MD-80: Lawn Dart or Efficient Design?
Dave Benjamin
Let me say up front that the MD-80 is among my favorite airliners to fly
in -- very quiet up front (not so in the rear, but I can normally avoid
the aft rows), good T/O and climb performance, POWERFUL flaps.
But I can't get over the far aft positioning of the wings, negative
incidence of the stab, and positive incidence of the thrust. How do all
of these combine to make the MD-80 an efficient flying machine (or do
they not)?
Steve Lacker
Dave Benjamin <db...@slip.net> wrote:
>Let me say up front that the MD-80 is among my favorite airliners to fly
>But I can't get over the far aft positioning of the wings, negative
>incidence of the stab, and positive incidence of the thrust. How do all
>of these combine to make the MD-80 an efficient flying machine (or do
>they not)?
As one of the more vocal MD-80 haters around, I'll stand up and defend it :-)
It *is* a pretty efficient machine. The rearward placement of the wings is
simply a result of the rearward placement of the engines. The engines
themselves are a relatively efficient design. It doesn't have THE most
efficient wing, THE most efficient engine, etc., but its a good combination
overall. What it lacks in efficiency in the air, it tends to make up for in its
reliability and apparently good serviceability (any airline mechanics here who
can comment on that?). No doubt it could be more efficient if it had been
designed from scratch as a 150+ pax airliner instead of being a mercilessly
stretched DC-9, but all in all its done well for itself.
But I still smash my head everytime I stand up in one :-)
--
Steve Lacker / Applied Research Laboratories, The University of Texas
512-835-3286 / PO Box 8029, Austin TX 78713-8029
sla...@arlut.utexas.edu
RD Rick
In <airliners...@ohare.Chicago.COM> Steve Lacker
<sla...@arlut.utexas.edu> writes:
>...It *is* a pretty efficient machine. The rearward placement of the
>wings is>simply a result of the rearward placement of the engines. The
>engines>themselves are a relatively efficient design. It doesn't have
>THE most>efficient wing, THE most efficient engine, etc., but its a
>good combination>overall. What it lacks in efficiency in the air, it
>tends to make up for in its>reliability and apparently good
>serviceability (any airline mechanics here who>can comment on that?).
>No doubt it could be more efficient if it had been>designed from
>scratch as a 150+ pax airliner instead of being a mercilessly
>stretched DC-9, but all in all its done well for itself.
It was the heavy weight of the new JT8D-217 engines that caused the big
stretch forward of the wing in the MD-80.
Before the two recent 757 crashes, the MD-80 was second in safety.
It must be in first place now.
The PSA avionics techs bitched long and hard when the first MD-80's
were added to their all-727 fleet. Avionics bay too small, etc.
You should have heard them when the BAe-146 arrived.. Pure misery.
Reno Air seems quite happy with the reliability and maintainability of
their all MD-80 fleet. Alaska A/L, OTH, has serious problems with
belly corrosion, etc., and find it very unreliable compared to their
737-400 fleet.
Karl Swartz
>Reno Air seems quite happy with the reliability and maintainability
>of their all MD-80 fleet.
*Almost* all MD-80 -- they now have several MD-90s.
>Alaska A/L, OTH, has serious problems with belly corrosion, etc., and
>find it very unreliable compared to their 737-400 fleet.
Perhaps that's why they plan on going to an all-737 fleet within the
next few years.
--
Karl Swartz |Home k...@chicago.com
|Work k...@netapp.com
|WWW http://www.chicago.com/~kls/
Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills
C. Marin Faure
In article <airliners...@ohare.Chicago.COM>, Dave Benjamin
<db...@slip.net> wrote:
> Let me say up front that the MD-80 is among my favorite airliners to fly
> in -- very quiet up front (not so in the rear, but I can normally avoid
> the aft rows), good T/O and climb performance, POWERFUL flaps.
>
> But I can't get over the far aft positioning of the wings, negative
> incidence of the stab, and positive incidence of the thrust. How do all
> of these combine to make the MD-80 an efficient flying machine (or do
> they not)?
I've had MD-80 pilots for an airline that will remain nameless say that
under certain c/g conditions, they run out of elevator up-trim on final
approach. As a result, they have to physically horse the nose up for the
flare, such as it is.
C. Marin Faure
author, Flying a Floatplane
David G. Davidson
>apparently good serviceability (any airline mechanics here who
>can comment on that?)
I can and I think you'll find that most mechanics that have had an
oppurtunity to work on any MD product versus Boeing (we'll just talk
narrow-body here) will think that the MD product is a big pain in the
butt, in general, to work on. Like anything they each have there good
and bad points.
*AC Packs - Boeing's system is better. Placing the components in the
belly is much better than hanging them from the top of the tail cone as
MD has done. It is very difficult to work on a MD pack. The tail cone is
always dark, hot and hard to move around in. Also the MD AC system
doesn't cool as well as the Boeings.
*Pneumatic System - Again Boeing has the edge, with components located
on the engine or in the airstair area on a 727. The MD system is more
complicated and the augmentation valve is located at the bottom of that
damn tail cone.
*Hydraulic System - servicing is more difficult on the MD product.
Working on the MD components is difficult since they are located in the
wheel well and you have to stand on the curved and always slippery
gear-door.
Not to be outdone though, the 727 'B' pumps are located in a miserable
location and are not easy to deal with.
*APU - Terrible on a MD, with the apu exhaust duct going through the
right half of the tail cone. That makes it that much harder to do
anything in the tail cone.
The 737 APU installation is far from perfect though. Oil servicing is
unreal and working on the thing requires the removal of the large,
stainles-steel "bath tub" that surrounds it.
727 APU installation is the best of the three, but also far from ideal.
The 757/767 are the one's to copy here.
*Flight Controls - much simpler on an MD, but just doesn't seem right to
fly an airplane that big with control tabs.
*Electrical System - goofy use of Cross-tie relay on the MD. Power
center located behind FC FA seat is bad. Changing power relays is a big
chore. Simpler and easier to understand system on the Boeings.
MD also has a habit of hiding relays and circuit breakers in odd and
inaccessable places
*Standby Compass - requires use of glareshield mounted mirrors to use on
the MD (extra cheesy!) Lot's better on the Boeings.
*Main Gear Downlock Spotlights - horrible on the MD. No excuse for this.
*Crew Seats - Much better on an MD than that over-engineered stuff found
on the 727 and 737. Seems newer 737s have the same seats that the later
MDs have.
IMHO.
Robert Dorsett
In article <airliners...@ohare.Chicago.COM> rick...@ix.netcom.com (RD Rick) writes:
>Before the two recent 757 crashes, the MD-80 was second in safety.
>It must be in first place now.
Definitely. Once one throws out the two crashes during the
flight-test program. And the crash in Argentina. And the NWA crash
at Detroit. And the SAS crash in Sweden. Oh, and the CAL RTO crash
at La Guardia...
Apologies if I missed any.
--
Robert Dorsett Moderator, sci.aeronautics.simulation
r...@netcom.com aero-si...@wilbur.pr.erau.edu
ftp://wilbur.pr.erau.edu/pub/av
Steve Lacker
several people variously wrote:
> Before the two recent 757 crashes, the MD-80 was second in safety.
> It must be in first place now.
First by what measure? Number of hulls destroyed, number of lives
lost, number of injuries per passenger mile?
Just curious.
>I've had MD-80 pilots for an airline that will remain nameless say that
>under certain c/g conditions, they run out of elevator up-trim on final
>approach. As a result, they have to physically horse the nose up for
>the flare, such as it is.
I had a retired pilot tell me a similar story, plus he said that the MD-80
"just didn't feel good" to fly.
I also liked David G. Davidson's list of good/bad serviceability items on
various narrowbodies. Interesting stuff! One comment interested me:
>727 APU installation is the best of the three, but also far from ideal.
It amuses me how many fellow passengers I hear complaining about how
loud that APU is in the cabin. Most of them don't seem to *know* that
its an APU and not a main engine, but they all know its loud if you're
sitting near the trailing edge of the stbd. wing.
Mark J. Bushnell
In article <airliners...@ohare.Chicago.COM>,
Steve Lacker <sla...@arlut.utexas.edu> wrote:
>As one of the more vocal MD-80 haters around, I'll stand up and defend it :-)
>
>simply a result of the rearward placement of the engines. The engines
>themselves are a relatively efficient design. It doesn't have THE most
>efficient wing, THE most efficient engine, etc., but its a good combination
>overall. What it lacks in efficiency in the air, it tends to make up for in its
>can comment on that?). No doubt it could be more efficient if it had been
>designed from scratch as a 150+ pax airliner instead of being a mercilessly
>stretched DC-9, but all in all its done well for itself.
In my experience of working on Boeing and Douglas aircraft, I've found that
they each have their good and bad points. I prefer the Boeings, since I've
worked on them more often & am more familiar with them. One area that I
definitely do not care for on the DC-9/MD-80 is the air conditioning
system. It's located in the tail of the aircraft, on either side of the
aft stairway. It's very cramped, no ventilation, and the exhaust duct from
the APU runs right thru the area occupied by the right air conditioning
system.
On the Boeings, the airconditioning system is located in the bottom of the
aircraft, just ahead of the main landing gear. It's accessed by opening
doors or panels located in the belly of the plane.
Speaking of APU's, I do wish that Douglas would figure out where to locate
the APU exhaust opening. On the DC-9/MD-80, it's on the side of the
aircraft, just above the right (#2) engine. If one should open up the #2
engine upper cowling while the APU is running (or start up the APU with the
#2's upper cowl open), you are going to have a hole burned into the
composite material of the cowling in very short order from the APU exhaust
heat. On the DC-10, the exhaust is also at the back of the aircraft, but
pointed down at about a 45 degree angle. Every time a person walks around
the back of the aircraft, they are going to be hit by a blast of hot air
from the APU.
Mark
RD Rick
In <airliners...@ohare.Chicago.COM> r...@netcom.com (Robert
Dorsett) writes:
>
>In article <airliners...@ohare.Chicago.COM>
rick...@ix.netcom.com (RD Rick) writes:
>>It must be in first place now.
>
>flight-test program. And the crash in Argentina. And the NWA crash
>at Detroit. And the SAS crash in Sweden. Oh, and the CAL RTO crash
>at La Guardia...
>Apologies if I missed any.
Yeah, you missed some. It's computed on deaths or accidents per RPM,
revenue passenger mile, or something. There are over 1,000 MD-80
racking up RPM's right now.
The listing I saw was at a Boeing presentation, where they were
discussing USAir 427 and the 737's fourth place.
RD
David G. Davidson
An aside to the Lawn Dart thread.
>On the DC-10, the exhaust is also at the back of the aircraft, but
>pointed down at about a 45 degree angle. Every time a person walks
>around the back of the aircraft, they are going to be hit by a blast of
>hot air from the APU.
This is that same as the L-1011 installation. The difference is that the
L-1011 APU (which is a derivative of the PT-6) is much louder and seems
to blow much hotter air than the DC-10 (which I think is a Garret unit).
Points to the DC-10 for this, but I still won't fly on one if I don't
have to.
Dave
http://rampages.onramp.net/~gerhard/tristar
Richard N. Rea
In article <airliners...@ohare.Chicago.COM> r...@netcom.com (Robert Dorsett) writes:
>In article <airliners...@ohare.Chicago.COM> rick...@ix.netcom.com (RD Rick) writes:
>>Before the two recent 757 crashes, the MD-80 was second in safety.
> ^^^^^^ only
>>It must be in first place now.
>Definitely. Once one throws out the two crashes during the
>flight-test program. And the crash in Argentina. And the NWA crash
>at Detroit. And the SAS crash in Sweden. Oh, and the CAL RTO crash
>at La Guardia...
>Apologies if I missed any.
Hee-Hee. Actually the two which "crashed" during flight testing shouldn't
count. The first was from the ham-fisted FAA official who tried to do a
carrier-landing into the runway. The second (can't remember who was flying
the plane) which overran the runway and ended up in some soft ground. The
crane which was trying to pick it up shifted and the plane bent in the middle.
Richard
John M. Hunt
>I've had MD-80 pilots for an airline that will remain nameless say that
>under certain c/g conditions, they run out of elevator up-trim on final
>approach. As a result, they have to physically horse the nose up for the
>flare, such as it is.
Interesting. Have you heard any similar stories of inadequate
nose-down available trim?
I wonder if the MD-80 designers might have been thinking about the
possible installation of more modern engines such as the CFM family or
the V2500. I don't have any numbers in front of me but imagine these
more efficient engines weigh more than the JT8D-217 and its close
relatives?
By the way, keep up the excellent work represented by your very
informative posts.
-
-
John M. Hunt
john...@ipa.net
Stefano Pagiola
Robert Dorsett wrote:
> >Before the two recent 757 crashes, the MD-80 was second in safety.
> ^^^^^^ only
> >It must be in first place now.
>
> Definitely. Once one throws out the two crashes during the
> flight-test program. And the crash in Argentina. And the NWA crash
> at Detroit. And the SAS crash in Sweden. Oh, and the CAL RTO crash
> at La Guardia...
>
> Apologies if I missed any.
There was an Inex Adria CFIT crash in Corsica very early on (1981 or so)
and an Alitalia crash near Zurich (also CFIT, as I recall) a few years
ago.
To be fair, several of the accidents above resulted in no or little loss
of life (SAS, CO). And the flight-test "crashes" were more in the order
of hard landings.
I'm not familiar with any MD-80 crash in Argentina. Can you supply
details? (Airline, date, location, cause, fatalities?)
In terms of hull losses, we should also add to the 757's ledger one loss
in China (when a hijacked 737 flew into a parked 757).
So in terms of hull losses, the MD-80 is indeed still ahead. How does it
work out in terms of fatalities? Those 757s were pretty full...
Stefano
Cole Pierce
>I've had MD-80 pilots for an airline that will remain nameless say that
>under certain c/g conditions, they run out of elevator up-trim on final
>approach. As a result, they have to physically horse the nose up for
>the flare, such as it is.
I don't know of ANY pilot who 'horses the nose up for the flare.' And
yes, I've found a lot of nose up trim on roll-out, but I've never 'run
out' of it. Would sure be a helluva forward c.g.
>I had a retired pilot tell me a similar story, plus he said that the MD-80
>"just didn't feel good" to fly.
I think the MD-80 feels very good to fly. It's not an F-4 or an F-8, and
I would like a little better speed stability in the dirty configuration,
but other than that, it flies great for a big plane.
Aside: how many of those other posts on MD-80 accidents were pilot error?
The Northwest/Detroit for sure, and probably the LaGuardia abort, altho
that one leaves a few unanswered questions. The rest?
gun one
MD-80 driver
usn (ret)
David Lesher
>This is that same as the L-1011 installation. The difference is that the
>L-1011 APU (which is a derivative of the PT-6) is much louder and seems
>to blow much hotter air than the DC-10 (which I think is a Garret unit).
Note the standard definition of an APU:
A device that converts Jet-A into noise.
I too have had to stand next to an a/c with a running APU.
After about an hour, you are not a happy camper.....
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close...........(v)301 56 LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead........vr vr vr vr.................20915-1433
Alecs Bains
John M. Hunt <john...@ipa.net> wrote in article
<airliners...@ohare.Chicago.COM>...
>
> >I've had MD-80 pilots for an airline that will remain nameless say that
> >under certain c/g conditions, they run out of elevator up-trim on final
> >approach. As a result, they have to physically horse the nose up for
the
> >flare, such as it is.
>
> Interesting. Have you heard any similar stories of inadequate
> nose-down available trim?
>
>I am currently working on my Commercial Pilot licence but I also work as a
ramp serviceman for a large company in Vancouver, B.C.. I service MD-80
aircraft on a regular basis and from a ramp standpoint the MD-80 is not one
of the most liked airplanes in the sky. It is very difficult to load when
Pax loads are high due to small baggage compartments and it is very very
tail heavy. When towing and pushing out EXTREME caution must be used as
abrupt accelerating or braking action will make the aircraft bob up and
down violently. Also it has a critical problem. In any weather from -5c -
15c the wings must be checked for ice due to a clear icing problem. This is
caused by a cold soaking problem when fuel is in the tanks after flight. It
is the only aircraft that needs to be de - iced in the summer. This is
almost comical. On a positive note however I must admit that rarely if ever
have I ever seen a mechanical delay to an Md-80.
-
--
Alecs Bains / Vancouver , B.C. , CANADA
Pete Mellor
>>Apologies if I missed any.
>
> revenue passenger mile, or something. There are over 1,000 MD-80
> racking up RPM's right now.
>
> The listing I saw was at a Boeing presentation, where they were
> discussing USAir 427 and the 737's fourth place.
In any kind of service reliability or safety assessment, one is
always faced with the choice of which incidents to record over
what measure of operation.
With air accidents, the two types of occurrence which are most
often cited are:-
a) deaths, and
b) hull losses.
Possible measures of operation are:-
i) revenue passenger miles (RPM),
ii) revenue passenger hours,
ii) revenue flight hours, and
iii) revenue flight cycles (take-off plus (hopefully!) landing).
There are no prizes for spotting that one obtains completely
different statistics depending on the choice of measure. Not only
that, but the ranking of two models of aircraft with respect to
"safety" will often vary.
If you want to make air transport the safest ever mode of travel,
quote "hull losses per RPM". If you want a slightly less optimistic
(more realistic?) picture, quote "deaths per flight cycle".
I discount another measure of "safety" that I have seen ("hull losses
per number of examples in service") as being totally misleading, and
not a well-defined measure of anything.
Peter Mellor, Centre for Software Reliability, City University, Northampton
Square, London EC1V 0HB, UK. Tel: +44 (171) 477-8422, Fax: +44 (171) 477-8585
E-mail: p.me...@csr.city.ac.uk
-----------------------------------------------------------------------------
Joe Curry
In message <airliners...@ohare.Chicago.COM>
Pete Mellor <p...@csr.city.ac.uk> writes:
> >>Apologies if I missed any.
Likewise for myself! Now that the subject is on MD 8's, perhaps some
one can let me know the difference between MD 80, 83 and 87?
What are the seating configs and capacities. Air speeds etc?
--
Edinburgh Airport is the UK's fastest growing. Insist on EDI flights.
Visit the text page on http://www.users.zetnet.co.uk/jcurry
Tim Takahashi
Alecs Bains <Pi...@netcom.ca> wrote:
>I service MD-80
>aircraft on a regular basis and from a ramp standpoint the MD-80 is not one
>of the most liked airplanes in the sky. It is very difficult to load when
>Pax loads are high due to small baggage compartments and it is very very
>tail heavy.
The MD-80/90/95/DC-9 family is the extreme example of how far
a basic airframe configuration can be stretched. It seems you've
noticed some of the deficiencies of such a configuration.
However, the configuration has the advantage of having a clean
wing... and this should have some real benefit in terms of
reducing pylon/nacelle related induced drag. If nothing else,
it is an easier wing to optimize.
What's the fuel economy like on a MD-80/90? Better or worse than
a equivalent 737? (or 727? given the length of the MD-90)
-tim
Andrew Muir
In article <airliners...@ohare.Chicago.COM>,
"David G. Davidson" <ger...@onramp.net> wrote:
>An aside to the Lawn Dart thread.
>
>>On the DC-10, the exhaust is also at the back of the aircraft, but
>>pointed down at about a 45 degree angle. Every time a person walks
>>around the back of the aircraft, they are going to be hit by a blast of
>>hot air from the APU.
>
bunch of us were pretty glad when the KC-10 started up its APU. There was a
warm dry place to stand.
GERWOCII
I too work for a ramp service company here in Dayton OH. Never had to
deice an MD-80 in the summer but sure sprayed alot of glycol this winter.
Dont know what airline you service but one of the ones we service here is
TWA. Not only do they balance the airplane for trim flight but thay have
very strigent weight and balance for fuel comsumption so it is difficult
to get all the bags and mail in the belly. Never had a problem with the
727 or 737 though.
Stefano Pagiola
Joe Curry wrote:
> Likewise for myself! Now that the subject is on MD 8's, perhaps some
> one can let me know the difference between MD 80, 83 and 87?
MD-80 is the overall name for the family.
MD-81, -82, and -83 are progressively higher gross weight versions, with
increasingly powerful versions of the JT8D-200. The -83 has the longest
range, accordingly.
MD-88 is a version with a glass cockpit.
MD-87 is a shortened version (the only one that is visibly different from
the other 4 versions).
Stefano
RD Rick
In <airliners...@ohare.Chicago.COM> Stefano Pagiola
<spag...@worldbank.org> writes:
>
>rickydik wrote:
>> >Before the two recent 757 crashes, the MD-80 was second in safety.
>> ^^^^^^ only
>> >It must be in first place now.
>>
>> Definitely. Once one throws out the two crashes during the
>> flight-test program. And the crash in Argentina. And the NWA crash
>> at Detroit. And the SAS crash in Sweden. Oh, and the CAL RTO crash
>> at La Guardia...
>
>There was an Inex Adria CFIT crash in Corsica very early on (1981 or
so)>and an Alitalia crash near Zurich (also CFIT, as I recall) a few
years>ago.
I calmly corrected:
The AZ crash at Zurich was a DC9-30. Crew was apparently following a
dead Glideslope indication.
>.. not familiar with any MD-80 crash in Argentina. Can you supply
>details? (Airline, date, location, cause, fatalities?)
Nobody seems to have data on that one, if it happened.
RD
Ed Hahn
In article <airliners...@ohare.Chicago.COM> t...@me.rochester.edu (Tim Takahashi) writes:
tt> What's the fuel economy like on a MD-80/90? Better or worse than a
tt> equivalent 737? (or 727? given the length of the MD-90)
The figure that was thrown around at the airline I used to work for
was that the MD82/83 could operate many of the same routes as a B727-200
at 65% of the operating cost (i.e. pretty significant), at the expense
of 7 fewer passengers in the cabin.
ed
-------- Ed Hahn | eh...@mitre.org | (703) 883-5988 --------
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really, I wouldn't kid you about a thing like this.
GWils...@aol.com
>727 APU installation is the best of the three, but also far from ideal.
Can anyone describe to me what the 727 APU installation actually is?
Thanks for any info.
Gerald Wilson
Jan-Erik Andelin
RD Rick (rick...@ix.netcom.com) wrote:
: >.. not familiar with any MD-80 crash in Argentina. Can you supply
: >details? (Airline, date, location, cause, fatalities?)
: Nobody seems to have data on that one, if it happened.
Oh yes, it happened. On June 12, 1988, Austral Airlines' MD81
on approach in dense fog crashed killing 22 people near Posadas.
More info on my MD80 homepage, welcome ...
-- erkki
* * * MD80 International Home Page * * *
http://www.clinet.fi/~andelin/md80.htm
--------------------------------------------------------------
Jan-Erik Andelin * phone +358-19-584 622
Agatan 63 * e-mail and...@clinet.fi
06100 Borga, Finland * WWW http://www.clinet.fi/~andelin/
Steve Lacker
GWils...@aol.com wrote:
>
> In article <airliners...@ohare.Chicago.COM>, "David G. Davidson"
> <ger...@onramp.net> writes:
>
> >727 APU installation is the best of the three, but also far from ideal.
>
> Can anyone describe to me what the 727 APU installation actually is?
>
Its in the starbord (right hand) wing root. The exhaust exits from the top of
the wing, a bit aft of the emergency exits. The only drawback I can think of to
this installation is that it is noisier inside the cabin than an APU buried
back in the tail, because the exhaust stream is literally a couple of feet from
the passengers. Maybe the maintenence guys on the list can give more details- I
*think* the APU is accessible through the starbord wheel well, so its much
easier to service than a tail-mounted unit.
--
Stephen Lacker
Applied Research Laboratories, The University of Texas at Austin
PO Box 8029, Austin TX 78713-8029
512-835-3286 sla...@arlut.utexas.edu
David Lesher
GWils...@aol.com writes:
>>727 APU installation is the best of the three, but also far from ideal.
>Can anyone describe to me what the 727 APU installation actually is?
ISTM it's not certified for in-flight use.....
JWizardC
The B-727 APU is mounted in the left wheel well. The intake is through the
wheel well and the exhaust is a port on top of it. The good news is that
is saves a lot of plumbing for fuel, hot air, and electricity. The bad
news is that if you forget to turn it off prior to takeoff, the passengers
get treated to a real pretty purple flame shooting out of the top of the
gear well as it starves for air.
TheFNG
David Lednicer
> Can anyone describe to me what the 727 APU installation actually is?
The APU is in the main gear bay, on the centerline, behind the
rear spar. The APU is actually situated in a hole in the fuselage keel
beam. Inlet air comes from the gear bay (I believe the gear must be
down to run the APU) and exhausts through a exit in the right hand upper
wing skin.
-------------------------------------------------------------------
David Lednicer | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc. | email: da...@amiwest.com
2133 152nd Ave NE | tel: (206) 643-9090
Redmond, WA 98052 USA | fax: (206) 746-1299
Keith R. Thompson
GWils...@aol.com wrote in article
<airliners...@ohare.Chicago.COM>...
> In article <airliners...@ohare.Chicago.COM>, "David G. Davidson"
> <ger...@onramp.net> writes:
>
> >727 APU installation is the best of the three, but also far from ideal.
>
> Can anyone describe to me what the 727 APU installation actually is?
The B-727 was originally designed without provision for an APU and was
later added to the design at the behest of the airlines. Because the engine
and aft airstair configuration ruled out mounting the APU in the tail,
Boeing basically cut a hole through the keel in the forward part of the
main gear wheel wells and mounted the APU there.
Air for the APU is drawn from the left wheel well and exhausted through a
port in the top of the right wing near the fuselage. The APU uses a flow
multiplier which draws from the right wheel well.
The main problem with this installation is that in extremely hot
environments, high temperatures in the wheelwell when the APU is operating
can result in a Lower Aft Body overheat warning light illuminating on the
engineer's panel. That's why under these conditions ground crew will
frequently drop the main gear doors if the aircraft will be idle for
awhile. This aids airflow to the APU and reduces the likelihood of getting
the warning light.
--
Keith R. Thompson
kei...@earthlink.net
Denver, CO
MikeM727
In article <airliners...@ohare.Chicago.COM>, "Keith R. Thompson"
<kei...@earthlink.net> writes:
>The APU uses a flow multiplier which draws from the right wheel well.
Only the -200 uses a flow multiplier. The flow multiplier allows the
running of both a/c packs on the APU. The -100 can only run one pack on
the APU.
>The main problem with this installation is that in extremely hot
>environments, high temperatures in the wheelwell when the APU is operating
>can result in a Lower Aft Body overheat warning light illuminating on the
>engineer's panel.
Never heard of that. Generally, there would have to be some kind of bleed
air duct rupture to result in a Lower Aft Body overheat warning. However,
if the APU is not shut down prior to takeoff, when the gear is retracted a
Wheel Well Fire warning light and bell could result.
>That's why under these conditions ground crew will
>frequently drop the main gear doors if the aircraft will be idle for
>awhile. This aids airflow to the APU and reduces the likelihood of
>getting the warning light.
Never heard of, seen, or done that. The only time I am aware of the
inboard gear doors being dropped is for maintenance. Seems like it might
help with cooling, though.
Mike,
ATP/FE, Boeing 727
-----------------------------
Props are for boats!
-----------------------------
GWils...@aol.com
In article <airliners...@ohare.Chicago.COM>, David Lednicer
<da...@amiwest.com> writes:
>> Can anyone describe to me what the 727 APU installation actually is?
>
> The APU is in the main gear bay, on the centerline, behind the
>rear spar. The APU is actually situated in a hole in the fuselage keel
>beam. Inlet air comes from the gear bay (I believe the gear must be
>down to run the APU) and exhausts through a exit in the right hand upper
>wing skin.
Thanks for the various answers to my question. Just one more
clarification....How high is the under surface of the wing? Are there any
problems with FOD being sucked up into the APU?
Gerald Wilson
Steve Lacker
JWizardC wrote:
>
> The good news is that
> is saves a lot of plumbing for fuel, hot air, and electricity. The bad
> news is that if you forget to turn it off prior to takeoff, the passengers
> get treated to a real pretty purple flame shooting out of the top of the
> gear well as it starves for air.
Well, I've never seen the pretty purple flame... but I have seen a "nervous
flier" in the seat in front of me nearly have a stroke when the flight crew
started the APU on a 727 and a lovely plume of thick white smoke poured out
the exhaust port right outside the window :-) Apparently that particular APU
was a bit of an oil burner.
David G. Davidson
>However,if the APU is not shut down prior to takeoff, when the gear is >retracted a Wheel Well Fire warning light and bell could result.
The 727 APU is not certified for airborne use and it should
automatically shutdown once the air/ground sw goes to air mode. Normal
ops is to shut it down once the engines have been started.
David G. Davidson
Ok, here's the deal on the 727 APU.
It is mounted in a hole in the keel beam in the forward end of the wheel
well and hangs from the ceiling of the wheel well.
The portion of the APU with the gearbox, electrical generator, starter,
fuel control, oil pump and oil filter is in the left wheel well.
The portion of the APU which contains the combustion chamber, ignitor
plug and box, turbine wheel and the APU load valve (the valve which
turns pneumatics to the airplane on and off) is in the right wheel well.
The APU exhaust exits through the top of the right wing, just a little
aft of the rear overwing exit.
The air inlets for the APU are in the left wheel well and are protected
from FOD by the left gear door which is normally closed. One of the air
inlets is for cooling the electrical generator. The other feeds air to
the APU compressor section.
The bottom of the wing is about 6 feet off the ground.
This is kind of hard to visualize. Is there a way to post pictures to
this group? Maybe I'll just throw some pictures together and put them on
a web page.