jetcareers - View Single Post - Vmc: Flap and Gear Positions, 5 degrees of bank and Max Gross

pilot602 · September 17th, 2003, 13:34

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My examiner insisted that I explain why having the flaps retracted increased VMC. The best I could answer was that having flaps extended creates more drag on the operating engine side due to propwash and therefore decreased the overall power of the operating engine and decreased VMC. Anyone have a better explanation?
I got complteley ripped apart on "keel effect". I tried to explain that the lateral profile of the landing gear creates resistance to uncommanded yawing movements and therefore decreases VMC but the DPE wouldn't accept that answer. Can anyone explain to me simply why having the gear down decreases VMC?

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Hmmm - It's my understanding that having the flaps EXTENDED indeed causes more drag and INCREASES Vmc...

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Anything that is stuck into the flow of air in a symmetrical fashion (i.e. flaps, gear, even cowl flaps, etc.) will help to stablize the yawing moment of the asymmetrical thrust condition. Drag does increase ... but so long as the drag is symmetrical it helps to stabilze the aircraft thus lowering the speed at which directional control is lost. Which is why, if you look, to determine Vmc the aircraft is in a completely clean, high power setting and then the thrust on the critical engine (if one exists) is immediately reduced to a zero thrust/windmilling condition.

Also, the phrase "raise or lower 'Vmc'" is technically wrong. We all say it but Vmc is a fixed airspeed as represented on the ASI (the red radial line). It will never change. The speed at which directional control is lost (what we refer to inn slang terms as "Vmc") will change depending on atmospheric conditions, pilot technique, weight, etc.

September 17th, 2003, 13:34	#5
pilot602 Old Skool Join Date: Oct 2001 Location: who haa Posts: 3,750	Re: Vmc: Flap and Gear Positions, 5 degrees of bank and Max Gross [ QUOTE ] My examiner insisted that I explain why having the flaps retracted increased VMC. The best I could answer was that having flaps extended creates more drag on the operating engine side due to propwash and therefore decreased the overall power of the operating engine and decreased VMC. Anyone have a better explanation? I got complteley ripped apart on "keel effect". I tried to explain that the lateral profile of the landing gear creates resistance to uncommanded yawing movements and therefore decreases VMC but the DPE wouldn't accept that answer. Can anyone explain to me simply why having the gear down decreases VMC? [/ QUOTE ] [ QUOTE ] Hmmm - It's my understanding that having the flaps EXTENDED indeed causes more drag and INCREASES Vmc... [/ QUOTE ] Anything that is stuck into the flow of air in a symmetrical fashion (i.e. flaps, gear, even cowl flaps, etc.) will help to stablize the yawing moment of the asymmetrical thrust condition. Drag does increase ... but so long as the drag is symmetrical it helps to stabilze the aircraft thus lowering the speed at which directional control is lost. Which is why, if you look, to determine Vmc the aircraft is in a completely clean, high power setting and then the thrust on the critical engine (if one exists) is immediately reduced to a zero thrust/windmilling condition. Also, the phrase "raise or lower 'Vmc'" is technically wrong. We all say it but Vmc is a fixed airspeed as represented on the ASI (the red radial line). It will never change. The speed at which directional control is lost (what we refer to inn slang terms as "Vmc") will change depending on atmospheric conditions, pilot technique, weight, etc.