H-9 33% Suhkoi SU-31 "Balancing Question"

[rcheliman]

I rememer reading a thread about the H-9 33% Sukhoi SU-31 kit that the balancing not being correct in the manual, I was wondering if someone could lead me to the thread or tell me what the recommened balance is and what the plane actually balanced at with a GT-80 up front. Just hate to surf thru 40 thread pages to find it.

[mmcconville]

If my memory is correct the CG should be 1/8" behind the rear edge of the wing tube. Thats where my model (the pic in your avitar ) was balanced.

[rcheliman]

	Quote: Originally Posted by mmcconville
	If my memory is correct the CG should be 1/8" behind the rear edge of the wing tube. Thats where my model (the pic in your avitar ) was balanced.

Thanks Mike, that gives me a good starting point.

[forgues research]

	Quote: Originally Posted by mmcconville
	If my memory is correct the CG should be 1/8" behind the rear edge of the wing tube. Thats where my model (the pic in your avitar ) was balanced.

Mike,
I have this same model from Hangar 9, my question to you is this, how can you get the model to weigh under 25 lbs. mine weighs 29 lbs and some.

I have an EVO 80 in the nose, use Lipo batteries, rudder servo is in the middle of the airplane and still had to add more then 3 lbs in front of the engine to balance.

Are people really saying there airplanes weigh only 23 to 25 lbs. with mine being stock all the way, I don't beleive these numbers..

If you can shed some light I would appreciate it.

Roger

[wylieruneyjr]

I was told that you could go 3/4 back from wing tube center, with no problems and another 3/4 inch for 3-D. However Itried that and found at 1 and 1/2 inchs back from center the airplane was too sensative to elevator on landings and would flare nose high when trying to level -off. this would cause a stall in short order. The only thing you could do was throttle up and go around for another try. DON,T try to push the nose down cause its too sensative on elevator and will plant itself right now like ohh shizts. Don,t ask how I know LOL rebuilt plane and tryed some weight up front. Now I,m not the best pilot, new to larger gas planes, never really got the CG perfect, plane would go from too sensative to kangeroo landings hipped hopp and plop. But there is a sweet spot in there. Plane hovered great was fast for gas, and man it had a hell of a roll rate on high. Fun plane ! I had 3W 80 AND WAS OVER POWERED. ONE POUND OF WEIGHT GOT ME CLOSE TO THE SWEET SPOT ON CG. Trees got the plane building another one right now. Can see mine fly at wwwcarolinaskydancers.com click on member vids andy fun flying suhkoi

[mmcconville]

Roger,

29 lbs seems pretty heavy. Its been a long time since I did that design and I havent had one for quite a while so I dont remember the exact weights. In fact the last time I flew the one I had was the same day we shot the photo in Rcheliman's avitar and thats been hmmmm, probably 5 years or so.

What do you have in your for batteries etc?
I believe mine was in the neighborhood of 24 to 25lbs with a ZDZ 80 nd about 2.5lbs of weight in the front of the cowl. That was with rudder on pull-pull (I think) and one battery pack on the rx.

The new SU-26 comes out a LOT lighter, more in the 21 to 23 lb range. 23lbs seems unrealistic for the SU-31 though, but 29 seems very heavy too.

[forgues research]

	Quote: Originally Posted by mmcconville
	Roger, 29 lbs seems pretty heavy. Its been a long time since I did that design and I havent had one for quite a while so I dont remember the exact weights. In fact the last time I flew the one I had was the same day we shot the photo in Rcheliman's avitar and thats been hmmmm, probably 5 years or so. What do you have in your for batteries etc? I believe mine was in the neighborhood of 24 to 25lbs with a ZDZ 80 nd about 2.5lbs of weight in the front of the cowl. That was with rudder on pull-pull (I think) and one battery pack on the rx. The new SU-26 comes out a LOT lighter, more in the 21 to 23 lb range. 23lbs seems unrealistic for the SU-31 though, but 29 seems very heavy too.

I have Lipos, 1800 for ignition in the engine compartment, 850 lipo for the receiver, and 2500 lipo for the servos, even my servos are light they are 77 oz Multiplex.

I have a Hitec 5995 in the middle of the airplane for pull/pull on rudder

The engine is a single cylinder EVO 80 about the same weight as the ZDZ.

I have even put the engine 1/2 inch further forward to help but still a whole lot of weight in the nose and I mean right on the side of the engine where it mounts..

I am using an electronic fish scale . unless the scale is wrong.

Roger

[mmcconville]

Really weird. I used a high precision digital scale we have here which I know is accutate. Hard to imagine where all of the extra weight would have come from.

I'm an advocate of keeping records, so I just looked up my notes from the model I had which i put together in 2001. From my notes:

"Weight ready to fly- 24.9lbs. w/ GT-80
23.5ibs w/ ZDZ 80cc

Note: When ZDZ engine was used, the rudder servos were moved forward and a pull/pull cable linkage was used. Additionally, 1 lb of weight was added to the front of the cowl to achieve optimum CG. However overall weight was still 1.5 lbs less than when equipped with the Zenoah GT-80."

My memory was a littl off but close.

I also found that the CG range I found was this:

"Center of Gravity range is located from ½” in front of center of wing tube to ½” behind center of wing tube."

The info I posted about the CG location above was wrong. Sorry for that guys. I must have been thinking of a different model.

[forgues research]

	Quote: Originally Posted by mmcconville
	Really weird. I used a high precision digital scale we have here which I know is accutate. Hard to imagine where all of the extra weight would have come from. I'm an advocate for keeping records, so I just looked up my notes from the model I had which i put together in 2001. From my notes: "Weight ready to fly- 24.9lbs. w/ GT-80 23.5ibs w/ ZDZ 80cc Note: When ZDZ engine was used, the rudder servos were moved forward and a pull/pull cable linkage was used. Additionally, 1 lb of weight was added to the front of the cowl to achieve optimum CG. However overall weight was still 1.5 lbs less than when equipped with the Zenoah GT-80." My memory was a littl off but close. I also found that the CG range I found was this: "Center of Gravity range is located from ½” in front of center of wing tube to ½” behind center of wing tube." The info I posted abou tthe CG location above was wrong. Sorry for that guys. I must have been thinking of a different model.

Thanks for all the information Mike, I will double check my scale for accurate reading, I certainly can't tell from 24 to 30 lbs by holding the airplane in my arms.

It would always lands fast because of being a bit tail heavy all year, so now I added a bit more weight up front , time will tell.

Roger