@FrancescoPeople who would potentially pay to go into orbit as a tourist will want to look out the window. Having super Hi-Def internal screens or VR headsets to show what's outside isn't going to cut it for these people, otherwise they could just look at a screen on the ground. Having windows would completely alter the structural integrity of Skylon. Skylon therefore isn't going to be used as a tourist operation. Something else that uses SABRE technology might, but for the moment all that we've ever heard from REL is SABRE/Skylon.
Ok, so if we're posting numbers now I might as well post mine. I make the tail area affected by the rocket plume to be approximately 99m2 based on the tail modelled as a Sears-Haack body, which it isn't perfectly, and the thermal image from the paper at Mach 16, which only shows the top and could be larger area than that at higher altitude.
Okay so now things get more hand wavy and I make no guarantee my maths is right, but the SABRE engines put out about 6.9Gw with a mass flow of 666 kg. If you imagine that energy spread over the surface area of cones moving back from the engines then the proportion of the energy intersecting with the tail could be said to be the area of the tail affect/the area of the cones. If that's the case then the tail might be seeing something like 3.3kw/m2 which over the 195 seconds from Mach 8 to orbit could raise the temperature of the skin by around 860K on top of the aerodynamic heating which tops out at 855K for certain parts of the fuselage skin. This is all hand wave and BOE stuff but it seems like a reasonable number. A peak of 1715K might seem bad but the tail probably doesn't seem that much aerodynamic heating and it seems managable with some active cooling or C/SiC.
@RonMI guess there is that possibility. But before that happens Skylon will have to become human rated. That might be a little ways off yet.
... If that's the case then the tail might be seeing something like 3.3kw/m2 which over the 195 seconds from Mach 8 to orbit could raise the temperature of the skin by around 860K on top of the aerodynamic heating which tops out at 855K for certain parts of the fuselage skin. This is all hand wave and BOE stuff but it seems like a reasonable number. A peak of 1715K might seem bad but the tail probably doesn't seem that much aerodynamic heating and it seems managable with some active cooling or C/SiC.
Quote from: lkm on 08/21/2015 10:53 pm... If that's the case then the tail might be seeing something like 3.3kw/m2 which over the 195 seconds from Mach 8 to orbit could raise the temperature of the skin by around 860K on top of the aerodynamic heating which tops out at 855K for certain parts of the fuselage skin. This is all hand wave and BOE stuff but it seems like a reasonable number. A peak of 1715K might seem bad but the tail probably doesn't seem that much aerodynamic heating and it seems managable with some active cooling or C/SiC.3.3kw/m^2 isn't all that much. Presuming the tail surface was heated by some other source to 855K (and the heat sink calculator I'm using is accurate) that come out to in the neighborhood of 30 degrees extra heating when you account for radiative cooling. 885K doesn't need active cooling with the right materials, or even really exotic materials.
Quote from: Citizen Wolf on 08/21/2015 10:55 pm@RonMI guess there is that possibility. But before that happens Skylon will have to become human rated. That might be a little ways off yet.Perhaps not as far as you think. Skylon is completely reusable. What's tested in certification is what will fly. Exactly what was tested, not a new piece built to the same design.
It may be *planned* to be completely reusable, but that can be a different thing altogether.
You have more absolute faith in Skylon specifications that REL engineers themselves do.
I have absolute faith both will use the best available models and modelling tools to ensure their plans are viable, or to scrap them and re-design their architecture if they cannot deliver the expected results.
What do you have absolute faith in?
I'm glad to hear it, because that is not how you come across when posting.
That change is a constant. And assumptions are often wrong. Among other things.
But in regards to Skylon - based on aerospace history - I have faith in that *IF* Skylon ever flies, it will have some significant differences to the current evolution of the design.
The problem they're trying to solve is not the fundamental economic viability of the vehicle.
Aren't you contradicting yourself a bit here? If the upfront costs are the problem the RLVs generally look bad, Skylon included.
That's also the reason why there was no way in the world a fully reusable F9 could ever have reduced the launch costs by a factor of 10, the fixed costs are still too high. 50%, maybe, 10% nope.
And that Skylon fudge to split up the business case also won't help, it just moves part of the financial uncertainty beyond the event horizon so that it can easily get forgotten. Problem just is that that doesn't mean it's going away the same way that sticking your head into the sand doesn't make the Lion go away.
While it's true that the way things have been done is not necessarily a good reason for doing it that way in the future the fact that no one else does it the same way it's interesting that ship yards don't run cruise lines, aircraft mfg's don't run airlines (even in countries where this does not break anti-trust laws) or 18 wheeler mfg run haulage companies.Should that not give people pause for thought that perhaps the way the rocket industry does things is a bit odd and needs to change?
In the early days of airplanes and ocean liners that IS what happened, Boeing for example used it's superior designs to run a very anti-competitive airline, government action forced them to stop (and they are still a notorious corrupt company). The WhiteStar ocean liner company was in a partnership with Harland and Wolff shipbuilders who agreed to not make any ships for WhiteStar's competitors.
The division of manufacturer and operator is always associated with a transportation system becoming, cheap, common, safe, reliable, competitive and regulated.
I don't think anyone disputes that WILL eventually how space travel is done the question is if this vehicle would achieve that kind of market transformation.
Skylon would need to make quantum leaps in all these areas before the ground would be ready for an airliner like division between manufacturer and operator.
It will probably also require a second company making competing substitute vehicles as no operator would run the risk of being completely dependent on a single vehicle supplier.
P.S. On a technical note, dose anyone think a closed wing https://en.wikipedia.org/wiki/Closed_wing#PrandtlPlane_.28Box-Wing.29 configuration would help Skylon, it would seem to present the possibility of both reducing drag while allowing a higher mounting of the engines thus reducing the need for the bent nacelle (which I assume is needed to keep the thrust through the center of mass which is above the nacelle).
And yet that "fudge" is exactly how every other transport system on this planet does business.