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--- I suspect that it [the clover leaf rule change] most likely came from one busy-body who likes to quibble about things like what the correct altitude for level flight is.
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For the record: "one busy-body" = Keith Trostle
Also for the record: I do not think that I ever "quibbled" about the "correct altitude for level flight".
Regarding the four leaf clover - let's go back a few years.
In the late 50's, George Aldrich essentially created the pattern that we have since flown. In that pattern he wrote the rule for the four leaf clover. As far as we know, he estimated the loops would have a diameter of something smaller that the 45
o loops and elevations defined for the rest of the pattern. (The FAI adopted our AMA pattern into their rules around 1960.) I am not sure what diameter George chose for the diameters of the four loops in the clover. The '72 rule book shows the entry to be at 45
o and the tops of the two top loops were to be at "3-7 feet below the 90
o point over the flyer's head." The diameter of those loops were not defined at that time. This description remained in effect until the 78-79 rule book where the entry point was to be at the 38
o elevation and the tops of the two top loops were to be "3.9 feet from the vertical plane through the circle center". This description was essentially interpreted by pilots to mean the loops were to have a diameter of 38
o. With 38
o diameter loops, the tops of the two top loops could not possibly get close the that "3.9 feet from the vertical plane through the circle center". Instead, the four leaf clover was essentially flown in front of the pilots face where the tops of the two top loops did not come close to the "vertical plane through the circle center" as specified at that time. The Clover essentially appeared as two sets of 38
o loops side-by-side, each with each set having one loop on top of the other. (In my experience, many pilots, even good experienced pilots, still fly their four leaf clover too small to this day.)
This description of the clover with the 38
o entry point remained in effect until about 2004. I was not a member of the Contest Board at that time. However, I knew that the entry and the 38
o diameter for the four loops of the clover could not fill the half hemisphere as described by the rule book where the tops of the two top loops were to be tangent to the "vertical plane through the circle center" (as defined at that time) coupled with the requirement all the loops were to be round and tangent to each other. I asked Pete Soule to look at the description of the four leaf clover and define what the diameter of those loops should be and what the entry level of the maneuver should be. Pete Soule is an aerospace engineer in Southern California that I have had the privilege to know and to have met with him regularly at that time. He prepared a report in July, 2004 that determined the size of the loops if they were to be tangent to each other and tangent to the 4-6 feet normal flight level altitude as well as tangent to the vertical plane through the center of the circle. Those loops were to be 42
o in diameter and the entry level was to be at the 42
o constant elevation given the manner on how the maneuver was to be initiated at that time.
Based on the Soule calculations, a proposal was initiated at that time and accepted by the Contest Board that defined the clover with 42
o diameter loops, that they were to all be tangent to each other, that the bottoms were to be tangent to the 4-6 foot altitude, that the top two loops were to be tangent to the vertical plane through the center of the circle and that the center of the maneuver was to be a constant 42
o elevation. The proposal was adopted at that time (around 2005 or 2006) and has remained essentially unchanged until this year.
(A few years later, the FAI changed their rules which essentially adopted our AMA rules change made to our four leaf clover.)
It was after the FAI adopted our change to the clover that Keith Renecle of South Africa generated his 3-dimensional simulations of what the whole pattern looked like on the hemisphere where our pattern is flown. It quickly became apparent that something was wrong with the description of the clover. The real problem was the specification that the center of the maneuver was defined by the constant 42
o elevation. With this constant elevation, either the loops could not be round or they could not all be tangent to each other and still meet the loops' tangency requirements at the top and bottom of the maneuver. Over the years, there was considerable discussion in Europe on this dichotomy. Those discussions eventually led the FAI to change their description of the clover several years ago which eliminated the constant 42
o elevation through the center of the circle.
Soule later modified his study to show that the path through the center of the maneuver could not be at a constant 42
o elevation but would be on the great circle path on a plane at 45
o through the center of the circle and that the tangent points between the top and bottom loops would be at the 42
o elevation, just as shown in the Renecle simulation.
I generated a proposal to the Contest Board about 3 years ago to initiate the change so that the maneuver could be flown as described. That initial basic proposal was withdrawn because it had errors. A revised proposal was submitted more than a year ago and was posted on the AMA web site for most of last year. This proposal was the subject of many comments on this Stunt Hangar forum for several years. This change eliminates the constant 42
o elevation through the center of the circle which made it impossible to fly the maneuver as it was then described. With the "upright" and "inverted" flight paths through the center of the maneuver, all of the tangency and round loop requirements can be met. The upright and inverted flight paths through the center of the maneuver are no longer required to be at a constant elevation but rather they are actually on a great circle path on a plane that is at 45
o from the center of the circle. These are great circle paths, just as are the vertical paths through the center of the circle. Rather than writing that 45
o elevated plane into the rule book, the wording explains that the paths be upright and inverted through the center of the circle and does not even suggest that those paths are to be at a constant elevation. This proposal was approved last Winter at the close of the last rule change cycle and is now in the 2022-2023 rule book.
The new FAI rule allows the entry to be either from normal level flight or at the "center" of the maneuver. We did not allow for this option because to properly maintain the tangency requirement, the model cannot be in level flight at the initiation of the maneuver for the option to start the maneuver at the "center" of the maneuver. Instead, it would need to be on a path on that 45
o plane through the center of the circle. There was also some discussion by a few board members on how the entry should be defined. One option was to have the start from the normal flight level with a sharp turn (as if putting a stem on the maneuver). Instead, it was decided to put the judging start and stop points to be at the 45
o elevation which also happens to be crossover point for the vertical and inverted flight paths through the center of the circle which is also the very center of the clover. The initial turn to a vertical flight path is not defined by the new rule book. The way the rule is written, the pilot has a choice as to how to establish the vertical path at the start of the maneuver. In addition, the new rule also allows the pilot to recover from the maneuver before flying through the top of the circle directly into the wind when there is a severe wind.
Another way to explain the need to change the rule is that until this change, the prior rule that required all loops to be round, that they all be tangent to each other, that the bottom two loops be tangent to the normal level flight path, that the top two loops be tangent to the vertical plane through the center of the circle, AND that the horizontal flight path through the center of the circle was to be a constant altitude (albeit the earlier 45
o, then the 38
o or the more recent 42
o), the maneuver could not be flown. In other words, it was impossible to fly a perfect maneuver because it was impossible to do as the description was flawed. I do not think a maneuver description should be so faulty that it would be impossible to perform. The real problem with any of the previous attempts to define the four leaf clover was the requirement for a constant elevation flight path through the middle of the maneuver. Or, it would be possible to leave the constant elevation requirement in, but then eliminate the requirements that the loops be round and the same size. If that choice were to have been made, the maneuver would no longer be symmetrical.
One more thing. The previous description for the clover required one 360
o loop and three 270
o loops. Now, the clover appears as four 270
o loops which, in my conservative unbiased opinion, gives a more symmetrical appearance.
Note to Derek: This proposal was on the AMA website for over two years. There has been discussion on this matter on this Stunt Hangar for longer than that. Also, for the record, the final vote on this proposal was completed in September of last year, before you became a member of the Contest Board. The vote among the 11 Board members was 10 for, 1 against the proposal.
(One note about Pete Soule. He is/was well known in the Team Race community and was on the US F2C team several times. He wrote the "Round and Round" control line column for Model Airplane News for several years. He has written or co-authored several technical papers regarding control line airplanes. He is a genuine rocket scientist.)
Keith Trostle
Chairman
AMA Control Line Aerobatics Contest Board
Topic: My thoughts on the New Clover (Read 11826 times)