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  #21  
Old 02-20-2011, 06:25 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
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Default moment of inertia and weight both important

As Scott pointed out, the moment of inertia is also important.

Since the fixture with the nose gear is pivoted on the trailer at the back, you will have a reasonable approximation of the motion, especially if the distance to the rear pivot is about the same as the distance to the main gear struts on the airplane.

It is still an issue that the trailer wheels crossing bumps will add an unrealistic motion and load, but you can get around that by towing over very smooth surface, with simulated bums that only the nose wheel goes over, not the trailer wheels.

In addition to simulating the static weight on the nose wheel, you can simulate the moment of inertia of the airplane by attaching a beam with weights at both ends, or just a long beam sticking out the front with the weight well forward of the nose wheel. This would have the added advantage of requiring less total weight. For example, if the beam extends twice as far forward as the distance from the pivot to the nose wheel, then only half as much weight would be required to simulate the static load. The trick is to calculate the right combination of weight and beam length that would simulate both the static weight and the moment of inertia.

Someone tell me the distance between the nose gear and main gear on an RV-(A) and tell me the distance from your pivot to the nose wheel, and I can take a crack at calculating that for you. I have a good enough idea of the airframe component weights to make a reasonable guestimate.
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  #22  
Old 02-20-2011, 07:09 PM
rubber314chicken rubber314chicken is offline
 
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Location: Cleveland, OH
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Default

Quote:
Originally Posted by scsmith View Post
Someone tell me the distance between the nose gear and main gear on an RV-(A) and tell me the distance from your pivot to the nose wheel, and I can take a crack at calculating that for you. I have a good enough idea of the airframe component weights to make a reasonable guestimate.
For the 9A I found numbers that varied from 56.5" to 57.5" The nose wheel is 34.5" aft of the datum, and the cg range is from 77.95" to 84.84" aft.
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  #23  
Old 02-20-2011, 07:14 PM
thinkn9a thinkn9a is offline
 
Join Date: Nov 2007
Location: Mississippi
Posts: 282
Default More Armchair comments

First - I think this is a great idea.
Second - I'd NEVER put the unit, post test, on a flying airplane

and now for the armchair comments
- Raiz has posted some calcs and comments in the last few months. He defined some "failure points". I would think if you could test a series growing closer and closer to replicate the step function failure or other failure with tire pressure differences he discussed, it would fill in the gaps between wonder, calcs, and real world.

- someone else mentioned the black and white blocks for scale/displacement. You could make up a plate very simply with a piece of metal or wood and black and white paint. This test won't be exact,.. so as long as you make the blocks about right,... video should be good. You could mount so you could see the tire/gear moving up and down, and possibly back and forth.. (need to figure out if the view would be "one to one" or due to angle the actual displacement is different than "shown" against the black and white checkerboard.)

Another means to figure out the movement is to make a "record" of the movement. Can be done in several ways,... for instance could use gorilla glue and put small cross piece on the gear by the wheel. Then mount something next to it that the cross piece could push aside (think clay) to show the maximum displacement. what you are trying to do is "isolate" the actual movement,.. and not get into "inertia" of something being displaced and total movement being more than that of the nose gear or object being studied.

now,.. if you could really get some of that neat electronic gear,... you might not need any of this
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  #24  
Old 02-20-2011, 09:57 PM
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billnaz billnaz is offline
 
Join Date: Jan 2005
Posts: 230
Default Gear leg to donate

I have my old nose gear leg and fork sitting in the hangar. It's the original 6A gear that I changed out after the service bulletin. You can test it to destruction if you'd like. Actually I'd like to watch too! I'm kinda close, up at Chandler.
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  #25  
Old 02-20-2011, 10:16 PM
vgb vgb is offline
 
Join Date: Aug 2007
Location: northern Cal
Posts: 111
Default gear leg

Now you guys are getting with it.I would like to see a gear leg video to destruction also.
I think you will see these gear legs tuck under instead of flexing up.
When I built my 7A I had a lot of comments on the spindly gear leg.
Your doing more than anybody else has done to test the gear.
I do think that when the nose dips you have the moment of the tail adding to the weight on the nose.
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  #26  
Old 02-21-2011, 08:24 AM
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MrNomad MrNomad is offline
 
Join Date: Mar 2006
Location: Tucson, AZ
Posts: 823
Thumbs up Hopefully, our efforts will lead to an improved design

Quote:
Originally Posted by billnaz View Post
I have my old nose gear leg and fork sitting in the hangar. It's the original 6A gear that I changed out after the service bulletin. You can test it to destruction if you'd like. Actually I'd like to watch too! I'm kinda close, up at Chandler.
Bill: At the risk of sounding like Tony Soprano, this sounds like an offer we can't refuse. YES, CHD is a stone's throw from 57AZ and YES, we'd like to meet and discuss so please send an email/phone number to

oldak at comcast.net or mrnomad57 at gmail.com.

In less than 12 hours since the initial post, we've been offered a gear leg, fork, and video equipment from a friend currently in S. Africa. While we wait for this loaner equipment to arrive, the initial non destructive tests will continue.

Later today Chet and I will discuss the engineering comments we received. Not being mechanical engineers, we appreciate the ideas and hope that the engineers in our RV community will play an increased role.

Just like building an RV, we firmly believe in teamwork and collaborating with others with the hope that our combined efforts will lead to demonstrable improvements in an area that's vexed too many pilots.
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  #27  
Old 02-21-2011, 12:16 PM
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Ron Lee Ron Lee is offline
 
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Posts: 3,275
Default

You can get close to eliminating the flipover at ZERO COST easily. Starting today.

Land on well-maintained paved surfaces only.
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  #28  
Old 02-21-2011, 12:50 PM
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Cadstat Cadstat is offline
 
Join Date: Dec 2010
Location: Greeley, Colorado
Posts: 199
Default Nose Gear

I applaud your efforts as will many 'A' drivers. But it is apparent from all the obsevations that recreating a failure many not lend much 'real world' information. There is likely gyroscopic loads involved in the equation that might be hard to reproduce in a static test stand under point loading.
Most of the rubber side up photos of the 'pole vaulting' RVs show the plane laying in grass. We know the gear doesn't do well off the payment. I hope your activities lead to a new design.
Your trailer experiment may only reinforce what we already know "Keep off the grass."
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  #29  
Old 02-21-2011, 02:17 PM
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L.Adamson L.Adamson is offline
 
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Location: KSLC
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Default

Quote:
Originally Posted by MrNomad View Post
Bill: At the risk of sounding like Tony Soprano, this sounds like an offer we can't refuse. YES, CHD is a stone's throw from 57AZ and YES, we'd like to meet and discuss so please send an email/phone number to
One thing to keep in mind, regarding older RV6A nose gear legs.........is how old is it? Around 1999 Van's issued an SB for older gear legs, which failed early. My 1996 kit/leg was replaced at that time. When testing with a high speed wheel & cam........the early legs failed quickly. The new models stood up to the abuse.

L.Adamson -- RV6A
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  #30  
Old 02-21-2011, 05:29 PM
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frazitl frazitl is offline
 
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Location: Las Vegas, NV
Posts: 488
Default Van's spec

for maximum nose wheel weight on the nose is 375#. As you progress with your tests, you might want to consider higher weights.

Would $5 or $10 from a bunch of us help to fund your experiment. If you set up a paypal donation account, Im in. Wish I was closer. Still have my old engineering text books .
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