Vmc...

[jdlilfan]

There has to be at least one Piaggio pilot on this board... Lets hear it!

On paper, that plane "just aint right!"

Technically though, all things would be based on the CG location, which should be a bit forward of the engines, which would give the rudder adequate leverage in a SEO scenario.

What do you want to know? Been flying one for about a month now. VMC feathered is 100kts, VS1 is 112, With all things considered, the plane would most likely stall before reaching VMC. Also the props counter-rotate so there is less of a factor of critical engine (without opening the can of worms with is a counter-rotating prop have critical engines or they are both critical, etc). Also the props sit far enough back that they really don't effect the rudder as much as a conventional twin. In most regimes of flight the CG is really far forward and a lot of times the plane is CG restricted rather than weight.

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

The powerplant systems are nearly identical to a King Air (and most likely are the same). The only thing different is that there are less controlling levers and the engines are facing the CORRECT side.

The plane has a few little weird behaviors but overall it flies like any other normal plane.

Didn't really add much to the discussion on VMC, sorry for hijacking the thread.

 

[nosehair]

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.

While I agree that there would 'never be a reason' in normal operations in the normal usual light twins that we all use for training and private and most commercial operations, ...the fact remains that most of these airplanes do get lower vmc's with the gear down. Likewise, so do most single retracts become more directionally stable with the gear down.

The main point of learning these aerodynamic factors is understanding how they can affect an airplane. We learn a lot about theory that we don't really need to know or even have a chance to apply because we never get into an airplane that requires a lot of our required knowledge.

I wasn't actually around these airplanes in WWII, but I like to use this story to help explain the 'gear up or down' decision in regards to Vmc.

I heard that the B-17 was the teacher on the gear position. These babies were loaded. Probably overloaded. When one of the four engines would quit on the take-off, probably with airspeed below published Vmc, and struggling to clear the trees, the pilot would raise the gear, and ..roll right over into the trees. They discovered from practice that taking out a few tree tops, or even 'landing' straight ahead into the trees was better than rolling over because of raising the gear.

 

[Hacker15e]

You guys all seem to be missing the most important answer in all of aviation (and it completely applies in this discussion):

"It depends...."

 

[tgrayson]

I heard that the B-17 was the teacher on the gear position.

I'm skeptical to draw any conclusions from anecdotes, particularly when they may be untrue. That's where too many of the OWTs come from. But assuming the event actually happened, I'd be interested to know if the decision to leave the gear down was decided by pilots or an engineering analysis of the aircraft performance. I raise the question because pilot in this scenario has other options. Reducing the power on the outboard engine on the other side would significantly lower Vmc, too, possibly with a smaller loss in excess thrust. There are many questions to be asked before accepting this as a good lesson.

Regardless, none of us should be lifting off below Vmc, so the point is moot. Our Seneca did have one option for a short-field takeoff that required rotating below Vmc, but I never used it and advised others likewise. We had an alternate procedure that required rotating at Vmc.

 

[Hacker15e]

I asked over on the Warbirds board about the B-17 story, hoping that some guys with actual B-17 experience could comment.

 

[tgrayson]

I asked over on the Warbirds board about the B-17 story, hoping that some guys with actual B-17 experience could comment.

I also sent an email to Randy Sohn, who has flown the aircraft.

 

[Hacker15e]

Here's what the B-17F manual says:

9: Engine Failure During Take-off

a) Failure of an engine during take-off may not be noticeable immediately except for a resultant swing. If, therefore, a swing develops, and there is room to close the throttles and pull up, this should be done.

b) If it is necessary to continue with the take-off, even though one engine has failed, hold the airplane straight by immediate application of rudder. Gain speed as rapidly as possible. See that the landing gear is up, or is coming up, and feather the propeller of the dead engine. Retrim as necessary.

 

[Hacker15e]

A current pilot of Sentimental Journey says:

I don't have my training materials to hand, so I'm talking off the top of my cranium but I've never heard of any effect raising the gear has on Vmc or stability. The AZ Wing uses 92kts for Vmc on Sentimental Journey. Our listed Vs1 is 87 and Vso is 77. Our gear retracts simultaneously or nearly so, and frankly there is not a lot of drag penalty with the gear extended so we usually leave them out on crew training patterns to save cycles on the gear motors. There doesn't seem to be any difference between doing a normal pattern and an engine-out pattern with gear up or down, at least in my experience, and I've never heard any of our experienced PIC's or instructors talk about not raising gear with an engine failure.

 

[Alchemy]

I present to you the ultimate VMC explanation: ta da

Well, at least it was the ultimate if you were taking a checkride from the author.

 

[dasleben]

I present to you the ultimate VMC explanation: ta da

Well, at least it was the ultimate if you were taking a checkride from the author.

Dear Lord. I think I understood about three words from that link. Just kidding, but it's amazing how much you forget when you just fly the line everyday. I haven't even thought about this stuff in 3 years or so.

 

[tgrayson]

I present to you the ultimate VMC explanation: ta da

That's about the most erroneous article that I've ever read on the subject:

Holding a bank in the direction of the operating engine may increase the performance of the multiengine in some respects, but it definitely raises Vmca.
​

 

[minitour]

Just kidding, but it's amazing how much you forget when you just fly the line everyday. I haven't even thought about this stuff in 3 years or so.

That should tell you something. I think instruction needs to be more focused on:
1) Decision making - "How can I make sure this never happens to me?"
2) Basic Knowledge - "Now that I've gotten into this situation I need to know what's going on so I don't freak out."
3) Problem-Solving - "Now that I'm in this situation, what do I have to do and why?"

...I don't think the lift formula fits into any one of these categories.

It's nice to know, but in the end it isn't going to save my bacon. I'm driving it, not engineering it.

-mini

 

[nutz4life]

Vmca is perhaps the dumbest things I heard of. There's just Vmc and I guess Vmcg

 

[AviatorGator]

Vmca is perhaps the dumbest things I heard of. There's just Vmc and I guess Vmcg

 

[Crism]

That's about the most erroneous article that I've ever read on the subject:

Holding a bank in the direction of the operating engine may increase the performance of the multiengine in some respects, but it definitely raises Vmca.
​

Other than that, have you found anything else significantly wrong?

 

[tgrayson]

Other than that, have you found anything else significantly wrong?

His listing of the criteria under which Vmc is tested are outdated and his explanation as to why gear affects Vmc (if it does) is speculation.

And his comment about the rear CG increasing the moment arm of the thrust is wrong.

 

[Hacker15e]

I'm thinking 'myth busted' with respect to the B-17 anecdote.

Somehow,I think that the person posting on the other website had an imperfect understanding of the situation.Retracting the gear won't cause the B-17 to roll even if only one main gear retracted.The only concievable theory that I can think of might be that the lowered gear could function as an additional vertical surface.

I looked in the B-17 Pilot Training Manual and have posted below what it has to say about the proper technique for single or two engine failure on take-off.It does mention that the airplane probably won't maintain altitude on two engines at weights over 58,000 lbs.Most B-17's at full combat take-off weights were probably at least 60,000 lbs.The published max gross weight for the B-17,at least according to the FAA for a type-rating was 59,000 lbs.

The instructions below also mention that you might be better off keeping an sick engine running as long as it's developing useful power and that it will be difficult mentally to hold the nose down when you're just barely flying and close to the ground.How true.By the way,I can confirm the last statement in red concerning the airplane floating more than expected on a single engine landing.

 

[tgrayson]

I'm thinking 'myth busted' with respect to the B-17 anecdote.

Agreed, good research.

 

[Mike H]

has anyone pointed out lately, that Vmc is ONLY about controllablity and has nothing to do with maintaining altitude?

lots of people don't seem to be able to keep that in mind

 

[Alchemy]

That's about the most erroneous article that I've ever read on the subject:

Holding a bank in the direction of the operating engine may increase the performance of the multiengine in some respects, but it definitely raises Vmca.
​

By all means send the author an email and let him know what you think: http://www.westwingsinc.com/#contact, it's the first name at the top of that page. I'd be interested to see how he responds to your arguments.

I don't care one way or the other, as Vmc is basically irrelevant to the type I fly.