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09-21-2010, 11:51 AM
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Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,658
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This should tell you Dave
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09-21-2010, 12:19 PM
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Join Date: Aug 2006
Location: Battle Ground, WA
Posts: 426
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Hollow Leg?
Quote:
Originally Posted by pierre smith
....in that the leg is stiff but hinged at the firewall and 4 rubber doughnuts provide the spring. Seems that the idea could fairly easily be adapted to the two seaters.
Best,
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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
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09-21-2010, 01:57 PM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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Since the Grumman gear...
Quote:
Originally Posted by LarryT
...
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.
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...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...
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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09-21-2010, 02:51 PM
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Join Date: Oct 2009
Location: Victoria, BC, Canada
Posts: 3,932
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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.
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.
__________________
Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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09-21-2010, 03:37 PM
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Join Date: Mar 2006
Location: Tucson, AZ
Posts: 823
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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.
__________________
Barry - Tucson
RV9A Superior O-360 (an amazing experience)
Dynon AP Garmin Sensenich F/P
2020 Dues paid. Thank u DR!
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09-21-2010, 04:10 PM
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Join Date: Sep 2010
Location: Sao Paulo, Brasil
Posts: 72
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Quote:
Originally Posted by Dmadd
Yup. ;-)
Some folks even retract the flaps to give the tail more authority after landing... It allows them to hold the nose up longer into the rollout... Works great.
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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 ?
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09-21-2010, 08:01 PM
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Join Date: May 2009
Location: KS
Posts: 110
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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. 
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09-21-2010, 08:16 PM
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Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,219
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Quote:
Originally Posted by LeeM_2000
I personally find it unlikely that so many RV pilots have forgotten good soft field techniques.
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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.
__________________
Kyle Boatright
Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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09-21-2010, 08:24 PM
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Join Date: Jan 2005
Location: Round Rock, TX
Posts: 3,778
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Quote:
Originally Posted by Kyle Boatright
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.
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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 
__________________
Reiley
Retired N622DR - Serial #V7A1467
VAF# 671
Repeat Offender / Race 007
Friend of the RV-1
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09-21-2010, 09:09 PM
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Join Date: May 2009
Location: KS
Posts: 110
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Quote:
Originally Posted by Kyle Boatright
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.
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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.
Last edited by LeeM_2000 : 09-21-2010 at 09:11 PM.
Reason: Forgot to add the quote. :)
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