|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

11-25-2011, 09:11 AM
|
|
|
|
Join Date: Apr 2006
Location: Arizona
Posts: 387
|
|
Tailwheel Nosewheel Neither?
LeeM_2000,
Are you building an RV tailwheel, nosewheel, or neither? If neither, which way are you planning to go? (Your profile says your RV of interest is the "7," but I suppose it could be 7A, since Doug doesn?t have an "A" designation option for the profile.)
Thanks,
Bill Palmer 
|

11-25-2011, 10:35 AM
|
|
|
|
Join Date: May 2007
Location: Quincy, Florida
Posts: 680
|
|
deficiency
I'll vote with the comment about the pilots of wrecked airplanes being the major problem. With proper training and experience and paying attention in the landing/taxi phase of flight, there is no reason to ground loop a taildragger and no reason to "doink over" an A model RV. I don't believe that any of Van's demonstrators have ever "doinked over" or ground looped. Of course, extreme conditions will be an exception to my comment. I believe that both models are safe, but both require a certain level of skill to fly without incident.
|

11-25-2011, 10:36 AM
|
|
|
|
Join Date: Apr 2006
Location: Arizona
Posts: 387
|
|
Happy Holidays
Lee,
I wouldn?t recommend concluding from the accident statistics that either RV model is ?deficient? from a design standpoint. The past accident data actually says that pilot error (proficiency, judgment, skill) is the main safety issue for both RV models; not design. If you strip-out pilot error and non-RV-design causes (engine outs, for example), there is virtually nothing left in the accident database; certainly nothing statistically valid for influencing a model choice decision. In other words, the past accident statistics prove, beyond a shadow of a doubt, that both RV models are historically safe from a design standpoint. Certainly, their mutual, relatively low stall speeds point to increased safety. Also, both RV models are constantly being improved; particularly the nosewheel models lately (Van's, Anti-Splat, new wheels/axles, spacers, etc.). Nosewheel RV pilots are clearly more aware and improving. In fact, nosewheel nose-overs may already be a thing mostly of the past; not the future.
Bottom Line: In my opinion, concluding that any RV model, nosewheel or tailwheel, is unsafe or ?deficient? based on past accident statistics which point overwhelmingly to pilot error is both an invalid exercise and a trip to the ?Dark Side? of Van?s Air Force! I would suggest that the glass is almost completely full for both RV models and not even close to empty for either! In the spirit of the holidays and Van?s Air Force camaraderie, if one has something positive and useful to contribute to the overall RV community, then go for it! Otherwise, it might be best to think twice before concluding that one RV model is more dangerous and not as good another RV model or that both RV model designs are somehow ?deficient.? There really is no objective, complete, or even possible database to prove that either RV model design is unsafe or ?deficient.? In fact, practical experience, numbers flying/building, and just plain common sense say that both RV models are the greatest homebuilt aircraft ever designed! Pick either one you like; you won?t be sorry! You?ll only risk being sorry if you select something else!
Happy Holidays to All RVers!
Bill (Sometimes ?Darth Nosewheel,? but Trying To Be ?Luke for All RVs? Skywalker) Palmer 
|

11-25-2011, 12:35 PM
|
 |
|
|
Join Date: Nov 2006
Location: Saint Simons Island , GA
Posts: 1,523
|
|
In the spirit of today
BLACK FRIDAY
So far unless I'm really missing something here we can draw no conclusions about A model safety here.
Unless you strip out everything but landing accidents all of this about which is safer is moot.
Just looking at the NTSB database about RVs as a group tells me nothing.
They are like any other aircraft in that YOU have to operate them safely and within your and their limitations.
Big wheel/little wheel, from all the above statistics in this post nothing tells me one is safer than the other.
Now, go out and go shopping.
__________________
Jerry "Widget" Morris
RV 8, N8JL, 3,000+ hours on my 8.
VAF #818
Saint Simons Island, GA. KSSI
PIF 2008, 2009, 2010, 2011,2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020
 I just wish I could afford to live the way I do
|

11-25-2011, 05:07 PM
|
 |
|
|
Join Date: May 2009
Location: KS
Posts: 110
|
|
Quote:
Originally Posted by Bill Palmer
Lee,
I wouldn’t recommend concluding from the accident statistics that either RV model is “deficient” from a design standpoint. The past accident data actually says that pilot error (proficiency, judgment, skill) is the main safety issue for both RV models; not design. If you strip-out pilot error and non-RV-design causes (engine outs, for example), there is virtually nothing left in the accident database; certainly nothing statistically valid for influencing a model choice decision. In other words, the past accident statistics prove, beyond a shadow of a doubt, that both RV models are historically safe from a design standpoint. Certainly, their mutual, relatively low stall speeds point to increased safety. Also, both RV models are constantly being improved; particularly the nosewheel models lately (Van's, Anti-Splat, new wheels/axles, spacers, etc.). Nosewheel RV pilots are clearly more aware and improving. In fact, nosewheel nose-overs may already be a thing mostly of the past; not the future.
Bottom Line: In my opinion, concluding that any RV model, nosewheel or tailwheel, is unsafe or “deficient” based on past accident statistics which point overwhelmingly to pilot error is both an invalid exercise and a trip to the “Dark Side” of Van’s Air Force! I would suggest that the glass is almost completely full for both RV models and not even close to empty for either! In the spirit of the holidays and Van’s Air Force camaraderie, if one has something positive and useful to contribute to the overall RV community, then go for it! Otherwise, it might be best to think twice before concluding that one RV model is more dangerous and not as good another RV model or that both RV model designs are somehow “deficient.” There really is no objective, complete, or even possible database to prove that either RV model design is unsafe or “deficient.” In fact, practical experience, numbers flying/building, and just plain common sense say that both RV models are the greatest homebuilt aircraft ever designed! Pick either one you like; you won’t be sorry! You’ll only risk being sorry if you select something else!
Happy Holidays to All RVers!
Bill (Sometimes “Darth Nosewheel,” but Trying To Be “Luke for All RVs” Skywalker) Palmer 
|
I think you misunderstand what I mean by 'deficient.' I never equated deficient with unsafe. I admitted that the numbers don't point necessarily to an unsafe design. To me they point to something that is less than perfect. Less than perfect = deficient or improvable. Hence, the Anti-Splat product.
However, to better explain what I consider optimal, it is my belief that airplanes should generally remain upright when they roll out after all but the hardest of hard landings (aka cartwheels, death spirals, etc...). I think they should remain upright during and after a nosegear failure. I also think you should be able to have an off-airport landing and remain upright. That does not seem likely in an A-model given the accident narratives I read.
Speaking of deficiencies; you know, the iPhone 4 receives a signal just fine if you hold it the right way or if you use one of their bumper covers. The vast majority of complaints about the "death grip" came from people holding the phone wrong or those not using a bumper. To the majority of folks, this was an acceptable design characteristic. I call it a deficiency, but it's not deficient enough to dissuade me from purchasing one. I like to think I am at least as good at holding a phone as I am at flying an airplane.
Last edited by LeeM_2000 : 11-25-2011 at 07:59 PM.
Reason: demoticonification
|

11-25-2011, 06:39 PM
|
 |
|
|
Join Date: Jan 2005
Location: Richmond, VA
Posts: 696
|
|
Quote:
Originally Posted by LeeM_2000
Definition of DEFICIENT
1: lacking in some necessary quality or element <deficient in judgment>
It is my opinion that landing gear should not tuck on landing or roll out under all but the most extreme conditions. In this case the necessary quality would be to NOT tuck and cause a rollover. There is plenty of evidence to suggest that this landing gear design can and will tuck under what I consider less than extreme conditions.

|
Lee,
Apparently I failed to convey my difficulty with your initial post and I will own my failure to convey what I was looking for. I wanted to know the data that you were using to reach your conclusion that the nose wheel design is deficient. It was numerical data and perhaps some statistical analysis that I was looking for, not a definition of a word you used.
And, I suppose you already know the "eye rolling" icon is somewhat demeaning and inappropriate in a discussion based on facts and rational deduction.
__________________
Don Alexander
Virginia
RV-9A 257SW Purchase Flying - O-320, Dynon D100
RV-9A 702DA (reserved) Finish Kit IOX-340
www.propjock.com
|

11-25-2011, 07:03 PM
|
|
|
|
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,574
|
|
pilot error, design deficiencies, durability
Its very easy to say that an airplane damaged during landing is from pilot error. Of course it is. If the pilot landed it better, there wouldn't be any damage. But that does not equate to "pilots with better technique/training/skill" would not ever have a problem.
A very skilled, high-time tailwheel pilot can still get caught off guard by a gust and groundloop. There are a number of those stories on this forum.
A very skilled, high-time tricycle pilot can still get caught off guard by an unexpected lip at the edge of pavement, or a pothole, or even let the nose down a bit too fast from a gust, and fold up a RV-6A/7A/9A nosewheel.
It doesn't add much at all to the discussion to just say it's all pilot error and stop considering that a characteristic of the airplane design is less forgiving and tolerant of less then perfect technique than it could/should be.
There is always a trade-off of strength/durability for weight and/or complexity. It is a matter of design judgement where to draw that line. But most good engineers would agree that if a very modest increase in weight or complexity can add a significant improvement in durability, it is a good trade.
Several engineering analysis have shown that the RV-6A/7A/9A nose gear strut is not stiff/strong enough in bending near the end, and striking a bump or a moderate impact can yield the strut. When it yields, it tucks under, which should be regarded as a DESIGN DEFICIENCY. A proper nose gear, when overloaded, should fail upwards, not tuck under. Given enough load, something is always going to fail. Good design should still manage that failure to minimize consequences.
The best solution for the nose gear would be to adapt the RV-10-style nose gear design to the RV-6A/7A/9A. A bit heavier and more complex, yes. Big payoff in durability, and when it does fail, it will fail upwards. The next best solution is to reinforce the existing gear - like the anti-splat device. The designer deserves cudo's for a simple, effective enhancement. And when it does fail, it will fail upward.
In the same way, there have been some discussions about making the RV-8 gear support structure a little more robust. Is it strong enough for skilled pilots and most all conditions? Yes, obviously. Could it gain more durability and suffer less widespread damage when there is a pilot mistake by some enhancement to the design. Yes. Should we just end any discussion by saying that good pilots can land it without breaking it? I don't think so. Same point: if a very modest increase in weight or complexity can add a significant improvement in durability, it is a good trade.
Examples of improving the RV-8 gear - a one-piece gear would be significantly stronger, and also heavier. Reinforcing some of some of the structural parts (the Z-channels under the floor that tie the gear towers together, and vertical stiffeners along the outboard edges of the towers) would add much less weight, and still provide a moderate strength increase.
To those that say, "if you are worried about your nose gear, look in the mirror" I would say, if you are positive that your excellent technique will never damage your nose gear, you better look in the mirror. We all make mistakes.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!! 
VAF donation Jan 2020
Last edited by scsmith : 11-25-2011 at 07:09 PM.
|

11-25-2011, 07:16 PM
|
|
|
|
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,574
|
|
Don:
There was a well-documented thread here a year or so ago that included a nice engineering analysis of the gear strut, and simulations of how it responds to a bump. You can search for that thread if you like.
I have also done simple engineering analysis of what the bending moment and stress is in the gear strut. It is evident that there is a moment inversion at a point directly above the axle, and forward of that, the bending moment is in the direction that makes it tuck. Further, it is evident that the bending stress is highest there, so at whatever load makes it fail, it will fail there first, instantly causing the roll-over.
My engineering opinion is that that is a design deficiency.
A small increase in the diameter of the strut in that region would prevent that. Then, at some higher load, it would yield and bend close to where the strut attaches to the engine mount. In that case, it would bend upward, not downward. This would give a progressive failure without immediate consequences. If it bent far enough, you would get a prop strike. Then, if it bent a whole lot more, the nose would hit - likely in a way that would not cause a roll over (in my opinion).
Quote:
Originally Posted by Don
I wanted to know the data that you were using to reach your conclusion that the nose wheel design is deficient. It was numerical data and perhaps some statistical analysis that I was looking for, not a definition of a word you used.
|
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!! 
VAF donation Jan 2020
Last edited by scsmith : 11-25-2011 at 07:21 PM.
|

11-25-2011, 11:15 PM
|
|
|
|
Join Date: Apr 2006
Location: Arizona
Posts: 387
|
|
Deficient?
Steve,
Certainly, we’re all entitled to our opinions and “deficient” is apparently a subjective term open to explanation and interpretation; at least that’s what I’m reading. My opinion is that neither the RV nosewheel models nor the RV tailwheel models are deficient from an overall, integrated design perspective (integrating weight, strength, load, performance, gear, etc.). Yes, improvements and changes can always be made, and individual systems can be evaluated in isolation, but there are trade-offs in terms of weight, performance, and other specifications as you have pointed out. Certainly, one man’s “modest increase in weight and complexity” is another man’s “I’ll lose 50fpm.”
I think we can all agree that Van has achieved a winning combination of low stall speed, excellent handling characteristics, sport aerobatic capability, high climb rates, and high cruise speeds. Overall RV performance is a major design achievement, at least in my opinion. Part of that is the simple (read “light”) tapered-steel-strut nosegear design; part of that is the RV-8’s relatively light gear towers, etc. Adding weight and complexity is usually not a good way to go for RVs; particularly adding weight. Van’s recent nosegear mod (new fork and shortened gear leg) actually lowered my 8A’s nosegear system weight by 1 lb. 5.5 oz. At 30 oz., the Anti-Splat looks like a reasonable modification weight-wise. A complete nosegear redesign might not be so reasonable from a weight (performance) standpoint.
If you are saying that RVs should be designed, or should have been designed, to reduced pilot proficiency standards as for, say, training aircraft such as the Piper Warrior or Cessna 172, then I would suggest that the resultant “RV” would be quite different and would probably not perform as well as what we have today. Certainly, a professional engineer such as yourself can undoubtedly achieve a more-robust, load-tolerant, and pilot-friendly RV nosegear/nosewheel design or a better, stronger main gear system for the RV-8. If you can do so without substantially impacting RV performance/weight, please do! I agree with you that the RV-10’s nosegear design is very attractive from an engineering perspective, but I would want to execute it in titanium or possibly (dare I say it?) composites, to keep the system light for my 2-place RV. Of course, I probably couldn’t afford to purchase such a titanium or composite nosegear system; a minor annoyance.
As your engineer’s goal is to eliminate pilot error through redesign, my builder’s goal is to modify what I can (Van’s, Anti-Splat, adjustable axle, etc.) and eliminate pilot error as much as possible through education and training. I suppose the optimum answer is somewhere in between. What influences my opinion is the fact that so many RVs, about 7,000, are flying with no reported damage history. Also, for nosewheel RVs, the historic nosewheel nose-over rate is 2% and the majority of that is, in fact, pilot error. Of course, I assume you would say that the “deficient” nosegear design is responsible for a lot of that pilot error, but the reported nose-over numbers also include nose-overs resulting from engine outs, off-airport landings, and the like. Certainly, the nose-over rate directly attributable to the original nosegear design, unmodified, is low compared to the 2,500 nosewheel RVs flying; it looks like less than 1%.
I personally don’t see the actual nosegear design performance/results as “deficient.” Engineering analysis of the nosegear geometry and materials is one thing; actual results are another. I would agree that the original nosegear design itself could be described as “marginal.” I don’t think Van would agree with that assessment, but maybe he’ll post?! (Not Likely!) Does the original nosegear design “need improvement?” I think the accepted answer for that one is yes. Is the RV nosegear design, particularly as it has evolved through recent modifications, “deficient?” I would conclude No! That’s my reasoning and “2 Cents” opinion anyway! I was going to say my “non-engineer’s” opinion, but that wouldn’t be true!
Bill Palmer
P.S. Steve, have you considered the potential legal/business ramifications to Van’s as a result of your posts? If you haven’t already been contacted by a product liability/aviation accident attorney, I suspect you might. You are the first professional aeronautical engineer I’ve seen who has been willing to publicly document that you consider Van’s 2-place nosegear design to be “deficient.”
Last edited by Bill Palmer : 11-26-2011 at 11:55 AM.
Reason: legal/business
|

11-26-2011, 07:44 AM
|
 |
|
|
Join Date: Jan 2005
Location: Richmond, VA
Posts: 696
|
|
Steve,
I appreciate the extensive reply but somehow I am no doing an adequate job of communicating my position and what I am seeking. In the past I've seen posts degrade when this happens and I don't want to belabor the point too much more.
To be clear, I don't have a position on whether the nose wheel design Van's sells is deficient or not. It appears to be sufficient based on the data presented (I am saying "appears" which is NOT a conclusion). It also appears to be the weakest link in the design based on the same data (again, no conclusion) and this is based on the relative frequency of nose gear failures. Note again, I am saying "relative frequency" - I am NOT concluding the frequency is too great. I am saying out of all the RV accidents/incidents, it is one you hear about more than any other.
So, what I have been doing is soliciting DATA from both sides of the debate. Lee made some fairly strong conclusions, which he seems to be backing off of, based on something. When asked for data he provide a definition and a smirk. It wasn't much support for his case. You have alluded to a structural analysis that you've performed and based conclusions on it and on a discussion on this website about a year ago. It would be informative to see your analysis and to have it vetted here by other engineers.
At this point, I'm trying to collect, understand, and evaluate both sides of the argument. Only then will I make a decision. In my experience, I am far more skeptical than most folks and I like to make decisions based on data, not on opinions and tradition.
It appears that both sides MAY have merit. Unfortunately, only one side has presented any substantive data or technical support (though I am hopeful you'll change this by sharing the analysis you alluded to).
__________________
Don Alexander
Virginia
RV-9A 257SW Purchase Flying - O-320, Dynon D100
RV-9A 702DA (reserved) Finish Kit IOX-340
www.propjock.com
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 05:36 AM.
|