OK gujys, I need help on CG
03-31-2013, 07:59 PM
#51
RE: OK gujys, I need help on CG
While on the subject of CG and balance
Do balance all RC planes left and right- after the front to back CG is established
You want the planes wings to come back to the planes center ,when you tip either wing a few degrees , left to right
Hang the plane by the engine hubfrom the ceiling -piston not on compressionturn the radio on and center your finger on the bottom of the rudder or the center rear of the fuseadd weigth on the wing that rises -until you come back to the center from both sides -
Balancing this way increases level flight stability very very greatly
Do balance all RC planes left and right- after the front to back CG is established
You want the planes wings to come back to the planes center ,when you tip either wing a few degrees , left to right
Hang the plane by the engine hubfrom the ceiling -piston not on compressionturn the radio on and center your finger on the bottom of the rudder or the center rear of the fuseadd weigth on the wing that rises -until you come back to the center from both sides -
Balancing this way increases level flight stability very very greatly
03-31-2013, 08:33 PM
#52
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RE: OK gujys, I need help on CG
does he include the ailerons? and what does he use for MAC %?
ORIGINAL: Speedy-Gonzales
Here!
Grab a measuring stick, fill in the blank boxes, and figure it out.
http://www.geistware.com/rcmodeling/cg_calc.htm
Speedy-Gonzales
Here!
Grab a measuring stick, fill in the blank boxes, and figure it out.
http://www.geistware.com/rcmodeling/cg_calc.htm
Speedy-Gonzales
04-01-2013, 01:05 AM
#53
RE: OK gujys, I need help on CG
Unless the instructions say otherwise, the measurement should be taken from the root of the wing.
Just for interest; If it is a parallel chord, then it will be the same as the tip and should be about 30% If it is a tapered wing then the measurement at the root will be greater than 30%.
MAC is more difficult to calculate so I wouldn't worry about it. But the measurement you have should be about 30% of the MAC.
Just for interest; If it is a parallel chord, then it will be the same as the tip and should be about 30% If it is a tapered wing then the measurement at the root will be greater than 30%.
MAC is more difficult to calculate so I wouldn't worry about it. But the measurement you have should be about 30% of the MAC.
04-01-2013, 04:37 AM
#54
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RE: OK gujys, I need help on CG
ORIGINAL: chadxp1
does he include the ailerons? and what does he use for MAC %?
does he include the ailerons? and what does he use for MAC %?
ORIGINAL: Speedy-Gonzales
Here!
Grab a measuring stick, fill in the blank boxes, and figure it out.
http://www.geistware.com/rcmodeling/cg_calc.htm
Speedy-Gonzales
Here!
Grab a measuring stick, fill in the blank boxes, and figure it out.
http://www.geistware.com/rcmodeling/cg_calc.htm
Speedy-Gonzales
It is astonishing how much highly technical information (some of it wrong) has shown up in response to a simple question in a beginners' forum. All he needs to do is use this calculator to check to see whether the manufacturer's 5 1/4 inch back from the leading edge recommendation (measured at the root) is right. If it isn't, go with the CG calculator's result. Beginners come here looking for advice, not a display of people's dazzling vocabulary of aeronautical jargon.
04-01-2013, 05:41 AM
#55
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RE: OK gujys, I need help on CG
While it's nice to know the technical stuff, if a guy is using the calculator mentioned above it's not necessary. The guys who made the calculator understand the technical reasons why it needs to be the way it is, and they designed the calculator to work properly. All a guy really has to do is make the measurements it asks for and plug them in.
As for fine tuning the trainer the OP is asking about, my thought is that the CG should be as far forward as possible while still allowing a good flare for landing. That doesn't mean making it so nose heavy you can't get the wing to stall and settle in, but rather nose heavy enough that the nose naturally wants to drop as the airspeed slows and the pilot has to hold it up. A perfect trainer setup has the pilot hitting the end of the stick travel just as the wheels are touching. If the plane is settling in on the mains first and then touching the nose wheel down a second or two later, the CG is right. Such a setup will be speed sensitive, which means the plane if trimmed for level flight at 60-70% throttle will pitch its nose up at 100%. That's very handy for aborted landings and instructor saves.
On a related topic, I find that our terms we often use regarding CG are confusing to the beginner, and sometimes to experienced guys as well. For any plane, there is a range of CG where the plane will fly safely. Forward of that range, the plane fights elevator inputs and becomes impossible to flare for landing and aft of that range it becomes aerodynamically unstable. The terms we use so much "nose heavy" and "tail heavy" don't make a distinction between whether we are talking about a preference within the acceptable CG range or going too far. If new pilots could get it explained to them more clearly that our advice applies to the acceptable CG range and how to recognize if their planes are outside of that range, I think we'd have a much easier time helping new pilots get their planes set up right.
As for fine tuning the trainer the OP is asking about, my thought is that the CG should be as far forward as possible while still allowing a good flare for landing. That doesn't mean making it so nose heavy you can't get the wing to stall and settle in, but rather nose heavy enough that the nose naturally wants to drop as the airspeed slows and the pilot has to hold it up. A perfect trainer setup has the pilot hitting the end of the stick travel just as the wheels are touching. If the plane is settling in on the mains first and then touching the nose wheel down a second or two later, the CG is right. Such a setup will be speed sensitive, which means the plane if trimmed for level flight at 60-70% throttle will pitch its nose up at 100%. That's very handy for aborted landings and instructor saves.
On a related topic, I find that our terms we often use regarding CG are confusing to the beginner, and sometimes to experienced guys as well. For any plane, there is a range of CG where the plane will fly safely. Forward of that range, the plane fights elevator inputs and becomes impossible to flare for landing and aft of that range it becomes aerodynamically unstable. The terms we use so much "nose heavy" and "tail heavy" don't make a distinction between whether we are talking about a preference within the acceptable CG range or going too far. If new pilots could get it explained to them more clearly that our advice applies to the acceptable CG range and how to recognize if their planes are outside of that range, I think we'd have a much easier time helping new pilots get their planes set up right.
04-01-2013, 08:18 AM
#56
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RE: OK gujys, I need help on CG
NASA has a web site for modelers to figure CG:
http://www.nasascale.org/howtos/cg-calculator.htm
Go figure...easy to use.
http://www.nasascale.org/howtos/cg-calculator.htm
Go figure...easy to use.
04-01-2013, 10:59 AM
#58
RE: OK gujys, I need help on CG
Yes, 25% is a perfect start up balance point for a model like yours.
.........and that is measured from the interception between the center of the fuse and the LE of the wing.
Here is the graphic method, just for your reference.
.........and that is measured from the interception between the center of the fuse and the LE of the wing.
Here is the graphic method, just for your reference.
04-01-2013, 11:55 AM
#59
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RE: OK gujys, I need help on CG
If I follow your drawing how come you show CG at 4,405 Where mine was 5,340. Guess I missed something on your drawing. Remember we are still working with a almost 3rd grade education[:'(][:'(]
04-01-2013, 01:41 PM
#60
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RE: OK gujys, I need help on CG
I sent you a PM. CALL ME! I will walk you through this.
Talking directly to you via phone will be much easier and we will work together to get your CG measurement.
You can ask all the questions you want and I will give you simple ( and correct ) answers.
You will need the wing, a yardstick, and a place to lay your wing on the floor up against a straight wall in your house.
Preferably on a carpeted floor so your wing wont slide around while measuring it.
No problem my friend!!
S-G
Talking directly to you via phone will be much easier and we will work together to get your CG measurement.
You can ask all the questions you want and I will give you simple ( and correct ) answers.
You will need the wing, a yardstick, and a place to lay your wing on the floor up against a straight wall in your house.
Preferably on a carpeted floor so your wing wont slide around while measuring it.
No problem my friend!!
S-G
04-01-2013, 03:55 PM
#61
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RE: OK gujys, I need help on CG
OK
Was nice talking to you on the phone. Glad we straightened this out.
Just for your reference here is your wing. The calculated CG is 5.47"
so 5 1/4" ( as specified ) is a forward and safe place to start for your first flights.
Double check to see if the back edge of your wing is straight like
the first picture/drawing. If it is straight then we have the correct CG.
The 3rd photo is of a G-Shark with a straight trailing edge.
If this does not look right to you then call me back and we will start over.
This plane really reminds me of a GILES 202.
Was nice talking to you on the phone. Glad we straightened this out.
Just for your reference here is your wing. The calculated CG is 5.47"
so 5 1/4" ( as specified ) is a forward and safe place to start for your first flights.
Double check to see if the back edge of your wing is straight like
the first picture/drawing. If it is straight then we have the correct CG.
The 3rd photo is of a G-Shark with a straight trailing edge.
If this does not look right to you then call me back and we will start over.
This plane really reminds me of a GILES 202.
04-01-2013, 05:11 PM
#62
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RE: OK gujys, I need help on CG
Ok,,i usually just sit here and read this stuff,,never giving my opinion cause i usually ruffle too many feathers,,,,you are ALL correct,sorta,even a couple of egineering types here getting sexy with big words and algorythms,,i think, cause i didnt read EVERY letter,,,Buddy,finish the plane,,bolt or screw or elastic the wing to the fuse,,im guesing bolt cause i cant find what plane it is so im going with low wing fighter,,bolt on the wing,,,measure back from the leading edge,, 3.5 or 5.5 in whatever they mentioned in the plans,,ALONG each SIDE of the fuselage,,heres the important part,,and i know you barely passed third grade, like me!!, so ill type slowly,,the plane needs to be UPSIDE DOWN,,,(that would be the side you DONT want landing first!),, with EVERYTHING in it cept fuel!! Also,,say its a p-40 or corsair (rearward folding gear),,the gear needs to be in the bays,,heavy wheels and tires can greatly affect the FLYING cg and the ACTUAL cg,,so fold emm,,,,plane upside down,,measure,,make a dot,,on the left side,,then the right side of the wing relative to the fusealage,,connect the dots,,find the center,,voila your FLYING cg,,but is it the ACTUAL cg??? if not ,,then you scrap that fancy set-up you made for the Li-po,s ,,shift everything forward or back(Back?? that would be a first,,for me anyway!! lol),,check again,,,still no go,,then add some Pb (thats LEAD for you grade twoers!),or a heavy hub,,,All this feather ruffling ive done only addresses the ACTUAL cg,,once you get this crate ?? balanced,,,,its FLYING cg may differ,,this YOU will only be able to "sense",,once your flying it,,,woulda helped had you mention WHAT plane we,re yakkin bout here,,or i just missed it,,anyway,,and before you theoretical mathematicians (ie-enginameers) try to amaze me with measurements and reasonning,,,ever heard of TRIM adjustments? even an f-2??? will have em (by puter no doubt) cause its one thing to DRAW a plane but sometimes it just flat dont work!,,ok gotta go the skinny waitress is yellin last call!!
04-01-2013, 05:23 PM
#63
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RE: OK gujys, I need help on CG
me again,,,,ignore my idiocy,,go read Jester s1 ,,he da man,,,,,the rest of you guys,,chill,,,diagrams,,calculations,,formulas??? really,,our buddy here built a plane from a kit or an arf,,hes not trying to back engineer something he found in the back forty to make it fly!! thats already been done,,,build it,,STRAIGHT!!!!!!!! follow the instructions,,,and repair often when nesacary!! (when! lol)
04-01-2013, 05:49 PM
#65
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RE: OK gujys, I need help on CG
ORIGINAL: warbirdmaniac
Ok,,i usually just sit here and read this stuff,,never giving my opinion cause i usually ruffle too many feathers,,,,you are ALL correct,sorta,even a couple of egineering types here getting sexy with big words and algorythms,,i think, cause i didnt read EVERY letter,,,Buddy,finish the plane,,bolt or screw or elastic the wing to the fuse,,im guesing bolt cause i cant find what plane it is so im going with low wing fighter,,bolt on the wing,,,measure back from the leading edge,, 3.5 or 5.5 in whatever they mentioned in the plans,,ALONG each SIDE of the fuselage,,heres the important part,,and i know you barely passed third grade, like me!!, so ill type slowly,,the plane needs to be UPSIDE DOWN,,,(that would be the side you DONT want landing first!),, with EVERYTHING in it cept fuel!! Also,,say its a p-40 or corsair (rearward folding gear),,the gear needs to be in the bays,,heavy wheels and tires can greatly affect the FLYING cg and the ACTUAL cg,,so fold emm,,,,plane upside down,,measure,,make a dot,,on the left side,,then the right side of the wing relative to the fusealage,,connect the dots,,find the center,,voila your FLYING cg,,but is it the ACTUAL cg??? if not ,,then you scrap that fancy set-up you made for the Li-po,s ,,shift everything forward or back(Back?? that would be a first,,for me anyway!! lol),,check again,,,still no go,,then add some Pb (thats LEAD for you grade twoers!),or a heavy hub,,,All this feather ruffling ive done only addresses the ACTUAL cg,,once you get this crate ?? balanced,,,,its FLYING cg may differ,,this YOU will only be able to ''sense'',,once your flying it,,,woulda helped had you mention WHAT plane we,re yakkin bout here,,or i just missed it,,anyway,,and before you theoretical mathematicians (ie-enginameers) try to amaze me with measurements and reasonning,,,ever heard of TRIM adjustments? even an f-2??? will have em (by puter no doubt) cause its one thing to DRAW a plane but sometimes it just flat dont work!,,ok gotta go the skinny waitress is yellin last call!!
Ok,,i usually just sit here and read this stuff,,never giving my opinion cause i usually ruffle too many feathers,,,,you are ALL correct,sorta,even a couple of egineering types here getting sexy with big words and algorythms,,i think, cause i didnt read EVERY letter,,,Buddy,finish the plane,,bolt or screw or elastic the wing to the fuse,,im guesing bolt cause i cant find what plane it is so im going with low wing fighter,,bolt on the wing,,,measure back from the leading edge,, 3.5 or 5.5 in whatever they mentioned in the plans,,ALONG each SIDE of the fuselage,,heres the important part,,and i know you barely passed third grade, like me!!, so ill type slowly,,the plane needs to be UPSIDE DOWN,,,(that would be the side you DONT want landing first!),, with EVERYTHING in it cept fuel!! Also,,say its a p-40 or corsair (rearward folding gear),,the gear needs to be in the bays,,heavy wheels and tires can greatly affect the FLYING cg and the ACTUAL cg,,so fold emm,,,,plane upside down,,measure,,make a dot,,on the left side,,then the right side of the wing relative to the fusealage,,connect the dots,,find the center,,voila your FLYING cg,,but is it the ACTUAL cg??? if not ,,then you scrap that fancy set-up you made for the Li-po,s ,,shift everything forward or back(Back?? that would be a first,,for me anyway!! lol),,check again,,,still no go,,then add some Pb (thats LEAD for you grade twoers!),or a heavy hub,,,All this feather ruffling ive done only addresses the ACTUAL cg,,once you get this crate ?? balanced,,,,its FLYING cg may differ,,this YOU will only be able to ''sense'',,once your flying it,,,woulda helped had you mention WHAT plane we,re yakkin bout here,,or i just missed it,,anyway,,and before you theoretical mathematicians (ie-enginameers) try to amaze me with measurements and reasonning,,,ever heard of TRIM adjustments? even an f-2??? will have em (by puter no doubt) cause its one thing to DRAW a plane but sometimes it just flat dont work!,,ok gotta go the skinny waitress is yellin last call!!
My brain hurts. I can't possibly top that.
04-01-2013, 05:59 PM
#66
RE: OK gujys, I need help on CG
ORIGINAL: goirish
If I follow your drawing how come you show CG at 4,405 Where mine was 5,340. Guess I missed something on your drawing. Remember we are still working with a almost 3rd grade education[:'(][:'(]
If I follow your drawing how come you show CG at 4,405 Where mine was 5,340. Guess I missed something on your drawing. Remember we are still working with a almost 3rd grade education[:'(][:'(]
What I did was showing you that there is also a graphic method that you could use now and in the future.
Note that I included the dimensions that you provided earlier, but I did not know the sweep of the wing and I just assumed same for LE and TE.
If your wing is swept back as shown in the above picture, then the diagram is inaccurate and the CG should be more aft.
Kudos to Speedy-Gonzales !!!
04-01-2013, 06:00 PM
#67
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RE: OK gujys, I need help on CG
I really really Hate throwing my hat in the ring,,honestly,,but really,,,this thread we are trying to help a guy balance his new love,,i just got done ranting about you enginameers trying to help a newbie with yer friggin confusing algorythyms and charts,,telling him,,Basically,,,,your ASS (oops can i say butt here?) will determine the REAL cG of said afformentioned flying homemade apparatus,,,rc type even,,,,,upon outting from here,,on my way to happily spend my kids college money,,,,another question in the Querry dept....HOW to get my plane to fly and correct and ,,,well just behave nicely to the in-laws,,,queery,,by?? another Engineer,,electron type this time,,,they dont didnt and never will understand the A factor (A- being ASS you A int in it!),,,wants to know how to get his plane to tell him what its doing,,,im guesing it Aint gonne be big enough for him to shove himself in it so,,,hmmm he may buck at the alternative,,,,ILL be back!,,,,,,,,,,,,1/4 inch of forward or back on the Cg?? THATS the sweet spot?? THAT plane will be back in the shop for somme,ummm RE-adjustements
04-01-2013, 06:44 PM
#69
RE: OK gujys, I need help on CG
ORIGINAL: warbirdmaniac
I really really Hate throwing my hat in the ring,,honestly,,but really,,,this thread we are trying to help a guy balance his new love,,i just got done ranting about you enginameers trying to help a newbie with yer friggin confusing algorythyms and charts,,telling him,,Basically,,,,your ASS (oops can i say butt here?) will determine the REAL cG of said afformentioned flying homemade apparatus,,,rc type even,,,,,upon outting from here,,on my way to happily spend my kids college money,,,,
I really really Hate throwing my hat in the ring,,honestly,,but really,,,this thread we are trying to help a guy balance his new love,,i just got done ranting about you enginameers trying to help a newbie with yer friggin confusing algorythyms and charts,,telling him,,Basically,,,,your ASS (oops can i say butt here?) will determine the REAL cG of said afformentioned flying homemade apparatus,,,rc type even,,,,,upon outting from here,,on my way to happily spend my kids college money,,,,
04-01-2013, 07:44 PM
#70
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RE: OK gujys, I need help on CG
For those po poing the wing tube after you figure it out let me guess, it is where he wing spar is. It is really not rocket science or maybe it is but they already figured it out for you. If it says the cg is 5.25 back from the leading edge measure it 5.25 back from the leading edge of the wing at the fuse. It may not be perfect but it will fly. You may want to side on nose heavy and start a 1/44 inch forward. If it is not on the wing spar I would be concerned and recheck your measurements.
