Building a RC Aircraft with Recovered Control System

[Lancelot59]

I recently extracted the control system out of a severely damaged RC aircraft (a very simple kit deal). It's got two servos, and a pretty good motor, which works out perfectly for me!

I want to build a new aircraft from scratch using the recovered control system. For the fuselage I'm thinking of using a simple truss type frame. Simple enough, but I'm getting stuck on what material to use. Balsa wood seems reasonable because of it's low weight. I can see it being fine for the wing ribs, but I doubt it'd work as well for the fuselage, wing spar and other flight surfaces.

Does anyone know of any materials that are simple to acquire and that will handle the load? The battery is the heaviest part at about 500g, along with the motor.

 

[Cyrus]

Balsa wood is plenty good for the entire airframe.

 

[Lancelot59]

Really? I'll look into getting some then. How about skin materials? Since it's not a monocoque I can get away with something simple. I could just pull a lightweight plastic over the frame and brush glue onto the sides of the bulkheads/members.

Are there any specific materials that work better in this situation?

 

[Cyrus]

Just use monocote, you don't want to be brushing glue and trying to get plastic over things - it's a nightmare.

 

[russ_watters]

You probably want the fuselage and certain parts (leading edge) of the wing to be a little more rigid, so you can just wrap them with balsa sheeting.

 

[Lancelot59]

Just use monocote, you don't want to be brushing glue and trying to get plastic over things - it's a nightmare.

Wow...that monokote stuff is pretty robust. I see stuff being quite useful! A quick question, can it be used to make a gas-tight seal? In this thread there's a fellow looking into making a small airship. Does it make clean enough of a seal to hold helium?

You probably want the fuselage and certain parts (leading edge) of the wing to be a little more rigid, so you can just wrap them with balsa sheeting.

That solves that issue. I've never tried to make an aircraft using balsa wood before, so I'm still trying to learn the ins and outs.

Well I'll take a look around and see where I can get the supplies from locally.

 

[Cyrus]

Wow...that monokote stuff is pretty robust. I see stuff being quite useful! A quick question, can it be used to make a gas-tight seal? In this thread there's a fellow looking into making a small airship. Does it make clean enough of a seal to hold helium?

Probably not, but you can try and coat the seams with something to seal it.

That solves that issue. I've never tried to make an aircraft using balsa wood before, so I'm still trying to learn the ins and outs.

Well I'll take a look around and see where I can get the supplies from locally.

Google building your own RC aircraft, you can find lots of stuff on how to do it. Model Airplane Magazine is a good place to start as well. It's really not that hard. I would just buy a kit and build that instead, less hassle. Crawl, then walk, then run. Get an ARF, then get a KIT, then design your own.

 

[Lancelot59]

Probably not, but you can try and coat the seams with something to seal it.

I'll see if I can find any compounds that will do the job.

Google building your own RC aircraft, you can find lots of stuff on how to do it. Model Airplane Magazine is a good place to start as well. It's really not that hard. I would just buy a kit and build that instead, less hassle. Crawl, then walk, then run. Get an ARF, then get a KIT, then design your own.

I have some experience with an ARF, the same one I took the control system from. I was pretty good with it, until a sewing machine destroyed it.

 

[Cyrus]

You should do what actually blimps do, have air sacks inside the main dirigible structure. Buy some balloons and fill them up (since you know they won't leak). And have the blimp shape hold, say, 3-4 of these balloons inside of it.

 

[Lancelot59]

You should do what actually blimps do, have air sacks inside the main dirigible structure. Buy some balloons and fill them up (since you know they won't leak). And have the blimp shape hold, say, 3-4 of these balloons inside of it.

Sounds like a solid idea. I could leave an opening in the bottom that I could actually insert the balloons in. How can you actually calculate the weight a volume of helium can lift?

 

[Cyrus]

Its just equal to the difference in densities of air and helium, times the volume. My concern with my half-brain idea is that the structure that holds the air sacks could be too heavy at your scale.

 

[Lancelot59]

Its just equal to the difference in densities of air and helium, times the volume. My concern with my half-brain idea is that the structure that holds the air sacks could be too heavy at your scale.

Well how much does monokote weigh? A rigid dirigible could be significantly lightened by carving bits out of the balsa wood (assuming that is what's used). The way I see it, is you have a bunch of ribs that form the shape of the dirigible, and then fill those with cells made of a lightweight material.

This seems like a bit of a design challenge. Will the cells have enough lifting power to deal with their own weight? I'll doodle around and see if I can come up with an effective system.

 

[Cyrus]

Well how much does monokote weigh?

Google that kind of information.

A rigid dirigible could be significantly lightened by carving bits out of the balsa wood (assuming that is what's used). The way I see it, is you have a bunch of ribs that form the shape of the dirigible, and then fill those with cells made of a lightweight material.

Right, and I am saying that's a non trivial weight.

This seems like a bit of a design challenge. Will the cells have enough lifting power to deal with their own weight? I'll doodle around and see if I can come up with an effective system.

Provided the balloons are not neutrally buoyant, yes.

 

[Lancelot59]

Google that kind of information.

Right, and I am saying that's a non trivial weight.

Provided the balloons are not neutrally buoyant, yes.

Well, it definitely won't work if it's too small. Given that the volume increases faster than the surface area, so long as the right materials are used it should be able to lift the frame and control equipment while being a reasonable size. That's if the cells are custom made, were you thinking of using some off the shelf mylar balloons? Another interesting question is how the balloons are going to get into the container. I'm guessing inflate them inside the main body somehow.

I'm drawing up a quick diagram right now, I'll post it in the morning.

 

[Cyrus]

No, not mylar balloons. Just any old vanilla birthday party balloon (Mylar does not have the elasticity to make for a useful balloon).

 

[Lancelot59]

The way I've designed the frame, those won't work. The mylar balloons hold more helium, but the real thing is that they're "flatter". Instead of being spherically shaped, which makes them ideal for this setup. You can just stack multiple banks of these things. I'll post the drawing shortly to help illustrate the point.

 

[Lancelot59]

Alright, this is the quick design. This is just to give a general idea of what I'm going for.

The space between ribs 3-8 are where the balloons would go. That's why I wanted to use mylar balloons, they stack better down this axis. This setup should be able to hold 4 per bank, with a total of 32. It'd be a little over a metre long, although I doubt 32 balloons would do the job.

On the bottom you see what frames 3-8 would look like. A ring, with a circular centre piece in the middle. Four spars would connect to that piece and also help prevent the balloons from slipping through. In case you can't make out the dimensions, the estimated diameter would be about 1.4m, with about 0.2m between each of the containing frames.

In addition there would be 4 spars running the length of the containing frames for reinforcement, and to create a nice flat bottom to mount equipment on. As well as one spar running down the longitudinal axis of the ship.