Vmc question
03-22-2013, 07:32 PM
#11
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Joined APC: Nov 2011
Position: Volleyball Player
Posts: 3,982
Yep, good resource when used judiciously 
Nice for showing stall patterns, lift equations, Vg diagrams, power/drag curves, etc. I think people are a little afraid of getting into that book, but it's really excellent if you know what to look for and how to read it.
My real world "factors", in other words, things that actually have an impact on control:
Power
Propellor condition
Control position
Airspeed
Angle of attack
Configuration
Which engine fails
CG
Weight
Some of these don't even make much of an impact much of the time, or highly depend on the airplane, but since they do vary at least some of the time, they are worth discussing, unlike conditions for certification. About the only thing to say about that is the 23.149 FAR tests the aircraft in a "worst case" scenario, which is takeoff due to the ground being close and the plane being slow, so it's set up according to this and the recommended takeoff configuration.
The useful parts of 23.149 include the definition of Vmc and understanding it. Realizing that above a certain weight there is required climb performance. There is such thing as Vmcg. Max rudder pressure required and max heading change maybe. These might be more at the CFI level, in terms of being able to look up and show/explain, rather than just "knowing it because I was taught".
Nice for showing stall patterns, lift equations, Vg diagrams, power/drag curves, etc. I think people are a little afraid of getting into that book, but it's really excellent if you know what to look for and how to read it. My real world "factors", in other words, things that actually have an impact on control:
Power
Propellor condition
Control position
Airspeed
Angle of attack
Configuration
Which engine fails
CG
Weight
Some of these don't even make much of an impact much of the time, or highly depend on the airplane, but since they do vary at least some of the time, they are worth discussing, unlike conditions for certification. About the only thing to say about that is the 23.149 FAR tests the aircraft in a "worst case" scenario, which is takeoff due to the ground being close and the plane being slow, so it's set up according to this and the recommended takeoff configuration.
The useful parts of 23.149 include the definition of Vmc and understanding it. Realizing that above a certain weight there is required climb performance. There is such thing as Vmcg. Max rudder pressure required and max heading change maybe. These might be more at the CFI level, in terms of being able to look up and show/explain, rather than just "knowing it because I was taught".
03-22-2013, 08:32 PM
#12
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Joined APC: Jan 2013
Posts: 834
Another myth is that the FAA's Vmca certification test is the worst case scenario; it is not, but close enough for it's purposes; and that also needs to be explained to a student. Addressing other points... What responsible instructors are doing or attempting to do is teach some additional information that can make the difference, be lifesaving or provide increased insight or understanding, Etc. It frosts me that, due to the construction and operation of our flight training system, most students are only trained and prepared with passing an examination as the goal. While the FAA stipulates minimum standards regarding rules, Regs, training and testing criteria, Etc. They are by no means the last word on safety, training or competence, Etc. Geez, spin recovery training is not even required; and that is just plain foolish. I also have never liked the fact that someone can get a multi rating in a low powered, counter rotating "trainer" twin, as most do. I think that is fine if that is all they will fly. I think there should be an additional ME rating to include a "real", conventional, twin. I always encourage everyone to learn as much as possible and I always give more then they are expecting; largely to prepare them for or better operate in the real world. Misinformation, misundertanding and inadequate knowledge abound in this business and that is also unfortunate. That is largely due to folks not taking the time to properly research, Etc. when it is easier to parrot or just believe what you are told. Students should be able to count on a flight instructor for correct information though many times that is not the case as even instructors fall victim to and contribute to this situation. On another note... I have a fairly large aviation library which of course includes Aerodynamics for Naval Aviators. One of my favorite books is an antiquated text from the "Empire Test Pilots School" (which trained many RAF students) It is titled "Anatomy of an Aeroplane" and is a first edition. "Cub driver" might find this interesting as well. You can probably still find a copy online.
03-22-2013, 08:42 PM
#13
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Joined APC: Nov 2011
Position: Volleyball Player
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Paragraphs save lives
Just after takeoff is the "worst case" engine failure scenario, apart from the engine coming off the mounts I suppose mid-flight.
The "factors" are the conditions to set it up for that. It doesn't mean that those conditions are all the "worst case". We don't take off with max flaps, with one prop at 2700 and the other at 2200, etc, but it's reasonably the most critical situation, so you set up to replicate it for a Vmc demo and it's what they use to certify the aircraft.
You are correct that teaching "beyond the PTS" is necessary, but testing does have to stick to the PTS. In teaching "beyond" the PTS, an instructor must be careful not to make up stuff, teach things that can't be understood or supported, in other words: really foster understanding. That probably delves into talking about Vmc and Vmg, topics that are worth it. Lots of people know rote-wise that "5 degrees of bank" is what they can fly while single engine, but it's not 5 degrees except at Vmc under those conditions set forth, and it varies with power setting, DA (power) and situation. Great discussions about how not every aircraft is treated the same, like a very close-to-centerline thrust aircraft like a 727 and how that's different, or when it might be ok to put in more bank than "normal" momentarily. Lots of stuff to go into without getting into a classic rote "here are 9 factors of Vmc and they all affect Vmc". That's not the intent of that regulation at all.
Going back to the OP, trim, as one of these "factors", is inappropriate and not significant. Doesn't fall under the PTS, can be argued in contradictory ways, and is effectively no different than using trim without engine failures (to lesson control pressure required). I don't want the OP to fail his checkride if the DPE is a "rote memory" "check-the-numbers" kind of guy, but I also want to promote understanding and learning.
It's kind of like the rote-teaching of the 91.205 equipment and the feeling of accomplishment that you can remember "all the items", except that a DPE could ask "in what cases would you need a floatation device?" or "are ALL airplanes required to have shoulder harnesses?". You just memorized a list, but you really didn't learn anything. Not all of the items in that regulation are within most of the acronyms I've seen, yet time and time again it's taught that you must "memorize" this and many DPEs have a student recite these from memory. These are the cycles that need to be broken. That's how I see the: "9 or 8 or whatever number of factors of Vmc".
Just after takeoff is the "worst case" engine failure scenario, apart from the engine coming off the mounts I suppose mid-flight.
The "factors" are the conditions to set it up for that. It doesn't mean that those conditions are all the "worst case". We don't take off with max flaps, with one prop at 2700 and the other at 2200, etc, but it's reasonably the most critical situation, so you set up to replicate it for a Vmc demo and it's what they use to certify the aircraft.
You are correct that teaching "beyond the PTS" is necessary, but testing does have to stick to the PTS. In teaching "beyond" the PTS, an instructor must be careful not to make up stuff, teach things that can't be understood or supported, in other words: really foster understanding. That probably delves into talking about Vmc and Vmg, topics that are worth it. Lots of people know rote-wise that "5 degrees of bank" is what they can fly while single engine, but it's not 5 degrees except at Vmc under those conditions set forth, and it varies with power setting, DA (power) and situation. Great discussions about how not every aircraft is treated the same, like a very close-to-centerline thrust aircraft like a 727 and how that's different, or when it might be ok to put in more bank than "normal" momentarily. Lots of stuff to go into without getting into a classic rote "here are 9 factors of Vmc and they all affect Vmc". That's not the intent of that regulation at all.
Going back to the OP, trim, as one of these "factors", is inappropriate and not significant. Doesn't fall under the PTS, can be argued in contradictory ways, and is effectively no different than using trim without engine failures (to lesson control pressure required). I don't want the OP to fail his checkride if the DPE is a "rote memory" "check-the-numbers" kind of guy, but I also want to promote understanding and learning.
It's kind of like the rote-teaching of the 91.205 equipment and the feeling of accomplishment that you can remember "all the items", except that a DPE could ask "in what cases would you need a floatation device?" or "are ALL airplanes required to have shoulder harnesses?". You just memorized a list, but you really didn't learn anything. Not all of the items in that regulation are within most of the acronyms I've seen, yet time and time again it's taught that you must "memorize" this and many DPEs have a student recite these from memory. These are the cycles that need to be broken. That's how I see the: "9 or 8 or whatever number of factors of Vmc".
Last edited by JamesNoBrakes; 03-22-2013 at 09:07 PM.
03-22-2013, 09:24 PM
#14
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Joined APC: Jan 2013
Posts: 834
Originally Posted by JamesNoBrakes
Paragraphs save lives
Just after takeoff is the "worst case" engine failure scenario, apart from the engine coming off the mounts I suppose mid-flight.
The "factors" are the conditions to set it up for that. It doesn't mean that those conditions are all the "worst case". We don't take off with max flaps, with one prop at 2700 and the other at 2200, etc, but it's reasonably the most critical situation, so you set up to replicate it for a Vmc demo and it's what they use to certify the aircraft.
You are correct that teaching "beyond the PTS" is necessary, but testing does have to stick to the PTS. In teaching "beyond" the PTS, an instructor must be careful not to make up stuff, teach things that can't be understood or supported, in other words: really foster understanding. That probably delves into talking about Vmc and Vmg, topics that are worth it. Lots of people know rote-wise that "5 degrees of bank" is what they can fly while single engine, but it's not 5 degrees except at Vmc under those conditions set forth, and it varies with power setting, DA (power) and situation. Great discussions about how not every aircraft is treated the same, like a very close-to-centerline thrust aircraft like a 727 and how that's different, or when it might be ok to put in more bank than "normal" momentarily. Lots of stuff to go into without getting into a classic rote "here are 9 factors of Vmc and they all affect Vmc". That's not the intent of that regulation at all.
Going back to the OP, trim, as one of these "factors", is inappropriate and not significant. Doesn't fall under the PTS, can be argued in contradictory ways, and is effectively no different than using trim without engine failures (to lesson control pressure required). I don't want the OP to fail his checkride if the DPE is a "rote memory" "check-the-numbers" kind of guy, but I also want to promote understanding and learning.
It's kind of like the rote-teaching of the 91.205 equipment and the feeling of accomplishment that you can remember "all the items", except that a DPE could ask "in what cases would you need a floatation device?" or "are ALL airplanes required to have shoulder harnesses?". You just memorized a list, but you really didn't learn anything. Not all of the items in that regulation are within most of the acronyms I've seen, yet time and time again it's taught that you must "memorize" this and many DPEs have a student recite these from memory. These are the cycles that need to be broken. That's how I see the: "9 or 8 or whatever number of factors of Vmc".
Just after takeoff is the "worst case" engine failure scenario, apart from the engine coming off the mounts I suppose mid-flight.
The "factors" are the conditions to set it up for that. It doesn't mean that those conditions are all the "worst case". We don't take off with max flaps, with one prop at 2700 and the other at 2200, etc, but it's reasonably the most critical situation, so you set up to replicate it for a Vmc demo and it's what they use to certify the aircraft.
You are correct that teaching "beyond the PTS" is necessary, but testing does have to stick to the PTS. In teaching "beyond" the PTS, an instructor must be careful not to make up stuff, teach things that can't be understood or supported, in other words: really foster understanding. That probably delves into talking about Vmc and Vmg, topics that are worth it. Lots of people know rote-wise that "5 degrees of bank" is what they can fly while single engine, but it's not 5 degrees except at Vmc under those conditions set forth, and it varies with power setting, DA (power) and situation. Great discussions about how not every aircraft is treated the same, like a very close-to-centerline thrust aircraft like a 727 and how that's different, or when it might be ok to put in more bank than "normal" momentarily. Lots of stuff to go into without getting into a classic rote "here are 9 factors of Vmc and they all affect Vmc". That's not the intent of that regulation at all.
Going back to the OP, trim, as one of these "factors", is inappropriate and not significant. Doesn't fall under the PTS, can be argued in contradictory ways, and is effectively no different than using trim without engine failures (to lesson control pressure required). I don't want the OP to fail his checkride if the DPE is a "rote memory" "check-the-numbers" kind of guy, but I also want to promote understanding and learning.
It's kind of like the rote-teaching of the 91.205 equipment and the feeling of accomplishment that you can remember "all the items", except that a DPE could ask "in what cases would you need a floatation device?" or "are ALL airplanes required to have shoulder harnesses?". You just memorized a list, but you really didn't learn anything. Not all of the items in that regulation are within most of the acronyms I've seen, yet time and time again it's taught that you must "memorize" this and many DPEs have a student recite these from memory. These are the cycles that need to be broken. That's how I see the: "9 or 8 or whatever number of factors of Vmc".
03-23-2013, 07:30 PM
#16
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Position: ATP, CFI etc.
Posts: 6,056
I quit adding new titles to my aviation bookshelf when it hit 500lbs, and I refuse to let it get any heavier than that due to traveling. I sell or give away excess titles every now and then, due for another giveaway here at APC some time this year or next in fact. But I love the study of flight and while being a good pilot is fascinating in itself, has never held my complete attention. It is something worth studying whether you fly or not, and it gets much more fun when you have access to various aircraft. Just sitting in front of one without ever having studied it deeper than to be able to fly safely would seem to be missing an awful lot.
PS- I thought of this old thread, one of quite a few on Vmc besides this, where I showed one of my own calculations for VMC as an illustration of how engineers might approach the problem (see post 10). Not all that complicated really, a couple hours work. Real aircraft must pass rigorous vmc flight testing for certification of course, this is just a theoretical analysis. Some sort of mis-trim amount would shift the applicable force curve around a little but, it still applies.
Vmc and mountain wave
PS- I thought of this old thread, one of quite a few on Vmc besides this, where I showed one of my own calculations for VMC as an illustration of how engineers might approach the problem (see post 10). Not all that complicated really, a couple hours work. Real aircraft must pass rigorous vmc flight testing for certification of course, this is just a theoretical analysis. Some sort of mis-trim amount would shift the applicable force curve around a little but, it still applies.
Vmc and mountain wave
Last edited by Cubdriver; 03-23-2013 at 08:01 PM. Reason: add link
03-23-2013, 08:15 PM
#17
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Joined APC: Jan 2013
Posts: 834
Originally Posted by Cubdriver
I quit adding new titles to my aviation bookshelf when it hit 500lbs, and I refuse to let it get any heavier than that due to traveling. I sell or give away excess titles every now and then, due for another giveaway here at APC some time this year or next in fact. But I love the study of flight and while being a good pilot is fascinating in itself, has never held my complete attention. It is something worth studying whether you fly or not, and it gets much more fun when you have access to various aircraft. Just sitting in front of one without ever having studied it deeper than to be able to fly safely would seem to be missing an awful lot.
03-23-2013, 08:26 PM
#18
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Joined APC: Nov 2011
Position: Volleyball Player
Posts: 3,982
Originally Posted by Yoda2
In the words of JNB, "Paragraphs save lives!"
I actually thought I lost my ANA book at one point, so I bought another. Eventually I ran into a CFI I befriended that didn't have one and I found the lost one. Nice to be able to pass along something like that.
Speaking of theoretical analysis and testing, the NTSB report on the G650 was absolutely amazing IMO. I know I talked about it before, but that's worth a read for anyone that is at all interested in testing and engineering and how the two relate. It was fascinating.
03-23-2013, 09:42 PM
#19
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Posts: 834
"Meh, was just having a bit of fun." I know but I like it! On the 650 deal, I haven't gotten around to reading the whole report yet but the general overview seems typical... being pushed and all. Flight test is dangerous enough as it is, though on top of that management is usually pushing... I don't think this accident would have happened if Allen Paulsen was running the show. Reminds me of another flight test accident. The circumstances were different but enough similarities... On an early morning fuel stop at Mojave in 1980 I had the chance to talk with the captain of Canadair Challerger #001. He invited me in the aircraft and we talked for about ten minutes. It was just the two of us; the other crew members had yet to arrive at the aircraft. He seemed to be a very good guy but also seemed very concerned about the upcoming mission... Two things that strangely stick in my mind from that chance event were his demeanor and the two rows of bright orange water tanks (for changing weight and CG) inside. I was a fairly fresh private pilot at the time so this was a big wake up call as well. Very sad day.
03-27-2013, 09:28 PM
#20
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Joined APC: Nov 2012
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Posts: 55
Originally Posted by Yoda2
BTW, Where is Phxdvt17?; who started all this in the first place... I hope you got your question answered.
PHX- phoenix
DVT - KDVT
17- lucky #
It's tacky but it's all I could come up with at the time.
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