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Naval Projects / Re: Small Surface Combatant Task Force concepts
« Last post by Kat Tsun on Today at 08:39:04 pm »
It's a bit curious to me why ships like the FREMM and F100, which are fairly massive and well armed/outfitted, are being considered, but smaller foreign designs like Asashi or Fridtjof Nansen seem to have been ignored. Were these proposed by any contractors at any point during FFG(X) run up, or is the USN only considering in production/in service designs rather than ultra-modern or out-of-production one? Asashi in particular seems to be well suited to the constraints of FFG(X), with a modest armament comparable to F100-class, but a superior combat system, and a supposed cost of less than a billion USD.
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Naval Projects / Re: Unbuilt White Star 1000" liner
« Last post by chuck4 on Today at 08:37:44 pm »
Could this be confused with an unbuilt white Star Project after WWI that was to have rivaled the normandie and queen mary before White Star merged with Cunard?
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So, it seems that we are uncovering this monster. I think that would be good to know who proposed the design, and if documents are availabe. I am thinking about a 3d model and a scale model 😊
Wich design seems more feasible for you, the Bel geddes m4 or this one?
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pdf of report on cancellation

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any drawing or original document regarding the bf 109 K1/K2/K3 ,and concept for the bf 109 K?

thanks for your answer.
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Space Projects / Re: Stratolaunch
« Last post by steelpillow on Today at 12:18:27 pm »
Following up on Archibald's comment. The big problem with a horizontal-launch space stage is the mechanical stresses in the body/fuselage. In a vertical-launch rocket, the optimum aerodynamic cylinder is also the optimal structure, with the fuel pressure able to provide sufficient structural rigidity. But in a horizontal position the cylinder tends to sag in the middle and the fuel pressure is nowhere near enough to stabilise it. A surprising amount of of structural reinforcement needs to be added, and that means weight.

The problem is even worse with Pegasus because the cylinder is chopped into discontinuous stages, with the structural forces having to be transferred across multiple joints.

A subsonic hike to a few miles up is no compensation at all. Whether SSTO or air-dropped, launch to orbit is on the edge of impossible. Stratolaunch could probably send up a sub-orbital second stage that could in turn launch an orbiter, but it's an awful lot cheaper to do it the SpaceX way. My guess is that this was why Elon Musk parted company - he woke up and smelled the coffee before Paul Allen did.
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Space Projects / Re: Stratolaunch
« Last post by martinbayer on Today at 11:37:21 am »
I do think that air launch could potentially make just enough difference (90% PMF vs. 94% - the STS ET had a PMF of 96%) to make a single stage orbiter a la Interim Hotol feasible.
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Postwar Aircraft Projects / Re: VTOL On Demand Mobility
« Last post by galgot on Today at 09:58:49 am »
Thanks for these precisions. Maybe one way to avoid such problems in case of a motor out, would be to have a big excess of power diverted to the remaining turning motor for a time, to be at least effective the duration of a fast automatic emergency landing , even in case of disrupting flow due to the upper or bottom non-turning prop… ? Dunno.
Or eject the non-turning prop all together… wait, in town… forget it  ;D
What is the reliability of that kind of motor anyways compare to a helo turbine ?
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Space Projects / Re: Stratolaunch
« Last post by Archibald on Today at 09:58:34 am »
There it is
https://engineering.purdue.edu/AAECourses/aae450/2008/spring/report_archive/reportfinaluploads/pdfs/Report_Section_7.pdf

"A study by Klijn et al. concluded that at an altitude of 15,250 m, a rocket launch with the carrier vehicle having a zero launch velocity at an angle of attack of 0° to the horizontal experienced a Δv benefit of approximately 600m/s while a launch at a velocity of 340m/s at the same altitude and angle of attack resulted in a Δv benefit of approximately 900m/s. The zero launch velocity situations can be used to represent the launch from a balloon as it has no horizontal velocity.  

Furthermore, by increasing the angle of attack of the carrier vehicle to 30° and launching at 340m/s, they obtained a Δv gain of approximately 1,100m/s.

Increasing the launch velocity to 681m/s (= Mach 2) and 1,021m/s (Mach 3) produced a Δv gain of 1,600m/s and 2,000m/s respectively."

Sure, 2 km/s helps... but only a little. And separation issues as mach 3 can be interesting, just ask the crew of Lockheed M-21, the SR-71 that carried a D-21 drone on its back.

A SSTO needs a propellant mass fraction of at least 0.94 that is, the complete vehicle with crew, payload, tank, represents 6% , and 94% is pure propellants.

No 0.94 and then no 9 km/s to Earth orbit;

Air launch substracts 2 km/s out of 9 km/s, fine, but even 7 km/s is still a very high hurdle. 7 km/s can be done with a PMF  of  0.90 - still 10% for the vehicle itself, and 90% of the mass allocated to the propellants.
At the end of the day, either 90% or 94% of the mass, being the raw propellants - doesn't change much, building such a thing is still a huge conundrum...

I wouldn't buy a car which would weight 1000 kg with the gasoline tank full, and only 50 kg with the tank empty.
Which mean that 950 kg of the car would have to be gasoline itself. Pure gasoline. no kidding.
The tank around the gasoline, the car around the tank, and the car payload could not mass more than 50 kg. Bad luck, I alone weight a little more than that. And then the car would not work.
Other example
A 450 mt 747-8 is 1/3rd structure (150 mt) 1/3rd payload (150 mt) and 1/3rd kerosene (150 mt). PMF is thus 33% or 0.33. A SSTO would need 95% or 0.95.  Air launch just can't change that, or not enough to make a useful difference. That's the issue...
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