Happy New Year!

2015 is upon us and it will be a bright an prosperous year! I look forward to new opportunities and plenty of fun in the new year.

I recently posted a comment on the MAN site about the Future of RC in response to the question: “What’s in store for RC aircraft in 2015?” While reflecting on the question posed (and my reply), it occurred to me that we are at a dawn of a Golden Age for the RC hobby and the Unmanned Aerial Vehicle industry. Yes, things are changing rapidly, and some of that change may be uncomfortable, but all in all, we have more options, better technology, and lower barriers to entry than at any time before the RC hobby.

The commercialization of drones and unmanned aerial vehicles IS going to happen (despite the FAAs bungling of the rule making process) and that will pour millions of dollars into technology and innovation that will cross over into the hobby market. Hobbyists will find new and innovative ways to adapt this technology and this will feed back into the commercial market. This cycle is unstoppable and will continue just like it has with every disruptive technology since the wheel.

Yes, there are growing pains that will need to be sorted through. The lower entry barriers means that irresponsible actors (both private and commercial) will end up causing problems that will likely lead to new regulations. But while those regulations may end up restricting certain elements of our hobby (and some will feel disenfranchised as a result), the core of the hobby/industry will thrive.

I don’t know what the future will bring, but I am sure it will be bright. We need to keep an open mind about the future and the AMA and our clubs need to continue to adapt and evolve with the hobby and with the industry it will spawn.

Be safe and have fun!!!

Cobra 4130 Brushless Outrunner Sketchup Model

So I have been distracted for the last several weeks learning how to use Sketchup. My first exposure to CAD was more years ago than I care to admit during my college days using a Computervision system. Back in those days, a 2D CAD systems ran on stand alone “mini” computers that would barely fit into a typical walk in closet. Since then have worked with a number of 2D and 3D CAD systems through 80’s and 90’s, but it has been over 20 years since I have touched any sort of CAD package. Needless to say, things have come a long way in the last 20 years, and it is quite amazing what you can do with a free CAD program like Sketchup today.

My initial goal was to use Sketchup to design a new custom cowl for my Hog Bipe project. I decided to start with an outline of the Cobra 4130 motor that I will be using on this model so that I could be sure that my new cowl would have sufficient clearance around the motor.

This was my first time using Sketchup, so there was a bit of a learning curve, but I found myself have more fun than I expected. I ended up getting carried away and doing a full model of the motor including the stator, magnets, bearings, etc. I did not go so far as to disassemble the motor, so many of the interior dimensions are just best guesses. Overall, I am extremely happy with the end result.

Cobra 4130 [2] Cobra 4130

It is quite amazing what you can do with this free package! There are some simple tasks that drive me nuts compared to the ‘industrial’ CAD packages I have used in the past, but in general it seems like there is no real limit what you can accomplish. My only real complaint is that as Sketchup was originally intended for architectural applications, it does struggle a bit with certain operations on smaller dimensions (e.g.; < 5 mm or so). The simple workaround is to scale everything up 10:1 for those operations.

If you have any use for this component model in your own applications you can download it here (I will also upload it to the Sketchup 3D Warehouse):

 

There was a bit of time investment here, but I found creating this model to be extremely satisfying! I am also sure that this investment will pay off in the future as there are plenty for 3D CAD applications in designing and/or customizing RC models.

Next up will be to start designing the Cowl around this motor.

Hog Bipe – Custom Battery Tray

Next up is to put together a custom battery tray. When performing a glow to electric conversion, often you can use the fuel tank floor for the battery tray. In this case, the floor needed to be lowered about an inch to have enough room for a 6S lipo pack. The stock floor is aligned by sitting in a notch formed by the fuselage doubler. Since I intended to lower the floor, I started by adding some balsa tri-stock to create an upper alignment point. I wanted an upper alignment so that I could easily add some cross-braces (see below) to reinforce the tray from beneath.

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I cut a new tray from 1/8″ lite plywood. Unlike the stock tank floor, I cut this to fit the full length between F1 and F3. This will give me plenty of room to adjust the pack fore and aft when balancing. I also wanted to add slots for a Velcro battery strap on either side of the middle of the tray. To cut these slots, I clamped a piece of straight scrap-wood to my drill press table, then drilled a series of holes along the length of the slot.  This arrangement allows you to quickly drill a series of holes along a line. The slots are then cleaned up with a popsicle stick with some sandpaper attached.

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The tray is then glued in against the tri-stock. Given that a 6S battery can weigh in at over 1-1/2 lbs, I wanted to reinforce the battery tray. I added some 1/4″ x 1/8″ basswood cross braces beneath the tray. This creates a light but rigid platform for the battery. I may add some balsa tri-stock to the corner formed by the fuselage side and the tray floor before is close up the bottom of the fuselage.

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Hog Bipe – Fuselage Top Sheeting and Battery Hatch

I finally got a few days to spend working on the Hog Bipe. I am deviating from the original kit a bit more now. I plan to add a custom scratch-made cowl (more on that coming in a future post), so I cut the fuselage cheeks off at this point.

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Another significant modification is to add a custom battery access hatch. I started by cutting the hatch floor from some 1/8 lite ply along with a new F1A and two sets of F2 formers. I used lite ply for the formers in stead of balsa since I felt balsa would end up getting damaged with routine handling of the hatch. One of the F2 formers was glued to the fuselage top at a slight rearward angle, allowing for easy installation and removal of the hatch with no interference. The new F1A was installed square at the front of the new hatch floor. I then positioned the hatch on the fuselage and glued the other F2 to the hatch floor at an angle to match the F2 previously installed to the fuselage top. Stringers were then added.

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To secure the hatch, I added a short 1/8″ hardwood dowel to the front and a pair of 1/4″ dia x 1/16″ thick rare earth magnets in the back. A strip of 1/8″ ply was added in front of F2 on the fuselage top for the mating magnets. The magnets were epoxied into 1/4″ dia by 1/16″ deep counter bores made with a forstner bit.

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Sheeting proceeded more or less per the kit instructions (sheeting the hatch and the fuselage front separately). I sprayed down the sheeting with a bit of ammonia based window cleaner to soften the wood, then  formed it around the fuselage using tape to hold it in place. After letting it dry overnight, I then trimmed it to final shape.

I added some scrap 3/16″ square stringer material to provide something to attach the sheeting bottom to.  Instead of CA, I installed each piece with Titebond, holding it in place with pins and tape. I let the glue dry for each piece before moving onto the next. A bit time consuming, but for me, this approach yields the best results.

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Sharp eyes will also note I also added a bit of sheeting to the F1 firewall bulkhead so that it would match the battery hatch. I am happy with how the sheeting came out. The hatch fits nice and snug, and all of the seems are nice and tight and will only require a small amount of filler.

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Next up is the battery tray, motor mounts, and then the custom cowl.

Site Moved To New Host

In addition to trashing my site with no warning, I recently discovered that sites hosted with the free hosting service 000webhost are blocked by many ISPs. Well, I guess you get what you pay for.

I decided to move my site to Host Metro, taking advantage of their $1.84 per month promotion. It took a bit of wrangling to get the site set up, but I think I have everything moved over now. Initial impressions are OK. Customer service seems to be helpful with rapid responses from their live chat support. The website itself seems a little slow though, but it is only been one day, so I will give it a bit of time before making a final judgment.

Site Problems

My site went down recently and had to be rebuilt. I am not sure what happened. I use 000webhost.com  to host my site. This is a free hosting site that has, up until now, been flawless. I was really impressed with how much functionality provided by a free site (but in the end, I guess you get what you pay for). I am not sure what went wrong, but noticed on the site forum that a few others also had the same problem. Fortunately, I had a backup from August and was able to recover with only two lost posts (and after a bit of head scratching, I was able to recover these from local Live Writer files).

I don’t mind paying a (reasonable) fee for hosting and was considering upgrading to a paid account at 000webhost, but I want to make certain that everything is stable there first. In the meantime, I’ll be sure to capture a new backup now.

Hog Bipe – Fuselage Construction Continues

Spent a bit of time working on the fuselage this weekend. After installing the T-Nuts for the Sullivan tail wheel in the fuselage bottom, I spent some time fussing about with the formers and the fuselage top and bottom pieces. I followed the basic approach that SeamusG used in his very well done Hog Bipe Build Thread on RCU. I used some 1/4″ balsa blocks to pin the forward section of the fuselage to the building board, I then dry fit the formers and other parts together with clamps, tape, and rubber bands, fussing about until everything was square.

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To ensure that I had everything straight, I set up my laser level with a vertical beam, and lined it up with the fuselage, checking that it hit the top center of each former. I also dry fit the rudder to ensure that it would install square. When happy with this, I went ahead and started to apply medium CA working from the bottom up as described in the instructions. Hopefully, everything stayed straight and square while gluing.

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Just like SeamusG described in his build thread, I also ended up with a bit of a gap between the in the fuselage bottom plate and sides near the front of the plate. I decided, the fill the gap in with a bit of aliphatic resin (Tite Bond). As a bit of extra insurance, I used some balsa triangle stock to reinforce the joint between the bottom plate and fuselage sides and F5. I probably would not have done this if I had gotten a good wood-to-wood bond joint between the sides and the bottom near F5, but the area right behind the wings tends to be a weak spot in many planes, and for a gram or two of weight, this will add a lot strength.

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I also started planning out the battery hatch. Although SeamusG built a glow plane, his build included a mod to add hatch to access the fuel tank. Following his lead, I will add a hatch between F1 and F2. With this in mind, I realized that I should not have glued F1A to the back side of the firewall F1. This double really is not there for strength, but as a place to attach the stringers used to help shape the forward section sheeting. Instead I want to use this piece as the front section of the hatch.

With a little care and a long X-Acto blade, I sliced F1A off from the firewall. The back side is a bit damages and the part will be too week to use for the hatch, but it is in good enough shape to be used as a pattern to cut a new piece. A little sanding and the back of the firewall looks like F1A was never there!

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Next up will be the creation of the hatch floor and bulkheads in order to prepare for sheeting. I also will need to modify  and reinforce the fuel tank floor to serve as a battery tray.

Hog Bipe – Tail and Fuselage Started

Now that the wings are done, I started work on the tail feathers. I wanted to give the plane more of a “vintage” look with a more rounded fin and rudder. I started by tracing the original outline from the plans. I then used my old flexible curve (an old drafting tool that you can bend to an arbitrary curve and it will hold its shape) to create a new outline. No science involved, just going by look. You can see the dotted line for the original and the darker line for the new shape.

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I then cut new pieces from 1/4″ x 4″ wide balsa sheet and assembled to the original kit supplied tail piece. I sanded a taper in the rudder from 1/4″ to 1/8″, like the original kit supplied part, but the rudder seems a bit too flexible to me now, so I may cut another and leave it un-tapered (or less tapered). I also may cut some lightening holes in the rudder (and elevators), but will wait for a trial balance first.

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The stabilizer has been built according to the plans, but I will probably give the elevators a similar rounding off treatment to the rudder. I ended up with a slight bow to the stab after sheeting (about 1/16″ total). Not perfect, but not enough to worry about either.

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My motor arrived earlier this week too. I settled on a Cobra C-4130/14 instead of the C-4130/12. The “14” had a slightly lower Kv (450 vs 540) which will let me run slightly larger prop. Equipped with the motor mount, I marked and drilled the firewall. I also added a few holes for air flow (one directly behind the motor and set along the bottom).

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I glued up the fuselage doublers using Titebond weighted down with some paint cans to hold them flat while the glue cured (no pic). Unfortunately, there are no positive features in the design of the doublers to guarantee alignment. and one of the doublers slipped forward. The notches in the doublers will set the firewall position, and if they are not perfectly aligend with each other, the firewall will not sit square. To compensate, I slightly widened the back of the notch to compensate for the slip, this will allow the firewall to sit square against the back of both notches and keep the fuselage sides in line with each other. If I were to build this kit again, I would drill a couple of 1/8″ holes and use a couple of dowels to pin the doublers before gluing. The dowels could then be cut flush and sand smooth and you would never know they were there.

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The cabane mounting blocks were next up. Thes must be positioned properly in order to ensure proper wing alignment and incidence. Here again, there is no positive alignment feature in the kit, so to ensure proper alignment, I used the following technique. First, I drew a line marking the proper position for the top of the block (1/8″ below the top of the fuselage side. Next I cut a short piece of 1/8″ dowel, and  inserted it into the laser cut hole in the fuselage side. I then slipped the aluminum cabane strut over the dowel (the dowel was cut so that it was flush with the cabane strut). I next positioned the mounting block over the cabane strut with the top of the block on the alignment mark (not seen in the picture, but the mounting blocks have a rabbet groove that the aluminum strut fits tightly into. This ensure that that the block is in the proper position and that the hole in the cabane strut will be aligned with the hole in the fuselage. Finally, I position the laser cut “C” shaped plywood positioning plate around the block (basically in the reverse order that the instructions call for). With everything lined up snugly, I tack the plate in place with a few drops of CA, then remove the block, the cabane strut, and the alignment dowel. I use CA to secure the mounting plate and a little Titebond to glue down the mounting blocks (being careful to keep the groove clear of glue). This is then repeated for the other three mounting blocks.

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The instructions call for then drilling a 9/64″ hole through the fuselage and into the mounting blocks. This allows you to install a 4-40 blind nut in the back of the mounting block, but a 9/64″ hole is way to sloppy for a 4-40 bolt. I start by drilling a 1/8″ dia hole from the outside through the mounting block, using the existing hole in the fuselage for alignment. I then drill a 9/64″ dia hole through the back side of the mounting block (not going through to the fuselage side) to accept the blind nut. Last step is installation of the blind nuts themselves. I did not want to take a chance at messing up my perfectly aligned assembly by hammering them in place, so I simply drew them in by tightening a screw and washer.

Finally, I epoxied in the firewall and F3 former, using my 1-2-3 blocks to ensure everything was square. This was done in two steps, first gluing the firewall and F3 former to one side, letting the epoxy cure overnight, then flipping this assembly over and gluing to the other fuselage side.

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Next up is to assemble the rest of the formers into the fuselage. Since I plan to use a Sullivan tail wheel assembly, I will need to drill and install blind nuts in the fuselage bottom. This will be much easier to do before everything is assembled, so I guess it’s off to the LHS before I can continue.

Hog Bipe – Wing Construction Complete

I have been picking away at the wing construction on the Hog Bipe on and off. Sheeting the wing tips went smoothly and I am happy with the end result.

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The lower wing is built in two pieces and glued together to obtain the proper dihedral. One little trick I used was to cut a block of scrap wood with the dihedral angle for the inner wing rib. This allowed me to position and clamp the rib in place before gluing to the spar. The first photo below shows the block against the kit supplied dihedral angle gage. The second photo shows it in use.

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The rest of the lower wing construction was uneventful and came out straight and true with the right dihedral.

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I bought my kit off e-bay, so I am not really sure when it was made, but I was fortunate enough to have one that included the parts for the optional dual aileron servo setup in place of the single servo in the original kit. The dual servo setup is much stiffer and is less likely to have flutter problems. My only deviation from a stock build so far has been to add a couple of paper tubes for the aileron wires and to use 2 inch wide fiberglass tape t reinforce the lower wing joint instead of the 1 tape supplied with the kit.

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The plans call for using medium or thick CA to saturate the tape weave. I chose to use epoxy instead. This was my first experience using fiberglass cloth and epoxy, and I considered it a small scale trial run for glassing a balsa plane. I sprayed a light coat of 3M-77 adhesive on the glass and laid it down between two strips of masking tape. I chose BSI Finish Cure epoxy. This is similar to laminating resin and was available at the my LHS. To ensure that the epoxy would flow smoothly and to get a good cure, I pre-heated the bottles for 10 seconds in the microwave before mixing. I applied the epoxy with and acid brush and spread it smooth with an old gift card. I rough sanded with 80 grit and applied a second coat after an overnight cure, sanding out with 80 and 150 grit after full cure.

Overall, I am happy with the result. Structurally, I am sure this will be plenty strong. Cosmetically, I am satisfied for this application. It sanded out quite smooth, and would be a good surface for painting (if I was going that direction). I did end up with a few dry spots where the epoxy did not wet through the fiberglass fully, but I know what to look for now and should be able to avoid that in the future.

The last major step was to shape the ailerons to the tip. This also went smoothly with no real surprises or major problems. One minor problem was that one of the supplied aileron blanks did not have a well shaped rounded leading edge – a few minutes with a long sanding bar took care of that.

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Next up is to start in on the fuselage, but I will need to order my motor so that I can properly drill the firewall first.

New Project – FT Viggen

It’s been a while since I last posted. Summer has been busy but I have found time to get out flying when I can. Like last summer, I got sidetracked with a scratch-build foamy EDF. This time I, went with an established design and put together an FT Viggen. I didn’t bother with documenting the build process at all since there is a great build video on the Flite Test site, and I just followed it along step by step.My only deviation from the FT build was to add a 1×2 mm carbon fiber wing spar. I re-used the fan and all of the electronics from my original (failed) Fan Trainer project, and I must say that I am pretty happy with end results.

I really enjoyed the build process. I transferred the downloaded plans onto the Dollar Tree foam boards by taping the plans down to the board, then pushing a pin through the plans at each corner, or intersection point. I then used a pencil and a straight edge to lightly “connect the dots”. Working with hot glue and foam may not be quite a s rewarding as a full on balsa build, but it fast, cheap, and surprisingly strong. Overall, I can’t argue with the results.

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I maidened it a few weeks back, and I must say that I was quite impressed with how stable she was. The guys at Flite Test did a great job with the design! Just a gentle underhand toss with the throttle at about 75% and she flew away and got right on step. She is very sensitive to aileron input and I kept looking for rudder while (i.e.; I’d move the rudder stick, but of course, since there is no moveable rudder so nothing would happen – duh). I may try to add a rudder (or just build another with one).

I did run into one problem and learned a good lesson about battery charging. In particular, that I learned that I need to be mindful of the power supply power/current capacity when charging.

I am using a 4s 3700 mAh batteries (slightly larger than the recommendation of 3300 mAh, but what I had available already). The last time I used these batteries was in my original Hanger 9 Alpha Trainer a few years back. Since then, I bought a new battery charger that allow supports much higher charging rates. While field charging the batteries using my Duracell Powerpack, the charger died about half way through the cycle. At first I was quite certain that my charger had crapped out (I have a Hyperion 1420i charger and they have a reputation for early failure). Fortunately, when I got home, I discovered that the 12V cigarette lighter pulg-to-banana plug adapter that I was using had a blown its 10 amp fuse (I didn’t even know it had a fuse!).

A little math shows the problem:

  1. Battery Voltage (3.7 per cell empty, but  4+ volts per cell charged):  4 x 4v = 16v
  2. Out power to battery:  16 x 7.4 = 118.4 watts
  3. Input current required at 12v (assuming 100% charger efficiency):  118.4 / 12 = 9.9 amp

Knowing that the charger is not 100% efficient, it is pretty easy to see why the 10 am fuse blew. Overall, a cheap lesson. But, given the reputation of the Hyperion 1420i (now discontinued), I may want to think about picking up a new charger before next year’s flying season.

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