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.

 

Top Flite 60-90 size P47 ARF… Gas to Electric P1: Decisions

I already posted a bit here about this airplane with the focus on the retracts I used.  You can see that post here.  This post will focus more on the Electric conversion process and the results of that.  Note that I never flew the plane with the DLE 20 that was on it when I acquired it so can’t compare to that… I can only tell you about my conversion process and the results I got.

Acquiring the airplane

I have a flying buddy that has been in and out of the hobby for the past several years named Martin.  Martin called me after not having heard from him for a bit (maybe a year or more) and reminded me of a P47 that we had worked together to get ready to fly.  It was a 60-90 size Top Flite ARF and we had gotten it pretty close to flyable with a DLE 20 installed, servos and linkage all installed and even radio gear all in place.  For whatever reason it had just never made it into the sky.

Martin asked if I was interested in the airplane.  If you look back at my previous posts you will see that I already own a nice FMS 1500mm P47 that flies very well on 6S.  While I have a particular affinity for the P47 (my grandfather helped build them in Evansville, Indiana during the war) I was hesitant because this airplane is only slightly larger than the foamy I have and I wasn’t sure I really needed two P47s in a very similar size… plus I’d have to consider whether to convert it which might be quite a job.  Add in that I really didn’t have any room in the RC budget at that moment for another airplane and I explained to Martin that I really couldn’t give him nearly what it was worth.  Martin however, explained that he simply wanted to get out of the larger airplanes like this and since I had spent so much time working with him on it, he was simply offering to give it to me!  I offered to at least pay something but Martin insisted that if I had an interest that it was mine.  He even offered to deliver to the field in a couple days when I was planning to fly.  What could I say?  Of course I accepted.

Here’s what she looked like just after delivery.

 

Modifications and Decisions

After a lite cleaning and a thorough inspection I made a couple decisions on things I wanted to change/upgrade or just tinker with a bit before I’d fly it.  A couple were easy decisions. 

First, I wanted to order a new set of graphics as the decals the came with the plane I knew would never last.  In my experience if you want good looking and long lasting graphics with few/no wrinkles or bubbles you buy vinyl… typically from Callie Graphics.  Callie is inexpensive, willing to work with you on any request and provides a great product.  I had a set of markings on a 50cc size Mustang for 3 or 4 seasons.  Many days the plane sat out in the sun all day and the vinyl never bubbled or faded.  I even had to peel the stars and bars from the wing and reapply them when I crashed the bird and bought a new wing.  They still looked like new when I sold the plane a few years ago.

Second, I knew I wanted to replace the landing gear, which I’ve already discussed.

The third issue was much more of a question and it took a couple weeks to come to a conclusion.  What to use for power?  Obviously leaving the DLE 20 in place would have been easy.  I knew the history of the engine and that it ran well before it came to be installed in this bird and it would certainly be an adequate power plant.  However, every other plane I currently own is electric and I had what I thought might be an excellent motor for the purpose.  In fact I had been looking for something to put the motor in ever since I acquired it.

Thus began several days of reading and research.  First I looked on various discussion groups about the airplane and what others had done.  90% plus had run gas engines… a few 2 stroke glow and a few 4 strokes rounded out the vast majority.  What intrigued was the 2 guys who mentioned they were running electrics.  Eureka!  Until I realized that there was just no easy place to put a battery hatch into the P47… at least not that I wanted to tackle.  the plane is pretty much all curves and being an ARF, access is limited unless you want to recover and rebuild extensively.  This didn’t seem promising.

While I mulled on that, I started to look into the electric motor I had and tried to figure out if it would be enough power for the P47.  The motor is a Hacker A60-5S-V2 and while the Hacker site has a fair amount of info there was only a bit of corroborating information that I could find.   It looked like it might be just a bit on the small side if you believed the Hacker site information.  Encouragingly, the actual users reported fairly uniformly that they were running this motor (and most Hackers it seemed) at the maximum ratings and even significantly above with no problem at all.  I picked up this motor at a swap meet NIB from a trusted source at about half the price of a new one… I could never bring myself to pay the full price when there were a lot of quality motors available at much lower prices… Could the Hackers really be that much better??  This was my chance to find out, right? 

With 90% of my previous electric setups I was always able to find a dozen examples of similar planes and power plants to compare to.  In this case, only a couple examples were out there… so lacking enough information to confidently pick a proper propeller and speed controller I decided to revisit an old standby… eCalc.  I won’t go into great details, but based on what it showed me I decided that the Hacker could “hack it” on the P47.   I might need to use 8S batteries (which I have none of) and the flights might be a bit shorter than I’d ideally like (6-7 minutes predicted) but I really wanted to try out this motor. 

So that issue aside I was back to the problem of a battery hatch…  I went back to all the groups and started reading again and after several hours of reading and making the firm decision to just keep the DLE-20 in place, I read a few more posts and one of the guys who was running electric power mentioned the hidden hatch… WHAT!?  I read on for hours and found nothing but then I saw reference that the hatch existed on this entire series of warbirds??  It was only 1AM by this point and I had to get up at least by 6 but this was important, right?  As I continued my research, I found a description of where the hatch was located and how to open it up on the sister warbird, the Mustang.  A quick trip to the shop and I confirmed the hatch did actually exist on my P47 as well… sort of… and the decision was made.  I had to try.

To see the next post on this subject click here.

 

 

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.

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!

Balsa USA 1/4 Scale Cub – Part 5 Finally back on the bench!

The cub has been sitting quietly in the corner of my shop for two and a half years now while other projects came and went including dozens of repairs/builds and modifications to my planes as well as many visitors projects.  It even survived the move that is nearly 2 years in the past now with no damage… so finally it has found its way back to center stage on my bench. 

If you want to catch up on the old posts, here are links to each:

Balsa USA 1/4 Scale Cub – Part 4 More Mods – Rudder Shape.
Balsa USA 1/4 Scale Cub – Part 3 More Mods – Flaps!!
Balsa USA 1/4 Scale Cub – Part 2 Modifications begin
Balsa USA 1/4 Scale Cub – Part 1 Acquisition and plans

Mostly getting back to this project came about because my flying buddy, Garry Bow, bought a Dave Partrick 1/4 scale Super Cub at the swap meet in Toledo this last spring and though he sold it before getting it in the air again, we have been talking about it enough that other folks in the club have decided to enter or re-enter the brotherhood of RC cub fliers.  I think almost every RC airplane enthusiast has already, or plans on getting, one variation or the other of the J-3, clipped wing, PA-18 super or maybe even one of the more modern variants like the Carbon Cub.  Cubs lend themselves to slow majestic flying and there are many different variations that allow for you to fly a cub that is at least semi-aerobatic, can tow gliders, carry a drop box, sky diver, camera or whatever.  Most Cubs are almost instantly recognizable to even those who don’t pay much attention to aircraft or RC and also make great entry points for scale building.  Cubs can be very simple 4 (or even 3) channel setups with a high wing and light wing loading.  This allows for slow and gentle landings and the typical Cub landing gear configuration can absorb some punishment in case of abrupt landings,  especially those outfitted with bush tires and working shock absorbers.   So it is time to get back to my latest endeavour into the the world of Cubs. 

My latest cub started life as a Balsa USA 1/4 scale J-3 Cub kit but I have been working to make it into something closer to a Super Cub.  I’ve detailed a lot of my modifications up to this point so I’ll try to just continue where I left off a couple years ago!

Looking back I realize that I did make one more significant change that never got posted and that has to do with the wing attachment method.  I really disliked the way the wing attached.  It seemed like it would take 3 people to get the wings on and off without damage to the airplane with just a location pin and bolts holding on those massive long wings.  I didn’t like the thought that damage to the root rib seemed likely if you didn’t get the struts on quickly before a gust of wind or careless bump to the wing caused an issue.  This design was made for someone who is much better organized and meticulous than I!

So right before I packed it away, I added a small wing tube arrangement to my Cub.  At first, I tried to put a straight wing tube and sleeve in place but then realized that a straight tube was not going to work well in a wing with dihedral!  So I assembled and shimmed and adjusted until the wings were sitting at the proper angles and then created a wing tube for each side utilizing the servo wire guide holes as a ready-made mounting point for the sleeves.  The tube itself is a carbon fiber tube from a friends wrecked airplane and the sleeve is an aluminum tube that the CF rod fits perfectly inside of.  I butted the tubes up in the center of the body and created a couple of new rib structures (complete with cutouts to make installing the mounting bolts easier) to hold them in place.  Now all I have to do is slide the tube into the wing and slide the whole assembly into the body and the wings have enough support for me to take my time bolting them in and attaching the struts.  Time will tell if this system works the way I hope it will.

Since I retrieved the Cub from its dark corner, I have started working on a couple of other changes too, including a new tail gear, engine mounting, and a glider tow release.  I’m still debating lighting options, float mounting (I have no appropriate floats yet), a possible belly pod (to mimic a baggage pod or fuel pod, both of which are in use on many Super Cubs) for candy drop or whatever, and possibly some hard points to carry a very non-scale sky diver drop mechanism I have.

Also, I have started to plod forward with the final steps the previous builder never completed like window installation, wing leading edge shaping, etc…  I’ll try to post on some of these activities soon.