JoeAirPort

My Feedback: (41)

I have a question (about any profile): I have a Katana 40 profile and the directions say to pick up the plane by the prop and the fin/rudder tip to check for lateral balance. When I do this it balances right according to their test. But I set the thing on my bench and every time it drops the right wing (duh, engine is side mounted so this makes sense). This is balancing on the edge of the flat fuse. So the question is shouldn't it balance on the fuse and not on the prop/tail? The engine has right thrust so grabbing the prop tip is not the true center of the plane. Isn't the center of the fuse the balance point?

Johnny Mojo

Hey Joe,

Easiest way I have found is to not do it Seriously though if you pinch the prop and the tail I agree that it would not be totaly accurate because the mere fact that you are pinching those areas will serve as resistance to any lateral movement. That's probably why it moves when you set the bird on the bench. I'm just not sure that it's totally necessary on a profile bird in this case. The side mounted engine difference should be able to be compensater for with gear being put in the opposite wing though, and remember that the tank will be on the left side too.

Don't burn too many brain cells over it though. It probably won't matter much and burning FUEL is much more fun.

J.

AeroDave

I would find the true center. I usually put s small screw in the top of the fuse above the motor mount. Then I can hold that and the top of the fin. One of mine was rocking in harrier when it shouldn't have, so I put a screw toward the back and hung plane by strings. Sure enough, it was off. Next flight the harriers were noticably better. I know there is probably a cleaner way to do this, but the small whole from the little wood screw doesn't amount to much.

Good luck!
Dave

JoeAirPort

My Feedback: (41)

If I did it with your test, it would be way off, the right wing would drop like a rock. So I'm wondering what the ARF really wants for solid harriers. Prop tip balance or the center of the fuse like your test uses?

aerofundan

Joe, a friend here tried to remove wing rock laterally balancing plane... it didn't make much difference at all, i would say just fly it like that

UltimateFlyer120

My Feedback: (5)

The way I laterally balancing my planes. I set the tail wheel on a table and hold the prop and watch which way the plane rolls several times. I try to adjust my battery to remove the out of balance problem. When my planes are out of lateral balance I have to trim the aileron to compensate and then everything else is screw up. After it's all balanced you add fuel and it's all screwed again but it seams to me to fly better once it's balanced laterally (without Fuel).

Jeffro

I laterally balance my profiles by putting an eye hook/screw in the bottom of the fuse at the CG point and hang it from the ceiling by a piece of string. It's BEST to do this before covering so you can add SMALL amounts of weight further out in the wing. If it's already covered you can usually balance by taping a coin(s) on the wing tip.

Good luck!

Jeffro

John Wells

My Feedback: (10)

Hey Joe, I've tried it every which way I can think of. I used to embed a piece of sullivan nyrod in the rudder and I made a stand for laterally balancing. The way I do it now is just fly the plane upright and inverted (on a calm day) and see if a wingtip drops one way or the other. If needed, I glue a small piece of lead on the light side and fly it again. It's your choice on how you want to do it. You can hide the lead under the covering or glue it on the outside.

JW

AeroDave

Joe, I'm just telling you what works for me. I'm sure there are many ways to get the same job done. I will say this: lateral balance can have a significant effect on 3D performance. I believe the gentleman who stated it didn't make much difference in his case. It could be there were other factors in play. since I started laterally balancing my planes I have found increased consistency in performance. Whether its really better or I just want to think it is, I'll continue to do it. I tend to get my jollies by trying to be really precise in my flying, whether in 3D or traditional "pattern" moves. So little things like this tend to delight me to no end. I wish you the best. I'm sure you'll arrive at what's best for you.
Dave

STLPilot

My Feedback: (21)

Best way to laterally balance a plane is in the air. Do a wall or parachute. If the planes dips then the wing it dips on is the heavy side. Add quarter oz of weight on light wing till you get it. Once you have nice and flat walls and parachutes, it's balanced.

AeroDave

STL,
that is definitely the way to go. What made me revisit the lateral balancing of the profile I mentioned above was doing harriers and walls. I noticed one wing would be low. If it was when doing a harrier, it would start low then rock. So I took it home and did the screw thing. I could have just added weight at the field and been done.....

STLPilot

My Feedback: (21)

It's hard to balance them laterally on the ground because you can't see center of mass even though it seems that it should be right in the middle of the profile. In some cases it may not be since there are small deviations in production no matter whose building it.

Parachutes seem to be the most accurate in my book, works every time. Once you have a nice flat parachute and you still have rocking in harrier then take out lateral balance from your list of probable causes.

majortom-RCU

My Feedback: (40)

My method for balancing profiles is to put a screw-eye into the fuselage at the CG point while the plane is still uncovered, but with everything else either glued in or dry-fitted. When I say everything, I mean absolutely every screw or little bit of hardware. I fill the tank half-full and try to position it out along the wing to balance the side-mounted engine. I mount it as close as I can to this position, then use a bit of lead for final balance.

If it's an ARF, I still use the half-filled tank, but now any lead will most likely be on the outside of the wingtip. Profile ARFs are born to crash anyway, so who cares about visible ballast. (Lotsa fun to fly 'em tho!)

Because I fly pattern, I am in the habit of getting my aerobats laterally balanced on the bench, and the practice spills over to even my cheap beaters. I will agree that much of profile 3D flying is not too sensitive to lateral balance, but some of it is. I can tell if I trim for straight & level with a full tank and then try flying s&l at the end of a flight (like on landing) that lateral balance is off.

seanychen

My Feedback: (4)

Come on you guys, it is really easy to laterally balance a profile. Just put it on a flat table that's short enough so that just the fuselage bottom portion between main gear and tail gear will sit on the table. Then if it does not fall off to one side, then it is laterall balanced.

STLPilot

My Feedback: (21)

Hmmmm ... I don't know Seany. Looking at how you have the sitting on the scale that will get you close, but the weight of the fuse needs should be on something that is no wider then the tip of a sharp object. But then that goes back to center of mass and slight discrepancies in manufacturing/design. But like I said, it will get you close, but only the plane can tell you exactly where it is. They all have a personality of their own and are happy to tell you where the real problems are in the air.

Also when testing your parachutes or walls make sure fuel is at half full since that's the average your tank will be per flight. If you're running a good a motor of course.

krayzc-RCU

My Feedback: (31)

i watching [8D]

JoeAirPort

My Feedback: (41)

Another test is to flip it inverted, fly it straight and level and see if a wing drops. Add weight to the one that does not drop.

STLPilot

My Feedback: (21)

I've never heard about that one, don't get me wrong if you know that will work I guess it will. But the torque or propwash from the engine alone could cause the plane to roll on either wing in flight, let alone other factors like trim.

When you smack into a wall or parachute your quickly chopping the throttle to stop and torque and propwash. Thus reducing rolling effect made by the engine. This give more accurate balance.

JoeAirPort

My Feedback: (41)

Check out the video that Joe McBride did on the Flying Circus forum (Trimming for success?). He describes it there. Also I have heard of this before seeing the video. There's more than one way to check for lateral balance. I heard another way of checking for dynamic balance. You fly straight down at idle, pull up and watch which way the plane turns (with no aileron input). If it rolls right the left wing is light. If it rolls left the right wing is light. Dave Patrick also uses both of these methods in his trim chart supplied with his ARF's (calls it Tip weight test 1 and test 2). Your method is another dynamic test and makes sense to me.

I still wondered about whether to use the prop tip or center of fuse at engine to do the static test. I guess you bring up a good point though. The static test is just a starting point. The dynamic one is probably more accurate.

STLPilot

My Feedback: (21)

This sounds like a parachute, only you do it at higher speeds and pull hard at the same time chopping throttle to reduce prop wash and torque.

Good thing about profiles you don't have to worry about planes snapping out and you have exaturated control surfaces for the static test. Thus it's going to take a lot to lose your plane or even close. I just pick it up by hand and eyeball it if it looks good it is good. It's good enough to get in the air for the final test.

JoeAirPort

My Feedback: (41)

Yes the entry is very similar to a parachute. But the one I was talking about is actually not a stalled maneuver, you pull up gradually and see which wing tip drops. The parachute is a stalled manuever. But they are very similar and both accomplish the same thing, the parachute being a little more violent.

Spacey

Dion's method of getting the lateral spot on is the easiest and most accurate. It's really simple to pop into a wall or do a quick parachute to see where what is going. Only problem I could foresee with this method is folks that don't have very solid stick skills that might jerk a little aileron in with the up elevator so beware of that. But yes if you want to get it accurate you are going to have to go this route.

Picking the plane up by the tip of the prop and the tail fin will NOT work! Not even by a longshot as most profiles have right thrust on the motor thus the motor's centre is usually off to the one side. Next as Dion also stated very clearly simply getting the exact centre of the fuselage and working from that is not always going to get you spot on unless the model is exactly symmetrical when looking from above (This is never the case unless the model as a whole was cut on a CNC machine or something).

So here's what I do. Simply pick it up with light fingers by the front of the fuselage (Centre as possible) and the tail fin before the maiden and position radio gear or add some lead to a wingtip to get it nicely into the ballpark. Next take her out for a spin and pop a couple of walls and parachutes as described by Dion above. Next just add some lead to the lighter wing untill the model either does the walls/parachutes perfectly level or you don't have a wing that's dominently lagging or dropping.

UltimateFlyer120

My Feedback: (5)

I have to disagree completely with Spacey and the reason is simple But I'll quote the designer of the Boxxer Jeremy Chinn
"While you are setting the CG, don’t forget the vertical and lateral CG’s. The plane should balance tip to tip (lateral), and should balance top to bottom. The lateral and vertical CG’s of most airplanes is on a line through the crankshaft of the motor, through the wing and the horizontal centerlines."

Funfly profiles are very forgiving. Build it straight and without warps and forget all this other BS!

Spacey

Ooof now I have to say I know exactly what Jeremy meant with that statement and it's all true but the wording might need to be refined a little to be accurate technically speaking. Now seeing as we want to get a little technical I'll start off by saying this. It would be impossible to draw a line through the centerlines of the wing, the horizontal stab and the crankshaft of the motor if the motor is not exactly in the middle of the fuselage vertically and horizontally and also if the motor is not mounted with exactly 0 degrees up/right/down/left thrust. On top of that it would be impossible to do so if the wing and the horizontal stab is not all mounted exactly in line with each other. Like for instance on a Cap it's going to be rather difficult getting that line in there.

Now all that Jeremy meant AFAIK was in order to get the vertical CG line figured out a good way to get it close is to get the centers of the wing, horizontal and the motor (Crank really) and take the average distance between them vertically on the fuselage when viewing it from the side and get that line to be perfectly vertical or well perpendicular to mother earth when you let the plane hang vertically from the centre of the crankshaft. I'm having a little difficulty explaining it but lets say both the wing and the horizontal stab is mounted with exactly zero incidence. If you were to then pick the plane up by the centre of the crank and let it hang tail down then both the stab and the wing would be perpendicular to terra firma. If you got that right it would mean the vertical CG is good most of the time.

Now if we were to look at the lateral balance of the model you have to keep in mind what happens when up elevator is pulled on any aircraft. Now we're talking perfect scenario here for this one where the elevator would be exactly symmetrical and well the whole plane for that matter like I described in my previous post. If you were to balance this exactly symmetrical profile with the engine mounted offset to the right of the fuselage (Like most of them are) and with also 3 degrees right thrust in the motor you have a line running quite skew when compared to the line of symmetry (Sp?) of the profile when looking at it from above. Simple enough that the area of the profile on the right of the line would be less than the area on the left. Now we know that the greater the area the more effect air has on it. The more the area for a given weight also comes back to the lighter wing loading thing. So yes in the end you would simply sit with a right wing that has a higher wingloading than the left wing and quite simply when you yank up elevator the right wing would drop and the plane would roll right (This all barring the elevator halves also deflect exactly the same amount).

My best suggestion is take a plane with the motor nicely offset like they normally are with some right thrust and balance it your method. Now go back and use Dion's method to balance it and go back home and see where the lateral ended up. Definitely not in the same line. Now also as we know not a single model is built exactly perfectly so the right side of the plane and the left side would hardly ever match up exactly area wise when looking at it from above. Also the deflection of the elevator halves would never be exactly the same in flight unless you have a rock solid control system. That is why I said to use the pick up thing at home to get yourself into the ballpark and then fall back to Dion's method as that'll get you the closest if you can pull up elevator perfectly without putting aileron in. If you can do this and you don't see one wing dropping the whole time but rather the wings taking turns and so on you know you have a well balanced profile laterally.

I hope I made sense.

scolpit

Excuse me, but what's a parachute? I probably know what maneuver is, but english is not my main language.