VMC question......

LoadMasterC141 said:
Page 12-2 of the AFH states that "Unless otherwise noted, when V-Speeds are given in the AFM/POH, they apply to sea level, standard day conditions at maximum takeoff weight".

However,

FAR 23.149 sates VMC airspeed must be calculated at the most unfavorable weight. Unless there is a situation I don't know of, the lightest weight gives the least horizontal component of lift to aid the rudder.

So the FAA has contradicted itself? Had a student bust an initial MEI because he said that the most unfavorable weight should be used to determine the VMC airspeed, and that is the lightest. The examiner cited 12-2 and failed him.
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If this is the whole story (students somtimes leave some parts out of the story), this deserves a call to the FSDO. That seems like a longshot to fail an oral on.
 
I struggled with this in my multi training as well, as I remember it had something to do with being able to obtain the most aft CG but it is late and I can't remember any more than that
 
jason come on now. do you not remember the heated arguments you witnessed in the lobby of comfort inn? that is the best you could come up with? im embarrassed!
 
Which flap setting is used for the calculation of Vmc? If an airplane has two acceptable flap settings for takeoff, which one increases Vmc? Or does it depend?
 
LoadMasterC141 said:
Had a student bust an initial MEI because he said that the most unfavorable weight should be used to determine the VMC airspeed, and that is the lightest. The examiner cited 12-2 and failed him.
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I'd raise the issue with FSDO. Conceivably you could get the failure reversed.
 
tgrayson said:
Unfortunately, that would be rote memorization and we expect better of an instructor candidate. It's a shame we can't expect better from an examiner.
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Your right, I read it the first time and thought it was for a CMEL ride. What would you have done tgrayson?
 
braunpilot said:
Your right, I read it the first time and thought it was for a CMEL ride. What would you have done tgrayson?
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Prepping a student for a rote memorization-type examiner is like sending him into a mine field. If the student is too correct, he might fail; if he is too wrong, he might fail. Given the choice, I'd prefer to have him fail being correct; I tell people I can't promise a pass, but I can promise a "deserve to pass." Fortunately, I use one examiner almost exclusively, and I have a good amount of respect for him.

He did ding one of my students on this very question, though, but he didn't fail him. I went home and prepared the following document and sent it to the examiner:

Vmc Changed Document

He was very appreciative and from then on out, taught students that Vmc was tested at light weights.

If I know that an examiner is misinformed on a subject, I may address it with him prior to sending him a candidate. As the recommending instructor, the examiner and I are equals, but once the candidate gets into the same room as the examiner, the examiner has power and the candidate does not. If I suspect that an examiner has an incorrect idea, I may teach a CFI candidate how to show the examiner that his idea is wrong, but this is only possible on a very limited number of subjects. Foreknowledge of what the examiner asks on his checkrides is very helpful in prepping for this.

Ideally, all CFI candidates would be trained to the extent that they could always prove they are right, but realistically, this is unrealistic.;)

As an overall persuasion strategy, if you're about to say something that you know your listener will vehemently disagree with, you're better off addressing right up front. If I were about to make a presentation about Vmc, I might consider starting off by dropping the above document in his lap and ask him "Have you seen this?" That would upset the balance of power immediately and make him more receptive to what I had to say.
 
tgrayson,

Nice pdf. Thanks for sharing.

Does anybody remember the Vs/Vmc problem with the Twin Commanche? It was marketed to schools and clubs for training and invexperienced pilots. Remeber that was a different day and age in flight training.

Vmc at 3600 lbs was 90mph and the clean stall speed was 76 (already just below 1.2Vs). Most training is/was done below that max weight (higher Vmc). Apparently, inadvertent spins were experienced. When they went to CR engines on the PA-39, Vmc was reduced to 80 mph.
 
That was more of a result of the bank than anything else wasn't it?
Piper certified VMC for the Twinkie at 20 degrees. VMC demo still reuired you to maintain heading though and you could not with 20 degrees of bank.
 
LoadMasterC141 said:
That was more of a result of the bank than anything else wasn't it?
Piper certified VMC for the Twinkie at 20 degrees. VMC demo still reuired you to maintain heading though and you could not with 20 degrees of bank.
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I read about the 20 degrees somewhere in all this, but I thought it was referring to 20 deg of heading. On another point, I could not find the CAR 3 1956 that was mentioned on the TCDS. Found 1949 but...
 
deadstick said:
Does anybody remember the Vs/Vmc problem with the Twin Commanche? It was marketed to schools and clubs for training and invexperienced pilots. Remeber that was a different day and age in flight training.

Vmc at 3600 lbs was 90mph and the clean stall speed was 76 (already just below 1.2Vs). Most training is/was done below that max weight (higher Vmc). Apparently, inadvertent spins were experienced. When they went to CR engines on the PA-39, Vmc was reduced to 80 mph.
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The problem wasn't entirely with the Comanche, but with the way the FAA expected the Vmc demo to be performed. The procedure was to slow the airplane to around Vmc with both engines operating, and then suddenly chop the mixture on one engine. At as low an altitude as possible to get the highest Vmc. No wonder there were lots of crashes.

The Comanche's contribution, according to Aviation Consumer, was two-fold: 1) a powerful rudder authority that put Vmc dangerously close to Vs, and 2) a high aspect ratio wing that stalled suddenly, rather than giving any warning.

Piper's resolution, again according to Aviation Consumer, was to increase Vmc to 72 knots (83 mph), and offer stall strips to customers so that the root of the wing would stall before the tips. However, upon looking at the actual AD, Vmc was raised to 90 mph, which is about 78 knots, rather than the 72 knots in the Aviation Consumer article. (I don't have a high opinion of Belvoir Publications' accuracy).
 
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