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Topic: What Is That Thing On An Airliners Butt?
Username: VC10er
Posted 2012-12-27 16:15:58 and read 5142 times.

If many parts of an airplane have an animal body part as a name (nose, tail, wings, belly) then I call the APU exhaust hole and the slope under the rear fuselage ...the butt. So on some ac (perhaps just Boeing ???) there is an external long vertical device that has a drop down piece which is a long piece of metal.

I am so curious what that is? I see it on all 747 and 767's (I think) perhaps other types.

My guess:

It is a condensation / water outlet?

It helps prevent a tail scrape on take off by scraping the runway first and signals the pilot?

???

This may not turn into the most interesting post, but I'd truly appreciate someone enlightening me,
Thank you!

Topic: RE: What Is That Thing On An Airliners Butt?
Username: HermansCVR580
Posted 2012-12-27 18:04:06 and read 5049 times.

If you look at this picture of a 737 the larger part on the back of the tail that is for a tail strike the smaller one is a drain port.

http://www.airliners.net/photo/SkyTe...d=b1e3191187692f51e3c096b73b3a4e37

Topic: RE: What Is That Thing On An Airliners Butt?
Username: rwessel
Posted 2012-12-27 20:56:48 and read 4903 times.

Not quite sure what you're describing but this is a tail skid (in the deployed position) on a 773:


View Large View Medium
Click here for bigger photo!

Photo © Cornelius Saayman



And the tail strike protection on a 739:


View Large View Medium
Click here for bigger photo!

Photo © Manolo Aldana
View Large View Medium
Click here for bigger photo!

Photo © Jason Wood



Those are usually only fitted on longer aircraft with a greater risk of a tail strike.

One some aircraft, a simple fixed skid is attacked in that location.

Or are you referring to a tail stand:


View Large View Medium
Click here for bigger photo!

Photo © Rainer Bexten



Which exists to prevent (freighters, usually) from tipping back while being loaded. On some freighters the tail stand is integral, and drops down, on others, it's an external stand.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: Skydrol
Posted 2012-12-28 01:02:21 and read 4787 times.

Quoting VC10er (Thread starter):
If many parts of an airplane have an animal body part as a name (nose, tail, wings, belly) then I call the APU exhaust hole and the slope under the rear fuselage ...the butt. So on some ac (perhaps just Boeing ???) there is an external long vertical device that has a drop down piece...

I am so curious what that is?

You know exactly what that animal body part is called.  



  

LD4

Topic: RE: What Is That Thing On An Airliners Butt?
Username: VC10er
Posted 2012-12-28 08:16:54 and read 4605 times.

Quoting rwessel (Reply 2):

I think it's the tail strike protrusion. Does it deploy and detract?
I see them most clearly on a 767 or a 747 as a taxi by the rear end of them. For some reason I can't recall noting one on a 777. So, are these tail strike instruments just on Boeing?

And yes, from a body part perspective I guess one could argue that is one way 2 airplanes mate  

Topic: RE: What Is That Thing On An Airliners Butt?
Username: tb727
Posted 2012-12-28 09:04:55 and read 4570 times.

Quoting VC10er (Reply 4):
I think it's the tail strike protrusion. Does it deploy and detract?

On the 727 yes, it extends and retracts with the landing gear. Hydraulic on the -200 and Electric on the -100. It's a fairly noticeable fuel penalty if it is stuck extended.


727 Tailskid by a2pilot, on Flickr

Topic: RE: What Is That Thing On An Airliners Butt?
Username: airmagnac
Posted 2012-12-28 10:33:03 and read 4513 times.

Quoting VC10er (Thread starter):
there is an external long vertical device that has a drop down piece


Quoting tb727 (Reply 5):
Quoting VC10er (Reply 4):

Does it deploy and retract?

yes, it extends and retracts [...] It's a fairly noticeable penalty if it is stuck extended.


"animal body parts", he said...

   

Topic: RE: What Is That Thing On An Airliners Butt?
Username: AirframeAS
Posted 2012-12-28 12:13:03 and read 4458 times.

Quoting VC10er (Reply 4):
So, are these tail strike instruments just on Boeing?

I think there are some on the A320 and the A321. But I am not entirely positive on that.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: RussianJet
Posted 2012-12-28 12:44:48 and read 4429 times.

What are the tailstrike skids made out of? I'm imagining they're designed to take serious punishment - so what substance is deemed to withstand such a hammering in the event of a careless rotation?

Also, is it just careless rotation that can cause strikes? Are there perhaps on occasion something unaviodable/unforeseeable that can lead to them (e.g. an insane gust of wind - keeping with the butt theme....)?

Topic: RE: What Is That Thing On An Airliners Butt?
Username: rwessel
Posted 2012-12-28 13:31:06 and read 4397 times.

Quoting RussianJet (Reply 8):
What are the tailstrike skids made out of? I'm imagining they're designed to take serious punishment - so what substance is deemed to withstand such a hammering in the event of a careless rotation?

They don't really need to be that rugged - they're easily replaceable after being worn down. So whatever the manufacturer decides is appropriate. Also most tail strikes don't put all that a huge load on the ground at that point.

For the maximum performance takeoff tests during certification, most manufacturers will fit an extra large skid (often made of wood), because that test usually involves deliberately dragging the tail.

Quoting RussianJet (Reply 8):
Also, is it just careless rotation that can cause strikes? Are there perhaps on occasion something unaviodable/unforeseeable that can lead to them (e.g. an insane gust of wind - keeping with the butt theme....)?

Basically it is just "careless rotation", but things like gusts can impact it, as can a sudden need to get off the runway (let's say an obstacle suddenly appears). As I understand it, most commonly these result from a too aggressive early rotation, where the aircraft does not leave the ground soon enough because the airspeed is still too low (normally the deck angle continues to increase after takeoff). The problem is that long aircraft have less margin for overrotation because of their geometry, so have various forms of protection - these days electronic protection in the FBW system is popular.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: RussianJet
Posted 2012-12-28 13:34:21 and read 4392 times.

Quoting rwessel (Reply 9):
The problem is that long aircraft have less margin for overrotation because of their geometry, so have various forms of protection - these days electronic protection in the FBW system is popular.

Can such automated protection not be dangerous in the event of obstacle avoidance being necessary? Conceivably there must be a one in a million situation where a tailstrike would be the lesser of two evils, particularly when the other option might be smashing into another aircraft in the event of a runway incursion.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: rwessel
Posted 2012-12-28 13:55:09 and read 4370 times.

Quoting RussianJet (Reply 10):
Can such automated protection not be dangerous in the event of obstacle avoidance being necessary? Conceivably there must be a one in a million situation where a tailstrike would be the lesser of two evils, particularly when the other option might be smashing into another aircraft in the event of a runway incursion.

While I'm not familiar with the details, it seems this would be the same as the old AvB hard-vs-soft limits debate.

On one side, being able to reliably pull to with an inch or two of dragging the tail would give the pilot the confidence to haul back on the stick as hard as necessary, while giving almost maximum performance. On the other side, letting the pilot pull that last little bit in an emergency might help sometime.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: beiaard
Posted 2012-12-28 14:13:14 and read 4349 times.

Quoting VC10er (Thread starter):
If many parts of an airplane have an animal body part as a name (nose, tail, wings, belly) then I call the APU exhaust hole and the slope under the rear fuselage ...the butt.

Would the proper appellation of this perhaps be the "empennage"?

Topic: RE: What Is That Thing On An Airliners Butt?
Username: tdscanuck
Posted 2012-12-28 14:45:08 and read 4322 times.

Quoting RussianJet (Reply 10):
Can such automated protection not be dangerous in the event of obstacle avoidance being necessary? Conceivably there must be a one in a million situation where a tailstrike would be the lesser of two evils, particularly when the other option might be smashing into another aircraft in the event of a runway incursion.

The automated systems will let the tail get within about 6" of the runway. The performance benefit of getting the extra rotation of that 6" is wiped out by the drag of running the skid down the runway and the risk of damaging the structure. Whether you have a physical skid or an electronic skid, you're better off not hitting the tail on the runway even if you're trying to get off the runway right now.

Tom.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: RussianJet
Posted 2012-12-28 14:49:24 and read 4319 times.

Quoting tdscanuck (Reply 13):
The automated systems will let the tail get within about 6" of the runway. The performance benefit of getting the extra rotation of that 6" is wiped out by the drag of running the skid down the runway and the risk of damaging the structure. Whether you have a physical skid or an electronic skid, you're better off not hitting the tail on the runway even if you're trying to get off the runway right now.

Thanks for that Tom - makes sense.

Can you shed any light on what they are usually made of? I must say I'm surprised to hear that they don't take that much of a pounding in a tailstrike situation - is that really so?

Topic: RE: What Is That Thing On An Airliners Butt?
Username: tb727
Posted 2012-12-28 15:48:32 and read 4285 times.

Quoting RussianJet (Reply 8):

What are the tailstrike skids made out of? I'm imagining they're designed to take serious punishment - so what substance is deemed to withstand such a hammering in the event of a careless rotation?

That red block in my picture is just a piece of sacrificial metal, I don' t know what it is exactly but it's just there to get scrapped instead of the #2 engine exhaust hopefully. The silverish cylinder is like a piston that gets pushed up into the white part if the tail is hit. There is a little tab and a wire on the silver part about 3 or so inches from the white, if you get it good enough to compress it that far, the clip breaks off and hangs by the wire and you have to inspect the damage. You can actually push up on it and it moves up freely for a couple inches.

The best FE's or flight mechanics out there have a can of red spray paint and JB weld for the clip in their bag  j/k of course.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: strfyr51
Posted 2012-12-28 16:15:10 and read 4270 times.

the installed tail skid is an option that many airlines like and take. what it does is to keep the lower aft pressure bulkhead
from being damaged on takeoff which might very well save a LOT of lives. . Ive seen where the over-rotation of a 747-200 and -400, 767-300 757-200 and on rare occasions the 777-200 result in tail strikes where the repair is over a Million Dollars in time and Labor which might include the Boeing AOG Team. Who are highly skilled and specialized in these types of repairs.
At United We've made repairs of this nature and many other critical repairs up to and including Cracked rear wing spar splices to the 737-322's, rework of DC-10, 747 and 757 Pylons etc. But THAT particular repair is not only Time Critical. But people have Died from that repair Not having been done Completely correctly. The tail skid is WELL worth whatever Boeing charges for it as an option.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: Starlionblue
Posted 2012-12-28 22:12:34 and read 4157 times.

Quoting RussianJet (Reply 10):
Quoting rwessel (Reply 9):
The problem is that long aircraft have less margin for overrotation because of their geometry, so have various forms of protection - these days electronic protection in the FBW system is popular.

Can such automated protection not be dangerous in the event of obstacle avoidance being necessary? Conceivably there must be a one in a million situation where a tailstrike would be the lesser of two evils, particularly when the other option might be smashing into another aircraft in the event of a runway incursion.

There's a trap here for pilots. Sure, you can instinctively rotate aggressively before normal rotation speed but this probably won't get you the best rate of climb. So instead of increasing your obstacle clearance chances, it decreases them. Unless the aggressive rotation puts you right on best angle of climb I suppose.

It's a bit like pulling up instinctively to extend a glide, putting you below best glide speed and thus actually shortening the glide.

Also as Tom says.

Quoting tdscanuck (Reply 13):
The automated systems will let the tail get within about 6" of the runway. The performance benefit of getting the extra rotation of that 6" is wiped out by the drag of running the skid down the runway and the risk of damaging the structure. Whether you have a physical skid or an electronic skid, you're better off not hitting the tail on the runway even if you're trying to get off the runway right now.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: tdscanuck
Posted 2012-12-28 22:36:17 and read 4153 times.

Quoting RussianJet (Reply 14):
Can you shed any light on what they are usually made of?

As far as I know, they're just aluminum blocks. The big skids used in flight test are oak planks but that's a very different application.

Quoting RussianJet (Reply 14):
I must say I'm surprised to hear that they don't take that much of a pounding in a tailstrike situation - is that really so?

In most tailstrikes, the pilot just miscalculated by a little bit...so it's not like the rotation is accelerating as the skid hits, it's far more likely that the rotation is actually decelerating and the pilot just misjudged the control a little bit. Since the skid is very far back on the tail it doesn't take a lot of force to put a big torque into the fuselage. It's important to note that the skid is only "in use" for a few, maybe five at most, seconds...after that you're either off the ground or not going flying and derotating. And then it will be inspected and possibly replaced, so it doesn't have to stand up to abuse for very long.

I've been involved in one inadvertent tail strike...we knew it had happened right away by the sound...we flew home depressurized (major pain in the rear) and did the inspection...canister wasn't crushed, just a little paint ripped off. Maintenance called us good to go and out we went. And that was an intentionally aggressive rotation, we just captured the wrong angle.

Tom.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: yeelep
Posted 2012-12-29 01:10:39 and read 4106 times.

Quoting RussianJet (Reply 8):
What are the tailstrike skids made out of?

On the 737 the skid is made from heat treated 718 inconel.

Topic: RE: What Is That Thing On An Airliners Butt?
Username: T prop
Posted 2013-01-04 23:34:04 and read 3344 times.

I have only read about one instance of early rotation saving lives. It happened in the early eighty's when a Korean Air DC-10 on take off roll out of Anchorage encountered a Piper Chieftain lined up for take off on the other end of the runway. The DC-10 crew pulled the nose up just before running over the Chieftain. The nose wheels left tire marks on the top of the Pipers fuselage and knocked off the vertical stab. The Pipers fuselage went between the left and center main gears of the DC-10, One of the Pipers wings was torn off at the root and the other just outboard of the nacelle. The DC-10 continued off the end of the runway, burst into flames and was destroyed. Amazingly, there were no fatalities.

NTSB AAR-84/ 10


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