Stop That Flickin! 

or

How to trim a F3F Model.

The first step for me is to build/assemble the model correct the first time. Solid linkages and a serviceable installation. No double centering and no slop. On tails I will test the pushrod linkage by pushing down on the control surface with enough pressure to move the servo (power off) and see if there is any excess pushrod flex. If so reinforce the pushrod to the fuse. Keep all pushrods as straight as possible. This means no bends, no kinks, no arcs. Its better to use as much servo travel to move a surface as possible. Using the inner hole on the servo arm and 100% EPA is MUCH better than using the outer hole on a long arm and dual rates! Why? When the servo moves 90 deg through its travel you get better resolution and torque with a small arm over a longer arm and 10 deg travel to get the same control movement. You lose torque, control and feel.

Stage 1 set up: First flight. 

  • Set up the control throws as recommended or like similar models you have. 

  • Set both Elevator & Aileron DR to 70% of what you set up as max throw. 

  • Set the CG per plans or instructions and add 1 oz extra (in the nose) for first flights. Nose heavy models can be flown safely. 

  • On first toss be smooth set the elevator trim ASAP for level flight. 

  • Get a feel for control inputs. Flip the DR if needed. 

  • Get some speed up and try a few gentle turns. Increase the turn rate and make a mental note of changes needed.  Roll rate or pitch rate changes etc.

  • Rock the wings +45 to -45 and check the differential.  I will post a video of this shortly.

  • Test the flaps at altitude. If the elevator comp is way off land with minimum flap or set it in the air with the program open if you know your radio that well.

  • Test the stall at altitude. 

  • Land and make a few adjustments, repeat. 

Stage 2 set up: Tweaking. 

  • Differential. Kevin Newton has a good description on differential set up on his web page. Do that. http://www.users.globalnet.co.uk/~knewt/Set%20Up.htm 

  • CG. I do the dive test. I am looking for a straight glide path at -45 deg.  Pull up = nose heavy. Tuck = nose light. 

  • Land and check the elevator for any extra trim. Shim the v-tail as required to get neutral flight trim. Repeat. 

  • Do this a few times to get where the model won't pull out of the dive AND still flies level across the slope with no trim.

Stage 3: Turning. Elevator set up. 

  • Open your program to set elevator throw. 

  • 1st. Get some altitude and make a medium fast run away from the slope and pull full up elevator for a tight loop. If the model spits out of the loop one side or the other by itself then decrease the max throw and try again. Keep decreasing the total elevator throw until the model can do a tight loop without loosing track. This is your max elevator throw.
  • 2nd. Make a race turn with extra altitude and pull through at a good rate. No problems = continue. Flick = cut down the throw.  You see where I am going with this??

  • Keep doing the turns and adjusting the total elevator throw until you get a quick turn without any problems. 

  • You need to enter the test turns smoothly and accurately. If you blow the turn entry try again. The model will not magically fix a poor turn entry, you will need to do that yourself.

If the model feels soft around neutral then a little reverse elevator exponential is needed. (I only needed this on one model in my life so don't get carried away) Don't increase the total throw to get that "feel" in neutral. Increasing the total throw will get you stuffed into the hill. Remember we just fixed that. Or. Learn to fly with the new feel. Your probably reading this because you want to move higher up in the comps and are having problems and your "Personal Feel" is not working for you. Try it this way and see if you get faster times.

Stage 4: Trailing edge. 

What does "snap flap" do? It adds camber with up elevator. Why? Most of our sailplane airfoils are more efficent in a turn with a little camber. The camber reduces the drag on the wing in a high alpha condition like a pylon turn. This extra camber is not needed in a straight line only where we ask the wing to carry more load. SOme

  • Set the flap/aileron mix so you can get the roll rate you want with the minimum of control throw. I like the complete T.E. moving a little than having the ailerons move a lot. Differential effects roll rate. Once you set the differential leave it alone and only adjust the amount of throw on the TE for roll rate. 

  • If the model now wants to Flick you night need to back off on the flap/aileron mix and try again. 

  • Repeat stage 3 and 4 until you get it right. You want minimum throw but positive control. 

  • Snap flap. Keep adding until the model slows down then back off some. Easy. Move the flaps the same as the ailerons. Put this feature on a switch just to see the difference. The best way for this mix to work is to set up each turn entry exactly the same, time after time after time.......

It looks like a lot of work but you can get real close on a good afternoon. Don't make 100 changes at a time or you won't know what worked and what did not. When you think you have it perfect do some tweaking on the CG and see if more performance is hiding in the model. 

A lot of problems can be dialed out or dialed in with the computer radio. Be careful. I like to adjust while flying but this might cause more trouble if your TX is too complicated.

Race day. KISS = Keep It Simple Stupid. Don't set up your radio so you need to flip 16 switches on and off to get through a flight. Don't make it so hard on yourself. Do a pre flight before you enter the ready box and be ready to launch with your helper by your side when the pilot on the course is at lap 5. Keep the contest moving. I love it when I hear the 'Experts" telling guys that 5 cell packs and long servo arms are needed for lightning quick response to get you out of trouble. If you do it right you don't need lightning quick response and the slop and double centering problems that come with it. Lightning quick response is what go you INTO trouble! Be Smoooooooooth.

Have FUN! 

Tom