This is the clearest, most concise article I've ever read on adjusting models for flight. I took the liberty of adjusting the article so it would pertain to, Hand Launched, Catapult Launched & Jet Cat gliders. I included some of Stan Buddenbohm's trimming methods to help clarify the article for gliders.
I'm going to drop it in here at outdoor general discussion to see if anyone has some comments or improvements to the article before I post it in the builders plan gallery. Bob
TEN-STEP TRIMMING PROCESS FOR RUBBER MODELS
https://freeflight.org/Library/TechLibrary/TrimmingRubberModels.pdfStarts Here
TRIMMING PROCESS For Gliders
There are two concerns with trimming that must be satisfied; CG and thrust line (incidence). The CG of the model must be located at the right location to provide stable flight and provide maximum aerodynamic efficiency. A CG that's too far forward spells loss of aerodynamic efficiency. A CG that's too far aft spells stability problems. The thrust line (incidence) determines how the model will fly under power through the air. Many modelers try to juggle each of these two problems at the same time causing unnecessary trimming confusion. The trimming procedure presented separates the two variables and treats them individually. You first get the most efficient "glide" you can with compromises allowed for free flight stability, then power the "glider" and adjust the thrust line (incidence). It's actually nothing new.
We will assume that your model has been built straight and true. Take the time to check this, but make sure you have no warps. This method of trimming also assumes the model has the right amount of dihedral and that all flying surfaces are of adequate size. Your model will also need a way to adjust the stabilizer incidence.
No Stabilizer Warps (see Stan Buddenbohm's Lit'l Sweep indoor glider article) "That doesn't mean just unwanted warps,that means don't warp the stabilizer to adjust incidents!! Why not, at extremely high launch speeds, stabilizer warps are too effective. Total control of the model is essential, warps in the stabilizer can make control of the model nearly impossible in the launch"
https://1drv.ms/b/s!AraUbrvqKoRLg6cses65dN_38lFLhg?e=tShvBK
Here are the steps for trimming. Each will be discussed in the text that follows.
No-Nonsense Trimming
1. Locate CG.
2. Glide model.
3. Adjust stabilizer for a smooth glide
4. Check stability by launching into slight dive and climb.
5. Readjust CG for stability if necessary.
6. Mark location of the new CG (if changed in step 5).
7. Test fly under power.
1. Use the Center of Gravity (CG) from your plan drawing, or use 50% to start with.
2. Launch the model smoothly towards an imaginary spot somewhere out in front of you The trick is to launch the model at it's glide speed. Do it a number of times to get the hang of it and to get some usable information on the gliding flight characteristics. If the glider does anything but a gentle downward descent with a slight left turn at the end you have a warp .
3. At this point the glide is adjusted using only the stab. The most efficient method for stab adjustment is to re-glue the stab with positive or negative incidence. Cement-type glues work great for this since the joint can be unglued with solvent and re-glued. Adjustable elevators can be used, but produce more drag. Take your time to obtain a smooth but not too floaty glide (best L/D not best sink rate theorists).
4. Check stability by launching into slight dive and slight climb This is the tricky step that requires some patience. If you are using a CG from a plan location then you might be able to skip this step, but it's worth checking. This idea came from flying R/C sailplanes. A neutrally stable sailplane can be put in a slight dive and will remain in that dive at constant speed. An unstable sailplane when put in a dive will not stay in the dive, but will return to it's original attitude. This is all based on center of lift and CG location. . Ideally, for maximum performance, neutral stability may not be the best way to go. Some amount of stability is desired because of the possibility of being upset during free flight.The closer you get to neutral stability, the more you’ll get out of your model, but you’ll sacrifice this stability. So glide your model and experiment with dives. The model should gently pull out of a dive. If forced into a dive, it should easily recover. If it doesn’t, then it’s time to move the CG!
5. Readjust CG location for stability if necessary. For a model that seems to stay in a dive add nose weight and negative stab incidence (leading edge lower). For a model that acts like a falling leaf or is overly stable (pulls out from a hard dive) remove nose weight and add positive stab incidence (leading edge higher). Continue gliding and adjusting until satisfactory results are obtained. Avoid TOO much stability. (Added-- too much stability will cause your glider to loop on the launch.)
6. Mark location of New CG (if changed in step 5) Easy enough. This is your permanent CG for your model! From this point on, you will not change this!
7. Test fly under power. Launch your model straight ahead with minimum power starting out. Observe the flight. Does it turn? Does it stall or dive? Remember how it looked when you were gliding it? What's different now? Ideally, the model should simply have an extended glide with a slight turn in the direction you desire. If everything looks good, try more power. With more power the glider should climb, but transition into its glide without stalling or diving.
It is usually safest to make your first hard launch straight up. It is very IMPORTANT that you observe your gliders transition. The amount of incidents in the glider determines the angle from the horizon & the angle of the bank that you will launch your glider. Test flying is the only way to determine this, make mental notes of how your glider reacts on every launch, you want your glider to transition into a glide without losing any altitude at the apex. Make these two adjustments (angle from the horizon and bank angle) until you get the transition the way you want it. Write the launch & bank angle on the bottom of your glider wing, plus the degrees of rotation your glider makes to transition at the top. To have your glider transition into a thermal, Position yourself with the degree of rotation counterclockwise to where you anticipate a thermal is coming through in relation to you. With your newly acquired skills, Good Luck. A good amount of luck is what it takes to make that MAX.
