Van's Air Force
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Year long discussion of "Another nosegear failure" -09/19/2010
- Thread starter rocketbob
- Start date
Hollow Leg?
This is an idea worth considering, Pierre. I do agree with the other engineer's statement that putting out one fire can lead to another different one (known by us engineers as The Law of Unintended Consequences).
Automobile suspensions separate the structural and movement functions, i.e. a control arm isn't ridgidly attached to the chassis at the inboard end and expected to deform elastically to provide suspension travel.
The current gear leg is a solid cross-section. It requires a machined/ground OD profile, forming and heat treating. If the functions of movement and structure were separated, perhaps a larger cross-section formed tube could be used as the leg, sized so the section modulus would be greater without a weight penalty, or even a reduction in weight. It seems like it would be less expensive to form a constant cross-section tube as opposed to machining/grinding the taper profile. Obviously there would be some added complexity at the firewall end of the leg that would also add some weight and expense.
It seems that separating structure and movement functions would be an excellent start. The Young's Modulus (i.e., "springiness") of all steels is the same. For a piece of steel to be used as a spring, the section modulus (think "stiffness") deliberately has to be reduced so the the steel will deform elastically under load. That means high stresses, which dictates alloy steels with high yield strengths, and finite fatigue life. Unlike many steel parts that can be designed for infinite fatigue life, there is a finite number of cycles a given spring can see before it fatigues and breaks. All automobile and truck manufacturers run lab tests to statistically determine that their springs will have "adequate" fatigue life. At every commercial truck scale in the US you will see vehicles taken "out of service" by commercial vehicle officers. The most common mechanical failure that results in a vehicle being tagged by a CVO is a broken spring. By separating structure and movement, the leg itself could be designed for "infinite" fatigue life (although nothing can be designed for "single event overload," aka "crash.") The rubber springs could be an easily replaceable maintenance item.
LarryT
This is an idea worth considering, Pierre. I do agree with the other engineer's statement that putting out one fire can lead to another different one (known by us engineers as The Law of Unintended Consequences).
Automobile suspensions separate the structural and movement functions, i.e. a control arm isn't ridgidly attached to the chassis at the inboard end and expected to deform elastically to provide suspension travel.
The current gear leg is a solid cross-section. It requires a machined/ground OD profile, forming and heat treating. If the functions of movement and structure were separated, perhaps a larger cross-section formed tube could be used as the leg, sized so the section modulus would be greater without a weight penalty, or even a reduction in weight. It seems like it would be less expensive to form a constant cross-section tube as opposed to machining/grinding the taper profile. Obviously there would be some added complexity at the firewall end of the leg that would also add some weight and expense.
It seems that separating structure and movement functions would be an excellent start. The Young's Modulus (i.e., "springiness") of all steels is the same. For a piece of steel to be used as a spring, the section modulus (think "stiffness") deliberately has to be reduced so the the steel will deform elastically under load. That means high stresses, which dictates alloy steels with high yield strengths, and finite fatigue life. Unlike many steel parts that can be designed for infinite fatigue life, there is a finite number of cycles a given spring can see before it fatigues and breaks. All automobile and truck manufacturers run lab tests to statistically determine that their springs will have "adequate" fatigue life. At every commercial truck scale in the US you will see vehicles taken "out of service" by commercial vehicle officers. The most common mechanical failure that results in a vehicle being tagged by a CVO is a broken spring. By separating structure and movement, the leg itself could be designed for "infinite" fatigue life (although nothing can be designed for "single event overload," aka "crash.") The rubber springs could be an easily replaceable maintenance item.
LarryT
az_gila
Well Known Member
Since the Grumman gear...
...has been mentioned previously - it may be noted that the nose gear leg is a heavy wall tube, with a pivot "axle" bonded on at the end.
The shock movement is provided by a torque tube that is the width of the cockpit just behind the firewall...
...has been mentioned previously - it may be noted that the nose gear leg is a heavy wall tube, with a pivot "axle" bonded on at the end.
The shock movement is provided by a torque tube that is the width of the cockpit just behind the firewall...
Thanks for the info on the Grumman gear, Gil, that's what I wanted to know. So while the design looks similar, it might not be all that much alike.
One thing that does stand out in my mind is that the gearlegs on the Grumman and other similar gear i've seen use a constant cross section member of some kind (solid or hollow, I don't know). Van used a tapered rod, which can be better from an engineering standpoint in that the load can be more evenly distributed along the rod, but that means it could fail anywhere long its length. It also means the curvature under load gets greater towards the tip, which might be part of the problem here.
Maybe just switching to a constant cross section, equal to the current dimensions at the firewall end, would be the simplest solution. Yes, it would move the failure point "up the line" as it were. But if it moved the failure to the mount point, or even right back to the firewall, I think people would still find an engine mount failure followed by skidding along on the cowling preferable to getting pole-vaulted onto their backs. If nothing else it should be reasonably easy to try.
I also like the idea of changing from the current fork design to a "Doug Bell" style fork, but I don't know how well that would work on the front of the plane. I know it works brilliantly on the back.
[size=-2]And yes, I am an aeronautical engineer, but I haven't put much more than back of the envelope thought into this... So standard disclaimers apply, your mileage may vary, etc. etc.[/size]
One thing that does stand out in my mind is that the gearlegs on the Grumman and other similar gear i've seen use a constant cross section member of some kind (solid or hollow, I don't know). Van used a tapered rod, which can be better from an engineering standpoint in that the load can be more evenly distributed along the rod, but that means it could fail anywhere long its length. It also means the curvature under load gets greater towards the tip, which might be part of the problem here.
Maybe just switching to a constant cross section, equal to the current dimensions at the firewall end, would be the simplest solution. Yes, it would move the failure point "up the line" as it were. But if it moved the failure to the mount point, or even right back to the firewall, I think people would still find an engine mount failure followed by skidding along on the cowling preferable to getting pole-vaulted onto their backs. If nothing else it should be reasonably easy to try.
I also like the idea of changing from the current fork design to a "Doug Bell" style fork, but I don't know how well that would work on the front of the plane. I know it works brilliantly on the back.
[size=-2]And yes, I am an aeronautical engineer, but I haven't put much more than back of the envelope thought into this... So standard disclaimers apply, your mileage may vary, etc. etc.[/size]
MrNomad
Well Known Member
Keep the momentum rolling......
The nose gear issue has been discussed many times on this forum. If there are two things we ALL agree on it's our love affair with these airplanes and our willingness to help one another with tips, suggestions, training, and ideas.
I propose we take this nose gear conversation to the next level. That we create a working environment for those engineers and mechanics in our community who are willing to commit some time and talent towards an improved design.
Raise money as required. My nose gear problem cost me $7200 "out of pocket" and two months of labor to repair. I'm happy to send $$ to a qualified effort whose goal is an improvement.
I'm certain our community has one or more lawyers who can compose the necessary documentation so that legalese does not preclude progress.
I'm also certain our community has one or more manufacturers who might be willing to produce the part.
Finally, our community has many talented flight instructors and photographers who are probably willing to photo proper landing technique so that all aspects of this situation are addressed.
Let's use the most recent disaster as the catalyst to reduce the incidence of this problem.
My two cents.
The nose gear issue has been discussed many times on this forum. If there are two things we ALL agree on it's our love affair with these airplanes and our willingness to help one another with tips, suggestions, training, and ideas.
I propose we take this nose gear conversation to the next level. That we create a working environment for those engineers and mechanics in our community who are willing to commit some time and talent towards an improved design.
Raise money as required. My nose gear problem cost me $7200 "out of pocket" and two months of labor to repair. I'm happy to send $$ to a qualified effort whose goal is an improvement.
I'm certain our community has one or more lawyers who can compose the necessary documentation so that legalese does not preclude progress.
I'm also certain our community has one or more manufacturers who might be willing to produce the part.
Finally, our community has many talented flight instructors and photographers who are probably willing to photo proper landing technique so that all aspects of this situation are addressed.
Let's use the most recent disaster as the catalyst to reduce the incidence of this problem.
My two cents.
A good friend of mine teaches never land full flaps, it just doesn't makes sense. 10 or 20 degrees ist just fine, if you need more, than jou are allready in a risky enviroment ( short or/and soft field ) anyway. What's all that drag at 40 degrees for, and the pitching forvard force it provoques ?
LeeM_2000
Well Known Member
I personally find it unlikely that so many RV pilots have forgotten good soft field techniques. As appears popular to say before making a judgment, I am not an engineer, but it seems quite clear to me from just looking at it that landing on soft fields is simply not a strength of that nose gear design. And, I am not sorry to point out that hundreds of successful landings on the same soft field does not qualify the airplane for soft field landings in my estimation.
It is a bummer because I would like the tricycle configuration otherwise. I have to be able to land on grass. I enjoy it too much and there are too many cool places at the end of grass strips. Maybe there will be an update by the time I get to the fuselage.
It is a bummer because I would like the tricycle configuration otherwise. I have to be able to land on grass. I enjoy it too much and there are too many cool places at the end of grass strips. Maybe there will be an update by the time I get to the fuselage.
Kyle Boatright
Well Known Member
More than a few RV pilots are careless with their short field technique. I go to quite a few fly-ins and whether on pavement or grass, see plenty of RV's where the nosewheel is plopped right down immediately after the mains touch and little or no up elevator is applied. No, it isn't a majority, but it is a surprising number.
I'm sure this has been a contributing factor in some nosegear failures - one lax moment can cost you. However, it is my belief that the nose gear should be more forgiving of less than optimal pilot technique.
LifeofReiley
Well Known Member
Amen... !!!!! I see abuse even on asphalt runways all the time, many crossing the #'s at 80-85kts burning the coal... bouncing everywhere, nosewheel landings and all
LeeM_2000
Well Known Member
Yeah, being relegated to spam cans leaves me pretty much local, aside from OSH, so my opinion of RV pilots may be slightly myopic. The RVs in my operating area seem to have it down, however. In fact, most of the regulars I see at my airport have it down. I think they have to because the grass can be pretty rough at times.
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Captain Avgas
Well Known Member
I'm with you Pierre. The RV10 leg is a far better option. Much heavier aircraft and none of them have ended up on their back sunning themselves
If there was an option provided from Van's to fit that on my RV6A count me in.
The RV10 option may be the way for Vans to go but you would not want to underestimate the problems associated with a retrofit of this type of design because it will involve replacement of both the engine mount and the nose gear (plus mods to the lower cowl and the potential redirection of some existing FWF systems). OK for new kit buyers but a disaster of sorts for existing owners.
See my post #36 on this thread for further explanation:
http://www.vansairforce.com/community/showthread.php?t=62815&page=4
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kentb
Well Known Member
two weeks ago at my airport.
I saw a guy in a piper make a three point landing. All three wheels touch down at the exact same moment.
Unfortunately it was a piper archer.
Don't know the pilot, he wasn't local to the airport.
You can get away with this on some planes. When I was learning in a C172, I remember more than once my instructor complaining about holding the nose wheel up.
Kent
I saw a guy in a piper make a three point landing. All three wheels touch down at the exact same moment.
Unfortunately it was a piper archer.
Don't know the pilot, he wasn't local to the airport.
You can get away with this on some planes. When I was learning in a C172, I remember more than once my instructor complaining about holding the nose wheel up.
Kent
Anything less than full flaps in my -6 and you can't three-point it. You'll one-point it on the tailwheel before the mains come down. Ideally, I land full flap, and wheel it on. The full flaps reduce the load on my brakes, and shorten the rollout.
Frank Smidler
Well Known Member
Full flare?
Are you trying to do a full stick back flare? In my transition training with Alex DeDominicis he made it very clear that before you take off you have to look out and get a mental picture of the airplanes attitude when on the ground. When you come in for landing you have to flare to the same attitude and hold it, letting the plane settle in on three points. If you try to do a full stick flare the tail will hit first then the mains will drop and bounce you back into the air. I do this no matter how much flap I have out and it works great. The only problem I have is flaring at the right height.
Are you trying to do a full stick back flare? In my transition training with Alex DeDominicis he made it very clear that before you take off you have to look out and get a mental picture of the airplanes attitude when on the ground. When you come in for landing you have to flare to the same attitude and hold it, letting the plane settle in on three points. If you try to do a full stick flare the tail will hit first then the mains will drop and bounce you back into the air. I do this no matter how much flap I have out and it works great. The only problem I have is flaring at the right height.
ScottSchmidt
Well Known Member
Really?
Is that true for the RV-6,7A's? In the -10 I can do a full stick flare with any flap setting and the tail will not hit.
I have only landed an RV-6A about 10 times and I had no problem landing on the mains and holding the front wheel off until the elevator lost authority.
I sure hate seeing these planes flip over. I'm sure sorry about that.
Pretty soon the insurance for a nose-dragger will be more than a tail-dragger.
Is that true for the RV-6,7A's? In the -10 I can do a full stick flare with any flap setting and the tail will not hit.
I have only landed an RV-6A about 10 times and I had no problem landing on the mains and holding the front wheel off until the elevator lost authority.
I sure hate seeing these planes flip over. I'm sure sorry about that.
Pretty soon the insurance for a nose-dragger will be more than a tail-dragger.
sprucemoose
Well Known Member
Uh, It looks like Frank is talking about taildraggers, while you (and the rest of this thread) are thinking 3 point attitude in a nosegear. Might explain the confusion.
That proves the nose down pitch full flaps provoques. In your taildragger it will help you force the tail up on the flare. On A models we seek just the contrary, we need the nose wheel up and tail down as long as is possible, specialy when allready on the ground, on rollout.
Have any 8A's experienced this?
I did a brief search and did not find any mention of 8A's experiencing this kind of nose gear failure. Does anyone know of any? I realize there are far fewer 8A's than 6A's or 7A's flying but am curious because the 8A can be very nose heavy depending on the load.
I did a brief search and did not find any mention of 8A's experiencing this kind of nose gear failure. Does anyone know of any? I realize there are far fewer 8A's than 6A's or 7A's flying but am curious because the 8A can be very nose heavy depending on the load.
Av8torTom
Well Known Member
Simple Solution?
It's been said before by many, and I completely agree. A larger nose wheel would be a huge improvement in the design, and less expensive than a re-do of the nose gear. It would minimize the effects of surface imperfections and raise the "nut" even further off the ground. This may also require larger main wheels, but that's been done by others as well.
When I look at that YouTube vid of the nosewheel on the grass, I can easily visualize a larger nose wheel riding more smoothly over the surface.
My $0.02
It's been said before by many, and I completely agree. A larger nose wheel would be a huge improvement in the design, and less expensive than a re-do of the nose gear. It would minimize the effects of surface imperfections and raise the "nut" even further off the ground. This may also require larger main wheels, but that's been done by others as well.
When I look at that YouTube vid of the nosewheel on the grass, I can easily visualize a larger nose wheel riding more smoothly over the surface.
My $0.02
Holding up nose wheel while braking
You can brake while holding up the nose wheel. It is just a matter of applying more back pressure on the stick as you apply braking pressure. It is a balancing act but very doable.
This was one of the things I practiced with Seager during transition training and emphasized during a recent flight with him while landing on Vernonia's grass strip. It also helps in safely shortening the landing rollout on any surface.
You can brake while holding up the nose wheel. It is just a matter of applying more back pressure on the stick as you apply braking pressure. It is a balancing act but very doable.
This was one of the things I practiced with Seager during transition training and emphasized during a recent flight with him while landing on Vernonia's grass strip. It also helps in safely shortening the landing rollout on any surface.
Av8torTom
Well Known Member
Well good point, but...
Even oleo struts nose struts can fail
http://www.youtube.com/watch?v=NMmHYWjEmkY
Even oleo struts nose struts can fail
http://www.youtube.com/watch?v=NMmHYWjEmkY
Av8torTom
Well Known Member
David Paule
Well Known Member
A larger nosewheel, and the larger fork needed to clear it, will lower the natural frequency of the existing strut. That could increase the deflection....
.
Av8torTom
Well Known Member
Yes, but...
I would be surprised if the small increase (1-2 inches) in CG would make much difference.
I think this guy has done some serious thinking about this:
http://mesawood.info/myrv7a/building/nosegearmodinfo.html
I would be surprised if the small increase (1-2 inches) in CG would make much difference.
I think this guy has done some serious thinking about this:
http://mesawood.info/myrv7a/building/nosegearmodinfo.html
PaigeHoffart
Well Known Member
8A vs 7A
If you read this:
http://www.ntsb.gov/publictn/2006/RV_Study.pdf
It sounds like every A model has been involved.
Having said that, there might be a reason why we don't hear about 8A nose overs as much. Looking at the 3-view drawings on Van's website gives me the impression that the 8A has a slightly greater distance between the nose wheel and mains than the 7A. It looks like about 8", but it would be interesting to measure. A nose wheel farther away from the CG might reduce some of the loading.
Looking at Van's published weight on nose wheel chart seems to confirm this. For the same weight and CG location, an 8A has about a 7% lower nose wheel weight when compared to a 7A. Perhaps the combination of slightly lower static and dynamic loading is significant?
Paige
If you read this:
http://www.ntsb.gov/publictn/2006/RV_Study.pdf
It sounds like every A model has been involved.
Having said that, there might be a reason why we don't hear about 8A nose overs as much. Looking at the 3-view drawings on Van's website gives me the impression that the 8A has a slightly greater distance between the nose wheel and mains than the 7A. It looks like about 8", but it would be interesting to measure. A nose wheel farther away from the CG might reduce some of the loading.
Looking at Van's published weight on nose wheel chart seems to confirm this. For the same weight and CG location, an 8A has about a 7% lower nose wheel weight when compared to a 7A. Perhaps the combination of slightly lower static and dynamic loading is significant?
Paige
RV7AV8R
Well Known Member
When you compare these photos of planes with a similar nose gear but two without the problem there are other differences as well. Gruman and DA40 have wider lower stances. Just looking at these photos, which looks more unstable?
rocketbob
Well Known Member
Which reiterates what I have thought all along: the leg itself is strong enough, but the fork needs to be redesigned such that it would be virtually impossible for it to make contact. If the fork is redesigned to make it similar in construction to one of the aftermarket tailwheels, machining of the leg would be necessary to mate the fork to it. It would also make the leg easier to make since a bend would no longer be required.
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Tuck
Seems to me that the issue is that the taper of the leg and geometry of the fork causes the nose assembly to tuck under. The flex in the gear leg is such that the front nut rotates closer to the ground rather than away from it under the landing loads (up and back) If the flex occurred closer to the firewall, like it does with sprung assemblies, the movement of the fork would be more vertical and less rotational.
In summary, make the gear leg stiffer near the nose gear, relatively less stiff nearer the firewall. In my opinion, all we need is a small change in taper of the gear leg, not a total redesign. If it was done correctly, the nut would get no closer to the ground when vertically loaded.
Vans got it half right raising the nut. It helps if you fall in a deep hole but I suspect many of the flips have a simple vertical load and tuck of the fork to blame.
I may winch mine down this weekend and watch what the fork does.
I also like the way that my old 6a's tail hugs the ground! (tricky problems are seldom the result of just one thing, nor is the fix)
Seems to me that the issue is that the taper of the leg and geometry of the fork causes the nose assembly to tuck under. The flex in the gear leg is such that the front nut rotates closer to the ground rather than away from it under the landing loads (up and back) If the flex occurred closer to the firewall, like it does with sprung assemblies, the movement of the fork would be more vertical and less rotational.
In summary, make the gear leg stiffer near the nose gear, relatively less stiff nearer the firewall. In my opinion, all we need is a small change in taper of the gear leg, not a total redesign. If it was done correctly, the nut would get no closer to the ground when vertically loaded.
Vans got it half right raising the nut. It helps if you fall in a deep hole but I suspect many of the flips have a simple vertical load and tuck of the fork to blame.
I may winch mine down this weekend and watch what the fork does.
I also like the way that my old 6a's tail hugs the ground! (tricky problems are seldom the result of just one thing, nor is the fix)
frazitl
Well Known Member
I've been wondering
what would be required to use 6A main gear legs on a 7A. I understand they are shorter. The tail low(er) stance created would, if nothing else, lower the CG and reduce the rearward force on the front wheel when it hits a hole or a bump. Besides, I still like the looks of my Mooneys...
what would be required to use 6A main gear legs on a 7A. I understand they are shorter. The tail low(er) stance created would, if nothing else, lower the CG and reduce the rearward force on the front wheel when it hits a hole or a bump. Besides, I still like the looks of my Mooneys...
another non engineer look and suggestion
If you look at the nose gear of the other planes pictured above compared to the RV the RV has a higher vertical angle and the other ones a more horizontal angle. So if an RV hits a "hole" the gear leg becomes more vertical and thus will bed backwards much easier. Strengthening the leg as it stands now would possible store more energy for a possible flip over. Not being an engineer, I would think that being able to mount the front gear leg lower on the firewall to increase the horizontal angle of the leg would allow the gear leg to flex up to absorb the energy and then spring down, instead of bending back to absorb the energy and spring forward that it appears to be doing now. In a perfect world the nose coming straight forward would never bend over, but then it would be tough to get the spinner to spin fast enough to get off the ground.
The other possible thing would be to possibly lower the mains to get a more horizontal angle on the front gear. Also by lowering the mains, if the front gear hits a "hole" then the horizontal plane of the rv would still be more horizontal then as it is now with the leg bending and putting the nose lower to the ground thus putting attitude of the plane less than horizontal, and making it ready to flip over.
Take it for what it is worth, my 2c
Bob K
If you look at the nose gear of the other planes pictured above compared to the RV the RV has a higher vertical angle and the other ones a more horizontal angle. So if an RV hits a "hole" the gear leg becomes more vertical and thus will bed backwards much easier. Strengthening the leg as it stands now would possible store more energy for a possible flip over. Not being an engineer, I would think that being able to mount the front gear leg lower on the firewall to increase the horizontal angle of the leg would allow the gear leg to flex up to absorb the energy and then spring down, instead of bending back to absorb the energy and spring forward that it appears to be doing now. In a perfect world the nose coming straight forward would never bend over, but then it would be tough to get the spinner to spin fast enough to get off the ground.
The other possible thing would be to possibly lower the mains to get a more horizontal angle on the front gear. Also by lowering the mains, if the front gear hits a "hole" then the horizontal plane of the rv would still be more horizontal then as it is now with the leg bending and putting the nose lower to the ground thus putting attitude of the plane less than horizontal, and making it ready to flip over.
Take it for what it is worth, my 2c
Bob K
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tadsargent
Well Known Member
nose gear
Gruman and DA40 have wider lower stances. Just looking at these photos, which looks more unstable?
No pilots are visable and they are on pavement, Neither.
Regards
Gruman and DA40 have wider lower stances. Just looking at these photos, which looks more unstable?
No pilots are visable and they are on pavement, Neither.
Regards
eric_marsh
Well Known Member
An interesting thread. I'm going to be thinking about this a lot as I build my 6a. It appears that anything to reduce the possibility of a flip over would be money and time very well spent.
Looking at that video what I find very disturbing is that much of the motion of the front wheel appears to be forward/aft rather than up and down. My experience with cars/motorcycles is that such motion is completely wrong. Evidently with an aircraft this is not so much the case. Still, looking at it makes me very uncomfortable. It just doesn't seem right.
Looking at that video what I find very disturbing is that much of the motion of the front wheel appears to be forward/aft rather than up and down. My experience with cars/motorcycles is that such motion is completely wrong. Evidently with an aircraft this is not so much the case. Still, looking at it makes me very uncomfortable. It just doesn't seem right.
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MrNomad
Well Known Member
Photoshop suggested idea and challenge for a solution!
RocketBob, Doug, others:
While I am not an engineer, the gist of many of the comments I've read seem to agree that if the gear leg nut was higher off the ground, the incidence of rollover would decrease.
Others have suggested a larger front wheel & increased tire pressure (amongst other ideas) will get the nut further from the ground and reduce incidents. To a retired software guy like me, that seems logical.
Please take a look at the following two photos. Using Photoshop, I altered the angle of the fork. Said change will raise the nut further from the ground. I suspect it also alters the load on the gear leg and maybe even the cg a bit but I am not qualified to validate such claims.
Photo of the original fork....
Photo-shopped altered fork....
I propose a concerted, RV community effort to address the problem. I have my original fork which, admittedly, has some deep gouges on one side where it scraped along the runway but it seems otherwise intact. I would happily mail it to any person who has the skills to change the fork angle and weld it back together again to further test the raised nut theory.
Based on emails received from Doug (and others), our community has the ability to engineer the expected outcomes of such an alteration and the ability to suggest the degree of change to the fork.
I propose a test wherein one or more RVer does the engineering, welding, and testing. As I said, I will happily mail my fork to the volunteer(s). I may also be able to get an old style gear leg from a 6A to further reduce the expense attached to such an experiment.
WHY US? My legal experience suggests that the existing vendors involved with this gear leg do not want to touch this issue with a 10 foot pole.
Also, if there is anyone out there who does NOT think their insurance premiums are based on the number of rollover incidents, they need to think again.
Therefore, we will all benefit from reduced incidents to say nothing of the human factor and expense. The community can help itself by stepping forward and facilitating an answer which a qualified vendor may eventually choose to provide.
I look forward to positive thoughts and ideas.
RocketBob, Doug, others:
While I am not an engineer, the gist of many of the comments I've read seem to agree that if the gear leg nut was higher off the ground, the incidence of rollover would decrease.
Others have suggested a larger front wheel & increased tire pressure (amongst other ideas) will get the nut further from the ground and reduce incidents. To a retired software guy like me, that seems logical.
Please take a look at the following two photos. Using Photoshop, I altered the angle of the fork. Said change will raise the nut further from the ground. I suspect it also alters the load on the gear leg and maybe even the cg a bit but I am not qualified to validate such claims.
Photo of the original fork....
Photo-shopped altered fork....
I propose a concerted, RV community effort to address the problem. I have my original fork which, admittedly, has some deep gouges on one side where it scraped along the runway but it seems otherwise intact. I would happily mail it to any person who has the skills to change the fork angle and weld it back together again to further test the raised nut theory.
Based on emails received from Doug (and others), our community has the ability to engineer the expected outcomes of such an alteration and the ability to suggest the degree of change to the fork.
I propose a test wherein one or more RVer does the engineering, welding, and testing. As I said, I will happily mail my fork to the volunteer(s). I may also be able to get an old style gear leg from a 6A to further reduce the expense attached to such an experiment.
WHY US? My legal experience suggests that the existing vendors involved with this gear leg do not want to touch this issue with a 10 foot pole.
Also, if there is anyone out there who does NOT think their insurance premiums are based on the number of rollover incidents, they need to think again.
Therefore, we will all benefit from reduced incidents to say nothing of the human factor and expense. The community can help itself by stepping forward and facilitating an answer which a qualified vendor may eventually choose to provide.
I look forward to positive thoughts and ideas.
N941WR
Legacy Member
Replacement axle
Do any of you that have gone over have the Matco front axle installed, or something similar?
It is possible that this is the solution and we don't enough samples to know.
The real problem is, it will take an upset but with this axle to know it doesn't work.
Do any of you that have gone over have the Matco front axle installed, or something similar?
It is possible that this is the solution and we don't enough samples to know.
The real problem is, it will take an upset but with this axle to know it doesn't work.
kentb
Well Known Member
I replaced mine.
Some day I'll get around to making another video clip with it in the grass. I don't know if the difference will be detectable.
I switch because I like the design better. It now rolls easier moving in and out of the hangar.
The problem with looking to see if I (or anyone else with a gear mod) tips over, you won't be able to know if the mod failed to do something for you or bad pilot technique.
Kent
Some day I'll get around to making another video clip with it in the grass. I don't know if the difference will be detectable.
I switch because I like the design better. It now rolls easier moving in and out of the hangar.
The problem with looking to see if I (or anyone else with a gear mod) tips over, you won't be able to know if the mod failed to do something for you or bad pilot technique.
Kent
nose gear question
Has a RV-10 flipped yet? Why didn't Van use the 9a/7a gear on the 10? Could a 10 style gear be adapted to the 7a? Nose wheel flips went from bad to worse when the 7a came on line ( the 9 lands at a much slower speed ) , The 6a leg is shorter and stiffer. Vans through their hands up once and had a independent recommend the new fork SB, to get them to do it twice ....?
Better wheels, bigger tire , new fork all good steeps to lessen the chances of this happening but until the leg is changed or improved the risk is still too great that more planes will be bent and people hurt.
liability is a strong motivation to blame the pilots for all of these failures. As a first step I am suggesting we all write a hart felt letter to Van himself about the need to revisit the nose gear problem, Resonate failure,yield point failure ,call it what you want the leg on its best day is barley adequate. There is no perfect solution a higher margin of safety is the best we can hope for.
Flame suit on
Bob
Has a RV-10 flipped yet? Why didn't Van use the 9a/7a gear on the 10? Could a 10 style gear be adapted to the 7a? Nose wheel flips went from bad to worse when the 7a came on line ( the 9 lands at a much slower speed ) , The 6a leg is shorter and stiffer. Vans through their hands up once and had a independent recommend the new fork SB, to get them to do it twice ....?
Better wheels, bigger tire , new fork all good steeps to lessen the chances of this happening but until the leg is changed or improved the risk is still too great that more planes will be bent and people hurt.
liability is a strong motivation to blame the pilots for all of these failures. As a first step I am suggesting we all write a hart felt letter to Van himself about the need to revisit the nose gear problem, Resonate failure,yield point failure ,call it what you want the leg on its best day is barley adequate. There is no perfect solution a higher margin of safety is the best we can hope for.
Flame suit on
Bob
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MrNomad
Well Known Member
RHILL suggests we write to Van. My letter follows. Feel free to copy any portion.
Van's Aircraft, Inc.
att: Mr. Van Grunsven
14401 NE Keil Road
Aurora, OR 97002
Dear Mr. Van Grunsven:
Let me begin this letter by commending you on some really great airplanes. My 9A is a joy to fly, efficient, fast, nimble, and looks great too. Your staff is helpful and the products you sell are generally quite good.
There remains one issue that concerns me, and based on the large volume of emails and posts to the RV website, this issue concerns others too. The issue is the nose gear on the "A" models. Just two weeks ago, an experienced pilot in a well built 6A airplane flipped while taxiing. While the pilot and passenger suffered injuries, they survived but the beautiful airplane was destroyed.
I've read the 2005 NTSB study, examined ideas submitted by others, but I won’t begin to tell you how to modify the front gear to reduce rollover incidents. However, in addition to pilot error and ground conditions, the consensus of opinion appears focused on three contributing factors and they are:
1) the distance of the front nut from the ground
2) the rolling resistance of the front wheel
3) and the capability of the front gear leg.
While no design can fully compensate for pilot error, ground conditions, or builder mistakes, I urge you to look into this matter again. Design, build, and sell us replacement parts that will reduce rollovers and bent front gear. I am certain there are many RV owners who would cooperate with a team effort should you choose to organize one. I am equally certain folks would submit their real world experiences for your review, and offer their design ideas for your consideration.
Please take this opportunity to work with us and make these great airplanes even better.
Barry DiSimone 90063
Tucson AZ
Van's Aircraft, Inc.
att: Mr. Van Grunsven
14401 NE Keil Road
Aurora, OR 97002
Dear Mr. Van Grunsven:
Let me begin this letter by commending you on some really great airplanes. My 9A is a joy to fly, efficient, fast, nimble, and looks great too. Your staff is helpful and the products you sell are generally quite good.
There remains one issue that concerns me, and based on the large volume of emails and posts to the RV website, this issue concerns others too. The issue is the nose gear on the "A" models. Just two weeks ago, an experienced pilot in a well built 6A airplane flipped while taxiing. While the pilot and passenger suffered injuries, they survived but the beautiful airplane was destroyed.
I've read the 2005 NTSB study, examined ideas submitted by others, but I won’t begin to tell you how to modify the front gear to reduce rollover incidents. However, in addition to pilot error and ground conditions, the consensus of opinion appears focused on three contributing factors and they are:
1) the distance of the front nut from the ground
2) the rolling resistance of the front wheel
3) and the capability of the front gear leg.
While no design can fully compensate for pilot error, ground conditions, or builder mistakes, I urge you to look into this matter again. Design, build, and sell us replacement parts that will reduce rollovers and bent front gear. I am certain there are many RV owners who would cooperate with a team effort should you choose to organize one. I am equally certain folks would submit their real world experiences for your review, and offer their design ideas for your consideration.
Please take this opportunity to work with us and make these great airplanes even better.
Barry DiSimone 90063
Tucson AZ
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A gear letter
Thank you Mr Nomad, My letter will go out today, We all talk a good game, here is something everybody can do for the price of a stamp.
I am committed to my build almost ten years now, I know Van to be a stand up guy, Vans aircraft a great company, I am convinced litigation concerns prevent the needed redesign of the "A" mount system. Two fresh designs have launched since RV-10,RV-12. both are nose gear ,both use a different system . I can see in the near future insurance company's will exclude nose wheel prongs from coverage, A warning sticker for the passengers " The Surgeon General has determined landing or taxiing a RV-A is Hazardous to your Health".
Look no further than what Boses has done to lightspeed on this TSO'd headset,Bose has forced the Faa into enforcing this reg to gain an advantage for the A20 headset. Vans hopes this will go away, it wont, the negative impact ( bad press)will hurt the company and aviation as a whole.
Van will have to act on this, the sooner the better, by writing a letter, We all are helping Van to "Do the right thing" Fix the "A" Gear.
Stop blaming the pilots, the builder, the runways. "Look in the mirror" anything else is an excuse. Write the letter, be Positive ,encourage vans to take action ,come out in front on this. Given enough time and a few more flips and it will go negative on its own. Take a 1/2 hour Write the letter,
do your part to fix this.Thank you in advance for your help!
Bob Hill
Thank you Mr Nomad, My letter will go out today, We all talk a good game, here is something everybody can do for the price of a stamp.
I am committed to my build almost ten years now, I know Van to be a stand up guy, Vans aircraft a great company, I am convinced litigation concerns prevent the needed redesign of the "A" mount system. Two fresh designs have launched since RV-10,RV-12. both are nose gear ,both use a different system . I can see in the near future insurance company's will exclude nose wheel prongs from coverage, A warning sticker for the passengers " The Surgeon General has determined landing or taxiing a RV-A is Hazardous to your Health".
Look no further than what Boses has done to lightspeed on this TSO'd headset,Bose has forced the Faa into enforcing this reg to gain an advantage for the A20 headset. Vans hopes this will go away, it wont, the negative impact ( bad press)will hurt the company and aviation as a whole.
Van will have to act on this, the sooner the better, by writing a letter, We all are helping Van to "Do the right thing" Fix the "A" Gear.
Stop blaming the pilots, the builder, the runways. "Look in the mirror" anything else is an excuse. Write the letter, be Positive ,encourage vans to take action ,come out in front on this. Given enough time and a few more flips and it will go negative on its own. Take a 1/2 hour Write the letter,
do your part to fix this.Thank you in advance for your help!
Bob Hill
I know you said "almost zero", but the number of incidents that have occurred on paved surfaces suggest that this is not an adequate solution. Take care while operating on rough fields is probably better advice, but that's something we should all know anyway.
Ron Lee
Well Known Member
Rob, the "rough runway" wording may be better. What were the factors surrounding flipovers on paved surfaces? What are the stats? How many on non-paved versus paved? Then of those on paved, what happened (PIO, severe cracks in the runway, etc). I know of one paved runway in Colorado that has significant cracks and I will not land there.
The one that inspired this thread was a pilot who LEFT this airport because he was supposedly concerned about the runway condition. Then he came back and encountered a bad area. Did he have a nose wheel nut skid like I have done?
One in Texas a few years ago happened around Christmas after mucho rain. I noticed on the pictures areas that remind me of gophers where I live. My comment then was that the field was not suitable for RV-A models.
While I have made changes in this area, I am not as concerned as others appear to be.
The one that inspired this thread was a pilot who LEFT this airport because he was supposedly concerned about the runway condition. Then he came back and encountered a bad area. Did he have a nose wheel nut skid like I have done?
One in Texas a few years ago happened around Christmas after mucho rain. I noticed on the pictures areas that remind me of gophers where I live. My comment then was that the field was not suitable for RV-A models.
While I have made changes in this area, I am not as concerned as others appear to be.
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Here is an old movie that shows the resonance of this NLG on a smooth runway that was posted awhile back. Sorry I can't remember the author.
http://www.eaa538.org/images/nosegear.wmv
It happens at some very low speeds. Add some surface undulations and you have a collapse.
http://www.eaa538.org/images/nosegear.wmv
It happens at some very low speeds. Add some surface undulations and you have a collapse.
ColoCardinal
Well Known Member
OMG that's pathetic!
On an earlier video it was possible to see that on a roufgh surface there is as much motion fore and aft as there is up and down. In this one it shows almost MORE fore and aft motion. All of that serves no purpose other than to stress the gear. It could be that a lot of that motion is started in the verticle section of thegear leg. Someone on an earlier post had a mod tht cut off the bottom section of the leg and replaced it with a stout connection with the nut on the top. If the verticle section IS the probelm, that would eliminate it as well as moving the nut away from being able to "trip" theplane when things get bent too far aft.
On an earlier video it was possible to see that on a roufgh surface there is as much motion fore and aft as there is up and down. In this one it shows almost MORE fore and aft motion. All of that serves no purpose other than to stress the gear. It could be that a lot of that motion is started in the verticle section of thegear leg. Someone on an earlier post had a mod tht cut off the bottom section of the leg and replaced it with a stout connection with the nut on the top. If the verticle section IS the probelm, that would eliminate it as well as moving the nut away from being able to "trip" theplane when things get bent too far aft.
