In this installment we will talk about one of the m phrasesás famous of the aviationón “Speed and height retain their teeth” ¿Whaté so true or not is this saying? Foto The A320 Study Guide
Post written by: William Casalins
Aeron Engineeráuseful
Foundationón SON
¿Speed and height preserve teeth?
NOT ALWAYS
It is the creed of the student pilot and the veteran pilot knows that he has reached the veteranía usáearrings.
Alejandro Torres, a young co-pilot Boeing 727 In the middle of the cruise he turns around and asks me about the Coffin Corner, I start by clearing my voice (to start the conference) the téflight cone, Hernán Buitrago, tune the oído and gets ready to see dówhere am I wrong and the captainán Ricardo Barragán looks at me out of the corner of his eye (You know I'm going to contradict everything) and he checks it when I tell the co-pilot: ¿tú you know that the avión does not enter péloss due to low speed and on the contrary it can do so due to high?
Péloss of sustenanceón
Many times we have orído to a pilot, when he gives the approximationóNo takeoff to his co-pilot, or an instructor to his student “increase your speed that you are going to enter péfiring” ¿CóWhat am I going to say to veteran and new pilots?, than the grandfatherón does not enter péloss due to low speed but rather due to high áangle of attack; but on the contrary, it can stall due to high speed.? ¿it's a paradox? if we see the fósupport formulasóIt doesn't seem like ití, that I am wrong, that speed defines liftón and what, yes I duplicate it, the sustenanceón is multiplied by four, what, if the speed drops, the sustenanceón también does it in that same proportionón. Don't even talk about Casalins this time if you're wrong, what abouté form.
S=Cs*a*p/2*V´´
¿But really how it is?
Let's start from backás forward:
¿Cócan stall due to high speed? Okay, Let's define what a stall is and differentiate the péloss with the decreaseón of supportón, when you decrease liftón forces you to descend if it isá below current weight, but the péloss forces you to reduce the áangle of attack lowering the nose of the aircraftón, ahí Eastá the difference, tú you can be in péloss if you áIt is from the corner of the attacká above a áthis crítico, it doesn't matter what speed you have. That's why; to fix the hight speed buffet, It is necessary to lower the speed and to correct the low speed buffet you have to lower the nose first (to get it out of the péfiring) and then increase speed if you don't want to go down.
On péHigh speed loss is promoted because, after a certain air speed, This becomes a fluid with characterícompressible statics (what the air is really like) while at lower speeds it is considered incompressible (like the water) density and other factors are considered constant; afterés (at high speeds) day fóformula we mentioned before doesn't work for anything (there are many factors that prevent it). The same as with a áwing angle of attack más allá of the crítico, beás in péloss of liftón regardless of whether you have a higher speed, without counting that it isés doing a maneuver with some extra Gs that will obviously aggravateíand la situationón.
On péhigh speed loss has been improved, by dérock, with the arrow of the wing, así, although the avión is flying más ráI ask, the wing makes him “believe” to air that is going at a lower speed and behaves as such, decreasing the separationón of the boundary layer and the formationón more shock waves than those that will be producedíeven on a straight wing with the same profile. This, however, is not free and at the time of takeoff and landing, you also needén complicated hyperlift mechanismsón, because the air continues” believing” what's up más slower than expected and neededía más approach speedódon't fire him, with the necessary extra runway length to achieve sufficient lift valueón.
Nevertheless, the expression continues to be usedón loss speed. Let's look at the fórmula (S=Cs*a*p/2*V´´) again for a given weight, with a áconstant area, the same height, We will see that to have a speed míanima we need a CL máximo, and that is achieved with a ágiven angle of attack (for a particular profile); Then, if there is a relationshipón speed and loss, but what really happens is that if the speed decreases below that value and the pilot wants to maintain altitude, instinctively he will raise his nose without realizing that doing so will complicate the maneuver, because everything is going to happen él wantíto be avoided and with often disastrous consequences if you don't have the height to recover. But this (to use a stall speed) it has its advantages, the speedímeter is the instrument that más watches a pilot for being the más important in the flight of the airplaneón, some aircraft also haveén indicator áangle of attack, but the oldestía has más well alarms so that the pilot knows that he isá exceeding (oh prólimit to exceed) that value. Other planes are going toún más allá and impart a forward force to the elevator column (to lower the áangle of attack). We can see that in these teams has no relationón with the speed or weight of the aircraftón y solo isá connected to an A.O.M sensor. which is activated a few degrees before it reaches the point crítico y así alerts the pilot a few knots before that péloss of liftón.
Coffin Corner
the ringón del féretro is as horrible as its name suggests, as weight and altitude increase, those speeds change for the worse. The low one increases and the high one decreases and they try to get closer, reaches an altitude where it isán very close (each other) and the pilot has a dilemma, if it accelerates it goes into péloss and if it decreases alsoén, ya isá Of course there is a height limit for a given weight..
Then it isá más clear toún, that speed and height do not always preserve teeth.
