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Author Topic: How do I set the CofG  (Read 11908 times)

skyhawk newbie

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How do I set the CofG
« on: October 19, 2010, 00:53:55 AM »
Hi to all...
I'm new here and new to flying ..
Just got meself a 4Ch SkyHawk Powered Glider..
http://cgi.ebay.com/New-4Ch-RTF-RC-EP-Aerobatic-TW742-SkyHawk-Glider-Plane_W0QQitemZ290326804731QQcategoryZ19164QQcmdZViewItemQQ_trksidZp3286.m7QQ_trkparmsZalgo%3DLVI%26itu%3DUCI%26otn%3D3%26po%3DLVI%26ps%3D63%26clkid%3D5078401181636134857
But I know you have to have a CofG for good glideing,but as the battery is held on with vercro , its not set for the CofG..
So how do I do it ...the vest and easyest way...  LOL

Thanks

Sean
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Richard Boyd

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How do I set the CofG
« Reply #1 on: October 19, 2010, 07:17:38 AM »
Hi Sean, is it possable for you to relocate your battery to make your CG in the correct position ?
You can add weight like small pieces of lead to position the CG correctly, but from my own personal experiances it is much better to move the battery or purchase a larger battery to give you the correct CG.
Hope this helps in some way,

Richard
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Richard Boyd
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Ron

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How do I set the CofG
« Reply #2 on: October 19, 2010, 07:50:55 AM »
Hi Sean,

That's very good value isn't it?
All that stuff for 47 quid.

I'm guessing that maybe you mean where should the CofG be, as well as how to adjust it.

As Richard says, moving the battery is the best way to adjust it, but the position of the CofG should be marked either in the instructions of even possibly on the model itself.
One theory I've seen is that it should be about 24% of the wing chord back from the leading edge, and I'd say that position would give you a reasonable starting point.
Then it's glide tests in the proverbial 'long grass'.
But as the silage and hay season is well over, it might have to be heather and furze :(
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skyhawk newbie

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How do I set the CofG
« Reply #3 on: October 19, 2010, 14:12:10 PM »
Thanks for all replys...

Theres not alot of info in the manual,very basic..
Theres only 6 pages in the manual and the first 4 tell you how to put the glider together...the other 2 are about setting the Tx
The Prop is called a Airscrew ! ! !

Found out some more info on setting CofG
measure the wing from leading edge to trailing edge...(215mm) devide that by 4 (=53mm) then mark the wing back from leading edge....
Then devide the 215mm by 3 (=71mm) mark wing again...
Your left with two marks on the wing...
Set CofG ,slightly more to the front mark of the two on the wing for gliding...
think I've got this sorted...????
If this is the wrong / right way ..Please let me know....

Sean
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How do I set the CofG
« Reply #4 on: October 19, 2010, 16:06:07 PM »
Yup, pretty much Sean, well done! :clap:

In case you didn’t know, the distance between the leading and trailing edge of a wing is called its Cord.
The centre of gravity of most planes is roughly between a quarter and a third of the chord back from the wings leading edge. :wink:  

For your first flight it’s safer to have the CoG a bit forward. So if I were you I’d set the model to balance on the forward mark.

In time, if you want to make the plane more aerobatic, you can move the CoG rearward, but generally your CoG should be somewhere between the two marks that you’ve made. :D

Keith
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Fred

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How do I set the CofG
« Reply #5 on: October 19, 2010, 19:40:31 PM »
If I may add, the CoG is roughly 1/3 of the average chord of the wing! (like for the Crystal, it's almost 50% of the root chord...)
But also depend of the calage to complicate the thing slightly further  :P

Saw on another forum, the greatest advice ever to find the correct CoG of a plane !... This is where the wing is the thickest ! Whatever wing shape, size, profile etc  :shock:

Anyway, centre the plane like they say in the manual, and you will refine it in flight.
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gerryb

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« Reply #6 on: October 19, 2010, 20:02:10 PM »
hi sean,
adding my tuppence worth.....everything said so far is spot on. now, to check cg in flight. fly the model to about 3 to 4 hundred feet. might seem a lot with what looks like a small model but you need to have plenty of sky under the model to recover. ok, at height, face model into wind, power off, apply down elevator to make the model dive (not too steep, mind you!) relax your grip on the stick and see what the plane does.
if it recovers in a long slow arc, your cg is spot on.
if it pulls up fairly sharply, cg too far forward. move battery back or remove lead.
if it continues to dive, cg too far back. move battery forward or add lead.
any changes you make should be one at a time and in small amounts.
have you anyone locally to help with your 1st flights?
gerry
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skyhawk newbie

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How do I set the CofG
« Reply #7 on: October 19, 2010, 21:25:19 PM »
Quote from: "Fred"
If I may add, the CoG is roughly 1/3 of the average chord of the wing! (like for the Crystal, it's almost 50% of the root chord...)
But also depend of the calage to complicate the thing slightly further  :P

Saw on another forum, the greatest advice ever to find the correct CoG of a plane !... This is where the wing is the thickest ! Whatever wing shape, size, profile etc  :shock:

Anyway, centre the plane like they say in the manual, and you will refine it in flight.


There's nothing in the manual about setting the CofG....
and as I'm totaly new to all this flying lark , your going to get lots of silly question from me....
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skyhawk newbie

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Re: cog
« Reply #8 on: October 19, 2010, 21:37:03 PM »
Quote from: "gerryb"
hi sean,
adding my tuppence worth.....everything said so far is spot on. now, to check cg in flight. fly the model to about 3 to 4 hundred feet. might seem a lot with what looks like a small model but you need to have plenty of sky under the model to recover. ok, at height, face model into wind, power off, apply down elevator to make the model dive (not too steep, mind you!) relax your grip on the stick and see what the plane does.
if it recovers in a long slow arc, your cg is spot on.
if it pulls up fairly sharply, cg too far forward. move battery back or remove lead.
if it continues to dive, cg too far back. move battery forward or add lead.
any changes you make should be one at a time and in small amounts.
have you anyone locally to help with your 1st flights?
gerry


Had my first flight last Saterday...
I crashed....Broken prop and cracked wing....
Fixed the wing,just waiting for 3 props to come from the UK
and another 2x SkyHawk gliders  from Hong Kong,just incase

Found out yesterday theres a local flying club
near where I live that meets every Saterday...
So hopefully they'll be there this weekend....
If the weather is OK

Sean
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How do I set the CofG
« Reply #9 on: October 19, 2010, 23:03:19 PM »
That’s what you need Sean……….a local flying club. :D  
They’ll be able to show you what to do and help answer some of your “silly” questions.

(Actually there is no such thing as a Silly question. It’s far sillier to try and fly a plane without knowing what your doing, than to ask someone what to do first. There isn’t a pilot alive how hasn’t asked ”silly” questions at some point. :wink: )

Good Luck, let us know how you get on.

Keith
(I still ask silly questions............... :roll: )
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Ron

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How do I set the CofG
« Reply #10 on: October 20, 2010, 14:15:40 PM »
Hi Sean,

Good to hear you've found a club near you, and presumably with a flying field?
As you live in Bandon it maybe the closest club to me (Bantry), so wonder where it is?
May just see you there on Saturday....

Ron
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skyhawk newbie

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How do I set the CofG
« Reply #11 on: October 20, 2010, 14:25:13 PM »
Quote from: "Ron"
Hi Sean,

Good to hear you've found a club near you, and presumably with a flying field?
As you live in Bandon it maybe the closest club to me (Bantry), so wonder where it is?
May just see you there on Saturday....

Ron



Rang a guy called Barry Leach..
Will PM you his phone number...
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skyhawk newbie

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How do I set the CofG
« Reply #12 on: November 05, 2010, 00:19:19 AM »
Quote from: "Ron"
Hi Sean,

Good to hear you've found a club near you, and presumably with a flying field?
As you live in Bandon it maybe the closest club to me (Bantry), so wonder where it is?
May just see you there on Saturday....

Ron



Met up with Barry last saterday at the flying field,great spot easy to find, he mailed me today as they mite be there this saterday aswell,if weather is OK.

sean
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Ron

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How do I set the CofG
« Reply #13 on: November 05, 2010, 12:18:12 PM »
Hi Sean,

Weather looks decidedly duff, but if I can escape from this job (that seems to be endless in this weather :( ), I may have a quick trip up there tomorrow PM.

Ron
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