I have the infinity retracts so my highest point in the system is just above the trunnion where the gear swings. My master cylinder is in the plans position. I pressure bleed my brakes, even with the nose down in the grazing post, and do not suffer the issues to which Marc refers. Just pump fast and it takes all the air with it. I do always empty the system before bleeding.
On Jun 11, 2022, at 11:49 PM, 'Chrissi Bush' via COZY Builders Mailing List <cozy_builders@...> wrote:
Marc,
I know this is a really dumb question but I'm going to stick my
neck out anyway and ask, if using a pressure bleeding system where
no pumping or actuation of brake apparatus is involved, if it were
possible or the brake system were laid out in such a manner, whats
to stop you from unbolting the components and stringing them up in
the air to get as much a vertical lineup as possible and then
doing the pressure bleed?
...Chrissi
On 6/10/2022 7:17 PM, Marc J. Zeitlin
wrote:
Folks:
I have to believe that we've discussed this in the past,
but it bears repeating. A customer's plane has been beating
the crap out of me for the past 5 hours of paid work time (and
I HATE charging customers for time spent due to design or
implementation issues), due to a brake system that is
extremely difficult to bleed. Although this is an OSH award
winning COZY MIV, which in almost all other ways is the
epitome of what to do on COZY MKIVs, the brakes have always
been marginal from a torque application (meaning pressure
developed) standpoint.
This is not the plans system, or even a laydown MC system,
but a "Velocity style" hanging pedal system, with the MC's up
high, and the reservoir only a bit higher (the lines from the
reservoir to the MC's are mostly BELOW the MC's). On a
Velocity, due to the much larger depth of the fuselage, it's
easily possible to have everything arranged well as described
below, but on a COZY, it's a lot more difficult due to the
small depth of the fuselage, particularly in the nose area.
In this case, the feed lines from the MC's to the LG
bulkhead route up and over the pedal torque tube and are
pretty much guaranteed to be air traps at the high point.
Given the lack of access in the nose due to the brake mounting
system, bleeding the lines (pressure bleeding from the caliper
to the reservoir, to try to push all the air out) has been
completely unsuccessful on one side, even after manipulating
the MC's to try to position them so that the lines are running
uphill all the way to the reservoir. We may resort to
replacing the tubing inside the fuselage; rerouting it and
using smaller tubing.
At any rate, when designing your brake system, ensure the
following:
- From the bleeder valve on the caliper to the top of the
reservoir, ensure that EVERYWHERE upstream (closer to the
reservoir) is higher than any place downstream. IOW, for
those of you with math backgrounds, the uphill slope from
the caliper to the reservoir MUST BE MONOTONIC - anything
else will be an air trap at a high point.
- Sometimes it's not possible to perfectly do #1 - in
these cases, use the smallest possible tubing, which would
be AN-2 or even 1/8" SS with a 0.020" wall. If you can't
use that, use nothing larger than 3/16" tubing.
- Unless you can GUARANTEE #1, do NOT use Matco 1/4"
tubing, or 1/4" Matco fittings, as shown here:
https://www.aircraftspruce.com/catalog/lgpages/matcotubefitting.php
These are air traps at the point where the tubing goes
into the fitting. The 1/8" tubing and fittings is probably
acceptable, but why not just use metal hard lines where
nothing moves, and SS/Teflon braided line where things
move.
- Position the calipers so that there will be a minimum
air trap in any attached fittings (and the smaller the
brake line and fittings, the smaller the air trap).
- Position the calipers so that the fluid flow is uphill
from the outlet to the inlet from the reservoir, and the
moreso, the better.
You will be far happier with the performance of your
brakes, and make things a lot easier when you need to bleed
them (and you will), if you stick to these rules of thumb.
The closer you can be to having all 5 things be the case,
the lower the chance of issues. Sometimes you can get things
to work even if you violate all 5, but your margin for
success is a lot slimmer.
--
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|
Keith Spreuer
Thinking outside the box there Chrissi. The problem is that the lines are routed thru the fuselage and attached in numerous places. Don't see any way to reinstall the system as an assembly
I have the infinity retracts so my highest point in the system is just above the trunnion where the gear swings. My master cylinder is in the plans position. I pressure bleed my brakes, even with the nose down in the grazing post, and do not suffer the issues to which Marc refers. Just pump fast and it takes all the air with it. I do always empty the system before bleeding.
Phil On Jun 11, 2022, at 11:49 PM, 'Chrissi Bush' via COZY Builders Mailing List <cozy_builders@...> wrote:
Marc,
I know this is a really dumb question but I'm going to stick my
neck out anyway and ask, if using a pressure bleeding system where
no pumping or actuation of brake apparatus is involved, if it were
possible or the brake system were laid out in such a manner, whats
to stop you from unbolting the components and stringing them up in
the air to get as much a vertical lineup as possible and then
doing the pressure bleed?
...Chrissi
On 6/10/2022 7:17 PM, Marc J. Zeitlin
wrote:
Folks:
I have to believe that we've discussed this in the past,
but it bears repeating. A customer's plane has been beating
the crap out of me for the past 5 hours of paid work time (and
I HATE charging customers for time spent due to design or
implementation issues), due to a brake system that is
extremely difficult to bleed. Although this is an OSH award
winning COZY MIV, which in almost all other ways is the
epitome of what to do on COZY MKIVs, the brakes have always
been marginal from a torque application (meaning pressure
developed) standpoint.
This is not the plans system, or even a laydown MC system,
but a "Velocity style" hanging pedal system, with the MC's up
high, and the reservoir only a bit higher (the lines from the
reservoir to the MC's are mostly BELOW the MC's). On a
Velocity, due to the much larger depth of the fuselage, it's
easily possible to have everything arranged well as described
below, but on a COZY, it's a lot more difficult due to the
small depth of the fuselage, particularly in the nose area.
In this case, the feed lines from the MC's to the LG
bulkhead route up and over the pedal torque tube and are
pretty much guaranteed to be air traps at the high point.
Given the lack of access in the nose due to the brake mounting
system, bleeding the lines (pressure bleeding from the caliper
to the reservoir, to try to push all the air out) has been
completely unsuccessful on one side, even after manipulating
the MC's to try to position them so that the lines are running
uphill all the way to the reservoir. We may resort to
replacing the tubing inside the fuselage; rerouting it and
using smaller tubing.
At any rate, when designing your brake system, ensure the
following:
- From the bleeder valve on the caliper to the top of the
reservoir, ensure that EVERYWHERE upstream (closer to the
reservoir) is higher than any place downstream. IOW, for
those of you with math backgrounds, the uphill slope from
the caliper to the reservoir MUST BE MONOTONIC - anything
else will be an air trap at a high point.
- Sometimes it's not possible to perfectly do #1 - in
these cases, use the smallest possible tubing, which would
be AN-2 or even 1/8" SS with a 0.020" wall. If you can't
use that, use nothing larger than 3/16" tubing.
- Unless you can GUARANTEE #1, do NOT use Matco 1/4"
tubing, or 1/4" Matco fittings, as shown here:
https://www.aircraftspruce.com/catalog/lgpages/matcotubefitting.php
These are air traps at the point where the tubing goes
into the fitting. The 1/8" tubing and fittings is probably
acceptable, but why not just use metal hard lines where
nothing moves, and SS/Teflon braided line where things
move.
- Position the calipers so that there will be a minimum
air trap in any attached fittings (and the smaller the
brake line and fittings, the smaller the air trap).
- Position the calipers so that the fluid flow is uphill
from the outlet to the inlet from the reservoir, and the
moreso, the better.
You will be far happier with the performance of your
brakes, and make things a lot easier when you need to bleed
them (and you will), if you stick to these rules of thumb.
The closer you can be to having all 5 things be the case,
the lower the chance of issues. Sometimes you can get things
to work even if you violate all 5, but your margin for
success is a lot slimmer.
--
You received this message because you are subscribed to the Google Groups "COZY Builders Mailing List" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cozy_builders+unsubscribe@....
To view this discussion on the web visit https://groups.google.com/d/msgid/cozy_builders/4c9159d4-8a1e-98ec-9cef-08fe7eae0dd6%40aol.com.
|
