Alright, get ready for a big info dump, first on general advice and my own experiences as well as getting started with the hobby, and then specifically about slender deltas...I'm going to try to make this as neat and concise as possible, yet cover all the bases in a hope to get you off to the right start and on the fast track to success. You are starting the hobby with almost the exact same goals and ideas as I had and an emphasis on custom designs just like me, right down to a tee in certain types of planes even. I started in late 2018, and was extremely stubborn about jumping in with my own designs with no real experience in the hobby or aerodynamic knowledge. There was a some waste in time and materials and a lot of frustration, but I still got my own designs to start flying after a few months of hard work and help/advice/studying here on the FT forums. My first more or less successful designs flew in March or April 2019. I know if you follow the advice you get here you'll be flying in a lot less time
The thing that was the tipping point and the key to getting my own designs to fly, was actually taking advice from the from members here and use a free sim to practice, and then build or buy a simple plane that is good for training a beginner(for me it was the Hobby Zone Champ). If you are looking at FT kit to train on, everyone swears by the
Tiny Trainer. If you are set on one of your own designs, I suppose the tandem wing may be a bit easier to work with than the slender delta, but somebody would have to probably build one with you and help you develop it in a way that makes it a good trainer, and also to guide you in flying it/trouble shooting it. I'd probably be willing to do this with my spare 1806 motor once I snag some new foam.
If you want a delta style plane that is easier for a beginner to handle(maybe not a first plane or trainer, but a good second plane) possibly try FT's basic delta, or my Arrowhead tailed delta design(which is really easy to build and fly and has a huge flight envelope that will grow with your skill.) There is printable plans for the Arrowhead, courtesy of
@Grifflyer here
https://forum.flitetest.com/index.php?resources/arrowhead-aerobatic-tailed-delta.93/ (just hit download button. Several members have built and flown this one with great success, so we can guide you through building and flying it. Dig around and you can find FT designs like the Tiny Trainer, FT delta, and tons more custom community designs.
Slender deltas
First off I'd like to say I'm stoked to see somebody other than me with an interest in these
! It's a unique niche in aerodynamic design, and though it's not a holy grail wonderplane and has its own quirks and weaknesses(like anything else), it has enough strengths and character to make a well performing RC plane that's enjoyable to fly and unique. I could link articles and pictures about the HP-115 and vortex lift and all that, but you've probably seen all that if you are even using the term "slender delta", so I'm going to skip ahead and come at this from the angle of how those design principles translate to RC with foam board and electric motors.
control system: If less experienced, I'd assume you'd want a 3ch control system VS 4ch, but I could be wrong. 3ch is easier to build and to fly for a beginner, but it will limit the overall flight envelope(amount of different stuff your plane can do) in certain ways that's a trade-off depending on whether you go 3ch elevons/throttle or 3ch RET(rudder/elevator/throttle). I've built both, and the RET slender deltas area a bit easier to fly for a beginner, but are a little quirky and can teach you bad flying habits if you haven't flown other planes before. This version can't really do rolls, but it can loop, fly around, and do high alpha(high angle of attack/hovering) very well. It needs dihedral in the wing tips, which makes turns a bit choppy if you don't do them right, but gives you some self-leveling, which is a plus.
Elevons on the other hand are a more realistic feel and give you full roll control(the axial rolls are like a drill-bit! nothing rolls as fast as a slender delta with powerful elevons) and nice graceful turns and banking, but are a bit more temperamental to slop and touchy for a beginner to fly. If you have 3ch elevons and no rudder, it limits your maneuverability and control while in sustained high alpha. 4ch gives you the best of both worlds, but is extra weight for the servo, a bit more work on the build, and harder for a beginner to fly.
Powerplant: No matter what size and scale your slender delta is at, it will want a motor that's on the larger/more powerful end with an aggressive multi-blade prop to get the full flight envelope potential. Slender deltas need "excess thrust" to meet their low speed and high alpha potential. Also, although slender deltas with a lot of wing and not much fuselage can be very light on wing loading when you do the math, they are still a bit sensitive to weight and will prefer a lighter battery. On 3s with a 15-17" span by 28-30" chord/length wing, my slender deltas have handled much better with a light 650 mAh batter as opposed to a heavier 850. With the 1806 motor, they fly well enough, but have some difficulty and wing rock in high alpha. 2205 or 2806 is enough power with an aggressive 5x5.5x3 prop to have an awesome flight envelope, but your flight times on 650 will only be a few minutes. So basically, your bird has to be a bit overpowered with poor "fuel efficiency" to get its best flight peformance.
Location of prop is also important, and a hard choice with slender deltas. A tractor is basically out of the question due to torque issues and air flow. I used high-mounted pushers. Great on 30" long designs, but go bigger and it is too far away from your control surfaces to give good prop wash, so your handling and control decreases. A prop in slot is hard for smaller models for durability and giving up precious lifting surface area on your skinny little wing. A straight rear pusher will be hard to get CG and require extension cables of various types to get you battery all the way in the nose while your prop is at the back. Also, little to no prop wash on that setup. I'd say if going with a prop and not EDF, the high mounted pusher is the easiest for a smaller plane, and a tail nacelle on the vertical stabilizer might work good on a bigger bird so you get great prop wash right over your control surfaces.
Flying, we'll talk about that when you've got something ready to maiden, or I can address any specific questions before this post gets too massive.
