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Author Topic: I'm going to build a DHC-3 Otter, because of a very generous Gift!  (Read 2642 times)
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Dan Snow
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« on: September 25, 2018, 08:31:43 PM »

I'm half way through the trimming flights on my DHC-1 Chipmunk, and 90% of the way to test flying my DHC-2 Beaver, in spite of distracting myself with scratching together a couple of faux No-Cal. Just waiting on an order from Peck Polymers

Then yesterday I received the most amazing gift!! Thanks to Dave Cowell of Aerowerks, and Paul Bradley of Paul and Ralph Bradley's Model Airplane Hangout, I am the humble recipient of a set of custom laser cut parts for the Pres Bruning DHC-3 Otter found on Paul's website. The wood is excellent quality and the laser cutting is crisp and clean.  I can't wait to get started on it.

Dave and Paul are great examples of the fine people in the sport/hobby of model aeronautics. Their generosity and willingness to help out another modeler is to be applauded.
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I'm going to build a DHC-3 Otter, because of a very generous Gift!
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« Reply #1 on: September 25, 2018, 08:39:38 PM »

It will be hard to not do a great job with that Dan. Amazing support from the Bradleys and Aerowerkes.

John
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Dan Snow
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« Reply #2 on: September 26, 2018, 07:56:26 AM »

Question for all you guru's out there. This is the side view from the Otter plans.  On the Chipmunk and the Beaver ya'll recommended moving the rear peg forward at least one bay.

Should I contemplate doing the same here? Moving it forward will put approximately 55% of the motor forward of the CG.
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« Reply #3 on: September 26, 2018, 01:29:56 PM »

I would move forward at least 1/2 a bay but probably 1 full bay would be better.  Look up the use of a rolling rear peg cover.  You can then use up to a 3 or 4 times hook to peg motor and have it unwind well.
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« Reply #4 on: September 26, 2018, 03:02:16 PM »

It's a Pres Bruning design.  He is one of the most prolific modelers (FAC) out there.   Leave it where it is shown. 
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« Reply #5 on: September 26, 2018, 11:01:50 PM »

Forward one bay.
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Dan Snow
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« Reply #6 on: September 27, 2018, 05:26:13 PM »

I admit, I'm like a kid at Christmas! I just couldn't wait any longer so I started on the Otter.  I built the stab, laminated and shaped the cowl and the nose plug, and am attempting to laminate the rudder outline. I don't think this one will work as I think I see a little cracking at the apex of the fin. Maybe it wasn't in the hot water long enough??
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« Reply #7 on: September 27, 2018, 07:03:32 PM »

It'll be just fine. Once all the structure is in place and covered, not to worry. Those gussets are your friends!

Aerowerkes wood and laser cutting is infinitely better than Dumas, no?

You've inspired me to finish my (now out of production) Thomas Designs Bostonian Beaver kit. Thanks Dan! It's a kit based on the Walt Mooney design.
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« Reply #8 on: September 27, 2018, 07:05:59 PM »

That's a great gift,enjoy the build.

Scott

https://i.imgur.com/cQ3xQXJ.jpg

https://i.imgur.com/BmerN4q.jpg
I'm going to build a DHC-3 Otter, because of a very generous Gift!
I'm going to build a DHC-3 Otter, because of a very generous Gift!
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Dan Snow
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« Reply #9 on: September 28, 2018, 12:17:25 PM »

I have a question Scott, what is a "2 wing flight"?

Not sure what color scheme I will use on the Otter yet.  Paul Bradley has an excellent covering print file for it, just not sure if that's what I want. Will research some other schemes and see.

Made progress on the wings. At the last moment I looked closely at the ribs and realized I needed a 1/32" shim under the leading edge to match it to the curve of the ribs!

(If I don't tell anyone I managed to install one of the strut support ribs upside sown, and had to cut it out and turn it right side up,no one will ever know? Right?)

We have a front about to come through so the next 2-3 days look to be a bit too gusty for test flights, so might as well build.
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« Reply #10 on: September 28, 2018, 05:46:43 PM »

Hi Dan,

 Wings are units within the Royal Canadian Air Force.2 Wing was a Reserve unit in the RCAF that
operated in Toronto.I think they may have transitioned to helicopters when the Otter was
phased out,but I could be wrong.

Scott

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« Reply #11 on: September 29, 2018, 03:22:08 PM »

Can someone tell me what I'm doing wrong here?!?!?!?  The plans call for the fin outline to be 2 laminations of 1/16"x1/32" balsa around a form, outline supplied.

I have tried twice so far and failed completely both times. First time I poured boiling water over the strips and let them soak for 5 minutes, then slathered them with thinned titebond and very slowly tried to bend them around the form. In spite of this they broke at the apex of the tight radius at the top and bottom of the fin.

Try #2, Got the water boiling and submerged the strips for 10 minutes, then tried the thinned titebond. Again they broke at the apex.

Help!!
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« Reply #12 on: September 29, 2018, 03:52:25 PM »

Strange - it looks like it should be ok. The bottom of the rudder looks worse. Maybe the strips aren't bendy enough. Try pulling the strips around rather than bending them around the form. Or fix them at the apex and pull around forward and back, rather than starting one end. Basswood would be better, soaked in ammonia.
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« Reply #13 on: September 29, 2018, 03:54:10 PM »

First thing. Soak your strips for longer.I like to leave them submerged ( i.e. not floating )  overnight, although a couple of hours can prove sufficient, depending on the density of the wood. Second. Secure your strips at one end of the former and gently pull and tape them around the former. Don't just press them against it and ease them around. The pulling really helps. If the strips aren't limp after soaking them overnight  the wood is too dense/stiff. Third. After taping them to the form, bake them in an oven at 150-200 centigrade. After all this, take them off the former, apply your favourite glue ( 50/50 PVA works well ) and tape them back around the former ( you did wax the former didn't you ? !!! ). Leave for 24 hours and  Bob's your uncle !!!  Smiley
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« Reply #14 on: September 29, 2018, 06:43:30 PM »

Royal Canadian Air Force

https://i.imgur.com/sJUAnYQ.jpg

https://i.imgur.com/jdmxSYk.jpg

US Navy

https://i.imgur.com/F228H04.jpg
I'm going to build a DHC-3 Otter, because of a very generous Gift!
I'm going to build a DHC-3 Otter, because of a very generous Gift!
I'm going to build a DHC-3 Otter, because of a very generous Gift!
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Dan Snow
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« Reply #15 on: September 29, 2018, 06:52:20 PM »

First thing. Soak your strips for longer.I like to leave them submerged ( i.e. not floating )  overnight, although a couple of hours can prove sufficient, depending on the density of the wood. Second. Secure your strips at one end of the former and gently pull and tape them around the former. Don't just press them against it and ease them around. The pulling really helps. If the strips aren't limp after soaking them overnight  the wood is too dense/stiff. Third. After taping them to the form, bake them in an oven at 150-200 centigrade. After all this, take them off the former, apply your favourite glue ( 50/50 PVA works well ) and tape them back around the former ( you did wax the former didn't you ? !!! ). Leave for 24 hours and  Bob's your uncle !!!  Smiley

150C is around 300F on this side of the pond    BUT BAKE FOR HOW LONG?Huh?  Don't want a crispy kritter when I'm done! Smiley Smiley

I tried wrapping it from the apex the second time and almost  immediately it started cracking, but I wasn't trying the pulling trick.  I also checked my wood and I would hazard a guess that the first two times I tried it I was using what looks like B or possibly C grain. I have another sheet that looks more like A grain so I will try the strips from that piece.
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« Reply #16 on: September 29, 2018, 07:01:36 PM »

I should have written 150-200 Fahrenheit. Balsa get's a bit flammable at 200 centigrade  Roll Eyes

Twenty to thirty minutes should be enough time in the oven. There's no need to bake it when gluing. Just let it air dry  Smiley
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Dan Snow
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« Reply #17 on: September 29, 2018, 07:33:03 PM »

Ah-thank you for clarifying that. I had visions of carbonized balsa!!  Smiley
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Dan Snow
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« Reply #18 on: September 30, 2018, 09:06:52 AM »

Well, that was a complete bust! Damn, it has to be me. I am cursed when it comes to forming balsa!  Grin Grin

Everything seemed to work fantastically! When I took the strips out of the water they formed easily around the form with no signs of cracking or splitting. I carefully taped them down, clamped the form together and popped it into a 175F oven for 20 minutes. After letting it cool down for a little bit I un-clamped the form, and then................. totally destroyed the strips trying to get the bleeding tape off!!!  It was my old fumble fingers to blame, I'm sure. I probably used the wrong tape, (scotch) which I'm sure didn't help 

The process works great Mefot, it was my implementation that was off.

I am going to give Paul Bradleys method of heat forming a try. If I screw that up I'm going to build the fuselage next and try again later on the rudder.  Grin
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« Reply #19 on: September 30, 2018, 09:49:32 AM »

Blue painter's tape.  Lowe's, Home Depot, Ace Hardware, Hobby Lobby, Michael's, etc.  We should have told you.  Sorry.
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Dan Snow
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« Reply #20 on: September 30, 2018, 10:01:48 AM »

I tried to use blue painters tape but it wouldn't stick to the form.
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« Reply #21 on: September 30, 2018, 10:48:57 AM »

I soaked a 1/16 square strip for about 90 minutes and then used Paul Bradley's technique with s soldering iron, and tah-dah, I have the fin outline done! I used 1/16 rather than 1/32 x 1/16 lamination because I could just envision the carnage with my fat fingers trying it!  Cheesy Cheesy

I will let this dry thoroughly and then figure out how much I need to shim it off of the building board. The rudder has a symmetrical airfoil when viewed from the top. Should be a fun challenge to keep it straight, huh?
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« Reply #22 on: September 30, 2018, 12:40:24 PM »

Hi Dan.  I know this is a little late but I use meat tray Styrofoam for my molds.  Its free, tape sticks to it very well and its not bothered by water.  Love the plane and am watching with rapped attention. Smiley
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« Reply #23 on: September 30, 2018, 02:37:20 PM »

Be fore I forget, I wanted to let folks know:

If you are interested in building one of these birds, contact Dave Cowell at Aerowerks. He is offering a set of laser cut parts for the Otter for $11 plus shipping. Excellent workmanship and balsa quality. Check if he has the new cut files from Paul Bradley yet as Paul made a slight tweak to a couple of the parts.
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« Reply #24 on: September 30, 2018, 03:13:22 PM »

Nice job, Dan!  And yes, updated cut files already in place.

Skyraider
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