Just curious, My manual says the CG should be 6" behind the LE. My buddy says it should be a bit nose heavy. Hes got alot of experience under his belt. I dont exaclty know what to do?...

Pete

would help if you included what plane you are refering to......and then......there are threads already in existence about most popular planes. A search would bring up the plane you have and reading through it, you'd find out what ppl are successfully flying their planes with.

Sorry, H9 P47 150, Found one thread with over 100 pages, Been reading it, Right now I'm at p. 50, Not much about CG issues yet.

Pete

Please tell us all why you don't trust the manual. You always start with what the manual says and then fine tune the CG to your liking. It's a very simple principle. What works for your buddy may not work for you.

Agreed.

Pete

I'll tell you what, there are more CG location mistakes made in manuals and on plans than any other mistake I can think of. You'd be well advised, Pete, to learn how to determine the mean aerodynamic chord and locate the CG yourself, at between 25-30% of MAC.

In 25 yrs of RC I've never seen a kit or plan CG location that wouldn't adequately fly the aircraft. Balance where the designer or kit mfg suggests and fine tune from there. I'm totally unfamiliar with what you seem to be calling a major discrepancy with kits, plans, manuals where the CG is concerned.

I've got to agree with mustang fever. I've seen mistakes in this area. Especially the chinese ARF's seem to be pretty mis-informed on CG location.

The CMP 50 size P-40 comes to mind real quick and is well documented that the manual is wrong. It listed the 140 size CG instead. It is always wise to ask those that have successfully flown their planes of the same brand/make to make sure the manual is accurate.

Even if the indicated CG results in a nose heavy plane, remember: A nose heavy plane may fly poorly, but a tail heavy plane may fly only once.

If the indicated CG looks to be about 25-30% MAC, I would use that to start.

your doing the right thing
I always read threw threads and take notes, search, and ask questions about the plane I'm working on..
will save you alot of headaches

I always start noseheavy and move back from there.. I like nose heavy planes... they track better and aren't are twitchy,,, but land fast

Ron

When in doubt, start with 25%. It might land hot, but it will fly without giving you a heart attack.

Here's the ones I know of where serious CG mistakes were made:

The Hangar 9 Camel. 4" from the upper LE gives you over 30% of MAC. Not good for an 11% of wing area stab.
Mikulasko's Arrow. (Plans) They say to balance with the tank empty, rear mounted tank. Guaranteed control problems.
Lanier Mariner 40. The CG measurement for the 120 size is used in the book.
Fun Aero Albatross DIII. Way tail heavy.

You beat me to it.....

Still only looks like a few kits when compared to the thousands of kits on the market. Maybe you guys should buy better quality kits. I still have never purchased a kit with the wrong CG indicated in the manual/plans.

Meister Scale's 102" Me109 plans indicate 8" from the leading edge.... turns out it's supposed to be 6". 2" is significant, even for a plane that size, and I have heard that several people have lost this plane on maiden as a consequence. Does this mean that Meister Scale plans are poor quality? Some might argue yes, but I don't think so. You just should never jump in blindly. It literally only takes a few minutes to do the calculation or search a thread to find the best balance point where the model flys best.

Calculate the 25% of the MAC yourself, or research, read, and ask from those that actually have experience flying your model it takes only a few minutes to get the answer you seek. A little bit of time spent up front can save you from serious heart-break!

Nothing is perfect I suppose but I have yet to need to calculate CG for any kit or ARF I've ever owned and that's a lot of kits in 25 yrs. It's a good thing that the vast majority of kits available don't have the problem you describe because most newbies to RC can't even size batteries for their airplanes let alone calculate thier CG's. lol This CG thing has to apply to a very very small amount of aircraft for sure.

Well Gentleman,

The main was the CG should be @ 6 inches behind the LE – my buddy says it should be a bit nose heavy.

HE GOT A LOT EXPERIENCE UNDER HIS BELT….

I don’t know exactly what to do…..?????


Number one for you Pete:
I see on regular bases “builder” with 20 years + experience, and their aircrafts look very bad and fly horrible. But with their experience on their models – these guys manage to bring that airplane down…

Number two:
This is a Hangar 9 ARF and I can assure you guys when you set that Aircraft on the Hangar 9 recommended CG – this plane will fly and it is easy to maneuver.

Number three:
There is no comparison ARF to kits, because the builder can make many mistakes. You change incidence on the wing or horizontal stab – you have to move around the CG to get that airplane fly a straight line without having 5 degree on the elevators up or down.


To sum that up, it’s always best to ask pilots who own your model and ask them for their experience. With that info and may some internet opinions you may be able to form your own…..



Happy landings (works well when the CG is right)

G-Pete

My TF P-40 CG was set with the plane level according to the manual. It was tail heavy and flew like crap. Set the CG according to the manual, but make sure the nose points at a slightly downward angle. You shouldn't have any problems and you can adjust later if you need too. It shouldn't be too far off.

Agreed. Usually the manuals are a good spot, but I tend to put mine a tad nose heavy from the manual just to be safe. On the H9 1.50 P-51, manual says 6 3/8" from LE against fuse. I got it balanced at 6 1/4" with a bit of nose down on the balancer.

If you have a yardstick and the model, you can get your own answer in about 5 minutes. And it'll be absolutely accurate and dependable.

http://www.geistware.com/rcmodeling/cg_super_calc.htm