Design Log for 2-Place Touring Plane

[niccof]

I've been spinning around designing an airplane off and on for a couple of years now. The biggest inhibitor of progress has been getting distracted by the shiny new idea that popped into my head, so I'm starting this log to set a stick in the mud and have some degree of accountability for progressing once the excitement of the original idea wears off.

One of the reasons I kept stopping on many of my previous concepts was I continually found myself succumbing, step by step, to the subtle allure of scope creep. In the moment it is easy to spend a few extra imaginary dollars for extra performance and, oh while I'm at it, this should probably be carbon fiber because stiffness is important and flutter would be bad and retractable landing gear can't be that hard to design...

Mission and Reality Checks
Ultimately, the goal for this project is to actually make this hypothetical airplane into a real, flying airplane and not a series of numbers on an excel sheet. To that end I've created a list of constraints and requirements that should help keep me on the rails here. Oh, and a mission. Simplicity is going to be the name of the game here. Side benefit is that simple is usually less expensive than complex.

• Mission - VFR day trips for the famous burgers or sight seeing in areas of interest with a dash of short cross country flights in there. Range is notionally around 500 NM (sans reserves) and really is going to be more limited by time in the air. A few hours straight in a small plane is enough for me, and most likely my bladder.
• Conventional Layout - Pretty straightforward here and that's the point. Engine in the front, tail in the back, people and wing in the middle. I've toyed with pushers, asymmetric designs and even a Facetmobile-esque design. Pushers have too many drawbacks in my opinion and I am simply not sufficiently skilled or experienced in aircraft design and construction to "push the envelope" with more exotic configurations.
• Fiberglass Moldless Construction - This one is mostly a budget check and somewhat dictated by the space available to me. I'm making this in a garage and I can't store a dozen airplane sized molds along with an airplane sized airplane and still have space to work. Moldless is going to be the method of choice for the majority of the aircraft because it is a well documented process and for a paletable cost I can build a series of test pieces to check the strength and consistency of my methods against predictions. I want to know with a high degree of confidence that I can consistently produce quality parts.
• Fixed Tricycle Gear - I'm not anticipating this aircraft to be fast enough to make retractable gear worth it. That and more mechanisms means more design work and more things that can break and more money etc..
• Ground Adjustable Propeller - Yes the efficiency offered by a $12,000 constant speed propeller is oh so enticing, but I haven't IPO'd my AI enhanced crypto blockchain marketplace yet, so I can't afford one. Even if I could afford it that is one more "complex" thing that is likely a poor balance of cost-per-performance.

Design Goals and Constraints
The "reality check" section above is mostly composed of constraints imposed by me, by choice to help keep the airplane more in line with my budget and skills. This section is more focused on the specifications of the aircraft and constraints imposed on it by my shop.

• Length < 18 feet - My garage is 19 feet long and about as wide. There's some stuff in there that cuts down on those dimensions a little, but I've worked out that I can realistically finegle an 18 foot long fuselage in there. This includes the firewall forward, but not the prop and spinner, neither of which I'm expecting to have on the aircraft for very long while it is in the garage.
• MTOW < 1320 lbs - After spending some time collecting specs on similarly sized aircraft and iterating through little Raymer's equations for preliminary sizing the length limitation puts my MTOW in the ballpark of LSA category aircraft like the Sonex and RV-12. That could really limit the useful load, especially if the empty weight ends up around the RV-12 end of the spectrum (about 800 lbs depending on equipment). Ultimately, I think this is acceptable given the mission parameters, but weight is really the enemy for this aircraft.
• Engine: Rotax 912iS - I'll admit I was already leaning towards a Rotax, but once I identified the above constraints it seems like the most logical choice. Many LSA category aircraft use it and the fuel efficiency is about as good as it gets. Bonus points for single lever control. The fuel efficiency and low installed weight are the two factors that ultimately made it the baseline engine. Low installed weight is obviously good when MTOW is limited, and the low fuel consumption in cruise means I can get by with a resonably small tank (most aircraft in this category are around 20 gallons).
• Removable Wings - Since I'm building this in my garage which is not connected to an airport I will have to trailer the aircraft to one. This combined with my garage not being the size of a T-hangar means the wings will have to be removable. This doesn't mean it has to be a trivial process, but I can't glue them to the fuselage or something. Trailering also means the max width for anything I can't take off the aircraft is 8 feet, though 7-7.5 feet is probably a little more practical.
• Plain Flaps - About as simple as it gets for flaps and that is one of the goals for this aircraft.
• VS1 < 55 Knots - This one is kind of an arbitrary limit but I'm putting it here for a reason. I've heard that in the event of a crash it is best to be going as slow as possible. I haven't personally tested this and I would love to continue not testing it. That said, to the best of my abilities I want to design a crashworthy aircraft, and then also never actually crash it. A nice side effect of this low stall speed is that the large wing area it demands will help takeoff and climb performance.
• Rate of Climb > 1000 FPM - In line with similar aircraft. It's nothing to write home about, but this is a threshold value.
• Standard Cruise > 120 Knots - This one is a low priority but I also don't think it will be a design driver for a reasonably clean composite aircraft with faired wheels. It is here for the record.

I think that about sums up the design goals and constraints. There might be a few stragglers or something I forgot to mention. Next post I'll put some of the actual numbers up here with some comparison aircraft in the hope that y'all will check my assumptions. Oh, and if it wasn't obvious my "AI enhanced crypto blockchain marketplace" is not actually a thing.