Not sure where to post this, but here I go. I finished a kit and it is time to balance, so I set it on my Great Planes CG Machine and in order to get it balanced properly as recommended, the battery has to be placed in the rear and it balances perfectly. So I velcro the battery in place set the model on the floor and it sits on its tail (it is a tri gear not a tail dragr). In order for it to sit on the tri gear I have to move the battery forward but then on the CG Machine it becomes nose heavy. Has any of you eno****ered a situation like this and what do you recommend to correct this?
TIA

I have a couple of questions.

what plane is this

how tail heavy is it?

I assume the the main gear at at the proper location?

have you confirmed the cg location and or have you tested the cg location with your fingers?

Hope these questions help

It's a trainer I built for my neighbor's son
Dunno how tail heavy, what do you mean?
Main gear is set at the proper location (pre-drilled placement holes)
Balances perfect from fingers and CG machine with the battery placed towards the rear.

I've never seen this happen before[&o]

If the CG is within the limits of the design, what is show on the plans, then the main wheels are to far forward. Check to see if the wheel wires have a different wheel location when moved side to side. It may be that they have a rake built into the wires and If you put them on the wrong side os the plane, then the rake is forward and that would give you the problem you are seeing.

Don

PS you didn't answer what plane it is, there are a ton of trainers out there and to give you a good reply, we need to know which trainer it is.

Don

I balance mine inverted with that machine. If you have used parts that the manaul recommends you should be very close to the netural CG and not tail heavy. you can always put the battery up futher and fly the plane, if you do not like how it flies nose heavy you will have a plane to adjust. Land it and move the battery futher back.

Here are some pics of the trainer on the CG Machine with the battery installed:
Edit: Thanks again for all the help I can get

If the model balances (at a slightly nose down angle) on your fingertips at the CG given in the instructions then I'd trust that. If that also agrees with what you get on the CG machine, that's great. If the model still falls back on it tail, then it's one of two things:

1. The CG given in the instructions is wrong. It happens. The CG should be at no more than about 25-30% of the wing cord.

2. As Campgems says, the main gear are too far forward.


I've never seen this type of trainer before, so I'm wondering if it would somehow "pull itself upright" with the engine running.

I'm sure once the tank is full of gas it will right it self, but it is just odd to see this behavior. The trainer is a Durabrick, oops sorry a DuraPlane.

OK, I don't want to steal anybody's thread, but this is the first one in a while talking about balancing. Always my nemisiss!! You balance a high wing right side up. You balance a low wing inverted, right? OK ,now, how about a mid-wing? I've just finished a MidWest Hots from plans & I'm having a terrible time balancing it. It seems I can get it (inverted) balanced slightly nose-down for a few seconds & then it will start nosing down & keep going untill I stop it. Sometimes I can hold it level & it will go " tail heavy" It will do basically the same balancing right side up, only it seems that the hesitation will be some what slower. Any ideas?

Outdoor. With this you can balance anything. Well worth the time to build.

http://home.mindspring.com/~the-plum...%20Machine.htm

Les

If the balance slowly falls on way or another and I mean slowly, those birds have always flown well for me. its when you put it on the CG spot and it just will not stay that i have seen issues if you fly it anyway......

I did not know about the high wing deal as its been a while since i did one of those maybe 9 + years. I would also do the mid wing inverted....balance

I had one of those birds before.... I don't remember the tail falling like that though. Some of my thoughts...

1. CG should be checked withOUT fuel...
2. If the tail falls back without fuel it should work well once fuel is added BUT when you come back after burning off the fuel that tail will simply drop like that again.
3. The purpose of checking for CG is not to control the way it stands on the ground... It's for how it will FLY.

I would maybe move the main mount aft about an inch or so.... Its NOT that scientific. If you move it way back... You will have a little added difficulty in taking off but that would probably if you put it back near the aft servos (elevator/Rudder). one or two inches shouldn't be close enough to the holes you drilled already to compromise the integrity and should still be able to lift off easily. Remember it's a PLANE not a CAR.... balance it to the WING and it will fly great... If you balance it to the wheels then in this case it will be REAL nose heavy and you'll have your hands full!!!

Good luck and let us know how you do! Keep sharing your info....

I just checked the online manual and it states that the CG is set at 3-5/8 inches behind the leading edge. It is usually set at the thickest part of the wing. Double check your measurements. That looks way too tail heavy on your first picture.

Well took this bad boy to the field today anyways, once there the guys looked at it and did the fingers balancing, the machine balancing and we all agreed with Huntster, if it balances on the spot it will fly well regardless of how it looks on the ground. So I hooked it up to the fuel pump and it just up righted it self; so I decided to maiden this bird today. I tell yah it flew like a champ, it is not a first timer trainer in my opinion but it sure is a blast of fun to fly and handles the winds very well. Mission accomplished [sm=thumbs_up.gif][sm=lol.gif]
Thank you all for your priceless input and advise/transfer of knowledge.

I had a Tiger 2 ARF that did the same thing. I would taxi in and when I killed the engine the tail would fall down.

David

Flybug,
Its been said several times already in this thread but I think the main gear are located too far forward. Perhaps there was a mistake when transfering a dimension to the fuselage from the plan or something. The designer wouldn't locate the main gear inside the CG range. Duraplane trainers have been around since about 1990 so I doubt an error that big has gone undetected without a revision in the plans or instructions. I bet if you retrace the build sequence you'll find something.

I will go back and retrace my steps, will start with the instructions and report back.
Thanks

CrateCruncher,

I reviewed the manual http://manuals.hobbico.com/dur/dura1111-manual.pdf page 6-7 and the main gear is right where it suppose to be according to book. So I guess since 1990 no one notice that the main gear was within the CG or perhaps it was designed that way. A lot of people complain of this plane but perhaps there is the issue they balanced it for ground and not for flight and it became a handful. This model flies as intended and balances perfectly at 3-5/8 inches, but empty it sits on its tail. I will call support to bring this to their attention, maybe I get a free revolver