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Pumpkin drop event

I've realized I don't check CG anymore

buzzbomb

I know nothing!
#1
When I started building multi-wings, the CG never seemed right. I just had to throw it into the air, and then modify the nose/tail weight as the flight characteristics dictated. I've since built and flown the FT Edge and just finished my Spitfire build, and then I realized: I don't bother to check CG anymore. I just build as designed, throw it in the air and see what happens.

It's not a factor of laziness. I've just learned over time that if you build the plane as designed, the CG kind of works out or it doesn't, and you don't know until you fly it. Even when you think you've got the CG right, and the plane balances on two poles right where it's supposed to, it probably needs adjusting and you won't know it until you fly it.

This goes against all established wisdom. It works for me, though. I'm wondering if I'm the only one who just throws it into the wind to see what it does.
 

SquirrelTail

Well-known member
#2
When I started building multi-wings, the CG never seemed right. I just had to throw it into the air, and then modify the nose/tail weight as the flight characteristics dictated. I've since built and flown the FT Edge and just finished my Spitfire build, and then I realized: I don't bother to check CG anymore. I just build as designed, throw it in the air and see what happens.

It's not a factor of laziness. I've just learned over time that if you build the plane as designed, the CG kind of works out or it doesn't, and you don't know until you fly it. Even when you think you've got the CG right, and the plane balances on two poles right where it's supposed to, it probably needs adjusting and you won't know it until you fly it.

This goes against all established wisdom. It works for me, though. I'm wondering if I'm the only one who just throws it into the wind to see what it does.
I typically fly bigger aerobatic planes, so no... but when I do the foamies I still check.. I glued like 10 pennies to the nose of my goblin so it would cg
 

BATTLEAXE

Well-known member
#3
I'm on the other side of the coin where I constantly check the CG to discount the CG as a problem in flight... by the way I fly up until recently, I had so many other contributing issues that CG wouldn't have mattered anyway lol. It's always something I take into account while the build is in progress in my mind but I never know for sure until the build is done, CG by design. Then of coarse the flight tells the story. Once the flight is done and I find the correct flight balance then I mark where the battery placement works best, which I am sure everyone else does.
 

Hai-Lee

Old and Bold RC PILOT
#4
When I started building multi-wings, the CG never seemed right. I just had to throw it into the air, and then modify the nose/tail weight as the flight characteristics dictated. I've since built and flown the FT Edge and just finished my Spitfire build, and then I realized: I don't bother to check CG anymore. I just build as designed, throw it in the air and see what happens.

It's not a factor of laziness. I've just learned over time that if you build the plane as designed, the CG kind of works out or it doesn't, and you don't know until you fly it. Even when you think you've got the CG right, and the plane balances on two poles right where it's supposed to, it probably needs adjusting and you won't know it until you fly it.

This goes against all established wisdom. It works for me, though. I'm wondering if I'm the only one who just throws it into the wind to see what it does.
GUILTY!
In my case though I have built, bought, test flown/Maidened and repaired so many planes that I cannot remember them all! I am forever getting balance points confused or wrong but I am able to fly them anyway!

Now like you I can take off, diagnose, land, adjust and take off again without a second thought. It does make my training sessions a little hair raising occasionally but nothing too serious.

I am trying hard to remember to mark balance points on all aircraft I fly now, (once sorted), and I demand that my students perform their own preflight tests so that they get to understand the handling differences if they get it wrong!

Getting better of late but it is a battle, especially when I can buy 2 batteries, (2 different brands), supposedly the same but their weights can be so very different!

Still a work in progress, but I am at least aware of my issue!

Have fun!
 

Merv

Well-known member
#5
When I create a plane from scratch or modify a plane from plans. I draw the wing in SketchUp and calculate where 25% & 30% of the wing area is. I will balance my plane at 25% for the madden, when I get the plane trimmed out, I will slowly move the CG aft until the plane flies the way I want it to. Generally around 30%.

CG @ 25% gives a very stable plane, which helps while trimming. After the plane is trimmed, moving the CG aft will add a bit instability. How much instability is a mater of personal preference.
 

Vimana89

Well-known member
#9
I don't usually bother to use a calculator. I go off in general where a type of plane likes the CG, Low aspect deltas are a no brainer by now, Nutballs and the like are 25% in, straight wing 1/3, etc. I do a little balance check with my finger before taking out to fly, and that's basically it. I make sure it's in the right ballpark and fine tune it from there. Didn't work out so hot with the T- Tray though that things finicky. Slender deltas and round wings are pretty forgiving, they will fly wonky and let you know when something's off, but at least fly.
 
#10
I have been getting a bit lazy as well about CG on “veteran” fliers; even after repairs or modifications. It hasn’t caused any problems a few clicks of trim can’t fix... yet...

But as everyone knows, when you have a plane in the air that is having trouble, there’s a great quote that can be applied.

“Flying is fun, until suddenly, it isn’t”
 

JGplanes

Active member
#12
I mark the battery locations in most of the foamie kits after a first flight, but on a "plans only" or scratchbuild I find that I'm constantly fiddling with the CG to get it to go a little faster or float a little more depending on the plane. Only last week I moved the battery way back from the recommended CG in a plane I've had for two years, and it changed the flight characteristics drastically. I used to hate that plane, but now it flies great.
 

rockyboy

Skill Collector
Mentor
#14
I check the CG once at the end of the build and keep track of what size battery and where it went to get things balanced right. From there it's all about how it flys and I'll nudge the battery one way or the other try to get to the flight behavior I want.

If I change battery sizes I do balance the plane again, but I try to pick and stay with a particular battery size for each model.

For me planning to go to the field is an exercise in figuring out a plane for each of the primary battery sizes I have - 3s2200, 4s1800, 3s1800, or 3s1300. There are some other odd balls in the fleet, but I have tried to standardize as much as possible :D
 

Hai-Lee

Old and Bold RC PILOT
#16
Whilst it it important to check the planes balance before each flight some value/information can be obtained by getting the CG or balance wrong. It was because of CG experiments that I noticed the standard simple cub, (built with heavier FB), flew better when tail heavy albeit in a tail down position. With the CG correct it barely flew at all. Mind you tail heavy was a real struggle at times and it definitely NOT recommended.

As a result of its performance when the balance was upset I investigated the wing incidence angles and the main wing lift. An increase in incidence made it fly perfectly when properly balanced. Just a result of flying a poorly balanced plane.

Another thing to consider is what I experienced locally just recently where a new club member was complaining that his favorite and oft repaired plane was flying "Like a dog". I asked him to take it up and fly it to show me the issues and so he carefully fitted the battery in the marked position in the fuselage and refitted the canopy ready for flight. I asked him if the balance was correct and he stated that he used the same battery position as always which had been marked after the plane had done its series of test flights. I picked up the plane and tried to balance it at the manufacturers recommended points and found that it was markedly tail heavy!

It seems that the poor old plane had endured many crashes and had the tail broken off a few times, Actually it was his first time out after his reattaching the tail yet again. It turns out that he had added a lot of glue and some wooden reinforcements!

I shifted the battery forward and got him to test the plane again. It flew brilliantly! If you plane doesn't fly as expected revise your balance BUT if it flies well do not mess with it!

Have fun!