Vmc
- Thread starter B767
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tgrayson
New Member
Nothing. When you say "Vmc" you're normally referring to Vmca (air), as opposed to Vmcg (ground),
meritflyer
Well-Known Member
Huh??
I always thought Vmc was vodka mixed w/ cranberry??
I always thought Vmc was vodka mixed w/ cranberry??
tgrayson
New Member
The FAA treats them as synonymous all through the FAA literature. There is no V-speed for the airspeed at which you will lose control at any particular moment. Some examples:
AC 25-7A Flight Test Guide for Certification of Transport Category Aircraft
The VMC (commonly referred to as VMCA) requirements are specified in § § 25.149(a), (b), (c) and (d); the ...
Pilot's Handbook of Aeronautical Knowledge:
VMCA
Minimum control speed in the air, with one engine inoperative, (critical engine on two engine airplanes) operating engine(s) at take off power, maximum of 5° bank into the good engine(s).
Flying Light Twins Safely, FAA-P-8740-19
Minimum Control Speed Airborne (Vmca)
Vmca is designated by the red radial on the airspeed indicator and indicates the minimum control speed, airborne at sea level. Vmca is determined by the manufacturer as the minimum airspeed at which it's possible to recover directional control of the airplane within 20 degrees heading change and, thereafter, maintain straight flight, with not more than 5 degrees of bank if one engine fails suddenly with:
* Takeoff power on both engines,
* Rearmost allowable center of gravity,
* Flaps in takeoff position,
* Landing gear retracted,
* Propeller windmilling in takeoff pitch configuration (or feathered if automatically featherable).
FAAO 8400.10 Air Transportation Operations Inspector's Handbook
(2) VMCA is the minimum speed at which directional control can be demonstrated when airborne with the critical engine inoperative. Full opposite rudder and not more than 5 degrees of bank away from the inoperative engine are permitted when establishing this speed. VMCA may not exceed 1.2 VS.
Dugie8
Well-Known Member
I couldn't find the AC that dealt with Vmc factors, but I could have sworn there was some blurb in there about Vmc and Vmca, the difference, etc. But the info you got here seems to say otherwise. Thanks for the clarification.
§ 23.149 Minimum control speed.
(a) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees. The method used to simulate critical engine failure must represent the most critical mode of powerplant failure expected in service with respect to controllability.
§ 23.149 Minimum control speed.
(a) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees. The method used to simulate critical engine failure must represent the most critical mode of powerplant failure expected in service with respect to controllability.
In the Baron I did my ME training in, the published VMC was 78. That number was determined in the following configuration:
most aft CG
max gross
critical engine windmilling
other engine at takeoff power
flaps and cowl flaps up
standard temp/pressure/sea level
and two others that I can't remember. Anyways, obviously, this number is not "worst case scenario", so it is common that the actual airspeed at which you lose control could be higher than 78. There is another airspeed published called VSSE which is 84. I assume this value is set as to always be higher than whatever VMC turns out to be.
meritflyer
Well-Known Member
Vmc is actually determined under a "worse case scenario" (for the most part). Most of the factors you have listed contribute to an increase in Vmc.
There are factors that will contribute to raising Vmc such as sideslip (not banking into your operating engine) so assuming those elements are eliminated, Vmc should occur as published or lower.
Here are a few thoughts -
Vmc is determined with weight being unfavorable, (light) not max gross, within the range of takeoff weights.
The power is fulll power on both engines initially.
Vsse is the intentional engine cut speed and should be higher than Vmc.
wheelsup
Well-Known Member
That's impossible, unless they had zero fuel and no people on board. For the baron it was determined at max gross. nbv are you ex-mapd?
wheelsup
Well-Known Member
There was a ground instructor at a school I worked at who actually asked Raytheon. The engineer source he had there told him it was done at max gross weight. FWIW.
tgrayson
New Member
I'm skeptical that this is the case.
First, the regulations in Part 23 require that it be done at most unfavorable weight. That would be light weight.
However, depending on when the Baron was certified, the regulation may have read differently. It used to say something to the effect of "Maximum gross takeoff weight, unless a lesser weight is necessary to show Vmc." The bold is the important part. Most airplanes will stall prior to losing directional control at max gross weight, so gross weight typically can't be used. Part 25 still reads this way.
However, the procedures during flight typically always use the lightest weight possible. Here's some material from AC 23-8B, Flight Test Guide to Part 23 Airplanes:
There are variable factors affecting the minimum control speed. Because of this, VMC should represent the highest minimum airspeed normally expected in service. The variable factors affecting VMC testing include:
[.....deleted....]
(4) Weight and C.G. For rudder limited airplanes with constant aft c.g. limits, the critical loading for VMC testing is most aft c.g. and minimum weight. Aft c.g. provides the shortest moment arm relative to the rudder thus the least restoring moments with regard to maintaining directional control. VMC should be determined at the most adverse weight. Minimum practical test weight is usually the most critical because the beneficial effect of banking into the operating engine is minimized. Light weight is also desirable for VMC testing because the stall speed is reduced.
Now is it possible that Vmc in the Baron was determined at max gross? I suppose so. But personally, I wouldn't put much stock into what your ground school instructor learned from Raytheon. My experience in trying to gain information from large organizations is that it's very tough to get anyone on the phone who both understands the question and knows the answer. He might easily have gotten some staff flunkie or random pilot who simply regurgitated what he learned during his own multi training.
wheelsup
Well-Known Member
I don't have the speeds for the 58, but I found these on the internet for the 55:
Vs1 = 76
Vmc = 80
So it would seem gross weight COULD be used. I'm not arguing either way; but like you said the possiblilty exists. I'm not sure when it was certified, early 70's I think, not sure if that would fall under the "old" regs you posted or not.
I'm 100% positive the Baron 55 (ours was manufactured in 1980) has a published Vmc that was determined at max gross, as well as other factors that do not make up a "worse case scenario". It specifically says go in the POH (I don't have one off hand to quote)
what does that mean? (I guess that answers your question)
meritflyer
Well-Known Member
How is that impossible?!?
"Unfavorable CG and weight" is how part 23 reads. Unfavorable weight, as tgrayson mentioned, is light.
I'd say that the "ground school instructor" that said it was tested at max gross, was talking "watercooler talk", if you know what I mean.
wheelsup
Well-Known Member
That AC, 23-8:
and it's predecessor, wasn't even around until 1972. The baron TCDS shows certfication of the 55 between 1963 and 1970, and 58 between 1969 and 1970 (for the 58A).
EDITed to add: There is a new model, the 58 G, certified in 2005. However, we had none of those.
wheelsup
Well-Known Member
Yes, that is it. You just hit the nail on the head. Glad we got that one figured out. Thanks for the education.
tgrayson
New Member
Note what it says, though: "to consolidate existing flight test policy." The policy pre-dated the AC, but by how much, we don't know.
As I said, it's possible that your aircraft measured Vmc at max gross, but it's counter to the policy that has existed for over 30 years.
wheelsup
Well-Known Member
And up until this year Pluto was a planet
.Also, AC 23-8 was published in 1989. 8110.7, which I don't personally have a copy of (in it's 1972 version), was published in 1972. How do you know that policy existed for 30 years?