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CS-TMX
5th Sep 2004, 05:04
Why do they have vortex generators?

http://www.airliners.net/open.file/653082/L/

Best regards

idg
5th Sep 2004, 16:09
To help energise the airflow over the outboard section of the wing to ensure the tip didn't stall. The a/c had extended wing tips as they are -500 airframes and had a problem at high speed where a jet upset situation could end up with the a/c 'winding up' to excessive G. There were several systems in the a/c to help prevent the problem which was initially triggered by the active ailerons simultaneously pitching up to relieve G load caused by a gust. These systems were called ACS (for active control system) MDLC (manouvering direct lift control) and RSB (recovery speed brake).

CS-TMX
5th Sep 2004, 16:34
Hi idg

Thanks for your explanation though I am aware of what vortex generators are and what they do as well as MDLC or ACS.

But those vortex generators are only found on RAF L1011s. No civil TriStars being -500 with ACS or standard lenght version have them. So I was searching for a specific reason related with their tanker role, if it exists.

I mean, ok they have vortex generators to prevent bondary layer separation on that zone, but why? Do RAF L1011's usually fly at a higher speed near from Mmo causing compressibility problems? Or is there another reason?


http://www.airliners.net/open.file/233612/L/


Best regards,

idg
6th Sep 2004, 00:21
CS,

Well the a/c weren't modified aerodynamically in any way. It's my recollection that all civil TriStars had the vortex generators.

There were two lots of a/c though...ex BA and ex PanAm. There were significant differences in that obviously they were certified by different agencies. The PanAm a/c had digital AFCS when they arrived no RSB, and different schedules for the MDLC. FAA had not found it necessary to fit this spec as did the Brits.

It is probable therefore that the photo youv'e posted is of an ex BA, since these were the only ones converted to tankers and that the the votex generators were only fitted to the BA a/c....memory is a bit hazy on this so will have to check.

Incidentally even the ex BA a/c had structural differences. The first two came from Lockheed with weaker outer wings since they were originally built on the line with 'normal' -200 wings and only during flight test were they stretched. All later production a/c had 'stronger' outer wing sections and thus had a different MDLC schedule!

Denzil
6th Sep 2004, 01:15
It was the digital vs analogue AFCS that made the difference. The analogue had the vortex genny's fitted. When the RAF had the ex Pan Am aircraft standardised with the analogue the vortex gennys were fitted as part of the mod.

CS-TMX
6th Sep 2004, 03:26
Thanks, I think now I have the answer. FLew many times TAP TriStar500s as a pax and they hadn't those vortex gennerators.

When you say digital vs analogue AFCS can we distinguish it externaly by looking to the glareshield?

Is this the analogue one:

http://www.airliners.net/open.file/423373/L/


and this the digital one:

http://www.airliners.net/open.file/458794/L/


???

Then, I think all standard lenght TriStars had analogue AFCS but had no vortex generators since they were bigger and weren't fitted with ACS which supposedly was a system that could aggravate the jet upset phenomena.

Sorry if I'm saying a big mistake:oh:

GlueBall
6th Sep 2004, 03:50
It's conceivable that the vortex generators were fitted at Marshall Aerospace at Cambridge during the tanker conversion, probably to minimize turbulence for trailing aircraft.

Volume
6th Sep 2004, 06:36
Do the L1011 tankers have pods, or just a central fuelling station at the fuselage ?
If they have pods installed to the outer wing, these might disturbe airflow there, so the VG had to be installed to counteract the effects. On other tanker conversions there were also some vortex generators added to the outer wing to minimise pitch effects occuring at high speed with the pods installed.
Does the 1011 have a supercritical wing ?

idg
6th Sep 2004, 15:07
Vol,
No the TriStar tankers were never fitted with the pods although the space was created during conversion to fit the control panels at the F/E's station. Might have a photo if anyone wants to see.

CS
I believe the statement that the long bodied (-1,-50,-100,-150,-200s) were all built with the analogue AFCS would be correct. The -250 I think only had 524 engines and uprated wing stucture to give higher zero fuel weight and more fuel capacity. Whether any operator reverted to the digital I don't know but I suspect the only one might have been Delta in the States.

Denzil,
Ah that would explain it...I heard rumours that they were reverting the PanAms to analogue.

Did you all know that Lockheed were considering a fuel tank behind/ above the S duct to enable CG control in flight? It was also one of the first a/c to be fitted with an experimental glass cockpit.

Way way ahead of it's time!

FE Hoppy
6th Sep 2004, 16:38
I think the VGs were to satisfy CAA certification at the time BA got the -500. Slightly different g loading requirements to the FAA. All the other operators were able to certify the aircraft as per FARs.
The APFDS doesn,t have an aerodynamic effect.

CS-TMX
6th Sep 2004, 19:06
idg

Here is the picture of the experimental EFIS ;)

http://www.pioneer.net/~fitzrr/efis.jpg

In http://www.pioneer.net/~fitzrr/index2.html

I would say, in certain way, still ahead of our time as the Concorde is/was :cool:

Dengue_Dude
15th Sep 2004, 18:12
I think Hoppy's along the right lines too.

If memory serves, the CAA were also not happy with the ex PanAm aicrafts' stall warning system.

I believe that they used the stick shaker for high speed warning AND incipient stall and their point (the CAA) was that up in Coffin Corner the spread between the two wasn't that much.

Clawing my memory I believe the aircraft were also cleared to FL430 - but it was a long time ago.

Super move changing the digital autoflight system back to analogue.

Remember being on the ZE706 (corrosion trial) RAF acceptance flight test. What a mix up of APFDS that was (is?)

Anyway, I though vortex generators were to keep roll control in the event of a stall.

Stir the airflow and delay flow breakdown and so the ailerons would retain roll control.

Remember too the outboard ailerons are locked out with the flaps up anyway - are they unlocked with a stall warning - can\'t remember.

Must get my copy of Handling the Big Jets out of the loft!!

411A
16th Sep 2004, 01:27
Max certified ceiling for the -500 was indeed FL430. Have been there several times (at lighter weights of course) and no problems noted.

Yes, the Lockheed TriStar was the first wide-body aircraft with a super-critical wing section.

-500 series aircraft with the analogue a/p were limited to 506,000 pounds all up weight.
510,000 pounds for the digital.

No TriStar that I ever flew (and I flew 'em all except the -150/-250) had the outboard ailerons locked out with the flaps up...ie: it ain't a Boeing.
Of course, once it arrived on the UK register, anything could happen, and sometimes did.

CS-TMX
16th Sep 2004, 05:38
411A, I must say I'm an eager reader of your posts here and on other forums;)

I remember a pair of years ago you questioned someone why there were restricted weight -500 versions.

Naw, that would be too easy...for you! But I'll give you a hint....try looking at the autopilot. Interesting stories there.

Another hint: think digital (ie: other than analogue).

Now I got partially the answer.

Other than the obvious difference between the glareshields what were the main differences between digital and analogue AFCS? Why an analogue version imposed a a lower MTOW to some of ex-BA -500s?

About the outboard ailerons I believe they where moved to a 2 down neutral position in cruise flight and would react to minimize gust effects.

My father worked as an AMT for TAP. Here is a detailed main panel schematic of our old L1011s and with digital a/p:

http://www.tristar500.net/files/painel_principal.jpg

ALso if anyone is interested, the flags of the AFCS modes annunciator:
http://www.tristar500.net/files/AFCS.JPG

Best regards;)

FE Hoppy
16th Sep 2004, 09:26
Out baord Ailerons are not locked but they do change their neutral position.
Three modes for the ACS don't remember all the details, like Homer Simpson, when ever I learn something new I have to forget something old.
The highest gross weight Tristars are the RAF (ex-BA) tankers all with analogue afcs.

allthatglitters
16th Sep 2004, 10:36
"cs
I believe the statement that the long bodied (-1,-50,-100,-150,-200s) were all built with the analogue AFCS would be correct. The -250 I think only had 524 engines and uprated wing stucture to give higher zero fuel weight and more fuel capacity."

The 524B02 engines were fitted to -200 and -500 series a/c BA recieved, the -500 524's were uprated to the B4 series when the 4.5 feet extentions were added to the wings, along with the active aileron system, this was carried out as the delivered aircraft had a range shortfall. I also remember that Gulf Air uprated some of there -100 to -200 series, part of the mod was to uprate the engines from the 22B's to 524B2 series engines.

But this was all so long ago, and many happy memories of a great aircraft.

Dengue_Dude
25th Sep 2004, 14:37
Sorry chaps about the duff gen (locking outboard ailerons)

Trouble is I'm flying DC10s at the moment and the last few years.

The phenomenon is called 'recency' when you forget the previous stuff - except in a crisis when you revert and confuse the hell out of yourself!

The DC10 DOES lock the outer ailerons when the flaps are up unless you get a stall warning.

Vortex generators though I still think are there to regenerate the boundary layer and retain roll control in the event the inner wing section stalls.