M.E checkride soon...

LS1 Life

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Lookin for a lil help on critical engine factors and descriptions. Im flying a Piper Seminole. This is the list and descriptions off my list. Any critiques of these would help.

Critical Engine Inop and Windmilling
-The critical engine inop and windmilling causes dead weight and parasitic drag which raises Vmc. Because the dead engine is not operating the opposite engine has to work even harder to maintin sufficient lift for flight at a given altitude. The drag is caused not just by the bulk of the engine/cowling but also by the windmilling prop, the prop should be feathered so it can become streamline with the relative wind, thus reducing drag.
Rearward CG
-CG location is plays a major role in the controlability of the aircraft. With a rearward CG the arm to the vertical stabilizer is smaller which means more rudder use is needed to maintain directional control, thus increasing Vmc. With a forward CG the arm to the vertical stabilizer is larger giving more leverage to the rudder to maintain directional control, thus decreasing Vmc. (think of it as prying a door open with a pen vs a crowbar)
Most Unfavorable Take-Off Weight
-Weight is plays a role with manueverability. The most unfavorable take-off weight would be a light setting. The less weight the aircraft has the higher Vmc will be due to the fact that the aircraft will be able to pitch and role the aircraft easier than a heavier setting. The heavier the setting the lower Vmc will be. (Think of what would be easier to move, a smart car or a semi truck)
Landing Gear Retracted
-The landing gear plays a role due to retracted or extended effects. With the gear retracted the aircraft is flush with the relative wind, giving no help with maintaining directional control, thus raising Vmc. With the gear extending, Vmc lowers due to Kheel effect. Kheel effect is the effect of the gear acting as miniature surfaces against the relative wind. The surfaces want to become streamline with the relative wind giving a bit of help along the vertical axis, thus lowering Vmc. (the only problem with the gear extended is that it increases parasitic drag reducing performance. If in flight, the gear should be retracted due to the fact that only a handful help is being given, yet a bucket full of drag is being produced)
Operation Engine
-This pertains to how much power/lift is being produced. The more power the engine is producing the higher Vmc is because of pitch and roll tendencies. The more power and lift you have the stronger these tendencies become, thus raising Vmc. The less power being produced lowers Vmc because the pitch and roll tendencies along with less lift are less. This can be usually be determined by altitude. The lower the altitude gives the engine more usuable air to produce more power. The higher the altitude the less usuable air the the engine can use to produce power.
Flaps in the Take-Off Position
-The Seminole's take-off position is 0 degrees. The more lift that is produced the higher Vmc will be due to the pitch and roll tendcies during takeoff. Flap settings such as 10 and 25 degrees increase lift more than drag, increasing Vmc. At full flaps, 40 degrees, more drag than lift is produced decreasing Vmc. (40 flaps should never be used for take-off....DUH) If engine failure is encountered flaps should be set to 0 degrees.
Trimmed for Take-Off
-Trim for take-off should be neutral. If rudder trim is used for take-off, this will increase Vmc due to the decrease in the camber line of the stabilizer. Trimmed rudder decreases the effective surface area of the airfoil. (these tabs are a good portion of the airfoil, keep them neutral)
Airborne or in Ground Effect
-If the aircraft is airborne Vmc will be higher because of the greater Angle of Attack (increasing P-Factor) need to supply sufficient lift. Wingtip vorticies are also greater airborne because they are not reflecting off the ground. In ground effect a lower AOA is needed to produce sufficient lift, thus lowering Vmc.
Cowl Flaps
-Cowl flaps can be debated but as far as I am concerned the are drag. More drag on the inop engine, raises Vmc.
Eliminate Sideslip
-A while back, pilots used rudder as the only means of maintaining directional control but with only rudder, sideslip would occur. If the aircraft is in a sideslip, the relative wind no longer flowing over the front of the aircraft. Instead the relative wind be pounding against the side of the inop engine reducing airflow over the operating side and reducing rudder effectiveness, thus increasing Vmc. To eliminate the sideslip we bank toward the operating engine no more than 5 degrees causing the relative wind to become more streamline over the aircraft, which will lower Vmc.


I know temperature also plays a role in Vmc but that also pertains to how much power is being produced (which i covered) If anyone has some add ons, please post! Thanks to anyone that reads it all, its alot but its checkride material. :rolleyes:
 
<<Because the dead engine is not operating the opposite engine has to work even harder to maintin sufficient lift for flight at a given altitude. >>

The engine has nothing to do with providing lift. It provides thrust and thrust is what keeps you in the air.

<<The less weight the aircraft has the higher Vmc will be due to the fact that the aircraft will be able to pitch and role the aircraft easier than a heavier setting. The heavier the setting the lower Vmc will be. (Think of what would be easier to move, a smart car or a semi truck)>>

This is not a correct explanation of the role of weight in Vmc. See a recent posting in the Technical section.

<<Operation Engine
-This pertains to how much power/lift is being produced. The more power the engine is producing the higher Vmc is because of pitch and roll tendencies. >>

Again, the engine has nothing to do with providing lift; the thrust is what makes the airplane hard to control, due to its yawing/rolling tendencies.


<<Airborne or in Ground Effect>>

This is all speculation. I’m aware of no published data that hints at whether Vmc is higher or lower in ground effect.

<<Cowl Flaps
-Cowl flaps can be debated but as far as I am concerned the are drag. More drag on the inop engine, raises Vmc.>>

Cowl flaps play no role in establishing *published* Vmc figures, since this does not appear in the list of required configuration in 14 CFR 23.149. Drag itself does not affect Vmc, but differential drag on the dead engine vs working engine can.
 
Trimmed for Take-Off
-Trim for take-off should be neutral. If rudder trim is used for take-off, this will increase Vmc due to the decrease in the camber line of the stabilizer. Trimmed rudder decreases the effective surface area of the airfoil. (these tabs are a good portion of the airfoil, keep them neutral)
Airborne or in Ground Effect
-If the aircraft is airborne Vmc will be higher because of the greater Angle of Attack (increasing P-Factor) need to supply sufficient lift. Wingtip vorticies are also greater airborne because they are not reflecting off the ground. In ground effect a lower AOA is needed to produce sufficient lift, thus lowering Vmc.
Cowl Flaps
-Cowl flaps can be debated but as far as I am concerned the are drag. More drag on the inop engine, raises Vmc.

When I teach Vmc to my students I only bring up seven things. I haven't had a student get in trouble for that yet.

As you know, the PA-44 does not have rudder trim. I would leave that out.
The check ride is very much a game and if you give too much info, the examiner will dig. Good luck.
 
When I teach Vmc to my students I only bring up seven things. I haven't had a student get in trouble for that yet.

As you know, the PA-44 does not have rudder trim. I would leave that out.
The check ride is very much a game and if you give too much info, the examiner will dig. Good luck.

Yes it does.... aft of the flap lever, in between the seats, in front of the fuel selectors.
 
I have completely blocked that out. I still can't picture it.

It is kind of weird to manipulate...although, so is the elevator trim. The rudder trim in a seminole does provide some nice leg relief when you're running around single engine though.
 
<<Because the dead engine is not operating the opposite engine has to work even harder to maintin sufficient lift for flight at a given altitude. >>

The engine has nothing to do with providing lift. It provides thrust and thrust is what keeps you in the air.

<<The less weight the aircraft has the higher Vmc will be due to the fact that the aircraft will be able to pitch and role the aircraft easier than a heavier setting. The heavier the setting the lower Vmc will be. (Think of what would be easier to move, a smart car or a semi truck)>>

This is not a correct explanation of the role of weight in Vmc. See a recent posting in the Technical section.

<<Operation Engine
-This pertains to how much power/lift is being produced. The more power the engine is producing the higher Vmc is because of pitch and roll tendencies. >>

Again, the engine has nothing to do with providing lift; the thrust is what makes the airplane hard to control, due to its yawing/rolling tendencies.


<<Airborne or in Ground Effect>>

This is all speculation. I’m aware of no published data that hints at whether Vmc is higher or lower in ground effect.

<<Cowl Flaps
-Cowl flaps can be debated but as far as I am concerned the are drag. More drag on the inop engine, raises Vmc.>>

Cowl flaps play no role in establishing *published* Vmc figures, since this does not appear in the list of required configuration in 14 CFR 23.149. Drag itself does not affect Vmc, but differential drag on the dead engine vs working engine can.

Critical Engine... Correct, what i was saying is that the engine has to work harder to produce sufficient thrust to provide enough lift to keep the aircraft in the air.

Weight... got a link to the thread your lookin at?

Operating engine... need to reword this. What i meant was that the more power being produced the more thrust is created. the more thrust you have the greater the pitch/roll tendencies will be.

Airborne and Ground Effect... my main point is that in ground effect the wing tip vorticies are decreased and a lower AOA is needed to create lift making less P-Factor, thus lowering Vmc. If Airborne, we need a greater AOA to create sufficient lift, which in turn creates more P-Factor causing more yaw, thus raising Vmc.

Cowl Flaps... as described in 23.149 the configuration is specified for take-off. For the take-off and landing configurations of the aircraft the cowl flaps are open. And yes, differential drag is the problem. That's why for the inop engine we close the flap to decrease the amount of differentail drag.

Douglas... our seminoles have both rudder and stabilator trim.
 
Critical Engine... Correct, what i was saying is that the engine has to work harder to produce sufficient thrust to provide enough lift to keep the aircraft in the air.

Except that thrust doesn't provide lift and descents are not caused by a lack of lift. If I were an examiner, I might start asking you about the four forces and their relationship in various phases of flight.

<<Weight... got a link to the thread your lookin at?>>

http://forums.jetcareers.com/technical-talk/84376-question-about-vmc-weight.html


<<What i meant was that the more power being produced the more thrust is created. the more thrust you have the greater the pitch/roll tendencies will be.>>

What do the pitch tendancies have to do with Vmc? And what do the roll tendancies have to do with Vmc? Vmc is determined by directional control, not pitch control and not roll control (usually).

<<Airborne and Ground Effect... my main point is that in ground effect >>

I understand your point, but I'm merely pointing out you have no evidence to indicate that Vmc is actually reduced in ground effect, so your explanation for why it's true is moot. Is it possible that ground effect reduces rudder authority?
 
What do the pitch tendancies have to do with Vmc? And what do the roll tendancies have to do with Vmc? Vmc is determined by directional control, not pitch control and not roll control (usually)

He means yaw tendancies also Vmc at least the way I was taught was defined as anytime you were unable to control any of the axis of the aircraft OR at an airspeed in which any change in flight condition would cause a stall.

Meaning if you had full left aileron at a certain speed (right engine inop) than that would be Vmc pending of course you used rudder properly as well.

Except that thrust doesn't provide lift and descents are not caused by a lack of lift.

Havn't you ever seen an airplane do a torque roll mister! :)
 
Sorry for the late response.

Evidence is the reduced aerodynamic factors within ground effect. It may not be documented but possibly seen or felt through the aircraft. Vmc at low altitudes is not tested in actual conditions because its dangerous. Tests in a wind tunnel or experimental facility is limited to what it can tell us because its not actual conditions. Replicated tests can only tell us so much. Rudder authority, my guess, is most likely decreased. Further explanation... haha I'd have to look into it.

Factors of a critical engine and effects.
P-Factor - yaw
Spiraling Slipstream - Yaw
Accelerated Slipstream - Roll and pitch
Torque - Roll

Each configuration of the aircraft causes differences in the airflow over the aircraft's surfaces. Pitch, Roll, and Yaw all play a roll in determining the limitation of the aircraft operating on a single engine because at a specific AOA, angle of bank, or rudder AOA the aircraft can become uncontrollable.

I passed my checkride, but I'm currently going after my CFI, CFII, MEI so im seeking all available knowledge and explainations.
 
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