Whether to balance wings of different weights:

The drivel from some posters never ceases to amaze me. Who really gives a damn about the miniscule weight of CA or how much is applied in the process of building two wing halves. I defy anyone to buiild two wing halves of identical weight. Always balance your wings laterally and then the entire plane. Maybe we can generate some posts on the differing weight of graphics applied to the wing after its built and covered. Some just can't resist flaunting their knowledge regardless of its relevance. Give us a break and keep it simple and pertinent like MJC.

Wow, that's great to know. Back to the original question, go ahead and balance your airplane laterally by carving out the wingtip of the heavy side and/or adding pennies or lead to the light wingtip. Make sure that the engine and muffler are installed when you balance it. But if I were you I wouldn't be concerned about glue weight. You probably didn't use enough glue to make a measurable difference.

Don't forget also that oil tends to collect more on one side than the other, which could cause the plane to go out of balance. And then it really gets bad when bugs and grass seeds start to collect in the oil.

When I built the wing panels for my Dynaflite Super Cub, I weighed the piles of wood for each panel, shuffled parts ( it is easy to feel the heavier wood ) between the piles to even the weight. When the panels were finished, they were within 1 oz of each other, and these panels weigh about 30 oz each!

It is like building a straight wing - build it straight, do not try to remove warps that get built in !!!

David

Hello Mike,

Good post, especially that first line. (biiig grin)

My first reaction when I looked at this thread's first couple of messages was, "I know CAs outgas when they cure, so there must be some loss of mass. Probably not enough to measure without some extremely high resolution scales, though." Seem you've proved my conjecture to be right. Thanks,

CR

M Dennett wrote:

He's not alone. Those of us who started in this hobby before ARFs were available picked up this trick early on. Dead weight is your model's enemy! Why add it when a little forethought can eliminate the need? Part of this hobby is the knowledge of a job done well.

I have a Lanier Extreme Stick ARF that flew well but was noseheavy as hell with a light .46 2-stroke. I'm just finishing up the mod of moving the servos back to under the h-stab in order to eliminate the 4 -5 ounces of weight I had to add back there to balance the thing. I already have the battery behind the wing, may have to move it further back. Won't know until I recheck the CG.

Cheers,

CR

strathboy wrote:

Charles, the knowlegeable builder ALWAYS does a pre-balance check BEFORE permanently installing servos and drilling the engine mounts. Takes a bit more time and effort but if ARFs are your idea of RC modelling, you should have lots of the former.

The first piles comparison started at 5oz difference! To be even pickier, I moved the heavier ribs toward the center of the panels. I could do this since all but the outer 2 ribs and root ribs were identical !

And like Charles said, I do not like to fix the radio gear location UNTIL I know about where the plane will balance. Sometimes this still does not help - I just finished assembling a Sig 4*60 with a Magnum 91

4-stroke in the nose. Even with the battery against the firewall, I still have to add ~1oz of lead to the nose. I'd hate to see the chunk of lead required to balance this plane with a 60 2-stroke!

David

You bet I was! We use enough CA around this joint that a little diddling around here and there to learn something is no problem. Besides the owner is an airpane fan. Our company back forty is a registered MAAC flying field, so I also have no problem finding something to do at lunch.. snicker. Although winter seems to be keeping a grip on us as this morning there is ice on the cars and a -15C windchill reported. Grrr..

Mike D.

There may even be slightly higher losses than what I measured, but the point is it seems like it is basically next to nothing as I'd consider losses like

2-3% to be effectively "no loss" in the greater scheme of things.

Mike D.

p.s. personally I use aliphatic glues to build wings but not due to the above, rather because IMHO they end up tougher. But I do use CA to tack parts (and my fingers) in place.

Strathboy,

This your second post to me, telling me to locate my servos to achieve the correct balance point. The first was in regard to the Kadet Senior ARF, now this one. In both cases you've shown your ignorance of the models in question. Both of them come out of the box with the servo trays permanently installed and with pushrod materials supplied to reach those trays. Seems logical to try these servo locations before electing to modify the model. In the case of the Extreme Stick, the servo tray is located about as far back as it can be, under the wing, even so, the stock model is noseheavy with any engine.

As for drilling the engine mount; in the case of the KSA, the engine is located on the mount so as to place the prop drive washer just clear of the cowl and still allow cowl removal for maintenance. In the ESA, I used a light DB mount with the engine as far back on it as it would go and still allow the fuel lines to clear it. The ESA required major surgery to balance it without ballast.

Your sarcastic remark about ARF building comes as a surprise to me, coming from someone who thought that preselecting wing wood in order to have the finished wing panels come out equal in weight was unusually meticulous. Aren't you the guy who suggested that adding weight to the finished wing was a lot easier?

You really ought to educate yourself a bit more before about the subject(s) before you expose your backside for all to see.

CR

strathboy wrote:

You lookin for any Industrial Engineers?

Alex.

Charles, wouldn't you expect the producers of ARF's to take balancing into consideration when they're designing them? Just imagine, "major surgery" required. As for adding weight to balance wings, I've never had to add anything more than an ounce to compensate for whatever created the imbalance be it glue, wood composition or whatever. Its really inconsequential. I must admit however, that the constraints you describe (fixed servo trays and prop clearance ) would preclude implementing my suggestions. I do indeed have limited experience with ARF's (only 2) and both have been very annoying including the reasons you mention. Both were low wing, had numerous design flaws and high wing loadings. They also had short lives. Charles, don't take take the sarcasm (bait) in newsgroup comments too seriously. Remember, hypertension can seriously shorten your flying years.

differential

Some folks seem to be worrying way too much about lateral balance. In full-scale aircraft maintenance we pay no attention to lateral balance, and close attention to longitudinal balance. In an FS airplane, the 30-pound battery is off to one side, sometimes the same side the solo pilot sits on, along with most of the instruments, and flap motors and autopilot stuff and so on might be in one wing or the other. When we weigh the airplane we might find a 30 pound difference between the mains of a 1400 pound airplane, and notice little or nothing in flight. It's the fore/aft imbalance that's the killer.

Dan

And these are aircraft your concerned with tracking in both inside and outside loops, right?