SpaceShip2 Crash 1 Fatality 1 Survivor

[Race5]

Re: SpaceShip2 Crash 1 Fatality 1 Survivor

I'm confused, which is nothing new. I've been reading the reports about the accident. my understanding is, they were at Mach 1.2 when the feathering device was unlocked, not activated. However for some unknown reason the aft portion of the aircraft started to move into the feather positioning, evidently leading to the structural failure. I've read that at Mach 1.4 this was suppose to be done as part of the flight test. So my question is.......if it did happen at Mach 1.2 by accident, and was suppose to be done at mach 1.4 where I assume greater forces would be encounter..........why did it fail at Mach 1.2?
Also, I thought the feather device was suppose to be deployed in space with minimal aerodynamic loads would be encounter due to lack of atmosphere. I've never figured out how the feathering system effects the reentry and what position the aircraft is in. I know if it doesn't work, the aircraft will burn up. I'm glad to hear the surviving pilot is out of the hospital and doing better.
Brian

You have to remember they are flying an almost vertical trajectory under power. By the time they reach Mach 1.4 they are so high up that aerodynamic pressures are much, much lower than when they are lower and slower. At that altitude, true airspeed is Mach 1.4, while indicated airspeed ( as it would be read by a normal pressure system) is almost zero. The feathering feature serves two purposes. One is to help slow the craft, the other is to orient it in the proper re entry angle while providing stability.

[GeoffS]

Re: SpaceShip2 Crash 1 Fatality 1 Survivor

...mach 1.4 where I assume greater forces would be encounter...

Here's a pretty accurate and readable explanation of the changing aerodynamic forces: http://en.wikipedia.org/wiki/Max_Q

Basically, the pressure (force) on the craft depends on the product of air-density and velocity squared.
For a craft climbing out of the atmosphere, the density is steadily dropping as the speed is increasing, so the forces increase to a maximum (i.e. "Max-Q") at some particular altitude & speed combination, and then decrease.

[supercub]

Re: SpaceShip2 Crash 1 Fatality 1 Survivor

Ok, thanks for the feedback, and I'm somewhat familiar with Q max. However, and I could be mistaken, but it appears that they weren't going vertical....they were more in a horizontal flight path, so P would be increasing as V increased due to constant atmosphere pressure.
Brian