Drunken Bungle Whore

Been flying a lot this year (work - nothing glamorous!) On one journey about a month ago I was sitting in the last but one row and the flight was incredibly bumpy (Heathrow to Glasgow). On the way back (same day) I'm in the very front row and not a single bounce. Now I quite appreciate that the conditions would have changed in the interim, but it got me thinking - is the back of a plane more bumpy than the front? (WILL SOMEONE PLEASE FIX THE PONDER2 SMILEY FFS! )

Physics was always my weak point, but I seem to remember something about energy transferring along an object - rather like when you crack a whip - the end is moving much faster than the bit in your hand.

Anyone know?

boxst

Hello

Yes the back of the 'plane is bumpier than the front. I don't know the physics behind it. I travel a lot and if I have to travel in economy or wander back to go to the toilet you can feel the difference.

Steve

FlightMan

Suppose being further away from the centre of the plane, any pitch movement will be amplified. Not sure if pitching is the same as bumping though.

Kuro

the further you are away from the wing, the more the effect will be amplified. The body will flex around the centre as that's where the highest lift factors are.

...although statistically you are slightly more likely to survive an air crash in the rear compartment.

you takes yer choice

Sbradley

Hiya.

(It's an illusion I'm afraid. The aeroplane is rigid so any bumping must be the same at either end or the middle. Otherwise you have a problem... ) In brackets 'cos it's wrong but I'm man enough to let people see when I screw up...

However.

Aeroplanes move (duh) and hit turbulence from one end at a time. So it's possible that the lurch could be more pronounced at the extreme ends as the fuselage will tend to pivot around the centre of lift.

I never notice, to be honest. I've spent too long flying and just dial turbulence out unless it's something I feel I should be worried about...

SB

PS I'll come back to this. Not slept for 2 days so it *may* be total bollocks...

PPS See edit below...

Edited to say that Les is a fine example of why you should listen to steely eyed jet jockeys rather than wild staring eyed helicopter pilots.

He's right, of course. I'm going to bed...

Leslie

The closer you are to the tail the further you will move up and down when the aircraft pitches when it hits turbulence. The aircraft will pivot in the fore and aft axis from a point approximately 1/3 of the wing fore and aft length (chord) from the leading edge of the wing.

It is possible of course that on the trip back the aircraft avoided the clear air turbulence because it was flying at a different altitude.

Les

FlightMan

Thanks Leslie, thats what i was trying to say! ;-)

Nick100

You tend to get lots of side to side movement at the back of planes, because of the yaw damper.

I'm not exactly sure why, but think it's something like this :
During turbulance most big planes have an automatic system called a yaw damper to try to stop control oscillations setting in, which would possibly be caused by the auto pilot if the damper wasn't there (?). The yaw damper/control drives the rudder side to side and eventually reduces the speed and travel of the rudder, however it does cause the aircraft tail to waggle around which feels like you're being shaken.

It's waggle waggle all the way, when sitting at the back

scoobyster

The yaw damper stops the sideways waggling, it does it very quickly indeed - I've had this demo'd on a Jetstream 31 and the waggling stopped within moments of the yaw damper being engaged, very impressive. I guess you may still experience waggling (great term ) if the aircraft is making unbalanced turns, these would be more pronounced at the tail or nose as you're further from the axis the a/c is turning around.

SWRTWannabe

Surely with all the taxes they charge for planes taking off and landing, they'd have some money to mend all the pot holes up there and prevent all these bumps

Listy

Yes very good Les but you do know nobody likes a smart ****!

fast bloke

It isn't pot holes - its speed ramps - you'll be seeing gatsos up there next

J4CKO

iTrader: (1)

I flew into Glasgow a couple of weeks ago,sat in the back of an Embraer (little jet) and that was scary, was coming into land and the pilot announced we had to have another go (cant remember why) and that was even more scary, thought the wing was going to hit the ground first, the way back was very smooth.

London into City airport on Sunday, apparently that is a fun descent, got told of by the missus for telling the kids I was going on a 'Fokker', my six year old found this highly amusing, dont know how !

Drunken Bungle Whore

Thanks for the info guys - always glad for the explanations behind things - I love to know "why"!

FlightMan

London City has a 5.5 degree glideslope, compared to the normal 3 degrees. Although I've never been to LCY, those that have tell me you really notice the extra 2.5 degrees. Nothing on the old Kai Tak approach though, do a search on airliners.net to see why!

Couldn't resist http://www.airliners.net/open.file?i...next_id=877985

mart360

the best bits when it roller coasters !!! came in to lhr on a flight back from luxembourg

very turbulent, and it was a few opposite locks and full power applications to get us smoothly on the runway..

like one of the earlier posters, if you fly a lot, you just tend to ignore the small stuff, its the unexpected ones that make you think...


30,000 ft clear day and bang almightty drop and away you go

only had one plane diverted for technical reasons we reckon we should have never taken off in the first place

Mart

FlightMan

LHR can be fun. Landing on 27R with a NW wind causes tremendous windshear off the BA hangers. We'd normally de-alternate to land 27L if required, but someone always has to be the first to give it ago when the wind shifts/drops. Happened to a EDI/LHR BA shuttle last year. Last I heard the "clean-up" squad was being called to the gate. Puke everywhere apparently.

douglasb

Haven't flown into London City but I have been to Belfast City in a BAe 146. I think that the glidepath is similarly steep and that there are rules about not flying over land to keep noise down.

Anyway, we came in over Belfast Lough approximately parallel with the runway. At what appeared the last moment, the pilot did a left hand handbrake turn to take us over land and then did a right hand handbrake turn to line us up with the runway. At a 5.5 degree slope in strong crosswinds this can be described as "interesting".

Adrenalin is brown

Drunken Bungle Whore

Flew into Belfast city only this week - always loved the approach along the Lough - especially the huge left hand turn right in the middle!

Kevin Groat

Having spent the last 2 years flying Aberdeen to Scatsta (Shetland) twice a week in a 146 I can confirm that a 5.5 degree descent with 30 knot cross winds leads to spirited landings. Also taking off with the 146 on a 1200m runway with 50 knot head winds can lead to damn near vertical take off (handbrake on full throttle departure...)

There is talk of a 7 degree descent to maximize payload on landings due to the short runway

carl

Flown into London City in a BAe 146 (RIP...) Pretty impressive as you come in over London, then come hurtling down the glide slope with water on both sides of you. Pretty similar experiences -- also in 146s -- at Innsbruck (mountains all around) and Moenchengladbach (1200m runway!)

fast bloke

hmmm - I thought Belfast City was a normal approach. Came into Dublin from CDG a couple of years ago. I could smell hydraulic fluid. Pointed it out to one of the crash chicks (you know - if we crash exit by... etc etc) - 10 seconds later we are being advised of crash positions. Pilot came on to say that everything seemed normal but they didn't know what was causing them smell... we would have a normal landing in about 2-3 minutes. Landed in Dublin accompanied by about 20 fire trucks, taxied to the far end of the runway and got off on the big bouncy castle slide thing. never found out what the smell was.

btw - if you think a normal Belfast City landing is interesting, try one with an east wind. Is seems the normal approach is up Belfast Lough, handbrake turn over the titanic quarter, drop over the BT building with about 10ft clearance, squeeze through between Samson and Goliath, touch down and come to a shuddering halt about 4 inches from the end of the runway

The Chief

Depends on where the engines are situated.

I was on a flight last year and it was incredibly bumpy in fact i crapped myself, when on my third and final flight of the journey i got speaking to the air hostess who was sat right next to me at the back and she said that aircraft with the engines on the wings are less rigid at the back and tend to flex a bit more, the final flight had the engines slapped on the back and she promised me the journey and landing would be as smooth as anything and you know what - she was right!!!

mark1234

The other factor is that the plane will yaw (as well as pitch which has already been identified) around the middle.. so there's a lot more lateral movement in the ends as well.

Another factor with rear engined planes is that the main wing is much further aft - more of the weight is carried aft, so the COG is further aft.. and the centre of pressure (lift) needs to be somewhere near it. Downside is it's bloody noisy in the back! In all honesty I can't believe the flex in the fuselage is sufficient to be noticable - any observable effect has to be down to being at a distance from the centre of any yawing and pitching moments.

Realistically, the biggest difference was likely to be the weather you flew through.. they try to avoid turbulence as much as possible.

Exchanging airline stories, had a comedy moment flying into LHR recently.. we're stacked waiting for a slot, the pilot points out the transatlantic 747 stacked ahead of us. 10 minutes later we go to seatbelts, and roll out the hold, turning downwind there's an almighty bang and lurch, followed by nothing. Half the plane screams.. 30 sec later the pilot comes on the intercom and comments. "In case you're wondering what that was folks, you'll remember I mentioned the 747 ahead of us? We just turned across his wake - they leave waves in the sky a bit like a boat moving through the water". Worst landing was with AA - smooth as you like.. or so we all thought as the engines wound up in reverse.. then the plane stopped flying and dropped the remaining 10 feet or so!

Only time I've really got nervous was on a bumpy approach to LHR with cloudbase at 800 feet. Kinda disorienting. Since then i've started learning to fly - On monday I experienced my first (deliberate) spin. Uuurrrgghhh! Not enjoyable

Drunken Bungle Whore

Yup - I've experienced one of those 10foot drop to the runway landings - those tyres must be really tough!


More questions then - why are Heathrows runways 27L/R - I get the L/R (I think- left and right?) - but why 27?

And all the planes from T4 - do they have to wait for a gap to nip across their runway, or is there a special 'road'? (Sorry if these are really dumb questions, but when I'm in the traffic jam waiting to take off at LHR I just get to wondering these things.....)

Thanks!

B!

Sbradley

OK, now I'm awake

Runway numbers show the direction. So 27/09 points West or East, depending on which way you are going down it. LHR has 4 runways, 27 left and right and 09 left and right. 2 physical strips of concrete but 4 runways. Everything goes in the same direction, traditionally to be closest to heading into the wind but more realistically these days to minimise the noise impact, and they land (I think) on the left while taking off on the right. That maximises the traffic.

Aircraft approach the runway on the ground from either side on a series of taxiways - big, wide, strong roads. They're controlled by a ground control team in the tower who have a microwave radar that allows them to see things on the ground even in thick fog or at night.

SB

Drunken Bungle Whore

Thanks for that - but the T4 question still puzzles me. T1/2/3 are all inbetween the 2(or 4) runways so can access them easily - but T4 is on the far side so to get to the runway nearest the A4 (sorry - not a pilot!) a plane would have to cross the runway nearest to T4 wouldn't it.....? Is there a special crossing place cos there wouldn't be a lot of time for them to 'nip accross'? (Though the idea of a 747 pilot revving the nuts of a plane ready to drop the clutch and shoot across amuses my simple mind....)

FlightMan

Almost right. but not quite.

We do have 2 runways, used to be 3 but R23 now has Concorde parked on it! Rwy 23 has no be decomissioned so we're officially a 2 runway airfield. Of course each runway can be used in 2 directions, so for take-off paths.
Anyway, LHR operates what is called alternation. So, when we're on westerlies, from 06:00 to 15:00 we will land on 27L, and depart on 27R, then swap at 15:00. The following week the runways are swapped. We publish the alternation patten every year on our website, but its always at the mercy of the weather. However on easterlies because of the Cranford agreement we would use 09R for deps and 09L for arrivals, with no alternation.

Anymore questions?

Drunken Bungle Whore

Cheers FlightMan - any answers to the question above...?

Leslie

Listy,

Sorry for being a "smart ****" as you said, but I used to lecture on aerodynamics and flight control systems!

Les