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Calling all experts about main wing position.

#1
Hi everyone,

I am making a new model with no plans at all, here is my problem, I don't know where I should put my main wing...

Here are the dimensions...

Main wing is 40" by 10.5" add 2" for control surface...
B-Plane 1.JPG

Fuselage is 46" long and about 3" square
B-Plane 2.JPG

Prop is a 8" attached to my 2200kv motor driven by a 30 amp esc
B-Plane 3.JPG

Elevator is 12" wide by 4" add 2" for control surface
B-Plane 4.JPG


So, how far from my prop should I put my main wing !?

Thanks guys!
 

earthsciteach

Moderator
Moderator
#2
Welllll..... Its not that straightforward. But, its not that complicated, either.

First, have you ever played with one of those cheap, wind-up rubber band balsa planes? If you have, you probably have messed around with moving the wing forward or backward to get it to fly nicely. Too far forward and it climbs, stalls and repeats. Too far back and it noses into the ground. It does this because you are adjusting the center of lift of the airplane.

But, on most flying models (and the real deal) the center of lift is at some set point optimized to carry the load of the plane with a "sensible" fuselage length. and balance is achieved by distributing the weight of "stuff" in the airframe so that the center of gravity is just a bit forward of the center of lift. Without going into too much detail, you want the plane to be slightly nose heavy if you were to suspend the plane from its center of lift point (which is approximately 1/2ish the distance from the leading edge to the trailing edge of the wing - that distance is called the 'wing chord'). The horizontal tail surfaces are the 'levers' that hold the nose level in flight. Think about you and a much heavier person standing on a board that is on a fulcrum. In order to balance you with the heavier person, your side of the board has to be longer (farther away from the fulcrum point). On an airplane, that fulcrum is the overall center of lift.

So, you have a couple of options at this point. One, slap the wing on where you want it to go, then adjust the center of gravity by moving around the battery, adding a bit of weight to the nose/tail as need be. Or, locate all your components, then position your wing just behind the center of gravity.

While option 2 sounds reasonable, its just plain (plane?) silly. Go with option 1. Personally, I'm a huge proponent of, "if it looks like it should fly, it will fly." Position your wing somewhere between 1/4 to 1/3 the distance from the front to the back of the fuselage, then adjust the location of your battery to balance it out so its slightly nose heavy. If you support the plane with two fingers under the wings, it should balance with your fingers about 1/4 the wing chord.

Let me know if what I said doesn't make sense. I'm a teacher, so I'm used to reexplaining the thoughts that get trapped in my brain!
 
#3
I think that you got the right answer for me, I've just received my parts and I'll try to balance everything tonight.
Thank you so much for clarifying this for me!
 

jetpackninja

More combat please...
Mentor
#5
I'm going to disagree with teach a little bit here. (not much)
Since you haven't finalized your wing position, I'd locate the battery and electronics in ideal locations as possible and then place the wing. Look at the wing and use the thickest part of the airfoil as the balance point. On experimental planes I have even used velcro on the top of the fuse and on the bottom of the wing so that I could move the wing until I could find the right location. This can come in really handy if you plan on experimenting with different power configurations or playing around with cameras etc.
 

earthsciteach

Moderator
Moderator
#6
Ninja's airplanes don't have fuselages and tails. Just sayin! ;)

Yeah, I would buy into that, as long as the wing doesn't end up ridiculously close to the nose or tail for it to balance out. A short-coupled airplane can be a handful.
 

jetpackninja

More combat please...
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#7
Teach
Good point! Ninja says if you don't need it don't put it on there, it's just gonna get smashed up anyway ;)

Bbjen-
Have a look at some of Ed's designs.
Your plane looks a lot like a noob tube.
Ed uses a lot of the "if it looks like it should fly, then it will fly" methodology with his planes.
 
#9
Follow up on my main wing position

Hey guys,

here is a follow up on my plane i followed Ed's video to determine my cg and I tried the plane. Sorry no video on that...

How off was my cg?

Look at this...
B-Plane 6.jpg

I would say a rock too far...
RockOn! :)
B-Plane 5.jpg
With the rock, it was heavy for my 2cell battery but it still flew well.

Should I adjust the main wing or cut the tail?
 

jetpackninja

More combat please...
Mentor
#10
Looks to me like you may be able to adjust the battery to a more forward position.
Will your power setup tolerate a 3s battery? A little more weight, a little more punch...
 

jetpackninja

More combat please...
Mentor
#15
How married are you to the design?

I wouldn't cut the tail.
If anything I'd lengthen the nose.

You could probabaly move the wing back a little further but like teach says too close to the tail and it may be pitchy.

How much does the rock weigh?
We are trying to give advice without having a good perspective of the dimensions etc.
But, my guess is, that a bigger (more mah) battery, closer to the nose (maybe even as far as it can go) will help you out.
3s give you more power so that you do notwon't feel the weight penalty as much.

How married are you to the design and your current components?
If it's flying around fine with a rock on it's nose you've probably done a pretty decent design job for just off the top of your head...
 

earthsciteach

Moderator
Moderator
#16
Another thing to consider is wing loading. Calculate the area of the wing and divide by the weight of the plane with everything installed. I'm curious to see what that number this is.
 
#17
With the battery up front, it was way too tail heavy, i just could'nt help myself and i've cut the tail.
I'll have pictures and i'll weight the rock tomorrow.
 

jetpackninja

More combat please...
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#18
Moving the wing further back would have accomplished the same thing...
But at the end of the day it's your plane, hope to see another flight report soon.
 
#19
Hy everyone,

Here are the pictures:

The plane final:
B-Plane 7.jpg

The modified tail:
B-Plane 8.JPG
B-Plane 9.jpg

I did a test flight today, sorry no video I was alone, and it flew not bad.
The main things now would be to make a bigger ruddler because I flew in the wind and I got tossed around.

And I need to get some 3s batteries. for now I am using my rc car's battery. I just did not have enough power to push it with the wind...

Total weight is 829 grams for the plane without the rock. The rock was 153g. alone...