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Herr "AT-6 Texan" Kit #114 Rubber Power to RC Conversion

speedbirdted

Well-known member
#41
It always amazes me how much you can bend balsa. This fuselage wing support has to be twisted drastically to mate up with the bulkhead.

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After soaking the piece in glass cleaner with ammonia for about an hour it twisted easily and smoothly without cracking.

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I need to mention how amazing the laser cuts are in this Herr kit. The cuts are extremely thin and there is remarkably very little scorching of the wood.
Jon
Looks like A-grain balsa. Not surprised it bends so nicely. It's usually used for leading edge sheet and planked/sheeted fuselages for this very reason.
 

TooJung2Die

Well-known member
#42
Looks like A-grain balsa. Not surprised it bends so nicely.
I need to learn how to recognize the different grades of balsa. I hit the mother-lode this Christmas. The only other balsa scratch builder in our RC club gave me what looks like a lifetime supply of balsa. There's everything you can imagine. The brown box in the middle has about a hundred sheets of 1/32" and 1/16". He builds big, 1/4 to 1/3 scale, and said he doesn't need this small stuff anymore. It's a mess, needs to be sorted and organized, but I will be eternally grateful.

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TooJung2Die

Well-known member
#43
At this point of building the fuselage the instructions have you add all the stringers to one side. I know from experience that is not the best way to proceed if you want a perfectly straight fuselage. With all the bulkheads and longerons glued the half fuselage is unpinned from the board.

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Bulkheads on the opposite side are glued on being careful to keep them square to the keel. Spot the one I glued upside down. 😖 Doh!

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Jon
 
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speedbirdted

Well-known member
#44
I need to learn how to recognize the different grades of balsa. I hit the mother-lode this Christmas. The only other balsa scratch builder in our RC club gave me what looks like a lifetime supply of balsa. There's everything you can imagine. The brown box in the middle has about a hundred sheets of 1/32" and 1/16". He builds big, 1/4 to 1/3 scale, and said he doesn't need this small stuff anymore. It's a mess, needs to be sorted and organized, but I will be eternally grateful.

View attachment 187837
Here's a good chart:

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As a hard and fast rule, A-grain is flexible and malleable where C-grain is very stiff and strong along the grain and should be used for things like stringers, longerons and spars. B-grain tends to be a mixture of A and C.

About that balsa... can I have some of it? :p
 

TooJung2Die

Well-known member
#46
Next the remaining longerons get glued in place. This is the last chance to make adjustments to be sure the fuselage is perfectly straight with no twist and the bulkheads are square to the keel.

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Looks straight and twist free from this view.

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The the last halves of the cockpit formers got sanded and fitted. Bevels are sanded where they fit the longerons.

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The last fuselage wing support gets soaked with glass cleaner and held in place with rubber bands.

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Both wing supports are glued in place. You can see how much they had to be shaped to fit the bulkheads.

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It was a puzzle how these two pieces are supposed to fit. The plan doesn't represent them well and they're barely visible in the box photo. There's no way they would fit into the cockpit former notches so the notches were filled.

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None of the fuselage stringers are in place yet. It's easier to build a battery hatch and install the electronics without having the stringers getting in the way. After that's all done the stringers can go on.

Jon
 
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TooJung2Die

Well-known member
#47
Building the nose cowl. Same as before, pin down the keel and attach the bulkheads square to the table.

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To keep the bulkheads flat pin them to the table and glue on the opposite side.

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Partially built nose cowl is dry fit.

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The nose block that goes on the very front is made of 3 rings of laminated balsa.

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Beginning to sand the nose block to shape. Shaping the inside of the curve is easier if you do it before final attachment. Checking the shape as sanding progresses.

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Jon
 
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TooJung2Die

Well-known member
#48
The rubber motor mount in the kit that goes behind the nose block is balsa. Because an electric motor will be mounted there it is replaced with a firewall made from 3/32" plywood.

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Nose block is glued and clamped to the plywood firewall.

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We don't need all that balsa behind the firewall so a circle was drawn where it'll be cut out.

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Nose block and firewall are glued to the rest of the nose cowl.

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Front view of the nose cowl. Still needs more sanding to bring it to the final shape.

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Jon
 
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TooJung2Die

Well-known member
#49
A hatch is needed to access the electronics and battery. To make the hatch I need another pair of formers for the front and rear of the hatch. The plans don't have outlines of the formers so I scanned the balsa sheet and glued the copy to 3/32" balsa sheet.

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Formers are cut out and sanded to shape. The notches for the stringers will get cut much later.

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Slots are cut in the fuselage formers for the sides of the hatch. There are two pieces per side. The top piece is part of the hatch and the bottom piece becomes part of the fuselage.

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Wax paper is put between the parts of the hatch and the fuselage so they don't get glued together. The wax paper also creates a gap between the hatch and fuselage. Use tiny drops, just enough CA to tack the parts in place. CA glue creeps where you don't want it!

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The wax paper is pulled out and the new parts are sanded to match the fuselage. Now the notches for the stringers are cut.

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The stringers are glued in. Glue them in one at at time alternating right side then left side so you don't create a twist in the fuselage. A couple of the stringers had to be soaked in glass cleaner to bend. Again, use the CA very sparingly so the hatch doesn't get glued to the fuselage.

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Using a razor saw cut through the keel and stringers to separate the hatch from the fuselage.

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Voilà! It's a hatch. Short pieces of bamboo skewer are glued in for locator pins. Magnets will be used to hold the hatch in place.

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Now go back over all the tacked glue joints with more CA so everything is glued securely.

Jon
 
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TooJung2Die

Well-known member
#50
Forget the cowbells, I got to have more clamps! 😁 Gluing the cowl to the fuselage.

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This is the motor I've been planning to use from the beginning of the build, Racerstar BR2304 1850kv. It kinda resembles a radial engine.

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Time to make some airplane noises. I taped everything together to get a very rough idea of where the CG is with just the motor mounted.

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At this point it weighs 4.6 ounces with all the electronics and a 500mAh 2s battery.

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I'm having serious second thoughts about this motor. It weighs 22 grams and can pull over 300 grams of thrust. That much thrust is overkill for an airplane that should only be 6 ounces ready to fly, maybe less. I don't think this airframe will take the stress for long and it's very nose heavy at this point. I have another motor that's less than half the weight and half the thrust.
 
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rockyboy

Skill Collector
Mentor
#51
I think you almost have enough clamps... just a couple more and you'll be set! :ROFLMAO:

Airframe is looking great - and agree the motor is dangerously oversized. Will be much better served with a lower thrust and slower turning motor.
 

TooJung2Die

Well-known member
#52
Airframe is looking great - and agree the motor is dangerously oversized. Will be much better served with a lower thrust and slower turning motor.
Thank you. This motor on the right is a better fit for an airplane of this size and weight. It's rated as 1811-1800kv, good for scale airplanes up to 200 grams. It only weighs about 10 grams with the propeller. I have smaller motors than that on bigger airplanes.

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#53
The motor is mounted. I'm not concerned about the holes. The front of the firewall will be covered with a graphic of a radial engine.

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Backside view of the motor mount. It's glued in at an angle like that to give the motor a down and right thrust angle.

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The servo rails are made from popsicle sticks. Push rod is carbon fiber. The z-bend wire is attached with heat shrink tubing. I added a few more stringers around the cockpit. I made a new instrument panel for the cockpit because the original one didn't fit the clear canopy and had visible gaps.

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The elevator parts are dry fit. They will be permanently attached after the covering is on.

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The elevator looks big. I'll have to be conservative with the throw.

Jon
 
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#55
The motor is mounted. I'm not concerned about the holes. The front of the firewall will be covered with a graphic of a radial engine.

View attachment 189093

Backside view of the motor mount. It's glued in at an angle like that to give the motor a down and right thrust angle.

View attachment 189094

The servo rails are made from popsicle sticks. Push rod is carbon fiber. The z-bend wire is attached with heat shrink tubing. I added a few more stringers around the cockpit. I made a new instrument panel for the cockpit because the original one had gaps around the clear canopy cover.

View attachment 189095

The elevator parts are dry fit. They will be permanently attached after the covering is finished.

View attachment 189098

The elevator looks big. I'll have to be conservative with the throw.

Jon
That is a GREAT lightweight pushrod set up!