Tuesday, September 19, 2017

TurboParker's Guide to UMX Radian Trimming

Copied from RCGroups:

Initial balancing & trimming:

1) MEASURE the CG on your plane. Do whatever is necessary to adjust it to 31mm, which is the factory recommended starting point. Do this before you try anything else.

2) Zero your tx trims. If your transmitter allows, adjust the trim-steps to the smallest setting. (Usually "1".)

3) Power-up the plane, but do not engage AS3X. Then disconnect the battery.

4) Mechanically trim the elevator so that it's neutral with respect to the stab.

5) Take the plane up for a flight with the CG @ 31mm & see how it behaves power-off & power-on.

6) If it glides smoothly & doesn't balloon under power, you're done.

7) If it porpoises during the glide and/or balloons under power - add down-trim until it glides smoothly, then zero your tx trim & transfer the tx trim to mechanical trim.

8) Note the degrees of down-trim with respect to the stab. If it's only a few degrees or so, you can call it good - unless you're trying to squeeze every last bit of glide performance out of the airframe that you can get. If you're trying to set a personal UMXR glide record, adjust the decalage accordingly, so that no visible trim is needed for best glide with the CG at 31-32mm. If the plane needs a lot of visible down-trim with the CG at 31-32mm, the decalage is off enough to warrant fixing it or returning the plane & getting a replacement.

Remember that you must re-trim the elevator for best glide whenever you change the CG. That is absolutely mandatory. If you don't, you will simply end up chasing your tail & get frustrated with the process of flight-trimming. When you get it right, you will be rewarded with a plane that glides smoothly & efficiently, and exhibits very little (if any) throttle-pitch coupling under power. See the video below for an example of how the plane is supposed to behave when it's trimmed & balanced correctly, and the decalage is about right. Be sure to turn up the sound, as I narrate during the flight. It's a bit long, but the 19 minutes it takes to watch the entire video will most likely be worth it for those who are new to sailplanes.

Here's another method of fine-tuning the CG:

1) Take the plane up high, trim for level flight @ say 20-25% throttle. Better yet, trim for the flattest stable power-off glide (no porpoising).

2) Enter a power-off dive at a 45-degree angle, then release the sticks, and observe the plane's behavior:

A. Plane pulls sharply out of the dive as soon as you release the elevator: The plane is extremely nose-heavy. Move the CG aft, take the plane back up, re-trim as described above, then repeat the test.

B. Plane starts to dive more steeply (tucks toward the belly) when you release the elevator: The plane is tail-heavy. Move the CG forward, take the plane up, re-trim as described above, then repeat the test.

C. Plane continues on its path: The CG is at the neutral-handling point (often called the sweet-spot), which provides the greatest sensitivity to lift (the plane will indicate weaker lift than it will when it's nose-heavy). A neutral CG also results in the lowest stall-speed & the least amount of drag. But it also makes the plane neutrally-stable in pitch, so it will not self-correct in a dive. Many competition sailplane pilots prefer a neutral CG, but some pilots prefer a slightly-forward CG.

D. Plane starts to gently pull out of the dive when you release the stick: The CG is just slightly forward of neutral. The plane will still indicate light lift (albeit not quite as well as it would with a neutral CG), and it will be more stable in pitch than it is with a neutral CG. Some sailplane pilots prefer this CG position, as the slightly positive pitch-stability makes the plane less-apt to suddenly enter a dive or climb on its own when it gets perturbed by the air currents. The slight loss of efficiency is rarely noticeable to casual sailplane pilots who are not concerned with getting every last bit of performance from the airframe.

Remember that at this scale, moving the CG just 1-2mm is noticeable in flight. Avoid making large changes unless you're sure that the the CG is way off. Also, remember to re-trim for level flight each time you move the CG. This is absolutely critical. Failure to re-trim as described above will negate the entire process.

Also remember that CG is not a fixed number. Move it forward a bit for better wind-penetration on turbulent days, or for increased glide speed on windy days. Move it back to the sweet-spot in calm conditions and/or when lift is very light & you want to stay aloft on the farts of field-mice alone.

If the decalage is correct, you'll end up with the elevator level or close to level with respect to the stab after the above tests. If not - then the decalage is likely off. Which means you'd need to do the decalage test.

Decalage test:

1) Zero your elevator trim on the tx, then mechanically neutralize the elevator with respect to the stab.

2) Take the plane up, but do not re-trim the elevator in flight. This is absolutely critical, as re-trimming the elevator after neutralizing it before the flight will screw up the test & render the results useless.

3) Perform a power-off vertical dive from high altitude, release the elevator stick, and observe the plane's behavior:

A. Model continues straight down: No change needed.

B. Model pulls to canopy: Increase stab incidence with respect to the wing.

C. Model pulls to belly: Reduce stab incidence with respect to the wing.

Adjusting the CG as described above is the next step after verifying that the decalage is correct.

Here's where the batt ends up on mine to get the CG to the sweet-spot for best glide performance & power-on behavior. You can also see the CG 'sweet-spot' marks on the wings:

TurboParker's Narrated Video:

blogodex = {"idx" : ["UMX Radian", "Trimming"]};

Sunday, September 17, 2017

NutBall Aerobatics

GoldGuy, the inventor of the NutBall, reveals some NutBall tricks and his propensity for poetry:

1.  Next time your out, experience the distinctive sound made by a NutBall. Here's how............

Take it to altitude with the nose up, instantly give it full down and full left. It will flip over and go into a violent but controllable spin. Hear that sound it makes? It's the only model I know that does it. To slow down it's decent, just cut the throttle. To get out of it, just relax the controls, then feed in a bit of up. Cool eh?

2.  The snap roll is similar. Flying straight and level fed in some up and then do the same, down and left. If you time it right, you'll get one complete violent snap in an instant. Practice at altitude and when you get it right, do it at eye level for best effect and you'll come out looking like a pro.

Also, in that inverted flat spin mode you can use the throttle and elevator to go up and down. Hold in the rudder the whole time..................throttle back, it will come down, add throttle and a bit more down and it will go up. You can go up and down in that inverted spinning mode as long as you wish.

You will have to move the battery back for a 30 to 35% CG for best flopabatics.

3.  Rolling the NutBall is an easy to do and a basic maneuver. Once you've mastered it, the roll becomes the basis for the snap roll, spins, inverted flat spin (complete with sound effects), the inverted 'elevator', both up and down, plus other silly weird stuff.

Rolling is more than just slapping over the rudder stick with the NB, although with models like the Simple Delta, flat and with elevons, that's all it takes to look good. What you want is to practice nice smooth rolls where the speed of rotation is the same throughout the 360 degrees of travel, it can be done almost axel, it's all in the timing and rolling to the left is easier to start off with. Make sure you set the CG at 25 percent to start, you can modify that as you progress, fly the maneuver at a MEDIUM speed at first and pay attention to the amount of movement on the rudder and elevator, not too much (???) is lots. The big problem in rolling the NutBall is that with too much rudder throw it wants to flip over very quickly once past inverted. How much movement is all apart of fine tuning. Having a low wing loading is a big aid in flying aerobatics as everything is much easier to do. If there's too much of a breeze, mount a bigger battery or some lead ballast, keeping the CG unchanged.

So, here's what to do to start off with.....................

Fly along straight and level at a brisk speed, but not full tilt (yet), and just before you enter the roll, add a tiny bit of up elevator to rise the nose, then feed in the rudder nice and smooth and when it goes inverted give it a tiny blip of down elevator and let off on the rudder just after is goes past inverted. What you need to do in the beginning is to form a pattern or tune in your brain. Practice in your shop with the model in front of you, try and picture in your mind what's happening. I learned four point rolls by repeating this to myself as I moved the sticks in the proper sequence and at the proper speed................ta da, ta da, ta da, ta da. It's like a tune in your head and you keep to the timing. Not sure what key I'm in, but it works. Got that from the best 3D pilot I know.

When you go out to practice, by yourself seems best and concertrate on the one thing and do just that.

#4 Here's another easy fun one anyone can do, the 'upright elevator', although it's all down elevator, no up. You'll need a rearward CG for this one, but start off with what you've got to see the difference it makes. Gain lots of altitude and point the nose straight into the wind. Now, hit full up and hold, and kill the thottle at the same time (again, it's in the timing) and use just the rudder to keep it facing into the wind. It should float down like a leaf, and with a low wing loading and a nice breeze you can plop it right down on the wheels. You can do this one inverted too.

Have fun with it.............all it takes is a bit of practice and a little more after that............your starting to look like a pro now...............keep it up

Most aerobatics it will do
And referring to how it flew,
If someone shouts, "a NutBall, WOW"
I wouldn't bother takin' a bow,
Cause they're probably talkin' about YOU

Wednesday, September 6, 2017

2017 Shopping List

Here's what you need to get started in Remote Control Aeromodelling!  This is everything you need except for actual aircraft.

Transmitter and Battery (one each)


4-Channel Receiver and Voltage Sensor (one each, for each model)


8-Channel Receiver (if you need more than 4 channels)

Get one of these instead of the 4-channel if your model needs more than 4 channels.


OrangeRX DSM2/DSMX transmitter module

If you want to fly a plane that uses a Spektrum DSM2/DSMX compatible receiver


Battery Charger and Accessories


Charging Cables:

Power Supply

The above Charger doesn't include a power supply.  You can use an old PC power supply or laptop power supply if you've got one.  If not, this one will do what you need.