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  #1  
Old 04-16-2006, 09:10 PM
jimski9's Avatar
jimski9 jimski9 is offline
 
Join Date: Apr 2006
Location: Tauranga, New Zealand
Posts: 27
Default Gear leg dampeners

The plans describe bonding wooden gear leg dampeners to the main gear legs.
Is there any concern about this permanent bonding? I wondered if it may make it difficult to inspect the gear legs for cracking later on. I am considering drilling five or six holes in the wooden dampeners and attaching them to the gear leg with beefy zip ties.
Has anyone else done this and will this provide enough dampening effect?

Thanks

Jim Talbot
Tauranga
New Zealand
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  #2  
Old 04-16-2006, 09:29 PM
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kevinh kevinh is offline
 
Join Date: Jan 2005
Location: San Mateo, CA
Posts: 1,419
Default

Quote:
Originally Posted by jimski9
The plans describe bonding wooden gear leg dampeners to the main gear legs.
Is there any concern about this permanent bonding? I wondered if it may make it difficult to inspect the gear legs for cracking later on. I am considering drilling five or six holes in the wooden dampeners and attaching them to the gear leg with beefy zip ties.
Has anyone else done this and will this provide enough dampening effect?
I think the plans also say something about some planes needing them and some not. I tried flying my plane without the dampeners and try as I might - no shimmy . Therefore my pieces of wood never got installed - saves weight, effort and servicabilty if you luck out.
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-kevinh, Track my RV-7A, flying, alas, sold in 2013 after 450ish hours. (I'm now building something different)
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  #3  
Old 04-16-2006, 11:34 PM
hngrflyr hngrflyr is offline
 
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Location: eugene, oregon
Posts: 206
Default

The thickness of the wire ties might interfere with the fit of the gear leg fairings. I just finished this job a few weeks ago, with satifactory results. The additional thickness of the fiberglass wrap did alter the fit of the fairings. I now plan to install the pressure recovery wheel fairings along with the fiberglass gear leg fairings. My RV-6 has the original two piece metal fairings on the gear legs at present.

Bob Severns
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  #4  
Old 04-17-2006, 02:09 PM
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gmcjetpilot gmcjetpilot is offline
 
Join Date: Jan 2005
Posts: 4,285
Default Make it "structural"

Quote:
Originally Posted by jimski9
The plans describe bonding wooden gear leg dampeners to the main gear legs.
Is there any concern about this permanent bonding? I wondered if it may make it difficult to inspect the gear legs for cracking later on. I am considering drilling five or six holes in the wooden dampeners and attaching them to the gear leg with beefy zip ties.
Has anyone else done this and will this provide enough dampening effect?

Thanks Jim Talbot Tauranga New Zealand
Jim don't worry about inspection access for cracks. You should be worried about corrosion. Some materials like instant foam, which some have used on gear legs can hold mosture corroding the steel.

The gear legs don't crack; they might bend, but I would not worry too much about cracks. If there's a crack it'll happen down low where it bends for the axial. I say that with some knowledge of metals, crack growth and damage tolerance. Certainly a crack can occur, but it will "grow" fast. It's unlikely you will catch it in time unless you do gear inspections frequently. So you can cover up the leg with out too much worry.

To avoid corrosion a good finish is important. I am not a huge fan of the powder coating on the gear as they come now, but that's what we have. I would rather an epoxy primer for this part. We don't need a pretty gun metal gray, like the canopy frame. No one can see it. As long as the PC coating does not chip, flake or crack, allowing mosture to contact the steel. Corrosion is not likely even if you do cover it with fiberglass.

There was one case where instant foam was used to fill the fairing. The combo of chemical reaction and foam holding mosture on the steel gear leg, which was not properly primed (pre powder coat days), was a disaster. In a year or so period of time, the thing was a corroded mess.

kevinh's right, consider trying with out at first. However with you will have a firmer more solid ride and reduce the chance of shimmy significantly, but it comes at an expense.

The twist ties may add too much "thickness" as mentioned, and I doubt they would be "structural". If you are going to put them on you might as well make them work.

Extra thickness from attaching the stiffener increases the gear fairing frontal area. Fiberglass wrap is my method of choice to attach the stiffener. It adds min thickness and is very strong. It is semi permanent but it is not impossible to remove.

You could try some stainless steel bands, like the steel bands around freight, but I would worry about the metal bands making a nick in the gear leg. I said cracks are not a worry before. I lied. If you put a notch or nick in steel you will increase the chance of a crack by a huge margin. Don't allow any nicks or gouges in your gear legs.


If you do add the stiffener, use some sealant between the gear leg and stiffener to keep junk out. Pro seal would work. The adhesive is not meant to be structural but helps the parts work together, reduces abrading of he powder coat and keeps mosture out.

They way I attach a stiffener is wrap it with carbon fiber or "S" glass tape, at the top, mid and bottom, at minimum. You don't have to go crazy, but a couple of wraps around at each location, about 3-5" wide will do. Added thickness will be min.

On my RV-4, the difference noticeable. I could taxi fast and never get shimmy. It was just more solid. I made may own stiffener out of OAK. Actually a woodworking genius friend make them for me. The fit between the stiffener and leg was like a glove. Making a double tapered wood stiffener with a concave mating surface to match the gear leg is a trick. Van's method of gluing two pieces of wood molding together, with a "V" notch fit, works and is way easier, but if you have the skill to make a one piece solid stiffener that nests onto the gear, verse just sitting on top a V-notch with two contact points, the better.

Flying (taxing) without the stiffener, I did get a main gear shimmy when taxiing (way too) fast, but I would just check speed, slow down and it stopped. No big deal. The solution without the stiffener was taxi a little slower. I put the stiffener on because I thought I had to. In retrospect I could have left it off.

With the stiffener the feel was solid and could taxi straight, in a turn, go fast with out worry of wheel shimmy. Taxi at any speed over any surface felt solid like a car. I guess it helped a little on landing, but no shimmy taxi was the main advantage.

On my current project I am leaving them off for the simple reason of build, time, weight and keeping the fairing "skinny".

The stiffener needs to work as one with the steel leg. Just throwing it on so it can move and shift decreases effectiveness. The tie wraps I think will not cut it. If you are building a RV-7A, I think stiffeners on the mains and even the nose gear may have positive affect on the nose gear issue.

G

Last edited by gmcjetpilot : 04-17-2006 at 03:22 PM.
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  #5  
Old 04-17-2006, 03:45 PM
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Chino Tom Chino Tom is offline
 
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Location: Chino, CA
Posts: 738
Default Using PVC pipe

On my -6 I used sch 40 (thick walled) 1/2 PVC pipe. I split it (half moon) and attached it using 3M 3/4 strapping tape wrapped the entire length of the landing gear leg. Not as stiff as wood but alot better than nothing. It is light and very easy. I even run the brake line inside the PVC. Cut and peal off the tape if you need to inspect (or in my case replace a brake line). Fits nicely inside the gear leg fairing. Going to do the same on my -8A.
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Chino, CA
RV-8A,180/CS/Carb, AFS 4500 EFIS/EMS
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  #6  
Old 04-17-2006, 03:57 PM
szicree szicree is offline
 
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Location: SoCal
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Believe it or not, they make shrink tubing in some ginormous sizes. Maybe you could just shrink-tube the whole thing together.
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Fullerton, Ca. w/beautiful 2.5 year old son
RV-4 99% built and sold
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  #7  
Old 04-17-2006, 06:47 PM
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fodrv7 fodrv7 is offline
 
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Location: Torquay, Victoria, Australia
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Default Bounce

First let me confess to not haing mastered the 'Greaser' in my RV-7, which I had pretty well mastered on my mates -8.
Seems to be a function of poor vis. over the nose (compared with the -8.) my ability (Inability) and maybe? the lower 3 point attitude than the -8.

From a recent pic of me landing I suspect I am touching down tail first and pitching onto the mains.
So, has any one noticed that wood dampers in the gear fairings dampens the gear on touch down. I'm not talking about dropping it on from three feet, but when you almost kiss it on and the rebound in the gear gives you a skip- not a bounce.

Pete.
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  #8  
Old 04-17-2006, 07:25 PM
Kyle Boatright Kyle Boatright is online now
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,219
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My experience is that the "greaser" 3-pointer is hard to repeat in anything but perfect conditions. The airplane is above stall speed, and any meaningful vertical motion causes a skip. In addition, the slightest gust can balloon you a foot or two, even if you had all three wheels on the ground rolling smoothly. I've had more than a few of these, where I got an "oooh" out of the passenger because of the nice touchdown, and then caught a gust, which ruined the whole effect.

The tail slightly before the main's landing may be a better overall solution because as soon as the tailwheel hits, the mains follow, reducing your angle of attack and minimizing the chance of a skip or balloon.
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Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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  #9  
Old 04-18-2006, 07:06 AM
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Jconard Jconard is offline
 
Join Date: Apr 2005
Location: Twin Cities
Posts: 438
Default

It seems to me that you could, at one time, buy pre-made wodden stiffeners, from GBI or someone similar.

Anyone know where you can still get these?

JC
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  #10  
Old 04-18-2006, 07:51 AM
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Chino Tom Chino Tom is offline
 
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Location: Chino, CA
Posts: 738
Default Try wheel landings

[quote=fodrv7]First let me confess to not haing mastered the 'Greaser' in my RV-7, which I had pretty well mastered on my mates -8.
Seems to be a function of poor vis. over the nose (compared with the -8.) my ability (Inability) and maybe? the lower 3 point attitude than the -8.

We can start another debate, but hopefully not..... If your 7 (just like my -6) has a 180 and CS it tends to be slightly on the nose heavy side and will WHEEL land a lot better than 3 point. But like a 3 point, the least amount of vertical component will result in the finest landing. IMHO you can wheel land your -7 much more consistantly in any kind of wind. Carry a little power all the way into the flare and about 75 -80 mph over the fence (with a CS prop they pay off very fast at idle) Try it with just a slight amount of nose down trim and it will almost pin itself. You will use a little more runway over the 3 point but not very much. Ask Dan C what he thinks.......
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