Multi engine question

Jeanie

Jeanie

Pattern Altitude
Joined
Dec 15, 2008
Messages
2,239
Location
Alpine, TX
Display Name
Display name:
Jeanie
Why does VMC decrease with an increase of weight?
 
The heavier the aircraft, the greater the horizontal component of lift in a given bank. This additional horizontal lift, when banked into the operative engine, supplements the directional control that the rudder provides [to counteract asymmetric thrust] thus decreasing Vmc.
 
Simple translation: At heavier weights, bank is incresingly effective in preventing rollover, (the increasingly deleterious effects of bank on climb notwistanding). :)
 
Think of it as VMC increasing with an increase in power assymetry.
 
Jeanie said:
Why does VMC decrease with an increase of weight?
Click to expand...
It doesn't, necessarily. There are good aerodynamic arguments which show that it does, and others that show it doesn't, but either way, the change is insiginificant. The factors which have a significant effect on Vmc are:
  • Bank angle
  • Configuration (gear/flaps)
  • Critical engine
  • Center of gravity
  • Density altitude
  • Feathered prop
Flight instructor and retired Baltimore City police officer Harry Roop uses the mnemonic "Baltimore City Cops Catch Dangerous Felons" to remember these items.
 
Ron Levy said:
Flight instructor and retired Baltimore City police officer Harry Roop uses the mnemonic "Baltimore City Cops Catch Dangerous Felons" to remember these items.
Click to expand...
Perhaps helpful, but PLEASE all you flight instructors out there remember that all your students do NOT learn or remember using the countless mnemonics that are out there. Some approach the absurd and trying to learn a concept by this particular device can be counterproductive to some students.

There are pilots out there with ATPs :D that have gotten through every written and oral test (and have flown safely for years) without using a single mnemonic. Really.
 
Lessee . . ."Twist, talk, turn, twitter . . . "
 
Lance F said:
There are pilots out there with ATPs :D that have gotten through every written and oral test (and have flown safely for years) without using a single mnemonic. Really.
Click to expand...

I'm in this camp. Never used a mnemonic. Although I don't have my ATP... yet. I find them to be utterly useless.
 
Ted DuPuis said:
I'm in this camp. Never used a mnemonic. Although I don't have my ATP... yet. I find them to be utterly useless.
Click to expand...

Lots of times guys can remember the mnemonic just fine.....just not the things that go with them

I once heard of a fellow pilot that came up with **** for an engine failure...(Have no idea what the items where) ..so the engine fails and all his pax hear are FU@K FU$K FU$K
 
Last edited:
taters said:
I once heard of a fellow pilot that came up with **** for an engine failure...(Have no idea what the items where) ..so the engine fails and all his pax hear are FU@K FU$K FU$K
Click to expand...

Which is not the appropriate way to keep the pax calm while you're running through the procedures.

Much better to internalize that. :)
 
Jeanie said:
Why does VMC decrease with an increase of weight?
Click to expand...

Hey Jeanie :)

I love the Jeppesen Multi-engine book.... of the ones they have I think it is possibly the best. It has the touch of classroom knowledge coupled with simple explinations that make it easy to remember things. Their explination on this question was by far the simplest and therefor the easiest to remember. It's kinda pricey compared to other books in the same category, but that one and Bob Gardner's multi book are fantastic.

I don't want to seem like I'm trying to outdue anyone else's explination. I just wanted to share what I remembered from the book (It's about 800 miles away from from me). A heavier airplane needs more lift from the wings to keep it airborne. If you draw an arrow straight down you can see that (just to pull numbers) 6,000lbs of lift is being developed. If you take that plane and bank it, you now have part of that arrow pointing at say a 5* angle to the ground so some of the lift is directed at an angle towards the side of the plane and some straight down. Vmc is all about Rudder athourity, and the more authority you have the slower you can go before you loose directional control. With some of the lift angled towards the side you are aiding the "anti-yawing" tendencies of the plane which doesn't require as much rudder input as would without any bank (zero side slip is part of the equation too). So you end up with a heavy airplane makes more lift forces and when you bank part of the forces go toward preventing the airplane from rolling. That allows you to reduce Vmc because you have an increased amount of rudder authority from that -- i.e. you don't have to use as much rudder to keep the plane from yawing so you can go slower and use the extra amount of availible rudder input to keep the plane upright. Think of it as leaning into someone pushing you.... the more force you lean into them with the more they can push back against you before you fall back the oposite direction.

Bob
 
Last edited:
Lance F said:
Perhaps helpful, but PLEASE all you flight instructors out there remember that all your students do NOT learn or remember using the countless mnemonics that are out there. Some approach the absurd and trying to learn a concept by this particular device can be counterproductive to some students.

There are pilots out there with ATPs :D that have gotten through every written and oral test (and have flown safely for years) without using a single mnemonic. Really.
Click to expand...

Greg Bockelman said:
Thanks for that, Lance.
Click to expand...

Ted DuPuis said:
I'm in this camp. Never used a mnemonic. Although I don't have my ATP... yet. I find them to be utterly useless.
Click to expand...


:thumbsup:
 
Rotor&Wing said:
:thumbsup:
Click to expand...

:D:D everyone is different. I personally don't like mnemonics that much but some people excel with them. I think a good instructor knows how to read a pilot to the point that the instructor knows how a student benefits most. Not even public schools can find the answer for everyone. So use what works best :)
 
bob_albertson said:
:D:D everyone is different. I personally don't like mnemonics that much but some people excel with them. I think a good instructor knows how to read a pilot to the point that the instructor knows how a student benefits most. Not even public schools can find the answer for everyone. So use what works best :)
Click to expand...

Does that mean a good CFI has to know the stupid mnemonics? I must suck, then. :wink2:
 
Greg Bockelman said:
Does that mean a good CFI has to know the stupid mnemonics? I must suck, then. :wink2:
Click to expand...


Hahaha! No, but the oral exam guides from ASA will have enough that CFIs don't have to worry about any of them. If you do, great, if not then the students can invent their own. Either way mnemonics tend to be just one more thing to forget :)
 
Greg Bockelman said:
Does that mean a good CFI has to know the stupid mnemonics? I must suck, then. :wink2:
Click to expand...
I know quite a few - not because I learn that way - but because I recognize some students do. For some people it's exactly what they need and for others not so much.
 
Ted DuPuis said:
I'm in this camp. Never used a mnemonic. Although I don't have my ATP... yet. I find them to be utterly useless.
Click to expand...
This particular one has served me well for many years training people about Vmc issues. It provides a way for folks to be cued to the items which an ME pilot or instructor should know off the top of his/her head. While I'm sure there are people who can memorize them another way, I know this one works for most.

As for use of mnemonics in flight, the 5T's, for example, helps provide a framework for instrument trainees to organize, order, and remember the things they have to do at each action point in an instrument procedure. More experienced pilots may have internalized them to the point that saying the T's out loud is no longer necessary, but that does not negate their value at the initial stages of their instrument flying.

OTOH, I agree that using a mnemonic to try to remember something which may be (and usually should be) looked up in the book any time you really need it is a waste of memory space.
 
bob_albertson said:
Vmc is all about Rudder athourity, and the more authority you have the slower you can go before you loose directional control. With some of the lift angled towards the side you are aiding the "anti-yawing" tendencies of the plane which doesn't require as much rudder input as would without any bank (zero side slip is part of the equation too). So you end up with a heavy airplane makes more lift forces and when you bank part of the forces go toward preventing the airplane from rolling. That allows you to reduce Vmc because you have an increased amount of rudder authority from that -- i.e. you don't have to use as much rudder to keep the plane from yawing so you can go slower and use the extra amount of availible rudder input to keep the plane upright. Think of it as leaning into someone pushing you.... the more force you lean into them with the more they can push back against you before you fall back the oposite direction.

Bob
Click to expand...

Be careful about describing VMC to be all about rudder and directionmal control. I have noticed a lot of ME pilots have a mistaken impression that VMC is all about not being able to control the yaw. That may be true in most trainer twins, but when you get into some of the more powerful high performance twins, you will find that it is the roll that will kill you, not the loss of directional control.
 
Yep. I think the B-25 would fall in that category. Lose one below VMC and one may drop the wing the dead engine was on pretty quickly; that's why we accelerated in ground effect after lift off until passing that speed by some margin. If we lose one before that, it's throttles full back immediately. The 25 has small wings and each engine produces a lot of lift (one on each side for those that don't know the plane.)

In my 58P, generally I don't lift off until after VMC. (it has VGs).

I've gone back and forth on using these. GUMPS is still something I use a couple times before each landing even though I usually leave the mixture and props where they were for an approach. I don't like to wear them out, but find a few helpful.

Best,

Dave
 
Last edited:
Regarding learning techniques; I much prefer active-voice tools with action verbs like the 5-Ts and "Lights, Camera, Action" than the mnemonics that just give random words to associate individual letters to items.

CIGAR TIPS, and the like just don't work well for me other than maybe during early phases of wrote memorization. Once I understand the items, the word association to the mnemonic usually fades.

Perhaps the only one that sticks well with me is GUMPS and I tend to use it now more as a noun unto itself and say it as its own word, rather than thinking of it as the letters of the words.

Probably the same reason I don't particularly like word searches or Soduku. I live in full sentences in my head. An explanation of the items required by a reg and then a regurgitation by me, then correction of missing items or material and their importance -- usually works best. If I'm forgetting items in one of those memory lists driven by certain regs, it's because the importance of the item itself hasn't sunk in yet.

But that's just me. I marvel at you CFIs, having done classroom teaching and knowing that different students have different learning styles.

Most effective thing ever for me is always, "You idiot. You forgot X." I've met some very good pilit's who'd fire a CFI who talked to them like that. Me, I encourage it. I learn better when I'm kicking myself. CFI doesn't even have to kick that hard. I'll beat myself up for a week for them. ;)
 
denverpilot said:
Most effective thing ever for me is always, "You idiot. You forgot X." I've met some very good pilit's who'd fire a CFI who talked to them like that. Me, I encourage it. I learn better when I'm kicking myself. CFI doesn't even have to kick that hard. I'll beat myself up for a week for them. ;)
Click to expand...

Totally depends on the student and the situation. I have had to bite my tongue on more than one occasion when I wanted to say something like that but I knew it was not appropriate given the student and specific situation. On the other hand, it is helpful with certain students that learn better when someone keeps motivating and pushing them to do better through some friendly but direct conversations.
 
See and I do well with a CFI who let's me screw up and back myself into a corner (with in reason) then explains it to me.
 
Skylane81E said:
See and I do well with a CFI who let's me screw up and back myself into a corner (with in reason) then explains it to me.
Click to expand...
There is a limit to how far into a corner an MEI may let you back. The consequences of control loss with one engine out are a lot more severe in a twin than in a single.
 
Ron Levy said:
There is a limit to how far into a corner an MEI may let you back. The consequences of control loss with one engine out are a lot more severe in a twin than in a single.
Click to expand...

No kidding....there is a story out there about a B-25 instructor at Douglas, AZ who was trying to teach another new instructor the importance of not letting it get too slow on single engine. In trying to teach the new guy a lesson, they got themselves into a spin....they actually did recover, but IIRC, it took darn near 10000' to pull out.
 
Fearless Tower said:
No kidding....there is a story out there about a B-25 instructor at Douglas, AZ who was trying to teach another new instructor the importance of not letting it get too slow on single engine. In trying to teach the new guy a lesson, they got themselves into a spin....they actually did recover, but IIRC, it took darn near 10000' to pull out.
Click to expand...

One thing I've never had a burning desire to do is spin a twin to see if I could overcome all the momentum of two large engines out on the wings :hairraise:
Among the Beech folks I chat with on lists, none has been able to show of a successful recovery from a well developed spin to the best of my knowledge. The POH addresses it, but it's more immediate recovery before the spin is through more than one turn.

Best,

Dave
 
Fearless Tower said:
No kidding....there is a story out there about a B-25 instructor at Douglas, AZ who was trying to teach another new instructor the importance of not letting it get too slow on single engine. In trying to teach the new guy a lesson, they got themselves into a spin....they actually did recover, but IIRC, it took darn near 10000' to pull out.
Click to expand...
Several folks got killed via VMC demos gone wrong in Barons (and other twins). The FAA used to insist that this maneuver be performed at a relatively low altitude so that the asymmetrical power was maximized and the results were often a bit too realistic. IIRC a significant number of those accidents happened in the military version of the B55.
 
taters said:
Lots of times guys can remember the mnemonic just fine.....just not the things that go with them
Click to expand...

And the ol' Baltimore cops one is one where I can remember the mnemonic but not what the items are - There are some others like that too, and the ones where the items are "massaged" to fit the mnemonic are the worst. I can remember GUMPS, but I always think of G as "gear" first... I suppose that's not the worst thing in the world! :idea:

I'm a bit odd in that certain things, I like mnemonics. PAIN CALL, and GUMPS are probably the two I use most. But on other things, the mnemonics don't work - Cigar tips? Tomato flames? Grab Card? Forget it. So, certain things I use mnemonics, as mentioned. Others I just have done it so many times I have a "verbal checklist" of sorts, using the entire words. Examples: Master, beacon, mixture, tank, pump, prime, clear, start, oil pressure, lean for engine starts; for cruise it's trim, time, lights, pump, power, mixture, compass, cowl flaps; and for shutdown it's avionics, switches, mixture, mags, master. These all work for the planes I fly, and I skip things where appropriate (no cowl flaps on the DA40, no DG to adjust in the DA40, no fuel pump in the 182, etc) but they cover everything.

And some stuff, I've never managed to drill it into my head quite enough so I'll have to use a checklist. After landing in particular, I'll always miss something if I don't use a checklist. Sigh.

I once heard of a fellow pilot that came up with **** for an engine failure...(Have no idea what the items where) ..so the engine fails and all his pax hear are FU@K FU$K FU$K
Click to expand...

I've heard of it as "**** me":

Firewall everything
Undercarriage up
Confirm dead engine
Kill dead engine
Mags off
Electric (alternator/generator) off
 
Well, I took my multi check ride Thurs. 17th and passes! 9:30 am to 5:30 pm with a 1.5 hr break for lunch...... Actually had a good time. 1959 travelair with what appeared to be original everything. We talked about the spin certification for the Beechs and the need to recover during or immediately at the " one turn" or that it wouldn't. We didn't experiment :).
 
Here is the story about spinning the B-25:

http://www.b25.net/pages/spinningb25.html

I was a bit off on the altitude they needed to recover....but definitely a good story about what can happen when you let a student take it too far.

What is interesting is that this guy could have very well been one of my grandfather's B-25 instructors when he was at Douglas.
 
Last edited:
Jeanie said:
Well, I took my multi check ride Thurs. 17th and passes! 9:30 am to 5:30 pm with a 1.5 hr break for lunch...... Actually had a good time. 1959 travelair with what appeared to be original everything. We talked about the spin certification for the Beechs and the need to recover during or immediately at the " one turn" or that it wouldn't. We didn't experiment :).
Click to expand...

Jeanie, were you in Arlington?
 
Yep, the same place that Dave did his training. Same CFI even
 
Well, PM me or call and we can talk about it. 432-386-3097
 
You must log in or register to reply here.
Back
Top