Airline Pilot Forums

Airline Pilot Forums was designed to be a community where working airline pilots can share ideas and information about the aviation field. In the forum you will find information about major and regional airline carriers, career training, interview and job seeker help, finance, and living the airline pilot lifestyle.




View Full Version : MD-11F takeoff distance empty


petersfreeman
07-25-2018, 08:12 PM
The MD-11F has an operating empty weight of 112,748 kg, and a maximum take off weight of 280,000 kg (standard).

The takeoff distance at the maximum takeoff weight (MTOW) is 3,100 metres.
What is the takeoff distance without any cargo (empty)?


TiredSoul
07-25-2018, 08:16 PM
Why you want to know?

Birdsmash
07-25-2018, 08:19 PM
Obviously not an airline pilot if heís asking for takeoff distance vs the way we normally calculate takeoff performance. I smell a lawyer!!!!


TiredSoul
07-25-2018, 08:25 PM
Or a flightsimmer or a tewwowist

https://coubsecure-s.akamaihd.net/get/b140/p/coub/simple/cw_timeline_pic/e5eb7fb5bc0/4595859eb0c0eaec96a1d/big_1482374220_image.jpg

petersfreeman
07-25-2018, 08:40 PM
I'm writing about the MD-11F. The technical specifications that I have gleaned from sources such as Wikipedia (https://en.wikipedia.org/wiki/McDonnell_Douglas_MD-11) and others do not mention the takeoff distance when empty. I did read a post from a pilot who has landed an MD-11F at Kos airport in Greece which has a runway distance of 2,400 metres, however he did not specify what load he was carrying.
The other discrepancy I have noticed in the Wikipedia entry for the MD-11 is that the maximum takeoff weight (MTOW) is 280,000 kg (standard), yet the maximum landing weight is only 222,900 kg. The question that immediately sprang to my mind is, how could you take off with 280,000 kg and yet not be able to land with more than 222,900 kg. Is the MTOW a theoretical weight and the takeoff distance derived from the MTOW designed to be a safety factor that takes into account variables such as the altitude of the runway, air temperature and air pressure, all of which would affect the air density and hence the lift generated by the wings. What I am looking for is how much runway would an empty MD-11F need to land and take off (the take off distance would be the greater).

Reactivity
07-25-2018, 09:11 PM
Itís not uncommon for an aircraft to have a maximum takeoff weight that is higher than its maximum landing weight. Itís the difference between simply carrying that weight on the ground vs running it into the ground at a vertical rate that I canít remember at the moment.

petersfreeman
07-25-2018, 09:46 PM
Thank you Reactivity, that was helpful. Can you tell me how much runway would an empty MD-11F need to land and take off.

JohnBurke
07-25-2018, 10:19 PM
Takeoff calculations are not single-number figures. Calculations depend on multiple factors, including pressure altitude, temperature, weight, wind, runway slope, and climb gradient with an engine failure. The latter in turn depends on the runway to be used, considering surrounding terrain and obstacles, and performance based on the previous elements: pressure altitude, temperature, weight, and wind.

A takeoff is not simply calculated in terms of pavement used, but stopping distance (what are the surface conditions? Wet? Dry? Slick?), which includes conditions, runway type, etc. Brake temperature may also be factor. Additional factors apply to the specific aircraft and it's condition, operative or inoperative equipment (autospoilers, takeoff autobrakes, etc).

Also to be taken into consideration and calculated for each takeoff is center of gravity and trim setting.

Not only must the aircraft leave the ground, but must climb at a minimum gradient with an engine failed or not producing thrust. Every takeoff is calculated not just with takeoff distance, but accelerate-stop distance, accelerate-go distance, balanced field length (when accel-stop and accel-go are equal), taking into account all relevant factors, including obstacles or temporary obstacles, and any equipment changes that affect performance.

An aircraft can get off the ground when empty in a fairly short distance; a choice of flap settings must be made, which in turn affects speeds and distances; these speeds are also established relative to the effects of asymmetric thrust: can the aircraft maintain directional control with one (or more) engines inoperative? An aircraft can get off the ground at a slow speed and climb slowly and steeply, but there are safety margins to consider, which require faster climb speeds, longer distances, and shallower climb gradients.

Aircraft departing above their minimum landing weight will either have to accept a higher landing speed and longer distance on landing (and overweight landing) in the event of a required return in an emergency (eg, fire), or must dump fuel down to the landing weight.

Maximum weights vary with the serial number. Typically 287,124 kg for taxi, 285,990 kg for takeoff, 222,941 for landing. There are also maximum weights for inflight landing flaps (224,301 kg) and zero fuel weight (209,242 kg). The last weight is the maximum allowable weight of the aircraft before fuel is included; anything above that weight must be fuel.

In the case of the MD-11, you must also take into account whether the aircraft has "deflected ailerons" or not. These impact performance and configuration (flap setting), including takeoff distance. Some aircraft have deflected ailerons, which which the ailerons lower incrementally with the flaps to increase camber over a larger span of the wing, increasing lift. Some don't.

An airplane that's fairly light, 185,000 kg for example, at Los Angeles on a standard day could expect a reduced power takeoff with a takeoff distance required of approx 7,300'. The same aircraft, returning to land on the same no-wind runway, at the same weight, would need approximately 4300 for actual ground roll, an a landing distance of 7200' on a dry runway. On a wet runway those figures would increase to approximately 5000' and 8300' respectively, with a final approach speed of 150 kts.

Reduce those weights to 150,000 kg, with a 26% CG, and the takeoff number is approx 5000'. Landing at the same weight/CG/runway conditions yields approx 3700/6100 dry, and 4200/7000 wet. Those are ideal numbers; pilot technique can lengthen them. They're simply calculations. Change any of the factors and those numbers change, too.

Remember that each takeoff requires a full runway analysis that looks at the specific runway, and any obstacles or conditions particular to that runway at that moment, taking into account the other information specified. There is no one number that's used; it's calculated for every takeoff based on actual data, every time, and if a runway change is made or any changes are made with respect to configuration, weather changes, winds, center of gravity, and so forth, the runway analysis and performance calculations are re-done in entirety.

petersfreeman
07-25-2018, 10:44 PM
Thank you, John Burke. This helps me a lot.
I found a good white paper on the subject: https://fenix.tecnico.ulisboa.pt/downloadFile/395143164280/Jo%C3%A3o%20Lemos%20Viana%20-%20Takeoff%20and%20Landing%20Performance%20Optimiz ation%20-%20Extended%20Abstract.pdf
I do appreciate the time and effort you have taken to provide me with a detailed and comprehensive understanding of aircraft performance. I'm writing about the McDonald Douglas MD-11 aircraft, in particular the F variant, and I do want to ensure that my statements are accurate and reflective of the aircraft's characteristics.
Cheers - Peter.

JohnBurke
07-25-2018, 11:43 PM
I'm writing about the McDonald Douglas MD-11 aircraft, in particular the F variant, and I do want to ensure that my statements are accurate and reflective of the aircraft's characteristics.
Cheers - Peter.

The information above regards aircraft in general, but the numbers were drawn from a quick performance calculation for the MD11F.

What are you writing? Is this for an article, or a book?

petersfreeman
07-26-2018, 12:23 AM
Hello John Burke,

The information is for a book which I expect to be finished around the end of October and published in the early spring. The information about the MD-11 comprises only a small percentage of the book, however I am a stickler for accuracy and want to ensure that I have it right. I find that I become irritated when an author writes about a topic of which I have knowledge and see that the author has not taken the care to ensure that it reflects reality.

Cheers, Peter

Reactivity
07-26-2018, 07:42 AM
Hello John Burke,

The information is for a book which I expect to be finished around the end of October and published in the early spring. The information about the MD-11 comprises only a small percentage of the book, however I am a stickler for accuracy and want to ensure that I have it right. I find that I become irritated when an author writes about a topic of which I have knowledge and see that the author has not taken the care to ensure that it reflects reality.

Cheers, Peter

I sincerely hope your sources are more authoritative than Wikipedia and APC forums.

JohnBurke
07-26-2018, 07:47 AM
Peter, is this book fictional, or non-fiction?

Depending on what he's writing, a detailed list of works and research sites isn't necessarily what's needed. It may be a matter of trying to flesh out an element of a story to make it as realistic as possible.

petersfreeman
07-26-2018, 07:47 AM
Hello John Burke,

I am writing a book which I expect to have completed towards the end of October and published in the early spring of 2019. The material on the MD-11F only comprises a small percentage of the book, however as I am a stickler for accuracy, I want to get it right. I find it frustrating when I read material on a topic on which I have expertise and the author has not taken the care to ensure that they have the information correct.

Cheers, Peter.

JohnBurke
07-26-2018, 08:12 AM
Fiction, or non-fiction?

petersfreeman
07-26-2018, 08:49 AM
I have published non-fiction, however the work is fictional.

No Land 3
07-26-2018, 11:23 AM
He should be asking on pprune.

Elevation
07-26-2018, 08:53 PM
So fiction gives you a lot of room to make believable, educated reasons for your story to work. You don’t have to have cargo wizards and fuel warlocks like I mentioned earlier.

Boeing has kits for the 737-200 and 727 to operate from unpaved surfaces. It’s entirely plausible that Douglas Co. would have had a team investigating suitability of the DC-10 or MD-11 for similar roles before ultimately abandoning the project. (As far as I know this never actually occurred, but fiction gives you room to make your alternate timeline.).