Virgin Galactic Tech
BOAC,possibly a static line to a stabilising drogue,then an auto barostat at 10-15k.....
Yo BOAC!
I have many friends that had the experience of being in free fall after being hit by AAA or a SAM. One guy told us that first thing he saw was no "floor" on his jet.
It's the luck of the draw.
Most of us had a barometric doofer that deployed the chute at 14,000 feet or so without any action on our part.
The biggie is being ejected from the wreckage via a system or blind ass luck. I would take either, heh heh.
I have many friends that had the experience of being in free fall after being hit by AAA or a SAM. One guy told us that first thing he saw was no "floor" on his jet.
It's the luck of the draw.
Most of us had a barometric doofer that deployed the chute at 14,000 feet or so without any action on our part.
The biggie is being ejected from the wreckage via a system or blind ass luck. I would take either, heh heh.
Per Ardua ad Astraeus
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A static line needs to be attached to something...
Gums - how many of your mates did it from 45k+ and supersonic? I know of only a few actual 'controlled' ejections from that environment, an X-15, a Lightning and probably a few others, but disintegration?
Gums - how many of your mates did it from 45k+ and supersonic? I know of only a few actual 'controlled' ejections from that environment, an X-15, a Lightning and probably a few others, but disintegration?
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Right after "ullage".
PJ2
At about 0:55, after "unlock" but before "feather", I think I see significant random independent buffeting of the 2 feathers, the worst of the entire 3 minutes or so. Suggests to me that "unlocked" allows quite a bit of uncontrolled movement of those surfaces.
At about 0:55, after "unlock" but before "feather", I think I see significant random independent buffeting of the 2 feathers, the worst of the entire 3 minutes or so. Suggests to me that "unlocked" allows quite a bit of uncontrolled movement of those surfaces.
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Physical lock
Cross reference of pchapman & Redredrobin's efforts on the rumours thread.
From New spaceship restoring hope after Virgin Galactic crash | Reuters
@BOAC tell if you don't want this posting here and I'll delete it
From New spaceship restoring hope after Virgin Galactic crash | Reuters
As the ship is rocketing upward, the tail is held fast by a large hook that is supposed to remain engaged until the craft reaches supersonic speed, Mike Moses, Virgin Galactic vice president of operations, explained in an interview with Reuters.
At that point, the pilots release the hook, though the tail remains pinned back by aerodynamic pressures. The command to actually move the tail into descent position comes after the rocket motor burns out, near the apex of the ship's altitude.
Unlocking the tail is done well before then so that if the mechanism fails, the pilots can abort the flight.
"It's a great safety feature, but if you use your safety feature in a regime that it's not designed to handle, bad things are going to happen," Moses said. "It's like your car airbag going off at 65 miles per hour."
At that point, the pilots release the hook, though the tail remains pinned back by aerodynamic pressures. The command to actually move the tail into descent position comes after the rocket motor burns out, near the apex of the ship's altitude.
Unlocking the tail is done well before then so that if the mechanism fails, the pilots can abort the flight.
"It's a great safety feature, but if you use your safety feature in a regime that it's not designed to handle, bad things are going to happen," Moses said. "It's like your car airbag going off at 65 miles per hour."
thcrozier;
Yes, I wondered about that too - lots of movement.
For me anyway, the issue isn't the "early" unlocking as attributed to the PNF "without orders from the PF" but the fact that a mere unlocking resulted in unintended deployment of the feathers.
By another description, it's the thrust reverser deployment in mid-air problem - it just shouldn't happen. However, simplicity of design and weight considerations may play a role in a more elementary mechanical or even electro-mechanical design which required stricter SOP requirements, (lots in that statement to unpack, I know).
I'm sure someone knows but I'm curious as to what Mach No. the feathers were unlocked in the third launch, (the one with the CVR where "unlocked" is heard about 17" after light-off). Probably it's above the required M1.4 but it would be interesting if it weren't...
Yes, I wondered about that too - lots of movement.
For me anyway, the issue isn't the "early" unlocking as attributed to the PNF "without orders from the PF" but the fact that a mere unlocking resulted in unintended deployment of the feathers.
By another description, it's the thrust reverser deployment in mid-air problem - it just shouldn't happen. However, simplicity of design and weight considerations may play a role in a more elementary mechanical or even electro-mechanical design which required stricter SOP requirements, (lots in that statement to unpack, I know).
I'm sure someone knows but I'm curious as to what Mach No. the feathers were unlocked in the third launch, (the one with the CVR where "unlocked" is heard about 17" after light-off). Probably it's above the required M1.4 but it would be interesting if it weren't...
center of pressure
I looked up my Viper chart for movement of the c.p. as we went from 0.9 M to 1.4 M.
We were not static stable until 0.95M, but went from a c.p. of 43% MAC at 1.1M or so to almost 60% MAC at 1.4M, and then it leveled off.
So looks like 1.4M is a good rule of thumb for less concerns about changes in center of pressure. Have to look at Concorde and Blackbird stuff to confirm.
My guess is the pneumatic system allowed the feathers to move, unlike a hydraulic system ( compressible versus not-so-compressible acting fluids). So the shock waves and movement of the c.p. seems to be an area of concern.
We were not static stable until 0.95M, but went from a c.p. of 43% MAC at 1.1M or so to almost 60% MAC at 1.4M, and then it leveled off.
So looks like 1.4M is a good rule of thumb for less concerns about changes in center of pressure. Have to look at Concorde and Blackbird stuff to confirm.
My guess is the pneumatic system allowed the feathers to move, unlike a hydraulic system ( compressible versus not-so-compressible acting fluids). So the shock waves and movement of the c.p. seems to be an area of concern.
Feathered re-entry system
I'm still mulling over the reason to unlock the feathering system in the early stages of the flight. The plausible argument, that the system is esential for a safe re-entry and that therefore the functioning of the system has to be tested before leaving to space makes sense, but does that apply to a testflight where neither achieved Mach nor achieved altitude would be high enough that usage of said system is critical?
In search for a more detailed description of the system i found the following patent, which was filed 2004 for the spaceship One re-entry system, and as Spaceship Two is known as being a scale up, it might still apply to the system used in Spaceship Two as well.
The unlock system and the feathering system are pneumatically operated.
Patent US20060108479 - Winged spacecraft - Google Patents
What is the reason behind to unlock a safety feature that early in flight? Is it to have it available already during ascent if stability issues arrive to slow the ascent or to stabilize the ascent by other means when flight control inputs or gas thrusters are not effective or failed?
Something does not sum up, there is no urgency at all in a test flight like that to arm the system that early in a flight.
In search for a more detailed description of the system i found the following patent, which was filed 2004 for the spaceship One re-entry system, and as Spaceship Two is known as being a scale up, it might still apply to the system used in Spaceship Two as well.
The unlock system and the feathering system are pneumatically operated.
Patent US20060108479 - Winged spacecraft - Google Patents
What is the reason behind to unlock a safety feature that early in flight? Is it to have it available already during ascent if stability issues arrive to slow the ascent or to stabilize the ascent by other means when flight control inputs or gas thrusters are not effective or failed?
Something does not sum up, there is no urgency at all in a test flight like that to arm the system that early in a flight.
Early unlock
@RetiredF4
Good find that patent!
About the unlocking, to my understanding:
The earlier in flight that you can allow unlocking - provided already having reached safe margin to uncommanded feathering through the transsonic regime - the earlier you can detect an unlocking failure, the earlier you can cut-off the rocket motor.
The earlier you stop pushing energy into the vehicle - which has been found to be unable to perform the nominal high drag reentry - the better the chances for surviving a non-nominal low drag re-entry.
In addition to that I would expect after engine cut-off the oxidiser to be dumped overboard thus reducing weight, to further improve re-entry margins.
My post perhaps superfluous, reading the later portion of yours.
Hmmm, ...
I guess that also in a lower energy testflight an earlier than engine cut-off verification would add to re-entry safety margin as well.
Other than that, to test the procedure as such as closely as possible to the procedure for nominal energy flight.
Or, ... perhaps to more precisely quantify the first safety margin, i.e. to step-wise determine in subsequent tests how soon you can safely permit unlocking.
Admittedly more speculatively all that ...
What is the reason behind to unlock a safety feature that early in flight?
About the unlocking, to my understanding:
The earlier in flight that you can allow unlocking - provided already having reached safe margin to uncommanded feathering through the transsonic regime - the earlier you can detect an unlocking failure, the earlier you can cut-off the rocket motor.
The earlier you stop pushing energy into the vehicle - which has been found to be unable to perform the nominal high drag reentry - the better the chances for surviving a non-nominal low drag re-entry.
In addition to that I would expect after engine cut-off the oxidiser to be dumped overboard thus reducing weight, to further improve re-entry margins.
but does that apply to a testflight where neither achieved Mach nor achieved altitude would be high enough that usage of said system is critical?
Hmmm, ...
I guess that also in a lower energy testflight an earlier than engine cut-off verification would add to re-entry safety margin as well.
Other than that, to test the procedure as such as closely as possible to the procedure for nominal energy flight.
Or, ... perhaps to more precisely quantify the first safety margin, i.e. to step-wise determine in subsequent tests how soon you can safely permit unlocking.
Admittedly more speculatively all that ...
Last edited by janrein; 9th Nov 2014 at 09:34. Reason: Had not read well enough what I was answering to
@Janrein
I agree with that view, if the flight profile itself could lead to a situation where that reconfiguration would be essential for a safe return profile. The more speed and altitude is planned for the special test profile, the earlier you would like to know if the system is working. In the end this only ensures that the unlocking is working, but not the feathering itself.
But as unlocking removes also an important safety feature against premature activation of the system, there has to be a tradeoff between removing that safety feature ( and thus the danger of deployment of the feathering system at an unwanted phase of the flight) and risking to be not able to unlock it in a later part of the flight. As a pilot i would not bother about a system, I most probably would not need anyway (except for testing purposes) and I would acttivate it at the latest (safest) time.
Next thing is, there must be thoughts about the reliability of this pneumatic feathering system concerning possible failure modes (to the feathered position without activation), otherwise a guarded switch would do the trick to prevent the pilots of inadvertent activation of the system.
I really would like to understand the operation of the system, which parts of the actuators are pressurized by what action, wether the locking and actuating system uses the same accumulator, and what the fail safe default modes are in case of loss of pneumatic pressure. Still searching though for that information.
I agree with that view, if the flight profile itself could lead to a situation where that reconfiguration would be essential for a safe return profile. The more speed and altitude is planned for the special test profile, the earlier you would like to know if the system is working. In the end this only ensures that the unlocking is working, but not the feathering itself.
But as unlocking removes also an important safety feature against premature activation of the system, there has to be a tradeoff between removing that safety feature ( and thus the danger of deployment of the feathering system at an unwanted phase of the flight) and risking to be not able to unlock it in a later part of the flight. As a pilot i would not bother about a system, I most probably would not need anyway (except for testing purposes) and I would acttivate it at the latest (safest) time.
Next thing is, there must be thoughts about the reliability of this pneumatic feathering system concerning possible failure modes (to the feathered position without activation), otherwise a guarded switch would do the trick to prevent the pilots of inadvertent activation of the system.
I really would like to understand the operation of the system, which parts of the actuators are pressurized by what action, wether the locking and actuating system uses the same accumulator, and what the fail safe default modes are in case of loss of pneumatic pressure. Still searching though for that information.
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When to unlock the feathers
@RetiredF4 Nice find
@ janrein
I tried to start a list of the pros & cons of the unlock timing in post #5. Perhaps we can start to expand on this.
Obviously it needs something like:
- After any potential sources of [high?] aerodynamic [upward?] tail forces:
--- shock waves?
--- clean engine burn?
--- uneven engine burn?
--- flight-path induced?
- Exactly where the point-of-no-return (without feathers) occurs in the flight.
BTW what is the likely split of responsibilities in a two-person rocket-powered test crew?
- PF/PM seems inconsistent with the PNF apparently making an unrequested & unannounced change (inconsistent with the flight plan as far as we know it).
- If the PNF was handling the engine (and perhaps stability) the unlock seems more within his remit.
The fact that the unlocking seems to have been very early in some other Virgin test flights suggests that the high & M1.4 'rule'
was not strictly adhered to. The apparent need to deploy the feathers early in some flights [in response to instability?] suggests
that might have been unrealistic (at least for test flights examining the planes stability).
@ janrein
I tried to start a list of the pros & cons of the unlock timing in post #5. Perhaps we can start to expand on this.
Obviously it needs something like:
- After any potential sources of [high?] aerodynamic [upward?] tail forces:
--- shock waves?
--- clean engine burn?
--- uneven engine burn?
--- flight-path induced?
- Exactly where the point-of-no-return (without feathers) occurs in the flight.
BTW what is the likely split of responsibilities in a two-person rocket-powered test crew?
- PF/PM seems inconsistent with the PNF apparently making an unrequested & unannounced change (inconsistent with the flight plan as far as we know it).
- If the PNF was handling the engine (and perhaps stability) the unlock seems more within his remit.
The fact that the unlocking seems to have been very early in some other Virgin test flights suggests that the high & M1.4 'rule'
was not strictly adhered to. The apparent need to deploy the feathers early in some flights [in response to instability?] suggests
that might have been unrealistic (at least for test flights examining the planes stability).
@RetiredF4
PeterH upthread had found some details about the pneumatic system.
http://www.pprune.org/tech-log/55054...ml#post8726231
More questions remain.
- Pneumatic cilinders single or double working?
- If double working, what are the numbers for the reverse stroke?
- What redundancies in the pneumatic system?
- Any redundancies for the pneumatic system? (e.g. aerodynamic and reaction controls "working" the configuration)
- ...
I would expect numerous failure mode effect and criticality analyses (FMECAs) have been performed prior to any flight including test flights, the details of much of that we cannot expect to ever see.
OTOH itīs amazing how much information over time can be gleaned from te public domain, I am sure we will see more answers coming.
PeterH upthread had found some details about the pneumatic system.
http://www.pprune.org/tech-log/55054...ml#post8726231
More questions remain.
- Pneumatic cilinders single or double working?
- If double working, what are the numbers for the reverse stroke?
- What redundancies in the pneumatic system?
- Any redundancies for the pneumatic system? (e.g. aerodynamic and reaction controls "working" the configuration)
- ...
I would expect numerous failure mode effect and criticality analyses (FMECAs) have been performed prior to any flight including test flights, the details of much of that we cannot expect to ever see.
OTOH itīs amazing how much information over time can be gleaned from te public domain, I am sure we will see more answers coming.
Patent with better pictures
http://www.spacepatents.com/patented...pat7195207.pdf
A PiRep about a simulator expierience in SpaceShipOne
SpaceShipOne Pilot Report
The project SpaceShipOne
http://robustdesignconcepts.com/file...ipOnePaper.pdf
http://www.spacepatents.com/patented...pat7195207.pdf
A PiRep about a simulator expierience in SpaceShipOne
SpaceShipOne Pilot Report
The project SpaceShipOne
http://robustdesignconcepts.com/file...ipOnePaper.pdf
@PeterH
My hunches for the main drivers:
Before unlocking:
- Assure sufficient Mach number (M 1.4 plausible number) to stay clear of transsonic regimeīs agressive and complex dynamics;
- Other factors assumed of lesser or no relevance.
Margins to respect after unlocking:
- Pressure distributions in the supersonic and hypersonic regimes (no complex transients) within prescribed limits, as determined by a.o.:
- - Trimmable elevons within prescribed trim angles
- - Other aerodynamic control inputs within prescribed limits
- - No reaction control inputs or within prescribed limits
- Sense and magnitude of actuation forces from pneumatic feathering system within prescribed limits
- Thrust vector misalignments within prescribed limits (determined from design criteria in combination with static motor tests and powered flight test data recordings), or else early motor cut-off.
Margin to latest permittable unlocking, determined mainly by:
- Aerothermodynamics of unfeathered re-entry, driven mainly by vehicle energy (altitude, speed, weight, i.e. by duration of motor burn)
Other than that I can say very little about the re-entry.
The aerothermodynamics of the re-entry is probably the least known of all factors involved, even for the vehicle designers.
The same can be said for Apollo lunar return re-entries at the time and for the first Space Shuttle Orbiter re-entries, the actual margins were only established after the first flights and there have been narrow escapes.
In comparison SS2 has no or limited thermal protection and the design concept is to not need it, hence the feathers and the unlocking as soon as safely possible, thatīs my best guess.
My hunches for the main drivers:
Before unlocking:
- Assure sufficient Mach number (M 1.4 plausible number) to stay clear of transsonic regimeīs agressive and complex dynamics;
- Other factors assumed of lesser or no relevance.
Margins to respect after unlocking:
- Pressure distributions in the supersonic and hypersonic regimes (no complex transients) within prescribed limits, as determined by a.o.:
- - Trimmable elevons within prescribed trim angles
- - Other aerodynamic control inputs within prescribed limits
- - No reaction control inputs or within prescribed limits
- Sense and magnitude of actuation forces from pneumatic feathering system within prescribed limits
- Thrust vector misalignments within prescribed limits (determined from design criteria in combination with static motor tests and powered flight test data recordings), or else early motor cut-off.
Margin to latest permittable unlocking, determined mainly by:
- Aerothermodynamics of unfeathered re-entry, driven mainly by vehicle energy (altitude, speed, weight, i.e. by duration of motor burn)
Other than that I can say very little about the re-entry.
The aerothermodynamics of the re-entry is probably the least known of all factors involved, even for the vehicle designers.
The same can be said for Apollo lunar return re-entries at the time and for the first Space Shuttle Orbiter re-entries, the actual margins were only established after the first flights and there have been narrow escapes.
In comparison SS2 has no or limited thermal protection and the design concept is to not need it, hence the feathers and the unlocking as soon as safely possible, thatīs my best guess.
I found the patent and other document descriptions of the unlock system disturbing.
Pneumatic unlock actuator?
I can understand the actual feathering being pneumatic, but the unlock? With all the simplicity of the design, why not a physical cable to rotate the "hook"?
Hell, at apogee, I could even see a cable system to move the feathers. Zero aero loads and simplicity. Hardest thing would be moving the feathers once back at 60,000 feet or so.
My prediction is that there was a physical problem with the deployment actuators that allowed the feathers to move once they were unlocked. As I mentioned, our Viper c.p. moved a significant amount in the transonic regime, but then essentially stopped moving aft at M 1.4 Who knows, waiting until M 1.4 may have helped keep the feathers "streamlined".
The NTSB statement "of fact" that the feathers deployed needs to be clarified, ya think? Did they simply move on their own or did the pneumatic actuators move them?
Pneumatic unlock actuator?
I can understand the actual feathering being pneumatic, but the unlock? With all the simplicity of the design, why not a physical cable to rotate the "hook"?
Hell, at apogee, I could even see a cable system to move the feathers. Zero aero loads and simplicity. Hardest thing would be moving the feathers once back at 60,000 feet or so.
My prediction is that there was a physical problem with the deployment actuators that allowed the feathers to move once they were unlocked. As I mentioned, our Viper c.p. moved a significant amount in the transonic regime, but then essentially stopped moving aft at M 1.4 Who knows, waiting until M 1.4 may have helped keep the feathers "streamlined".
The NTSB statement "of fact" that the feathers deployed needs to be clarified, ya think? Did they simply move on their own or did the pneumatic actuators move them?