Brake lines

[painless]

Folks:

I am in the process of getting my brake lines installed on the landing gear legs (6A) and am concerned about the aluminum tube they are made out of flexing and eventually failing.

Plans say to run the brakelines down the forward side of the main gear, and loop them prior to attaching to the brakes. Is that loop enough of a buffer to flexing of the line? How has everyone's held up that are flying?

Thanks in advance. Finishing up things....yeah right!! I've been "finishing up things" all summer!!!!



Regards,

[sf3543]

I installed exactly according to VAN's plans and when I sold my plane at 900 hrs they were dirty but as good as new. I'd do it that way again.

[gmcjetpilot]

Here are some pictures of brake line failure and fire:

http://www.matronics.com/photoshare/...Brakeline2.jpg

http://www.matronics.com/photoshare/...om.07.02.2005/

I often say build it per plans, keep it simple, light and least weight and least expense. Obviously the stock hard aluminum line is per plans and works, BUT this is one area I did not follow plans.

There are a few cases of aluminum lines failing. In fact to early original RV designs, RV-3/4/6, used, per plans, the nylon-flow plastic line all the way to the brake caliper! This worked but if you abused the bakes and got it hot, the line melted. Van changed to the aluminum many years ago.

OK, what do I suggest? For a little expense, weight you can get some -2 or -3 stainless steel braided line and run that all the way from the firewall to the brake caliper. An option is run solid aluminum tube down the leg and transition to braided line for the last foot or so. I don't care for that because of the extra fittings, but it works. Some have found a cheap source of a braided line by using the flex hose for grease guns that come in different lengths. They come with 1/8" NPT fittings at each end, have a rubber outer layer with a braded inner layer and than an inner liner. The operating pressures are 3000-7500 psi. The liner is Polyamide or polyester Elastomer (Dupon) and should be OK with the Hyd fluid. Another source of short high pressure hoses is paint ball guns!
http://www.stinggroup.addr.com/quake...l#anchor211232

You can always have a custom small dia. hose made up. You will need to do that if you want a full length firewall to caliper hose since the grease hoses top out around 18" lengths. Some of the hot rod shops make braided hose for brake lines. Summit racing has some longer lengths off the shelf up to 53" with AN fittings for less than $30.


The braided lines are going to weigh more and cost more. If you have some custom lines made it will be at least $30-$60 each with AN fittings. One advantage, is for maintenanace; you can move the claiper out of the way on the flex hose. Of course the real advantage is it should be safer and less likely to fail than a solid aluminum tube.

George

PS: The subject for barke fluids comes up. Some people who know more about the subject than I state the Mobile 1 synthetic ATF works well and has double the flash point temp. The down side is there are other additives, not really needed for a brake system (but for wear issues in an auto trans); however they have no negative affect on the brakes; some claim it worked well for them for years. Easy to get and in small qts amounts.

There is a better Mil spec brake fluid, MIL-H 83282, but only comes in 4 gal quantities. It has twice the flash point (237C) of the older MIL-H5606 fluid (105C) that we use. It would be nice if Van or someone who sells parts would buy MIL-H 83282 to sell in small amounts to builders in smaller amounts. We can always make our RV's better and safer. No need to use 65 year old MIL-H5606 brake fluid formulas when MIL-H 83282 is available. The two MIL specs are NOT compatitable, one is mineral base and the other synthetic.

The current fluids of choice in the aerospace industry are:

* MIL-H-5606 - first introduced over fifty years ago and still used on many aircraft. Used on business jets and many U.S. Air Force aircraft, it is highly flammable and considered responsible for the loss of at least one military aircraft, due to the fire created (and many GA & commecial aircraft).
* MIL-H-83282 - first used by the Air Force in 1982 and the U.S. Navy in 1997, it is less flammable than 5606, but much more viscous at low temperature. The lower temperature limit of MIL-H-83282 is considered &endash;40? F, and it is used in virtually all Navy aircraft.
* MIL-H-87257 - this newest fluid is used in C135, E3, and U2 aircraft; it is less flammable than 5606 (similar to 83282) but its viscosity at low temperatures allows use down to &endash;65? F. Considered the fluid of choice for newer aircraft being developed, and
* Skydrol and Hyjet - these alkyl phosphate ester based fluids are used on commercial aircraft, and are less flammable than the military fluids described above. Maximum temperature limit is 160? F. These fluids have been around at least since the 1960's.

[robertahegy]

I followed Van's plans with the loop and they seem to be fine after 18 months and 100 hrs flying time. Lots of landings on a short turf field. Make sure your wheel pants don't cause the brakes to rub on the disc by creating side loads on the lines and calipers (clearances) and don't ride the brakes as many inexperienced pilots do. That loop really absorbs a lot of the vibration and twisting forces. Make it as large as permissable, roomwise.

Burning in breaks is totally unnecessary. A few low speed taxis with frequent, short brake applications is all that is needed to remove the protective coating from the new discs and seat the pads.

Roberta

[osxuser]

I like the idea of running aluminum down the gear leg, and then a nice AN hose from there to the caliper. Thats how the most certified aircraft do it, although some stick with the hard line the whole way.

I also prefer to stick with 5606 because of it's availablity. If something breaks on a flight and you need repairs, there is a lot higher chance your gonna be able to get 5606 than the later mil-specs.

[az_gila]

Originally Posted by osxuser

I like the idea of running aluminum down the gear leg, and then a nice AN hose from there to the caliper. Thats how the most certified aircraft do it, although some stick with the hard line the whole way.

My certified 28 year old Grumman Tiger has a single aluminum line down the gear leg all the way to the brakes.... doesn't even have a real loop in the end....

It's still on the original brake lines, but I'm replacing them at the next annual... 28 years of landings has to work harden the lines somewhat...:^)

gil in Tucson

[mark manda]

dumb question #506--- the plans called for running the line down the front side of the main gear?

I'm not close to the airplane-- I can't go look until tomorrow morning.

[gmcjetpilot]

To each is own and I agree the aluminum works as does 5606 fluid, but I think both of these are one step closer to a very hot fire.

The higher flash point fluids will reduce the chance of fire for sure. Granted the 5606 is easier to get, but than in several years of flying my RV, the brake system never need much service. Basically the need for a field repair is small. The 83283 fluid is not rare, any commercial FBO or service center has it. 5606 is only around because of the 60 year history, it has been identified as an extremely flammable fluid with a low flash point. Add hot brakes and.... Since we are building our own plane there is no need to follow the crowd for the sake of inertia, but that is just my opinion.

As far as flex line or flex brake line? Well if it does not crack there will be no leak and thus no fire regardless of fluid used. However if it ever does leak and you have 5606, you could have a bad fire. The cost, weight of using flex line is small to nil compared to the advantage. What I am hearing is a few folks have had good success with the aluminum line, one for 900 hours,while others obviously not. I guess by casual observation I have not heard of any flex lines breaking and therefore may be considered "better". Even if you don't have a fire a failed brake line could result in a ground loop if you are not aware of the problem.

IF you are going to use aluminum all the way, DO NOT bend it too much. Forming will work harden the tube (strain harden or cold working), making it stiff and more subject to craking and fatigue. I think Van uses 5052-O or 3003-O which is soft. If you really wanted to do it right, you could anneal the brake line after forming, but that requires kiln (oven) large enough for the whole line. To anneal 5052 you need to heat to 650F (775F for 3003-O) long enough to make sure its evenly heated and than air cooled. Some guys with talent say they can anneal it with a tourch. Since it must be heated throughout it would be hard to use a tourch on a long tube. The next best thing is just make sure you bend the tubing a min amount duing forming. You can also heat the tube to at least 500F to hot work duing forming, reducing strain harding. Caution if annealing a used line all trace of 5606 must be removed or you will have a hella of a fire, it is nasty stuff when too hot.

I mentioned some older RVs have nylon brake lines. If you have an old kit or bought a used kit or flying RV, you should replace the nylon with aluminum lines or flex line. Read the last three Par's in link below, RV-3 accident:

http://www.tc.gc.ca/civilaviation/sy...-05/brakes.htm

Brake fires in general are not just a RV thing, many a plane have had brake fluid feed fire, some resulted in total loss of aircraft. Many of these are from the pilot riding the bakes during taxi.

The other part is of the equation is NOT getting the brakes hot in the first place. The BEST way to check you speed during taxi is use the bakes to get to a slow speed and than release the brakes completely. Allow the speed to build a little and then check the speed again. The brake, release, brake, release, method builds the least heat. The wheel fairing is very tight, and not a lot of air is going around the brake. So if you ever lean hard on the brake, for whatever reason after landing, especially from a higher speed, allow them to cool before using them again. G

[moodyjr]

FWIW I purchased prefabbed Earls #4 Speedflex ss braided teflon brakelines 36 in long for about $13 each from an online speed shop. Lines are tested to 4000psi .Fits perfectly between the pre-punched fuselage hole & the caliper in my -8A. #3 lines are also available.

The OD of the line is about 5/16" & I am running the entire length of the braided line in split 1/4 ID polyurethane tube for abrasion protection for the leg & fairing.

John Moody
#82025

[mrreddick]

"An option is run solid aluminum tube down the leg and transition to braided line for the last foot or so. I don't care for that because of the extra fittings, but it works."

I have to agree with this exerpt from a previous posting. I have a solid line down the gear leg that terminates at a fitting and it has been flawless in the past 400 hours.