Aircraft speed & aircraft skin temperature question

[Don Stauffer <stauffer@xxxxxxxxxxxx>]

> I recently read some entrepreneur purchased a Learjet and intended to 
> install a rocket engine on the aircraft. It made me think what would prevent 
> you from taking the aircraft into suborbital flight assuming you could keep 
> the nose pointed in the proper direction. It's the trip back down I see a 
> problem; the heat of reentry. At what speed does the skin temperature start 
> becoming an issue? 

You got it!  Actually, even as low as Mach 3 is a bit too hot for 
aluminum.  Not only is pointing in the right direction for boost 
important, but, even assuming the skin would survive temperature, you'd 
need some way to control attitude in re-entry.

Remember the Valkyrie?  Mach three.  Not only did it have high temp 
metals, it used fuel to cool skin in some areas.

Seems to me I have an old F-4 manual somewhere, and there were some 
restrictions on sustained flight at certain parts of the envelope 
because of skin heating concerns.