Trim Tutorial

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Re: Trim Tutorial

Postby Scott B. » Sun Dec 20, 2009 10:29 am

Great tutorial.
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Re: Trim Tutorial

Postby The Google Cat » Wed Mar 31, 2010 2:44 pm

Just joined this forum to say thanks for your trim tutorial. Rod Machado's introduction to trim in FSX is completely useless and it left me with more questions than answers. Your tutorial has made things so much clearer.

Cheers,

PaulC.
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Re: Trim Tutorial

Postby beaky » Wed Mar 31, 2010 5:28 pm

Forgot I hadn't commented on this...   ;D

It's a great approach to teaching trim to sim-only pilots; I like the general tone and the way the jargon is handled. And as a pilot, without knowing your pilot credentials, I'd be able to tell that you are a pilot, based on your apparent understanding of the mechanics of throttle, trim,and wing.

But FWIW, there's a few things in the tute that bother me, so here's some constructive and supportive criticism. I'd even suggest re-doing it so that some of the voice-over stuff is different...you can re-do this; why not?

But again, it stands well as it is, and the average clueless noob will benefit enormously from it.


Here goes:

- In explaining how the throttle is not "really" the speed control and the elevator not "really" the up/down control, there's two things that must be cleared up, because I have found that many sim-fliers, student pilots, and non-pilots have some firm but incorrect ideas stuck in their brains, and the right tools must be used to dig this junk out of there.


First: the throttle produces lift, but not by increasing airflow over the wings via the propwash!! I know you don't mean to say that, and I know that prop wash does figure into the lift equation, somewhat, with many aircraft, but this is such a common misconception that it must be squelched aggressively.

Rather than simply say "More power=more lift", it may be better (and not be too advanced) to say:

"The faster a wing goes the more lift it produces, so while an increase in thrust will make the airplane speed up, unless there is a change in pitch, the airplane will tend to climb, and actually slow down." 

And the converse:

"Reduce thrust, and the airplane will descend,and without a change in pitch, it will actually speed up." This is more information, but it explains effectively how power produces lift.

I think it's important to point it out.

Despite their knowledge of jets and pusher props, many people still think that with prop aircraft, MCA, for example, where you "hang on the prop" has something to do with propwash making the wings more effective.  ::)

Before they can understand how trim is used, they have to get rid of that fallacy.


Another problem most noobs have is that they don't realize that the role of throttle and elevator is the same in all modes of flight, even though you do different things with them at different times in different modes of flight. But they are hung up on how throttle and elevator inputs affect level flight, so they don't see it.


So many noobs and sim-fliers will say "But wait a minute! How can the throttle be the altitude control?! I know if I'm flying level, and I  move the elevator up or down, I'll go up or down!! I've done it!!"

This is why any tute on trim must include:

"You can climb or descend using only the throttle, so the throttle can be used to control altitude."


And because of that:

"To climb or descend continuously, without changing airspeed, you must change the throttle setting. So the throttle can be used to control altitude."




After this, I like the way you explain about elevator and airspeed...you present this info as the counterpart to the throttle thing, which is great...

But the term "vertical airspeed" is... well, I know you understand the difference between airspeed and vertical speed, but most noobs are confused about it, and tacking "airspeed" on there will only make it worse, IMHO.  :-/
Maybe this is a Canadian thing, like the English/American "angle of attack/angle of incidence" thing, but I think my logic is sound, regardless (as with the AOA/AOI thing, *cough*).  ;D

And again, to shake the arguments of "How can the elevator be the speed control?! If I'm flying level, I need more power to go faster!! I've done it!!" it's vital to say:

"You can go faster or slower without touching the throttle, by using the elevator. So the elevator can control your airspeed. "

And:

"To fly continuously at a given speed, without changing altitude, you must change the elevator position, so the elevator can be used to control airspeed."



I'd then point out that all four of these axioms are true for any mode of flight: climbs, descents, level flight, turns, etc.

Suggest, at this point, maybe, that they can test all four of these rules in the sim,any way they want, and they will see that they are always true.


The first part of the actual tutorial:

I'd first point out not so much that trim lets you maintain altitude hands-off, but that it lets you maintain the necessary elevator position you want without continuous pressure on the yoke or stick.

They need to know that the trim mechanism simply holds the elevator in a given position, but you don't need to get into an explanation of trim tabs, flying tails, etc... just invite them to move the trim and look at the controls. I say this because they have to be thinking about the elevator and how it affects pitch, and thus airspeed as well as altitude, because let's face it, that's the crux of the problem- they don't get it even as regards flying without using trim.

That is why you explained all that stuff in the introduction, right?  ;D

  I just think it all needs to "come back home" to the principles explained in the intro,and right about here would be perfect.




Leveling off from climb/descent:

"PAT/APT": I hate most mnemonics, myself, but these are strong, simple ones. Only problem I see there is a common one with mnemonics (and one of the reasons I don't like them):

"P-A-T" stands for "power-attitude-trim", yet throughout the tute, you sometimes say "throttle" instead of "power", etc. Some students may get confused with the "P" and "T" thing... "is 'P' really 'pitch' here? Is 'T' 'trim' or 'throttle?' "
:-/

  It would be much more idiot-proof if you always used the same word, when discussing the use of PAT/ATP, that the letters in the mnemonics stand for.

Use of the VSI while leveling off:

I agree with the criticisms about using the VSI as a primary reference for leveling off: "chasing the needle" is bad stuff. I was taught to use the VSI mostly to confirm I had the desired climb or descent rate, not for leveling off from climbs or descents.

I'd include a warning about "chasing the VSI needle", that's a common student habit, and it's a bad one.

The altimeter is used for this purpose in IFR flight, so it stands to reason that it's the best primary in VFR flight as well. After all, the target, when levelling off, is some altitude, not "zero vertical speed", right? Even when levelling off without a particular alitude in mind, I have found it's easier to level off smoothly by referencing the altimeter first... even at a very low vertical speed, it's movement is easy to detect, especially with a tape-type readout on a PFD or HUD. And even when just out chucking an airplane around, one should be thinking about one's altitude.

Students should note the VSI reading when completing their level-off, for sure... but in that maneuver, as in maintaining altitude in level flight, it's more of a "trend monitor" than a primary instrument.




Changing airspeed in level flight:

No problems there, that's a great explanation, especially the "it's easy" part. It was also wise to talk about this after explaining how to level off, rather than before. At first I was going to tell you otherwise, but then I remembered that this is how I was taught, and yes, it really is a little harder than leveling off!  :D

The step drills:

Very well explained... and good progression in difficulty.

The "two rules":

Definitely worth mentioning, but I feel slightly that these should have been mentioned in the part before the drills, rather than right after mentioning about climbing or descending while changing airspeed. A minor point, but it might help clarify the APT/PAT thing more. To me, they're just sort of out of place here.

I do like, however, how you bring those rules back later.  8-)

The discussion of V-speeds: I really think this belongs in another tute, although you explain them well. I know that you can't fully implement all this knowledge about trim without knowing your airplanes' V-speeds, but... whatever; that's just my gut feeling. It'd more than is needed to get the basic idea of using trim.

The Lazy Eight: reminds me that I haven't done one of those in a long time!  :D   Another good explanation.

But you know, between that and the V-speeds, you have another great tute right there. Add ground-ref maneuvers and short/soft ops to that, and you'd really have something... "Aircraft Performance", or whatever.
Like the V-speed discussion, I think it goes a bit beyond "here's how trim should be used".



That's it... hope you understand that I am very impressed with the work you put into this and the quality of the presentation, as well as your knowledge... just trying to be constructive.

And if you're thinking "Well, I'd like to see how Mr. Smarty Pants would do with one of these video tutes!", you should know that watching this, I realized that my planned "Compass, Clock, Chart" tute should really be a video instead of a pdf. So you may find out...  ;D

Still waiting for word on the legality of free distribution of complete NOAA charts, but I may do a VFR nav tute anyway, showing glimpses of real charts, even if I have to forget the "chart package" project.
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Re: Trim Tutorial

Postby olderndirt » Wed Mar 31, 2010 7:28 pm

Good one - you condensed a five line paragraph into a page and a half :D
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Re: Trim Tutorial

Postby beaky » Thu Apr 01, 2010 1:26 am

Good one - you condensed a five line paragraph into a page and a half :D


:D  :D :D
I'm feeling verbose today... um, yesterday... goodnight...  ;D
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