Devin -
You are about to hear a common refrain; so let me be the first to start the chorus: Get the biggest air-compressor (tank-wise) that you can. :D
I have a 26-gal upright Craftsman that I bought about 7 years ago on sale. It comes on at about 110 psi and cuts off between 140 and 150 psi. If I'm using an air drill (at 90-100 psi) then the compressor will come back on every 15-20 holes that I drill. Unless you have a separate shed/room you can put the compressor in, you will come to be annoyed at the compressor running all the time. Even with short bursts of drill noise or rivet-puller puffsyou can still hear the radio (or your music-playing device of choice) when you have hearing protection on. But once most modern compressors kick on, their continuous racket drowns out anything else for many minutes at a time.
Air drills
really suck down your tank - much more than anything else you'll use when building a Sonex. For thin materials you can get away with using a cordless drill if its powerful and you use sharp drill bits. But thicker materials really benefit from a fast-turning drill. You'll find you get much better holes & results from an air-drill on anything that's major structure. RPMs are much slower on a corded or cordless drill, and high RPMs + moderate pressure are what give the best results with a soft metal like Aluminum. They also leave less of a bur to get rid of (and trust me, you will be tired of deburring holes by the time you complete your project!!)
IMHO, there are essentially 4 tiers of air drills: Super-cheap crap, Cheap-but-usable, Somewhat expensive and nice, VERY expensive and slightly nicer. Skip the lowest tier. The price difference between the bottom two tiers is maybe $20 or so. You can get "tier 2" drills from various supply shops for around $50 - $60. That's where I started, and it worked OK for me for awhile. Then I saw a sale on the 4000 RPM ATS Pro Palm Drill (
https://www.aircraft-tool.com/shop/deta ... D=ATS61101). It was double the cost of my original drills, but I was getting tired of my bigger air drills and thought the ATS might be a little lighter and fit in some slightly tighter spaces - so I took the plunge. WOW, what a difference! I have since bought another one, because I like them so much. I literally have never used my original air-drills since I switched. The palm drills are definitely more maneuverable and spin faster; but the biggest benefit is their light weight! A heavier drill really makes it harder to keep your drill bit in proper alignment with the parts (especially as you start working on big assemblies and aren't drilling straight down all the time). The light weight also saves a bunch on hand fatigue over time. Finally, I find that the "palm" term is accurate - I often now drill with my middle finger on the trigger, so the heel of my hand can slide up on the drill grip and press straight along the axis of the drill bit (rather than pressing with my hand down low on the grip, which can make the drill want to cock at an angle, especially when the bit breaks through to the far side of a piece and the resistance suddenly changes). I've handled (but never used) a Sioux or other $300 - $400 drill. They felt really nice, but honestly they didn't feel like 3x or 4x better than the ATS palm drill.
BTW: Why two drills? Well, its often handy to have a short drill bit and a long drill bit of the same type chucked up and ready to go;
or to have a #40 and a #30 chucked up at the same time to make it easy to switch back and forth (or if you are lucky enough to have an assistant and 2 air hoses, one of you does the #40s while the other person follows behind and does the #30 holes - but be sure your compressor can keep up).
For most other tools you can go with simple & cheap - my Harbor Freight riveter is still going strong after 6 years; although you have to tweak it and then lock the adjustable components very tightly to stop it from annoyingly and frequently falling out of adjustment.
I hope this info helps, and feel free to ask if you have further questions or want clarification on anything!
--Noel Wade
Sonex #1339
TD, Center-Stick, Acro-Ailerons, Turbo AeroVee, Flush pulled rivets
Wings & Empennage complete, Fuselage nearing completion
P.S. I see that others are starting to talk cordless drills. While you
can use them, do understand that the weight and size of a cordless drill can be fatiguing and/or a hindrance. They also lose RPMs as you use up charge with each hole you drill, so be prepared to invest in a couple of spare batteries! As I said above, I use my cordless drill for thin materials and when I only need to drill a couple of holes in a part. But for thick items or anything with a lot of holes (such as skins), a compact air drill is a much faster & nicer solution!