Chitty Chitty Bang Bang!

[altbob]

I am attempting to teach myself Sketchup in an effort to make a 2D flyer of Chitty Chitty Bang Bang. I'm hoping someone out there in FT land has the same passion I do for seeing something like this actually fly and is willing to help me with using Sketchup.

The plan is to have a pusher prop, put an elevator hinge on either the front or rear horizontal stabilizer and as for a rudder, I was thinking the wheels could actually be made as separate circles and be hinged to turn! The stubby wings may not give enough lift when the weight of a motor and battery are added, so I am keeping open the possibility of putting 3-bladed autogyro props on the ends of each wingtip.

Feel free to jump in!

I seem to be hitting all sorts of walls with the program and it's taken me about 20 hours to get just this far:

 

[Flynn]

I did some searching and found this. He has some plans linked on his page. I'm sure you could try in dollartree foam

http://www.flyelectric.ukgateway.net/chitti.htm

Ain't the Internet great?

 

[altbob]

Hey Flynn, believe it or not I found that Chitty on the web too, and it's really nice and clearly a lot off work, trial and error went into it. But I really think I can do better with a 2D foamie and am determined to at least try. My main problem in sketchup right now is drawing surfaces and finding out the corners don't join up or parts that I want to cut away can't be. I'm sure it's something obvious, but I'm finding sketchup difficult to learn. If anyone is willing to lend a hand I would be very grateful to send them my file to look at.

 

[rcspaceflight]

A profile style of plane is probably the way to go. I agree with that. I think you're either going to have to make the wings a little bigger or go with a very light set up. Possibly both. You can increase the wing size an inch or two without changing the overall look.

Keep at Sketchup. Once you learn it, it's an extremely valuable tool. Not just in this hobby. My biggest advise with using Sketchup is to group objects together. If you have the wings and fuselage "exploded", then they will stick together. If you try to move one, it will take the other with it. If you make the wings a group and the fuselage a group, then you can move them separately. When you want to create tabs and slots, only explode one of the objects and keep the other grouped. Then when you cut out the slots, then re-group it and explode the other and add the tabs. It's a mandatory process.

If everything is exploded and sticking together, you don't have to start over. Just select a side, copy it, paste it somewhere else, and then add thickness to it again. Then group it right away.

I hope that advise helps. Because learning the software is going to help you out further down the line.

 

[Flynn]

Hey Flynn, believe it or not I found that Chitty on the web too, and it's really nice and clearly a lot off work, trial and error went into it. But I really think I can do better with a 2D foamie and am determined to at least try. My main problem in sketchup right now is drawing surfaces and finding out the corners don't join up or parts that I want to cut away can't be. I'm sure it's something obvious, but I'm finding sketchup difficult to learn. If anyone is willing to lend a hand I would be very grateful to send them my file to look at.

Yeah after I posted that I said, well that really didn't answer his question, sorry bout that.

 

[altbob]

Yeah after I posted that I said, well that really didn't answer his question, sorry bout that.

No worries man, I appreciate any help at all! I appreciate all contributions!

 

[altbob]

A profile style of plane is probably the way to go. I agree with that. I think you're either going to have to make the wings a little bigger or go with a very light set up. Possibly both. You can increase the wing size an inch or two without changing the overall look.

Keep at Sketchup. Once you learn it, it's an extremely valuable tool. Not just in this hobby. My biggest advise with using Sketchup is to group objects together. If you have the wings and fuselage "exploded", then they will stick together. If you try to move one, it will take the other with it. If you make the wings a group and the fuselage a group, then you can move them separately. When you want to create tabs and slots, only explode one of the objects and keep the other grouped. Then when you cut out the slots, then re-group it and explode the other and add the tabs. It's a mandatory process.

If everything is exploded and sticking together, you don't have to start over. Just select a side, copy it, paste it somewhere else, and then add thickness to it again. Then group it right away.

I hope that advise helps. Because learning the software is going to help you out further down the line.

I'll post an update on the wing soon. I figured out how to put a camber in it that might work. I can also try using the scale tool (?) to lengthen the wingspan a little and hopefully this won't throw off the appearance too much. Still have to figure out what to do about that front canard. Not sure if it should be a control surface or just be used to add lift. A front lifting canard will probably create all sorts of turbulence and induced drag on that wing, which will be just barely adequate as it is. A control surface might make more sense, but I'm not sure about how control surfaces in the front will work on a pusher prop setup. This could get interesting...

I'm continuing to struggle with Skeptchup...I am using groups and components but I keep getting weird results. Things don't select the way one would always expect. I'm surprised there isn't a command that you can use (like holding down the ALT key or something) to force a line to draw on a particular axis or on a particular face. I'll keep working at it...I'll watch some more youtube tutorials today...

 

[altbob]

What I'd like to do with Sketchup is cut a section of the foam board out. Drawing a line on a face does not go all the way through to the other side. What would be the equivalent of a virtual x-acto knife?

 

[rcspaceflight]

What I'd like to do with Sketchup is cut a section of the foam board out. Drawing a line on a face does not go all the way through to the other side. What would be the equivalent of a virtual x-acto knife?

I usually cut out a slot and then use the pull tool to pull it to the other side. You could do the same if you're cutting a piece off. Or you could copy and paste it then re-pull it to the 3/16th thickness.

Oh, and Sketchup can snap to the green, red, or blue axis when drawing, but it's rather picky. I too wish I could push a button to force it to one of those three options. Generally I find it easiest to go to the top view and draw everything out on the floor. You could also make a giant square and draw on that. It's likely to stay on the face of the square when drawing out a shape. Then you could copy and paste the shape.

One thing I have found with the rotation tool is that it's a lot more likely to snap to the green, red, or blue axis when the point of origin in the software is between the piece you're rotating and the camera.

 

[altbob]

The issue I seem to be having with cutting out slots is the lines don't seem to end up on the face. In this project I'm trying to cut a slot for where the canard will go after placing the canard on the body. I make lines but they seem to go off into space somewhere. Anyway, I'll try to figure it out. Meanwhile, I did some work on the wings today, putting an undercambered airfoil and 5 degree dihedral into them. Here's what that looks like:

 

[altbob]

I usually cut out a slot and then use the pull tool to pull it to the other side. You could do the same if you're cutting a piece off. Or you could copy and paste it then re-pull it to the 3/16th thickness.

That was really useful, thanks!

One thing I have found with the rotation tool is that it's a lot more likely to snap to the green, red, or blue axis when the point of origin in the software is between the piece you're rotating and the camera.

I'll have to try that. What makes me crazy and I still don't know how to fix is when I draw a closed polygon and yet Sketchup does not recognize it as a face. How do you deal with that?

 

[rcspaceflight]

I'll have to try that. What makes me crazy and I still don't know how to fix is when I draw a closed polygon and yet Sketchup does not recognize it as a face. How do you deal with that?

I'm 99% sure I know that you're talking about. It's something that's annoying. I just draw a diagonal line. Usually that will add the face and pretty much show you why it's not quite working. For making plans it being that "little off" is fine.

 

[altbob]

Yeah, it's something like that. Sometimes I can figure it out, looking very closely I can see where two lines don't actually touch. Other times I search and search and try everything and there just doesn't seem to be anything wrong with my polygon, but Skeptchup refuses to consider it a face. I definitely made things harder by adding a texture material to my fuselage/car body. I might just go ahead and redraw that as a flat plane without any texture... Sadly I don't see a way to flatten it out or delete the texture once you put it on.

 

[altbob]

So I went ahead and did a redraw. Now my problem is that I am trying to intersect faces to get the shape of my airfoil on the side of the fuselage so I will know where to cut, and the intersection line keeps appearing on the wing instead of the fuse. This is driving me a little nutty! Help!

 

[altbob]

Well, I'm putting Sketchup aside for a day just to clear my mind...I swear when I woke up this morning everything in the room seemed to be outlined in dotted blue lines. That's a sign that you need to step away from the monitor for a while....

So for today's task, I made a paper model, about 1/5th the size of the actual Chitty 2d Flyer I ultimately want to make, and did some down and dirty glide testing with it. After some messing around with the control surfaces I found that I could manage consistent straight and level toss glides of about 2 feet by adding just a touch of up elevator to the horizontal stab. Having said that, the paper model also stalls very easily. Once power is lost, if it has any vertical pitch is stalls like crazy, and if I toss it with a degree of downpitch forget it, it's crash city! Making the wingloading light enough to fly the actual plane gently is going to be a stretch.

The wings on the paper model were printed from my Sketchup design. The other parts on the paper test glider were just eye-balled. The resulting model is a bit too short, and the rear stab is a little undersized, but I don't think lengthening the fuse/chassis or enlarging the stab/elevons is going to make things worse. If anything those will be improvements (hopefully!)

 

[rcspaceflight]

Now my problem is that I am trying to intersect faces to get the shape of my airfoil on the side of the fuselage so I will know where to cut, and the intersection line keeps appearing on the wing instead of the fuse. This is driving me a little nutty! Help!

I think if you explode everything, it will cut everything up that is intersecting for you. So you could explode the fuselage and the wings and then select all of the faces on the wings and then paste it. (Hold "Shift" to select multiple pieces. You do not have to have the outlines of a face selected. If you copy and paste a face, it will automatically draw the outlines for you.)

 

[rcspaceflight]

Having said that, the paper model also stalls very easily. Once power is lost, if it has any vertical pitch is stalls like crazy, and if I toss it with a degree of downpitch forget it, it's crash city!

That does not mean it won't fly well. That just means you'll have to know how to fly it. If you know a plane is going to fall out of the sky if it drops below 5mph, then you just keep it above that speed. It's actually a common tendency for planes to just fall out of the sky if it goes too slow. Each plane just has a different definition of "too slow". Bad things happen when a Boeing 747 "flies" slower than 100mph.

 

[altbob]

Thanks man, I really appreciate the help. I got pretty frustrated and ended up redrawing a huge portion of the model to get it to do what I wanted it to. Part of the problem I think is that I don't really understand all the pros and cons of making something a group. It was making me crazy that I could intersect faces and get the lines from part A onto part B, but not the other way around. I tried everything I could think of for about 2 hours...!

Meanwhile, back to Chitty - the proof of concept model seems stable in roll and yaw. Pitch is a little dicey, probably because of the front canard...which is a liability I am willing to put up with for now, because it's so integral to getting Chitty to look, well, like Chitty! My hope is that with actual moving control surfaces I can learn to avoid nosing down into an unscheduled dive, or nosing up into a stall. As you say, there is going to be a certain stall speed to any model. I'll be happy if this can just make gentle turns and fly slowly enough that you can really tell what it is as it goes past. I'm definitely not expecting acrobatic performance here

The good news at any rate is that the wings really work well. A gentle toss results in lift and the model floats along for a few feet and lands level. That's very encouraging

 

[Montiey]

I would be impressed if this works..

Good luck!

 

[rcspaceflight]

Basically making something a Group makes it no longer editable. If you're using Sketchup to design a house, then you for sure want to make all of the furniture separate Groups so you can move each piece around individually without changing the piece of furniture it's self. When designing planes it's great for moving the wings, stabilizers, and fuselage around without changing any of the individual pieces. Once you have everything where you want it, then it's great to explode it all.

Sorry about the confusion. I just like to keep things Groups so I don't accidentally change the individual pieces.