WEDJ

Well, with the fall leaves on the ground, my thoughts turn towards balsa and glue.

Here's a look at the "short kit" from Klarich - very nice work, all the curved pieces, none of the stick wood.

WEDJ

Now, I will be building it as r/c assist, with a 450 brushless motor and folding prop for getting to altitude. One of the biggest problems is where to put the equipment, since the body is rather narrow, and the CG should be at 65% (thanks, Ustik)

So obviously, the motor has to go in the nose. With the battery being the heaviest part, I am placing it right at the CG, where it can easily moveforward or back by 2 to 3 inches. There is no room for servos to go side by side, so they have to go in tandem.

Oh yea, tandem servos. The elevator will be aCF pushrod, and the rudder pull-pull. They have to start at different heights, or they will interfere. The only practical way is to put the elevator servo towards the tail, then the rudder at the wing TE. Remember, the battery underneath the servo has to come out the wing opening, which is only about 5 x1.5 inches.

Anyway, here's a shot of the plan, and then the placement of the major parts.

WEDJ

Oh, one last start-up detail, weight.

The total weight of motor, battery, and r/c gear is 7 ounces!  Since the SC (Super Condor) has a 324 sq in wing area, I am hoping for all-up weight of 1 1/2 pounds, for a loading of 10 2/3 oz per sq ft.

WEDJ

So, now that I have started, I had to at least glue something together. Here's the rudder. What you see is the fixed post, and the major part will be moveable, It will have a section ahead of the hinge line, which reduces the air load on the rudder.

WEDJ

Yea, those little gussets will add a lot of strength to the finished static rudder. Now we have another problem, the motor mount does not fit within the forward fuselage former. I'm thinking that I will have to build the fuselage front, then cut it back and add a firewall that will take the motor mount.

Anyone have an alternate suggestion?

UStik

Maybe yes. I don't know that brand of motors you're using, but wouldn't it be natural to choose the front mount in a glider? Seems your motor isn't prepared for that, or might the shaft be shifted? Comparison between front mount (left, motor attached to a front bulkhead behind the spinner plate) and rear mount (right, with a separate cross mount like you have) on an [link=http://www.modelmotors.cz/index.php?page=61&product=2212&serie=34&line=GOLD]AXI[/link].

Strat2003

My Feedback: (1)

If you have access to the rear of the firewall you could mount the motor directly to it without the mount, using the screws and holes that usually attach the mount to the rear of the motor. You might even want to install it early in construction, motors are reliable enough to be considered for built-in status.

WEDJ

Actually, I can reverse the shaft, but the motor housing turns w/ the shaft, the only static part is the rear plate. I am relictant to mount the motor internally due to heat. I like the idea of permanently mounting it to the firewall, that may be the best solution.

In fact, I'm thinking of usinga 1/16 ply backplate in the shape of that first former, and then using RTV to attach it. That way, I can still separate the motor if need be.

UStik

Not quite. Actually, what you call rear plate is the front plate with four holes for mounting the motor directly to the firewall. (That front plate extends internally as the stator with the wire windings. The shaft runs through the stator and has the rotor attached, which you call the housing. These motors are named outrunners because this rotor with the permanent magnets is outside and the stator inside. But you will know that...)

Anyway, that cross-shaped "radial" mount is in addition if you want to mount the motor in front of the firewall. You may have the cross mount directly attached to the firewall, or the other way around with long bolts. I attach a picture of a motor attached with the cross-shaped mount as rear mount, and another picture of the same type of motor mounted as primarily intended.

I think that's what Strat means, even if he also calls the stator the rear of the motor. If you take for granted that it's the front you know how they are usually mounted in gliders. [link=http://www.chk-modelle.de/deutsch/modelle/simba_neu.htm]Here[/link] is an example which shows that you can even dismantle the prop/spinner, remove the 4 motor mounting screws and pull the motor out of the front fuselage, pulling the wires. You might even re-mount the motor, holding the fuse vertically and letting the motor down on the wires. The shaft will fall into the hole in the firewall and you just have to find the holes in the motor and screw in the screws. I think Strat means it's just convenient to mount the motor as long as it's even easier to mount in early construction.

As to heat, you'll notice that the gliders shown on the webpage have no cooling air inlets. That's because the brushless motors don't produce much heat and because they are run only shortly, anyway. Typically, the glider is flown to thermal altitude at full power and then the motor stopped and breaked by the ESC so the prop folds. Fly a while until you need a climb again and the motor has cooled down. The glider guys do it that way all day. Of course, it does no harm to have a small air inlet to lead the heat away. Not much flow needed, but the outlet has to be bigger than the inlet. You'll even need that bit of cooling for continuous power flight, but that's not typical glider flying. Don't ask how I know.

WEDJ

OK, so not worrying about heat gives me some more options to consider. I will probably do the stab next, then the wings (can you say - plug-in tips?) and wait on the fuselage until last.

WEDJ

OK, progress time. Here's the finished vertical stab/rudder assembly. Glued, trimmed and finish sanded.

WEDJ

So yesterday I looked at the horizontal stab, and there are several considerations.

First, how to do the moveable elevator? I decided for simplicity to only move one side of the stab. I mean, it's a glider, not a precision aerobatic plane. Besides, the pylon guys have done that for decades very successfully. So here's a shot of the partially finished stab, with the right side split into fixed and moveable pieces.

WEDJ

So now I'm thinking about the extra forces on the stab vs the free flight original design. In the center, I will need to add sheeting, so I cut 1/16 off the top of the center ribs. On the bottom, I will just scarf in some sheeting between the ribs and spars. This also has the advantage of providing a better gluing surface to mount the vertical stab. Here's the center ribs and their cut-off portion. I left just enough to make a small land for the 1/16 spar.

WEDJ

So here's the stab, all finished except for the center sheeting.

WEDJ

And with the center sheeting added. After the glue dries, we will pull it off the board, add the bottom sheeting, and do a lot of careful sanding. I guess I'm running out of excuses to do the wing.......

WEDJ

For anyone interested, I did get the plans scanned at Staples Office store, it is a 10 Meg Jpeg file.  PM me you email address if interested.

WEDJ

So I've spent a lot of time looking at the wing construction, which as drawn would be very weak and not suitable for RC assist and electric power. I have identified 5 changes to the structure to improve load carrying ability, look at the diagram and notes. I will also sheet the center and figergalss the joint. Hmmm, the gif image did not translate clearly, let me work on it......

WEDJ

Let's see if this works better. I pasted the image into a word doc. Never mind, word docs are not supported.

WEDJ

So I converted it to a JPEG

WEDJ

Finally, it worked!

For anyone who is starting to build something, I really reccomend starting a build thread. It does several positive things:

1 - we like to read them
2 - it generates interest for your plane
3 - It motivates you to keep going (keep the fans happy)
4 - You get a real sense of satisfaction
5 - you may give others new ideas

It is not difficult, just type as if one of your buddies was looking over your shoulder and asking "What are you doing?" or "Why are you doing it that way?"

WEDJ

And so I finished sanding the horizontal stab, cut out the elevator, and notched it for a plywood control horn. Looking at the hinge line, I remember that the silk on the Jr Skylark actually warped the hinge line a bit, so I will add some support strips (like a "T" beam)

WEDJ

I haven't posted since last week, because There is a lot of thinking to do here.

First, I have to figure out how to attach the wing to the body, since access will be important. The original, of course, did not have to worry about that, it was just glued on and done.

So what I have decided is to add a 1/32 plywood root rib between the wing panels, and have a tab at each end, to capture a horizontal nylon 6x32 bolt. In other words, the wing will be put on the body, then two transverse bolts willl hold it on. Here's a phot so you can get the idea.....

WEDJ

The next question I had to attack was how to split the wing, since a one-piece 7-foot wing is out of the question for transportation. Since the root is going to be solid, the only place to split the wing is at the gull junction, halfway out each panel. The kit only has one rib there, and if it's split, there must be two ribs there. In addition, I will be using square aluminum tubes to make the join. Each of the 4 rib pieces should be faced with 1/32 ply, so here is the sandwich I made to get all these ribs correct.

WEDJ

And, of course, remember that I was adding spars, etc to the wing, so here is the rib stack, all ready to get assembled

WEDJ

Here's the ribs and TE stacked up, Notice the spacers on the bottom of the lower spars to accomodate the undercambered airfoil.