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Old Yesterday, 06:46 PM
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YellowJacketsRC's Avatar
United States, SC, Pawleys Island
Joined Jul 2003
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Sorry to bug you AP,
But while you have my lipo numbers, can you do the same thing for the 60 Edge and Laser for me? Since I fly those as well I would love to know the difference!
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Old Yesterday, 06:56 PM
Not as Good as The Kid
Aeroplayin's Avatar
South Pasadena, FL
Joined Sep 2009
6,246 Posts
Quote:
Originally Posted by Brashair View Post
Aero,
I'm wondering, when you do your WCL figures do you use the manufacturers advertised wing area or your own measurements of the actual wing area? I find typically there's a huge discrepancy. For instance, the 60" EF Extra is listed at 760sq's. My measurements of the actual wing area comes in at around 600sq's. Even if you consider the span across the fuselage it would only be about 660. Well short of 760. The 60" Edge has about a 1" wider cord throughout the span but is also listed at 760. This probably explains why pilots generally suggest the 540 is floatier, it simply has more squares supporting the weight.
The 78" Extra's advertised squares are listed at 1225, but I measure 1146. That's pretty close but still represents about a 7% difference which can have quite an effect on WCL calculations.
I totally agree with your premise with respect to the importance of wing loading, BTW.
I calculate the wing area from actual measurements and if I were not able to get them myself, other contributors here are nice enough to make the effort.

I do use the area to the fuse median as well. There is a lot of rounding going on out there and there are four planes on a site that have the same 1000 sq-in as the area, even though they are different models with different wing configurations and different wingspans.

The tricky part is when the racing tips are involved, and the shapes of some are different than others. Sometimes, the trailing edge curve can equal what's missing from the leading edge, and unless to you do a weight comparison, or use calculus to determine area under the curve, you may never get it right.

The best way to do it is to outline the wing tip on cardboard, cut it out, and weigh it. Then measure, cut, and weigh a few known square cm of the same cardboard as the constant, and calculate the relative difference in weight. So if I get 6g per 100 sq-cm of cardboard, and the cardboard outline of the tip weighs 18g, then the wing tip is 300 sq-cm.

The 'common way that most people measure wing area is:

((Root Length + Tip Length) / 2) x Wingspan

So that would mean that my 78 Extra 300, with a tip length of 10.750 inches and a root length of 19.625 inches, and a wingspan of 78 inches, has a wing area of:

((19.625 + 10.750) / 2) x 78 = 1185

Now you may be surprised to see that the website says 1225, but I agree with the website, because there is another way to extrapolate the root length to the fuse median, and if you do it this way, you come up with 1227. Here is how you do that....

The length of the wing panel of the 78 inch wingspan is 34.75 inches and the root of the 34.75 panel is 19.625 inches, but if we extrapolate the root length of the panel to the fuse median, the panel root it is 20.71 inches.

If the cord changes from 10.750 inches to 19.625 inches over 34.75 inches, then it will change to 20.71 inches over a 39 inch distance. So....

((20.71 + 10.75) / 2) x 78 = 1227 inches.

So this is how EF calculated the wing area of the 78, and it's the way I like to do it too.
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Last edited by Aeroplayin; Yesterday at 07:02 PM.
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Old Yesterday, 07:11 PM
Not as Good as The Kid
Aeroplayin's Avatar
South Pasadena, FL
Joined Sep 2009
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Quote:
Originally Posted by YellowJacketsRC View Post
Sorry to bug you AP,
But while you have my lipo numbers, can you do the same thing for the 60 Edge and Laser for me? Since I fly those as well I would love to know the difference!
I have the Laser weight higher than the Edge weight to begin with, so it starts off with a little higher wing loading and cube loading too. But the Laser goes from an 8.56 oz/cu-ft to an 8.72, and the Edge goes from an 8.13 to an 8.29.
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Old Yesterday, 07:24 PM
They Call him Dead!
YellowJacketsRC's Avatar
United States, SC, Pawleys Island
Joined Jul 2003
6,618 Posts
Quote:
Originally Posted by Aeroplayin View Post
I have the Laser weight higher than the Edge weight to begin with, so it starts off with a little higher wing loading and cube loading too. But the Laser goes from an 8.56 oz/cu-ft to an 8.72, and the Edge goes from an 8.13 to an 8.29.
Thanks. So the MXS with tips (thats how I fly it) should be noticeably floatier. I am not sure I feel that. But I do feel the difference between the smaller and larger lipos in the same plane.

I also feel the Edge is floatier than the Laser. What I don't quite get is that the MXS has a lower WCL than the Edge. It just does not FEEL that way to me.

How come that???
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Old Yesterday, 08:55 PM
Not as Good as The Kid
Aeroplayin's Avatar
South Pasadena, FL
Joined Sep 2009
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Quote:
Originally Posted by YellowJacketsRC View Post
Thanks. So the MXS with tips (thats how I fly it) should be noticeably floatier. I am not sure I feel that. But I do feel the difference between the smaller and larger lipos in the same plane.

I also feel the Edge is floatier than the Laser. What I don't quite get is that the MXS has a lower WCL than the Edge. It just does not FEEL that way to me.

How come that???
Well, potentially three things to consider.

I'm going to guess that your weights are different than mine, but I think the real difference is that the Edge wing configuration gives it an advantage in slow speeds. Not only is the leading edge straight and stalls evenly, but the 1/4 cord is also swept forward, which give it a little more yaw stability. In essence, the wing tips are also more stable, which is not always a good thing in XA.

But I also have the Edge about 41g heavier than the MXS, and that's probably because I had a heavy HV ESC after I chucked the HK thing that was in there. There were also decals on the Edge, and I did reinforce the battery tray and the LG platform with triangle stock and epoxy. 2658g.

Finally, the big reason, and somewhat related to the first about wing configuration....

The aspect ratio of the MXS is high in comparison. High AR means longer and narrower wings as opposed to shorter, wider wings. The Edge has the lowest AR of all three, and the Extra has the highest with the MXS very close behind the Extra.

The triple tapered wings of the MXS and the Extra. along with a higher AR, creates a specific characteristic that most XA guys like... snap and tumble. It destabilizes the tips just a little more to make these maneuvers pop. The design challenge is to get the snap to stop when you want it to and EF is one of the best at this. Bob Godfrey used to be the king of this capability when he was alive, and if you watch videos of Andrew flying his Extra 300 in TAS, you'll see what I mean.
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Old Yesterday, 09:12 PM
They Call him Dead!
YellowJacketsRC's Avatar
United States, SC, Pawleys Island
Joined Jul 2003
6,618 Posts
So the Edge can FEEL Floatier without BEING floatier....
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