Center of Gravity

[M.Schmavs]

Curious what I'm doing wrong here. I'm getting back into the hobby after ~11 or so years so I'm definitely rusty with setup details. Just to mention, the flybarless stuff is all new to me too. I was flying 450 and 600 sized flybared electrics with FM crystals. I ALWAYS wanted a Synergy. They were so cool looking back then and even now. I think it was the N9 that I fell in love with. Soooo, new transmitter and new model and a 500 size is perfect for my property.

Anyway, I'm wrapping up the build and decided to measure the COG while I have everything mocked up. Unfortunately, it's tail heavy. I was surprised because I have a non-recommended and heavy GensAce 5000 mAh battery. Even all the way forward, it's still tail heavy. Unfortunately, I can't run it all the way forward because the canopy won't fit. I don't imagine a smaller battery would help but what do I know after all these years.

My method is to set my blades perpendicular to the tail, disconnect the grip links so the grips swing on the feathering shaft without servo resistance and pick the model up and set it back down. I mostly observe which end of the skids hit the table first when setting it back down. Obviously, the rear skids hit first.

I know there's a carbon boom available but I'm just surprised the battery isn't heavy enough to center the model even all the way forward with the unmounted canopy drooping off it.

Setup:

Futaba CGY760R mounted on the gyro plate
All servos are the recommended MKS
GensAce 5000mAh
XNova 4020-1200kV (16T main and 18T tail)
Hobby Wing 120
The whole thing comes in at ~2850g if I remember correctly.

So, what am I doing wrong?

Edit: 18T tail gear, not 20

[alan]

I have run gensace 4000’s, pulse 4500 and most recently Scorpion 4500’s. Never had a problem getting a reasonable CG.
How are you checking your CG? The blade down your arm method is how I spot check CG and works well. You may be over reacting. Modern day flybarless units do not require spot on CG. The only time I get obsessed with CG is an F3C setup.
Cheers
Alan



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[M.Schmavs]

From above, this is my method:

"My method is to set my blades perpendicular to the tail, disconnect the grip links so the grips swing on the feathering shaft without servo resistance and pick the model up and set it back down. I mostly observe which end of the skids hit the table first when setting it back down. Obviously, the rear skids hit first."

Can you explain the "down your arm" method?

With today's technology, you're right, I'm probably overthinking this but no one never accused me of not being thorough!

[Wolf51]

Hi,

My 516 spec is very similar to yours.
Xnova 4020 1350, hobbywing 120 v4.
I use gens ace 4400 65c and 5000 60c packs.
With the 4400 onboard i get good cog with battery tray locked in 3rd hole from front.
With 5000 onboard its 4th hole.
I am using the option carbon fibre boom which saves about 50g and gives 1 locking hole toward the rear difference from the std alloy boom.

COG check, like Alan, is blades down the arm method. i.e.
Hold the heli on its side by the main blade grips with grips/blades vertical - resting on your arm to take the weight if necessary.
If the boom wants to rotate downward its tail heavy, if upwards its light, etc. Good cog will have the heli not rotating, regardless where the boom is pointing. It may help to back pinion off maingear to eliminate drag from the motor.

The 516 is an awesome model, I hope you enjoy it.

Cheers

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[M.Schmavs]

You guys are awesome. Thanks so much for the info!

I'll likely pick up the carbon boom anyway. The only reason I don't have it now is because I actually forgot to add it to my cart when ordering the gears. Ha!

Thanks again!

[M.Schmavs]

The carbon boom fixed the issue! Probably no surprise to anyone here but I just wanted to provide an update.

Just looking forward to finishing it up now. It's been a fun build!

[Wolf51]

Getting the build how you think it should be is a big step toward happy flying.

Good luck with the maiden


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[M.Schmavs]

Funny you say that. I was reconfirming all my pitch curves and found my transmitter collective stick was not calibrated from the factory. I reached out to Futaba and thankfully they replied quickly with how to fix it. I found the instructions they gave me on the very last page of the manual beginning with "The settings here are special settings that are unnecessary during normal use." Haha

So what that means is, I programmed everything uncalibrated. Luckily, I think I got away without redoing everything by calculating the difference and reprogramming the servo neutrals in the CGY and adding a couple twists on the pitch links. Everything seems good except I'm still getting different pitch values from negative to positive and right/left and fore/aft cyclic.

I'm going to start a new thread because I think I need some more assistance. Hopefully, it's not much to worry about like CG!