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convair880mfan
Topic Author
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Joined: Fri Jun 25, 2021 12:33 am

Flap setting differences on DC-9-10 and other DC-9 types

Sun Aug 22, 2021 11:21 pm

Does anyone know if the flap settings on the DC-9-10 was different from later versions? I read a report entitled "Bye Bye Baby: DC-9 from the Flightdeck" by Max Kingsley-Jones in Aircraft Illustrated magazine* and he mentions a Flaps 10 takeoff and then Flaps 20 approach and Flaps 30 landing. The aircraft covered in the article was a British Midlands DC-9-10 according to the author.

But I thought the DC-9 flap settings were 0-5-15-25-40-50. I know the series 10 models of the DC-9 did not have slats. Were the flap settings also different than later DC-9 models.

Thanks for any information.
_______________________
* Max Kingsley-Jones. "Bye Bye 'Baby': DC-9 from the Flightdeck." Aircraft Illustrated. May 1994. pp. 24-28.
 
DiamondFlyer
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Re: Flap setting differences on DC-9-10 and other DC-9 types

Mon Aug 23, 2021 3:11 am

Having flown both a -10 series and a -30 series, yes, what you see is correct. The 10 series flaps were 0, 10, 20, 30, 40 (50 was blocked in noise compliance efforts).
 
convair880mfan
Topic Author
Posts: 217
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Re: Flap setting differences on DC-9-10 and other DC-9 types

Mon Aug 23, 2021 5:34 am

Thanks for that information DiamondFlyer. I had the opportunity to fly once on a Delta DC-9 10 series from Boston to Manchester, NH. One thing that has stuck in my memory is that that plane seemed to have a downward deck angle during the approach. I thought it was sort of unnerving as though the plane were diving toward the ground. Maybe my memory fails me here, but that is what I remember..

I also seem to remember that I sat by the very loud engine and there was a kind of throbbing or pulsing sound at certain times.
 
GalaxyFlyer
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Re: Flap setting differences on DC-9-10 and other DC-9 types

Mon Aug 23, 2021 1:44 pm

Fans or turbines out of sync
 
LH707330
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Joined: Fri Jun 15, 2012 11:27 pm

Re: Flap setting differences on DC-9-10 and other DC-9 types

Mon Aug 23, 2021 3:19 pm

The downward deck angle is common on aircraft with no slats, the CRJ100/200 do the same thing.
 
DiamondFlyer
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Re: Flap setting differences on DC-9-10 and other DC-9 types

Mon Aug 23, 2021 5:03 pm

LH707330 wrote:
The downward deck angle is common on aircraft with no slats, the CRJ100/200 do the same thing.


I don’t think I’d generalize that widely, as the 145 family doesn’t have slats, but doesn’t land nose down.

Yes the DC9-10 does land with a distinct nose down attitude on approach
 
LH707330
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Re: Flap setting differences on DC-9-10 and other DC-9 types

Mon Aug 23, 2021 11:19 pm

DiamondFlyer wrote:
LH707330 wrote:
The downward deck angle is common on aircraft with no slats, the CRJ100/200 do the same thing.


I don’t think I’d generalize that widely, as the 145 family doesn’t have slats, but doesn’t land nose down.

Yes the DC9-10 does land with a distinct nose down attitude on approach

Fair criticism, let's go with a more complete version: slats, when extended, lower the chord line and leading edge of a wing and re-energize the boundary layer behind them, allowing the wing airflow to remain attached longer. One consequence of this is that the wing can be put at a higher angle of attack than if it didn't have slats, which is why many slatted aircraft have nose-high attitudes on approach. On types like the DC-9 and CRJ, where heavier versions have slats to allow lower approach speeds, those versions typically have a more nose-up attitude than the non-slat versions.
 
e38
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Joined: Sun May 04, 2008 10:09 pm

Re: Flap setting differences on DC-9-10 and other DC-9 types

Tue Aug 24, 2021 1:08 am

Quoting convair880mfan (Topic originator), "Does anyone know if the flap settings on the DC-9-10 was different from later versions?

I thought the DC-9 flap settings were 0-5-15-25-40-50. I know the series 10 models of the DC-9 did not have slats. Were the flap settings also different than later DC-9 models."


convair880mfan, exactly what DiamondFlyer wrote in Reply # 2 above.

This following is just additional information for your interest:

DC9-10

Flaps 0 - not used for takeoff or landing
Flaps 10 - takeoff setting
Flaps 20 - takeoff setting
Flaps 30 - approach and landing setting used for abnormal situation such as engine out approach and landing
Flaps 40 - normal setting for landing, i.e., company standard
Flaps 50 - not used, see below *

DC9-30/40/50

Flaps 0 - could be used for takeoff only in "Flaps 0, Slats extend" configuration
Flaps 5 - takeoff setting
Flaps 15 - takeoff setting
Flaps 25 - approach and landing setting used for abnormal condition such as engine out situation
Flaps 40 - normal setting for landing, i.e., company standard
Flaps 50 - not used, see below *

* The DC-9 was designed such that Flaps 50 would be the "standard" flap setting for all normal approaches and landings. However, it was discovered that the thrust required to maintain Vapp with Flaps 50 exceeded standards for noise compliance. As DiamondFlyer stated in Reply # 2, the Flaps 50 detent was retrofitted with an FAA-approved blocking device to enable the aircraft to be FAA Stage 3 noise compliant by the year 2000. The blocking device was secured with safety wire such that if Flaps 50 was needed for an emergency landing due to a short runway being the only option available (think 3,000 feet perhaps), the safety wire could be broken, the blocking device rotated, and Flaps 50 selected. Approach speed at Flaps 50 would have been 5 KIAS less than Flaps 40. At my operator, 5000 feet of runway was the minimum acceptable for normal operations.

Two other comments:

1. convair880mfan, your awareness of the downward deck angle on approach is very perceptive. However, from the flight deck, the difference in the angle (DC9-10 versus other models) was almost undetectable as the aimpoint used on approach in all the models was identical--aimpoint approximately 1/3 up from the bottom of the windscreen.

2. Reference your comment, "throbbing or pulsing sound at certain times," and comment by GalaxyFlyer above, Reply # 4, "Fans or turbines out of sync."

On the DC9-50 series, the aircraft had an engine synchronization system designed to reduce or eliminate this condition, although it didn't always work all that well. It was required to be "OFF" for takeoff, approach, and landing. It was also installed on the MD-80 series (Pratt and Whitney JT8D engines). I do not know if the MD-90 aircraft with the IAE V-2500 engines had it.

On earlier DC-9 series, 10, 30, 40, the pilots had to manually "sync" either the N1, N2, or simply slightly adjust the throttles by "sound" to reduce or eliminate the pulsing sensation.

e38
 
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DL_Mech
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Re: Flap setting differences on DC-9-10 and other DC-9 types

Tue Aug 24, 2021 1:32 am

Interesting. I went searching for a picture of a DC-9-21 on approach.



http://en.wikipedia.org/wiki/McDonnell_Douglas_DC-9#/media/File:SAS_DC-9-21_SE-DBR.jpg

vs a DC-9-10



Image
From: https://www.skybrary.aero/images/8/81/DC91.jpg
 
DiamondFlyer
Posts: 3547
Joined: Wed Oct 29, 2008 11:50 pm

Re: Flap setting differences on DC-9-10 and other DC-9 types

Wed Aug 25, 2021 3:54 pm

LH707330 wrote:
DiamondFlyer wrote:
LH707330 wrote:
The downward deck angle is common on aircraft with no slats, the CRJ100/200 do the same thing.


I don’t think I’d generalize that widely, as the 145 family doesn’t have slats, but doesn’t land nose down.

Yes the DC9-10 does land with a distinct nose down attitude on approach

Fair criticism, let's go with a more complete version: slats, when extended, lower the chord line and leading edge of a wing and re-energize the boundary layer behind them, allowing the wing airflow to remain attached longer. One consequence of this is that the wing can be put at a higher angle of attack than if it didn't have slats, which is why many slatted aircraft have nose-high attitudes on approach. On types like the DC-9 and CRJ, where heavier versions have slats to allow lower approach speeds, those versions typically have a more nose-up attitude than the non-slat versions.


Yes, I'd agree with that statement. Having flown both the CRJ2 and the DC9-10, they are a bit of an odd duck on landing for sure.

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