RES Polybreaks

[soholingo]

Which is better multiple poly breaks or a single poly break. For instance, the Bubble Dancer has a two breaks for Polyhedral and the Topaz only has one break at for polyhedral.

Is there much difference in the performance?

[Andy W]

If properly designed, no.
I prefer a flat center section, as it allows for a single spoiler, and reduces worries about the strength of a joint at the center (although, as Fred's Trinity demonstrated, that's no guarantee)..
..a

[OVSS Boss]

Soho,
If I was getting an RES ship. I would go Topaz for one reason, getting the thing around. They all fly very nicely, but everything is flat and that means that whatever conveince you use to carry it, less hanger rash will occur. My .02$...

Marc

[soholingo]

Marc,

You are hitting the nail square on the head. That's why I am asking, storage. Most planes can fit in a 53" gun case, but the double break causes issues when storing/transporting.

j

[IP Freely]

Jay, you probably already know this but I thought that I would throw it in anyway. The Topaz S center section is not completely flat. There is a small amount of dihedral in it.

B

[soholingo]

I am asking so I know what to build. I guess that would qualify as a double break.

[histarter]

Soho,
If I was getting an RES ship. I would go Topaz for one reason, getting the thing around. They all fly very nicely, but everything is flat and that means that whatever conveince you use to carry it, less hanger rash will occur. My .02$...

Marc
After flying Mirages (and hauling them all over in small cars for over 10 years), with various forms of wing tunning, I really cannot find fault with the 3 panel system, and believe the center panel spoiler to be the best addition to a competent design. ;)
To me the Topaz represents the best upmanship for the Mirage, however I would probably build my version with the tailboom cut in two, and a large 115 degree articulated V tail installed, because simplicity, efficiency, and short coupling is my interest. :D

[tonyestep]

Quote from Mark Drela: "on a rudder/elevator glider, the ideal
dihedral distribution is more like a shallow circular arc or parabola,
not an ellipse. The arc has a minimum induced drag penalty from the
sideslip during an established turn. "

The new Topaz with a little dihedral in the central panel matches this well and the flat tips are eay to transport as Marc sez, although the fuse is quite long and it takes a big bag to fit the plane.

[georgeg]

Each to his own and all that, but a single spoiler in the center panel is the last thing I'd want. I know some people like it but I think a center spoiler disturbs the airflow around the tail and makes landing approaches more interesting than I really want. Just my opinion.

[ChuckA]

Quote from Mark Drela: "on a rudder/elevator glider, the ideal
dihedral distribution is more like a shallow circular arc or parabola,
not an ellipse. The arc has a minimum induced drag penalty from the
sideslip during an established turn. "

The new Topaz with a little dihedral in the central panel matches this well and the flat tips are eay to transport as Marc sez, although the fuse is quite long and it takes a big bag to fit the plane.

Back in the early 70's, I did a lot of research in NASA reports about stability and ran across a report by a man named Cone about non-planer wings. One of his findings was that wings with parabolic dihedral had better lateral-directional stability. Sounded like a good idea but I didn't want to build a wing so I used a 5 panel wing that gave a linear approximation to parabolic dihedral. I used that in my 1973 Tern III and 1974 Tern IV and really liked it. Got away from the five panel wing for my RES models until 2001 when I returned to it for my first LilAn.

[soholingo]

Chuck do you have any pictures?

[Andy W]

Each to his own and all that, but a single spoiler in the center panel is the last thing I'd want. I know some people like it but I think a center spoiler disturbs the airflow around the tail and makes landing approaches more interesting than I really want. Just my opinion.

A lot of people agree with you, but a lot of people also fly models with substantial spoilers (i.e. AVA - myself included) and do not find this to be the case. Perhaps design plays a role here..
..a

[OVSS Boss]

And actually GG, some folks are kit bashing and splitting that one big one into two smaller ones and getting all they want. The one thing some folks do like though about the one big juan, it that in burning altitude, 90 dgree throw gives you darn near flap effect. Tomatoe or Tamatoo, you make the call.

Marc

[ChuckA]

Chuck do you have any pictures?

Here are pictures of the original Lilan from 2001 and the current version I am flying. The center wing of the LilAn is 47.5 inches so that it will fit in my van without removing the center wing panel. I can be ready to fly in a couple of minutes after reaching the field since all I have to do is plug in the outer wing panels and tape them. The pictures do not show the dihedral so I included a picture of the first Lilan before covering to show the dihedral. Dihedral of the outer wing and tip panels were increased for LilAn II to improve handling.

[StevenatorLTFO]

I have an older Topaz with the flat center panel, and the single spoiler, and 1. It will turn on a dime, and 2. with proper elevator comp (it took a big bunch), it settles down fine in and around the landing circle.

Steve

[tonyestep]

Chuck, that's a nice-looking plane.

[soholingo]

Non of these gliders look like Parabolas. They all look like they are closer to ellipses.

And if you were to draw a best fit line with the bubble dancer it appears that you would be very close to the topaz's arc.

What am I missing?

Jay

[Soar_dude]

Non of these gliders look like Parabolas. They all look like they are closer to ellipses.

And if you were to draw a best fit line with the bubble dancer it appears that you would be very close to the topaz's arc.

What am I missing?

Jay

The only wing that comes to mind with a parabola is the Hobie/Super hawks series. http://www.hobiehawk.com/default.htm

Soar Dude

[bobby legue]

And dont forget that every poly break adds some more drag.......

[Neil Stainton]

Yes, but do many small ones add more drag than few big ones?

Neil.

[histarter]

Yes, but do many small ones add more drag than few big ones?

Neil.
That is a very good hitech question and it becomes a struggle with designers.
Seaking the perfect arc for poly to control roll rate at a myriad of airspeeds is tough. Then realizing the employment of a thin profile is an aggrevation because dihedral breaks are more massive (heavy) making the Topaz design (for example) a very strong competitor because wing mass is more centrally located. Then adding the little bits of extra drag for the multiple breaks, it hardly seems worth the effort. Of course the perfectionists will disagree with this simple overview. ;) :)