The first step in any buld is basic design considerations. Things like size and weight aren't just a consideration for such mundane considerations like transportation, but also compatability with radio and powerplant components are also a critical consideration. When I first envisioned building a F-23A, I was thinking about about making it the same size as my Freewing F-15 which is ~ 1:17.7th scale. The F-15 sizes out to about 44 inches long and a wingspan of about 29 inches. A F-23 built to the same scale is 48 inches loninches has a wing span of 29.5 inches. This is a perfect size since it'll fit easily in the back of my SUV and will leave me enough space to bring a couple more airplanes.
To make sure that this was a good plan I printed out some engine mount bulkheads to various scales. To my surprise, the engine bays in the F-23 are quite streamlined, with minimal structure around them, not doubt for aerodynamic and signature reasons. So at roughly 1:17th scale I could clearly see that even a 64mm fan would be a very tight fit and I'm not certain that a 70mm fan would work at all. Another consideration is that the nozzles aren't placed right along the centerline at the end of the fuselage like previous generation of fighter designs but are run through troughs. The only way the bigger fans will work is by placing their thrust lines considerably lower in the fuselage and this would require exhaust ducting that bends upwards then straightens out which would undoubtedly incurr a performance penalty and would require larger nacelles. The latter is highly undesirable because I really want to capture the gracile lines of the production jet.
As you can see in the above photo, there's very little room to work with and a key consideration is running of electronics and associated wirring as well as I'm planning on belly landing and I'd feel much more comfortable with a smaller hole in the bulkhead. Printing out some more sizes I saw that while I could go up to say 1:15th scale and run 64mm fans, I'm not convinced that the jet would be much lighter than going a bit bigger and choosing a high performance 70mm setup. So more printing I came up with this:
The above photo is 1:12.6 scale and as you can see the 64mm fan is now the same size as the actual duct opening. A 70mm fan should fit fine! The good news is that the inlet, minus the diverter cone, is about 117% of the FSA of the changesun 10 blade fan Im looking at. While a bit bigger than I was planning its still manageable for transportation and stowage with a total length of 70.5" and a wingspan of 43.5".
Finally my last concern is my approach to construction. I've seen various methods and one in particular was appealing since it seems to be fairly easy and straight forward. This approach is to cut out the plan-view shape, wings and fuselage, in one lage piece of thick depron then attaching bulkheads as required to form the basic shape. The jet would then be skinned with thin depron. As I've seen on build threads on the various RC forums, this approach looks to be too heavy. So I'm leaning towards a more traditional bullet up approach by using bulkheads strung up along a jig with longitudinal stringers for the basic structure, certain areas will have extra support such as the radio and battery compartment along with the ducting as well as the engine mounts. Most of the bulkheads will use 6mm or maybe 9mm depron with some reinforced with light plywood. While I'm failry convinced that's the way to go, I was not sure if I had enough bulkheads on the scale plans I have. So to make sure I printed out the two side views that shows bulkhead placement side by side and it appears to me that I should have enough:
I apologize for the poor lighting but you can see I have about 28 locations although some are too close to each other to be usefull.
All I have for the next few days, stay tuned as I'll be starting up the profile "PAV" here real soon.
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