Fins on Engine Cowling

[mmrassi]

Hi,
Have alook at this picture:

http://www.airliners.net/photo/Lufthansa/Airbus-A340-642/0596750/M/ (http://www.airliners.net/photo/Lufthansa/Airbus-A340-642/0596750/M/)

Here is mentioned that these fins are used to reduce turbulence, I would like to know more about these devices and why they put them on engine cowlings? Is there any major source of turbulence around the engines AND Does this method affect the noise (thanks toolowtoofast (http://www.pprune.org/members/187317-toolowtoofast) ) polution made by the plane?( I heard this somewhere but still unsure about the truth?)

Does Boeing use the sameway?

[barit1]

The "fins" (or "strakes") are really vortex generators, and are an important part of high AOA aerodynamics for the wing. I recall on the DC-10 they reduced the stall speed perhaps 10 kt. or more. They are your friends.

[toolowtoofast]

sound polution????? (sic)

clowns on the tube/train/bus with loud doof doof music on their I-pods - now THAT'S noise pollution.

aircraft engines - music :)

[kijangnim]

Greetings
Indeed they are vortex generators, and usually vortex generators are uses to put some energy back to the boundary layer, in this case they act exactly at the pods (engine to wing fixing), avoiding the area just behind the pods to become turbulent at high AOA. i.e., during takeoff, approach and landing :)

[NinerVictor]

ASFKAP got the name right. There is a write up on this in the smartcockpit.com website. You can download the document here (http://www.smartcockpit.com/pdf/flightops/aerodynamics/42).

9V

[OSCAR YANKEE]

Take one off, and you suffer a performance penalty.
If memory serves me right it's about 4-6 tonnes on both the 737 (CFM) and A319 (CFM).......:eek:

M

[Tacolegend]

Airbus calls them strakes. :ok:

[getsetgo]

vortex generators delays the separation of airflow( profile )arround the airframe thereby reducing the drag which is created when the airflow separates from the skin.
nothing to do with turbulance as your post indicates.
see book MECHENICS OF FLIGHT BY A.C. CERMODE:ok:
it explains allmost all aspects of air.
theory of flight:ok:
good luck

[Blinkz]

The picture is a little misleading to the actual angle of the vanes as the engine cowling is up.

I think the vanes are used to produce a stabilising force to stop the engines from vibrating/moving too much, as well as acting as vortex generators.

[kijangnim]

Grettings
GETSETGO
I have spelt it turbulent as turbulent airflow (drag) as opposed to laminar airflow.:ok:
turbulance is something else :}

[wonderboysteve]

They are there to compensate for the cut out in the leading edge devices caused by the engine pylons. As well as the obvious reduction in slat span, the cut out affects the three-dimensional lift distribution. As the LE devices have a critical role in defining CLmax, this accounts for the effect on stall-speed (and hence weight).

[kijangnim]

Greetings
Wonderboysteeve :ok::ok:

[sinkingship]

Just to add the main use is for high AOA and pre stall characteristics, if you look majority are only installed inboard only, because fan cowls can be fitted either side of an engine it can be un-noticed defect. I think some a/c such as an A319 may have fins either side though.

[Antunes]

if you look majority are only installed inboard only, because fan cowls can be fitted either side of an engine it can be un-noticed defect. I think some a/c such as an A319 may have fins either side though.


You will find strakes on both sides on all A319 aircraft and on A320 LIP (Lift Improvement Package) aircraft. This is also the easiest way to distinguish a standard A320 from a A320 LIP. :8

This extra engine strake together with several modifications on the leading and trailing edge of the aircraft enables you approach about 6kt to 7kt slower than the standard aircraft.

[Farrell]

Have seen pictures one or two 737s with the cowlings mixed up so two vortex generators on one engine and none on the other or maybe it might have been with one on each nacelle but on the wrong side.

I think Boeing may have modified the cowlings at this stage to prevent this.

[kijangnim]

Greetings
Two on either side and none on the other, is a bit odd, on day in one airline I have flown with maintenance put them on the other side the boeing rep went mad, I think that it is better tol look into the CDL to check that it is normal configuration :ok:

[getsetgo]

Kijangnim

Warm greeting

Turbulence I was referring to mmrassi”s post not yours. I did not read or reply to your post.

Vortex generators are always fitted on the upper side of lift generating surfaces ,at an angle to the airflow to generate vortex and delay separation of air on the upper side of the wing ,this increases the lift generated by the wing.
Vortex generator increases the lift/performance, doesn’t reduce drag.
In this picture the small fin on the engine cowl is bifurcating the the airflow and optimizing its distribution around the pillion and the wing, by directing more towards lift producing surface and less towards pillion.
Thereby generating better performance .
Fin position, angle ,size & shape is the result of extensive wind tunnel tests. (NO GRAB)
There is no need to create vortex ahead of aerofoil.
that’s why this fin is not called vortex generator.
Other aspects
Could be this small metal piece is the waist left over after the a/c was complete and manufacturer thought of some cosmetic work around the engines.
And When it breaks manufacturer can sell new one for exorbitant amount as spares.:)
or to make pilot work harder while doing the walk around:}

[Leave 5 on the glide]

I believe the idea is to direct the nacelle vortice over the wing, so as it doesn't interact with the wing flow and destroy the boundary layer (causing separation).

[ChristiaanJ]

Thanks for this discussion about an interesting example of a vortex generator!

Ever looked at a Concorde?

There are two 'vortex generators/chines/strakes' (whatever you want to call them) on the forward fuselage, roughly under the cockpit windows.

They don't look prepossessing at all, but they really "stick down'' the airflow over the entire top of the fuselage, even at quite high angles of attack, and prevent the lower part of the vertical tail ending up in a highly turbulent airflow. It's one of the reasons the Concorde vertical tail isn't all that big, compared to some subsonics, even if she lands at a higher angle of attack.

And an interesting snippet: they were already in place for the first flight of the first prototype in 1969.....

CJ

[barit1]

Ever looked at a Concorde?

There are two 'vortex generators/chines/strakes' (whatever you want to call them) on the forward fuselage, roughly under the cockpit windows.

Ditto later DC-9's beginning with the series 50. Probably the MD-80/-90/717 too, although I haven't taken time to look up photos. :)

[Brian Abraham]

From SmartCockpit - Airline training guides, Aviation, Operations, Safety (http://www.smartcockpit.com/pdf/flightops/aerodynamics/42)

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.

[Lightning5]

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!

[Checkboard]

Previous thread on topic:

nacelle fins? (http://www.pprune.org/tech-log/9228-nacelle-fins.html)

[ChristiaanJ]

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

[ARINC]

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.

[quartermilltopo]

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."

[fnp90]

i found picture for this discussion.http://www.globalsim.web.id/publicservice/Vortex/NacelleChineVortexPhoto.jpg

[ChristiaanJ]

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

CJ

[john_tullamarine]

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.

[lomapaseo]

All good words above

But just how critical are they for dispatch?

[Dan Winterland]

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.

[keel beam]

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.

[john_tullamarine]

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 ...

[Dan Winterland]

''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.

[fnp90]

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/publicservice/Vortex/NacelleNoChineVortex.jpg

to overcome, chine placed. (vortex started from chine)
http://www.globalsim.web.id/publicservice/Vortex/NacelleChineVortex.jpg

[ernie blackhander]

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)

[ChristiaanJ]

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

[dixi188]

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.

[fnp90]

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..!-

[fnp90]

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/aerodynamics/area-rule/mach09-oil-vis.jpg
b) virtually eliminated by antishock bodies

[HarryMann]

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.Could some please stop confusing turbulent boundary layers with separated flow... a turb b.l. is not going to do that, heavily separated flow might cause buffeting & noise though

Turbulent boundary layers are much more resistant to separation than laminar ones.. some obviously know this, quite a few don't. That's why we stir up the flow in the boundary layer (with say voretx generators), to get an early transition to turb b.l and re-energise it.

It's interesting some of the differences in minimum speeds quoted for flow modifiers around the nacelle/wing junctions - they're quite significant.

To whoever it was suggested that Boeing 'invented' the nacelle strake or vortex generator - sounds like another re-writing of history to me :rolleyes:

[ChristiaanJ]

Sorry, Harry, wrong terminology... blame extreme age of poster.

CJ

[CV880]

Back in the late 70's when I briefly worked for a DC10 operator I came across a file of newsletters produced by Douglas (I think they were titled "Know Your DC10" or something similar). One of them discussed the reason for nosecowl strakes which was as described in depth in several earlier posts (disturbed airflow off the nosecowl in the landing configuration interacting with the gap in the LE slats for the pylon was going to result in missing their target landing distance due to too high a reference speed). According to the article they started out with a strake on the inboard side that extended from the nosecowl right across the fan cowl and then shortened it bit by bit until they established the minimum size of strake that allowed them to acheive their target landing distances. Another stake was installed on the outboard side to make the nosecowl fully interchangeanle L & R.

[barit1]

And then one operator noticed the techs were leaving spanners, etc. in the valley between the cowl and strake, and so removed the latter to prevent FOD. :}

[Dan Winterland]

FNP's picture in post 28 has 4 CFM56s, but isn't a 340 as i) judging by the engines, the wing is too small ii) the wing has vortex generators which the airbus FBW designs don't and iii) that wing has Kruger style LE devices which airbuses don't. It's either a 707 airframe which would make it an E3 or a C135 derivative or a DC8 conversion. The CFMs weren't certified on civil 707s and as the engines have the CFM logo which wouldn't be put on a military aircraft, I reckon it's a DC8.

[Runaround Valve]

Not a DC-8 as none had leading edge flaps/slats. By the vortex generators on the wing it has to be a 707. Not up to speed re Airbus but think that they would have an extendable leading edge like a B767.

[Dan Winterland]

They do. In fact, I think it's this aircraft. The one and only prototype 707-700.

http://www.simviation.com/hjg/aircraft/boeing/b707-700/b707-700_boeing_cfm_test_1979_700_n707qt_NEW.jpg

A website on the 707s history mentions that it wasn't continued because it would compete with the 757. However, someone I know who was partly responsible for the introduction of the KC135R (with CFM56s) into the USAF mentioned that the aircraft had handling issues which Boeing realised would make civil certification difficult.

[fnp90]

Dan Winterland, thanks man...