Hi Thomas, afraid not exactly an old wives tale.   Here is an extract from an  old NACA report that appears to take the position that submerged (NACA?) ducts are not the best suited for radiators or anything requiring much diffusion or pressure recovery. Unfortunately,  I don't have the full report but the report number is listed on the summary below if you wish to try and find it.   Any extract can be misinterpreted taken out of the context of the total report - but, it seems to take a position.  Also while NACA ducts may not be the BEST possible for our type airspeeds and radiators - there are always other factors to consider in trying to fit systems to aircraft - space, location,weight, possible inlet locations, etc, etc.  So while the NACA ducts may not be the best possible solution for a theoretical installation, its other attributes may make it the best of possible systems for the pushers.  Just an opinion of course.

While looking through my files I also found a copy of the report you cited which I though a comprehensive discussion of NACA inlets, vortexes and boundary layer - appears to have some good material in it - although I'll admit I have never done more than just skimmed it.

http://naca.larc.nasa.gov/reports/1951/naca-tn-2323/


Ed A


----- Original Message ----- From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, October 19, 2005 10:05 AM
Subject: [FlyRotary] Re: NACA scoops

rijakits wrote:

    Remember the inventors of the NACA-duct did recommend to NOT use
    it as a pressure-recovery intake (what we need for our our car
    style radiators)

I've heard this repeated so many times, and yet I've never been able to find the report that said it.  I believe it is well on its way to becoming an old-wives-tale.  I've looked for a while in vain to find the exact quote this morning, but the closest I've been able to find was more along the lines of "we didn't test that, so we don't recommend it."

"We don't recommend it, because we haven't tested it" is NOT the same as, "we don't recommend it because we found it doesn't work."

All of the reports are online at naca.larc.nasa.gov.  That address starts you at the search page.  'submerged inlet' brings up the reports on NACA scoops, with the most germaine for our purposes being located at http://naca.larc.nasa.gov/reports/1951/naca-tn-2323/ .  I'll keep looking for the quote I'm referring to above, but I would really appreciate a pointer to the report that says, "We found submerged inlets to be deficient for use with radiators."

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