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Author Topic: Another Boston Cub  (Read 4195 times)
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Yak 52
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« Reply #25 on: February 24, 2012, 10:25:42 AM »

Thanks Russ  Grin.

I've made some simple wheels, just two laminations of 3/32", nothing fancy. The hubs are thin brass tube which was chucked into my drill for turning. The yellow detail is tissue pritt-stuck (?) to white paper and glued on to the painted wheels.

Not very scale but not too heavy at a third of a gram each.
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crashcaley
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« Reply #26 on: February 24, 2012, 12:45:43 PM »

Nice work Jon.  Wrinkles, what wrinkles; you've not seen wrinkles until you've seen my models.   Grin  Still do not get how you experts get tissue wrapped around compound curvies.  That is definitely a nicely covered nose block.  Caley
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Yak 52
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« Reply #27 on: February 24, 2012, 04:02:31 PM »

Thanks Caley, I certainly wouldn't put myself in that catagory  Embarrassed The compound curves are just covered with wet tissue and stuck with dope. The wrinkles can be carefully smoothed out, any that are left when it's dry, I sand a bit to flatten them and remove some of the double thickness (deeper colour). It looks pretty rough... but then when you dope it again the colour magically reappears  Smiley Took me about 6 tries to get it acceptable  Shocked

I've now done the little tail wheel. It's the same as the main gear but as the compass cutter's minimum radius is too big, I used a hole punch to cut the yellow circles.
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OZPAF
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« Reply #28 on: February 24, 2012, 06:48:36 PM »

I looked and I looked Smiley at the highlighted areas on the noseblock and couldn't notice anything Jon. I'm afraid I agree with Caley. As a jaded old RC glider flyer  I doubt whether I could produce tissue covering of that quality under the threat of torture Cheesy.
You must be looking forward to seeing that fly.
John
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Yak 52
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« Reply #29 on: February 24, 2012, 06:54:08 PM »

Thanks John, says more about the quality of my camera than my covering I'm afraid  Cheesy

It's coming together... I hope to get it to an indoor competiton in a week or two so the pressure is on, especially with the BD5 too. Fuselage was covered tonight... I'll post some pics tomorrow when the light is better.


Jon
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Yak 52
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« Reply #30 on: February 25, 2012, 06:31:31 AM »

Well here's the fuselage covered... Quite pleased with the tail wheel. I nearly forgot to fit it before covering!  Embarrassed
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« Reply #31 on: February 25, 2012, 05:25:58 PM »

Very nice Jon. Will that be doped?
John
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Yak 52
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« Reply #32 on: February 25, 2012, 05:54:55 PM »

Yes that's the plan, just a thin coat. I will probably be flying it outside too.

Jon
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Yak 52
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« Reply #33 on: February 27, 2012, 11:57:48 AM »

The wing is now covered too... not far to go now. The weight is up to 12 grams so I'd imagine I've missed the 14g target when you consider the prop and windscreen weight  Angry
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Mr Blue Sky
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« Reply #34 on: February 27, 2012, 03:34:50 PM »

Hello Jon,
Yes, the covering is good. What tissue are you using, it looks a very nice, dense yellow?
Don't worry about the odd wrinkle, I have quite a few and I'm told it adds character.

Tony.
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Yak 52
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« Reply #35 on: February 27, 2012, 06:39:44 PM »

Hi Tony, it's just yellow esaki, bought from my local (proper) model shop. It will probably lose a bit of opacity when it is doped.

Jon
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« Reply #36 on: March 04, 2012, 12:31:09 PM »

Hi Jon,
Your work is very impressive to me. The bones pictured in your early posts look very clean. Which is how I wish my bones looked,maybe someday. I have not really tried the lamination technique on any of my builds, and I'm so impressed with how nice your stab and tail look that I think it's time I explored this method. I'm wondering if you, or anyone else reading this could direct me toward some detailed info/tutorials on this building technique? 

I am currently building (just started) the Walt Mooney Boston Beaver and would like very much to try out some new building techniques. Any and all help,suggestions or advice is appreciated and welcome.
Please keep posting pics of the your Cub. It's beautiful work.

DL.
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« Reply #37 on: March 04, 2012, 01:00:08 PM »

Thanks DL.

I'm actually having a few problems with warps in the fuselage. I'm not sure if it's because of my covering sequence or the light structure around the cabin...


The laminating is really quite easy - there are lots of ways to do it but my sequence is:

1) Cut the form. I use a spare copy or print of the plan, glue stick it to 3/32 sheet balsa and cut around the inner edge of the tailplane etc. Then mask up the edge with packing tape. This form is then pinned to my building board. (Some people use foam for this.)

2) Prepare the wood. This time it was strips of 1/16 x 1/32". They are soaked in the sink or bath  Grin for a few hours in warm water.

3) The first strip is gently moulded around the form and held with pins (actually with little balsa blocks with pins through them to avoid marking the wood.

4) I then run a bead of thinned PVA (white glue) around the first strip while it's still damp. Mould the second strip around the first removing and replacing the pins as neccesary. It's just a case of getting it tight, pinning it against the form and then moving on. Applying more glue as neccesary as you go. (In fact for longer parts it's best to just glue as you go anyway.)

5) I release the component from the form after the glue has 'grabbed' (10 mins?) to make sure it isn't stuck to the form - but then hold it to the form with masking tape until it is thoroughly dry.

To finish up the part I stuck it down to some double sided tape to hold it while gently sanding. The tape had to be cut to remove it though.

The laminated part is then pinned to the plan as per normal for adding the rest of the structure. I've found it's sensible to make the laminated parts over size in both thickness and depth because they sand away very quickly and you end up with less wood than you might want.

Hope that'll get you started...


Jon
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DLphotog
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« Reply #38 on: March 04, 2012, 02:12:24 PM »

Thanks for the detailed info Jon. I'm going to go build a rudder and stab right now using this technique.

DL.
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« Reply #39 on: March 04, 2012, 03:13:20 PM »

Hello Jon,
I'm sorry I have taken so long to get back to you. Thanks or the tissue info (Feb 27th). I see you are having a little trouble with fuselage warps, this is something which always worries me, I have avoided some designs which I feel would distort badly. Like you I tend to use Esaki but it has a very fierce shrinkage. I have tried pre-shrinking with varying results, my method is to attach a sheet of tissue to a frame and soak it. The shrinkage is usually quite good but it can shrink a little more, sometimes too much for a light structure. I am trying to figure a way that allows the tissue to be removed from the frame then re-attached to the frame and shrunk again, maybe up to three times, and I would like to do this without wasting too much tissue. One thing I have noticed is that the shrinkage seems to be greatest during the summer, must be something to do with the heat or maybe the dry atmosphere. One final thing, how do you stop the laminations sticking to the former, my method is to use the PTFE tape that plumbers use. It stretches and can be wrapped around the edges of a former quite easily and PVA does not stick to it. One final, final thing, do you go to the Impington Sunday events? Next one is this coming Sunday 11th.

Bye for now,

Tony.
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Yak 52
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« Reply #40 on: March 04, 2012, 04:08:22 PM »

Nice one DL - keep us updated...

Tony, I've up till now never bothered with pre-shrinkung esaki and not had any problems... I wish I had now though! I have been gradually dampening it to see if it goes back (stuck it in the bathroom  Grin) and I've seen some improvement. It was probably just too humid when I first covered it, although I did a few bits and pieces at the same time and they were ok. I may replace one of the panels but like as not I'll just put up with it.

I use brown parcel/packing tape on the form - nothing will stick to it not even CA. I used to use sellotape but it's not as good.

I was planning to come to Impington this time but now I'm not sure if I can get there...  Undecided If I can I the Cub should be done in time but the BD5 is still 'in build'.


Jon
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« Reply #41 on: March 04, 2012, 11:36:09 PM »

Your Cub looks great, good job. I always pre shrink the tissue when building small birds like this, or I just use Domestic tissue.  For the tail surfaces, I shrink and dope the tissue on the picture frame, then cut it our and apply it to the tail surfaces.  Also I use real stiff/hard 1/16 balsa and I have never had a fuselage warp.
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Yak 52
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« Reply #42 on: March 05, 2012, 06:37:28 AM »

Thanks Scigs. I should have pre shrunk it... I am gradually migrating to lighter wood for my builds and I should have considered the effects!
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« Reply #43 on: March 06, 2012, 12:08:36 AM »

Jon...
Cub looks great...all the guys advice sounds good....I usually pin the structure down on the board again over plastic wrap and lifted off the wrap for air to circulate underneath using pieces of scrap stringer material and spritz it with isopropal alcohol and let it dry pinned down.  So far that has worked for me...worked with the peanut Vagabond I did a while back....

I am just amazed at your ability to cover with no really visible wrinkles...super job.

Tom
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« Reply #44 on: March 07, 2012, 06:12:00 AM »

Thanks Tom, I've not tried the alcohol trick yet. I was playing around by wetting certain panels to see which was pulling it out.

I managed to get it aligned by using a couple of strips of tape to pull it back into shape. The flat top of the fuselage (wing mount) wanted to go trapeziodal and the glazed part of the cabin had a slope to the left.

I've added some gussets which has helped a lot - not perfect but better....
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« Reply #45 on: March 09, 2012, 02:43:34 PM »

Looks like the gussets have really helped...good luck with this.  Hope you can get it stabilized soon.

Tom
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Yak 52
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« Reply #46 on: March 09, 2012, 05:06:28 PM »

Thanks Tom - it seems to be holding better...
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« Reply #47 on: March 13, 2012, 03:07:11 AM »

Jon, glad you found a way to straighten the fuselage. It happens to my planes a lot more than I like.... But mostly it's not as bad as it looks like. It's not possible (for me) to build 100% straight anyway and in many cases the different warps nearly compensate each other at the end. So if the warps are not to big and dont affect the sensitive parameters such as stab incident to much, I try to fly the "warped" plane. In many cases the plane flew great and I am sure I would have worsen the problem with fighting against the warps... We build in warps such as washout... and trimming sometimes includes some intended warping to...  Roll Eyes

Dont get me wrong, I really try to build straight and I use the known techniques to reduce the warping. I just want to say that I have accepted (to a certain level) that the material is "living" a bit. At least for a certain time. After some weeks / month, the material seems to have found a "stable" form.  In many cases I was not successful to fight the warps. I was able to reduce them to a certain amount, but mostly they came back after some time.....

Best regards Roman
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Yak 52
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« Reply #48 on: March 13, 2012, 06:22:14 AM »

I just want to say that I have accepted (to a certain level) that the material is "living" a bit. At least for a certain time. After some weeks / month, the material seems to have found a "stable" form....

Thanks for the encouragement Roman. I don't mind the odd warp normally either but this was affecting the wing saddle, making it twist, so I was worried a bit about the effect on flying. I've done what I can and having left if for a while it seems to have settled down...

Cheers!
Jon
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« Reply #49 on: April 04, 2012, 06:55:42 AM »

Well I've started a push to get this finished. I'd left it a while because of the warp problems - the fixes have mostly worked, not perfectly, but it has at least stabilized. I've been doing the trims and details like the UC fairings. Just assembly, prop fitting and the windscreen to do now. I'm in two minds whether to attach the wing first of the screen first. Either way will mean clamping issues for the other part  Undecided

I'm also waiting for new ink cartridges for my first colour printer Smiley so hopefully I will be able to print the Cub decal for the fin.
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