Ducting Losses

[Dynoroom]

OK. We talked hood scoops. We talk pressure recovery. Lets try this.....

Several teams have inlets in the front of there cars. The air travels through a tunnel to some type of defuser (maybe) the to the throttle.
How do you calculate ducting losses?
How much expansion should be used in a given length?
Given options would you use this type of inlet or a standard hood scoop?
Opinions welcome.

Newbes, this is your chance to get in on so "what if" type engineering.

[Peter Jack]

There are obviously going to be some ducting losses but then how do those compare to the aerodynamic losses caused by the hood scoop? The size and shape of the ducts and the hood scoops must also be taken into account.

Pete

[Bville701]

How much power are you gaining from the scoop, rather than the duct? Is it enough power to compinsate the drag that the scoop will cause.

[interested bystander]

Don't want to sound Bitchy ,but you LeFever's might want to query Doug Kruse who did the aluminum panel work on your roadster -and of course many others-about the EIGHT FOOT LONG duct he fabricated for the Red Baron P-51 and the pressure it picked up. Lockheed's Skunk works was involved in the design ,unofficially. Doug may still have the drawings.

You're just gonna get OPINIONS, not DATA with this Landracing group, even as well informed and as helpful as they are.

Doug may be able to help you through the forthcoming confusion that will appear on this topic.

[Bville701]

I spoke with Doug today.   

Just trying to get everybody else interested in the subject. We kind of know the direction we would like to go in.   

[jl222]

Don't want to sound Bitchy ,but you LeFever's might want to query Doug Kruse who did the aluminum panel work on your roadster -and of course many others-about the EIGHT FOOT LONG duct he fabricated for the Red Baron P-51 and the pressure it picked up. Lockheed's Skunk works was involved in the design ,unofficially. Doug may still have the drawings.

You're just gonna get OPINIONS, not DATA with this Landracing group, even as well informed and as helpful as they are.

Doug may be able to help you through the forthcoming confusion that will appear on this topic.

   Where's the fingerface when you need one

         JL222

[Dean Los Angeles]

You're just gonna get OPINIONS, not DATA with this Landracing group, even as well informed and as helpful as they are.

I beg to differ!
Here is a calculator for "Pipe Friction Calculation for Fluid Flow in a Pipe".
http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm
This if for a section of uniform pipe cross section. For a non-round section you will have to add some further losses.

Type "pipe flow losses" in Google for tons more.

[Sumner]

.............You're just gonna get OPINIONS, not DATA with this Landracing group, even as well informed and as helpful as they are......

I'm interesting in why you believe that "no one" on here has any data on this subject or the previous one?  I feel there is a lot of "data" available from this group and of couse "opinions" from some of us that are just guessing, but who have still managed to do pretty well.

Why post your concern about getting "opinions" vs. real "data" on Mike's questions and not others?

c ya,

Sum

[Bville701]

Dean,

Thanks for posting that web-site. It's really cool and I like the way you can enter your own deminsions into the formulas.    

[interested bystander]

Got the hair up on some folks necks, I see.

We're not fabricating air conditioning ducts or piping systems here. Instead we're dealing with a DYNAMIC system with parameters changing by the millesecond.

Let's hear some good sound DATA with that in mind.

(I'm really not a BAD person).

[Rex Schimmer]

Interested bystander,
This does not happen to be opinion or theory but fact: The aero drag caused by internal flow of a duct is related to the ratio of the inlet area and the outlet area. If the outlet area is zero then there is no aero drag casued by the duct becasue there is no flow thru the duct. In the case of an engine inlet duct the outlet is the engine intake, this is assuming that the duct is sealed and does not leak air, the aero drag internal to the duct is very low, assuming that the duct and the inlet plenum are designed to expand and reduce air velocity, simply because the air velocity is very low. If you run a long, non expanding duct back to the engine inlet you can calculate the velocity thru the duct by calculating the amount of air that the engine is comsuming in cu. inches/min and divide by the area of the duct in inches squared and you will get the air velocity in inches/min. You may be surprised what the internal air velocity is. If you have an 8 inch dia duct and it is connected to a 500 cu. in engine at 8000 rpm and the VE is 100% the air velocity thru the duct is 37.7 mph. If you go to a 10 inch duct it is 24 mph. This shows two things: First you want to expand your inlet to get the velocity of the air down which will reduce the internal drag and you want the duct as big as possibile and also as short as possible before you expand it to get air velocity down and recover pressure. D.B. still rules here.

Not theory! FACT!

Rex

[Jonny Hotnuts]

If you really want to open a can of worms the volume of the airbox is made to take advantages of resonate frequencies. There are natural harmonics that the engine will generate by the intake pulses and if you can build a box with the correct internal volume you can gain HP overall and have this gain peak at different levels depending on the airbox tuning.

YOu can take a lightly modified busa *especially with a larger bore, and gain HP (I hear up to 5 hp) just by increasing the volume of the box based on changing the resonate tuning of the box.

[1212FBGS]

Nutz...how exactly would you do that on a Busa? the cut and paste version would be OK
Kent

[fredvance]

Kent, how much bigger is your air box than a stock busa?  Fred

[interested bystander]

Going back to the query that started this thread, what I believe is that LeFever was trying to encourage comments specific to the the modified roadster.

Rex , you've enlightened all with your clear description of what I deem a laboratory scenario of which Mike's credentials  indicate he's well aware of.

My impression was "How would one design a duct system specific to my application?" was what he asked.

In  other words, how does one design a system that takes the specifics of the vehicle and then optimize its' intake duct to allow for optimum air delivery over the range of, for instance, a fifty mile an hour push-off to a 300 mph clocking exit speed.

No criticism EVER intended Rex with your comments on the forum!

Someday we'll talk!