flight dispatchers

Today we will talk, in the form of homage, about the importance andé This is what flight dispatchers do., a positionón key for operations toéreas.

Few jobs are as thankless as being a flight dispatcher for a aircraft of transport toéprisoner of charge, no one remembers them cuándo the avión comes out like a áalg angelún airport crítico (height, short track temperature, fruitáasses etc.), They don't remember them eitheráWhen the aircraft leaves so heavy or poorly loaded that the pilot feels like the blue planet is falling on him and uses all his skill and experience to be able to obtain a successful although precarious climb.; at that moment it is not the dispatcher himself who comes to mind but the being that brought him into the world.

Post written by: William Casalins
Aeron Engineeráuseful
Foundationón SON

flight dispatchers

Hardly anyone gives them the importance they have., ¡nor themselves!. Many aircraft and lives have been lost due to poor clearance procedures, because the aircraft were más heavier than reported, badly loaded (misplaced the load), the cargo was loose or they were merchandiseídangerous, poorly packaged, etc..

The planes, whether ultralight or a jumbo jet, son mámachines that must be perfectly balanced; The manufacturer gives exact instructions for weight and position.ón of the center of gravity (C.G.) and the mátolerance ranges where this can go without harming performance, the stability or structure of the aircraftón.

The manufacturer, además, according to the charactersídeparture and destination airport statics (height, temperature, RH, wind, length, tilt usón and type of surface  track, etc.) and  a few pesos máwe moan  de operationón; It should be noted that these weights are calculated with the critical motor inoperative in V1, óbe the engine that más affect it´(when it fails) at the moment más crítico,  where the pilot must decide whether to take off or abort takeoff and brake, to stay within what is left  track available.

The first Creole flights were madeístill according to the manual, afterés the pilot (which was normally the ownerñor your ancestoróno of the airínea) when they getítrust him  decíto the dispatcher (almost always empírico)  “SALI SOBRAO, étake a ton más”  and thenés a más y andí until the avióin the hallíto really bad, in the líhalf of the track and narrowly avoiding the obstacleságlasses (with all engines operating at mámaximum power) then  decía “good bápull half a ton and that's it”, those were the onesátrack analysis that they used and that never took into account conditionóNo. of engine inoperative in V1.

In my judgement, I saw oneón poorly loaded is más dangerous than an avión very heavy; And if those two events are combined ¡GOD SAVE US FROM A LOSS OF ENGINE DURING TAKE-OFF! They have already been heard nervously  To some pilots “How we go an ADF (radio locator) We fall”, The above doing alusión that if there is a motor strike there will be noíNothing to do, as has effectively happened in some bimorectors that are so diffíciles to control and although it isén correctly loaded, an exceptional expertise and m is neededás that, what they really need is a place to fall, which unfortunately does not always beá Available for the large number of buildings near the slopes.

The trajectory of an object that moves in the air  It is really that of its center of mass or center of gravity (C.G.) And an aircraft is not the exceptionón, for his C.G.. pass the 3 AVI control axesón, what  It is achieved by aerodin surfacesámicas that exert a force proportional to speed and áangle of said surface or stabilizer referring to relative wind and distance (lever arm) from where this force is applied to the center of gravity (C.G).

From the early aviationón have comeó A serious stability and control problem, almost all aerodin partsáAvi micasón are destabilizing (the grandfatherón tends to get worse the situationón in functionón of time) The pilot Teníto maintain this control all the time with great effort and concentrationón; The pilot is human and only podíTo do this actionón by smallñtime intervals before finishing exhaust fíSica and mentally.

At first this was enough, But as the flights were doneían más long and m planesás large, a priority was made that the avión will be self-stabilized aerodinánot at all, This is achievedíand by carátically only yesíAmos el C.G. ahead of the center of pressure  (C.P.), point where support is considered concentratedón)  And it depends on áwings, the queue and its distances, but as we will see itálateness has dire consequences on performance and weight, because as we say in engineeringía : “nothing is free in life, and everything has to be paid one way or another”, in airplaneáutica says them “commitment” forks  improve some important things by sacrificing others that are not a priority for that designñor in particular.

The main wing is the one that provides the greatest amount of lift.ón under normal conditions, provides an upward force equal to the weight of the aircraftón or sometimes much más (depending on the maneuver beingé doing). In a straight and level flight, as it is in almost the entire cruise (is the one that spends almost the mostía flight time), the wing alsoás to support the weight of the aircraftón has an additional load, which is the downward force of the tail due to having the C.G. advanced (see graph).

It is obvious that being the C.G. más advance or the avión más heavy, This value tends to increase and require moreás upward force from the wings and this entails más resistance to advance, más weight because it has to be done más strong structure and higher fuel consumption. On the contrary, if the weight was behindás of the aerodynamic centerámonkey, the vector provided by the horizontal stabilizer aimingía upwards and although it consumes additional power per  the resistance to advanceñadidas in the tail (same as the previous case), this force  is added to the supportón created by the main wing, which means that it must work less and for that reason have a greater structural resistance.ás smallña, máIt is light and has less resistance to advance, which translates into less fuel consumption and más speed, albeit to a substantial detriment to the stability and control of the aircraft. Fortunately today when I designed themñaircraft manufacturers have left the electrificationóonly the “responsibility” of stability, the operationón of control surfaces and the possibility más remote from entering a stallón, isán building  aircraft with artificial stability and given the advantages in benefits  and fuel savings are very desirable; This really startedó in aviationón military when the requer fightersíAn less stable, In the end they were más ráask for maneuvers so that they could evade más fáCilically to enemy aircraft and missile. With artificial stability systems, they can be designedñar slightly unstable aircraft that will haveíAn better yields, that only couldíto keep them in flight powerful and redundant computers.

Combine itón of having an over-peed aircraft and with the C.G. too far ahead is highly undesirable especially in takeoff conditions, approximationón and landing, When hypersustrating surfaces  They printed a very strong nose hipper, además The low speeds of these maneuvers make the elevator and their horizontal stabilizer do not have enough authority (force) to keep the nose in positionón up, and the loads imposed on the wings and nose landing gear couldíto make them collapse.

As we said before, the positionón del C.G. with respect to the aerodynamic centerámonkey is what Iás affects the stability in the avión; stable if isá past, neutral sí match and unstable if found behindás.

How an image is worth máI know a thousand words, we are going to use several gráyou stay (exaggerated) to better understand all this mess. We will start with the conditionótakeoff or landing number, with the C.G.. advanced, and on a cruise with C.G. late.

Warning: mourningágo ahead

Hahaha it's a joke.

Stability isática and dinámica

The stability isáethics is the natural tendency of the birdón in trying to return to its original attitude when it is disturbed in its straight and level flight by a ráwind gust or any other reason.

din stabilityámica consists of the shape like the avión tries to reach or arrives at its original flight state afterés of said disturbanceón.

¿Cóhow does position affectón de C.G. stability and control?

The alas are those that fly and the total weight of the aircraftón must be very close to the point where the sum of all the supporting forces occurs (pressure center), otherwise the moment (the arm of the lever multiplied by the intensity of the force) between weight and liftóto beíto so large that the surfaces of the risers will beístill insufficient to maintain stable flight, especially at low speeds. For example, if there are conditions of heavy weight and too much lead added to the low takeoff and landing speeds together with the nose down pitching moment due to the deployed high lift surfaces, to beíto the event más unfavorable for control, performance and structure, but better for stability. the solutionón más likely to resort to increasing speed to make más effective tail force, use fewer degrees of flaps and soí decrease positive pitch moment.

in performance (performance)

When the avión has a nose-down pitching moment (positive), the tail has to do some downward force. This will dependá of the sizeñor the moment and length that exists between the horizontal stabilizer and the C.G.) We can consider that downward force as an additional weight that theóIt has to be supported by the main wings, That requires más resistance to advance, that is máS Available power of engines.

in the structure

Analyzing event MáS unfavorable (nose-heavy and over-heavy at take-off), We said that the wing alsoén has to be responsible for the additional weight, This means that the stabilizer is pulling down to counteract the positive pitch moment. (nose down). This suggests that wings have to be MáS strong and lógicamente más heavy, In the landing you are going to stress a lotás the nose train (and everything in general) since the pilot does not have enough control to land smoothly on the runway; If it's the revés (heavy tailed) to beíTo a miracle that the pilot puts it in the right place on the track.

The aircraft dispatcher is a linkón very important in the operation chainón of aircraft; así As are the flight assistants who are notán to load the bags or serve the coffeeé, but really están to get us out of the avión in less than 90 seconds in case of evacuationóemergency number. The dispatcher is notá To load the avión, éHe is in charge of ensuring that the flight is prepared correctly, with the right fuel to go to the destination airport, to alternate and fly over the determined time before landing, make the flight plan along the route and at the height máadequate s, depending on weight and winds, informing the pilot of weather conditions at all airports and aerovías involved, of the grandfather's statusón and maintenance notes, that the goodsíhow dangerous it isén  well packed, documented  and his positionón well defined, people on board etc.. etc. ÉL, together with the pilot in command, They are the ones who, after all, plan the flight; That's why every time an avión makes a safe and on-time landing at a destination airport, it is because in large part the flight dispatcher HE DID HIS JOB WELL.

Some examples can be investigated:

• Overweight without consequences: Max Conrad, who establishedó réworld distance records aboard a Piper Twin Comanche that carried twice the load úutil allowed flying almost 12,700 Km between SuráAfrica and Florida.
• The accident of Boeing 747 than Afghanistanán is an example of not exceeding the weight otherwise the poorly secured load will shiftó backás during takeoff.
• One that never fails in CRM courses is the accident of the ValuJet DC-9 that caught fireó by merchandiseídangerous as poorly managed.

Thanks to my friends FIA, Jaime Sada and Freddy Higuera for the collaborationón este artíass.

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