flaps/slats wet V1 speed

[flyin74]

I was out flying with some friends and was asked, "what do you think creates more lift, flaps or leading edge slats?" I responded quickly with flaps, just because of the camber created by flaps.
What do you all think creates more lift?

Also, how does a wet V1 speed effect weight, performance, etc.?
I told him that the V1 speed would be lower and your weight would be limited and finally your obstacle clearance would be degraded from 35ft to 15ft.
Does this sound right?

Thanks in advance!

[HotDog]

Lufthansa 747-130 crashed on T/O in Nairobi, 20 Nov. 1974 due to the failure of the LE flaps to extend although TE flaps were in the T/O range.

V1 is reduced by 10KTS and this will produce screen heights between 15 - 25ft.

[mutt]

You will find that a number of aircraft are approved to takeoff with only leading edge slats extended, flaps zero. I dont know of any that are approved with only flaps extended. This would lead me to say that slats are more effective.

Wet V1 changes really depend on the aircraft date of manufacture. 4 engine aircraft usually only have a speed decrement, twin engined aircraft will have a speed and weight decrement. The V-speed decrements can be a lot higher than the 10 knots mentioned above.

Mutt.

[Zoner]

A few years back I had to do a ferry flight out of Sao Paulo with the LEDs retracted on a B-747-100. Even with low gross weight and greatly increased takeoff speeds Boeing told us to expect some buffeting after liftoff. They were right. I did many zero flap takeoffs with slats extended on the DC-9-30 and everything was pretty normal. So I'd have to say I would want the LEDs if I could only choose one.

[Tonic Please]

Reminds me of the 727 (i think) aircraft that crashed on departure from Heathrow back in the 70s.(27L/R runways - it hit ashford or somewhere west of airfield I know that) Dad was one of the first people on the scene!!

The truth emerged about the slats (leading edge), being retracted too soon, thus resulting in increased drag and reduced lift due to decreased accel.

Anyone care to elaborate for me?

Dan

[HotDog]

I think you mean this one?

Heathrow, England, June 18 1972 - 118 killed
British European Airways HS-121 Trident 1C, crew failed to diagnose premature Leading edge flap retraction.

[EFP058]

Excuse my ignorance please, but what exactly do you mean by the term "wet V1 speed"? Rainy weather? :confused:

[HotDog]

Wet runway surface V1.

[Jagbag]

Slats improve the low speed handling of an aerofoil by a large amount due to delayed separtion of boundary layer, increased lift generating surface etc. while TE or LE Flaps increase the camber/ total surface area and thereby the lift and drag.

This becomes critical in a swept wing planform which has LE Flaps near the wing tips where the BL separation is ahead due to the transverse flow across the wing.

If the Angle of attack and the speeds which are meant for slats extended are used when slats have failed- then the aircraft is very close/in the region of reverse command, where there could be a large rise in drag for a correspondingly reduced rise in lift. if this is not detected quickly by a pilot then it could lead to a descend because the lift equation of the aircraft is not matching up. Hence the need to critical monitor airspeed and attitude during take off/go around by BOTH pilots. Hence any failure either LE or TE could result in disaster. Its happened to me when my co pilot raised the flaps to 0 by mistake instead of flaps 15 during a single engine (raw) go around at minima of an ILS. Luckily managed to control it. thank god it was in the simulator (but during a test). However my stick shaker did come on momentarily.

The situations enumerated by other contributors have been when the slats have failed but one knew that he/she had no flaps. A crash may happen even if the flaps fail. So beware of drawing half conclusions.

Hope this helps.

[Tonic Please]

Spot on thats it. Thought id mention it to shed light on how serious LE and TE issues can get.

Smooth skies

Dan

[aviate1138]

Tonic Please said...
'Reminds me of the 727 (i think) aircraft that crashed on departure from Heathrow back in the 70s.(27L/R runways - it hit ashford or somewhere west of airfield I know that) Dad was one of the first people on the scene!!'

Captain had heart attack just after takeoff. Confusion on the flight deck led to the Trident deep stalling into a postage stamp field near Staines by-pass and missed the 150,000 volt pylons by just a few feet. Virtually no forward velocity and full fuel [ nearly] it did not catch fire but the massive vertical G component killed everyone. Sad thing was the BBC and Independant Radio had to keep broadcasting on all their radio/TV channels for ghoolish rubberneckers to get the f**k out of the way as Fire, Police and Ambulances couldn't get to the scene! Then the souvenir hunters moved in - some sick people were out there that week. Made me sad to be a Brit for a while.
That one accident made the CAA paranoid about cardiac assessment from then on.

Aviate 1138

[Tonic Please]

Awful. Just like to make clear Dad didnt get any souvernirs. He tried to help. :) He was only in his teens and not particularly into aviation.

[EFP058]

Wet runway surface V1.
Ah, okay, thanks. I thought it would be something much more complicated, but I guess sometimes even in aviation things can be simple. ;)


Lufthansa 747-130 crashed on T/O in Nairobi, 20 Nov. 1974 due to the failure of the LE flaps to extend although TE flaps were in the T/O range.
I believe the LE flaps didn´t fail to extend but were rather accidentally retracted again prior to t/o.

This is what my level of information is about this particular accident: The 747 was taxiing to the active RWY, and due to the taxiway having quite a bit of downslope the crew was using idle reverse in order to avoid riding the brakes. Problem is, the 747 retracts the LE flaps when reverse thrust is applied. Apparently this can be overridden somehow (sorry for the lack of details, but I´m not exactly an expert about the systems of a 747, I´m sure someone else will correct me if I´m wrong), but for some reason the crew neglected to do so.
Problem number 2 was that the warning light for the retracted LE flaps was only present on the FE´s panel, but he didn´t notice the warning since he was already facing forward for the departure.

So the crew started the t/o roll and rotated at the calculated Vr speed. The aircraft actually lifted off, but instead of climbing out it wobbled along a few feet above groundlevel (would it be possible that it was flying only due to the ground effect?), and of course since it lifted off without LE flaps it was extremely close to stall speed. The crew was puzzled by the unexpected behavior of the aircraft, and as a first measure they decided to get the gear up in order to gain airspeed. However, when the gear bay doors opened, that was all that was needed to cause enough increase in drag, pushing back the airspeed just enough for the aircraft to stall.
The aircraft hit the ground about one kilometer behind the runway and skidded for another half kilometer before it came to a rest and burned out. A total of 59 people lost their lives in this accident, 4 crew and 55 pax. :(

The accident report claimed "the lack of warning of a critical condition of leading edge flap position and the failure of the crew to complete satisfactorily their checklist items" as major contributory factors.

[denachtenmai]

Ref the Lufthansa 747 crash. If my memory is correct, then I think that a little while before this a similar situation occurred with a BOAC 747, it did not result in an accident. I seem to recall that the incident was reported to Boeing but the information was not promulgated before the Nairobi crash. Maybe someone more knowledgable than myself can add further comments.
Regards Den.

[52049er]

Just for completeness a quote from the AAIB report


"The field was sufficiently inaccessible to prevent all but themost persistent sightseers from reaching it. The police were successfulin controlling spectators, and contemporary reports that membersof the public had impeded rescue services by their presence nearthe scene are not borne out by the facts"

52

[HotDog]

The 747 was taxiing to the active RWY, and due to the taxiway having quite a bit of downslope the crew was using idle reverse in order to avoid riding the brakes. Problem is, the 747 retracts the LE flaps when reverse thrust is applied. Apparently this can be overridden somehow (sorry for the lack of details, but I´m not exactly an expert about the systems of a 747, I´m sure someone else will correct me if I´m wrong), but for some reason the crew neglected to do so.

The leading edge devices take 7 seconds to extend with T/O flaps selected so they would have been well and truly out long before VR. The East African Community Accident report stated the
cause of the accident was the failure to select the pneumatic power source for LE device extension.