Katana S - 72"
 

I have the Extra and it balances at about 5" which is centered over the wing tube. For a lot of other owners' tastes it is a bit futher aft. I am an advanced pilot. It would be good to start at the front of the wing tube. The more aft the cg, the less elevator throw you should have and the trailing edge of the elevator should move about 9/16" on low rate, these elevators are large. When you see a plane going crazy and the pilot is yelling, "it's tail heavy!" there is way too much throw. If the plane gets airborne then it is flyable (is that a word?).
On the pump, be sure the adjustment screw is backed out if its a Perry VP 30. the OS needs the minimum pressure from the pump. Adjust the engine like normal but you will find it will be set a lot leaner on the low end than without the pump. Keep leaning it out 1/8 turn at a time until it quits when you jam the throttle full then back it out 1/8 or so. Your throttle response should be instant like a F1 race car and very reliable. Mine had two flights on it and would idle at 1800 rpm. Use a quality prop like Menz or Mezjlik 18x8. Zinger doesn't make a quality prop. An APC 18x8W would be ok but not the pointy one that looks like a two bladed letter opener.

hmm
 

all good advice but, i can fly some as well(not way advanced)... but your quote "If the plane gets airborne then it is flyable " is sort of general....or vague..... i have flown a few real tail heavy planes(if you want to call it flying) and it was all i could do to get it back to the ground...was not very pleasant to fly and a handfull.
i would say start nose heavy and work back. the ole"fly inverted and see how much elevator is needed to stay level" test... seems to get you close to the ball park.......but i agree with the huge control surface.... and to much throw stuff.. i looked at the size of my rudder and elevator on this katana i am putting together and went holy moly!..
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they sent a smallish looking fuel tank in kit looks to be 12-14 oz.and the plans show it in the nose(way in front) i want to put a larger tank....i have a 24... but i was wanting to put it closer to the CG.....does that make sense>?)move it back) a 24 oz tank in the nose would seem to change the CG considerably when going full to empy.

thoughts...idea`s>?
and if i move it back......my thoughts were to put it about 2/3`sin front of the cg...or so......

Katana S - 72"
 

I would go with a 20 oz tank to start. On the cg is optimum but you will probably need a pump.

Not saying it will be easy to fly but, in a tail heavy situation just ease back on the throttle and go way easy on the controls.

There is anothe CG test the sailplane guys use. Put the plane in a 45 deg dive at low power and see what happens. If it starts to level off the cg is forward, if the dive steepens it is aft. Optimum is no change. Assuming your incidences are correct and trimmed out otherwise.

Katana
 

h82crash, thanks for the advice. Since I acquired this plane second hand, did not know where to put the CG or how to set the pump. You are right, I keep leaning the low to get it to run. I used a Zinger Pro Z 18x6 yesterday. Seems to pull it very well and failrly slow, especially on down lines. Flew it again today and found the tank is small and I need to tinker with the engine a liitle more. But, plane flies great.

Should get mine tomorrow!!
 

Hi all,
I should be getting my GSP Katana S 72in tomorrow.
Anyone have lightening tips, construction hints, ect. to share??

Motor will be an RCS 1.40.
HS-475 servos.
1850 mah AA 5 cell pack
8-10 oz tank

Hope to keep it around the stock weight of 10-11 lbs RTF.

Thanks!
CrazyHerb