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HelicopterAudacity Models P6 Pantera - Tiger 50 › Just how important is CG?
12-19-2008 02:07 PM  9 years agoPost 1
The Dude II

rrVeteran

IN - USA

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Fellows,

As we already know, our Pantera tends to be a bit tail heavy if we go light on the electronics.

Do a search here on RR on Balance & CG...you'll see we are not alone on this issue.

I had excepted that helis are somewhat more difficult to fly than it was to make a good cup of coffee.

After all, every heli I've owned/flown always wanted to "go where it wanted" and I thought that was part of the equation...you have to be a real good pilot to stay on-top of the machine at all times and make it look good.

I didn't use a large battery up front to balance it out...because I was splitting hairs on the over-all weight and hadn't given much thought to CG placement.

I've been balanced on the main shaft shaft with an empty tank most of the season...and thought that was "good enough". Keep in mind, at a full tank it was significantly tail heavy.

Recently, I've been able to REALLY FOCUS on the machine and how it's handling...Night flying in really quiet/calm air exposes "flight handling issues" that I previously thought was just the wind messing with me.

I've been experiencing "quality of flight" issues as I spend more time inverted.

Specifically: (with heli trimmed for hands-off upright hover and SWASH mixing setup for true vertical climb-outs both inverted & upright)
Inverted hover...had to hold a good bit of back pressure (aft cyclic - in order to keep it level).

Aileron Rolls...(stationary & in FF) first couple were just OK... but keep it up and you'd be flying backwards if you didn't nudge forward cyclic every time you passed through upright.

Inverted Circuits...in order to maintain level flight had to keep pulling aft cyclic.

I've been torn...I've swapped CF for metal were I could and just recently moved the gyro sensor forward and chopped-up the tail fin.

http://www.runryder.com/helicopter/t478599p1/

Do I add weight and fly a heavier bird?

Thought about it after combing through search results here on RR and applied some "learned" things from another area of the hobby.
On planes (yes...heli guys...you can learn a thing or two from playing with a lesser machine)...we fiddle around with CG to get it handling just right...especially if you're flying IMAC.
In IMAC, it's very important the machine flies "true" with hands-off...or the work-load on the pilot goes UP to the point the "average" pilot just can't make it look good.
IMAC is to a large extent about symmetry and correct geometry on maneuvers.
How close to a "perfect circle" is that loop?
Does the aileron roll look like axial...or like a cork-screw?
Does the plane fly straight & level line from end-to-end across the flight line...upright & inverted?
etc.

If the plane is designed/built correctly...you can shift the CG around and achieve these results with just a few flights.

Finally, I came to the conclusion to try and ADD some dead-weight to the front of my Pantera.

Filled the fuel tank to 50%...locked the blades in the grips and put the canopy on.

It needed 1.8oz of weight up front...so I went from 7lb-13oz to ~ 7lb-15oz (empty weight).

So how does it fly?

After 4 tanks the other night...all I can say is...

Wish I looked at the CG closer earlier!

It will do as many aileron rolls in a line as the field is long with little to no corrections (like 9 rolls in a row...either left or right handed). Rolls are axial! No more cork-screwing...unless I miss the timing on the collective or put in elevator inadvertently.

It will fly hands-off in FF... straight & level(inverted or upright) as far as I will let it...maybe 8-10 seconds @ ~ 30mph.

And because the load under the blades is more centrally located...the head doesn't bog as easily when pulling and pushing the sticks.

Reality is, from about 3/4 to 1/4 tank, the bird balances on the main shaft. Full tank...the tail is heavy enough to rotate to about a 45 degree angle downward...likewise...empty tank is nose heavy about the same amount.

I'll take knowledge that I'm 2oz heavier any day... knowing that it HANDLES better!

lotta ins, lotta outs

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12-19-2008 03:11 PM  9 years agoPost 2
Kjarman

rrApprentice

noblesville, IN

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I know what I'll be doing on a cold winter day..... Ballancing!!! Thanks Gus.

I sold another one to Terrafirma...... wife wants to know where the money's at!!!!

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12-19-2008 07:07 PM  9 years agoPost 3
bclong211

rrApprentice

Columbia ,SC

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Yea i am with you kjarman. Pretty compelling info. I have one pretty close by shaving everything off the tail that I could but my other heavier pantera is very prone to the tail swings you mentioned. That is what caused the only crash I have had with it. I was doing elevator loops stationary and the tail kicked around about 90 deg while I was inverted and it was just enough to bog the head to where it could not be flipped back up right before the blades struck the field.

I meant to do that!!!

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12-19-2008 09:40 PM  9 years agoPost 4
kmaxphil

rrNovice

Prince George,B.C.-Canada

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I am glad you wrote this post. I know c of g is important I just didn't bother. I guess that explains some of the issues with trim I have been haveing. The best part is I have a reason to go into my hobby room and play helicopter engineer. As for waiting for a cold day it was minus 28celsius here this morning so I no time like now.

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12-19-2008 09:52 PM  9 years agoPost 5
Santiago P

rrProfessor

South West, Ohio

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slightly fwd bias on the CG will improve hovering stability and fwd flight tracking.
Slightly aft, will improve the rection for aerobatics.

Neither one is right or wrong, is whatever works or feels best for you.

Happy medium would be balancing the heli level at mid tank.
good luck

Team Minicopter - PeakAircraft.com
bavarianDEMON- Team Kontronik - Scorpion Motors-

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12-20-2008 01:25 AM  9 years agoPost 6
The Dude II

rrVeteran

IN - USA

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MoneyPitVictim,

That's what I'd heard...but never paid much attention too.

Always thought tail heavy = 3D...so why change?.

That's what I had aspired too.

Reality is, I'm an O.K. 3-dr at best... as if to place on platform...but certainly prefer smooth moves first.

lotta ins, lotta outs

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12-20-2008 01:59 AM  9 years agoPost 7
Heli_Man_Bob

rrApprentice

Miamisburg, Ohio, US

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To Balance my Pantera I had to add 6oz to the radio tray used stick on derby car weights .

Using 3cell lipo with ubec for the rec I think this is why I needed more weight.

Have not weighed the heli

Aileron rolls are amazing with the Pantera

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12-20-2008 03:09 AM  9 years agoPost 8
billm

rrElite Veteran

Liberty Lake, WA

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Gus,
Your on the mark as always. Hate to say it but all the years of plank flying the CG was the key. In the heli world nothing with the laws of physics have changed. Thats why (some of you in the past have poo pooed me) I use the longer tray. Instead of dumping lead in the mix. I decided to have "working" weight. Larger battery pack and a regulator. The down side is a bit more mass. the up side is faster servos (the regulator can pump the juice) and flying all week without a charge.
In the plank world you have a large fuse to fuss with CG. IE moving things around. In our heli world you have very limited wiggle room.
Nice post and this is my 2 cents. I would love to fly but we just got 19 inches of snow the last 24 hours. No wait!! I have a pantera snow blower! I just get to hover over the car park to clean things off.

My name is Billm. Cough, and I'm a Heli Holic

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HelicopterAudacity Models P6 Pantera - Tiger 50 › Just how important is CG?
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