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food for thought for those overly concerned

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amyvega2005(at)earthlink.
Guest

Posted: Wed May 14, 2008 4:44 pm Post subject: food for thought for those overly concerned

This is from a manual on Vne, and how it effects structure and flutter"

Q- I like flying my aircraft fast. If I stay below Vne, I wonâ€™t have to worry about structural failure, right?



A- Vne is assessed at or near MTOW with the cg within the fore and aft limits for the aircraft's specified category; it does not apply if weight, manoeuvring loads or cg position are outside the specified limits. As a maximum airspeed it applies only in smooth atmospheric conditions, for gentle control movements and symmetrical aerodynamic loads; even gusts associated with mild turbulence or control surface movements greater than perhaps a few degrees travel will lead to some nasty surprises, if operating close to but below Vne. At high speed the controls are very effective with a probability of over-control applying extreme loads to the structures. Asymmetric aerodynamic loads such as combined rolling and pitching reduce the maximum airframe load allowable by perhaps 30%. Take care because some aircraft control systems provide an inadequate feedback of the load being exerted i.e. a high load can be applied with a relatively low stick force. 



If an aircraft is operated within its specified flight envelope and weight and balance, observing the limiting accelerations and control movements; and maintaining airspeeds commensurate with atmospheric conditions; then the only possibilities of inflight structural failure relate to: 

improper modification, repair or even repainting of the structure, 

excessive free play in control surface hinges, torque tubes or control circuits, 

cumulative strain in ageing aircraft eroding the designed safety margin, 

failure to comply with the requirements of airworthiness notices and directives, 

or just poor care and maintenance of the airframe.

Flight at airspeeds outside the designed flight envelope (or when applying inappropriate control loads in a high-speed descent or, indeed, at any time) is high risk and can lead to airframe failure. 



Be aware: deliberately exceeding Vne is the realm of the test pilot â€“ who always wears a parachute! The following text is an extract from an RA-Aus accident investigation report: 



"(Witnesses) observed the aircraft in a steep dive at what appeared to be full power. The port wing appeared to detach from the aircraft ... 



That wing had the attach points intact but had pulled the mountings out of the top of the cockpit. This action would have released the door, which landed close to the wing. The wings were intact but the ailerons were detached. There was no delamination of the fibreglass structure. The ailerons were not mass balanced.

steveadams

Joined: 10 Jan 2006
Posts: 191

Posted: Thu May 15, 2008 5:14 am Post subject: Re: food for thought for those overly concerned

I'm trying to envision some commonality between the wing failures.  I was reading a little sidebar in Kitplanes magazine about AVEMCO's experience with LSA's thus far. One of the things they said was that overall pilot experience made little difference in predicting risk because many of the LSA flying qualities are quite different than common certified aircraft. Time in type was a much better predictor of risk. Then looking at these accidents, there are a lot of differences; experimentals, factory built (from 2 different factories with some differences in materials and construction techniques), brand new planes, older planes, new pilots, very experienced pilots, planes with extensive modifications to the design, different phases of flight etc. However, there does seem to be a few common themes. First, those accidents that were witnessed had some reports of attitude changes prior to the breakup. Secondly, (correct me if I'm wrong) but it seems most of the pilots, regardless of their overall experience, were fairly new to the 601. I have never flown a 601, but it seems to me most likely that there is some flying quality of the 601 (i.e.- low wing loading and low stick force/G combined with a lot of elevator authority) that allows pilots used to a more conventional aircraft to overcontrol the aircraft under certain conditions and literally pull the wings off (something akin to pilot induced oscillations in autogyros). If I was building a 601 I would build to plans, spring the $100 or so to get an instrument to measure cable tension, inspect control attachments frequently for slop, make the changes that CH recommended, and get a lot of transition training before attempting to fly the 601. With that I would feel comfortable with the design.

amyvega2005(at)earthlink.
Guest

Posted: Thu May 15, 2008 6:04 am Post subject: food for thought for those overly concerned

BINGO! you hit the nail on the HEAD!



Juan



--

amyvega2005(at)earthlink.
Guest

Posted: Thu May 15, 2008 6:04 am Post subject: food for thought for those overly concerned

BINGO! you hit the nail on the HEAD!



Juan



--

frankroskind(at)HOTMAIL.C
Guest

Posted: Thu May 15, 2008 6:04 am Post subject: food for thought for those overly concerned

While I haven't flown a 601, I have flown taylrocrafts, which have similar weight and flying speeds (although slower at cruise), if not similar handling.  A taylorcraft at cruise handles much like a 152, warrior or even a Colt at cruise.  At slower speeds the differences are huge.  I stlll think the variations among aircraft at cruise speeds is not as serious as the variation among aircraft near stall speed.  In the cases of the wing failure accidents there is no reason to believe the planes were in slow flight, and every reason to believe they weren't.  The thing that makes a much lighter aircraft a little trickier to handle near stall speed is how quickly it slows down because of the low speed involved, and lack of momentum.  At cruise there should be less difference in how to handle a very responsive LSA and any other very responsive aircraft.  Further, if you are overstressing the aircraft, you are also experiencing a fair number of g's yourself.  This would be very evident to an experienced pilot.  the handling would have to be so squirrelly that a pilot could touch a contol and exceed g force limits from a cruise in order to get the kinds of crashes we saw.  This seems unlikely.

  

 I have read three plausible, although in one case, unlikely scenarios described in posts.  Flutter, which has been beaten to death, and which I think is not likely, pilots deliberately exceeding design parameters, which seems likely in at least one case, and incipeinet cracks progressing to failure, which theory does a good job of explaining how an airplane in straight and level cruise suffers a wing failure.  The incipient crakcs might have been initiated by exceeding design parameters, or through an as yet unexplained mechanism.  I would bet that there are other explanations for the crashes, but I don't recall reading them here.  There is, in addition, one implicit theory that pilots exceed design parameters unintentionally be pushing forward too rapidly on the stick.  This is implicit in the message to reduce evevator travel.  I find it hard to believe that experienced pilots might do something like that, although the forward puch might have been unintentinal, such as in response to a sneeze.  Unfortunately we lack cockpit sneeze recorders.

  

 What can you do to avoid all of the scenarios?  To avoid flutter install your controls correctly, without slack.  To avoid overstressing the aircraft deliverately, don't.  To avoid the excessive down elevator, install the stops recommended.  The best way to deal with incipient cracks is detection.  Inspection could help, but maybe there is where some additional thought would help.



 	  Quote: 	
		   Subject: Re: food for thought for those overly concerned

 From: dr_steve_adams(at)yahoo.com

 Date: Thu, 15 May 2008 06:14:38 -0700

 To: zenith-list(at)matronics.com

 

 --> Zenith-List message posted by: "steveadams" <dr_steve_adams(at)yahoo.com>

 

 I'm trying to envision some commonality between the wing failures. I was reading a little sidebar in Kitplanes magazine about AVEMCO's experience with LSA's thus far. One of the things they said was that overall pilot experience made little difference in predicting risk because many of the LSA flying qualities are quite different than common certified aircraft. Time in type was a much better predictor of risk. Then looking at these accidents, there are a lot of differences; experimentals, factory built (from 2 different factories with some differences in materials and construction techniques), brand new planes, older planes, new pilots, very experienced pilots, planes with extensive modifications to the design, different phases of flight etc. However, there does seem to be a few common themes. First, those accidents that were witnessed had some reports of attitude changes prior to the breakup. Secondly, (correct me if I'm wrong) but it seems most of the pilots, regardless o!

 f their overall experience, were fairly new to the 601. I have never flown a 601, but it seems to me most likely that there is some flying quality of the 601 (i.e.- low stick force/G combined with a lot of elevator authority) that allows pilots used to a more conventional aircraft to overcontrol the aircraft under certain conditions and literally pull the wings off. If I was building a 601 I would build to plans, spring the $100 or so to get an instrument to measure cable tension, inspect control attachments frequently for slop, make the changes that CH recommended, and get a lot of transition training before attempting to fly the 601. With that I would feel comfortable with the design.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=183274#183274

 

 

 

 

 

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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Thu May 15, 2008 6:11 am Post subject: Re: food for thought for those overly concerned

Excellent post Steve,



Until further information from the accident develops I'd suggest, and will implement myself if I ever get flying, the following.



Reduce Vne to 170 MPH.

Reduce Va & Vfe by 5 to 10 MPH.

Install the Elevator Stop Modification.

Perform no maneuvers that exceed 2G +/-

For new 601 pilots: Receive 10-20 hours of dual in a 601 before acting as PIC. 



None of these actions will in any way reduce the utility of your aircraft and will add a huge margin of safety.





 	  steveadams wrote: 	
		  I'm trying to envision some commonality between the wing failures.

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

jmaynard

Joined: 27 Feb 2008
Posts: 394
Location: Fairmont, MN (FRM)

Posted: Thu May 15, 2008 6:42 am Post subject: food for thought for those overly concerned

On Thu, May 15, 2008 at 07:11:28AM -0700, Gig Giacona wrote:

 	  Quote: 	
		   Reduce Vne to 170 MPH.

 Reduce Va & Vfe by 5 to 10 MPH.

 Install the Elevator Stop Modification.

 Perform no maneuvers that exceed 2G +/-

 For new 601 pilots: Receive 10-20 hours of dual in a 601 before acting as

 PIC.


	


Okkay, now this makes some sense. I'm not sure the Vne reduction will make

any practical difference, but it's a good thought.



I need to call AMD anyway; I'll ask if the elevator stop modification is

going in my aircraft.

-- 

Jay Maynard, K5ZC                   http://www.conmicro.com

http://jmaynard.livejournal.com      http://www.tronguy.net

Fairmont, MN (FRM)                        (Yes, that's me!)

AMD Zodiac CH601XLi N55ZC (ordered 17 March, delivery 2 June)

_________________
Jay Maynard, K5ZC
AMD Zodiac XLi N55ZC

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Thu May 15, 2008 6:55 am Post subject: Re: food for thought for those overly concerned

The Vne reduction is there because Vne was mentioned in one of Chris H's letters concerning the failures. The point of all the temporary changes is to address issues the designer mentioned and increase the safety margin. 



If I need to fly faster than 170 I'll fly something other than a 601XL. If I need to pull more than 2Gs I'll go fly a Pitts.



The exception to this is the dual time. That just makes good sense and I was going to do it from day one any way. I did it when I've gotten checked out in every airplane I ever flew. Why stop now?



 	  jmaynard wrote: 	
		  Okkay, now this makes some sense. I'm not sure the Vne reduction will make

any practical difference, but it's a good thought.



I need to call AMD anyway; I'll ask if the elevator stop modification is

going in my aircraft.

--

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

jmaynard

Joined: 27 Feb 2008
Posts: 394
Location: Fairmont, MN (FRM)

Posted: Thu May 15, 2008 7:15 am Post subject: food for thought for those overly concerned

On Thu, May 15, 2008 at 07:55:26AM -0700, Gig Giacona wrote:

 	  Quote: 	
		   The Vne reduction is there because Vne was mentioned in one of Chris H's

 letters concerning the failures. The point of all the temporary changes is

 to address issues the designer mentioned and increase the safety margin.


	


The main reason I think reducing Vne won't make any pracical difference is

that I don't think the aircraft will exceed 170 MPH in a screaming dive,

anyway, at least not if built to LSA standards. I could be wrong; I don't

particularly intend to find out. (Aside from asking how AMD managed to do

that so I won't...but I suspect they pointed the nose more or less straight

down.)



 	  Quote: 	
		   If I need to fly faster than 170 I'll fly something other than a 601XL. If

 I need to pull more than 2Gs I'll go fly a Pitts.


	


I don't intend to do either, period. I'm somewhat susceptible to motion

sickness, and pulling much in the way of positive Gs is one sure way to set

it off.



 	  Quote: 	
		   The exception to this is the dual time. That just makes good sense and I

 was going to do it from day one any way. I did it when I've gotten checked

 out in every airplane I ever flew. Why stop now?


	


True. I'll have a minimum of 8 hours of Zodiac dual before I ever fly mine

as PIC, and more wouldn't hurt.

-- 

Jay Maynard, K5ZC                   http://www.conmicro.com

http://jmaynard.livejournal.com      http://www.tronguy.net

Fairmont, MN (FRM)                        (Yes, that's me!)

AMD Zodiac CH601XLi N55ZC (ordered 17 March, delivery 2 June)

_________________
Jay Maynard, K5ZC
AMD Zodiac XLi N55ZC

DaveG601XL

Joined: 27 Oct 2006
Posts: 351
Location: Cincinnati, Oh

Posted: Thu May 15, 2008 7:52 am Post subject: Re: food for thought for those overly concerned

FYI, according to my 2006 dated drawings, Vne is listed as 160 MPH.



do not archive

_________________
David Gallagher
Cincinnati, OH area

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Thu May 15, 2008 8:33 am Post subject: Re: food for thought for those overly concerned

Really, mine show 180 mph, but are 1st Edition 04/02.



Taking that into account I may drop my Vne further. maybe as low as 155 mph. Not that I'll ever get to that speed but the Vne is there for more than just a don't go over this number kind of thing. If I were to go over the Vne it would trigger me doing what for all intents is an annual on the airplane.

 	  DaveG601XL wrote: 	
		  FYI, according to my 2006 dated drawings, Vne is listed as 160 MPH.



do not archive

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

tonyplane(at)bellsouth.ne
Guest

Posted: Thu May 15, 2008 8:34 am Post subject: food for thought for those overly concerned

My XL will EASILY EXCEED Vne in a SHALLOW  dive at max rpm (during Phase one I took it, in VERY gradual steps in CALM  air, to 195mph IAS.  Have not taken it to red line since)

  

 I have no idea what the terminal velocity is and do not  plan on finding out.

  

 My XL is probably one of the draggiest" XLs with no wheel  fairings and bigger tires/wheels/brakes (6x600s) 

  

 I built the airframe from a stock kit following the plans.  

  

 Also, you can easily go past the "white" line with full  flaps.

  

  

 Tony Graziano

 601XL/Jab3300;N493TG; 374 hrs of fun flying in the  XL/Jab3300.  It is a tough bird and easy to fly.

  

 ---------------------------------

 "The main reason I think reducing Vne won't make any  pracical difference is

that I don't think the aircraft will exceed 170 MPH in  a screaming dive,

anyway, at least not if built to LSA standards. I could be  wrong; I don't

particularly intend to find out. (Aside from asking how AMD  managed to do

that so I won't...but I suspect they pointed the nose more or  less straight

down.)"



   [quote][b]

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Thu May 15, 2008 8:37 am Post subject: Re: food for thought for those overly concerned

I don't know about the AMD version but I know two 601XLs that have in fact either made it to the Vne or exceeded it. 

 	  jmaynard wrote: 	
		  

The main reason I think reducing Vne won't make any pracical difference is

that I don't think the aircraft will exceed 170 MPH in a screaming dive,

anyway, at least not if built to LSA standards. I could be wrong; I don't

particularly intend to find out. (Aside from asking how AMD managed to do

that so I won't...but I suspect they pointed the nose more or less straight

down.)

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Thu May 15, 2008 12:57 pm Post subject: food for thought for those overly concerned

A 601XL is definitely capable of exceeding 170 MPH. The dive angle  

needed to do this is not that steep either. Testing to Vne should be  

part of the Phase 1 flight test program. In fact, Vne is usually  

defined as not more than 90% of the maximum speed the aircraft has  

been test flown to. To claim a Vne of 180 MPH, the aircraft must be  

flown to 200 MPH at some point in the test flight program and it is  

not too difficult to do this.

On May 15, 2008, at 11:12 AM, Jay Maynard wrote:

 	  Quote: 	

 On Thu, May 15, 2008 at 07:55:26AM -0700, Gig Giacona wrote:

> The Vne reduction is there because Vne was mentioned in one of  

> Chris H's

> letters concerning the failures. The point of all the temporary  

> changes is

> to address issues the designer mentioned and increase the safety  

> margin.

 The main reason I think reducing Vne won't make any pracical  

 difference is

 that I don't think the aircraft will exceed 170 MPH in a screaming  

 dive,

 anyway, at least not if built to LSA standards. I could be wrong; I  

 don't

 particularly intend to find out. (Aside from asking how AMD managed  

 to do

 that so I won't...but I suspect they pointed the nose more or less  

 straight

 down.)

-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Thu May 15, 2008 1:03 pm Post subject: food for thought for those overly concerned

One good thing to note about that is that the person at the controls  

rarely gets motion sickness even if that person would normally be  

inclined to get it as a passenger.



On May 15, 2008, at 11:12 AM, Jay Maynard wrote:



 	  Quote: 	
		  

 I don't intend to do either, period. I'm somewhat susceptible to  

 motion

 sickness, and pulling much in the way of positive Gs is one sure way  

 to set

 it off.

>


	




-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

amyvega2005(at)earthlink.
Guest

Posted: Thu May 15, 2008 2:44 pm Post subject: food for thought for those overly concerned

Vne is 160 on mine as per specs.

It easily goes to that at 5500 ft and at full rpm.  easily.  I think that is the main issue with the  plane.  It can hit "hull speed" pretty darn quick, and people need to keep in mind, Altitude, speed, DA, weight and manauvering speed.  

Juan



--

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