Vmc demo trouble?

[Timebuilder]

Here's another question..how much do you reduce power on the operating engine if you experience loss of directional contorl? When do you bring the power back in?

If you are in danger of the roll, and this is the avoidance you are demonstrating with the Vmc demo, then you want to pull the op engine power to idle. You lower the nose (we used 5 degrees below the horizon) and let the plane reach Vmc plus ten before coming back in with power on the operating engine.

Timebuilder, don't mean to be rude or anything, but why look at the heading indicator? Were you doing this for an IFR Student. I've always covered up the instruments and had the student use a reference point outside, if that point starts to move, its the same thing as the heading indicator moving. Remember, see and avoid. I'd venture a guess more people die each year in Mid-Air Collisions that single engine situations.

I think that's a reasonable question. Here's my answer.

If you teach the student to judge loss of directional control by means of an outside reference, then a power loss in instrument conditions does not lead to recall of a previous training scenario when and if this happens. If you use the HI, you can see immediately when loss of directional control happens, while properly scanning for traffic and the 1 kt per second you lose as you gently pitch the nose up, and you can begin the recovery immediately. The HI is good for drilling for use in either VFR or VMC, and the outside reference is only engrained for VFR conditions, making the correct response less likely as a result of that training.

If you train to the "first indication" of the stall, you have not yet stalled.

 

[IP076]

Inside vs outside....

Yeah, that makes sense. I've always taught students that went Private/Single to Private/Multi before starting an Instrument Rating....that's why we always emphasize the outside stuff.

Agreed, I was talking "first indication" and I think most people were referring to "Stalling".

Try this....when you're stabilized at Vyse prior to starting the actual Vmc portion of the manuever, note the pitch attitude. Now, pitch up for an attitude that will bleed off airspeed at approximately 1 knot per second. At the first indication of loss of control, reduce the throttle on the operating engine enough to stop the roll and pitch to the attitude you were at when you started the manuever (Holding Vyse). Increase power slowly on the operating engine until full power is again attained. You should be established back at Vyse by then. If you increase the power slowly, you should never reach a point at which the aircraft will roll again.

That's they way we used to teach it (Basically) and it was the method that yielded the "least ammount of altitude loss" that I think we're all going for.

 

[SpocksBeard]

I have to chime in here with a comment because this was a big problem I saw as a check instructor at my old flight school. I found that the reason many students would get a stall buffet before a loss of directional control was because they were preventing the aircraft from rolling by increasing aileron pressure instead of correcting with rudder. I constantly preached that they should initially put just enough aileron in to establish the 5 degree bank at the beginning of the manuever and STOP there. Then only correct for the yaw with the rudder as the airplane slows, and you almost always get a loss of directional control first. Everytime I have demonstrated it this way I NEVER got a stall indication first. If you think of what you are doing with the ailerons otherwise it makes sense. By deflecting the aileron on the good engine's side up to compensate for the resultant roll you are simply deflecting it into mostly dead air - the airflow is mostly separated in front of that aileron as you slow down and increase your angle of attack. That aileron is not helping to keep that wing down to counteract the roll at high angles of attack. The aileron on the bad engine's side is deflected downward. This dramatically increases the angle of attack on this wing which is exactly the wing you DON'T want to stall. I believe this has alot to do with stall/spin scenarios that occur as a result of a VMC Demo. I used to tell students that once the initial amount of aileron you put in was not enough to keep the airplane from rolling towards the bad engine, it was time to recover. That is more than sufficient as a demonstration of loss of directional control. Personally, I never blocked the rudder. If the manuever is done without increasing aileron input as you slow I don't think there is any need to - at least not in a duchess or apache.

 

[tathepilot]

SpocksBeard

this is a good point. I never thought about it that way. By not using full aileron deflection, directional would be lost quicker without using full aileron which prob would ag·gra·vate an im·mi·nent stall.

I'll have to give it a try.

 

[EDUC8-or]

I never thought about it that way. By not using full aileron deflection, directional would be lost quicker without using full aileron which prob would ag·gra·vate an im·mi·nent stall.

That's the way I was taught and the way I teach my students. If you limit the amount of aileron input you will lose directional control before the stall.

However, on my MEI ride the DE wanted me to maintain 5 degrees of bank throughout the maneuver, which meant increasing aileron input until the loss of directional control. Remember, as you slow down your control surfaces become less effective due to the decreased airflow over these surfaces. By the time we began to lose directional control, I believe I had in full aileron and full rudder deflection.

I DON'T teach my students to use full aileron deflection, but the DE wanted me to see how you can lose control in a hurry and how to prevent these situations with my students.

 

[nosehair]

Vmc Demo Recovery

Here's a different twist on the recovery technique:
I teach recovering as if you were having an engine failure on take-off. Reduce throttle on the operating engine AND lower the nose ONLY enough to regain directional control with a minimum loss of altitude. Imagine that you are trying to clear an obstacle at the end of the runway with an engine out, and you begin losing directional control. Pull the throttle back slightly, while lowering the nose slightly, and you will discover that you can regain directional control and airspeed while leveling off slightly. In most cases, throttle reduction to 65 - 75% power and nose down to a slight climb angle will produce a flying aircraft. This technique may allow you to maneuver around or over an obstacle on climb-out.
I also teach stall recovery with a very minimum loss of altitude.
Most students recover from stalls by diving excessively to regain excessive airspeed because they are recovering at an altitude that will allow that. Then, when they actually stall one on a go-around or high flare/bounce, they slam the throttle forward and punch the nose over into the ground - just like they have been rotely trained.
Stalls, Vmc Demos, Engine-cuts, all these things should be responded to and recovered from as if you were within a hundred feet of the ground.

 

[CUEBOAT]

5 degrees of bank, do not limit yourself to this. PTS calls for angle of bank that gives best control and performance(which is a contradiction itself-different topic). It seems everyone gets hung up on 5 degrees, if you need to bank more or less to stay alive wouldn't you do it. In a BE-76 5 degrees is too much you'd be side slipping into the good engine which would increase drag also, may be the case in other light twins. VMC recovery is done at first indication of stall or loss of directional control, says so in the PTS.

 

[SpocksBeard]

I guess in 400 hours of teaching in a BE-76 I never looked at the actual angle of bank I was holding. Obviously it doesn't have to be 5 degrees - I always just went with whatever prevented any sideslip. Then again, in a manuever with this much going on at once I never wanted students to be splitting hairs over whether they were holding 3 degrees or 7 degrees of bank either. 5 degrees is just an approximation and is useful during a verbal explanation. Whatever you do you don't want to be increasing your aileron deflection as you slow unless you are doing it to demonstrate how something very bad can happen in a hurry like it was mentioned earlier.