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morris knife balancing

Old 03-21-2003, 11:30 PM
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Default morris knife balancing

I trying to balance morris the knife with the following setup :
saito 72
aluminum spinner with dave brown adapter
kit (not arf)

1) lateral balance:
i tried to hold the the model on both edges with finger tips (or sharp wood edge ) . it seems that the right wing is fulling very fast (this is the right side where the engine installed)

2) cg balance
at 4.5" inch i have to add something like 10g to the tail in order to balance the model (using greatplane balance machine) 5" cg requires even more.
the battery (1500 map) was moved to the most left and aft as could as i did with the engine.

* i repeated the balance test for several times

did someone got this behavior
is the lateral balance so bad with saito 72
what should i do

thanks
Old 03-22-2003, 12:32 AM
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Default morris knife balancing

Easiest way to balance the Knife is to place a little screw hook into the fuse at the balance point then hang it upside down.
Old 03-22-2003, 06:02 AM
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Default morris knife balancing

Hehehe... Great idea. In fact, my knife has a permanent screw-hook on top at the balance point. That's what it hangs from in the garage.

To try to answer the original question, Mine lateral and fore-aft balanced with the TT 46 Pro all the way forward and the battery out in the wing as far as I could get it. If you only have to add 10g to the tail for fore-aft balance, that's not too bad. I'm guessing you can't move the engine back any more?

Warning: It flys great at the recommended CG 4.5". When I take off the 12.25x3.75 APC and put on a wood 11x4 it shifts the CG back a bit and you can really tell the difference - it gets trickier so be careful to move the CG back slowly.
Old 03-22-2003, 10:25 PM
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Default morris knife balancing

thanks guys but

1) did someone installed morris the knife with saito 72 and had big lateral balance problem ?
2) it seems to me that installing these screw hooks on such a flimsy fuselage will ended with cracked fuselage !?
Old 03-22-2003, 10:34 PM
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Default morris knife balancing

There was no way I could balance my TopCap with a Great Planes C.G. machine. I made a mark on the fuse were it should balance and used my finger tips to hold the fuse to balance it that way you don't have to drill any holes. By the way mine balanced perfectly with an O.S. 70 4 stroke.
Old 03-22-2003, 11:07 PM
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Default morris knife balancing

The screw won't crack the fuse.

Screw it in
Take it out
Put some thin CA in the hole and let it cure
Screw it back in
If the hole gets loose, repeat the CA or stick in a toothpick and re-CA it to give the screw some bite.

Hang it from the screw to check balance.
Old 03-23-2003, 01:17 PM
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Default morris knife balancing

I will try the screw hooks method but just to be clear .

i have to install two screw hooks on the bottom of the fuselage one near the engine and the other one just beneath the rudder then hang it from the ceiling using some kind on nylon wire
is that correct ?

thanks
Old 03-23-2003, 02:02 PM
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Default morris knife balancing

Sorry I don't have a photo handy, but what I did was put the screw-hook in the top of the fuse at the CG point. I believe it's 4.5" back from the wing leading edge. Just one screw-hook is all. I hang it from a heavy string or light rope.
Old 03-23-2003, 02:23 PM
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Default morris knife balancing

Originally posted by rcFp
I will try the screw hooks method but just to be clear .

i have to install two screw hooks on the bottom of the fuselage one near the engine and the other one just beneath the rudder then hang it from the ceiling using some kind on nylon wire
is that correct ?

thanks
Just one screw on the CG is fine... top or bottom doesn't matter...

I have an O.S. 46fx and the engine is all the way back as I can get it...

I used a 1650 mah pack in the trailing edge of the wing OPPOSITE of the engine-head-side...

In addition, my fuel tank, receiver and switch is on that side too...

Basically you'll NEVER have perfect lateral balance for any amount of time due to the fuel tank having to be left or right of the lateral balance point...

However, with the tank on the opposite side, you'll offset more of the weight with simply the weight of the tank, clunk and lines AND when fuels in, you'll be left heavy for part of the flight and perhaps right heavy the second half...

For CG... the kit is already 1 lb lighter than the ARFS so adding some tailweight wont hurt too much... also going with the carbon fiber gear might help a tad... (get info on gear here:Profile Brotherhood

ALso let me say that the plane is a real performer despite the lateral balance issues... The plane with fly great a bit noseheavy and you can add tailweight to your liking... With a Saito 72, you won't be hurting for power.


Lastly if I build another, I will weigh the sheeting and put the heavier sheets on the "light" side...

I'm strongly consdeiring building a 150% scale version with sheeted foam wings and fuse... I'll also make the wings removable via wingtube. I will leave the nose longer than the plan and test the CG with the servos in the tail.... I'll then adjust the length of the nose to achieve balance.

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