[ExI] Skylon heat exchangers

[The Avantguardian]

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On Fri, Dec 19, 2014 8:32 PM PST spike wrote:

>>... On Behalf Of Keith Henson
>Subject: [ExI] Skylon heat exchangers
>
>On Fri, Dec 19, 2014 at 4:00 AM,   "spike" <spike66 at att.net> wrote:
>
>snip
>>
>>... The next trick they must have solved is figuring out how to make this 
>> heat exchanger stand up to a shock wave.  Now that's technology 
>> indistinguishable from magic.
>
>>...The heat exchangers are not exposed to the shock wave.  The air goes
>through two shock waves on the way i engine so it's all subsonic when
>it goes through the heat exchanger... Keith
>
>Keith after two oblique shock waves the air flow is so turbulent they might
>be better off facing supersonic flow.  But if they can make this work, it
>will be the biggest breakthrough in space technology in my lifetime.  I am
>cheering for them.

So am I. Single stage to orbit is Buck Rogers stuff. 

>Here's why I haven't completely lost faith in the whole notion, an
>experiment you can do at home.  Go get a garden hose and find a spider web.
>Check out how much flow you can spray at that web and still it stands.
>Every notion I have about flow and strength of materials would tell me there
>is no way that web could hold up to a garden hose, even with a nozzle on it,
>but it does.  Now don't take my word for it; go out there and start
>spraying.  I have no equations that would explain why the heck that happens.

That's spider silk for you. It has approximately the same tensile strength as steel but can deform a lot further before failing. So it can withstand similar forces through a longer distance, ergo it takes more work to snap a spider web than a steel wire of the same diameter.

Also the spider web is incredibly thin, so very low surface area is presented to the pressure wave or fluid flow. So the drag forces on the web would be pretty low. A relevant bit of trivia is that some South American tribes weave fishing nets out of orb weaver silk for fishing in rivers.

Stuart LaForge