Landracing Forum
Tech Information => Technical Discussion => Topic started by: Ratliff on June 12, 2008, 07:23:48 PM
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NACA used to feed turbocharger in Honda Hawk.
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Anything left in the library?
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Anyone that wants to see a properly designed one just stop by our car.
If you think you have a good one, paint it, if it is easy, then it is not working properly... Don't bother with any of the prefab ones, most don't work.
Hey Slim, I have the NACA research papers on the duct development, should I post that book here... :evil: I think it is only 40 or 50 pages :-o
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Before we get too carried away, here is a quote from page 18 of the original NACA report,
NACA ACR No. 5120;
"Submerged inlets do not appear to have desireable pressure recovery characteristics for use in supplying air to oil coolers, radiators, or carburetors of conventional recirocating engines. "
Jim
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... Don't bother with any of the prefab ones, most don't work.
Stainless: Why do you say that? Is this opinion? Do we have data?
(Please don't read attitude into this, its a question, ok?)
OK, I've opened my big mouth, its off to post my "intro" and figure a way to run a test (has anyone tested??) - I think I can get a transparent duct to wool-tuft.
Thank you.
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I will jump in here David, according to the NACA report submerged inlets must be located in an area where the flow is attached and the boundary layer is relatively thin. The slope, depth of opening and size must account for this. Putting them way aft on a flat sided vehicle makes them no better than a plain hole.
Jim
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Well, we have tried the plastic ones, didn't get any more air than with no scoop at all. Installed the one that is on there now, it was a proven performer with a lot of development, beyond the NACA work, by Boeing. The air box we had at that time was instrumented for pressure and showed a steady rise starting about 190 and at 220ish MPH developed almost 1 PSI at WOT. It is on a flat sided car and mounted aft of the center. We have had very good success with it but your luck may vary. Proper design makes the difference. There was a lot of work done after the NACA report by several aircraft companies. The original posts looked like hood type designs. The one we have came from the flat side of an airplane...
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http://www.landracing.com/forum/index.php/topic,4033.0.html
Other examples of how NACA ducts can be applied are shown in the thread on the Alex Tremulis design for Kitty O'Neil.
Tremulis proposed using them for engine air inlets on a jet land speed car. NACA ducts were used on the roof of the Lew Arrington rocket Funny Car to supply air that aided chute deployment.
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Thank you, gentleman, for the info. I appreciate it.
(Stainless, jdincau, and Ratliff).
I understand the boundry must be thin -obviously the duct will work better on the nose than towards the back. good reminder!
I look forward to seeing the duct Stainless has procurred (-2 for spelling?) and how that differs from others.
best to all, keep the rubber side down.
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Just to revisit the comment about plastic ducts not working . . .
My assumption is this: the ducts would work if placed in a high pressure area, and would not work in a low pressure area/area of this boundary flow.
Am I still on the right track?
thanks again!
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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.
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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..
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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.... :-o
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.
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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
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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.
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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!
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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
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I will proceed cautiously. Thanks guys.
Jim B.
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Just a note - the political discussion that was under this heading has been split off an moved to "Formerly NACA Ducts".
Chris Conrad
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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
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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.
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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.