Scale Plans Reccomendations

[bob152637485]

Hello, I am fairly new to the RC world, but I have been flying RTF planes for about a year now. A friend of mine and I built our first RC plane from scratch, but it sadly did not perform too well. I was hoping to get some recommendations from some of the veterans in the hobby for some plans that would be good to follow. I have a couple objectives for a plane I would like to meet:

1) Fully Scalable. The initial motivation for wanting to get into RC flying is due to my passion for flight. I am currently working towards my private pilot's license, and was hoping to make my own FAR Part 103 ultralight from the ground up. I wanted to grow some building skills before setting out to such a large feat, so I decided that RC versions of my future ultralight would be a safe way to go. That being the case, I would essentially want my RC to just be a smaller version of the future plane, using the same building materials and techniques.

2) Electric. I definitely believe the future of aviation will be in electric motors, with how much denser battery capacity has become. I have seen an electric ultralight done before, so I would like to continue on that path. I do have a decent amount of practice and experience with all of the electronics involved in RC planes, so this part should be fairly easy for me.

3) Light. For those not familiar with FAA Part 103, the empty weight of the plane must be less than 254 pounds. so if I made a 1/5th scale RC, we would be looking at 25 pounds or less. I want to play it safe regulation wise as well, so I will say that this should include the weight of the battery.

4) Power. The full scale version will need to hold not only the weight of the batteries, but also my own weight(about 120 pounds). I want to make sure the smaller scale will handle a scaled version of this weight as well.

5) LOTS of hand holding! I am very inexperienced at reading plans, blueprints, etc. If at all possible, I would like something that has more of a step by step feel, and/or has lots of pictures, cutouts, etc.

I am well aware that there are high ambitions with this project, but I would definitely appreciate any and all advice you may be able to offer!

[fhhuber]

5000 watts is appx 6.2 hp. Minimal power for ultralight aircraft is generally considered to be 50 hp, with 62 hp or more usually being recommended. So you need a 50,000 watt motor to hve a reasonable chance.

However, ultralight and electric man carrying are close to mutually exclusive. The weight of the batteries displaces most of the weight carrying capacity of the aircraft. (or a huge chunk of the part 103 empty weight limit...)
Maybe with another battery technology jump...

Your 25 lb model will need 1500 to 2000 watts appx for flight. 3000 to 5000 watts to be aerobatic.

Nothing in aviation is fully scalable... some things scale better than others. Models tend to have far lower than scale wing loading (thus our EDF jet models don't need150 knots to get off the ground) You have to do the engineering calculations for the structure and as the aircraft gets larger the calculations get harder, because the bigger the wing,the more important it is that the wing can flex under load, to prevent it from breaking. You would have a hard time seeing the flex in a Cessna 172's wing, even under extreme load, but you should be worried if you don't see the wing of a 737 flexing in what feels like smooth level flight. Even with that... we have models with VERY significant wing flexing.

[fhhuber]

There ARE now electric aircraft the size of a C-152 (2 passenger) which have realistic 1.2 to 1.5 hr flight durratin capability per charge. That's good enough for getting flying lessons... not good enough fr cross country flight.
These do not come close to part 103 weight limits.

[bob152637485]

Ok, so what if we were to put the idea of electric on hold for now, and just focus on the idea of a ~200 pound ultralight. Do you feel as though scaling something like that down to the RC world is just not feasible? Also, thank you for the feedback.

[fhhuber]

Ultralights scale down just fine... I have a kit for a "Weedhopper" sitting on the shelf waiting its turn. It will be my second Weedhopper. The first used scale aluminum tube structure and was unflyable because engine vibration made the framework cause terrible radio interference for the 72 mhz AM radios of the time.

[bob152637485]

Great! I'll check out the weedhopper. Any other designs you would reccommend?