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  #31  
Old 09-23-2019, 02:23 PM
rapid_ascent rapid_ascent is offline
 
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I'm certainly not an expert in this area but I do think that Tom may have a point. Sometimes it's easier to look at the symptom of the problem and not realize that there is an underlying root cause for the problem. That in fact may be returning on the updated install.

In my EE work we try to minimize the number of variables when we are trying to track down problems. The fact that you changed the type of brake line could actually have nothing to do with the real cause of the problem it is only a change that was made. Or it could be a different problem entirely. My generic suggestion is to try to break the problem down and minimize the number of variables.

As I said before I don't know a lot about this area. I have worked on car brakes and that is the extent of my experience. Just trying to provide my 2 cents to help were I can and learn from others experiences.
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  #32  
Old 09-23-2019, 02:35 PM
TS Flightlines TS Flightlines is offline
 
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Charles----just for giggles---there is a temperature indicating paste that is available---most race care shops sell it----that will indicate the max temp of the area. Might be a good idea to get a temp reading----

Tom
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Joint Venture with Aircraft Specialty
Teflon Hose Assemblies for Experimentals
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  #33  
Old 09-23-2019, 03:59 PM
BobRV7 BobRV7 is offline
 
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Location: Loveland, Co
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Vans DWG C2 shows the fuel line on top and the bleed valve on bottom, Matco Brakes says you can switch the bleed valve on top or bottom but bleeds better on top as the air goes up but with wheel pants on the RV's the aluminum tube would fit better. If it's not rubbing on anything and its a matco brake, you are suppose to tighten the axel cap so the rubber seal on the bearing stops turning with the wheel then tighten it a1/4 turn not any tighter, if it's spinning with the wheel it may make a noise or if it's too tight. Get a brake manual if you don't have one, I know Matco uses Nord-lock washers so different Torque. Also you might fly it without the wheel pants to test for noise. Good look
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  #34  
Old 09-23-2019, 05:19 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by rapid_ascent View Post
I'm certainly not an expert in this area but I do think that Tom may have a point. Sometimes it's easier to look at the symptom of the problem and not realize that there is an underlying root cause for the problem. That in fact may be returning on the updated install.

In my EE work we try to minimize the number of variables when we are trying to track down problems. The fact that you changed the type of brake line could actually have nothing to do with the real cause of the problem it is only a change that was made. Or it could be a different problem entirely. My generic suggestion is to try to break the problem down and minimize the number of variables.

As I said before I don't know a lot about this area. I have worked on car brakes and that is the extent of my experience. Just trying to provide my 2 cents to help were I can and learn from others experiences.
I agree, there are a lot of variables and zeroing in on a cause of this type of condition can be a challenge. Further proof of that is that chatter with hard lines happens occasionally as well.

But based on past experience and the fact that the major change that was made was adding a flexible hose, I think there is a strong possibility that the cause is related to the hose.

Replacement of the hard lines with hose is nothing new. Builders have been trying it for far longer than Steve and Tom have been making and selling custom hoses. The first chatter/squeal instances related to the use of flexible hoses thatI was made aware of occurred in the mid to late 90’s.

I am not aware of anyone ever identifying anything specific to explain why it works in one installation and not another. Could it be that the use of rubber lined hose allows for more expansion than when Teflon lines hose is used?

It might be of some help if Steve or Tom we’re willing to post the installation specifics of their hoses that allow them to always work with no problems (type of hose, clocking of fitting, etc.)
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  #35  
Old 09-23-2019, 06:25 PM
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RV6_flyer RV6_flyer is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
I agree, there are a lot of variables and zeroing in on a cause of this type of condition can be a challenge. Further proof of that is that chatter with hard lines happens occasionally as well.

But based on past experience and the fact that the major change that was made was adding a flexible hose, I think there is a strong possibility that the cause is related to the hose.

Replacement of the hard lines with hose is nothing new. Builders have been trying it for far longer than Steve and Tom have been making and selling custom hoses. The first chatter/squeal instances related to the use of flexible hoses thatI was made aware of occurred in the mid to late 90’s.

I am not aware of anyone ever identifying anything specific to explain why it works in one installation and not another. Could it be that the use of rubber lined hose allows for more expansion than when Teflon lines hose is used?

It might be of some help if Steve or Tom we’re willing to post the installation specifics of their hoses that allow them to always work with no problems (type of hose, clocking of fitting, etc.)
Would be nice to know the details.

I can say that I had my "per plans" aluminum lines brake setup make noise once after a caliper rebuild and brake pad replacement. My fix was to "bend" the aluminum line slightly (left or right I do not remember) from the fitting changing the side load on the brake caliper. Any time I would get noise after that, I knew the alignment of the tubing to the fitting on the caliper was off and needed an adjustment.
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  #36  
Old 09-23-2019, 11:15 PM
Aircraft Specialty Aircraft Specialty is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
I agree, there are a lot of variables and zeroing in on a cause of this type of condition can be a challenge. Further proof of that is that chatter with hard lines happens occasionally as well.
It is definitely difficult to pinpoint exactly what the major change in this situation is as there seems to be a lot of them.

1. Fire 2. New Tire 3. New Tube 4. New Pads 5. New Brake line 6. New O Ring 7. Bleeder Valve Swap 8. New Rotor 9. Second set of new Pads.

However, what I find interesting is this. After the initial change, the problem didn't present itself until after a couple of flights and then got progressively worse.

After the Rotor Change, the same thing happened. Initial testing was fine and then it appeared again and got progressively worse.

After the second pad change, the same thing occurred after about 5 minutes of heating up.

Quote:
Originally Posted by WingnutWick View Post
Figuring I had the problem licked, my initial first brake attempts had no sound, then to my dismay, about 5 minuted into taxi test it came back again!
I am curious if this happens if you test it now. Does it start immediately, or does it still first start after about 5 minutes of taxiing?

Quote:
Originally Posted by RV6_flyer View Post
I can say that I had my "per plans" aluminum lines brake setup make noise once after a caliper rebuild and brake pad replacement. My fix was to "bend" the aluminum line slightly (left or right I do not remember) from the fitting changing the side load on the brake caliper. Any time I would get noise after that, I knew the alignment of the tubing to the fitting on the caliper was off and needed an adjustment.
This is very true. Jan also mentioned this. We have heard (no pun intended) that side loading on calipers with either flex or rigid tubes can cause noises.

Quote:
Originally Posted by rvbuilder2002 View Post
It might be of some help if Steve or Tom we’re willing to post the installation specifics of their hoses that allow them to always work with no problems (type of hose, clocking of fitting, etc.)
Happy to answer this question

Our brake hose assemblies are all PTFE Teflon with a stainless steel braid in -3 or -4 size. Most are clear coated with an anti abrasion clear plastic. The hose has an approx 3,000 PSI working rated pressure and a >9,000 psi burst pressure. We do NOT utilize any rubber lined hoses for any of our assemblies.

Fittings utilized are -3 or -4 stainless as are the collars utilized to crimp the assemblies.

Collars are all crimped utilizing a CNC crimper for repeatability. Assemblies then undergo hydrostatic pressure testing prior to shipment.

For more detailed information, here is a link that has fabrication and testing videos.

http://aircraftspecialty.com/howwemake.html

As far as the second part of the question regarding installation specifics....that would be impossible to post as we have over 30 build sheets just for gear leg hoses on a variety of aircraft. They come in a variety of configurations. Some hoses utilize straight fittings, some have angled fittings, some have banjos, some go straight down the gear leg, while others wrap around the axle. The "Standardized" assemblies were all designed and built with the help of beta testers around the world. Many others are built custom based on owner specifications.

WingnutWick- There are some good comments and suggestions in here, and I'm sure you'll get to the root cause of this. If Tom and I can be of any assistance, we are happy to help.
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  #37  
Old 09-24-2019, 09:52 PM
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WingnutWick WingnutWick is offline
 
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Alright folks, here's the breakdown of yesterday’s work and findings. I wanted to be able to see if I can isolate it to one thing for future information vice doing all the suggestions at once so I started with the easiest and went from there.

First I tried to "clock" the fitting. I moved it so that it alleviated the bend that was previously there. Initial taxi test seemed good, I was excited, and how easy a fix. But then it came back after a little more taxiing and braking. The tendency for it to happen after a little bit of operation I’m guessing has to do with being heat related? Either the pads or the fluid in the lines as it occurs after everything is warmed up a little. Not enough info though to say for sure.

I tried clocking it further both inward and outward. No luck. I tried removing some of the zip ties I had to prevent any undue pressure being applied on the caliper. No luck. Next I jacked the wheel up, and made sure everything was looking normal and tight with the bearings, axle, pressure plate, etc. I beveled the leading and trailing edge of the pads a little as suggested, and added brake quiet. Cleaned the rotors and pads. It was just as bad as before.

My final option before deciding to belligerently throw bundles of money at the problem and buy a whole new wheel, bearing, and brake assemblies, was to fabricate a rigid line as I had before. I had the tools and tubing in my hangar so I did just that. Lo and behold - the horrible noise and vibration was gone! Not a squeak, just as silent as the other and my 8's! I did plenty of taxiing and a high speed abort to simulate landing followed by a flight. Nothing at all! Just to be sure I waiter until today to test it agin before posting this, and after much operation, the noise is gone! Sigh of relief.

While I was keeping an open mind about it, my gut was telling me after I had read a lot of previous archives of "brake groan" following installation of flex lines, that this was the case. Now let me say, these lines are absolutely beautiful and extremely well crafted. Super high quality. (Steve I'm sure yours are the same as well ) Not to mention recommended to me by a lot of people. But there seems to be the occasional RV'er out there that these do not work well with. The interesting question I'm curious about (for Tom and Steve) is why they work on most, but cause this resonating vibration sound on others? A couple people stated "hydraulic resonance". My lines in particular ran from the fuselage to the brake assembly and were on the long side from what I gathered (50.5 inches), I'm not sure if that contributed.

I wonder if a -3 line would have made a difference. It may be that whatever setup I had was imparting some pressure on the system that was causing this. Short of making some support bracket, I tried manipulating the position and support via zip ties. I'm tempted to test out different lines (like a -3) to figure it out but as of now I (and my girlfriend) are just happy her plane is back functional so I'm going to take a "brake" from meddling underneath it and enjoy flying it!

Thanks all for the great help, as always this has been great learning experience and I've furthered my skills and knowledge in the brake department with this whole fire debacle. And thank you Tom for the lovely lines, and to both Tom and Steve for sharing their insights into their lines. I am going to see if they will work on my 8 at some point without the same issue. This is obviously a one in thousands occurrence. I wonder if we can figure it out! It may simply boil down to the possibility that the nature of flex lines results in a smaller tolerance for positioning than what you can get with rigid lines, in the fact that with rigid lines you can essentially sculpt a spiral straw with them and they will work as long as the end ends up aligned with the fitting with no pressure (which is easy to do). I’m sure that this was just a matter of amateur craftsmanship on my part. I shall re-attack these at a later date.

Thanks again all!

Cheers!

Wingnut
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  #38  
Old 09-24-2019, 10:44 PM
maus92 maus92 is offline
 
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Interesting. I will be installing flex lines in the next week or so to replace rigid tubing that has some workmanship issues, and a nick from the wing root fairing that I discovered during my annual CI. The original installation is not exactly what is shown in the plans, and the bends are a bit "flat," so I hope to improve on the current configuration. While I'm at it, I'll be removing surface corrosion from the gear legs, and repainting with epoxy paint.
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Last edited by maus92 : 09-24-2019 at 10:49 PM.
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  #39  
Old 09-25-2019, 05:04 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by WingnutWick View Post
The interesting question I'm curious about (for Tom and Steve) is why they work on most, but cause this resonating vibration sound on others? A couple people stated "hydraulic resonance". My lines in particular ran from the fuselage to the brake assembly and were on the long side from what I gathered (50.5 inches), I'm not sure if that contributed.

Wingnut
From discussions over the years with people that have had this occur, my theory has always been that it is related to the expandability of the long hose under high pressure.
Any object will expand under pressure. On some, they are stiff enough that it is only at a molecular level and for others it might even be measurable with a caliper.
My theory is that in some cases, there is an interaction between the brake system and the expansion of the hose that occurs at a natural resonance. Perhaps because of run-out of the disk, or a slight thickness variation?
I think it is the long length of hose, having a lot of expansion area along its length, that it acts like a compression spring under the high pressure.
I think that if you had a hard line with just a short length of flexible hose at the end (like is typically done on certificates aircraft), you probably wouldn’t have seen the problem.
I imagine some types of hose material can expand more than others when exposed to high pressure. I don’t know if that is a factor in the hoses working in a lot of installations but not in some, but it could be.
Do you know whether your hoses have rubber or Teflon liners?

Regardless, glad to hear that you narrowed down the cause.
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  #40  
Old 09-25-2019, 08:13 AM
TS Flightlines TS Flightlines is offline
 
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Charles---very glad that you isolated the problem. Kinda weird, but stranger things have happened. Yes the liners are teflon, and yes we've had some gear hose that were longer---and no problems. As Scott said, quite possibly there is something in this install that has a natural resonance.

Tell you what----We'll be glad to make you short hoses coupled to rigid tube when you get to that point if you wish. Also---obviously you can return the hoses for a full refund including the shipping.

This has been one of those experiences that get filed int he memory banks---

Tom
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Joint Venture with Aircraft Specialty
Teflon Hose Assemblies for Experimentals
Proud Vendor for RV1, Donator to VAF
RV7 Tail Kit Completed, Fuse started-Pay as I go Plan
Ridgeland, SC
www.tsflightlines.com, www.asflightlines.com
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