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Old 04-30-2010, 05:33 AM   #1 (permalink)
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Default Last 5% of setup - flight tests

I only know a few things to try in flight to make sure my Vbar setup is optimal.

updated for 5.0

I'm assuming you can already hover your v-bar heli with precision, if you are fighting to hover with vertical precision you have bigger and more traditional setup issues to solve than v-bar software settings. I'm assuming also the heli isn't vibrating excessively, usually the whole tail fin will exhibit any excessive vibration.

Prelude: Vibration
The transition to 5.0 revealed to me just how much vibration can throw out 4.0 accuracy without the vibe being obvious to the pilot. 5.0 is much more vibration immune than 4.0 so upgrading a 4.0 vibrating heli to 5.0 can make it fly much better without any other change! But 5.0 also has better vibration reporting. So your first step with 5.0 is to check if excessive vibration is reaching the sensor. Unfortunately 5.0 Pro is required for two critical vibration tools: flight log and spectrum analysis. After your maiden flight review the flight log from the v-bar software (menu "Info.." "Event log" "Get last 100 entries"). If you have any of the yellow or red vibration alerts you need to chase vibration. This subject is so big look for existing topics in this forum on it. Suffice to say that the most common sources are unbalanced tail blades, unbalanced rotor blades or previous mechanical damage or wear to spindles, axles. Also gears that are meshing without any slop can add vibe. Finding where this vibe is can be done by elimination of much rotating parts (removal!) run up, and measure, then add back one by one re-measuring each time.

Field tests:

1: do increasingly aggressive vertical ascents and make sure that the heli doesn't rear back due to tail drag, or pitch forward (ie: make sure the boom is level to the eye). The fix is to increase/decrease the tail elevator pre-comp which counters tail drag. If the elevator tipping is worse at full pitch vs mid power ascents, then consider if you really have level swash at max pitch (and min pitch).

2: from flat, pull the heli over onto its back with just elevator then either punch away from you, or continue the rotation back to where you were originally, does everything stay in line with your eyes. Make sure not to give any accidental aileron. The fix is to check mechanical phase is correct or to adjust software phase. See the next step.

3. Hover above ground effect tail in and get it sitting at a spot (you can do this in a steady wind), then smoothly rotate 90 degrees to the right without any other input. Does the heli start un-commanded forward flight? If so you need some swash rotation. On a heli with rear elevator servo and front cyclic servos, using the control panel, go to "swash rotation" and rotate the swash 2 degrees by turning the control wheel in the direction the heli moved. Eg, if it moves right, turn it right so it indicates 2 degrees. No need for reboot, just remove the panel and take off again and do the same thing. Is it worse, or better or even reversed? Remembering where you are from 0 (now +2 degrees), either add or subtract more. Within ~5 degrees you should find you can piro on the spot from a stable hover to any compass position without any un-commanded flight. Getting this right is the difference between a great flying machine ("like a sim!") and a sloppy one. The auto-trim flight also does this adjustment but do you ever have a real windless day? I prefer to do it manually. If phasing isn't right a slow piro while hover will nod the heli (and if you stop at the nod it will start forward or reverse flight). Even if mechanically phasing looks perfect, can you spot a 3 degree error? I can't.

4: on a windless day take off and hover then stop giving cyclic corrections. Does the heli move off purposefully in any direction? is it the same direction each time? The fix is ensure level swash first, then auto-trim flight, and good CG. If the direction is random, the source of the problem is likely to be vibration.

5: Do some pitch pumps, is the tail locked entirely, or does it react a bit late and then recover. If it reacts a bit late then recovers, check and change collective pre-comp.

6. Do some CW and CCW piro sudden stops, do they feel identical (stop just as fast)? change stop gain A and B if not. added: also do FFF then piro at full speed, both CW and CCW, is there any tail authority loss vs doing it stationary.

7. Do FFF and then piro slowly into the prevailing wind on either side or... fly fast away from you and go into a high fast banking turn and during the turn, piro the tail faster than the turn -- so it should move smoothly into the wind. Does the tail struggle, or oscillate during the move or even just make a sound like .? if reducing tail gain doesn't help or removes too much of the pinpoint tail stop behavior you want, then the fix is to focus on the entire tail system: servo, servo arm length, slop, pitch slider, maximum slider movement, tail blade length, head speed, tail rod clamp .. etc etc.

8. Do some full pitch moves, does the heli bog, especially near the end of the pack, if so consider reducing pitch.

9. Do some fast sudden turns at the end of a forward flight, does the heli bog or the blades stall? consider reducing CG (cyclic gain).

10. Do continuous full pitch aileron flips and elevator flips. You should do this with the agility optimizer on to let the v-bar try to find the adjustments to make flip speed the same in both directions. After you've had one flight with some full pitch flips, the optimizer will have selected some numbers, so turn it off.
If it is flipping too fast, reduce agility and/or cyclic gain, re-check optimizer, and start again.

So what other in-flight tests can one do that can highlight a setting that might need tuning?

Last edited by nyc863; 08-19-2010 at 07:50 PM..
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