Author Topic: NACA vents vs. Hood Scoop question  (Read 16805 times)

0 Members and 1 Guest are viewing this topic.

Offline QikNip

  • Full Member
  • ***
  • Posts: 123
NACA vents vs. Hood Scoop question
« on: September 05, 2018, 05:55:45 PM »
I've been reading up on hood scoops and have thus far concluded that they can create additional drag if oversized, oxygen starvation if undersized, unexplained negative aero effects even if right sized ... and that they are in general a black art!  After reaching the foregoing conclusions, I began to wonder about the use of NACA vents mounted in the hood, collectively plumbed into a fairly large collector box, feeding the carburetors - what I hope would be more equalized doses of cooler air than occurs under the hood at speed.

At issue is the question of how many vents would be needed to provide the requisite air to supply a 122 cubic inch motor spinning at 8300 RPM's achieving a top speed of 155-160. Secondary consideration would be any boost that might come as a bi-product of the cooler, calmer intake air.

These specific questions aside, I'm fully open to hearing that this is a thoroughly dumb idea! I throw myself on the mercy of the aero educated here. :-D 

Rick
138.0 G/CPRO 4/18 Arkansas Mile Challenge Record
145.632 G/CPRO 8/17 Bonneville Record
149.825 G/CPRO 8/18 Bonneville Record
142.443 G/CPRO 9/20 Loring 1.0 Mile Record
156.343 G/CPRO 9/20 Loring 1.5 Mile Record

Offline WOODY@DDLLC

  • Hero Member
  • *****
  • Posts: 1803
  • ECTA made it to AR-Kansas!
    • Design Dreams, LLC
Re: NACA vents vs. Hood Scoop question
« Reply #1 on: September 05, 2018, 06:07:16 PM »
All models are wrong, but some are useful! G.E. Box (1967) www.designdreams.biz

Offline QikNip

  • Full Member
  • ***
  • Posts: 123
Re: NACA vents vs. Hood Scoop question
« Reply #2 on: September 05, 2018, 06:23:34 PM »
Woody:
I read it once. Now I'll read it some more! I think your comment in the article..."It isn't that simple" belies your message above!  :-D
Rick
138.0 G/CPRO 4/18 Arkansas Mile Challenge Record
145.632 G/CPRO 8/17 Bonneville Record
149.825 G/CPRO 8/18 Bonneville Record
142.443 G/CPRO 9/20 Loring 1.0 Mile Record
156.343 G/CPRO 9/20 Loring 1.5 Mile Record

Offline tauruck

  • Hero Member
  • *****
  • Posts: 5126
Re: NACA vents vs. Hood Scoop question
« Reply #3 on: September 05, 2018, 06:39:07 PM »
NACA ducts work as long as you use the correct formula.
I've seen many advertised by online vendors in the automobile
arena and none if not all are real NACA ducts. My experience
with them was in road racing. Ask George Poteet why he got rid
of his big scoop when building the new speed demon. Just my
2c from an amateur wannabee aerodynamacist.

Offline Stan Back

  • Hero Member
  • *****
  • Posts: 5879
Re: NACA vents vs. Hood Scoop question
« Reply #4 on: September 05, 2018, 06:45:02 PM »
Maybe you need an "Air Intake" – like this Monza that's held the C/CFAlt records at both Bonneville and El Mirage since 1992.

And, same motor, set 7 Street Roadster records at El Mirage and Bonneville, too, in a barn-door Model A that's way outclassed now.

PM me for a description.
Past (Only) Member of the San Berdoo Roadsters -- "California's Most-Exclusive Roadster Club" -- 19 Years of Bonneville and/or El Mirage Street Roadster Records

Offline Sumner

  • Global Moderator
  • Hero Member
  • ***
  • Posts: 4078
  • Blanding, Ut..a small dot in the middle of nowhere
    • http://purplesagetradingpost.com/sumner/sumnerindex.html
Re: NACA vents vs. Hood Scoop question
« Reply #5 on: September 05, 2018, 09:57:39 PM »
NACA ducts work as long as you use the correct formula....

Won't name names but someone real famous with a big world record that uses them told me he wouldn't use one on a NA vehicle, they run blown.  A blown engine can suck in the air it needs if you give it a place for that to happen. Not that a NACA duct wouldn't work, but a lot of variables that would almost dictate wind tunnel testing to make sure in your situation that it would work.

This might possibly help with scoop design that wouldn't hurt drag too much....

http://purplesagetradingpost.com/sumner/bvillecar/bville-scoop%20info-1.html

Sumner
« Last Edit: September 07, 2018, 05:25:27 PM by Sumner »

Offline Rex Schimmer

  • Hero Member
  • *****
  • Posts: 2625
  • Only time and money prevent completion!
Re: NACA vents vs. Hood Scoop question
« Reply #6 on: September 07, 2018, 04:44:45 PM »
Stainless and the guys with the Bockscar have ran a NACA duct inlet for years and have the data to show that if it is correctly designed and made and put in the proper place on the car surface they do work. As I remember they actually got theirs from some military aircraft and it works for them. I have a piece to that is to fit where my present scoop fits that will allow me to make a NACA duct inlet, but it is a next year project. Flat out to make the WOS meet next week!

 Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline Stainless1

  • Administrator
  • Hero Member
  • ***
  • Posts: 8948
  • Robert W. P. "Stainless" Steele
Re: NACA vents vs. Hood Scoop question
« Reply #7 on: September 07, 2018, 07:41:24 PM »
If you want to know if your NACA duct works, paint it... if you can, it doesn't...  :-o
If is really difficult to paint, because the paint shoots through it when the gun passes to paint the floor, then it probably does.. there is more to it than just the shape...

Yes ours came from our favorite airplane, was part of an engine pod that was scrapped after a fire...
 :cheers:
Stainless
Red Hat 228.039, 2001, 65ci, Bockscar Lakester #1000 with a little N2O

Offline panic

  • Sr. Member
  • ****
  • Posts: 845
    • My tech papers
Re: NACA vents vs. Hood Scoop question
« Reply #8 on: September 08, 2018, 02:47:55 PM »
I missed the part in any of this that says "air flows from high pressure to low pressure".
I guess it's not important.

Offline Interested Observer

  • Sr. Member
  • ****
  • Posts: 433
Re: NACA vents vs. Hood Scoop question
« Reply #9 on: September 08, 2018, 05:58:43 PM »
Quote
"air flows from high pressure to low pressure"

Generally true, but if the air has mass, which it does, and velocity, which it may, the converse is possible.
So, "Ramcharging".

Offline Stainless1

  • Administrator
  • Hero Member
  • ***
  • Posts: 8948
  • Robert W. P. "Stainless" Steele
Re: NACA vents vs. Hood Scoop question
« Reply #10 on: September 08, 2018, 10:47:22 PM »
I missed the part in any of this that says "air flows from high pressure to low pressure".
I guess it's not important.

If you are using a NACA duct I think that is the principle that makes it work, as long as you have velocity and a correctly shaped duct which I think maximized the amount of air captured.... but like I said, there is more.... the correct shape on the rear lip has a lot too do with how well the duct works.  It also needs go be sized for your needs.  In the past we have measured positive pressure in the airbox fed by the duct. 
If you think 1 is good so 2 must be better..... nope tried that.... no positive pressure.

But Panic, if you wish to educate us on the theory behind the NACA duct, feel free to do so... whatever you think is important  :-o
Stainless
Red Hat 228.039, 2001, 65ci, Bockscar Lakester #1000 with a little N2O

Offline Speed Limit 1000

  • Hero Member
  • *****
  • Posts: 1396
Re: NACA vents vs. Hood Scoop question
« Reply #11 on: September 08, 2018, 11:44:29 PM »
And the quest began :cheers:        https://ntrs.nasa.gov/search.jsp?R=20090012113
John Gowetski, red hat @ 221.183 MPH MSA Lakester, Bockscar #1000 60 ci normally aspirated w/N20

Offline John Burk

  • Sr. Member
  • ****
  • Posts: 695
Re: NACA vents vs. Hood Scoop question
« Reply #12 on: September 09, 2018, 01:11:35 AM »
An air inlet in the center of an aerodynamically shaped nose may be better than a NACA inlet or a scoop . It gets full ram air pressure for any speed and actually reduces drag on the body slightly compared to a hood scoop by reducing the amount of air the nose needs to push aside . This only applies to a correctly streamlined nose .

Offline MAYOMAN

  • Sr. Member
  • ****
  • Posts: 438
Re: NACA vents vs. Hood Scoop question
« Reply #13 on: September 09, 2018, 08:51:07 AM »
Some of this was discussed in "Engine Compartment Venting" in Aerodynamics. I may have more to share from an earlier project - but need to get an okay from Woody.
The road is long - Life is short - Drive fast

Offline SPARKY

  • Global Moderator
  • Hero Member
  • ***
  • Posts: 6908
Re: NACA vents vs. Hood Scoop question
« Reply #14 on: September 09, 2018, 11:06:13 AM »
to Woody sharing  :cheers:
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!