The Magic of Independently Trimmed Flight Modes
Joseph Vilella
In a recent paper posted on the club’s website titled “Nuances of Tailwheel Airplanes Handling”, I introduced the concept of setting up our transmitters with Independently Trimmed Flight Modes (ITFMs). However, I soon realized that this very important feature deserves its own discussion, so club members can fully understand and appreciate their outstanding benefits.
I have been flying RC aircrafts on and off since I was 22 years old. I have flown monoplanes and biplanes, slope and thermal gliders, as well as gas powered RC helicopters. Today, at the age of 75, I fly an E-flite 1.2 meter Timber X and an E-flite 1.2 meter P-51 Mustang. I like to keep my RC flying less stressful,more enjoyable, and safe. The use of ITFMs has allowed me to achieve that.
The person that made me aware of ITFMs functionality is John Weaver. He is the owner of Discount Hobbies and he uses ITFMs to safely fly his RC turbine jets as well as his other RC planes. He configured my Spectrum NX8+ transmitter so that I can take advantage of ITFMs. John and his Discount Hobbies team will be able to set up ITFMs in the transmitters of interested members of our club.
This paper will not deal with the topic of how John configured ITFMs on my transmitter. It will deal with how I have been able to use ITFMs to make my finicky E-flite P-51 Mustang much more user friendly and enjoyable to fly.
Flying the Mustang Without ITFMs
Well, that was an interesting and painful journey! Without ITFMs, I was forced to choose the best flight condition (takeoff, cruise, or landing) to perform the Mustang trims. For me this was cruise flight at 80% throttle with the landing gear up. My Mustang’s Sub Trim settings were zeroed out as shown below,
because I had no control surface misalignment issues out of the box to deal with. In flight, my ailerons, elevator and rudder were perfectly true. All I needed to do was to add down pitch to deal with the Mustang’s desire to climb at high throttle settings. This required a +32 down elevator trim. The plane flew straight, level and predictable. I allowed it to fly three seconds into the wind unassisted in order for the receiver to learn the correct settings to optimize AS3X gyro performance.
Once I achieved that, I had to do the best I could to manage its takeoffs and landings with that considerable down trim. This was not fun! I ended up having to fix the landing gear because of two minor crashes, one at takeoff and one during landing. There was too much operator overload for me to deal with at my tender age of 75 (My Timber X was much more user friendly…actually, a piece of cake under similar circumstances). I destroyed three propellers because of drastic nose pitch downs during takeoff. On top of that, I had to deal with its sensitivity to weathervaning and its sudden occurring left yaw if I was too quick at the throttle.
My landings attempts were a bit better, however, it was always hard to slow down the plane with those cruise trims. I didn’t dare to use flaps under those circumstances. Safely deploying them with the right elevator mixes was a guess that if done wrong, would have complicate matters further. The bottom line was that the Mustang was living up to its well deserved reputation…a truly beautiful flyer that can bite your head off if you don’t handle it EXACTLY as required during its takeoffs and landings.
Flying the Mustang with ITFMs
Then John Weaver came to the rescue! While telling him about my frustrations, he suggested that I use ITFMs to better control and enjoy flying my tricky Mustang, as well as my well behaved Timber X. I agreed and he set them up on Switch D of my transmitter, which is where I also activate my flaps deflections.
On it, I chose Position 0 to be my takeoff flight mode, Position 1 to be my cruise flight mode, and Position 2 to be my landing flight mode. Incidentally, the ITFMs are different from the SAFE and AS3X gyro modes. The gyro modes are set in your selected SAFE and AS3X switch and the ITFMs co-exist with the flaps on the D Switch. The reason is that if you want to use flaps for takeoff (Pos 0) and/or landing (Pos 2), you can deploy them in conjunction with the required ITFMs trim modification of the surfaces, by having them co-exist on the same switch.
How the ITFMs Are Setup for the First Time on the Mustang
1. I went through the ITFMs trim process as if I had the Mustang on a maiden flight. I placed the D Switch to Position 0 (takeoff) and after doing the usual pre-takeoff checks, I took off the Mustang as best as possible with neutral trims.
2. Once the plane was up, I retracted the landing gear and proceeded to set the D Switch to Position 1 (cruise). I slowly advanced the throttle to 80% and started applying elevator down trim until the Mustang flew straight and level. I did not need to do any rudder or aileron trim corrections. Once the plane was consistently flying straight and level into the wind, I went hands off for three seconds. This allowed the receiver to learn the trims in order to optimize AS3X gyro performance.
3. Once I did that, I reduced throttle, deployed the landing gear and set the D Switch to Position 2 (landing). At this time my flaps deployed to the 30% deflection I had selected for them in the Flap System setup screen (see image below). I usually like the 30% flap deflection because it is enough to slow down the plane, while giving me a more shallow and manageable landing glide. That is strictly my preference. I proceeded to add the required trims to fly the Mustang in a slow and stable manner. The only trim required was up elevator. Once I had the plane trimmed in a straight and level flight, I flew it hands off into the wind for three seconds. Once again, this allowed the receiver to learn the trims to optimize AS3X gyro performance in my landing mode.
4. Having achieved the cruise and landing trims I landed the Mustang. Now I had to decide what trim settings would work best for my takeoffs using Position 0 of my D Switch. This took several takeoffs in order to understand how to get the P-51 plane safely off the ground without a nosedive. I found a workable up elevator setting to keep the nose parallel as the tail is up and problem solved. I did not deploy flaps because they can cause the nose to pitch down as the tail comes up.
My Actual Mustang ITFMs Settings
Takeoff: Prior to takeoff, I set the D Switch to Position 0. A -18 up elevator trim is automatically applied for a controlled takeoff.
Cruise: After takeoff, I retract my landing gear, set Switch D to Position 2 and advance my throttle to 80%. A +32 down elevator is automatically applied for a stable cruise flight.
Landing: I reduce throttle, deploy the landing gear, and set Switch D to Position 2. Results: My flaps are deployed to 30% and -40 up elevator trim is automatically applied for slow and stable flight. With that configuration, I fly the Mustang around the landing pattern and bring it slowly to a good landing.
