[AR] Re: Pogo Accumulator Assembly
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Fri, 15 Dec 2017 11:42:06 -0500
On Fri, Dec 15, 2017 at 11:11:35AM +0100, Uwe Klein wrote:
Am 14.12.2017 um 23:30 schrieb William Claybaugh:
Brian:
Pogo is a system level interaction between thrust variation and the
vehicle structure; to the extent that your systems has thrust
pulsation--from whatever source--pogo is a possibility.
so the solution is to somehow reduce thrust on short term increase of
acceleration? "fluid High pass filter" ??
I think the idea is that pogo arises from rocket acceleration
producing increased pressure at the pump inlet. In big rockets, one
has a long column of fluid, which yields a proportionately large
pressure increase from acceleration. This pressure increase
translates to increased pressure at the pump outlet, which translates
to more thrust. By itself, this would just be a mechanism for
runaway, but the control system senses it and reduces thrust; thus it
becomes an oscillation.
Of course this explanation makes it sound like instead of adding an
extra device to stop pogo one could put more cleverness into the
design of the control system.
This particular anti-pogo device is described as an "accumulator",
which I think is something like the anti-water-hammer devices one puts
on home water pipes: it has a gas-pressurized volume into which the
fluid can move when its pressure increases. It's more of a low-pass
filter than a high-pass one.
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