Alexia said:
i did the math. if i build the whole thing like an oversized model i can easily do it under $1k.
rebuilding a car was my original idea but that would be over 10x as expensive. i had my eye on a 1964 DeVille but it was in bad condition and cost almost $5k, nevermind that i don't even have a single piece of proper equipment to work on it or the finances to keep its gas tank full. besides, my dad never had a cool car that he'd one day pass on to me. that made me really sad and is part of the reason i decided to forget about it and come up with something else.
I can agree with you about the cost of a car. I'm rebuilding a '31 Chevrolet as a street rod in my garage that used to belong to my wife's grandfather. The car was $9k (had to buy at auction to support her grandmother being in a home), engine and transmission was $5k, rear end was $3k, wheels alone will be another $3k...I'll be into this thing for probably $40-50k by the time I'm done.
With that said, don't think you can build a plane like an oversized RC model. Engineering and physics does not always scale in a linear fashion, i.e. sizing up beams to 10X larger does not mean they can handle 10X the load. I have formal engineering training, please understand I am not speaking off the cuff. I have had classes in statics and dynamics, thermodynamics, and that is the limitation of my mechanical engineering and I wouldn't try taking on building a home-brew aircraft because I know the challenges and difficulties. If you have all the aerodynamics engineering training needed to design an aircraft from scratch, then I won't tell you no, but I have yet to see any information that indicates you understand the magnitude of your undertaking.
i think you underestimate my abilities. the only time consuming issue is sourcing the materials and the only real issue is trying to find a propeller. seriously, it seems like it's impossible to buy a simple wooden prop anywhere.
for a powerplant i thought about one of those 20hp single cylinder gokart engines. it has enough power and light weight (not to mention low price) so i can't see why it wouldn't work.
the whole thing being illegal is absolutely the last thing i care about. i mean, i don't care about that at all.
i already built an RC model when i was 12 and once i figured out how to get it in the air with its underpowered stock motor i flew it like it was nothing. keep in mind, that wasn't one of those toys that uses differential thrust steering. it was an actual model with 100cm wingspan, elevator, rudder, and ailerons. if i was able to fly that underpowered model on my first try without any training at the age of 12 then i should be able to fly a real plane. after all, laws of aerodynamics are exactly the same for a small model and a huge jumbojet
Your abilities to build something is not something I am going to call into question. What bothers several of us is that you haven't given indications that you understand the implications here. Getting a propeller isn't hard--a carbon fiber model would likely be your best bet as wooden props are heavier and require a lot of work from the manufacturer to make one that can handle the stress without blowing apart. Even with that, you'd probably be looking at a minimum of $1k for a prop (look them up online, they can be had).
For a powerplant, I don't think 20hp will do it for anything beyond an ultralight aircraft (i.e. powered hang-glider with a seat under it). A full aircraft will need a lot more power just to overcome the additional drag of it's size, generate enough speed to get the lift needed to get airborne, etc. The Wright Brothers were able to get their plane in the air because it had massive wings that were basically fabric stretched over the smallest skeleton of wood. They didn't get enough speed to stress the airframe to breaking point. They still risked their lives getting it in the air.
As for legality, there's a lot you can do in the ultra-light arena without needing much government oversight. Still, if you want to get a full aircraft built and try to find somewhere to get it off the ground, good luck. Be prepared to faces fines, arrest, confiscation of your craft, and possibly jail time for going against the rules. Those rules are in place to protect the public, not you. I'm a licensed skydiver, I can't just jump into any given location on a whim (exiting aircraft due to emergency is a different matter). There needs to be a NOTAM (notice to airmen) filed to let other aircraft in the area know that jump activity will be taking place, and most places not designated as drop zones will require several million in insurance coverage to give you permission to land there to cover you possibly hitting someone on the ground and injuring or killing them. I get zero coverage on my life. I'm only a couple hundred pounds of weight, imagine the damage a full-size aircraft can do.
You last paragraph is what gives most of us pause. Getting an RC aircraft into the air isn't a big deal. You run it into a few things or do some low speed crashes, no big deal. Getting something off the ground and flying it around isn't a big deal. Landing anything safely IS a big deal. Handling emergencies is important training. Early flight training teaches you basic control of the aircraft, takeoffs and landings, and emergency procedures. Navigation, communication via radio, etc. is all secondary. As a skydiver, 98% of our first jump course is recognizing and handling emergencies. Keep in mind that if you screw up a landing with an RC aircraft, it just cost money to repair or replace. You screw up a landing in a full size aircraft, you get seriously injured or die.
Yes, the laws of aerodynamics are the same for a small model as a huge jumbo jet. The laws of aerodynamics do NOT scale in a linear fashion from a model to a jumbo jet. Drag and the power required to overcome it is a major factor. Look at high performance cars--why is it that a 40hp engine can get an old VW on the freeway up to 75mph yet putting a 400hp engine in a car doesn't get you 750mph? Why is it supercars with well over 1000hp top out under 200mph? It's not a linear scale. Also, items that aren't major effects for small RC models (ground effect is one that comes to mind) are a real issue with larger aircraft. Get the education you need before undertaking a project like this, please.