Balance CG Problem with Arf Nobler

So far I haven't had much luck with my Nobler with the 5 flights. I have a CG problem with it for balancing it. It is WAY Nose heavy. With an empty tank it takes 4 oz of tail weight with the spinner off. I have an os fp 35 in it with stock muffler and a great planes uluminum spinner. I alreay added two oz of tail weight but it still is way nose heavy and down want to climb up. Should I have 2 more oz's?? I'm going to go flying tomorrow probably with it, so hopefully I can get it flying right even with it getting to be a brick. Anyone have this problem?
Ryan

The stock muffler is primary culprit, although the metal spinner isn't doing you any favors.

While I wish to emphasize that I have absolutely *no hands-on experience* with the O.S. 35FP, based upon a fair amount of flying and testing with the 20FP and 25FP motors, I wouldn't automatically toss that stock muffler in the trash.

In any case, the model *must* balance properly. At some point ya just have to stick in the extra weight. And then lie about it to your buddies.

So THAT'S how it works...

Right!, Craig! I don't know how that heavy weight got spread around about my 58 oz. Impcat. I lied about it to everyone I saw. How's your 51 oz. ROJett Bear doing?

LAST EDITED ON May-12-04 AT 12:58 PM (CDT)
 
You have probably thought of these things, but consider getting a tongue muffler and replacing the metal spinner with a lighter plastic one. You might still have to add a little tail weight, but the end result will a whole lot lighter than adding all of the tail weight you propose.

I have a tongue muffler from my K&B 40 that isn't in use. I will have to see if that fits tomorrow. I also have some plastic spinners. I hope that the tongue muffler will fit.

>So far I haven't had much luck with my Nobler with the 5
>flights. I have a CG problem with it for balancing it. It
>is WAY Nose heavy. With an empty tank it takes 4 oz of tail
>weight with the spinner off. I have an os fp 35 in it with
>stock muffler and a great planes uluminum spinner. I alreay
>added two oz of tail weight but it still is way nose heavy
>and down want to climb up. Should I have 2 more oz's?? I'm
>going to go flying tomorrow probably with it, so hopefully I
>can get it flying right even with it getting to be a brick.
>Anyone have this problem?
>Ryan

I'm not sure if this is the answer but with my arf nobler, I used a Brodak 40 with a tongue muffler and set the motor as close to the firewall as possible and then used a 3/4" prop spacer adaptor made by Fox. While the motor is mounted close to the firewall I had hoped this would help any possible vibration problems. Mine seemed to balance fine with no added tailweight.

Hi

Sound to me that changing the muffler and spinner is not going to be enough.

When I build, I set everthing up together and find where the motor needs to be to ballance the plane before comitting to engine placement. Depending on size of plane, compensate about 5 -10 mm for finish adding tail weight due to the surface area of tail. Then modify the design to get the motor where it needs to be. The reason for all this is that while you can add weight to ballance the plane, the lighter it is, the tighter it turns and the faster it flies but more important is to keep mass out of the extremities of the plane. Mass in the extremities means the turning moments are working against extra enertia that both resist turning and resist straightening up out of a turn.

If it were me, I'd be doing surgery to move the motor back to get the CG around 20% of the mean chord behind the LE.

Same here, Brodak 40 all the way back, I also must have measured wrong as I ended up cutting about 3/4 inch of the engine mounts and working the cowl back. But with the tounge muffler and an itty bitty aluminum spinner and balance was right on.

You have the same setup as mine. I put 2 oz of weight on the tail to get the CG right. My total flight weight was still under 41 oz. I doubt the extra 2oz. will make it fly like a pig.

>You have the same setup as mine. I put 2 oz of weight on
>the tail to get the CG right. My total flight weight was
>still under 41 oz. I doubt the extra 2oz. will make it fly
>like a pig.

Considering it was designed to fly around 45-48, I would probably agree with you!

If the engine runs well, just put weight in the tail until it balances. Don't mess up a good engine run to save a piddling amount of weight. Of course if it doesn't run well, then fix it.

The 2 Ounces Ryan already put should have been enough to make it stuntable, he says it won't even climb up. Mine with a Fox35 required no lead at all. But a buddy of mines with a Fox35 would not turn at all, it was like a pig. The trick is he never got it inverted or tried outsides. What I'm getting at Ryan is to check 2 things. When the motor quits, pay close attention to see if the plane noses up. This could indicate downthrust in the engine mount. The second thing is control flex. Did you upgrade the controls? With the heavier engine set up, the pushrod rigidity becomes more critical. Lock your leadsouts with one hand and push/pull on your elevator and see how much "spring" is in the pushrod.
I put a piece of aluminum tubing over the stock pushrod, and it stiffened it up fine. Dixon and Morris sell graphite tubing that fits over the wire also.

Hope this helps.
Eric Viglione

Hey Ryan, bring it to the contest Sunday, or come over on Sat. and we'll take a look at it. Is there a flying session scheduled for SAT?

Phil,

I haven't heard a word from Frank yet. If he doesn't call tonight, perhaps we should make some arrangements.

>So far I haven't had much luck with my Nobler with the 5
>flights. I have a CG problem with it for balancing it. It
>is WAY Nose heavy. With an empty tank it takes 4 oz of tail
>weight with the spinner off. I have an os fp 35 in it with
>stock muffler and a great planes uluminum spinner. I alreay
>added two oz of tail weight but it still is way nose heavy
>and down want to climb up. Should I have 2 more oz's?? I'm
>going to go flying tomorrow probably with it, so hopefully I
>can get it flying right even with it getting to be a brick.
>Anyone have this problem?
>Ryan

Ron B.
F4Fguy

I'm a little confused by your comment about it's behaviour.Do I read correctly that it wants to climb,unless you add down?If so,the problem is most likely mis-alignment rather than fore/aft balance.
Re-check the wing /tail/thrust alignment to be sure it's 0-0-0.Also check the flap/elevator setting to ensure they are both at 0.It sounds as if you may have a little down flap at 0 elevator.

The one I have is balanced at the spec point with an O.S.35S with stock muffler.The FP35 is a little heavier but not enough to need 2+oz. of tail weight.Adding tail weight to compensate a mis-alignment problem is courting disaster.

If the problem really is balance point,removing weight from the front is preferable to adding tail weight.The tongue muffler is one way to do this.Another way is,as has been suggested,moving the engine closer to the firewall,reducing it's moment.

Ron, No I have to hold up just to make it go level. I didn't have time to work on the Nobler today but my tongue muffler off my KB40 don't fit the OS, so I will have to get a muffler for that. I have my engine in the right spot where my spinner is right infront of the cowl.

Phil and Chip, Frank hasen't called here yet about flying. Hopefully we will be this saturday. I'll bring my new bi-slob with. I just got home from flying it and it is a blast!

Ron B.
F4Fguy

Ryan:

One other point;is the spinner back plate distance set per the revised Great Planes/Goldberg instruction?The original instructions had this dimension from the edge of the fuselage side to the back plate.The revised,and correct,dimension is from the FIREWALL to the back plate.this could be the reason you need so much tail weight.