Hey all,
Well after a bit of distraction I finally got the trim on my pt-40 finished up. Got kinda impatient near the end, but oh well. Anyways, I'm working on balancing right now before finishing up the radio install. First balance came out REALLY nose heavy. I pulled the battery out of the battery bay and moved it all the way to the back of the electronics bay. Tested balance again. Still nose heavy but not as bad. I'm wondering if I should try to modify the F3 former to allow the battery pack to be moved further back, or just install it like it is (full back in electronics bay) and go ahead and add some weight to the tail.
Thanks
-John

striderjg,
Unless you're 100% sure of what you're doing I wouldn't recommend modifying structural components such as the formers. It's too easy to weaken one to the point that it could break. Do as you've already done and move the battery back as far as you can first. Then you need to add weight to the tail to balance the plane.

I would recommend that you install all of your radio equipment before you balance the plane. The radio components could change the balance of the plane. It's also possible that you could use the receiver itself to help shift the balance of the plane back some. But if you balance the plane and then install the radio equipment there is a good chance that you'll chance the CG of the plane.

Hope this helps

Ken

THanks Ken,
I'll just add weight. After moving as far back as I can it doesn't look like ti will be that much weight. Probably a oz at the tail. Everything is installed jsut not finalized. (ie, control hookups to servos, tray ca'd, wires tieded, ect. Everything is inthere though. I'll hold off putting the weight on till I get it ready for flight then I'll balance again and put the weight on.
-John

Striderjg,
If an ounce is all that you need in the tail then you are going great. An ounce is next to nothing. You won't have anything to worry about at all!

Ken

Striderjg: What size engine you you have on your PT-40? I'm in the process of completing a PT-40 with a OS .50SX, and from what I can tell - it'll be tail heavy too. I may have to put the battery behind the F3 former, but don't know how to secure it there, as there's a lot of space between F3 and F4. Any suggestions? if all else fails, I probably make some sort of a tail skid with the right amount of lead weight in it and epoxy it the the bottom tail section.

Johnmpa,
I'm using a os .46fx. I assume when u say tail heavy u mean nose heavy I'm hopeing I got the name of the former right. I was thinking of moving it behind the former that's at the trailing edge of the wing. I was trying to think of how to secure it. Hadn't come up with anything yet. I'll keep thinking on it, and if I come up with anything I'll let u know. As I have it now at the very back of the compartment under the wing, I built a little box out of scrap for the battery. It's wedged in pretty tight with some foam. I will probably do the same with the skid for the bit of extra weight I'll need. I'll just grab a piece of steel and pull out the trusty dremel and cut off wheel to cut it down to weight, then epoxy to the bottom of the tail.
-John

Be SURE it's out-of-range nose heavy before you add tail weight. This trainer can balance as close as 25% of the wing chord and fly well. Remember: Nose heavy planes may fly poorly. Tail heavy planes may fly ONCE.

Dr.1

If you're within an ounce, and you're nose heavy, if I were you, I'd fly the thing before going to any effort. Matching up the exact CG when you're building is often a waste of time. Getting close is not. And you're close. Flying it to work out the CG the plane actually needs is worthwhile. But nose heavy and close when building it is good enough to go the next step.

When you first fly the plane, take it up high and see how slowly it will fly. Then keep it high and throttle it to go about 1/3 speed and trim it for level flight. All of this will take very little time. Now put it into about a 60degree dive and move the elevator stick to neutral. If the nose comes up fast on it's own, then take it home and add that ounce of tail weight. Don't worry about that CG until the plane flies nose heavy.

BTW, if the nose tucks down, then the model is tail heavy and you'd want to move the battery back forward. Yeah, those reactions don't sound right, but they are.

And btw....... If you're wanting to move a battery back into the fuselage to get weight back there then don't worry about adding extra wood back there to hold the battery with some supporting structure. Add the structure. You want weight after all. The rear fuselage isn't designed to hold concentrated masses like a battery, so if you move it back "into the stringers", give the stringers some help. Get a sheet of 1/8" balsa at the hobby shop and use it to build a box back there. It's really simple to do. Make sure the box spreads out to strengthen the fuse area it's in, and the plane will be better for it. You can also use balsa sticks to bridge and support. It don't have to be pretty, ain't nobody gonna see it nohow. But make sure it spreads the load. Nothing ruins a flight like having your battery g-force it's way through the aft fuselage covering.

Thanks darock. That sound like sound advice to tailer the balance with flight. I have to run out to lhs today to pick up a charger/switch jack, I may pick up some stick on weights as well to take with me to the feild. Just about evertyhign is done. Woot. Just need the charger/switch jack, then tweak the Aliron throws. I must have gotteen the wholes on the servo wheel wrong. To much differantial. 10+ mm down and only about 5 or maybe less up. So I need to play with that too. I'll try some of the stock holes and see if I can make it work with that, or just increase the throws and use epa to tune it down.
-John

edit --
Oops, wasn't thinking. One side goes up and one side goes down either way. Epa won't do **** for that. Lol. So looking at the hole placement on the servo wheel I guess.
-John

Striderjg,

The aileron differential should be much more up than down, Much! Wouldn't criticize, but you call it too much when you have way not enough good differential, needing more up than down.

Adverse yaw is caused by the drag of the lowered aileron on a flat bottom wing. It is only a concern when flying slowly. However, on some high-performance aircraft, with symetrical wing, adverse yaw is used to help rolls stay axial.

Ken, AMA 19352

Damn. I don't know what I was reading. 14mm p 10mm down. hmmmm. Lol. thanks for that. Gonna go reverse the servo wheel now. *slaps head*


Fixed. Reversed the wheel. Luckly I had some extra pushrods. Thanks
-John