Triple swept constant chord... - RC Groups
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Jul 27, 2006, 04:59 PM
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kral27's Avatar

Triple swept constant chord...

What do you think the flight characteristics for constant chord triple swept wing with a conventional cruciform tail would be like? Here is an illustration of a recent idea I've come up with. The wing is allready built and spans 2090 mm. The root chord is 304 mm with the tip chord at 152 mm. The tip panels are set at 38% up from the center which is 0% The inner panels have 3.8% of dihedral each. Each panel is 380x304mm (span x chord). The first panels are 7.6% swept, the second are 15.2% swept, and the third panels are 28.5% swept.

After completing the wing I noticed that it became quite stiff and very rigid for the weight of 750 grams.

I built it primarily for concept reasons. No immediate flight plans yet.
Last edited by kral27; Jul 27, 2006 at 05:16 PM.
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Jul 28, 2006, 05:04 PM
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kral27's Avatar

Does anyone have an opinion?

I would appreciate any opinions regarding this design. Critical, non critical, good advice, bad advice, educated, and non educated feedback is most welcome with absolute sincerity.

Any comments would be greatly appreciated regardless.
Jul 28, 2006, 06:19 PM
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davidfee's Avatar
It looks like it would make for a very nice, stable platform for slow flying. Do you have something really heavy in the nose? The nose is pretty short, so you may have trouble getting the correct CG.

I like the lines.
Jul 28, 2006, 07:22 PM
B for Bruce
BMatthews's Avatar
I like it too. The sweep angles should promote some nice Schumman like spanwise airflow without the complexities of the tapers.

But I'd remove the trailing edge joggles at the root. Why make it more complex than it needs to be?

I'd also suggest a smoother and more tapered transition to the boom instead of the lumpy one that's shown. There would be a lot of turbulent drag off this sort of shape.

Frankly I think this would make a very nice 2 meter floater that not only flies well but would have a lot of character.
Jul 28, 2006, 08:19 PM
Registered User
The sweep back, combined with those tapered tips may produce nasty tip stall characteristics.

I don't think the short nose will cause balance issues because all that sweepback will move the neutral point back heaps.

Jul 28, 2006, 10:22 PM
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kral27's Avatar

Trailing edge croped...

I decided to crop the trailing edge in the center section in the interest of noise reduction in reference to the pusher prop arrangement. I've read that thicker trailing edges reduce the buzzing sound when compared to a clean thin TE.

If this option generates negative attributes towards the flight characteristics I would then make the design modification. I think that it might be a minor trade-off seeing that the popular Wingo also has this design feature. The Wingo uses a NACA 4408mod airfoil for it's wing. This design is using a NACA 6409 airfoil generated by a program I use called Profili.

I decided to add the tip panels in efforts to create a hybrid 50% winglet and 50% stabilization panels. This is the most difficult design feature during this project. Not only was designing the panels on computer difficult, but the building of them as well. Every single rib of this wing had to be shear sanded to conform to the the three different shear angles presented. Fortunately, after building the first 2 prototypes this became considerably easier.

After completing all seven panels it came time for the actual joining. At that particular point in the project the panels were quite stiff and unsheeted. The panels contain nothing more than a 16mm leading edge combined with a 31.7mm trailing edge and a 8x8mm carbon fiber square (1mm thickness). This arrangement may be sufficient for a plank design but after clamping the panels together for a structural test I soon realized that sheeting was mandatory.

I started sheeting just the first 30% of the airfoil top and bottom and soon reclamped for a second look. Much improvement was gained at a penalty of 150 grams but there was still an uncomfortable amount of flexing. I was soon forced to sheet the last 57% on all panels top and bottom. Carefully selecting the lightest 1.5mm balsa stock I managed to complete the wing ready to cover at a weight of 789 grams.

The only section remaining for attention before covering is capping the top and bottom portion of the ribs which remained unsheeted. Capping will be a relatively easy but tedious job since all caps must be sheared to angles that are never provided common tools. I wish I could find a nice balsa shear that allows you to adjust the angle of the cut much like the way you set the angle on a good quality tripod.

I appreciate the comments made greatly. Slow flight is one of the overall design goals for this project. I also wanted to see a little bit of that spirited track-on-rail effect you get when flying a 747-400. This is my favorite airplane to fly (at least on simulator) because it feels the most intuitive both the instrument panel and flight characteristics of all the planes I've flown. Outside of flight simmulator I have only flown a Cessna 152, 172, 182, 310, 340, 421 and some of the Mooneys. The Monneys were suprisingly less demanding to fly than the 152's.

Once again your input is greatly appreciated and hope to continue providing updates as well as photos in the future.
Jul 29, 2006, 12:58 AM
B for Bruce
BMatthews's Avatar
WOW! So you set the angles on the outer panels so the ribs are all still vertical? That's very unusual since standard model practice is to make all the panels flat and just let the ribs cant inwards as the dihedral is put in. On the inner panels what you did is not a big deal but on the outer ones you just reduced the apparent thickness of the airfoil. You see, the air sees the shape that is normal to the lower surface of the panel as the airfoil. Yes, fitting all the angles that resulted must have been a chore and a half!

Do a search for D tube. A D tube leading edge sheeting results in a lot of torsional stiffness thanks to the fully joined tube shape that tends to let the sheeting, leading edge and spar all join in supporting each other to form a stiff tube form. If your sheeting does not bond to the spar then you lost a lot of free stiffness.

Also don't fret about some flexing. The covering will help a lot when it's on and shrunk.

Rear motor and prop. That explains the cutouts in the trailing edge and also the odd looking blunt'ish ending of the pod as seen in the top view.

Well, if you've built most of it already. No point in avoiding flying it once it's done or you'll never know if your ideas are on the right track.
Jul 29, 2006, 04:10 PM
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kral27's Avatar

Panel construction...

actually all of the panels were built on a flat surface with all ribs maintaining a 90 degree relation to the flat work board. The dihedral was set by simply sanding the thicker end ribs at the desired angle. The inner carbon tube was then stuffed with a variety of .5, .7, 1, and 2 mm carbon rods which added little weight. I wetted the carbon robs with 30 min epoxy cout with milled fiberglass. This solution was also applied to the square tubes with a syringe immediately prior to joining the panels.

I wish a had that boook about model aircraft building that seemed to have valuable informatie. Forgot the name of it, read about it here on the forums somewhere.

The end panels of this design play the key element in creating that visualy dramatic look. I plan to put forth a great deal of effort and further R & D to abtain both the desired visual and flight results.

Please tell me more about D-Tube construction and if possible post links as to where there is more information. The great thing about building from scratch is that your insight seems to multiply endlessly after completion of a project.
Last edited by kral27; Jul 29, 2006 at 04:16 PM.

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