From SmartCockpit - Airline training guides, Aviation, Operations, Safety

The large vortex generator installed on the inboard side of the nacelle is commonly called a nacelle chine. These devices are used on both the 767 and 737 airplanes. Modem efficient aircraft utilize high bypass ratio engines mounted from pylons off the wing. In order to minimize landing gear length (minimize weight) and to maintain adequate runway clearance (minimize foreign object ingestion), the engines are installed in relative close proximity to the wing.

This close coupling of the large engines with the wing results in increased flowfield interaction between the engines and the wing at high angles of attack, and can result in reduced airplane performance unless special consideration is given to counteracting these effects. One such adverse interaction is a loss in maximum wing lift capability in the landing configuration. At the high angles of attack required at low airspeeds, vortices are shed from the fan cowl. For engine installations where the nacelle is located further below the wing, such as JT9D installations on the 747, these vortices pass underneath the wing. For more close coupled nacelle configurations, these vortices flow over the top of the wing and interact with the wing flowfield. The effect of these vortices is generally favorable as long as they remain intact. Unfortunately the wing, at high angle of attack, will impose large adverse pressure fields on these vortices as they flow rearward along the wing surface.

These vortices will break up and burst, causing the boundary layer air over the wing behind the engine to separate. This results in lower maximum lift levels than would be the case with less closely coupled nacelles.

The solution was the development of a large vortex generator installed on the inboard side of the engine nacelle which was sufficient to delay the nacelle vortex bursting phenomenon. The Boeing invention disclosure identifies this as a vortex control device (VCD), but it is more commonly known as a nacelle chine. The nacelle chine was sized and positioned on the inboard side of the nacelle to control where the nacelle vortex is shed so that it will not attach to the wing. The strong vortex shed by the nacelle chine will cause the nacelle vortex to flow over the wing delaying the wing influence to burst the vortices until a higher angle of attack. The result is that the lift loss is essentially regained.

Due to air condensation under certain atmospheric conditions, the vortex shed by the nacelle chine can be clearly viewed from the cabin. In terms of airplane performance, the nacelle chine reduced approach speeds by 5 knots and landing field lengths by approximately 250 feet for the 767-200. The nacelle chine is a significant contributor to the short field performance of the 767.

Chines/strakes whatever they are called are there to direct airflow onto the leading edge devices, thus reducing stall margins. From my distant 767 days, Boeing reckon 4 knots, but like I said , distant days!

Previous thread on topic:

nacelle fins?

Thanks for the link, Checkboard!

Al this goes to prove how inobservant one can be... I've seen vortex generators in all sort of places, but never noticed them on the nacelles.

CJ

They also reduce spanwise flow and hence induced drag. Fitted to many fighter types too. The cold war quip was they were fitted to prevent airflow defecting.

They fly better
 

Many moons ago, I asked a Flight Engineer why the strakes were attached to the engine cowling on the DC10.
"Hmmm.." he said, "I think it makes them fly better when they come off."

very good example
 

i found picture for this discussion.http://www.globalsim.web.id/publicse...ortexPhoto.jpg

fnp90,
Many thanks, magic photo.
It's not often a discussion subject is so well illustrated.

CJ

Main point is that the nacelle chines result in stall speed reduction. I would be extremely surprised to see any MMEL/AMM permission for an asymmetric absence of chines.

From consideration of the certification effect on performance data and OEM workload to cover the delta, I would be surprised to see any MMEL permission for symmetric absence.

Different matter for the "usual" rows of small VGs - there may well be permissions for some to be missing.

All good words above

But just how critical are they for dispatch?

On the A320/1, not too critial. The CDL allows one or all of them to be missing with various penalties. For example, the 320 has a penalty of about 1.3 tonnes to the RTOW, 5kts to be added to the VApp and LDR increased by 8%.

The 320 has them on one side of the cowling, the 321 both. Flying a 321 with one missing isn't that unusual if a 320 cowling has been fitted as a temporary measure.

I have a photo of a B767 with the left engine with 2 strakes and the right engine with none! Not intentional that's for sure.

The CDL allows one or all of them to be missing with various penalties

Clearly

(a) I stand surprised

(b) AI saw a commercial advantage for the CDL entry.

No performance problem operating without them with stall-related penalties. The concern relates more to what happens at stall ... one presumes that the stall characteristics of the A320/1, with asymmetric chines, are relatively benign ?

Flying a 321 with one missing isn't that unusual if a 320 cowling has been fitted as a temporary measure

I don't think one would expect to see any noticeable (to the pilot) difference regardless of what was missing ... other than in the stall regime.

A quick looksee through the FAA MMEL doesn't immediately show an equivalent MMEL provision. What does AI term the devices ?


As a consideration, I am aware that some of the light twin VG mods (which have the same intent to control stall speed) can demonstrate "interesting" roll character at the stall ...

''AI saw a commercial advantage for the CDL entry. ''

Possibly, but the FBW Airbus designs have so much low speed protection, they and the regulating authorities don't consider the risks significant.

''No performance problem operating without them with stall-related penalties. The concern relates more to what happens at stall ... one presumes that the stall characteristics of the A320/1, with asymmetric chines, are relatively benign ?'''

The A320 series is unstallable in normal law.

''I don't think one would expect to see any noticeable (to the pilot) difference regardless of what was missing ... other than in the stall regime.''

As above. You can't stall it in normal operations. In Alternate law, the protections are replaced by a stall warning at 1.03 VS1g. I don't know if the stall characteristics aren't affected, or the it wasn't considered significant - or if the margin takes a missing strake CDL into account. The instances of going into alternate law are very rare. And the crew will have aded the 5 knts to VApp for added protection anyway.

''A quick looksee through the FAA MMEL doesn't immediately show an equivalent MMEL provision. What does AI term the devices ?''

'Nacelle Strakes'. And they are a CDL (Configuration Deviation List) item and not an MMEL item.

some more
 

as i stood in front of 737 i saw this cowling chine and wonder of its purpose. so i dug internet and found those discussion from indonflyer dot net. since they discuss in indonesian it is relatively difficult to understand (although I'm Malaysian). guess need time to understand. here some pictures from indonflyer...

(translated)
at low speed nacelle generate it's own vortex (vortex started before chine)
p/s: this picture should be without chine to avoid confusion.
http://www.globalsim.web.id/publicse...hineVortex.jpg

to overcome, chine placed. (vortex started from chine)
http://www.globalsim.web.id/publicse...hineVortex.jpg

i know its a little off topic and a little smaller than an a340 but on en emb 120 on the r/h wing root faring there is a "vortice generator" (i use the term lightly). Its whole purpose in life is to reduce vibration on the vertical and horiz stabs, was making pax in the back sick, fit one of these and the pax stopped getting sick. Could it be something similar? (just asking)

ernie,
Probably much the same thing.
A boundary layer going turbulent can cause a lot of low frequency noise and/or vibration, and even if not really audible, it can still make the pax uncomfortable, and possibly even sick.
Any photos of the 'vortice generator'?

fnp90,
Very clear drawings! Thanks.
Looking at your photo again, what aircraft is it? A340?
Are the two "dotted lines" on the wing, in line with the vortex and the nacelle, also two rows of vortex generators?

CJ

Vortex generators
 

Slightly off topic, but.

On the Airbus A300-B4 (and probably -B2) there are Vortex Generators on the upper wing surface, forward of the outboard (low speed) ailerons.
I always thought these were to keep the airflow active over the ailerons in the low speed configuration when approaching or in the stall.

So my question is, Why do these vortex generators still appear on the A300-600 when it does not have low speed ailerons?

Any ideas.

Safe flying.

CJ,

in my opinion the picture was A340. but this one looks "VERY CLEAN" and small chine also... correct me if im wrong.
http://img137.imageshack.us/img137/88/a340300wingw.jpg

-a picture worth a thousand words..!-

CJ quoted: "Are the two "dotted lines" on the wing, in line with the vortex and the nacelle, also two rows of vortex generators?"

im no expert, from the picture seem yes. but from what i read it is not nessasary vortex generator (VG) to be in-line with vortices but it help to channel or to smooth the vortices hence reduce seperation. here some pictures again...:}

a) Large region of shock-induced flow separation on a swept wing
http://www.aerospaceweb.org/question...09-oil-vis.jpg
b) virtually eliminated by antishock bodies