Depron, a few naive questions.

[David Davis]

I was once described as a "traditional modeller." Inasmuch as all of the models I have built have been made from balsa and ply that is correct. This includes some Chris Foss designs with foam veneered wings. However, with the dramatic increase in the price of balsa some modellers have started using depron to replace balsa. Having never even seen depron, I am curious as to how I could use it should I ever want to hence the following questions:

 

1. Is depron the same as foamboard? If not how do they differ?
2. If I were to build a wing like a Keil Kraft Super 60's wing with a balsa leading and trailing edge and three spars, could I use depron for the wing ribs? For those unfamiliar with the Super 60 it is a three channel model with a 63" (1600mm) wingspan: https://www.benbucklevintage.com/index.php?main_page=product_info&cPath=1_4&products_id=11
3. If I were to use depron wing ribs on such a model which glue should I use to stick it to the balsa? I assume that the same glue could be used for the balsa sheet of the leading edge and centre section.
4. Could I use depron instead of balsa sheet for the leading edge and centre section sheeting?
5. What problems could I anticipate if I were to cover a wing built with depron wing ribs with Oracover or Oratex?
6. I plan to build a 1/4 scale Fokker triplane. Could I use depron for the wing ribs of of this model, if not why not?

 

If it makes any difference, I do not build or fly models with a wingspan of less than 54" (140cms) in the wingspan.

[GrumpyGnome]

1. No, foamboard tends to have a paper covering - Depron is more like the trays you get chips in...

2. Yes. Some ic/electric fun fly types kits (e.g. Fusion) do just that

3. Ali works - uhu por may 'eat' the foam...

4. Yes, but it'll be less resistant to 'dings'

5. Shrinkage may distort the structure, too much heat could damage the foam

6. Don't see why not - just make sure structural loads are catered fir, e.g. interplanes....

 

[Don Fry]

Two areas I use depron is in ribs and fusalage bulkheads. Especially as I’m trying to save weight, but not alter the appearance. 
Ribs are not structurally hard working, and I find depron a good substitute for the cross cut balsa we used to use for ribs. I’ve used it for 2 meter hooligan hacks, 3mm depron ribs, vertical performance and two rolls a second

Bulkheads, behind the wing, I tend to glue balsa spars to the depron, 2 uprights to the front, cross pieces to the back. (Saves joint cutting)

Note I do this to save weight, for no structural compromise, cheaper, easier to cut is a bonus.

For information, I get mine from a local Bricomarché, it’s in the plumbing section, sold in 3mm and 6mm sheets, 1000 by 1500 mm sheets. From memory about €5 a sheet

 

[Lima Hotel Foxtrot]

2 hours ago, David Davis said:

1. Is depron the same as foamboard? If not how do they differ?
2. If I were to build a wing like a Keil Kraft Super 60's wing with a balsa leading and trailing edge and three spars, could I use depron for the wing ribs? For those unfamiliar with the Super 60 it is a three channel model with a 63" (1600mm) wingspan: https://www.benbucklevintage.com/index.php?main_page=product_info&cPath=1_4&products_id=11
3. If I were to use depron wing ribs on such a model which glue should I use to stick it to the balsa? I assume that the same glue could be used for the balsa sheet of the leading edge and centre section.
4. Could I use depron instead of balsa sheet for the leading edge and centre section sheeting?
5. What problems could I anticipate if I were to cover a wing built with depron wing ribs with Oracover or Oratex?
6. I plan to build a 1/4 scale Fokker triplane. Could I use depron for the wing ribs of of this model, if not why not?

1. No. FB has a paper covering either side that can be as much as 2/3 of the total weight, but it is much stiffer and takes spray paint well. Most glues work on FB, including cyano, because it is a different foam.

2. Yes.

3. PVA, Aliphatic, Uhu Por, Foam 2 Foam, Epoxy, hot glue, silicon and probably foam safe cyano. Most cyano will melt depron.

4. Yes. May want to glass or use Foam Armour.

5. Heat melting or distortion? Although lots of advice on the web from people claimng they have successfully ironed onto foams of various types.

6. Probably.

[Ron Gray]

2 hours ago, Don Fry said:

From memory about €5 a sheet

So is that memory foam you get Don?

[Ron Gray]

2 hours ago, Lima Hotel Foxtrot said:

FB has a paper covering either side that can be as much as 2/3 of the total weight

Paper covering can be removed by applying heat from a covering iron 

[john davidson 1]

4 hours ago, GrumpyGnome said:

1. No, foamboard tends to have a paper covering - Depron is more like the trays you get chips in...

2. Yes. Some ic/electric fun fly types kits (e.g. Fusion) do just that

3. Ali works - uhu por may 'eat' the foam...

4. Yes, but it'll be less resistant to 'dings'

5. Shrinkage may distort the structure, too much heat could damage the foam

6. Don't see why not - just make sure structural loads are catered fir, e.g. interplanes....

 

Point 3---- por will NOT eat the foam odourless superglue also will not , normal wil

[Don Fry]

Superphatic from deluxe materials is good.

[Simon Chaddock]

David

Conventional balsa construction techniques are the result of decades of trial and error so most people have confidence in what they do.

The thing to remember is that basic XPS foam sheet is nothing like as strong or stiff as balsa but then it is only about 1/10 the weight.

To use it effectively you need to understand the sort of loads involved to make best use of its properties.

It is not a like for like substitute.

To take the Triplane rib example. The wing is a 'shrunk' material covered structure so the ribs are under compression forces particularly towards the trailing edge as well as any aerodynamic loads.

The full size Triplane ribs were ply with capping strips either side as well as a couple of vertical stiffeners.

The capping strips are a vital part of the structure.

It follows that foam alone would not be an ideal material but it could replace the ply and being so light could be much thicker, at least the width of the capping strips and it would not need lightening holes. The foam under the capping strips would be strong enough to resist the compressive effect of the shrunk skin and also any 'handling' loads. An important consideration in a model, 

So what you end up with is a 'composite' rib cut from a relatively thick (3 or 6 mm?) foam and slightly under size but with a balsa? capping strip glued on top and bottom.

I will leave you to contemplate the best alternative to emulate the wire trailing edge!

 

Of course if a wing is entirely sheet foam covered so there are no skin shrinking forces then a composite rib is less likely to be needed. Closely spaced simple foam ribs should be adequate.

I hope this helps.

 

On a historical note the War Ministry had a fully detailed set of sketches made from a captured Triplane. The wing section, the detail of the unbraced wing structure and the welded tube fuselage were all a bit of an eye opener but such construction techniques were largely ignored by UK manufacturers for at least a decade.    

 

Edited December 6, 2022 by Simon Chaddock

[Don Fry]

Arrrrrrrr, but Simon, this is a proposed quarter scale model. Now, is David is the only man on earth proposing to reproduce that substructure? Or he wants (thinking) to change balsa to depron. A rib is not a structurally stressed component. As you say, 1/10 of the weight, don’t cut holes in it. Capping strips in balsa, you don’t know it’s difference, when covered. Just analyze where the skin shrink stress loads go. The cap strips take them to the TE, SPAR, D BOX AND LE.

Modern materials, smaller structures.

[Simon Chaddock]

Don

"A rib is not a structurally stressed component" 

Surely the wing loading although not uniform is spread over much of the wing area. The ribs have to transfer that load to the spar. They are loaded as beams when in flight.

   

I specifically did not suggest a scale structure but simply a foam rib with cap strips so a scale rib section and spacing would be stiff enough to withstand any variations in skin shrinkage.

 

Edited December 6, 2022 by Simon Chaddock