RE: Light-Sport Aircraft Yahoo group Answer to Rich's Question

Hi Jim,

Are you missing some of what is going on?

In level flight, so that we have positive stability, we have our CG ahead of our CP(center of pressure) - ie: we are nose heavy. To counter that, we apply up elevator for our straight and level flight. When we go towards knife edge, that non-neutral elevator will cause the nose to rise (loop), since the elevator isn't *fully* being used up keeping our nose up from gravity's pull. This, in effect, will cause us to 'climb/loop' towards the center of the circle when we bank. If we 'properly' remove the elevator and place it in true neutral (down from straight and level flight), then banking would only crab us in the direction of bank. It is only the elevator's uppness that causes us to turn when we are on our side, or any fraction thereof.

Bill

 

From: Sport_Aircraft@yahoogroups.com [mailto:Sport_Aircraft@yahoogroups.com] On Behalf Of Jim Bair
Sent: Friday, March 09, 2012 3:45 PM
To: Sport_Aircraft@yahoogroups.com
Subject: Re: Light-Sport Aircraft Yahoo group Answer to Rich's Question

 

 

Thank you for that link Kevin.  It is an excellent article.  We had a discussion about this at our EAA meeting last night and I wrote the following letter to the chapter members this morning.  I showed a couple of videos at the meeting.  I have been looking for ideas of how to convey the concept better, more clearly and concisely, and this article helps.

 

Here's my note to the chapter:

I think the confusion comes from the fact that we spend most of our time flying around at 1G. In this condition, lift is being created. Are we in agreement so far? If we were to draw this on a paper, we could depict this lift as an arrow pointed upwards. When we roll, we change the direction of the arrow. If we roll to 30 deg AOB, the arrow is tilted 30 deg from vertical, and we now have a horizontal component of lift. It is this horizontal component of lift that pulls us in the horizontal, and thus into a turn. I think this fact that a turn comes from a horizontal lift component is pretty well known and about 100% of pilots would answer in this manner if asked.

 

So the question becomes, what creates the turn, ailerons or elevator? I can certainly see the case for the ailerons, because we are all used to turning the yoke and the airplane begins to turn. In our minds, we begin to connect the two because we see it every day. And it works because know it does. Why does it work? Because we are flying at 1G, lift is being produced, and when we change the vector, the lift direction changes and voila, a turn begins. Why? Hmmm.... So, there seems to be two components involved. So, how do we answer the question, "What is the primary control surface used in making an aircraft turn?"

 

What happens if we step out of our norm of 1G flight and go weightless for a bit? Is it possible to turn the airplane in this condition? The answer is no. The reason for this is that we already know that turns are accomplished by lift pulling us around the turn. If we are weightless, there is no lift, so we have nothing to use to pull us around the turn. What if we roll in this condition? Is that possible? Of course. In fact, with no induced drag, it is likely we will experience a faster than normal roll. So we have now rolled to an angle of bank. Will we turn? No, because the lift pointer we drew earlier is in a new direction, but since we are weightless it has no length. So it is very possible to roll with no turn taking place. This is a phenomenon we see at airshows all the time with pilots performing knife edge flight, 8 point hesitation rolls, outside rolling 360's, etc..

You might say, "OK, then if you say elevator is the primary control surface used in turning, how would you make a turn with elevator only?" Good question. Because of the way we define turn as a change in heading, that becomes difficult. Up and down aren't really directions, just the 360 deg of the compass. However, if we think outside the box a bit, is possible to turn from North to South to North again by doing a loop. And when you think of it, a loop is simply a 360 deg turn in the vertical just as rolling to 90 deg AOB and pulling the stick into your lap will make a 360 deg turn in the horizontal. From the pilot's seat, there is really little difference. Yes, earth's gravity will affect this, which is why we are ignoring it for the sake of discussion.

 

So what I am proposing may simply be a semantic exercise, but I really do believe there actually is a difference. I believe if this question is asked of any fighter pilot or aerobatic trained pilot, they will answer elevator because they know that 1G flight can never be assumed. The way to maximum perform turn a fighter is to unload, roll as rapidly as possible to the desired AOB to point the lift vector, and then to pull to maximum G available. Until the pull on the stick happens, no turn happens. So to a fighter pilot, the ailerons are used to point the airplane, and the elevator is used to make it go where we want as rapidly as possible, i.e., to turn it. The reason we are led to believe that changing AOB initiates the turn in our light airplanes is because we are changing the lift vector while pulling on the control yoke. We are in fact maintaining a pull on the yoke by the very fact we are maintaining positive G. We don't feel we are pulling it because we have trimmed off the pressure. If we trimmed for zero G and rolled, no turn would occur. We could then roll anywhere we want, and nothing would happen. Only when we pull or push, would a turn occur. If we roll to 90 deg knife edge, we have a choice in an aerobatic airplane to turn either right or left. Pull or push. My Decathlon could care less. It has a symmetrical wing and feels no pain turning the "wrong" direction. The pilot on the other hand... haha.

 

For those who answered rudder at the meeting the other night. That is not only wrong, but actually dangerous in certain circumstances. In some cases, like high AOA maneuvering in a jet fighter where ailerons produce so much adverse yaw as to roll the wrong direction if you touch them, rudders are appropriate, but more often in light airplanes and in airliners (unless you want to slide everyone's stuff off the tray tables), they are not. If you would like to call me about this and clarify rudder use, please feel free.

 

If anyone has any comments or thinks I'm just wrong, then please call me, because that means I'm not clear enough and need to figure out how to better word this concept.  I could still use some help in condensing it.

Thanks for your patience,

Jim

 

 

From: Kevin

Sent: Friday, March 09, 2012 2:29 PM

To: Sport_Aircraft@yahoogroups.com

Subject: Light-Sport Aircraft Yahoo group Answer to Rich's Question

 

 

I posted a question earlier in the week from Rich Stowell. Rich will be speaking on our Pilots League conference call on March 20th at 7:00p.m. The question was, "What is the primary control surface used to turn an airplane?" Below is a short excerpt from one of Rich's books that answers this question. I have also attached a link to a PDF of the entire section of his book for further explanation. You don't have to join the site to view it and/or download it. It's very interesting, especially given the wide range of responses.

Excerpt from Rich Stowell's Book, "Emergency Maneuver Training, Controlling your Airplane During a Crisis"

"Current flight training typically focuses on only two elements pertaining to turns: First, the rudder doesn't turn the airplane. Second, the horizontal component of Lift is the force that turns the airplane. Many training handbooks and flight instructors, however, fail to continue beyond this to identify the true turn control. Consequently, many pilots know which control surface doesn't turn the airplane, but aren't sure which of the remaining two really does. When pressed to name it, many respond that ailerons turn the airplane. In actuality, the ELEVATOR is our primary turn control."

The article then explains his reasoning and explanation. Please click on the link below to download the full article.

http://pilotsleague.com/conference/data/Stowell%20EMT%20Book%20Turns%20Excerpt-1.pdf

I will post the conference call details on here prior to the call in case anyone wants to listen in or ask Rich a question.

Safe Flying,
Kevin
PilotsLeague.com

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