View Full Version : Bump due to Autospeedbrake at Landing
FCeng84
24th Sep 2010, 18:39
On some models and for some conditions activation of autospeedbrakes at touchdown results in adding a bump to an otherwise smooth landing. Is this something that pilots notice? Are there particular models that exhibit this worse than others? Does this become such an annoyance that pilots intentionally land without arming automatic speedbrakes chosing rather to extend speedbrakes manually following touchdown?
SNS3Guppy
24th Sep 2010, 18:46
Do you mean that you think the autospoilers are activating prior to touchdown? That perhaps the spoilers are deploying and making the airplane "drop" into an otherwise smooth landing? That's not happening.
Not only do the autospoilers deploy after touchdown, but there is a slight delay before they deploy.
con-pilot
24th Sep 2010, 18:53
The auto-spoilers on the 727-200 was either a blessing or a curse. With the built in time delay, if you made a firm landing it would prevent a bounce, however, if you kind of just kissed the runway and had a slight hop, the blasted things would slam you back down on the runway.
So I didn't use them that much, except on contaminated runways, then I always armed the spoilers.
FCeng84
24th Sep 2010, 19:28
SNS3Guppy,
A variety of types of logic are used to determine the air-to-ground transition and to activate autospeedbrakes. The ones that I am familiar with are main gear truck tilt angle, main gear strut compression, and gear spin-up. These three events usually happen in that order. If the autospeedbrakes are triggered on truck tilt (or actually truck untilt) they can deploy before there is very much weight on the main gear. The airplane will tend to settle in due to the loss of lift from speedbrake deployment. This can generate a bump once the gear truck is fully untilted and the strut oleo is loaded to it fully compressed position.
Even if the control logic includes a delay, the speedbrakes can end up deploying before the gear struts are fully compress for a very low sink rate landing.
SNS3Guppy
24th Sep 2010, 19:55
The ones that I am familiar with are main gear truck tilt angle, main gear strut compression, and gear spin-up.
Right. Gear on ground, delay, autospoilers extend...exactly as I said.
FCeng84
24th Sep 2010, 20:15
The height difference between when the gear first touches the ground and when the gear are fully loaded can be several feet. This can be enough to result in quite a bump if lots of lift is shed quickly when or shortly after the gear first touches down cause your bird to "drop in".
In an effort to reduce the length required for the landing runway there is motivation to get the speedbrakes up ASAP. Every second of delay cost you approximately 200 feet of pavement.
Maurice Chavez
24th Sep 2010, 20:22
The auto-spoilers on the 727-200 was either a blessing or a curse. With the built in time delay, if you made a firm landing it would prevent a bounce, however, if you kind of just kissed the runway and had a slight hop, the blasted things would slam you back down on the runway.
So I didn't use them that much, except on contaminated runways, then I always armed the spoilers. :D Absolutely right! The trick with the 727 is put the left gear down first (Z-Rod), that prevented the bounce. Same works for me on the B732 (works on wheel spool), an airplane I absolutely hate, after coming off the 72... Anywho, try landing on either the left or right gear (depending on what seat you fly) with auto spoilers. Works for me....
Maybe I shouldn't have said that, I'll probably get slammed again for being unprofessional...
con-pilot
24th Sep 2010, 21:55
Maybe I shouldn't have said that, I'll probably get slammed again for being unprofessional...
Not by me you won't.
Cheers. :ok:
CommanderRiker
25th Sep 2010, 00:50
Absolutely right! The trick with the 727 is put the left gear down first (Z-Rod), that prevented the bounce. Same works for me on the B732 (works on wheel spool), an airplane I absolutely hate, after coming off the 72... Anywho, try landing on either the left or right gear (depending on what seat you fly) with auto spoilers. Works for me....
No, no, no....if a little wind comes from the right, the Alteon checker will fail you right away! This happened to a mate who went for the KAL sim training after the company accepted him. Be warned!
By George
25th Sep 2010, 04:41
On the 747, the truck touches heel first. The length of the 'fall' is 8 feet which is why at the gate the RAD ALT shows -8ft and not zero. Sometimes, especially if you are trying to hold off for a greaser the initial gentle touch results in a slight thump due to the auto-spoiler activating on first contact dropping the truck. Best not to try too hard and she goes on nicely.
Not all 727-200s have auto spoilers.
On the 747, the truck touches heel first. The length of the 'fall' is 8 feet which is why at the gate the RAD ALT shows -8ft and not zero.
The 8ft drop is mostly due to body angle during flare and the distance of the main gear from the RA Antennae. You're not going to get an 8 foot drop if the spoilers slam you down on the main gear. The drop would only be due to strut compression and bogey tilt.
Bogey tilt on the body gear is only about 7 degrees, and the drop because of this would only be a few inches.
Rgds
NSEU
SNS3Guppy
26th Sep 2010, 07:19
With autospoiler application in the 747, no "drop" occurs. The airplane has a natural pitching tendency, nose-up, when the autospoilers deploy. A smooth landing in the airplane doesn't produce a drop. In the cockpit, a smooth landing is heralded by the movement of the speedbrake handle, but no sensation of actually touching down.
misd-agin
26th Sep 2010, 14:21
Main strut compression.
Without autospeed brakes armed you can sometimes feel the aircraft wheels on the ground while still 'flying'. If you have autospeed brakes they deploy and the a/c 'drops' by the amount of strut travel available. It's not as noticeable if you already had a fairly consistent descent rate while the struts were compressing.