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Need expert help balancing a giant scale stinger.

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Need expert help balancing a giant scale stinger.

Old 09-04-2008, 10:23 PM
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raulcroes
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Default Need expert help balancing a giant scale stinger.

Gentlemen,

I've bought a Lanier Stinger giant scale ARF. I've assembled it as per it's manual. I've chosen to use a DL-50 to power it. Sadly when I went to balance it, it turned out to be tail heavy. it required almost four (4lb.) to get it balanced. this was a hard blow for me since I've did my best to assemble it as light as I could. first I thought I could move the four tail servos up front but that's a mere 164gr. and that would shorten the separation between the ignition and the radio gear. Next I thought I could extend the nose a few inches by making an engine box and putting the engine there hoping it would eliminate or at least minimize the amount of counter weight I would need to use to balance the plane. If I were to do the latter, would this affect how the airplane flies?? Is there any other solution to this problem?? Any advise will be highly appreciated.
Respectfully,

Raul G. Croes[8D]
Old 09-05-2008, 09:48 AM
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da Rock
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Default RE: Need expert help balancing a giant scale stinger.

Both of your ideas have merit.

Servos for giant models usually have significant weight. Moving 'em forward will have an effect.

Moving the engine forward will have little effect on the flight characteristics. A number of fullscale aircraft designs got the same treatment during development. The P47 comes to mind. They added something like 5" to the Jug before putting it into production.

If I were in your predicament, I'd move that engine first. It ought to be fairly easy to temporarily rig the mount an inch or so forward. Masking tape and scrap wood can do wonders. See what it'll take and then decide.
Old 09-05-2008, 10:06 AM
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da Rock
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Default RE: Need expert help balancing a giant scale stinger.

BTW, 4 pounds to balance a roughly 14 pound model is A LOT OF BALLAST.
Old 09-05-2008, 01:29 PM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

da Rock,

Thank you for your insight. I will try to lengthen the nose a little and see at where abouts it balances. I'm happy to hear it doesn't affect the fiying characteristics of the airplane, since I want it to be a gentle/easy flier. I have had three eye surgeries and have not flown for a couple of years. I trying to get back in to the sport so I need all the help I can get.
Once again, thank you for your help, much appreciated.

regards, Raul [8D]
Old 09-05-2008, 02:25 PM
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Jim Messer
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Default RE: Need expert help balancing a giant scale stinger.

Raul:

I can't believe what you are saying. There must be something wrong with your arithmetic. The Stinger is a normal airplane with normal percentage dimensions, and many have been built and flown. Seems then if it is a design problem, others would have had the same problem, and we haven't heard this story before that I know of, just reading everyday posts here on RCU.

Tell us how you went about balancing, and just where is the balance point. Maybe we can sort this thing out, as adding 4 lbs. just doesn't sound right. It's way way too much!
Old 09-05-2008, 03:21 PM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

Jim Messer,

First of all, thank you for responding to my call for help. I can't believe it myself! I'm bummed out. My son and I held the wings at the tips at the 5" mark from the leading edge, no dice. Then we moved till the 5 1/2" mark and it sort of start to dip the nose. what I plan to do now is build a balancing device to try to balance it as precise as posible. I really wish I am wrong on this one. I can't understand it. Like you said there must be many modellers out there with this particular model and I have'nt heard of complaint's. As soon as I've build the contraption and tried the balancing act, I'll post the results.
Regards,

Raul[8D]
Old 09-05-2008, 03:33 PM
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John Sohm
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Default RE: Need expert help balancing a giant scale stinger.


ORIGINAL: raulcroes

.... first I thought I could move the four tail servos up front but that's a mere 164gr. ....
164 grams is about 5 3/4 ounces. Depending on the ratio of the tail moment to the nose moment, that could easily become 3 to 4 times that in added weight at the nose. Still that's a far cry from 4 pounds. What did you use? Ironwood? Just kidding.

What method did you use to finish this Stinger? Iron-on plastic film like Monokote? Or did you glass it? Let me ask you this, what engine did they originally call for? Because a lot of the newer engines, especially those from China, are coming in with electronic ignitions and aside from the added battery to power it, they are usually much lighter than the older magneto type engines. Some of those were really heavy. I mean what's a DL-50 weigh compared to say a G-62 or something a bit smaller. This could be part of the issue. At least it's something to think about.
Old 09-05-2008, 03:57 PM
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Default RE: Need expert help balancing a giant scale stinger.

First of all how did you measure that 5 inches from the leading edge? Did you just measure along the wing from the leading edge? Or did you draw a line up from the leading edge and measure 5 inches from that line? it will make a difference...move your battery as far forward as possible and check again
Old 09-05-2008, 04:12 PM
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Default RE: Need expert help balancing a giant scale stinger.

Just for grins try the CG right next to the fuse instead of the wing tips, something is real wrong!!
Old 09-05-2008, 04:25 PM
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Default RE: Need expert help balancing a giant scale stinger.

I hate to ask but are you balancing it inverted?

David
Old 09-05-2008, 05:51 PM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

John Sohm,

It's an ARF, so I have no control on the building and or materials, just the assembling of the kit. It is fairly light with the engine (without the four pounds of ballast weight of course) and all but I don't have the exact numbers. I will try to weigh it using a bathroom scale. The engine they used in the assembly manual was a Fox 4.2 ci gasser. it looks bulky and is definitely heavier. I've tried to look-up the spec's for this engine, but no luck. I agree with you that, that is one of the contributing factors of this problem.[]

jetmech05

I've measured on the wing tip (which is flat) in a straight line from leading edge to trailing edge, five inches. I've put a mark there, and with the "finger" balancing technique under each wing tip,brought the airplane level and released it. the tail just dropped. I have the ignition battery resting in a craddle on top of the engine stand-off's. I will take pictures and post them for clarity.

Gray Beard

I am willing to try anything. I will definitely give it a try. I will report back how it panned out.

daveopam

I have done it in the non-inverted position. which is the best way to balance this type of aircraft??? I'll probably have a balancing contraption build tomorrow. [&o]


Gentlemen, I thank you all for taking the time to help me out. It is highly appreciated.

Raul G. Croes
Old 09-05-2008, 10:28 PM
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Default RE: Need expert help balancing a giant scale stinger.

This will barely help , but get the lightest tailwheel possible! Sometimes The ones they supply in kits are chunky.
Old 09-06-2008, 07:24 AM
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Default RE: Need expert help balancing a giant scale stinger.

there is part of the problem...draw a line up on the fuselage at the leading edge and measure 5 inches from there...you don't measure along the wing 5 inches either at the tip or at the root...sorry but this will make you even more tail heavy....on a low wing airplane you must check CG inverted.....that way the weight is below the pivot point...try flipping her over
Old 09-06-2008, 11:41 AM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

jetmech05

I will do what you've suggested. by the way this is a midwing airplane, so should it be balanced inverted or right-up???
Thanks for you help.

Raul
Old 09-06-2008, 01:29 PM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

Ok guys, I borrowed my daughters bathroom scale and weighed the stinger on it. it gives me 14.4lb. (without the ballast weight) for the airplane RTF, , and 18.1lb. with the ballast. I don't know how precise that bathroom scale is but I've repeated the test several times with the same results. I'm building the jig to balance the plane. I'll keep you posted.

Raul
Old 09-06-2008, 01:41 PM
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Default RE: Need expert help balancing a giant scale stinger.

On a midwing you'd think it doesn't make a difference but it does...you kinda gotta get a feel for where the weight is above or below the wing....in other words is your battery and receiver plus your servos above or below the midway point on the fuselage from top to bottom you want the weight below the pivot point on the CG machine or in this case your finger
Good Luck
Old 09-09-2008, 05:06 AM
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Default RE: Need expert help balancing a giant scale stinger.

Yes, the DL is much lighter than the G62 that the kit form of this plane was designed for-from your weights, the ARF must be much lighter in its construction. I can see you prob. having to add some weight to obtain the cg (if the servos being moved doesn't handle it) but as allready mentioned, 4lbs. is crazy![X(] What is the cord of the wing? Also, is that 5" the starting point for the cg-many times the listed is a slightly nose heavy condtion for first timers and can be moved back quite a bit. That stinger sure would be awesome if you could keep it around 15lbs.
Old 09-09-2008, 07:59 AM
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da Rock
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Default RE: Need expert help balancing a giant scale stinger.

When the CG is really hard to nail down, use some rope and hang the sucker.

Not kidding.

Running some cord from the nose to the tail and hanging the airplane up by that rope works like gangbusters and is absolutely accurate. You hang the sucker somewhat level ("somewhat" is sometimes better than "perfectly" level, so don't sweat it) and then hang a plumb bob from the same hook that got the cord. The plumb bob will point exactly at the CG. Make a guess where that'd be on the wing and NOW adjust the sucker to be close to level. I like to do this "twice level" deal to get a better idea where the CG is vertically, to see if it's a lot higher or lower than the wing, and how much.

Hanging the sucker is very easy to do accurately. It's especially good when the airplane really isn't easy to balance on a "two sticks" tool. A huge number of the bigger models are done this way. But it works for all of 'em.
Old 09-10-2008, 11:01 AM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

flygilmore

The CG recomendations in the manual are; from the wings leading edge 5" to 5.5". thats very little. What I strive for is make this bird as easy as posible to fly.

da Rock

That sounds brilliant! I will get the hook, rope and plumb bob. As soon I have it hanging from the ceiling I'll take pictures. I'll place masking tape denoting the manufacturer recomended CG settings, so we cab see how far off it is. I've put the plane on the so called "two sticks" tool and the sticks almost went trough the wings!!! It crushed the balsa a little bit. So I'm not so keen to that method anymore. I need some clarification on one point and pls. excuse me because my english is not so good. You've said and I cuote "I like to do this "twice level" deal to get a better idea where the CG is vertically, to see if it's a lot higher or lower than the wing, and how much. Are you saying that I have to balance it horizontaly and vertically??? Pls. elaborate.
I thank you guys very much for your help.

Raul[8D]
Old 09-10-2008, 11:42 AM
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da Rock
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Default RE: Need expert help balancing a giant scale stinger.

If you balance it level, the plumb bob points down through the CG and the wing. And you won't exactly know where the CG is (above or below the wing).

You've got the idea, I just do it less radically. After I get some idea of where the CG is along the wing with the airplane hanging about level, I do a couple of tilts. Tilt the nose down a little and then with the nose up a little to get an idea where the CG actually is. Knowing that helps a lot with actually placing the exact fore/aft location on the wing. Plus, we all know if our airplane is a high wing or low wing, but whether or not the CG is above or below the wing matters sometimes too.

In practice, once you've gotten a plane and bob hung up, it's so quick and accurate to do a number of different checks, with a little nose up, then more, then nose down, then more, that it takes no time at all to pinpoint exactly where the CG actually is.

BTW, hanging the airplane can also show you the lateral balance or imbalance.
Old 09-10-2008, 11:58 AM
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da Rock
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Default RE: Need expert help balancing a giant scale stinger.

BTW, when you're balancing a heavy model on points, you can protect the wing and not affect accuracy at all. Just tape on something thin and stiff. I've got scrap plywood that's flexible and tape it where the points are going to press against the wing.

You can also use "thick points". I do it all the time. I make foam cradles for all my airplanes out of sheet foam insulation. It's about an inch thick. And when the airplane is moved so the wing is over the front cradle, the cradle top supports the wing just like a balancing device would. Only it does the supporting with a wide surface, not a sharp point. I move the airplane to balance then move it a bit forward a little at a time until it tilts on it's own. I mark a line for that and then start moving the airplane aft. When it tilts on it's own going the other way, I mark a line for that. Halfway between the two lines is where the CG is. If you're fairly consistent and accurate, the CG found that way will be as good as any other method will give you. How is that possible? Isn't the most accurate way of finding the CG the best way? Nope.....

All we need is a starting point, and EVERY CG suggested by the plans is a very safe starting point. They aren't some magic location where the airplane suddenly comes alive and won't fly well if the CG isn't there. The suggested CGs are always safe and the safe range on some of our airplanes is a couple of inches, sometimes more depending on the size and how far aft the horizontal tail is. And almost every method we use to find the CG can beat a couple inches of accuracy with no problems.
Old 09-15-2008, 09:09 PM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

Ok guys, I've finally have the stinger hanging from the ceiling with the plumb bob also hanging from the hook. I've taken some pictures and I think they speak for themselves. I have the stinger pretty much level in these pictures. According to the manual the CG should be between 5" and 5.5" but from the pictures you can see that it is almost 8.5". There is also a picture of the dreaded 4lb. divers belt weight. Da rock you've suggested I move the plane a little of level, nose up and then nose down but I don't understand why. Cloud you pls. explain what I would be looking for??? I thank you all for your help, much appreciated.

Raul[8D]
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Old 09-16-2008, 03:53 AM
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da Rock
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Default RE: Need expert help balancing a giant scale stinger.

Hanging at an angle just gives you a different perspective that helps show where the CG actually is vertically. The line drawn (with the laser) nose up will cross the line drawn nose down and that's exactly where the CG is. With a midwing model like yours, it's not really a big deal. It'll be in the wing somewhere.

I'm sure the cowl and spinner aren't as heavy as the diving weight, but they'll have an effect.

The plane is already at max design weight @14lbs. I'd guess the mfg really screwed up with the wood that went aft of the wing. Something is out of the ordinary aft on that plane.

Darned if I'd add nose weight with it already being heavy. I'd move the engine forward. However far the cowling will allow. Heck, I'd extend the fuselage sides to reach the cowl if needed. And no need to make the extension light, is there.
Old 09-16-2008, 11:06 AM
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raulcroes
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Default RE: Need expert help balancing a giant scale stinger.

thanks Da Rock for your reply,

I agree with you 100%. the cowl won't allow any more movement. It overlaps the nose about 3/8". I will extend the nose, as you said. The contraption you've suggested will make it alot simpler to find the CG when trying to determine how far forward the engine will have to be moved.

I want to thank everyone who helped me find a solucion to my problem. In the process we all learend something new.

Thanks again.

Raul[8D]
Old 09-16-2008, 07:41 PM
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Default RE: Need expert help balancing a giant scale stinger.

I've got the kit built Stinger with a G-62 on it.........the plane was designed with the stock G-62 in mind.....the plans show a G-62 mounted to the plane...I thought I'd lighten mine up by putting a G-62 with electronic ignition on it.....threw the CG out of wack and I ended up tail heavy. Look at how short the nose is from the cockpit forward.....it needs a heavy engine to balance it.
Like you said.....the cowl won't let you move the engine much...
If I were you......I'd set the cowl off to the side and leave it out of the equation till you get the motor out front enough to get the CG back in line........I bet you have to move it out at least 3 to 5 inches..........................stand back and look at how short the nose is.

Set the motor out front a ways.......get the CG you want.......fly the plane and get it dialed in........then you can decide how and if you want the cowl mounted for looks.

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