Hood Scoop

[stratman59]

Rex,

Thanks for the formula.
Thats alot better than what i had.

Robbie

[interested bystander]

Mr Schimmer and Mr Bettes, Boyle eclipsed Bernoulli by a few years with that formula -he published it in 1662. (One of the few things I retained from HS Physics.) And Charles added temperature, as I recall.

To add to Rex's description of scoop requirements, you can't WISH the air to go places.
You can MANAGE it as witnessed by the strange tabs, winglets and bumps the F1 people come up with. Like Larry  McReynolds said a 'couple weeks ago  "There's no free lunch in aero."

A simplistic scoop shape might be to picture the exhaust valve throat as the open airstream and the header flange as the "target" for your airflow. I.E the carburetor (s) or injector ram tubes.
 

[836dstr]

Rex,

Stan and I have had discussions about Air Scoops vs. Air Ducts. We both run Street Roadsters and the rules regarding Hood Scoops have changed in 2009 to limit the front of the Scoop to the front hood line. The rule was intended for other body types but we got swept up by it for this year at least.

With a non-taped Air Duct such as Stan runs, the expansion of the cross section is internal to the Duct. He also said that this should be just inside the inlet (opening quickly). Should that divergence be a certain angle in relation to the distance from the inlet to the carb, say 45 degrees, or 90 degrees to airflow at the inlet face, or some other angle?

I understand that in addition to pressure recovery the goal is also to reduce turbulance in the plenum.

Tom

[SPARKY]

I was told the objective was calm air at 10,000 below sea level

[Glen]

As I recall a couple of years ago Tom Bryant did a lot of research on hood scoops for the Tom Thumb coupe.
It's probably on his web site that's listed under links on this site. Tom I am sure would be glad to talk with anyone on this.  www.bryant automotive redding Ca.

[stratman59]

Glen,

Thanks for the info.

Robbie

[Rex Schimmer]

Tom,
I am not completely up to speed on the new air scoop rules for your roadsters class but the general rule is that the inlet should expand at around 7-9 degrees per side, so if you did a cone the included angle would be 14-18 degrees. The idea of course is to keep the air attached to the interior of the scoop and try to prevent turbulance, also if the air has to turn 90 deg from the scoop/plenum to the engine inlet then you should probably think about some sort of turning vanes to help the air to go into the engine. Lots of big time research is being done on air scoops by the F1 guys and they have been doing it for years so just keep the sides smooth, no sudden transitions, try to not have sharp corners and good luck.

Rex

[836dstr]

Thank you Rex!

That gives me a good idea where to start.

Tom

[jimmy six]

Tom, remember unless the rule has changed the taper or anything you want must be on the inside of the part that protrudes in front of the grille shell. I believe the rule still states that the air device must not taper and that has always been the outside dimensions....JD

[stratman59]

Jimmy Six,

You are talking about roadsters or all cars.

Robbie

[836dstr]

Robbie,

JD and I were talking about a roadster application, but applies to cars of all types. Look at the SCTA Rulebook for definitions. Hood Scoops and Air Intakes/Ducts are two different animals and have different specifications.

Tom

[Stan Back]

All cars -- but he's referring correctly to Air Intakes, not Hood Scoops.  

Stan

[Stan Back]

Tom --

I've got to learn how to type faster.

Stan

[floydjer]

How about a variable inlet like the SR-71 uses?

[Rex Schimmer]

Floyd,
If I was doing a "cost is not object" project I would certainly do something like the SR-71 inlet. It would give you the best of both worlds, large inlet for low speeds and reduced area for high speeds and great aero. As one of my more favorite sayings goes "Only time and MONEY prevent me from doing this!""

Rex