08Mastering.lt1.doc
[headline: Mastering the Immelmann and Cuban 8]
[subhead: Lessons in proactive vs. reactive flying]
[author: Dave Scott]
[Graphics by the author]
[sidebar in text file]
[sidebar]
Dave Scott founded the 1st U.S. R/C Flight School and has professionally trained more than 1,500 pilots. His accelerated RC flight training techniques have resulted in 98% of his Basic Solo Courrse students achieving solo flight in less than a week, and 100% of his Aerobatics students achieving in only days what traditionally takes years.
More information about Dave’s flight school and manuals can be found at www.rcflightschool.com.[dingbat]
As soon as a pilot has become proficient performing loops and rolls, the different ways that loop and roll elements can be combined are practically infinite. This article applies the timeless efficiency of the crawl-walk-run process to the Immelmann turnaround and the Cuban 8.
It is important to note that regardless of what maneuver you’re practicing, adding refinements is much easier after first mastering the basic elements. Furthermore, by adding refinements individually, each receives the majority of your attention and is more quickly mastered.
Immelmann Turnaround
The problem with an ordinary turn is that it takes the airplane away from the ideal line that it was on before the turn (Figure 1). The pilot is forced to make several adjustments after the turn to reestablish the preferred line coming back. Consequently, the pilot has less time to think about what he or she wants to do next.
The Immelmann is an aerobatic maneuver that allows you to do a 180° turnaround while maintaining the same line of flight coming back—albeit higher—and thereby makes flying easier (Figure 2).
Phase I: Sequencing Steps
An Immelmann should be treated as two separate parts: a half loop, and then a half roll to upright, with a return to neutral between them to help ensure that the half roll is axial and not barrel shaped (Figure 3).
As with any loop, the key to performing a good half loop is a wings-level entry to ensure that the loop starts out tracking vertical, rather than veering off to the side with the wings banked. You should target a specific fixed amount of elevator, (e.g., half) in order to establish a consistent initial loop radius.
When you execute the half roll at the top, use full aileron in order to complete the half roll before it has a chance to lose undue altitude or wander off heading.
Tip: professional pilots cheat a little and neutralize the elevator and start rolling a few degrees before the airplane reaches the top of the loop to ensure that the roll does not finish sinking or lower than where it started (Figure 4).
Phase II: Floating the Top
The half loop will tend to tighten or “pinch” near the top because of the effects of gravity. The pinch typically starts at roughly 10 o’clock or 2 o’clock, depending on the direction from where the maneuver is entered. These “key points” are where you should reduce your elevator input slightly to “float the top” of the half loop in order to keep it round (Figure 5).
For the final refinement, input a slight amount of forward elevator pressure at the start of the half roll to keep it more axial and level at the start (therefore reducing how much you have to cheat). Just remember to remove the elevator push soon after you start the roll to avoid barreling the roll and causing a loss of heading.
Altogether, the refined Immelmann is performed by pulling a fixed amount of up-elevator to establish a consistent loop radius. Between the 10 o’clock and 2 o’clock key points, the elevator input is reduced slightly to float the top of the loop. Then a fraction before the airplane reaches the top of the loop, quickly return the elevator past neutral into a slight push while simultaneously rolling upright.
Phase I Cuban 8: Looping Over the Top
The half Cuban 8 is one of the most frequently performed turnaround maneuvers because it finishes close to the same altitude and flight path from where it started. Performing a basic half Cuban turnaround is similar to the Immelmann, except that the elevator is held in past the top of the loop to a 45° downline before rolling upright (Figure 6).
Developing the ability to judge a precise 45° downline takes practice. In the meantime, a simple approach of neutralizing the elevator as soon as you see the airplane fly over the top of the loop works amazingly well to achieve a ballpark 45° coming down (Figure 7).
Make sure that you quickly return the elevator to neutral at the instant that you see the airplane fly over the top. If you attempt to finesse or smoothly take out the elevator, you will most likely overshoot the 45° and find yourself rushing to recover (Figure 8). Also, make sure that you apply full aileron when rolling upright in order to complete the half roll quickly before it uses up too much altitude and causes you to rush the pullout.
The half Cuban 8 should contain a line before and after the half roll. During the early stages, this is accomplished simply by pausing at neutral before and after the roll. You can reinforce this by pacing the 45° downline with the time it normally takes to say or think, “Pause, roll upright, pause, pull out.” Most important, the pauses at neutral before and after the roll will help ensure that the roll is axial and not barrel shaped, as well as provide time to be certain that the wings are level before pulling out.
Phase II: Floating Over the Top
As your skills increase, start reducing your elevator input slightly at the 10 o’clock or 2 o’clock key point to keep from pinching the top of the loop (Figure 9). Floating the top of the Cuban 8 not only adds precision, the float also buys a little more height and therefore time to apply additional precision to the 45° downline.
You can also buy some time on the 45° downline by smoothly reducing the throttle to one quarter after floating over the top of the loop. If you continue to feel rushed on the 45° downline, try pulling less elevator at the start of the loop to affect a larger/higher loop and buy more time to execute the 45° downline and the half roll.
Flying a larger loop requires a higher power setting in order to perform a nice arc over the top of the loop. As a consequence of flying larger loops, floating over the top, and reducing throttle coming down, the airplane will likely lose so much airspeed that gravity will cause it to drop noticeably out of the 45° downline. You will likely need to input a little forward elevator pressure during the inverted segment of the 45° downline, as well as during the first part of the roll, in order to maintain a precise 45° downline throughout.
There won’t be enough time to fine-tune the forward elevator on the 45° downline. Rather, you should commit to a certain (slight) amount of forward stick pressure, complete the maneuver, and then reflect on whether to stay with that amount or target a different input next time.
At this point, you should put an emphasis on maintaining lines of equal length before and after the half roll, centering the roll on the 45° downline. This is accomplished by accounting for the airplane’s gravity-induced acceleration on the downline and holding the upper portion of the 45° downline a half beat longer to match the length of the faster lower section (Figure 10).
The process of learning to fly a precision half Cuban 8 can be summarized as first mastering the round loop segment, turning your attention to maintaining a precise 45° downline, then working on maintaining lines of equal length before and after the half roll.
Full Cuban 8
When comfortable with the half Cuban 8 turnaround, you can double your fun and perform a full Cuban 8 in front of yourself simply by pulling out of one half Cuban 8 directly into another (Figure 11).
The length of time required to complete the full Cuban 8 demands that you start each loop with perfectly level wings if you expect to finish this maneuver anywhere close to the heading on which it was started. The most common error performing full Cuban 8s is hurrying into the second half using more elevator than was used during the first half, resulting in a much tighter loop and having to rush the shorter 45° downline. Plan to use the same amount of elevator for both loops, and not only will they be the same size, but the pace along the 45° downlines will predictably match as well.
Conclusion
Many aerobatic maneuvers have foreign or intricate-sounding names than might prevent people from giving them a try. But when it comes down to it, the vast majority of aerobatic maneuvers are composed of partial loops, lines, and rolls that follow a predictable sequence. You can take comfort in knowing that it’s possible to put on an amazing aerobatic display simply by rearranging those elements.
Master the Immelmann and Cuban 8 and you haven’t just learned two new maneuvers, you will have also opened the door to hundreds of different maneuver possibilities. Good luck![dingbat]
—Dave Scott
[email protected]
SOURCES:
1st U.S. R/C Flight School
www.rcflightschool.com