Triangulation Trimming

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In the world of precision competitive flying we are faced with a couple of challenges. First, a reliable set up: whether it be propulsion selection or airframe selection, what we choose to use can make or break us in the heat of competition. We go through enormous amounts of effort to build, install equipment, arrange our schedules to practice, and generally dot every I and cross every T to get ready for the local events and even the Nationals.

We pride ourselves as being the pros at the local clubs when it comes to engine setting, servo selection, and being up to date on all the latest gadgets available for our models. In general, we make great strides to be on top of the hobby except for one area: trimming.

While we are better than most of the sport fliers, some of us lack the devotion to follow the rabbit completely down the hole, so to speak. With our high end radio equipment we have become spoiled with the technology and allowed ourselves to get trapped into quick fixes so we can spend more time flying the sequences – not entirely a bad plan. Some of the top fliers just amaze me with their ability to fly a poorly trimmed model. I have learned a lot working with some of the top fliers in the world today. Anything is possible and there is always more than one way to reach the end goal.

What I will try to do is teach you how to get the most reliable results from your setup no matter what design you are flying. So bear with my rambling at times, and I will do my best to fill you in on what I have learned in the last twenty plus years designing and trimming top shelf pattern designs.

The bottom line is there really is no poor design out there in the ‘main stream’ of pattern.

Right now there are so many airplanes to choose, from garage operations to the Naruki ten-thousand-dollar-a-copy machines in Japan. The bottom line is there really is no poor design out there in the “main stream” of pattern. I’m not talking about the pattern look-a-like hobby shop sellers, “it flies just like a pattern plane” types. I’ll stay away from these in this series of articles because there are too many variables. However, the same trim rules apply to these as well. To quote an old friend, Paul Verger, “You may not turn that frog into a Prince but you might make him a Duke.” Keep this in mind for the entry-level airplanes as they are not quite as refined as the top choices out there, but some can be helped with a little TLC and trimming.

Using our modern radios we have learned to satisfy the judges with condition switches for snaps or spins and have convinced ourselves this is the only way it can be done. It’s even crept into the rules and downgrades for the maneuver descriptions. With the conditions switches we can manufacture a fake spin or snap through manipulation of the stick and slight of hand to display what is accepted as a perfect maneuver instead of trimming the airplane to perform the maneuver without being a Houdini.

Am I against condition switches? No! I do believe they are a great tool, but 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 you can get before we resort to flipping switches.

The closer you start to perfection the better the outcome.

First I want to start out by saying the number one rule in trim perfection is SET UP SET UP SET UP! I hope I get my point across. The closer you start to perfection the better the outcome. With this in mind, 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. I have refined what I call a “Plus Plus” set up. The wing and the stab are both set positive to the centerline or the desired flight angle that the designer had in mind when he drew the fuse on the plans. This set up goes against the grain of the old accepted way of trimming so my set up rules will not transfer to what I will call the “Zero Zero” method of trimming that came around in the nineteen seventies when guys started experimenting with more streamlined designs – more on this progression later.

Most of the new designs out there have come about from the top FAI pilots so airframes are designed around the hardest schedules in the F3A aresti catalogue. 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? This is all the more reason to get the most out of the airplane for your best competitive results. We just don’t get to know our airplanes very well anymore before we have to buy the latest airframe on the market. I can remember some of the old designs staying strong on the market for at least ten years in the eighties; that’s not the case anymore. 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. However, our trimming skills have stayed the same.

Now, 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. The people who consistently do well are those that have learned how to set their airplanes up for the most durable usage and consistent performance.

 

Let’s review some Pattern design heritage…

 

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 mix was required. To do this, we installed retracts and had what amounted to pencil like fuselages to keep the drag down. The “Zero Zero” set up was in full swing. The schedules were not very demanding and the only maneuver we had to really worry about, as far as mixing was concerned, was the 4 point roll and a reverse knife edge every once in a while. So, the need for mixing was kept to a minimum because the maneuver demand was not very high or complicated.

Now fast forward this about ten years and Christophe spanked every one at the World Championships with a new airplane and flying style using the more powerful YS Motors. It was throttle management! I can remember a former F3A team member, Bill Cunningham, coming back from the World Championships and telling me, “this kid, Christophe, is the future and I’m not sure he can ever be beat. His style is light years ahead of the rest of the world with this slow and deliberate style of flying.” He set the bar that we still strive for today.

At the same time Dean Koger, Ron Chidgy, and a few others like myself decided to slow an airplane down. We knew we were going to have to build some drag into the airplanes and increase the wing size. Hence, 1150 square inch wings and fixed gear came about. There was only 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 were especially difficult, because the wings were so hard to stall or keep stalled during the snaps or spins. We all started reducing the wing size, eventually getting down to the 900 or 950 area and even larger fuses for transitional lift. We also needed longer fixed gear for the giant power plants. We now use 22 plus inch props. All this added drag and we became quite happy with ourselves, however there is a down side.

Let me explain briefly. 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 our trimming issues we have today. Remember, we went from 1150 to 950 squares. In essence, we reduced lift and increased drag so as to compensate. A smaller wing produces less lift, therefore requiring more down force (up elevator trim) at the horizontal stab to stay level at the same CG.  To make up for this, we started moving our CGs rearward for a more comfortable inverted feel.  With these few changes, we increased our workload trimming and setting up an airplane that’s happy through the whole flight envelope.

There is just too much misinformation out there

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) it makes the airplane have a left rudder tuck to the belly that’s pronounced mostly on four point rolls, reverse knife edge, stall turns, knife edge loops, etc. 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 upline pull, we increase down thrust. I have seen upwards to 3.5 degrees 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 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. Why is this not just common sense? And we wonder why it’s so hard to come up with a common comprehensive trim guide! There is just too much misinformation out there.

Now lets talk about the snaps and spins. Most of the snaps and spins performed today are just tomfoolery. By that I mean they are set up with condition switches so it 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 – it just appeared to have done it through slight of hand or trickery. 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 spins is just more of the same and is accepted today as a required setup. WHY? One big setup flaw, CG position.

The T-cantilizer is… generally another band-aid for a poorly trimmed machine in the first place

Recently the T-cantilizer phenomenon has come about, 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 is generally another band-aid for a poorly trimmed machine in the first place, not a bad design. Yes, it will reduce rudder mix. This is mainly because the cross section of the gadget is acting as a lifting surface and helping the rudder authority. More authority means less rudder use required, therefore less mix. However, most of the time it creates another issue in the vertical up or down line lines that you have to chase with mixes and can be abusive to the surface it is mounted on, usually the canopy.

I think I have laid a good foundation to help you fundamentally 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 is something I have developed over the last 20 years. It is an extremely important tool for your advancement in pattern flying and will dramatically increase your chances to advance 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.

I will teach you how to read the feed back from your airplane and triangulate a correction that will fix more than one thing at a time. When you are done with this article you will walk away understanding more about trimming and setup than you ever though you would want to know.

I will start with the basic foundation to my trimming method on the next page but just wanted to give you a good background of where we came from first. I wanted to describe what you are fighting so you can be assured you know what direction to go in using my methods.

Part 2