PDA

View Full Version : MD-80's most kept secret


verticallimit
6th Nov 2011, 00:49
I have for over a year asked pilots, aircraft mechanics, asked on various forums and peered in the manuals.
I have not found the answer yet, so I think that the best kept secret on the MD-80 is what forces is used on the flight controls in manual flight:

aileron
elevator
rudder

All people I have asked says that the MD steering is very heavy.
I have tryet a ride in a Diamond 42 simulator and the instructor was previously MD pilot and he told me that MD had heavier controls, and the Diamond 42 simulator could well give sore arms if not trimmed in flight.

I still hope that there is a friendly person who can tell me the data, and preferably in a graph.
Thank you in advance.

Best regards
Claus Norgaard

vapilot2004
6th Nov 2011, 02:06
MD-80 aileron movement is controlled by aerodynamic tabs. This is also the case for the elevators in normal flight conditions. Rudder movement is hydraulically boosted in normal operation while during manual reversion, a tab system is unlocked and takes over.

General:
A control tab works by extending itself upon which aerodynamic forces cause the larger control surface to deflect in the opposite direction. For example, in commanding an aileron up movement, the tab is driven downwards forcing the aileron to deflect upwards.

Tabs, tabs, and more tabs:
Each aileron has an additional smaller tab located outboard of the control tabs for lateral trim. The elevators have two additional tabs located outboard of the control tabs for surface deflection assist and float control respectively. Longitudinal trim is accomplished via a conventional moving stabilizer. The rudder has a single tab used solely for control during manual (no boost) operation.

Feel and performance:
MD-80 control column forces are not extreme but they can be higher than the artificial forces generated on the 737 depending on the flight regime. It has been suggested by some that the DC-9 series is a bit mushy in the lateral axis thanks to the tab arrangement and down-wing spoiler linkage but I have never personally found nor heard it to be a problem even during gusty, crosswind landing conditions.

Let me know if you are interested in more information regarding the cable layout, control column and surface interconnections, or tab arrangements VL.

verticallimit
6th Nov 2011, 11:04
Hi vapilot2004

Thanks for the fine explanation.
But do you know how many pounds the pilot have to use for moving the various flight control surfaces, I assume that the force is also according to speed, so controls are easier to operate near stall speed.

Best regards
Claus Norgaard

vapilot2004
8th Nov 2011, 03:53
Aileron:
Breakout 5-6 pounds at the horn. 25 degree bank ~8-10 pounds.
Elevator:
Breakout at least 10 pounds. 5 degree nose up 20-25 initial then 15 pounds untrimmed.
Rudder:
25 pounds or more breakout. around 35 pounds for 15-20kt crosswind landing correction. V2 engine out before trim over 75 pounds in the sim (CAE)

Aircraft speed vs control column forces:
In comparing cruise vs approach speed control forces, we need to remember the deflection angles will differ by a factor of 2-4x or more for the same command request. Add in the by-statute (FAR/JAR) force gradient requirements and we are entering complex ratio territory, however, generally inputs at slow speeds require more force for the same maneuver.

verticallimit
9th Nov 2011, 21:12
Hi, Vapilot2004

Many thanks for this information. :ok: It is a tremendous help you have provided here.

To my surprise, I found out yesterday that the MD80 rudder pedal movement becomes smaller the faster you fly and therefore you should use less force at "full" rudder. I found this on the web.
"As the airplane speeds up, the rudder authority is limited, but the gearing
between the rudder and the rudder pedal does not change. Since rudder authority is
limited, rudder pedal travel is also limited; i.e., full rudder pedal deflection is not
required to get full available rudder deflection. Rudder pedal force is a function of
rudder pedal deflection, so less force will be required to achieve maximum available
rudder deflection as airspeed increases"
http://www.ifalpa.org/downloads/Level1/Safety%20Bulletins/Operations/03SAB001_Use%20of%20Rudder%20on%20Boeing.pdf
Page 8-9

I always thought that the faster you was flying the more force was needed to move the flight controls and it is apparently opposite on this big mashines.

I have also read this, and this fits very well with the data you have written.
"A pull force of approximately 16 pounds would have been required for lift-off"
http://www.icao.int/fsix/sr/reports/03002120_final_report.pdf
Page 24

I can understand that, the necessary force on the columns for lift-off may fluctuate some kg. depending on trim, aircraft weight and CG.

These are important data for me because I try to create a super realistic MD-80 simulator. And the time for building flight controls is near.
Links for simulator: Google Oversæt (http://translate.google.dk/translate?sl=da&tl=en&js=n&prev=_t&hl=da&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fsites.google.com%2Fsite%2Fdanskemd80cockpitpr ojekt%2F)

http://www.md80project.dk (http://www.md80project.dk/)

MD 80 is a fantastic airplane and is my favorite.

Best regards
Claus

vapilot2004
11th Nov 2011, 05:49
Very happy to hear I was of some small assistance Claus.

Congratulations on a unique and ambitious project. I particularly appreciate your choice of aircraft number one, and the idea of sharing your finished creation via caravan is a winner.

A well-respected airline and long-time operator of the Super 80 is of course SAS. Across the water from you in Sweden, I believe the training arm of SAS still operates a few MD-80 sims. Perhaps interest in your simulator 'gift' to the public, coupled with a shared appreciation for the Super 80 might get you some free/sponsored time in one of their simulators. Wouldn't hurt to ask.

verticallimit
11th Nov 2011, 22:50
I've tried to get in touch with SAS but without much luck, maybe I'm not in touch with the right people.

Danish Air Transport (http://www.dat.dk/home-30644.htm) in Denmark has provided a incredible help to this project.

ZFT
11th Nov 2011, 23:19
Possibly because all their FFSs are now operated by Oxford Aviation. See PM

verticallimit
13th Nov 2011, 14:30
As I wrote at the top of my post
"I have for over a year asked pilots, aircraft mechanics, asked on various forum"
This includes SAS, Oxford Aviation, Boeing and others, but without the big breakthrough.
It must be said that Boeing has offered me a real full-motion simulator for an extremely low price, but unfortunately I could not raise the money. Transport to Denmark alone would cost about $ 25000.
I think if I do not get hold of the right contact person at these big companys, I belive my mails often is moved to the spam box.

Best regards
Claus