Virgin Galatic Spaceship Two down in the Mojave.

[TIMTS]

How fast would SS2 be accelerating at this point? I mean, would the time between M1.0 and M1.4 be just a few seconds, 30 seconds, or longer?

[janrein]

Mach versus time

Timings and statements from the various videos:

Powered flight 1, rubber fuel, 17 seconds
Powered flight 3, rubber fuel, 20 seconds, Mach 1.4
Powered flight 4, plastic fuel, 9 seconds to break-up at around Mach 1

Ultimate operational goal Mach 3.4 (?) ...

[The Old Fat One]

The FT title is...

Space tourism is a high risk publicity strategy

and you could see it easily if you head down any of the multiple links to the FT coverage, including the one posted above.

It is of interest because it examines the motivation for the enterprise. As aviators of one form or another here, we might be prone to excepting that this project is all about "what it says on the tin"...pushing forward human boundaries, advancing technology etc etc etc

The article reviews yer man Branson's commercial savvy where large scale PR is concerned as well as his appetite for self-promotion.

Nothing wrong with any of that IMO...I'm just as much a capitalist as he is. What he does with his billions is his own affair, just so long as not one penny of tax payers money flows into his coffers.

As for the people involved (whether employees, or hugely over-optimistic potential passengers) if they did not know the risks before they do now.

[Mozella]

Enlighten me as to why the feathering of the tail would be more dangerous at mach 1 that at 1.4 ?

I think the information is either incomplete or someone has gathered a fact and reported it without understanding what it means.

My understanding is that the wing/tail feather mode is normally used only during re-entry and perhaps M 1.4 is the Mach number at which is is normally deployed. I don't really know, but that factoid might be inadvertently or incorrectly blended into the current news. Anyway, I imagine going into feather mode would most likely be at very high altitude with low dynamic pressure. In other words, the true speed, measure in either mach number or true airspeed, would be rather high but because the air is so "thin" the airframe wouldn't have a lot of load on it; i.e. indicated airspeed (dynamic pressure) would be low............ very low.

Contrast that with going into feather at 50,000 feet and Mach 1.0; i.e. shortly after release. Working from memory (you should look it up to get the real number) the indicated airspeed would be about 250 knots and that, I would imagine, is too fast to feather the wing/tail system. I have no idea how high they are when they go into "normal feather mode" during re-entry, but if it's up around 150000 feet, the indicated airspeed would be way down, perhaps 50 knots or so at M 1.4. Again, look up the real figures. My brain isn't what it used to be and high mach number flying as well as my university aerodynamics training are both now only a distant semi-memory.

Of course, depending on who you talk to about flying around on the fringes of "Space", the measurement of the speed of sound and the concept of indicated airspeed begin to unravel a little bit, but you get the idea. That is to say, M 1.4 at high altitudes might be perfectly safe for a major configuration change while doing so at M 1.0 at low altitudes would be a disaster. It has a great deal to do with the dynamic pressure (indicated airspeed to most folks).

I think we're victims of bad reporting and/or lack of aerodynamic understanding and/or ignorance of just what the flight profile is normally like.

[John Farley]

Well said Mozella

So far as the future of this programme is concerned I would comment that given the NTSB statement it seems likely that the breakup was caused by a simple mechanical/electrical system failure. That is a very much simpler thing to sort compared to a failure in the rocket system which the flight set out to test.

In this life it is so often what you least expect that gets you.

[what next]

I think we're victims of bad reporting and/or lack of aerodynamic understanding and/or ignorance of just what the flight profile is normally like.

Exactly. And I don't believe for a second that the switch selection the may have lead to the feathering of the tailplane was done by mistake. A little way up someone posted the credentials of the crew. They were highly qualified and had over half a year of preparation for this flight. These pilots would not arm (or activate) a system at Mach 1 that must not be armed before Mach 1.4 unless they had a reason for it. Engine problems, control problems, whatever. But "by mistake"? Certainly not.

[NigelOnDraft]

that must not be armed before Mach 1.4

I do not believe that was what the NTSB said... but more along the lines of "would be armed at M1.4" i.e. that was what the SOP / Checklist / Test Card etc. said.

One needs to understand the rationale for the "locking" lever.. what "hazard" was it trying to mitigate? What eventually might have happened? Or was the greater hazard considered that of "feathering" whilst under WK2? Or might one need the feathering quickly in an emergency hence it was armed well in advance of when it would normally be needed.

As others have said, under 60Klb of rocket thrust, the acceleration from M1 to M1.4 I doubt would be many seconds, and guess feathering equally catastrophic at either on the ascent phase?

The NTSB updates / docket system will be interesting...

[Dogma]

I don't get the sensitivity of the question over the Pilots "Piloting Qualification". It's pretty straight forward did they fly complex fast jets solo, were they qualified Test Pilots? In truth, the advances we enjoy in Commercial aviation today were hard earned by very specialist flight test Test Pilots.

It relevant to ask - did they go to Empire or USAF TPS for example. If not, why not?

[TIMTS]

Anyone know what speed this test was meant to reach?
Since it was the first live test of a new propellant type, maybe M1.4 was the final speed sought for this flight, as opposed to VNE for the feathering mechanism? Reporters have been known to get numbers mixed up...

[deptrai]

In truth, the advances we enjoy in Commercial aviation today were hard earned by very specialist flight test Test Pilots.

you're probably referring to test pilots like Brian Binnie here: Scaled Composites: SpaceShipOne

if he's a qualified test pilot, in your opinion, I suggest you ask him if he thinks his former colleagues at scaled are qualified or not. He worked alongside them for many years, he should know.

[peekay4]

I think the information is either incomplete or someone has gathered a fact and reported it without understanding what it means.

My understanding is that the wing/tail feather mode is normally used only during re-entry and perhaps M 1.4 is the Mach number at which is is normally deployed.

Dynamic pressure is greatest at transonic flight (Max Q), then reduces as the aircraft goes supersonic and accelerates past Mach 1.2.

So for safety, the feathering mechanism must be locked when flying through this region. Otherwise, the aerodynamic forces can twist SS2 into feather mode.

Which is what apparently happened.

[MG23]

Originally Posted by NigelOnDraft

As others have said, under 60Klb of rocket thrust, the acceleration from M1 to M1.4 I doubt would be many seconds, and guess feathering equally catastrophic at either on the ascent phase?

Presumably, you want to verify you can unlock it before you go flying off into space, so you can cut the engine and abort the flight if you can't?

Though that may not make sense in this case, if it was just a short engine test.

[PrivtPilotRadarTech]

Doesn't seem like there would ever be a case when you'd want to feather while the engine was producing any appreciable amount of thrust.

[thf]

Originally Posted by what next

And I don't believe for a second that the switch selection the may have lead to the feathering of the tailplane was done by mistake.

Me neither. Two questions:

• Is unlocking the feather mechanism something the captain has to order verbally and the co-pilot to acknowledge before unlocking?
• If the answer is yes: did the captain order it?

[thcrozier]

Feather Lock

Is the "lock" an electronic switch or a mechanical cover?

[WingNut60]

So you can select reverse while in top gear?

Sorry crew, but why would you be able to select (unlock) an unsafe flight mode at any time during the flight envelope.


If the craft is so sophisticated, and feathering intrinsically dangerous (as identified by a thorough design risk assessment) I'd have thought that "
Feather Unlock" might be handled by something a bit more " sophisticated" than a handle.


Giving the crew the ability to UNLOCK in an emergency and outside of the normal envelope is, surely, different from giving them the ability to UNLOCK by mistake and / or inadvertently.

[gums]

Beg your pardon, Wingnut

The U.S. N. jets with wing fold use a MECHANICAL system to enable the hydraulic wing fold feature. My A-7 had a cable on the cover of the electric switch. Raising the handle pulled a cable that removed a mechanical lock on the wing fold mechanism for each wing.

So we had a two step safety system. You couldn't get to the switch unless you raised the cover that mechanically removed something to enable the hydraulics to move the large metal rod connecting the outer wing segment to the inner. And then another system cranked the outer segment up or lowered it.

As with others, I question early removal of the feather lock. However, I understand an earlier mission had a bad pitch moment excursion and used the feather system to stay under control. If subsonic at a low mach, seems O.K. At transonic conditions, all bets are off.

[WingNut60]

Thanks GUMS. Got that and agree
But what I was chasing was an interlock to prevent inadvertent selection at some unsafe phase of flight.


Mechanical or electrical doesn't matter provided the selection is possible either a) within design parameters or b) with an explicit procedure that knowingly overrides the protection features


Reports so far indicate that feather unlock was selected outside of design parameters.
Looks like it might have been an oops moment. And sophisticated systems just should not allow oops moments.

[west lakes]

However, I understand an earlier mission had a bad pitch moment excursion and used the feather system to stay under control.

So did the knowledge of this prompt the removal of the lock in case of another instability?
i.e. a situation that arose during testing has shown up a possible failure in the design parameters.
Isn't that what test flying is partly about?

[thcrozier]

September 29, 2011

"Upon release, the spaceship experienced a downward pitch rate that caused a stall of the tails. The crew followed procedure, selecting the feather mode to revert to a benign condition. The crew then de-feathered and had a nominal return to base," according to an updated flight log posted by Scaled Composites, builder of the WhiteKnightTwo/SpaceShipTwo launch system."

Space.com

http://www.space.com/13297-virgin-ga...ht-glitch.html