As I mentioned on t’other thread.
Speculating is bad, but I find this kind of thing morbidly fascinating. I don’t understand why there weren’t multiple locks on the logic for the feathering to prevent inadvertent actuation.
Speculating is not necessarily bad. It lets you hone your reasoning skills, and provides delayed feedback about if you inferred/guessed correctly or not. And it is fun.
Likely some engineer thought that the ones present were good enough, test pilots did not object (or did? we may get told later if there is a dissenter within the ranks willing to talk), and there were no problems before with many flights before.
Low-probability-deemed hazards usually get addressed only after a problem actually appears, especially so with trailblazing prototypes.
Every design more complex than a yo-yo has a number of obscure weak-ish spots that can go wrong; even the yo-yo has a string that can give way. Budgets are limited, time as well, and sometimes people die. But people also die falling from stairs so that’s not an absolute condemnation either; mistakes happen.
If a lock fails and doesn’t allow the feather process to occur at the right time, they will crash. Therefore, adding more locks is also adding more points of failure.
Of course, if the prelim findings hold out to be true, I would imagine they will need to implement more checks into the process before the feather can be unlocked. It does seem odd to me that the feather can be unlocked during rocket burn. The article states the unlock should not occur before mach 1.4. So is that fast enough that the unlocked feather will remain in place? Or is that a speed at which they know they are outside of the atmosphere and the feather is ineffective at that point? Also… is the feather powered, or is it a spring loaded type of device??
I want to know so much more! For example, I didn’t know they carried parachutes and could escape out of the ship. With everything going on in that disintegrating ship, I’m amazed the pilot could even climb out of there.
Do any of you aviation fans care to share some links to the more technical discussions happening out there?
My guess is that they were ejected. No climbing feasible out from something wildly spinning and subjected to several g.
Presumably they have a FMECA somewhere. They must have run the safety numbers.
I haven’t looked, but PPRuNe and airliners.net might be good places to start. I don’t know equivalent space forums.
http://www.airliners.net/aviation-forums/military/read.main/163074/
It’s always a massive balancing act of a seesaw-setup with (n+1) axis’ to consider. Press down on one side and another might rocket out of the construct and hit something that’s not even connected.
Observers point out that the feather deployment could have been secondary to engine vibration or some change to the vehicle’s aerodynamics:
http://www.parabolicarc.com/2014/11/02/ntsb-spaceshiptwo-feather-mechanism-deployed-prematurely/
It’s fast enough that you’re out of the transonic range (where there’s a mix of subsonic and supersonic airflow), so the airflow is less turbulent and there’s actually less drag. But still early enough in the flight that if the feather doesn’t unlock they can abort. From what I’ve been reading, during the burn they’re accelerating fast enough that the difference between just over Mach 1.0 and Mach 1.4 is at most 10 seconds. Not a very long time.
But if it turns out that the feather locking mechanism wasn’t designed to withstand the stress of transonic flight, as opposed to unlock at Mach 1.4 just being the SOP, then the question becomes, why didn’t the test pilots know this?
[quote=“shaddack, post:5, topic:44756”]
My guess is that they were ejected
[/quote]No, one article said that the vehicle didn’t have ejector seats. The pilot would have had to get out of the vehicle through a hatch and deploy his parachute on a single lung full of air (this being at 45000 feet altitude) so it is no surprise that only one made it out. If one guy had tried to help the other they would both be dead.
Ejection seats are way too heavy for this kind of craft. The actual system that I remember seeing is removing the nose (presumably with exploding bolts), leaving unobstructed egress where the flight crew can tumble out even if half conscious. As for the celebrityes in the peanut gallery behind them, well, that’s what memorial reels are for at the Oscars.
OK, but I’d just like to point out that when we say someone was ejected from an automobile, such as during a roll-over accident, that doesn’t mean they punched out through the roof while strapped into a rocket-powered seat … Ejected can also mean involuntarily expelled.
Then there’s also the passive/active verb tense (or how the grammar nuts call it). “ejected from” implies voluntary action (and implies an ejection seat), “was ejected from” implies third-party action, whether it was automatically activated ejection seat or another mechanism.
In this case I expected the thing to have ejection seats. The trick with separating nose is a nice compromise of weight saving vs giving at least some chance to the pilots.
So what you’re saying is they’re gonna charge even more for that extra carryon bag. DAMN YOU AND YOUR FEES!
Just a note - ejection seats aren’t fool proof. Especially at those heights and speeds. IIRC several SR-71/A-12 pilots were lost even when they ejected.
According to @smut_clyde’s link above, there are two levers that require actuation in order to fully unlock and deploy the booms, something like Unlock (lever one) and deploy (lever two). Their procedure might be to set the system to unlock (lever one) and then actuate lever two at some future point determined by any number of circumstances (altitude, speed, etc.). However, the article states that the booms deployed with only the first lever actuated–this may point to some flaw in the locking system itself, but it’s clearly way too early to say.
It’s often easier to recognize hazards in retrospect.
Consider the AS-204/Apollo 1 fire. Nasa had decided on a pure oxygen atmosphere to minimize the risks of the bends. Nasa somehow failed to list pure oxygen at one atmosphere as a hazardous condition requiring any special precautions, beyond limiting ignition sources. Nasa was concerned that the outward-opening hatches in Mercury and Gemini might blow open in-flight, killing the crew, so a new inward-opening hatch was introduced for Apollo, preventing escape, and another outward-opening hatch had to be introduced for later Apollo.
Yes, this is very early speculation. But I meant, why they didn’t know that it was dangerous to unlock it early.
My assumption is that with the removal of the lock the aerodynamic forces were just too great, and that this will come out later in the investigation. That at some point there needed to be a conversation where the engineers said to the test pilots, “Now look, the timing on this is critical. Too late, and you might get stuck up there in a free fall with no brake. Too soon, and there’s a chance you could deploy the feather unintentionally. You need to watch your speed very carefully and time it just right.” But that, because it was a large and complex project, that conversation never happened.
It’s just a guess. I could easily be wrong.
Indeed. And/or why wasn’t there software or mechanical systems in place to ensure that it wasn’t unlocked too early. Of course, the USAF KC-135 will allow stick jockeys to lower the flaps at any speed despite a warning buzzer* that sounds if the airspeed is too high. But that’s 50s and 60s tech.
*Supplemented by the bitchings of the a/c crew chief for all the required inspections after overspeeding the flaps.
Which would be a crying shame given that it’s a system way up on the “critically important” list. It also makes me curious as to how it was designed–is the first lever intended only to lock/unlock the movement of the second lever, or does it actuate some mechanical lock on the booms themselves? I’m also curious how much of that spacecraft is software locked/actuated as opposed to being purely mechanical. At the very least I suspect Virgin and the NTSB have a great deal of solid information (whether video, instrument, or airframe data) available to their inspection teams to help troubleshoot the issue.
