Parallel Charging… don’t do what I did!

For those of you who are at least somewhat seasonal flyers like I am, you may recognize the dangers of the first few trips to the RC field after being mostly away from flying for some weeks or months.  There are new planes to fly, old problems with existing planes that you promised yourself you’d fix over the winter and of course just the early season issues caused by being out of the groove.

I recently had one of those “early season” moments (at least that’s what I’m going to blame it on) where I did something stupid because I didn’t have my head in the game when it mattered.  Here’s what I believe occurred.

My first mistake was in not being prepared.  Usually, when I get to the field I have already charged up flight packs and my radio, insured I have all the right bolts, tubes and whatever for the planes I intend to fly, etc… but this time I just didn’t get the proper time to prep so I arrived at the field with the two batteries I had for the plane I most wanted to fly in storage mode.  So I pulled out the generator, hooked up my power supplies, grabbed the high power charger and popped the two 5S batteries on the parallel board to charge.  Of course I did this all in a hurry and without putting my glasses on.

That’s when the fun began.  As I was starting to program my charger, the smell of burning plastic and some smoke started to issue from the area of the batteries!  I quickly yanked the battery connections lose and tossed the batteries into an open grassy area away from any nearby cars and my trailer.

Investigation showed the parallel board and connectors on the batteries to both be partially melted including the absence of several pins in the connectors on the board itself!

I later noticed (as you may have already) that the melted connectors on the board were the 6S connectors??? So somehow I had gotten the two 5S XH balance leads at least partially seated in the 6S connectors.  And I had done so consistently!!

I’m guessing that I managed to connect the ground part of the balance lead to the first positive wire on one or both, essentially grounding cell 1’s positive wire!  In any case whatever I did caused a enough current to flow through those pins so as to melt the plastic around them and de-solder some of them from the parallel board!

So main lessons learned:

  1.  Always wear your glasses when making these connections!
  2.  Don’t get in a rush.  There’s a lot of energy involved in this process and releasing it in the wrong way is dangerous!  Rushing anything involving RC airplanes is typically a bad idea.  If you don’t have time to take your time… don’t fly!
  3. Don’t count on the locator pins on the balance plugs to protect you.  Use your brain and your eyes to insure proper alignment!

While I was at the field I decided to cut the balance plugs (now mangled beyond use anyway) from the batteries as there were exposed pins etc… and I didn’t want to transport the batteries with any chance that a short might occur and cause another event in my vehicle or trailer!  I cut them off cleanly with minimal wire left exposed, one at a time, and staggered nicely so they couldn’t easily touch.  Also I was there for 3 or 4 hours after this occurred and the batteries weren’t swelling, getting hot or showing any other signs of distress so it seemed they might be salvageable and I wanted to examine them later on my bench.

 The next day at home I started going through and measuring the voltage and labeling each wire to identify the individual cells.  All measured in the vicinity of a storage charge level and by measuring each relative to ground I was able to figure out and mark the cell order.  Here’s my test setup with a battery in the midst of the labeling process.  I have the negative test lead clamped into the ground on the main load connection and that connection rubber banded down to keep it safely away from all the positive wires.

I found a place to purchase 5S extension leads, so as soon as I get those I will attempt to safely put a balance plug back on the battery.  Once I do that I can further test and cycle to insure the batteries are still good.  I’ll post again or add to this post when I finish that process to tell you the results.

In the meantime I’m wondering if a “safer” balance board would be a worthwhile investment?  Some have not only a fuse for the main connector (which mine does also) but protective self-reset able “polyfuses” on the balance connectors.  Right now those sound like a wise investment and I encourage you to consider that option if you start parallel charging.

Don’t get me wrong.  I don’t think that parallel charging is unsafe… just that it requires a bit of caution and attention to keep it safe!

Spektrum connect issues… resolved?

One of my largest aircraft currently is my Extreme Flight 74″ 12S powered Laser.  It is also one of my favorites due to ease of assembly at the field, unlimited vertical performance and the fact that it is capable of such beautiful aerobatics!  Sometimes it even looks good when “I” fly it!  Yep, the plane is certainly more capable than her pilot.

Really the only issue I have had with this plane for quite some time is on that occasion when I get it assembled and ready to fly… except the iX12 radio and 12 channel power safe receiver will not connect on power up!  It’s very frustrating.  It’s not that it has lost bind…  I’ve occasionally gotten it to work again by cycling power once or twice or even just taking it back home and trying again…  It’s was never obvious what I actually did to fix it… and sometimes it seemed nothing would.  It happens very rarely and usually if I just go through a rebind process it works perfectly from that point on for a long time.  This typically only occurs if the plane has been sitting idle for a period of times… week or months (like first flight of the spring) is the most likely time to have this occur.

So being as it is just getting to be good weather for flying on any kind of consistent basis here in Indiana, I just ran into this issue again!  This time I was at home and had decided to tinker a bit with the Telemetry when it once again refused to talk!  Power up the radio, power up the plane, pull the pin switches for both receiver and speed controller and… nothing.  Everything is sitting at centers and the usual sing/buzz from the servos but no link…  

I tried a couple of power cycles and still no luck so this time I decided to post on the Spektrum group on Facebook.  After several posts back and forth and a number of excellent suggestions, one gentleman pointed out that the power safe receivers would not link to radio if the proper number of remotes (he even said if just the A receiver was down, that would do it)  didn’t come on line and suggested checking the contacts and coating them with electrical grease to shield them from problems.  An intriguing idea so I went back to the airplane and did some more testing.  As I did so, I also noticed that I had not done my normal strain relief on these cables so I decide to take care of that before all was said and done.

What I found was that in fact the A receiver was certainly not linking up (no lights if I recall correctly… or at least no steady light) and once I re-seated the cable, everything linked up instantly.  Repeated testing showed it all working perfectly from that point on.

I have a fair amount of pride that few of my planes crash due to “avoidable” assembly and maintenance issues so I like to track these issues down and resolve them whenever possible and then apply the fix wherever it makes sense on the rest of the fleet.  This airplane for instance has redundant flight packs separate from the power packs that run the motor, nylon insert nuts on all of the ball linkage bolts, Telemetry monitored battery levels, etc… in order to make sure it is as reliable and survivable as is possible/reasonable.  So I decide to see if I could eliminate this issue for good.

After collecting the necessary items (all shown here except the liquid tape) I started to work to resolve this issue.

The process went something like this…  First pull the remote receiver (they are all attached with sticky back Velcro, so this is not hard to do) and the cable from the airplane.  Inside the box (I’m working in the living room so protecting the furniture/carpet from harsh chemicals and spills) I spray some contact cleaner into the end of each cable connector and into the remote receiver connector.  Once dry, I took a toothpick and forced some dialectric grease down into the holes on the cable connectors and then coated the pins in the connector as well.   I did the same on the receiver while still installed in the airplane… luckily it’s somewhat roomy in there… and then reconnect everything and wipe away any excess that squeezes out.

That should eliminate the possibility of corrosion in the future so once all was back in place I moved onto painting on some red “liquid tape” right on the back of the connectors and onto the first 1/4″ or so of wire for each of the four cables that connect to the remote receivers.  This helps to share the stress on those wires and eliminate the most likely break point for the connections.  The liquid tape will flex but doesn’t allow for kinking or pulling on the individual wires.  I have had a few of these wires break before but never had an issue once I applied this little “hack”.  I apply this while everything is plugged in typically.  If a bit gets on the receiver or over the outside of the connectors it doesn’t hurt a thing and simultaneously it can’t get in the way of the actual electrical connections if applied this way.

Here are the two plugs on one side of the receiver.

And here is one of my receivers sitting on top of the motor box under the cowl.  You can see how I have coated the connection, further protecting the wires against stress and contaminates to some extent.

We will have to wait and see how this works out.  I have high expectations that this problem is likely resolved and I feel very positive that this improves the likelihood that this plane will fly for years to come… or at least until I make a mistake behind the sticks!

UMX P-47 Electrical Issues Resolved

I received this UMX P-47 as a Christmas gift a couple years ago.  I have a warm place in my heart for the P-47 as my Grandfather helped put thousands in the air while working in the Republic plant in Evansville, Indiana.  I checked the markings and this model is based on an Evansville bird!  Excellent.

Here is what the little UMX looks like:

The P-47 was one of the primary work horses of WWII.  It was a favorite with a lot of pilots as it offered that most favored of qualities, survivability.  With plenty of armor protecting the pilot, a reliable air cooled engine and (as long as you had altitude) a dive speed that almost no other plane could match providing an escape if worse came to worse, a lot of pilots survived missions in a P-47 that would have had different results in other birds.   This led to a popular saying during WWII “If you want to get the girl fly a P-51, if you want to go home to your girl strap on a P-47.”

It was also heavily armed with 8 fifty caliber machine guns and could carry 3400 rounds of ammo along with an impressive load of bombs equal to more than a third of what the B-17 bomber could carry and so became a favorite with the ground troops as well, providing a lot of support to the boys below.

For all these reasons, I love a P-47 and though I don’t get to fly it often I do enjoy it.  It flies well for its size, is fast enough to look like its doing what it should be, and it tracks nicely, I’m sure partly due to the on board AS3X stabilization.  It requires a good size space to fly indoors and can’t take too much wind so outdoors is limited, thus the limited flying time.

Starting last year I’ve had the opportunity to fly at one indoor venue over the winter months that is large enough to enjoy flying this bird in.  It was during one of these events that I started having a weird issue with the aircraft.

Occasionally, the bird would suddenly and completely lose power while taxiing.   This happened once and I thought I just had a bad battery.  The second time it started working again when I picked it up and re-plugged the same battery…  odd.    After that flight it went back in it’s portable hangar and sat for a couple weeks ’till the next indoor at which time I took it out and tried to fly again… It was only when the spark happened as I plugged in the battery that I recalled the previous issues.  I quickly disconnected a rather warm battery…  YIKES!  A close examination of the area helped locate the issue…

As you can see, the insulation has pulled back and several strands of the multi-stranded wire are trying to make some “non-approved” connections!  

To cure this problem I first cut off the remaining strands and then reattached them with the use of my handy “helping hands” soldering clamp.

 

Once that was accomplished I used some liquid tape to insure that no more unapproved connections were going to occur.

Then to help further protect the connection I applied some shrink wrap.  Here’s the final product.

I’ve since gotten 4 flights on the “Jug” without issue.  Unfortunately, with the recent outbreak of Covid-19… further flights are probably months away, but I am happy to report that the P-47 is back to mission ready status.  Here’s hoping we can all be healthy and back to this wonderful hobby soon.

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.

 

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.

 

Mini Convergence VTOL – First forward flight, and first repair!

Back around Xmas a relative gifted me with a nice little micro flyer for indoor use.  It was definitely a beautiful little plane… as a matter of fact it was something that I liked so much that I had purchased one for myself just weeks earlier!  So back to local shop I went to make a trade… and on a whim I picked up a Mini Convergence VTOL from E-Flite.

I flew it a couple times over the winter at some of our indoor events but I was not about to try forward flight in the limited space available so it sat mostly unused through the winter and for most of the summer before I really recalled it was over there in the corner in a pile with my other indoor flyers!  After I dug it out and charged some batteries I took it out to the field, rechecked all my programming to find the right switch setting to get into a forward flight mode and lifted off.

Forward flight mode went well and I was getting a pretty good handle on how the plane handled life as a fixed wing when the radio timer started warning me I should start to think about landing.  I slowed a bit and then flipped the switch to go back to vertical flight mode when things started to get “interesting”.

The plane began to immediately flip end over end and no control input made a lot of difference.  It didn’t fall very fast but all I could do was throttle down when the ground came up to grab the airplane.

Back on the bench here is a view of the culprit…

As you may have noticed there’s something missing on the rear motor… two things in fact.  The prop and the spinner nut!  No wonder if flipped end over end!  There were also a couple of foam “piercings”.  One in the wing and one in the canopy.  Neither of those are any real concern.

Luckily the bird comes with two spare props.  The rear prop, I found, is the same as the port/left prop.  This has it’s pitch in what I would consider the “standard” direction for aircraft with a counterclockwise rotation creating rearward/downward thrust.  Luckily, I just happened to have an aluminum prop nut/cone with the correct thread in the shop and the plane comes with one of each type of spare prop so that problem was quickly solved.

Unfortunately when I powered the plane back up I quickly found another issue.  The port side motor did not rotate up into the same position as the starboard. 

I quickly realized something was not right with the servo that performed the “tilt” on that motor.  Opening it up, you can see why.

To get this view I had to remove that servo which required removing a couple screws to get the servo unmounted and a few more to remove the plastic faring that covers the bottom of the boom.  Also, I disconnected the linkage and finally I had to split the tape with a razor blade (careful not to cut wires) and once removed, open up the servo.  Some of that disassembly is shown below.

Reassembly had to wait a couple weeks but was not particularly challenging.  For once I didn’t lose any screws, linkage, etc.  The only real gotcha was to make sure you have taken note of where and what orientation the plug goes into the receiver/main board and be sure to power up the aircraft and allow it to pivot the servo to the starting point so you can line up the servo arm on the new servo so that the two engines are pointed in the same direction for startup.

So, moral of the story.  When you read on line that folks have had some issues with the prop nuts loosening up and you should check them before each flight… listen.  For my part, I decided to do something to help the nuts stay in place so I put a bit of clear finger nail polish on the threads of all three of the motors before replacing and tightening them down.  I find it works pretty well as a thread locker for such things without risking any damage to plastic (like the props).  Some thread lock compounds have been known to make plastic brittle over time!  It is also fairly easy to muscle the nuts back off with the finger nail polish but in my experience does a fair job of eliminating any loosening due to vibration and the like.  IE it can broken free again but won’t generally fail under normal use.

I’ve made one flight since this repair and the aircraft did well.  So if you have one of these, do yourself a favor.  Go unscrew all three prop nuts and find some non-permanent thread lock (or raid the wife’s nail polish stash) and take out a little insurance.  

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.

“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.

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!

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!