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Aug 04, 2018, 10:22 AM
Light flies right!
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Build Log

Gambler DLG 1-Meter Wing


Among several projects that I'm wanting to get done, a new wing for my Gambler+ DLG is one that has been on my mind for a while. Ever since I got it last year, I've had a ton of fun chucking the Gambler around and learning to thermal with it. However, I've noticed the plane's limitations, namely launch height and penetration. The S3021 airfoil, while a good airfoil for larger thermal sailplanes, has been superseded by numerous other foils designed specifically for DLGs. The Gambler's designer, Allan Wright, is currently selling an updated version of the Gambler with a slightly increased wingspan and the Drela AG36 airfoil, which seems to work very well from what I've seen.

However, since I crashed my Gambler and rebuilt the fuselage, I'm thinking that building a larger wing would not be very beneficial. During the rebuild process, I somehow removed 1.7 oz/50 grams of weight, which changed the plane's AUW from a porky 7.5 oz/215 g to an underweight 5.8 oz/165 grams. Because of this weight difference, the Gambler is a lot more floaty now, but it also seems to be more sluggish in turns. The slower flying speed and higher percentage of mass in the wing probably contributes to this. All of this has led me to the conclusion that to get the best overall performance from the new fuselage, I should build a wing of the same size or smaller to keep the wing loading from getting too low, improve turning response, and offset any possible strength deficit of the new fuse. The fuselage dimensions also seem to fit a 1-meter DLG better than a 1.2-meter, being similar in length to the MiMi I'm also working on.

With all of this in mind, I started with redesigning the wing in XFLR5, testing out the following different airfoil and span configurations:

AG03 root and mid, AG11 tip - 1.2-meter and 1-meter spans
AG37 root and mid, AG38 tip - 1.2-meter and 1-meter spans
AG38 root, mid, and tip - 1.2-meter and 1-meter spans

My focus for the redesign is on flat-bottomed airfoils that can be built up with balsa, since I am a fairly inexperienced builder and this is what I have access to. I have included wing models for the Gambler+ and newer Gambler-AG to serve as a baseline for comparison. I performed fixed speed LLT, fixed lift LLT, and fixed lift VLM1 analyses on each wing configuration. For the VLM1 analyses, I tried to approximate the CG for each configuration as best as I could, but regardless I think the Cm v. Alpha graph should be taken with a grain of salt.

I found that the designs using the AG03/11 performed the best out of the bunch, with the 1.2-meter version having the best overall performance. However, the most surprising thing I found is that the 1-meter AG03/11 wing actually performs similarly to the AG36 Gambler-AG wing, despite having much less area and span. The only areas I see where the 1-meter design may suffer are in launch and dead-air sink rate. I decided to go with the 1-meter design because I feel that the size and weight of my particular fuselage would fit the smaller span and the smaller wing should require less strength, and therefore less carbon fiber than the original Gambler wings. Less external carbon fiber would also help clean up the airfoil profile and improve efficiency as well.

I've started drafting some plans using AutoCAD, and I'm using this project as an opportunity to learn the program. While I'm quite familiar with Inventor and SketchUp, I really have to get used to the workflow of AutoCAD. Back to the subject, the new foils create a wing that is much thinner than the S3021, so I've opted to use different construction techniques than the original wing used, including basswood instead of iron-on unidirectional CF spar caps, shear webs, and a CF blade instead of tubular throwing peg. Overall, it will be similar to the built-up MiMi wing design by Frans Bal and JetPlaneFlyer.

Stay tuned for more as I finish the design and get building!
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Aug 31, 2018, 09:23 PM
Light flies right!
Thread OP
Well, it turns out that I must have made some errors in my XFLR5 analysis, as could be expected since I am learning the nuances as I go. While interpolating the wingtip airfoils for the plan, I realized that some of my airfoil polars and wing geometry data looked off, so after making the necessary updates and changes, it looks like my original analysis results were overly optimistic. The new results show the 1-meter AG03/11 wing as it probably should be, in that it doesn't perform as well in max L/D and sink rate when compared to the 50" AG36 wing, although I think it will still have an edge over the AG36 in windy conditions. The 1-meter wing is still a vast improvement over the S3021, however.


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