Radio Control Aerobatics - 2009/11
If it doesn't fly straight up-and-down lines, you need to tame that dog. If it doesn't fly straight and level at different throttle settings, you need to tame that dog!
As we have written in previous columns, preparation is crucial. Flying an aircraft that is not properly trimmed can be time-consuming.
We learned something the hard way. If a few test flights were needed every time to remember how to fly a certain model before practice or competition, we had a poor plan at a contest and a frustrating situation at practice.
Sometimes, to be the best takes more than skill; it takes a tamed airplane. Time spent trimming a model at the beginning of the season can make the difference between a successful contest season and one where, "I'm just here having fun."
Interview: Bryan Hebert — Hebert Competition Designs
The first aircraft Whisperer we will talk to is Bryan Hebert, who owns Hebert Competition Designs. He is known for such models as the Storm, Patriot, Shinden, and his latest, the Valiant monoplane and Shark biplane.
Bryan said:
"In the world of precision competitive flying, we are faced with a couple of challenges, the first being a reliable setup. Whether propulsion selection or airframe selection, what we choose to use can make or break us in the heat of competition.
We go through enormous effort to build and install equipment, arrange our schedules to practice, and dot every 'i' and cross every 't' to get ready for the local events, as well as the Nationals. I will teach you how to get the most reliable results from your setup, no matter what design you are flying.
Right now there are so many airplanes from which to choose, from cottage operations to the Naruki $10,000-a-copy machines from Japan. The bottom line is there really is no poor design out there in the mainstream of Pattern.
I'm not talking about the Pattern look-alikes, hobby-shop sellers, 'it flies just like a Pattern airplane' type model. We will have to discuss those another time.
Using condition switches that our modern radios come equipped with, we have learned to satisfy the judges with snaps or spins and have convinced ourselves this is the only way it can be done. We can manufacture a fake spin or snap through manipulation of the stick and sleight of hand to display what is accepted as a perfect maneuver, instead of trimming the airplane to perform the maneuver.
While I do believe that condition switches are a great tool, I hope I can share some insight as to how to get a more consistent result without the need for so much programming, by making the airplane as perfect as possible.
The Number One rule in trim perfection is setup, setup, setup! I hope I get my point across. The closer you start to perfection, the better the outcome.
I'm amazed at how many guys don't know what their throws are in degrees or measurements of any kind. This is a must in order to know how to improve or refine your setup in the trimming process and to record and be able to transfer this information from one airplane to another.
I would like to briefly go over my trim method. I call it the Triangulation Trimming Method, because I use three flight angles for feedback to let the airplane tell me what to do.
In order to boil it down to the essentials, and get to the fine-tuning, I have refined what I call a 'Plus-Plus' setup. The wing and the stabilizer are both set positive to the centerline or the desired flight angle that the designer had in mind when he drew the fuselage on the plans. This setup goes against the grain of the old accepted way of trimming.
The last few rules cycles have raised the bar for what is expected out of a modern airframe. Who would have thought that a top airframe would have about a three-year life span because of constantly evolving technology, building techniques, and schedules? We just don't get to know our airplanes very well anymore before we have to buy the latest airframe on the market.
Because our modern airplanes are expected to be able to perform maneuvers we would have only dreamed about just five years ago, the demand for a perfect airframe has gone up exponentially, while our trimming skills have stayed the same.
I'm going to let you in on a big secret. There are no bad designs out there. There are designs better than the others, but they all have some good points.
For the most part, we are just bad trimmers. Those who consistently do well are those that have learned how to set their airplanes up for the most durable usage and consistent performance.
In the old days of retracts, we were mostly interested in going as fast as we could for the ease in manipulation of the controls. The less we moved the sticks, the less a mix was required. To do this, we installed retracts and had what amounted to pencil-like fuselages to keep the drag down of the zero-zero setup that was in full swing.
The schedules were not very demanding, and the only maneuvers we ever had to really worry about, as far as mixing was concerned, were the four-point roll and a reverse knife edge. So, the need for mixing was kept to a minimum because the maneuver demand was not very high or complicated.
Fast forward about 10 years, and Christophe Paysant-Le Roux spanked everyone at the World Championships with a new airplane and flying style, using the more powerful YS engines. It was his throttle management. His style was light-years ahead of the rest of the world, with this slow, deliberate throttle-management flying that set the new trend for flying.
At the same time, Dean Koger, Ron Chidgey, and a few others like myself decided to slow the airplane down. We knew we were going to have to build some drag into the airplanes and increase the wing size; hence 1,150-square-inch wings and fixed gear came about.
But there was one problem: F3A started using down-line and up-line snaps, which really made this style of airplane hard to fly. The snaps and reverse spins especially, because the wings were so hard to stall or keep stalled during the snaps or spins.
So we all started reducing the wing size; eventually getting down to the 900- or 950-square-inch area and even larger fuselages for transitional lift, and longer fixed gear for the giant power plants. We now use 22-inch-plus propellers. All this added drag and we became quite happy with ourselves. However, there is a downside.
Briefly put, no drag is good; it robs the airplane of efficiency. If the drag does not produce lift, it is a detriment. That's why you see some taking the gear legs and making them lifting devices. However, our cool, user-friendly landing gear is responsible for most of the trimming issues we have today.
Remember, we went from 1,150 to 950 squares; in essence, we reduced lift and increased drag so as to compensate. We started moving our CG more rearward, which allowed our wing angle of attack to increase, thereby producing more lift at level flying conditions. With these few changes, we increased our workload trimming and setting up an airplane that's happy through the whole flight envelope.
Here are the problems we encounter with the conditions laid out above:
- First, with the CG moved rearward—it's usually around 35% of the MAC (mean aerodynamic chord)—the airplane has a left-rudder tuck that's pronounced mostly on four-point rolls, reverse knife edge, stall turns, knife-edge loops, etc., generally whenever we use the left rudder. Right rudder does not get affected by this unless your CG is really rearward.
- The next problem is an up-line pull to the canopy and a down-line pull to the canopy. To take care of the up-line pull, we increase downthrust. I have seen upwards to 3.5° to correct this problem. Then to fix the down-line pull, we mix it out with the transmitter.
These Band-Aids all seem to work okay, and they are commonly accepted as normal correction practices. Some are even proponents of a rudder-to-throttle mix, because they fly so tail-heavy.
Now let's talk about the snaps and spins. Most of the snaps and spins performed today are just tomfoolery, set up with condition switches so the airplane appears to be performing the maneuver. We can use stick-switched conditions that enable the elevator to come in and out of the maneuver, to give the appearance or resemblance of the descriptions required by the rule books, while the airplane has never actually snapped or stalled.
Stalled spin entries are the same. Using the famous elevator rate switch from high to low rate to show a nose drop, which looks like a stalled entry right before the spin, is just more of the same and is accepted today as a required setup. Why? Because of one big setup flaw: CG position.
Recently, the T-cantilizer phenomenon has come about (that side-force generator seen mounted behind the canopy), touting the end-all for rudder mix. While I agree it works for the most part, and I respect Christophe as a World Champion designer, you have just added another surface on the airplane to trim, and it generally is another Band-Aid for a poorly trimmed machine—not a bad design.
Yes, it will reduce rudder mix, mainly because the cross-section of the gadget is acting as a lifting surface and helping the rudder authority. More authority, less rudder use required, therefore, less mix. But most of the time, it causes another issue in the vertical up- or down-lines that you have to chase with mixes, and can be abusive to the surface it is mounted on—usually the canopy.
I will start the basic foundation to my trimming method in the next article. But I hope I have laid a good foundation to help you understand where we are coming from and where we need to go to improve your flying and trimming understanding and skills.
The method I want to share with you for correcting these issues, which most of us have come to accept and live with, is something I have developed over the last 20 years. It is an extremely important knowledge tool for your advancement in Pattern flying and will dramatically increase your chances for advancing your understanding in setting up an airplane every time.
It is not design-exclusive. It's fundamental knowledge that will transcend all designs and classes. When you are done with this series of articles, you will walk away understanding more about trimming and setup than you ever thought you would want to know."
Thank you, Bryan, for your insight. It's likely that many fliers are surprised by your thoughts and, we hope, will be encouraged to try some of your trimming ideas and learn more about how they can be better pilots by understanding how their airplanes work. MA
Sources
- Hebert Competition Designs — www.hebertcompetitiondesigns.com
- National Society of Radio Controlled Aerobatics — www.nsrca.org
Transcribed from original scans by AI. Minor OCR errors may remain.
