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fredymac

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Longer duration video with better shots of landing. With Allen gone I wonder if the money to fully prove out the flight envelope will be provided. Maybe the Missile Defense Agency could use the aircraft to carry their boost phase laser. Not sure how high up this thing can fly or if MDA could settle for a lower altitude for a demonstration test.

 
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sferrin

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That looked like an exciting landing. :eek:
 

kitnut617

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sferrin said:
That looked like an exciting landing. :eek:
Watching the first flight of the XP-82 after it's restoration a few weeks ago, the pilot did the same thing when it landed. Admittedly, doing it in something this big certainly would get the pucker factor up I think.
 

Byeman

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fredymac said:
Longer duration video with better shots of landing. With Allen gone I wonder if the money to fully prove out the flight envelope will be provided. Maybe the Missile Defense Agency could use the aircraft to carry their boost phase laser. A
There is no laser. Also, it is a poor platform for such a task.
 

fredymac

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Byeman said:
There is no laser. Also, it is a poor platform for such a task.

They are developing one. How do you know what the turbulence field is? Did you run the numbers? What shape did you use for the pod structure? Can you show me your Schlieren graphs? You provoke this kind of response if you don't provide any details for the brush off replies you give.
 

Jemiba

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Please, back to a reasonable tone !
 

steelpillow

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I do agree that arbitrary payloads in arbitrary flight regimes could lead to unwelcome oscillatory modes, via interaction of arbitrarily distributed mass and aerodynamic characteristics. Even with the fuselages roc steady (sic), the wing is so wide and thin that its centreline could oscillate significantly. Vertical displacement and pitching come immediately to mind. Due to the structural size, these oscillations would be of unusually low frequency, which means unusually high absolute displacement for a given energy and therefore also higher structural stresses.

Each such flight configuration would need to be de-risked through modelling, backed byl in-flight characterization of the airframe characteristics.

But I do not agree that a degree in rocket science is necessary before such a risk may be taken seriously on a public forum. Rather, the burden lies on the proposer to "run the numbers, design the shape of the pod structure and produce [wind tunnel data]" in order to demonstrate that the regime is safe and, in the case of a precision-aimed laser, adequately stable. Such risks are commonplace enough. Many UK residents will remember the Millennium Bridge fiasco, when this supposedly stable bridge opened and an unexpected vibration mode developed when under operational loads. Nor in an aerospace context do I need to dwell on the safety regime under which the 737 MAX stall-management system was deployed. The "no rocket scientist has proved it unsafe" argument just does not wash.
Of course, low-amplitude, low-frequency unwanted oscillatory modes may be corrected for using software-controlled electro-mechanical systems. But that will not help if there is insufficient mechanical damping to prevent destructive divergence from building up under some unforeseen flight condition.

On the other hand, if all that can be achieved then a central payload will be better insulated from engine-induced vibration than say the US experimental laser installations in a 747 were. But I remain unconvinced that the Roc would be a laser scientist's first choice.
 

fredymac

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All fine and well but “arbitrary”? This vehicle was designed from the outset to carry a large, heavy cylindrical mass under the center wing. A presumption of malfeasance or incompetence is necessary to imply the principal design function will fail. It will undoubtedly require fine tuning and validation but again, how do you presume aerodynamic, stress, and turbulence modelling was not rigorously conducted by the engineering staff during the design process? Indeed, g-loads and vibration levels would have to be assessed because customers would require that information for their payloads.

I am not too familiar with the Millennium Bridge. I thought it was a curved pedestrian bridge and the design staff forgot about the pedestrians (shifting masses on balance and load). I didn’t follow that story but I assume a finding of design failure would have resulted. It is always possible for a company culture to go dysfunctional and allow a serious fault to get by. In this country that would be followed by all kinds of lawsuits and possible bankruptcy.
 

steelpillow

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I think you are taking the suggestion that something might fail as a claim that it will.
In the case of the Millennium Bridge, the specification of the structural analysis software was prescribed by national engineering safety standards. However the standards did not recognise the particular failure mode that occurred and so the software did not check for it. That the mode was induced by pedestrians instinctively adjusting their step to the oscillations was pure coincidence from the structural point of view. The safety standards have since been updated to include the particular oscillatory mode and I understand this has happened globally.
Similarly, nobody is presuming that Stratolaunch have not done their job properly. But there remain those mathematically arbitrary conditions - the known unknowns - that one cannot model in advance. And the aerodynamic-inertial coupling of a large, heavy pod on a slim, wide wing is a biggie.
 

fredymac

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I am no expert on the state of Finite Element Analysis and Computational Fluid Dynamics software so I can't assess how comprehensively it can cover all possible perturbations. On the other hand, I would think experts who use the software would have a feel for where they are uncertain of the results and give themselves some design margin. In the end, its a matter of expertise and thorough consideration of risks.
 

Mark Nankivil

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I have yet to see a failed design from Scaled Composites - time will tell if Roc maintains that track record. I wonder far more about a mssion for the airframe with Paul Allen's passing and the near immediate cancellation of the efforts for those launch loads.

Anyone know how long before the expected Pegasus XL launch?

Enjoy the Day! Mark
 

Byeman

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They are developing one. How do you know what the turbulence field is? Did you run the numbers? What shape did you use for the pod structure? Can you show me your Schlieren graphs? You provoke this kind of response if you don't provide any details for the brush off replies you give.
It is intuitively obvious. The "pod" would have poor visibility being slung between two fuselages. That is why the ABL had the mirrors in the nose.

And what does Schlieren have anything to do with it? It will fly nowhere close to trans-sonic.
 

Byeman

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On the other hand, if all that can be achieved then a central payload will be better insulated from engine-induced vibration than say the US experimental laser installations in a 747 were. But I remain unconvinced that the Roc would be a laser scientist's first choice.
It would be less insulated, since it is on the wing which the engines are attached.
 

FighterJock

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Anyone know what has become of the Spaceplane (shuttle) that was under development until the death of Paul Allen? The Stratolaunch website is still showing that it is active, yet I have seen news on the web that it has been canceled. :confused:
 

Moose

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Anyone know what has become of the Spaceplane (shuttle) that was under development until the death of Paul Allen? The Stratolaunch website is still showing that it is active, yet I have seen news on the web that it has been canceled. :confused:
Stratolaunch has cancelled all their rocket/spacefraft development. At the moment, they plan to fly Pegasus and hope to attract a customer with their own vehicle.
 

FighterJock

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That is sad that they have cancelled all rocket/spacecraft development, let's hope that Pegasus gets customers soon so that they can restart development at some point in the future. By the way the Spacecraft was my favorite of all the Stratolaunch designs.
 

TomS

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Pegasus is a really marginal launcher right now. Its cost ($55 million plus) isn't that far off a Falcon 9, for much, much less payload. It's going to have to cut its price by about 80% to compete against other launchers coming out in its weight class. That includes the Virgin Orbit LauncherOne (target price of $12 million), another air-launched option coming soon if you really need to hit weird orbits.
 

steelpillow

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On the other hand, if all that can be achieved then a central payload will be better insulated from engine-induced vibration than say the US experimental laser installations in a 747 were. But I remain unconvinced that the Roc would be a laser scientist's first choice.
It would be less insulated, since it is on the wing which the engines are attached.
I trust you are aware that there are no engines on the wing centre section. Are you suggesting that there is an absorbent coupling between a one-piece wing and bolt-on fuselage structures? Otherwise, being out along the next wing section is further from the engines than being in the separating fuselage.
 

Byeman

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The ABL laser was nose mounted for turbulence minimization, not visibility.
It was visibility. It allowed the turret the most view. turbulence is not a problem from the side of the fuselage. See SOFIA aircraft
 

fredymac

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It was visibility. It allowed the turret the most view. turbulence is not a problem from the side of the fuselage. See SOFIA aircraft
Here is the ABL with a 1.5 meter telescope mounted externally in a sealed, rotating turret.
Also, the predecessor ALL with a 60cm telescope mounted externally in a sealed rotating turret. Experience with this configuration (boundary layer, turbulence) led to the switch to the ABL location.

And finally, a picture of SOFIA. Notice what's missing. I've mentioned before that my profession is optical engineering (including HEL systems). And that is all the time I am going to spend on this.
 

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sferrin

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Supposedly the Russian IL-76 laser testbed also has its laser in a nose turret. (I say "supposedly" because all the pictures I can find show a turret-shaped fairing rather than an actual turret.)
 
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