JR X9303 2.4 and XP9303 (72mhz) setup instructions for the elevators.


Make sure the radio is on a clean slate zero elevator trim and make sure the subtrims are at zero. The instructions here are for the JR 9303.

On a new model:

Hold the ENT button and power on the TX. This will enter the system menu.

Got to MDL Name and name the model. I chose “FOCUS”

Once the name is set, got to the DeviceSEL and push the roller bar to enter the menu.

Scroll to the bottom of the screen under each channel that says “ACT” and change it to “INH” This will turn off all the other switches and channels that are not being using in this models setup. It also allows us to setup the dual elevator servos using the 9303’s Servo MATE function.

Once all the channels (gear, Flap, Aux2, aux3 and aux4 are “INH” press the List button.

Scroll to Wing Type and press the roller bar.

Under Wing: set to “Flaperon” this turns on the dual aileron servos so we can setup aileron differential. This means Right aileron servo plugs into the Ail channel and the left aileron servo will plug into Aux1 or the Flap channel.

Next using the roller bar scroll down to the “INH” that is just below the ELEV channel. Press the roller bar. This will bring up a little box to choose the servo you want for the dual elevator channel. In my case I use the Gear channel #5.

Now you have dual elevator servos programmed. The trims will work and you have dual aileron servo and dual elevator servos programmed. This is about as easy as it gets setting up the dual servos.

Press ENT twice to take you back to the main screen of the radio and out of the system menu.

Plug the right elevator into the ELEV channel and the Left Elevator servo into the Gear channel on the RX.

Power up the servos for the elevators.

The next step is to get the servo arms aligned properly. JR servo wheels have an odd number of teeth on the spline. This means that if can get good alignment with one position rotate the horn 180degs and it will be within ½ tooth of its position before. Now this is where we use subtrim. See you guys though subtrim was for moving the surface to the center point. NOPE it’s for getting the servo arm aligned properly to give equal travel on both sides. The goal of a precision setup is to get everything as mechanically correct first. Then use the electronics in the TX to fine tune it. The larger the subtrim values the harder it will be to match up the two elevator servos so they throw exactly the same at all travel points. We want these elevators to be absolute mirror images.

To get this step correct you are going to have to play a little bit. Slide a pushrod tube section onto the clevis or control horn side of the titanium ends. This is shown in the photo on the 2nd from the left. Bring this pushrod up servo arm. We want the pushrod connection to the center of the servo wheel screw to form a 90deg angle. This means that the servos movement will be equal as close as we can get it off this center position. I use a Motel room key or old credit card to get the angle as close as I can. The photo below will show you the connection and the 90 deg angle. You can’t set the servo arm 90degs to the case of the servo. This is a common mistake. You need it 90 deg to the pushrod. This means that the servos rotation of equal angles each side will give the same linear distance of travel to the pushrod. This 90deg point means is getting your linkage as symmetrical as possible.

If your servo wheel needs some subtrim to get it perfect. Then adjust it with subtrim. See how much it takes. Say a value of 10 is really good. Yet a value of 35 or 60 is not so good. If you have a really low value like 10 you are good. If not then try and rotate the servo wheel 180degs to the other side of the wheel. This will get it closer on the spline and require less subtrim. Again subtrim it perfect and then look at the number. Your goal here is to pick the number that is the smallest. I was lucky. The R-elev servo was dead on with no subtrim at all. The L-elev needed about 6 for a subtrim to get it perfect. Why is this. Well the servos are brand new, so its not worn servos. It has to due with the electronic differences very small differences in the servos. Today’s digital servos are awesome and so close to each other its great. But there can be minor little differences. I want to minimize these differences. This subtrim is the first step in this task of matching up the two sides.

In the photos I had to cut a Days Inn card key to make my tool. Just be sure to use the true edge so that you get the 90deg angle. Align to the center of the 2mm bolt on the ball link or DARE link, and the servo screw. The photo shows the 90 deg angle after the pushrod is assembled. We are not there yet. But right now you get it as close as possible. The final adjustment of the pushrod length will get us dead on…The idea now is to choose the proper side of the servo wheel. If you choose the wrong side your sub trim values will be high and can affect your elevator tracking down the road.

While the servos are still powered up….Place a section of masking tape on the pushrod. This will give you an accurate mark location. This is gives an accurate location to cut. Remember the threaded sections on the titanium ends are smaller than original and we want to get the pushrod length as close as possible some only maybe a single turn or two is needed to center of the elevator mechanically. Place masking tape on the elevator at the tip to align it with the tip. Again this will not be the final location for alignment but we want to get it really close. Then the fine thread of the 2mm fitting will give use precise adjustment

I use a fine tip Sharpie for this mark the CF tube where to make the cut.

Using that Dremel cut off wheel again cut the CF pushrod tube at the Sharpie mark. You don’t want to use a saw or anything like that it can damage the end of the pushrod tube. The cut off wheel makes a fairly clean cut. The masking tape not only holds your mark, but also helps to keep the end of the tube from fraying as its cut.

Once cut use a sanding block in the photo is 150grit. The will clean up the edge and square it up.

Once it’s all squared up its time to get ready to glue the ends. Clean the barb side of the pushrod ends. I use denatured alcohol. You have been touching them with your fingers and the oil on your skin will prevent a good bond for the glue. You will notice the barb side has little grooves; this is to allow glue to flow into these grooves and act as teeth to grip inside the CF tube. Yet the grooves are spaced to not create stress risers like a section of all thread might. Clean the barb sides up with denatured Alky and let them dry it. It will happen pretty fast.

Glue is our next choice. Several options exist for the glue. A slow set epoxy will work. It gives a long work time but sometimes can get messy. The epoxy is usually pretty thin if you are using 30min. DO NOT USE a 5min epoxy. This stuff is poor at strength. We want a good solid bond. A popular choice is JB weld. Again don’t use the 5min JB Qwick stuff it will fail. The slow set JB weld is fine. 30min epoxy or JB weld will require you to leave this to cure overnight or at least many many hours. CA work in this application well and its done in about 15-20mins.

In this case I’m using the med CA from Bob Smith. It’s the Purple stuff. I have also used the Dark red which is the super thick stuff. DO NOT USE KICKER………………

Once the titanium ends are dry from the alcohol cleaning then start at one end. I’m choosing the clevis side. So take the servo wheel off the servo being careful to not touch the barb side of the pushrod end.

Get a paper towel handy as you will need it to wipe off excess glue right away. Later up the barb. Make sure you get good coverage in all the grooves. Slide the pushrod tube on the barb and rotate it and plunger motion it in and out. This is to get good coverage of the adhesive. You may need to add a little glue. Wipe off excess right away. Once it has good coverage leave it alone and go tot the other end. Lather this barb up with the thick or medium CA and plunger it in and out of the CF tubing. Rotate it to make sure the adhesive is in all the grooves and coverage is good.

Now for a trick from my experience: The air inside the pushrod tube will expand as the CA heats up and kicks off. You don’t want the pushrod end pushing out of the CF tube as the glue sets. So use a rubber band or several depending on the length. This will hold the ends tight on the CF tubing for the glue to cure. Again DO NOT USE KICKER. Just let it set for 15-20mins. To keep things from flopping around I unplug this elevator servo from the Receiver and attach the servo wheel to the spline of the servo. Look close at the photos and you will see the rubber band.

Repeat the process on the other side. The pushrods are now glued and go have a soda, beer or favorite beverage of your choice. I go pet the dog, and play catch for a while. He is young so it takes about 15-20mins of exercise to get him worn out.

Come back and just cut the rubber band with a #11 blade. Remove the servo wheel and pull on the linkage. Grab it at both ends the clevis ad the servo wheel and try to pull it apart…it should be solid and this is a test to make sure your bond is good. Don’t go King Kong on me and break your model. Just test pull the linkages. It’s all done now we have to dial it perfectly. This is why we left the rudder off the model when we were hinging

This one is long. I’ll break into 2 parts

Linkage work part #1

First remove the masking tape form the tips of the elevators so when you power up the servos you don’t break something.

Plug the servos back in to the RX and turn it on. The servo wheel screws are still missing from the servo wheels. This is good it will help us make adjustments easier.

Adjust the length of the control horns from the middle of the hinge to the center of the 2mm clevis pin (bolt) Make sure both sides are identical. Mine were set at 31mm. Match both side as absolutely close as you can. My servo wheel connection choice was a hole about 12mm out from the center of the servo wheel screw. This gives me a mechanical advantage of over 2.5 to 1. This gives the servo better power over the surface and minimizes any slop or wear in the servo. In a precision setup you never want 1 to 1. Not even on the pull-pull rudder, but we will discuss that later. For now think using the maximum servo resolution. Servo wheel 12mm and the control horn on the elevator is 31mm. These are just starting values and we may change them later. Taking your time now will mean matched up changes later. If you need to shorten the control horn length to less than 31mm to get more travel…then its easy just a turn two on both sides and they stay paired up. Making these measurements accurately is very important to how the model will fly and trim later. I like to do it one time and that is it. This is the reason I use the more expensive MK clevis and NMP DARE links. Once you do this work it will not need to be changed. Even changing out servos the linkage will not need to change. Some folks don’t mind putting in the work… That’s cool I prefer to fly it and not have to spend time in the shop trimming…and adjusting.

Back to it; the servo wheels were setup at the 90degs pint as close as we could get. For now ignore the elevator and if it is centered up on the stab tip. Instead look at this 90deg pushrod to servo arm again using the Days Inn card key tool. This time it needs to be spot on. Align the card key down the center of the pushrod and slide it up to get the center of the bolt in the DARE link to align with the center of the servo wheel screw. This is super important here also. The more it’s off the variation you are going to have to put in electronically in the TX to get the elevators moving together. If they are matched mechanically then the differences will be very small as you will see in a bit. Use subtrim to get the servo arm pushrod relationship just right. Small changes in subtrim make a difference so work hard to get it as close as you can.

Since the servo wheel screws are not installed its easy for the next task. Look at the elevator and its relationship to the stab tip. For now I want you to get one side adjusted perfectly to the tip. For adjustments just pop the servo wheel off and rotate the pushrod in the clevis. This will have to be whole turns at a time. For the first side get it as close to aligned as possible. Don’t freak out if its not dead on. We are going to match the other side to it. Right now we don’t know where the elevator trim is going to end up so aligned with the tip is good for this one side. Knowing that Dave Guerin designs a model that is really close here we know the eventual center or neutral point will be close to this tip location. Once you have the linkage adjusted for length to get the elevator centered up on one side you are ready to move to the other side. Install the servo wheel screw on the side you just finished. I turn off the radio so that tightening the servo wheel screw will not strip the gears in the servo. The 3421Sa servos have a small nylon gear train. If you really crank on them while they have power the gears will easily strip. So power them off and tighten the servo wheel screw.

Next elevator side. Dial in the pushrod to servo arm relationship to the 90degs again. Subtrim is the way to do this and ignore the elevator location to center for now. Get that 90degs right. If you screwed up in picking which side of the servo wheel to use and your sub trim is high values….then switch the servo wheel around and re-attach the DARE connector. I screwed mine up and had to do this. In the end one servo had zero subtrim and the other ended with a value of 6. This is a good and low value. Next is to adjust the length of the pushrod to get the elevator in the proper center or neutral location.

This process is the same as the first side….get it close to the tip as you can…but this si not the definitive reference. We want the two sides to match each other. If the tips are sanded just a little off or maybe a little extra heat on the covering can pull one tip down or up. These tips are small and can bend a little bit one way or another. So don’t trust the tip….We used it on one side as a reference. This time eye ball the surfaces of the two elevator halves from the rear. Align your eye with one surface on the original reference side. Use the first side as your reference and adjust the current working side to it. In my case it was up compared to the tip about 1/64th of an inch. This is OK. It doesn’t mean the stab is warped. It just means the tips could be sanded a little different. You likely will not feel it flying. Just make sure the elevators match perfectly. I learned this from Tony Frackowiak. The Mark One Eye Ball is awesome for setting this up. Make full turn adjustments at first to get it close. If you have to, remove the clevis pin bolt. And turn it over to get a ½ turn adjustment.

Note: the MK clevis doesn’t come with a nut for the bolt. So if you turn the clevis over the threaded side of the clevis will be on the head side of the bolt. This means tightening the bolt will not pull the clevis together. That is OK for now…We are going to put little 2mm hex nuts on these bolts later. Its more important to have precision in this setup now. ½ turn on a 2mm clevis is pretty small movement. This is why I use the 2mm over the 4-40 or 2-56. The 4-40 is heavier and not needed due to the titanium…and the 2mm is more threads per inch than the 2-56. This means finer adjustment.

Once you have these elevators all setup at the center position and the servo arm to pushrod relationship is all 90 degs shut the radio off and tighten the servo wheel screw in the second elevator servo.

Now is time to match the servos or rather the elevator surfaces as they move. The servos and linkages are setup the same and we need to make sure for any given stick movement the elevators will track together. Our reference of centered and matched at neutral elevator will be our basline.

Part 2

Elevator linkages continued


There are a couple of tools we can use or make work in this situation. One method is to extend the elevators out the back of the model about 10-12”. Years ago I made a set of tools for this task.

A clothes pin with a piece of metal rod works great. I put small square patches of 1/64” ply on the jaws of the pins to keep them from digging into the surface. Align the pins as close to the same spot on each elevator as you can. Bring the ends of the metal rods to the rear of the model and have them meet as close to the middle as possible. Reminder the radio needs to be turned on the servos plugged into the proper ports. JR 9303 setup we did made the Right elevator in the elevator slot and the left one goes into the channel 5 or Gear slot.

We don’t have the rudder installed yet but this you can use your eye ball for. Some folks will use tape and CF rods….This works too. But I use the metal and here is why. We know the surfaces are aligned by the Mark One Eye Ball. So when we attach the extender rods they should match up. Guess what they rarely do. Why is this? It could be the fact that the elevator on one side is sanded a little more rounded at the rear than the other…so the clothes pin doesn’t sit as good on and flat on one side as the other. Or it could be the clothes pins are not the exact same pivot points. It doesn’t matter we know our Mark One eye ball made them the same….so I will put a small bend in one metal rod up near the clothes pin. I put this small bend in to get the two rods to come almost dead on at the rear. If they are close enough to be within the diameter of the rods its good to go. You just need to see that offset distance stay the same as the servos move up and down full travel.
Now I want to use the maximum servo travel that I can. Setting it up this way means my D/R will be close to 100% so that I’m using the full travel of the servo and not losing resolution. Go into the Travel Adjust menu on your radio. Futaba calls this EPA or ATV. On the JR it’s called Travel or Travel adjust. On the 9303 You can run the values up to 150%...We don’t want this as we need to possibly adjust each side for end point. Since each servo is a little different and there is no way to get the linkages absolutely 1000% perfect this is why we use the travel adjust….to make them electronically perfect as we can.

Lets back up….If you didn’t spend the time doing the first parts of this step by setting up the 90deg relationship and the Mark One eye ball center then these Travel Adjust or ATV values will be way off to get the servos to track. We want them to be so close to the same value. I have found that if you do your linkages correct you can get it within just a couple of % points of each other for each end. This also means that the elevators will move at the same speed to those end points as well.

Ok back to the Travel adjust. We want some room to adjust a few % each way…we also don’t want the servos moving to their mechanical stops as this can damage servo gears or the control surface. I ran my Travel adjust up to 135% for each side of the elevator channel and the gear channel. By the way cool thing about the JR 9303 it renames the servos from elevator to R-elev and the Gear channel to L-elev. Both of these servos need to get the travel adjust setup to 135%. We match the surface travels up here in travel adjust to get the surfaces paired and mirror images through the travel. We want the % values to be close but they are not going to be the same very often. We want accuracy and here is where the computer radio helps us. Slowly move the elevator first to full up position. Watch the relationship of the pointers. Keep the same. Usually at the end one will have gotten a little ahead or behind the other. I always adjust the second elevator….in this case the Left elevator gets its adjustment to match the perfect 135% and 135% of the right side.

In the case of my model it needed 137% up on the left side to match the right side. Then it took 136% down elevator on the left side to match the right side.

This is really tight. When I move the elevator through its motion the extension sticks track perfectly with each other. If for example one side needs like 10% more travel in both directions…you can shorten the length of the surface control horn by say 1 turn and then go through this whole setup from the beginning. Your center will change and you need to start over to match things up on that side.

Please let me emphasize this fact. It will make the plane fly better if you get really picky during this step. IT will affect things and the plane will fly better if you take the time to do this the one time.


Special NOTE: If using old or used servos. The servo pots can get a little worn and it will affect the end point travel of the servo. So I recommend new servo for this install. If not new servo fresh rebuilds of the servos. Both JR and Futaba Servo centers can put new gears and pots in the servos for you. Its cheap at about $15-20 per servo and this will make your life easier in this task. Besides if you have a $100 servo it will act like new with a new pot and gears. If you can’t get it just perfect or the values seem to change every time you move the stick…then your servos are not as accurate as the higher priced servos. This is a case where I recommend the high precision servo. If your choice is a less precise servo this is where it will show up no doubt. Can a cheaper servo work…yes

There are some choices that are better than others. Again I pick the best servos for the task so we don’t have to mess with but this one time. This is tedious work and many folks get lazy at this step. With the D/R at 100% and setting the values for the travel to match here with the pointers….if you dial in say 80% dual rate or even 50% dual rate the surfaces are going to travel together. If the Travel adjust values are way off from each other or the sub trim is not set right…then when you switch your dual rates the servos will not move the same at 50% as they did at 100%. Mechanically sound means the D/R adjustments keeps everything paired up and perfect.

Part 2.5

Neat trick………………..

I have another little trick to check our work. Sometimes its 3am and looking at the little points is tough. They bounce a little as they move….

We left the rudder off the model for a reason. Here is why, take a small section of the pushrod tubing. Masking tape it to one side of the elevators. Because of the taper on the stabs and elevators it will have a gap on the opposing elevator. The photos below show the idea. Get it as straight and square to each side as possible. I left masking tape in the end that was not taped down to help it show up.

If the elevators are moving together 100% of the time…this gap will stay the same at all times. Again the gap is a result of the taper on the stab and the elevators. So the gap on mine was about 3/32” maybe 1/8” the photo shows the setup.

I moved the elevator stick up and down and watched this gap. If it stays the same the entire time then the elevator was hinged straight and the settings for ATV or travel adjust are set properly.


Mine by the way confirmed the proper setup. Now I can dial my D/R back to a flyable rate say 80% and it will stay tracking together. I don’t know what the values are for degrees of throw yet. I do know I’m likely close thanks to my ratio of servo arm to control horn length. My guess now is about 80% D/R will be about 15 degs of travel. That is not important now. What is important is that the travels are the same…and the total travel is not way too little or way too much for what will be needed to fly, snap, and spin the model.

Anyone set a Focus Sport up for a single Elevator servo and/or an OS120AX yet? I just got my and opened the box. I plan on going with the OS120AX and single pitch servo route.

Randy,

I decided to build it stock for now. Based on CG and other things I'm likely going to convert it to the DEPS setup. Its really easy to do and the fuse has only a couple formers back there and neither one will get in the way. Dave designed it around the servos in the tail and the YS and Hyde mount up front. I have found its better to trust the results of others than to totally re-invent the wheel all the time. Especially on a plane like this. I want to build it the way it was intended and evaluate just how good it really is. So far I'm very pleased with the way it has gone together.

If the model is tail heavy then it will get the DEPS before I fly it. I can stick the DEPS in the model in about 1 night maybe 2 if I have been flying all day long... On the DEPS a 9411SA would be a good choice here.

But if it balances out I think it will be fine. The 3421SA's are pretty good on the elevators. I have these in my Naruke Bipe. I've been happy with them, but just don't like the long setup process to get them dead on. For me the DEPS deal is a better solution. it takes me less time to setup and stays more accurate over time. As noted above if you change servos in the tail of the model. Then you need to do that all big process again. If the DEPS is installed just pop the servo in..both elevator stay synched up...and the only thing different could be a few clicks of elevator trim on the first flight with the new servo. The plane will still loop correctly because you never changed the relationship between the sides. Dual servos you are changing everything about the relations just just bolting another servo in place.

Example 2007 NATS. I was practicing a couple days before. Got done flying at near dark, and we were headed for the Texas Road house. Putting my Model in the car I bumped the elevator and stripped a gear in my single elevator servo. I replaced the servo that night. One trim flight the next day to set the elevator neutral trim position and the model flew exactly the same as it did the day before. basically in 10mins work and two passes of the flying field the model was repaired and flying the same. If that had been on the Naruke bipe, man it would have taken me an hour plus maybe two hours to get the servo replaced and the settings just right. Then I would have to fly it and make sure everything was tracking together.

I'm big on making the model easy to replace a part, change out a servo, drop in a new engine. Swap in a landing gear or the likes. I try to make it so that I can fix easily all the things that can go wrong....Don't bury a RX battery to where you can't get to it in a few minutes. Don't glue in an adjuster than could get broken off putting it in the car.

make things simple and easy to take apart and replace. For me the single servo on the DEPS is that way.

I'm putting it in the Naruke Bipe this winter.
I say a little thank you to the Ron Chidgeys' and Tony Frackowiaks' of the world every time I find something to use that works as well as the DEPS. If it had not been for seeing that on the plane Chidgey built and Tony Frackowiak had I would be still searching for a better system.

The fuse of the Focus is a perfect candidate however from what I'm seeing with the YS and the Hyde Mount up front the weight will do me good in the tail. We'll see. Cg is one of things I have not checked on the model. And we have a ton of rain coming for the weekend...so it won't fly this weekend. Maybe first of next week.

Troy Newman

Great Detail

This is awesome. I see Central has this model on sale now. I think its time to get one.

Thank You Troy for the effort you put into this. I seem to learn every post.

AM

Fuel tank mounts are installed. I used Medium “Purple” CA to attaché the rails. There are plywood doubler pieces that slide over the Rail “U” shapes then you glue the rail into the router grooves on the inside of the fuse wall. The plywood doublers are then glued up tight against the fuse side. This makes a strong and lightweight tank mounting system. The laser cutting on these parts was excellent and they fit tight but no extra sanding or fitting was required on mine. If your needs a little sanding its no big deal just clean up the edges a bit and it will all fit nicely.

Some minor force was needed to get the rails into place. The technique I use was to align one side then pivot the rail into place straight down from the canopy opening. If you tried to plant one side then slide it in at a angle say front to back horizontally you could break the rail assembly apart. Coming straight down kept everything together. Only a small amount of force was needed to spread the fuse sides as the rail pops into place

We are going to jump around a little bit on the finish. This is the order in which I did things. It made it easier for me. Right now the model has the majority of everything done. The engine was installed then removed for easier handling on the bench, the servos in the tail are all done. The rudder is still not attached nor the rudder cables setup. I usually leave the rudder cables to a last minute thing. No specific reason. Right now we are ready to do the landing gear. This means that sitting the model on the table will be fairly easy now and we don’t need a stand of some sort to finish up the details.

The aluminum landing gear that comes with the model is pretty heavy. If you wanted to you could replace this gear some Carbon Fiber Bolly gear and probably save 5-6oz. The wheels and wheel pants supplied with the kit are pretty large. The pants are heavy do to their size yet the wheels are very light. This model was setup to work on the rougher grass fields around the country. The wheels and pants work well together and fit.

Landing gear install was a pretty easy task. This is where the quality of the model parts suffers a little bit. It’s not a bad thing but the gear could be aluminum and much lighter than they are. They could also have been finished to some extent. From the looks of the gear they came off a plasma type cutter and were stuck right in the box. The edges are not cleaned up in anyway. Please be careful with this edge mine were extremely sharp with a burr from the cutting process on the edge of the aluminum. I took mine to a bench grinder with a wire wheel and this cleaned them up a little. Be careful the wire wheel can eat of the aluminum if you are not careful. The goal was to get it to a point that I could use some sand paper. Then I sanded with some 100grit then down to some 320grit paper. I will likely paint the gear legs white as they will look good on the model. For now I need to get them bolted in the model. Another notable was the printed lettering on the raw metal stock before it was cut is still on the gear legs. This is shown in one of the photos below. Acetone made short work of this lettering. Once I had the edges all rounded off and smoothed over it time to get the gear in the model and bolted in place.

The gear plate in the fuse came pre-drilled and 4mm blind nuts or “T” nuts were installed on the bottom ply plate. The way this landing gear design is the strut is sandwiched between two plywood plates. The bolts just keep the strut from sliding out of the slot. When bolted all together this creates a very strong structure. The landing gear struts are pushed into the slots about as far as they will go. Mark the locations from inside the canopy area of the model using a Fine tip Sharpie marker.

Next remove the gear strut and mark it so you know which side it was. This is done just in case the right and left gear plate holes don’t match up. It’s easier to mate the system up now and know which are the Left and the Right. For this I used a regular Sharpie marker as shown. As you can see I marked in a location that is hidden when the gear are bolted in place. Another neat trick is using a sharpie marker on the strut before painting like this will mean that the paint will not bond properly over the marks. So the marks will be permanently on the strut in a hidden spot. This will keep them from getting mixed up down the line. Another little trick in using the sharpie marker on the strut is to mark which model it goes to or maybe a date. This way you if you have more than one of the same models like I do with some of my 2M models you can keep the parts separated and know instantly which model they go to. When I was a kid one of my mentors as a modeler was Lee DeMary in Denver Colorado. I always remember Lee putting the test flown date on his model. I can still vividly see the marking he would put on the fin or rudder. I always thought this was a neat thing to do.

Back to the landing gear install. Once the holes for the gear bolts are marked I used a #10 drill bit to drill the holes. These holes are a little bit oversized for what is needed on the 4mm bolts but I wanted to make sure that I had no issues installing the bolts. Besides the plywood box that the strut sits in doesn’t allow for much movement if any. The holes were drilled then a Counter sink bit was used to clean up both sides of the holes. A quick bump or two will de-burr the edge of the holes and make a nice clean surface. Landing gear struts are then bolted in place using the supplied 4mm Phillips head bolts and flat washers. I installed them once to make sure all was correctly fit then I removed and added thread lock to each bolt, one a t a time. The gear struts are now installed.

Moving to the tail wheel installation is next on the hit list. I don’t like the tail wheel bracket supplied with the model. The wheel is good and light but the bracket is a bit cheesy and I make my own. The tail wheel bracket furnished with the kit attaches the tiller arm of the bracket to the rudder in a “hard” connection. So every bump and chuck hole you hit will translate directly to the rudder. For years I used fuel tubing to connect the tiller of the tail wheel to the rudder. This would give some shock absorber action yet the wheel would move semi “OK”. Today I just install a pin in the bottom of the rudder and then use rubber bands to connect the tiller to the rudder. This way the rubber bands are tight enough o keep the wheel moving with the rudder, yet if you hit a clump of grass there is some shock protection. We don’t want those impact loads going to our rudder hinges, or the back through the cables to the rudder servo. The rubber band isolates the wheel from the rudder just enough. It’s easy to replace and works perfect. Plus Peter Goldsmith always told me that a model airplane has to have a rubber band in it. That’s the rules. So this is my fulfillment of that unwritten rule. Since I make my own tail wheel assemblies I keep a spare or two in my box all the time for a quick change out. The model has a plywood plate installed at the rear of the fuse for the tail wheel. I drilled and used a tap to thread it for a 1/4-20 SAE Bolt. My homemade tail wheel assembly uses a ¼-20 nylon bolt as its attachment device and also the bearing for the wire strut. Drill the hole and run the tap in slowly. Once the threads are cut you can use some thin CA, again the Bob Smith Blue is the best here. Soak the threads with thin CA. Don’t use any kicker we want the wood to absorb this CA and make the wood very hard and the threads durable. After about 5-10mins the CA is good and cured it helps to run the tap through the threads one more time just in case the CA clogged up the threads. Now the tail wheel just bolts in place by hand. It doesn't need to be super tight. I will show some better photos of this next post I need to get some good photos of it.

The rudder of the model is still not installed but we will get to it very soon. I want to get the wheels and pants installed on the struts then its time to do the rudder hinges and finish of up the tail wheel install.

Tail wheel on the model is installed as shown in the photos. You don’t have to install it before you glue the rudder hinges. I found it easier to get the wheel pants setup at the proper angle with the tail wheel installed. It doesn’t really matter too much as we block the tail for the model up so that the fuse is “zero” to out table. This is the same thing we did when setting up the main wing incidence. However this time the main gear struts are on the model. Due to the fact the landing gear plate could be installed at a slight angle or there could be minor differences in the struts after the last bend before the axle we want the model to sit level on the runway. Using a reference from the end of the strut say measuring up ¼” on both sides may work but then is the struts are slightly different now the wing could be unlevel to the runway when its just sitting there. This is nit picking of course but a sure way to make sure the model looks as good sitting there as it does flying it this little trick.

Using a square on the rear of the fin align the hinge slots so that the fin is 90degs to the table. You may have to add small scrape of the balsa under one landing gear strut. Some models might need a 1/16” balsa scrap and other might need more depending on how well the gear plate was installed and if the end of the struts is finished the same length. In the case of my Focus Sport no shims were needed. So now since our table is flat I used a spacer under my sharpie marker to give me an equal distance mark from the table surface. The fin is square to the table and when we glued the fin on the fuse it was square to the stab. The stab is parallel to the wing so now the wing is parallel to the table. This means equal height marks from the table will mean our axles will be the same distance from the table and the axle line will now also be parallel to the wing. So when its sitting on the ground the wings will be level with the ground.

A horizontal mark is made for the axle…then a vertical mark is placed in the middle of the strut front to back. This cross hair is where we drill the hole for the axle.

STOP everything. At this point before you drill your holes….The supplied axles are not long enough to handle the supplied wheels and wheel pants. They are about 3/8” too short. So I replaced the bolts. I used 6-32 bolts 2” long. You could use a 1.75” long bolt as I had some extra to be cut off. The supplied bolts are a 4mm, If you want to replace the 4mm bolt and use the supplied lock nuts and washers great. Those bolts can be found at just about any good ACE hardware or True Value. Unfortunately the Lowes and Home Depots of the world don’t tend to have the extensive fastener section of the ACE. Home Depot wants to sell you 100pcs of a given bolt and you only need 2 of them. Plus the selection of metric stuff is pretty small. I have a ACE right by the house nad they are awesome at little metric fasteners. I was lazy and choose to just use a 6-23 bolt and hardware I had in my supply. The holes in the wheels are slightly larger than the 6-32 but I placed a small brass tube section on the bolt as the axle part to take up the extra diameter and to give the wheel a smooth surface to spin on. If you leave the bolts bare the threads can grind away at the plastic wheel hub. The small brass tube fits over the bolt and inside the wheel hub as a spacer. I then was able to bolt it all up together.

If you are not going to use the wheel pants then the supplied axles work very well and are sized perfectly. The supplied wheel pants are rather larger and as a result the supplied axles don’t get the wheel in the middle of the wheel pant.


So when drilling the holes in the aluminum gear struts you either need to drill for the 4mm supplied axle or for the smaller 6-32 bolt. Decision is yours. But I wanted to make you aware of this little issue. That way you can make your decision before having to go to the hardware store and find a 4mm bolt due to the fact you hole in the strut was too large to take the 6-32 bolts.

Below are the photos of the tail wheel and the marking for the axle holes.

Once this is all aligned and setup I want to finish up the tail wheel and to do this I need the rudder hinges glued. We are at point where I have everything I could with the rudder off for alignment of the axles, elevators and so on its time to finish this dude up and glue the rudder hinges.

The techniques are the same as we used on the elevators and ailerons. But this time I tried new glue. Bob Smith CA has a new glue product that is for CA hinges. On some urging from some other modelers I tried it out and its really good stuff. I recommend it over the regular thin (Blue) CA. This is called Insta-Flex Flexible Thin CA. The bottle has a greenish blue label. Its low odor which is cool, and its flexible. This means it works great for CA hinges as will not make them brittle. In fact on the label they call it CA hinge glue. This is the stuff to use.

http://www.bsiadhesives.com/Pages/hobby/ca.html

Remember to drill that little 1/16’ hole in the center of the hinge slow to allow the glue to wick down into the joint. This new CA is not quite as thin as the Blue stuff and it wicks a little slower. But it works the same way and I’m sold on its flexible properties.

Center the rudder vertically using the ultracote stripes. If the overhang on the top or bottom is too much for your taste you can carefully cut the covering back and sand the balsa rudder top or bottom to fit perfectly. The pull the original covering back in place and iron it down. This should be done before hinging. Another thing I mentioned but had not done yet was I used some flame red ultracote to seal up the gap when the fin glues onto the fuse. This also should be done before hinging the rudder.

Rudder is now hinged let it sit for 10-15mins for the CA to fully cure. Toby gets a around the block to keep his energy level at the right spot.

Once this is all aligned and setup I want to finish up the tail wheel and to do this I need the rudder hinges glued. We are at point where I have everything I could with the rudder off for alignment of the axles, elevators and so on its time to finish this dude up and glue the rudder hinges.

The techniques are the same as we used on the elevators and ailerons. But this time I tried new glue. Bob Smith CA has a new glue product that is for CA hinges. On some urging from some other modelers I tried it out and its really good stuff. I recommend it over the regular thin (Blue) CA. This is called Insta-Flex Flexible Thin CA. The bottle has a greenish blue label. Its low odor which is cool, and its flexible. This means it works great for CA hinges as will not make them brittle. In fact on the label they call it CA hinge glue. This is the stuff to use.
Remember to drill that little 1/16’ hole in the center of the hinge slow to allow the glue to wick down into the joint. This new CA is not quite as thin as the Blue stuff and it wicks a little slower. But it works the same way and I’m sold on its flexible properties.

Center the rudder vertically using the ultracote stripes. If the overhang on the top or bottom is too much for your taste you can carefully cut the covering back and sand the balsa rudder top or bottom to fit perfectly. The pull the original covering back in place and iron it down. This should be done before hinging. Another thing I mentioned but had not done yet was I used some flame red ultracote to seal up the gap when the fin glues onto the fuse. This also should be done before hinging the rudder.

Rudder is now hinged let it sit for 10-15mins for the CA to fully cure. Toby gets a around the block to keep his energy level at the right spot.

Rudder is hinged…Now I install a 1” long piece of the yellow nyrod pushrod into the bottom of the rudder. This will be the “hard” point for the rudder tiller arm. The same nyrod material I used for the cowling. Just drill with a #25 drill bit. Then cut a 1” long section of the nyrod pushrod. Drill the hole about 3.25” from the center of the tail wheel bolt. CA the 1” long nyrod in the rudder with Medium (Purple stuff) into the bottom of the rudder. Leave 1/8” of the nyrod sticking out the bottom of the rudder. Now you can screw a #4 socket head sheet metal bolt ½” long with washer on it into the nyrod. This now gives you a connection for the rubber band. With the washer it the rubber band will not slip off.

I use a small rubber band it gets 3 folds and loops from the hook on my tail wheel tiller arm to the bolt with washer. This is the exact same setup I use on the expensive 2M models. This tail wheel is light simple and easy to change when the rubber band breaks. The tail wheel is a quick change is something goes wrong…To me it’s a nearly perfect setup.

Now the landing gear is 100% complete.

Cut the head off the 6-32 bolt for use as the rudder control horn. Drill and tap the hard point in the rudder to accept the 6-32 bolt. The hard point is installed and already drilled. You may need your covering iron to help you find the hole. Mine was right at the meeting point of the red and yellow covering. Once the wood dowel is threaded for the 6-32 bolt I run the bolt in about 80% of the way. I then apply a small amount of Medium CA (purple again) to about 4-5 threads just as they are going into the rudder. I then run the bolt/control horn in the rest of the way. Center bolt on the rudder. Then use some thin CA (Blue) and put a couple drops on the threads right where they go into the rudder. The wood will be dry and the thin CA will wick into the hole with the bolt. Don’t use any kicker or accelerator just let the thin CA wick down into the connection.

For rudder cables I tend to use the normal threaded adjusters and Dubro clevis for the pull-pull connections. This is because the cables will keep the linkage tight. If it gets a little loose the cables can be tightened. On a pull-pull setup you can use the Mk ball bearing clevis links but these will work just as well for pull-pull. The vibrations don’t take their toll as much on this linkage due to the fact that it’s always under tension with the pull-pull setup. I run the 6-32 tap about ½ way through the adjustable links. Then thread these links on the 6-32 rudder control horn.

The photos show the detail.

Next task: the rudder pull-pull exits in the fuse. These are shown in the photos also. I use a hot cheapy soldering iron to melt/open the holes. A Hot knife works well for this task also. The rudder cables and servo I will leave to later in the mix. Right now the rudder is ready to string the pull pull setup.

To finish up the flying surfaces the control horn 6-32 bolts are installed in the ailerons. The process is the same as the elevators. The aileron servos are setup the same way as the elevators. Build the linkages the same way as the elevators. Right now we are not going to program the travels and adjust the control horn lengths. We will get to that when we finalize the radio programming. For now we just build the linkages and mount the servos the same as with the elevators. I used JR 9411SA servos they are a mid-size servo and save some weight. These servos are very good; I used them on my 2M models on the ailerons also. You have to use a 6” extension on the servo lead to get it into the fuse. Again the heavy duty gold extensions are the ones to use. Part # JRPA095 is the JR HD gold 6” extension. Use the same technique described above for securing the leads to each other. Dental Floss and a little drop of CA will ensure the extension never comes un-done unless you want it to. I used the small round wheels that come with the standard JR servos. Leave the aileron horn as long as possible. We’ll adjust as needed later…for now these lengths are fine.

NOTE: On my wings I found the aileron extension holes in the foam cores had some glue in them. What it appears has happened is the poly U glue like Gorilla glue was used to sheet the wings and attach the false ribs out inside the foam. This glue foams when it cures. In this case it foamed and plugged up the servo lead holes. I thought this was going to be a major issue however after sitting and thinking about it for 2 days…The only real solution ended up being a very fast fix. Use a small flash light look down the aileron servo lead holes and see if they are plugged up. This will be about 8” down hole from the root of the wing. What appears happed is a little too much glue was used on the false rib. Since this rib cuts across the servo lead route the glue foamed up and blocked the hole.

I used a 12” long, 1/2” diameter brass tube with a serrated end. A dremel cut off wheel is used to make the small notches as shown in the photo. This tube was slid into the hole until it contacted the glue. The serrated edge toward the glue blockage will cut the glue very easily…Just twist and push twist and push. The action is much like a drill bit. It took about 10 seconds on one side and about a 45secs to a minute on the other side. The glue popped out like a plug. They are shown in the photos. While I was concerned about the best way to do this fix the answer was very simple and fast.


Good news the rails installed in the wings for the aileron servos fit the 9411SA servos perfectly. No need to modify them.

Linkages: the pushrods are built the exact same way the elevator pushrods are built. Remember to clean the barb area with alcohol and let it dry before gluing the ends on the pushrods.
Things are finishing up fast and it’s a matter of cleaning up loose ends right now. Once the ailerons servos and linkage are all installed the wings are done until final programming in the radio.

Throttle and rudder servo installs.

NOTE: the servo rails in the front of the model are too wide to accept a normal size servo. They are also a little to low and the bottom of the servo will hit the former at the rear of the landing gear plate. So in order to use these rails on just about any servo I tried I needed to put small blocks on top of the rails and also add a small extension to one side.

This again was a no big deal but a little disappointing to need the fix. In the end its not going to affect the flying and the weight added was maybe 1 gram. You will have to adjust the fix to your servo.

I also wanted to align it properly to give a straight shot to the throttle arm on the engine. So the engine needs to be bolted back in place. I used a long 12” 1/8” drill bit to align the pushrod exit in the firewall. See the photo below for the alignment.

I use a bolt through ball link like the heli guys use for the carb side of the throttle pushrod. Then on the servo side I use an EZ connector style adjuster. Actually the one I use is the Tettra. It has a little threaded nut that holds it onto the servo wheel. It’s also a low profile looking clean and neat. This type of adjustment is really good for a throttle linkage. Being that the Tettra has a locking nut on the bottom of it…there is no worry about it coming off the servo wheel. I use a little blue thread lock and never had one fail.

For pushrod material I use 0.047” music wire. It is stiff enough to handle the task yet can flex side to side with the movement of the Hyde mount. I really don’t like throttle cables and use this small music wire for various reasons. It needs very little support and it gives a positive control of the throttle arm. Use a 2-56 sold link on one side of the pushrod. The other one will pass through the Tettra adjuster. Sand the music wire with some 100 grit before you solder it. A little Silver solder is perfect for this mechanical connection.

While the engine is back on the model, mark the location for fuel line exits on the firewall. These don’t need to be drilled just yet…

The engine will have to be removed one more time before we fly it. So just mark the holes for the fuel lines. Keep the engine in the model for right now….Time to cut the air exits and muffler hole in the side of the cowling. For right now just get the throttle linkage aligned and ready to be finalized.

The engine is then all mounted up. The cowling needs to have the access holes cut, and clearance holes to get the cowling on when the muffler is on the engine. To do this you can use just normal printer paper. Tape the paper to the side of fuse as shown in the photos. Now the holes are made on the paper to fit the specific locations. Since the paper is attached to the fuse with Masking tape remove the muffler and attach the cowl. Transfer of the hole and access locations and sizes are made to the cowling. Cut the cowling as needed. The re-install the muffler and make sure you can get the cowl on and off with the muffler on. You will need to have a slightly oversized hole to the rear to get the cowl to clear the muffler and then stretch over the end of the crankshaft. The general holes and access for the needle valve, low speed air bleed and glow plug hole are then matched up.

Since the cowling has no venting for air exit in it you need to cut some. I choose to put a larger square hole in the bottom. This combined with the extra clearance for the muffler will give a good amount of exit air for engine cooling.

Time to get the rudder cable strung up. Mounting of all the misc stuff, RX, switch, battery, fuel tank, plumbing and so on needs to be done. The model is not just about ready to fly. I always leave mounting of the switch and battery pack to the end after I check the CG. The RX doesn’t tend to weigh much and the length of servo leads will limit the location a bit. So I mounted up the RX just behind the fuel tank. I made a small tray that span the fuse and used thick CA to attach the tray to the lower ¼ x ¼ stringer on the floor of the fuse.

Leave the Battery loose and just stick it in the model. We are going to check the CG location and perhaps have to move the battery. I selected a JR 1650nimh 4 cell pack to power the system. I will be using the JR X9303 2.4ghz system. I flew this system last year in my 2 meter models on the 1650 4 cell and also the 2300mah 4 cell packs. These are fairly light. I think the battery pack weighs in at about 4.5-5oz. You could save some weight here doing a smaller pack also. Saving weight on this model may be an issue we will know in a little bit. Rich now my guess is about 8.5 to 8.75lbs. This is just a guess. I'm using heavy stuff like the battery pack and wanted to get an idea of where it could come in with just normal stuff.

For now I want to check the CG. Since the battery pack could move in the end, I don’t want to mount up the switch just yet either. The location of the switch could limit how far I put the battery away without adding an extension. Again I want to get it close and save the weight of an extra lead. So just leave the switch in a “middle location in the Fuse….after checking the Cg we can choose were to put in and the battery pack.

The photo shows a 5 cell 2300mah pack. I first tried the Cg location with this pack as the 1650 was charging. Yes this pack weighs more but from the photo you can see the battery is right about on the center of the fuel tank. So it is very close to the CG. This pack weighs about 1 oz more than the pack I will use in the model. I sometimes will take a larger pack to have better leverage in moving it around. I was concerned about the model being tail heavy as a previous poster had shown. So I grabbed a larger battery to give me a little more mass to move to help get the CG…..

Now for the magic part. The CG was right on with the battery in this location. Sorry could not keep that secret long.

I want to explain how I calculate the Cg location. The designer asked for a CG of 6.5in behind the LE of the wing. I want an accurate CG location being an engineer I came up with a method about 8years ago to get my CG and also the models weight very accurately. Here is the radio compartment install and the battery pack location photos. Next post I’ll explain the method I use to get the CG…it has huge advantages over a couple fingers under the wing, and is even better than picking up the fuse without the wing and trying to guess if it hanging tail low. This method gives you accurate number.

To get the CG I do it the same way they do it on a full sized aircraft. I measure the reference distances, then I place all 3 wheels on scales and measure the load be taken by each wheel. To calculate this takes a bit of Physics…You have to know about moments and force arrangements. I’ll try to make it simple. Assemble the model with all its parts and bits. Ready to fly except the battery pack is not mounted yet. Its loose as in the photos above.

I run the models nose up tight against the wall, and measure my references from that wall. These numbers will vary on each model. The key is you measure from the same reference. We are going to calculate the moments around the tip of the spinner. Then divide the total moment by weight of the model. This will give us the distance from the tip of the Spinner that the entire mass is centered on. This is the Center of Gravity. The problem is we can’t easily measure from the tip of the spinner to a reference on the side of the plane of the wing. But if we measure the distance say from the LE of the wing to the tip of the spinner then its easy to calculate how far back our CG location is from the Wing LE. The designer referenced the LE of the wing at the root and says the CG location should be 6.5” aft of the LE of the wing at the root.

Another thing to realize is the model needs to be “flying level” while sitting on the table or the mass would not be distributed absolutely correctly. Will it get it super close….yes much better than the guy sticking his fingers in the wing tube socket of the fuse and trying to determine how far the tail hangs down from level.

#1 Push the model up against the wall. And block the tail up so the model is level. I used some empty JR servo boxes as my blocks. These will sit on to of the scale when getting the weight from the tail wheel. Since we will have to “TARE” or zero the scale with the blocks on it…we don’t want heavy blocking material. Foam works the empty servo boxes are also light. I think I used 4 servo boxes. Get the model close to square with the wall surface.

#2 Measure from the wall to the Main gear axles, and to the tail wheel axle. These are the distances that will be used with the weight carried by each wheel. In my case this was 14” from the wall-tip of the spinner to the main gear axles. Tail wheel axle is 64-5/8” or 64.625”

#3 Measure the distance from the wall to the LE of the wing. This became a slight problem as the landing gear was in the way of my square. So I measured to the LE of the Landing at the fuse then used a ruler to get the extra distance back to the LE of the wing. This is shown in the photos. The distance to the Landing gear is just under 13.75” and the distance from the landing gear to the LE of the wing is just over ¼” The result is the LE of the wing is 14” from the tip of the spinner. This is the same distance as the main gear axles. This doesn’t have to be the case but on this model it worked out to be that way. So the LE of the wing is 14” from the tip of the spinner.


#4 You have to have a scale. I use actually 3 digital scales. One scale placed under each wheel. You can use just one scale. I would recommend getting a small foam or balsa block that is the same thickness as the scale to go under each wheel that is not on the scale at the time. This will make sure the model is not sitting at an angle and distributing the weight unevenly. I place the empty servo boxes to block the tail up. Then each scale is the same so the model is sitting level on the table. NOTE you can’t do this on carpet…the carpet will give a low reading on total weight. I did this a few years ago and the model weight was about 6oz off. I thought the plane was 6oz under the limit and it was really about 2g under the limit. So make it a hard surface….My bench is what I use.

#5 Turn on the scales one at a time lifting the models wheel off the scale while it calibrates and zeros its self.. With the tail wheel one zero it with the servo boxes on it and not the tail wheel. Write down these numbers. I use grams….the scales are more accurate in grams and are good to 1g increments. The mass will not matter in the CG calculation as it will be divided out. You could use oz’s lbs, tons if you wanted. The unit you choose should be as accurate as possible. We don’t want to record a number that is 0.0050tons.

The scales you choose will either make this easy or hard. A scale with 1g resolution is excellent for this application. Fishing scales that are accurate to 1/4lb is probably not the best tool . Same as the bathroom scale. The bathroom scale is designed to read 150-250lbs….your model is lighter than that…so get a good scale that is for reading small numbers. The ones I have are EBay Specials about $35 each and are 1g resolution to 13kg. They also ready lbs and ozs. Being an Engineer type I prefer the grams…its easier…1000g is a Kg and the weight limit is 5 of those Kg. The weight limit in F3A doesn’t say 11lbs it says 5kg so this is the mass unit we will use. The reason for this is resolution. We want the Cg as accurately as possible. If you are like me and have 3 scales…great if not you need to move the scale and your balsa or foam block around to keep the model level while measuring the weight on each wheel. Write down the numbers for each wheel.

The next post will show my numbers and the math to get the CG location. You now have all the numbers you need.

Below are the numbers.

Left wheel 1686g
Right Wheel 1664g
Tail wheel 489g

This along with our distances we can determine the Center of Mass of the model. This is out center of gravity. To get engineering terms…the Center of gravity is where the entire mass of the plane will be acting. This is one point on the model. Right now we have 3 points that the mass is acting and its not acting evenly at these points either. The majority of mass is being carried by the main wheels. Then a small portion is acting on the tail wheel but this lever arm is much longer than the one acting with the main gear. We are going to calculate the moments around one point. That tip of the spinner reference. Engineering education tells us that is we add up all moments about a point it’s the same as one big moment around that same point. This makes it easy for us.

I use a spread sheet and just plug the numbers in for each model and the sheet calculates it for me. But the math is simple and can be done by hand.

Mass left wheel + mass right wheel = mass of the mains

Mass mains * distance to mains = moment of the mains

1686g + 1664g = 3350g


3350g * 14 in = 46900 in-g -----ďƒ* don’t worry about the units it will end up with inches.


Tail wheel moment

Mass of the TW * distance to the tail wheel = moment of the TW

489g * 64.625 in = 31601 in-g


Total moment

Moment of Mains + moment of TW = Total moment around the spinner tip.

46900in-g + 31601in-g = 78501 in-g

This is the number we need. We now know the total moment about the spinner tip and the total weight of the model 1664g + 1684g + 489g = 3839g

So now we need to point at which this moment would be centered knowing the total weight of the model. So we divide the 78501 in-g / 3839g this gets the mass units to go away and the resulting number is just inches.

78501 in-g / 3839g = 20.44inches

So the CG is 20.44in from the tip of the spinner. Dave Guerin designing the model tells us we want the CG to be 6.5” behind the LE of the wing. We know the LE of the wing is 14” behind the reference we used as the tip of the spinner. So 20.44 in is 6.44in behind the LE of the wing at the root. WOW

It came out just about perfect. The CG is about as close as we could get. Its within about 1 to 1.5mm from the designed CG. This is with the Heavy battery 5 cell 2300mah right on the center of the wing tube. I could not ask for a better balance than that. Usually you have to move the battery and repeat the math to get your new CG…That is why I plug the numbers in Excel spread sheet and let it do the work for me. You may have to move things around. The cool thing about this method is you can add weight and fly it….changing the CG then come home remove the weight and shift battery packs to get the CG back in the exact spot you had when you flew it. This allows for a reference.

Notice you could use the wing tube as the reference. The trailing edge works too. You just have to keep track of the numbers in relation to that tip of the psinner location. Once you find these distances you never have to get them again. The relationship between the mains and the tail wheel will not likely change so you just keep the references and use a spread sheet to calculate it fast and easy. However the math is not hard to do or understand.

I hope I have not confused you guys too much.

Of by the way we also have the weight of our model. It will be pretty close within a few grams. Each scale has a error associated with it. To reference it comes out at 3839g which is 8.46lbs or 8lbs 7.4oz. Reminder this is with the big 5cell pack.

So the CG of the model came out excellent. The weight of the model came out excellent. Now why is this. First using smaller servos in the tail. Being light with the glue in the tail, Using the Hyde Mount with the YS engine gave enough mass in the front to balance it considering the lightweight servos in the tail.


Digest all this and tomorrow I'll have the radio programming stuff on the JR X9303 2.4ghz system. I also have flight reports as we are planning to get it in the air tomorrow. Since I'm lucky enough to be in Phoenix with temps suppose to be in the mid 60's I think we can get it in the air. Things are looking good on it though.

I have not put any graphics just yet. I'll likley have some graphics and stuff on it in the morning.

Radio programming is very simple and straight up.

Troy Newman

Thanks Troy,
very informative thread!!!

Keep on the good work

I get to see the maiden flight today (hopefully). :-)

Quick post since everyone wants to know.

Yes Flew it today. Got 3 flights. Its good. I'll talk about some radio setup and some trimming things.

For the most part the model is correct as it sits. I did play with rates to get the feel to my comfortable level. Things like expo and so on...

Model locks in well and has gobs of power at the 8.5lbs with the YS 110S. The JR X9303 2.4 system also performed flawlessly. The CG was very good perhaps it could scoot a little aft of where I have it now but its close.

Ran through some of the trim tests which we'll talk about in detail a bit here in a future post but it is doing things correctly. Snaps well, spins well. I had so much fun checking it out I flew it out of fuel on each of the first 2 flights. Engine was rich for sure but I would say they were 10-12min flights.

For mixing and setup it doesn't need any right now and its way to early to start putting that stuff in. Right now I need to make sure the rates are good, the model is tracking as well as it can, and then we'll tweak knife edge mix if it needs much if any. Right now I was doing point rolls and it shows no signs of coupling. There will be some mix when I get done, never had a model that didn't have any.

It also got about 2-3% down elevator mix at idle throttle. I set this before we flew it the first time.

I flew some of the figures in the P-09 and tried some the F-09 stuff too but didn't fly a sequence. My goal was to get the model tracking properly then the sequence will be easier.

The only big change I have on the boards right now is some wing tip weight. The left wing panel is dropping a little. I'll get to this in detail. For now the loop tracking is ....well just ok, its not doing anything funny but will be tracking much better. Vertical uplines are dead straight in pitch, looks to be drifting slightly left at the tops. The engine has great gobs of power and you don't need full power anywhere I can see in the Prelim sequence.

Rudder is a little soft at the moment but I had the rate dialed down and some higher expo than probably is needed. Then again I have been flying my Astral and the bipes and they have the best yaw ability of any models I have ever owned. This is not a Bipe when it comes to the rudder....but a little fine tuning will give the feel I want.

Overall its a solid model, it tracks nice and I think its a going to be locked in very well with just a little tweaking here and there.

Minor stuff right now, but it will get better quickly as there is not much to fix.

OK for the quick update on the flying and we'll get into the details of the setup. Right now I'm going to clean it up,a nd put it on charge for tomorrow. Weather looks good again 60 and hope to be in the high 60's to 70 by the first of the week.

Troy

Troy
I am building the Focus Sport and am at the install hinges part. I believe the wings, ailerons, horizontal stabilizer and elevators are foam cores with balsa leading and trailing edges. You stated that you used CA to bond the hinges. Is there enough wood at the leading and trailing edges to avoid the CA from leaking on the foam cores as the CA will eat the foam. Would it be better to use foam safe CA?
Thanks

John Kruger