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Author Topic: Want to use balsa sheets as Skin and wing covering. Anyone done this?  (Read 1433 times)
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bjornS
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« on: March 29, 2016, 01:20:53 AM »

Hello everyone.

I am not good at tissue nor want to spend all that time building up a wing. I want to instead use very thin balsa sheets as my covering. I purchased a bunch of 1/32ns inch balsa sheets, 4-5 inches wide by like 2-3 feet long. Under 5 bucks each which is super thin and easily bends to form a wing. I built a small mockup to see and it works great.

I have been trying to find resources on the web and I see huge amounts of pictures of people doing this but only for small pieces of the fuselage but haven't seen a wing. I saw one forum on the topic and they talked about this not being practical because of the weight, but these sheets weigh next to nothing and don't seem to weigh much more than a foam core wing with balsa covering.

Anyone think this is doable. FYI I did build a very small plane, all balsa doing this and it flew, albeit fast and a little squirly, but it fled. The plane is tiny and had some heavy gear in it, so I expected it to need some speed. Also I built using my eyeballs with no plans so the wing was think for the plane and the stabilizer was also built up with a proper wing which should have been just a thicker piece of balsa and nothing else. The rudder was also very tiny so that helped make it a little less stable. But the think flew.

So, back again to my question, anyone think this is nuts or is there some legitimate reason this will not work. Am I leading edge here ? It just seems so much simpler to use balsa and certainly stronger. Keep in mind my plane size target is about 26-30 inch wing span maybe even as small as 24 inch total wingspan tip to tip.

That little plans had a 17 inch wingspan tip to tip with a 1.5 inch fuselage fully enclosed gear, magnet latch, etc. It was pretty heavy for a small plane, about 90 grams fully loaded. I can send pictures if people are interested. The balsa is not sealed in any way so it can't get wet at all. I will have to account for that of course.

Thanks on any feedback or shared experience in building smaller sized planes using all balsa.
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DavidJP
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« Reply #1 on: March 29, 2016, 04:20:07 AM »

A bit curious..... are you making a conventional framework/structure with ribs and spars etc and simply using the balsa instead of tissue?  I guess not.  Have you considered using Depron foam and making the wings etc. out of that?  Very quick method.
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« Reply #2 on: March 29, 2016, 06:36:26 AM »

Bjorn:

Fully sheeted wings were common for FAI Power, F1B Wakefield rubber, and F1A towline gliders in the 1970s-1980s. But these are much bigger models then you are building.

I've built an number of F1B wings using 1/32 sheet balsa top and bottom, with 1/16 balsa ribs spaced about 1" apart and 1/8 square balsa leading edge. Spars were tapered 1/32 spruce let into top and bottom sheeting with balsa webbing. Actually fairly quick to build. For an under cambered airfoil you do need to make a building board that is curved to match under camber.  Weight is dependent on how light the 1/32 sheet is. But that can easily be calculated by weighing sheets and comparing area to area of wing. If I remember correctly 3x36x 1/32 sheets I used were in the 6g range. 

FYI a typical F1B wing back then (1970s) was around 4.5 to 5 inch chord and span was around 50-55 inches.  The sheeted wings were considerably heavier then a modern carbon fiber D-box wing (42g uncovered/52g covered is typical). The new wings are much higher aspect ratio (1.8m span) and much, much stiffer then the sheeted wings.

It would be helpful to have an idea of what type of model you are building (free flight, RC, glider, etc). Another option would be a solid balsa wing. Again not as light or as stiff as with more modern composite construction. With a solid balsa wing you need to keep the airfoil thin to reduce volume of balsa. For the 24-30 inch size, consider a Jedelsky type construction--Typically the front 1/3 of wing would be 3/32 or 1/8 balsa sanded to airfoils shape with thinner curved portion aft.

As you have no doubt figured out, 90g for a 17 inch span a very heavy wing loading.  Depending on what you are trying to do, weight should be about a fifth of that.

Louis
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billdennis747
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« Reply #3 on: March 29, 2016, 07:59:48 AM »

Start by googling ken willard schoolboy
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p40qmilj
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« Reply #4 on: March 29, 2016, 12:17:14 PM »

 Grin if you want to see sheet balsa in action www.paramodels.com   
jim Grin Grin
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bjornS
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« Reply #5 on: March 29, 2016, 03:01:25 PM »

Thank you everyone for the wealth of replies and information. I am at work and will review in more detail a little later. Here are some answers to various questions posed.

1. I am building something akin to a warbird, rather would like to.
2. It is all Electric, which I still also have challenges with in matching motors with batteries and figuring out flight time and airplane size. I have experience with what I happened to buy a lot of, smaller motors running off of typically 2s 500-600Ah. Now that I think about it my biggest issue really is figuring out prop sizes. That is why to date I have been sticking with the proposed size model. I have motors that I think will fly a plane of that size.
3. My thought on wing construction is ribs and then covering using balsa instead of tissue. I can leave a little more space between ribs this way.
4. The body of the plane is slightly thicker balsa and mostly a single piece for the sides.
5. I have Depron sheets at home but it seems so flimsy and snaps easily. I am worried about how fragile this would be but I thought about using it lately for a 3d plane, similar size as the balsa one I want to build.

Thanks. i will research some of the feedback. Thanks again everyone, really appreciate the responses.
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lincoln
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« Reply #6 on: March 29, 2016, 10:32:42 PM »

There's a typo in Jim's link above. It should be parmodels.com
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Some all sheet models:
http://flying-models.com/centerfold/fm_centerfold_may2013/FM_BabyBiwinger_Plan.pdf
Note the modifications called out in the article:
http://flying-models.com/centerfold/fm_centerfold_may2013.php

Walt Mooney designed a number of all-sheet peanut scale models:
http://www.hippocketaeronautics.com/hpa_plans/categories.php?cat_id=66

With sheet on the top and bottom of the wing,  you should be able to go much larger.

Note Dave Robelen's Kestrel. 73 inch span wing for RC with 1/16" top and bottom sheeting on the wing. Presumably,you could make a similar model using 1/32" balsa that was half the span. Much more span if the wing has a lower aspect ratio.  I'm pretty sure you could use 1/32" for the fuselage too, especially if it's curvy.
http://outerzone.co.uk/plan_details.asp?ID=3719

For lower aspect ratio models, you can probably leave off the bottom sheet. You'd probably want to have some ribs on the bottom to hold the shape.
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« Reply #7 on: March 30, 2016, 06:28:10 AM »

Bjorn:

I'd suggest that you think twice before increasing rib spacing.  On a stressed-skin structure the "skin" (1/32 balsa sheet in your case) is carrying most of both bending and torsion. To be effective, the top and bottom skins need to work together, much like the top and bottom flanges of an I-beam. One option is to vary the rib spacing, with ribs closer together near the center, where loads are higher, then gradually increase rib spacing towards the tips.

Louis
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pd1
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« Reply #8 on: March 30, 2016, 09:02:34 AM »

Ken Willard used balsa sheets for wing coverings on a lot of his small RC models.
http://www.outerzone.co.uk/search/results.asp?page=1
I did a Willard Roaring 20 with electric power and RC, 20 inch span and a lot of fun.

Carl Goldberg did too.
Some warbird types with plans here.
http://www.parmodels.com/Plans/jigtime.htm
Some warbird types with plans here.
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lincoln
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« Reply #9 on: March 30, 2016, 10:14:05 AM »

Changing rib spacing may be a good idea. Many of the ribs could be sliced out of foam sheet. You might try putting extra half ribs, since 1/32 top and bottom may be overkill for a 26 inch model.

I'm not sure how much work you'll save over a built up, tissue covered wing. Unless you need inverted performance, a single surface wing out of 1/32 might be just fine if you keep the weight down. Not for a TA152 though. Maybe for a Wildcat.
Bjorn:

I'd suggest that you think twice before increasing rib spacing.  On a stressed-skin structure the "skin" (1/32 balsa sheet in your case) is carrying most of both bending and torsion. To be effective, the top and bottom skins need to work together, much like the top and bottom flanges of an I-beam. One option is to vary the rib spacing, with ribs closer together near the center, where loads are higher, then gradually increase rib spacing towards the tips.

Louis
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julio
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« Reply #10 on: March 30, 2016, 08:52:46 PM »

I just uploaded an article to the Builders' Plan Gallery at Miscellaneous Articles. It's about all sheet scale models, with balsa sheet single surface wings (not skin covered wings). The file is a .pdf but couldn't upload it as such, so I uploaded compressed as .rar. Hope it could be available soon.

Julio
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I think I will stay a novice forever.
Daithi
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« Reply #11 on: April 24, 2016, 04:24:30 AM »

I did, many years ago, convert Keil Kraft Junior Scale kits to control line, with an Allbon Dart (0.5 CC) up front and used sheeted wings. You have to undercut the ribs by 1/32" top and bottom to maintain the wing section. however, this wasn't necessary in the end as the thicker section (using the original ribs unmodified, gave better lift). For C/L I used a 1/8" plywood keel and the port side formers were reduced by 1/16" and the starboard increased by the same amount (to keep the original centre line) and I filled in the gaps between the stringers with 1/16" scraps. This produced a very strong fuselage. Tail feathers were replaced with 1/8" sheet ones.

For free flight/radio electric, the same setup for the wings should work, but keep the weight down elsewhere. Depron isn't as weak as you seem to think, especially when used as sheeting and will be fine for the fuselage and tail.
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It's not that modelling is in my blood. My blood is on a LOT of balsa Wink
packardpursuit
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« Reply #12 on: June 13, 2016, 10:37:30 AM »

For those interesetd in some unique sheet balsa building techniques, you may want to go to this site's  "Outdoor FF" heading, under" FF Scale" and review all threads by a fellow named" Prosper". 

From a practicality point, finishing thin balsa as a sheet covering is the real problem. Prosper seems to be onto something!
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F4FGuy
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« Reply #13 on: December 15, 2017, 01:15:57 AM »


  Bjorn,

  I came across your post from some time ago as I was just cruising the site. If you still have questions, here's my "Lil Zero".  It was built for 1/2A CL Stunt and performed fine(note past tense).

Specs: Span 28", Area 180+, Wt. with fuel 10+oz., Engine Norvell .061
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Hepcat
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« Reply #14 on: December 15, 2017, 06:28:25 PM »

Bjorn,
There is nothing new, different or unusual about making model aeroplanes from thin sheet balsa. In my eighty odd years of aeromodelling I have seen many types of model built that way in sizes from a few sqaure inches wing area up to several square feet.  It is a method which suits some models well and is completely inappropriate for others, therefore I urge you to do a lot of looking at old plans otherwise you stand to waste a fair amount of money and to suffer quite a lot of dis- appointment.  With most things intended to fly the wing loading is usually important and the wing loading on an 'all sheet' structure is not always easy to estimate.  Do look at plans of some models of similar size to what you intend to build.
John

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lincoln
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« Reply #15 on: December 19, 2017, 01:11:06 AM »

Someone mentioned solid wood wings. The 36 inch version of the Apogee rc hlg weighed only 104 grams. A 24 inch version's wings would weigh a bit over 20 grams, and would be more than adequately stiff and strong.
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lincoln
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« Reply #16 on: December 19, 2017, 01:14:31 AM »

BTW, the Apogee design is predicated on very light, c-grain wood. If you're going to use 10 lb wood on that 24 inch plane, better make it a Ta-152.
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F4FGuy
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« Reply #17 on: December 24, 2017, 04:28:08 AM »


 Bjorn,

  Don't let the naysayers get to you. What you propose is imminently feasible and practical. There are a few things to keep in mind:
(1) Unless you are a reasonably accomplished flier, you may find it a little more "brittle" than you'd like. Even at 1/2 A size a major crash is usually not reparable.
(2) As mentioned above material selection is critical. Use only 5-6 # balsa in the covering (preferably  4# in the wing from HP back).
(3)Use only the thinnest material needed for the job it has to do. In the "LIL" Zero the entire structure is from 1/16", 1/20 and 1/32" 4-76# balsa with 1/64" basswood fuselage stringers. The 1/16" was for wing ribs(the only structure inside the wing) and fuselage bulkheads. In a small model, the distance between supports is small so the thin material does just fine.
(4)As to the apparent preference for solid plank or carved balsa, unless you just want to go roundy-round or look good and not fly at all, it makes little sense. You'll end up with an airfoil that's too thin for efficient maneuvering or too heavy if it is thick enough.
 Finally, as I see it, especially in 1/2A, balsa skinning or old fashioned built-up and tissue covered are the only answers to a good performing 1/2A model.         
 I do know a little of conventional plank wing 1/2A, as you can see in the pics. They can be lots of fun, but accurate maneuvering, not so you'd notice.


  Ron Burn (F4FGuy)





                                                             
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