FlooredCOBRA

I originally had a title asking what percent is used when trying to find CG. But now that I am more into my build I figured I would change the title.


I am about to make a plane off the top of my head to see if it will fly. I been thinking of what control method to use so I figured I would use elevons like used on delta wings or flat platform type planes such as the flying stop sign. My question is where do you determine the correct CG for these? What percent from the leading edge?

jumper666

http://www.inlandsloperebels.com/Calc/cgcalc.html

http://www.adamone.rchomepage.com/index5.htm

http://www.nasascale.org/howtos/mac-calculator.htm

http://www.airfieldmodels.com/inform...ulas/index.htm

http://www.airfieldmodels.com/inform...amic_chord.htm

FlooredCOBRA

Aha just what i needed. thanks! I will post some pictures of my contraption when I get it together more.

FlooredCOBRA

Okay so now I am in a bind. I need to post pictures but the camera is out of town with wife. I think I am going to need help with this.

I am making a model hopefully flying model of the Star Wars Interceptor Tie Fighter. I have it built up pretty much the way I want it to look. For test model at least. I am using a flying lawnmower approach for the main wing set up. Prop in front and Elevons in rear. Up front I have a canard stabilizer to hopefully keep the long nose from going in.

So with the canard set up is the CG in the same spot? Does this formula still apply?

FlooredCOBRA

I have the Tie-Fighter complete and will take some pictures with my phone. It came out pretty big but thats the cool part of it. I used pretty thick styro foam i got from home depot. If this works I will clean it up with some thinner foam used in foamies and use thin carbon fiber rods for the front canard. I plan to use transparent covering for the canard to make it less visible and help keep the original look.

It is about 3' long and about 1' 1/2 tall. So far it looks pretty cool but it wont mean nothing if it wont fly. I am totally making this off the top of my head. But if it does work it is Very simple to make again.

As for power I have a E-Flight 450 motor and 20amp speed controller. For the prop I will try a 12x6 and see how it goes. I pulled the motor from my E-Flight Edge 540. On the Edge I used a 11 x 3.8 SF and it worked out great. But for this thing I wanted to try a larger prop since it was a big larger. So fa the power feels pretty strong, I just hope it has enough to tug it with all that drag. I set it on the tail nose up and it had enough power to take off vertical pretty quickly. So was happy to see it pull its own weight.

I will take some pictures tomorrow and test fly it and see how it goes. I will probably hand launch it if I can find a good spot to grab it by. Below is the actual model I made it after. Nothing about it should fly but I think with some messing around it will work. I will sure as heck keep trying until I get it down.

FlooredCOBRA

Moderator, Can I get this thread moved to The park flyers section. I thought I was in the correct one when I posted but was in here instead.

Thanks

CWHFSR

I am SO going to follow this. Did you take photos of the entire build process? I wish you luck in a successful flight!

CWHFSR

Oh yea, are you going to have plans or anything if it does work?

FlooredCOBRA

Okay I am back after some testing. I did not take pictures of me building it. But it is very simple to make. Everything is measure by 1' sections and 6''. I can make a drawing pretty easy of it. I tried to keep it simple so I can go back and make more of them.

So anyways I did some testing today after the rain finally stopped. This thing has been a load of fun. I think I crashed it more in one day than I crashed the entire 20 years I been flying haha. But the thing is it crashes so slow so its more or less a funny landing so not bad. every now and then it would break and I would have to get the glue gun out and glue it back. This is my test subject so I'm going nuts with the glue and tape. Normally I would be picky and keep it clean but since it a test one no biggie.

I built this thing with a main wing in mind and a canard wing up front. I never balanced something like this before so this is all new to me. Looking at this thing I see all sorts of things that should not allow it to fly but I am going to ignore them.

As for flying this was the fun part. The very first time i tested it I held it by the vertical canopy in center. Added throttle and let go. Right off it has plenty of power so weight and power doesn't seem to be an issue. It climb about 15' and started to loop over and over very fast in a diameter about the same size ass itself. I gave some down input and it had no effect. I don't think I laughed so hard in a long time to see this thing flipping around like this. To funny. So my CG was off by a tad to say the least.

So I moved the battery all the way to the front and tried again. The same thing happened but I did have a lot more control, just not enough. Full down was not enough. From there I glued on larger elevons to see if I can get more movable surface. It worked and now I was able to control it a Lot better. But it still wanted to loop over but in a different way not CG feeling like before. Looking at my front stabilizer seen it was off and that was one of the reasons to making it want to loop over. It did fine until it got a little airspeed them started to loop over.

So I adjusted it to keep nose down and tried again. This time it flew straight and I was able to move around much better but it ended up flipping back over again. I think I will add some weird way up front on the front stabilizer and see how that goes also. But what I did do was add some down thrust with the motor. I tossed it in the air again and WOW what a difference! Flew pretty good but ended up loosing control of it and it slowly did a flat spin type decent and went in.

No major damage. But I am making progress and even though I crashed a good bit it has been a lot of fun. I had to stop flying because I ran out of day light. I will do some more testing tomorrow if it does not rain. I have plenty more ideas to try out and I am stubborn so I do plan to make this thing fly right haha.

Here are some pictures I took. Its rough but its a start!

FlooredCOBRA

Woohoo it flies!!!! The darn thing flies!!! haha

So what it came down to was my CG, it was WAY off. I had to balance it using the entire front of the plane as the L.E. Weird..
I kept crashing so finally decided t make a small model of it to see exactly where the CG was at. Then I copied it to the big one and it worked first try. I had to tape a bunch of weight to the nose to balance it out. I used what I had laying around like C size batteries AA's and small battery packs and taped it to the nose. Pretty messy but it worked out to test.

Next I will mess around the the actual cockpit and see what I can get away with. I was thinking of trying a foam ball from a craft store or something. Maybe cut out the inside and hollow it out for air. If that is to bulky or messes with air flow I will try something more open. I know what would work but my idea is to make it as close as possible as I can and work backwards from there. I would hate to make a simple cockpit and leave it simple when something better looking would actually work.

Now the next step is to remake it much lighter and relocate the electronics forward so I can remove all the weight I added. I have a couple ideas how I want to do it so will have to test out 2 different versions. After that I will make the final version clean everything up and make it look as close to the model as I can. Put some details in it paint it and so on.

I just cant believe the darn thing flies haha. And it looks pretty cool in the air too. You can definitely tell what it is supposed to be in the air. I'm pretty excited about it.

Oh yeah here is the small model I made. Made it out of foam plates.

CWHFSR

So, do the front spars have to stay on or was that just you figuring the CoG?

FlooredCOBRA

As for the front spar it will have to stay on. I tried to work around it but that would require a much longer main wing. Pretty much from a couple of inches from the front LE all the way to the rear. Then it would look all chubby. I pulled it off just to see how it would fly and it was not stable at all. Once it started falling it did not want to recover, it kept flipping over. I really hate to leave it but that was something I had to add, Bummer.

What I plan to do is make up the front spar with balsa then cover it with clear covering. I dont think it will be to terribly visible in the air with it clear. As it is now you really cant see the stick that holds the motor on while it is in the air.

I flew it again before I lost sun light and it is Very stable and easy to fly. I flew it low and putted around in a harrier and there was no wing rock at all. The funny looking thing is stable. I could not get over how easy it was to fly and with all the weight I had to add. I did notice I had to fly almost wide open the whole time. Once I got up there I could cut it back down to a little under 3/4 throttle. But I think with it cleaned up and a bunch of weight stripped off it will get even better.

I did not try any loops or rolls yet. I was afraid it would break in the air seeing how much its been through. I hope it will be as aerobatic as those small Hydro Plane Boats since they are using the same control surfaces. The cool part is how big it is I think.

Wish I had my camera back so I could have better pictures. But here are two shot with my phone. Not very detail but it is in the air! ;-)

CWHFSR

Very nice!

Is the front spar only to hold the wings together, something that a small carbon rod might do? Or is it for something else?

FlooredCOBRA

Both.

My plan was to use a carbon rod at first to hold all four corners from spreading apart when picking up speed. But come to find out I needed a stab up there.

FlooredCOBRA

I'm starting the second build right now. Had to take a break my hand is cramping from cutting.

This time I am using DOW Blue board foam. I seen the fan fold stuff at Lowes and debated between the two. I went with the 1/2'' Foam for now. I may try fan fold next or order some foam from online. The stuff they had their was pretty beat up flimsy. I will try different versions and see what would build the fastest and work better.

I have the side wings cut out. They seemed kind of on the heavy side so I hollowed the inside out some. Now trying to think of best way to stiffen it up. I was going to try one main spar on bottom of wing the covering over the hollowed out part. Any ideas what would work? I thought maybe fan fold to cover up the sides but then I think I would be back in same boat with weight with the glue and all. I think.

Heres some pictures of what I have cut out so far. Any ideas are welcome seeing I am making this up as I go.

Ion01

That is insanely cool! You might try just running two carbon rods with clear covering between them to make the front stabilizer. This would be plenty strong and would be even harder to seen in flight. Also, I think the hollowed out ball would work just fine! Keep us updated!

FlooredCOBRA

actually after thinking about it I dont think I will use the wings I cut out. I think it will end up being heavy after I cover the holes up. I'm going to go with Blue fan fold and fold it over a spar to give it thickness and strength. I think It would be stiffer once The edges were sealed and a spar in the middle.

As for the front stab I may do that with the carbon rods. If our shop has some, Last time I was there all they had was square rods

CWHFSR

Something else to look for are carbon tubes. They may be a little lighter but just as strong.

How about regular plane covering to cover the cut-out wings? I would think that would be light and would cover nicely. Then again, didn't you say before that the last one didn't seem to have a weight problem? Also, what about just carving out the back of the wing and leave the front solid, wouldn't that help with the balancing? Or if you do carve out the front you can add some lead inside the cut out before covering it up.

FlooredCOBRA

Just got back from Lowes and got some Fan fold. I'm going to put the cut out wings on hold for now.

I have an idea how I can make it lighter build it easier. I'm going to have balsa internals and build up the entire thing. Then cover with clear covering and foam on parts needed. The internals will be a very basic skeleton just enough to give some thickness needed for strength.

The other one started out very light. But to get my CG correct I had to add a bunch of weight to nose. By making the rear much lighter on this one it will move some weight to the nose. My original was light but after crashing it and re gluing about a couple dozen times it was one big glue bomb. But on the bright side it still flew. So anything lighter will be a plus.

FlooredCOBRA

Past few days I been getting off work very late so have not had a chance to work on it. I gave it a shot one night to try to get some work done. I woke up in a pile of blue foam and a spilled Pepsi.

But today I got home at a somewhat decent time and finished putting together the 4 wings. I sat there debating to use wood inside or use foam. I must of changed my mind a hundred times. I cut out some pieces and lay down some foam inside to give strength and some thickness to the wings. They came out pretty sturdy and I feel satisfied with the weight.

So now next I need to make up the side vertical wings that join the top and bottom. After that I can move on to the main Wing and cockpit. I am going to try my best to hide everything inside the cockpit when I get to it.

When I get to the painting part. Is there a brand that works best on foam? I read water base spray paint. This is my first foam plane build so open to any tips out there. Also how much additional weight does the paint add? I am using a E-Flight 450 with 20 amp speed control for now. What is my limit for that set up weight wise?

FlooredCOBRA

Okay thought I would post some pictures of my progress. It is going very slow. Been working long hours so have not had much time. Then on top of that I now have the flu.

I did have the main wing complete but ended up scrapping the idea. It just did not work at all and was flimsy. So I bought some more carbon fiber rods to help stiffen it up some. I think I have better Idea how to go about it and much simpler. I got out of hand and just over done it on the last one. Going to work on second main wing this weekend.

But here is what I have done so far. Not a lot but it is progress. It is very easy to make just so time consuming to get a little bit done.

CWHFSR

I like that detail piece you put on there, looks great.

FlooredCOBRA

Okay so I done a bit more building. It don't look like much but took some time to make the parts. Each part I have to measure cut and sand down. I think It would go faster if I did'nt sand anything. I took a few more pictures. Still dont have the camera back so been using my chezzy phone for pictures.

So far it still feels fairly light and feel pretty good about it. I just have to finish building the LE and TE of the wing and then the front spar and it will be done. Then just have to paint it.

I found finding the right paint has been a real pain. I got the black but cant find any foam safe grey. I am going to use KRYLON H2O for the black. I found that paint worked out good on the foam. Actually that was the only foam safe paint I found out of all the places I been to. I tried Walmart, Micheles, Hobby Lobby. Maybe Home Depot may have some

ALSO to MODERATOR could you please move this thread to the PARK FLYERS section. I hate to keep posting in the 3D thread when it has nothing to do with it.

CWHFSR

I like the way it looks so far. Have you decided how you are going to put that front airfoil on? Is the foam strong enough in that middle area from the cockpit to the wings? having those skinny connectors onto the wings would scare me especially if it flexed. Perhaps some carbon fiber rods in there too?

FlooredCOBRA

Hey thanks.

Yeah there is a carbon rod on the bottom. There is hardly any flex if any in that skinny wing. I was scared about the flex but those carbon rods are awesome. The LE and TE of wing will be build up like I did the elevators. So when done the wing will actually be a long rectangle.

I am hoping they wont be to visible and take away from the main foam part. Trying to keep it looking like the real thing as possible. It will have the wings of the first model but just see through to give the shape.

Its been fun messing with so far.