JulianUK
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Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 7:12 am

Reading about tail strikes, surely it should be automated, if you are going to tail strike there should be an automated warning that you are seconds away from scraping the back, and if you persists a forced pitch down through perhaps a radio altimeter at the back or some sort of distance protector. From what I understand you can still, even in the most modern of aircraft, pull the stick back strike the tail and cause a lot of "issues" as my pilot friends likes to call them..... Smile

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dw747400
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 7:19 am

I believe the A340-600 and 777-300ER have some form of electronic tail protection. Both are very long aircraft that require a significant amount of rotation at MGTOW. I'm sure someone has more detailed information.
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David L
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 7:32 am

Quoting Dw747400 (Reply 1):
Both are very long aircraft that require a significant amount of rotation at MGTOW.

Isn't it more to do with the fact that they require less rotation to strike the tail on the runway?
 
dw747400
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 7:48 am

Quoting David L (Reply 2):
Isn't it more to do with the fact that they require less rotation to strike the tail on the runway?

That is true too. The point I was trying to make is that both the 777-300ER and A340-600 represent dramtic increases in MGTOW compared to the baseline aircraft. Both have some wing modifications, but in general they either need to go faster or rotate to a higher angle of attack in order to produce enough lifts so that lift=weight. Not being a heavy pilot nor having performance charts, I don't have exact numbers, but there is a limit on takeoff speed set by both RTO needs/runway length, and tire speed limits. Thus, simply reducing the rotation angle for a stretch is not an option, and a long, heavy plane will be more prone to tail-strikes than a plane that is either lighter or shorter.

In short, the comment above was a poorly worded way of saying that you can't just reduce the rotation angle.

[Edited 2006-05-22 00:51:49]
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EssentialPowr
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 8:48 am

Quoting JulianUK (Thread starter):
Reading about tail strikes, surely it should be automated, if you are going to tail strike there should be an automated warning that you are seconds away from scraping the back

By the time of a warning, the tail strike has occurred so such a system would probably be of minimal value.

Tail strikes on the 737-800/900 are very possible in both takeoff and landing regimes. For takeoff, a slow rotation rate of about 2 degrees/sec is optimal. There is plenty of energy at Vr to accomodate the takeoff w/ the desired rotation rate.

In the case of the 777-300, I believe the gear truck is levered, in that it is locked for takeoff and rotates to remain in parallel with the fuselage. This enables the a/c to rotate off the aft axle as opposed to the center of the truck, which allows a higher initial rotation angle, which in turn provides some tail strike relief and enables shorter t/o distances. Landing is normal, in that the truck will rotate.
 
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Starlionblue
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 9:48 am

Quoting EssentialPowr (Reply 4):
Quoting JulianUK (Thread starter):
Reading about tail strikes, surely it should be automated, if you are going to tail strike there should be an automated warning that you are seconds away from scraping the back

By the time of a warning, the tail strike has occurred so such a system would probably be of minimal value.

As Mr Powr says, warning times are too short for anything but an automated tailstrike inhibitor.

Regarding the "surely it should be automated" part, you would be amazed how precise pilots can be in their handling of the big birds, and how precisely they can be handled. Just because a 380 or 747 looks ungainly and hard to maneuver doesn't mean that it is. Control surfaces are scaled up to match the rest of the plane.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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HAWK21M
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 2:01 pm

I've heard that the B777-300ER is equipped with Tail skid that senses the Proximity of it from the Surface below & accordingly sends a signal to Trim the Aircraft nose down to avoid the Strike.
Maybe someone having worked on the B773ER would know in detail.
regds
MEL
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David L
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 8:48 pm

Quoting HAWK21M (Reply 6):
I've heard that the B777-300ER is equipped with Tail skid that senses the Proximity of it from the Surface below & accordingly sends a signal to Trim the Aircraft nose down to avoid the Strike.
Maybe someone having worked on the B773ER would know in detail.

http://www.boeing.com/news/releases/2003/q4/nr_031016g.html

"If the tail gets too close to the ground, the system moves the elevator for slower nose rotation. During abuse takeoff testing, where Santoni has deliberately rotated the airplane early and fast, the system has responded as designed."
 
avioniker
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 9:43 pm

The Marconi/BAE HUD provides indications of an impending tailstrike. AA uses it in their 737's
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EssentialPowr
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 10:06 pm

David L, thanks for the reference...

Quoting HAWK21M (Reply 6):
I've heard that the B777-300ER is equipped with Tail skid that senses the Proximity of it from the Surface below & accordingly sends a signal to Trim the Aircraft nose down to avoid the Strike.

There's no sensor in the tail skid of any kind; its just that the flight computer computes the geometry...from the same article:

""It's in the primary flight computer," said Frank Santoni, Boeing 777 chief pilot, of the special feature. "It's a function that looks at rate of closure of the tail to the ground during rotation, measuring how fast and at what distance the tail is moving toward the pavement."
 
Qantas744er
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 10:10 pm

Correct, in the case of the 340-600 the Fly-by wire system always knows the max AOA (angle of attack) so that if the pilot would accidentaly not be aware of the the AOA the system would bring the nose back down again.

On any airbus model exept the a300 and a310 the pilot can set a digital pitch bar in the PFD so that he knows he shouldnt pull over that bar. But there was an incident in JNB 2 years ago, were a EK a340 on TO the pilot didnt calculate the V1 Vr V2 properly and accidently used a lower TO speed than needed, and because it was only his second flight on the a340 as a captain, and previously he learned on the a330 that using the pitch bar technique was ok, but a pilot should never only rely on this method.

So on TO the pilot tried to rotate the plane struck its tail for several hundred feet, and finally after the pilot engaged TOGA thrust mode the plane just made it off the RWY dumped fuel and made a successfull emergency landing.

Cheers Leo
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David L
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RE: Tail Strike Protection - Is Any Automated?

Mon May 22, 2006 10:19 pm

Quoting EssentialPowr (Reply 9):
David L, thanks for the reference...

No problem - I remembered it from one of those "FBW is Dangerous" discussions!  Smile
 
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RE: Tail Strike Protection - Is Any Automated?

Tue May 23, 2006 5:22 am

Tail strike protection is usually achieved with a tail bump... Basically a structure that hits the ground first and doesn't let the real tail hit.

I don't think indication is a solution, as time is very short during rotation. A FBW function to avoid tail strike through limiting elevator deflection in case of tail-ground proximity is possible... and already exists.
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VC-10
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RE: Tail Strike Protection - Is Any Automated?

Tue May 23, 2006 6:47 am

Quoting Qantas744ER (Reply 10):
Correct, in the case of the 340-600 the Fly-by wire system always knows the max AOA (angle of attack) so that if the pilot would accidentaly not be aware of the the AOA the system would bring the nose back down again.

That is not correct. A system such as this was tried during development but they found if the a/c pitched down the pilot just pulled back on the stick further. Instead now they have an idication on the PFD


 
EssentialPowr
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RE: Tail Strike Protection - Is Any Automated?

Tue May 23, 2006 8:55 am

Quoting HiFi (Reply 12):
Tail strike protection is usually achieved with a tail bump... Basically a structure that hits the ground first and doesn't let the real tail hit.

UUhhh...no. That skid is designed to protect the a/c as much as possible, but is certainly not to be used intentionally. If it is hit, the a/c is grounded for a fairly extensive inspection.

Tail strike protection, in the case of both manufacturers, consists of procedures and or software protection to prevent the skid from being hit in the first place.
 
Bobster2
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RE: Tail Strike Protection - Is Any Automated?

Tue May 23, 2006 9:27 am

Would a pilot ever want to do a tail strike on purpose? For example, the KLM pilot in the Tenerife crash caused a tail strike in his attempt to get over the Pan Am plane. I don't know if that was intentional, nor do I know if it helped get the plane off the ground quicker, or if it delayed getting the plane in the air.

If there was some advantage to a tail strike in an emergency, that would affect the protection system.
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EssentialPowr
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RE: Tail Strike Protection - Is Any Automated?

Tue May 23, 2006 10:30 am

Yes, that has happened. About 2 yrs ago an incident in DFW was avoided when a CAL crew rotated to the skid in a 737 to avoid a Delta a/c.
 
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Starlionblue
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RE: Tail Strike Protection - Is Any Automated?

Tue May 23, 2006 9:19 pm

Quoting Bobster2 (Reply 15):
Would a pilot ever want to do a tail strike on purpose?

During unstick speed testing the tail is dragged on the ground. But there's a skid installed to protect the tail.

Also as EssentialPowr says, you could do this for collision avoidance. But could it be that drag from the tail would exceed the advantage?
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don81603
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RE: Tail Strike Protection - Is Any Automated?

Tue May 30, 2006 7:18 pm

I believe Concorde equipped with a small tire in at the end of the fuse to deal with a tail strike. Could such a system be implimented in other long fuse aircraft, or would it entail a major redisign? I don't know what hydraulic or electrical systems are routed in the area, so...


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Photo © Fergal Goodman



[Edited 2006-05-30 12:23:39]
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Vimanav
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RE: Tail Strike Protection - Is Any Automated?

Tue May 30, 2006 8:22 pm

Quoting Don81603 (Reply 18):
I believe Concorde equipped with a small tire in at the end of the fuse to deal with a tail strike

As is the IL62.

just an observation.

rgds//Vimanav
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Starlionblue
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RE: Tail Strike Protection - Is Any Automated?

Tue May 30, 2006 9:11 pm

Quoting Don81603 (Reply 18):
I believe Concorde equipped with a small tire in at the end of the fuse to deal with a tail strike. Could such a system be implimented in other long fuse aircraft, or would it entail a major redisign? I don't know what hydraulic or electrical systems are routed in the area, so...

I'm sure it could be, but today you have tail skids doing the same thing.

It should also be noted that the situation might have been a bit more serius with Concorde since the engine exhausts would have hit the ground before the tail if not for the tail wheels.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Tom12
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RE: Tail Strike Protection - Is Any Automated?

Tue May 30, 2006 10:55 pm

While we are on the subject of tail strike on a jet, i noticed in one of the photos the other day there that the pad to prevent serious damage had hydraulics of somekind behind it and so i was wondering does this pad come down with the landing gear?

Tom
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Tom12
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RE: Tail Strike Protection - Is Any Automated?

Tue May 30, 2006 11:02 pm

http://www.airliners.net/open.file/0675034/L/

This is the image with the 763 and 764's tail strike pads down


Don't have the time to put the image in, sorry!

Tom
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HAWK21M
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RE: Tail Strike Protection - Is Any Automated?

Tue May 30, 2006 11:26 pm

Quoting Tom12 (Reply 22):
Don't have the time to put the image in, sorry


View Large View Medium
Click here for bigger photo!

Photo © Tony Marlow - WorldAirImages


regds
MEL
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Matt72033
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RE: Tail Strike Protection - Is Any Automated?

Wed May 31, 2006 12:01 am

Quoting Dw747400 (Reply 1):
I believe the A340-600 and 777-300ER have some form of electronic tail protection. Both are very long aircraft that require a significant amount of rotation at MGTOW. I'm sure someone has more detailed information.

i'm sure Airbus garunteed at some point it was impossible to tail strike a 600!
 rotfl 
 
AJ
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RE: Tail Strike Protection - Is Any Automated?

Fri Jun 02, 2006 3:50 pm

Quoting Tom12 (Reply 21):
While we are on the subject of tail strike on a jet, i noticed in one of the photos the other day there that the pad to prevent serious damage had hydraulics of somekind behind it and so i was wondering does this pad come down with the landing gear?

Tom

Hi Tom, on the 767-300 the tail skid extends and retracts with the landing gear.
 
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HAWK21M
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RE: Tail Strike Protection - Is Any Automated?

Fri Jun 02, 2006 6:31 pm

Quoting AJ (Reply 25):
Hi Tom, on the 767-300 the tail skid extends and retracts with the landing gear.

How is that Sequenced.Any details.What Logic.
regds
MEL
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sulman
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RE: Tail Strike Protection - Is Any Automated?

Fri Jun 02, 2006 7:56 pm

The trouble with automating the protection is that it limits the pilot's options should they want to over-rotate for any reason.
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HAWK21M
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RE: Tail Strike Protection - Is Any Automated?

Fri Jun 02, 2006 8:37 pm

Quoting Sulman (Reply 27):
The trouble with automating the protection is that it limits the pilot's options should they want to over-rotate for any reason.

Isn't that a Good thing.
What reasons are you qouting.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Pihero
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RE: Tail Strike Protection - Is Any Automated?

Fri Jun 02, 2006 8:57 pm

Quoting HAWK21M (Reply 28):
Quoting Sulman (Reply 27):
The trouble with automating the protection is that it limits the pilot's options should they want to over-rotate for any reason.

Isn't that a Good thing.
What reasons are you quoting.
regds
MEL

Don't pretend to be so innocent,MEL !
Real Boeings are supposed to be airplanes in which real pilots have the last say and will never ever ever be overruled by a computer !
Call NAV20 asap !
(Sorry, I couldn't help !)

[Edited 2006-06-02 13:59:35]

[Edited 2006-06-02 14:00:39]
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Tom12
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RE: Tail Strike Protection - Is Any Automated?

Sat Jun 03, 2006 3:16 am

Quoting HAWK21M (Reply 23):
Quoting Tom12 (Reply 22):
Don't have the time to put the image in, sorry



Quoting AJ (Reply 25):
Quoting Tom12 (Reply 21):
While we are on the subject of tail strike on a jet, i noticed in one of the photos the other day there that the pad to prevent serious damage had hydraulics of somekind behind it and so i was wondering does this pad come down with the landing gear?

Tom

Hi Tom, on the 767-300 the tail skid extends and retracts with the landing gear.

Thanks AJ, Mel
"Per noctem volamus" - Royal Air Force Bomber Squadron IX
 
bri2k1
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RE: Tail Strike Protection - Is Any Automated?

Sat Jun 03, 2006 3:55 am

Quoting HAWK21M (Reply 26):
How is that Sequenced.Any details.What Logic.

I'm gonna have to take a guess here that when the landing gear lever is in the "DOWN" position, the tail skid goes down too?
Position and hold
 
OldAeroGuy
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RE: Tail Strike Protection - Is Any Automated?

Sat Jun 03, 2006 11:41 pm

Quoting Pihero (Reply 29):
Don't pretend to be so innocent,MEL !
Real Boeings are supposed to be airplanes in which real pilots have the last say and will never ever ever be overruled by a computer !
Call NAV20 asap !
(Sorry, I couldn't help !)

The 773ER pilot can still put the tail skid on the runway to satisfy the Vmu speed requirement but the vertical velocity at skid contact will be very low.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
David L
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RE: Tail Strike Protection - Is Any Automated?

Sat Jun 03, 2006 11:47 pm

Quoting OldAeroGuy (Reply 32):
The 773ER pilot can still put the tail skid on the runway to satisfy the Vmu speed requirement but the vertical velocity at skid contact will be very low.

But would it get the aircraft airborne more quickly?
 
VC-10
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 1:42 am

Quoting Pihero (Reply 29):
Real Boeings are supposed to be airplanes in which real pilots have the last say and will never ever ever be overruled by a computer !

Famous last words, we'll revisit this in 5 years time.
 
OldAeroGuy
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 7:02 am

Quoting David L (Reply 33):
But would it get the aircraft airborne more quickly?

Not sure what you mean.

Vmu is about the lowest possible speed for lift off, not how quickly you can lift off.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
David L
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 7:41 am

Quoting OldAeroGuy (Reply 35):
Not sure what you mean.

Vmu is about the lowest possible speed for lift off, not how quickly you can lift off.

Sorry, I have a habit of forgetting that others may not be pursuing the same line of thought as I am  Smile. I meant in the context of deliberately "performing" a tail-strike to avoid an obstruction on the runway, addressing questions such as these...

Quoting Bobster2 (Reply 15):
Would a pilot ever want to do a tail strike on purpose? For example, the KLM pilot in the Tenerife crash caused a tail strike in his attempt to get over the Pan Am plane. I don't know if that was intentional, nor do I know if it helped get the plane off the ground quicker, or if it delayed getting the plane in the air.

If there was some advantage to a tail strike in an emergency, that would affect the protection system.



Quoting Starlionblue (Reply 17):
Also as EssentialPowr says, you could do this for collision avoidance. But could it be that drag from the tail would exceed the advantage?



Quoting Sulman (Reply 27):
The trouble with automating the protection is that it limits the pilot's options should they want to over-rotate for any reason.
 
Pihero
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 8:14 am

Quoting OldAeroGuy (Reply 32):
The 773ER pilot can still put the tail skid on the runway to satisfy the Vmu speed requirement but the vertical velocity at skid contact will be very low.

I had a conversation with a T7 instructor on the subject and he told me the software had been "changed" to allow the test ; he confirmed the impossibility to scrape the tail of a 773 in normal ops.

Quoting David L (Reply 33):
But would it get the aircraft airborne more quickly?

A pilot attemting that maneuver would find himself :
1/-airborbe with a very poor climbing performance and acceleration
2/-very close to a stall. He'd need some real fine precision flying.
3/-probably crashing into the obstacle he was trying to avoid.
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David L
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 8:28 am

Quoting Pihero (Reply 37):
I had a conversation with a T7 instructor on the subject and he told me the software had been "changed" to allow the test ; he confirmed the impossibility to scrape the tail of a 773 in normal ops.

Ah, I'd forgotten about that! So, Airbus may be more "evil" but Boeing are sneaking in there.  biggrin 

Quoting Pihero (Reply 37):
A pilot attemting that maneuver would find himself :
1/-airborne with a very poor climbing performance and acceleration
2/-very close to a stall. He'd need some real fine precision flying.
3/-probably crashing into the obstacle he was trying to avoid.

That was my suspicion but far be it for me to suggest it myself.  Smile
 
FlyDeltaJets
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 11:26 am

My guess to as to why the -600 doesn't have a tail skid is it's height off the ground. Am I correct in this thinking
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OldAeroGuy
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 11:34 am

Quoting Pihero (Reply 37):
I had a conversation with a T7 instructor on the subject and he told me the software had been "changed" to allow the test ; he confirmed the impossibility to scrape the tail of a 773 in normal ops.

The instructor is incorrect. The flight test was performed with the same software that is on the airplane today.

If the instructor was correct, the Vmu test performed would not match the Vmu capability of the airplane. There the scheduled Vmu speed would be incorrect.

Think about this as an anology. Initial airplane models establish a Vmu consistent with their ground contact angle. Later stretched versions of the same airplane (no wing changes) will have a higher Vmu at the same weight and T/W since their ground contact angle is less due tio their longer body length. If they changed the 773ER software to no allow tail skid contact, then the Vmu would need to change due to the lower body attitude the pilot could actually achieve.

Plus I've discussed this with the 773ER Flight Control software engineers and they ought to know.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Pihero
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 5:57 pm

Quoting OldAeroGuy (Reply 40):
The instructor is incorrect. The flight test was performed with the same software that is on the airplane today.

I'm going to have a serious argument with this guy !
What he told me was that the Vmu test is just about performance. They established the Vmu/Vlo couple on which to base the further V computations as "it was agreed with the FAA that the difference between a tail-scrapping Vlof and the protected-tail Vlof would be epsilon" (me quoting my friend).
After some research, I found this link which explains the take off performance for ground angle restricted airplanes.
It would be interesting to know for sure how the T7 performance was really established.
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chksix
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RE: Tail Strike Protection - Is Any Automated?

Sun Jun 04, 2006 8:02 pm

Are the Vmu speeds from testing available somewhere or are they kept secret?

I can't find any data in the 737 flight manual. It claims that detailed data is calculated in the dispatch computers so they kept all tables simple in the manual.

I've tried googling but no results yet except this:
http://www.wingfiles.com/files/safety/tailstrike.htm
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chksix
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RE: Tail Strike Protection - Is Any Automated?

Mon Jun 05, 2006 7:45 pm

What I'm looking for specifically are:
FAR A16WE-§25.101 to §25.149

I guess they are locked up by Boeing  Sad
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EssentialPowr
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RE: Tail Strike Protection - Is Any Automated?

Tue Jun 06, 2006 4:36 am

Quoting FlyDeltaJets (Reply 39):
My guess to as to why the -600 doesn't have a tail skid is it's height off the ground. Am I correct in this thinking

Yes and no...Tail clearance is a function of the geometry of the a/c (theoretically) rotated about the mains until the tail touches. It is a function of height off the ground, ANd the length of fuselage past the mains. For landing, its about 12 degrees nose up for a -500, and probably similar for the -600, since in order to maintain the same type rating, the cockpit sight picture had to be very similar b/t the NG and classic a/c.

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