NACA Ducts

[Dr Goggles]

If a NACA Duct was fabricated incorrectly or placed in the wrong location on the vehicle could it pull a vacuum on the air box? Jim B.

seem to recall that the Rice-Vigeant guys had that very problem with their Busa Lakester....they had Naca ducts on the cowl and it went slower with the cowl than w/o til they sorted the location of them...or built a snorkel...don't remember the end of that movie..

[Stainless1]

The inlet and top of the inlet are the most important factors.  The correct design creates the pressure area in the inlet.  As I mentioned earlier, if you try to paint it and the the paint will only seem to suck through and not stick inside the base of the inlet then it is working properly.  We found it a little bit amazing....     
We weren't smart enough to design it from the NACA papers, but we were smart enough to recognize how well it worked in its designed application and apply it to ours. 

[Vortex1]

I have a book written by Carroll Smith called Tune To Win and there are drawings and dimensions of a NACA Duct in one of the chapters. I am using these to build a test duct. I figure the Indy car guys must be pretty smart on this stuff.


Thanks.

Jim B

[Stainless1]

I have a book written by Carroll Smith called Tune To Win and there are drawings and dimensions of a NACA Duct in one of the chapters. I am using these to build a test duct. I figure the Indy car guys must be pretty smart on this stuff.


Thanks.

Jim B

Jim, Yea, but they should be smart enough to just procure one from a military airplane, then copy as required, pay attention to the design, something should look like a wing when you are done.

[interested bystander]

FFRANKLIN has everbody worked up about NACA ducts.

They're usefull if applied properly, otherwise, they are just "trick" looking.

My suggestion would  be - if you have no real world test facilities available, to look at the ALMS and F-1 websites among others, and  attempt to apply their solutions (if any) to your landspeed project.

Be careful!

[Peter Jack]

I remember reading a very technical article in Road & Track of all places probably in the late 60's, early 70's on NACA ducts. They gave all the critical dimensions, but the thing they really emphasized was that all the corners must be sharp. Most of the accessory ones that you buy tend to be rather generously radiused. That may be why most aren't very effective.

Pete

[Vortex1]

I will proceed cautiously. Thanks guys.



Jim B.

[Milwaukee Midget]

Just a note - the political discussion that was under this heading has been split off an moved to "Formerly NACA Ducts".

Chris Conrad

[High Gear]

I have used this NACA duct calculator and it seems to be accurate when compaired to stor bought items. The link is below

sports.racer.net/tech_info/aero/naca_profile_calculator.xls

[Blue]

The biggest single problem with NACA or any other type of flush duct is the pressure recovery.  Absolute theoretical maximum is only 90% at mass flow ratios of 30 to 50%.  That means we can put a pitot type inlet (like an LSR hood scoop) out there that is 1/2 to 1/3 the size of an equivalent perfect NACA and get 10% more ram air (pitot inlets are good for 100%).

NACA's are good when we need varying amounts of air flow or if we are regulating flow with downstream restrictions.  They tend to be used on aircraft for accessory inlets where air demand will vary.

Engines use pitot inlets, not NACA's.  Otherwise, we're giving away power and fuel, and no aircraft designer worth a dime does that.

[Ratliff]

The biggest single problem with NACA or any other type of flush duct is the pressure recovery.  Absolute theoretical maximum is only 90% at mass flow ratios of 30 to 50%.  That means we can put a pitot type inlet (like an LSR hood scoop) out there that is 1/2 to 1/3 the size of an equivalent perfect NACA and get 10% more ram air (pitot inlets are good for 100%).

NACA's are good when we need varying amounts of air flow or if we are regulating flow with downstream restrictions.  They tend to be used on aircraft for accessory inlets where air demand will vary.

Engines use pitot inlets, not NACA's.  Otherwise, we're giving away power and fuel, and no aircraft designer worth a dime does that.

Don't have a photo of Al Teague's car handy, but attached is a photo of the pitot inlet on Bob Herda's 357 mph streamliner. I think Herda, a professional aerodynamicist, also designed the pitot inlets used on Goldenrod's 425 mph pass.