You know how said I’d never 3d-print Chuckranoplan again?

Well, technically I didn’t say that; I just said I’d never print a whole model except for geometry studies and laughs. However, I still intend to use the capabilities of MaB where it would make things convenient. Some of those Areas of Convenience include the front and back of the fuselage. Planes and ships alike are usually pointy, but that implies curved surfaces that I don’t really have the patience to carve by hand.

So here’s a picture of the biggest thing by enclosed volume that MaB has ever printed.

The hull of 0004 is about 4 inches square. The tapered portion of the nose is 7.5 inches long by itself, and that’s just a bit under my 200mm maximum Z axis travel limit. The above print is just a raw single shell export of the nose, with no internal ribbing features. And it definitely shows in the wobbly, bowed sides and corner splits. This was mostly a quick test to see if MaB would even be able to pull it off.

The answer: Yes, but just barely.

This revision has lots of internal ribbing added to keep the sides stable as the whole thing is built up. Those indents in the back are eventually where I’ll mount the pivot hinges for the ducted fans. The total weight of this thing is about 1.8 ounces.

What this view doesn’t show is some of the back corner lifting that occured. When you’re building a part this huge without surround-heating, inevitably the thermal stresses in the plastic rise above what the masking tape interface can handle.

It seems like the largest parts I can realistically make without that warping are about 3″ x 3″, or something like 50% of the way up this part. So I might actually not print off the entire nose of 0004 at once. I might take another cross section at said 50% mark and make the back 50% from foam. It’s probably better off that way, since I don’t particularly trust a thin wall plastic part to hold onto a pair of screaming ducted fans. The result would be that only the tip of the nose, about 3-4″, will be hollow ABS.

So what’s this thing going to be made of anyway? I spent a bit of time splitting the parts up into their different anticipated materials to get a better weight estimate:

I swear that is not the final color scheme…

Most of this thing is going to be chunks of blue Home Depot XPS insulation foam (or pink – it could end up pink, depending on which one I see first!). The tailplane is “wing stock” EPP foam, shown here in white, and the vertical stab is balsa. The balsa tail is surrounded by two hollow shell prints that round out the stern area. I’ve also thrown in 4 A123 cells for kicks, though realistically I might use a 4S / 3Ah lithium polymer pack for maximum energy density. The A123 cells are easily available, but not that energy dense. The little HK939MG servos I got were also meticulously modeled and inserted.

I also modeled the HK3720B 70mm EDFs. I got a chance to actually spin one up…. and it’s beastly. A pack of them can probably take on Fankart, and I’m tempted to buy like 10 more because why the hell not. I definitely got one up to almost a kilogram of thrust, and I was running into the power supply current limit.

The calculated weight of everything shown is about 2.5 pounds, with slightly low estimates for foam density. If I assume the foam is closer to 1.3 lb/ft^3, the weight increases to about 2.8 lb. The two EDFs by themselves outweigh the entire superstructure. I still find it mildly wrong to think about something 1.2 meters long only weighing 3 pounds.

But, in other words, 0004 will have a greater than unity thrust to weight ratio with both fans installed. If it still fails to do anything, I’m going to commit a very slow and ritualistic suicide somehow involving a waterjet (because that would be the best way for someone like me to go, right?!). This thing better hang itself in the air for absolutely no reason.

Still looking for feedback from real Crazy R/C Airplane People… I know at least one of you read this site!

I speak as if I’ve built it already, crashed it, and am in the process of rebuilding it.

Sadly enough, this is not the case. With CPW activities in full swing, I’m pushing the fleet around all over the place for demos to prefrosh. In the mean time, I’ve been slowly planning out the advent of Chuckranoplan 0004, which will be my first attempt at building a large model. I’ve been skulking around the rcgroups forums extensively looking at other peoples’ builds (sadly, not many of GEVs, but the ones that have been built are pretty awesome). I also purchased a copy of the WhizzyWIG build plans, which I have found to be less than helpful since they’re geared towards advanced modelers. It amounts to me handing someone random a 3-view technical drawing and telling them to “make it” – it presumes a certain amount of knowledge about the subject which, if present, would greatly aid the “making” process, but otherwise would probably cause more confusion than anything.

At least it’s a massive print, so I can hang it on my wall as a poster and occasionally stare at it to sanity-check my own design.

To recap the goals for 0004, they are:

• 4 to 5 foot length overall (LOA)
• Using the hot wire foam cut approach with cross section templates and a hotwire cutter I have yet to build
• Weight of under 2 kg absolute max
• Actuated control surfaces including flaps (flaperons?), rudder, and elevator

The geometry of 0004 will be outwardly similar to 0003 and its slightly derpy brother, using the DACWIG approach. I’ve settled on the 70mm EDFs for propulsion, and also ordered a single 90mm unit. I decided to forego the 125mm this time because of its requirements for 36+ volts, whereas the rest of the power system will only be running 14.8 volts (4S lithium cells). On a random side note, I found out that the Chinese technical term for the “Dynamic Air Cusion” GEV is 动力气垫地效翼船, which really does say Dynamic Air Cusion Ground Effect Ship. The Chinese seem to be the only ones who built that type of vessel (and theirs is in as bad of a shape as the Russians‘)

Here’s the preliminary solid geometry study for Chuckranoplan 0004.

 

 

Unlike all my previous “builds”, 0004 will have a more conventional hydroplane hull. I’ve sort of gathered that hull steps are most effective if they are placed at the center of gravity and at the stern. I’m not even sure if on a craft this small the steps even matter, but what they allow me to do is conveniently divide the hull into four major sections – the nose, the forward hull, the aft hull, and the stern section. Being steps, I am able to take advantage of them as dividing planes for fabricating the four parts separately.

Right now the plan is to use the cross sections at the forward and aft hull to cut those two parts out of foam (probably expanded polystyrene from Home Depot), and then hollow-shell 3d-print the bow and stern sections. The reason I’m still even thinking of 3DP is that I can thin-shell those two parts, which are of substantially more complicated geometry and need to contain mounting points anyway, and not impact the weight substantially. Essentially, I hope to use the 3DP only in situations where it is actually advantageous, like the aforementioned complex integrated geometry.

And now the top:

Looks pretty conventional (and empty). The main wings will have their profile hotwire-cut from foam. The tailplane, however, will be purchased “stock”. As it turns out, you can just straight up buy pre-cut airfoil stock made of polystyrene or polypropylene foam (EPS and EPP).

What. Why didn’t I know this before?

Well, they didn’t have the profiles I wanted in HOLY CRAP THAT’S HUGE, but the tailplane is more conventional. It will be a 20 inch chunk of their NACA 2415 x 4.5″ chord in EPP material.

The vertical portion of the T tail will be a single plane of 1/4″ balsa wood, laser-cut to shape. The rudder surface will hang off the back with hinge pins, and will just be another chunk of balsa sanded to a taper.  The other control surfaces will just be cut-out portions of the same airfoil they’re part of, also attached with hinge pins.

I have yet to arrange mounting points for any servos or controllers, and I’ll probably just take the standard R/C modeler approach of carving cavities into the foam to stuff these things in.  I have also yet to design the ducted fan mounts, which will be servo-actuated so they can pivot the fans for pressure augmentation or forward cruise.  The servos will probably be a handful of <20 gram park flyer servos, since while this thing is pretty big, I like the idea of having a flock of little servos instead of several large ones and long routed pushrods or cables.

And a 3/4 back view. The large side pontoons will also be profile-cut and then have the end chamfer sanded to shape.

As far as foam models go, I think this is actually pretty straightforward, and someone who’s done it before can probably bang it out in 5 minutes.  It will be an interesting learning experience, which is mostly what I’m after. If it does The Thing, then all the better because I have an excuse to build one 10 times bigger.

Right now, the weight breakdown is as follows:

• If I make everything in that picture from 1.0lb/ft³ foam (which seems to be a median value for XPS foam), the weight is 380 grams.
• The EDFs weigh in at 140 grams each
• I’m likely to run a 4S, 3.0Ah to 5.0Ah battery, which seems to weigh between 300 to 550 grams.
• I’ll toss in 200 grams, a very liberal estimate, for the weight of control electronics, servos, pushrods and actuators, glue, random hardware, and dust from the floor.
• I’ll additionally add 50 grams to the estimate because of the pivoting fan mount (which will add weight, but I don’t actually think it will be 50 grams over the assembly)

That totals out to about 1.4 kg, or 3.1 pounds, or exactly where I think I should be.

 

hey rc airplane people does this sound legit to you