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Old 02-10-2009, 07:33 AM   #1
hpais
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Default How to ensure the head is balanced?

I just finished assembling the Spectra (will post pics) and got the first flight through.

I have a few comments and a question:

1. How to verify that the head is balanced? Is it enough to put the heli sideways, disconnect links to the head, ensure the main shaft is level, blades are balanced and see that the head stays put in all positions? (blades horizontal, vertical, 45 degrees?)
-- If the head is not balanced, is it enough to put a couple of washers until it does? Will this also establish dynamic balance?

2. How do you take the head apart? The part of the assembly that scared me the most was putting the circlip that hold the dampers on the head blade shaft. how do you remove those circlips without breaking them? -- BTW I Hate those circlips, they´re awkward

3. On spinup the whole heli wobbles as if the center of spin of the blades is not through the main shaft. On idle, blades not spinning, the fuel on the tank seems to be boiling. After spin up and when the heli is off the ground, everything is smooth --- but the wobble makes me think the head is off balance... - - Can it be or is it my paranoia

4. First lift off required almost full stick... then after one minute of flight I started reducing the stick as if the engine was gaining a lot of power. After five minutes it was hovering right at mid stick Yes the needles are 1 1/2 turns open. It smokes a bit and there is a tiny amount of unburnt oil blowing out the hatori muffler. 1:30 mineral oil as stated in John Garst's instructions. 25C (77F) temperature. 750m (2460ft) above sea level (it's Sao Paulo). It drank 250ml (8oz) of fuel on this first 5 minute flight. The TRM engine is now smoothing out.

First engine start was done with blades off, the heli securely strapped to a hobby table. This gave me the chance to set engine cutoff and other throttle servo setpoints in safety. I was careful not to give it gas enough to make the clutch engage and the unloaded head spin.

This first flight I did on top of a concrete pavement. Glad I did because everything that wasn't loctited came off. Nothing serious: the tiny screws that hold the graphite tail pushrod holders to the tail boom; the screws that hold the air filter bling cover; the head cap screw (I always loctite it last); the screws on teh pull starter (I forgot to take the pull starter off the first three starts - then kept it off for this first 5 minute flight). Concrete helps find screws that fly off the machine!!! On grass they'd be lost forever.

As stated in the instructions, with the muffler hot I managed to get another 1/4 turn of the screws on the muffler, and almost a full turn on the screws of the carburator -- these aren't loctited as they touch the engine which gets hot and melts the loctite.

The jewel generator is appropriately named! Steady full greens on the bar voltmeter. The BLS451 do draw a lot of current. Without the jewel connected I could see the voltmeter fluctuate a dot or two when moving the servos under the load of the head. With it connected, everything full green.

No interferences on the Futaba 2.4GHz radio -- I did keep the engine original as recommended, did not install the RF shields.

I managed to set the GY611 at 60% gain. Steady tail. I did not try to set it any higher as I believe that with the engine breaking in and such there are still vibrations that will make the GY611 overworked and overstressed.

Man this thing is huge in the air!
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Old 02-10-2009, 07:50 AM   #2
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1. you described static balance, dynamic balance requires the addition of a flybar weight and you then move it around on the flybar to achieve a vibration free RPM range. this will be pretty specific in range and requires a bit of trial and error, a friend and a tachometer.

2.loosen the clip and slide it partway off the shaft. Use magnetized pliers to remove it completely from the shaft. You will get better at it as you perform it.

3.vibration induced fuel 'boiling' is normal at idle, one big cylinder banging around tends to do that. Vibration at flying RPM is what you need to be concerned with.

4. As the engine breaks in, you will notice an increase in power as internal drag is diminished. with the break-in oil content you will also see the oil dripping from the muffler. Once you change over to the 'normal' mix, this will disappear and you will have more power as well.

Glad to hear you got it in the air! You started well before me on my build, and I haven't been really motivated to spend hours at the bench.
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Old 02-14-2009, 02:21 PM   #3
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Hey Hermann sounds like you are doing great!

I have just about got the main body of the kit built, need to order electronics now...
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Old 02-16-2009, 10:19 AM   #4
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Hermann, did you have to but a larger servo wheel for the BLS451's or did it come with one that does the job okay?
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Old 02-17-2009, 03:27 PM   #5
hpais
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Hi Kevin,
I used the standard arms that came with the BLS451. They're OK, throws are correct and they introduce very little exponential throw at the ends of the throw. I made sure I had them centered and that the bellcranks were centered when all servos were at mid position. Blades were at 0 degrees in all quadrants.Swashplate also absolutely level. I purchased the MinAir swash level tool but it wasn't necessary. Instead I used a small bubble level I had purchased at Home Depot. And I made absolutely sure I had zero subtrim. All adjustments were made to the pushrods to ensure everything squarely aligned at mid-position and zero degrees.

With this setting I was able to get beyond 12 degrees of full up and down deflection, and made sure the swashplate wasn't hitting on the corners (low left, upper right extremes of elevator/aileron deflector).

The wheels that come with the BLS are 27mm, while the large futaba wheel is 30 mm. The bellcranks on the Spectra are 28.5mm, so they are neither the same size as the large wheel nor the BLS arms. Both will introduce a non-linear response which gets corrected when you set the pitch curves on the radio.

All I can say is the precision of this helicopter blows my mind!

My previous experience was building a Trex600 electric, which is also very well made, but not at the same level, feeling-wise - on the Spectra there is no play at all in all subassemblies, perfect fit, great machine work. The Trex has several plastic pieces which require filing and a very delicate hand not to overdo the fitting of parts.
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Old 02-17-2009, 03:29 PM   #6
hpais
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And By the way, I did have the large futaba wheels at hand. I didn't use them because they'd be a bear to shave to allow fitting of the Servo doublers. The arms just fit with the doublers without interference.

I haven't put many flight hours - it's been raining daily here, but with the BLS451 it flies like it's on rails, very stable (I set the expos at -30% on the futaba radio).
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Old 02-17-2009, 04:05 PM   #7
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Sounds good Hermann thanks for the report!

Looking forward to been able to order my electronics soon, I have been looking out for used stuff but I think for the difference in price I will buy all new...

Hope to report back on my first flights soon :o
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