[AR] Re: Embry-Riddle Prescott Liquid Rocket Engine Hot-fire
- From: Craig Fink <webegood@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Fri, 7 Jun 2019 07:59:38 -0700
On Thu, Jun 6, 2019 at 10:16 AM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 5 Jun 2019, Craig Fink wrote:
Why not just put the engine on a rocket and chain it down, like SpaceX...
Because, for one thing, the rocket usually isn't instrumented to measure
thrust and flow rates.
Although SpaceX hasn't been talkative about the details, you can be sure
most of their engine development is done on traditional test stands.
Many things can be done in more relaxed ways, with greater flexibility and
bigger margins and more instrumentation -- and lower cost -- if the test
stand doesn't have to be flightweight.
Why are you trying to discourage this young man and others from having fun?
Flow rates, any good engine controller should be looking at flow rates and
doesn't require a test stand. Thrust measurement are F=MA for a rocket,
strain gages. Reconstruction of the Space Shuttle ascent could more
accurately compute the weight of the Orbiter than could be measured on the
ground, the thrust, ISP, mixture ratio, also. Going the test stand route
is twice the work for half the fun. They don't have to build everything
lightweight/flightweight until the last one. Printed engines, heavy tanks
can hop too. Just making the test stand a boiler plate rocket that hops.
Go look at SpaceX timeline for the Raptor Engine. I could be wrong, but
they build the first one, took it to the test stand ran it for a second or
two, then mounted to the heavy, non-flightweight rocket and did the next
test using it. Another second or two of run time. It probably came apart or
damaged itself a little bit, or they just wanted to take it apart and
examine it. Now they have mounted the next one, probably new and improved
in some way, ready for the next tiny hop. They essentially skipped the test
stand to go right to integrating the engine on their boilerplate test
vehicle. Exactly how many full length burns has Raptor Engine successfully
completed? Zero.
Test Rockets straining against the chains holding them down are way more
sexy than Test Stands. Just take the chains off after the engine stops
coming apart. Teaching rapid development and deployment using 3-D printers
is ....... Electric Compressors are much simpler, more controllable and
don't require batteries to run your engine for short hops.
Just my opinion.
--
Craig Fink
WeBeGood@xxxxxxxxx
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