Zenair safety?

[LarryMcG]

Moderators, please move this, if not appropriate here.

Off the sonex forum,

SNIP

Like most here, I looked at the 601 series as well. The XL was rather
new when I was making the big decision, but had suffered two in-flight
breakups:
http://ntsb.gov/ntsb/brief.asp?ev_id=20 ... 0209&key=1
http://ntsb.gov/ntsb/brief.asp?ev_id=20 ... 1677&key=1

I then considered the 601HDS, but the factory said they considered it
an inferior design, in spite of the much better accident history.
They weren't really interested in selling a HDS kit to me. Then about
the same time I attended the Sonex workshop, another 601XL broke up in
flight:
http://ntsb.gov/ntsb/brief.asp?ev_id=20 ... 0539&key=1

Then, last month:
http://ntsb.gov/ntsb/brief.asp?ev_id=20 ... 0519&key=1

Note that these aircraft were built by different parties and that at
least one of the aircraft was built professionally by AMD. My humble
opinion: there is a design problem with the wings. The FAA has been
working with Zenith trying to resolve the issue, I read somewhere.

This is a very sad set of facts for those who died and for the rest of
the experimental aviation community. The Zodiacs are very comfortable
aircraft, although not as much fun to fly, from my limited experiences
flying two 601XLs and a Sonex.

Note that the RV-3 went through a similar series of accidents years
ago, and that the main spar of the wing was redesigned as a result.

The one Sonex that crashed resulting in the death of the owner/pilot
(but not the builder) sole-occupant likely went down due to, in part
at least, the medical condition of the Sport Pilot's undiagnosed diabetes.
http://ntsb.gov/ntsb/brief.asp?ev_id=20 ... 1218&key=1

Last time I checked, no Sonex had broken up or suffered a structural
failure in-flight. A few have crashed and even inverted due to the
usual causes (fuel exhaustion, for instance) and not come apart.
Seems to be a very tough airplane, in addition to being a rather
inexpensive one.

The AeroVee doesn't come up much in the NTSB database either, although
I haven't been as diligent in my research since I'm going with the
Jabiru 3300. (Mountains out here on the west coast!)

[justin.schoeman]

NTSB Accident Data for Zenith, Zodiac, Zenair, 801, 701, 601, amd, czech as of 05/12/2008 04:04 PDT:

http://www.cleanh2o.com/633z/nstb/

The Zodiac XL does seem to have a bad record, but the HD and HDS don't seem to have any structural failures - only the usual assortment of engine failures and pilot error.

The Sonex is an aerobatic plane, so is structurally much stronger. Just has an extremely narrow cabin...

[grostek]

Hi All,

I Had look at the Matronics list and found the post quoted below about the wing failures.

Certainly food for thought.

Makes sense that the 601 HD and HDS are slower with their thick wing , so probably do not get near "flutter" speeds, wherever that may be.

Balancing the control surfaces on any aircraft makes good sense, Bud Evans even did it on the lowly VP1 and VP2 and they certainly are not speed machines.

IMHO balancing control surfaces on any aircraft is insurance against the unexpected.

Kind regards,

Gunter Rostek.

PS Are the control surfaces of the Sonex/Waiex balanced?



Quote
Subject: Re: Recent crashes From: "ashontz" <ashontz(at)nbme.org> Date: May 13, 2007

I think it's definitely worth looking into.

[quote="robert.eli(at)comcast.net"]David and other interested folks,

After reading the latest flurry of Emails on the 601 wing structural failures,
I will attempt to clarify what I was hypothesizing about wing flutter. It is
my understanding that flutter problems most frequently involve control surfaces,
for which designers have methods to reduce the probability of its occurrence.
It is also my understanding that there are problems that occasionally
occur involving divergent structural vibrations (flutter) that cannot be predicted
even by the best designers, of which Chris Heintz is certainly one (I have
the greatest respect and admiration for Chris).

I recall many years ago the difficulties the turboprop Lockheed Electra had with
a string of wing failures traced to a type of torsional flutter introduced
by the engines. The Electra wing was extremely strong and withstood every load
test that the engineers could throw at it, and it took months, if not years,
of work by 100's of the best engineers Lockheed had to finally pinpoint the
problem. The point to be made is that structural strength alone cannot save
a wing if it can be induced to flutter in a divergent (unstable) fashion.
Even the strongest wing (or any other structure) can be failed if it has a mode
of vibration that is unstable (has a vibration for which the amplitude is
increasing with time). Another classic example is the "Galloping Gertie" suspension
bridge failure that I am sure everyone has seen in the famous documentary
film.

The hypothesis is (and it is just that; a long shot, out-of-the-box possibility)
that the 601XL wing has a torsional stiffness (resistance to twist) that
would normally be sufficient for a safe design; however, due to some combination
of structural and aerodynamic characteristics, it is insufficiently stiff
to damp a particular type of torsional flutter. This characteristic would not
necessarily have any relationship to the wing's strength as normally measured
by load tests or design calculations. A further feature of this hypothesis
is that the center of lift of the outer sections of the wing produces a twisting
force moment that tends to increase with the angle of twist (angle of attack).
The process would be initiated by some abrupt maneuver, wind shear, or
whatever, that produces some greater than typical twist in the outer section
of the wing, which in turn, introduces more twist due to the local increased
angle of attack. The whole process would depend on a natural torsional frequency
of vibration of the wing that is "in tune" with an oscillating aerodynamic
load that tends to produce progressively more twist with each oscillation
of the vibration. This process, if it were to occur, would progress very quickly
(a matter of a second or two), until finally the structural strength of
the wing skin and rivets would be exceeded. Using some educated guessing, I would
suspect that the primary mode of failure would be the wing skin rivets where
they attach to the ribs and spar (by hole elongation and rivet shear). As
this mode of failure progresses, the spars would be twisted beyond the yield
point (leaving a twisted spar) and the failure would cascade on down to the
fuselage attach points.

All of this is probably, as someone suggested, overdone hysterics; but I can't
shake the two very strange incidents that were reported here with regard to
the observed wing flutter immediately prior to the wings "folding back" in the
one crash, and the observations of a pilot who experienced the severe wing
vibration over the powerplant cooling towers. Maybe these two reports are not
based in fact, but I took them to be reliable accounts.

Bob Eli

> ---


--------
Andy Shontz
CH601XL - Corvair
www.mykitlog.com/ashontz


Read this topic online here:

http://forums.matronics.com/viewtopic.p ... 613#112613

End Quote

[LarryMcG]

Hi Gunter

Yes, got a big chunk of lead on the Aileron, extending into the wing, and gives us specs etc for balancing before finishing, on both the sonex and waiex.

L

[grostek]

Hi Larry,

Glad to hear that the Sonex/Waiex surfaces are balanced.


Kind regards,

Gunter Rostek.

[Morph]

to me the wierdest thing on the Zenair CH601 is the ailerons. (See attached pic) the top surface aluminium skin extends all the way over the top of the wing to the back of the airleron. The up and down movement of the aileron relies on the flexing on the aluminium sheeting at point A.

[grostek]

Hi Morph,

Chris Heinz explains his Hingeless Aileron here including the testing to make sure it is safe.

http://www.zenithair.com/kit-data/ht-aileron.html

Kind regards,

Gunter Rostek.

[Rudix]

to me the wierdest thing on the Zenair CH601 is the ailerons. (See attached pic) the top surface aluminium skin extends all the way over the top of the wing to the back of the airleron. The up and down movement of the aileron relies on the flexing on the aluminium sheeting at point A.

I agree, a bit strange and some pilots complain that it leads to higher stick forces.

Mine has normal hinges.....

Fly safe,
Rudi

[grostek]

Hi All,

Just to add a bit more information.

The perception has been created both in SA and abroad that all series 601 aircraft have serious problems with wing design.

Firstly the 601 series falls into two distinct and different classes design wise.

The older 601 HD and HDS series have a thick airfoil section and a planform wing (Square) well not quite because the HDS has tapered wing panels but of the same airfoil section as the HD.

Also the HD/HDS wing design is a 3 piece wing with a center section protruding out board of the fuselage.

There have been 0 (Zero) reports of wing failures/inflight breakups with these thickwing 601 models.

The South African Raven from Carl Babst is of this type 601HD, and has not had any problems either. There are approx 30 Ravens flying in SA with no problems.

Now the 601 XL has a completely new wing design which enables the xl to carry more load at a faster speed for the same horsepower as the HD types.

The 601 XL is the only one that is under investigation by the FAA for wing problems.

But as with all things on the Internet it is important to check and verify everything.

I have added a quote below from a Yahoo group that maybe puts a different slant on the "Wing failure" allegations.

Kind regards,

Gunter Rostek



Quote


-----Original Message-----
From: 601_HD-HDS@yahoogroups.com [mailto:601_HD-HDS@yahoogroups.com] On Behalf Of Ron DeWees
Sent: Monday, April 28, 2008 11:40 AM
To: 601_HD-HDS@yahoogroups.com
Subject: Re: [601_HD-HDS] XL Wing Problems

Hi Mike and other HD/HDS drivers and builders.
I copied an email from this morning's Zenith list re the recent XL wing failures. Many owners are so concerned that they propose an independent engineering analysis of the XL wing. This Zenith list poster thinks they are about to put themselves in a double bind. If they get an analysis done of the failures and don't share it they are screwed, and if they share it and it grounds the fleet they shoot themselves in the foot with values. Sure seems like CH would be doing all this work for them. Shining light in a dark corner will relieve a lot more fear than just worrying about what's there. Seems like CH would be jumping on this problem/question with both feet but it's not forthcoming, it seems.
Ron
N601TD (HDS)
186 mph VNE (verified)








RE: [601_HD-HDS] XL Wing Problems

You are a little miss informed, Zenith and AMD have done several structural tests due to these incidents and have even had a 3rd party do such testing both physical and mathematical. All paperwork from these tests and stacks more from Chris Heintz Zenair and Zenith has been remitted to the FAA and cannot be released to the public as it has become part of the investigation. With all the data, in the FAA’s hands we have to realize one thing. The Job of the FAA is to determine if the Aircraft design has a possibility of a future problem. If a problem is perceived then the SLSA model of the 601XL series would be instantly grounded by FAA order. If several accidents have the same cause then the series would be halted in sales and production until a resolution by the designer is made. This simple fact has not happened!

The problem over the last 2 years is that [b]4 failures have happened that look similar to the observer, but the FAA is finding different faults[/b], one involved not wearing a seat belt in a thunderstorm by a novice pilot, another seems to have been an unsecured wing spar ( either no bolts or no nuts on the bolts). One possibly over gross with near limits maneuvers, even a pelican strike through the canopy had first been announced as a failure, when in reality none had happened, another ran out of fuel but instantly the wrong information gets published by the armchair engineers.

The other list members are creating a self generated hysteria, we have to remember that there are several 601XL’s with over 500 hrs on them and a few with over 1000 hrs on them. IF flown in the parameters of design and not stressed beyond capacity I believe the 601XL is a safe and fun to fly aircraft. I will even be having my daughter learning on my XL this fall. I have spent a lot of time in the 601HD and did in fact enjoy it very much, but the 601XL is a nicer plane to fly in my opinion.

Mark Townsend
Can-Zac Aviation Ltd.
president@...
www.can-zacaviation.com

Unquote.

[LarryMcG]

Many thanks for all the Input, especially Grostec!

Important for all concerned to know ALL the details!

LM

[swiftprop]

Very interesting post. It must be noted that Carl Babst is also an engineer although civil and not aerolautica. He has also had his CAA static tests with good results.