Synergy-II wing development - RC Groups
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Apr 23, 2014, 12:27 PM
Registered User

Synergy-II wing development

Hello everyone,

I've been working this year on a Synergy-ish wing designed for a somewhat higher aspect ratio lighter weight plane. Much of the development info has been buried at the back of the original Synergy thread so I expect it is mostly being ignored. Work has progressed far enough that it is well past time this subject had its own thread.

Discussion started somewhere on page 30 of the original Synergy thread. For those who are interested, start reading about there:

Originally it was supposed to be a "quick" project to bang out a higher AR Synergy wing design. I've seen some poor designs and thought it worth putting out a reference wing design people could build or use for comparison purposes.

But during the process, I learned that the missing region of points in the flat region on the bottom of the flaperon for most of the Synergy foils was causing XFLR5 to generate erroneous analysis. The predicted performance of Synergy went down a little when the missing points were restored.

I endeavored to replace the existing Synergy foils with new foils which matched the original erroneous performance characteristics. I was about half successful. Some foils I could match essentially perfectly, but others couldn't be done at the existing thickness.

After beating my head against that wall for a while, I decided it was time for Synergy-II.

I've been through about 50 wing variants and perhaps a hundred candidate foils. The current wing version is #30, along with its variants. Current performance is quite good. There is a fair bit of work remaining to be done but it is coming along nicely.

In current form, the root foil is rather similar to a Synergy-50. The tip is Zone-V2-20. In between it is more like Synergy than anything else. Flight characteristics should be very similar to the existing Synergy wings.

What one should expect from the new wing when finalized is slightly improved minimum sink rate, fairly high launches, and phenomenal L/D.

However, being higher aspect ratio is not without its penalties. The falloff of performance from being flown poorly will be a little greater. But since performance starts out higher, this is tolerable.

Synergy-II will be a wing design, not a foil family! The foils are being developed based on their contribution to wing performance and handling, rather than being developed as a family of foils with a wing design which follows afterwards.

This approach has plusses and minuses. I may end up with a higher performance wing this way. That's certainly a plus! But if one looks at parametric progression across the span of the wing, one will likely see oddities. I do hope to minimize this, but it isn't the highest priority. I'd like to minimize it mostly from the philosophy that a smoother wing design is more elegant and likely a better wing.

The wing is designed in cruise camber. Speed camber would likely be best somewhere around -2 degrees from there. Float is whatever works. Launch climbout would be best at about -2 degrees.

For more background info, feel free to dig into the previous Synergy thread.

One other thing - this time around the foils are designed without any consideration of turbulation.

Gerald Taylor

PS - The question came up on whether I was done with Synergy-II. At this point, yes. It was hard to do better than the 20141225i version and that version is already in use by many. So that version is Synergy-II by default.
Last edited by G_T; Nov 01, 2017 at 02:13 PM. Reason: Synergy-II considered done
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Apr 23, 2014, 12:55 PM
nickbox's Avatar
Can't wait!

seems I have a long article to read..nice
Last edited by nickbox; Apr 23, 2014 at 01:05 PM.
Apr 23, 2014, 03:23 PM
Charles Martin
BavarianCharles's Avatar
Originally Posted by G_T
Synergy-II will be a wing design, not a foil family!

will you be designing the wing strictly for molding, or also with a configuration suitable for bagging?

Thanks, Charles
Apr 23, 2014, 03:33 PM
Registered User
Strictly for molding, but, one can readily take slices wherever desired to panelize the wing. The more panels, the more accurate the wing. I expect 4 panels per side would be sufficient to get the wing pretty close, to where flying characteristics would be hard to distinguish compared to fully molded.

It is possible that with a single wing design provided, people with CNC routers may offer fully contoured cores for bagging. One could use a machined upper or lower surface bed, along with mylars, to produce a good quality wing at reduced cost and effort compared to the usual molding approach. Accuracy should be higher than the usual bagging approach. A variety of material could be machined into a suitable bed, and the surface need not be of polished quality. I'd like to see this approach considered and tried by hobby builders who already are familiar with bagging techniques. Wings on a half shell... Solid cores allow this to be done.


PS - When the wing design is done, I plan to ask/impose on Tom Siler to generate some CAD for the wing. We'd then make the CAD available to everyone. One of the big issues getting to a molded wing is the cost of the software and the degree of expertise required to accurately transfer a theoretical wing model into a lofted wing and/or lofted molds. Having that part already done or at least well under way may enable more people to make the transition to making molded planes. This may also encourage manufacturers to stick with the wing design rather than tweaking it out of its expected performance.
Last edited by G_T; Apr 23, 2014 at 03:40 PM.
Apr 23, 2014, 05:06 PM
Aurora Builder

I applaud the effort. I also agree with your approach. An upper surface bed machining out of MDF and a semi-bagged solid core wing machined out of 40 psi XPS is a nice way to go, and something I have been thinking about for some time. MDF molds are used for hollow molded sailboat foils on a regular basis fyi. It is too expensive to machine an aluminum mold for a one-time pull.

If Tom is too busy to generate a model, I can create the base wing CAD in about an evening and maintain 100% accuracy with the XFLR5 file. Building a mold from the base CAD is where the time will be spent on a wing with washout.

Apr 23, 2014, 05:53 PM
launch low, fly high

I can also sort out a CAD model if you need one generated. It would be kind of interesting to have several people generate CAD models and compare the various results!
Apr 23, 2014, 06:10 PM
Aurora Builder
It would be interesting, but really only to CAD users. I use Solidworks, Tom uses Rhino (which IMO handles complex curves, i.e airfoils, better than Solidworks). I am curious what you use for design work Joe?

To me, the more interesting aspects of CAD design are how one models the tip and the mold. In Solidworks for example, it is difficult to taper to a zero thickness tip, yet relatively easy to use the exact same method XFLR5 uses for terminating a wing. The methods used for generating a mold can vary quite a bit depending on the part, and some methods are superior than others...

In reality, most of this is an academic exercise. I could take a .OBJ or .STL output of a CAD wing design and load that into a full Reynolds-averaged Navier Stokes flow simulation to compare wing models, but that is a lot of effort and can require tweaking on the models to generate a proper mesh. All of which is moot as it is likely minor changes in wing design from XFRL5 to CAD will be lost in the noise when polishing out a mold surface.
Apr 23, 2014, 06:59 PM
launch low, fly high
I have a large amount of experience with CATIA, although I've a little experience with Solidworks and have dabbled with Rhino.

The accuracy of the airfoil blending is something to check carefully, regardless of the tool used to generate the surfaces. This is where many wing lofts go astray. And yes, the wingtip region typically is as much art as science in terms of how the surfaces are generated (and which rules are used to generate said surfaces).

There are sometimes annoying artifacts and errors that occur when converting CAD lofts from one format to another. As to a converting to a tessellated file, well, that has its own set of annoyances.

It appears that there are several people that are willing to loft whatever Gerald generates. I am curious to see what results from this exercise.
Apr 24, 2014, 12:43 AM
Registered User
I might be interested in creating a fuse mold to match this wing. I have a low wing plug I'm currently working on, and if I hadn't already molded the wing saddle to match a high AR ZV2 I'd wait for this series to be released. I might still make a second mold. I'd just have to reshape the wing saddle, so it wouldn't be much extra work. How soon do you anticipate releasing the design?
Apr 24, 2014, 03:53 AM
the answer 42 is
dear Gerald

it is nice to see that you started this new thread, hopefully the Synergy will get the attention it deserves (more builds is what we need)

I still love the Synergy I and I am looking forward to build the Synergy II

Looking with great interest


Apr 24, 2014, 11:13 AM
Registered User
As to when it will be done - when it is done! That's always a tough call. My current version - wing 30k, is nearing completion. There is a region perhaps 6" wide most of the way to the tips that is slightly more active than I'd like when the transition point is near the hingeline. I want to tone that down a little to reduce wing rocking in turbulence when flown slowly or flown in thermal turns. But otherwise the wing is a good performer. When I've done this I'll release this variant so you all can see the current status for yourselves.

I've got so many foils and so many wings in the XFLR5 project file now that it might take me an hour just to get it down to where I can post the wing. Plus there is a foil family in there (not F3K) that I'll be releasing in a couple of months; that's last year's work. I don't want to accidentally release it early.

I'm alternating days working on Synergy-II and working on my CNC machine. I want the CNC running this summer, so I can potentially make some molds for myself and others. So tonight should be making metal chips. I'll likely release some variant of wing 30 tomorrow. Really it should only take a couple more hours to get 30k sorted out.

Then I'll need to make a parametric examination of the wing to see how physically consistent the design might (not) be. That is looking at things like thickness progression across the wing.

The foils for the initial 30k release are not really finalized. They have slightly different number of points for instance, which can drive CAD and CNC hot wire cutters batty. I'll fix that as I clean up 30k.

So then 30k - or whatever the version ends up being - becomes the first candidate Synergy-II. I'll have to spend a few hours running numbers for other camber settings as I'm doing nearly all the work in cruise mode.

From there it is looking at what can be done to make further improvements. From about wing 21 I've been working to improve the float. I've traded off a very tiny bit of L/D to reduce the sink rate and improve the handling. I'd like to continue working to reduce the sink rate even further. But it is worth noting that the sink rate is already very good. I don't think it will take a Reto to get three minutes in dead air.

The other thing I want to consider is how much lift reserve we would like to have in the wing. Edge had a lot, Zone-V2 much less. The benefit is being able to crank tighter in thermal turns without the wing mushing out. The disadvantage is a bit more active wing when flown slowly or flown in high turbulence. I'll control this primarily through sharpness of the front 20% of the wing. But, I'll need to know what all of you would like in that regard. So please think on it a bit.

Apr 24, 2014, 11:22 AM
Registered User
I really like being able to pull my DLG into a very tight turn without worrying about stalling. That's one of my biggest pet peeves with the ZV2 and one of the main reasons I don't use it anymore. I like having plenty of lift reserve in tight turns.
Apr 24, 2014, 04:12 PM
Registered User
Do you have enough stick time on Synergy to comment on its lift reserve? It is between Edge and Zone-V2.

PS - Perhaps try increasing coupling of elevator to camber, if you fly a Zone-V2 again.
Apr 24, 2014, 10:16 PM
Registered User
I've never actually flown a Synergy wing, so I can't comment on how it compares. The evening I spent with an Edge was one I really liked, but possibly not enough to make a complete judgement. I've flown 6 different ZV2 planes, two of which were mine, and all but one exhibited that behavior (though I know nothing about the way the 4 that weren't mine were set up). The one that didn't seem to struggle weighed only 7oz, and the ability to circle really tightly is definitely dependent on weight. I can't recall if I experimented with elevator-camber coupling or not. I know with my ZV2 I spent a long time playing with CG, differential, reverse diff, and tried flying faster than I'm accustomed to. I never found a setup that brought me to love the plane.

To be fair none of the ZV2 wings I flew were molded, so that could very well make all the difference. Clearly others like it or it wouldn't be on more DLGs currently being produced than any other foil series. I'd love to try a molded ZV2 wing, but I have a hard enough time justifying buying a $350 complete DLG. A molded wing by itself costs more than that.
Apr 25, 2014, 06:56 PM
not bad for one eye
Thank you Gerald for the time you put into all of your projects.

Can you comment on the best way to set the trailing edge gap? I've used the method Tom described in his DLG Molded project but the kink at the hinge line failed to loft strait. Recently I set the gap in XFLR by dividing my desired TE gap by the airfoil cord, then multiplying by 100. I then use the hinge line as the blend value. I think that's right, though I am unsure because I'm not on a computer with XFLR. Either way, I'm worried I'm making a mess of the airfoil that others have spent so much time creating. I'm looking forward to a new project, soon after you finalize the wing I'll be using my cnc router to cut cores.

Thanks Paul.

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