Well, I went out and bought an Alpha ARF. The assembly of the plane was easy and straightforward, everything went together as it was supposed to. I put the plane on the CG machine, at 3 inches from the leading edge, and the tail dropped like a rock. It took 11! ounces of weight right behind the engine to balance it correctly. This setup was with the reciever and battery pack between the fuel tank and servo tray. I have since moved the battery up under the front of the fuel tank. What else can I do to get this thing to balance, short of adding a lot of lead?
Thanks,
-Sam

Can you please supply more details of the model?
Pics or a descrpition.
Is it a Semi Scale ? Radial? Ducted Fan? Biplane? Sports Model?
What wingspan? Motor Size?
What sort of motor have you got installed? 2 stroke? 4 stroke?
What is the all up weight of your completed model?
Many semi scale models of short nosed, radial engined airplanes, such as AT6's, Mitsubishi Zeros etc, need lots of ballast weight up the front to get the C of G right.
I have seen scale models of the Hawker Typhoon, powered by large 4 stroke motors, with over 1.5 pounds of ballast up front.
It's just something that the owners have to live with and if the model, with ballast, is still within the accepted weight range of the motor's capability, it's no big deal.

The alpha is a RTF trainer from hanger9. This thing should have balanced out of the box with everything installed.
Well, on second thought, I see you said ARF, not RTF. Therefore, you're putting your own stuff in it. What engine did you use? The evolution is a farily heavy engine, but not 11 oz heavier than other 46's. Aside from moving your battery up, you don't have much other choice but to use weight in the nose.
let me restate that--you have plenty of choices, but none of which would be real good for a beginner. Some choices are:
1) Lead weight in the nose (easiest fix) after moving battery as far forward as possible.
2) Weighted prop nut--will decrease performance substantially in a smaller engine.
3) Move throtle servo to the front--but this might be impossible with the fuse cheeks on the Alpha.
4) Get smaller, lighter servos--the servos for this plane sit behind the CG, so lighter ones will help, but will set you back another 75 bucks or so. The HS 81's from Hitec will operate this plane beautifully, but--like I said--will cost you more. If you're going to spend another 70 bucks, then you might as well spend it on suggestion number 5:
5) Get a bigger engine to help balance it.

Of all of the suggestions, I'd think number 1 would be the most logical for a beginner flying a trainer. I still can't believe this thing is that tail heavy. You are sure you had it at the correct CG?

I agree with 2slow2matter, this plane is an ARF and it should be pretty close to balanced when assembled. If you need that much weight in the nose to balance it then something is not right. I would ask what engine you have mounted on the plane. But I would also look at what is making the tail so heavy. Before you go adding weight you need to figure out what is so out of balance. Once all is said and done if you still need to weight then so be it, but I think you can balance without using all that weight.

Hope this helps

Ken

I'd say that if he is using any of the more common 40 size engines he MUST be doing something wrong in the balancing. I can not believe an alpha is that far off. Has you made any other changes back in the tail area. Extra glue, fittings, anything?

Unless someone left a pipe wrench under the covering, Bruce has to be right! Sam, did you change anything? Like the pushrod system. etc? If no, recheck your method of using the CG machine.

Thanks guys,
I think the main thing is that I've got an O.S. 46LA on the nose, instead of the heavier Evolution. I think I was probably a bit heavy on the epoxy on the tail and securing the control horns as well (I removed most of the glue where I applied it to the control horn backplates though, but it couldn't have been more than a quarter ounce of glue). As for balancing the plane correctly, I had the LHS check it as well, it came in 11 ounces tail heavy.
-Sam

I don't know, the Evo just isn't that much heavier. I sure hate to add that much weight to the plane. Can you move the batteries up under the tank? Can the engine slide forward any and I do mean ANY? Move as much "useful" weight as you can before adding "dead" weight.

By having to add 11 ounces to the nose (which means there is more weight in the tail than necessary), then you will be coming in at about one pound overweight--which is going to increase your wing loading substantially. Maybe not quite a pound since the motor is definitely lighter than an evolution. However, the motor isn't more than a couple of ounces lighter, I'm sure. I'll have to check out the weights of the two motors and get back to you.

Ok, the LA is a little lighter and a little weight in the tail goes a very long way due to the distance from the CG. You are stuck with the weight. Do like Bruce said and move the battery as FAR forward as you can. Next, find a scale and weigh it. (balanced w/weight) You can check your wingloading and "see" what the effect of the weight is.
First get your wing area in inches. span x chord = area (sq in)
Divide by 144 to get the area in square feet. sq in/144=sq ft
Now divide the weight in ounces by the sq ft. oz/sq ft= wing loading
You've got the wingloading!
Now compare that with others. I think the average trainer is 16-20oz per sq ft.

OK, here's the deal. I checked it out, and the LA comes in at 9.6 oz without muffler (according to towerhobbies), and the evolution comes in at 16.3 ounces without muffler (according to horizonhobby), so that is your difference. The alpha was designed for the heavier evolution trainer system. Your motor is nearly 7 ounces lighter than the intended power plant! For 10 more bucks you could have bought the evolution. The OS is an excellent engine, but the evolution will produce much more power at the prop than that LA will. Probably not quite as much power as the AX (or FX), but way more than the LA. But, I digress. That's your decision, and now you'll need to add dead weight to balance it out. For 25 bucks or so, you might consider going and buying a 1500 or more mAh battery. It will not only be heavier, but it will be useful weight--you can fly many more times than on the standard 700 mAh battery! Move it all the way to the front, and you might not have to add as much weight. Also, consider putting a slightly heavier nose wheel on the front--or lighter ones on the back. You could put foam wheels on the back, and leave the heavy rubber one on front--that will help redistribute some weight as well, and actually make the plane a little lighter at the same time!

Even with the extra weight it will fly OK, it just won't glide/float quite as well. On the bright side, it will penetrate a wind better when dead sticking much like when they add ballast to a glider. Do what you can with moving weight, get a heavy prop nut and put any weight you do add as far forward as possible.(secure it well)

Out of curiosity I just put my Alpha RTF on the GP CG Machine and it is showing tail heavy also. This plane flies great the way it is and is the same as it came out of the box (no extra glue or balsa).
I don't know how much it would take to make it level but it would be a lot of weight as the tail easily drops to the ground when on the machine.
The plane does balance at 3 3/16 inches if that helps.

Anything between 25% and 30% of the mean average chord will fly. The further back the CG, the touchier the elevator.

The evolution manual puts the EVOE0400 at 14.08 w/o muffler. Still @4.5 ounce difference. Evolution data downloaded from Horizon web site. Still don't understand you needing so much weight.

Bruce,
that is the weight of the evolution 40, but I had looked up the evolution trainer system that normally comes with the alpha. It's a different motor that is actually .455 CI, and has a weighted flywheel and so on. But you are correct, no matter the weight difference, it doesn't take much at the extreme end of the plane (tail or nose) to make a difference.

Agreed.

Didn't read the whole post, short on time...

I have a alpha trainer ARF with .46 LA and it was very tail heavy, I have put a heavy prop nut and glued with epoxy some weight on the nose. I also moved my battery in the fuel tank compartment, my plane is not even slightly nose heavy (Because I got tired of adding weight) It's actually level, maybe 1 degree tail heavy (Without fuel in the tank) and my plane flies great, to me anyways...

So yeah It's normal I think for that plane to be tail heavy, I think it was designed for the evo .46 engine wich is probably heavier then the la,

I think I slapped a 1 ounce prop nut and 4-5 square lead on the nose.

I looked up your ARF and it has a constant cord wing. Can you measure the distance from the leading edge to the trailing edge of the wing. With this measurement you can determine where to set your CG (center of gravity). I would reccomend setting it at 27% measured back from the leading edge.

Example: Cord Width equals 10"

27% = .27

Multiply .27 x 10 = 2.7" = 2 11/16"

Measure back from the leading edge 2 11/16"

I've read through this and I think that the weight problem has been found. The OS is lighter than the Evolution, so the extra weight you add in the nose will be just about where the plane was designed to fly. So you should be ok. But what did catch my eye was the comment you made about epoxy on the control horns. Did you use epoxy to mount the control horns on the elevator and rudder??

Ken

I think maybe he put some on the backplate of the control horns--I believe that is what I read. I noticed that as well. Probably should have used CA, if anything. I usually don't put any glue on at all, unless it's the kind without backplates--and I really hate to use those. In fact, I usually replace them with real horns utilizing backplates. I once built a little 1/2 A kit that used control horns with screws--no backplates. They were dubro's, and all I could find. On them, i put some CA down and then screwd them into place--they didn't go anywhwere.

flycatch - That would make the situation look even worse and the manual does say 2.75 - 3 inches. That would put your calculation at the forward end but it would probably take over a pound of weight to get it there. []

Move what you can and add weight for a 3 inch balance point. IMHO

You guys are right about the weights of an OS LA and any .46. I have several different .46's and, with muffler, they run between 16.5 & 17.5 ounces. The OS LA's are much lighter at about 10 ounces. If the plane was balanced with the flywheel, you can add a few more ounces to the 17.5, which is what I get for an Evo .46. This could account for your balance problem.

In addition, during production when building a large number of planes, it is not uncommon to occasionally get some heavy balsa for the tail. You could have a slightly heavy tail, plus the epoxy you added may have tipped the scales.

One of the things about RC building, whether a kit or an ARF is you must watch any weight added to the tail. A tail is typically 3 times longer than a nose so any little extra weight added to the tail will take 3 times as much added to the nose to compensate.

You also might consider a brass heavy hub. I have used them numerous times to correct a minor out-of-balance condition.