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Author Topic: Stratolaunch  (Read 71822 times)

Offline TomS

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Re: Stratolaunch
« Reply #360 on: April 14, 2019, 01:58:49 pm »
and
Any ID on chase plane?

No reg number but I think it's a Cessna Citation II or similar.

Edit: that's how FlightRadar24 idented it (but no ADS-B data from either aircraft.)

https://twitter.com/samerfarha/status/1117089673921335296?s=20
« Last Edit: April 14, 2019, 03:37:19 pm by TomS »

Offline fredymac

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Re: Stratolaunch
« Reply #361 on: Yesterday at 02:32:15 am »
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.


Offline sferrin

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Re: Stratolaunch
« Reply #362 on: Yesterday at 05:12:11 am »
That looked like an exciting landing.  :o
"DARPA Hard"  It ain't what it use to be.

Offline kitnut617

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Re: Stratolaunch
« Reply #363 on: Yesterday at 07:06:18 am »
That looked like an exciting landing.  :o

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.
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Offline Byeman

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Re: Stratolaunch
« Reply #364 on: Yesterday at 08:04:15 am »
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.

Offline fredymac

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Re: Stratolaunch
« Reply #365 on: Yesterday at 08:42:28 am »

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.

Offline Jemiba

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Re: Stratolaunch
« Reply #366 on: Yesterday at 10:31:54 pm »
Please, back to a reasonable tone !  
It takes a long time, before all mistakes are made ...

Offline steelpillow

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Re: Stratolaunch
« Reply #367 on: Today at 01:08:39 am »
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.
« Last Edit: Today at 01:18:30 am by steelpillow »
Cheers.

Offline fredymac

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Re: Stratolaunch
« Reply #368 on: Today at 02:50:57 am »
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.

Offline steelpillow

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Re: Stratolaunch
« Reply #369 on: Today at 04:37:00 am »
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.
Cheers.

Offline fredymac

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Re: Stratolaunch
« Reply #370 on: Today at 06:36:33 am »
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.

Offline Mark Nankivil

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Re: Stratolaunch
« Reply #371 on: Today at 06:55:19 am »
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