Snohomish Fun Fly Chronicles

Well, the Snohomish fun fly 2011 came and went.  What a super fun time Friday-Sunday.  Matt Botos was absolutely nuts with the new Synergy E6 and E7.  They are very quiet and very fast.  The Futaba flybarless unit really looked solid with all the intense fast and sudden maneuvers they were doing.  I was looking forward to witnessing the Futaba units in action by some good pilots.  So far I like the Vbar, BeastX, and Futaba.

Tim S. from Oregon put on amazing shows during the day and especially at night.  Holy cow he improved big time!  Super fun to watch at night for sure.  I was having so much fun Saturday that I crashed about 8:30pm.  I was kinda tired but I was confident I could fly a fun flight with my yellow glasses on.  I could see the heli perfectly fine, but 10 seconds into the fight while doing some low maneuvers the brain signal did not send to my thumb and I crashed.  It was like I was in simulator mode or something.  It was a sure sign my brain was fried and was time to call it a day.  Here’s a little picture:

Tail shaft bearing replacemtent

Hello, Frank.
I recently made a short 1 minute video on replacing my tail shaft bearings by pressing out/in with an Arbor press.  It was easy as pie.

Tail shaft bearing worn out

During inspection I discovered the inner race of one of my tail shaft bearings was badly worn out.  Here in the video you can see wobble.  The bearing is secured, and the shaft is not wobbling within the bearing – it is the inner race wobbling  between the outer race.  Thanks to a friend I have a new set I will install Saturday.

I also took time to balance my tail assembly (hub & grips).  I used a magnetic prop balancer and simply filed away the tip of the heavy grip.  Now it is balanced, so before it might have been vibrating and maybe the reason for this bearing wear, and/or it could just be normal wear over time.  Lord knows I pirouette like mad too, so maybe that’s why.  :-D

Tail setup essentials

Summary:  Do you have a tail kick that just won’t go away?  Does your tail blow out on hard maneuvers?  I believe you can fix both and have a solid “sim-like” heli performance, either flybar’d or flybarless.  Your confidence will definitely improve when that damn tail stays put!  You may already know some of this stuff, but dissecting every bit of the art of tail perfection is another story.

Thoughts:

• Mechanical setup is crucial.
• The gyro’s software expects a specific hardware configuration, from servo, to servo horn, to lever, to blade size, to blade type, and if any right thrust is present at servo center.
• “Chinese” tail grip weights takes an enormous amount of stress off the servo and allows the servo to do its job much more efficiently.
• The job of the servo is to only put the tail blades in the precise angle required, and quickly.  It is the tail rotor assembly’s job to bite air and do the work of holding the tail and moving the tail.  The servo should not have to fight wind resistance hardly at all.

The steps I took:

1. At servo center (in rate mode or setup mode) mechanically set the tail blades for 3 degrees of right thrust (pirouette clockwise).  Or maybe your particular gyro requires a different amount of degrees of right thrust, if any at all.
2. Take note if you had any right thrust at all, or even left thrust!  This will help you make adjustments to your tail gyro.
3. Calculate 3 degrees by the tool with the vbar software here.  Even if you don’t have a vbar you can still download it and use this useful calculator.
   Note: with the Vbar you can perform a trim flight for 60 seconds and that will trim your tail.  Then you can mechanically adjust to the point where you have zero trim in the Vbar software.
4. Set your tail end points to equal values (or distances).  For example: I set mine to 120/120 left/right.
5. If you lessened the amount of right thrust you must increase the gyro gain (aka: common gain).
6. If you had to add right thrust, first try leaving the tail gain where it is at and proceed to the testing section below.
7. I installed “Chinese” tail weights to the tail blade grips.
8. I installed 115mm tail blades.
9. After testing gyro gain (see below) you may need to increase torque pre-compensation on the tail rotor to fine tune tail kick with collective climbs and rainbows.

Testing:

1. Test gyro gain by flying extreme fast forward flight from one side of the field to the other, or a big fast smooth circuit.  I mean full collective and pitch forward like in a drag race and keep it moving!!  Increase the gain by 5 points until you have a shutter or wag on the tail, then back down 1 or 2 points and test fast forward flight again until perfected.
2. After that, a very high tail slide may be used to test.  Again look for a shutter or wag.  If you get a shutter or wag, very gently abort the tail slide.  You don’t want to break anything.  Perfect gain should hold solid as a rock without shutter noises.

Results:
After tweaking the tail gain to the edge of possibility (value of 100), then I added torque pre-compensation (value of 70) on the vbar.  My tail now virtually has no tail kick – so tiny it’s almost undetectable.   The combination of mechanical setup, peak common gain, and supplemented with torque pre-compensation was a winning combination.  However it is only as good as a solid mechanical setup… all the way to carbon fiber blades.

Warnings/Taboo:

• Plastic tail blades are a no-no.  Use carbon fiber for superior tail performance.
• Regularly apply oil between the tail shaft and pitch slider.
• The tail pitch assembly must be totally smooth in all movement.  If a screw is too tight or if locktite is binding up a joint, do what ever is necessary to have a perfectly smooth operating tail pitch slider.
• Slop between the linkage ball and ball link means you need to replace one or both.
• Slop on the lever driving the linkage ball attached to the pitch slider means you need to replace the lever and/or linkage ball.
• Slop on the tail pitch slider on the tail shaft might means it’s time to replace the pitch slider, and if you haven’t replaced the tail shaft after hundreds of flights without crashing then the shaft might be worn out from all that sliding.  (the solution is to crash more!)
• Wobble on the blade grips isn’t a biggie, so don’t worry too much.
• Tight tail blades is not an issue (but snug them so the blades are not flopping around).

Vbar changes and calculations

I did a little more homework and remembered I can plug in two numbers in a calculator within the Vbar software that will assist with determining the blade pitch on a rotor.  Here’s what it looks like:

http://www.vstabi.info/en/collective

That picture is showing using it for the main rotor, but I thought a rotor is a rotor, so I plugged in 115mm for my tail blade size and determined 12mm for the distance value to achieve 3 degrees of blade pitch.  The Vbar recommends 3 degrees of right thrust at servo center and so now I think I finally got it.  The 12mm distance is pretty small – a little less than 1/2 inch.  Because I have play in my tail grips and a little play on the pitch slider I held the tail assembly rigid with my fingers and then measured the distance of the blades while rabbit ear’d.  I noticed too that the 12mm distance more narrow than my pinky finger (but I might have fat fingers?).  The distance would be slightly more narrow for 105mm tail blades and 95mm tail blades.  Basically 3 degrees of tail pitch isn’t much, but folding your blades rabbit ear’d amplifies the movement so you can see it loud and clear.

I will keep experimenting with the 3 vbar banks with tail precompensation by increments of 5 this time.  before I might have been way too aggressive and went from 22 up to 100 with large jumps.  I’m thinking perhaps too large of a value might be backfiring in results?  I’ll find out this way.  Also the newly set 3 degrees tail right thrust might make a difference, but not too sure.  I will test it all tomorrow.

Since I lowered my tail i value from 75 to 60 I notice the tail pirouette consistency both felt and looked more consistent… which is perfect because I was battling whipping in my pirouettes while moving in hurricanes and piro flips.  I also increased the P value from 75 to 80.  The P & i values of 80 & 60 is the software default values now with the latest Vstabi PC software so it made sense to stick with that for now.  The tail P & i values are advanced settings and even I dare not to play with them unless I have MrMel’s instructions.  MrMell said to lower the tail i value if you have whipping (aka: inconsistency in pirouettes while traveling and/or in wind).

I like the bank switching because it allows me to try settings much quicker and without landing.  Later I tried 2 more settings and toggle while in the sky.  I say only 2 more settings because you always want to have a known-good setting to fall back to if something bad were to happen, or if you loose track of your settings.  I also keep a written log of what I’m doing and settings’ results.

Vbar changes

I’m going to be playing more with my vbar gov settings.  The first step was to enable bank switching.  That was simple to assign the Aux channel number to a physical 3-way swtich and it was done.  The first bank will have default settings.  Bank 2 & 3 will have different settings to experiment with.  The one setting I’m going to play with first is the gov collective dynamic.  Collective Dynamic is the feed forward to the gov for preemptive rpm maintenance to account for what the gov cannot see coming (like pitch pumps).

I’ve already changed the tail P and I values to the software’s new defaults of 80 and 60 respectively.  I was running 75 and 75 and I experienced pirouette inconsistency.  I learned from MrMel lowering the I value will help piro consistency.  I also returned the tail collective torque compensation to the default value of 15, but I had it at 100.  I did well especially during aileron tictoks where a Jamie Robertson tail wiggle will be present if not optimized.  I’ll play with all this next time I’m out.  If I get frustrated I will simply load in my saved settings from before which worked pretty well.  I’m just looking for optimizations.

Video of 1900RPM

I finally captured some heavy flying with the 1900RPM headspeed.  I used a helmet cam on my head.  I edited the video to cut out some boring stuff and to highlight  the more maneuvers that stressed the machine and proved the strength while at 1900RPM.

Video here: http://www.youtube.com/watch?v=9UYo5cbtQkk

I played with 1800RPM headspeed but while it flew well too the motor ran higher temperatures due to ~400RPM less motor RPM.  The fan built into the motor that cools it was spinning less but the motor was working as hard or harder than 1900RPM head speed.  If the motor spins less then the less it is cooled by the fan, and the ~400RPM less made a negative difference.  That’s ok because I feel 1900RPM is what I want to fly with now.  I would be able to run 1800RPM or less safely and easily with a 12T pinion but maybe another time.