Rutan "EZ" aircraft structural discussion

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Aircar

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MODERATOR NOTE: I've moved the first seven posts in this thread thread here from the "Deleted Posts" thread in the Rules of Conduct section, since it has well-diverged from that topic. The material begins below with Aircar's post, intact, answering this post by Toolbuilder, which remains in the original thread. The only edit I've made to Aircar's post here is to add this note at the beginning. - Topaz.

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Sheesh ! -- I could fill a book with professional engineers who decry Burt Rutan's approach to things (eg no wind tunnel investigation most times and debateable structural integrity from the accumulated opportunities for error etc etc --after one Vari Eze shed a winglet he found that the wing was only good for 2.5G and then imposed this 'working limit' on all other Ez's because it was (and is) impossible to test or verify the structural strength --(as in material properties plus fabrication etc ) --it is on the web and while candid is also stunning in terms of the implications (and ethics..?) Given that Burt had always said he designed in such large margins for builder variations and quoted 12Gs at one stage this is a worrying wash up . I personally concluded (in 1973 ) that it was unwise to expect first time builders to have to make primary structure without any real quality control and the avenues for getting it wrong --the foam core and 'lay up in a day' method of wing fabrication in particular --molded glass removes the vast majority of possibilities for error and avoids the drudgery of hand finishing in this example .

It depends on what you define as 'unconventional' also --in 1970 Paul Bikle said that "composite construction cannot still be said to be novel or unconventional " --42 years ago but composite homebuilders even of tractor monoplanes still try to make it seem somehow innovative (Bikle managed the X 15 program and was responsible for the building and testing of the first lifting bodies by 'clipping' various NASA Edwards budgets and getting a few homebuilders at Edwards to help Gus Brieglib (wooden glider designer builder) make the first one which was tested by towing behind a souped up buick then behind a DC 3 'unofficially' --THAT was unconventiona/,on a shoestring and truly experimental . The space Shuttle indirectly grew out of this initiative (I know about Dynasoar being sidelined etc but this work made it possible to think about flying re entry and conventional landing --the originator Dale Reed also was responsible for the ancestor to the Vari eze -mini sniffer/super snooper --these things truly justified the experimental category.

It is NOT a case of boofheads doing the unusual or unorthodox in their ignorance while the real engineers get good honest results from the tried and true (the RV4 etc ethos) and there are all sorts of examples of apparently sub adequate bits of engineering around on the most stock aircraft --if you want to lose some sleep just go through the AD updates and reflect a bit (I think it was Raymer who wrote a book about his career experiences with major failures in production aircraft and the tracing back of the underlying reasons --I have read it in a library but cannot recall the title .

Given that the 'beef' being aired on this thread was EXACTLY the 'friction' between designers wanting to do new and hence un precedented or un fully verifiable things versus the advice that does TEND to decry that basic impetus to experiment I find it a bit surprising to deny it again . I came across a Smithsonian website about "the reinventors" and an article with you tube (not viewable in Australia) about them re inventing the flying car --curious given that there is still no satisfactory flying car and it can still be said to be in the still to be invented category if compared to anything established and worked out . That is a case in point about the difference between "leave it alone -no one has succeeded at it" versus "beauty! this thing still hasn't been nailed, let's find a way !" .....
 
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Topaz

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Re: Deleting posts

Sheesh ! -- I could fill a book with professional engineers who decry Burt Rutan's approach to things (eg no wind tunnel investigation most times and debateable structural integrity from the accumulated opportunities for error etc etc --after one Vari Eze shed a winglet he found that the wing was only good for 2.5G and then imposed this 'working limit' on all other Ez's because it was (and is) impossible to test or verify the structural strength --(as in material properties plus fabrication etc ) --it is on the web and while candid is also stunning in terms of the implications (and ethics..?) Given that Burt had always said he designed in such large margins for builder variations and quoted 12Gs at one stage this is a worrying wash up . I personally concluded (in 1973 ) that it was unwise to expect first time builders to have to make primary structure without any real quality control and the avenues for getting it wrong --the foam core and 'lay up in a day' method of wing fabrication in particular --molded glass removes the vast majority of possibilities for error and avoids the drudgery of hand finishing in this example . ...
I'd like to see a link or cite to this particular version of this particular story. The only case I know of where an EZ shed a winglet and subsequently crashed as a result involved the builder leaving out most or all of the attachment plies for the winglet. The only thing holding it on was the wing skin and, at the point of failure, only the foam. This was very much a builder issue and not a design issue, and it did not result in changing the G-loading limits of the aircraft. If there was some other incident and this kind of restriction has been placed upon the airframe, I'd surely like to see the details, but the "shed a winglet" accident sounds very suspiciously like the one I'm referencing, and a builder leaving structure out of the wing can't be laid back on the designer or his methods. I know of no "2.5G" permanent restriction being placed on the various EZ designs, and I'd like to see a reference for that, too, if you please.

Here's a link describing the accident to which I refer above: http://v2.ez.org/cp33-5.htm

As for "not possible to test" structural properties, etc., I'll point out that Rutan did extensive structural testing for the materials and methods used in the various EZ designs, and that there are very definite structural inspection procedures and criteria distributed to every builder. Those inspection methods and criteria are published at the back of Rutan's book, Moldless Composite Sandwich Aircraft Construction, which was distributed with every set of plans that were purchased from the RAF. Building to the plans and meeting those inspection criteria, combined with the safety margins and testing used in the original designs, has resulted in decades of good safety stats for the various EZ designs. They're not exactly falling from the skies in droves. I'm having a hard time tracking how you say that they're suddenly suspect, when the in-service experience speaks so strongly otherwise. The same goes for hand-layup composite construction in general - it's not just the EZs that use it, but many other designs, with similar successes.
And I'll further note: Rutan based his hand layup methods on those of the German Akafliegs in building the first generations of composite sailplanes. Any indictment of that building method is going to have to resolve the fact of the success of the method in-service both in US homebuilding practice and German sailplane practice, and would have to show a definite pattern of higher-than-average structural failures when the method is properly used. I know of no such data. If you have it, it would be a service to the forums to publish it here. You're entitled to your personal opinion, of course, but let's not try and state that as fact.

...I think it was Raymer who wrote a book about his career experiences with major failures in production aircraft and the tracing back of the underlying reasons --I have read it in a library but cannot recall the title ...
It was Jan Roskam, and I have the book here on my shelf: Roskam's Airplane War Stories

It should be noted that, in many cases, the "failures" described trace back to either unrealistic requirements placed upon the design by the customer, specification "creep", or mis-assembly at the production level*. There are certainly some engineering errors responsible for some of the failures, but it would be incorrect to characterize even the majority of the failures described in the book as being from that source. In fact, the description of failures is not the majority of the book's content. Mostly he's just talking about what it was like to work on various programs. The "lessons learned" described in the text go far beyond structural, systems, or mechanical failures, and into teaching methods, administrative methods, and just plain "dealing with people". As an indictment against engineering, the book is extremely weak tea.

*One of my favorite "lessons learned" from the book involved one of these (War Story 83, p.188), where Roskam states as a lesson learned: "Always assume that if something can be installed the wrong way, it will be. ... When possible, design for a one-way fit."

If we're going to continue with this sidebar to the original topic, I'll move it to a more appropriate place in the forums.
 
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bmcj

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Re: Deleting posts

The only case I know of where an EZ shed a winglet and subsequently crashed as a result involved the builder leaving out most or all of the attachment plies for the winglet. The only thing holding it on was the wing skin and, at the point of failure, only the foam. This was very much a builder issue and not a design issue.
That's the only one I recall too.
 

Apollo

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Re: Deleting posts

The only case I know of where an EZ shed a winglet and subsequently crashed as a result involved the builder leaving out most or all of the attachment plies for the winglet. The only thing holding it on was the wing skin and, at the point of failure, only the foam. This was very much a builder issue and not a design issue, and it did not result in changing the G-loading limits of the aircraft. If there was some other incident and this kind of restriction has been placed upon the airframe, I'd surely like to see the details...
You are correct that the winglet failure was the result of a builder leaving off most of the attachment plies. There has never been a structural failure of any Rutan design that was built correctly and flown within the operating limits. Although Aircar mixed up the facts, Burt did recommend a 2.5G operating limit for all Vari-EZ aircraft. This had nothing to do with the winglet failure and was based on a separate incident.

I'm at work and don't have my reference materials, but as I recall: A preflight inspection by a new owner revealed excessive displacements at the wing tips. The owner confirmed it was way beyond specifications and traced it to the wing attachment. Progressive disassembly (and eventual destruction) of the wing attachment fittings revealed two things: 1) Lots of corrosion in the wing attach fittings, and 2) A vertical joggle in the spar cap plies where the splice plate attaches. The joggle was much larger than the plans indicated and the original builder did not realize the implications. The splice plate appeared to be cutting into the spar cap plies at the joggle. The parts were sent to Scaled for further inspection and testing.

In this particular case, the vertical joggle was an inadvertent consequence of the assembly method used by the builder. But there was no guarantee that other builders hadn't done the same thing. There's no way to inspect the spar cap plies without cutting into the area and rendering the wing un-airworthy. Burt requested that Vari-EZ pilots/owners restrict their maneuvers to 2.5G while Scaled investigated. There was hope that Burt/Scaled would publish an inspection and repair method, but they never did as far as I know.

The 2.5G limit is voluntary and pilots that have already pulled higher G's on their Vari-EZ may assume (rightly or wrongly) that their wings do not have the defect. The Long-EZ, Defiant and other Rutan designs have completely different wing attachments and are not affected. The above details are based on recall. A Google search can probably locate the actual documentation, which I also have at home. Topaz, I am in complete agreement with the rest of your post.
 

Topaz

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Apollo, thanks for the great post with details on this. I hadn't heard most of it before. Do you have a link to any source materials? I'm sure a lot of people would like to follow that and explore the rest of the details.

EDIT: Ah, I see Hot Wings has already done so. Thanks, guys!
 

SVSUSteve

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Re: Deleting posts

Roskam states as a lesson learned: "Always assume that if something can be installed the wrong way, it will be. ... When possible, design for a one-way fit."
It reminds me of something I was taught back in my first career (emergency medical services) when I first became a supervisor and had to help to write treatment protocols. I was writing them for a well educated, conscientious and proactive provider (in other words: for someone like myself). My medical director rejected them and when I asked why he stated the following: "You never write a protocol for the smartest person out there. You develop them with the dumbest person: the one who barely passed his class, took multiple attempts to pass the certification exams and whom none of their coworkers would let treat anyone they cared about if given any say about it. Assume that the person who will be using your instructions has a tendency to drool excessively and leaves his helmet at home to avoid frightening his patients. Give them one option at a time and make it the one least likely to be bungled."

That has carried over into my theory of design for my aircraft, both the LSA I will be selling plans for and the turboprop that is just for my own personal enjoyment. The latter is because of the fact that I don't fully trust mechanics and in some aspects of the construction, even myself.

That said, the only aspect structural I have any beef with Rutan (and most of the rest of the major composite designers) is the area you would expect me to take issue with: occupant protection. It's an issue inherent in foam core composites as used in homebuilding (the practical limits of weight vs. strength; there's a point at which layup becomes too impractical for the techniques available to a homebuilder and a point at which composite loses its weight advantage) and not something specific to Rutan's design work in particular. If someone came out with a "homebuilder's autoclave" for composite work that could handle large pieces and not be prohibitively expensive, then things get a little better but there are a lot of design issues that continue to exist. The fact that Rutan's designs are among some of the better composite frames from a crash survivability standpoint (I'd choose a forced landing into trees with a Vari-EZ or Long-EZ over a Lancair any day) is something I would point out.
 
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Apollo

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Re: Deleting posts

It reminds me of something I was taught back in my first career... "You never write a protocol for the smartest person out there. You develop them with the dumbest person: the one who barely passed his class, took multiple attempts to pass the certification exams and whom none of their coworkers would let treat anyone they cared about if given any say about it. Assume that the person who will be using your instructions has a tendency to drool excessively and leaves his helmet at home to avoid frightening his patients. Give them one option at a time and make it the one least likely to be bungled."
That is an excellent lesson that should be heeded by all aircraft plans developers. I've mentored a dozen or so younger engineers and one lesson that comes up regularly is:

"When presented with many design variables or requirements, prioritize their importance and decide which ones are critical design drivers and which ones can be be compromised to achieve design objectives rather than treating all variables the same."

This seems like common sense, but I still run into new engineers that can't converge on a solution because they assign the same priority to all variables/requirements.
 

SVSUSteve

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Re: Deleting posts

That is an excellent lesson that should be heeded by all aircraft plans developers. I've mentored a dozen or so younger engineers and one lesson that comes up regularly is:

"When presented with many design variables or requirements, prioritize their importance and decide which ones are critical design drivers and which ones can be be compromised to achieve design objectives rather than treating all variables the same."

This seems like common sense, but I still run into new engineers that can't converge on a solution because they assign the same priority to all variables/requirements.
Yeah, prioritizing was also an issue that I encountered when I first started working on my larger design (I'm not an "engineer" in the sense of having a degree; trying to figure out how to get back into school full time to get one, but that's another story). The LSA design was a piece of cake since many of the things that people need in a "regular" aircraft (functional use, speed, cruise altitude) become less and less important given the handicaps placed on LSAs. I was left with gentle handling characteristics, an obscenely low stall speed, comfort and safety.

With the turboprop, it was (in order of priority):
-Speed
-Safety
-Comfort
-Range
-Service ceiling
-Utility (payload)
 

Aircar

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The link to the Cozy newsletter (itself a reprint from the canard pusher) is the article referred to (although I first learnt of it in correspondence to a Cozy builder) --there was a very similar -in terms of the underlying reason for failure ,case of a DG sailplane that failed due to the out of straightness and loss of compressive strength at the wing root top spar cap.

Bob Kuykendall of HP LLC sailplanes informed me of the details on that one aghain in private correspondence and if I trawl my memory as to exact date and the rest it will likely be wrong -there are thousands of ADs and engineering notes on hundreds of aircraft and the distillation of all this to 'lessons for designers' is what I believe would be of great value to intending designers (and a positive benefit from this forum if it could be collated in a more readily accessible form)

the substantial facts are I believe true and the lesson drawn valid (the 2,5Gs is in the story as well as the cause --I was actually thinking it was a wing failure but had a little doubt if my memory was 100% sure --I knew also about the incorrectly built winglet failure (and other canard flutter incidents etc plus of course the fatal accident to the second Vari Eze built in Australia that rolled inverted during high speed taxy tests at Bankstown airport killing Kevin Roby . -- I was invited to examine the wreckage by the airworthiness authority and at the time I was the only approved organization certified to perform major primary structure repairs --on sailplanes and GA aircraft plus had worked for both domestic airlines on bonded structures and composite repairs (inc radomes )

Additionally I had had to 'negotiate' with the Australian airworthiness authority --over a period that stretched to YEARS -- to accept the German LBA qualifying tests and inspection procedures for composite airframes --bearing in mind that ,then and until 1999, EVERY NON "OVERSEAS" amateur built/homebuilt/one off HAD to be FULLY compliant with FAR 23 PLUS additional demands to PROVE fatigue life and FLUTTER margins --small wonder that there WERE NO Australian designs - and only my Fully molded composite tail pusher etc etc Opal was ever presented to get approval --as a kit -- meanwhile almost ANYTHING could get the OK to be built BY Australians without ANY form of certification or any tests to prove integrity or handling etc . The Alvarez Polliwagen was 'knocked back' by an engineer,then acting as the intermediary with the airworthiness authority --and good friend of mine nowadays --on the basis of known deficiencies and falsified history 'data' but one was imported 'illegally' and used as the basis for a somehat misbegotten clone that has created many problems,crashes etc since and that I was involved in trying to redesign and correct to at least a minimum standard
( There was a question of what is an "Australian" design --even if designed overseas --as was my Opal ,in the USA --don't even think of asking about the hair splitting intricacies of all this legislative buggery that you guys in the US have never even had to think out with homebuilding or kits --not since George Bogardus and the Oregon Outlaws won the right to 'seek happiness' via homedesign and homebuild. Letting untrained people make primary composite structure in the fashion involved in mold LESS construction -- the mixing accuracy,temperature control etc etc is fraught to say the least .

It gets down to HOW you are SURE that your composite aircraft is and will remain 'airworthy' and being able to get someone employed by the government to sign their name that it is beyond question.

The quality control of ANY foam core composite aircraft would never come close to being certifiable --and REAL issues with reproducability and integrity certainly exist --at the least I think my point that the Vari Eze is NOT so overdesigned as to account for all possible builder errors is not true. -there are always 'debateable' design details on aircraft and there must be a weakest link somewhere (the attachment of the metal tail cone to the fobreglass nose on the HP 18 sailplane was one case where I locked horns with Dick Schreder who had designed a one inch wide step 0.032 deep to join the two parts with no understanding that at the END of a layup the material is subjected to ragged run outs and sagging of any overhang,bleed out of resin etc unlike just a cut edge in alumimium --adding a considerable amount of 45 degree fine weave tapes interleaved with the basic course mesh woven roving likely saved the day there )

The crashworthiness of the Varie Eze is another sore point --firstly the manual instructs you to sit so that there is NO MORE than ONE INCH between your head and the canopy --with tight straps (for visibility ..) -the so called 'roll over structure" is LOWER than this and consists of a foam and glass 'pyramid' taped to the seat back of the front seat - in the Kevin Roby fatal (itself an outcome of heat radiation from ther brake discs softening the room temperature cure undercarriage legs ...) this 'structure' was simply peeled off with onlt minimal evidence of any abrasion --the imprint of the glass was perfectly visible on both sides of the seat and pyramidal piece.

Kevin Roby's head was ground down to the level of the eyeballs .

The fusealge sidewalls were split open as though sliced with a huge knife -right down the centre of the foam and the remains of the rest of the nose were shredded --one micro second after impact it looks like the glass and foam delaminated ,the foam shattered and the uncoupled thin skins and thick but gutless foam provided little protection --stiff equals little deflection or energy absorption possibility .

I could go one but don't have time right now on the subject of crash survivability and composites and design or the larger subject...
 
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Autodidact

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Simply not true. The Cirrus uses divinycell foam core in its primary structure and is FAA certified. See the link below:

http://www.aircraftinteriorsexpo.com/__novadocuments/4563
Apollo, i think you've confused "quality control" here with "design". I think Aircar means the quality of the work done by a disparate group of individuals scattered accross the globe, which would be impossible to measure and standardize.
 

Apollo

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Apollo, i think you've confused "quality control" here with "design". I think Aircar means the quality of the work done by a disparate group of individuals scattered accross the globe, which would be impossible to measure and standardize.
Perhaps. Other wording in the post and the statement that quality control for "ANY" foam core composite aircraft could not meet certified standards caused me to take the sentence literally. The post seemed to be a rant about all composite aircraft. I'll concede that I may have misread the meaning.

But if we're talking about homebuilt aircraft only, there's no need to single out composite aircraft in that way. Disparate groups of individual builders scattered across the globe could not meet certified quality control standards for metal, wood or fabric aircraft either.

Putting that aside, it's clear that Aircar is concerned about the difficulty of inspecting and verifying composite structures. What happens when critical plies are buried inside other composite structure? If you're purchasing a Long-EZ, how do you really know that all the winglet tension plies are there? Or that the builder used UNI tape instead of fabric? Or that the ply angles are correct and the layup isn't dry? Or that the fibers are straight and not curved? Those are good questions and it IS an issue. But metal aircraft are not immune to quality control problems. There's been plenty of accidents in plans-built metal aircraft because the builder fabricated a part badly, used the wrong rivets, didn't use the right bolt, used a thinner gage of metal, substituted a weaker alloy or didn't follow instructions. Many of those mistakes can't (or won't) be inspected either.

The solution for composite and metal aircraft seems to be the use of prefabricated kits. This allows more of the critical work to be done by the vendor. Today's kits (by reputable vendors) provide much better quality than most plans built aircraft. But since Long-EZ's and Cozy's aren't falling out of the sky due to structural failures, it IS possible for plans-built composite aircraft to have reliable structures (ie, no in-flight failures) on a consistent basis.

On the issue of crashworthiness for composite aircraft, I do agree with Aircar - some of them are deficient. But I only have to look at the BD5 to know that metal aircraft can be just as deficient.
 
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Autodidact

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Disparate groups of individual builders scattered across the globe could not meet certified quality control standards for metal, wood or fabric aircraft either.
My own feeling is that you can't study aerodynamics and structures too much, even if you have no intention of designing your own. It will make you better able to choose a design, and will make you a better craftsman than you would have been.
 

SVSUSteve

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Kevin Roby's head was ground down to the level of the eyeballs .
To quote the title of a chapter in a book written by a friend's brother: "There was brain for half a block....". It's shocking how many folks die because the designer and/or builder didn't look at what would happen in a crash often for want of nothing more than a couple of pieces of bent metal.

Simply not true. The Cirrus uses divinycell foam core in its primary structure and is FAA certified. See the link below:
Apollo, i think you've confused "quality control" here with "design"
Apollo also may be confusing "FAA certified" and structurally sound from a crashworthiness perspective. There's a reason why the difference in occupant fatality rates for Cirrus versus a comparable metal framed aircraft is something like 2-3 times as poor. Cirrus is a prime example of how not to use composites to protect the pilots and passengers. Actually about the only things Cirrus has done well so far (besides providing plenty of data for my research although I wish they would stop doing so) is inclusion of the CAPS/BRS chute and showcase how to market aircraft when your sole concern is profit at the expense of everything else.

There was one that ran off the runway at Chapel hill and hit a tree while going slower than Vr. It killed one of the front seat occupants and seriously injured the other. The front of the plane pretty much totally sheared away back to the leading edge of the wings.

But if we're talking about homebuilt aircraft only, there's no need to single out composite aircraft in that way. Disparate groups of individual builders scattered across the globe could not meet certified quality control standards for metal, wood or fabric aircraft either.
Agreed 110%. I have yet to see a single homebuilt that during a post-crash teardown that doesn't have at least one significant sign of poor construction technique or just overt cutting of corners to save money. It's kind of frightening the number of boneheaded substitions people make (using hollow or under strength bolts to secure the restraints, etc), misplaced drilled holes, etc.

There's been plenty of accidents in plans-built metal aircraft because the builder fabricated a part badly, used the wrong rivets, didn't use the right bolt, used a thinner gage of metal, substituted a weaker alloy or didn't follow instructions. Many of those mistakes can't (or won't) be inspected either.
The rate is probably a lot higher than many of us want to admit because a lot of the mistakes get overlooked as the NTSB tends to just kind of "check the boxes on the paperwork" when it comes to experimental crashes even more so than they do with GA crashes in general. One of the only crash investigations I look at as being sufficiently thorough was the death of Dan Lloyd.

But I only have to look at the BD5 to know that metal aircraft can be just as deficient.
There's not a plane out there today as either a kit or a commercial manufactured design that comes close to being "good enough" for crash survivability. Well, except for cropdusters...

My own feeling is that you can't study aerodynamics and structures too much, even if you have no intention of designing your own. It will make you better able to choose a design, and will make you a better craftsman than you would have been.
Amen. Thinking "worst case scenario" on both subjects is also probably a good idea.
 

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-the so called 'roll over structure" is LOWER than this and consists of a foam and glass 'pyramid' taped to the seat back of the front seat -..
It was never meant to be a 'roll over' structure. If it was, Burt would have designed it correctly. To insinuate a design flaw or lack of proper engineering is just uninformed and wrong. Please get your facts straight. There is a whole world of information in the Canard Pushers and later in the CSA newsletters that applies to these canards and most, if not all, of the naysayers know nothing about them and make a lot false statements without knowledge of what they speak, particularly in the wonderful world of forum trolling.
Mike Melvill designed an excellent roll over structure in carbon as have many others in steel.
 

plncraze

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http://www.niar.twsu.edu/agate/ This is a link to some crashworthiness info on composite aircraft. I beleive Orion posted this some time ago.

What is frightening about aircraft design is how little thought is given to how the structure will dissipate energy in a crash. I remember the JAARs Helio Courier at Oshkosh and talking with one of the people who had helped design the crashworthy seats. They had two or three different kinds of seats depending on location and crush space underneath and some of their ideas were not perfectly obvious at first glance. The seats were "tuned" to collapse at a certain rate and then not rebound, which is the real killer, I believe. I would bet that the super stiff composites would just break like an egg in a crash. There was a quote I heard somewhere that if you overload aluminum that it becomes modern art while if you really overload composite you will be picking it up in a dust pan.
 

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The seats were "tuned" to collapse at a certain rate and then not rebound, which is the real killer, I believe
Yes and no. Yes, recoil isn't a good thing (beyond a certain point or rate). No, it's not the primary killer in terms of vertical deceleration and stroke. You can look at a lot of the standard GA aircraft and get this demonstrated pretty plainly. The "simple" compression of the vertebrae is sufficient to kill (through upper cervical spine trauma, basilar skull fracture, incapacitation in the face of fire or sinking, or through associated vascular trauma) in most cases and recoil of the seat isn't a significant issue because they can't stroke in the first place in a meaningful way.

There was a quote I heard somewhere that if you overload aluminum that it becomes modern art while if you really overload composite you will be picking it up in a dust pan.
More often than not in the real world of crashes, you overload composite and you don't have to pick it up at all because of the ensuing post crash fire. There's a reason why some of my friends at the NTSB refer to Cirri as "Ronsons" after the old lighter brand with the slogan "Lights the first time, every time".

The major problem with crashworthiness in composites is not that you can't make composites that are sufficiently strong. The problem is that you generally can't do it in your garage or hangar because of the manufacturing processes required. Also some of the resins used in the really, really high end crash protection roles makes uncut Bolivian marching powder look cheap.

What is frightening about aircraft design is how little thought is given to how the structure will dissipate energy in a crash.
I would bet that the super stiff composites would just break like an egg in a crash.
You're looking at two separate roles there. A lot of people oversimplify the design requirements for crashworthiness to either "Tough as possible" or "it needs to break to dissipate energy" when in fact, you need to do both but in different parts of the aircraft. That's why there's the acronym "CREEP":
-Container: structure of the cabin stays largely intact to prevent impinging or entrapping of the occupants
-Restraints: fairly straightforward but needs to be strong enough to withstand a 95th percentile survivable crash with a 95th percentile adult man in the seat.
-Energy management: either dissipate or route the energy around the occupants rather than through them. Also, designing so that the aircraft decelerates gradually on soft soil, water, etc rather than 'digging in' and worsening the impacts
-Environment: design the cockpit/cabin to be as unlikely to produce injury as possible, including if the shoulder harness, etc fails. No sharp knobs, flush mounted switches, etc.
-Post-crash environment: Design the systems so that a dazed and injured person (with reduced motor or cognitive skills) can get out of their restraints, get around in the vehicle and get the doors open. This also includes taking into consideration the effects of vision obscuration from smoke, minimizing the production of toxic gases, etc.
 
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