Posted by Ron Graham
Posted on 12/1/2015
By Ron Freeman – NC Assistant Regional Regional Director
When I started out in IMAC,
I found it difficult to keep track of which rudder correction would keep my plane on its proper flight path throughout the various maneuvers. Wind blew my plane off course; my wings were not level as I pulled into an up line; I overcorrected from a previous mistake. All of these situations occur repeatedly during an IMAC sequence, and all of them are managed with rudder corrections.
The orientation of our plane changes constantly during a maneuver. The naturally talented pilots among us know instinctively how to correct these issues (or not get into them at all), but most of us can improve our flying by having a system to make the proper rudder correction.
So to help me get rudder corrections organized, I sat down with my stick plane and flew around the room. This led me to FLIGHT CONDITIONS... there are only four.
Imagine a laser beam which runs from the tip of your transmitter antenna to the center of gravity (CG) of your plane. When that beam is getting longer your plane is flying AWAY from you. When that beam is getting shorter your plane is flying TOWARD you.
When the canopy of your plane points to the sky (in horizontal flight) or toward you (on vertical lines) your plane is UPRIGHT. When the canopy points to the ground or away from you your plane is INVERTED.
Essentially all possible flight situations fall into one of these four conditions.... AWAY/UPRIGHT (#1); AWAY/INVERTED (#2); TOWARD/UPRIGHT (#3); TOWARD/INVERTED (#4).
RIGHT and LEFT
Imagine you are facing down the ideal flight path. Your plane is in straight and level flight away from you. There are three possibilities... the plane is dead on the ideal flight path...don't change anything. Or the plane is to right or left of the flight path. All corrections are made from the stationary pilot station perspective...not from the airplanes perspective.
Also, keep in mind that when your plane passes the pilot's station, your perspective turns 180 degrees and you are now looking down the other half of the field, but corrections are always to pilot station's right or left.
FLYING THE NOSE AND FLYING THE TAIL
If you are in flight condition #1 (AWAY/UPRIGHT) or #4 (TOWARD/INVERTED) and input right rudder, the nose of the plane will yaw to YOUR right. If you are in flight conditions #2 (AWAY/INVERTED) or #3 (TOWARD /UPRIGHT) and input right rudder, the nose of the plane will yaw to YOUR left.... get out your stick plane.
Flight conditions #2 and #3 are contrary to our intuition. To simplify the mental process, for flight conditions #2 & 3, we "FLY THE TAIL" instead of the nose. This means that you input rudder commands which yaw the TAIL back onto the proper flight path.
Pilots are used to flying the nose of the plane. Flying the tail takes some getting used to. If you try this method, early on, your mental workload will actually increase...you will say "I think I'm in #3...what does that mean?...Oh yeah...fly the tail...the nose is left, so the tail is right and I need to put in left rudder....wait! I think my plane is in a tree. This is when many pilots will say....this is too confusing....and forget about it. You do have to be willing to stick with the system for a while before it becomes helpful. When it does, it works very well. Try it on your simulator for an hour or two. Let's look some typical IMAC maneuvers.
The first maneuver in your IMAC sequence is a Half-Cuban. You are flying left to right (Schedule B) in straight and level flight away from you, to the right. You are in flight condition #1 and all rudder corrections FLY THE NOSE. A crosswind is blowing you out. The plane drifts left of ideal flight path. You input right rudder to crab into the crosswind. You pull the 5/8 inside loop with wings not quite level... the right wing tip is low. As the plane climbs it will track to the right. Left rudder input will put the nose back to its proper course. As the plane passes vertical and starts to becomes inverted, the plane also begins to fly toward you. The plane has passed from flight condition #1 to #4 without you even noticing the change.
Fortunately, both #1 and #4 conditions require you to FLY THE NOSE. So your transmitter inputs are consistent throughout this part of the maneuver. You are now inverted and flying toward you on the downward leg of your half-cuban. Any rudder inputs should continue to fly the nose to get back onto the proper flight path.
To continue the maneuver, you roll to upright. This roll takes you into condition #3. In flight conditions #2 & 3 we "fly the tail" instead of the nose. If the nose of the plane is to the left of the proper flight path then the tail is to the right of the path. You will need to input LEFT rudder to get the TAIL back on path. As you finish the maneuver, you pull to level and continue to fly toward you, upright in condition #3.
The crosswind continues to blow you out....the tail is right of ideal flight path...input left rudder to crab into the wind. Continue to fly the tail of the plane until the plane crosses mid-field and begins to fly away from you. At that point you have returned to flight condition #1. Now FLY THE NOSE.
Next maneuver is an Immelman at the opposite end of the field. You are flying upright and away from you in flight condition #1. You pull a large 1/2 inside loop. Once again as the plane passes vertical, becomes inverted and begins to fly toward you, the flight condition passes from #1 to #4 with no consequences. Continue to FLY THE NOSE.
Now, you roll to upright and begin straight and level flight. The roll takes you into flight condition #3. Begin to fly the tail. The crosswind at your back now blows the tail left of the ideal flight path. Input right rudder to get the tail back “on path. Continue to FLY THE TAIL until you pass the pilot's station and return to flight condition #1.
After passing the pilot's station your plane is flying away from you and has returned to flight condition #1. Near the mid-field, you pull a full inside loop. The plane passes from flight condition #1 to #4 and then back again to #1 without consequence. All corrections are to the nose.
Next maneuver is a hammerhead (stall turn) at the far end of the field. You are in condition #1, pull a 1/4 loop to a vertical up line, still in condition #1.The crosswind blows the nose left of ideal. Correct with right rudder, ease off of the throttle, and complete the stall turn. As you pivot, and begin the down line, you enter condition #3. Now the wind correction requires left rudder to get the tail back on path. As you pull the quarter loop and return to level flight, you remain in condition #3 and fly the tail until your plane passes the pilot's station.
I think you get the basic idea. Try flying the Humpty Bump and the Cuban on your simulator or stick plane. You begin to notice that 1/2 rolls on internal lines of maneuvers always change the flight condition. If at first, you find the system too confusing, you may start by simply noting... I have rolled the plane 180 degrees... my rudder corrections are now reversed. That is the doorway to start using the whole concept.
One last advantage is that regardless of which direction you fly your sequence (schedule B vs C), the corrections are always consistent. You don't have to learn two different sets of corrections.
Some of you will hate this from beginning to end and pay no attention. Others will say... hmm.. there's something there...we'll see. And a few will say...this is what I'm looking for...organization and structure. To each group...give it a chance. I love it.
About the author....
My father was a B-17 pilot in WW II, and my interest in airplanes started as a child. My room was filled with wood and plastic model planes. I worked as an engineer on the B-1 bomber (1 of about 2,500) for North American Rockwell in the early '70's (note the little flippers on the forward fuselage...to minimize buffeting at the pilot station). I later left engineering to became an oral surgeon. RC airplanes always fascinated me, but I never had the time until later in life. Sport flying was fun but IMAC gave purpose to my flying. I started in IMAC in 2007 and compete in the intermediate class. While the flying and competition are big parts of IMAC, over time, the people you meet and the friends you make become the most important aspect of the hobby.
Thank you IMAC