V Speeds, Part Two


Flying - - Contents - By Richie Len­gel

VLOF — Liftoff speed. Speed at which the air­craft be­comes air­borne. Back pres­sure is ap­plied at VR (ro­tate) — a some­what lower speed — so that liftoff ac­tu­ally hap­pens at VLOF.

VMCA or VMC — More com­monly known as VMC (al­though VMCA is more cor­rect). Min­i­mum con­trol speed with the crit­i­cal en­gine (usu­ally the left) in­op­er­a­tive out of ground ef­fect in the air — “red line” — and most crit­i­cal en­gine inop and wind­milling; 5 de­grees of bank to­ward the op­er­a­tive en­gine; take­off power on op­er­a­tive en­gine; gear up; flaps up; and most rear­ward CG. In this con­fig­u­ra­tion, if air­speed is al­lowed to di­min­ish be­low VMC, even full rud­der can­not pre­vent a yaw to­ward the dead en­gine. At slower speeds, the slow­er­mov­ing wing — the one with the failed en­gine — will stall first. VMC is not a con­stant; it can be re­duced by feath­er­ing the prop, mov­ing the CG for­ward and re­duc­ing power.

VMCG — Min­i­mum speed nec­es­sary to main­tain di­rec­tional con­trol af­ter an en­gine fail­ure dur­ing the take­off roll while still on the ground. De­ter­mined us­ing aero­dy­namic con­trols with no re­liance on nose­wheel steer­ing. Ap­plies to jets, tur­bo­props or trans­port-cat­e­gory air­craft.

VMO/MMO — Max­i­mum op­er­at­ing limit speed for tur­bo­props or jets. VMO is in­di­cated air­speed mea­sured in knots and is mainly a struc­tural lim­i­ta­tion that is the ef­fec­tive speed limit at lower al­ti­tudes. MMO is a per­cent­age of Mach lim­ited by the change to the air­craft’s han­dling char­ac­ter­is­tics as lo­cal­ized air­flow ap­proaches the speed of sound, cre­at­ing shock waves that can al­ter con­trol­la­bil­ity. As alti­tude in­creases, in­di­cated air­speed de­creases while Mach re­mains con­stant. MMO is the ef­fec­tive speed limit (“bar­ber pole” on the air­speed in­di­ca­tor) at higher al­ti­tudes. MMO is usu­ally much higher for swept-wing jets than for straight-wing de­signs.

VMU — Min­i­mum un­stick speed. Slow­est speed at which an air­craft can be­come air­borne. Orig­i­nated as a re­sult of test­ing for the world’s first jet trans­port, the de Hav­il­land Comet. Dur­ing an ill-fated take­off at­tempt, the nose was raised so high and pre­ma­turely that the re­sul­tant drag pre­vented fur­ther ac­cel­er­a­tion and liftoff. Tests were then es­tab­lished to en­sure that fu­ture heavy trans­ports could safely take off with the tail touch­ing the ground and main­tain this at­ti­tude un­til out of ground ef­fect.

VNE — Never-ex­ceed speed — “red line.” Ap­plies only to pis­ton­pow­ered air­planes. This speed is never more than 90 per­cent of VDF. G loads im­posed by any tur­bu­lence can eas­ily over­stress an air­craft at this speed.

VNO — “No” go there. Max­i­mum struc­tural cruis­ing speed. Be­gin­ning of the yel­low arc, or cau­tion range. The­o­ret­i­cally, a brand-new air­craft can with­stand the FAA’S 50 fps gust at this speed. Un­for­tu­nately, the pi­lot has no way of mea­sur­ing gust in­ten­sity.

VR — Ro­ta­tion speed. Rec­om­mended speed to start ap­ply­ing back pres­sure on the yoke, ro­tat­ing the nose so, ide­ally, the air­craft lifts off the ground at VLOF.

VREF — Cal­cu­lated ref­er­ence speed for fi­nal ap­proach. Fi­nal ap­proach speed. Usu­ally 1.3 times VSO or higher. Small air­planes: bot­tom of white arc plus 30 per­cent. Jets: cal­cu­lated from land­ing­per­for­mance charts that con­sider weight, tem­per­a­ture and field el­e­va­tion. To this speed jets typ­i­cally cal­cu­late an ap­proach speed (VAP) by adding (to VREF) half the head­wind com­po­nent plus the gust fac­tor (to a max of 20 knots).

VS — Stall speed or min­i­mum steady flight speed at which the air­plane is con­trol­lable. VS is a generic term and usu­ally does not cor­re­spond to a spe­cific air­speed.

VS1 — Stall speed or min­i­mum steady flight speed in a spe­cific con­fig­u­ra­tion. Nor­mally re­garded as the “clean” — gear and flaps up — stall speed. Lower limit of the green arc (re­mem­ber, “stuff in”). How­ever, this is not al­ways

the case. It could rep­re­sent stall speed with flaps in take­off po­si­tion or any num­ber of dif­fer­ent con­fig­u­ra­tions. So VS1 is a clean stall, but the def­i­ni­tion of “clean” could vary.

VSO — Stall speed in land­ing con­fig­u­ra­tion. Lower limit of white arc. Stalling speed or the min­i­mum steady flight speed at which the air­plane is con­trol­lable in land­ing con­fig­u­ra­tion: en­gines at idle, props in low pitch, usu­ally full wing flaps, cowl flaps closed, CG at max­i­mum for­ward limit (i.e., most un­fa­vor­able CG) and max gross land­ing weight. Max­i­mum al­low­able VSO for sin­gleengine air­craft and many light twins is 61 knots (re­mem­ber, “stuff out”).

VSSE — Min­i­mum safe sin­gleengine speed (multi). Pro­vides a rea­son­able mar­gin against an un­in­ten­tional stall when mak­ing in­ten­tional en­gine cuts dur­ing train­ing.

VTOSS — Take­off safety speed for Cat­e­gory A ro­tor­craft.

VWWO — Max­i­mum wind­shield­wiper op­er­at­ing speed.

VX — Best an­gle-of-climb speed. De­liv­ers the great­est gain of alti­tude in the short­est pos­si­ble hor­i­zon­tal dis­tance. The speed given in the flight man­ual is good only at sea level, at max gross weight and with flaps in take­off po­si­tion. VX in­creases with alti­tude (about ½ knot per 1,000 feet) and usu­ally de­creases with a re­duc­tion of weight. It will take more time to gain alti­tude at VX be­cause of the slower speed, but the goal is to gain the most alti­tude in the short­est hor­i­zon­tal dis­tance.

VXSE — Best sin­gle-en­gine an­gleof-climb speed (mul­ti­engine, 12,500 pounds or less).

VY — Best rate-of-climb speed. De­liv­ers the great­est gain in alti­tude in the short­est time. Flaps and gear up. De­creases as weight is re­duced, and de­creases with alti­tude. Lift-to-drag ra­tio is usu­ally at its max­i­mum at this speed, so it can also be used as a good ball­park fig­ure for best glide speed or max­i­mu­men­durance speed for hold­ing.

VYSE — Best sin­gle-en­gine ra­teof-climb speed — “blue line” — (mul­ti­engine, 12,500 pounds or less).

FAA reg­u­la­tions could change at any time. Please re­fer to cur­rent FARS to en­sure you are le­gal.

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