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What Price A Masterpiece? By Dick VanGrunsven

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As an engineer myself, I have been put in the position of customers "using up some of the margins" that I have used in the design. Usually it has taken the form of asking me what the "real" instead of the "nameplate" payload of the machine. I always stated very firmly that the "nameplate" payload is the only one there is. And as the customer walked away I knew very well that he was going to overload his machine.

I had a conversation with one of Van's engineers about this very topic and we both agreed that the "margin of safety" or "factor of ignorance" is the property of the designer, not the right of the customer to use however he desires. Van makes this point in his comments as he has a right to do.

As an aircraft designer in my day job, I have learned to repect other designer's opinions, anaylsis, and decisions. Unless I have experience or analysis of my own, I do not think I am in a position to question their judgement. Design is a very personal thing. I have been asked many times in my 26 years of designing airplanes to "give up the margin". My company has me sign a Ethics Committment form every year to remind me from doing just that.

By the way, it really is a safety margin for failure not for permanent deformation- strain. We design to not have failures up to 1.5 times design limit load. At and above design limit load you can have permanently deformed parts but not structural failures. If you surpass the limit load you need to inspect for areas of strained structure. There is also no requirement on how often you can surpass design limit load. You only have to show no structural failure to 1.5 times deisgn limit load once. That does not guarentee that you can go to 1.4 times limit load twice or to 1.05 times limit load 20 times and not have failure.
 
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Fatigue

You only have to show no structural failure to 1.5 times deisgn limit load once. That does not guarentee that you can go to 1.4 times limit load twice or to 1.05 times limit load 20 times and not have failure.

Philip, you bring up a really good point, and perhaps another topic for consideration - fatigue. As the cyclic stress on a structure increases, the number of cycles that structure will tolerate before failure decreases. Sometimes dramatically. And while RVs are not typically used daily like an airliner and are not pressurized, the designer analyzed the structure for a certain number of cycles at some assumed gross weight. Increase the load to a new gross weight and who knows how many cycles that structure will take before failure.

Hand-in-hand with fatigue comes damage tolerance, or the structure's ability to resist crack growth for an amount of time between mandatory inspections, so that you can see or otherwise detect a crack and have a chance to repair it before the structure actually fails. Our airplanes, along with other GA aircraft, are required to be inspected once a year. Once again, increasing the cyclic load can have negative consequences on crack propagation, causing crack growth to failure in something less than the one year inspection interval.

Any changes to the design can certainly be analyzed by a competent and knowledgeable engineer. And if one chooses to go that route, great. But so many times we just don't know what we don't know. Please be safe out there.
 
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I don't know enough about what the -10 pedal assembly should look like to comment on this one, hence why I didn't. I can't even really tell what's going on there.

The clevis of the rudder cable should connect directly to the tab welded to the rudder bars. The builder used a stand-off in order to not bring the rudder cable out of the tunnel as per the plans. Van's concern is that the stand-off applies a rotational force to the tab.
 
Boy, as soon as I read this article on FB last night I knew this would be a hot topic here on the forum...I wasnt wrong.

My thoughts when I read it were,

1. Van repeatedly called the builder by name, I think he could have toned that down a little. As someone already mentioned, making it more of a general message to all builders about mods and using a couple of examples from the specific builder would have been a better approach. I didnt read it that way, it sure seemed like this builder/plane was square in Van's sights. I wouldnt have wanted to be that guy to be called out by Van himself for all the world to read, thats tough.
2. I understand what Van is trying to get at though. We, as builders, get carried away sometimes with our mods. It just seems to be a situation of more and more stretching of the design...encroaching on the design limits. When are we going too far? I personally have tweaked my build, and love the fact that I have that luxury but I do try not to get carried away and deviate too far from the original design.
3. Lastly, I havent seen anyone bring up this point. What will this do to builders that are making mods to their plane? If SA approaches me to do an article about my plane when its done, I would more than likely decline after this whole deal. No thanks to opening up that potential. Same thing on here, I know a lot of guys that do mods to their planes dont post about it on here because of getting flamed for it...sometimes warranted, but a lot of times not. This kind of thing will drive builders to be less forthcoming about their mods.

All in all, good discussion...certainly made me think about my own mods, which is always a good thing. If Van was trying to stir up some serious discussion on the topic...mission accomplished.
 
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3. Lastly, I havent seen anyone bring up this point. What will this do to builders that are making mods to their plane? If SA approaches me to do an article about my plane when its done, I would more than likely decline after this whole deal. No thanks to opening up that potential. Same thing on here, I know a lot of guys that do mods to their planes dont post about it on here because of getting flamed for it...sometimes warranted, but a lot of times not. This kind of thing will drive builders to be less forthcoming about their mods.

Well, that's unfortunate. If you know enough to change the design then you should not only be willing, but WANT others to look at it and comment. Granted, maybe not for the whole world to see. I've done that numerous time with changes (See Rocket Fuel Vent Line for example), and sometimes I've changed things again because more knowledgable people than me found something I failed to see. But I agree that sometimes, you have to have thick skin. Such is the nature of social electronic media.

I sure would rather get beat up here on VAF, SA or by Dick VanG, than by.....physics!

I think this quote is perfect! Well done.
 
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Boy, as soon as I read this article on FB last night I knew this would be a hot topic here on the forum...I wasnt wrong.

My thoughts when I read it were,

1. Van repeatedly called the builder by name, I think he could have toned that down a little. As someone already mentioned, making it more of a general message to all builders about mods and using a couple of examples from the specific builder would have been a better approach. I didnt read it that way, it sure seemed like this builder/plane was square in Van's sights. I wouldnt have wanted to be that guy to be called out by Van himself for all the world to read, thats tough.
2. I understand what Van is trying to get at though. We, as builders, get carried away sometimes with our mods. It just seems to be a situation of more and more stretching of the design...encroaching on the design limits. When are we going too far? I personally have tweaked my build, and love the fact that I have that luxury but I do try not to get carried away and deviate too far from the original design.
3. Lastly, I havent seen anyone bring up this point. What will this do to builders that are making mods to their plane? If SA approaches me to do an article about my plane when its done, I would more than likely decline after this whole deal. No thanks to opening up that potential. Same thing on here, I know a lot of guys that do mods to their planes dont post about it on here because of getting flamed for it...sometimes warranted, but a lot of times not. This kind of thing will drive builders to be less forthcoming about their mods.

All in all, good discussion...certainly made me think about my own mods, which is always a good thing. If Van was trying to stir up some serious discussion on the topic...mission accomplished.

Great prospective.. +1
 
In Australia we give Americans lots of stick for going on about the land of the free, and the right to free speech and all that hoohar.

But to be honest I read every single post and it made me smile because it was a testimony to people having their say.

The protective inventor, the over zealous builder, those that agree with Dads harsh words, those who say you leave him alone and those that just looked at the facts.

All of that got expressed and can be read by anyone with an internet connection. No one got litigated against ( I am hoping ) and some of us readers learnt a few things about design safety and testing the edge in a reasonable way or not.

Truth be told, every person had the right to say what they did.

This was a very good post, for more reasons than just what is relevant to aviation.

Really great post and one all of us in the states should appreciate!
 
If you look up "tactful" in the dictionary, Van probably isn't going to be defined there. He tells it like he see's it and those who listen will be the wiser. If you think he is going to sugar coat anything at this point in his life, uh,...probably not going to happen. He is generally a quiet man, every time I have engaged him in conversation. But he listens, and when he speaks, you know something important is going to be said, or he just doesn't speak.
I appreciate him countering the SA article. SA looks for general interest articles that appeal to their readership. Nobody wants to read an article about a built per plans, run of the mill airplane, so cut them some slack too.
Point and counter point, I think this is all good stuff.
 
** Because of all of the ?I gotta have? added features, empty weight creep erodes the aircraft?s useful load.**

I've experienced this not only personally, but on other aircraft that I have weighed. Re-weighing an aircraft after a few years of "upgrades" can have a startling and sometimes significant effect on useful load. With the addition of paint, leather interior, improved seats, avionics upgrades, auto pilots, better tires/brakes etc. etc. it's sometimes shocking on how much this stuff adds to the empty weight of an aircraft. The above changes can easily add 50-100 lbs.

Something to think about if you haven't re-weighed your aircraft after a few years of upgrades/mods, especially if your are planning on going to OshKosh fully loaded and if you're like me, come back with even more "stuff" :eek:
 
Well, that's unfortunate. If you know enough to change the design then you should not only be willing, but WANT others to look at it and comment. Granted, maybe not for the whole world to see. I've done that numerous time with changes (See Rocket Fuel Vent Line for example), and sometimes I've changed things again because more knowledgable people than me found something I failed to see. But I agree that sometimes, you have to have thick skin. Such is the nature of social electronic media.

Very good counterpoint Randy, doing these things "in the shadows" is not healthy either. I will say pick your knowledgable sources wisely though, there are a lot of people who claim to be 'experts'.
 
JonJay;552585... If you think he is going to sugar coat anything at this point in his life said:
Yikes, when I opened this thread, my monitor jumped off the table and my coffee cup fell to the floor!

JonJay, your assessment above nails it.
 
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I'm with Randy....my RV8 includes more than a few mods and I've laid out all of them here at one time or another. They are subject to review by any reader. You'll have my respect and thanks if I've done something unsafe and you object based in physics, engineering, or realistic test.

There are very smart people here.....

As for the FB article, I understand Van's frustration. To pick just one thing, I can imagine hundreds of copies of the rudder pedal mod following that SA article. Heck, I can imagine a vendor popping up next week selling the parts. It would become a popular mod. Some knowledgeable folks would object. They would be blown off because nobody had died yet. And so on.....if you've been around this game long enough you know how it works.

Someone mentioned judging standards. The official standards make safety a very high priority. Please see Section H, Judging Criteria, pages 11 and 12, and note subsection #1:

http://www.airventure.org/awards/judging_manual10.pdf

The seat belt and rudder pedal issues should result in a loss of points if observed by the judges.

Here's the problem. Judges are volunteers, great guys, willing to work and generous with their time. However, they are not necessarily engineers, and not all are as observant as they could be. And you can say the same about magazine writers.
 
I think some of you are missing the whole point of Van's article.

He was impressed with the beauty of the workmanship of the airplane but he also wanted to let everyone know that changing the design limits of any airplane can come with penalties and possible danger.

Van knows better than anyone the design limits of the RV10 and I for one am glad to see that he is not afraid to publicly point out that changing those design limits may come with consequences.
 
I'm going to get flamed--but

I did not see the article, nor have I seen Gregs plane or know him. But in my very limited experience in helping some of you, we all refer the project that we are working on as a VANs RV--. No matter what we do to modify it, it is still a VANs RV---unless of course you change the name. Van has his name on it.
I'm pretty sure that when Paul and Louise fly 'junior', that they will refer to it as a RV3, and not a PDLH1. So as long as it has Vans name on it somewhere, I think he has the option to voice his opinion. If some of the other engineers on here want to design, and market their own planes, then that would be a great thing. It would be very interesting on things they would come up with.

Van has his 'name' on every one of the RV's flying. All of them are his children, so I think that gives him some lattitude for scolding us if we do something that isnt in the best interest of the family. I do have to agree with Paul--if you put your project out there, someone will find something about it that they didnt like, or would do different.

Tom
 
I think some of you are missing the whole point of Van's article.

He was impressed with the beauty of the workmanship of the airplane but he also wanted to let everyone know that changing the design limits of any airplane can come with penalties and possible danger.

Van knows better than anyone the design limits of the RV10 and I for one am glad to see that he is not afraid to publicly point out that changing those design limits may come with consequences.

To add to this... pushing the design limits to accomodate bling is an unwise thing to do.
 
I'm with Randy....my RV8 includes more than a few mods and I've laid out all of them here at one time or another. They are subject to review by any reader. You'll have my respect and thanks if I've done something unsafe and you object based in physics, engineering, or realistic test.

There are very smart people here.....

As for the FB article, I understand Van's frustration. To pick just one thing, I can imagine hundreds of copies of the rudder pedal mod following that SA article. Heck, I can imagine a vendor popping up next week selling the parts. It would become a popular mod. Some knowledgeable folks would object. They would be blown off because nobody had died yet. And so on.....if you've been around this game long enough you know how it works.

Someone mentioned judging standards. The official standards make safety a very high priority. Please see Section H, Judging Criteria, pages 11 and 12, and note subsection #1:

http://www.airventure.org/awards/judging_manual10.pdf

The seat belt and rudder pedal issues should result in a loss of points if observed by the judges.

Here's the problem. Judges are volunteers, great guys, willing to work and generous with their time. However, they are not necessarily engineers, and not all are as observant as they could be. And you can say the same about magazine writers.
This is valuable information on how aircraft are judged. . . At the EAA Airventure airshow/fly-in.

However, this particular example of an RV10 was judged at Sun n Fun. Sun n Fun is not an "official" EAA airshow. EAA has no direct involvement in the operation of Sun n Fun. As a consequence I am not too sure Sun n Fun judges are following the same judging standards as the EAA Airventure judges. Someone tell me if I am wrong on this thought and I will stand (aside) corrected and voice no further opinions on the subject.

I would also like to comment on the posts concerning the manner in which this article from the mother ship has been presented.

Having no engineering degree or background I will only offer my opinion on the subject only as a fellow builder and as a fellow modifier of my own build. To those who feel it "wrong" to openly call out, by name, a builder who has made some alterations to design that can have some dire consequences I say: Sometimes we as individuals need someone to call us out by name. Often times it is the only way to get our attention. "Hey, Steve, you should not be doing things "that way"!"

Look fellas, we are all grown ups (well, at least we should be). For those who feel Greg was unduly chastised, I see this like a person who does not want parents, preachers or God knowing about his/her personal transgressions. Perhaps, if the transgression only ends up hurting oneself we can hide behind anonymity and, therefore, feel vindicated in hiding the transgression from the world. On the other hand, if our transgression will end up hurting others the transgression should no longer be hidden behind closed doors. It should be "outed" for what it is: a violation of fundamental truths that we all must live by. Physics and basic aerodynamics are the fundamental truths that will ultimately be the tell for the mentioned transgression(s).

We all know this feeling we see in this story. We have experienced it first hand. This is the reason many have posted their objection to the "offender" being named outright. It is too bad too many of us refuse to accept guilt as a proper teaching tool. It is a very powerful one if we would allow it to do its work.

Greg, Sun n Fun judges, Sport Aviation editors, EAA all contributed to "outing" Greg on this issue. Now comes the "Piper" to say that some serious transgressions have occurred. Not only does Mr. V (RV parent, RV preacher and RV deity) have the right to do so, he most assuredly has the justification in doing so.

We can be cynical in our belief that he is only saying these things to look out for his "Cash Cow" of a product but the truth, I am convinced, is much more basic than that. He does not want any individuals hurt from his creation. It is as simple as that.

I, myself, feel the terrible weight of guilt when I am individually named for some transgression. However, bad it makes me feel though, I hope in my personal life to be able to be man enough to accept the exposure and learn from it in order to better myself.

I wish this for Greg as well. He has shown he has the skills and the fortitude to build exceptional quality machines. I hope he is also exceptional in his character to accept direct criticism for his actions and become a better builder and a better man for having experienced it.

Live Long and Prosper!
 
Under normal use, this rudder cable attachment will fail first. The cables take the load of applying the brakes, and that tab will not hold up...... this makes me cringe............:eek: Not only dose the rudder fail, but you lost the brake with it.

The seat belt may never get a chance to be tested............... if the rudder cables are corrected.

Yeah, I saw that and thought "not good". The bending loads on that tab under hard braking are going to be substantial.
 
Very good counterpoint Randy, doing these things "in the shadows" is not healthy either. I will say pick your knowledgable sources wisely though, there are a lot of people who claim to be 'experts'.

Amen to that, although I thought the Matronics list cornered the market on experts! :rolleyes:

In Indy, we are blessed with a great bunch of fellow builders who are not shy and are very knowledgable. I've also had Mark Fredericks and Tom Martin critique my stuff. They politely pointed out a few things along the way and I was much wiser (and safer) for it.
 
To those who feel it "wrong" to openly call out, by name, a builder who has made some alterations to design that can have some dire consequences I say: Sometimes we as individuals need someone to call us out by name. Often times it is the only way to get our attention. "Hey, Steve, you should not be doing things "that way"!"

SDI hit the nail on the head with this comment. We as a community of builders and pilots should not be shy about giving or receiving criticism. It?s this criticism that can very well save your life. I always say to another pilot when I fly with them that I have no ego in the cockpit, if anything I do makes you nervous or gives you pause please speak up. I?m a big boy, if I?m being dumb I want to know. If I don?t agree with you I?ll let you know that too. No offense taken, we're just looking out for each other. After all, isn't that what friends do?

I can think of at lease one life that may have been spared if he received more criticism AND listened to the criticism that he received. And his family that he was planning to fly in that plane later that day, I?m guessing, didn?t have a clue how far this builder deviated from Van?s design.

You as a builder absolutely have the right to make mods and changes to the design. However, remember as Van points out, your passengers most likely have no clue whether or not those mods are safe and prudent. They are trusting you, literally, with their lives, nod that trust shouldn?t be taken lightly.
 
This is valuable information on how aircraft are judged. . . At the EAA Airventure airshow/fly-in.

However, this particular example of an RV10 was judged at Sun n Fun. Sun n Fun is not an "official" EAA airshow. EAA has no direct involvement in the operation of Sun n Fun. As a consequence I am not too sure Sun n Fun judges are following the same judging standards as the EAA Airventure judges. Someone tell me if I am wrong on this thought and I will stand (aside) corrected and voice no further opinions on the subject.

Steve, I am not saying you're wrong; I am very aware of the fact that Sun'n Fun is not an EAA event. But you do need to know that Dan Horton knows something about aircraft judging since he won awards for a previous airplane at Sun'n Fun as well as SERFI and Oshkosh. Go to this page, fifth one down on lower part of the page:

"...N22EB
Grand Champion, Oshkosh 1998, SERFI 1998, and Sun 'n' Fun 2000."

And I think he has won awards for other aircraft he has built, too.

In addition, I believe, but I could be wrong, that he has been a judge at Sun'n Fun, perhaps even this last year. The point being, whether or not the correct book is quoted, I believe Dan knows that Safety should be high on the priority list when an aircraft is judged at Sun'n Fun, SERFI or Oshkosh.
 
"Quote of the Thread"

...
I can't afford either a perfect or unsafe plane...

This is a HOT thread, and I appreciate all the perspectives. Every once in a while, a sentence just STANDS OUT. This comment sums it up for me.

"I can't afford either a perfect or unsafe plane"
 
Steve, I am not saying you're wrong; I am very aware of the fact that Sun'n Fun is not an EAA event. But you do need to know that Dan Horton knows something about aircraft judging since he won awards for a previous airplane at Sun'n Fun as well as SERFI and Oshkosh. Go to this page, fifth one down on lower part of the page:

"...N22EB
Grand Champion, Oshkosh 1998, SERFI 1998, and Sun 'n' Fun 2000."

And I think he has won awards for other aircraft he has built, too.

In addition, I believe, but I could be wrong, that he has been a judge at Sun'n Fun, perhaps even this last year. The point being, whether or not the correct book is quoted, I believe Dan knows that Safety should be high on the priority list when an aircraft is judged at Sun'n Fun, SERFI or Oshkosh.
Oh, I absolutely agree with your points. I was making no statement at all about Dan H, his building principles or his statements about judging. I was just making a point that I am not too sure that the Sun n Fun judges were following the actual EAA Airventure standards for judging.
 
Liability?

Van MUST speak out when he sees something that he, as the designer, considers problematic. To not do so would be to give tacit approval for the modifications------and in this crazy lawsuit happy society that equals Van accepting the liability for those changes.



This lawsuit issue has been mentioned on the thread several times. Just curious (I honestly don't know)...has Van's Aircraft ever been successfully held liable for a kit aircraft? On the other hand, if the builder can show damages caused by this article during a sale attempt...hmmm.
 
...I am not too sure Sun n Fun judges are following the same judging standards as the EAA Airventure judges.

You're correct in that only AirVenture uses the exact format detailed in the Judging Manual. However, I believe every show uses the EAA standards.

For example, a Sun'nFun or SERFI may not have the same class structure, will not have as many classes overall, and may not offer the same awards, but quite likely will use the standard 0-10 point system for rating safety, craftsmanship, etc (see "Decision Tree"), and follow most everything in the textual guidance.

We now return you to your regularly scheduled discussion
 
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The material in Van's article is true. What would the legal basis for a lawsuit be?
 
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It infers that the rudder system will not work and that the airplane may not be safe. Truth is not the issue, damages is....my buyer backed out because he read this article and decided the plane wasn't safe. The buyer had done his own pre-buy (in person) and was ready to go. He discovered all these things and was fine until the designer and half the forum said they wouldn't fly in it. It's not fair for the designer to do a negative "pre-buy" from a magazine article.
 
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are you a lawyer and this line of reasoning is based on legal principles?

i *think the truth is a defense in a libel lawsuit, and i would bet that Mr. Vansgrunsven would be considered an expert on his own for a case like this, so his statements would not be considered for damages. but i'm not a lawyer, and have found that these ideas about the law are often not worth even the 2pennies. If it is really a concern often a short consult with a real lawyer specializing in the subject is enlightening. and that is my actual experience: two separate occasions, of about an hour were well worth the several hundred dollars they cost.
 
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Anybody anytime for any reason

Anybody can sue anyone else for any reason at any time. You'd be amazed at what I have seen. That's not to say they can win, but they can initiate a lawsuit.

Van has a lot less exposure to this builder, though, than he would have to others if he accepted these sorts of things without saying anything about it. In fact, his exposure to this builder is so slight that it is almost nonexistent. But, the key word is almost.

What I try to tell people about litigation is that you can never eliminate exposure. All you can do is the best you can -- build your product as well and as intelligently as possible, tell the whole truth, identify your risks and manage them, and let the chips fall. If someone is determined to sue you, just as if someone is determined to kill you, they can figure out a way to do it.
 
PeterK....
You need to sort out how to quote others. It appears that you have MikeS and szicree(?) (post 78 & 79) making quotes that are yours! This thread is getting way too serious for mistakes like this.
Over and out!

[ed. I fixed the quotes (removed them to avoid confusion). dr]
 
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RV10/Vans

One more comment and then I will get out of this.

Safety is a very big concern and our hobby is under attack so I understand the need for Van to comment, I just wish he had done it generically vs. directly at a fine builder and long standing contributor to this hobby.

The seat belt deign is certainly an issue. The rudder cable is debatable. For those who do not have an RV10, the rudder cable attach point is not effected by braking unless this rudder pedal is also custom which I cant tell from the picture. He can add all kinds of extra fuel capacity, heck I know moderators on this site that have done that. Its up to the pilot to perform weight and balance and insure he does not overload the aircraft and the assumption that he will do something unsafe is not fair. As far as mods, its a good thing we can do that. The tunnel issue in the 10 is a good example.

Ok I'm done.

Pat
 
Knowing Greg's back ground, he knows what he's doing...

Judging only by the pictures of the rudder pedals and seat belt attachments... No he does not. He clearly does not understand structural loading and a very quick analysis by a first year engineering student would illustrate the error of his ways. The cantilevered bolt on the rudder pedals (and the incredible twisting load that the thin little tab is now expected to endure) would be unsafe on a kids go cart.

Somewhere else in this thread someone brought up the point that design is a very personal thing - and in the sense that designers will often find their own preferred solutions to a problem, this is absolutely true. However, all "real" engineering solutions will reconcile with the laws of physics and fundamental engineering principles.

Sure, there are countless ways to deviate from Vans design and still stay true to basic engineering principles, but simply claiming the E-AB status as your only justification is not going to impress the forces of nature.

So good on Van - not for pointing out that someone had "changed" his design, but for pointing out that the change was now contrary to basic engineering principles (and merely for aesthetics, at that!).
 
Judging only by the pictures of the rudder pedals and seat belt attachments... No he does not. He clearly does not understand structural loading and a very quick analysis by a first year engineering student would illustrate the error of his ways. The cantilevered bolt on the rudder pedals (and the incredible twisting load that the thin little tab is now expected to endure) would be unsafe on a kids go cart.

Somewhere else in this thread someone brought up the point that design is a very personal thing - and in the sense that designers will often find their own preferred solutions to a problem, this is absolutely true. However, all "real" engineering solutions will reconcile with the laws of physics and fundamental engineering principles.

Sure, there are countless ways to deviate from Vans design and still stay true to basic engineering principles, but simply claiming the E-AB status as your only justification is not going to impress the forces of nature.

So good on Van - not for pointing out that someone had "changed" his design, but for pointing out that the change was now contrary to basic engineering principles (and merely for aesthetics, at that!).

Full engineering analysis on rudder cable attach bolt based on one marginal picture.... debatable at best. :rolleyes: I'll defer to his back ground and experience

The seat belt redesign... If the crash is enough to overload the attach points, you've probably got bigger problems. Was there a sacrifice of function for form? Only one way to find out.
 
I'll agree that the pic of the rudder cable attach is not that great, although another view of the same area appears in the SA article and is pointed out as an example of the fine build quality. I think it's fair to say that such an article/photo might inspire others to do likewise. Now, if these pics are fair representations of the pedal arrangement then I'd say the tension placed on that tab is about three times what it would be with the original configuration. Now, if the tab was overbuilt by a factor of three then all is fine, otherwise not.

As far as the restraints go, the belt attach points look hokey but might be tough as needed. On the other hand, the location of the shoulder harness attachments is a joke.
 
PeterK....
You need to sort out how to quote others. It appears that you have MikeS and szicree(?) (post 78 & 79) making quotes that are yours! This thread is getting way too serious for mistakes like this.
Over and out!

[ed. I fixed the quotes (removed them to avoid confusion). dr]

post 78 wasn't mine, post 79 didn't quote anyone, it was simply a reply to post 78 by szicree. What Doug fixed I have no idea.(electronic?) you are correct however that this post is way too serious when you feel certified to tell me what I "need to sort out" and the self imposed authority to identify the source of all mistakes. And yes of course...over and out, sir.

[ed. To clarify, what I did was remove the little blue box in (3) replies. Did not touch a character of the replying person's words. dr]
 
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Full engineering analysis on rudder cable attach bolt based on one marginal picture.... debatable at best. :rolleyes: I'll defer to his back ground and experience...


I?m not trying to be argumentative here, but that thin little tab is designed to take load in plane with the weld. As designed, it will see essentially zero side load, and you could probably hang a small car from it with no problem. However, the addition of the bolt provides a significant lever arm to a flat tab with zero triangulation. As a result, the tab WILL flex at the weld, and it eventually WILL fatigue and break with almost absolute certainty. This conclusion does not need any more analysis than a quick glance to determine.

There is likely a fairly simple and safe modification to offset the rudder cables if desired, but this ain?t even close! Let?s also keep in mind that this is a PRIMARY flight control and subject to a single point failure.


The seat belt redesign... If the crash is enough to overload the attach points, you've probably got bigger problems. Was there a sacrifice of function for form? Only one way to find out.


Again, the out of plane leverage that this "modification" adds to the attach points has almost certainly reduced the load carrying ability to the point that it's useless in a crash. There's a good chance that a simple nose over at the end of the runway will pop every rivet head off that structure as it is twisted out of plane. I hope he never finds out...


Modifications are fine, but let?s not celebrate unsafe and overweight just because it's pretty!
 
My 2 cents

Main issue is additional weight which seems to be the same "problem" addressed with the RV6 whereas lots of builders used higher gross weights. Van argued against this BUT elected to use higher gross weights in the 7. One of the reasons given for this was that there had been lots of 6 owners safely using higher gross weight. Maybe when there's a 4 seat RV-11 it'll have a higher gross weight.
Vans has always been a minimalist and has ALWAYS cautioned against added weight and equipment--this is nothing new.
Also, having experience with air carrier weight and balance it's worth stating that Vans example doesn't really ring true. While freight carriers like Fedex and UPS weigh every container going on board, the passenger airlines are simply taking a guess on passenger weight and carry on bags, being a few percent over is not that uncommon. Also, they don't care where the weight watcher convention folks all wind up sitting so CG is questionable also.
 
post 78 wasn't mine, post 79 didn't quote anyone, it was simply a reply to post 78 by szicree. What Doug fixed I have no idea.(electronic?) you are correct however that this post is way too serious when you feel certified to tell me what I "need to sort out" and the self imposed authority to identify the source of all mistakes. And yes of course...over and out, sir.

[ed. To clarify, what I did was remove the little blue box in (3) replies. Did not touch a character of the replying person's words. dr]

Hmm...Somebody needs a hug and a nap!
I know what I saw...Thanks DR!.
 
Main issue is additional weight which seems to be the same "problem" addressed with the RV6 whereas lots of builders used higher gross weights. Van argued against this BUT elected to use higher gross weights in the 7. One of the reasons given for this was that there had been lots of 6 owners safely using higher gross weight.

Van did not arbitrarily assign a higher gross weight to the RV-7 because some builders were getting away with it in the RV-6. The RV-7, while being derived from the RV-6, is a different design. It was designed and tested for, among other things, a higher gross weight than the RV-6. As far as I know, Van's has not raised the max gross weight specification of the RV-6. It is still lower than the RV-7 (1600 vs. 1800 lbs).

Also, having experience with air carrier weight and balance it's worth stating that Vans example doesn't really ring true. While freight carriers like Fedex and UPS weigh every container going on board, the passenger airlines are simply taking a guess on passenger weight and carry on bags, being a few percent over is not that uncommon. Also, they don't care where the weight watcher convention folks all wind up sitting so CG is questionable also.

There are margins built into the loading specifications for a small amount of statistical variation inherent to how the airlines operate as you described, as well as other uncertainties in the design and construction of the airframe. That does not mean that there is sufficient margin left over for you to also knowingly overload the airplane, on top of those other uncertainties that still exist for which that margin was allotted. That is exactly Van's point, and he is absolutely correct.
 
Overload Question

Since I have never done this I have to ask the question. When ferry pilots far exceed the gross to load fuel for transoceanic flights (I realize they get a permit to do so) how do they avoid damaging the aircraft? Or do they only go to the manuf margin number?

Pete
 
I?m not trying to be argumentative here, but that thin little tab is designed to take load in plane with the weld. As designed, it will see essentially zero side load, and you could probably hang a small car from it with no problem. However, the addition of the bolt provides a significant lever arm to a flat tab with zero triangulation. As a result, the tab WILL flex at the weld, and it eventually WILL fatigue and break with almost absolute certainty. This conclusion does not need any more analysis than a quick glance to determine.

Exactly right evaluation.

There is likely a fairly simple and safe modification to offset the rudder cables if desired, but this ain?t even close! Let?s also keep in mind that this is a PRIMARY flight control and subject to a single point failure.

Say, perhaps using a single long bolt through the pivot points of the brake pedals, but make it extra long so that the head of the bolt sticks out the required 1 inch or so. Also increase the diameter of the bolt to 1/4 or 5/16 diameter and use a bushing around the the bolt to prevent the bolt from sliding side-to-side. Simple, easy, and way better than the existing design. Only downside is the cost of the long bolt.

Again, the out of plane leverage that this "modification" adds to the attach points has almost certainly reduced the load carrying ability to the point that it's useless in a crash. There's a good chance that a simple nose over at the end of the runway will pop every rivet head off that structure as it is twisted out of plane. I hope he never finds out...

The biggest problem I see with this picture is that the tremendous forces the seat belt will see during a crash are going to just fold up this skinny little rod. I remember years ago doing an calculation of the deceleration experienced in a 35mph car crash...it was in the neighborhood of 30 Gs. A 200lb pilot or passenger will exert 6000 lb on the seat belt attach points in such a scenario. Assuming equal distribution of force among three attach points, that's 2000 lb per attach point, but this rod will see double that if there's a passenger onboard, too. 4000 lb will just fold that 1/4" diameter rod in half. This might be an acceptable solution if the rod diameter is significantly larger to handle the bending load, but the best thing to do would be just attach the belts directly to their respective brackets so all the load is in-line.

268036_157245434346396_121827541221519_334223_2940540_n.jpg
 
It is ironic to me how some high time ATP/Military types on this board made a huge deal a few weeks ago out of lowly private pilots even thinking of questioning their flying behavior and potentially blowing the whistle to the FAA on them. Yet, when the tables are turned and assuming they are not aero engineers, they are quick to question Van and others who have been professionally designing aircraft for years. Van had no choice but to take issue with the article. The political correctness of how he handled it can be debated, but that issue is much less important than the point he was trying to make.
 
Van did not arbitrarily assign a higher gross weight to the RV-7 because some builders were getting away with it in the RV-6. The RV-7, while being derived from the RV-6, is a different design. It was designed and tested for, among other things, a higher gross weight than the RV-6. As far as I know, Van's has not raised the max gross weight specification of the RV-6. It is still lower than the RV-7 (1600 vs. 1800 lbs).


There are margins built into the loading specifications for a small amount of statistical variation inherent to how the airlines operate as you described, as well as other uncertainties in the design and construction of the airframe. That does not mean that there is sufficient margin left over for you to also knowingly overload the airplane, on top of those other uncertainties that still exist for which that margin was allotted. That is exactly Van's point, and he is absolutely correct.

OK--but in reality vs engineering you now have 2 similar designs with different gross weights. It has been argued that the 6 is actually a stronger frame and the shorter wing will handle more load. Only point I was trying to make is that similar statements were made by factory in regard to the 6 and then they jumped on the bandwagon.

Isn't the "extra margin" the same point that overweight builders always use? On cargo airlines, jumpseaters would be bumped if the plane went one pound over gross. "Small statistical variations" is not the case in passenger airlines as flights can easily be several thousand pounds different even given identical passenger loads. CG is also a **** shoot when you don't know where the heavier/lighter folks are sitting or where carry-ons of various weights are stored. I was simply trying to shoot a hole in the reference to passenger airlines as they are the worst example of specific loading.
 
OK--but in reality vs engineering you now have 2 similar designs with different gross weights.

The two designs are similar, but different. Their max gross weights are also similar, but different.

It has been argued that the 6 is actually a stronger frame and the shorter wing will handle more load.

I've heard only speculative hand-waving arguments to that effect. I'm not aware of any actual engineering or test data to support that hypothesis.

Only point I was trying to make is that similar statements were made by factory in regard to the 6 and then they jumped on the bandwagon.

I'm not aware that the factory jumped on any such bandwagon. As far as I know, the factory still specifies a max gross weight of 1600 lbs for the RV-6 (see specs on Van's web site).

Isn't the "extra margin" the same point that overweight builders always use?

Yes, that is the error that wishful-thinking builders make when they assume that there is sufficient extra margin for them to arbitrarily raise the max gross weight.

On cargo airlines, jumpseaters would be bumped if the plane went one pound over gross. "Small statistical variations" is not the case in passenger airlines as flights can easily be several thousand pounds different even given identical passenger loads. CG is also a **** shoot when you don't know where the heavier/lighter folks are sitting or where carry-ons of various weights are stored.

Again, yes, there is uncertainty in airline passenger weight and distribution. And presumably, the statistical variation associated with that uncertainty is characterized and accounted for in the margins built into airline loading calcs. And again, that doesn't mean that there is sufficient margin for you to also knowingly overload the aircraft on top of that uncertainty.

I was simply trying to shoot a hole in the reference to passenger airlines as they are the worst example of specific loading.

Ok, no problem. So let's use cargo carriers as a simpler, less muddy analogy. The more precise methods used by cargo carriers for loading calculations, and how strictly they adhere to the max gross weight specifications, only strengthens the point Van was trying to make.
 
..... He clearly does not understand structural loading and a very quick analysis by a first year engineering student would illustrate the error of his ways. The cantilevered bolt on the rudder pedals (and the incredible twisting load that the thin little tab is now expected to endure) would be unsafe on a kids go cart.

....!).

I read his documentation of the rudder cable mod (on his build site) and he DID consider the bending moment of the cable attach tab. To that end, the head of the machined bolt lies against the vertical rudder pedal post, by design, negating any bending of the attach bracket.

Best,
 
I know i am going to catch a lot of flack for my comment because it is just the nature of all forums.... but here it goes.

1. The rv is an EXPERIMENTAL aircraft. If VANS wants to regulate or prevent all from doing as you wish with your property, they should certify the aircraft and be done with. Otherwise, thank you very much for a great product. It is my right under the privileges given by the faa and my responsibility as the builder to do as i see in my own interpretation what i want with my experimental aircraft. Right or wrong...my aircraft....see next point.

2. If the aircraft passed the DAR INSPECTION, it is done! No one questioned this small detail. If it is so unsafe, who was the dar that gave the certificate?


I seen a lot of Rv,s built to specs and i will not fly in them. Where is Vans on this? Imho, i think vans crossed the line here....

Ok fire away now.
 
actually i would like to see Mels comments on the DAR responsibility in this area.

I've always had the impression the DAR sign off is not a piece of paper that says the airplane is safe to fly, the airplane has not been flight tested, how can it be so?

What the pink slip means it has all the required placards, the engine runs, and the required forms are correctly completed and for some reason, the builder has a pilots license and current medical. (that was checked the last time the FAA looked at one of my airplanes - that was a re-certification to get the new ops specs regarding major changes)

This thread has gone slightly ballistic and over the edge to boot. Read the SA article, Vans response to it and get on with life. The airplane looks great and is a tribute to Mr. Hale but like it or not, Vans comments are appropriate.
 
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