Unbraided "Pressureflex" from Hosemaster is rated to 450 or 400 psi
for 1/4 or 1/2" hose, respectively. But it's probably still stiffer
than their Masterflex hose, which is rated to 90/70/70 psi for 1/4,
3/8, and 1/2 unbraided hose respectively, or 1800/1558/1186 psi with a
single braid.
It would be interesting to see what the burst pressure a short section
of the unbraided Masterflex really is.
It's all stainless though. So compatible with your propellants, but
the connection to the plumbing would have to be anodized to prevent
galvanic corrosion with peroxide.
Since the rocket is fairly long you likely only need five degrees or
so of gimbal. I wonder if there's some clever origami seal-less joint
that can do a few degrees at low pressure.
On Thu, Aug 4, 2016 at 12:38 AM, Paul Breed <paul@xxxxxxxxxx> wrote:
About 300 psi feed, H2O2 and hydrocarbon (currently gasoline)
On Wed, Aug 3, 2016 at 3:21 PM, Jonathan Goff <jongoff@xxxxxxxxx> wrote:
Out of curiosity, what pressure are you running and what propellants?
Jon
On Aug 3, 2016 4:05 PM, "Paul Breed" <paul@xxxxxxxxxx> wrote:
I'm doing a really tiny motor, the inertia of the motor is almost
trivial...
3/8" clear ID Teflon lined flex tube seems order of magnitude stiffer
even pressurized than the motor
inertial force... realize that my tiny 3d printed motor has thrust to wt
of >125.
On Wed, Aug 3, 2016 at 2:08 PM, Ben Brockert <wikkit@xxxxxxxxx> wrote:
I did the full math on hose forces. The forces you have to deal with
are:
* Base unpressurized, room temperature bending force.
* Additional bending force due to change in Young's modulus due to
cryogenic temperature
* Additional bending force due to mass and velocity of propellant,
i.e. force needed to curve the propellant
* Additional bending force due to pressurization of the hose.
The first two additional forces turn out to be trivial and can be
ignored. The third one added about 3 times the original bending force,
so it ended up being roughly 4 times the bending force needed when
empty and unpressurized. One lesson from that is if the GNC guy wants
to tune the gimbal PID at high fidelity, pressurizing the system with
gas at room temperature to operating pressure gives a high fidelity
result.
But in the end it doesn't matter at all. The actuator on a gimbal is
usually sized for the inertial loads of gimbaling the engine. Any
normal slew rate is going to have a wild excess of power over the
force needed to bend the hoses. The last time I ran the numbers the
system had about 32 times as much force as needed just to bend the
hoses. Its actuators were a bit big for the size of the engine, but
even if they were a tenth the size inertia would still be the dominant
force acting against the gimbal.
I don't know that it's the source I used, but
http://www.engineeringtoolbox.com/forces-pipe-bends-d_968.html gives
equations for the pressure and massflow components.
I can see the rotating seal making the whole thing package better, but
it also means more dynamic seals are added to the propulsion system.
Definitely easier with your storables than LOX/kero, but still another
moving seal. And a much bigger one than the ones in the valves.
Ben
On Wed, Aug 3, 2016 at 9:44 PM, Paul Breed <paul@xxxxxxxxxx> wrote:
I've designed a gimbal that routes both propellants through the
structure
with a couple of rotating seals, all bearing supported...
My personal feel is this will be lighter than flexible hoses and the
upgraded actuator
necessary to bend them, alas I don't really know.
Is there any data or ideas on how stiff flexible pressurized hose is?
Paul
