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weights and balance in a Big Stik

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Old 11-11-2012, 06:34 PM
  #1
Iherling
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Default weights and balance in a Big Stik

I am building an ARF Big Stik 40. How important is it to locate the engine (OS 40) as per the instruction manual. I built an ARF Big Stik 60 and located the engine per the manual and it was very nose heavy. I built aTower Hobby 60 ARF and located the engine per the manual and it was very nose heavy. Sooo... I am thinking of moving the OS 40 aft of the recommened location to help. Will moving it back 1 - 1.5 cm make much difference in the CG. Itgoes against my nature to have to add a lot of weight to an airplane.

When I built a full scale clipped wing cubI was fanatical about keeping the weight down and it really paid off in performance. Would an RC respond in a similar fashion.
thanks
Irvin
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Old 11-11-2012, 07:05 PM
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Default RE: weights and balance in a Big Stik

You can always mount the engine with a constructed plane, meaning with everything installed, wings mounted, and check the CG. When mounting the engine, you can carefully put the engine on the mounts without bolting it down and carefully checking the CG to see where it is. If it is to nose heavy, well, move the engine back a tad and re-check it. Once you are happy with the CG with the battery placement, yes, that matters, you can secure the engine.

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Old 11-11-2012, 07:40 PM
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Default RE: weights and balance in a Big Stik


Quote:
ORIGINAL: Iherling

I am building an ARF Big Stik 40. How important is it to locate the engine (OS 40) as per the instruction manual. I built an ARF Big Stik 60 and located the engine per the manual and it was very nose heavy. I built aTower Hobby 60 ARF and located the engine per the manual and it was very nose heavy. Sooo... I am thinking of moving the OS 40 aft of the recommened location to help. Will moving it back 1 - 1.5 cm make much difference in the CG. It goes against my nature to have to add a lot of weight to an airplane.

When I built a full scale clipped wing cub I was fanatical about keeping the weight down and it really paid off in performance. Would an RC respond in a similar fashion.
thanks
Irvin
Having built a 1:1 scale with success, you probably are far ahead of most of us. As far as an RC model is concerned they all live under the same physical laws of sub sonic convergence airflow.

I seldom pay much attention to directions reference engine placement. I put it where I want it, depending on the type of model and what it is to be used for. Then I make certain that the CG definitely is not aft of 28% of the Mean Aerodynamic Chord, (MAC).

Once the pilot makes a few flights, then the pilot can make adjustments as said pilot so desires. For models with less than 800 sq. ins. wing area, one can usually obtain a good CG without much effort, generally shifting batteries, tank, etc. Then there are the big birds that will require added weight.
My funny is that I have a Baby Bipe, 101" wingspan, with a G-62. I bought it from a guy that built it but never flew it. CG was about 25%. Very good. It flew very well but I was not satisfied with the G-62 and its difficulty in starting. So I had it converted to electronic ignition. Then when I went out to fly, it started very easily, choke, get gas and flip and all was fine.

Started that take-off, into the wild blue, and all devil broke loose. I had a bucking bronco, but how, I know not, I got it back on the ground. I FORGOT THAT THE MAGNETO WEIGHS A POUND AND A HALF AND THAT WAS BACK IN THE SHOP. So I added weight up front. It quickly became a very nice smooth flier soon as the CG was moved up to about 28% as it was with that magneto junk pile there. I now fly two G-26 engines with magnetos, both very dependable. One is a 100" w/s Eiendecker. I added 16 oz. of lead up front. Without that lead, it acted like I was a 3D pilot and I can't even spell 3D! CG is now25% of MAC. My first flight was almost the last one. The kit plans call for a 33% CG. I knew that was WRONG but I took off first time at about 32% or slightly forward. Almost lost it.

BTW I was in the USAF B-47 between 1958 to '62. Wanna' know about CG! Find one of those guys to talk about it. Those that started a TO roll with fuel misloaded to place CG aft of 35%, all I can say is that 90,000 lb. of JP-4 will roast a heck of a lot of hot-dogs and marshmellows. [:@]

Don't sweat a little weight. Start definitely NOT aft of 28% MAC. To L with plans. They simply sell kits!!
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Old 11-11-2012, 07:46 PM
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Default RE: weights and balance in a Big Stik


Quote:
ORIGINAL: Iherling

I am building an ARF Big Stik 40. How important is it to locate the engine (OS 40) as per the instruction manual. I built an ARF Big Stik 60 and located the engine per the manual and it was very nose heavy. I built aTower Hobby 60 ARF and located the engine per the manual and it was very nose heavy. Sooo... I am thinking of moving the OS 40 aft of the recommened location to help. Will moving it back 1 - 1.5 cm make much difference in the CG. It goes against my nature to have to add a lot of weight to an airplane.

When I built a full scale clipped wing cub I was fanatical about keeping the weight down and it really paid off in performance. Would an RC respond in a similar fashion.
thanks
Irvin

Moving your engine forward or back 1 to 1.5 cm will only move your CG approx. 1/4". It will by no means correct for a "very nose heavy" setup.

Kurt
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Old 11-11-2012, 09:41 PM
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Default RE: weights and balance in a Big Stik

I chose to mount the engine per location in the instructions. Before gluing the vertical stab, i checked CG and added weight inside the fuse through the vertical stab's opening. Once satisfied, glue the vertical stab. Nice, clean setup and you don't have the lead weight squares showing on the exterior.
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Old 11-11-2012, 09:56 PM
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Default RE: weights and balance in a Big Stik

Hey - I just sent my daughter off to Mizzou! She mentioned the Jayhawks...

Kurt
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Old 11-11-2012, 10:49 PM
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Default RE: weights and balance in a Big Stik

Those little stick on lead weights.....badges of shame.
I once saw a model that had them both fore and aft.
We build our planes with the lightest possible materials and techniques, then decorate them with lead.
I admit to using it when remodeling the plane just doesn't make any sense...OTOH I have remodeled a few planes that were tail heavy, including moving the wing back.
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Old 11-12-2012, 06:15 AM
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Default RE: weights and balance in a Big Stik

Sticks tend to run nose heavy anyway. It's a common mod to mount the servos at the back of the fuselage, especially when running a bigger than necessary engine. You should be able to get it right though by finding the right battery placement and cutting a hatch on the bottom of the fuselage to mount it in.
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Old 11-12-2012, 10:22 AM
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Default RE: weights and balance in a Big Stik

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ORIGINAL: combatpigg

Those little stick on lead weights.....badges of shame.
Yup.

To at least make the weight "usefull"... on my 40 and 60 size sticks I built a little tray for the batteries and mounted the packs BEHIND the wing inside the fuse.

I put them as far back as I could while still being able to remove them ( they were velcro'd in ) with hemostats.

I also went with larger packs than I would normally use ( 3200 mAh ) on a plane this size. That turned out to be a very wise move as my typical flights with this plane are 20 minutes or more, particularly on windy days when I can fly the plane at just above idle most of the time.

On my Giant Big Stik I mounted the fuel tank on the C.G. and did the same thing with a pair of big flight packs.

The stated C.G. on the GP Big Stiks are way too far forward.

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Old 11-12-2012, 01:41 PM
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Iherling
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Default RE: weights and balance in a Big Stik

thanks to all for help.  since i have already glued tail feathers I will try placing battery as far back as i can access, use a larger battery pack, move the engine back on the mount a bit and then if I still need weight I may open a bit of the fuse in the rear and mount it out of site
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Old 11-12-2012, 09:06 PM
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Default RE: weights and balance in a Big Stik


Quote:
ORIGINAL: jester_s1

Sticks tend to run nose heavy anyway. It's a common mod to mount the servos at the back of the fuselage, especially when running a bigger than necessary engine. You should be able to get it right though by finding the right battery placement and cutting a hatch on the bottom of the fuselage to mount it in.
Yep. I was also running an OS95AX on the Big Stik 60. I also placed the elevator servo in the tail and still needed to added weight to the back.
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Old 11-12-2012, 09:07 PM
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Default RE: weights and balance in a Big Stik


Quote:
ORIGINAL: Bozarth

Hey - I just sent my daughter off to Mizzou! She mentioned the Jayhawks...

Kurt
I'm sorry to hear that.
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Old 11-13-2012, 06:15 AM
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Default RE: weights and balance in a Big Stik

On my 60 Ultra Stick I made a rear hatch in the bottom of the fuse and placed the battery back as far as I could get it.  Still, was nose heavy.  So, I used some stick on lead weights on the battery itself to get CG perfect.

If I wanted to mod and move the servos to the rear of the fuse I could probably do away with the lead...but it flies very nice like it is now.  I could probably go with a larger flight battery with same result. 

Just confirming that sticks usually are nose heavy from the get go.
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Old 11-13-2012, 11:27 AM
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Default RE: weights and balance in a Big Stik

CG with an ARF is often a problem. When you are really building a plane and not assembling an ARF you have a lot more control of how the CG will come out just by where you locate the gear. On a ARF you can get close by moving things around but they limit you unless you know how to build and make mods to the plane. Stick on weights on an ARF isn't any big deal, I wouldn't worry about putting them on the outside at all. As long as the plane flies correctly who cares. Just put them on under the stab as far back as you can and be happy. You can develop an ego when you start building. Just have fun with your plane.
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