Virgin Galatic Spaceship Two down in the Mojave.

[Peter H]

Aerodynamic forces and feather booms

janrein: Excellent post.
Can I suggest that an uneven rocket burn might also increase aerodynamic forces.
Regards, Peter

[Flash2001]

Janrein

Please don't mix units, you're bringing yourself down to the level of the EPA!

After an excellent landing etc...

[peekay4]

Would yield for dynamic pressure:
q = 11 kPa at 45kft and M1
q = 8.5 kPa at 70kft and M 1.4

The math is a bit off.

Using solely the above parameters:

q = 10.2 kPa at 45kft and M1
q = 6.2 kPa at 70kft and M 1.4

So roughly 40% less.

[SKS777FLYER]

Double post

[Radix]

I put my money on either:
- the pneumatic (!) system failed to pre-pressurize causing the tail booms to move without much effort
- or the aerodynamic forces at the transsonic region were so different from what they thought them to be that the design couldn't cope unless being fully locked. E.g. good old sound barrier strikes again.

Sounds the most plausible from these 10 pages of expert opinion on PPruNe.

The other pilot will be able to tell why they moved the unlock lever at a point different to the brief and whether this was ever discussed with the engineering team.

edited

[RichardC10]

@janrein
Agreed that transonic loads could be highly non-linear. However, the locks are out during the period the speed is reducing through the transonic regime in the test flights, though admittedly at a somewhat higher altitude. If there was marginality in holding the feathers in the correct position at any (high) speed why plan to withdraw the locks above some (low) speed limit?

[TURIN]

I put my money on either:
- the hydraulic system failed to pre-pressurize causing the tail booms to move without much effort

Then you've lost your bet.

My understanding is the booms are pneumatically operated.

[mostlylurking]

I am interested in why the booms feathered prematurely, but I expect there was a simple cause and the solution will also be relatively simple.

More interesting is why the craft broke up. I think that is also relatively simple - the booms deployed while the motor was running. This would cause the centre of resistance to be way above the thrust line. i.e. the forces would cause the craft to tumble violently. At mach 1, no craft could stay together.

Looks like an interlock is needed, or that there was an interlock but failed.

[MichaelJP59]

Anyone know, was this the only prototype? is there another one under construction by Scaled?

I know the order was for more than one, but it must take a lot of time, I get the impression that the build team is not very big?

[skadi]

The second one, VSS Voyager, is under construction:

VSS Voyager - Wikipedia, the free encyclopedia

[peekay4]

The second one is 65% complete, should be ready for ground and flight testing in 2015.

[FlyingCroc]

What I don't understand. How did the pilot survive this crash. He is at 50'000 ft at Mach 1 and the airplane breaks apart. I don't think there are ejection seats? How is this possible?

Did any military pilot ever eject at Mach 1?

[Heathrow Harry]

actually it didn't totally break up - I expect it came down spinning like a
sycamore leaf with a fair bit of "wing" attached - at least on one side

And I guess a crew compartment built to go into low space at 2500 mph is fairly robust

[robdean]

Supersonic ejection has been survived, but it is somewhat high-risk and non-enjoyable. Notable for facial blast injuries (colossal hemorrhaging) and for knees and elbows bending in the opposite direction to that usually preferred. The Russians came up with a few interesting innovations to try to improve survivability.

In this case there may have been chance benefits of 'ejection-by-disintegration' - Siebold may have been subsonic before being 'ejected' into the windblast and possibly this occurred with his back to the direction of travel.

I very much doubt Siebold 'did' much about escaping SS2. More likely 'WTF?' followed by 'I appear not to be dead, to have mislaid my vehicle, but happily still to be in possession of a parachute'. The very nature of intense chaotic events is that all manner of outcomes are possible, even those which are genuinely or apparently very improbable. In fact, 'WTF?' may have come immediately after rather than before the detailed change in situational awareness.

[A_Van]

To FlyingCroc


First ever ejection at M > 1:


26 February 1955 - This Day in Aviation

[AreOut]

apparently if you are lucky enough you can survive even 3 Mach ejection

Lockheed SR-71A (61-7952) - At 78,000 feet without an Airplane

[WorkingSection]

Agreed about the maths...

peekay4 agreed:
At 45000ft, the local standard atmosphere temp is 216.5K, speed of sound=295.04m/s, density is 0.2438kg/m^3 so stagnation pressure is 10.6kPa.

At 70000ft, we have T=217.99, a=295.95m/s, TAS=412.9m/s so stagnation pressure is 6.4kPa, and I agree a 40% reduction.

[RetiredF4]

What I don't understand. How did the pilot survive this crash. He is at 50'000 ft at Mach 1 and the airplane breaks apart. I don't think there are ejection seats? How is this possible?

Survivability of a high speed ejection depends on multiple factors. But consider air is denser at lower altitude than at 50.000', therefore the forces at 50.000 feet and Mach1 are less than the same speed at 10.000'. So the speed would not have been a problem here, but the uncontrolled sequence of separation from the aircraft and environmental factors like oxygen and temperature. A crew of our wing had an ejection below 300' and going 540 knots IAS, they both had their helmets torn off their heads and they suffered bruises like boxing with M.Ali for an hour from the air blast. The frontseater had both arms dislodged from his schoulders with multiple fractures. The body position of the WSO was drastically better, as he was the guy who initiated ejection and he therefore was prepared for it and had no fractures at all.

[mickjoebill]

Windchill at Mach 1 at 50,000ft?

[RF4]

Similarities to Blackbird Crash 1966

Actually there are a number of similarities between the survival of the SS2 pilot and the survival of Bill Weaver after the in-flight break-up of the SR-71 in 1966.
Both broke up at high speed at high altitude, with the pilots being torn/tossed out of the flight deck - Siebold torn from his seat and Weaver torn from his ejection seat.
Pressure suits have not changed much from those days, and both owe their lives to an intact pressure suit, parachute and supplementary oxygen. I am presuming these things for the case with SS2 - if I am wrong please correct me.
It will be interesting some day to hear Siebold's experiences after his exit from SS2 his free-fall, chute deployment and rescue - a harrowing experience with a decent ending.