Interesting Delta flight, MD88

[fdcg27]

Nothing to worry about WRT the old girl you flew on. Delta has taken good care of these old things and I flew on Delta MDs when they were still new.
You should have caught the build date on the plate which would have been on the frame of the door through which you boarded. I always do.
Anyway, other developments of the original Douglas design will be around for awhile.
Delta has the largest MD90 fleet in the world as well as the largest 717 fleet.
Not saying much, since neither type was build in much volume.
Delta has invested in an engine shop for the 717 (really MD95), so those derivatives of the original DC-9 will be around for some time.
Yes, the last few rows of any of this family of aircraft are loud.

 

[Mr Nice]

Originally Posted By: PimTac
Many years ago I flew on a MD of Alaska airlines while on military orders. I do remember the noise, it was deafening.

Seeing loose screws anywhere on a aircraft would make me nervous.


I flew on one from Charlotte to St Louis and unfortunately sat near the engine. I agree they are loud inside the cabin.

 

[CincyDavid]

They are really quiet toward the front...not so much in the rear. McDonnell Douglas built a heck of a sturdy aircraft.

I generally just look out the terminal window and get the registration #, then google it for the production date, etc, but we boarded at gate E66 at TPA, which is on the corner and it's the only gate where you really can't see the bird out the window. I tried to look at the build plate but it was a mad rush to board and I didn't get more than a quick glance and couldn't read it that fast.

I was thinking...if someone had told a bunch of Douglas engineers in the early 60s that DC9 derivatives would still be in commercial service with mainline American carriers 50+ years later they would have thought you lost your mind. Surely we'd all be flying high-tech supersonic planes by now. I wonder how well "modern" aircraft would/will respond to Delta's philosophy of maintaining them well and keeping them forever...how well will electronics age, as opposed to more mechanically-oriented craft? It's similar to cars...a 65 Mustang is a heck of a lot simpler than a new one. Will anyone be able to get parts for, and repair a 2018 Mustang 50 years from now?

 

[Nyogtha]

I've certainly had more comfortable flights in MD-80, MD-88, & MD-90 aircraft than similar design DC-9's, back when I was a smoker and rules changed where smoking was only allowed in the rear of the aircraft. The DC-9 turbines produced a whine at a really annoying frequency for me. I have no idea if this was simply a performance charachteristic of the engine used or a reflection of maintenance practices by Continental at the time, which used the DC-9's I flew on.

 

[john_pifer]

I work at BNA (Nashville), and I watch a few planes take off every day - mostly SW 737s, but also a lot of Delta MD-80s.

The MD-80s are always my favorite to watch take off. I don't know if it's my imagination or if it's a sort of optical illusion, but the rotation and climb-out of the DC-9 variants always seem a lot steeper than the boring 737s. Maybe it's the fact that the wing is set so far back on the fuselage, but when they rotate and take to the air, they seem like they "settle back onto the wing" and that tube is pointed almost 45 degrees towards the sky!

 

[Mr Nice]

John,

Which airline do you work for ?

I agree the MD-80 looks to climb steeper after rotating.

 

[bunnspecial]

My last commercial flight was two flights on MD-90s and two on MD-88s.

One MD-88 out of Atlanta had a terrible set of brakes that sent a grind/shimmy through the entire plane. Needless to say, I noted the tail number and when I flew back out of Little Rock, AR on the same plane the following day it had been fixed. None the less, it was a bit worrying. I wasn't the only one who had been on the flight the previous day, and it was a conversation while waiting to board.

I do have to say that the last leg of my trip was on what seemed to be a relatively new or at least recently refurbished MD-90 and it was quite comfy. It helped that the plane was at less than half capacity and they let us spread out as much as we wanted(within reason). I had a 3 seat row to myself, which is nice for a 6'2" guy who's also a bit on the rotund side in economy class.

I know the old McDonall-Douglas planes are indestructible. Still, though, I think back to my last flight on a DC-10 probably 10 or 12 years ago and like every other flight on them it was loud and rattly but still ultimately fairly comfortable. The MD-88 and MD-90 definitely brought back memories of a DC-10 flight for me.

 

[CincyDavid]

I've never flown a DC10, biggest bird I've been on was a Delta L1011 back in the early 80s. I was maybe 12-13 years old and don't recall much about it.

The only 4-engine plane I've been on was also a Douglas product...Braniff DC8 to Panana City Panama in 1981. My parents shipped me off to Panama for the summer to learn Spanish, staying with a family they knew. Only issue was, nearly everybody I encountered in Panama spoke at least passable English. The main thing I recall about the plane was big brown leather seats.

 

[john_pifer]

Originally Posted By: Mr Nice
John,

Which airline do you work for ?

I agree the MD-80 looks to climb steeper after rotating.


I work at Embraer’s overhaul station.

 

[Astro14]

Originally Posted By: john_pifer
I work at BNA (Nashville), and I watch a few planes take off every day - mostly SW 737s, but also a lot of Delta MD-80s.

The MD-80s are always my favorite to watch take off. I don't know if it's my imagination or if it's a sort of optical illusion, but the rotation and climb-out of the DC-9 variants always seem a lot steeper than the boring 737s. Maybe it's the fact that the wing is set so far back on the fuselage, but when they rotate and take to the air, they seem like they "settle back onto the wing" and that tube is pointed almost 45 degrees towards the sky!


The nose on the MDs may indeed be much higher than the nose of a conventional airplane, but that means little when comparing climb...there are several angles at play here.

First is the angle of incidence: the angle at which the wing is mounted on the airplane. IF the wing is mounted with a lower angle of incidence, then the nose of the airplane is higher for the same angle of attack, which, in conjunction with airspeed, is what generates lift...and that brings us to angle of attack.

Angle of attack: the angle at which the airflow is hitting the wing. Some airplanes fly at a higher AOA at low speed (like takeoff) than others. The 737-800 and -900 fly at a very LOW angle of attack when taking off (and at a higher speed) so they don't hit the tail of the airplane on rotation. Since angle of attack is actually defined as the angle between the air flow and the mean chord line of the wing...we should consider...

Mean chord line: The chord is the line between the leading edge point and the trailing edge point. As flaps are extended, the chord line changes, often dramatically.

Flaps are selected for takeoff, but the degree of their extension, and the design of that wing, varies among airplanes. So, flaps 5 in a 757 gives you good takeoff performance. But flaps 15 or 20 might be needed based on field length, altitude, wind, terrain, weight, etc. The wing has a far different shape at 20 than at 5.

The chord line has changed with each change in flap extension...

So: take one airplane with a much lower angle of incidence than another, and it will have a higher nose on climb out. If the flaps are extended to a greater degree on that airplane, then the mean chord line has shifted, too. Add a change in airspeed and the AOA will be different between airplanes.

It's entirely possible that the nose on the MD is at twice the pitch (relative to the horizon) than the 737 for similar climb performance. Due to differences in the angle of incidence, and angle of attack, and flap setting, the two airplanes may be flying the same climb profile, the same vertical path in relation to the terrain, but at very different airspeeds and pitch attitudes.

https://en.wikipedia.org/wiki/Angle_of_incidence_(aerodynamics)
https://en.wikipedia.org/wiki/Angle_of_attack
https://en.wikipedia.org/wiki/Chord_(aeronautics)#Mean_aerodynamic_chord

 

[SEMI_287]

Oh I'll miss the Mad Dog. I've always wanted to fly one but that will never happen. I remember my first flight on one. USAir from DCA-MCO in 1995. It was great for short flights but not anything longer than 2.5 hours. I flew a Delta MD88 ATL-TUC and it was horrible. Cramped and there wasn't anything more than snacks. 4 hours on one wasn't fun.

 

[john_pifer]

Originally Posted By: Astro14
Originally Posted By: john_pifer
I work at BNA (Nashville), and I watch a few planes take off every day - mostly SW 737s, but also a lot of Delta MD-80s.

The MD-80s are always my favorite to watch take off. I don't know if it's my imagination or if it's a sort of optical illusion, but the rotation and climb-out of the DC-9 variants always seem a lot steeper than the boring 737s. Maybe it's the fact that the wing is set so far back on the fuselage, but when they rotate and take to the air, they seem like they "settle back onto the wing" and that tube is pointed almost 45 degrees towards the sky!


The nose on the MDs may indeed be much higher than the nose of a conventional airplane, but that means little when comparing climb...there are several angles at play here.

First is the angle of incidence: the angle at which the wing is mounted on the airplane. IF the wing is mounted with a lower angle of incidence, then the nose of the airplane is higher for the same angle of attack, which, in conjunction with airspeed, is what generates lift...and that brings us to angle of attack.

Angle of attack: the angle at which the airflow is hitting the wing. Some airplanes fly at a higher AOA at low speed (like takeoff) than others. The 737-800 and -900 fly at a very LOW angle of attack when taking off (and at a higher speed) so they don't hit the tail of the airplane on rotation. Since angle of attack is actually defined as the angle between the air flow and the mean chord line of the wing...we should consider...

Mean chord line: The chord is the line between the leading edge point and the trailing edge point. As flaps are extended, the chord line changes, often dramatically.

Flaps are selected for takeoff, but the degree of their extension, and the design of that wing, varies among airplanes. So, flaps 5 in a 757 gives you good takeoff performance. But flaps 15 or 20 might be needed based on field length, altitude, wind, terrain, weight, etc. The wing has a far different shape at 20 than at 5.

The chord line has changed with each change in flap extension...

So: take one airplane with a much lower angle of incidence than another, and it will have a higher nose on climb out. If the flaps are extended to a greater degree on that airplane, then the mean chord line has shifted, too. Add a change in airspeed and the AOA will be different between airplanes.

It's entirely possible that the nose on the MD is at twice the pitch (relative to the horizon) than the 737 for similar climb performance. Due to differences in the angle of incidence, and angle of attack, and flap setting, the two airplanes may be flying the same climb profile, the same vertical path in relation to the terrain, but at very different airspeeds and pitch attitudes.

https://en.wikipedia.org/wiki/Angle_of_incidence_(aerodynamics)
https://en.wikipedia.org/wiki/Angle_of_attack
https://en.wikipedia.org/wiki/Chord_(aeronautics)#Mean_aerodynamic_chord


Excellent explanation! Thanks!

 

[Astro14]

If I had flown the MD series, I might be able to provide some first hand observations, instead of just discussing aero...but I can see how one airplane would appear to be at a far higher pitch than another on the same field.

Incidentally, on the 747-400, you could select the flight path vector to be displayed on the PFD (Primary Flight Display). The usual display is pitch, but the FPV shows where the airplane is going, relative to the horizon. It includes crosswind and horizontal path as well as vertical path.

On a max gross climbout (875,000#), at 283 KIAS (which was allowed by the FAA below 10,000 feet as it was the minimum safe maneuvering speed) the 747 would be about 10 degrees nose up. That's the pitch attitude.

But that FPV was only about 3 degrees above the horizon...the big jet was climbing out at about 7 degrees AOA...quite slow, really, and it liked to be about 330 KIAS, or more, in the climb, once above 10,000 feet.

282 KIAS really was the minimum speed for it...the FPV confirmed the high AOA of the climbout. Climb rate at 330+ KIAS was much better than at 283...the high AOA resulted in a lot of induced drag from the wing. Higher speed and lower AOA yielded much better climb...

 

[oil_film_movies]

Originally Posted By: john_pifer
I work at BNA (Nashville), and I watch a few planes take off every day - mostly SW 737s, but also a lot of Delta MD-80s.

The MD-80s are always my favorite to watch take off. I don't know if it's my imagination or if it's a sort of optical illusion, but the rotation and climb-out of the DC-9 variants always seem a lot steeper than the boring 737s. Maybe it's the fact that the wing is set so far back on the fuselage, but when they rotate and take to the air, they seem like they "settle back onto the wing" and that tube is pointed almost 45 degrees towards the sky!


The Pitch Angle during climbout is more a function of the weight of the airplane during climbout.
If the aircraft (any kind) is relatively light, the pitch angle can be quite high. When fully loaded up, the pitch angle is less.

For example, I've seen 737's take off empty and they appear to fly straight up almost at a high pitch angle.

This is due to flying "speed-on-pitch" takeoffs. They choose a target airspeed, and then adjust pitch angle to maintain that target speed. They use a fixed throttle position at hight thrust, so the only thing a pilot needs to do is pitch up a little if he is going too fast, and pitch down a little if going to slow.

 

[SEMI_287]

Originally Posted By: Astro14

On a max gross climbout (875,000#), at 283 KIAS (which was allowed by the FAA below 10,000 feet as it was the minimum safe maneuvering speed) the 747 would be about 10 degrees nose up. That's the pitch attitude.

and it liked to be about 330 KIAS, or more, in the climb, once above 10,000 feet.

282 KIAS really was the minimum speed for it...the FPV confirmed the high AOA of the climbout. Climb rate at 330+ KIAS was much better than at 283...the high AOA resulted in a lot of induced drag from the wing. Higher speed and lower AOA yielded much better climb...


You have my attention.

 

[E365]

The MD88/90 flight director pitch command on takeoff is often just above 20°. Usually the pilots don’t (told they shouldn’t) pitch past 20° though.

Climb out speeds on a heavy MD90 will also be past 250kt, like some heavies. OLD wing design.

The chattering brakes on the MD88 is 100% normal when they get warm/hot. The MD90 has carbon brakes with no chattering.

 

[E365]

Here’s some takeoff pitch angles of various airliners. MD88/90 is higher pitch than average.
https://www.bangaloreaviation.com/2009/05/typical-takeoff-and-climb-angles-of-all.html

 

[oil_film_movies]

Originally Posted By: E365
Here’s some takeoff pitch angles of various airliners. MD88/90 is higher pitch than average.
https://www.bangaloreaviation.com/2009/05/typical-takeoff-and-climb-angles-of-all.html

http://www.boeing.com/commercial/aeromagazine/articles/qtr_02_09/pdfs/AERO_Q209_article04.pdf is the main article.
The Mad Dogs on the graph illustration show the MAX pitch angle (theta), while the 7x7's show the typical range.
Notice there is the climbout airspeed targets, which, after liftoff is followed, as the normal transition from liftoff to climbout.

With an airspeed target, thats speed-on-pitch, with a max pitch limit, but note you adjust pitch angle to maintain a target airspeed.
And when you do that, a heavy aircraft has a lower pitch angle and lighter ones have more pitch.

 

[E365]

Up to 1,000’ AGL, the 20° max is also very typical for the 88/90. The command is often higher than 20°. So you don’t end up pitching for speed, because pitching for V2+10 would put you higher than 20°. Often are pitching for 20° and accepting the speed faster than V2+10.

 

[oil_film_movies]

Originally Posted By: E365
Up to 1,000’ AGL, the 20° max is also very typical for the 88/90. The command is often higher than 20°. So you don’t end up pitching for speed, because pitching for V2+10 would put you higher than 20°. Often are pitching for 20° and accepting the speed faster than V2+10.
I'd like to see what pitch is for max weight (mtow), vs. a flight that's half full. Wondering if a MTOW climbout really hits the 20 deg theta max.