Plane balancing question
 

I just finished putting together my first plane a Tower Trainer MKII ARF 40. The engine I chose is a SuperTigre GS-40. The battery is as far back as it will go. The plane is ~ 6oz nose heavy with the weight as far back as I can put it, is this unusual? It looks like my only option is to stick the weight on the outside on both sides of the rudder which is really ugly. I can paint the weights but still... Any suggestions?

RE: Plane balancing question
 

Can you move the engine farther back on the engine mount? Can you move the receiver or servos farther back?

Whatever you do, DO NOT put the weights on the rudder! You will risk ripping the rudder off it's hinges! Put the weight on the back of the fuselage as far back as you can.

RE: Plane balancing question
 

Oh I didn't mean stick them to the rudder itself I meant on the stabilizer on both sides of the fin. Nothing can be moved further back than it is.

RE: Plane balancing question
 

the tower trainer should still come with the clamp type engine mount. can you push the engine all the way back to the rear bolts?

also your balancing the model dry( meaning without fuel in it) right? 6 oz to the tail in any trainer is not normal, unless you put a .61 on it.

Never put weight on a control surface, ever.

What do you mean the battery is as far back as it can go? you can put and extension on the battery and put it in the tail. It not generally good advice but most of my own builds I just glue the battery in, in the tail since I have no intention of removing it for a couple years. Also move the receiver back

RE: Plane balancing question
 

You can get an "extension cord" for the battery to allow you to move the battery back, or just move the tank back... if that's possible.

RE: Plane balancing question
 

Keep additional weights as low as possible; better under the stabilizer than above.
Servos can also move back, eliminating the pushrods.
Only the engine and the tank need to remain at front.
Review the balance point and verify lateral balance as well.
Empty tank for any balance.

RE: Plane balancing question
 

You have a lot of good suggestions on how to bring it into balance, but that is a lot of weight for a trainer. Are you really sure you need that much tail weight? A rule of thumb is for a rectangle wing, the CGshould be 25 to 28% of the cord, measuring from the LE. Please check that you have the right measurements. If you balance it out to the wrong measurement, chances are very good that the plane will not last 30 seconds in the air. I just did a rebuild on a plane I've had and flown for three years. My first flight with it after the rebuild was almost its last, I was off on the CGby one inch and any hint of touching the elevator resulted in a 90 turn up or down. Iwas so happy to get it down in one piece.

Double check the CGmeasurement before adding weight. Have an experienced guy double check it for you.

Don

RE: Plane balancing question
 

I am using a Great Planes C.G. machine. The plans say 89 mm from the leading edge which I have double and triple checked, I even tightened the screws on the rulers to make sure they were not slipping. The engine is back as far as it will go. On the bright side with an extension on the battery I can get it way back there and that has dropped me down to 2 oz which seems much more reasonable doesn't it? This brings up another question for me though. I have to use a dowel to get the battery back there (its wrapped in foam) I don't think I could glue it or secure it without ripping the covering off. When I get it back there its wedged in pretty tight do you think that will be good enough or is there some trick to securing stuff like that?

RE: Plane balancing question
 

You don't have to glue it, but you should block it in some way so it doesn't slide forward. The last thing you want is to jerk up on the plane and have your CG shift by 1/2 inch. Glueing in a dowel or piece of balsa in front of it will do fine if you can get it back there.

RE: Plane balancing question
 

Use some velcro to make it stick where you want. Also, I have used the foam sheeting that comes in boxes for shipping to create a wrap for the battery, make it large enough to jamb in (carefully) between a couple of fuselage formers and use a small leftover piece of balsa or lite ply to make a trap for the foam and screw it to a former so the foam is trapped, and can't move.

RE: Plane balancing question
 

89mm seems too far. Has anyone else balanced this plane? How wide is the wing chord? 89mm is 3.5 inches and that seems to be a little too far back. Good luck with this.
Curtis

RE: Plane balancing question
 

there is no reason to get it to the milimeter, the tower trainer balances on the main spar can go 1/4 inch either way.

loose the foam and wick some CA back there

RE: Plane balancing question
 

I'm going to go a completely different direction here...

Rather than offering suggestions for how to bring the CG within an acceptable range (though to be sure, the suggestions above all have merit), i have to ask...

WHY is it so far out of whack?

I can't get past the feeling that "something is wrong, here". As RedFox said....6 oz to the tail of any trainer is NOT NORMAL....something, somewhere, is amiss.

I HAVE to believe that we've either got something heavy placed in the wrong spot, or we're using something that's far smaller/larger than it should be, or a measurement is off somewhere (perhaps measuring from the wrong point?), or a CG machine is set up wrong or being incorrectly used, or SOMETHING.

I suppose it's POSSIBLE that tower built one that far out of whack...but I sure would like to know what the heck IS out of whack before flying that airplane.

RE: Plane balancing question
 

Looks like that's right (see a clip from the manual below). I bought one of these for my son, but haven't finished building it yet. I'm putting an OS 40LA on it, so hopefully mine will balance out a little better!

RE: Plane balancing question
 

I think whats wrong is that this SuperTigre has a big clunky muffler on it. It seems overly heavy to me... While this is my first plane I am no novice to building things to specifications. I am confident I am using the CG machine properly and as far as having something heavy in the wrong place the only option is the engine and like I said that is back as far as it will go. The plans call for a .40 motor and thats what I have. I ordered it at the same time as the plane so its not some old whacky thing I found at a garage sale or something. As far as the radio components go I am using Futaba 3004 servos and a R617FS receiver which if anything is lighter that what would be expected. Everything else is what came with the kit. It's not that complicated an assembly so I am back left with the weight of the muffler on the engine.

RE: Plane balancing question
 

By all means lock the battery firmly in place.
Wrap a dowel to the battery, and then screw down the other end of the dowel to the plane structure.
You could also use a battery of bigger capacity, in order to make the extra weight useful.
Having such a heavy muffler, a lateral balance is also necessary.

RE: Plane balancing question
 

That could well be it, I suppose. Probably the best way to be sure is to simply remove it from the motor, and see if the balance changes significantly. If removing it only changes the weight needed by an ounce or two, that ain't it....if, on the other hand, it goes from needing 6 oz at the tail to 1-2, then you may have found your issue.

I'll take your word that your setup/use of the CG machine/etc is all correct. I did not mean to suggest you HAD made incorrect decisions or HAD used them incorrectly, simply that SOMETHING is "not quite right", and those were a few of many possible causes. Just things worth double-checking. :)

RE: Plane balancing question
 

Well, the St40 with the muffler weighs 19oz. The Tower 40 weights 17oz with motor(AHthat would be with muffler), and the O.S. La40 weighs 12.5 oz muffler included.. It depends on which engine it was designed around, it could take a less than 3 oz on the tail to accomidate the weight difference figuring a 2 to 1 lever arm ratio.

There is something else at play here. What kind of prop nut, spinner,prop,etcdo you have,

Don

RE: Plane balancing question
 

The prop nut is the one that came with the motor, the spinner is the plastic one that came with the kit and the prop is a Top Flite 10x7 Power Point. If the OS is only 12.5oz and the SuperTigre is 19oz then it seems to me as though the difference in motor weight could very well be what is causing the problem. I think I am going to get an OS for the next motor. I am thinking on the battery I am going to see if I can put some screws back there, stuff the battery back there with some extra foam and then stretch a rubber band across on the screws to hold it into place. Like I said before with the battery back there it only needs a little less than 2 oz additional weight on the tail (probably less once I get all the stuff back there to secure it).

RE: Plane balancing question
 

Sometimes on a forum where we can't get the voice inflections and body language its hard to interpret tone (I am talking about the tone of my reply). I am sorry if my response seemed gruff it was not intentional :). I understand and truly appreciate your input and experience. There are people that have little mechanical or technical experience or a very young and just learning these sorts of things. I just wanted to give you a feel for my overall ability to do these sorts of things. Again I REALLY appreciate everyones help.

RE: Plane balancing question
 

No worries, gold. Just wanted to make sure MY post didn't come across as 'talking down" to you. :)

We're all good.

RE: Plane balancing question
 

Ok, so I just took the muffler off and with the battery in the back its only about 1/2 oz nose heavy. Just for fun I weighed the muffler and it comes out to 3.445 oz. I am guessing with the OS at 12.5 I would balance just right. So in the end I think I am just going to stick the muffler back on and add the 1.75 oz to the tail. On a side note if anyone else has a SuperTigre 40 and thinks it's muffler is big, heavy and ugly there is this option:

http://www3.towerhobbies.com/cgi-bin...?&I=LXZ653&P=7

Their web site says "up to 50% lighter than stock mufflers". I am not going to get one because this is just a trainer and it not worth the $40 to me. If I had this to do over I would have gone with the OS 46 LA. Its considerably lighter and is only about $20 more and hey I would have gotten .06 more displacement :D. I guess the old adage holds true here "you get what you pay for" ...

RE: Plane balancing question
 

I built this same plane 2 years ago and still fly it. It required 4.5 oz. of weight in the tail to balance. I put a n OS 46AX on the nose. I used the same balancer and thought it was alot but had an OS 40 LA on anoither plane and the weight difference is what gets you. Good luck and have fun. Be sure to do the latteral balance as well with that muffler. I have 1.75 oz on the opposite wing as well.

Mike

RE: Plane balancing question
 

Balance is critical but you could not be with more of a safer plane than what you have. Trainers are so forgiving.

I remember doing all sorts of things with mine when I had it. We would remove the .40 and slap on a .60 with tuned pipe. Or take a .20 size and put on a .40 and dog the heck out of it. The cg would change and we would adjust but sometimes we could not. Everything was set as far back or forward as possible. And for me I refuse to add weight so just ended up going with it. But I will add I already knew how to fly so any change I could compensate.

I am surprised on how off your plane is. Normally going by the book is dead on more or less depending on setup. Kind of makes me wonder what is off on your plane. But for sure you said your doing balance without fuel. I would maybe check for wing placement. Kind of far fetched but perhaps your wings location slide a little bit more rearward than normal. Could be a manufacture defect but easily fixed. I seen this before on a smaller electric trainer I had. The wings would not settle correctly on the fuselage and cause for up incidence and wrong CG location. I little trimming and shaving and problem corrected. It happens.

Also as for the balancer. It is a nice one as I have one also myself but I did notice inconsistency with I was setting CG on a small electric profile. The little stopper arm would move around allowing a diagonal contact and that small amount would move the measurement a little enough to cause a different outcome. For the heck of it take your tape measure and measure out 3 1/2 inches and put small black tape on the cg. Then put your fingers there and see where it goes. It may be the same or you may get something different. But worth a shot to try out a few different angles.

Hope all works out! Let us know how it goes

RE: Plane balancing question
 

The 'trick' to keeping the battery in place according to the guy at the local hobby shop is to wad up a black garbage bag and stuff it back there. "That way when you wreck it you have some place to put the pieces" he says... Thanks for the vote of confidence[X(]