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#1480
by
ugordan
on 25 Jan, 2018 16:14
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The flames lengths are about proportional to the thrust
F 5000KN - about 60 feet long.
SV 35000KN - about 400 feet long.
They're also incredibly strongly dependent on atmospheric conditions. You posted a Saturn image taken during max Q and compared it to a F9v1.0 very shortly after liftoff. I could have just as easily dug up a F9 plume at around T+2min and compared it to a post-liftoff Saturn V plume and it would prove precisely nothing, even though it would be bigger.
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#1481
by
gongora
on 25 Jan, 2018 18:14
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I'm hopeful that this bird flies twice. It's an expensive piece of hardware why not use it twice.
Also, Hawthorne will be busy with F9 Block 5's. producing a Block 5 FH could eat into their available resources.
Gwynne has already said the next FH will be Block 5. If most of this vehicle comes back put it on display somewhere and move on to the new configuration.
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#1482
by
yokem55
on 25 Jan, 2018 18:23
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I wonder if overall Falcon Heavy will be nearly as loud as the shuttle SRB's or Saturn since even though the total thrust is lower, the exhaust velocity will be a bit higher, with an isp of 259 for the Shuttle SRB's, 265 for the F-1 vs 285 for the Merlins.
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#1483
by
JonathanD
on 25 Jan, 2018 19:41
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I wonder if overall Falcon Heavy will be nearly as loud as the shuttle SRB's or Saturn since even though the total thrust is lower, the exhaust velocity will be a bit higher, with an isp of 259 for the Shuttle SRB's, 265 for the F-1 vs 285 for the Merlins.
I didn't think exhaust velocity was necessarily the arbiter of that. Otherwise, a flashlight would be really loud, right?
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#1484
by
yokem55
on 25 Jan, 2018 19:44
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I wonder if overall Falcon Heavy will be nearly as loud as the shuttle SRB's or Saturn since even though the total thrust is lower, the exhaust velocity will be a bit higher, with an isp of 259 for the Shuttle SRB's, 265 for the F-1 vs 285 for the Merlins.
I didn't think exhaust velocity was necessarily the arbiter of that. Otherwise, a flashlight would be really loud, right?
Well, combination of thrust and exhaust velocity. The flashlight doesn't produce all that much thrust....
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#1485
by
AUricle
on 25 Jan, 2018 19:53
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I hope I'm in the right place for this. I'm an uber newb here.
Does anyone know the time between firing of the engine pairs for the FH test yesterday?
I've see 200ms in other places, which I find hard to believes, since that would mean almost 3 sec. to get up and running.
I thought I'd read an earlier article here that said the timing was every 20ms, which in real time would appear simultaneous to the naked eye, and seems more correct.......
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#1486
by
envy887
on 25 Jan, 2018 20:14
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I hope I'm in the right place for this. I'm an uber newb here.
Does anyone know the time between firing of the engine pairs for the FH test yesterday?
I've see 200ms in other places, which I find hard to believes, since that would mean almost 3 sec. to get up and running.
I thought I'd read an earlier article here that said the timing was every 20ms, which in real time would appear simultaneous to the naked eye, and seems more correct.......
Does anyone have information indicating whether it's 2 engines at a time, or two engines
per core at a time, for the staggered start? The latter is 3x as fast and would light the whole stack in under a second even at 200 ms intervals.
The latter also make a lot more sense to me, because if only 2 of the 27 are lit at each interval, all three cores will frequently have very different thrust levels, and the thrust will never be balanced around the hold-downs on an individual core.
ISTM that they would light 2 engines per core at once, with the two being lit always across from each other. The center engine would be lit simultaneously with one of the 4 pairs, and all 3 center engines on the 3 cores would light simultaneously.
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#1487
by
Torbjorn Larsson, OM
on 25 Jan, 2018 21:10
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I hope I'm in the right place for this. I'm an uber newb here.
Does anyone know the time between firing of the engine pairs for the FH test yesterday?
I've see 200ms in other places, which I find hard to believes, since that would mean almost 3 sec. to get up and running.
I thought I'd read an earlier article here that said the timing was every 20ms, which in real time would appear simultaneous to the naked eye, and seems more correct.......
Does anyone have information indicating whether it's 2 engines at a time, or two engines per core at a time, for the staggered start? The latter is 3x as fast and would light the whole stack in under a second even at 200 ms intervals.
The latter also make a lot more sense to me, because if only 2 of the 27 are lit at each interval, all three cores will frequently have very different thrust levels, and the thrust will never be balanced around the hold-downs on an individual core.
ISTM that they would light 2 engines per core at once, with the two being lit always across from each other. The center engine would be lit simultaneously with one of the 4 pairs, and all 3 center engines on the 3 cores would light simultaneously.
According to this sound analysis the cores ignite one engine per core with about 30 ms intervals:
Here are the audio waveforms at the ignition of a typical F9 and the FH static fire. The F9 engines all appear to start simultaneously, but as advertised, the FH ignitions appear staggered over about 0.32 seconds, with 9 distinguishable events. Perhaps the engines were ignited 3 at a time, one on each core? I've also attached the audio files in case you want to do your own analysis.
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#1488
by
JDTractorGuy
on 25 Jan, 2018 22:42
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Threw this together in paint. Falcon Heavy vs STS-135.
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#1489
by
ValmirGP
on 25 Jan, 2018 22:49
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I may be way out and wrong but after hearing the videos, specially the Robin Seemangal one, and also after viewing the beginning of the test on the official SpaceX video, I got the impression that the central core fired all at once (louder rumble and sudden bump in the smoke coming out of the trench) and then I believe I counted nine quieter rumbles. My take of it was a core firing as as a normal F9 and then the side boosters firing two at a time, maybe one from each side. Just what I thought.
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#1490
by
AUricle
on 25 Jan, 2018 23:13
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I may be way out and wrong but after hearing the videos, specially the Robin Seemangal one, and also after viewing the beginning of the test on the official SpaceX video, I got the impression that the central core fired all at once (louder rumble and sudden bump in the smoke coming out of the trench) and then I believe I counted nine quieter rumbles. My take of it was a core firing as as a normal F9 and then the side boosters firing two at a time, maybe one from each side. Just what I thought.
As Envy887 said in #1505, balancing the thrust forces would've been critical. So I'm inclined to believe the original reporting of the staggered firings calling for a pair of engines to fire every 20ms, would cause momentary imbalances.
Your suggestion would seem to imply a serious imbalance too.
The best suggestion I've seen is lighting 1 engine from each core simultaneously, and repeating that 9 times. That keeps the forces balanced throughout the firing sequence. The audio files suggest that. 9 firings 35ms apart using a total of 315ms.
I'd really like a definitive answer to this, and I'm sure on launch day, the webcast will cover this topic. I'm just impatient
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#1491
by
Grandpa to Two
on 25 Jan, 2018 23:25
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From the sound alone:
There's the initial boom, then ~4s pause before the main rumbling of the engines. The main firing seems to only be 6 seconds from listening to it.
I attached the sound file I used.
I may be way out and wrong but after hearing the videos, specially the Robin Seemangal one, and also after viewing the beginning of the test on the official SpaceX video, I got the impression that the central core fired all at once (louder rumble and sudden bump in the smoke coming out of the trench) and then I believe I counted nine quieter rumbles. My take of it was a core firing as as a normal F9 and then the side boosters firing two at a time, maybe one from each side. Just what I thought.
There’s good discussion on sound files here as well as reply #1449 have fun.
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#1492
by
Roy_H
on 26 Jan, 2018 00:37
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While it's nostalgic to compare thrust clouds comparing the FH 5Mlb to the Shuttles 6.8Mlb and Saturn's 7.5Mlb, I really don't think these pictures belong in Updates.
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#1493
by
AC in NC
on 26 Jan, 2018 02:09
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Threw this together in paint. Falcon Heavy vs STS-135.
Nice. I tried to adjust for the different framing here. The original made STS look like it was dwarfing FH. This may bring them a little closer to an easy comparison.
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#1494
by
OneSpeed
on 26 Jan, 2018 05:55
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As Envy887 said in #1505, balancing the thrust forces would've been critical. So I'm inclined to believe the original reporting of the staggered firings calling for a pair of engines to fire every 20ms, would cause momentary imbalances.
Your suggestion would seem to imply a serious imbalance too.
The best suggestion I've seen is lighting 1 engine from each core simultaneously, and repeating that 9 times. That keeps the forces balanced throughout the firing sequence. The audio files suggest that. 9 firings 35ms apart using a total of 315ms.
I'd really like a definitive answer to this, and I'm sure on launch day, the webcast will cover this topic. I'm just impatient
Due to thrust torque (a thrust-induced rotation) scenario that could destroy or severely damage the octawebs at the base of each Falcon core that house the Merlin 1D engines, the Falcon Heavy’s 27 engines will not be lit simultaneously like the Falcon 9 engines.
I take it from ChrisG's statement that the risk to the octawebs is not from pure thrust, but from a rotational moment or torque. There are a few ways for the Merlin engines to generate torque (as opposed to thrust).
1. First is to gimbal them whilst they are running, applying axial torque to the octaweb (around the z axis). That torque can be cancelled by eliminating the gimbal, and should be as easily controlled on FH as F9. I can't see how staggered firings would help control this mode of induced torque, but maybe someone else can.
2. Next, a 'tipping' moment in the x and/or y axis can be applied, by varying the thrust in the engines and/or gimbaling. Staggering the ignition sequence would also cause this 'tipping' moment, so it is extremely unlikely that the stagger was introduced to solve this mode of induced torque.
3. The Merlin gas generator also induces some z-axis torque at startup, as a reaction to the quick spoolup of its turbines after ignition. F9 can obviously handle this torque, but what happens when three cores are connected? The cores would all be pushed in the same direction about the z-axis, but where they are connected, they would be pushing in opposite directions. Staggering the engine ignitions would definitely help here, reducing the peak load to 1/9 of instantaneous startup.
4. Some other mechanism I haven't thought of?
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#1495
by
Lars-J
on 26 Jan, 2018 06:11
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Not the torque issue again... Please watch the last 40 or so F9 flights and see what kind of torque induced rotation you see when the hold-downs release. (hint: none)
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#1496
by
woods170
on 26 Jan, 2018 06:38
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IIRC the rain bird sound suppression system was mainly for potential acoustic damage the the Shuttle's tiles and during Apollo water was mainly for cooling...
For Shuttle, it was the payloads
You are both wrong in that you are both only one-third right. The substantial beefing-up of the sound suppression system after STS-1 was due to:
1. Reported damage to the orbiter and anomalies (body flap structural deflection, airframe cracks, tiles [16 lost, 148 damaged], forward RCS strut buckling) from SRB ignition over-pressure.
2. Concern for the payloads (courtesy of data coming from the DFI payload)
3. Reported damage to the mobile launcher (9.1 meter long crack in upper deck due to shuttle drift over the platform with insufficient shielding from SRB accoustics).
All this information is readily available from NASA and other public source.
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#1497
by
Shanuson
on 26 Jan, 2018 06:46
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Not the torque issue again... Please watch the last 40 or so F9 flights and see what kind of torque induced rotation you see when the hold-downs release. (hint: none)
I thought its about spin up of the turbo pumps, which is done while the rocket is still hold down (to abort if something goes wrong during this spin up / engine startup). This torque is absorbed by the hold-downs and short lived (lot less than 1sec). So at the moment of release of the hold-downs (>2s after startup) there is not torque anymore to rotate the rocket and you see like you said nothing.
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#1498
by
ZachF
on 26 Jan, 2018 11:54
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I wonder if overall Falcon Heavy will be nearly as loud as the shuttle SRB's or Saturn since even though the total thrust is lower, the exhaust velocity will be a bit higher, with an isp of 259 for the Shuttle SRB's, 265 for the F-1 vs 285 for the Merlins.
The figures I posted above included liftoff power, which takes exhaust velocity into account. Liftoff power of the shuttle is still higher than FH.
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#1499
by
dglow
on 26 Jan, 2018 12:12
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Not the torque issue again... Please watch the last 40 or so F9 flights and see what kind of torque induced rotation you see when the hold-downs release. (hint: none)
I thought its about spin up of the turbo pumps, which is done while the rocket is still hold down (to abort if something goes wrong during this spin up / engine startup). This torque is absorbed by the hold-downs and short lived (lot less than 1sec). So at the moment of release of the hold-downs (>2s after startup) there is not torque anymore to rotate the rocket and you see like you said nothing.
I recall that the first F9 launch exhibited a great deal of rotation directly off the pad. To what cause was this attributed?
