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How do you balance your model?

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Old 10-17-2006, 10:36 AM
  #1  
fadi
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Default How do you balance your model?

Hello
I nearly finished my sig 4star ARF plane now.
It looks gorgeous, but I still have the problem of center of gravity.

I put it on the great plane CG machine at 74mm as suggested in the manual... and the nose is heavy!!!

What to do? I tried moving the battery to the max, still, I need to add some small weight to the tail? In fact I need to add a zinger 11x6 propeller equivalent of weight bcs this is what I placed on the stabilizer to make it perfect funny, but I don't have any pre determined weight :P

How do you usually do it? What weight can I add to my plane if I can't buy those great planes stick-on leads? Any idea?


Please help, I can't wat to maiden it This is my first plane I ever build. I just love the idea to see it track perfectly !!
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Old 10-17-2006, 11:36 AM
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Default RE: How do you balance your model?

YES! By all means, add the stick on weights under the stab to balance the plane. This in addition to moving your radio gear as far aft as possible. It's much more fun to fly a perfectly balanced model that weighs a couple more ounces than a lighter, nose heavy pig.
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Old 10-17-2006, 11:41 AM
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Default RE: How do you balance your model?

I've used copper coins (our "penny"), fishing sinkers, wheel weights, cast lead balls for muzzleloaders, chilled shot (like used in shotgun shells) mixed in epoxy, washers (the kind bolts pass through), heavy gauge wire, lead fuse wire (on light free-flight models), wood screws, nails . . .

It doesn't matter as long as you can attach it solidly. If you have rear mounted servos you can remove them and tape coins to them with electrical tape. Easy to adjust the weight and requires no additional holes in the covering. Works with aileron servos for lateral balancing, too.

And then when your model dies it has something to pay Sharon the ferryman on the River Styx to get into the netherworld.
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Old 10-17-2006, 12:45 PM
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Default RE: How do you balance your model?

You can get those flat stick-on weight at the tire shops. They use them on cast aluminium wheels.
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Old 10-17-2006, 02:49 PM
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fadi
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Default RE: How do you balance your model?

ok I finally found them didn't know it was really cheap!!
I had to add 55g to the tail to balance properly. I sticked them directly to the cover, but I am afraid they will rip the cover or simply fall.

Shall I use CA? epoxy? should I cut and remove the cover before?

I am happy the plane is perfectly balanced now, but boy they look ugly!! Grr!!
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Old 10-17-2006, 03:22 PM
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Default RE: How do you balance your model?

I had to move the battery to the tail behind the wing to get mine to balance. You might try a little more weight and CA it inside the fuse at the tail. You don't want the weights coming off in flight!
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Old 10-18-2006, 01:17 AM
  #7  
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Default RE: How do you balance your model?

I maidened it this morning!!!!!!!
It tracks like an arrow, it is so smooth and nice!!! Can't believe it, I will just go and trash my trainer, nothing to compare!!

It lands relatively fast with the 10x6 propeller. I've put the 11x6 and it is very easy to control...
However my engine is not running properly with the 11x6 I don't know why. It is an OS MAX 46AX
I believe the top level of the fuel tank is not at the same level as the carburator valve... could it be the reason why it cuts on idle?

Anyway, now i have to just remove the weights and permanently glue them on the tail with CA.

By the way, these nylon pushrods are crap, i hated them. Tonight i will replace them with metal ones and the plane will be excellent but the engine.
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Old 10-18-2006, 02:10 AM
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Default RE: How do you balance your model?

G'day Fadi,
You should have the centre of the fuel tank level with or no more than 10mm below the level of the fuel inlet, & you will find that an 11x6 is the starting point for prop size, a 10x6 is a 40size prop & too small for the 46AX, & please define "running properly" what do you mean?
remember to keep it rich for at least a couple of flights, as per the instructions, & check your low speed mixture, with the pinch test after that.
Keep us posted as to your progress.
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Old 10-18-2006, 07:07 AM
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Default RE: How do you balance your model?

Yeah well this is the problem then... it seems as though my sig 4 star 40ARF has a relatively high engine mount in relation to the fuel tank. I don't know how to change that, it is quite a complicated job to readjust the nuts in the firewall

I know the 10x6 is too small, I just used it for running-in (around 20 flights of 15min), but my OS46AX won't rev up with the 11x6. Or did I got used to the engine with the 10x6? It used to reach 14500rpm :P
Now it barely reaches 10500rpm with the 11x6 zinger prop.

Running properly means sounding smooth without continuous mini speed-ups and slow-downs while airborn. it also means that it should idle smoothly without spitting fuel or shiver like hell!
I hope this is not too much asked from an expensive OS46 AX model
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Old 10-18-2006, 08:21 AM
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Default RE: How do you balance your model?

10.5 K with an 11X6 sounds ok to me. 14.5 K sounds really high...to high. High RPM dosen't mean more power or speed. As far as the rough running it sounds like the low speed mixture is to rich.
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Old 10-18-2006, 08:03 PM
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Default RE: How do you balance your model?

try a 11x5 on the .46
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Old 10-19-2006, 02:15 AM
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fadi
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Default RE: How do you balance your model?

ok I changed the glow plug, and retuned the engine. 11x6 is fine now.
It just rarely cut offs when i drop below 2500rpms... I think this is not perfect but should be acceptable for now.

I noticed that after flying for 7 to 9mins, the engine cuts more often when dropped to idle. I am relating this to the fuel supply.
Can a loop in the fuel line affect this? I am not going to lower the engine mount this is too much trouble

But I can cut the fuel line shorter between the fuel tank and needle valve..
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Old 10-19-2006, 03:36 AM
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Default RE: How do you balance your model?

G'day Fadi,
Yes shorten your fuel line, & remember, as you lean out your idle mixture, the engine will speed up, & you must slow it down with your throttle trim.
Sounds like you are getting there mate,
Enjoy.
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Old 10-19-2006, 05:32 AM
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Default RE: How do you balance your model?

Ah good point Yes, throttle trim...

Nevertheless, I am still unable to determine what really causes the engine to stop. What's happening on the inside that can stop it from firing... I am sure when I discover all the tricks of it, I will be able to properly remedy
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Old 10-19-2006, 06:31 AM
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Default RE: How do you balance your model?

Did you change to metal pushrods? That might have helped change your CG in the direction you needed.
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Old 10-19-2006, 07:28 AM
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fadi
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Default RE: How do you balance your model?

Yup, I replaced the nylon crap *&%#@# with metallic pushrods. the surfaces have more "authority" now!
When they move, they really MOVE!! and same travel distance every time
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Old 10-19-2006, 09:18 AM
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Default RE: How do you balance your model?

What woodbutcher was implying is that with the metal pushrods, your CG might have changed (Since they are heavier and they are completely behind the CG) So re-check before you fly.

Two things you have said have piqued my interest.

First, you say the engine keeps quitting at idle. Sounds to me like you need to adjust the low end needle valve. It is a small screw in the center of the throttle arm (See pic) The picture below is for a different engine. Yours does not have the "Blue Collar" but the adjustment is in the same place.

Bring the throttle to idle, let it idle for a few seconds, then pinch the fuel line with a pair of pliers - the engine should rev slightly, then die.

If the engine dies almost immediately, you're too lean and need to turn the screw out (CCW) - Note, only turn the needle by 1/8 turn each time.

If the engine revs a pretty good amount, then dies, the low end is too rich and you need to turn the needle IN (CW)

In either case, try it again, and repeat if necessary.

The next thing I wanted to mention is: Once you have the engine idling properly, if the plane still lands fast, try adding a little more tail weight. Not being able to slow down on landing is very often a sign of being nose-heavy.
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Old 10-19-2006, 10:18 AM
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Default RE: How do you balance your model?

Minnflyer, is the idle mixture tuning the only reason why an engine quits on idle?
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Old 10-19-2006, 10:42 AM
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Default RE: How do you balance your model?

Well, it's not the only reason, but it's the most obvious
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Old 10-19-2006, 10:44 AM
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Default RE: How do you balance your model?

I will try to tune one more time to see... when i had the 10x6 prop it was the best engine among all my friends at the field They envied my idle speed and smooth transits. I tuned it myself thought, I don't understand why I am not able to perfect it with the 11x6 now
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Old 10-19-2006, 10:47 AM
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Default RE: How do you balance your model?

What type of fuel are you using?
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