underdog71

Hi all,
I am relatively new at electric flight and am unsure if an electric airplane is to be balanced with the flight battery installed or not. I just completed assembly of a Great Planes sport scale Mustang, and it seems to be relatively close to being balanced without the flight battery, and when I install the flight battery, the nose is very heavy. HELP!

JohnBuckner

My Feedback: (1)

Yes balance the airplane with the battery and any hatchs or lids installed. Move the battery to the rearmost position to acheve the balance point noted in the manual and failing that move something else.

Now note to balance the airplane at what ever selected point it will sit level not nose down. If you do that you have just made the airplane nose heavy and not really balanced at your desired spot.

John

daveopam

My Feedback: (9)

Underdog1, be sure you are balancing it inverted. A low wing needs to be balanced that way.

David

chuckk2

Here is the problem.
The plane flies with the Battery. If the instructions have a balance point for glow or gas, it's without fuel.
Then, the question becomes how much would a full fuel tank weigh, more or less than the battery?
To add insult, the model's wing is not a "Hershey Bar' so figuring out where the balance point should be
on a percentage basis from the leading edge gets complicated.
If I have the correct P-51 (GP Sport .46). the manual lists 3-1/2" +/- 1/4"
This should correspond to the approximate change between full and empty tank if a gas or glow engine is involved.
(Empty Tank, Landing, A Bit Nose heavy is OK, tail heavy is disaster, unless you have enough effective elevator, and even then
things can get really sticky, with an unwanted stall close to the ground.)
What I usually do is use the center measurement (3-1/2" in this case) to balance with when I'm using electric power
(With the battery in place) The logic is that the 3 1/2" is supposedly the design CG, and so forth.
Occasionally, I've run into a model that the balance point was specified incorrectly. In that case, nose heavy is a bit safer than tail heavy.
Too nose heavy, and the model will not fly. Too tail heavy generally makes it uncontrollable or "flighty" to say the least.
If you end up moving the battery to the rear, a spacer made of stiff foam insulation may be a simple solution,
and, in the event of a crash, may help prevent battery damage.

Some time ago, I built/assembled a Hanger 9 P-51 ARF version of their P-51 PTS, and powered it with an E Flite 52 instead of the 46 called for.
It turned out that was a very good idea, since the all up weight was about 10 1/2 pounds with electric retracts and functional flaps.
The resulting T/W ratio was slightly better than 1/1.

underdog71

My P-51 is last years model with a 56 inch wing span. They list the CG as 411/16" back from the wing root. Someone else told me that a low wing plane must be balanced inverted. True? I modified the battery box to allow me to move the battery fore and aft as much as necessary. I'm using an O.S. 50 motor with a 6S 5000mAh flightpower battery and a Castle Edge 100amp esc. The prop I want to test first is an apc 13x10 electric. Flying weight is 8.2 lb.

JohnBuckner

My Feedback: (1)

Underdog you have the topflight recommended CG (4 11/16) Simple balance the airplane at that point (yes, upside down and gear extended if you have them) with the battery installed and assure that it balances level at that point, not slightly nose down for mother and country. This last point is probably why your last flights were nose heavy if you did attempt to balance previously at 4 11'16.

John

SeaJay

My Feedback: (6)

Daveopam,


Could you please explain the reasoning behind having a low wing aircraft in the inverted position while balancing? I have heard this before, but never understood the physics behind it! Does this rule apply to mid-wing aircraft too, like my Edge 540? Improper balancing technique might explain why my Giles 202 is so squirrelly, as I think I balanced it upright!!

Thanks, Craig.

dirtybird

My Feedback: (5)

The balance point does not change if the aircraft is inverted. Its just easier to do with a low wing aircraft.
If your Giles 202 is squirrely your balance is too far aft or you have too much control.

jrf

My Feedback: (551)

It's really very simple. A low wing plane will not stay in a level position when it is upright on the balancer. Turning it upside down allows it to stay in a level position while you are trying to set the proper CG.

A high wing plane will stay level when upright. A mid wing plane will usually stay level when upright, but if not, try it upside down.

If the CG is set with the airplane level on the balancer, there will be no difference whether it was set upright or upside down.

Jim

SeaJay

My Feedback: (6)

DirtyBird, and JRF,

I kind of suspected that that might be the reasoning behind the inverted balancing proceedure, but I wasn't sure..

JRF, I think that the issue might be with my surface throws, and my not having and Expo set.. I guess I should set in about 30% expo, and give it another flight to see if that settles her down!


Thanks, Craig.

flycatch

My Feedback: (26)

Plug in the numbers' and you will get your question answered.http://adamone.rchomepage.com/cg_calc.htm

pkoury

My Feedback: (7)

The CG of an aircraft is in 3 dimensions: front to back, left to right, and top to bottom (vertical). The ideal way to check front to back balance would be with the fulcrum point at the vertical CG location. If you balance a low wing airplane upright the vertical CG is above the fulcrum. If the aircraft tips forward or back the vertical CG will move either in front of the fulcrum or behind it. Depending on the design of the aircraft that can be enough that a perfectly balanced airplane resting on the fulcrum when pushed nose down would not return to level giving the impression it is nose heavy. Long story short the vertical CG should be at or below the fulcrum point.

SeaJay

My Feedback: (6)

Pkoury,

To have the best CG for aerobatics and/or 3D flight, would one need to have the vertical CG on the thrust line of the aircraft, or centered (if possible) with the center of thickness of the wing? Does my question make sense, I sometimes have difficulty in describing my question correctly!


Thanks, Craig.

underdog71

I want to take a moment to personally thank each one of you for your input regarding my C.G. question. The information all of you gave me was extremely helpful, as well as being interesting with your explanations regarding the "how and why" of the balancing physics involved. Super!

schhiqiul

I sometimes have difficulty in describing my question correctly!

JohnBuckner

My Feedback: (1)

Welcome to the forum schhiqiul Don,t be shy and take a shot at a description of your question and try to include as much info as you can. If it's about a CG issue a lot of folks struggle with this or even worse ignore this important step but it's really pretty simple and you can get a lot of good answers here so take a shot.

John

daveopam

My Feedback: (9)

Great advice on the CG question ^^^^^

SeaJay

My Feedback: (6)

John,

The member schhiqiul doesn't really have a question, or real comment.. He just copied and pasted the last sentence of my previous post!! If you go to his profile, and look at all of the posts that this person has made, you will find that all of his posts were also copied and pasted from previous comments contained within that thread, and all 5 posts from this username were done in a 15 minute time span..

I have had this happen twice now, from two different user names, I kind of wonder if the same person is behind both usernames, in fact, one thread has a post from both usernames that were copy/paste from previous comments..

Craig.

daveopam

My Feedback: (9)

SeaJay, I would hope it is a language barrier issue. I have not gone back and read his previous post, but if you think it is done with malice or troll intentions I will send him a PM and try and get a handle on what is going on.

David

SeaJay

My Feedback: (6)

David,

I have sent 1 possibly 2 PM's to you, but I am not sure if they went through to you though. Let me know if you didn't receive them!!

Thanks, Craig.

JohnBuckner

My Feedback: (1)

Thanks SeaJay probably another of those weird Bot things

SeaJay

My Feedback: (6)

No Problem, John... I have had the same thing happen on other threads, where a "Bot" or "troll" would copy and paste a section of a previous post I had made!! I guess there isn't really any damage done by it, just more posts to sort through!

Craig..

Post #500 for me!! I am now 1/2 K old!!