I have a Great Planes PT-60 trainer with an OS.61FX. During construction I checked the balance several times and things always seemed fine. Now that I am 100% done I fear it might be a tad tail heavy. If the RX and battery are as far up as they'll probably go and the servo tray is now glued in how can I balance it better?

I'm gonna recheck the balance today and mabe if still tail heavy I might try putting the battery and RX next to each other sideways instead of along the fuse. If that dosen't work I'm not sure how to get more weight to the nose.

I went to a garage and asked for the old wheel balance weights. I got a whole box full for free.
Cut off the metel holder and just use the solid lead pieces until you get the cg right. When you determine how much weight you need then glue the weights against the inside of the cowl cheeks beside the engine. If you need a couple of weights to balance, then try to keep them more or less even by gluing some weight to one cowl cheek and some on the other. Use canopy glue. It stays flexible and won't fall off from vibration and its fuelproof. Everything must be installed except the fuel to check the CG. For a trainer the nose should tilt down slightly, say 1 or 2 inches from level when you hold the plane up at the cg locations. You should also check your lateral balance after. It won't make a lot of difference at speed but will make a big difference if you stall the plane.

to add to Fatskys reply........ try to see if you can slip that battery under the fuel tank

Doug

Fastsky said: You should also check your lateral balance after. It won't make a lot of difference at speed but will make a big difference if you stall the plane. This is VERY good advice and something that should not be taken lightly. I have made little "stands" and rest the crankshaft on a razor blade edge on one, and the tail rests on a dull nail sticking out of the other little stand. The upright stands are about 7" high in front and 5" on tail stand. I use scrap wood for shims to raise /lower planes so I CAN KEEP THE MAIN WHEELS ABOUT 1" FROM THE FLOOR. There are other methods.....this one works good for me. :) ... lownslo

Rekitter...My first kit was a PT40 with a Super Tigre 40 up front. I had a similar problem, so I built a shelf for my battery pack above the servo tray, which in this plane is immediately behind the fuel tank. Using scrap thin ply, I made a channel on each side of the fuse to slide the battery tray and then banded it down. Two small hooks on the servo tray catch the bands to keep the battery tray from moving in flight. In my case, that seemed to be enough. On another plane, to hide the lead I used I opened the hatch and glued them to the bottom side of the hatch where they were out of sight. Got my lead from the hobby shop in 1/4oz pieces..easy to work with, but don't trust the adhesive. I scraped it off and used thick CA. Hope some of this helps.

Rekitter: My suggestion would be move weight first before adding any. That way the whole plane stays lighter and will fly better. The battery is a very good suggestion, move that as far forward as needed. Be a little careful of the receiver right next to it, because close proximity of the battery and antenna may cause interference problems, it can be done, you just need to be careful of antenna routing. You can verify this with a range check.

If you must add weight to the nose after this, I have used the brass heavy hubs a lot since they add the weight as far forward as you can get it.

If that still isn't enough, then use lead, but move weight first, then add.

I don't even begin to have an answer, but I understand tail heavy is a very bad thing. I took my RealFlight sim and set a plane up to be slightly tail heavy, I can not begin to fly it. My first plane has a nose heavy problem, I took it to the local club and had them look at it. It needed some trim but was very fliable. I recommend the experiance of the local club and their instructors..

FreeBird

Thanks Everyone! Those are really great suggestions!

I will try to move some weight first. I think I will try your idea Spadiator to put the battery in the little compartment under the fuel tank first. Just gonna be tough padding it under there but I think I can do it.

Then Ill Look into adding weights. Fastsky, please define canopy glue. I'm sorry but I just have never used it or heard of it. I was just gonna use epoxy but don't want to go that way if anyone thinks it would just get brittle and fall off.

Currently I have a Great Planes plastic spinner on the plane. During a ground check with an instructor at my club, he told me he didn't like the plastic spinners because they crack off. He suggested the Du-Bro Aluminum Spinner Prop Nut. So I bought one but haven't decided to put it on yet. Others told me they have been using the plastic spinners forever without a problem. So I'm just confused about that. Not sure if the prop nut is heavy enough but if it is or the other type prop nuts are and help with balance maybe I'll give them a try. Only thing is I have the Hobbico TorqMaster starter with a standard starting cone so it would have to be a prop nut like the one I have that doesn't require the small hole starting cone.

Rekitter> i respect Spadiators opinion on the "heavy hub" type of prop nuts. they can be useful if you need extra weight at the nose.. but i and several other fliers ive talked to tend to shy away from adding any kind of spinning weight to the shaft of the engine. when you get that weight spinning, it becomes a flywheel (which is basically a gyroscope) and has high moment or inertia.

as im sure you know when you try to change the plane on which a gyroscope is rotating (by applying a torque against the axis of rotation), you get an equal reaction from the gyro exactly 90 degrees perpendicular to the applied force. Ask any helicopter guy, and he will tell you.. :)
basically thats why one of those lil toy gyroscopes tries to rip itself out of your hands when you change the direction of the axis.. AND thats also why a spinning top, for example, will start to wobble when it starts to slow down and get affected by the pull of gravity.

..basically it breaks down to quite a bit of extra force being applied to the engines bearings.. and isnt really great for wear..

the way I look at it, i have enough rotating mass up front with the prop and spinner tuggin on my engine parts.. i dont want a big old weight up there spinning away trying to help my engine fly apart as well. :)

..its all left up to personal preference.. ;)
to one modeller it may seem trivial.. and to another it may seem like a big deal.. so take everything people say about spinners and (pretty much anything else) with a grain of salt.. gather ALL the facts about the situation, then use your best judgement and you should be good to go.

and incidentallly.. the only time ive ever broken a plastic spinner is when i accidentally stepped on it. :p haha

>edit<
sorry about being long winded again guys. ;) and Spadiator, like i said before, this wasnt a crack against your (perfectly valid) opinion and practice.. i just thought that Rekitter might be able to benefit from hearing from both sides of the fence.

Rekitter, I switched to canopy glue for holding weights after I has one falloff that was held on by epoxy. The canopy glue that I like to use is called RC 56. It comes out of the tube white, drys clear and has no bad odours. There are other brands as well if you ask your hobby shop guy. Stick to plastic spinners. They will protect the engine from an impact by absorbing some of the forces. Metel ones will allow your crankshaft to get bent if you nose in. I have heard of 2 plastic spinners break in 5 years of flying. I am including a pic of the Rc56 glue. Its about $3.00 for a good sized bottle. Give the battery under the fueltank a try first though. Fast!

Rekitter, you may also wish to replace your battery with a higher capacity (heavier) one. You might also be able to move the engine further forward and use a heavier (APC) propeller.
If I have to add weight, I usually try to put the "extra" weight to good use...