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Giving new life to a classic?

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Giving new life to a classic?

Post  batjac on Thu Mar 27, 2014 5:20 pm

As I posted earlier, I got myself a TD-4 for my birthday.  Ron suggested that I fly it at least once, as how many people can say they’ve flown a TD-4? Well, the plane is a 60 year survivor, so I’m not going to make it suffer the indignity of proving itself long into its retirement.  So, after I disassembled it for cleaning, I decided I’d build a replica TD-4.  I measured the weight of the plane and its components as I was taking it apart, and then traced everything out.  Normally I just jump in on a build, but I figured that before I start this build, I’d scan my working drawings and post them here in case someone else wanted to try their own.  These drawings are in .jpg format, but I also have them in .pdf if someone wants them in that format.











The wing weighs 111 grams.  The stab weighs 19 grams.  The fuselage minus engine weighs 60 grams.  The fully assembled plane weighs 257 grams, or 9.07 ounces.  Hopefully I can build it lighter, then strategically add weight to make it exactly match the TD-4’s original flying weight and balance.  Then it should give a reasonably accurate simulation of the original flight characteristics.

I’ll update this thread as I go.

The Working Mark
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re: TD-4 Classic

Post  happydad on Thu Mar 27, 2014 8:14 pm

batjac wrote:As I posted earlier, I got myself a TD-4 for my birthday.  Ron suggested that I fly it at least once, as how many people can say they’ve flown a TD-4? Well, the plane is a 60 year survivor, so I’m not going to make it suffer the indignity of proving itself long into its retirement.  So, after I disassembled it for cleaning, I decided I’d build a replica TD-4.  I measured the weight of the plane and its components as I was taking it apart, and then traced everything out.  Normally I just jump in on a build, but I figured that before I start this build, I’d scan my working drawings and post them here in case someone else wanted to try their own.  These drawings are in .jpg format, but I also have them in .pdf if someone wants them in that format.




The wing weighs 111 grams.  The stab weighs 19 grams.  The fuselage minus engine weighs 60 grams.  The fully assembled plane weighs 257 grams, or 9.07 ounces.  Hopefully I can build it lighter, then strategically add weight to make it exactly match the TD-4’s original flying weight and balance.  Then it should give a reasonably accurate simulation of the original flight characteristics.

I’ll update this thread as I go.

The Working Mark

Thanks for the memories Mark.  My dad and I owned one of the red-yellow versions of the TD-4 back in 1955-1956 or so. I finally crashed it so many times it was in too many pieces to repair.
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Re: Giving new life to a classic?

Post  Cribbs74 on Thu Mar 27, 2014 9:27 pm

Cool Mark, I appreciate the leg work.
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Re: Giving new life to a classic?

Post  batjac on Tue Sep 06, 2016 3:54 am

Well, being the easily distracted me, Roddie got me got me back on this, leaving my current projects in limbo.  There’re a lot of photos, so I’ll break this up into two or three posts.

Here’s the TD-4 taken apart to make templates.  




I cut out a paper copy of the fuselage and pasted it to a sheet of ¼” balsa.  After that I copied the cutout fuse onto 1/32” ply which I laminated to either side of the ¼” balsa.





I cut out a fin and stab from hard 1/16” balsa.  I also cut a piece of 2-56 all thread rod to make the stabilator pivot.






Fuselage slotted for fin and fin test fit.  I really don’t like that extended fin.  Seems like it’s gonna break pretty easily.  What was Cox thinking?





The all thread glued to the stabilator and reinforced with thread.

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Re: Giving new life to a classic?

Post  batjac on Tue Sep 06, 2016 4:05 am

I was going to make this all from scratch, but found a TD-4 firewall assembly and bellcrank cheap on eBay, so I went ahead and incorporated them into the build.  I cut the front of the fuse to match the holes in the TD-4, then made some balsa doublers for the firewall assembly to pivot on.  Then slotted the doublers for the radial spokes in the plastic pieces.










The firewall assembly test fit.  First in the Beginner setting, then the Sport setting.






Next I took a carbon fiber tube and cut it to length and split it in half for the stabilator saddle, glued it in place, and then put gussets in to hold it firmly.  





I cut a ply hook piece for the rubber band that holds the stabilator in place and glued it in.  Test fitting with fin in its slot and stabilator rubber banded in place.  The rubber band obviously won’t go under the bottom when the plane is finished, I just don’t have any small rubber bands yet so I had to go the long way around with the #33 rubber bands that I have on hand.






Lastly, I made blocks to hold the screw for the bellcrank.  



That’s all for now.  Next is to make up the wing.  That may take me a few days, as I’ve a few things to do in real life before I can put more time into the plane.  But again, who knows…


The Photojournalist Mark
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Re: Giving new life to a classic?

Post  KariFS on Tue Sep 06, 2016 4:22 am

Cool project! Any chance you might scan those templates into a pdf and distribute? EDIT: Oops, you've already done that, do you still have them?

Greenie and a big Thank You plus Congratulations to you for using high quality Finnish airplane birch plywood on your project Finland

Kari the Patriot
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Re: Giving new life to a classic?

Post  getback on Tue Sep 06, 2016 7:12 am

Looking Good Mark, This is a interesting build . At some time in my life as a kid I remember seeing one of these planes the engine thrust adjust is the give away , I thought it was strange at the time but has its advantages for easy set up . The wing should be a joy to make I would think. Popcorn
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Re: Giving new life to a classic?

Post  batjac on Sat Sep 10, 2016 1:16 am

Okay, I’ve decided to take the easy way out on the wing, but I need two sheets of medium and light 1/16” balsa, and all I have is hard 1/16”.  I can’t get to the hobby shop until tomorrow, so I’ll just post a couple of pics of the fuselage finished and ready for paint.

In the Beginner setting:




In the Stunt setting:




The Delayed Mark
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Re: Giving new life to a classic?

Post  roddie on Sat Sep 10, 2016 2:19 pm

OMG.. you have the patience of a SAINT!! That's a lot of work there! Wondering if you could build a wing "saddle" from two pieces of airfoil-shaped 1/4" balsa, with a 5/16" core-piece to match the contour of the fuse's wing cut-out.. except; size the curve on the bottom-side of the saddle to match the airfoil of your wing. A Sig airfoiled sheet-wing probably falls short of the TD4's chord.. but you could extend it (if you had one..) The saddle would be glued to the wing-root.. and the 5/16" thickness fuse would sit-down into the saddle. Not sure if I'm conveying this in words.. in a way that you understand.. but it would allow for rubber-band mounting.. yet keep the wing perpendicular to the fuse. You would connect your lines directly to the bellcrank.. in the event that the wing either separates the fuse.. or moves forward. A nose-in crash would likely cause the wing to move forward and downward.. which the saddle would allow. The fuse-mounted bellcrank "should" protect the pushrod.. and the stabilator.

I had thought about building an engine-mount that swivels as such.. by facing the bearing-surfaces with four discs made with coarse sandpaper. I felt that it would allow for a "friction-fit" (grit facing grit) that would hold, when sandwiched-together with a central machine-screw and another in the radial adjusting-slot. Incidentally.. the engine-mounting could incorporate a similar "saddle-mount" as the wing.. if desired. Unlike the PT-19; the TD4's engine-mount is rigid.
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Re: Giving new life to a classic?

Post  rsv1cox on Sat Sep 10, 2016 2:34 pm

Ok Mark I'm seriously impressed. A couple of dozen thumbs up.

Bob
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Re: Giving new life to a classic?

Post  fredvon4 on Sat Sep 10, 2016 3:21 pm

Build at least one spare fuse tail assy to use the plastic nose

Build up three wings... original span 21+/- inches...Bee engine

a 26 inch one Gold or Black engine...even Purple Python...grin

and a 30 inch one ----and have fun with tip shapes

A 049 Medalion with Screw in back plate redial mounted with the larger wing will be a real cool toy with the adjustable features of the nose...tail and maybe even lead out rake

I would make a mold to form the wings to shape ...perhaps with a LE out of spruce or bass, a spruce or bass mid chord spar and Heavy CA trailing edge

I might even try 4 or 6 bottom ribs to help hold the shape better

BUT even better is my initial notion when I saw how you were doing this...There are dozens of replacement pre formed wings for park flier trainers ...I have a formed wing here from a long dead HobbyZone Vtail commander but only 4" chord

Some sort of thin foam core with laminated covering and quite sturdy for the weight

Another thought is a set of tapered or Constant chord ACE foam wing cores

too many projects right now but these type projects spark a whole lot of TLAR bashing
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Re: Giving new life to a classic?

Post  RknRusty on Sat Sep 10, 2016 3:58 pm

Gorgeous work. When I grow up I wanna be a Craftsman too.

If you really want to go all out replica, you could add some cap strips around the edges so when painted, it will look almost just like the plastic model. There are some raised portions that would be hard to get right. The extra weight too... don't mind me, I'm just dreaming, living vicariously through your work.
Rusty

P.S. If this is a TD-4, then the little one with aluminum wings and a Spacebug Jr, is that a TD-3?

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Re: Giving new life to a classic?

Post  Mark Boesen on Sat Sep 10, 2016 4:49 pm

TD-1 had the aluminum wings, TD-3 was thin styrene, there was no TD-2
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Re: Giving new life to a classic?

Post  batjac on Sat Sep 10, 2016 6:17 pm

Thanks for all the compliments, guys.  It’s been a long time in progress.  Hopefully it’ll be done soon.

Roddie, I misspoke (mistyped?) when I said it was paint ready.  I do have a plan for a wing saddle other than the one on the original.  After I make the wing, I’m going to take a strip of 1/64 ply about an inch wide and sandwich it between the wing and the fuselage.  After making sure the wing is at a 90 degree angle to the fuselage, I’ll tack it in place with thin CA to the bottom of the fuselage, then remove the wing and glue it firmly in place with a bead of thick CA.  I also plan to have two dowels along the wing centerline sticking up about ¼” inch that will fit into a couple of sockets in the bottom of the fuselage between the ply doublers.  Between the dowels and the saddle, the wing should stay securely in place with the rubber bands fastened.

Rusty, I spent a lot of time debating whether I’d do 1/16” square strips along the edges and around the cockpit to replicate the original, but decided to leave it off.  The only place on the model that it’d be of real interest to me is to delineate the canopy lines for the pilot stickers I’ll try to make.  Low ROI.  But then, I still haven’t painted it yet, either…

Fred, lots of good ideas there.  But my limited “attention span per model” has already been exceeded on this one.  Once it’s complete, it gets flown a few times and then hung up in the garage until the Spring Tune-Up at Delta Park where I’ll pull out my off the wall designs to show off in the 1/2A circle.

The ADHD Mark


Last edited by batjac on Sat Sep 10, 2016 6:38 pm; edited 1 time in total
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Re: Giving new life to a classic?

Post  batjac on Sat Sep 10, 2016 6:35 pm

A quick request for info here.  I’ve read about the Cox “Thimble-Drome Training Aid Kit” that could be bought from hobby shops in the 50’s/60’s for about 50 cents.  It was just an aluminum disk with a hole for the prop bolt and a black rubber spinner.  The purpose was to create extra plate area to create drag and degrade the prop efficiency and to provide a rubber nose for a little extra weight and for the plane to bounce off of when it nosed in.  I have a few rubber spinners with the heavier hub, but I have no idea of the diameter/thickness of the aluminum plate.  I don’t even know if the plate was bare aluminum or painted/anodized.   I don’t really plan on using it when flying this replica, but I’d still like to make one up for display purposes.

Does anyone have any info on these kits?  Maybe one of the more senior members remembers seeing them when they were a kid?

The Bouncy Mark
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Re: Giving new life to a classic?

Post  Cribbs74 on Sat Sep 10, 2016 8:16 pm

That's a new one on me. Should be easy to re-create if needed. Especially with your building skills.

A little experimenting could help you figure out what diameter disk kills prop efficiency. I bet there is some info out there as it pertains to R/C and cowls.

Ron
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Re: Giving new life to a classic?

Post  Ken Cook on Sun Sep 11, 2016 5:24 am

Mark, I've seen the disc that you mention. I have never seen it on a control line model. Anytime I've seen it, it was on a free flight plane typically .020's. This disc that I have seen was just mill finish aluminum and it had some info stamped onto it.This was not a home made part but I didn't think it was a Cox related item. I recall seeing it in a American Modeller mag.
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Re: Giving new life to a classic?

Post  roddie on Sun Sep 11, 2016 7:30 pm

Not sure if this would interest you.. but I machined some discs made of 3mm (.118") thick "Dibond" with 1/8" center holes.



Dibond has a .094" polyethylene core; faced ea. side with .012" aluminum.



I use them for wheels with O-rings for tires. They're very lightweight.. although that wouldn't really matter for display. The largest discs are 1.5" diameter.

Just to give you an idea how they'd look mounted with a prop..



The ones with holes make a patented whistling jet-engine sound when running.. (just kidding.. but who knows.. I'll have to try one!)  



If functional.. forget about using a zero-drag starter-spring. That's a Tee Dee style aluminum spinner shown.. which I'd never actually run.. because even with the 1" long 5-40 prop-screw, there's only about 1/4" of thread in the crankshaft. A bottoming stub-screw with the threaded spinner-hub would be the way to go.
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Re: Giving new life to a classic?

Post  dckrsn on Sun Sep 11, 2016 9:00 pm

Here's one. I've seen one before, and I remember it being 2.5 to 3" dia.
http://www.ebay.com/itm/RARE-Cox-Training-Aid-Kit-/370381273980?hash=item563c71bb7c:m:mVs1ugsDpKujtaMriTU1MDg
Sorry, trouble grabbing a picture.
Bob
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Re: Giving new life to a classic?

Post  roddie on Sun Sep 11, 2016 9:05 pm

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Re: Giving new life to a classic?

Post  batjac on Sun Sep 11, 2016 9:06 pm

roddie wrote:

Cool!  Where did you find the picture?

The Amazed Mark

edit: Never mind, I just saw it.  $22.29 for a disk that originally cost 50 cents?  I'd be tempted if it were a little cheaper. I looked at his other Cox items. 171 of them. They all seem to be made of gold, maybe platinum.


Last edited by batjac on Sun Sep 11, 2016 9:19 pm; edited 1 time in total
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Re: Giving new life to a classic?

Post  roddie on Sun Sep 11, 2016 9:11 pm

batjac wrote:
roddie wrote:

Cool!  Where did you find the picture?

The Amazed Mark

From Bob's link. It's a really lo-res image though. I can't read the text on the label.
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Re: Giving new life to a classic?

Post  roddie on Sun Sep 11, 2016 9:20 pm

Just throwing this out there.. "If" you end up a little tail-heavy or.. want a little more training nose-weight on any Cox .049 powered airplane.. look for a Cox "Super-Stunter" hub-nut.



They're 3 times the weight of a standard one..



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Re: Giving new life to a classic?

Post  batjac on Sun Sep 11, 2016 9:27 pm

Roddie, I've already got three or four of those in my parts box. And what should be the proper rubber spinner. Looking at the picture on the package, it looks like the disk is half the diameter of the prop, so I'd guess its a 3" disk.

The Proper Mark
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Re: Giving new life to a classic?

Post  dckrsn on Sun Sep 11, 2016 9:29 pm

roddie wrote:
Hey, thanks for doing that Roddie.
I always wondered if there would be an
overheating issue, using one. Huh...
Bob
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