Fly RC

January 24, 2021

Hangar 9 Carbon Cub 15cc ARF … Part 3

In part 2 of my commentary and running monologue on the Hangar 9 Carbon Cub, I mentioned that I would cover the bottom vent that I added and some other mods so I will show you a couple of those here as well as try to relate my sense of how she flies. First the build and modifications update.

Bottom Vent

Looking at the cub I realized there is not a lot of accommodation for air flow and even if it isn’t much I’d like to have at least a modicum of air passing over my batteries inside the cockpit area. So without just cutting open a whole section between formers/bulkheads in the bottom of the tail I needed another solution. What I came up with was to cut open a section in the only solid area behind the cockpit, which is the hatch for servo access. I happened to have some louvers laying around that I picked up at a swap meet so I cut an appropriate sized hole and drilled a few holes for button head #2 screws and created a nice louvered exhaust vent. It’s very nice looking (even if not quite scale!) and looks like it belongs there. Was it enough exit area… well read on.

Top Hatch blows off!

Taxiing out for the first flight on the airplane, everything seemed great. I had done a balance check, the prop seemed to be well balanced, producing a minimum of vibration, all the surfaces were moving in the proper direction and with the proper authority… Nothing left to do but fly. Unfortunately upon reaching about half throttle, about 10 feet into the takeoff roll the top hatch that I had created decided to eject. Testing a second time showed the same issue. It hadn’t been jolted loose on a bump either it was simply being swept up by some combination of the air moving over the top of the wing and the air pressure forming inside the plane as the motor forced air into the various openings in the firewall. While the louvers I had installed on the bottom of the plane might insure a good vacuum to pull some air past the batteries once she was in flight, they didn’t do enough while the plane was just starting to roll to avoid the top hatch getting popped open. For the day, I simply applied some box tape along the front and rear edge of the hatch and things were fine from that point on. For future flights I had to do something to make the latch mechanism a bit stronger. Clearly the magnets I had in place were insufficient.

Before the next flight I eliminated the magnet and screw head that I had used to secure the hatch and cut a groove in the wood and created a tab using a servo horn to form a rotating latch that would insure the hatch stayed in place. Ten or so flights later, this seems to work well.

Servo arm loose on rudder!

The final lesson re-learned on the second or third flight of maiden day for the Carbon Cub was that you should always tighten all the screws and check all of your servo arms, linkages, etc… before flying. The rudder and elevator servos are under that bottom hatch and so not observable without unscrewing and removing the bottom hatch. Apparently, when I was setting up the plane, adjusting throws and linkages and such I had neglected to make sure all of these were tight. The servo arms are metal and are a decent fit but slightly loose on the servo shaft. If the teeth are engaged there is zero slop but if you don’t tighten up the servo shaft screw the arm will slip off and rotate out of place… especially when sitting in the trailer, bouncing down the road under the force of gravity I imagine?

So 2 or 3 flights in was doing some stall turns and I was getting adjusted to just the right inputs to get an acceptable looking maneuver when it flopped out of one of my attempts. Since I was low on battery I decided to come down and check out my throws and see if I could improve on the next flight. When I landed, my plane was crabbing slightly toward the pit area so as soon as the tail dropped down to join the mains on the runway I started to feed in just a touch of rudder to straighten the roll out… It wasn’t enough so I pushed in more but nothing occurred. I was far to close to the pilot line and rolling fairly slowly so throttling up without being able to change heading was not an option, especially with a plane I had only a couple flights on and knowing someone was occupying the flight station I was quickly approaching. Instead I hit throttle kill and watched it roll up and bump the flight station. Other than a startled fellow pilot, no harm was done. He maintained focus and control of his airplane and I went down and apologetically retrieved my errant bird.

Of course as soon as I saw the rudder “freely” swinging in the breeze I dug in and found the culprit quickly. I applied just a small amount of nail polish (thread locker is known to attack some of the “plastics” used in servos… Hitec Karbonite in particular but others as well… so I largely avoid it around my servos) and tightened the screw and have had no further issues with this connection since.

Flying with the Power 60 on 6S

The Hangar 9 team recommends the Power 60 for the Carbon Cub if you are going electric and I think they have a pretty good combo here. With my 6S 5000mah packs I believe the plane is capable of handling about anything the real world plane can do, and perhaps a bit more. This does NOT include an unlimited vertical climb with out assistance from the wings but it is not far from it.

My impression is the plane flies just a little “heavy” on the wing and thus requires a bit more speed than I would like, but keep in mind I fly mostly very light, overpowered aircraft like my EF Laser on an Xpwer 35 and 12S, the Timber X on 4S, the Uproar on 4S, etc… For a war bird guy, this thing would probably feel lighter on the wing than most and most scale pilots I suspect would see it as being “about right”. You have to remember that while it has “Cub” in the name it is NOT the ubiquitous yellow J-3. It is not a floater that is hard to get on the ground but it is predictable and smooth. If you incorporate the flaps into your landings (as you should), the plane will land at a very manageable moderate speed with only a little time spent with the tail still flying after touchdown. It’s not a total kitten either in the air or on the ground but in return it is a very capable flyer and a beautiful airplane both close up and in the air.

December 15, 2020December 17, 2020

Top Flite 60-90 size P47 ARF… Gas to Electric P3: Motors, Speed Controllers and Batteries

This is part 3 on my journey of converting this aircraft to Electric power. To see the previous post on the topic, click here.

As I have mentioned previously, I had picked up a nice Hacker motor from a flying club member and it seemed like it might work out as a power plant for this aircraft. I needed to get that mounted and also figure out what sort of ESC might be appropriate as well as selecting an appropriate battery and then figure out placement and mounting for all of that. So here was my process.

First I researched the airplane, including expected weight, wing area and ground clearance. I also read a bit on any balance issues folks reported to see if I was likely to need nose weight or tail weight and the weight of the suggested power plants. Armed with that I logged into ECalc and filled in the blanks with the wing area, weight and the motor type I had on hand. I then started plugging in appropriate speed controllers, props and battery combinations to see what I was going to need to get a good power to weight ratio. Something in the 1.2:1 or higher range seemed like a good goal for a fighter aircraft like the P47!

I like to keep the voltage high and amperage low in an RC aircraft power system. Higher amperage is hard to accommodate as most of our common connectors are not rated for it. If you overtax them, they get hot and waste power and eventually this causes a catastrophic failure. For similar reasons, our LiPo batteries will fail quicker when you run demand high current rates from them, plus they cost and weigh more as you try to accomplish this with batteries that have a higher “C” rating.

A little rant about LiPo C ratings… Feel free to skip the next two paragraphs if you like.

In general, C ratings are useful only in that a higher C rating within a manufacturer battery line indicates the ability to supply more current without damage to the battery than the batteries with lower C ratings. Beyond that they are deceptive at best and almost useless for comparison between manufacturers. Feel free to disagree but I am convinced that this is the state of things at this time and don’t expect it to change anytime soon so don’t put to much faith in C ratings.

So, while my large aircraft could (according to the manufacturer C rating) run on 20C cells, typically 40C cells get pretty hot and therefore fail sooner rather than later. The 50-60C packs simply perform better, don’t get as hot and outlast the lower C ratings… at least in the brands I most commonly run. I don’t bother to purchase from companies who advertise 100C and better as they are pure fiction in my opinion. A continuous draw at the advertised C rating is almost always a recipe for battery destruction in very short order and in the case of larger capacity packs is likely going to result in batteries dying from internally generated heat and wires/connectors or something similar failing anyway as the system quite literally “melts down”! It’s a joke to say you have a 4000mah 100C pack (that equates to 400A draw) and then putting a connector on it that is rated to handle, maybe 100A for short periods before it literally “melts down”! The cells in these packs might handle 150A draw with perfect ventilation but I doubt it. OK, rant over.

Back to sizing the system I came to the conclusion that running an 8S system with a 16×10 prop would be a good starting point with a predicted 1.3:1 thrust ratio. Partly this choice was based on the power I wanted and partly due to available speed controllers. Spektrum had just released a line of Avian speed controllers and one of them was capable of 8S (which I estimated was close to the biggest packs I could likely get into the airplane) and was rated at 80A continuous with 100A peaks which was as much as I really wanted to run through the EC5 connectors anyway! It was also far less expensive than the Castle Creations options in this same range and had Telemetry built in that I was going to want. I can do that with Castle Creations and most other speed controllers as well, but with even more expense. This setup also allowed me to prop up a bit for additional power if I later decided I needed to, which is always a nice option to have. The tradeoff if I did was that a 16×10 would likely give me 7 minutes or more in the air with a 5000mah pack while a 17×10 or 18×10 would start to cut into that as they would draw more amps.

In order to take advantage of the telemetry capabilities I wanted to access from the Avian speed controller I also would have to acquire a new receiver. I settled on a new AR6610T. That wouldn’t be a terrible expense as I had a project that needed a simple receiver like what was currently installed in the P47 so one way or another I was going to be buying one soon anyway.

Decisions made, I placed some orders and started looking to mount the motor. This came down to simply finding the right size spacers and then a hole for the wires to get through the firewall and some judicious trimming of the dummy engine.

The spacer length I needed turned out to be the same as some readily available standoffs for a DLE 30, which simplified things a bit.

Then to allow the prop to clear the cowl I added a couple washers behind the prop collet assembly.

Accommodating an already existing 6S 5000mah pack plus a 2 cell pack of equal size and rating in series (which the speed controller accommodates simply as it already has a series harness attached!) was a bit tricky as the tray exposed under that hatch was simply too shallow for this setup and I didn’t want to buy several batteries for which I would have no other use. Here’s the original space.

So, I did some cutting and regluing to create a “ramp” that allowed for easy insertion of some of the packs I had. I had already determined that having the batteries up against the back of the firewall was appropriate to get the balance where I wanted it and while it was a bit tricky to cut out, the existing structure, thusly relocated, works well for the new battery compartment “floor”.

I needed some 2S “booster” packs (as I think of them) to add to my 6S packs in order to run an 8S system so I started looking for something appropriate. I ended up with some APower branded 5000mah, 60C rated packs I picked up from RCBatteriesusa based in Arizona. I had read an article about the company recently and decided to give them a try. They are not the cheapest place to buy packs, but not at the very high end either and offer a good warranty as well as being reputed to have top notch service. The folks there were as good as advertised in taking care of what I wanted, including the fitting of my requested EC-5 connector even though that was not an option on the web site when I first started shopping. At no additional cost I might add. After unpacking, examination and a few cycles they appear to be high quality.

That about covers the power system… I think. Next time I’ll try to run down my experiences and impressions of the first dozen or so flights.

December 1, 2020December 17, 2020

Top Flite 60-90 size P47 ARF… Gas to Electric P2: The Hidden Battery Hatch

For Part 1 of this article, click here.

It was the wee hours of the morning before I really made the firm commitment in my mind that the P47 had to make the conversion to Electric. At the next opportunity I started the process.

First order of business was to pull all the gas accoutrements from the airplane. First, I pulled the prop and cowl and started stripping out the gas motor mount, ignition and the supporting switch, battery etc… I knew a guy who was looking for a DLE-20 so I made him a deal on the engine to help finance the needed items to complete the conversion. I had the motor but needed a speed controller and maybe some additional lipo packs.

As soon as all that was out of the way it was time to explore the “hidden hatch”. For reasons that are beyond my comprehension, Top Flite built a hatch into the top of the P47 (and other models in this line of ARF warbirds). They framed it out in ply, put magnets in place along with pins to hold it in place… and then put a solid balsa sheet skin over the entire nose (including the hatch) and covered it with no markings or indication that it existed. Nor is it documented in any way in the manual!

With no guidance it became quite the task to figure out how to outline and cut the hatch free. What I eventually settled on was to take a pair of forceps with an extremely sharp needle locked in it’s jaws and reach down into the wing saddle and force it up between the two plywood plates at each end and side of the hatch until it emerged through the covering. By doing this repeatedly, working my way around the hatch perimeter I outlined the hatch on the covering. Then while holding my breath, holding my head at just the right angle and sending up prayers to the modeling gods (a more fickle lot I have yet to meet) I took an Xacto knife and inserted it into one of the pin holes and slid it by feel between the plywood plates. Working my way around the perimeter of the hatch, I managed to slice my way through the vast majority of the sheeting. With the judicious use of my razor saw, I got the hatch loose with only one problem… I managed to cut through the pins at the aft most part of the hatch!

Don’t worry about the wasp decal… I was planning on ordering replacement graphics anyway!

As you can see it wasn’t a perfect cut but it came out well enough!

Luckily, I had on hand an appropriate sized dowel and replacement of the pins proved to be a fairly minor task. I would later go on to add a hatch latch on the leading edge of the hatch… or at least on the new one I had to build after I found out the hard way that those magnets just aren’t strong enough!

Next time I’ll discuss the power system choices I made and how that is working out.

To see the next post on this topic click here.

September 20, 2020December 17, 2020

E-flite 60-120 size retracts

I recently came into possession of a Top Flite 60-90 size P47 ARF. It had a DLE 20 on it and was nearly in a ready to fly state and had never been in the air, but of course I couldn’t just leave it alone. I have zero non-electric aircraft in my fleet at the moment and it so happened I had the perfect electric motor sitting in the box… so of course I converted it immediately! I also knew that one of my flying buddies was in the market for the exact gas engine that was installed in the plane. Thus it began.

I won’t go into detail here about the whole conversion. For more details on that there are several posts starting with this one: P47 Conversion. Suffice it to say that just when I thought it was fully ready to fly, now under electric power, I ran into a problem with the landing gear.

The landing gear that came with the plane was a mechanical retract system with “plastic” mechanisms and it had a lot of slop in the system. Even when fully locked up or down the gear could rotate… perhaps 3-5 degrees. The result was the wheels would not stay tucked up in the wheel wells, nor did they maintain the proper angle when down and “locked”. I first realized how big a problem this was likely to be when I taxied the plane around in my driveway. After rolling 5-10 feet it was like applying the brakes. You could see the wheels tilt inward at the pavement and twist inward so that they started scrubbing against the concrete. It was obvious this was not going to work. If I got off the ground at all, surely any landing with the wheels deployed was going to result in a flip over. With an 11lb plane, a flip over was likely to result in some consequential damage.

Then the question became, what to do? I disassembled the existing retracts and looked at any possibility for improving/repairing what was there but I could not come up with an adequate plan. I could also go to one of two “big names” and get retracts for the airplane… whether they be mechanical, electric or air driven. I was concerned the mechanical systems from the big names might put me right back where I was (at worst) or work OK, but cost me $150 at best… and of course their electric sets, which I have used before are very pricey. I could easily have spent $300 or more on those. I had not intended to spend much money to get this airplane flying but there was no fixed gear option so I had to do something. I really wanted to go electric but the cost…

Fortunately I read on some forums how guys had put some E-Flite electric retracts in the plane and claimed they worked well. I take anything I read on the forums with a grain of salt. I’m convinced most will not admit that they are unhappy with something they spent a lot of money on and are now stuck with so I wasn’t sure. I tried to read the specs/look at dimensions etc… but unfortunately this is a brand from Horizon Hobby and their web site is simply pathetic. Not only is their search engine on the site total crap, but they typically provide very limited information on their products on the site and these were no exception. No indication of the build material, no dimensions, no complete description or listing of what parts come in the box, etc…but having few other options coupled with some good reviews in the discussion threads I was reading combined with an affordable price convinced me to take the plunge.

Immediately on picking them up from my local hobby store I was cautiously impressed. These thing looked like they were machined from aluminum and what’s in the box is very complete, down to the necessary allen wrenches provide (3) to fit all the set screws!

Here’s the box contents…

And here is a closer shot or two of the mechanism itself.

To me, these are things of beauty, and I only paid about $155 for the pair through my local hobby shop, including tax!

It took a little work to get them into the bird… nothing terrible and none of it reflecting badly on the retracts. Since installing these I have made I think 10 flights. I fly off of grass and Geotex runway and there has been no rain in the last 10 days before my last flights yesterday so the ground is hard and there are some bumps out there as well and so far these things have worked flawlessly. Not one time have I had an issue with either retract failing to move when commanded, coming up short of full motion, twisting wheels, nose overs… etc… From a functionality perspective, I have nothing but high praise for the E-Flite retracts.

If your looking at these and trying to decide if they are worth the money, I’d say yes. Further if you are trying to figure out how well built they are, I would say they are top notch. I’ve seen nothing to indicate that this is anything but top quality throughout. Finally, of course the information you need to see if these will fit is not to be found. So here are some measurements for you in case you need them.

I’m using English/US measurements and I’m sure these were made using metric measurements so these are approximate.

Across the mounting tabs the retracts are 1.75″ wide and 1.5″ long. Each tab is 15/32″ (just under a half inch) across the outer face. The depth of the units measured from the back of the mounting to the bottom is 1 and a 16th and the part that extends down into the wing is about 13/16ths wide. The mounting tab itself is approximately 3/16ths thick. The units themselves are approximately 3.25″ long (measuring the metal “frame”) which includes the motor mount etc… The strut is 5mm in diameter which allowed me to use my existing strut with just a minor trim at the top so that the “curly q” shock absorber bend in the struts lined up with the cutout in the wing.

Hopefully some of that will be useful to others out there. Wouldn’t a dimensional drawing from E-Flite be nice!! Still the units are top quality and reasonably priced! If your in the market, I don’t think you’ll be unhappy with these.

January 15, 2020July 27, 2020

Hangar 9 Carbon Cub 15cc ARF … Part 2

One of the first things I’m always concerned about with an RC airplane is just how easy it is to get flying once I get to the field. I really don’t want to be fiddling with 15 bolts and nuts that require special tools to attach, nor do I want to have to crawl around on the ground to assemble the airplane, etc… At least not if I have a choice.

With the H9 Carbon Cub I felt like it was going to just be to “fiddly” to assemble as designed from H9. The wing attachment method with screws that would have to be put in from the bottom of the wing, up in a hole and then adding in the wing strut bolt attachments, the battery placement and mounting method which was going to have to be done reaching under the wing and into the cockpit area and then a screw inserted to hold it in place?? Did they really think I was going to do that for every flight? I found it frustrating to do with no windows in place and the cowl off! I certainly didn’t want to try this reaching in only through the door on the side of the cockpit.

All of this screamed out for some modifications so here is what I went with. First, I decided that I wanted to reverse the wing mount tabs. IE. I decided to permanently mount them in the wing and make the body end be the area where any attachment task was done. To accomplish this I needed to remove the tabs from the body. This was fairly quick and easy with the proper application of a ball peen hammer. Here is one still mounted in the fuselage.

They have a shoulder on the inside of the fuselage so you need to push them into the plane body if you want to remove them. A few raps and they pushed into the body and were easily removed.

A tiny bit of wood came off with them but not enough to cause any concern. I then used the phenolic tab material as a pattern to make replacement pieces out of similar thickness aluminum. Since I want them to extend a bit further into the fuselage so I can attach them on that end, each of mine are about 1/2″ longer than the originals and don’t have a tab. I did drill the hole so I could attach them to the wing (I just intend to only do this once)!

Once all cut out and the hole drilled in each I did some sanding to round the corner and cut some slots into them so I would have a way to pull them together to keep the wings from sliding on the wing tube and opening up a gap between the wing root and the fuselage.

Even with this mod, I didn’t want to have to reach up into the cockpit through the door and put screws in, rubber bands on or attach a tie wrap or whatever. Between this and the need to swap out batteries I decided I wanted to have a removable top window.

This meant I needed to build some sort of frame to mount the window in and create a hatch assembly. This sounds easy until you realize that the top of the cub is a curved surface AND the opening narrows as it goes toward the rear of the airplane! So first step was to make some custom shaped window frames for each side. I began by tracing the shape onto some light card stock (sometimes having a greeting card crafter across the shop comes in handy!). I then proceeded to attach the template to some wood and then cut and sand to shape.

I then used some of my finer TLAR engineering skills (That Looks About Right) to make a rounded cutout in the bottom of these pieces in order to provide clearance around the wing tube. After that I cut a couple of appropriate length 1/4″ square sticks to use as the front and back. Each of these is custom of course due the aforementioned narrowing of the opening.

Once that was all completed and some careful fitting done, the frame was assembled (I laid all the pieces in the place in the top of the fuse and used CA to tack glue them together then removed them from the airplane and finished the gluing process).

After a test fit of the full (one piece) window, I carefully marked and cut off the material for the top window. Before attaching it, I colored the frame with a black permanent marker and then glued and clamped the window material to the frame with canopy glue.

This was allowed to dry for a few hours and then the clamps came off and I added a bit more glue around the inside edges to make sure it was not coming off anytime soon. From there I started working on ways to mount the frame to the top of the airplane. First I made a tab out of a couple pieces of popsicle stick and glued it to the front bottom edge of the frame at an angle so it would catch the front of the fuselage. This prevents the front from lifting. You can see this here.

I had to just do a bit of adding a layer of popsicle stick and then sanding a bit off to make it have a close enough fit. More black marker to cover up the wood grain took care of hiding it.

The final stage involved another stick of wood on the back edge of the frame to add some “meat” to the frame (my original 1/4″ frame I felt was just to small) and allow for the attachment of a “handle/antenna” for easy removal of the top hatch when needed, along with a block of wood to house a magnet to hold down the trailing edge. Adding some black pin striping around the edges to give it a truly finished look was the final step in building the top window/hatch.

After all this was said and done I decided with this easy access I could use a turnbuckle to hold the wing panels together. Its very quick and easy to put in place and because of some fitting issues at the wing root of the port wing, I needed something to put a fair amount of pressure on to hold the wings where they belong.

Here are a couple shots showing the final product. I feel like it came out pretty decent and I wouldn’t have been happy with the original setup.

Next time, I will discuss the bottom air vent I decide to add and a couple of other minor adaptations I made.

January 8, 2020January 15, 2020

Hangar 9 Carbon Cub 15cc ARF … Part 1 of ???

A couple months ago my flying buddy Gary picked up a Hangar 9 Carbon Cub 15cc ARF that someone else had begun assembly on. After he had done a bit more work on it he decided it wasn’t for him so I acquired it in turn. I have always thought it was a beautiful airplane and wanted one so while I’m not sure how good a flying craft it will be, I decided to give it a go.

First, I had to decide what I would power it with. For me that was an easy decision. I doubt I will ever have another glow engine… expensive to run and messy. Other than having good memories that pop up when I smell hot glow fuel, there’s just no good reason I can think of to put one on an airplane these days. I may do another gas powered RC airplane one day, but not glow. It doesn’t hurt that I happen to have a slightly used Power 60 and 100A Castle ICE sitting in a drawer. Decision made, I started going through the manual and deciding what still needed doing to get it flying.

In addition I needed to go over the airplane and see what the previous owners had done that might need some attention. I also started researching the airplane online and noting what I might want to add or modify. So far I’m still not quite to full flight status! Like most of my builds, this one has been interrupted, delayed waiting on some parts or just to give me time to decide how I wanted to do things, and has taken about 10 times as long as the manual suggests! I’ll start to add some articles soon detailing the changes/issues and challenges I’ve had getting the Cub ready to fly.

June 9, 2019July 27, 2020

Balsa USA 1/4 Scale Cub – Part 6: Wing Mounting and Struts

It seems like the work on the Balsa USA Cub never ends. Some of it is just that the BUSA kit seems to be more complicated than most and the way the designer/manufacturer chose to do things sometimes makes no sense to me. Also, since I got this as a partially constructed kit, I’m having to go back over everything to see what parts the previous builder changed, skipped or just didn’t follow directions well!? Of course the fact that I’m “converting” it to a super cub is not helping the process along either!

One of the things I have spent significant time on concerns the wing attachment methods. The original plans call for a couple pegs through the wing roots and two bolts as well to hold each panel in place. In addition the struts are load bearing. They are bolted to the ply plate that makes up the fuselage floor and screwed into hard points on the wing. When I first tried to assemble them I quickly found the whole process to be frustrating and overly difficult. Getting the wings in place and holding them there while installing the bolts was difficult and that was without any windows in place! I can’t imagine what a PITA this would be once the plane was all covered and the windows all in. I quickly realized something had to change. In addition, it seemed entirely possible to cause some damage to the plane while installing the wing struts as the entire weight of the wings at that point is hanging on the wing roots and the structure between doesn’t seem all that strong. Thus the need for load bearing struts!

So I first added a wing tube to each wing and fashioned some bracing inside the top of the cockpit area to give it some strength. Now there is something a bit more substantial to hold the wings while the struts are being installed at the flying site. You can see the aluminum tube in the wing center joint and inside the wing panels below. There is a carbon fiber tube inside.

The strut attachment method seems a bit ridiculous as well with no concession to ease of installation or transport. The vertical wires that connect to the wing mid-point don’t seem to be movable or easily removable so transporting the struts looked to be a pretty interesting prospect. Add to that the directions for attaching the struts to the wing hard points uses wood screws… which to me is just a uniquely bad idea. How many times reassembling this bird before a screw is over tightened, stripping the wood and weakening this critical attachment point?? I understand these kits are designed to be very scale like and that most builders are going to modify all of this to make it even more so. Maybe they don’t intend to fly the plane all that often… but for me, if it isn’t reasonably simple to assemble when I get to the field it will likely get little flight time and become a hangar queen. I’ll take slightly less scale like and more functional and easy to get in the air over scale in this case. BUSA might as well just say “figure out a method that will handle the stresses and that you find acceptable to assemble” , and leave it at that. The directions they do provide seem to me to be a poor attempt at best.

After a lot of fits and starts and coming up with several plans and then rejecting them I came across some struts and connecting hardware from a 1/4 scale clipped wing cub at a swap meet. The struts were far to short but I cut off the ends in hopes of using the attachments.

I don’t know why he had them but the gentleman had 2 or three sets so I picked up a set for myself. I looked at them twice with great regret that they were for a clipped wing cub but then figured if nothing else I could use much of the hardware. Once I looked closely at the hardware the wheels started spinning and I realized the hardware alone was more than worth the price. So I created some Frankenstein struts.

Below is a snapshot of the mid-wing attachment point. Using the threaded “eyelets” with threads tapped into the hardwood blocks in combination with the hollow aluminum tubes with built in attachment points, a 4-40 bolt and nylon insert nut makes for a secure attachment point. The tubes and wires were trimmed and epoxied together after adding some grooves to the wire to insure the glue gets a good grip.

On the other end of the wire, I used some nylon landing gear wire straps and #2 screws to create an attachment point that is both strong and allows for an easy pivot point for storage. This shows them pivoted down against the struts for storage.

At the outer attachment point, the main strut connections are bolted to the hard point with 4-40 bolts and blind nuts. The ends of the wood struts were trimmed to fit inside the aluminum tube ends as well and attached with glue and screws to the wood strut ends. This took extensive trimming and measuring to get the correct length and support the wings in the correct position. Each is somewhat custom! The nice thing is the ends of the struts that I recycled have a threaded rod at each end for fine adjustment.

I attached the outer aluminum ends with expanding gorilla glue and some #2 screws to “pin” them in place. Now I have a nice pivoting attachment point that I don’t intend to disassemble often as the struts can be pivoted down to sit flat on the wing for storage.

Each strut, once adjusted on final assembly, should take only 1 bolt at the attachment point on the bottom of the body and 2 more at the mid-strut attach point in order to easily assemble or disassemble the aircraft and still provide plenty of needed support.

Combined with the wing tubes, which require a single bolt on each side to attach, the entire assembly process shouldn’t take more than about 5-10 minutes and I expect it to be both strong and fairly straight forward to accomplish.

There is still a long list of projects to get this plane ready to fly, some small like hinging of the wing surfaces, and some large like getting the cabin windows, windshield and door assemblies all finished. More updates soon.

January 23, 2019June 12, 2019

“Balsa USA Bristol M-1 Part 3: Final adjustments and test flight.

After making the previously documented adjustments I had some on line conversations with the local WWI enthusiasts and found that one of the reasons my Bristol flew so poorly was likely related to adverse yaw. I took it back out and flew it and I could obviously tell this was the case.

For those lucky enough not to experience it, here is my attempt to demystify a bit. Yaw is the motion around the vertical and along the horizontal axis that causes the nose of the airplane to point left or right. This is typically provided by the use of rudder… at least when it’s intentional! Adverse yaw is the motion that occurs around the vertical axis when you roll the aircraft by the use of ailerons. For instance, when you attempt to roll and turn to the left the left aileron will extend to the top of the wing and the right aileron will extend to the bottom (downward if the plane is upright). Both ailerons will immediately increase the overall drag of the airplane but in some cases (especially on flat bottom airfoils) the downward motion of one aileron creates more drag than the aileron that extends to the top (upward) side. If you think about what that means, the pilot is attempting to roll and turn right (for instance) but the drag on the left wing aileron extending downward is pulling the nose to the left! This is not the direction of motion the pilot intends, thus it is adverse! The quick fix is to input rudder in the direction of the intended turn. This can be done either by the pilots input or by creating a mix. Either can work, but I’m not a fan of this solution no matter which way you implement it.

It seems to me we have a problem that is created by an excessive amount of drag on one side of the plane that we now plan to correct with more drag applied to the other side of the air frame. More drag means the airplane slows and we get closer to stall. Depending on how close we already are to stall… this can be bad. Of course if more power is available we can overcome this problem but we are just adding more complication and more difficulty to make all these forces balance out. The pilot’s chances of correcting with just the right amount of rudder and power while executing a turn in an aircraft experiencing adverse yaw are decreased markedly versus an aircraft that does not have this issue. I want a smooth coordinated turn, not a wiggling, jerky, abrupt maneuver that looks like the pilot has had to much to drink, so I decided to use the aileron differential feature of my radio and let it handle this for me.

Aileron differential requires that the two aileron servos be connected on two different channels so they can be controlled independently. By programming differential the two ailerons will extend by different amount. So when the port (left) aileron goes up, the starboard aileron goes down but by a lesser amount. Less down means less drag and the nose is not pulled toward this side and the maneuver can be completed without the necessity of rudder input. Some rudder may be desirable for things like a coordinated turn but that is a whole different topic.

For the Bristol this was the final piece of the puzzle that made it fly the way it should. At least the way it should as I understand it! A return to the field for more tests and the adverse yaw seemed to be under control.

After all of this I began to realize that this airplane would never fly up to my hopes and expectations. It is a WWI design after all and it just will never be what I regard as a “good flying” airplane. It’s nice to watch it fly… and I had no problem getting it up and down and performing the basic aerobatics that it is designed for but it was not a floater (which I enjoy) nor a precise maneuvering acrobatic ship. It just always feels like its slogging along to me. For that reason I am in the process of stripping the power system and electronics and will pass it on to someone who is more interested in this type of airplane and can really appreciate it for what it is. So long Bristol.

December 6, 2018January 23, 2019

FMS T-28 Trojan V4 Yellow 1400mm – Cursed?

A club member recently picked up the FMS 1400mm T28 as a step toward getting back in the air. He’d been ill and hadn’t flown much for most of a year but he has flown a bit of everything and now does mostly Turbines so he wanted a war bird with retracts and flaps… something to get his fingers re-awakened but still with the extra “complications” of flaps and retracts so he wouldn’t get out of the habit of using those! After a bit of debate he went for this bird:

I never did hear the whole story but apparently, right out of the box the plane had issues. I heard stories of at least one speed controller swap, retract issues and a bad aileron servo… I don’t know exactly the list or the sequence of events but he quickly ran out of patience to troubleshoot all the issues and offered to sell the bird at a bargain basement price.

A second club member (let’s call him Gary) picked it up and got a warranty swap on the bad aileron servo which he replaced. He planned to bring the plane to my shop to troubleshoot any other issues he found but as fate would have it, he was in the midst of one of his infamous multi-part swap/purchases and the plane one again changed hands, landing now with Steve. One part of the plan didn’t change and that was to get it to my shop for a thorough once over.

Once the plane arrived Steve and I started testing and going over the plane to see what all was or wasn’t working. We did a quick bind and testing of the plane and quickly found one issue… NONE of the three retractable retracts actually did anything! Not a buzz, beep, wiggle or shake to be seen! No amount of coaxing, servo reversing, battery swap, rebinding, driving with a servo tester or anything else would make them budge.

Over the course of a few days I traced down all the wiring to each retract and nothing would convince any of them to move! This is not as simple as it sounds as the receiver drives a distribution board in the body of the plane which then is wired via a multi-wire connector (looks like a balance connector on a 5S lipo) to another distribution circuit board/box buried in the wing root where the retracts, flaps, ailerons and lights for each wing are plugged in. This is all starts to quickly look like a spaghetti bowl but eventually I pretty much had it mapped out in my mind.

Eventually I plugged in a servo at the wing root connection and proved that signals were getting to that point as the servo moved appropriately. I did this for all three retracts and every one of them tested the same… bad retracts! Now I have no idea how the retracts got to this point. I’m fairly sure they are not shipped in the down position and all were now in that position. They did not stink or have obvious damage so it was not obvious if they were somehow abused but it seems crazy that all 3 would fail in this manner. I guess we will never know.

Fast forward a week or so and 2 of the 3 needed retracts have arrived at the shop. Swapping them out is not overly difficult. I found the simplest way was actually to completely open up the retract housing (split it after removing the 4 plate screws AND the 6 small diameter screws that hold the two sides together and just replace the whole trunion, strut and wheel assembly.

Seemed easier than fiddling with all the set screws etc… especially for the nose gear with its’ C clip. As best I can tell the electrical parts are all the same for nose and mains so I swapped out the Port main and then the nose gear and both worked perfectly after that! So, confirmation that they were indeed bad.

Two or three weeks later another couple retracts came in and I once again dug into the T28. Third retract install complete and it is working… Reassemble everything and then suddenly it doesn’t!! Double check all connections and no go… time to take the plane apart again and recheck all those connections. Re-seat all the connections and everything works fine again.

OK, so back together and checking everything and what’s this… both Ailerons move in the same direction?? Long story short (this story is long enough) the servo that was supplied as a warranty replacement turns out to be a reversed servo! So call the local hobby store and order a replacement (correct) servo… wait and then take it apart again and swap that servo out. Now it should all be good, right?

Reassemble, checking at each step, and all looks good with the new servo functioning correctly until after the final wing assembly. Plug the battery back in to do a final check and what the what?? When the battery is plugged in nothing happens… and I mean nothing! No lights, no beeps, nothing!! Try different batteries… nothing. This is an ARF… when will we get to the ALMOST part of this??

At this point my cursing skills are well exercised and I’m beginning to think I might go pro… Something with the new servo?? One more time to check all the wiring… disassemble the whole plane again and trace wires when I notice something. One of the “wing root” connection boards looks like this:

Bare wires seem bad… especially when some of those little hair thin wires look like they might be touching?! I have no idea but my theory now is this is what started all the issues… It’s possible that these wires were pulled out as repairs were done… by me, perhaps… by the other 2 guys that have had their hands in the plane… maybe. But to my eye the insulation on the wires seem to have none of the white “goo” on them and a couple of the stray wires do. I think this was something the factory missed on. I’ll never be sure.

So while I have the plane plugged together BUT still all connected, I unplug the white XH style connector that feeds this side of the wing and try again and… Beeps, buzzes and all the other “correct” noises issue forth!! I think I may have heard some angels singing… just sayin…

So under a magnifying glass I went through and separated all the wires and painted that connection point with liquid masking tape. Once finished the final product looked passable:

Once reassembled it all looked great. Flaps, ailerons, rudder, throttle… check. Retracts… all three down and locked and back up again… check. This thing might just fly yet! Just as I was doing the happy dance… Hey, why is that landing light not on… At that point I had to make a decision… smash this thing into a hundred pieces and make up a good story for Steve on what unfortunate event had claimed the ill fated T28 or one more time time through the wiring. OK, so this one was simpler. About a 90% chance that the 2 wire, unkeyed connector (OK, its color coded but why not use a standard servo connector so idiots like me have a better chance to get it right?) is plugged in backward. Yep, that did it.

After all that, she looks to be ready to fly… finally. After purchasing the plane at less than half of what it originally cost, Steve has spent enough on retracts and a servo that he is pretty much up to having paid full retail and then a bit! If I charged minimum wage, I think he’d have to tell the wife “Sorry honey, no Christmas this year”! Good thing we do this for fun.

Hopefully all this will be worth it when this bird take to the air. T28s are typically great flyers so we are looking forward to seeing it in the air. Maybe we should schedule an exorcism instead of a christening!

September 11, 2018

Balsa USA Bristol M-1 Part 2: Straighten up and fly right??

After arranging a battery compartment, getting servos installed, repairing the landing gear mounting holes, radio setup, etc… etc… I took the Bristol out for a couple flights. It was… underwhelming. I have a Great Planes DR1 Tri-Plane so not totally unaccustomed to draggy aircraft that need coordination to turn but for some reason I could not get the Bristol to make a smooth turn no matter what I did, nor even fly straight and level without constant inputs. After 3 or 4 flights I was getting a bit better at herding it around, but if that was as good as it gets… this thing would never find a lasting place in my fleet.

I am not accustomed to just giving up on an airplane after a couple flights… especially if I can’t identify why or what exactly isn’t working the way it should so I started checking, rechecking and gathering info about the plane. Certainly there are aircraft that I simply don’t enjoy flying, but that doesn’t mean they aren’t doing what they are designed to do, and doing it well and consistently. I’m fairly sure I started out tail heavy which just amplified all/any other problems. Later flights I shifted the battery forward and things improved but still not stable/reliable the way any simple aircraft like this one should be!

Eventually I started going through the way it was built and started looking at things that I would pay attention to if I had built it. Eventually, I found at least one issue that could account for some of the odd flying I experienced. During any build from scratch, kit or even ARF you should always check the Horizontal alignment of the wing to the thrust line of the aircraft as well as the tail to the wing and the alignment of the vertical fin at a true 90 degrees to the horizontal. Since the Bristol looks kind of like a cigar with attached flying surfaces there is no really obvious way to check out the wing alignment to the thrust line but nothing jumps out on that score and frankly, if that’s off a little it probably won’t make nearly as much difference as the tail alignment to the wing. That is where I found an issue.

If you sit the plane up on a table top and prop up the tale a bit you can visually line up the horizontal tail surface with bottom edge of the wing. This will show that the two surfaces are at least level with each other. Well, you can if both surfaces are in alignment. The Bristol, not so much. Just to add insult to injury the vertical wasn’t vertical to the wing nor the horizontal stabilizer!

A bit more scientific method was in order, so I set the plane up on a stand and (using a piece of aluminum channel across the wing saddle as a flat rigid platform) set a level across the wing saddle. I then adjusted the plane to level.

Once the baseline was established, I measured the tail feathers to see how close to level they were. As you can see… not so much.

Left stabilizer

Right stabilizer

Verical fin… not so vertical.

So what to do… If the vertical had been perpendicular to the horizontal and the body structure had been something more traditional… like my Telemaster for instance… then I might have tried to do some twisting and heating to straighten things up. But with this cigar shaped body I couldn’t figure out how to make that work or if it was even possible!

So I went with plan B and created some wedges out of small pieces of popsicle stick and did a little cutting, wedging and regluing. Here is how it looks.

3 wedges, literally hammered into place on the starboard side of the vertical fin.

Then added a couple more on the top starboard side of the horizontal stab. I also put a couple on the port side bottom of the horizontal stab as well. The result was this.

Left stab now…

Right stab now…

Vertical now…

I’m pretty happy with the improvement and I’m debating adding some flying wires to help get the last couple degrees of adjustment I need to get to “perfect”. I think it may be the only way to maintain the proper alignment between the surfaces under flight loads in any case.

I’m hoping to get a test flight in again soon and hoping that now that I have the tail all straightened up, the Bristol will start to fly right!