Author Topic: STS-117 Landing Gear Slow to Drop?  (Read 14635 times)

Offline gordo

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #20 on: 06/25/2007 12:03 pm »
This is very interesting.

I assume the gear is electrically signaled to deploy.  The GPCs should be able to show when the signal was sent compaired to the other gear.  

I actually wonder if a "non-deploy" message came back and it was sent again, or one of the back up systems were signaled.  With the design of the system it would be very hard to get this sort of lag unless something had gone a bit wrong somewhere.

Offline shuttlefan

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #21 on: 06/25/2007 01:45 pm »
Quote
rdale - 24/6/2007  8:57 PM

What would the "hardware" be "saying" in this instance?

It would POSSIBLY be saying: "I have a more serious problem and you had better check to make sure it's not a generic problem that could be more serious on future landings." ;)

Offline johng

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RE: STS-117 Landing Gear Slow to Drop?
« Reply #22 on: 06/25/2007 02:08 pm »

You know, after I read this thread, I spent some time on youtube looking at landing videos and regardless of orbiter or mission, they all have some time lag between the two mains, with the right one deploying last.  Looks like a non-event to me.

Offline psloss

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RE: STS-117 Landing Gear Slow to Drop?
« Reply #23 on: 06/25/2007 02:28 pm »
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johng - 25/6/2007  10:08 AM


You know, after I read this thread, I spent some time on youtube looking at landing videos and regardless of orbiter or mission, they all have some time lag between the two mains, with the right one deploying last.  Looks like a non-event to me.
Out of curiosity, which landings did you find?  I was thinking of posting just the deploy sequence from the last handful of Edwards landings for illustrative purposes (and FWIW, I'm seeing the same thing as you).

Offline johng

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RE: STS-117 Landing Gear Slow to Drop?
« Reply #24 on: 06/25/2007 02:43 pm »

I dunno. Just some surfing before bed last night...

Offline JWag

Re: STS-117 Landing Gear Slow to Drop?
« Reply #25 on: 06/25/2007 03:23 pm »

Quote
DaveS - 24/6/2007  1:11 PM  

I have attached an MP3 of the MLG doors slamming shut, where you can really hear the delay between the left and right doors being closed.  There's a whopping 1.25 second difference between both doors, with the right MLG door closing first and the left door closing last.

If I'm not mistaken, the MLG and NLG are deployed entirely by gravity, and are incapable of retracting themselves.  I don't have Dennis Jenkins' book in front of me, but I'm mostly certain that I've read that locking the gear in place and locking the doors shut is done entirely by workers.  It wouldn't surprise me that there was a delay.

It makes some sense - why have the weight and complexity of all the hydraulics to retract the landing gear, when it will only ever need to be done while workers were swarming over the vehicle anyway?

It would seem reasonable for there to be a specification that defines the maximum allowable time from when gear deploy is signaled to receipt of signals that it is down and locked.  This could be tested in the OPF (though without benefit of a ~200 knot wind).

Offline Namechange User

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #26 on: 06/25/2007 03:50 pm »
The gear is deployed by the crew.  That is one of the reasons the orbiter cannot fly completely automated.  There are two switches that need to be thrown.  The gear is gravity assisted but hydraulically driven.
Enjoying viewing the forum a little better now by filtering certain users.

Offline mkirk

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RE: STS-117 Landing Gear Slow to Drop?
« Reply #27 on: 06/25/2007 04:29 pm »
Here is a public link to a section of the SCOM that describes landing gear deployment for the orbiter.

http://www.shuttlepresskit.com/scom/214.pdf

Page 2 discusses the deployment sequence.

I am just hearing about this issue since I have been traveling since Friday so I can’t confirm anything yet or offer any educated comments.

I will say that “IF” the deploy times for any of the gear were really “out of family”, this issue MUST be well understood prior to the next flight.  So no matter how easy or hard it is to get a handle on this it will be talked about in excruciating detail within the program as they head into the 118 flight readiness review.

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Offline JonSBerndt

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #28 on: 06/27/2007 04:20 am »
Quote
OV-106 - 24/6/2007  7:43 PM

The orbiter would not survive a belly landing.  Glide slope and landing speeds are much steeper and higher, respectively. than a regular aircraft.  

The gear have "thrusters" on them as well.  This is what they are called but do not think of them as the rocket-type thrusters.  They provide an extra push to extend the gear if necessary.  

As for deploying the chute pre-touchdown, that would be a bad idea.  The was concerns this was going to happen on STS-95 during approach the scenerios were not good as I recall.  This was the flight where the door fell off at launch.

The glide slope doesn't matter - the flare is executed regardless of gear state. I didn't see anyone suggest deploying the chute prior to touchdown. Ground effect might mitigate slapdown a bit, allowing a shallower AOA. Deploying the chute at first contact (given the orbiter CG location and the chute mount point above it) might help reduce slapdown - although there is a delay between chute deploy and full inflation that would probably render that utilization useless.

Jon

Offline mkirk

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RE: STS-117 Landing Gear Slow to Drop?
« Reply #29 on: 07/01/2007 04:21 pm »
It should be pointed out that at this point they believe the deployment was “within specs” and therefore not an issue.

As for landing gear up, this was always a sensitive subject in the short time that I worked in training.  The general consensus is that it would be a really bad day especially with a full payload bay like in an ascent abort scenario.
 
There is an established failed tire technique which is intended to help maintain directional control and help keep the orbiter from yawing into the bad tire.  There is no generally accepted, published (i.e. in the FDF checklists) procedure for landing gear up.

Since someone brought up the use of the drag chute I will relate this little story about “none traditional - uncertified uses”.

I was working with one of my senior instructors and John Young in the SMS (shuttle mission simulator) as we looked at some short field landing techniques and capabilities.

I was flying right seat while John was in the left.  On some of the approaches John had me pop the chute while we were crossing the threshold (i.e. still in the air at around 20 feet).  His intent was to have the chute unreefed by the time the main gear hit the runway, thus allowing us to slow down all that much faster.

I told one of my closest friends who happened to work in the MMACS group (mechanical, maintenance, arm, and crew systems) of the mission control center – among their responsibilities are the landing gear and the drag chute systems.  She and her fellow MMACS types were not too happy to hear what we were doing…they thought it was an exceptionally bad idea and began listing the reasons why…In fact current procedures expressly say DO NOT DEPLOY the chute prior to main gear touchdown or above 230 knots.

I should note however, that at least in the SMS, the technique worked well and we were able to perform some very short field landings by combining the early deploy with some other techniques.


Mark Kirkman
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Offline gordo

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #30 on: 07/01/2007 05:09 pm »
I wonder what were the thoughts going round the MCC when Columbia's telemetry intially reported 2 flat tyres on 107? "this could be an interesting landing?"

Offline psloss

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #31 on: 07/01/2007 05:17 pm »
Quote
gordo - 1/7/2007  1:09 PM

I wonder what were the thoughts going round the MCC when Columbia's telemetry intially reported 2 flat tyres on 107? "this could be an interesting landing?"
Bailout, speculatively.  This was discussed in e-mails during the mission and was then extensively reported after the disaster; here's Bill Harwood's story:
http://www.spaceflightnow.com/shuttle/sts107/030226email/

You can find the e-mails here, along with the transcript of the teleconference with JSC flight engineers Bob Doremus and Jeff Kling (Kling was the MMACS officer in the MCC):
http://www.nasa.gov/columbia/media/Media_Resources_Archives.html

Offline gordo

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #32 on: 07/01/2007 05:34 pm »
thanks for these, very sobering

Offline brahmanknight

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #33 on: 07/01/2007 06:10 pm »
Wow.....those articles are VERY sobering.  Sent chills down my back.  Even if Columbia had made it to Florida, the gear may not have worked.  With such a heavy payload, they would have been doomed in almost any landing possibility.

Offline psloss

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Re: STS-117 Landing Gear Slow to Drop?
« Reply #34 on: 07/01/2007 06:18 pm »
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gordo - 1/7/2007  1:34 PM

thanks for these, very sobering
I shouldn't prolong this tangent unless it is disassociated with the unrelated observation that prompted this thread, but if you read the transcript in Harwood's story, they lost the tire pressure measurements (the measurements went off-scale low).  Which isn't the same thing as a "flat."

Offline rkoenn

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RE: STS-117 Landing Gear Slow to Drop?
« Reply #35 on: 07/05/2007 12:43 am »
I work mechanisms for NASA on OV-104 which includes the landing gear and tires.  We actually own the mechanism and not the hydraulic systems.  The delta between the left and right main gear was 1.2 seconds but I have heard nothing about any concerns with this.  There are pyro explosives to blow the gear open if the hydraulic systems fail but they have never had to be used from what I know.  Also, there is a large delay between door closures during landing gear retract.  In the early days it was very large and also funny to watch someone uninitiated observe a gear retract.  The gear go up with right going first.  In those days the right would close with the left gear about 80% retracted.  However when the right gear closed completely it would release hydraulic pressure and the left would fall back to about 25% closed which would really freak out anyone not prepared for that to happen right behind their back.  There was a mod done later to the hydraulics to prevent this large pressure drop so the gear actually barely falls at all anymore.  And for those who don't know, the nose gear cannot retract and close the doors completely under hydraulics.  Hence there is a broom brigade that uses push brooms wrapped in foam at 4 locations to push the door tightly closed.

Offline psloss

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RE: STS-117 Landing Gear Slow to Drop?
« Reply #36 on: 07/05/2007 09:48 am »
Quote
rkoenn - 4/7/2007  8:43 PM

I work mechanisms for NASA on OV-104 which includes the landing gear and tires.  We actually own the mechanism and not the hydraulic systems.  The delta between the left and right main gear was 1.2 seconds but I have heard nothing about any concerns with this.
Thanks.

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