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Author Topic: Balsa: Changing the paradigm  (Read 5542 times)

Online Bob Hunt

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Balsa: Changing the paradigm
« on: September 29, 2020, 07:02:58 PM »

Note: I posted a version of the following a few years ago, but I feel it needs repeating here again. A few sentences have changed from the original post, but the gist of it all is still the same, and I feel critical.

Hi all:
This post will be my attempt to help all of us understand the realities of the current balsa situation and how we can help ourselves immensely from now on into the future to deal with these realities. I’m posting this piece because I believe the need for the following information is critical to model airplane building in the 21st century.

First the medicine:

The days of 4 to 6 pound, clear, straight grain, 3 to 6 inch wide in-one-piece, readily obtainable, inexpensive balsa wood are essentially over and gone. Please read that sentence again. It is essential that all of us face the realities of the situation. Sure, we will occasionally be able to find isolated stashes of Ecuadorian Gold, and we should snap up those opportunities when and where they present themselves. Those of us who have been at this for awhile can remember the amazingly clear and consistent contest grade balsa that we used to be able to get on a regular basis from several suppliers. That type of wood in the quantities in which we used to receive it simply isn’t available anymore.

Where has all the balsa gone? (Sounds like an old Peter, Paul and Mary song…) The real question is, “Where is all the balsa going?” What I’m going relate now may seem incredulous, but I have checked the facts with several people who really know the balsa business and it is apparently true. A few years back most of the balsa was going to the ship building industry to line the holds and hulls in super tankers. Perhaps someone who knows more about that construction will jump in here and elaborate. Today most of the wood that’s imported is going into (and this is so ironic…) making propellers! No, not 12 x 6 inch props and the like, but rather 30 and 40 and 50 and 60 foot diameter wind farm props. The word I get is the manufacturers of those devices are purchasing huge amounts of mill run balsa from which to make the blades for those props. They apparently don’t care too much about the densities of the wood and so are just buying it up wholesale. And with it, virtually all of the “good” stuff as well.

Add to that fact that there just isn’t as much soft, light, straight grain wood coming out of the forests anymore, and you can understand that we are lucky to get what we do get! The above will no doubt cause much debate here, but all the debate in the world will not change the central fact (The 4 to 6 pound Gorilla in the room if you will…) that “our father’s balsa” is not the kind of stuff we are able to get in quantity these days. Nuff medicine?

Now the Honey:

Take great heart, because there is an answer to this problem for us. However, that answer will involve all of us accepting some new paradigms. As most of you know I’m back pretty much full time in the model airplane component business. As that fact became more known, my business doubled. I’m a happy guy… What has been difficult is getting enough wood in the sizes and densities requested to fulfill my covered foam wing orders. This is not the first time this has happened to me. Back in the late 1960s and all through the 1970s I had a very successful concern that specialized in custom foam wing manufacturing (Control Line Specialties/Control Specialties). At that time I was able to purchase reasonably good quality wood, but even then getting a sufficient amount of 1/16 inch thick, 4 to 6 pound stock was a bear.

The answer was simple: Use thinner wood in heavier densities. I started producing wings covered with .045 (3/64 inch thick) balsa, and even many covered with .032 (1/32 inch thick) balsa. Look at the logic: A piece of 1/32,  10 pound density balsa, in a given length and width, weighs EXACTLY the same as a piece of 5 pound density 1/16 inch thick balsa of the same length and width dimensions. Please read that sentence again…

I’d say that 90 to 95 percent of the wings I produced in the aforementioned era were covered with the .045 material, and that included many, many wings used by the very top competitors in Stunt in the country. The overall result was the ability to keep pace with the incredible number of wing orders and provide strong, light components.

Once my clientele had bought into this concept, they found many other advantages to the shift in the wood paradigm. The heavier density wood had much better grain integrity. A good deal of soft wood contains “wind checks.”  Wind checks are chord wise cracks in the balsa sheet caused by the parent tree having swayed in the wind while growing. These cracks typically form across the trunk of a light density wood tree in several areas. This wood is not ideal for model building; especially where we need the strength of uninterrupted grain structure – such as in foam wing skinning. 

The heavier density wood has a couple of other advantages: Being denser it will not soak up as much glue during the covering process, nor finishing materials during the finishing process! Soft wood acts just like a sponge! You can also apply a better quality finish over a harder surface than you can over a softer one.

Okay, the facts are that by using the denser balsa in thinner sections we can achieve as light or even lighter wings of a given size that will also accept a lighter, better finish. But the biggest factor is that this type of balsa should be easily available to us through any one of the balsa suppliers on an ongoing basis.

My advice is that when you are ordering custom thickness balsa wood, don’t order just a few sheets of it. Balsa suppliers will gladly adjust their cutting and sanding equipment to supply you with the thicknesses you desire, but meet them half way by ordering enough to make it worth their while to make those adjustments.

The above was accepted technology in the foam wing business back in the 1970s, and I don’t know what happened to change the paradigm back to the use of lighter density, thicker sizes in the interim. The good news is that we can once again use this avenue to have our cake, eat it too, and then all go out for a big desert afterwards.

My wood supplier has informed me that he can supply virtually all the wood I need in thinner, higher density form. That’s the direction I’m heading. I will continue to order and offer 4 to 6 pound 1/16 and/or 3/32 as requested, but the prices will be staggering as this type of wood is at a super premium these days. My prices will, in turn, reflect what I have to pay to get it. Which brings me to the last point I want to make in this post: Major manufacturers do not cater to us in large part because we are unrealistic in our perception of what hobby items should cost. Times have changed, and we must face the facts that the prices we paid for quality merchandise 20 years ago are not the prices we should expect to pay today. This is especially true of the balsa we use. If you think about it, balsa is about the least expensive major component in any Stunt model. If we had to pay double or even triple to get good balsa materials for our projects, it is still a bargain. So a shift in paradigm in our expectations of what we will have to spend to receive satisfaction is also in order. We cannot expect the manufacturers to keep the prices to us low while at the same time they are paying more. That is just an understanding of simple economics.

Yours for a viable modeling future – Bob Hunt     

Offline john e. holliday

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Re: Balsa: Changing the paradigm
« Reply #1 on: September 29, 2020, 07:45:51 PM »
Thanks for the info.   I my self have not looked for what people called contest balsa.  Even when I started building and constructing stunt planes I never worried about density or weight.  The current plane I am working on has so called contest balsa for the ribs.   So far I have glued almost every rib back together as they keep breaking with my clumsy handling.   Even scratch building I go to thicker wood for ribs.  I have had discussions with one person about the so called contest sheet wood.  Especially the 1/16 sheet.  Lost count how many times a thumb or finger would go through the sheet shile trying to finish a wing,   Any way keep up the good work. H^^
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Offline FLOYD CARTER

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Re: Balsa: Changing the paradigm
« Reply #2 on: September 29, 2020, 08:09:31 PM »
Bob is correct.  If you would like your stunter to last more than one season, forget 4 to 6 lb. balsa. Thinner and stronger wood, better-designed structure, and strong, durable surface finishes will result in acceptable flying weight and long flying life.
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Online Bob Hunt

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Re: Balsa: Changing the paradigm
« Reply #3 on: September 30, 2020, 05:13:08 AM »
Floyd hit it on the head; using thinner/denser balsa in most places in our models will produce models that are stronger and lighter. For several years now I have been using fairly dense 1/16 balsa for the fuselage sides on my models, and also either 1/16 or 3/32 balsa for the formers. I built two crutches for my new design twin motor Turning Point; one was made using fairly light 3/32 balsa and one was made using medium density 1/16 balsa. They were identical in design and size and were built in the exact same fuselage fixture (using the Tru-Fit Fuselage Construction method, for which I have a free manual available, simply send me an email asking for it. My email address is robinhunt@rcn.com), and the one built using 3/32 weighs 2.36 ounces and the one built with the 1/16 sides weighs 1.70 ounces. That's more than significant weight reduction for one component. They are each more than strong enough for the job they have to do.

What we really need to achieve - and I've been preaching this for many years - is a light weight consciousness about our models. Removing even a gram or two from every component will add up to a lighter model. Our models are said to sustain up to 15 times the weight of gravity when doing a tight corner. For the sake of this discussion let's round that up to 16 Gs. So, using that number every ounce in our models becomes a pound under cornering load. If that doesn't make you want to count every gram while building...

Study every component in your next model as you are building it and ask yourself these questions: "Is this component as light as I can make it?" "Is it strong enough to do the job without breaking?" "Is it too strong for the job it has to do?" Chances are if the component is deemed too strong for the job it has to do then it is also too heavy.

My dear departed friend, Buddy Wieder built five models in my shop when he returned to modeling after a nearly 50 year sabbatical from the hobby/sport. He needed to relearn all the building skills he had forgotten over the years. My job was to oversee every part of the construction process, give guidance, and bring him up to date on new materials and building practices. During the construction of his version of my Caprice, Buddy had made the small fairing pieces that blend the inboard end of the flaps to the fuselage. He showed them to me before installation and I told him to hollow them out from the side that would be attached to the fuselage. He looked at me with a look that I wish I could convey in words here. He said, "You're kidding." I said, "Nope, take some material out." (Or words to that effect.) In reality all that was removed was a couple of grains of weight. What I was trying to convey to Buddy was that aforementioned "Light weight consciousness." And, he totally got it. From that point forward Buddy searched diligently for ways to safely remove even the tiniest bit of weight from each component that went into his models. He produced some gorgeous and light models from that point on.

There is no need to panic about the lack of light density balsa; all we need to do is change the paradigms of how we use the materials available to us. This might even be a blessing in disguise...

Later - Bob Hunt

         
« Last Edit: September 30, 2020, 05:44:15 AM by Bob Hunt »

Offline Dick Byron

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Re: Balsa: Changing the paradigm
« Reply #4 on: September 30, 2020, 08:54:50 AM »
I can't sit here and see  what is being said without mentioning something very special in my heart. A few weeks ago an old friend from Kansas City , Mr. Dave Tribble came to our labor day contest and I sold him all my 35 year old Sig contest balsa supply. It wasn't huge, but for a few bucks he got some very good wood, plus all my Sig dope.
I also gave him my flight box, electric starter and line holder box. They are to be given away at next years Nast as per Dave's wishes. Wait till you see them. 

Thanks Dave for your friendship.

Dick Byron

Offline Randy Powell

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Re: Balsa: Changing the paradigm
« Reply #5 on: September 30, 2020, 09:03:05 AM »
I started using heavier density wood awhile back. I just adjust by, as Bob said, using thinner stuff or in the case of built up wings, cutting parts thinner. My last wing looked like a spiderweb before covering.
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Offline GERALD WIMMER

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Re: Balsa: Changing the paradigm
« Reply #6 on: October 05, 2020, 02:26:14 AM »
Hello We recently brought six plywood combat kits from F2D services in Russia that were nicely laser cut to minimize the weight. No balsa present but reasonable weight compared to other F2D models I have. The careful laser cutting of the 3mm ply and accurate assembly made them easy to assemble and they fly very well too. My son Otto assembled one in an hour . They had provision for both a bladder compartment and hard tank.
Makes you wonder what could be made with ply and a careful design thought.
Regards Gerald

Offline Tom Luciano

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Re: Balsa: Changing the paradigm
« Reply #7 on: October 05, 2020, 03:45:43 AM »
Gerald
 Cool planes! I would like to further inquiry about these. do you have a website adddress?

Tom
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Offline GERALD WIMMER

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Re: Balsa: Changing the paradigm
« Reply #8 on: October 05, 2020, 04:22:34 AM »
Hi Tom

The site was F2D service run by Andrey Shkatov :
https://f2abcd-store.ru/products/40772013
The prices are very reasonable and being able to ship as a flat pack shipping was good too but it did take a while to get to New Zealand due to all the lockdowns .

May try to set two up with an electric set up like Bob Mears details on the MACA forum, like they use for the Air to Air Combat

Regards Gerald

Online Dennis Toth

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Re: Balsa: Changing the paradigm
« Reply #9 on: October 05, 2020, 06:27:16 AM »
One other area that we could explore is a balsa/rigid foam composite using 1/32 balsa and open cell foam sandwich. This could be used for fuse sides and even ribs. I have used this on gliders and the foam is light can be formed with a heat gun. The type I've used is Cellfoam 88 from Midwest also known as Depron online. It comes in 3mm (~3/32") and 5mm (3/16"). There may be other foams that are lighter maybe Bob H knows which ones would work even better and where to get it. I used the Midwest product because it was available at my LHS.

Best,   DennisT

Offline Mark Legg

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Re: Balsa: Changing the paradigm
« Reply #10 on: October 09, 2020, 02:32:41 AM »
Great topic!

Here in the UK, finding good, lightweight block balsa has always been a pain. So now for my builds that call for hollowed out block (so wasteful anyway) I'm using blue builders foam.

Its half the weight of balsa, cheap (well free to me, I work on a lot of construction sites) doesn't need hollowing, and when skinned with some light 1/32 balsa, very rigid!

Not sure about the legality of it in UK classic stunt rules... but it's an option in the current climate.

Cheers

Mark

Offline fred cesquim

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Re: Balsa: Changing the paradigm
« Reply #11 on: October 09, 2020, 04:45:04 AM »
Note: I posted a version of the following a few years ago, but I feel it needs repeating here again. A few sentences have changed from the original post, but the gist of it all is still the same, and I feel critical.

Hi all:
This post will be my attempt to help all of us understand the realities of the current balsa situation and how we can help ourselves immensely from now on into the future to deal with these realities. I’m posting this piece because I believe the need for the following information is critical to model airplane building in the 21st century.

First the medicine:

The days of 4 to 6 pound, clear, straight grain, 3 to 6 inch wide in-one-piece, readily obtainable, inexpensive balsa wood are essentially over and gone. Please read that sentence again. It is essential that all of us face the realities of the situation. Sure, we will occasionally be able to find isolated stashes of Ecuadorian Gold, and we should snap up those opportunities when and where they present themselves. Those of us who have been at this for awhile can remember the amazingly clear and consistent contest grade balsa that we used to be able to get on a regular basis from several suppliers. That type of wood in the quantities in which we used to receive it simply isn’t available anymore.

Where has all the balsa gone? (Sounds like an old Peter, Paul and Mary song…) The real question is, “Where is all the balsa going?” What I’m going relate now may seem incredulous, but I have checked the facts with several people who really know the balsa business and it is apparently true. A few years back most of the balsa was going to the ship building industry to line the holds and hulls in super tankers. Perhaps someone who knows more about that construction will jump in here and elaborate. Today most of the wood that’s imported is going into (and this is so ironic…) making propellers! No, not 12 x 6 inch props and the like, but rather 30 and 40 and 50 and 60 foot diameter wind farm props. The word I get is the manufacturers of those devices are purchasing huge amounts of mill run balsa from which to make the blades for those props. They apparently don’t care too much about the densities of the wood and so are just buying it up wholesale. And with it, virtually all of the “good” stuff as well.

Add to that fact that there just isn’t as much soft, light, straight grain wood coming out of the forests anymore, and you can understand that we are lucky to get what we do get! The above will no doubt cause much debate here, but all the debate in the world will not change the central fact (The 4 to 6 pound Gorilla in the room if you will…) that “our father’s balsa” is not the kind of stuff we are able to get in quantity these days. Nuff medicine?

Now the Honey:

Take great heart, because there is an answer to this problem for us. However, that answer will involve all of us accepting some new paradigms. As most of you know I’m back pretty much full time in the model airplane component business. As that fact became more known, my business doubled. I’m a happy guy… What has been difficult is getting enough wood in the sizes and densities requested to fulfill my covered foam wing orders. This is not the first time this has happened to me. Back in the late 1960s and all through the 1970s I had a very successful concern that specialized in custom foam wing manufacturing (Control Line Specialties/Control Specialties). At that time I was able to purchase reasonably good quality wood, but even then getting a sufficient amount of 1/16 inch thick, 4 to 6 pound stock was a bear.

The answer was simple: Use thinner wood in heavier densities. I started producing wings covered with .045 (3/64 inch thick) balsa, and even many covered with .032 (1/32 inch thick) balsa. Look at the logic: A piece of 1/32,  10 pound density balsa, in a given length and width, weighs EXACTLY the same as a piece of 5 pound density 1/16 inch thick balsa of the same length and width dimensions. Please read that sentence again…

I’d say that 90 to 95 percent of the wings I produced in the aforementioned era were covered with the .045 material, and that included many, many wings used by the very top competitors in Stunt in the country. The overall result was the ability to keep pace with the incredible number of wing orders and provide strong, light components.

Once my clientele had bought into this concept, they found many other advantages to the shift in the wood paradigm. The heavier density wood had much better grain integrity. A good deal of soft wood contains “wind checks.”  Wind checks are chord wise cracks in the balsa sheet caused by the parent tree having swayed in the wind while growing. These cracks typically form across the trunk of a light density wood tree in several areas. This wood is not ideal for model building; especially where we need the strength of uninterrupted grain structure – such as in foam wing skinning. 

The heavier density wood has a couple of other advantages: Being denser it will not soak up as much glue during the covering process, nor finishing materials during the finishing process! Soft wood acts just like a sponge! You can also apply a better quality finish over a harder surface than you can over a softer one.

Okay, the facts are that by using the denser balsa in thinner sections we can achieve as light or even lighter wings of a given size that will also accept a lighter, better finish. But the biggest factor is that this type of balsa should be easily available to us through any one of the balsa suppliers on an ongoing basis.

My advice is that when you are ordering custom thickness balsa wood, don’t order just a few sheets of it. Balsa suppliers will gladly adjust their cutting and sanding equipment to supply you with the thicknesses you desire, but meet them half way by ordering enough to make it worth their while to make those adjustments.

The above was accepted technology in the foam wing business back in the 1970s, and I don’t know what happened to change the paradigm back to the use of lighter density, thicker sizes in the interim. The good news is that we can once again use this avenue to have our cake, eat it too, and then all go out for a big desert afterwards.

My wood supplier has informed me that he can supply virtually all the wood I need in thinner, higher density form. That’s the direction I’m heading. I will continue to order and offer 4 to 6 pound 1/16 and/or 3/32 as requested, but the prices will be staggering as this type of wood is at a super premium these days. My prices will, in turn, reflect what I have to pay to get it. Which brings me to the last point I want to make in this post: Major manufacturers do not cater to us in large part because we are unrealistic in our perception of what hobby items should cost. Times have changed, and we must face the facts that the prices we paid for quality merchandise 20 years ago are not the prices we should expect to pay today. This is especially true of the balsa we use. If you think about it, balsa is about the least expensive major component in any Stunt model. If we had to pay double or even triple to get good balsa materials for our projects, it is still a bargain. So a shift in paradigm in our expectations of what we will have to spend to receive satisfaction is also in order. We cannot expect the manufacturers to keep the prices to us low while at the same time they are paying more. That is just an understanding of simple economics.

Yours for a viable modeling future – Bob Hunt   

Bob Hunt since the beginning of the times ahead on the game! 100% down to earth and perfect analysis of actual situation and a solution that´s just right. I always talk about how hard balsa is easy to finish and needs less material to fill than contest wood, but, unfortunately, i ain´t Bob Hunt. Please keep enlightening us ! thank you

Offline phil c

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Re: Balsa: Changing the paradigm
« Reply #12 on: October 12, 2020, 10:31:45 AM »
Hi Tom

The site was F2D service run by Andrey Shkatov :
https://f2abcd-store.ru/products/40772013
The prices are very reasonable and being able to ship as a flat pack shipping was good too but it did take a while to get to New Zealand due to all the lockdowns .

May try to set two up with an electric set up like Bob Mears details on the MACA forum, like they use for the Air to Air Combat

Regards Gerald

Sounds pretty good.  Light ply is fairly strong, but brittle, compared to balsa.  Have you compared the crash resistance of these planes.  Most of the ready-built planes with paper-covered foam leading edges, carbon fiber trailing edge, and 3mm balsa ribs can crash straight in over reasonable turg at F2D maneuvering speeds with minimal damage.  Used for 75-80 mph conbat they are even less likely to break without a direct hit.
phil Cartier

Online Bob Hunt

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Re: Balsa: Changing the paradigm
« Reply #13 on: October 12, 2020, 11:39:13 AM »
Bob Hunt since the beginning of the times ahead on the game! 100% down to earth and perfect analysis of actual situation and a solution that´s just right. I always talk about how hard balsa is easy to finish and needs less material to fill than contest wood, but, unfortunately, i ain´t Bob Hunt. Please keep enlightening us ! thank you

Woo boy! Thanks Fred for the kudos, but I'm quite certain that many of my so called buddies will get a good laugh at that "100% down to earth" comment; especially Ted Fancher...

But I do appreciate the thought!

Later - Bob

Offline GERALD WIMMER

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Re: Balsa: Changing the paradigm
« Reply #14 on: October 12, 2020, 02:29:02 PM »
Sounds pretty good.  Light ply is fairly strong, but brittle, compared to balsa.  Have you compared the crash resistance of these planes.  Most of the ready-built planes with paper-covered foam leading edges, carbon fiber trailing edge, and 3mm balsa ribs can crash straight in over reasonable turg at F2D maneuvering speeds with minimal damage.  Used for 75-80 mph conbat they are even less likely to break without a direct hit.

Hello Phil. My 11 year old son Max has tested the crash resistance with the ply models and they seem to flex well on impact. Probably up to me and my older son Otto to see what a mid air does to them but not yet, lots of old models to wreck first. Some of our old clunkers, which are based on the Rasputin design with pine reinforcements but still come apart with a good mid air and our newer foam LE models get prop eaten too.

With the price of balsa and freight, it leads me back to the desire to cut out cheap easily replaced foamies for general hack combat in our back yard flying circle or at club level where the amount of practice needed consumes lots of models quick. Here in New Zealand getting foam and ply is easy but balsa, spruce and carbon gets expensive or difficult and freight is the killer unless you can bulk buy materials at the DIY building stores .

Regards Gerald

Offline TigreST

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Re: Balsa: Changing the paradigm
« Reply #15 on: October 16, 2020, 04:56:48 AM »
Just a link to share on where to find all that balsawood that's gone missing to industry:

https://www.bloomberg.com/news/features/2020-02-05/wind-turbine-blades-can-t-be-recycled-so-they-re-piling-up-in-landfills


Tony Bagley
Ontario, Canada

Offline Gary Dowler

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Re: Balsa: Changing the paradigm
« Reply #16 on: October 16, 2020, 10:40:17 AM »
Was very happy to run across some balsa at my local hobby shop that came from an estate. 4” wide, 48” long 1/8” sheets.  Bought 5. Wasn’t real cheap, $6 each, but it’s straight, flat, 8lb wood.  I might grab a few more next week if it’s still there.

Also got a piece of 3” x 36” x 3/8 that was 5lb wood. A few more of those too.

Gary
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Offline Peter Nevai

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Re: Balsa: Changing the paradigm
« Reply #17 on: October 16, 2020, 06:36:31 PM »
The Hard dense stuff is fine except for Cowlings and wingtips where much carving needs to happen. Then it is a royal pain in the A#%
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Online Bob Hunt

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Re: Balsa: Changing the paradigm
« Reply #18 on: October 16, 2020, 07:01:53 PM »
Rock hard balsa challenge: Make a light weight stunt ship using all 1/32" "Very Hard" Sig balsa.


Motorman 8)

Well, no one suggested using "rock hard" balsa. The suggestion I made was concerning somewhat denser, and thinner materials. Yeah, I'd take the challenge on that assumption. How much are you willing to risk on this, uh, challenge? Please understand that I've already done this many times and have come up with some amazingly light, strong models. Like, try a 36 ounce 575 square inch Genesis 35 with engine and tank in place and only lacking fuel. Yeah, that was some time ago; 1974 to be exact. Ask Ted Fancher about the day he picked that plane up at the 1974 Nats. He told his friend, Bill Fitzgerald, "It weighs nothing!" That model was sheeted with about 8-pound 1/32. It was a foam wing model. The attached photo shows that model in 1974 with Lake Charles in the background. Note: The model in question is the smaller one of the two in the photo. The larger one was also covered with fairly dense, thin balsa. It had a 720 square inch wing and weighed 54 ounces with an ST.46 and tank on board, less fuel. It received, if memory serves, 18 appearance points that year, and the top model received 19 points and weighed a lot more than did my Genesis 46Mk I.   

Yes, softer materials will be needed for such things as cowlings and wing tips, but virtually all the sheet stock - wing sheeting, fuse sides, formers, molded shells for fuselage top and bottom - can be denser, thinner stock than normal and be much lighter in the end result due to less finish soakage. This is not an untried idea, Walt; I've been using this philosophy for many years. My friends and competitors will tell you that my planes are always among the lightest.

Later - Bob Hunt   
« Last Edit: October 16, 2020, 07:21:47 PM by Bob Hunt »

Offline Peter Nevai

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Re: Balsa: Changing the paradigm
« Reply #19 on: October 16, 2020, 10:25:57 PM »
Well, no one suggested using "rock hard" balsa. The suggestion I made was concerning somewhat denser, and thinner materials. Yeah, I'd take the challenge on that assumption. How much are you willing to risk on this, uh, challenge? Please understand that I've already done this many times and have come up with some amazingly light, strong models. Like, try a 36 ounce 575 square inch Genesis 35 with engine and tank in place and only lacking fuel. Yeah, that was some time ago; 1974 to be exact. Ask Ted Fancher about the day he picked that plane up at the 1974 Nats. He told his friend, Bill Fitzgerald, "It weighs nothing!" That model was sheeted with about 8-pound 1/32. It was a foam wing model. The attached photo shows that model in 1974 with Lake Charles in the background. Note: The model in question is the smaller one of the two in the photo. The larger one was also covered with fairly dense, thin balsa. It had a 720 square inch wing and weighed 54 ounces with an ST.46 and tank on board, less fuel. It received, if memory serves, 18 appearance points that year, and the top model received 19 points and weighed a lot more than did my Genesis 46Mk I.   

Yes, softer materials will be needed for such things as cowlings and wing tips, but virtually all the sheet stock - wing sheeting, fuse sides, formers, molded shells for fuselage top and bottom - can be denser, thinner stock than normal and be much lighter in the end result due to less finish soakage. This is not an untried idea, Walt; I've been using this philosophy for many years. My friends and competitors will tell you that my planes are always among the lightest.



Later - Bob Hunt

Absolutely!

BTW I like the original the best back from the 1970's  ;D #^ #^ Kills me that I had 8mm footage of that model flying at Flushing meadows. Oh how I wish I knew what ever happened to that reel. Bob was flying his F86 on the same reel.
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Offline john e. holliday

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Re: Balsa: Changing the paradigm
« Reply #20 on: October 17, 2020, 12:04:36 PM »
Bobby, is that really you with all that hair?   I think that is the year I first met you as you were carrying your airplane through the hanger as my team mate(Bob Hill) and I were making a set of lines for F2C competition.   I really need to construct/build one of your planes,  but I probably would not do it justice.  You are still one of my heroes. H^^
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Online Bob Hunt

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Re: Balsa: Changing the paradigm
« Reply #21 on: October 19, 2020, 06:13:36 AM »
Well, Walt, if you don't like or want people responding to your posts, perhaps that is the best thing.

Bob Hunt
« Last Edit: October 19, 2020, 08:06:26 AM by Bob Hunt »

Offline Dane Martin

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Re: Balsa: Changing the paradigm
« Reply #22 on: October 26, 2020, 05:32:19 PM »
Bob, thanks for the write up and insight. Lee Letchworth designed the "Tigger" for slow combat to match the WAM rules. It's designed around that 75-80 mph speed limit, and I figured with the thick wing and neat design, it'll be a fun Sunday flyer that can do a brisk pattern. I omitted some stuff and added some stuff in the way of construction, but didn't change any shapes or numbers.
Any way.... I went to Hobby lobby and picked out whatever balsa they had and got the "best" out of there. I'll add these pics as big as possible to see, but small enough to fit. If you can see, it's what we could consider pretty bad, hard and heavy wood. My covered wing is 192 grams ( I believe 6.8oz). I'm not 100% done building, but wanted to weigh in on the weight discussion... ha!
For a 42 inch wing, built, covered and excess push rod;  I thought it was coming out reasonably light. So in my opinion, if this is as good as we can get, i think i can still build nice strong models without huge weight penalties.

Offline Dane Martin

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Re: Balsa: Changing the paradigm
« Reply #23 on: October 26, 2020, 05:32:38 PM »
Wing pic. Zoom in. The first 4 ribs are made from some nice sig wood I had left over and didn't want to cut up a full sheet for 4 ribs. See the contrast between sig and the rest!

Offline Dane Martin

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Re: Balsa: Changing the paradigm
« Reply #24 on: October 26, 2020, 05:33:09 PM »
Adding color

Online Bob Hunt

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Re: Balsa: Changing the paradigm
« Reply #25 on: October 26, 2020, 06:57:17 PM »
That wing looks beautiful, Dane!
Bob

Offline Shorts,David

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Re: Balsa: Changing the paradigm
« Reply #26 on: October 26, 2020, 07:20:06 PM »
This is a new idea for me, Bob. I assumed that contest balsa was equal strength, just lighter weight...magic I suppose. So, the take-a-way is that I should be using thinner balsa than what the plans say as long as I'm using the cheap heavy stuff. Which kind of negates using the wood supplied in the kit I suppose.

Offline Dane Martin

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Re: Balsa: Changing the paradigm
« Reply #27 on: October 26, 2020, 09:35:14 PM »
That wing looks beautiful, Dane!
Bob

Thank you sir. Now, I'm not suggesting this Doll House wood can replace everything. But! When used in moderation and using known construction methods from our control line and free flight forefathers.... I personally think the future is not so bleak. I know the real builders here, and those who are not very internet savvy could certainly come up with even better results than my efforts. Once complete, I'll post videos of a few  4 min pattern flights. Lol

Offline Brent Williams

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Re: Balsa: Changing the paradigm
« Reply #28 on: October 26, 2020, 11:13:11 PM »
Bill Smith and Mick Castell from the UK have a really interesting tutorial on using blue foam for the bulk of the wing construction and using balsa only for the sheeting.  Quite a different construction approach than most sheeted foam wings. 
Clever self jigging system with foam ribs and a carbon tow reinforced spar.  I have posted a few pictures from the article.

Aside from the variability in weights of balsa for the sheeting, the foam raw materials for the structure are always going to be a consistent weight.

Here is a link to the PDF.
https://web.archive.org/web/20160705084830/http://www.clapa.org:80/BLUE%20FOAM%20CONSTRUCTION%20FOR%20CONTROL%20LINE.pdf
« Last Edit: October 28, 2020, 03:14:27 PM by Brent Williams »
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Offline Brent Williams

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Re: Balsa: Changing the paradigm
« Reply #29 on: October 26, 2020, 11:20:44 PM »
More.
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Offline mccoy40

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Re: Balsa: Changing the paradigm
« Reply #30 on: October 28, 2020, 03:43:45 AM »
What if we just vacuum bagged fiberglass onto the wing core? Similar to what the glider guys do for there wings. That would eliminate balsa altogether on the wing, does that sound like a good idea?


Oh - who is doing foam wing cores nowadays?


 H^^    /DV   S?P
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Offline Dwayne Donnelly

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Re: Balsa: Changing the paradigm
« Reply #31 on: October 28, 2020, 07:25:41 AM »
What if we just vacuum bagged fiberglass onto the wing core? Similar to what the glider guys do for there wings. That would eliminate balsa altogether on the wing, does that sound like a good idea?


Oh - who is doing foam wing cores nowadays?


 H^^    /DV   S?P

Or  carbon fiber, I'm sure Bob Hunt and others  have explored this idea, I knew a rc flyer that once used news paper to cover a foam wing...lol
« Last Edit: October 28, 2020, 05:51:59 PM by Dwayne Donnelly »
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Offline katana

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Re: Balsa: Changing the paradigm
« Reply #32 on: October 29, 2020, 06:09:22 AM »
I knew a rc flyer that once used news paper to cover a foam wing...lol

Why do you find that amusing - back in the 70's when foam combat wings were the 'in thing', we used brown parcel paper, christmas wrapping paper, wall paper - anything cheap and usually quite resilient !

Offline Dwayne Donnelly

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Re: Balsa: Changing the paradigm
« Reply #33 on: October 29, 2020, 06:54:13 AM »
Why do you find that amusing - back in the 70's when foam combat wings were the 'in thing', we used brown parcel paper, christmas wrapping paper, wall paper - anything cheap and usually quite resilient !

I thought it was genius...lol It was a RC plane with retracts, he didn't have any balsa on hand so he tore  a bunch of newspaper into small pieces  and applied them with resin, can't remember how many layers he used but it came out a bit heavy, the finish was very nice and it flew ok  but yeah a bit heavy...lol

« Last Edit: October 29, 2020, 08:57:16 AM by Dwayne Donnelly »
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Offline Brent Williams

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Re: Balsa: Changing the paradigm
« Reply #34 on: October 29, 2020, 10:53:34 AM »
In the spirit of changing paradigms and lowering balsa dependency, there are legit methods to consider.  Covering raw foam with clear film or thinned white glue/titebond and silkspan, newsprint, various craft papers, light fiberglass and and of late, carbon veil isn't a new practice.  It is good for strength and rigidity.  It's good for rapid building and for test-bed purposes.
 -This construction method proved to be good enough for a big, competitive, modern, 650 sq" twin design built by some random world champ.    (see Bob Hunt's testbed twin)

Paper (film,silkspan, fiberglass, veil, ect.) covered bare foam is not that good for traditional beauty however.  If you're looking to make a legitimate 15-20 point, Nats quality finish, look elsewhere.  It is susceptible to hanger rash and dents, but...it is a low effort method and shouldn't be perceived as an alternative to balsa/dope/auto clear finishes.

This method is very worthy of consideration and is effective if your goal is to make a bunch of good sport flying or pattern training planes with low emotional attachment. 
More flying, less building.  Good trade-off for most people (in my opinion, of course).

Lengthy tome on covering foam with newsprint: https://www.rcgroups.com/forums/showthread.php?1552848-Newspaper-glue-covering-improvement

« Last Edit: October 29, 2020, 06:44:50 PM by Brent Williams »
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Offline Mike Alimov

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Re: Balsa: Changing the paradigm
« Reply #35 on: October 29, 2020, 12:58:10 PM »
What if we just vacuum bagged fiberglass onto the wing core? Similar to what the glider guys do for there wings. That would eliminate balsa altogether on the wing, does that sound like a good idea?

 H^^    /DV   S?P

That sounds like a really, really good idea.  In fact, the 2020 Open Nats winner and the 2020 Advanced NATS winner were using all-composite airplanes, while the 2020 Jr. NATS winner was using some composite parts.  So, this is not a new idea.  The use of composites in CL stunt goes back to at least 1980's, but was not really widely adopted until 10-20 years later at the Worlds level, while not seeing virtually any adoption in the US to this day.
Look up the thread called "Revolutions" on the Building part of this forum, started by TDM (Traian Dorin Morosanu).  It shows the steps involved and the resulting product. 

Offline BillP

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Re: Balsa: Changing the paradigm
« Reply #36 on: October 30, 2020, 07:32:14 AM »
Why do you find that amusing - back in the 70's when foam combat wings were the 'in thing', we used brown parcel paper, christmas wrapping paper, wall paper - anything cheap and usually quite resilient !

Ditto. A lot of these methods were being used decades ago by sport flyers. In the late 80s I flew foam RC combat wings with variations of no covering, plastic covering, paint, paper, tape only, thinned Elmer's glue painted on, etc.
I've always reduced (drastically) scantling size to reduce weight...even to the point of replacing ply doublers with balsa on full fuse planes.  There are a lot of ways to get around using contest balsa but it appears the times are forcing people to start paying attention to it.
Bill P.

Offline John Park

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Re: Balsa: Changing the paradigm
« Reply #37 on: October 30, 2020, 08:20:19 AM »
About 25 years ago, I built a 'proof of concept' model to try a hollow foam wing built in two separate panels, each with two embedded spars (positioned at about 15% and 70% chord).  The spars had boxes at their root ends, locating on vertical ply tongues integral with two fuselage formers, one at each end of a substantial bellcrank platform.  The white 'bead board' foam was covered with nothing but the kind of gift-wrap paper sold for wrapping Silver Wedding presents, applied dry with an adhesive sold for use with hessian wall-coverings.  No finish was applied to the paper except clear polyurethane fuel-proofer.
The rest of the 'Stunt Stick' was conventional balsa-and-ply construction, except the tailplane and fin, which were 1/32" balsa over a foam core.  The model was 40" span, 360 sq. in. wing area for an OS-Max .15-III, and was a little heavier than I'd hoped - 25 oz.  It flew well, and the sharpest square and triangular corners I could fly did not (as I'd feared they might) pull the wings off.  The wing panels were simply epoxied to the fuselage sides and the tongues, but I envisaged a detachable arrangement if I ever got round to building a larger model to a similar layout.  As a proof of concept, I considered it successful, and only the loss of my local field at that time prevented me from developing it further.
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Offline Scott Richlen

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Re: Balsa: Changing the paradigm
« Reply #38 on: October 30, 2020, 11:41:23 AM »
Be careful with how you use foam ribs.  I recall an Edison NJ meet where a guys outer wing panel came off in the middle of the pattern.  In order to be "lighter" he used foam ribs.  Under aerodynamic load they compressed.  Once they compressed the wing started "flapping".  And one too many flaps later....

Offline John Carrodus

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Re: Balsa: Changing the paradigm
« Reply #39 on: October 30, 2020, 12:01:29 PM »
I have been using large black foam (unused) supermarket meat trays in most of my models for about five years. In the beginning I ran a few tests and found this pressed foam in some applications stronger than balsa, more stable, light and shock absorbing and split resistant. Certainly cheaper hands down! For better glue adhesion , slight roughing up of the contact area is helpful, although not always needed as the internal foam is exposed when cut to shape with a blade. Attached is an example of one of my foam ribbed models, ME262 I designed and built.

On another note , I can say Gerald Wimme's laser cut plywood combat wings are amazing and go really well. 

Offline Mike Morrow

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Re: Balsa: Changing the paradigm
« Reply #40 on: October 30, 2020, 02:17:55 PM »
John,
In the ME 262, which parts are foam?

Mike

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Offline Steve Dwyer

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Re: Balsa: Changing the paradigm
« Reply #41 on: October 30, 2020, 03:08:19 PM »
I think it was about a year ago or more when Eric Rule was experimenting with different building materials in lieu of balsa. Did he come back with any recommendations? I may have missed his input.

Steve

Offline John Carrodus

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Re: Balsa: Changing the paradigm
« Reply #42 on: October 30, 2020, 05:48:28 PM »
Reply to MIKE MORROW.
Hiya Mike
The ribs only in this case.
I have however made sandwich tailplanes with i/16 or thinner each side of 3mm foam. Very light and incredibly rigid. Sections or holes can be cut out and covered with silkspan or film for weight reduction. Wingtips too. I have also used straight foam ( or sandwich )as bulkheads in built up models. Hot glue and foam formers can make light and resilient internal parts that are cheap and easy to make and look ugly as hell, but who cares when it's internal and outa sight.
You'd be surprised just how tough this stuff is!
Cheers



Online Ara Dedekian

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Re: Balsa: Changing the paradigm
« Reply #43 on: November 06, 2020, 04:33:41 AM »


       This showed up as a pop-up ad on YouTube. balsawoodinc.com

       Ara

Offline Scott Richlen

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Re: Balsa: Changing the paradigm
« Reply #44 on: November 06, 2020, 06:38:45 AM »
Quote
This showed up as a pop-up ad on YouTube. balsawoodinc.com

I see that for an additional 30% they will pick for hard, medium, soft; but does anyone know if they will pick for contest grade (I didn't see that listed) or weight?

Offline john e. holliday

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Re: Balsa: Changing the paradigm
« Reply #45 on: November 06, 2020, 02:24:49 PM »
May have to give them a try.  Thanks for the link. H^^
John E. "DOC" Holliday
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