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Guillow's de Havilland Chipmunk (Read 4812 times)
Reply #76 - Oct 9th, 2019 at 7:53am

Dan   Offline
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No further progress has been made on the Chipmunk, but I have done some planning. Though it may seem like an insane amount of work, I am going to scratchbuild a replacement for every die-crunched part. After all that work, I would likely be upset if it were to crash, so it is definitely going to be a static display model. I even have a color scheme planned out for it, but I'll get a few covering jobs under my belt before I attempt it.
 

Building stick-and-tissue models is a hobby, not work.
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Reply #75 - Sep 25th, 2019 at 5:09pm

Dan   Offline
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Thanks to both Tom and alfakilo for the advice. I'll make a copy of the wing rib templates on the plans and make some new ribs. Hopefully I can make some progress on the Chipmunk this weekend. I am also considering modeling it for static display purposes...good thing I have yet to start on the fuselage!

 

Building stick-and-tissue models is a hobby, not work.
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Reply #74 - Sep 25th, 2019 at 9:09am

alfakilo   Offline
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When making copies of a part such as a rib, remember to use the original master to make the other copies. Using a copy to make another copy often results in the parts getting progressively larger because we inadvertently cut on or over the pencil/pen line instead of inside it.
 
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Reply #73 - Sep 24th, 2019 at 8:07pm

Sky9pilot   Offline
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There are many ways to make ribs...here's one that you can use.  Make templates of the ribs (root rib and tip rib).  Sandwich balsa planks long enough and high enough to cover the templates.  Then pin or drill holes through them and bolt them together with long bolts in two places.  Once bolted/pinned together carve the planks close to the templates and then finish by sanding down to the templates.  Once the shape of the ribs has been completed you can notch all the ribs with a sanding tool for the spars as needed.

Here's a link to Airfield Models site on making constant chord ribs: Click Here
Below are a few pics from their site...
 

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If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #72 - Sep 24th, 2019 at 7:22pm

Dan   Offline
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A little update on the Chipmunk: I inspected the ribs and found that some of their notches were not done very well. Therefore, I will be making a dozen new ribs and going to great pains to get each pair identical. If anyone has suggestions or advice on how to make than happen, I would be most grateful. A piece of balsa suitable for making the notching tool Tom described will be a Friday purchase.
 

Building stick-and-tissue models is a hobby, not work.
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Reply #71 - Sep 22nd, 2019 at 12:02pm

Dan   Offline
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pb_guy wrote on Sep 21st, 2019 at 11:37pm:
Remember what the carpenter said? "I've cut it twice and its still too short!"

He should have been taught to measure twice and cut once...remind me to never hire that guy!

All joking aside, I believe you're right about the ribs being intentionally left a little long. I will do a test fit later today to confirm.

Edit: instead of a test fit (which is what I did yesterday), I checked the wing ribs under a bright light. None showed any evidence that they were intended to be notched for spar clearance at the TE during manufacture. The plans did not show notches at the TEs, either. I have a little bit of sanding to do...

Edit number two: I have decided to construct an entirely new vertical stabilizer structure from 1/16" stock. I have given some thought to replacing the four die-crunched pieces with a single-piece structure. Is that a bad idea?
« Last Edit: Sep 23rd, 2019 at 7:57pm by Dan »  

Building stick-and-tissue models is a hobby, not work.
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Reply #70 - Sep 21st, 2019 at 11:37pm

pb_guy   Offline
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The ribs are probably left a little long on purpose. Remember what the carpenter said? "I've cut it twice and its still too short!" Match the front of the ribs to the Leading Edge (LE) and cut off, or better yet sand, the excess at the Trailing Edge (TE).
ian
 
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Reply #69 - Sep 21st, 2019 at 4:30pm

Dan   Offline
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Sky9pilot wrote on Sep 21st, 2019 at 4:12pm:
I'm sorry...how do you measure that amount of movement????

Quite honestly, I don't know. I'm more worried about eating my pizza and test-fitting the Chipmunk's wings!

Edit: I did a little test-fit, and I'm glad I didn't spread any glue! Either the ribs are too long or there was an issue with their trailing edges (a notch that didn't get cut at the factory or I neglected to cut). Back to brainstorming a solution...
« Last Edit: Sep 21st, 2019 at 5:56pm by Dan »  

Building stick-and-tissue models is a hobby, not work.
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Reply #68 - Sep 21st, 2019 at 4:12pm

Sky9pilot   Offline
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I'm sorry...how do you measure that amount of movement????  My bionic eye doesn't calculate to that many decimal places!!! Cheesy Grin Wink
That's not enough to worry about!
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #67 - Sep 21st, 2019 at 2:42pm

Dan   Offline
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I have not made such a tool, but I definitely will! The balsa I have now is rather soft, so I'll source out a new piece when I return to the hobby shop.

As regards the wing ribs, they would only be moved 0.0125 inches...just enough to make them easier to align. Trying to perfectly center them, with a space of 0.00625 inches per side, would drive me nuts! Of course, if that amount is miniscule enough that it isn't worth worrying about, I'll get cracking on the Chipmunk's wings!
« Last Edit: Sep 21st, 2019 at 6:51pm by Dan »  

Building stick-and-tissue models is a hobby, not work.
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Reply #66 - Sep 21st, 2019 at 2:26pm

Sky9pilot   Offline
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Dan,
Have you made any sanding tools for notches, fitting ribs to leading edges, trailing edges etc.  With diecut/die-crunched parts you'll find sanding parts to fit the locations on the plan are a real help.  I wouldn't shift the ribs in or out...rather sand the ribs to fit where noted on the plan.  This is where the fingernail files/emery boards come in handy. 
I use a hard piece of 1/16" balsa and glue it to a piece of 220 or rougher grit of sand paper.  Once the glue has dried I trim the sandpaper to the 1/16" balsa and even sand the sandpaper flush to the 1/16" balsa.  This becomes my "notcher".  I don't cut notches anymore...I sand in the notch.  This tool makes a perfect fitting notch for 1/16" sq stringers etc.  A sanding tool is one of your greatest assets in Stick and Tissue model building!
Sky9pilot
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #65 - Sep 21st, 2019 at 10:40am

Dan   Offline
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I just finished cutting a new wing rib. The rib in question, W-6, is a bit of a weak point; there isn't much room to work with when cutting the notch for the bottom spar. I have also found another hurdle to overcome: Guillow's apparently didn't update the plans with 1/20" between the outlines for the wing ribs. Trying to get all those wing ribs perfectly centered between the lines would drive me up the wall! My plan is to shift all the ribs slightly toward the wing tip or the wing root. Is one way any better than the other?
 

Building stick-and-tissue models is a hobby, not work.
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Reply #64 - Sep 19th, 2019 at 6:11pm

Dan   Offline
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Sky9pilot's advice about the gussets made me consider making new gussets. However, as it was intended for future reference, I decided not to. Instead, I sanded the corners to what should be their final form. It took much less time than I thought it would. The horizontal stab shouldn't need much more than a little filler, final sanding, covering, and installation on the fuselage.

Thanks again to all who have offered help, advice, suggestions, and positive feedback. I am glad to have found this board!
 

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Chipmunk_Horizontal_Stab_Shaped.jpg

Building stick-and-tissue models is a hobby, not work.
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Reply #63 - Sep 19th, 2019 at 12:03pm

alfakilo   Offline
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Nicely done! That should do just fine!
 
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Reply #62 - Sep 18th, 2019 at 10:34pm

Sky9pilot   Offline
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Just a little pointer re: the gussets.  the grain of the balsa is suppose to run along the line of  the longest side of the triangle.  This is where the strength of the gusset comes from.  Just for future reference.  You shouldn't need to replace any gusset that aren't like the above suggestion.
Sky9pilot
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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