-------------- Original message from Ernest Christley <echristley@nc.rr.com>: --------------


> Bulent Aliev wrote:
>
> > Bob, if the cabin does not have exhaust path for the incoming air,
> > the cabin pressure will build up and the NACA scoops will be
> > ineffective.
> > Buly
>
> That is correct. But it is also correct for any other type of inlet
> you'd care to mention. I'm not trying to be a smarta$$, just trying to
> point out that there is so much sound and fury around NACA inlets, but
> without a system approach it all signifies nothing.
>
> The radiator doesn't care what sort of scoop is out front. And it has
> no idea what sort of exhaust is behind it. All that matters is the
> pressure DIFFERENTIAL across it. Differential implies that there are
> TWO values to consider. You could have a working system with negative
> pressure compared to ambient in front of the radiator, if and only if
> you had a much more negative pressure behind it. Flatly stating that a
> NACA will or won't work is like talking about voltage without a
> reference ground.
>
> The Honorable Mr. Crook has done us all the favor of showing how to
> create a water manometer for less than the cost of a Coke at the
> movies. The only number for pressure differential that I've seen for a
> working system is Tracy's. I recall that to be 5" H20, so let's go with
> that and make up a few more numbers. You need 5" of pressure across the
> radiator to get adequate cooling. A P-51 style scoop stuck out in the
> wind could probably give you 4" of ram pressure. A properly designed
> exit could possibly give you -2". There you go. Your done. You'll get
> more than enough airflo w to cool the engine.
>
> But you want to cut the drag down, so you consider an submerged inlet.
> Use John Slade's approach, the partially submerged inlet. Don't just go
> straight for the fully flush inlet, but start slowly sinking the scoop
> into the skin. As it moves in, the positive pressure in front will
> drop. You still have the -2" on the back, but if you drop below 3" on
> the front you won't have adequate cooling. You start to slowly pull the
> scoop in, but before it is even halfway in you hit the 3" mark.
>
> Hmm? Maybe work on the exit. Change the shape a little, clean it up
> and maybe it will push the exhaust pressure down to -3". Now you only
> need 2" on the front, and you can get the scoop down to only half the
> original obstruction. What else? Maybe you can fit a K&W streamlined
> duct in before the radiator. Now that your duct is using the air it
> doe s have more efficiently, the frontal pressure is higher with the same
> scoop. Mabybe you have 2.5" instead of the 2", and you can sink the
> scoop just a little more.
>
> Hmm? But what happens if you scoop out a little bit of the air frame
> and put the scoop in the rut that is formed? Would that let you sink
> the scoop even further? You have the same sized opening, but it isn't
> sticking out in the wind as far for less profile drag. What if you gave
> the rut a carefully designed shape so that air will get a little extra
> pull into the rut instead of just flowing right over the top? Could you
> sink it still further? Maybe you can even play with negative pressure
> gradients and vortex sheets. Damn, now we're having to head over to
> naca.larc.gov to pull up old studies where 50 years ago they derived
> actual equations to predict what will happen.
>
> I guess my point is t o not think of the NACA scoop as anything more than
> one end of the spectrum that starts with a pot-belly stove flue sticking
> out the belly. I will be using a scoop that will be eerily similar to a
> NACA, except that it isn't. Due to it's location just below the leading
> edge on the thick airfoil of the delta wing, it will work much more like
> a traditional scoop at high AOA. During cruise, it will flatten out and
> begin to work more closely but not exactly like the submerged inlet.
> The exit will be on the top of the wing, just behind the max thickness.
> I have high hopes, but the water manometer will tell the true story. 8*)
>
> --
> ,|"|"|, Ernest Christley |
> ----===<{{(oQo)}}>===---- Dyke Delta Builder |