Subject: hydraulic problems with DC-10's??

From: [email-masked]
Date: Wed, 18 Nov 92 10:02:08 -0500

Great new newsgroup!

Perhaps now I can get a more definitive answer to the following:

Some of my pilot friends have accused the DC-10 as having a
particularly bad history of hydraulic problems (which have contributed
to a few crashes).  But do the statistics really support the notion
that the DC-10 really has a significantly worse safety record than
other wide-body jets, or is this just a myth?  Also, have all these
hydraulic problems been corrected, or does the DC-10 still suffer from
hydraulic problems even today?

---

From: [email-masked] (Karl Swartz)
Date: Wed, 18 Nov 1992 20:50:05 GMT

In article <[email-masked]> [email-masked] writes:
>particularly bad history of hydraulic problems (which have
>contributed to a few crashes).

Two, at least.  AA 191 at Chicago/O'Hare on May 25, 1979, and UA 232
at Sioux City, Iowa on July 19, 1989.  The Turkish Airlines crash near
Paris on March 3, 1974 helped set up UA 232 though I'm never seen any
reference to the hydraulics as being contributory to that crash.

>But do the statistics really support the notion that the DC-10 really
>has a significantly worse safety record than other wide-body jets, or
>is this just a myth?

After the A320 crash at Strasbourg early this year I saw something
that said the A320 had overtaken the DC-10 as having the worst safety
record of any large jetliner and that both were an order of magnitude
worse than the third-place contender.  I really wish I could find the
reference, but alas, I can't.  I don't recall the metrics used, and
one could certainly debate the statistical validity given the small
samples involved.

Another view is to look at the number of airworthiness directives (AD)
issued by the FAA in the US for the DC-10 versus its contemporaries.
As of January 1, 1982, the DC-10 had 148, far ahead of Boeing's 747
with 57 and Lockheed's L-1011 with 51.  The FAA clearly found a lot
more to worry about in the DC-10.

Probably the best general interest discussion of the DC-10 and all its
problems is in The Sporty Game, by John Newhouse (Alfred A. Knopf, New
York, 1982).  Chapter 5 in particular goes into great detail, though
it of course predates the Sioux City crash.

>Also, have all these hydraulic problems been corrected, or does the
>DC-10 still suffer from hydraulic problems even today?

The DC-10 (and the MD-11) haven't "suffered" from them recently,
though the problems still exist.  Fundamentally, the DC-10's hydraulic
system shortcomings as compared to the 747 and L-1011 are that there
are only three, instead of four, giving less redundancy, and they tend
to be routed together so that something which affect one probably will
affect all three.  Boeing and Lockheed (and I believe Airbus) used
three hydraulic systems in any one area of the plane, providing the
mandated redundancy, but used four overall so that a problem which
caused the failure of all three systems in one part of the aircraft
would still leave control in other areas via the intact fourth system.
They also chose to route the three systems independently, again to
minimize the possibility of complete failure.

As mentioned, I don't believe the Paris crash involved the hydraulics,
but it did lead McDonnell-Douglas to relocate the control cables and
hydraulics from under the cabin floor, where the cables had been
severed by a collapsing floor, to the top of the cabin.  This simply
left them vulnerable to a different failure mode -- demonstrated 15
years later when the fan on UA 232's #2 engine disintigrated and sent
shrapnel through the top of the aft fuselage, including all three of
those hydraulic lines.  Clearly a more reasonable solution would have
been to move only *some* of the lines after the Paris crash, but this
was not done and has not been done since, though some check valves
were added to minimize the impact.

The vulnerable location of the hydraulics at the leading edge of the
wing, instead of a mid-wing and/or trailing edge location as used by
other manufacturers, precipitated the Chicago crash, and the lack of
any mechanical locking mechanism to prevent uncommanded flap retrac-
tion also played a significant part.  (The largest blame was placed
on American Airlines for improper maintenance practices, though the
airframe certainly received its share of blame.)  While I believe the
locking mechanism was later added, nothing was done about the routing
of the hydraulics.  Indeed, American requested a modification kit to
move the hydraulics and was willing to pay for it, but McDonnell-
Douglas refused.

I'll leave you to draw your own conclusions, but I certainly do not
feel comfortable flying on the DC-10, even though I've flown on them
many times.  I fly SFO-ORD somewhat often and do my best to catch one
of the 747 flights United offers or a 757.

-- 
Karl Swartz	|INet	[email-masked]		
1-415/854-3409	|UUCP	uunet!decwrl!ditka!kls
		|Snail	2144 Sand Hill Rd., Menlo Park CA 94025, USA
 Send sci.aeronautics.airliners submissions to [email-masked]

---

From: [email-masked] (Michael Weiss)
Date: 24 Nov 92 17:40:41 GMT

In article <[email-masked]> [email-masked] (Karl Swartz) writes:
>at Sioux City, Iowa on July 19, 1989.

I have a hard time believing that an intact hydraulic system would have
prevented AA191 from crashing.  Let's face it, a wing-mounted engine falling
off produces such a rediculous unbalance that even full aileron wouldn't be
able to counter it.
-- 
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---

From: [email-masked] (Karl Swartz)
Date: Wed, 25 Nov 1992 00:40:06 GMT

>off produces such a rediculous unbalance that even full aileron wouldn't be

I don't see that ailerons have much to do with it -- the biggest
effect would be a substantial yaw, which would require rudder input.

In any case, start believing.  A United 747 (N4713U, now N4724U)
operating a HNL-SYD flight on Feb. 23, 1989 lost both engines on the
right side due to debris ingestion after a cargo hatch failed.  They
dumped fuel and limped back to Honolulu, well over an hour's flying
time.

Having lots of altitude and airspeed to work with is certainly quite
helpful, but isn't a requirement.  A few years ago a Piedmont 737-200
lost #2 immediately after takeoff from O'Hare.  The pilots promptly
declared an emergency, turned around, and landed several minutes later
on another runway.  They didn't even realize that the engine had
litterally fallen off until the got off he plane and looked.

Getting back to AA 191, what really killed AA 191 was a stall of the
left wing after the uncommanded retraction of the flaps on that side.
Even this was recoverable had the pilots known that their stall speed
was suddenly higher -- alas, McDonnell-Douglas didn't bother with any
redundancy for the flap retraction warning and that happened to be
powered by the engine that fell off.  In simulator tests after the
crash, every pilot crashed when confronted with the same scenario.
When given this indicator, and thus some indication of what was going
on, every pilot managed to maintain control of the aircraft.

An engine separation, while certainly not a normal event, should not
be a fatal event, and indeed the certification process requires some
consideration of an engine separation.

---

From: [email-masked] (Randolph Bentson)
Date: Wed, 25 Nov 1992 04:54:00 GMT

>off produces such a rediculous unbalance that even full aileron wouldn't be

The problem was that when the hydraulics failed,  leading edge
slat retracted on one side and that wing stalled.  No indication
was given in the cockpit so the flight crew didn't use the
appropriate recovery mechanism.

Ref: "The DC-10 Case", John H. Feilder & Douglas Birsch, eds.

-- 
    Randolph Bentson                 Colorado State University
    [email-masked]         Computer Science Department
    303/491-5792                     Ft. Collins, CO 80523

---

From: [email-masked] (Robert Dorsett)
Date: Wed, 25 Nov 92 06:58:52 CST

>effect would be a substantial yaw, which would require rudder input.

In the NTSB report on the DC-10 crash, a considerable amount of both yaw
and rudder were necessary to regain level flight, in the simulator tests--
80% right rudder and 70% right-wing-down aileron; roll angles didn't
exceed 30 degrees before recovery.  

Normally, given asymmetric thrust, you bank into the good engine(s): rudder's 
normally used to augment the ailerons as necessary to control sideslip.

>litterally fallen off until the got off he plane and looked.

There are actually two issues at work, here: one is the *power* lost by 
the engine.  To maintain level flight, the power required for flight must
equal the power available.  If the power available is less, one will start
to descend; if it's a lot less, one will descend faster.  The real issue is 
just power: it has little to do with where the failure was: losing two
of three engines on a 727 at MTOW means you'll go down, too.

The second issue is the moment produced by the combination of the "dead"
engine (with its drag) and the "good" engines.  This is generally a minimal
issue, assuming the airspeed is there, and the pilot applies correct 
technique.  Most transport aircraft can fly with all engines out on one side, 
although I do not know if this is an explicit regulatory requirement.  As 
long as the inherent longitudinal stability of the airplane (contributed
by the vertical stabilizer, rudder, wings, and fuselage) is sufficient to 
overcome the yawing moment, the airplane can be controlled.  So *correcting*
for a lost engine is a near-instantaneous correction, applied by the pilot, 
needing no altitude reserve.

During the El Al discussion on sci.aero, rec.av, and rec.travel.air, there
seemed to be considerable confusion between the role each factor took. 

---
Robert Dorsett
[email-masked]
...cs.utexas.edu!cactus.org!rdd

---

From: [email-masked] (Terrell D. Drinkard)
Date: 01 Dec 92 02:10:49 PST

>off produces such a rediculous unbalance that even full aileron wouldn't be

Not true.  An engine departing the airplane is a planned for event, in
terms of stability and control.  An aileron would have no problem
countering just the imbalance of thrust (and it would actually be mostly
rudder), in fact, without the added drag of a windmilling engine, the
problem is a bit simplified.  Flight AA 191 lost the slats on the left hand
wing (if memory serves) because of Douglas' failure to include mechanical
lockouts on the slat actuators.  They were not required to certify the
airplane.  But then, why build a 'just barely good enough' airplane?  The
#1 engine departed the wing, taking the hydraulic lines that run along the
front spar with it.  This cause a major loss of pressure in the slat
actuators which were then pushed back into the wing by dynamic pressure.
The assymetrical loss of the leading edge high lift devices was a major 
contributing factor in this crash.

Interestingly enough, the DC-10 is often used as an illustration of how NOT
to design hydraulic systems.

-- 
Terry
[email-masked]
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."

---

From: [email-masked] (Michael Weiss)
Date: 03 Dec 92 00:40:16 PST

In article <[email-masked]> [email-masked] (Terrell D. Drinkard) writes:
>problem is a bit simplified.

After the third post with this answer, I figure it's time to clarify my
statement.  I am referring to the unbalance of WEIGHT, not THRUST.  Nonetheless
I suppose we should go on...
  
>Flight AA 191 lost the slats on the left hand
>airplane.

Which doesn't disprove my theory.  As it is, though, the loss of the slats
(which, according to all my aero classes, only lowers the stall speed but does
NOT increase the coefficient of lift!) was enough to stall the wing, more than
"countering" the loss of weight on the wing.
-- 
\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | /
-  Michael  [email-masked]   |  School of Engineering & Applied Science  -
-   Weiss   [email-masked]  |   University of California, Los Angeles   -
/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | \

---

From: [email-masked] (Terrell D. Drinkard)
Date: 04 Dec 92 22:30:32 PST

>I suppose we should go on...
  
It doesn't matter, the loss of weight on that wing was actually a
short-term plus in that incident (effectively generated a right-hand
(positive) roll moment to help counter the loss of lift on the left wing).
The adverse affect (aside from the obvious one of damage occuring during
the departure of the engine and strut) is the increase in wing-root bending
moment.

>"countering" the loss of weight on the wing.

You may wish to recheck your math.  It isn't possible to lower the stall
speed without improving the coefficient of lift (assuming constant weight,
air density, and wing area).

What is not increased is the total amount of lift produced, assuming
unaccelerated, level flight.

---

From: Keith Barr <[email-masked]>
Date: 04 Dec 92 22:30:39 PST

Subject: Re: hydraulic problems with DC-10's??
> normally used to augment the ailerons as necessary to control sideslip.

Actually, you have this backwards.  Rudder is used to control the yaw,
and by controlling the yaw you introduce some sideslip that should be
counteracted by banking into the good engine (raise the dead is the way
I was tought to remember that :^)

The way this works is as follows....we will have to make due with ASCII
graphics:

Normal Flight (Multi-Engine, Both turning)
     Left thrust  Right thrust    
             |     |              
             |  A  |              
       ------X--A--X------        
                A                 
                A                 
              --A--               
                |                 
                |                 
                |                 
                |                 
               Drag               

Engine Out Flight (no correction)
        left thrust               
             |                    
             |  A                 
       ------X--A--X------        
                A          CW Moment
                A            |_   
              --A--               
                |                 
                |                 
                |                 
                |                 
               Drag               

Engine Out Flight (Yaw (moment) correction)
       left thrust                
             |                    
             |  A                 
       ------X--A--X------        
                A                 
                A                 
              --A--===>Rudder Force to counteract rotation
                |                 
                |                 Now you can see we have fixed the
                |                 Rotation with rudder, but we have an
                |                 unbalanced vector diagram, so the aircraft
               Drag               will sideslip to the right

By raising the dead engine we tilt the lift vector to the left which balances
the force from the rudder.

> needing no altitude reserve.

Correct, but here is an added explanation for those who care:
There is really only one concern of the pilot in an engine out situation, that
is airspeed.  The pilot, if he has done an appropriate preflight, will know
whether he/she is able to climb on one engine out, so that is not a suprise.  
The biggest problem with an engine out is loss of control.  This airspeed,
called Vmc (Velocity Minimum Controllable) is the speed at which the rudder
doesn't have enough air flowing over it to create enough force to counteract
the moment from the good/dead engine.  As long as you are above this speed,
you should be controllable (ignoring the fact that one wing may stall if
the slat comes up, but I am not talking about that case in particular).

On the same thread, but different argument...

>I suppose we should go on...

The change in weight from a lost engine is minimal.  A fully loaded DC-10-30
weighs 572,000 pounds.  A GE CF6-50C2B weighs only 8,731 pounds.  This means
that in normal flight each wing needs to support 286,000 pounds.  If each
wing supports the weight of its engine, now the left wing only needs to
create 277,269 pounds of lift, a 3.05% decrease.  I would imagine that 
ailerons easily can create a 3.05% increase in lift per side.

References:  Aviation Week and Space Technology 3/16/92 p. 102
             Illustrated Encyclopedia of Commercial Aircraft pp 148-157
 _____________________________           _____
| Keith Barr                  \           \ K \__      _____                  
| [email-masked]           \___________\   \/_______\___\_____________    
| Comm/AS&MEL/Inst/IGI         /           < /_/   .....................  `-.
|_____________________________/             `-----------,----,--------------'
When you think how well basic appliances work, it's   _/____/               
hard to believe anyone ever gets on an airplane.--Calvin

---

From: [email-masked] (Gregory R. Travis)
Date: 08 Dec 92 15:50:51 PST

>ailerons easily can create a 3.05% increase in lift per side.

It seems to me that they each have to perform at only half this figure:
I.e. - the aileron on the wing that lost the engine needs to increase lift
by about 1.5% while the aileron on the "good" wing needs to go negative
and decrease that wing's lift by 1.5%.

This is quite muddled though, as other anti-lift devices (such as spoilers)
will deploy at a given amount of aileron deflection.  In fact, and I don't
have my DC-10 refs handy, I imagine that the ailerons on a -10 are locked
in place when the flaps are up (not the case in the Chicago crash, I know)
and that the loss of an engine AT CRUISE would have to be countered entirely by
lift spoiling devices (i.e. spoilers) on the opposite wing with a
suitable increase in the aircraft's overall AOA.

In any case, the ORIGINAL poster's position that the loss of an engine
from a wing, considering the engine's moment and weight, would render the plane
uncontrollable is not supported either by analysis or historic precedent.
Engines depart planes all the time...

BTW, just to be pedantic:  The wings do not each contribute exactly
50% of the total lift.  Remember that that fuselage itself contributes
a SUBSTANTIAL amount of lift at cruise as do the horizontal stabilizer
surfaces (in certain flight regimes!).

greg, the math bimbo
--
Gregory Reed Travis				D  P  S  I
Data Parallel Systems Incorporated   [email-masked] (For MX mailers only!)
Bloomington, IN			     [email-masked] (For the others)

---

From: [email-masked] (Lars-Henrik Eriksson)
Date: 08 Dec 92 15:50:56 PST

In article <[email-masked]> [email-masked] 
(Terrell D. Drinkard) writes:
   In article <[email-masked]> [email-masked] 
(Michael Weiss) writes:
   >NOT increase the coefficient of lift!)

>From what I've learned, slats don't increase the coefficient of lift
*for a given angle of attack*, but they do increase the critical angle
of attack. That is, using slats you can get a higher coefficient of
lift by having a higher angle of attack than normally possible.

(So you are both right :-)

Of course, this means that when the slats retract, either nothing
happens to the lift at all (if the angle of attack is below the
no-slats critical angle of attack), or the wing stalls instantly.
----
Lars-Henrik Eriksson                     Internet: [email-masked]
Swedish Institute of Computer Science    Phone (intn'l): +46 8 752 15 09
Box 1263                                 Telefon (nat'l): 08 - 752 15 09
S-164 28  KISTA, SWEDEN                  Fax: +46 8 751 72 30

---

From: [email-masked] (Michael Weiss)
Date: 08 Dec 92 15:51:09 PST

In article <[email-masked]> [email-masked] (Terrell D. Drinkard) writes:
>>I am referring to the unbalance of WEIGHT, not THRUST.

I'll reply to this below.

>>NOT increase the coefficient of lift!) was enough to stall the wing
>It isn't possible to lower the stall

Actually, assuming constant wing GEOMETRY, which includes, besides area, shape
as well.  Slats change the geometry.  Their benefit is a reduction of the
stall speed, through delay of separation.  I believe the way that it does this
is by directing a stream of air along the upper surface of the wing.

In any case, my point is that there would have been a severe weight unbalance
between the wings, and I have doubts that it could have been countered by the
ailerons.  The whole reason that there was a negative roll moment was that the
left wing STALLED, not that it lost lift directly from the retracting slats.
I'm still not convinced that even WITH the slats extended it could have been
prevented.
-- 
\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | /
-  Michael  [email-masked]   |  School of Engineering & Applied Science  -
-   Weiss   [email-masked]  |   University of California, Los Angeles   -
/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | \

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From: [email-masked] (Paul Raveling)
Date: 08 Dec 92 15:51:12 PST

> >>lockouts on the slat actuators.  They were not required to certify the

	I'd be inclined to phrase that a bit differently.  The certification
	requirements were satisfield by demonstrating safe flight with
	asymmetric slats.  The catch is that (a) flying safely in this
	configuration requires keeping airspeed above the minimum (or
	AOA below the maximum) needed with slats retracted and (b) the
	crew didn't have a sufficient indication to judge immediately
	that they had asymmetric slats.

	This fits in with a pattern that's shown up in virtually
	all breeds of airliners where the cockpit's 'human interface'
	fails to supply needed information.  This shows up in a fair
	variety of accidents in various forms -- unloading the autopilot
	produces surprising gyrations, aircraft FBW control logic reacted
	to factors other than the pilot's directions and the pilot
	didn't anticipate it, etc.

	One human factors problem is how to best inform the crew of
	simultaneous failures that each can be critical.  For this
	DC-10 accident, they experienced loss of an engine at low altitude,
	followed quickly by partial loss of hydraulics and asymmetric slats.
	Each of these three primary circumstances call for prompt attention,
	and cockpit warnings of these and other consequent failures
	can overload the crew with failure alarms, becoming more of a
	problem than a solution.

	Bottom line:  IMHO human factors engineering in the cockpit
	is more a more important target than airframe engineering
	for risk reduction.

------------------
Paul Raveling
[email-masked]

---

From: Robert Dorsett <[email-masked]>
Date: 10 Dec 92 00:52:08 PST

Before starting: the left pylon assembly weight, btw, was 13,477 lbs, from 
the accident report.  A whole bunch of figures had been floating around...

>I'm still not convinced that even WITH the slats extended it could have been

Allow me to throw in my $0.02 worth.  

1.  A slat increases the maximum effective lift coefficient for a wing section. 
How this is done is irrelevant to this discussion: the result is that the 
lift coefficient goes up.  Slats permit the wing to produce a greater lift at 
slower airspeeds, i.e., they drive the stall speed down.  When used with 
trailing edge flaps, they offer even better lift characteristics, and improve 
handling characteristics.

2.  If we take away the slats, then the maximum lift coefficient goes down.  
By definition.  This means the stall speed goes up for the resulting 
configuration.  By definition.

3.  The accepted procedure was to climb at V2 until 800' AGL, then to lower 
the nose and accelerate. 

For a normal, undamaged aircraft, at 379,000 lbs, V2 was 153 knots.  

In the damaged aircraft, the minimum controllable airspeed, with a 4 degree 
left bank, into the missing engine, was 159 knots.

Therefore, if the crew were to fly a standard engine-out profile, at 153
knots, they would have been beneath the minimum controllable airspeed for
the damaged aircraft (159 knots).

During the investigation, the NTSB asked 13 qualified pilots to fly various
takeoff profiles.  70 takeoff simulations were flown.  All crashed the
airplane when flying the crash profile.  Several pilots, when left to their
own devices, and with extensive knowledge of the events, managed to control 
the airplane, nonetheless, by recognizing the initial roll and applying full
opposite aileron and significant rudder, and lowering the nose to gain air-
speed.  All pilots who received appropriate feedback, via a functioning 
stickshaker, and who increased their airspeed to stay above the stickshaker 
value--168 knots--saved the airplane.

I really fail to see what the problem is, here.  The engine fell off after
V1.  This didn't affect the aerodynamic characteristics of the wing itself: 
it became a control problem.  It also killed the electrical system driving 
the captain's stick-shaker, and killed a hydraulic system.  The latter 
caused the slats to retract within 20 seconds of failure.

The slat retraction DID affect the wing: it then became both a control and 
aerodynamic problem.  Exercising established control practices in an 
unknown aerodynamic regime crashed the airplane (I'd love to know whether
this went into Airbus's "pilot error" database :-)).  Had the slats remained
down, the airplane would have survived the engine failure, even with the 
failure of the stall warning system.  Other airframe manufacturers have 
manual locking mechanisms for their slat jackscrews.  McDonnell Douglas 
relied on hydraulic pressure to hold it all together.

Incidentally, this problem wasn't corrected: the SUX DC-10 also experienced 
extension of its slats after it lost all its hydraulics.

I'd suggest you obtain a copy of the accident report (NTSB-AAR-79-17), and
look it over, closely.  It has more than enough data for back-of-the-
envelope calculations.  Nothing in it suggests that weight or moments 
following engine separation played a significant role.

Lastly, I'd note that there was SIGNIFICANT public and industry concern 
about the DC-10's safety after this crash: the FAA's extraordinary grounding
of the airplane, inappropriate though it may have been, is testimony to 
that.  All of the manufacturers had something to contribute, and a great 
deal of manpower was invested in finding the cause.  There was REAL concern
that the airplane wasn't airworthy, even by FAA's standards.  Every analysis 
or comment I've ever seen on this crash has concentrated on the slat retrac-
tion being the proximal cause for the crash.  I've never seen the weight 
issue raised.  If you have "hard" evidence that it HAS been, some references 
would be useful, since it's not a well-publicised theory.  If you're
basing your comments on classroom experience, as I believe you indicated,
it might be a worthwhile learning exercise to raise it in class, or print
this discussion and privately  discuss it with your professor: but be sure 
to let us know the outcome.

--
Robert Dorsett
Internet: [email-masked]
UUCP: ...cs.utexas.edu!rascal.ics.utexas.edu!rdd

---

From: [email-masked] (Keith Barr)
Date: 10 Dec 92 00:52:10 PST

> surfaces (in certain flight regimes!).

What flight regimes might those be?  Unstable flight, as in the F-16?

Actually, in most aircraft the horizontal stabilizer is downlifting, so
the wings have to create more lift, and the body contributes to the
pitching moment, but contributes very little lift (unless we are talking
about the B-2).

For the horizontal stabilizer to lift up, the CG would have to behind the
Center of lift, which is not usually allowed.  I would bet a dollar that
the DC-10 has a down lifting tail, although I don't know for sure.

If you want references for either of these points, I recommend that you
look at Etkin's book on stability (an engineering text I used in my
aircraft design class that would explain in painful detail why you need
the CG in front of the Center of Lift), and you might check out K.D.
Wood's text on aircraft design for discussions about pitching moment and
lift created by the fuselage.

(is it just me, or is this thread becoming less and less appropriate for
this newsgroup?)

---

From: [email-masked] (Greg Wright)
Date: 10 Dec 92 00:52:13 PST

>surfaces (in certain flight regimes!).

 This is not as substantial as one might think. While some lifting bodies
are very good at producing lift the typical commercial fuselage is not.
Because of it's inablility to be a very efficient producer of lift, ie. 
it makes LOTS of drag in doing so, we try to keep the lift of the body
to a minimun. As far as the stab's go, at cruise they will be counter-
acting a nose-down or nose-up pitching moment depending on the CG and
gross weight at that particular time in the flight. Because, again, with
lift you get drag, the horiz. stab. is best kept at zero lift if possible.

-- 
 ________Greg Wright____________     "I struggle to be brief     
| [email-masked]  |     and become obscure."         
|     [email-masked]       |                             
|____uunet!bcstec!gregory_______|               NOT A BOEING SPOKESPERSON.

---

From: [email-masked] (Pete Babic)
Date: 10 Dec 92 16:07:11 PST

>extension of its slats after it lost all its hydraulics.

Does anyone know if the MD-11 has a proper locking mechanism for the slats?
I'm a layman when it comes to aircraft design, but the DC-10 really looks
like a substandard design that has killed a bunch of people due to cost
cutting short cuts.

-- 
Pete Babic  -  [email-masked]          ///
LIVE TO PARTY, SKI TO DIE!!!           ///  /\
Member of ACE                    \\\  ///  /--\MIGA  
(American Coaster Enthusiasts)    \\\/// MS-DOS or a Mac? What's that?

---

From: [email-masked] (Gregory R. Travis)
Date: 10 Dec 92 16:07:13 PST

>pitching moment, but contributes very little lift (unless we are talking

As I understand it (and I'm not an aero geek, just an historian geek :-))
there are flight regimes in which the horizontal stabilizer on conventional
(i.e. dynamically stable) aircraft contributes POSITIVE lift, even when
said aircraft is loaded within acceptable C.G. ranges.

It is possible (and likely) during slow flight for
the center of lift to move forward of the center of gravity on the wing.
At such time, the horizontal stabilizer becomes a LIFTING surface, restoring
normal stability to the aircraft and the pilot's never the wiser.

If you look at many horizontal stabilizers, especially on small GA aircraft,
you'll note that the airfoil is completely symmetric top and bottom.  If
the horizontal stabilizer contributed ONLY to negative lift, one would think
it more efficient to design it as an upside-down wing and shorten its overall
span.

I've talked to a couple of Cessna engineers about this (when I was completely
incredulous that it actually happened) and they agreed that the horizontal
stabilizer does contribute positive lift and that Cessna routinely measured
this lift with strain gauges when evaluating stabilizer structure.  The
lift is not present only during extreme maneuvering (such as a violent
pitch-down) but also during straight and level flight.

My good friend Moshe Braner ([email-masked]) can give you a much
better technical explanation of the phenomena and, no doubt, correct all
my mis-explanations and errors.

greg

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From: Robert Dorsett <[email-masked]>
Date: 10 Dec 92 20:58:52 PST

>like a substandard design that has killed a bunch of people due to cost

I had wondered about this, and researched it about a year ago.  I wasn't
able to find a clear-cut answer.

Otherwise, my conclusion is that the MD-11 is a very marginal upgrade of the 
basic DC-10 design.  The systems layout is almost identical; none of the major 
"complaint areas" have changed.  There's a high degree of commonality between
the DC-10 and MD-11, the "hydraulics plug" adopted after the SUX crash being a 
good example.

The changes incorporate a 6-meter fuselage stretch, the winglets, composites
in the tail, new engines, and a new cockpit.  The latter appears to be the 
most radical change, but other than that, what characterizes the industry
media is a lot of manufacturer "gee whiz" propaganda, long on "radical 
changes," but short on specifics.  

I recall an Av Leak article a couple of years ago, which suggested the
full new type-certification wasn't necessary, but McDonnell-Douglas did it
anyway, to try to exorcise itself from the political "ghosts" of the DC-10:
a regulatory face-lift, if you will.  Problem is, not much has changed.  

So: I see no objective reason to conclude the MD-11 is any "safer" than the 
DC-10, if one accepts the existence of the problems that characterized the 
DC-10's development.  

More detailed information would be welcome.  I was really appalled by how 
little "hard" info was out there, and I spent quite a bit of time on it.  
Literally hundreds of articles on 767-X and 777 aerodynamic and systems
development, dozens on Airbus, but only two or three "skimpy" treaments on 
the MD-11, the kind of things you'd find in "Aerospace America."  Does MDC 
have some kind of anti-publishing policy or something?

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From: [email-masked] (Paul Raveling)
Date: 11 Dec 92 17:42:34 PST

Several people:
	[email-masked] (Lars-Henrik Eriksson)
	[email-masked]
	[email-masked] (Michael Weiss)
write about the question of whether slats do or don't improve Cl (coefficient
of lift), in addition to affecting stall speed (critical angle of attack)...

	I'd surmise that slats should increase Cl at any given AOA.
	The reason should be that they should delay boundary layer
	transitions (laminar-to-turbulent, turbulent-to-detached),
	increasing the wing area that's working efficiently.  It's
	also true that this allows using a higher AOA, as noted by
	Lars-Henrik Eriksson; deployment of slats (and flaps too)
	DOES increase the AOA at which the wing achieves max Cl.

	An exaggerated example of this is adding a jib to a sailboat
	that formerly had only a mainsail.  Adding even a small jib
	improves the main's Cl substantially.

------------------
Paul Raveling
[email-masked]

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From: [email-masked] (Michael Weiss)
Date: 12 Dec 92 00:06:28 PST

>in place when the flaps are up (not the case in the Chicago crash, I know)

Not true, at least in the case of the inboard ailerons.  I still can remember
back in 1984 flying a DC-10 from LAX to HON, and noting that when the inboard
ailerons deflected to a certain point, the spoilers came up, too.  I don't
remember about the outboards (at the time, the inboard ones were more
interesting to me).

>uncontrollable is not supported either by analysis or historic precedent.

And I stand (sit?) corrected on this issue.  It struck me as an awfully large
moment at first (and second, and third) glance, but I didn't have any actual
weight numbers to compare.  Now that I do, it makes perfect sense.
-- 
\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | /
-  Michael  [email-masked]   |  School of Engineering & Applied Science  -
-   Weiss   [email-masked]  |   University of California, Los Angeles   -
/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | \

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From: [email-masked] (Terrell D. Drinkard)
Date: 16 Dec 92 04:19:50 PST

In article <[email-masked]> [email-masked] (Michael Weiss) writes:

  [Much aero-techie argument deleted]

>I'm still not convinced that even WITH the slats extended it could have been

As one gentleman pointed out earlier, there is a history of airplanes
losing engines and remaining perfectly controllable.  A 737-200 lost one, I
believe it was the #2, on takeoff just last week.  It impacted along the side 
of the runway, the airplane turned around without further incident and
landed safely.  While certainly not as common as an airline misplacing your
luggage :-), engine departures do happen and the airplanes do tend to land
without further damage or excitement.