Need aero calculation ---

[Christopher Crowe]

-- or a really good guess.

Okay. We have a flat bodywork surface that is directly parallel to the dirction of air travel on the side of a formula car. Let's assume that flow is stuck pretty well to the car in this area and not wildly turbulent. How large would a by-the-1940's-book NACA duct have to be to feed the plenum of a GSXR 1000 cc engine in this situation?

I'm hoping for some kind of a CFM matchup; the duct's size vs the volume of air being sucked by that hungry little 1000 cc pump at 13,000 r's.

Maybe someone's done some kind of calculation like this -- maybe someone's just a good guesser.

Or maybe this. Maybe the NACA duct just too passive an intake for an engine like this... and perhaps a scoop should be used for the ram-air deal... with all the attendant aero violence that comes with it. (Which I'd love not to have).

I know this is a kind of impossible question. But for the hell of it, I wonder if anyone has run any kinda-sorta numbers on something like this.

Thanks for any opinions or info!

C

PS: Figure that the ducting post the intake is not a-factor... that is, it correctly sized and appropriately gentle and smooth, etc.

[RobLav]

Many of us believe that a NACA duct for engine air intake is too passive.

[Christopher Crowe]

-- I question those great big scoops too. I mean, not only the obvious drag where it's gulping air, but the aero turbulence that takes place behind it *far behind it) as well.

Which of course asks the usual trade-off question; just how much ram-air really makes more power in these engines balanced against the negative aspects of a flat-to-the-wind scoop? I wonder if anyone's done a back-to-back comparison on a GSXR -- passive intake vs ram air. Clearly, ram air has got to make for some more power (I've heard it does in GSXRs)... but enough additional power to matter in a big way?

I know that big central scoop is F1-looking... but every time I see one something in my brain (the Tourettes part of my brain) yells "bull****."


So I dunno...

Other thoughts in this area?

Chris

[Jnovak]

Many of us believe that a NACA duct for engine air intake is too passive.

Rob is correct. A NACA duct dues not do well with pressurezing a plenum at these speeds. They are great for lower drag ducts and can have great pressure recovery.


Thanks ... Jay Novak

[provamo]

you could check out "Aircraft Design: A Conceptual Approach" by Daniel P. Raymer

i just don't think you have enough "space" to out-peform the "pitot" inlet

[rperry]

-- I question those great big scoops too. I mean, not only the obvious drag where it's gulping air, but the aero turbulence that takes place behind it *far behind it) as well.

Which of course asks the usual trade-off question; just how much ram-air really makes more power in these engines balanced against the negative aspects of a flat-to-the-wind scoop? I wonder if anyone's done a back-to-back comparison on a GSXR -- passive intake vs ram air. Clearly, ram air has got to make for some more power (I've heard it does in GSXRs)... but enough additional power to matter in a big way?

I know that big central scoop is F1-looking... but every time I see one something in my brain (the Tourettes part of my brain) yells "bull****."


So I dunno...

Other thoughts in this area?

Chris

"Ram air" isn't going to get you much. You can quickly look at atmospheric pressure (101325Pa) and pressure due to "ram effect" (½*1.225*V^2 (in m/s)) to see that ram air is a very small effect until you've moving very quickly.

That said I recommend against a NACA duct for an engine intake. You will have a lot of losses inside the duct and the inlet itself will have to be quite big, whereas a nicely faired and properly placed traditional inlet (above driver or on side of car) can be quite low in drag.