Vmc...

[Blackhawk]

it continues to say:



While it doesnt state that the flaps, gear, trim, and power have a negative affect, it is true that these conditions which must be met are unfavorable. Vmc would be lower if the aircraft is not configured this way

Again, you need to re-read what you quote.
"... with the most unfavorable weight and center of gravity position..."
Stop right there. That is it about most unfavorable. It does not say ANYTHING about the subsequent conditions being unfavorable, just that Vmc must be determined with the configuration listed. As I pointed out earlier, the landing may, or may not be unfavorable.
But if you don't take my word for it, from the FAA in a letter dated 24 May 2000 (note, my emphasis):

"The next question asks, “Explain why a change in landing gear position affects V​

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mc.” The author gives the answer as “Extension of the landing gear has a directionally stabilizing effect on the airplane (much like the keel of a boat). Vmc will be lower.” This is true if the landing gear configuration is stabilizing, which is not always the case, and is dependent on landing gear design relative to the aerodynamic center of lift. The analogy might be “add more feathers on the arrow to make it more directionally stable instead of making the point larger.”
The reality of the question is that Vmc is a takeoff configuration test with the landing gear up. Leaving the gear down causes other problems and is not a realistic condition on most airplanes.
In normal circumstances, as soon as the airplane is airborne the gear is retracted to reduce drag. If an engine fails at this point the pilot does not put the gear down to lower the Vmc (even if the design is directionally stabilizing) because the airplane is going to fly away with the gear up at minimum drag. Now, if the airplane does not have the performance to fly away it may have to land and it is usually advisable to land with the gear down. In this case the Vmc may change, but it is not a case we use in certification (the pilot also has the option of reducing power for the landing and this is directionally stabilizing)."​

 

[SIUav8er]

OK, how about this. would you rather loose an engine immediately after retracting the gear with full power, high AOA. OR on approach with lower power, gear and flaps down? from my experience doing multi engine training, the airplane is going to much more stable about the verticle axis (directionally) when the engine is lost in the landing configuration than it is when power is cut on climbout. Thats my experience, not just theory.

I see what youre saying about part 23 NOT saying that the configuration is "most unfavorable", but understanding how each condition affects the controllability leads us to this conclusion. Of course there are acceptions... but for the vast majority of light twins, this is the case.

As for the gear, you would never lower the gear or flaps during an engine failure because the loss in PERFORMANCE would outweigh the loss in controlability.

 

[SteveC]

Looks like you're kind of wandering away from this: "all the factors that must be met to during certification to determine Vmc for an aircraft are actually set up to be the least favorable conditions (to create the highest Vmc speed)."...which was the whole point of your guys' discussion, at least the way I read it. :bandit:

 

[Blackhawk]

OK, how about this. would you rather loose an engine immediately after retracting the gear with full power, high AOA. OR on approach with lower power, gear and flaps down? from my experience doing multi engine training, the airplane is going to much more stable about the verticle axis (directionally) when the engine is lost in the landing configuration than it is when power is cut on climbout. Thats my experience, not just theory.

I see what youre saying about part 23 NOT saying that the configuration is "most unfavorable", but understanding how each condition affects the controllability leads us to this conclusion. Of course there are acceptions... but for the vast majority of light twins, this is the case.

As for the gear, you would never lower the gear or flaps during an engine failure because the loss in PERFORMANCE would outweigh the loss in controlability.

Which is why the FAA requires you to have gear and flaps up during certification. It has nothing to do with this being an unfavorable condition but the understanding that this is the most likely worst case scenario- on take off after gear retraction. After all, if the gear is down you will/should land straight ahead. If the gear is down, however, you are not likely to lower it (same with flaps). To go from this FAA requirement to "this is the most favorable condition", however, is a great leap that is not supported by any scientific testing that I am aware of.
As for specific cases, you would need to actually take the specific airplane to altitude and test Vmc with flaps up/down (same engine power settings, weight, CG, etc), and the same with landing gear. I've seen some airplanes where landing gear is stabilzing, some where it is not.

 

[Mike H]

I'd like to hear a bit about the Vmc characteristics of a Piaggio.

I've milled it over a bit, but all things involved seem convoluted.

Does that thing have a beta setting for the props, and could you fly backwards?

 

[Roger, Roger]

When would you drop gear and flaps just to get an extra knot of Vmc?

 

[Cessnaflyer]

When would you drop gear and flaps just to get an extra knot of Vmc?

Exactly the extra drag would kind of ruin the need for lower Vmc when you can't even keep it above Vso

 

[derg]

I think it's more about figuring the worst case scenario while certifying Vmc rather than methods of reducing the Vmc speed.

 

[Polar742]

When would you drop gear and flaps just to get an extra knot of Vmc?

So, good question.

Here's my non-technical explanation.

You run out of rudder, you've hit Vmc.

You have two options at this point. 1) Increase airspeed 2) Reduce power. Part 23 airplanes, as I remember, could make either option quite sketchy. The guys I feel for are the ones flight the DC6s and C46s out of ANC. That could get interesting real fast.

Well, I guess you have 3, but #3 is one you really wanna avoid.

 

[oktex88]

When would you drop gear and flaps just to get an extra knot of Vmc?

I remember in my Multi Engine ground school class we were introduced to the topic of Vmc by reading the NTSB report of a multi-engine plane taking off off from a short field with obstacles. After takeoff the pilot kept pulling up to try to clear the trees near Vso and then raised the gear and raising the gear was just enough to reach Vmca and the plane flipped over. So maybe it's more not when you want to drop the gear but when you do not want to raise it.

Anyone know any acronyms or someway to help remember all the factors that can affect Vmc? Are there 11 or 13 total, I can't seem to recall the correct number. I have my ME checkride coming up soon.

 

[Roger, Roger]

I remember in my Multi Engine ground school class we were introduced to the topic of Vmc by reading the NTSB report of a multiengine plane taking off off from a short field with obsticles. After takeoff the pilot kept pulling up to try to clear the trees near Vso and then raised the gear and raisng the gear was just enough to reach Vmca and the plane flipped over. So maybe it's more not when you want to drop he gear but when you do not want to rasie it.

Anyone know any acronyms or someway to help remember all the factors that can affect Vmc? Are there 11 or 13 total, I can't seem to recall the correct number. I have my ME checkride coming up soon.

That story seems sketchy to me on several counts. First, who's to say that in the process of retracting the gear he didn't just let the airplane get that extra knot slow, or let up on the rudder just a touch? Second, WHY on God's green earth was he that close to Vso anyway, rather than Vxse? I think any speculation that the gear retraction caused the Vmc roll due to the increase in Vmc is just that-speculation.

 

[tgrayson]

After takeoff the pilot kept pulling up to try to clear the trees near Vso and then raised the gear and raisng the gear was just enough to reach Vmca and the plane flipped over.

I'm skeptical the NTSB would have enough data on a GA crash to know this. The story sounds more like the hypothetical scenario described in the article "Always Leave Yourself an Out". Failing to bank into the good engine can raise Vmc by 15 knots or so, which might be enough to produce a rollover at Vxse.

There would never be a reason to lower the gear to reduce Vmc; if you've gotten that slow, you're hurting your performance as well as risking loss of control. Both situations would improve by increasing airspeed.

 

[wjmiller3]

Does that thing have a beta setting for the props, and could you fly backwards?

Yes it does, and when the two engines spool up differently in beta the thing is as squirrely as it gets.. My boss flies one and he says its the scariest plane he has ever flown. He lets us fly right seat in it, a PC-12, and a 414 on occasion.

 

[SIUav8er]

When would you drop gear and flaps just to get an extra knot of Vmc?

Never because the loss of performance would outweigh the gain in controllability.

Reducing the power on the operating engine is what you do when approaching Vmc (as well as lowering the nose)

 

[V1_cut]

I remember in my Multi Engine ground school class we were introduced to the topic of Vmc by reading the NTSB report of a multi-engine plane taking off off from a short field with obstacles. After takeoff the pilot kept pulling up to try to clear the trees near Vso and then raised the gear and raising the gear was just enough to reach Vmca and the plane flipped over. So maybe it's more not when you want to drop the gear but when you do not want to raise it.

Anyone know any acronyms or someway to help remember all the factors that can affect Vmc? Are there 11 or 13 total, I can't seem to recall the correct number. I have my ME checkride coming up soon.

Well 1st post on Jet Careers, lets see how I do...

The way we teach Vmc at my school relating to the factors of VMC is, as the very 1st post to this question states, SMCFUM (say it aloud by say smack fum)
(lower) S- Standard Day 15*c and 29.92 with the altitude computed to sea level.
(lower) M- Max power into the operating engine
(lower) C- Critical Engine inoperative
(lower) F- Flaps up/Gear up trim/cowl set for takeoff condition
(raise) U- Up to 5* into the operating engine
(lower) M- Most unfavorable weight and aft cg (arm of rudder)

These are combinations of all the factors. When I say lower, that means if you change that in any way, it should lower the Vmca. When I say raise, for the "up to 5* into the operating engine" they say (PHAK) for every degree of bank that you take out, you can add 3 knots. So say you are at 0-side slip or around 5* of bank into your operating engine and your Vmca speed is 55, if you were to change bank from 5* to 0* you would have increased your Vmca speed to 70knots. This could potentially cause VMC.

I hope this helps some....

 

[shdw]

Well 1st post on Jet Careers, lets see how I do...

The way we teach Vmc at my school relating to the factors of VMC is, as the very 1st post to this question states, SMCFUM (say it aloud by say smack fum)
(lower) S- Standard Day 15*c and 29.92 with the altitude computed to sea level.
(lower) M- Max power into the operating engine
(lower) C- Critical Engine inoperative
(lower) F- Flaps up/Gear up trim/cowl set for takeoff condition
(raise) U- Up to 5* into the operating engine
(lower) M- Most unfavorable weight and aft cg (arm of rudder)

These are combinations of all the factors. When I say lower, that means if you change that in any way, it should lower the Vmca. When I say raise, for the "up to 5* into the operating engine" they say (PHAK) for every degree of bank that you take out, you can add 3 knots. So say you are at 0-side slip or around 5* of bank into your operating engine and your Vmca speed is 55, if you were to change bank from 5* to 0* you would have increased your Vmca speed to 70knots. This could potentially cause VMC.

I hope this helps some....

That is for certification. It doesn't necessary help with all the, "debated," factors that effect Vmc.

Edit: However, this is important and should be known by all multi rated pilots. IMO of course.

 

[Blackhawk]

That is for certification. It doesn't necessary help with all the, "debated," factors that effect Vmc.

Edit: However, this is important and should be known by all multi rated pilots. IMO of course.

And therein lies the problem. What is necessary for certification is being taught at many places as what lowers Vmc.

 

[shdw]

And therein lies the problem. What is necessary for certification is being taught at many places as what lowers Vmc.

I think both are necessary. Then again I think a pilot should know the lift formula and other rudimentary aerodynamics, which in the eyes of many, or so it seems, makes me look insane. :dunno:

 

[mikecweb]

I think both are necessary. Then again I think a pilot should know the lift formula and other rudimentary aerodynamics, which in the eyes of many, or so it seems, makes me look insane. :dunno:

So unless I can write down on a piece of paper right now the formula for lift you believe my knowledge as a pilot is lacking?

 

[dasleben]

I think both are necessary. Then again I think a pilot should know the lift formula and other rudimentary aerodynamics, which in the eyes of many, or so it seems, makes me look insane. :dunno:

I used to be able to rattle all that stuff off, particularly when I was teaching. I don't need any of that information on a daily basis anymore, and hence, I don't remember it.

I can still hand-fly an ILS to mins and land on a snow/ice covered runway though.