I'm working on a 3D printable model of the F9 v1.1...
Hmm, SpaceX Falcon9 main page reports this:"The first stage engines are gradually throttled near the end of first-stage flight to limit launch vehicle acceleration as the rocket’s mass decreases with the burning of fuel."http://www.spacex.com/falcon9
Available data from first v1.1 flight on altitude and velocity fit quite well with a full throttle simulation with a reasonable trajectory.
Quote from: pagheca on 12/14/2013 01:57 pmAvailable data from first v1.1 flight on altitude and velocity fit quite well with a full throttle simulation with a reasonable trajectory.Because MECO-1 happened earlier than on an expendable flight, roughly at the time it would normally start throttling down due to G limits. I would expect the SES-8 flight did involve throttling to some degree.
43 sec after throttling down started if the 2 min marker is taken for granted. However, a fit with the first 2 mins is enough to get some indication on the trajectory to be checked with available imaging.
Hi everyone,this question maybe obvious for many of you - please excuse me if this is the case but I'm just in learning mode.As well known, the Merlin 1D engine can be throttled down from 100% to 60%.The vacuum thrust of a rocket engine is proportional to the exhaust velocity and to the mass flow rate of the gas exhaust: dm/dt * V_exh.In vacuum and if also the gravity drag is negligible, when a Merlin 1D engine is throttled down, is dm/dt only changing, OR also V_exh (aka Isp_vacuum) is affected someway, with a consequent reduction in the engine efficiency in using the available propellant?If the second hypothesis is right (as I would say by looking at the physical principles the engine is based on), does someone know a reasonable way to write the relation Thrust(%) = f(%,dm/dt, V_exh)?Thanks for any hint,
[Changing thrust settings will change the chamber pressure, the chamber temperature, the characteristic velocity and correspondingly the specific impulse. And in the process also the mass flow.It will leave key characteristics unchanged, such as the exit area, throat area, the oxidizer-to-fuel ratio and thus the ratio of specific heats , the vandenkerkhove function, the exit to chamber pressure ratio and therefore the thrust coefficient.Since the throat area and the thrust coefficient stay constant, a change in thrust leads to a linearly corresponding change in chamber pressure and from this pressure ratio, a change in chamber temperature can be found using Poisson’s equationThis leads in turn to a change in characteristic velocity and specific impulse.At 50% throttle a decrease of specific impulse from 340s to 317s is to be expected On top you can expect some losses due to combustion efficiency that gets lower with lower throttle in a pintle engine.
Why that? Maybe just because progressively throttling is more efficient, at the end of the day, because it allows to follow much more carefully the thrust demand than just switching off engines?
IMO a big reason would be if another engine unexpectedly shutdown, as has happened with STS and Falcon9, then they just throttle up the remaining engines, with much shorter delay and avoiding the effects of restarting an engine in flight.
While trying to understand Merlin 1D and in particular "Merlin 1D+"* in depth, I've iterated my calculations a few times and have reached internal coherence and good balance with reality using the following characteristics/specs. Merlin 1D..Merlin 1D Vac..Merlin 1D+..Merlin 1D+ VacNozzle diameter, m1.073.031.073.03
Quote from: malu5531 on 12/12/2013 12:37 pmWhile trying to understand Merlin 1D and in particular "Merlin 1D+"* in depth, I've iterated my calculations a few times and have reached internal coherence and good balance with reality using the following characteristics/specs. Merlin 1D..Merlin 1D Vac..Merlin 1D+..Merlin 1D+ VacNozzle diameter, m1.073.031.073.03I've tried to draw the Falcon 9 first stage with your diameter, but I can't get it to fit. A circle of 8 engines with a diameter of 1,07 m each is going to have an outer diameter of at least 3,8 m as drawn in my CAD program, and that's with the engine nozzles touching each other. But if you look at images of the launch, the engines do not protrude outside the first stage diameter. And there's a gap between the engines. If I limit the outer diameter of the 8 engines to 3,66 m and allow some spacing between them, the nozzle diameter is around 96,5 cm (my drawing was in 1:144). I've also tried measuring the diameter from the second photo. Ignoring the distortion, the space between the center engine and the outer engines is 0.452 times the diameter of the center engine. So the total diameter of the ring of 8 engines is (3 + (2*0.452)) times the diameter of one engine nozzle. If the total ring diameter is 366 cm, then one engine must be 93,5 cm in diameter.
I might just not be looking in the right place, but has the Isp of Merlin-1D-VAC been confirmed or even reliably estimated yet?
I fully agree, nozzle diameter should be something like ~93-94 cm. I'm not fully there with the model. I have a similar issue with the RD-0162, not sure yet if those are related or there is a more trivial problem with the 1D model (such as adjusting the chamber pressure a bit, since that info might be old). Quote from: malu5531 on 12/31/2013 01:39 amI fully agree, nozzle diameter should be something like ~93-94 cm. I'm not fully there with the model. I have a similar issue with the RD-0162, not sure yet if those are related or there is a more trivial problem with the 1D model (such as adjusting the chamber pressure a bit, since that info might be old).
I fully agree, nozzle diameter should be something like ~93-94 cm. I'm not fully there with the model. I have a similar issue with the RD-0162, not sure yet if those are related or there is a more trivial problem with the 1D model (such as adjusting the chamber pressure a bit, since that info might be old).
There is a picture up the nozzles of the Merlin C posted here.http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838It looks to me as though SpaceX has done something to suppress flow separation at sea level. I would call it a duel bell nozzle design except it looks like quadruple bell design would be more accurate.I can see that the nozzles are uniformly divergent on the outside but on the inside it is different. What do you all think?
Quote from: aero on 02/19/2014 09:49 pmThere is a picture up the nozzles of the Merlin C posted here.http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838It looks to me as though SpaceX has done something to suppress flow separation at sea level. I would call it a duel bell nozzle design except it looks like quadruple bell design would be more accurate.I can see that the nozzles are uniformly divergent on the outside but on the inside it is different. What do you all think?What are you drawing *that* conclusion from? That is just an engineering drawing with different sub-component coloured differently. I think you are reading more into those colours that you should.
Quote from: Lars_J on 02/19/2014 09:52 pmQuote from: aero on 02/19/2014 09:49 pmThere is a picture up the nozzles of the Merlin C posted here.http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838It looks to me as though SpaceX has done something to suppress flow separation at sea level. I would call it a duel bell nozzle design except it looks like quadruple bell design would be more accurate.I can see that the nozzles are uniformly divergent on the outside but on the inside it is different. What do you all think?What are you drawing *that* conclusion from? That is just an engineering drawing with different sub-component coloured differently. I think you are reading more into those colours that you should.You're right. That's not a picture, my bad. Does anyone have a picture of the inside of a SpaceX rocket engine nozzle?