acronym for Vmc factors
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zerouniform
Well-Known Member
I usually use a story/timeline to remember the Vmc factors. It goes something like this...
A guy goes to the airport on a standard day. He loads the airplane to maximum gross weight, and with the most legal aft CG. He starts the engines and then taxis to the runway. He then places the flaps and cowls in the takeoff position. He takes off and brings the gear up, then departs straight out. Once at altitude he windmills the critical engine, sets takeoff power to the good engine, and banks no more than 5 degrees into the good engine.
I hope that helps a little.
A guy goes to the airport on a standard day. He loads the airplane to maximum gross weight, and with the most legal aft CG. He starts the engines and then taxis to the runway. He then places the flaps and cowls in the takeoff position. He takes off and brings the gear up, then departs straight out. Once at altitude he windmills the critical engine, sets takeoff power to the good engine, and banks no more than 5 degrees into the good engine.
I hope that helps a little.
dakovich
Well-Known Member
MULTTTTI OPS
M-max takeoff power
U-unfavorable CG(aft and lateral)
L-landing gear(up)
T-takeoff weight(max allowable)
T-takeoff position(flaps up or in t/o position)
T-trim tab(nuetral or t/o position)
I-into the operative engine(max bank 5 degrees for zero sideslip)
O-out of ground effect
P-prop(windmilling)
S-standard day(ISA)
also:
-must recover w/in 20 degrees
-150 lbs. max rudder pressure
not what i used to use, but i have this great book called "acronyms for pilots" and thats what they give for a Vmc acronym. great book for any CFI, tons of acronyms.
M-max takeoff power
U-unfavorable CG(aft and lateral)
L-landing gear(up)
T-takeoff weight(max allowable)
T-takeoff position(flaps up or in t/o position)
T-trim tab(nuetral or t/o position)
I-into the operative engine(max bank 5 degrees for zero sideslip)
O-out of ground effect
P-prop(windmilling)
S-standard day(ISA)
also:
-must recover w/in 20 degrees
-150 lbs. max rudder pressure
not what i used to use, but i have this great book called "acronyms for pilots" and thats what they give for a Vmc acronym. great book for any CFI, tons of acronyms.
GaTechKid
Well-Known Member
I'm not sure why people believe Vmc for every aircraft was tested at max gross weight but perhaps you've read something I haven't. Piper tested Vmc for the Seminole at a weight of ~2730, which is the most unfavorable weight with regards to directional control. Read below:
[ QUOTE ]
§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.
[/ QUOTE ]
[ QUOTE ]
§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.
[/ QUOTE ]
Skinnah
Well-Known Member
Actually, "Most Unfavorable Weight" would be a lighter aircraft. Vmc decreases as weight increases.
and here is a good acronym: SMACFUM
S - Standard day conditions. (increases Vmc, bad)
M - Max power on operational engine. (increases Vmc, bad)
A - Aft legal C.G. (increases Vmc, bad)
C - Critical engine prop windmilling. (increases Vmc, bad)
F - Flaps up, Gear up. (increases Vmc, bad)
U - Up to 5 degrees of bank into operating engine. (decreases Vmc, GOOD)
M - Most unfavorable weight: light. (increases Vmc, bad)
hope that helps.
Skinnah
Well-Known Member
[ QUOTE ]
Care to explain that? As I understand it, more weight = higher angle of attack = higher P-Factor = higher Vmc
[/ QUOTE ]
Yes, for the FAA certification test for aircraft manufacturers to determine Vmc they allow up to 5 degrees of bank into the operating engine. The heavier the aircraft in a given bank angle, the greater the horizontal component of lift. The horizontal component of lift aids the rudder force and in turn reduces Vmc.
Vmc decreases by about 3 knots per degree of bank. 5 degrees = 15 knots.
But, since we are talking about the standards set forth by the FAA in determining Vmc and they allow up to 5 degrees of bank for the test. So in that condition the heavier the plane the lower the Vmc.
Care to explain that? As I understand it, more weight = higher angle of attack = higher P-Factor = higher Vmc
[/ QUOTE ]
Yes, for the FAA certification test for aircraft manufacturers to determine Vmc they allow up to 5 degrees of bank into the operating engine. The heavier the aircraft in a given bank angle, the greater the horizontal component of lift. The horizontal component of lift aids the rudder force and in turn reduces Vmc.
Vmc decreases by about 3 knots per degree of bank. 5 degrees = 15 knots.
But, since we are talking about the standards set forth by the FAA in determining Vmc and they allow up to 5 degrees of bank for the test. So in that condition the heavier the plane the lower the Vmc.
As far as i understand there are several theories:
Vmc will decrease (at max takeoff weight) because:
1. Because weight is significant to the HCL that is generated when the airplane is established in the allowable fine degrees of bank. For the same 5º of bank the HCL increases with an increase in weight, due to an increase in AOA. The force is directed towards the good engine side, directly reducing the rudder required for counteracting the yaw/roll tendencies
2. Becase of inertia. An object in motion tends to stay in motion unless acted upon by an outside force. Therefore it is more difficult for a heavier aircraft to loss directional control (but harder to recover once lost).
Vmc will increase because (at maximum takeoff weight):
1. Because of P-factor in a conventional twin. With an increase in weight you have an increase in AOA, an increase in AOA moves the thrust lines towards the tips. Thus creating a greater yaw towards the dead engine when the critical engine is failed.
When i teach this, i bring up all the theories stated above but tell my students that they should say Vmc increases with weight because thats what it says in the FAA handbook (they shouldnt be able to argue with the book)
Vmc will decrease (at max takeoff weight) because:
1. Because weight is significant to the HCL that is generated when the airplane is established in the allowable fine degrees of bank. For the same 5º of bank the HCL increases with an increase in weight, due to an increase in AOA. The force is directed towards the good engine side, directly reducing the rudder required for counteracting the yaw/roll tendencies
2. Becase of inertia. An object in motion tends to stay in motion unless acted upon by an outside force. Therefore it is more difficult for a heavier aircraft to loss directional control (but harder to recover once lost).
Vmc will increase because (at maximum takeoff weight):
1. Because of P-factor in a conventional twin. With an increase in weight you have an increase in AOA, an increase in AOA moves the thrust lines towards the tips. Thus creating a greater yaw towards the dead engine when the critical engine is failed.
When i teach this, i bring up all the theories stated above but tell my students that they should say Vmc increases with weight because thats what it says in the FAA handbook (they shouldnt be able to argue with the book)
[ QUOTE ]
When i teach this, i bring up all the theories stated above but tell my students that they should say Vmc increases with weight because thats what it says in the FAA handbook (they shouldnt be able to argue with the book)
[/ QUOTE ]
opps i messed up....I meant to say that Vmc decreases as weight is increased as stated out of the FAA airplane flying handbook
When i teach this, i bring up all the theories stated above but tell my students that they should say Vmc increases with weight because thats what it says in the FAA handbook (they shouldnt be able to argue with the book)
[/ QUOTE ]
ricecakecm
Well-Known Member
"Carrie Wants Diamonds Like Famous People Should"
CG
Weight
Density Altitude
Landing Gear
Flaps
Propeller (windmilling or feathered)
Slip
Chris
CG
Weight
Density Altitude
Landing Gear
Flaps
Propeller (windmilling or feathered)
Slip
Chris
Simple explanation without the HCL, VCL stuff......heavier aircraft is more stable and has more inertia; lighter aircraft, less weight, less resistance to movement, easier to be affected by a higher (or worse) VMC.......same concept, fewer words.
Best to keep explanations simple, as John H learned in his latest interview. Taking a newbie student, and getting into the meat of HCL, VCL, etc, is all well and good, but it's better to crawl before you walk, walk before you run, with many of these concepts. HCL, VCL is all well and good if we're talking heavy maneuvering such as air combat maneuvering, where you control HCL/VCL constantly, and how you control it directly affects the outcome of the engagement. For a VMC discussion, it's good to describe in the meat of an in-depth discussion of aerodynamics, but for a simple description, it's excess fluff.
And John, it's not so much saying what a DE wants to hear, it's keeping things simple at the appropriate times, in-depth at the appropriate times. For example, if giving academics (oral) on VMC, then an in-depth discussion is appropriate provided it follows the crawl/walk/run method of teaching. For a flight brief, a quicker "shotgun" explanation gets the basic point across.
Then again....there are those examiners/DEs that if it isn't "their way", it's wrong........and those are the ones I like to schwack across the head, multiple times, with the FAR/AIM.....or local yellow pages.....then put them on the receiving end of this:
Best to keep explanations simple, as John H learned in his latest interview. Taking a newbie student, and getting into the meat of HCL, VCL, etc, is all well and good, but it's better to crawl before you walk, walk before you run, with many of these concepts. HCL, VCL is all well and good if we're talking heavy maneuvering such as air combat maneuvering, where you control HCL/VCL constantly, and how you control it directly affects the outcome of the engagement. For a VMC discussion, it's good to describe in the meat of an in-depth discussion of aerodynamics, but for a simple description, it's excess fluff.
And John, it's not so much saying what a DE wants to hear, it's keeping things simple at the appropriate times, in-depth at the appropriate times. For example, if giving academics (oral) on VMC, then an in-depth discussion is appropriate provided it follows the crawl/walk/run method of teaching. For a flight brief, a quicker "shotgun" explanation gets the basic point across.
Then again....there are those examiners/DEs that if it isn't "their way", it's wrong........and those are the ones I like to schwack across the head, multiple times, with the FAR/AIM.....or local yellow pages.....then put them on the receiving end of this:
moxiepilot
Well-Known Member
I know you already have a few responses for pneumoics, but here was how I learned it for my checkride: memorization and correlation.
My personal feeling is that if a student only has the list memorized they still have a ways to go understanding Vmc, however, soapbox aside I liked the Mulllllti ops one.
I used
TO
TO
TO
TO
TO
CG
CG
WI#
Take Off (flaps, trim, cowl, power, weight)
CG - unfavorable
Gear
Critical Engine
Ground Effect -out of
Windmilling prop
ISA
5* bank - up to, zero sideslip
150# rudder
---
20* heading
To explain it to students (like a pro)
I draw out the chart and explain the relationship between the factors, for example:
Take Off Flaps: can be either up or down depending on your airplane, so Joe student how would Vmc be affected when flaps are up as compared to when flaps are down all other things being the same?
Hopefully Joe student will get to the point where he says that when the flaps are down it is a stabilizing factor, performance is increased and Vmc decreases; however if flaps are raised control is effectively reduced which increases Vmc and decreases performance. Vmc is predicateed on rudder effectiveness, so although flaps increase lift, drag is also created. Drag counteracts thrust, thrust being the most important cause of Vmc loss of directional control....blah blah blah.
You can see what I'm getting at, while the memorization of the factors are important because you can't get to correlation without having gone through rote memorization. getting your student to that point is an objective. Its also really satisfying to see someone be able to actually understand Vmc factors and smile when you throw them a curve ball because they actually know how to answer.
That being said I also teach how critical engine is identified by comparing p-factor, torque, accelerated slipstream and spiraling slipstream on counter rotating engines vs. conventional. That seems to help in the understanding of Vmc as well. Finally asking the student which are the top three or four most critical out of all the factors and why is a good way to understand if they are getting it.
If the student can understand that power is the cause of the loss of directional control I get happy. I have them use #'s going through each factor startig with max power, then zero sideslip, etc. When they come up with how many knots (or mph) change from most unfavorable to favorable they actually SEE why each affects Vmc.
e.g.) max power @ 90 kts vs no power = difference of 90 knots.
zero sideslip (lets say 2*bank) vs. 5* bank = 15 kts.....
then they have a chart also explained in knots of the differences in the factors. Overkill? I don't know, they seem to have a grasp on it by this time. Will I think it will save a life? I hope so, I just didn't want to underestimate that for a checkride they can actually impress the examiner by actually knowing their stff as opposed to regurgitation.
Hope I don't come across as swaggery, this is just my experience and I hope it helps; besides It's 4 am and I just woke up for my flights.
My personal feeling is that if a student only has the list memorized they still have a ways to go understanding Vmc, however, soapbox aside I liked the Mulllllti ops one.
I used
TO
TO
TO
TO
TO
CG
CG
WI#
Take Off (flaps, trim, cowl, power, weight)
CG - unfavorable
Gear
Critical Engine
Ground Effect -out of
Windmilling prop
ISA
5* bank - up to, zero sideslip
150# rudder
---
20* heading
To explain it to students (like a pro)
Take Off Flaps: can be either up or down depending on your airplane, so Joe student how would Vmc be affected when flaps are up as compared to when flaps are down all other things being the same?
Hopefully Joe student will get to the point where he says that when the flaps are down it is a stabilizing factor, performance is increased and Vmc decreases; however if flaps are raised control is effectively reduced which increases Vmc and decreases performance. Vmc is predicateed on rudder effectiveness, so although flaps increase lift, drag is also created. Drag counteracts thrust, thrust being the most important cause of Vmc loss of directional control....blah blah blah.
You can see what I'm getting at, while the memorization of the factors are important because you can't get to correlation without having gone through rote memorization. getting your student to that point is an objective. Its also really satisfying to see someone be able to actually understand Vmc factors and smile when you throw them a curve ball because they actually know how to answer.
That being said I also teach how critical engine is identified by comparing p-factor, torque, accelerated slipstream and spiraling slipstream on counter rotating engines vs. conventional. That seems to help in the understanding of Vmc as well. Finally asking the student which are the top three or four most critical out of all the factors and why is a good way to understand if they are getting it.
If the student can understand that power is the cause of the loss of directional control I get happy. I have them use #'s going through each factor startig with max power, then zero sideslip, etc. When they come up with how many knots (or mph) change from most unfavorable to favorable they actually SEE why each affects Vmc.
e.g.) max power @ 90 kts vs no power = difference of 90 knots.
zero sideslip (lets say 2*bank) vs. 5* bank = 15 kts.....
then they have a chart also explained in knots of the differences in the factors. Overkill? I don't know, they seem to have a grasp on it by this time. Will I think it will save a life? I hope so, I just didn't want to underestimate that for a checkride they can actually impress the examiner by actually knowing their stff as opposed to regurgitation.
Hope I don't come across as swaggery, this is just my experience and I hope it helps; besides It's 4 am and I just woke up for my flights.
moxiepilot
Well-Known Member
[ QUOTE ]
[ QUOTE ]
Hope I don't come across as swaggery, .
[/ QUOTE ]
You sanctimonious prick!.............
[/ QUOTE ]
I have to google that word
* Sanctimonious- to act morally better than others.The most obvious of examples would be Jesus Christ, who basically had no faults, acting morally and justly throughout His life
lol
gotta love google
[ QUOTE ]
Hope I don't come across as swaggery, .
[/ QUOTE ]
You sanctimonious prick!.............
[/ QUOTE ]
I have to google that word
* Sanctimonious- to act morally better than others.The most obvious of examples would be Jesus Christ, who basically had no faults, acting morally and justly throughout His life
lol
[ QUOTE ]
I have to google that word
* Sanctimonious- to act morally better than others.The most obvious of examples would be Jesus Christ, who basically had no faults, acting morally and justly throughout His life
lol
gotta love google
[/ QUOTE ]
LOL........my only chance to use that big word, I had to!
I have to google that word
* Sanctimonious- to act morally better than others.The most obvious of examples would be Jesus Christ, who basically had no faults, acting morally and justly throughout His life
lol
[/ QUOTE ]
LOL........my only chance to use that big word, I had to!
