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  #51  
Old 10-07-2017, 10:39 AM
Bob Kuykendall's Avatar
Bob Kuykendall Bob Kuykendall is offline
 
Join Date: Sep 2006
Location: Douglas Flat, CA
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Here's the thread where Steve Smith and I showed that it pays to use good hardware on the landing gear clamps.
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  #52  
Old 10-07-2017, 10:48 AM
foxhound57 foxhound57 is offline
 
Join Date: Dec 2013
Location: Gold Coast Australia
Posts: 33
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Here is an interesting post from 2012 regarding Grove Gear indicating very similar thought processes we considered before committing to engineering our particular gear design.

Quote:
Originally Posted by 624832

I had originally bought the Grove 2 piece airfoil gear but after spending a lot of time discussing the gear with Robby Grove I decided to return them and get the 1 piece gear. Robby and I spent a number of hours discussing the various issues and I really couldn't come up with any downsides to the 1 piece gear and there seems to be a lot of advantages.

My biggest concern is what happens when you side load the gear. As a low time pilot, I feel I am likely to do this and I wanted minimise any impact that might have.

In looking at the geometry of the standard gear, in a normal landing, the outside of the gear tower takes a compression load and the inside of the gear tower takes a tension load. The gear tower is designed to take these loads easily.

If you side load the gear, however, the outside of the gear tower takes tension load, which it can handle well and the inside of the gear tower takes a compression load. Imagine and old style beer can opener levering the inside of the gear tower with the outer mount point as the fulcrum. There have been a couple of instances where this has caused the inside of the gear tower to crumple.

Now look at the 1 piece gear. In a normal landing the outside of the gear towers still take the compression load and the centre of the gear flexes to absorb some of the impact. The inside of the gear towers are no longer involved. If you side load the gear, the outside gear tower of the loaded side gets tension load and the outside of the opposite gear tower gets compression load. Not a problem.

I believe that the best way to mount the gear is with the outside clamp bracket only as this allows the gear to flex in the middle as it is designed to. This takes the gear tower out of the picture. In fact you could probably remove much of the gear tower assembly if desired. I didn't as I had already built them when I decided on the 1 piece gear.

The only possible downside of the 1 piece gear which we could identify was that if you side load the gear to a great extent, especially if you were on 1 wheel at a high horizontal angle, that the upward force on the opposite side of the aircraft could cause the aircraft to roll since the upward force is applied on the far side of the fuselage rather than a few inches inboard as it would be with the standard gear. I doubt if this is likely though.

In addition to a number of discussions with Robby Grove, I also cornered Ken Krueger in the Van's booth at Oshkosh a few years ago. I asked his opinion of the 1 piece gear and we spent a few minutes drawing out the geometry and looking at the issues. Ken would not, of course, endorse the idea, but he also could not come up with any negative issues either which I took a a good sign.

One of the best aspects of the 1 piece gear is that it is very easy to align. I shot a laser line down the centre of the fuselage onto a wall about 20 feet away from the gear. I also mounted a laser on one of the axle mounting holes on each leg and aimed the at the wall as well. Then I only had to adjust the gear so that the distance from the centre laser dot to each of the others was the same.

For my brake lines, I had Robby put the fitting on the top of the gear in such a location that it comes up through a hole in the floor in the middle of the gear tower. My flexible brake line runs into the tower and screws right down onto the AN fitting. Very clean with no bending of tubing.
The Grove Gear performs faultlessly and is very easy to install. We designed our particular gear for the conditions in Australia and very much in consideration of certain aspects of the above quote. Needless to say I am very happy with the outcome.
  #53  
Old 10-07-2017, 11:12 AM
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skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
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Default Engineering Data?

Quote:
Originally Posted by foxhound57 View Post
BTW Dans Maths is totally wrong. The stress increase (if any) is absolutely nothing like he incorrectly asserts!
It would be nice if you provided some actual data to show why you think Dan is wrong. The stress that Dan is referring to is from aft-loading of the gear caused by heavy braking or striking a pot-hole during roll out. This is a loading scenario that using a 1 piece gear does not eliminate, and the gear clamp/bolt loads will in fact be increased with taller gear legs.

Skylor
  #54  
Old 10-07-2017, 12:12 PM
foxhound57 foxhound57 is offline
 
Join Date: Dec 2013
Location: Gold Coast Australia
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Hi Sklor

No worries! Once I am back in Oz, I will copy and send through our data and plans by PM and you can run your own determination as a Mechanical Engineer.

That will be a few days as the aircraft, and all my build data live in, Australia, and I am currently in New York pushing "Heavy Metal" back to the West Coast this evening.

It should, however, be noted, (from a Mechanical Engineering point of view) that we are Not discussing a standard Grove Gear (error by some I might think...). My track is vastly wider (and far more stable) than a conventional Grove Gear and the radius from the cross-beam to the leg completely different. Given the design, thickness and therein ability of the Gear to resist a distorting influence or deforming force (your example of a pot-hole) it is extremely elastic. We designed it that way for the rough Aussie conditions. As a design, we looked at dissipation of the kinetic energy of a landing impact thereby reducing the impact loads to the airframe. Using larger wheels and brakes (as well as Auto Speedbrake and lift-dump on landing) deals with the scenario as well.

From a personal point of view, Experimental Aviation to me is the ability to develop and improve upon design using Engineering and Science as well as Common Sense and a degree of Artform (if you will…). I realise there are some “personalities”, who refuse to accept any deviation from “planned building”. Regardless of one's position, I do not see openly criticising anyone, or making ill-informed assertions adds to any discussion. Just my humble opinion of course!
  #55  
Old 10-07-2017, 12:17 PM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
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Seriously...

Quote:
Originally Posted by foxhound57 View Post
...no knowledge of the Width and the Tapering, the Thickness at the Mid-Point, Radius of Bend (and therein the distortion angle) or the Flare of the Pneumatic Type Coupling or the Size of the Pneumatic Wheel
It is not necessary to know any of those things. All that's needed is the relative gear height, measured from the floor to the underside of the radius block. Perry was kind enough to supply this photo:



1000 mm is roughly 39". My RV-8 (standard length Grove gear) measures about 29" in the same place. So, a reasonable estimate of relative bolt stress, tall gear vs standard gear, looks like this:



It's just law of levers. Dimension "d" is roughly 6". It doesn't matter if it is 5" or 7", as it would change the relative result less than 1%.

Assume d = 6", pick any force, and the 39" gear height loads the forward bolt 1.28 times that of the 29" gear height.

My previous statement was "stress applied to the bolts, clamps, and gear box structure would be roughly 25% higher for the same braking or chuckhole loading". It was based on simple head math, no equations needed. Round up 39 to 40, and 29 to 30. 30 is 75% of 40, or 40/30 = 1.33. Close enough.

Why is it important? A few owners have stripped a clamp bolt nut rated at 12,500 lbs, thus we have a pretty good idea of the potential bolt stress in service. The gear leg extension increases bolt stress by a factor of 1.28. 12,500 x 1.28 = 16,000, but the 0.375" NAS clamp bolt is rated at 14,000.

POSTSCRIPT: Located a note where I had jotted down the actual dimension "d" from measurement. It's 3.5"
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Last edited by DanH : 10-07-2017 at 08:01 PM.
  #56  
Old 10-07-2017, 01:38 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,202
Default Post a Link to the Documents

Quote:
Originally Posted by foxhound57 View Post
....fails to understand the Elasticity Mechanics of Material and Design and Kinetic Energy Disruption.....
Actually, those aren't necessary to understand this.

Perry, if you'd post a link to the Loads Analysis Report and also to the Stress Analysis Report, people interested could see for themselves what the engineering is here. This would be helpful, as people like myself, who don't have an -8, don't plan on getting one but do have an engineering background, just don't see what seems to be obvious to you.

Instead we're seeing the basics: there's a load. There's no obvious way for that load to be absorbed by the fuselage. If there's valid engineering that says differently, please provide it. Don't merely assert some of this. Please back it up.

Thanks!

Dave
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