Vmc...

[Papoo]

I'll freely admit that aerodynamics is not my strong point... but isn't the idea behind the split ball to give you zero sideslip? and wouldn't that give you the lowest drag?

It will give you the lowest parasite drag, yes. Some helicopters (Gazelle springs to mind) have a lightly weighted string hanging in the front center of the windshield, so the pilots know they are in a zero sideslip condition, presumably because sideslip flying is very easy to do in a helicopter.

However, when splitting the ball in an asymmetric thrust scenario, you are inducing more lift from your wings. In turn, you will experience a substantial increase in induced drag. Test pilots have proven that this increase in induced drag is far greater than the decrease in parasite drag. As a consequence, total drag increases, so performance decreases.

Incidentally, this increase in induced drag is accentuated in low airspeed scenarios, such as a Vmc demo or engine failure on climb-out, due to the low speeds involved, because as I'm sure you know, induced drag is greatest at low speeds.

Made a good point

There are plenty of variables, you're right. My point is that I agree that using bank will aid in directional control (useful only for the purpose of Vmc demo, IMO). But, in the event of an engine failure, maximum performance will be achieved with the ball centered. The difference is quite noticeable in the 4 twins I have experimented with.

My concern is that this 'split ball mentality' may, in the event of an engine-out on climb out, will cause pilots to bank in to the operating engine, because that's what is drummed into them. The performance difference is vast, and certainly enough to make a critical difference on a hot day in AZ.

Tgrayson;

The evidence is all there in test pilot reports. That same pilot group tends not to advocate training Vmc demonstrations in the first place, their reasoning being that it is a procedure for certification purposes.

The optimal condition of 2-3 degrees typically equates to the lowest Vmca speed. That, we both agree on.

 

[MikeD]

There are plenty of variables, you're right. My point is that I agree that using bank will aid in directional control (useful only for the purpose of Vmc demo, IMO). But, in the event of an engine failure, maximum performance will be achieved with the ball centered. The difference is quite noticeable in the 4 twins I have experimented with.

My concern is that this 'split ball mentality' may, in the event of an engine-out on climb out, will cause pilots to bank in to the operating engine, because that's what is drummed into them. The performance difference is vast, and certainly enough to make a critical difference on a hot day in AZ.

Flown the majoirty of my time in AZ, both actual engine failures I had were in the AZ summer, one low alt and heavy, and the other high DA and heavy; both using split ball (to the best of my ability, mind you.....I was a little pre-occupied to stare at the ball at the time), and I'm still alive and the plane flew fine, as much as it could with an engine out and the conditions I was in.

How exactly did you carry out your experiments? Maybe I was doing something wrong, but I didn't see a "vast detrimental performance" you speak of. In a real engine-out scenario, the ability to center the ball vs have it a bit off center, just may be something one might not have a ton of leftover SA to notice, what with the rest of everything going on. Of course, you'd then have the rest of your life to make whatever work, work.

and reduces throttle (another idiotic habit) when loss of directional control comes,

Food for thought.

And why would this be an idiotic habit? You do know there may be times you need to do this in order to stay alive? Writing off a particular technique that should be in your "bag of tricks" as idiotic, without truly understanding where and when it may have a place, isn't the wisest course of action. Have you ever been in a true single-engine situation? With the stress, the uncertainty? Not having the safety net of knowing that you can "just bring the other engine back online"? The not knowing if you're about to plow the ground straight ahead shortly? I'm not slam dunking you, am simply just asking. Because you're making some pretty bold definitive statements, indicitive of someone who hasn't seen or experienced all the human as well as technical aspects of a situation like this, and the mass of variables therein. That's why it depends.

 

[tgrayson]

The optimal condition of 2-3 degrees typically equates to the lowest Vmca speed. That, we both agree on.

Wrong. Lowest Vmca speed occurs with something like 10 degrees of bank.

The evidence is all there in test pilot reports.

No, it isn't. If you have evidence, then supply it. I don't think you have any.

 

[tgrayson]

Here's a flight test report by Melville Byington, a professor at Embry Riddle. He conducted experiements on a number of twins to determine optimal bank angle for performance and the performance penalties for failing to achieve that bank. I think this is one of the greatest articles on ME flying. Sorry, they're TIFs. If you want to skip to the flight test results of zero bank vs zero sideslip, just get page 4.

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