Boeing 717 and Horizontal Stabiliser Jackscrews

[Justin Wigg]

Hi all...

Watched that air disaster investigation thing on 7 last night and am
now wondering...

Did Boeing make any alterations to the MD-80 design when it became the
717, and in particular does the 717 retain the single-point failure
problem with the horizontal stabiliser jack-screws? I know that the
NTSB recommended a design change (see <http://tinyurl.com/52cov>), but
this newbie is unaware how much clout a "recommendation" from NTSB
really carries. I'm guessing that there has been no change.

(I was thinking that you could overcome the single-point failure by
using two screws with independant drive motors, but then you would
still have the same problem if *one* of the screws jammed up I
guess...)

Thanks in advance.

[JB]

I wonder how the horizontal stabilisers are moved on all (Airbus and Boeing)
of the other types?

JB

Post by Justin Wigg
Hi all...
Watched that air disaster investigation thing on 7 last night and am
now wondering...
Did Boeing make any alterations to the MD-80 design when it became the
717, and in particular does the 717 retain the single-point failure
problem with the horizontal stabiliser jack-screws? I know that the
NTSB recommended a design change (see <http://tinyurl.com/52cov>), but
this newbie is unaware how much clout a "recommendation" from NTSB
really carries. I'm guessing that there has been no change.
(I was thinking that you could overcome the single-point failure by
using two screws with independant drive motors, but then you would
still have the same problem if *one* of the screws jammed up I
guess...)
Thanks in advance.
--
SQL> select * from users | Justin Wigg - Melbourne, AUSTRALIA
where clue > 0; | http://www.dws.com.au

[BB]

Post by JB
I wonder how the horizontal stabilisers are moved on all (Airbus and Boeing)
of the other types?
JB

Same JB... They're all just jackscrews (overgrown worm and nut drives
I guess).. The differences is in what drives the mechanism - some are
fully electric (a la 707, 727, 737 etc.) and others are driven
hydraulically but with electric control (767, 747, DC-10 & Airbus
etc.)...


Regards,
BB.

[JB]

That's exactly what I expected. It strikes me as a simple, powerful, and
accurate way of controlling the stab.

JB

Post by BB

Post by JB
I wonder how the horizontal stabilisers are moved on all (Airbus and Boeing)
of the other types?
JB

Same JB... They're all just jackscrews (overgrown worm and nut drives
I guess).. The differences is in what drives the mechanism - some are
fully electric (a la 707, 727, 737 etc.) and others are driven
hydraulically but with electric control (767, 747, DC-10 & Airbus
etc.)...
Regards,
BB.

[Graeme Hogan]

Does the nut consist of a re-ciculating ball as per the flap jacks.

Post by JB
That's exactly what I expected. It strikes me as a simple, powerful, and
accurate way of controlling the stab.
JB

Post by BB

Post by JB
I wonder how the horizontal stabilisers are moved on all (Airbus and Boeing)
of the other types?
JB

Same JB... They're all just jackscrews (overgrown worm and nut drives
I guess).. The differences is in what drives the mechanism - some are
fully electric (a la 707, 727, 737 etc.) and others are driven
hydraulically but with electric control (767, 747, DC-10 & Airbus
etc.)...
Regards,
BB.

[BB]

Post by Graeme Hogan
Does the nut consist of a re-ciculating ball as per the flap jacks.

Yes, they all have recirculating balls to minimise wear and
friction..... As for the nuts - on the 747 and 747-400 there are 2
nuts - a primary nut and a secondary nut... The two are splined and
bolted together... The primary nut has recirculating ball bearings and
takes all the load in normal operations... The secondary nut comes
into play if the primary nut fails... The secondary nut also has
internal threading if the ball return path fails... The 767 is the
same but I can't comment specifically on other types (I'd be surprised
if they were different though)...


Regards,
BB.

[Trevor Fenn]

Post by BB

Post by Graeme Hogan
Does the nut consist of a re-ciculating ball as per the flap jacks.

Yes, they all have recirculating balls to minimise wear and
friction.....

Looks like that's not the case with the MD80

Loading Image...





As for the nuts - on the 747 and 747-400 there are 2

Post by BB
nuts - a primary nut and a secondary nut...

OK, I have to ask.....

Could it be that a 747 has bigger nuts than...oh, say an airbus?


:)
:)

TF

[BB]

Post by Trevor Fenn

Post by BB
Yes, they all have recirculating balls to minimise wear and
friction.....

Looks like that's not the case with the MD80
http://www.ntsb.gov/events/2000/aka261/GimbalNut.jpg

There you go... Apparently that a/c uses an Acme nut... Consider me surprised..

:-)


Regards,
BB.

[Brian May]

JB> That's exactly what I expected. It strikes me as a simple,
JB> powerful, and accurate way of controlling the stab.

Experts on the TV show were quoted as saying it was unacceptable to
have a single source of failure[1]. They said this was an exception to
basic safety principles in aviation, where there should always be
numerous backups of anything that could fail, and this issue should
never have occurred. The show never said how this single source of
failure could be avoided.

Notes:

[1] Not sure I buy this argument, there are plenty of potential single
sources of failure in aviation. e.g. if a rudder falls off...

[Rob]

Post by Brian May
JB> That's exactly what I expected. It strikes me as a simple,
JB> powerful, and accurate way of controlling the stab.
Experts on the TV show were quoted as saying it was unacceptable to
have a single source of failure[1]. They said this was an exception to
basic safety principles in aviation, where there should always be
numerous backups of anything that could fail, and this issue should
never have occurred. The show never said how this single source of
failure could be avoided.
[1] Not sure I buy this argument, there are plenty of potential single
sources of failure in aviation. e.g. if a rudder falls off...

I think in the aircraft industry whilst they do have backup systems if
one fails -- the term used is "fail safe" and should have been applied
in this instant.

[Sylvia Else]

Post by Rob

Post by Brian May
JB> That's exactly what I expected. It strikes me as a simple,
JB> powerful, and accurate way of controlling the stab.
Experts on the TV show were quoted as saying it was unacceptable to
have a single source of failure[1]. They said this was an exception to
basic safety principles in aviation, where there should always be
numerous backups of anything that could fail, and this issue should
never have occurred. The show never said how this single source of
failure could be avoided.
[1] Not sure I buy this argument, there are plenty of potential single
sources of failure in aviation. e.g. if a rudder falls off...

I think in the aircraft industry whilst they do have backup systems if
one fails -- the term used is "fail safe" and should have been applied
in this instant.

It seemed to me that the pivot point could be positioned so that a
catastrophic jackscrew failure caused the tailplane to adopt a neutral
position that didn't make the aircraft unflyable.

The jackscrew could be duplicated. A jam in either would lock the
tailplane in position, but that's not such a huge problem compared with
total failure of the screw.

Sylvia.

[matt weber]

Post by Justin Wigg
Hi all...
Watched that air disaster investigation thing on 7 last night and am
now wondering...
Did Boeing make any alterations to the MD-80 design when it became the
717, and in particular does the 717 retain the single-point failure
problem with the horizontal stabiliser jack-screws? I know that the
NTSB recommended a design change (see <http://tinyurl.com/52cov>), but
this newbie is unaware how much clout a "recommendation" from NTSB
really carries. I'm guessing that there has been no change.
(I was thinking that you could overcome the single-point failure by
using two screws with independant drive motors, but then you would
still have the same problem if *one* of the screws jammed up I
guess...)
Thanks in advance.

What makes you think the 717 is an MD80 derivative?

hate to disillusion you, but it isn't. It is really a re-worked
D9-40!
.
MD80/90 have 1209 ft^2 wings, 107.8 feet wingtip to wingtip.
717 has a 1001ft^2 wing, 93.3 feet, same as all D9's
D9-40 is 125 feet long, 717-200 is 124 feet, EW's are within a few per
cent. One of the reason the 717 was so cheap to design and build, is
that it is built from existing D9 tooling.

[Bernie Samms]

Wouldn't they have been able to build an MD80/90 derivative from MD 80
tooling or had they scrapped that? One just assumes that the later aircraft
would be a better platform than the older DC9 series??
--
Bernie Samms
Kingston Beach Tasmania

Aero Club of Southern Tasmania www.acst.com.au
Prologic Pty Ltd www.prologic.com.au

Out Mail has been checked by Norton Anti Virus but no absolute guarantee is
made that mail or attachment(s) are virus free.

Post by matt weber

Post by Justin Wigg
Hi all...
Watched that air disaster investigation thing on 7 last night and am
now wondering...
Did Boeing make any alterations to the MD-80 design when it became the
717, and in particular does the 717 retain the single-point failure
problem with the horizontal stabiliser jack-screws? I know that the
NTSB recommended a design change (see <http://tinyurl.com/52cov>), but
this newbie is unaware how much clout a "recommendation" from NTSB
really carries. I'm guessing that there has been no change.
(I was thinking that you could overcome the single-point failure by
using two screws with independant drive motors, but then you would
still have the same problem if *one* of the screws jammed up I
guess...)
Thanks in advance.

What makes you think the 717 is an MD80 derivative?
hate to disillusion you, but it isn't. It is really a re-worked
D9-40!
.
MD80/90 have 1209 ft^2 wings, 107.8 feet wingtip to wingtip.
717 has a 1001ft^2 wing, 93.3 feet, same as all D9's
D9-40 is 125 feet long, 717-200 is 124 feet, EW's are within a few per
cent. One of the reason the 717 was so cheap to design and build, is
that it is built from existing D9 tooling.

[matt weber]

On Sat, 30 Oct 2004 03:23:27 GMT, "Bernie Samms"

Post by Bernie Samms
Wouldn't they have been able to build an MD80/90 derivative from MD 80
tooling or had they scrapped that? One just assumes that the later aircraft
would be a better platform than the older DC9 series??

To be blunt it was easier just to cost improve an existing 100 seat
design (the D9-40), than it was to try to shrink a more recent design
(and much heavier design) to 100 seats. On a short haul aircraft, the
drivers for cost are maintenance and fuel economy. The old D9's are
very simple machines. They tend to be cheap to look after because they
are simple, and tend not to have corrosion problems.

The BR715 is immensely more fuel efficient than the original JT8's,
and still significantly better than the JT8 200 series (a re-fanned
version).

When you stretch an air frame, it usually doesn't cost a lot in EW,
by the same token, when you shink one, you get very little back. The
result of working from the 9-40 is an EW savings of about 15,000
pounds over the smallest MD-80 (the MD87)

The much higher operating weights of the MD80 series necessitated a
new wing, and new tail section for the higher loads and larger
engines. The 717 actually has the MK II version of the D9 wing (the MK
I version had no leading edge devices and was only used on the -10 and
-15). The MD80/90 needed a substantially stronger tail section, as
the original JT8 engines only provided about 12-16000 pounds of thrust
and weighed about 3500 pounds each. The V2500 and JT8-200's used on
the MD80/90 are 20-22,000 pounds thrust for the -2xx series and 4500
pounds, the V2500's are 25,000 pounds and weigh 5600 pounds each.
The much higher MGTOW meant that the tail assemblies had to be
stronger in order to provide the attitude authority needed and carry
the additional engine weight. . MGTOW on the 9-40 is 114,000 pounds,
on an option 717 it is 121,000 pounds, so the original D9-40 tail
assembly is probably adequate. MD80/90 MGTOW start at 140,000 pounds
and can be as high as 172,000 pounds. The high weights also implies a
stronger undercarriage, fuselage, and wheel assemblies, while the
original D9-40 system would have adequate strength for the 717, and
weigh considerably less.

The BR715 is similar in weight the JT8-200 series, but with much
better fuel consumption, and the 717 EW is much more in line with the
D9-40's than the MD80/90 family.

[Bernie Samms]

Thanks Matt. That is very enlightening and makes heaps of sense. Just shows
that simplistic views like I had are just that!
--
Bernie Samms
Kingston Beach Tasmania

Aero Club of Southern Tasmania www.acst.com.au
Prologic Pty Ltd www.prologic.com.au

Out Mail has been checked by Norton Anti Virus but no absolute guarantee is
made that mail or attachment(s) are virus free.

Post by matt weber
On Sat, 30 Oct 2004 03:23:27 GMT, "Bernie Samms"

Post by Bernie Samms
Wouldn't they have been able to build an MD80/90 derivative from MD 80
tooling or had they scrapped that? One just assumes that the later aircraft
would be a better platform than the older DC9 series??

To be blunt it was easier just to cost improve an existing 100 seat
design (the D9-40), than it was to try to shrink a more recent design
(and much heavier design) to 100 seats. On a short haul aircraft, the
drivers for cost are maintenance and fuel economy. The old D9's are
very simple machines. They tend to be cheap to look after because they
are simple, and tend not to have corrosion problems.
The BR715 is immensely more fuel efficient than the original JT8's,
and still significantly better than the JT8 200 series (a re-fanned
version).
When you stretch an air frame, it usually doesn't cost a lot in EW,
by the same token, when you shink one, you get very little back. The
result of working from the 9-40 is an EW savings of about 15,000
pounds over the smallest MD-80 (the MD87)
The much higher operating weights of the MD80 series necessitated a
new wing, and new tail section for the higher loads and larger
engines. The 717 actually has the MK II version of the D9 wing (the MK
I version had no leading edge devices and was only used on the -10 and
-15). The MD80/90 needed a substantially stronger tail section, as
the original JT8 engines only provided about 12-16000 pounds of thrust
and weighed about 3500 pounds each. The V2500 and JT8-200's used on
the MD80/90 are 20-22,000 pounds thrust for the -2xx series and 4500
pounds, the V2500's are 25,000 pounds and weigh 5600 pounds each.
The much higher MGTOW meant that the tail assemblies had to be
stronger in order to provide the attitude authority needed and carry
the additional engine weight. . MGTOW on the 9-40 is 114,000 pounds,
on an option 717 it is 121,000 pounds, so the original D9-40 tail
assembly is probably adequate. MD80/90 MGTOW start at 140,000 pounds
and can be as high as 172,000 pounds. The high weights also implies a
stronger undercarriage, fuselage, and wheel assemblies, while the
original D9-40 system would have adequate strength for the 717, and
weigh considerably less.
The BR715 is similar in weight the JT8-200 series, but with much
better fuel consumption, and the 717 EW is much more in line with the
D9-40's than the MD80/90 family.

[BB]

Post by Justin Wigg
Hi all...
Watched that air disaster investigation thing on 7 last night and am
now wondering...
Did Boeing make any alterations to the MD-80 design when it became the
717, and in particular does the 717 retain the single-point failure
problem with the horizontal stabiliser jack-screws? I know that the
NTSB recommended a design change (see <http://tinyurl.com/52cov>), but
this newbie is unaware how much clout a "recommendation" from NTSB
really carries. I'm guessing that there has been no change.
(I was thinking that you could overcome the single-point failure by
using two screws with independant drive motors, but then you would
still have the same problem if *one* of the screws jammed up I
guess...)
Thanks in advance.

The B717 is a re-named MD-95... IIRC it's the only civil McDonnell
Douglas product Boeing still make..

Every Boeing (and Douglas for that matter) since the 707/DC-8 use a
similar system to trim the stab. It's simple and, if maintained
correctly, reliable too. I couldn't imagine there being major changes
- a complete redesign (rather than detail changes) mandated by an AD
for example would be a can of worms because it could be argued that it
would have to apply to all aircraft moveable stabilisers (and that's
every jet flying)...

Regards,
BB.

[alpha]

Isn't this setup (screw jack) the same as the Rack & Pin steering
arrangement on our cars? 100km approaching a left hand bend and she jams
not looking good Jan, with the semi coming the otherway!!!!

Single point of failure...think i will get that bit serviced this w/end.

food for thought
Alpha

Post by BB

Post by Justin Wigg
Hi all...
Watched that air disaster investigation thing on 7 last night and am
now wondering...
Did Boeing make any alterations to the MD-80 design when it became the
717, and in particular does the 717 retain the single-point failure
problem with the horizontal stabiliser jack-screws? I know that the
NTSB recommended a design change (see <http://tinyurl.com/52cov>), but
this newbie is unaware how much clout a "recommendation" from NTSB
really carries. I'm guessing that there has been no change.
(I was thinking that you could overcome the single-point failure by
using two screws with independant drive motors, but then you would
still have the same problem if *one* of the screws jammed up I
guess...)
Thanks in advance.

The B717 is a re-named MD-95... IIRC it's the only civil McDonnell
Douglas product Boeing still make..
Every Boeing (and Douglas for that matter) since the 707/DC-8 use a
similar system to trim the stab. It's simple and, if maintained
correctly, reliable too. I couldn't imagine there being major changes
- a complete redesign (rather than detail changes) mandated by an AD
for example would be a can of worms because it could be argued that it
would have to apply to all aircraft moveable stabilisers (and that's
every jet flying)...
Regards,
BB.

[budgie]

Post by alpha
Isn't this setup (screw jack) the same as the Rack & Pin steering
arrangement on our cars? 100km approaching a left hand bend and she jams
not looking good Jan, with the semi coming the otherway!!!!
Single point of failure...think i will get that bit serviced this w/end.

There are so many SPOF's in your average car that you have to learn to live with
mortality. Errr, that didn't quite come out the way I intended.

[John Ewing]

Post by budgie

Post by alpha
Isn't this setup (screw jack) the same as the Rack & Pin steering
arrangement on our cars? 100km approaching a left hand bend and she jams
not looking good Jan, with the semi coming the otherway!!!!
Single point of failure...think i will get that bit serviced this w/end.

There are so many SPOF's in your average car that you have to learn to live with
mortality. Errr, that didn't quite come out the way I intended.

Yes, but I suspect the overwhelming SPOF is the driver of the vehicle.
My guess is that mechanical deficiencies are rarely the principal factor in
serious motor vehicle accidents.
In aviation, however, mechanical failure is a major factor in many
accidents.

John

[Johnie]

"John Ewing" <***@needed> wrote in message news:418587b1$0$22806$***@news.optusnet.com.au...

without taking the piss out of anyone, why would it be different just
because it's a pilot and not a car driver?

johnie

[budgie]

Post by Johnie
without taking the piss out of anyone, why would it be different just
because it's a pilot and not a car driver?

As I point out to my commercial pilot son, if he has an engine fail in his car,
it's an inconvenience. In the plane, it's an issue.

[Brian May]

budgie> As I point out to my commercial pilot son, if he has an
budgie> engine fail in his car, it's an inconvenience. In the
budgie> plane, it's an issue.

No, an engine failure in a car could be dangerous too (consider
pulling out in front of a semi-trailer truck with the expectation of
accelerating but finding the engine dies), just the chances of it
being dangerous in an aircraft are much higher.

[budgie]

Post by Brian May
budgie> As I point out to my commercial pilot son, if he has an
budgie> engine fail in his car, it's an inconvenience. In the
budgie> plane, it's an issue.
No, an engine failure in a car could be dangerous too (consider
pulling out in front of a semi-trailer truck with the expectation of
accelerating but finding the engine dies), just the chances of it
being dangerous in an aircraft are much higher.

True, but I was relating to single-vehicle situations, straight and level.

[Coop]

Post by John Ewing

Post by budgie

Post by alpha
Isn't this setup (screw jack) the same as the Rack & Pin steering
arrangement on our cars? 100km approaching a left hand bend and she jams
not looking good Jan, with the semi coming the otherway!!!!
Single point of failure...think i will get that bit serviced this w/end.

There are so many SPOF's in your average car that you have to learn to live with
mortality. Errr, that didn't quite come out the way I intended.

Yes, but I suspect the overwhelming SPOF is the driver of the vehicle.
My guess is that mechanical deficiencies are rarely the principal factor in
serious motor vehicle accidents.
In aviation, however, mechanical failure is a major factor in many
accidents.
John

Many, perhaps; but not most. I would have thought that human factors
were a greater concern in aviation, as you point out is the case with
car accidents.


Coop

[budgie]

Post by John Ewing

Post by budgie

Post by alpha
Isn't this setup (screw jack) the same as the Rack & Pin steering
arrangement on our cars? 100km approaching a left hand bend and she jams
not looking good Jan, with the semi coming the otherway!!!!
Single point of failure...think i will get that bit serviced this w/end.

There are so many SPOF's in your average car that you have to learn to live with
mortality. Errr, that didn't quite come out the way I intended.

Yes, but I suspect the overwhelming SPOF is the driver of the vehicle.

Quite often a/c incidents are the result of a long chain. Initially may have
been mechanical/structural/electrical, but the chain invariably seems to include
human links.

Post by John Ewing
My guess is that mechanical deficiencies are rarely the principal factor in
serious motor vehicle accidents.
In aviation, however, mechanical failure is a major factor in many
accidents.

Thta's certainly not a tribute to the level of servicing or certification in
cars, rather to the lesser certainty of serious outcome when travelling in 2D.
A wheel falling off (with or without suspension parts) is very often survivable
without significant injury. When a wing falls off, ...... (recalling RMO or was
it RMQ?)

[Andrew Puddifer]

No, a rack and pinion setup is like a piece of flat metal with
teeth cut into it, which has a round pinion gear which turns and slides
it side to side.
The recirculation ball and nut setup is used in lots of older vehicles
(60's through early 80's) with steering boxes. It is a very simple and
reliable system in that application, and even with severe wear will
continue to work safely.

Regards, Andrew.

Post by alpha
Isn't this setup (screw jack) the same as the Rack & Pin steering
arrangement on our cars? 100km approaching a left hand bend and she jams
not looking good Jan, with the semi coming the otherway!!!!
Single point of failure...think i will get that bit serviced this w/end.
food for thought
Alpha

[BB]

Post by alpha
Isn't this setup (screw jack) the same as the Rack & Pin steering
arrangement on our cars? 100km approaching a left hand bend and she jams
not looking good Jan, with the semi coming the otherway!!!!
Single point of failure...think i will get that bit serviced this w/end.
food for thought
Alpha

Different to rack and pinion (as in steering)... It's more like the
"worm and recirculating ball" system used in some cars...

Regards,
BB.