Reducing the drag of a two element wing through stall

[forty-two]

This whole thing reminds me of an old Loony Tunes cartoon, where an elephant is pitching in a baseball game, and the players are up in arms. I can't beleive I can remeber this, and the umpires answer.

"There's nothing in the rule book that says an elephant can't pitch"

http://www.youtube.com/watch?v=7dIdBz_OdpQ

3:10!

Wierd thing is, I remember seeing this too!

[Sean H]

Bobo even had a "snorkel", maybe that is where the Macca guys got the idea?

[cornermarker]

Just to show the behaviour a single element wing would exhibit with a blown section. Done on one of my home computers very very quickly, maybe 15 mins from drawing the section to acceptable convergence.

I'll bite. My liberal arts degree doesn't help me read these, but: I see a couple of things. An overall increase in velocity under the wing (good for a diffuser?). But at the wing itself a large vortex has formed downstream of the jet. And air upstream of the jet has slowed.

Also, the velocity above the airfoil has increased, but above and behind the airfoil it is slower. Velocity immediately under the wing is very low. Higher pressure below than above.



The overall effect is like changing the profile of the wing. With this new profile (shaded area) the flow stays attached and highly energized much longer than without the jet.

Overall, less disturbance to the air downstream of the airfoil.

I only wish I could see a higher aoa model, just with a lower pressure jet, say, yellow/green I'm guessing the size of the vortex correlates to the pressure of the jet.

Kelpster

[Ciro Pabón]

Well, there was also this film about a mule that could kick the ball during football games... Perhaps they could use it as a driver. There is nothing in the regulations saying that a mule cannot drive.



Now, if we could train a monkey to drive F1 cars, we could save some weigt for use as ballast...

[tinhouse]

Now, if we could train a monkey to drive F1 cars, we could save some weigt for use as ballast...

Tried.



Failed.

[forty-two]

Probably someone else has asked this already so apologies if I am going over old ground here... BUT

Has anyone considered what effect running the snorkel/airbox solution employed by the MP4/25 in heavy rain might have?

Presumably, if the theories about "driver covering hole with foot/knee/other" are correct, in a wet race, the cockpit will begin to fill with rainwater from snorkel whenever "hole" or vent is not being covered?

Doesn't sound like such a good idea to me if that IS the case.

Thoughts anyone?

[autogyro]

Probably someone else has asked this already so apologies if I am going over old ground here... BUT

Has anyone considered what effect running the snorkel/airbox solution employed by the MP4/25 in heavy rain might have?

Presumably, if the theories about "driver covering hole with foot/knee/other" are correct, in a wet race, the cockpit will begin to fill with rainwater from snorkel whenever "hole" or vent is not being covered?

Doesn't sound like such a good idea to me if that IS the case.

Thoughts anyone?

Just carry a patch. There is no proof yet that there is a knee hole. I still believe the job can be achieved with a tunable volume of bleed air set to break the slot flow at chosen speeds.

[DaveKillens]

Probably someone else has asked this already so apologies if I am going over old ground here... BUT

Has anyone considered what effect running the snorkel/airbox solution employed by the MP4/25 in heavy rain might have?

Presumably, if the theories about "driver covering hole with foot/knee/other" are correct, in a wet race, the cockpit will begin to fill with rainwater from snorkel whenever "hole" or vent is not being covered?

Doesn't sound like such a good idea to me if that IS the case.

Thoughts anyone?

That's a good point, and I anticipated this problem. That is why I specified some form of "plenum", where the hole is. I never went into detail about this "plenum", but it would be deep, and the incoming air would have to circulate inside this box first. By adding a small drainhole in the bottom, this would prevent water from flooding the driver's feet and legs in case of rain. It's basically an air/water separator.

But then again, if rain was expected, having a device that reduces rear wing downforce is a very bad idea. If any race is forecast to definitely rain, I expect McLaren to remove the scoop and disable the system.

[forty-two]

People, I apologize. I haven't noticed that this thread and the McLaren MP4/25 Air Intake were the same. I'll merge that thread with this one in a couple of days, so everybody notices and (I hope) knows where to post.

Nice one! Thanks Ciro.

[Balt23]

has anyone considered that what the the slot is always active, thus it is always acting as an active flow control device to keep the second element of the rear wing working (unstalled).

when the driver closes the duct, the blowing is inactive and so the wing stalls.

as mentioned on the first page of the thread, the induced drag due to the increased lift when the second element is unstalled is higher than the form drag. so when you stall the wing by turning off the blowing element you get reduced amounts of drag.

also on the official f1 site they also show a second element blowing air upwards from just above the light structure above the diffuser. this could also serve to increase circulation over the rear wing which would dissapear when the slot is closed.

[forty-two]

Probably someone else has asked this already so apologies if I am going over old ground here... BUT

Has anyone considered what effect running the snorkel/airbox solution employed by the MP4/25 in heavy rain might have?

Presumably, if the theories about "driver covering hole with foot/knee/other" are correct, in a wet race, the cockpit will begin to fill with rainwater from snorkel whenever "hole" or vent is not being covered?

Doesn't sound like such a good idea to me if that IS the case.

Thoughts anyone?

That's a good point, and I anticipated this problem. That is why I specified some form of "plenum", where the hole is. I never went into detail about this "plenum", but it would be deep, and the incoming air would have to circulate inside this box first. By adding a small drainhole in the bottom, this would prevent water from flooding the driver's feet and legs in case of rain. It's basically an air/water separator.

But then again, if rain was expected, having a device that reduces rear wing downforce is a very bad idea. If any race is forecast to definitely rain, I expect McLaren to remove the scoop and disable the system.

Or maybe a bit of high-tech gaffer tape over the inlet like they used in testing?

[autogyro]

has anyone considered that what the the slot is always active, thus it is always acting as an active flow control device to keep the second element of the rear wing working (unstalled).

when the driver closes the duct, the blowing is inactive and so the wing stalls.

as mentioned on the first page of the thread, the induced drag due to the increased lift when the second element is unstalled is higher than the form drag. so when you stall the wing by turning off the blowing element you get reduced amounts of drag.

also on the official f1 site they also show a second element blowing air upwards from just above the light structure above the diffuser. this could also serve to increase circulation over the rear wing which would dissapear when the slot is closed.

The outlet above the diffuser could be the alternate flow outlet when the flow is cut off from the wing slot. It would flow air into the low pressure area behind the car, which would reduce diffuser DF and reduce drag from the diffuser.

[forty-two]

has anyone considered that what the the slot is always active, thus it is always acting as an active flow control device to keep the second element of the rear wing working (unstalled).

when the driver closes the duct, the blowing is inactive and so the wing stalls.

as mentioned on the first page of the thread, the induced drag due to the increased lift when the second element is unstalled is higher than the form drag. so when you stall the wing by turning off the blowing element you get reduced amounts of drag.

also on the official f1 site they also show a second element blowing air upwards from just above the light structure above the diffuser. this could also serve to increase circulation over the rear wing which would dissapear when the slot is closed.

The outlet above the diffuser could be the alternate flow outlet when the flow is cut off from the wing slot. It would flow air into the low pressure area behind the car, which would reduce diffuser DF and reduce drag from the diffuser.

I speculated earlier on about this for a while and wondered if McLaren might make this a tri-stable device where the airflow has THREE possible destinations. One could perhaps be to "stall" the wing (for the straights), one could be to add diffuser DF (the default outlet), and finally another could be to INCREASE drag in order to act as an air brake to help reduce the workload of the brakes with these new heavier cars (perhaps the "trigger" for this could be hidden beneath the brake pedal?). I imagine that the final suggestion would require a secondary snorkel to supply signal air, but the MP4/25 has a matching panel on the R/H side of the tub which COULD be used for such a thing.

[kalinka]

ScarbsF1 wrote this on his blog :
"As no flow passes to the rear wing vent the rear wing produces its normal amount of downforce to aid cornering. However on long straights the driver can move his leg from the brake pedal and press it against the opening in the duct, this sends the airflow from the snorkel through the duct to the rear wing vent. This airflow disrupts and stalls the wing adding some 3-4mph (6kmh) to the cars top speed. As he moves his leg from the duct to the brake pedal the airflow returns to the previous condition and the rear wing gains downforce once more."

I a bit confused about this. I was following this forum for a long time, and I thinbk most of the people here agreed, that blowing the wing reduces possibility of stalling, and increases downforce. I found some studies myself about this on internet. So for me, ScarbsF1 is wrong. The effect is opposite. When you go on straight, you have to CLOSE the snorkel, therefore disabling the blowing of the wing, to INDUCE stall. Am I wrong ?

[hollus]

It depends on in which direction the air is being blown trough that slot.
If it is blown parallel to the wing chord, then probably the normal mode of operation is blown and cutting the airflow in the straight causes the wing to stall partially.
On the other side, if air is blown perpendicular to the wing's chord, then probably the normal mode of operation is non-blown, and blowing in the straight would disrupt the normal flow reducing both drag and downforce.
What is really happening, unless one works for Mclaren, is AFAIK unknown.