The purpose of Air-intake/Scoop?

[xpensive]

An enginnering collegue of mine, with little interest in F1 per se, asked me the other day about the purpose of the Air-inlet/Scoop on the cars.

I am certain this topic has been discussed on several occations here and please correct me where I'm wrong.
Anyway here goes, all based on the conventional formula for dynamic pressure, "speed sq. times density over two", where density is set to one.

Imagine that a 2500cc/1900Rpm four-stroke engine, with 100% filling of combustion chambers, would consume 380 liters (0.38 m^3) of air, in an F1 car travelling at a speed of 300 km/h (83.3 m/s). This means a need for an air intake area of 45.6 cm^2 to have the same intake-speed as said travelling speed.

The extra static pressure in the air-intake to force-fed the engine comes from the difference between travelling-speed and intake-speed. When an intake area of 200 cm^2 seems about right, it makes for a speed difference of 64.3 m/s, which creates an extra static pressure of 2.07 kPa.
Theoretically translating to some 15.7 extra horsepower if we started out with 760.

But the extra static pressure acting on the flat intake surface also creates an increase in additional air-resistance on the car. An extra static pressure of 2.07 kPa over 200 cm^2 at 64.3 m/s means a loss of 3.6 Hp.

Conclusively, a net gain of a mere 12 Hp, is the above too simplified, anyone?

[xpensive]

I am hoping for an aerodynamacist here.

[Ian P.]

When it comes to aerodynamics....some say I suck... oh well.

A quick independant run at your concept comes up with pretty much the same result.
If the engine is 2.4 L at 19,000 rpm it will draw in around 570 L/sec. This is based on a 150% cylinder filling efficiency. Not out of line as I understand for a modern "tuned" intake and exhaust system.
For a 40 square inch intale (6x6 inch roughly) the scoop inlet air velocity will be around 20 ft./sec.
If the car is travelling at 180 mph (300 kph) the differenc in air velocity would generate a net positive pressure of 0.29 psi, or 1.99 kPa.
Either we are both geniusses or we made the same errors.
Bottom line is around a 2% gain in air density at the intake plennum.
A bigger inlet will yield a geater pressure gain but at the expense of drag. All in all, I would expect the additional pressure to be beneficial and at least cover the losses across the air filter and to improve the overall balance inside the air-box to ensure equal filling of all cylinders.

[xpensive]

When a 2% gain in air density is pretty close to 102.07 kPa, I settle for the genius explanation, thank you.

[xpensive]

Well Ian P., no takers on this topic, not even Ciro found it worthwile to comment.
Wonder if it was too theoretical, handled many times before or simply uninteresting?

[Ian P.]

Me BORING..what next.
Probably acuse me of being sarcastic too.

The scoops do look better than NACA ducts and provide loads more room for sponsors.
Probably the biggest benefit.

[xpensive]

Well, I guess I failed to initiate a technical thread on this subject, i wonder why Ian P.?

[xpensive]

Anyway, my aim was to initiate a technical discussion over why F1 engineers finds it worthwhile to carry around such a piece of bodywork, disturbing the airflow to the rear wing, for a contribution of a mere 10 Hp at full speed?

Just providing room for sponsor logos?

[twoshots]

You might find this discussion helpful, it has some views on the change in airboxes from 70s onward. Interesting pics and scarbs' helpful post (as ever).

viewtopic.php?f=6&t=4007

[xpensive]

Interesting twoshots and many thanks.
I am surprised however that nobody bothered to back up their speculations with any corresponding calculations.

Fact of the matter is, that no matter how big your scoop/snorkel/air-intake is, the additional pressure will never be higher than the dynamic pressure generated the car's travelling speed.

Even at 300 km/h (188 mph), this corresponds to no more than 0.035 atmospheres,
while due to the squared relation to the speed, at 150 kmh only 0.009 is left, which is next to negligable in the context.

After you added the substanial increase in drag and disturbance of the rear-wing, this makes me very puzzled. Advertising space, is that it?.

[twoshots]

See tech reg 3.16 for the toblerone rule scarbs mentioned in the other thread. This gives you your advertising space.

3.16.1 With the exception of the opening described in Article 3.16.3, when viewed from the side, the car must have bodywork in the area bounded by four lines. One vertical 1330mm forward of the rear wheel centre line, one horizontal 550mm above the reference plane, one horizontal 925mm above the reference plane and one diagonal which intersects the 925mm horizontal at a point 1000mm forward of the rear wheel centreline and the 550mm horizontal at a point lying 50mm forward of the rear wheel centreline.
Bodywork within this area must be arranged symmetrically about the car centre line and, when measured 200mm vertically below the diagonal boundary line, must have minimum widths of 150mm and 50mm respectively at points lying 1000mm and 50mm forward of the rear wheel centre line. This bodywork must lie on or outside the boundary defined by a linear taper between these minimum widths.

[xpensive]

Thanks again "Junior", for clearing things up.
This is what I figured, once engineers and wind-tunnels came into play in the nineties, it was discovered that those arrangements were of little use performance-wise.

But the Intel logo fits nicely on the BMW scoop, no?

[twoshots]

The airbox size is probably determined by engine considerations with aero having very little to do with it. The drag is offset by the small ram effect and the engine gets enough clean air throughout it's operating range.

With the engine mounted with the weight at the bottom the intakes are on the top. Much easier to get a nice clean airflow from the top as well as the airbox being lightweight it doesn't raise the cg. Being above the drivers head the air will be as cool (I wonder if the air 1m above the track is actually cooler?) and 'clean' (both particulates and turbulence) as is possible. Stick that with the roll structure and toblerone rule and I guess it's just the optimum place for it.

[xpensive]

Now that you (twoshots) have explained that the structure in question is in the rules, I am absolutly certain that John Barnard was correct with the original atmospheric Ferrari 640 in 1989, which had no snorkel, but an elegant intake on either side behind the driver's helmet.
See image from F1Technical database.

[timbo]

Now that you (twoshots) have explained that the structure in question is in the rules, I am absolutly certain that John Barnard was correct with the original atmospheric Ferrari 640 in 1989, which had no snorkel, but an elegant intake on either side behind the driver's helmet.
See image from F1Technical database.

I read somewhere, that intake area is subtracted from cross-sectional area. Anyway, it acts differently than the flat section, and as engine consumes air, the pressure build-up is lower. There's still drag penalty (otherwise everyone would use intakes like on Jordan 198 or Williams FW13B), but it is well offset by more power.
As for 640 original intakes it was abandoned because it worked worser. Air volume that is going thru intakes is very sensitive to boundary layer and vortices, you can see how Newey created intake with boundary layer "detacher" on Williams FW19 (compare to Williams FW18), and on next year every other car had same solution.