Minimum Control Speed

[loopa]

Hi, could somebody help explain the conditions Minimum Control Speed in a multi engine aircraft? I there's like 10 or 12 right?

[Hedley]

I wrote this a couple years back:

http://www.avweb.com/news/airman/184438-1.html

[loopa]

I wrote this a couple years back:

http://www.avweb.com/news/airman/184438-1.html

As a matter of standardization, Vmc is determined at
maximum gross weight,
with the center of gravity [C of G] at the maximum aft position,
at sea level,
with the flaps set to the takeoff position,
the landing gear retracted,
with all engines developing maximum power at the time the critical engine fails and windmills,
with a maximum of 5 degrees of bank into the good engine.

I thought you were supposed to think how the conditions affected the CONTROL of the plane... ?

I thought gears down would provide more stability of the aircraft and thus improve control ability and thus decrease Vmc ?

[Tim]

Vmc in seminoles is not determined at gross wt. the POH says 'the min t/o wt or any lesser wt to demonstate Vmc' or something to that effect, although i think that's an amendment.

in addition to the horizontal lift component inceasing, stability also increases with wt - which contributes to a lower Vmc

[E-Flyer]

It's not just seminoles, but rather all multi engine aircraft according to transport.

It's even in the multi engine flight test guide. That Vmc is found at the minimum permissible gross weight. The reason being that the lift vector on heavier airplane has to be even greater, thus the horizontal component of lift (in a 5 degree bank) would be greater.

[Big Pistons Forever]

It's not just seminoles, but rather all multi engine aircraft according to transport.

It's even in the multi engine flight test guide. That Vmc is found at the minimum permissible gross weight. The reason being that the lift vector on heavier airplane has to be even greater, thus the horizontal component of lift (in a 5 degree bank) would be greater.

What is a "minimum permisable" gross weight

[FlaplessDork]

Because I was bored I found these for you. Seeing how most twins we fly were manufactured in he States I pulled the FARs for you.

Sec. 25.149 - Minimum control speed.

(a) In establishing the minimum control speeds required by this section, the method used to simulate critical engine failure must represent the most critical mode of powerplant failure with respect to controllability expected in service.

(b) 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 maintain straight flight with an angle of bank of not more than 5 degrees.

(c) VMC may not exceed 1.13 VSR with --

(1) Maximum available takeoff power or thrust on the engines;

(2) The most unfavorable center of gravity;

(3) The airplane trimmed for takeoff;

(4) The maximum sea level takeoff weight (or any lesser weight necessary to show VMC);

(5) The airplane in the most critical takeoff configuration existing along the flight path after the airplane becomes airborne, except with the landing gear retracted;

(6) The airplane airborne and the ground effect negligible; and

(7) If applicable, the propeller of the inoperative engine --

(i) Windmilling;

(ii) In the most probable position for the specific design of the propeller control; or

(iii) Feathered, if the airplane has an automatic feathering device acceptable for showing compliance with the climb requirements of §25.121.

(d) The rudder forces required to maintain control at VMC may not exceed 150 pounds nor may it be necessary to reduce power or thrust of the operative engines. During recovery, the airplane may not assume any dangerous attitude or require exceptional piloting skill, alertness, or strength to prevent a heading change of more than 20 degrees.

(e) VMCG, the minimum control speed on the ground, is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane using the rudder control alone (without the use of nosewheel steering), as limited by 150 pounds of force, and the lateral control to the extent of keeping the wings level to enable the takeoff to be safely continued using normal piloting skill. In the determination of VMCG, assuming that the path of the airplane accelerating with all engines operating is along the centerline of the runway, its path from the point at which the critical engine is made inoperative to the point at which recovery to a direction parallel to the centerline is completed may not deviate more than 30 feet laterally from the centerline at any point. VMCG must be established with --

(1) The airplane in each takeoff configuration or, at the option of the applicant, in the most critical takeoff configuration;

(2) Maximum available takeoff power or thrust on the operating engines;

(3) The most unfavorable center of gravity;

(4) The airplane trimmed for takeoff; and

(5) The most unfavorable weight in the range of takeoff weights.

(f) VMCL, the minimum control speed during approach and landing with all engines operating, 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 maintain straight flight with an angle of bank of not more than 5 degrees. VMCL must be established with --

(1) The airplane in the most critical configuration (or, at the option of the applicant, each configuration) for approach and landing with all engines operating;

(2) The most unfavorable center of gravity;

(3) The airplane trimmed for approach with all engines operating;

(4) The most favorable weight, or, at the option of the applicant, as a function of weight;

(5) For propeller airplanes, the propeller of the inoperative engine in the position it achieves without pilot action, assuming the engine fails while at the power or thrust necessary to maintain a three degree approach path angle; and

(6) Go-around power or thrust setting on the operating engine(s).

(g) For airplanes with three or more engines, VMCL-2, the minimum control speed during approach and landing with one critical engine inoperative, is the calibrated airspeed at which, when a second critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with both engines still inoperative, and maintain straight flight with an angle of bank of not more than 5 degrees. VMCL-2 must be established with --

(1) The airplane in the most critical configuration (or, at the option of the applicant, each configuration) for approach and landing with one critical engine inoperative;

(2) The most unfavorable center of gravity;

(3) The airplane trimmed for approach with one critical engine inoperative;

(4) The most unfavorable weight, or, at the option of the applicant, as a function of weight;

(5) For propeller airplanes, the propeller of the more critical inoperative engine in the position it achieves without pilot action, assuming the engine fails while at the power or thrust necessary to maintain a three degree approach path angle, and the propeller of the other inoperative engine feathered;

(6) The power or thrust on the operating engine(s) necessary to maintain an approach path angle of three degrees when one critical engine is inoperative; and

(7) The power or thrust on the operating engine(s) rapidly changed, immediately after the second critical engine is made inoperative, from the power or thrust prescribed in paragraph (g)(6) of this section to --

(i) Minimum power or thrust; and

(ii) Go-around power or thrust setting.

(h) In demonstrations of VMCL and VMCL-2 --

(1) The rudder force may not exceed 150 pounds;

(2) The airplane may not exhibit hazardous flight characteristics or require exceptional piloting skill, alertness, or strength;

(3) Lateral control must be sufficient to roll the airplane, from an initial condition of steady flight, through an angle of 20 degrees in the direction necessary to initiate a turn away from the inoperative engine(s), in not more than 5 seconds; and

(4) For propeller airplanes, hazardous flight characteristics must not be exhibited due to any propeller position achieved when the engine fails or during any likely subsequent movements of the engine or propeller controls.

(a) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane 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.

(b) VMC for takeoff must not exceed 1.2 VS1, where VS1 is determined at the maximum takeoff weight. VMC must be determined with the most unfavourable weight and centre of gravity position and with the aeroplane airborne and the ground effect negligible, for the takeoff configuration(s) with:

(1) Maximum available takeoff power initially on each engine;

(2) The aeroplane trimmed for takeoff;

(3) Flaps in the takeoff position(s);

(4) Landing gear retracted; and

(5) All propeller controls in the recommended takeoff position throughout.

(c) [For all aeroplanes except reciprocating engine-powered aeroplanes of 6,000 pounds or less maximum weight, the conditions of paragraph (a) of this section must also be met for the landing configuration with:

(1) Maximum available takeoff power initially on each engine;

(2) The aeroplane trimmed for an approach, with all engines operating, at VREF, at an approach gradient equal to the steepest used in the landing distance demonstration of 523.75;

(3) Flaps in the landing position;

(4) Landing gear extended; and

(5) All propeller controls in the position recommended for approach with all engines operating.

(d) A minimum speed to intentionally render the critical engine inoperative must be established and designated as the safe, intentional, one-engine-inoperative speed, VSSE.

(e) At VMC, the rudder pedal force required to maintain control must not exceed 150 pounds and it must not be necessary to reduce power of the operative engine(s). During the manoeuvre, the aeroplane must not assume any dangerous attitude and it must be possible to prevent a heading change of more than 20 degrees.

(f) At the option of the applicant, to comply with the requirements of 523.51(c)(1), VMCG may be determined. VMCG is the minimum control speed on the ground, and is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane using the rudder control alone (without the use of nosewheel steering), as limited by 150 pounds of force, and using the lateral control to the extent of keeping the wings level to enable the takeoff to be safely continued. In the determination of VMCG, assuming that the path of the aeroplane accelerating with all engines operating is along the centreline of the runway, its path from the point at which the critical engine is made inoperative to the point at which recovery to a direction parallel to the centreline is completed may not deviate more than 30 feet laterally from the centreline at any point. VMCG must be established with:

(1) The aeroplane in each takeoff configuration or, at the option of the applicant, in the most critical takeoff configuration;

(2) Maximum available takeoff power on the operating engines;

(3) The most unfavourable centre of gravity;

(4) The aeroplane trimmed for takeoff; and

(5) The most unfavourable weight in the range of takeoff weights.

[just curious]

For what it's worth, because of an accident in Red Lake with a Twin Otter in the early 90's, the chief pilot or person responsible for training in a Twin Otter used for maximum performance STOL operations must go through a day's training in the DHC-6 Sim. While the accident itself wasn't caused by a failure below VMC, the investigation revealed a gap in training and awareness of VMC, and STOL ops generally, since there is a variation in flap seting between Twin Otter Series.

The Twin Otter in Max STOL operations or MPS rotates below VMC. At that speed, without an exceptionally sharp crew, autofeather, and training, the earth revolves around the windscreen well before you can finish saying "Oh Sh...!"

I decided I like autofeather and a well-trained crew after that.

[FlaplessDork]

Occurrence InformationOccurrence Type: Accident Occurrence Date: 2009/03/14
Occurrence Time: 1104 Z Day Or Night: day-time
Fatalities: 0 Injuries: 3

Canadian Aerodrome ID: Aerodrome Name:
Occurrence Location: Approximatley 25 miles north of Fredericton (CYFC) Province: New Brunswick
Country: CANADA World Area: North America

Reported By: NAV CANADA AOR Number: 105083-V2
TSB Class Of Investigation: 5 TSB Occurrence No.: A09A0017
Event InformationCollision with terrain
ELT/SAR/comm search
Loss of control - inflight
Missing aircraft
Aircraft InformationFlight #:
Aircraft Category: Aeroplane Country of Registration: CANADA
Make: PIPER Model: PA44 180
Year Built: 2007 Amateur Built: No
Engine Make: AVCO LYCOMING Engine Model: O-360-A1H6
Engine Type: Reciprocating Gear Type: Land
Phase of Flight: Cruise Damage: Substantial
Owner: THE MONCTON FLYING CLUB (MONCTON FLIGHT COLLEGE) Operator: THE MONCTON FLYING CLUB (763)
Operator Type: Commercial

Detail InformationUser Name: MacQuarrie, Jack
Date: 2009/03/16
Further Action Required: Yes
O.P.I.: General Aviation
Narrative: At 15:26Z, several strong ELT reports were heard from aircraft in various areas (100 miles south of Fredericton (CYFC) to 40 miles north of Fredericton. The Rescue Coordination Centre (RCC) was advised. At 15:55Z the Fredericton Flight Service Station inquired about an overdue aircraft, C-GMFY, Piper PA44 180. At 16:00Z, the RCC advised that there was an overdue aircraft at Fredericton. At 17:30Z, search and rescue located an aircraft in the woods north of Fredericton. RCC advised Moncton ACC that all three persons survived and were airlifted to hospital. TSB Case Closed.

User Name: MacQuarrie, Jack
Date: 2009/03/16
Further Action Required: No
O.P.I.: General Aviation
Narrative: UPDATE TSB: During the flight, the student was asked to do a stall manoeuvre. The aircraft was approximately 3500 ASL. During recovery the aircraft abruptly entered a spin. The instructor immediately took control and started spin recovery procedures. During the ensuing dive and pull out from the spin, the aircraft impacted trees and came to rest right side up, with the wings separated from the fuselage. The aircraft was extensively damaged. The crew evacuated the aircraft by smashing out the front window. The door was unable to be opened due to trees up against the door.

User Name: MacQuarrie, Jack
Date: 2009/04/09
Further Action Required: No
O.P.I.: General Aviation
Narrative: UPDATE TSB: A09A0017: C-GMFY, a Moncton Flight College Piper PA44 with one instructor and two students on board, had departed Fredericton for a local training flight. During stall recognition and recovery training, the aircraft inadvertently entered a spin. The instructor took control of the aircraft and recovered from the spin; however, not before the aircraft struck trees. The aircraft continued through the trees and came to rest in an upright attitude at ground level. The three pilots exited the aircraft through the windshield with non-life threatening serious injuries. The aircraft was reported overdue and an unsuccessful radio search was carried out. The crew of another aircraft in the area had detected an ELT signal, JRCC in Halifax was advised, and a SAR C-130 and Cormorant were dispatched. The aircraft and crew were found and the three occupants were airlifted to Fredericton, transferred to waiting ambulances, and taken to a local hospital for treatment. Two of the occupants were kept in hospital overnight for observation while the third was released.

Me thinks someone did a power-on stall, or one engine spoolled up quicker than the other. Never jam the power forward in a twin. If I remember correctly Vmc in the Seminole is close to or the same as stall.

[Barney]

That's why we recover at first sign or 65 kts about 10 kts before the published stall speed on the PA44.

[Strega]

so then really youre not doing a stall. just a "pretend" stall.

What happens if one day you really screw up and do really stall?
How will you handle it having never performed the recovery?

[Barney]

No more like recovering at first sign of a stall which usually occurs at 65kts. It
can be either an audible warning or a buffet.

[Tim]

Me thinks someone did a power-on stall, or one engine spoolled up quicker than the other. Never jam the power forward in a twin. If I remember correctly Vmc in the Seminole is close to or the same as stall.

you are, of course, 100% wrong with your guess about the crash in YFC

[Tim]

so then really youre not doing a stall. just a "pretend" stall.

What happens if one day you really screw up and do really stall?
How will you handle it having never performed the recovery?

+1

from the multi instructors guide

http://www.tc.gc.ca/civilaviation/gener ... 75/Ex8.htm

Advice to Instructors
...
■The aeroplane is to be fully stalled for this exercise
...

in another thread a while back someone suggested that the stall recovery should be to shove the nose way down, as opposed to just low enough to break the stall. their reason was (if i recall correctly) that you're probably toast anyways if it happens at low alt...whereas i tend to think that just breaking the stall is the only thing that WILL save you if you stall at low alt. all that shoving the nose down accomplishes is a rapid loss of alt, which - in a seminole anyways - results in anywhere from 2-5 times as much alt lost from a smooth recovery.

[Big Pistons Forever]

Me thinks someone did a power-on stall, or one engine spoolled up quicker than the other. Never jam the power forward in a twin. If I remember correctly Vmc in the Seminole is close to or the same as stall.

you are, of course, 100% wrong with your guess about the crash in YFC

It appears that a perfectly servicable airplane went from 3500 ft to impacting trees which by great good fortune did not result in a smoking hole and 3 dead bodies.
Twin engine "trainers" can kill you just as dead as larger aircraft. This incident seems to speak to the reason why you want to do multi engine training with someone who is:

1) A very effective teacher

2) An instructor with lots of multi engine time so that when things are starting to go sideways he/she has the expereince to recognize the situation and the skills to correct it before things get out of hand.

[the goal is soul]

I found this PowerPoint online and felt it added a lot after having read the material I had around me on Vmc. I'm 'special needs' with respect to physics, but I still managed to follow along.

Aircraft Control at Airspeeds Near Air Minimum Control Speed VMCA


I liked the quote at the end:

JFK once said :

"They who forget their history are deemed to repeat it."

After this training material is finished we can say:

"They who forget about VMCA are deemed to lose control some day."

[loopa]

How would trim affect the control of the airplane?

Would it have to do with the fact that when it's in Take Off position it will force the nose to be set up in a higher angle of attack, thus increasing pfactor and more yaw?

How about cowl flaps?

I just don't seem to understand why those two are so important in determining how it would affect the control and the Vmc numerical Value...


If anybody could explain that would be great !


Thanks

[Hedley]

Using rudder trim increases Vmc, because there is less rudder
to do the oppose the yaw.

[loopa]

Using rudder trim increases Vmc, because there is less rudder
to do the oppose the yaw.

I was asking about how the Trim of the Elevator or Stabilator affects Vmc ... ? and also Cowl Flaps ?

[FlaplessDork]

Me thinks someone did a power-on stall, or one engine spoolled up quicker than the other. Never jam the power forward in a twin. If I remember correctly Vmc in the Seminole is close to or the same as stall.

you are, of course, 100% wrong with your guess about the crash in YFC

It was a guess. Can you enlighten us to the cause? Airplanes don't usually spin unless someone did something stupid.

There's a reason why on the flight test all stalls in a twin are power off. You are to fully stall the airplane when clean, but in the landing config you are to recover at the first sign.

[FlaplessDork]

Using rudder trim increases Vmc, because there is less rudder
to do the oppose the yaw.

I was asking about how the Trim of the Elevator or Stabilator affects Vmc ... ? and also Cowl Flaps ?

Vmc is only for directional control. You may have to be quite nose down to maintain the airflow over the vertical stab and rudder in certain conditions of weight, alt, temp, and pressure.

[TC Aviator]

Gentlemen, please refer to the Advisory Circular 23-8B that explains the methodology for determining crtification of the light twins.
The statement..."the aeroplane is at a minimum practical test weight with a rearmost centre of gravity" comes from Advisory Circular 23-8B that explains the procedures for the conduct of certification tests under AWM 523.149 (FAR 23.149).

You will find that in reference to "Weight and C.G." the circular reads as follows:

(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 63AC 23-8B 8/14/03, 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.
In this reference, it is advised that the aeroplane be loaded with the minimum practical loading that will bring the centre of gravity to the aft limit. At the aft limit, the vertical control surfaces will have the shortest possible moment arm for directional control as the aeroplane will yaw around it's centre of gravity. The minimum practical weight allows determination of Vmc with minimum interference from the effects of wing stall because at lighter weights the stalling speed is slower.