P-51 Redtail… More progress. Wing repairs progress.

Further work is occurring on my quest to reassemble the Redtail without spending significant dollars and simultaneously lightening it up a bit in the hopes of improved flying traits.

The latest is around the port side (that’s left if you were to sit in the cockpit of the P-51 facing forward) main landing gear mounting area and wheel well.  That area took significant damage during the abrupt meeting between the retracts and beans at about 35mph!  Yep, that is about stall speed… or at least is was that day.

Here is a sequence of pictures showing the progress.  Most of this was simply measuring, cutting, fitting and a fair injection of TLAR engineering methods to try to get something put back together that will stand the strain.  TLAR… you know… “That Looks About Right”!

After cutting out the sheeting and getting rid of the various splinters and unidentifiable fragments here is what I was left with.

 

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I cut away even a bit more before adding back a bit of structure…  Rebuilding the rails so that the screws have something solid to bite into required some temporary bracing…

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Then I started building the actual rail structure and piecing them together with an eye toward making sure there was some interlock to help add some strength.  This rail notches into the rib and creates a lip for the rear rail to rest on.

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Here, all the rails are in place and all of the mounting screws have been drilled and put in place… lots of advanced TLAR to get the placement right (I hope).

 

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Then came the puzzle of re-sheeting around the fiberglass wheel wells.  I cut the existing sheeting back to expose a bit of the top of the spar and then pressed the sheeting down over the fiberglass to give me a cut line.  This created shapes like this ones.

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Then I added some small “railing” to catch the sheeting and give me some glue surface for the larger span of this piece of sheeting.  There was also some reinforcing and rebuilding of the ribs that contact the wheel well that had to be done.

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Here are the pieces going into place.

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And the final bits of woodwork are glued in.

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From here is will just be some recovering work, though I have considered adding a bit of light fiberglass reinforcing underneath the landing gear mount area…  We’ll see.

Next up is finishing up the covering and the last of the repair work on the fuselage.

Glow Carburetor Adjustment

Just a note to let folks know I just unearthed a little gem of an article on how to adjust your glow engine carburetor.  I believe this was originally posted to RCU back in 2004 but couldn’t find it when I needed it.  Now that I found a copy I did manage to locate it on RCU as well but I decided I would just post it here to my articles page just to insure I could always find it when I want it.  You can click on Articles above or you can just click this link to pull up the article directly.

Tim Mills Carburetor tuning 101

This was originally written by my late friend Tim Mills who passed on February 20, 2011.  Tim had an amazing touch with engines from Motorcycles to Airplanes… Gas or Glow, 2 or 4 Stroke.  Tim always said that you just had to listen to what the engine was telling you but he was one of the most fluent in that language that I have ever known.  I’m happy to share just a bit of his wisdom on the subject.

 

 

Throttle lock/Kill Switch programming on the DX8

A couple years ago I was taxiing back toward the pits with one of my smaller gas powered planes and had stopped to observer another flyer doing a nice touch and go… My plane was sitting by my feet at a sedate idle during this distraction.  When I turned back, I returned my left hand to my radio and inadvertently slid the throttle stick to full!!  Luckily I was pointed at the pit chain link fence 6 feet away with no other obstructions… like people… so as I grabbed the stick and returned the throttle to idle the plane made a dash for the fence and quit as a result of the impact and the prop breaking into several pieces.  It did no real harm to anything except the prop and my pride… but it woke me up and from then on I have been much more attentive to my models while they are running.  When I am idleing, my thumb is hooked across the top of the throttle stick so that it cannot easily be moved upward.  As well, I now have a kill switch on every fuel powered airplane and it is always in the same position on the radio so I don’t have to hunt for it!  With gas planes I have a mechanism hooked into the ignition circuit that kills power to the ignition.  Depending on the type of engine and ignition system it may work a bit differently but each disables the ignition which kills a gas motor immediately.

With the advent of more electrics in my fleet this became even more problematic.  Electrics, once the battery is connected, should be considered to be “running” in all cases and therefore treated with the respect that would be due any idling engine.  Since you can forget the battery is plugged in at times, I try to be especially careful to restrain my electric powered aircraft whenever I’m not holding on to them and a battery is installed.  I have also setup a throttle cut switch that limits the throttle channel output to zero or as close as possible.  In some radios this is simpler than others.  In my Spektrum DX-8 there are two ways to accomplish this… maybe more… but I’ll show one of them here that I use most.  (I believe the 7s, 9 and 18 all do it similarly)

Note: You can do all of the following without the plane even being present and certainly don’t want to play with this with the plane powered up!  I highly recommend you test after you finish however with the plane well restrained or the prop removed.

First, the DX-8 has a throttle cut option in the setup menu.  If you go into that menu and change the inhibit to a switch label (I tend to use Gear0 as I’ll show below) you get a screen that looks like this.

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You’ll notice that the switch is set to Gear0 (that’s a zero).  I use this setting as I tend to setup my radio so that starting point for all airplanes when I fuel up or attach a battery is with all switches pushed away from me.  It really doesn’t matter which way you do it.  I’ve worked with computers and electronics so long and the way I was taught logic you generally consider 0 to be off and 1 to be on…. I guess position 2 is “really on” in the case of a 3 position switch!

With my radio set this way the throttle is locked so it cannot inadvertently start up without moving both the throttle stick and moving the gear switch out of its starting “safe” position.  The other thing you may notice is that the position reads 30%.  I played with this and came upon this setting by trial and error.  I believe this has to be done because of two factors.  First, the designers created this for (I believe) primarily fuel powered aircraft where the stop/kill position is significantly different from the idle/standard starting position.  In an electric aircraft you generally don’t want an “idle” with the prop moving when you pull back to the lowest position on your stick.  You want a full stop.  Second, most speed controllers in my experience will look at the throttle setting on power up (as long as it’s at least somewhere near one end of travel or the other) to be the zero/stop point.  That’s fine until you combine with point 1.

So imagine you plug in the battery with the throttle 30% lower than “idle”… which is what the throttle position would be if you left that setting at zero and had the switch pushed forward/off when you plugged it in.  All seems fine… Your speed controller makes its little tunes and if you move the throttle stick nothing happens but your servos are energized (this may vary by manufacturer of the speed control).  Great, you are ready to taxi and you flip the switch to the armed/on position and immediately the prop spins to a “high idle” setting!!!  That’s not convenient, nor especially safe.  This is because with the kill switch in the forward/off position the throttle was at a point 30% or so below the idle point and when you plugged in the controller reset that to be “zero”.  By testing I have found 30% to be about the right point to avoid this issue.  Now the kill switch doesn’t really change the position of the throttle at all and acts more like a throttle hold then a cut.  Ideal for what we want when dealing with electrics.

There are other ways and other radios do it differently.  On my DX-18 which I fly more than anything else I use the F switch instead of gear because I use the gear for other things… like retractable gears!  But whichever switch you use, I suggest you keep it consistent.  This way your routine on each plane is the same at least as regards to a safe “startup” and also because occasionally you may want to hit it in a hurry and not having to think about which switch it is can make a big difference in response time.

I’ll try to post on a different method in the near future.  Hope this is helpful.  Fly safe!

 

Packs, Chargers, Power Supplies and more – Power Supplies

With the FMA PL6  chosen as the charger I ran right into the realization that I could never use the full capability without some increased power supply capacity…  My standard rig at the field was a low end, unlabeled supply that I got surplus at a hamfest.  It had never failed to deliver but I also don’t think it was designed for more than about 20A at ~12-13VDC.  In the shop I have a bit better solution where I have a 52A 12-15 VDC supply available.

However…  there is a limit on the charger in that the input side of the charger can only accept 40A maximum.  That translates to a max of ~500W of charging power on 12VDC.  In order to get near the full 1000W you would need something closer to 25VDC at 40A.  Of course no charger is fully 100% efficient so the real numbers are 15% or so less but the basic idea holds.  So what am I to do?  My first thought was to start hauling my 52A bench supply to the field but that has two drawbacks.  One, is I would be limited to the 12V max of something less than 500W.  Not terrible, but having the max power available at the field could be even more important that back in the shop where I have (figuratively speaking) all day to charge batteries.  So, off in search of a way to get 25V or so at 40A.

First, I started looking for commercially available, purpose built supplies to do the job and quickly realized that such supplies are both unusual and very expensive!  I really didn’t want to spend 2-3 times as much on the power supply as I did on the charger.  Keep looking… and then I happened to come across high amperage 12V supplies for what I thought were very reasonable prices.  $60 each.  They were converted from computer (Dell server) power supplies and could supply 57A at about 12-13V.  Ok, that’s much more reasonable… maybe I could just use one of those and get along with slightly less than 500W of charge power… at least for now.  But then I recalled I had seen information mentioning using two identical supplies in series to get twice the voltage… Now we’re talking!!

Based on that vague remembrance I bought two of these supplies.  Both together were cheaper than I had paid for the bench supply a few years ago and each was more capable.  After a modicum of research I started experimenting and found that I could get a good working 25V supply at 57A by wiring the two supplies in series.  My first attempt resulted in one of the supplies shutting down… but with a little more research I found that by isolating the ground I could avoid the second supply from seeing a short when both were plugged into the same AC source.

I believe the power supplies likely include bonding the DC output ground terminal to the AC ground.  This means that when the two supplies are plugged into a common outlet and are sharing the same AC ground they are also sharing a common DC ground.  The result is that when the positive lead of supply A is plugged into the negative side of supply B… it is essentially creating a dead short.  Luckily, these supplies are very sophisticated and include the ability to clamp down the output in a case such as this so no damage was done.

Once the grounds were isolated from one another the supplies powered up and supplied a nice steady 25VDC.  I created a carrying case from a Styrofoam cooler and built a power panel in order to have a single 24V output as well as the availability of either 12VDC output if desired.  It is well protected in the cooler (which opens up when in use for better cooling) both from the elements as well as vibration and “bumping” around in the trailer.  I’ll update this post with a picture or two in the next couple days.

This whole rig worked great on my bench, so I took it to the field and after 3 flights on the CZ Cub decided to do a nice 1 hour parallel charge.  I fired up my low cost 900W generator, plugged in my new power supplies and… nothing!!  Further testing back at the shop confirmed that the whole rig worked but just not with my generator.  I’ll go into that in the next post on the subject detailing my search for a new generator.

Lots of LiPos… maybe parallel charging is one answer?

I recently picked up a higher power charger… In my case, I chose the Revolectric FMA PL-6.  This is a very highly regarded charger and I did not pick it for just the power but that was a basic requirement in the decision making process.  So far, I am enjoying it and I will have another post up shortly with more info on that product.  The important plot point for now is that this is a single output charger that can crank over 400W of charge power at 12V and over 800W at 24V.  Compared to my previous chargers that have always (at most) been limited to 50W per output this thing is a real power house… but I was thinking I had to trade off quite a bit to get the big power.  For instance…

The first big trade off when looking at these higher wattage chargers is that they typically have fewer outputs.  On my old trustworthy Hitec X4 I have 4 outputs, each capable of 50W of charging power.  When you start looking at chargers with 400W or so you usually get 1 output or occasionally 2 outputs with 200W of power each.  By the time you get to 600W or higher you are typically going to get one output.

This was an acceptable trade off for me because my main goal in purchasing this charger was to allow me to charge my 6S 3300-4000mah LiPos in a reasonable time.  A 4A charge (one hour recharge for the 4000s) at 25V (approx.) requires a 100W charger.  With my 50W, charge times were in the range of 1.5-2 hours.  With my new charger I can charge at 2C (8A) which at 25V is 200W and charge in 30 minutes or less.  Not bad!  In a pinch I can even charge faster as the batteries are rated for 5C (20A) max charge rate which would bring me to a 12 minute charge provided I have at least a 24V supply!  I don’t like to push the batteries that hard normally but it’s nice to have that ability.

The problem, it would seem is that I now can only charge one battery at a time so if I charge at 2C or so I could charge another battery every 30 minutes.  That’s great but it sure would be nice to be able to charge multiples… Oh well, I guess I have to give up something for progress… or do I!  As it turns out there is a way to get there, and it really isn’t that difficult.  Enter the parallel charging board…

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With this nifty little board plugged into the 6S balance port on the included balance board as well as the main charge ports of the PL6, I can now connect up to 6 similar batteries at a time and using the high power charging capabilities of this charger I can charge all 6 at once!!    There are many versions of this board with various types of charge plugs, so be sure to get the version that is right for your batteries.  It’s really fairly simple to use and quite effective.  Basically as long as the batteries are all similar cell counts and are starting the charge cycle at fairly similar states of charge, you can simply plug all of them into the board (main charge lead first, then the balance plug from each battery) and you’re ready to charge.

As an example, let’s say I’ve flown 6 flights on my T28 using 3S 2200 mah LiPo batteries.  Assuming I’ve run them all down near exhaustion I simply plug in the main leads and then the balance plugs to the balance board, set the charger for 2200mah charge rate as normal but specifying that I am charging 6 parallel batteries.  The charger will then multiply the charge rate and start charging at 13.2A.  In an hour or so, all 6 will be charged.  If all the batteries can handle a 2C charge rate of 4.4A then we could charge them all in about 30 minutes as the charger would be pumping out 26.4A.  26.4A at 12V (all approximations) would require a bit over 300W which is easily attainable with even a fairly modest 12V power supply or battery.

There are a couple things to keep track of when parallel charging.  You should take it seriously when I say that the batteries need to start the process at near similar charge levels.  Any difference in voltage between the packs will equalize by current rushing from one pack to the other through whatever connections are available (thus the advice to connect the main load connectors first since they can handle more current).  This rush of current if pretty much unrestricted and could overheat another battery or smoke the balance board if the difference is to great.  Also, note that all the packs need to be of equal cell count so no mixing 3S and 6S etc…

When this really gets to be impressive is when you look at what happens if I want to charge up all six of my 6S batteries.  I have 2 4000mah, 3 3300mah and 1 3700mah 6S packs for use in several of my planes.  Using my old 50Wx4 charger getting all 6 packs back to charged state after a full day of flying would take at least one full charge cycle of 1.5 hours (at least) for the first four and an additional 1.5 (or more) hours for the second batch of 2.  This is 3-4 hours of charging.  Now, I can hook up all 6 packs in parallel and even if I pick a modest 3.3A charge rate the charger will then do the match and start charging at about 20A (assuming adequate DC power).  The charge cycle will likely take only a bit over an hour and all 6 packs will be race ready again!

I’m not sure I’d want to do this with packs that were hugely different in capacity… have to think about what will happen and whether this might cause issues but I’m not concerned with this particular scenario.  Of course parallel charging is possible with other chargers… this is not something only this charger can do… but to be useful the charger needs power to spare.  Your average 50W charger need not apply…  Here are links to both the charger and the  balance board in case you are interested in purchasing one or both for yourself.


 

 

“Wax” coating for foam airplanes…

As I have ventured into more Electric powered flight I have acquired more and more foam aircraft.  Foamies are great as they are durable, easily repairable in most cases and very light.  Foam is also easier for manufacturers to shape into all sorts of shapes and allows them to mold in a lot of intricate detail if desired.  Sometimes the downside of foamies is that the foam tends to get dirt and dust embedded in it, grass stains and other scuff marks etc… As well, whatever paint has been applied often wears away quickly.  That’s not a big deal when the plane is the $30 variety but as the foam and electric planes get bigger, more detailed, and more expensive, you tend to become more interested in preserving them.  Even my T28, which is cheap at twice the cost (but don’t tell Parkzone) gets dirty and ugly far to fast in my opinion.  I am on my third and have probably 1000 total flights on them, and wanted a way to protect the latest edition.

I have seen folks using a clear spray coating of either urethane or something similar but it can damage the foam (either the spray itself or sometimes the propellant used).  As well, many of these eventually yellow and are hard to remove once that occurs.  Looking for something better, I ran across some information recommending a coating of Pledge Future floor polish to help preserve the foam and whatever finish has been applied to it.  I hunted a bit and found the product had since been renamed and re-marketed as Pledge Multi Surface Floor Cleaner so I went out an hunted down a bottle and first did a test coat on a scrap of foam with promising results.

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I have since coated part of my FlyZone Tidewater and all of my Parkzone T28 with it and I have to say the surface seems to be quite tough and very slick and shiny.  In both cases I covered the airplanes by simply painting it on with a foam brush but you really can’t tell that by looking at them.  I have read that many folks have applied it with an air brush with great results as well but aside from giving you a thinner and lighter coating (which may be important to you if weight is a critical in your application), I don’t think you will be able to tell the difference in finish as the product seems to be self leveling in nature and I ended up with a very smooth, slick finish on both aircraft.  Here’s a view of the T28…  it may be hard to tell from this but the finish is much slicker now than it was before.

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So aside from a small amount of weight there are a couple possible downsides to watch out for.  As I learned first hand on the Tidewater, the paint on your foamy may be soluble by the coating!  Yep, the paint on the Tidewater started running as soon as I applied the “Future”.  So test first with a very small amount of finish in an unobtrusive spot before applying widely.  With care, I did manage to coat all of the colored areas with a minimum of runs (a bit of dabbing with a paper towel works wonders).  On the plus side the T28 finish had no issues at all.

Secondly, while the viscosity of the product (just a bit thicker than water) lends itself well to application via foam brush or airbrush, it also can run easily so apply lightly.  The good news is a little reapplication will often soften the area and allow the aforementioned self leveling to occur.  If worse comes to worse, ammonia based cleaners will take it off so you can start over!  Keep this in mind while cleaning the aircraft in the future as many window type cleaners will contain ammonia and dull or remove the finish.

Based on my experience so far, I’m planning on having a buddy do a coat of Future with an air brush for my Carbon Z Cub.  He has more experience with air brushing than I so once I do a little bit of customization/decoration I plan on handing it off to him for the actual application.

If you need to get some Pledge Multi Surface to try it out for yourself and can’t easily find it locally, here’s a link to Amazon for the correct product.  Pledge Floor Care Multi-Surface Finish

It’s cheaper there than I found it locally, even with shipping!  I’ll update this post with my experience once flying season is in full swing.  Please comment with your own experience here as well.

“Bargain” battery? Maybe now it is..!

While working with a new pilot at our club field the other day he mentioned that in order to get his charger to properly work with the battery he was using for his on board glow (a pretty standard 4.8V NiMH pack) he had to bend the wires just right and/or stick pins in the connecter, etc…

I immediately told him this was NOT the norm and he should not continue this practice.  This is a warning that something isn’t right and we need to figure out what and why.  He took the battery out and we tried to check the voltage and sure enough the connector was almost impossible to get a good connection on…  I volunteered to take it home for further investigation and likely swap out the connector.  It was clearly labeled as a 2300mah NiMH from one of the more recently arrived web based resellers and a quick browse showed claims that it is a low discharge NiMH variant.  Some call these Hybrid NiMH and there are other terms.  The nice thing about this type of NiMH is that have a low discharge rate when stored so they don’t tend to drop their capacity between flight sessions like many NiMH batteries do.  I wouldn’t use a standard NiMH if I could avoid it because I just can’t count on them to be ready when I am and I don’t always know I’m going flying, sometimes until a couple hours before leaving for the airfield.  Standard NiMH with their high on the shelf discharge rates just don’t work for me.  This is especially true when you combine that with the low charge rates most will tolerate.  I can’t store them fully charged and expect them to hold for long and I can’t fast charge them…. just doesn’t fit my flying habits at all.

This battery looked like a nice combination of low price and a reasonable battery technology for our needs in RC aircraft.  Combine that with a low price and maybe there was something to be happy about here.  But what about that connector?  When I got the battery home I decided the connector was just not very good quality.  The pins (sockets really) were moving to much in the plug and didn’t appear to have been crimped evenly.  Next I noticed that the wires were significantly smaller than the average servo wires I’m used to.  Maybe 26 gauge instead of 24?  I’d rather replace the lead than splice it anyway so I took off the outer shrink wrap and this is what I found….

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First of all, I wonder if using what appears to be masking tape as the insulator to keep the wires from laying directly on the battery ends is the best choice or just an economical one?  I guess it’s not terrible since I presume it’s there to prevent chafing more than electrical insulation or perhaps just to aid in assembling the battery.  I’m used to seeing strapping tape/fiberglass tape here.  Seems like the masking tape might attract some unwanted moisture though.  Anyway, that isn’t so bad but the wires being so thin I did not like.  Seems like some slightly larger gauge silicon wire would be ideal but I guess you can only expect so much for single digit (dollars) pricing.

I then started to strip the tape and de-solder the wires when I noticed the following.

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Do you see the insulation cut on the black wire?  This was caused by the outer shrink wrap around the battery cutting into the insulation on the wires.  Either the shrink wrap should have been applied differently/softer heat shrink used or perhaps a wire shield/wrap/guard of some sort used around wires.  I’ve seen others use a nice rubberized sleeve (maybe just some appropriately sized heat shrink) to keep this from happening and add some stress relief in this area.  Hmmm… bad connectors and questionable construction/poor quality control…  Makes me think the savings on this battery might not have been such a bargain after all.

My point here is really just a long winded way of saying that very often in this hobby, “you get what you pay for” applies.  Even when you are buying something as mundane as a basic 4.8V NiMH pack.  I have no idea how good the cells that make up this pack really are.  Time will tell.  But even if they are top end like Sanyo Eneloop, the short cuts they took to make this pack more of a “bargain” could easily have resulted in a high cost to the user.  If the cut had been in the red wire and it had shorted to the negative can of the battery it was sitting on top of, the best cells in the world wouldn’t have helped.  Same for the connector that wouldn’t reliably do its job.  Every little bit of quality I can get in my airplane products is welcome.

Hopefully, with the new lead attached and a few wraps of some decent quality electrical tape, this “bargain” battery pack really will be.

PVC… Great for plane holders, wing racks, etc…

I needed to create a wing rack for when I’m carrying a larger number of planes in my trailer such as when I go out for trainer night at the field when I usually displace my 30% Edge with some combination of my Telemaster 40, Sturdy Bird and a sport/fun fly plane along with my Radian glider.  Usually 2 or 3 of these join the mix.  It becomes a problem to find a place for all these 4-6′ one piece wings so I decided to build a small wing rack and of course to do that I reached for some trusty PVC pipe.  This stuff is cheap, strong and there are a variety of “joint” pieces available to join two, three or 4 pieces together at 90, 135, and 180 degree angles, plus caps, etc…  You can build all sorts of stuff useful in RC.

I will add a few example photos for you to give you some ideas about where this can be useful.  Here is a pic of a stand we created to hold the Giant Scale P40 while we worked on it last winter on the bench.  Also in the pic is the pipe cement and the special cutters that work kind of like ratcheting scissors to give you a quick and easy PVC pipe cutting ability.  A wood or hack saw work OK too but they make a mess and take about 10 times as long to accomplish the task.

PVC Plane Holder

Here is a boat holder I created.  The two posts sticking out were used to hold the surface radio I used to carry with it.

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And this one is the new wing rack I just completed.  It will get some padding added soon.

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Sitting next to it and housing my P51 mustang is a combination structure using 2x8s along with PVC and velcro.  I took one piece of PVC and drilled holes through it to match the wing mounting block in the body to give me a cross piece that drops into notches in the 2x8s for a very reliable and secure hold down method.

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I have created wing racks in the garage that hung on the wall, plane stands for holding a couple of planes nose down and many other useful items.  With the different sizes available and combining velcro, pipe insulation for padding and even combined with wood at times where some heft or additional strength is required, you can create a whole host of useful stands, racks, carrying aids and much more.  Best of all you can assemble and do some “custom fitting” without using any glue and then go back and disassemble and reassemble as many times as necessary to get what you want before applying the cement.  And the material is relatively inexpensive!

Let your imagination go wild.  With a few sticks of PVC you can do a lot for less than you might think.