I got my self a CMP Katana 140 http://www.nitroplanes.com/katana-ae...version-2.html . I plan on powering it with a DLE 30 and it is either going to need a lot (about 30-40ounces) of lead in the nose to balance or it will need some redesigning. I was wondering if I extend the nose an move the engine forward 5 or 6 inches will it fly worse than adding 2 or 3 lbs of lead. I have done this with smaller planes but nothing this size and never really noticed a difference. I haven't installed servos in the tail yet but I doubt if I moved them in front of the prop they would make a difference. This thing must have concrete in the tail. Frustrating to say the least. Thanks for any help.

Look at the image of the plane on the web page you posted the link to, where the plane is upside down.

The C.G. should occur just forward of the Yellow "Katana" on the right wing ( right as viewed from a pilot in the plane ) or anywhere up to the front of the word "Aerobatics" in yellow. The former is best for 3D and the latter if you are not used to a 3D plane.

While the DLE is a relatively light engine... 2-3 pounds is excessive... to get the C.G. into this range.

Try the following:

- Move the engine as far forward as you can on it's mounts WITHOUT this requiring that you modify anything.
You should be able to use the cowl as it comes, but don't cut it out until you've flown the plane and have it in it's final configuration.
You may need to use longer mounts, but make sure anything you do permits you to utilize the cowl once you do cut it.

- Move all of your battery packs onto the engine mounting box

- Install the throttle and choke servos on the mounting box.

- Make sure the tank is as far forward as possible.

If after doing all of the above the C.G. does not occur in the area I indicated WITH everything except the cowl in place, then also

( If I recall correctly the servos mount in the tail )

- Move the servos as far forward as possible, and use a pull-pull on the rudder and pushrods on the elevators

- Try to balance the plane again, and if required place weights right on the motor or spinner to see how much additional weight may be required.

If only a few ounces you are done.

If more, see if there is anything else you can move forward. Are you using a pitts or canister muffler? A muffler closer to the front may help.

Finally if all else fails, try adding longer mounts just to see how far forward the engine has to go to achieve balance.

Once you have established that you can make a hardwood spacer to increase the distance from the engine box as long as you can get the cowl to fit properly.

On my CMP Edge 540T I added a 2" hardwood mounting block, but I did so because I really did NOT want to use long engine mounts.

The balance came out perfectly.

See: http://images.rcuniverse.com/gallery.../lg-132683.jpg

I'm not kidding. With nothing else installed I have to hang the engine out of the front of the cowl to get it to balance at the recommended range. when I start adding servos and linkages to the rear of the plane it is going to get real bad. I could move all of the servos under the cowl and add 15 more and it still wouldn't balance with the engine inside of the cowl.

Are you balancing it where I told you to?


Are your battery packs on the engine mounting block?

Don't add servos to the rear of the plane. Do as I indicated above.

Remember that 1-2oz on the tail may be the equivalent of 8-10oz+ on the noze due to the different lever moments.

Also balance the plane with the prop and spinner installed. You want everything in it to establish the C.G.

I understand what you are saying, I have been building flying models for 37 years. I understand where the CG should be. I uploaded pictures to show where I am attempting to balance. Right where the plans call for.
I have not installed anything in the plane yet. So to demonstrate I put all of the electronics: batteries, servos, tank, prop, spinner, extensions, switches, bec, and everything else I intended on installing in the plane and put it in a bucket. If I put that bucket with EVERYTHING going into the plane on the cowl it will balance. There is no way that I can put everything in the cowl. there will be more weight in the tail no matter what I do. So even if I put half of everything inside the cowl I will have to make up for that and whatever additional weight gets put into the tail. The bucket weighs about 4 lbs 13 ounces total, and about 30 ounces without the engine, prop and spinner. So I need 30 ounces of weight in the nose with nothing in the tail. Whatever I could not jam into the cowl would have to be made up by lead and whatever gets put in the tail times the moment arm will also need to be added as lead. If I move the engine forward the servos go where they are supposed to and no lead gets added.

Yup, you have it dead on what the instructions say.

The plane will fly just fine with the C.G. another 1-2" further back than that.... but don't go beyond 2". With the latter it will tend to pitch up a bit when climbing inverted.

But then so does my Funtana and newer Katana.... yet they 3D beautifully and roll axially.

Your engine is lighter than what the plane was originally designed for exacerbating things.

In the picture you have everything in the bucket sitting on the cowl.

With the engine installed it will actually sit a few inches forward of where it's weight is distributed via the bucket.

So it is likely you will need less actual weight to get things to balance. Maybe a few ounces less, but that may be offset by any servos in the tail, which I'd advise against.


I had one of these planes with a Magnum 1.80 Four Stroke and moving the batteries and servos forward did the trick for me.

I crashed the plane and put everything into the newer orange version the website shows, where things remain.


That said, as long as the mountings are secure, there is no reason you can't move the engine forward more.

Given where you have the C.G. marked that solution would probably be the best.


At worst you can use small "L" shaped brackets to mount the cowl right to the edge of the firewall without looking unsightly.


How much further forward can you move the cowl without resorting to having to build something to hide a big cowl gap?

The weight of the unassembled parts is 12.125 lbs. This Katana does not have much wing area, 992 sq inches. I would like to keep the wieght down.
After 1" it starts to leave a gap, after two inches the cowl would be no longer touching. (see pic)
I put tape 2" behind the original CG range (2" center to center of tape). That puts it about 6 1/2" back on a 15 1/2" cord. The plane will balance at this point even with the servos in their original spot. But to move it forward to the original center it takes 2 lbs on the engine box.. That really seems like a long way back. That is about 42% cord, I checked my Pheonix Models Katana and I fly it at about 35 % cord and it is quite aerobatic. I think I might go ahead with the build an try to epoxy 10 or 12 ounces in the cowl as far forward as I can. Along with moving the engine as far forward as I can and still have the cowl on. Since I don't have the supplies to move servos forward I guess they go where designed. I sure could use another opinion on this. I guess I will sleep on it.
I see the orange one has more wing area even though it has a shorter span and the nose is longer and the gear is farther forward. Why did yours crash?
Thanks for th help so far opjose

There is a simple device you can buy to have the elevators pull-pull. you will end up with no servo weight in tail. You could make you own even, if you seen one. I will try to find a photo of how the set-up looks and works. Capt,n

The rudder pull pull I think I can do. And since it is the heaviest servo it should help.

If you can do the pull-pull on elevator....you only need one servo working both elevators. Also you get the weightoff the tail. Capt,n

MORE...Drawing on possible do it youself pull-pull for elevator ! Look at Drawing.

That would be extra work on this plane. It has a different elevator servo mount.

What you have is perfect.

You can slightly modify the servo cover to become the pull-pull exit. Just don't feel you need to over do it.

Also remember that moving 2oz off the tail removes the requirement for 8+10oz off the nose.

The lever arm moment of that long tail has a dramatic effect on small weight offsets.

The Pull-Pull is worth doing.

Good advice from opjose! He helped me with my cg questions as well!

I just maidened mine last week. I kept the servos in the rear and used a heavier 40cc SPE I had laying around. Balanced one finger in front of the wing tubes with the batteries on either side of the fuel tank (about 6.5" back) which is further back than the instructions tell you. It was still a tad nose heavy requiring a little bit of down elevator when inverted. Even with all of the weight (mine was 13-1/2 lbs. without fuel), it floats like a trainer. It's not going to be a big time 3D monster with all of the weight (they weigh in at about 9.5-10 lbs., but it still hovered (up high), and tumbled very well. It goes into a flat spin very easily, but took some time to get it to stop spinning. If I had to do it over again, I would do your setup with the lighter DLE30, and move the servos forward, and mount the batteries on the firewall. It's a beefy airplane, but built tough. I dropped a wheel on the last flight and was able to land on one wheel for a foot or so before the right landing gear dug in, then it flipped. No damage found other than creasing the fin. I did change the landing gear to a huge beefy alum. gear I had off another airplane, and land on grass so I needed more clearance and strength to handle the bumps. I left the wheel pants off as well. I now have 6" clearance with a 20" prop. I upgrade the tail wheel assemby as well. I added fl. yellow trim sheet stripes to the wing tips, horiz. stab, and top of the fin/rudder which totally improved the visiblity in the air, and looks decent on the airframe. I'm digging it for sure, and got lots of folks looking it over at the field. For $179, it's a very nice flyer, my fellow pilots were very surprised and impressed with it's flying capability and ultra slow landing speeds. DG

In the early days of this Katana 140 ARF there were issues with the CG but nothing as extreme as what has been posted in this thread.
I bought two of them back in 2003 and assembled them stock out the box and didn't add any weights to balance them. The three Futaba servos that I used in the tail were lighter than the heavier Hitecs that most people were using. The engines were OS 1.60's with Bisson Pitts mufflers.
If it will help, I'd like to state that my CG was located at 135mm back from the leading edge and both planes were very good aerobatic fliers.. The instruction manual specifies a CG range of 110 to 130mm at a distance of 150mm out from the wing root.

Your plane balances at 6 1/2" back, 150 mm out from the fuse? Do you have any pictures of the yellow trim you added? I have gear off from an Extra 300S 1.60, should I use it or do you think the supplied gear will be strong enough? Thanks for all the help.

I bought mine 2nd hand, but with only a dozen flights on it with a G23 glow engine. He wasn't happy with the pull from the ST2300. He also told me the original landing gear was too weak for the weight of this airplane and replaced it with a decent size alum gear, but shaped like a 4-star gear (low to the ground). I needed clearance for a 18-22" prop for my 40cc gasser so I replaced it with the one I have on it. I just took the SPE40 off tonight to replace a broken ring and check the bearings so there won't be an engine or cowl on the front to show you. I'll double check, but I'm pretty sure the 6.5" is to the center of the wing tube from the indent, and I cg'd at 1 finger width in front of that or at about 6" and was a tad nose heavy still. Like opjose said, there is a pretty broad range that this airplane likes. It's best to be less than 6.5" or less to start with. Go safe and start at 5" and keep moving things around until you get the cg where you like flying it for your particular style. I'll put the wings on and snap some photos of the trim scheme for ya tomorrow. DG

I don't know what seems to be going on but the plane now balances at 115mm (4 1/2") with the engine, tank, ignition, throttle servo and ignition battery in the nose and nothing in the tail. Which is in the range in the instructions. So all I have to is account for whatever weight I put in the tail. The location for the elevator servo's are about 33" behind the wing tube and the end of the motor box is about 11 inches in front. So whatever I put in the tail I will have to put 3 times in the nose.
Two servos with extensions are about 4 ounces plus pushrods if I can rig a push/pull for the rudder. I went to the local hobby shop and all he had was a 2-56 push-pull kit. Does anybody think that will be strong enough? I was thinking about other ways to rig it just using the cable. Any ideas on that?
That is starting to sound reasonable. Probably between 12 and 18 ounces maybe less depending on where I balance it. I don't know what I have been doing wrong but if I keep waiting to get started on it I will end up needing weight in the tail.

Ok I installed all but the rudder servo...it looks to be about 17 ounces minus the spinner which I think is 3 or 4 ounces. So I am 13 or 14 ounces light in the nose and if I balance on the original cg recommendation. The tail servo will add another 6 ounces if I don't go pull-pull. I have also been considering a Tacon Bigfoot 1.60 I have as an electric option. With an 11 cell 3300 It only appear to be about 8 ounces light so far and if I use Higher capacity lipo's in the future it will need less. I am going to have to make some sort of cable guides for the push pull because the elevator servos are in the way.

A little late, but here are the photos of the trim sheet look. It really made a huge difference in being able to see the top of this airplane, and the fl. yellow didn't look out of place with this color scheme. The 3rd photo shows the landing gear I added, quite beefy, tall and wide. The last photo is my SPE40 gasser I just tore down last night. Had to buy a gear puller today to get the old bearings out. As soon as I get some Loctite 620 bearing adhesive I'll be ready to assemble. As long as your cg is somewhere around 4-6" back from the leading edge at the indent you should be fine. Fly and adjust to the way you like it to fly. Let us know how it goes! DG

Thanks F4U for the pictures. So you added trim to the top to make it more visible. Is there any lead in that plane at all? And if your not tired of questions is the thrust angle changed any other than what is built into the motor box?

No problem with the questions. No extra lead anywhere. Mine has 3 metal gear servos in the tail, SPE40 on the front (approx. 52ozs.), 1100mAh A123 ignition battery inside the fuel tank compartment, and 2300mAh A123 rx battery between the fuel tank and wing tube supports. 13.5 lbs. with super beefy landing gear, and no fuel. No change in thrust angle, just used the fire wall as is. Yes, trim sheet added to make it more visable. It's really blends in with the sky on top, the white bottom is ok.

As you can see, your DLE 30 is about 18-20 ozs. less than the SPE 40 I'm using, so you may end up needing to add extra lead up front, or moving the tail servos as suggested by Opjose. If you haven't tried it yet, move your batteries to the sides of the motor box and see if that helps get more weight up front. Let us know how it works out for you. I hope to get mine back in the air later this week if the winds get slow down under 20mph[>:]. This is my first gasser, and I'm really impressed with the ease of starting, no oil slime all over to clean up, and the stability of this airplane in the air (low rates). It spins as fast as my delta wing on high rates. You will love it! DG

Actually this is my second gasser. My first was a tragedy on the maiden due to reversed ailerons. You'd think after 5 years of flying I wouldn't miss something like that. This DLE runs fantastic, alot better engine that the Fuji BT24EI that I just got rid of. Here in Mi I am hoping to finish before the snow flies.

After moving things around, if you have to add the weight as lead, don't worry, this airframe can handle the weight. I was really surprised how well it floats in for a landing.

I got tired of trying to figure out how to rout the pull-pull past the servos..it would have needed guides inside of the fuselage or a long run outside to get past the elevator servos. So the rudder servo is where it was designed to be.
I installed the engine as in the manual. Here is a picture of the cowl, it is acceptable.
The plane weighs 10 lbs 11 oz plus tank, ignition, switches, batteries, spinner, and throttle servo. They add up to a little over 26 oz. It will need about 23 oz of lead depending where I can put it to balance at the extreme of the manual...less depending if I put it in the cowl or on the engine box. That seems to be a lot of weight to epoxy to the cowl. The total will be 13 3/4 lbs empty and well over 14 lbs with fuel. Does that sound heavy? That's about what my 74" Extra weighed with more wing area.
One more thing, after the DLE was installed it doesn't quite center with the hole in the cowl. Should I put adjust the engine angle to match the cowl or adjust the cowl to match the engine or leave it alone? I have never had a cowl with the holes pre drilled.
This plane is actually one of the fastest building planes I have owned. If I wasn't running into these weight issues it could be built in a day or two.
Thanks again.