doxilia

My Feedback: (3)

Ehsan,

I had a chance to look at the Mystic airfoil and incidence issues. As you mention, we don't have a reliable source to determine or know exactly what airfoil was used by Hanno in his WC '93 Mystic 60. Barring an email exchange with Hanno himself (which might be a possibility), the choice of airfoil is something that can be decided somewhat independently. So your model wouldn't be an exact replica (which it wouldn't be anyway since Greg's 3-view you'd be building from is based on a photograph) but a reasonably faithful reproduction.

Airfoils

We recently had a chance to do a little research on aerobatic symmetric foils in order to assess what airfoil was being used by the Japanese in a number of their classic aerobats including their semi-scale 120 size FAI classics (Chipmunk, Zlin, Akromaster and Laser). After comparing several designs and their airfoils we determined that they were, by enlarge, using a slight variation on the Helmut Quabeck 14% aerobatic airfoil known as HQ/A-0-14. Basically what Kato (MK) did was to pronounce the LE slightly in all likelihood to improve on the snap entry maneuvers. While I personally haven't flown this airfoil yet, many others have and it is well proven (both in competition and for sport flying) and apparently very good at least for classic pattern designs. It is also more modern than some of the older airfoils such as NACA 0014 (and thicker) and Selig S8035-14 so in a sense well suited to a late AMA/early FAI turn-around design such as Hanno's Mystic. In short, if I were to scratch build a Mystic 60 (or 45 as in your case), I would use the modified HQ MK airfoil. I have posted a picture of the different airfoils I was comparing when doing the research for an MK Super Chipmunk S that we developed. The bottom airfoil is the MK airfoil in question and the one I would use and suggest for the Mystic.

Incidence

As far as wing/stab incidence goes, again, there is no indication of what he might have used. Judging from his previous designs such as the Calypso, Supra Fly and Supra Star though, he likely had a smidgen of positive incidence on the wing and 0 degrees on the stab. Hanno notoriously tweaked this sort of thing extensively even during competition including engine thrust angles which is the reason why many of his competition models didn't have spinners on them. He said it was too inconvenient as it would wind up interfering with the fuse as he changed thrust at will. He recently went through he same sort of exercise in setting up the re-created Austrian Curare ARF and provided extensive details on the best power and radio setup for the new lighter model. In any case, what I would suggest is to build the model with 0.5 degrees of positive wing incidence and 0 degrees of stab incidence. Ideally, with a 60 size (or larger) model, the wing would be built with plug-in panels and incidence adjustors so it could be fine tuned. The Mystic is particularly well suited to this as it basically has a mid-wing fuselage configuration. The fact the wing goes right through the middle of the fuse also makes the plug-in approach more convenient as it provides more room in the fuse for radio gear. I built a pair of Mystic 30's with one piece wings and I wanted to design a CAD version to allow me to scale the design as well as fine tune it to my liking. The first thing that I wanted to do with the design was to take out the one piece wing and build it with plug-in panels. Whether the model is built with a once piece wing or plug-in panels, I would build the fuse as if it had plug-in panels and then, when it came time to fit the one piece wing, cut away the fuse portion that would become a belly pan on the wing.

Thrust

Thrust is much less of an issue especially with the Mystic since it is a fully cowled design. Adjusting thrust is something that can be done as part of the trimming process. I'd design the fuse to allow the use of a standard glass mount (or whatever you have available for the MVVS) with the engine mounted squarely on to it as it should. The down and side thrust can then be set by shimming the engine mount. If you wanted to build-in some thrust into the firewall, I would build in down thrust but not side thrust. I find it much easier to design and build a model with only one thrust angle built into the model and down thrust is generally easier as it allows you to build a symmetric fuse. With built-in side thrust, your fuse ends up being asymmetric in top view (at least from a former perspective). With a cowled design, it is much easier to produce the asymmetry in the glass cowl portion of the model - basically thrust angles in the front "spinner ring" area. I would start with 1 degree of down and right thrust. The 1 degree down thrust can be built in to the FW and any further changes (whether increasing or decreasing) can be done by shimming the engine mount. Side thrust would be produced entirely by shimming the left side of the mount. How much shimming is needed can be determined with a CAD drawn front end.

So in summary my suggestions would be:
[*] MK modified HQ 14% wing airfoil. (Stab I'm still thinking about.)[*] 0.5 degrees positive wing/0 degrees stab.[*] 1 degree down/right engine thrust to start. Down thrust built-in, right thrust adjusted through trimming process.

As far as fuse formers go, you should decide whether you want to build the model with foam decks or all wood. There is a good thread of a Supra Fly 60 build here using foam decks that you might find of interest:

http://www.rcuniverse.com/forum/m_9607575/tm.htm

There is also another SF2500 (the large demo version) scratch build somewhere here that would be interesting to check out. I'll look for the link.

I hope this helps and might provide a starting point for your Mystic build.

David

PS If you send me a PM with your email address, I can send you the airfoil suggested that I drew up in CAD. By the way, the airfoils shown all have 1/32" skins as they were to be used with foam core wings. Naturally, a built-up balsa wing would use thicker sheeting either 1/16" or 2mm.