL was from flutter, however, since-98% of the fleet has not
lost its wings and yet reports continue to surface of severe vibration, lo
ose cables, etc., it seems to me that there-must be-a combination of pr
oblems that occur simultaneously that result in destruction of the wings.
-
Anyone who has experienced-severe turbulance should carefully look over t
heir wing roots for damage and avoid flight, especially if they also have l
oose cables!
-
Scott Thatcher, N601EL
601XL with WW Corvair, 25 Hours
Just finishing first Condition Inspection
-
Message 7
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| Subject: | Re: Thoughts regarding Flutter |
Seeing as how the NTSB notice is based on assumptions as well I think the forwarding
of other theories is most certainly in order.
ciuro wrote:
> you should not assume anything at this time. Assumptions in aircraft accidents
are usually wrong'.
>
>
--------
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=239712#239712
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| Subject: | Re: Thoughts regarding Flutter |
Well, I don't understand how you guys think? It's beyond me.
I for a period of time, got to spend right seat time with a now retired 747
captain, who had flown C-46's in WWII over the burma trail. I always
greatly admired him, because his decision making process was crystal
clear. He would get the info, and regardless of whether it was the answer
he "wanted" or not, he simply made the decision based on safety. Never
once did I see him ever say, "well maybe ..." No, he simply accepted that
something wasn't safe and he went with it as called.
Regards,
Jeff
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=239717#239717
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| Subject: | Re: Thoughts regarding Flutter |
Thatcher, Can you tell the older timer what is the difference between
"simple harmonic" and " flutter" ? Jerry of GA DO NOT ARCHIVE
In a message dated 4/17/2009 9:06:46 A.M. Eastern Standard Time,
s_thatcher@bellsouth.net writes:
My opinion is that we are seeing a simple harmonic vibration of the
ailerons that, depending on the tension in the cables, can be considered
as scary
enough to cause real concern.
**************Join ChristianMingle.com=AE FREE! Meet Christian Singles in
your area. Start now!
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atforma&adid=aolfooter&newurl=reg_path.html)
Message 10
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List,
I know everybody seems to have an opinion on the NTSB and FAA situation; however,
a couple of us are continuing to build and still need some questions answered.
My next question is: How much "re-bending" of the rear and front tubes did you'all
have to do to get the tubes to lay against the canopy smoothly, prior to
drilling for screws? I find I have as much as 1/4" off the rear tube as I move
down from top-center toward either longeron.
...in other words:
>From "top-center, in either direction, about a foot of canopy rests against the
rear tube." Then canopy comes off tube gradually until perhaps 1/4" at longeron.
Re-bending those tubes is REALLY fun.
Thanks for any input.
Mike
--------
Mike Miller @ millrml@aol.com
601 XL, 3300, Dynon
Remember, "the second mouse gets the cheese"!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=239803#239803
Message 11
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| Subject: | Re: Thoughts Regarding Flutter |
Sorry guys but all of this to me is nothing more than wild speculation. I am finding
all the bantering to be depressing at best. It's gotten so bad for, I
haven't touched a rivet or drill since all of this mess came out. I honestly
don't expect anyone from Zenith Aircraft to step up and work with the NTSB willingly.
Zenith has stated and restated that the problem is wing flutter. Their
claim is its being caused by poorly or improperly maintained tension on the
cables tensions. I think there has been a line drawn in the sand and neither
the NTSB or Zenith is going to give one iota. The NTSB is forcing the issue
by posting their statement publicly and asking the FAA to ground all of our aircraft
until further notice. Once again, Zenith claims poor tension. Nothing
gives. The next decision will most likely come from the FAA in a formal notice.
If they do ground all 601's (and 650's) this will force Zenith to work with
the NTSB. If Zenith refuses,
then we, the customers are left out in the cold. As I said before, I'm finding
this all depressing so I am going to STOP reading all these posts and WILL search
on the FAA daily for any updates or notices. I just hope the Heinz family
realizes very soon, SOMETHING has to be done - even if its nothing more than
to sit down with the NTSB AND the FAA and acknowledge there COULD possibly be
a design issue - EVERYTHING has to be ruled out. It's our lives we are talking
about here. To stand back as Zenith has done and claiming its poor maintenance
is a cop out, big time. Its VERY POOR customer service. I just hope Zenith
Aircraft can see this.....Of course this is all my opinion. Stepping off
my soapbox now.
Larry Hursh
Edwardsburg, Michigan
Zenith CH650 (N650LM Reserved)
I hope someday I can be the person my dog thinks I am.....
Message 12
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| Subject: | Re: Thoughts Regarding Flutter |
Zenith doesn't have to work with the NTSB. The NTSB has absolutely no
authority in the matter. It's the FAA that has the authority, all the
NTSB can do is advise. The FAA is free to ignore that advise as they
see fit. The NTSB notice does not make any mention of the 650 so, so
far that model is in the clear. The FAA may be able to ground the S-
LSA version to the 601XL as they have a standard certificate of some
sort to go after. As far as the E-AB versions of the XL are concerned,
the FAA would have to ground each airplane on an individual basis,
because there is no type certificate to take action against. Each is
considered a one of a kind airplane and the paperwork does not even
have to contain Zenith or Zodiac or CH 601 XL, the builder can call it
anything he wants to and many builders probably have done so. The FAA
doesn't have the resources to track down every homebuilt variant of
the 601XL to make the attempt to ground them.
On Apr 17, 2009, at 8:13 PM, Larry Hursh wrote:
> >
>
>
> Sorry guys but all of this to me is nothing more than wild
> speculation. I am finding all the bantering to be depressing at best.
--
Bryan Martin
N61BM, CH 601 XL,
RAM Subaru, Stratus redrive.
do not archive.
Message 13
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| Subject: | Re: Canopy install |
Mike,
I marked the coordinates for the tubes (from the drawings) on one of those large
thick corrugated cardboard sheets that was in a packing crate from ZAC.? I cut
along the line.? I took that template to the fuselage and tried it out on the
bubble.? I made a few iterations of the curve to get it to fit the bubble,
trimming it as needed.? I adjusted the tubes to fit the final cut.? I still had
some gaps of 1/8" or less in the rear one.? I had no trouble fastening the bubble
to the tubes. I started drilling and clecoing from the center and worked
outward. ? Just make sure that any work you do with the bubble is at 80 degrees
or above, preferably above.?
Jay Bannister
-----Original Message-----
From: AZFlyer <millrML@AOL.com>
Sent: Fri, 17 Apr 2009 7:05 pm
Subject: Zenith601-List: Canopy install
List,
I know everybody seems to have an opinion on the NTSB and FAA situation;
however, a couple of us are continuing to build and still need some questions
answered.
My next question is: How much "re-bending" of the rear and front tubes did
you'all have to do to get the tubes to lay against the canopy smoothly, prior to
drilling for screws? I find I have as much as 1/4" off the rear tube as I move
down from top-center toward either longeron.
....in other words:
>From "top-center, in either direction, about a foot of canopy rests against the
rear tube." Then canopy comes off tube gradually until perhaps 1/4" at
longeron.
Re-bending those tubes is REALLY fun.
Thanks for any input.
Mike
--------
Mike Miller @ millrml@aol.com
601 XL, 3300, Dynon
Remember, "the second mouse gets the cheese"!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=239803#239803
________________________________________________________________________
Email message sent from CompuServe - visit us today at http://www.cs.com
Message 14
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| Subject: | Re: Re: Thoughts Regarding Flutter |
Bryan, don't try to fool yourself or anyone else on this list. When I originally
purchased my wing kit, it came with the hinge-less ailerons and the new style
fiberglass wingtips. I "converted" my fuselage kit to the 650 within the week
of it being introduced at Oshkosh last year. MY WINGS ARE THE EXACT SAME
WINGS AS THE 601. To "upgrade" them, I added the "L" brackets for the oil canning.
I added the gussets at the first and second rib on the ailerons. THAT'S
IT. The only major differences (besides the new style rudder) is the angle
of the main spar center section. On the original 601 the angle was set at 9 degrees.
With the 650 the main spar center section is now 7 degrees. It's for
better "forward visibility". Don't try kidding anyone on here about "being in
the clear" Bryan - your NOT in the clear. Its exactly the same wing with the
same flaps and same ailerons because mine WAS a 601. I know. You don't, so
quit trying to mislead people
about that on here. If you doubt me, call Zenith. You need the number???
Larry Hursh
Edwardsburg, Michigan
Zenith CH650 (N650LM Reserved)
Message 15
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| Subject: | Re: Re: Thoughts Regarding Flutter |
I'm not trying to fool anybody, all I said is the CH 650 is not
mentioned in the NTSB report. We are dealing with buearocrats here,
nomenclature is everything. If it's not specifically mentioned, it is
not included. It doesn't matter if it's physically the same.
Don't tell me what I don't know, You don't know what I don't know.
On Apr 17, 2009, at 10:24 PM, Larry Hursh wrote:
> >
>
>
> Bryan, don't try to fool yourself or anyone else on this list. When
> I originally purchased my wing kit, it came with the hinge-less
> ailerons and the new style fiberglass wingtips. I "converted" my
> fuselage kit to the 650 within the week of it being introduced at
> Oshkosh last year. MY WINGS ARE THE EXACT SAME WINGS AS THE 601.
> To "upgrade" them, I added the "L" brackets for the oil canning. I
> added the gussets at the first and second rib on the ailerons.
> THAT'S IT. The only major differences (besides the new style
> rudder) is the angle of the main spar center section. On the
> original 601 the angle was set at 9 degrees. With the 650 the main
> spar center section is now 7 degrees. It's for better "forward
> visibility". Don't try kidding anyone on here about "being in the
> clear" Bryan - your NOT in the clear. Its exactly the same wing
> with the same flaps and same ailerons because mine WAS a 601. I
> know. You don't, so quit trying to mislead people
> about that on here. If you doubt me, call Zenith. You need the
> number???
--
Bryan Martin
N61BM, CH 601 XL,
RAM Subaru, Stratus redrive.
do not archive.
Message 16
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| Subject: | Re: Thoughts regarding Flutter |
Additional thoughts, Scott
Sounds reasonable. I thought about replacing cables with push rods, but
then thought that the natural freq of a rod would probably be lower than
a tensioned cable and more likely to resonate.
Today as I was up enjoying the sky in my XL, I crossed mid-field and
broke to down wind and it reminded my of another reconstructed crash at
the crash lab at March AFB during a course I took in Aircraft Accident
Investigation at USC thirty years ago.
It was an AeroCommander Twin that shed its wings.
The physical investigator instructor, (who was also my undergraduate
instructor in Rotary Wing Aerodynamics years prior) related that he was
requested to investigate the wing failure of another Twin Commander, I
believe that occurred in Co. If I recall correctly, the Commander made
a mid-field crossing and broke to down wind and had a wing structural
failure which was attributed to pilot error causing the overload. The
instructor related that there were also other Commanders that had had
the same failure.
What he discovered (and I have the plot somewhere in my class notes,
buried ?) was that the stick forces per G went NEGATIVE at about 4 Gs.
Imagine the yoke coming back in your lap and the wing fails due to
overload, if above Va. (There was an AD issued to require a weight in
the control system to pull the stick under G loading (bob weights have
been used in many aircraft control systems).
The reason I bring this up is that I still believe the XL light stick
forces can easily result excessive G loading and are quite possibly the
REAL reason for the wing failures. Not that light stick forces are bad,
but one has to not be ham fisted above Va. (I previously related giving
an older pilot a ride in my XL during a pretty turbulent day and he
pushed the stick rapidly nose down such that I would have gone through
the canopy without a seat belt. This happened during climb out at
about 80 - 90kts and the gusty conditions had caused a pitch up.(still
can not believe another pilot would have done that, but possibly his
Tomahawk had a much different elevator response).
Somehow, some people jumped on the flutter bandwagon, and as another
matronics "inputer" stated - "and so it was"
What really concerns me is that the NTSB might wish to make a "Science
Project" (Note) over additional flutter testing of the XL. They
evidently do not wish to accept the successful flutter tests already
done by Zenith (see page 6 of the NTSB report).
Note:
A Science Project is where you spend all of your resources
but never come up with a result that is acceptable to the government
because additional tests or analytical parameters are ALWAYS required.
("You only tested (or modeled) down to -40F. We require additional
testing at -65F ......and on ....and on ..and ..............").
Tony Graziano
Buchanan, Tn
XL/Jab; N493TG; 483 really great hours in my XL
----- Original Message -----
From: s_thatcher@bellsouth.net
To: corvaircraft@mylist.net ; zenith-list@matronics.com ;
zenith601-list@matronics.com ; ZBAG@yahoogroups.com
Sent: Friday, April 17, 2009 8:55 AM
Subject: Zenith601-List: Thoughts regarding Flutter
I believe the problems that we are experiencing with the 601XL are not
the result of flutter or any other single issue but instead the result
of 4 specific and simultaneous factors that have caused the wing
failures of our aircraft.
First, why not flutter? Because in the instances that have been
reported to be flutter, the time that was required to identify the
vibration and to escape from its destructiveness has been too long (more
than a few seconds). My opinion is that we are seeing a simple harmonic
vibration of the ailerons that, depending on the tension in the cables,
can be considered as scary enough to cause real concern.
My first theory is that the problem we are seeing with the ailerons is
harmonic vibration, not flutter, and is dependent on the tension of the
cables. In my flight, the cables had loosened to the point that I could
feel a 1-2 inch movement of the stick without any corresponding movement
of the ailerons. As I went over the Valley River Mountains near Andrews,
NC, I could see the ailerons start to vibrate, so I decreased the
throttle and the vibration stopped. In another case locally, the pilot
had loose cables and, during flights above Va, experienced severe
vibration. He tested this by purposely flying into that portion of the
envelope repeatedly (observing the same type of vibration each time) and
then to test it again after tightening his cables. In his case, the
vibration stopped above Va. I believe that depending on the combination
of engine, aerodynamics and cable tension, the vibration of the ailerons
could be seen as mild or severe... but not flutter. Another possible
instance of severe vibration was a 601 in Georgia that experienced
vibration after flying over a power plant and which required a dive to
eliminate the vibration. It is known that to reduce flutter, you need to
reduce airpseed and pray. But in this case the means of reducing the
aileron vibration was to dive at speeds that were close to Vne. Not the
usual way to stop flutter and in any case, the resulting actions took
considerably longer than required to avoid desctruction from flutter. In
two of the three cases mentioned, the vibration was severe enough to
apparently cause movement of the wing, as stated by the pilots.
So, if the problem is just vibration how does that cause destruction
of the wings? My second theory is that the wings of every aircraft that
has failed to date was structurally compromised at some point in the
history of the aircraft. Recently, I was talking to a gentleman here in
Andrews, NC that was in the Lakeland bound 601 just a week or so before
it lost its wings and was destroyed. He stated that while flying with
the pilot over the mountains near here, they experienced what he
described as severe turbulance. He mentioned to the pilot how really bad
the turbulance was and the pilot stated that "this was nothing compared
to a week earlier". Apparently the turbulance was so bad that the pilot
called the experience "bone crushing". As for the Yuba City 601, the
owner of that aircraft had stated that there was an indication of
"smoking rivets" on the bottom of the wings. This condition usually is
the result of rivets becoming loose and creating a condition that
results in a decrease in structural integrity. The Yuba City aircraft
also (I believe) was flying near or in mountainess areas during its
history.
The third condition that must be met is looseness of the aileron
cables. I believe that vibration will not occur while the cables are
tight.
And the fourth criteria for these wing failures is flying above Va
(maneuvering speed).
So to summarize, if these 4 conditions are met, the probability is
high for the aircraft to be lost even in mild turbulance.
Once again, they are:
1. Aileron Vibrations
2. Previous structural damage to the wings.
3. Loose Aileron Cables
4. Speeds above Va
I had originally thought that the only way we could explain the loss
of wings on the 601XL was from flutter, however, since 98% of the fleet
has not lost its wings and yet reports continue to surface of severe
vibration, loose cables, etc., it seems to me that there must be a
combination of problems that occur simultaneously that result in
destruction of the wings.
Anyone who has experienced severe turbulance should carefully look
over their wing roots for damage and avoid flight, especially if they
also have loose cables!
Scott Thatcher, N601EL
601XL with WW Corvair, 25 Hours
Just finishing first Condition Inspection
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