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Old Jan 19, 2012, 01:21 AM
G_T
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Some speculative work for a different direction for DLG wings for 2012 (Synergy)

Hello everyone,

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.

Gerald Taylor

PS - This first version has a name now - Synergy.
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Old Jan 19, 2012, 01:31 AM
Team Hong Kong F3K
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Awesome, just in time for me to play around with it in the computer on one of the next projects
Thanks Gerald!
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Old Jan 19, 2012, 02:11 AM
Team Hong Kong F3K
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Gerald, is this the series you mentioned earlier where for a bagged plane, it will need 5p to perform? Will the performance drop of a 3p or 4p be noticeable enough to not bother with it? Theoretical ofcoarse, as no one has built one yet. Thanks.
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Old Jan 19, 2012, 02:41 AM
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Intresting work.
I've seen quite some improvements in XFLR5 when adding a fixed transition point. I guess the polar comparison is made from the Zone without turbulator and the new design with turbulator. Have you done the comparison to add turbulator to the Zone design for reference?

Best regards
Mattias
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Old Jan 19, 2012, 08:07 AM
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Gerald great topic!!

some related remarks:

- For a first guess of the thickness of a turbulator see: http://www.mh-aerotools.de/airfoils/...gTheTurbulator

- The turbulator should be placed a few percent upstream of the transition location.

- The optimal angle of the zigzag turbulator is 60 degrees. It is important that the points heading to the trailing edge are sharp (not rounded).

Bas
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Old Jan 19, 2012, 08:26 AM
Father of Fr3aK, DLG Pilot
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Mattias,

I've been playing with turbulators on the molded Zone V2, with Gerald's guidance of course. Results are mixed right now because of a lack of good flying weather
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Old Jan 19, 2012, 10:20 AM
Oleg Golovidov
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Very cool! Thanks again, Gerald.
It looks to me like a higher performing wing, not just forgiving. About 1+ points of L/D over the Zone-V2 wing! wow!
Interesting, does turbulating the flow at 85% have a really noticeable effect on performance? I was expecting to see the transition points set at well under 70% where the hinge line is. Gerald, you must have run the same airfoils without turbulation - what is the result? Much worse? About the same?
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Old Jan 19, 2012, 10:22 AM
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This is cool! I'll be keeping an eye on this thread to see how it develops!

BMW
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Old Jan 19, 2012, 10:35 AM
Aurora Builder
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Oleg,

Due note that the drag of the turbulator isn't accounted for in XFLR5, so I suspect the L/D difference might not be as large. I do wonder what the performance is with and without the turbulator? I'm assuming no turbulator is modelled in xflr5?

Gerald,

Your initial wing design seems good enough to build. I'll generate the GMFC cut files when I get a spare moment and build a test wing. Likely will be late Feb. before I get a test wing cut so if refined foils appear between now and then I can switch to those.

-Sam
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Old Jan 19, 2012, 01:38 PM
G_T
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If I get the chance I'll put out versions of the foils with the flap position set at 0. I put these out at 2 degrees because honestly that is where I developed them for the majority of the work.

I have not analyzed these foils as extensively or refined them to the level of my usual standards. There is likely room for some improvement here and there. Given the number of foils in the sequence, this is a fair bit of work. But I figured they are good enough to do a proof-of-concept test to see if this idea delivers the performance that the graphs suggest is possible. If so, then this might just be the new direction for DLG wing design. Or at least one possible new direction.

For those making bagged wings, 4 panels is likely sufficient. The airflow over the last few inches of the tips is going to be funky anyway, except at very high speeds where lift coefficients are rather low. So use the inner 4 panels, and trim the tips to shape and do a little sanding. It should be good enough.

Using fewer than 4 panels is not an option. Sorry folks. That's the price of getting the wing well synchronized from root to tip.

I'll generate some graphs to show the non-turbulated results. The differences are shocking.

Zone-V2 was not designed for turbulation. It could be re-designed for it... And it can use turbulation in the current form though probably without quite as large a performance boost. I haven't done much in the way of testing with it. It is its own thing.

This new beta series was designed for turbulation from early on. I generated the core set of foils without turbulation but went back and adjusted them once I decided on having full span turbulation for the series. Turbulation simply solved so many issues in one shot that it was a no-brainer.

The series looked like it had the potential for high performance but there have been many I've looked at that appeared good until tested in a wing design. The issue has always been one of having the foils sufficiently synchronized across the span. Perhaps these beta foils could be better as individual foils, but since they ARE fully synchronized, they give what they've got. Unsynchronized series are not capable of giving their full performance potential in a wing design. That is the critical point. Foils don't have to be as good to make a better wing if they are synchronized.

By synchronized, I mean that all the foils have their performance peaks lined up to match the intended lift coefficient for their station (or alpha if washout is intended). That should show quite well in one of the graphs I presented in the first post.

If someone created a foil series that each foil could give 30:1 L/D, one might think this could produce a great wing. But if one can't make a wing from them that lines them up so each gives 30:1 at the same time, then the resulting wing won't capitalize on the foils potential. That is the state of DLG wing series foils IMHO. Great foils that don't quite capitalize fully.

A lot of my work on series such as the Zone-V2 was to get the foils as synchronized as I could. But the last third or quarter of the wing becomes essentially impossible to get right. So as one approaches the tips, my optimization criteria changes. The tips on Zone-V2 are designed to minimize drag. Any lift they produce is a bonus. The reason for this direction is to limit the damage that the un-synchronized tips can do to the performance of the rest of the wing. It works... I consider the resulting series quite good for a conventional DLG wing design. I do think this is an area of reasoning that has been overlooked by many designers. Of course there are a lot of fine details I'm ignoring on this presentation but they are not relevant here.

This beta series on the other hand has foils which are very well synchronized. There is no need to design the tips specifically to minimize drag as an overriding criteria. Due to the Reynolds numbers penalty of smaller chords, it will still be important to minimize drag for such series but not to as much of an extent as is the case for normal wing series. Paying some attention to the tip's L/D and power factor is warranted.

In this wing design we are deliberately controlling the turbulation. It would be advantageous to use full span gap seal, even for a bagged wing. We want the turbulation action to occur where we want it and not at other locations.

Gerald
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Old Jan 19, 2012, 01:40 PM
G_T
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It's funny; anytime I post a series, far more people grab copies of the root airfoil than of the rest of the series. Honestly folks, the root is not where it's at.

Gerald
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Old Jan 19, 2012, 02:37 PM
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Kudos Gerald. The series looks very interesting, I look forward to hearing how it performs in real world testing.

Quote:
Originally Posted by G_T View Post
It's funny; anytime I post a series, far more people grab copies of the root airfoil than of the rest of the series. Honestly folks, the root is not where it's at.
People probably download the first zip file, look inside it, don't know what to do with a .wpa file, and give up.

Is the turbulation on the top surface only?

Neil.
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Old Jan 19, 2012, 03:06 PM
G_T
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Turbulation is top surface only. The bottom is fully laminar.

Funny, it must have been when I looked at it this time. Now the download of the foils is fairly uniform.

Gerald
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Old Jan 19, 2012, 03:39 PM
Father of Fr3aK, DLG Pilot
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Gerald,

Is the hingeline thinner than the Zone V2? Just curious. It looks like it may not be "moldie friendly" there.

I guess it's been a while since I looked at a V2 closely.
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Old Jan 19, 2012, 03:48 PM
G_T
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I do not think the hingeline is thinner. It should be similar. Others have gone much thinner than I...

The wing itself is thicker of course.

Gerald
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