AggieMike’s Multi Engine questions…

AggieMike88

AggieMike88

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The original "I don't know it all" of aviation.
As I progress through my training for the commercial multi engine add on, I know I’ll have questions. So this thread is to keep them collected in one spot.

Any knowledge you wish to share to improve the experiences of training, oral exam, check flight, and time building are welcome.

To provide aircraft specific information, I am using N125Y, a 1963 PA-23-250 Aztec operated by In The Pattern in Denton, TX.
 
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(General power plant)

One of the learning references discusses conventional versus counter-rotating. For the counter-rotating, the book showed information from a POH showing the engine designation with an L to indicate the propeller turns to the left.

How is this accomplished?

Is the propeller connected directly to the crank and the crank spins CCW (and what makes it do that versus a “regular” engine)?

Or is there a gear system that takes the CW motion of the crank and reverses it?
 
Aztec Specific

During lesson 1, I was encouraged to experience stalls, power off, on, and accelerated.

This Aztec does not have a stall warning buzzer or horn. Just a light activated by the small metal vane on the leading edge of the left wing. This is located on the upper left area of the instrument panel. The light cover is old and pretty opaque.

My experience with this plane during the stalls is I never saw the light illuminate. And I was really feeling for the buffet.

The question: Am I right that the buffet is kinda subtle?

My instructor announced “There is the buffet, recover” before I really noticed anything over the usual vibrations. At least compared to the 172’s I’ve been flying recently.

Or is it more pronounced, and I should wait a touch more before recovery?

(Next lesson, I am bringing some painters tape with me to check the stall warning light during preflight. Tape the vane in the activated position, then go back to the cockpit and turn on the master. Determine the lamp is working and figure out just how bright it is, and maybe what color.)
 
AggieMike88 said:
One of the learning references discusses conventional versus counter-rotating. For the counter-rotating, the book showed information from a POH showing the engine designation with an L to indicate the propeller turns to the left.

How is this accomplished?
Click to expand...

Making an engine run backwards is just a matter of swapping a few parts. Older diesel tractors will run backwards as the fuel is introduced directly into the cylinder, and they don't care whether the air comes in the intake valve or the exhaust valve. Obviously it's hard on things.

Lifted from another website:

Reversing the direction in which the crankshaft of a given engine rotates is not particularly difficult. But reversing the engine can add considerable extra expense because of the nonstandard pieces needed, including:

  1. a special crankshaft with the rod-journal oiling passages drilled to the opposite side of the rod throws in order to support the reversed bearing load phasing,
  2. a special camshaft because reversing the crankshaft reverses the firing order (no, you can’t just use a gear-drive to run the cam in its normal direction, and running it backwards opens the intake during the exhaust cycle and the exhaust during the intake cycle),
  3. special accessory drive provisions,
  4. reverse rotation crankshaft seals,
  5. specially-engineered oil pan (especially critical in dry sump systems);
  6. reverse-rotation starter and alternator,
  7. and a host of other details depending on the ignition and oiling systems used.
 
AggieMike88 said:
Aztec Specific

During lesson 1, I was encouraged to experience stalls, power off, on, and accelerated.

This Aztec does not have a stall warning buzzer or horn. Just a light activated by the small metal vane on the leading edge of the left wing. This is located on the upper left area of the instrument panel. The light cover is old and pretty opaque.

My experience with this plane during the stalls is I never saw the light illuminate. And I was really feeling for the buffet.

The question: Am I right that the buffet is kinda subtle?

My instructor announced “There is the buffet, recover” before I really noticed anything over the usual vibrations. At least compared to the 172’s I’ve been flying recently.

Or is it more pronounced, and I should wait a touch more before recovery?

(Next lesson, I am bringing some painters tape with me to check the stall warning light during preflight. Tape the vane in the activated position, then go back to the cockpit and turn on the master. Determine the lamp is working and figure out just how bright it is, and maybe what color.)
Click to expand...

The Aztec will provide plenty of noticeable buffet prior to a stall if you take it far enough. Sounds like either you didn't notice it or the instructor had you recover pretty early.

Now the question is, what risks may be associated with different types of stalls? Knowing this may provide insight to possible reasons why an instructor may have had you recover as soon as they felt the first sign of a buffet.
 
As Jim said in more detail, the ones that have engines that spin the other way are essentially engines made in a “mirror image”.

(Surprisingly they’re not always more expensive either.)

Lots of Russian stuff spins backward to our stuff, single-engine. Throw out all you learned about left-turning tendencies in singles when you fly one of those, and you’ll need left rudder for takeoff...

Not too tough to build an engine to spin either direction. We just think a particular rotation as seen from the cockpit is “standard”. Then we teach right rudder, right rudder, RIGHT RUDDER until we believe it. Haha.
 
Same. I find the Aztec to have a mundane stall.. like running a big boat aground on a sandbar. You hardly feel it happening.

I never understood the point of a stall horn tbh.
 
Does anyone have a photo to share of
  • the older Aztec throttle quadrant, both the upper part where the levers are and the lower, somewhat hidden, area with the switches?
  • the airspeed indicator (real one, with the correct speed marks)
  • the fuel selection switches between the seats
  • the trim cranks on the overhead, especially showing the "crank this way" labels and trim setting indicator.
I want to add photos to my chair flying "shadow boxing" wall to aid in visualization when practicing the maneuvers.

My lessons for today and tomorrow are canceled due to rain, so need to do so,etching to keep progress going forward
 
For this interested, here are two of the reference texts I am using. Others include the AFH, POH, Bob Gardners book, and a few more.
 

Attachments

  • Welcome to Twin Time.pdf
    579.6 KB · Views: 13
  • FAA Light Twins Safety.pdf
    1.7 MB · Views: 4
The "Right Engine is Wrong"...

Meaning the right engine on a Seneca is replaced so that there is no critical engine. Remember Critical doesn't mean important, it just means means losing it causes the most Yaw
 
ja_user said:
The "Right Engine is Wrong"...

Meaning the right engine on a Seneca is replaced so that there is no critical engine. Remember Critical doesn't mean important, it just means means losing it causes the most Yaw
Click to expand...
And since they now cause the same yaw, wouldn’t both engines be critical?
 
As an aside Mike...

Books.

I thought this one was worth the money...
ea397e6dc57e2f14988e5cdd346b36a8.jpg


I thought this one was “meh”.

a28a25b375d85036119ff893a71943a5.jpg


Happy to mail you a care package of these and any other multi goodies I have stuffed in my CFI box in my office if you’d like more material.

I’d want the ASA book back sometime. But unlikely any rush. Ha.
 
denverpilot said:
Happy to mail you a care package of these and any other multi goodies I have stuffed in my CFI box in my office if you’d like more material.
Click to expand...
I'll take the ASA book.

Are you craving any Texas created items? Happy to send you a care package as a thank you.
 
Martin Pauly said:
Watch and understand this, and you will likely ace the oral:

Click to expand...
Thanks! That and the other two videos you did for multi have been tagged for watching.

PS. Ping me next time you find your self in the DFW corner of the world. Would love to meet up in person.
 
MauleSkinner said:
And since they now cause the same yaw, wouldn’t both engines be critical?
Click to expand...

A very common question. The Definition is the engine that "causes the most adverse yaw", so no Critical engine if they are the same.
 
Martin's videos are required viewing for any student of mine :)
 
ja_user said:
A very common question. The Definition is the engine that "causes the most adverse yaw", so no Critical engine if they are the same.
Click to expand...
No, per Part 1, “Critical engine means the engine whose failure would most adversely affect the performance or handling qualities of an aircraft.”
So how do they determine Vmc if there’s no critical engine, when one of the conditions of Vmc, as stated in the AFH, is that “VMC is determined with the critical engine propeller windmilling...”?
 
MauleSkinner said:
No, per Part 1, “Critical engine means the engine whose failure would most adversely affect the performance or handling qualities of an aircraft.”
So how do they determine Vmc if there’s no critical engine, when one of the conditions of Vmc, as stated in the AFH, is that “VMC is determined with the critical engine propeller windmilling...”?
Click to expand...

Overthinking this. If one engine failing is worse than the other, that is the higher number that is used. If the Numbers match, well then you also use that number.

The criteria for publishing VMC is to keep manufactures on the same playing field as much as anything, it is a variable number...

But whether one engine is worse than the other should be a provable situation.
 
ja_user said:
Overthinking this. If one engine failing is worse than the other, that is the higher number that is used. If the Numbers match, well then you also use that number.

The criteria for publishing VMC is to keep manufactures on the same playing field as much as anything, it is a variable number...

But whether one engine is worse than the other should be a provable situation.
Click to expand...
No, I’m reading the FAA definitions, and if there’s no critical engine, Vmc can’t be determined per the definition in the AFH.

nor does the definition of critical engine require that one be worse than the other.

of course, the AFH doesn’t necessarily match regulatory definitions...Part 23 doesn’t use the term “critical engine” like Part 25 does.
 
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What does "would most adversely affect" mean to you? Serious question.
 
I would agree that whether both are critical or neither is critical is largely academic.

But, I do know that a Seneca 1 has a VMC published and it will roll over with either side failed.
 
ja_user said:
I would agree that whether both are critical or neither is critical is largely academic.

But, I do know that a Seneca 1 has a VMC published and it will roll over with either side failed.
Click to expand...
As I indicated earlier, a “critical engine” is not part of the Part 23 definition of Vmc.

But a manufacturer is bound by the regulatory requirements for determining Vmc, so whether neither or both are critical is only academic where the term doesn’t apply.
 
I guess I just don't understand what you are trying to argue here.
 
ja_user said:
I guess I just don't understand what you are trying to argue here.
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Paraphrasing is great for helping people understand certain concepts, but if the paraphrase doesn’t actually match the meaning of what you’re explaining, it can cause confusion.
 
MauleSkinner said:
Paraphrasing is great for helping people understand certain concepts, but if the paraphrase doesn’t actually match the meaning of what you’re explaining, it can cause confusion.
Click to expand...

But very few of us have met each other, so how would we know how others would receive what we are trying to transmit?
 
Have not read all responses, but the #1 thing (IMO) is pitch for blue line.
That said, it’s been a long time since I’ve flown light twins (Jets a bit different), but at blue line you will not VMC roll, and have a bit of time to get things feathered & secured.
 
ja_user said:
But very few of us have met each other, so how would we know how others would receive what we are trying to transmit?
Click to expand...
If you have to meet face to face in order to communicate properly, don’t try it elsewhere.
 
MauleSkinner said:
If you have to meet face to face in order to communicate properly, don’t try it elsewhere.
Click to expand...
Ok. We set the standards on the internet, face to face has no relevance here. got it.
 
MauleSkinner said:
No, face to face is relevant here if, per your post, you can’t communicate without it.
Click to expand...
relevance is "critical" as they say.

As usual in POA form, we will agree to disagree. No further education will be had by anyone reading this. Really it is too bad.
I'm out,
 
Kritchlow said:
Have not read all responses, but the #1 thing (IMO) is pitch for blue line.
That said, it’s been a long time since I’ve flown light twins (Jets a bit different), but at blue line you will not VMC roll, and have a bit of time to get things feathered & secured.
Click to expand...

One thing I saw results of and it impressed me greatly was an engine failure soon after takeoff, no runway remaining - this was DA of 7500, light twin, decent load, in a mountainous bowl.
Pilot pulled both back and bellied in to a pasture, they walked away.
This could have turned out so. much. worse. Like so many others which ended upside down or augered in.
The best option is not always to try to keep on going, on one engine.
"Fly The Airplane" includes doing so by purposely pulling both engines back in order to maintain aircraft control. I don't think this is taught enough.
They teach that you will be a perfect pilot and do everything right during OEI events and land on a runway. Well, we know how that's turned out statistically.
 
Let'sgoflying! said:
One thing I saw results of and it impressed me greatly was an engine failure soon after takeoff, no runway remaining - this was DA of 7500, light twin, decent load, in a mountainous bowl.
Pilot pulled both back and bellied in to a pasture, they walked away.
This could have turned out so. much. worse. Like so many others which ended upside down or augered in.
The best option is not always to try to keep on going, on one engine.
"Fly The Airplane" includes doing so by purposely pulling both engines back in order to maintain aircraft control. I don't think this is taught enough.
They teach that you will be a perfect pilot and do everything right during OEI events and land on a runway. Well, we know how that's turned out statistically.
Click to expand...
No doubt that may have been a good decision, but the *initial* response is blue line. After that all decisions are open to the situation at hand.
 
Let'sgoflying! said:
They teach that you will be a perfect pilot and do everything right during OEI events and land on a runway.
Click to expand...

Hmm. My multi instructors taught me no such thing. Especially at this elevation.

It was very clear if you wanted to survive, blue line probably results in an immediate landing and excursion through the airport fence or an off airport landing/crash under some control — vs rolling it over out of control.

Light twins fully loaded on hot days here are pretty much going nowhere but down, fast, if you trash one.

Unless you buy a bigger one and load it lightly. :)
 
In the texts and different videos, the term "light twin" is used.

At what weight does the aircraft become a "heavy twin" and what might be an example at the low end of that spectrum?
 
An observation: multi engine training has a similar track as Advanced SCUBA diver.

You learn how to do something more challenging, but the emphasis is how to manage and solve problems when it goes wrong.
 
AggieMike88 said:
In the texts and different videos, the term "light twin" is used.

At what weight does the aircraft become a "heavy twin" and what might be an example at the low end of that spectrum?
Click to expand...
12,500# is generally where certification rules change, and it’s no longer a “light twin”, although I think there are some things that change at about 6000#.

But as you’ve probably noted, there is no official FAA definition of that.
 
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