A Useless Geek's blog View Details
Posted by A Useless Geek | Sep 27, 2011 @ 01:45 PM | 11,158 Views
So, I was cutting out wings for a pile of Pinkstars and ended up with these two cutoffs that looked like moth wings. Instant "brain" (as I like to call it) storm: a slow flyer that uses big, fat wings. How original. Here's what I ended up with:

Span: 880 mm
O/A length: 784 mm
Mass: 168 grams
Motor: Turnigy 2204-14T (19 gram, 1400 KV)
Prop: GWS 8x4.3 EP slow (EP-0843)
ESC: SS 8A
Servos: hexTronik HXT500 x 2
Rx: OrangeRX 6 channel, minus useless plastic casket dead weight

The surfaces are almost completely 6 mm Dow Protection Board III. The fuse is 1/2" (actually 14 mm) Pink Foamular. 3M Extreme tape holds the whole airplane together, particularly in the back where I used no spar embedded in the fuse and paid the price for that. I actually broke the plane in half by holding it up from the tail surfaces. After using foamed-up yellow Gorilla Glue to put it back together I added tape to hold the tail end stiffly into place. Duh!

So, now I've got another plane to loan out to people trying to learn to fly. I'm not really happy with the stall characteristics of this plane, so I can do one of two things to fix that; either add a KFm2 step on the top side to make it fly slower and have gentler stall, or cut the wings back to a Skinny Boy configuration (there's plenty of meat on the wings to achieve that shape) and have the plane actually fly a little bit faster, but with easier handling characteristics. I don't know which approach I prefer. In either case I ain't gonna be the one flying this plane a whole lot.
Posted by A Useless Geek | Jun 05, 2011 @ 10:18 AM | 10,373 Views
This thread may get a lot of traffic, or none. Who knows? I'll keep updating as I get more photos made of assemblies on which I'm working.

To start with, let's take a look at how I build wing assemblies for the Skinny Boy, Eluder, Longhorn, Lunatic, etc. These are flat pan wings with a dihedral in the middle. The wing roots are cut at an angle so that they meet in a vertical line when the halves are put together. The underside of the assembly gets support from balsa trailing edge wedges cut down to size. After the wedges are put in place the entire underside of the wing root is sanded flat to meet with the flat top of the airframe.

Put the wings top down on a flat surface, then use blue tape down the centerline to hold the assembly together. Flip the wing over and apply puffed up Gorilla Glue to the seam. Weigh down one wing and prop the other one and the correct angle. Prevent the GG from puffing up too much on the top side by applying blue painter's tape. (The cat isn't necessary, but may help relieve tension.) The extra GG puff on the top side of the wing supports the wing during high G maneuvering.

Balsa trailing edge wedges are available at the LHS in long strips. Use a slitter to cut them down to size. You only need enough width to make contact with the top of the airframe, typically 10-16mm wide depending on what you are using. Glue the wedges along the underside of the center seam. The thin edge goes toward the center. The idea is to make a flat surface so that you can glue the wing to the airframe without gaps.

After the glue is cured you can sand the underside of the wing root to get a completely flat surface that can then be glued to the top of the airframe. You gots a basic airplane!
Posted by A Useless Geek | Jun 03, 2011 @ 02:25 PM | 10,088 Views
So, I've sorta fallen down on the really fast park jets the last year or so. The indoor/outdoor sport planes have been so much phun that I've ignored the realm of fast park jets almost completely. A couple of my fast projects are coming back to life now that I have everything (except batteries) to finish them.

I considered doing the Multiplex Blue Shark TwinJet first, since it already has servos mounted and such, but I know how much effort will go into getting the motors aligned on that beast. Instead I'll do the Electrifly Firebat first because it's a little simpler and has some features I want to mess with anyway.

My plan is to enhance the maneuverability with my own stiff balsa elevons, separately-controlled anhedral canards, and linked rudders. Needless to say it will be brushless and carbon fiber supported. I'm not going to go nuts with power; I figure 500 watts or so ought to get it moving pretty good. Maybe a little more.

The naked airframe as shown is at 193 grams, so it won't be a lightweight. (By comparison, a good Longhorn is 180 grams all up.) I'm not really worried about weight at this point because I know I can get it to fly fine with the amount of power I have in the motor box. I am thinking I can get this planes put together at 500 grams or maybe a shade less. And that's with an 80 gram motor, so it ought to scoot pretty good.

Stay tuned as this one comes together.

Later:

Okay, so I decided to try something a little less expensive and maybe...Continue Reading
Posted by A Useless Geek | May 31, 2011 @ 11:12 AM | 8,795 Views
So, I end up with a lot of these planes that kinda suck wind. Sure, everybody builds a stinker now and then, but how long are you gonna stick with a plane that obviously doesn't perform? A couple of years ago I was plowing through planes at a rate of two or more per week. If I hit on a plane that smacked I tried working with it for a little bit, but then I'd scrap it if it didn't get any better.

Why is it now that I can't seem to let go of any of these lousy planes? Take that Son of Blue Star, for instance. The first pass wasn't horrible, but it wasn't very good, either. I kept hacking at it and hacking at it because the plane showed some glimmer of promise, even though my changes weren't getting the kind of improvement I wanted to see. Duh! The plane eventually mutated into something completely unrecognizable from the original, and I scrapped it because it was too heavy.

Now I have this Pinkstar thing, which was supposed to be an hour and a half project completed just ahead of a club meeting a few months ago. Yet Another example of a plane that I just can't seem to get rid of. I have massaged and mutated this poor thing so much that I can't tell any more what was there originally and what was added later. It's been flown and smashed up so much that it's mostly repairs and add-ons now, I think. Why can't I just let go?

Grrr!

Later:

Well, the first version of the Pinkstar certainly wasn't very good. In fact, that plane flew better inverted than it did right...Continue Reading
Posted by A Useless Geek | Apr 30, 2011 @ 02:41 PM | 7,939 Views
So, the 2010-11 indoor season out at White Pines Golf Dome is ending tonight. I didn't do my shift last night or last week because I had an emergency appendectomy last Friday afternoon. That means I missed the Swap 'Til You Drop event a week ago today, also. That's really too bad, because I was looking forward to getting rid of some indoor stuff and maybe picking up a couple of outdoor planes for the summer. Oh, well.

I'll swing by the golf dome for a while tonight, but I ain't staying until 01:00 in the morning. Perhaps I'll have a new plane to try out. Not expecting a real big crowd; the last couple of weeks are usually pretty dry out at the dome. Everybody is getting ready for the summer and the indoor stuff is mostly finding its way back on to the upper shelves.

A week from tomorrow (Mother's Day) is the swap meet out at Lake Barrington Field House. Perhaps I can move some of the excess indoor stuff that didn't make it to Swap 'Til You Drop. Sure hope so, because this surgery stuff is going to cost more than my current net worth. Heh.
Posted by A Useless Geek | Mar 06, 2011 @ 10:57 AM | 7,604 Views
Unit B is a much better implementation of the Longhorn II Lunatic than the first pass. Hanging the control surfaces out the back and getting some real surface movement made this a completely different plane. I also reshaped and added some anhedral to the horizontal stabilizer/elevator. The results were far closer to what I expected.

I was able to construct this plane without the typical wood or carbon fiber structural bracing in the back because the moving surfaces left a clean fuselage for taping. So far the 3M Extreme tape is all that is needed to keep the back end held together. We'll see if that is true over dozens of flights.

(As a side note, I plan to attach a pinhole camera to the plane to watch the rear end in flight and look for flex.)

The Lunatic is a radical departure from the performance of the "normal" Longhorn with its conventional control surfaces. Death spirals, for instance, look like the airplane is chasing its own tail. Rudder spins are stupidly tight. Invert loops happen in the blink of an eye and almost within the airplane's own length. Outside death spirals are possible with this plane, something I haven't managed to do with anything other than a real 3D plane.

The 24 gram motor is bigger than this plane really needs. I can cut back to a 19 gram motor and 8A ESC and shave another eight grams or so off the front end. As it is the C/G is a little far forward of optimal for maximum flight stupidity, so moving the C/G rearward with component selection is actually a benefit.

I'll post up some video when I get a chance.

Specs:

Length: 840 mm
Span: 560 mm
Mass: 177 grams (dry)
Motor: hexTronik 2730-1700; 24 gr, 1700 KV
ESC: TowerPro 12A
Servos: hexTronik HXT500 (2)
Battery: 2S Turnigy 500 20C
Posted by A Useless Geek | Feb 14, 2011 @ 11:53 AM | 7,172 Views
So, I built the first pass at the Longhorn II (full floating stabs). The performance was less than spectacular, and I know why. Although the plane is okay, it isn't great -- and that was the target. The next one will have the whole tail section hung out a good eight centimeters back from where the first one was done. I shoulda know better than to mess with the dimensions of the original Longhorn. Duh!
Posted by A Useless Geek | Jan 15, 2011 @ 03:53 PM | 6,982 Views
So, I'm getting my stuff assembled for the Dome E-Niter tonight. Gots a few airplanes ready, but there are a bunch more not sufficiently put together to make it. Too bad, because I really wanted to fly some of my MS Composit stuff that I've modded to the hilt. Got a Bat Glider that works pretty well if I don't roll it on the ground and destroy the motor (done that twice already). The Swift II is finally flying properly, so I can use that tonight. Scott Barrie's Maxi Swift is almost ready to put back together; I might actually get that ready to fly. If it comes in under two pounds (900 grams) then I can fly it at the dome! That would be a trick, getting that behemoth to turn in such a confined space. Heh.

Also, I am providing one of the simulators for newbs to use in training. I'm planning to bring in my 42 inch LCD TV as a display, but I might have to settle for the 27.5 inch LCD off my desk if I run out of room in my car.

Anyway, it looks to be a good time tonight. We'll see about turnout. Stan Warden was getting all kinds of phone calls about the event, so that may be an indicator.
Posted by A Useless Geek | Dec 09, 2010 @ 10:19 PM | 7,871 Views
Anybody else have a DX7 that has given you the nice "BACKUP ERROR" message? Isn't that a treat?

The way the stoopid DX7 works if there is a brief -- like, measured in tens of milliseconds -- disruption of power then the darn thing tries to write a bunch of data to the FLASH. If the power comes back up before that write cycle completes then the radio trashes a bunch of FLASH data and goes in the tank.

If the FLASH contents take a complete header then the radio just reports "BACKUP ERROR" on the display and does nothing else at all. In the case of my radio, it trashed the contents of the Model 9 memory station in such a way that anytime I try to access the Model 9 slot the radio hangs.

The DX7 is a pile of horse poop as far as memory protection goes. First off, they couldn't figure out a more reliable scheme for backing up the long term memory? Second, the radio can't figure out how to validate its own internal storage before trying to use the data contained therein? (Think CRC.) Third, the user data space and operating program space are not kept separate and protected from each other? Last, the stupid-ass radio can't detect that the FLASH contents have gotten scrambled and re-initialize itself back to factory default?

What? Huh? What? This is the only FLASH-based embedded device I have run into in the last thirty years that had this level of stupidity designed into its behavior. Had I been responsible for this mess I'd expect to be kicked off the client's property covered in tar and set on fire. If I had worked next to the engineer(s) responsible I'd have killed and eaten him(them).

Here's to hoping that the DX8 cures a lot of these problems. It couldn't possibly be any worse.
Posted by A Useless Geek | Dec 05, 2010 @ 06:23 PM | 6,646 Views
The stench from the Ironing Board fiasco still fresh in my nostrils, I made another prop-in-slot mid pusher park jet real quick to clear my palette. Another basic delta. In fact, an actual delta! Nothing wrong with an isosceles triangle that proper C/G placement can't cure.

Balsa leading edge rounds used as longitudinal stiffeners. [By the way, the balsa used for leading edge rounds seems to be denser and stiffer than the wood used for wings and such. Works out well.] One piece of carbon fiber round tube (rescued from another plane) used as a lateral stiffener.

Flew fine out at the golf dome last night. Two batteries and no objectionable behavior.

Length: 774 mm
Span: 484 mm
Height: 167
AUW: 260 grams (186 dry plus 74 battery)
Battery: Turnigy 800 mAH 3S 20C
Motor: Welgard 2208-08 2600 KV (400 class)
Prop: APC 5x4
ESC: SS 20A, with mods
Servos: hexTronik HXT500 (2)
Rx: AR6100e
Posted by A Useless Geek | Dec 01, 2010 @ 01:17 PM | 6,649 Views
So, I was running low on planes to fly out at the golf dome. (I sold some off, crashed a few, and loaned out a bunch.) This was just an idea from some leftover foam that had a certain shape to it. I used a balsa leading edge strip running down the middle of the underside to stiffen the backbone. There's a GWS plastic stick mount to hold the motor in place. Not much to this thing.

After the fact I thought up ways to improve it, of course, such as an iron-shaped vert stab, a cross-braced undercarriage (to look like the folding legs) and some other stuff. Still, not bad for the little work I put into it.

The Ironing Board will get its debut out at White Pines tomorrow night at the SRCB club indoor. We'll see. Hey, look -- I needed another plane, okay?

AUW: 209 grams
Length: 815 mm
Span: 217 mm
Servos: (3) HXT500
ESC: Hobby King 15/18A
Motor: E-Max CF2805 2840 KV
Battery: Turnigy 2S 800 mAh 20C
Rx: Spektrum AR6100e

Later:

Um...not so great. Flies Like Chicken. (Tastes like it, too.) Gonna hafta add polyhedral extensions to the sides to get it stabilized. Maybe I ain't as smart as I thought I were...?

Later still:

Did a bunch more to try salvaging this beater. Flew like total kaka. Uhn-uh. Scrap.
Posted by A Useless Geek | Oct 20, 2010 @ 06:34 PM | 7,236 Views
As much as I whine about (w)Horizon's nasty pricing schemes and the way they've suppressed digital signaling development through their Draconian patents and such, even I am forced to admit their customer service can't be beat. I sent them a dead Vapor brick, a dead AR6100E, and a "BACKUP ERROR" DX7 with a broken antenna mast. They sent back a new-in-the-bag Vapor brick, a new-in-the-package AR6110 (I had asked for them to change the connector on the AR6100E to the straight pin type on the 6100), and a fixed DX7 with the display polished, the antenna mast replaced, and even a battery compartment cover (which I hadn't sent with the radio) and some little support extras. Total turnaround time: one week. Pretty nice.
Posted by A Useless Geek | Oct 14, 2010 @ 12:40 PM | 6,977 Views
So, it may be time to retire #1 pretty soon. It still flies really well when I don't put it into a fence post or a mailbox or tree or some other stupid obstruction to flight. Why do people put mailboxes out in front of their houses anyway? And on a post sticking up out of the ground where they can get in the way of an R/C plane? Dumb.

Fortunately I have a bunch more SDXSs on the way.

Later:

Okay, so I couldn't bring myself to retire #1 just yet. Instead I tacked on a bamboo brace across the wings and added a bunch more area to the control surfaces. Net result: like a new (albeit slightly heavier) aircraft. With good batteries this thing does wild and crazy stuff, as well as or better than the later ones. Now I'm thinking that I have to revisit all my plane designs and try them with stupidly large control surfaces to see if they'll improve.

Bah. I hate R/C airplanes. What a pain.
Posted by A Useless Geek | Aug 16, 2010 @ 02:21 PM | 7,061 Views
So, I broke my SDXS #2 totally in half by hitting a three rail fence in the wind. Not smart, you say? Well, it's a Smart Dart, but that's just the plane. I never said anything about the operator.

Took the wreckage and made something else out of it.

Later:

Okay, so I couldn't stand not having another SDXS at my disposal. I fabricated a new tail end for #2 and grafted it to the backside of the wreckage. Result? "New" SDXS, but I'm sticking with the designation of SDXS #2. Currently in the hands of a buddy who loves it and flies it off his DX6i.
Posted by A Useless Geek | Jul 26, 2010 @ 11:59 AM | 8,840 Views
So, I missed flying yesterday. I went to a memorial on Saturday with about 200 strangers. Somewhere along the way I picked up a flu that completely wiped me out by yesterday afternoon. I spent all yesterday after church shivering and sweating. Oy.

However, I think that's the only day other than one really windy one that I haven't flown since the end of May. Even on the days when it's been raining like crazy I wait for a lull in the rain and then boogie outside to run a battery through one of my front yard planes. Heh, heh, heh. "Nor wind, nor sleet, nor dark of night/Shall keep me from my appointed rounds..." or some such.

By June 1 of next year I will be able to claim that I've flown every day of the year with only a handful of exceptions. (I am not flying inside to make up those days -- that's cheating.) Anybody else flying literally all year 'round?
Posted by A Useless Geek | Jun 28, 2010 @ 03:04 PM | 6,691 Views
So, I wanted to do something a little different than the NextGenMid that was such a pain. I put this thing together without much forethought, but it came out all right.

Length: 790 mm
Span: 600 mm
Mass: 225 grams, all up
Motor: Emax CF2805-2840
ESC TowerPro Mega-8 12A SuperSimple 18A
Servos: hexTronik HXT500 (2)
Rx: Spektrum AR6100
Battery: Turnigy 800 mAH 3S 20C
Prop: GWS EP-4530 (4.5" x 3"), although I'll prolly go to a 4x4 later

You know, I was careful to shoot pictures even before glide testing because I was worried that the ultra-pointy nose would not survive the first time the plane left my hand. I need not have worried so much. The glide tests went fine, revealing my SWAG C/G placement to be only rearward by about 3cm. For the first powered flight I moved it up where I figured it oughta be and the plane flew great. Well, you know.

On this little Emax motor the plane really can't get going too fast, so maybe I shoulda used the KF step on the wing. I didn't use any CF in the wing itself. The only carbon in the whole plane is the strip between the front and rear pan halves, and that was just to make sure the thing stayed flat at the joint. The rest of the wing is pre-tensioned with tape.

Maybe I can get some video of this little guy in the air if there's a calm day this week. With the amount of wind blowing today I'm surprised I got the plane back at all, much less without any damage or nicks. Coolness.

Later:

Well, the Blue Star gets...Continue Reading
Posted by A Useless Geek | May 31, 2010 @ 06:35 PM | 6,680 Views
Well, anyway, I wanted a very crashable airplane for a newbie product. Something that they can essentially drive into the ground repeatedly without damage. I figured it has to be a mid pusher, with dihedral, and RET. My first pass at this sucked pretty badly, but this one less so.

Only the front end is EPP for the test bed. I wanted to see how I could eliminate flex as much as possible without braces. The dihedral and KFm2 wings are plenty stabilizing, and have all the lift you can shake a stick at. The wide center section going back to the tail is hefty enough to prevent torquing, which was a problem on the first unit. The long, tall tail fin prevents flex in the vertical axis.

So far the Crashable isn't working out too badly, but there are some issues with it that I don't like. Let me gather some more data and flight experience and I'll let you know what I'll try next.

Later:

Well, this is lousy.

The Crashable is junkable. It's just too flexible along the longitudinal axis to be of any real value. There are lots of ways I can reduce the flex, but all of them get away from the basic concept of a low cost, indestructible trainer. This was a nice try, but goes into the ashcan.

Next up I'm gonna try a variation on the Trainer One concept and see if that gets me anywhere.
Posted by A Useless Geek | May 25, 2010 @ 01:33 AM | 6,531 Views
I built another one to make sure I could do it the same way again. Details here.
Posted by A Useless Geek | May 13, 2010 @ 04:59 PM | 6,076 Views
So the guys at Slot and Wing (http://www.slotandwinghobbies.com) showed up for the SRCB Swap 'Til You Drop in April. They had piles of inexpensive goodies, including a barnload of static display models of the Swarm. These kits had no motor, no electronics, nuthin' -- perfect for scratch builders. I grabbed a couple, got another naked airframe for zero, and won another kit in a club raffle.

These are great planes to start from. 780 mm wingspan and 610 mm overall length. Wing chord is 125 mm. Lots of room inside to put electronics and batteries. Good structural design with enough bulkheads to keep it stiff but not too much structure to add mass.

The airframe is a two piece affair with the top and bottom halves held together with some form of RTV. A fresh #1 blade will zik right through the bond and split the fuselage halves cleanly.

The wings, horizontal stab, and vertical stab are all made of 2 mm foam that is kinda crusty with the color (ink or paint, I can't tell). The graphic stickers are all kinda wrinkled, though, so I just peeled most of them off. You can see from the picture that the wings end up looking like some post-modern op art piece, but that's okay by me.

I got rid of all the hard plastic pieces that are attached to the plane, including the motor mount and the whole front bulkhead. Even the cowl is too heavy (8.4 grams by itself). By hacking off the whole front end I removed 18 grams per plane! The other plastic parts aren't so heavy, but they have...Continue Reading
Posted by A Useless Geek | Mar 16, 2010 @ 08:33 AM | 5,978 Views
You like Velcro? I like Velcro.
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I settled on a technique for making the Smarty Pants wings that goes like this: put the wings together upside down on a flat surface. Tape the bottom of the seam together with packing tape, something that will release later on. Flip the wing assembly over and apply pre-wetted Gorilla Glue to the seam. Prop one wing up at the proper angle. Weight down the wing lying flat. Wait.

Later, I glue the wing assembly to the fuselage with more GG. Clamp that little bugger into place.

After it has thoroughly cured take it out to the garage and use the belt sander to grind the whole front end to a flat that's at the correct down and right thrust angle.

Make a Smarty Pants out of it.
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So, you need to squash that assembly you're working on to make it flat? Don't go running all over the house looking for heavy junk to put on top of the spreader panel -- just use a bucket of water. Lots o' mass and simple. Plus you can dump the water on the rose bushes afterwards to store the bucket without weight.