VMC Factors Need Help

[mnixon]

It has been forever and a day since I have seen this stuff. Anybody help a brother out. I always used "Lucy will buy fat cows" as an acronym, but I can not remember all the stuff. Any help is greatly appreciated. Thanks

 

[User546]

This is all you need to know: Lose an engine, stay as FAR away from that red radial line as you can and you'll be allright!

If your referring to the requirements of the manufacturer to determine Vmc for their aircraft, I use FLAPSPUTZ.

F - Flaps Up
L - Landing Gear Up
A - Airborne, Out of Ground Effect
P - Power Max For Takeoff
S - Sea Level - 15C & 29.92
P - Prop Windmilling
U - Unfavorbale Weight Balance
T - Trimmed For Takeoff
Z - Zero Sideslip Condition

 

[DGdaPilot]

Let's see what I remember:

Flaps: initial addition increases VMC, once set, VMC decreases

Landing gear: decreases vmc

Internal cowl flaps (like on a C310R): increase vmc when closed on dead engine

external cowl flaps (like a C340): increase vmc when open on dead engine

Adding power: increases vmc

Altitude: vmc goes down with altitude

Adding bank: decreases vmc


Hmmm...that's all I got right now...

 

[DGdaPilot]

Dang, you beat me.

Oh yeah

Fore CG: decreases vmc...i think...

Weight: vmc goes down as weight is reduced

Hot air (temperature): decreases vmc

Feathered engine: duh

 

[DC8 Flyer]

Well, lets see if I can remember it all:


Factors that effect Vmc

Weight
CG location
Zero Side Slip
5 deg of bank
Critical engine
Ground Effect
Flaps (wing and cowl)
Gear
Prop (feathered/unfeathered)
Max fuel imbalance (I know I know...)
Full (Authorized not available) Power
Altitude (engine power)
Trim (rudder trim)


I think thats all for factors and they are all the same for certification except for one is switched out with something else, but I can't remember which one.

Hope this helps. Are you studying for your MEI, if so, good luck!

 

[mnixon]

Yea I am working on my MEI, and it is truly amazing how much you can lose if you don't fly a multi in over 2 years. I have to do a presentaion tomorrow in g/s on Vmc factors so I am crapping myself

 

[User546]

To clarify some of the above, some are vague as to which way Vmc goes.

Flaps:
Raising flaps, raise Vmc
Lowering flaps create more drag, making it harder for the thrust to yaw the airplane.

Landing Gear:
Raising the gear, raises Vmc. (Same theory as flaps)

Ground Effect:
Leaving ground effect raises Vmc, due to increase in induced drag.

Prop Windmilling:
Raises Vmc.
High drag created helping to yaw the airplane in same direction as the asymeticral thrust.

Sea Level Conditions:
Raises Vmc. Decreases with increase in altitude.
At sea level, air is thickest, causing engine to produce more thrust.
As plane climbs, and air becomes thinner, resulting in less thrust, therefore less rudder input is needed to maintain control.

Power Max For Takeoff:
Raises Vmc.
Having full throttle increases thrust, requiring more rudder input to control.

Zero Sideslip:
Lowers Vmc.
If you sideslip towards the inop engine, the entire rudder and vertical stabilizer has a lower AOA - thus requiring more airspeed to counter-act the yaw.

 

[Flechas]

Just a couple things:

Flaps:
Raising flaps, raise Vmc
Lowering flaps create more drag, making it harder for the thrust to yaw the airplane.
.

Also, when adding flaps, the nose attitude is lower, changing the angle of attack of the props, decreasing P-factor on the operating engine . This also lowers Vmc.

Landing Gear:
Raising the gear, raises Vmc. (Same theory as flaps)
.

The gear doors and the gear itself also act as vertical stabilizers, like a dorsal fin, also called keel effect, this also lowers Vmc.

Sea Level Conditions:
Raises Vmc. Decreases with increase in altitude.
At sea level, air is thickest, causing engine to produce more thrust.
As plane climbs, and air becomes thinner, requiring less thrust, therefore less rudder input is needed to maintain control.

.

I think you mean "when the air is thinner, the engine produces less thrust", not requires

 

[DC8 Flyer]

To clarify some of the above, some are vague as to which way Vmc goes.

Flaps:
Raising flaps, raise Vmc
Lowering flaps create more drag, making it harder for the thrust to yaw the airplane.

Keep in mind, that flaps are airplace specific, lowering flaps in the seminole (PA44) increased Vmc, I have no idea why.

Also raising the flaps in most transport aircraft does resticts either rudder power (hydraulic pressure) or rudder movement, or both thus raising Vmc. The DC8 Vmc is about 220 with flaps up, and 170 with flaps 5 deg or more.

 

[User546]

I think you mean "when the air is thinner, the engine produces less thrust", not requires

Noted and corrected... good catch Flech!

mnixon... what airplane are you doing your MEI training in?

DC8... explain more if you could about the Seminole's Vmc raising when you lower the flaps. I did my multi in the Seminole, and I don't recall that being the case. Maybe you can enlighten me or refresh my memory about it?

 

[Tarzan]

I want to know what test pilot had the cojones to Vmc an airplane in ground effect. Wheres the FAA come up with this stuff?!?!

 

[Flechas]

I want to know what test pilot had the cojones to Vmc an airplane in ground effect. Wheres the FAA come up with this stuff?!?!

You don't need to try everytging to know how it works.
They know that if you have less induced drag, Vmc will be lower, and they also know than when you are out of ground effect you have more induced drag. So they sat together and determined that Vmc would be lower in ground effect.