-ft/m touchdown question

[RingwaySam]

Hi all,

Curious SLF here. Hope you don't mind me posting this. Im not sure if it's possible, but do pilots ever have an idea what there decsent rate is on touchdown (-ft/m) If so what is usually a the rate of decsent for a greaser/firm/hard landing? Im pretty sure acars records it, but im not to sure.

Im not if it has a specific name or not...

Sam

[chornedsnorkack]

By certification rules, every plane has to endure touching down at descent rate of 3 m/s at MLW and 1,8 m/s at MTOW.

Planes do not have very much more spare strength beyond that. When a Concorde touched down in Dakar at 4,2 m/s, the tail bumper wheel was crushed and the plane suffered tailstrike. The frame was repaired and flew again; but it was always heavier than the other Concordes because of the extra weight of repairs, and it was scrapped alone of all Concordes.

[RingwaySam]

chornedsnorkack (http://www.pprune.org/forums/member.php?u=117795)

Thanks alot.

[HarryMann]

By definition a greaser would be nearing 0 ft/s of course

[RingwaySam]

Wouldn't that depend on the aircraft type though. Surely a 767 will touch down harder than 737. Now like I said, I don't know much about this so please take it with a pinch of salt. For example, if a 737 greased the landing, and was, say -20ft/m surely the 767 wouldn't be able to match that because it's alot heavier.

[400Rulz]

Sam,
The weight of the actual aircraft is irrelevant - any aircraft can be "greased on" with the correct combination of speed (and hence lift) and correct body angle. You are right re. the 767 - it is harder to land, but only because the bogeys are tilted the wrong way. The aircraft has a predilection for "stubbing its toes" because of this, but it is still possible to "squeak her on".
As for the certification process, I understand that the u/c must be able to withstand 1200FPM rate of descent:uhoh:.
400R

[RingwaySam]

I see. That explains why the A330 seems to touch down alot smoother than A300s. Thanks for the info :)

[Pontius's Copilot]

On our large turboprops 200fpm to 300fpm at touchdown is OK, 700fpm is 2.1g (according to our Flight Data Analysis system) ... and that's not OK.

[Doors to Automatic]

I wonder why the 767 has the bogeys titing the wrong way? If they could be turned round it would transform the aircraft's landing perception with the punters.

[Chris Scott]

The A310 was the same. Perhaps the perceived state of the art in 1982? The VC10, on the other hand (1963) gave you 2 bites at the cherry.

[Random75]

Doors to automatic....

The reason the 767 gear hangs forward is to do with gear retraction. The other way wouldnt work.

Maybe there are other reasons and I am sure we will be enlightened....

All the best....

[Doors to Automatic]

Thanks Random

I did actually experience a real greaser on a Brunei 767-300 at LHR a couple of years ago so they are possible!

[Check Airman]

If I recall, The 777 autopilot aims to touch down at 1.5 fps, or 90fpm. I guess you can use that as a reference value.

[jettison valve]

A340-600:
Trouble starts at around 13 ft/s...

Unfortunately, the DMU and DFDR sometimes tell you different numbers... The sampling rate, you know... :\

Various MLGs have already been scrapped... Must be a bitch to land - or to detect a "hard landing" from the flight deck....

Cheers,
J.V.

[PierceAviation]

You are correct, most companies set up their ACARS to monitor touchdown velocities. The last company I flew for had the ACARS set up to immediately notify Maintenance Control of a hard landing...when I say immediately I mean we got a SELCAL from Control as we taxied off the runway to tell us to write up a hard landing.

Takes the argument out of the cockpit if it was a hard landing or not.

Regards,
Greg
********************************

[chornedsnorkack]

700fpm is 2.1g (according to our Flight Data Analysis system) ... and that's not OK.

3,5 m/s is the speed reached after 60 cm or so freefall.

Which means that after 60 cm falling at 0g, you need 55 cm to decelerate the airframe at 2,1g to stop.

How much distance does the landing gear allow for deceleration?