Virgin Galatic Spaceship Two down in the Mojave.
Join Date: Feb 2009
Location: Toronto, Canada
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
For high speed ejections we always have to look at the equivalent airspeed (EAS). That's what basically matters for wind blast. (Although I guess there are heating effects which might not relate directly to EAS - I don't know my high speed aerodynamics.)
So if SS2 were doing Mach 1.0 at say 50,000', the EAS would be only 250 kts. Rough but nothing like ejecting at Mach 1 at sea level, with an EAS of 660 kts!
(It can also be remarked about ejection stories is that it can be hard to tell what the actual speed was at the moment of ejection, which might sometimes be slower than at the moment the pilot last had a chance to look at the gauges.)
I'd just guess Siebold was lucky to not have sustained much injury during the breakup, and despite loss of consciousness from hypoxia, and happened to wake up sufficiently to unlatch the seat belt at some lower altitude and pull. One news article I saw suggested he was just in his seat with little structure around, but I'm unsure about how accurate the article might be.
So if SS2 were doing Mach 1.0 at say 50,000', the EAS would be only 250 kts. Rough but nothing like ejecting at Mach 1 at sea level, with an EAS of 660 kts!
(It can also be remarked about ejection stories is that it can be hard to tell what the actual speed was at the moment of ejection, which might sometimes be slower than at the moment the pilot last had a chance to look at the gauges.)
I'd just guess Siebold was lucky to not have sustained much injury during the breakup, and despite loss of consciousness from hypoxia, and happened to wake up sufficiently to unlatch the seat belt at some lower altitude and pull. One news article I saw suggested he was just in his seat with little structure around, but I'm unsure about how accurate the article might be.
@RichardC10
Maybe because of the following procedure drivers/considerations.
Imagine locks are discovered blocked or the locks operation system is discovered unserviceble. If this is discovered earlier in the burn, an engine shut-off, venting of remaining oxidiser to reduce weight and a reduced energy unfeathered re-entry may be feasible. You would not enter this abort mode unless you knew of the problem.
Imagine locks removed at e.g. Mach 1.4. Now imagine feathering pneumatics are discovered unserviceble much later, after nominal flight profile engine burn-out (2 minutes or so). Same problem! Or perhaps not quite? There may be redundant procedures for e.g. passive feathering (use RCS for correct attitude, then let it fold up "by itself" and keep it so using the trimmable elevators(?)
Fine, but you must unfeather again before hitting good old earth. Perhaps there are "tricks" for that as well. Or else bail out at lower speed and altitude?
In any case, with stuck locks that you´re not aware of, when you wait until full motor burn-out (for the nominal flight regime up to 380kft) there may be no alternatives left. I believe that may be a major driver for a not-too-late unlock action.
Admittedly speculative, but that´s what came up.
@Flash & peekay
I believe I did half rho v-squared on the numbers in SI units,
but will look it over, maybe a blind spot there ...
... why plan to withdraw the locks above some (low) speed limit?
Imagine locks are discovered blocked or the locks operation system is discovered unserviceble. If this is discovered earlier in the burn, an engine shut-off, venting of remaining oxidiser to reduce weight and a reduced energy unfeathered re-entry may be feasible. You would not enter this abort mode unless you knew of the problem.
Imagine locks removed at e.g. Mach 1.4. Now imagine feathering pneumatics are discovered unserviceble much later, after nominal flight profile engine burn-out (2 minutes or so). Same problem! Or perhaps not quite? There may be redundant procedures for e.g. passive feathering (use RCS for correct attitude, then let it fold up "by itself" and keep it so using the trimmable elevators(?)
Fine, but you must unfeather again before hitting good old earth. Perhaps there are "tricks" for that as well. Or else bail out at lower speed and altitude?
In any case, with stuck locks that you´re not aware of, when you wait until full motor burn-out (for the nominal flight regime up to 380kft) there may be no alternatives left. I believe that may be a major driver for a not-too-late unlock action.
Admittedly speculative, but that´s what came up.
@Flash & peekay
I believe I did half rho v-squared on the numbers in SI units,
but will look it over, maybe a blind spot there ...
Join Date: Feb 2009
Location: Toronto, Canada
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Video from 2nd powered flight is instructive about one normal sequence of events, as it looks back over the tail and includes cockpit audio that seems synchronized:
https://www.youtube.com/watch?v=0mCFxAsmnk0
In line with what janrein was talking about, the unlock is done early while the engine is burning, and they are accelerating and indeed still pitching up. The "Unlocking" call came right after the "5 seconds to go" callout, apparently about fuel remaining. About 15 sec into the burn.
Background: Another source [a space.com article] notes about the flight in the video:
https://www.youtube.com/watch?v=0mCFxAsmnk0
In line with what janrein was talking about, the unlock is done early while the engine is burning, and they are accelerating and indeed still pitching up. The "Unlocking" call came right after the "5 seconds to go" callout, apparently about fuel remaining. About 15 sec into the burn.
Background: Another source [a space.com article] notes about the flight in the video:
Sept. 5 2013: Second Powered Test Flight - SpaceShipTwo burned its engines for 20 seconds—four seconds longer than on the previous flight. The craft beat its previous record for altitude and speed, reaching a maximum altitude of 65,000 feet (21031 meters) and a top speed of Mach 1.6 or 1,217 miles per hour at sea level. The craft was piloted by Mark Stucky and copiloted by Clint Nichols.
Join Date: Mar 2014
Location: Arizona
Age: 77
Posts: 75
Likes: 0
Received 0 Likes
on
0 Posts
Uncommanded Feather
I keep seeing post here about "the crew unlocked the feathers...." I have gone back and watched again the NTSB briefing videos and reviewed the reports. Let's be clear about the facts:
1. "... the copilot, who was in right seat, moved the lock/unlock handle into unlock position."
2. In order for feathering to start, two things have to happen: someone has to unlock the feathering system, and someone has to activate the system with a different handle.
3. “This was what we would call an uncommanded feather, which means the feather occurred without the feather lever being moved into the feather position,” Hart said.
To me, the co-pilot removed the SAFETY LOCK so the feather handle could be moved later when needed. This might be a mechanical blocking handle that prevented the physical movement of the feathering handle. At this point we only know that some unknown failure caused the feathers to move. I see no reference to LOCKS on the feathers being removed, unlocked or actuated by the crew.
1. "... the copilot, who was in right seat, moved the lock/unlock handle into unlock position."
2. In order for feathering to start, two things have to happen: someone has to unlock the feathering system, and someone has to activate the system with a different handle.
3. “This was what we would call an uncommanded feather, which means the feather occurred without the feather lever being moved into the feather position,” Hart said.
To me, the co-pilot removed the SAFETY LOCK so the feather handle could be moved later when needed. This might be a mechanical blocking handle that prevented the physical movement of the feathering handle. At this point we only know that some unknown failure caused the feathers to move. I see no reference to LOCKS on the feathers being removed, unlocked or actuated by the crew.
Join Date: Jun 2008
Location: Cambridge UK
Posts: 192
Likes: 0
Received 0 Likes
on
0 Posts
Uncommanded Feather
@Niner Lima Charlie
I agree that there is some lack of clarity, and IMHO most [all?] press statements could be interpreted as referring:
- either to a physical lock on the feather mechanism/structure itself
- or to a safety lock on the feather handle.
However the current story is that telemetry indicated that there was an uncommanded feather deployment. Which I can only take to mean
that the feather activation handle wasn't involved in the deployment.
So, is it a physical lock or a safety lock? In the absence of known documentation on the question, lets think about the press releases.
- If it is a physical lock on the mechanism its state could well be important (e.g. in failing to prevent aerodynamic forces triggering deployment).
- If it is a safety lock on the handle its status is unimportant, as the event it might have prevented (movement of the activation handle) didn't happen.
So are the press releases about unlocking the feathers stating potentially important facts, or raising unimportant issues? I feel justified in believing
that a physical lock on the mechanism is involved, but would love to see the matter clarified in official documentation.
I agree that there is some lack of clarity, and IMHO most [all?] press statements could be interpreted as referring:
- either to a physical lock on the feather mechanism/structure itself
- or to a safety lock on the feather handle.
However the current story is that telemetry indicated that there was an uncommanded feather deployment. Which I can only take to mean
that the feather activation handle wasn't involved in the deployment.
So, is it a physical lock or a safety lock? In the absence of known documentation on the question, lets think about the press releases.
- If it is a physical lock on the mechanism its state could well be important (e.g. in failing to prevent aerodynamic forces triggering deployment).
- If it is a safety lock on the handle its status is unimportant, as the event it might have prevented (movement of the activation handle) didn't happen.
So are the press releases about unlocking the feathers stating potentially important facts, or raising unimportant issues? I feel justified in believing
that a physical lock on the mechanism is involved, but would love to see the matter clarified in official documentation.
Join Date: May 2012
Location: Australia
Posts: 131
Likes: 0
Received 0 Likes
on
0 Posts
Clarifying the "subsequent aerodynamic forces then deployed the feathering mechanism"
Originally Posted by http://www.virgingalactic.com/statement-from-virgin-galactic/
The NTSB also evaluated the vehicle’s feathering mechanism, which is the unique technology that turns the wing booms into position for re-entry. The NTSB indicated that the lock/unlock lever was pulled prematurely based on recorded speed at the time, and they have suggested that subsequent aerodynamic forces then deployed the feathering mechanism, which resulted in the in-flight separation of the wings and vehicle. At this time, the NTSB investigation is still ongoing and no cause has yet been determined – these are purely facts based on initial findings. We are all determined to understand the cause of the accident and to learn all we can.
... is 6.4kPa, and I agree a 40% reduction.
Thanks.
Previous commenters were right, I used pattern´s reported graphs but had not read them very accurately, especially density at 70kft is lower than what I mentioned.
Join Date: Feb 2009
Location: Toronto, Canada
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
I found the following in a forum without any attribution to the original source - so it isn't the best evidence. Still, on the face of it, it confirms that it is a physical lock. It also confirms that the tail is not held in place by the pneumatic system pressures.
(Now in the 2nd powered flight video, the unlock command came before the engine burnt out -- but that was for a lower profile flight where burnout and the apex were closer together. The quote appears to refer to the planned full altitude flights.)
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.
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.
Join Date: Mar 2009
Location: Bognor Regis
Age: 73
Posts: 26
Likes: 0
Received 0 Likes
on
0 Posts
The quote from Mike Moses is in a Reuters article published 6th Nov 9.04am UTC entitled 'New spaceship restoring hope after Virgin Galactic crash' available on Breaking News, Business News, Financial and Investing News & More | Reuters.co.uk
Join Date: Jun 2008
Location: Cambridge UK
Posts: 192
Likes: 0
Received 0 Likes
on
0 Posts
Physical lock
@pchapman & @Redredrobin Nice find, thanks. That URL didn't work for me, but this one did.
New spaceship restoring hope after Virgin Galactic crash | Reuters
New spaceship restoring hope after Virgin Galactic crash | Reuters
Join Date: Feb 2008
Location: UK
Posts: 66
Likes: 0
Received 0 Likes
on
0 Posts
I thought Virgin Galactic were not going to be commenting on the causes of accident.
Anyway, the quote is pretty clear. Move the unlock handle in a regime where the net aerodynamic forces work in the pro-feathering direction and the aircraft will be lost. The lack of interlocks made sense for SpaceShipOne but looks terrible in a vehicle designed for passengers.
Anyway, the quote is pretty clear. Move the unlock handle in a regime where the net aerodynamic forces work in the pro-feathering direction and the aircraft will be lost. The lack of interlocks made sense for SpaceShipOne but looks terrible in a vehicle designed for passengers.
Join Date: Jun 2008
Location: Ventura, California
Age: 65
Posts: 262
Likes: 0
Received 0 Likes
on
0 Posts
At the lower left corner of this diagram it says "feather actuation and lock pneumatically operated":
Size comparion - Virgin Mother Ship's SpaceShip Two versus White Knight's SpaceShip One
Size comparion - Virgin Mother Ship's SpaceShip Two versus White Knight's SpaceShip One
Join Date: Oct 2005
Location: Classified
Posts: 314
Likes: 0
Received 0 Likes
on
0 Posts
Actually it confirms the tail is held into place by another mechanism than the locks. He talks about being able to command feather i.e. there is a feather actuator.
Join Date: Nov 2010
Location: Nova Scotia
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Disaster at the speed of sound: the tragedy of SpaceShipTwo’s final flight
theguardian
Disaster at the speed of sound: the tragedy of SpaceShipTwo?s final flight | Science | The Guardian
The article explains how the feathering system is supposed to work and present evidences that pilot error caused the accident.
Disaster at the speed of sound: the tragedy of SpaceShipTwo?s final flight | Science | The Guardian
The article explains how the feathering system is supposed to work and present evidences that pilot error caused the accident.
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes
on
0 Posts
Now, that's not quite accurate.
To be fair, as far as mainstream media outlets go, The Grauniad is fairly trustworthy - but the only time the term "pilot error" comes up is in one quote (emphasis mine):
If you read between the lines, what this actually means is that neither the NTSB nor VG are currently commenting on the causes of the accident, so the journalist has called up a former VG bigwig for a comment in lieu of anything official.
To be fair, as far as mainstream media outlets go, The Grauniad is fairly trustworthy - but the only time the term "pilot error" comes up is in one quote (emphasis mine):
Originally Posted by The Grauniad
“There’s nothing that tells me that this was anything other than pilot error, sadly,” said Will Whitehorn, the former president of Virgin Galactic, speaking from the UK.