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dynamite dean
5th Mar 2002, 23:02
I am embarking on my next stage of career. .development - my multi instructors rating and getting a simple answer is becoming difficult please clarify.... .. .My current twin knowledge and what I was taught by a very experienced instructor was that vmca and we did plenty of 'em , that it is where the a/c is at it's max all up weight most aft centre of gravity with 5 degrees towards the live engine with the critical engine inoperative with flaps at the take off configuration and gear down... .. .I said to my very experienced insrtuctor this is the definition of Vmcg NOT Vmca "No no he replies it can't be!!!" is Vmca with gear down or not because in my dodgy atp notes it says gear up....who do I listen to? 10000hrs of experience or dodgy atp notes and my 8oo hrs of single flying? thanks dd. . <img border="0" title="" alt="[Cool]" src="cool.gif" /> <img border="0" title="" alt="[Cool]" src="cool.gif" /> <img border="0" title="" alt="[Cool]" src="cool.gif" /> <img border="0" title="" alt="[Cool]" src="cool.gif" /> <img border="0" title="" alt="[Cool]" src="cool.gif" />. . . . <small>[ 05 March 2002, 19:05: Message edited by: dynamite dean ]</small>

Zeke
6th Mar 2002, 00:48
Excerpts of the design regs are below, Vmca = gear retracted.. .. .§ 23.149 Minimum control speed. . .. .(a) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees. The method used to simulate critical engine failure must represent the most critical mode of powerplant failure expected in service with respect to controllability. . .. .(b) VMC for takeoff must not exceed 1.2 VS1, where VS1 is determined at the maximum takeoff weight. VMC must be determined with the most unfavorable weight and center of gravity position and with the airplane airborne and the ground effect negligible, for the takeoff configuration(s) with -- . .. .(1) Maximum available takeoff power initially on each engine; . .. .(2) The airplane trimmed for takeoff; . .. .(3) Flaps in the takeoff position(s); . .. .(4) Landing gear retracted; and . .. .(5) All propeller controls in the recommended takeoff position throughout. . .. .(c) For all airplanes except reciprocating engine-powered airplanes of 6,000 pounds or less maximum weight, the conditions of paragraph (a) of this section must also be met for the landing configuration with -- . .. .(1) Maximum available takeoff power initially on each engine; . .. .(2) The airplane trimmed for an approach, with all engines operating, at VREF, at an approach gradient equal to the steepest used in the landing distance demonstration of § 23.75; . .. .(3) Flaps in the landing position; . .. .(4) Landing gear extended; and . .. .(5) All propeller controls in the position recommended for approach with all engines operating. . .. .(d) A minimum speed to intentionally render the critical engine inoperative must be established and designated as the safe, intentional, one-engine-inoperative speed, VSSE. . .. .(e) At VMC, the rudder pedal force required to maintain control must not exceed 150 pounds and it must not be necessary to reduce power of the operative engine(s). During the maneuver, the airplane must not assume any dangerous attitude and it must be possible to prevent a heading change of more than 20 degrees. . .. .(f) At the option of the applicant, to comply with the requirements of § 23.51(c)(1), VMCG may be determined. VMCG is the minimum control speed on the ground, and is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane using the rudder control alone (without the use of nosewheel steering), as limited by 150 pounds of force, and using the lateral control to the extent of keeping the wings level to enable the takeoff to be safely continued. In the determination of VMCG, assuming that the path of the airplane accelerating with all engines operating is along the centerline of the runway, its path from the point at which the critical engine is made inoperative to the point at which recovery to a direction parallel to the centerline is completed may not deviate more than 30 feet laterally from the centerline at any point. VMCG must be established with -- . .. .(1) The airplane in each takeoff configuration or, at the option of the applicant, in the most critical takeoff configuration; . .. .(2) Maximum available takeoff power on the operating engines; . .. .(3) The most unfavorable center of gravity; . .. .(4) The airplane trimmed for takeoff; and . .. .(5) The most unfavorable weight in the range of takeoff weights. . .. .[Doc. No. 27807, 61 FR 5189, Feb. 9, 1996]. .. .§ 25.149 Minimum control speed. . .. .(a) In establishing the minimum control speeds required by this section, the method used to simulate critical engine failure must represent the most critical mode of powerplant failure with respect to controllability expected in service. . .. .(b) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative and maintain straight flight with an angle of bank of not more than 5 degrees. . .. .(c) VMC may not exceed 1.2 VS with -- . .. .(1) Maximum available takeoff power or thrust on the engines; . .. .(2) The most unfavorable center of gravity; . .. .(3) The airplane trimmed for takeoff; . .. .(4) The maximum sea level takeoff weight (or any lesser weight necessary to show VMC); . .. .(5) The airplane in the most critical takeoff configuration existing along the flight path after the airplane becomes airborne, except with the landing gear retracted; . .. .(6) The airplane airborne and the ground effect negligible; and . .. .(7) If applicable, the propeller of the inoperative engine -- . .. .(i) Windmilling; . .. .(ii) In the most probable position for the specific design of the propeller control; or . .. .(iii) Feathered, if the airplane has an automatic feathering device acceptable for showing compliance with the climb requirements of § 25.121. . .. .(d) The rudder forces required to maintain control at VMC may not exceed 150 pounds nor may it be necessary to reduce power or thrust of the operative engines. During recovery, the airplane may not assume any dangerous attitude or require exceptional piloting skill, alertness, or strength to prevent a heading change of more than 20 degrees. . .. .(e) VMCG, the minimum control speed on the ground, is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane using the rudder control alone (without the use of nosewheel steering), as limited by 150 pounds of force, and the lateral control to the extent of keeping the wings level to enable the takeoff to be safely continued using normal piloting skill. In the determination of VMCG, assuming that the path of the airplane accelerating with all engines operating is along the centerline of the runway, its path from the point at which the critical engine is made inoperative to the point at which recovery to a direction parallel to the centerline is completed may not deviate more than 30 feet laterally from the centerline at any point. VMCG must be established with -- . .. .(1) The airplane in each takeoff configuration or, at the option of the applicant, in the most critical takeoff configuration; . .. .(2) Maximum available takeoff power or thrust on the operating engines; . .. .(3) The most unfavorable center of gravity; . .. .(4) The airplane trimmed for takeoff; and . .. .(5) The most unfavorable weight in the range of takeoff weights. . .. .(f) VMCL, the minimum control speed during approach and landing with all engines operating, is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and maintain straight flight with an angle of bank of not more than 5 degrees. VMCL must be established with -- . .. .(1) The airplane in the most critical configuration (or, at the option of the applicant, each configuration) for approach and landing with all engines operating; . .. .(2) The most unfavorable center of gravity; . .. .(3) The airplane trimmed for approach with all engines operating; . .. .(4) The most favorable weight, or, at the option of the applicant, as a function of weight; . .. .(5) For propeller airplanes, the propeller of the inoperative engine in the position it achieves without pilot action, assuming the engine fails while at the power or thrust necessary to maintain a three degree approach path angle; and . .. .(6) Go-around power or thrust setting on the operating engine(s). . .. .(g) For airplanes with three or more engines, VMCL&hyphen;2, the minimum control speed during approach and landing with one critical engine inoperative, is the calibrated airspeed at which, when a second critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with both engines still inoperative, and maintain straight flight with an angle of bank of not more than 5 degrees. VMCL&hyphen;2 must be established with -- . .. .(1) The airplane in the most critical configuration (or, at the option of the applicant, each configuration) for approach and landing with one critical engine inoperative; . .. .(2) The most unfavorable center of gravity; . .. .(3) The airplane trimmed for approach with one critical engine inoperative; . .. .(4) The most unfavorable weight, or, at the option of the applicant, as a function of weight; . .. .(5) For propeller airplanes, the propeller of the more critical inoperative engine in the position it achieves without pilot action, assuming the engine fails while at the power or thrust necessary to maintain a three degree approach path angle, and the propeller of the other inoperative engine feathered; . .. .(6) The power or thrust on the operating engine(s) necessary to maintain an approach path angle of three degrees when one critical engine is inoperative; and . .. .(7) The power or thrust on the operating engine(s) rapidly changed, immediately after the second critical engine is made inoperative, from the power or thrust prescribed in paragraph (g)(6) of this section to -- . .. .(i) Minimum power or thrust; and . .. .(ii) Go-around power or thrust setting. . .. .(h) In demonstrations of VMCL and VMCL&hyphen;2 -- . .. .(1) The rudder force may not exceed 150 pounds; . .. .(2) The airplane may not exhibit hazardous flight characteristics or require exceptional piloting skill, alertness, or strength; . .. .(3) Lateral control must be sufficient to roll the airplane, from an initial condition of steady flight, through an angle of 20 degrees in the direction necessary to initiate a turn away from the inoperative engine(s), in not more than 5 seconds; and . .. .(4) For propeller airplanes, hazardous flight characteristics must not be exhibited due to any propeller position achieved when the engine fails or during any likely subsequent movements of the engine or propeller controls. . .. .[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-42, 43 FR 2321, Jan. 16, 1978; Amdt. 25-72, 55 FR 29774, July 20, 1990; 55 FR 37607, Sept. 12, 1990; Amdt. 25-84, 60 FR 30749, June 9, 1995]

gingernutter
6th Mar 2002, 01:08
Zeke, have you got nothing better to do than reproduce articles from a book? Just give the guy an answer in plain English, preferably in one paragraph!

Zeke
6th Mar 2002, 01:35
Gingernutter,. .. .For your benefit to repeat the first line of my post. .. . Vmca = gear retracted . .. .Retracting the gear increases Vmca in aircraft configurations where gear is in the slipstream of the prop wash. The drag caused by the prop wash over the gear offsets slightly the thrust as the drag from the live side gear is slightly greater than the dead side gear.. .. .Z

john_tullamarine
6th Mar 2002, 03:04
dynamite dean . . . .I wouldn't get too knotted up about the definitions in this case as they are of more relevance to the certification flight test program people than the line pilot.. .. .More important to remember that. .. .(a) Vmca, as quoted, is a somewhat artificial thing and specific to conditions which you are not likely to reproduce.. .. .(b) you indicate that you did plenty of "Vmca" practice during your endorsement training. Be aware that what you saw probably was not Vmca as demonstrated during the certification program but a static demonstration under conditions where the thrust output was reduced due to altitude and at a CG somewhat forward of the aft limit. Two dangers arise here. .. .(i) you can get the idea that the handling problems are less of a difficulty than they really are. .. .(ii) you can easily end up playing with such demonstrations at heights where the aircraft can be controlled directionally at speeds somewhat less than the published Vmca AND where Vs comes into play .... stall during a static Vmca demo and you invite a spin.. .. .(c) bank angle has a powerful influence on directional handling, hence the restriction on the manufacturer so that the test cannot use more than 5 degrees into the live engine(s). For the line situation, if the aircraft is somewhere near Vmca when a failure occurs, then the pilot has to control bank VERY aggressively or else the aircraft will easily be lost. This is the basis of a simulator exercise I use to great effect during endorsement training. I am of the opinion that the great majority of pilots have a totally unhealthy disrespect for handling problems in the vicinity of Vmca, especially during the dynamic excursions associated with a failure.. .. .As for me, I see very little benefit in exposing the real aircraft to the not inconsiderable hazards associated with Vmca demonstrations when, in reality, we should have a healthy respect for, and be staying well away from, that speed range.. .. .In general, if you are near Vmca in a lightie with one failed and at a decent AUW/DH, then the chances of successfully continuing flight are severely limited due to the abysmal excess thrust situation.. . . . <small>[ 05 March 2002, 23:26: Message edited by: john_tullamarine ]</small>

yxcapt
6th Mar 2002, 06:07
Your instructor might be correct, if he is really old and not up to date on current regulations.. .. .Under the old CAR 23 certification requirements, Vmc was done with the gear down. On some older twins, the piper Apachy being one, Vmc was determined with the gear down. . .. .FAR 23.149, as list above, is correct for most of the twins out there.

john_tullamarine
7th Mar 2002, 02:37
yxcapt highlights a very important point. . .. .The design standards regularly change to reflect both industry design and manufacturing capability and public (political) will.. .. .If one looks up the current rules, they should be viewed as a guide, as their application will be limited.. .. .If you want to find a likely answer for a specific aircraft, you need to check the relevant type certificate data sheet for the design standards issue for which the certification was determined .... then find a copy of the superseded rules to find the answer which you seek.

aztruck
7th Mar 2002, 03:45
I've had a beer or two but in reply to the original post...the "a" is for airborne and the "g" is for ground. I'm guessing that the instructor's angst was caused by the thought of someone applying 5 degrees of bank whilst still firmly on the deck.. .Difficult to do as well.

411A
8th Mar 2002, 02:08
JT's comments here need to be read and understood by instructors...otherwise they might find themselves on their back in that light twin...not good at all.

somewhatconcerned
8th Mar 2002, 03:55
Aztruck, whether or not the originator of VMCA or VMCG intended the A to be airboune or G to be ground I don't know. But it is a very good way of remembering what they stand for as far as i've been taught. ie VMCG .minimun conrol speed ground. (simplified I know but works for me).. .. .Along the same line, as a PPL I was taught VSO as Sh~t Out. Takes a little bit of lateral thinking but hey, that was was one definition I never had to revise

4dogs
8th Mar 2002, 06:28
gingernutter,. .. .I would suggest that the way Zeke presented his answer is the most professional way of doing it, since most of the questions come from folks who have never seen or been told of the source reference and who have to contend with all of the "experts" who know everything but can't tell you why they know they are right.. .. .A careful reading of the certification rule extracts often reveals the flaws in the knowledge of the self-appointed experts. That is also what I believe is the underlying principle that JT was pointing out.. .. .For the rest, I like to use the helicopter term "Vmin" meaning minimum speed for safe flight when discussing or demonstrating what is commonly (but erroneously) described as Vmca. Vmca is an artificial construct used in certification to ensure that a standard for controllability is met. The prerequisite criteria are rarely met in practise and the method used in certification testing is rarely replicated because it is not particularly representative of how you operate. The dynamic yaw and roll effects of sudden stoppage at maximum take-off power are not reflected, nor is the "ahh, sh*t" time to recognise and respond. Therefore loss of control can realistically arrive considerably earlier in real life than the static certification number might suggest.. .. .And please, please note that 5 degrees of bank is the maximum permissible for the certification test not the mandatory solution!!