wayne260

My Feedback: (4)

I have been told by people before that that best way to balance an F3A model is to have it inverted, however when I ask why I have never been able to get an answer. Is this true? Is it better to balance inverted than upright and if so why? Thoughts / comments.

pattratt

My Feedback: (1)

Wayne
It really doesn't matter as to which way you balance the aircraft as this only gets the c/g in the ball park. Final determination is done through a series of actual maneurves such as knife edge flight, inverted flight, 45 upline-1/2 roll-release controlls and watch the nose, watch roll characteristics, to determine actual c/g that works best for you and the specific pattern schedule that you are flying.
Dick

MachLoop

My Feedback: (3)

You can get the explanation here:

http://www.rcuniverse.com/magazine/article_display.cfm?article_id=601

Note that this explanation is generic to any aircraft and intended for determining where the C/Gactually is.That is different than tweaking the C/Glocation to establish that whichworks best for you based on your flying style and comfort zone(as mentioned by Pattratt).

VerneK

Hi Wayne,
I always balance my plane from upright, out of convenience more than anything else. Flying electric, the location of the batteries is pretty much going to dictate everything on the balance so installing the battery tray is the last thing I do after everything else is finished. I normally do a lot of research on the plane I'm building and rely on the reports of others who have already built the model I'm working on. A quick search on RC universe will usually turn up numerous reports of where the CG should be for any given plane.

Let's say the recommended location is at the leading edge of the wing tube. I install a servo screw into the lite ply root rib immediately above and in line with the leading edge of the wing tube and screw it in so there's just enough room to slide on a piece of nylon coated rudder cable. I do this on each panel and slide the wings on wing tube to where I can just slide the rudder cable over the screws. The nylon cable itself is attached to a 1" diameter piece of wooden dowel about 6 or so inches long that I use as a handle. The ends of the cable each have a crimped loop that I put on the servo screws in the root ribs.

Then I place the batteries in the fuse about where I think they'll need to be to balance the plane which is usually right over the landing gear mount. Then I slide the canopy in position and lift the plane by the handle. The balance will be immediately obvious by the nose or tail dropping. I keep tweaking the battery location until neither the nose nor tail drops and mark the location of the batteries in the fuse. Then I install the battery tray with some adjustment room available in case I want to adjust the CG after my trim flights. Once the tray is glued in, I re-install the batteries on the tray and double check the balance.

After that, I remove the screws from the root ribs and do my final CG tweaks based on flight trim. By starting off with the CG real close to where it needs to be, you can avoid any nasty surprises on your first flight. Hope my explanation makes sense.

Verne Koester

Bozarth

My Feedback: (15)

Simple physics. If your fingers are far from the cg when you pick it up, it might be a handful and want to flip itself over since the actual cg is above your fingers. Turn it over and you get more of a pendulum effect while you slowly adjust to find the correct spot.

Kurt

MTK

Wayne,

The answer to your direct question lies in the fact that the CG of most any low wing model will be located above the wing, vertically, in the fuselage. When you invert the model and are holding it up by the wing, the CG will be below the hold point and help stabilize the model. You make gravity your friend.

On the other hand, a pattern model's CG is not that far away, vertically, from the wing but is usually still above it. It will be easier to balance it inverted but upright is no deal breaker either.

Think of it this way....is it easier to balance something on top of a ball or easier to hang something below it

Jason Arnold

Do a static balance (on the bench) and then read this http://www.hebertcompetitiondesigns....ngulation.aspx

To answer your question, F3A models are balanced upside down due to the vertical CG. Don't confuse this with CG along the length of the model. A high wing trainer would be balanced upright because most of the weight (vertical CG) is below the wings. Trying to balance a trainer (on the bench) inverted would be next to impossible.

Regards,
Jason.

wayne260

My Feedback: (4)

Thanks for the feedback. Michael thanks for the link made for some interesting reading. Vern, your explanation made complete sense, Kurt and Matt K thanks for the simple explanations. Dick the DaJeVu is in the air so I am into the fine tuning and playing with CG location, haven't weighed it yet but think it's going to be over as the weight I had to add to the right wing on static balance was significant, but you are right it is a nice plane to fly.

pattratt

My Feedback: (1)

Wayne
How did you determine the amount of lateral weight required and where did you put it? Even Marcelos heavey composite wing De Ja Vu made weight at the worldsand nationals! I have two of them and they will make weight. If you still have my cell number call me. If not email me with your number and I will call you.
Dick

bjr_93tz

In the few F3A planes I've had the vertical CG has tended lie within the wing itself so inverted or upright the "pendulum effect" has worked against me.

Using a set of scales to determine the CG via maths works well and for those with a bolt on wing and suitably stronge fillets, so does a 4mm wide cable tie slipped between the wing and plane with the wing bolted loosely in place. Just slide the tie along and keep lifting the plane until the wing rests level.

There's lots of ways to skin the cat, but as has been previously stated it's only a ballpark figure as you'll fine tune it later to what you feel the plane needs.

Another handy tip is if you want to move the CG a set amount, multiply the weight of the plane by the distance you want to move the CG (eg 10lbx1/4") , then divide that number by the distance from the CG to where you can put the weight ( down the back 50 inches ? ), and that will give you how much weight you need to add... (10lbx1/4")/50" = 0.05lb or 0.8oz

Of course you'll reposition your gear later so as to remove the dead weight