Jan 19, 2012, 12:21 AM
Joined Apr 2009
Some speculative work for a different direction for DLG wings for 2012 (Synergy)
I have a little project to share with you. This is something I've been working on occasionally over the last couple of years. My previous attempts have been failures but I'm sort of liking this one. It meets all my initial objectives, sufficiently so to release it for community review.
The purpose of this series is to be forgiving. Forgiving flying characteristics. Easy to design good wings. Easy wings to make.
This series should be considered a beta version. But the concept needs to be tested in real life to see what it will really do. This may become the final version, or it may need tweaking, or after testing we may decide it really doesn't work well enough to be better than available alternatives.
There are two main concepts behind this series.
The first is that the behavior of the foils is required to be pretty perfectly matched from root to tip. To my knowledge this hasn't been done before for DLG wings. That is the part which stumped me for a couple of years. I could start a series but only get a little over half a wing well synchronized. The rest became a nightmare. I've scrapped more than a few attempts because of this.
The second concept is to use turbulation. This has some plusses and minuses. But the reason it is used for this series is two-fold. First off, it allowed me to fulfill the first concept as one approaches the tips. Second off, it allowed me to make the wing more forgiving.
Some words about the foil naming. The name is of the form "<date>-<Re>T<trip_point> + <camber_setting>"
<Re> is the Type-II Reynolds number for the foil. But really it should be used as a ratio number. The root foil is 60. If one is looking at the 40 foil, it should be 40/60 of the chord of the 60 foil. Exactly that value; don't deviate at all. Deviating messes up the synchronization.
<trip_point> is where the airflow is forced to transition to turbulent for low alpha. The physical turbulator should be a zig-zag strip (pinking shears are good for making this) or something equally effective whose back edge is at about this location or a few mm in front of it (it may have to be farther forward; TBD). For a mold, obviously the turbulator can be molded in place. Since the turbulator is not optional, this is a good idea.
The height of the turbulator needs to be determined. It needs to be high enough to work at low alpha, and low enough to be masked at higher alpha. Starting with a really low turbulator on one wing only, and testing when flying a little too fast should really show whether it works or not. Flown a little slow, the plane should fly level. Flown a little fast, it should turn away from the turbulator side. If it meets this criteria, then just duplicate the turbulator on the other side and let us all know what you did!
All of these foils are turbulated. Turbulation runs root to tip. The turbulator is fairly far back. At moderate to high alpha, the turbulator should be masked within the boundary layer and therefore should contribute no additional drag compared to an un-turbulated version of the wing. At low alpha the turbulator does its work. What the analysis will not show is the extra drag of the turbulator when it is doing its thing. XFLR5 does not account for drag of turbulators. This is what testing needs to determine - when the wing is flown moderately too fast, does it fly super flat or does it fly like a normal DLG or does it become a pig with wings? If the wing does either of the first two, then the design is a success. The third indicates scrap it and go back to the drawing board.
The hingeline is at 70%.
A note on the wing design I'm including - it is the first one I generated. It isn't optimized in the slightest. I just took the foils at their respective chords, and strung them out to make a wing with no washout with a lift distribution that is slightly excess at the tips (tends to be better for low Re wings). I haven't even tried anything else. These foils are intended to be that easy to use for designing wings. Keep the chords in their exact ratio, don't bother with washout, and space them to give the desired lift distribution. Done.
Don't build this one heavy; it isn't designed to be extra lifty. I'd aim for something in the 260s or even a little lighter. After all, one can always add ballast. But it will float better if it is lighter.
Launch should be decent if the turbulation doesn't mess with it too much. That is also something which remains to be seen.
Most might appreciate that this wing is a little thicker than my usual practice.
As usual, free to use! I'll come up with a name at some point.
PS - This first version has a name now - Synergy.
Last edited by G_T; Jul 26, 2012 at 10:55 AM.