Depron Wing For A Baron.

[David Davis]

The experience of modellers who have made models from depron is keenly sought!

 

As some of you know, I compete every year in La Coupe Des Barons, a daft competition for a three channel French trainer in which most of the entry gets trashed. I am quite well-known in the competition being the only Englishman and a four-stroke exponent as well. This year I built a new wing for one of my Barons using depron for the wing ribs for the first time instead of balsa. This involved capping each wing rib with balsa top and bottom in order to be able to cover the wing in film. I have two Barons in case I crash one just before the event! 😏

 

I have recently acquired a Laser 50 which I intend to use in next year's competition. This engine is heavier than it's Japanese or Chinese equivalents so I will have to build a Baron with a shorter nose. You are allowed to alter the dimensions +/- 10% of the original. While contemplating this change I thought, "Why not build a Baron with a wing made completely out of depron?"

 

If I were to do this how would I go about it? A standard Baron wing has a 61" span and a 10" chord, (155cms x 25cms) and a 3.5" (9cms) dihedral at the last rib. The raked back wing tip is not compulsory, several competitors have rounded or squared off wing tips. The wing area has to be +/- 10% of the original.

 

If I were to make a depron wing how would I fuel proof it or is depron only really suitable for electric powered models?

 

Pictures of my two Barons in their latest manifestations below for those who do not know what a Baron looks like.

[Graham Davies 3]

Hello David,

 

I've followed with great joy your exploits at the Coup. 

 

I've a fair bit of experience using depron in various forms to make both sports and scale models, although all electric. However, I see no reason why we can't adapt for IC. There are a number of techniques and routes you can make use of. I started by viewing the excellent and inspiring videos on the FliteTest website. These fantastic chaps really make anything seem possible. For me though, their approach of using foam board entirely was a bit restricting, so I have taken ideas from FliteTest and used traditional modelling techniques as well.

 

What I now do is reasonably similar each time:

 

I tend to use laminate flooring underlay. This is available from B&Q in the UK and comes from 2 main sources and is either black or white. The white comes in 3,6 and 9mm, I think the black just 6mm. For your usage, I'd go with 6mm anyway. You can use foamboard from art shops, but the paper adds a lot of weight, and not much else! I tend to remove it with an iron, which takes ages. However, my latest build it's staying on the outside to add a bit of ding resistance.

 

So once I have my preferred foam, I cut out the LOWER wing profile. Cut the UPPEr profile around 10mm deeper chord (to allow for the camber) There is a slight 'graining' to depron where it is easier to bend and less likely to crack in one direction than the other, but there's not much in it, to be honest. I make 4 or 5 ribs, not many more and don't worry about spar cut outs etc at this stage. The lower panel need to be 10mm shorter chord than the overall wing at the leading edge to make space for a few strips to make up the LE.

 

If your wing profile has any camber on the underside, gently curve the wing panel by gently dragging it across the edge of a table. This will preform the foam so it accepts your ribs more easily.

 

Then add your main spar. If the model is a lightweight, a few thicknesses of foam will do, but I generally add more strength here. My current favourite (cheapskate) method is to use 6mm square pin from B&Q, one top, one bottom. If you have balsa, 1/4 square is probably ideal. Start by gluing the lower spar to the foam profile at around 25% chord. Then notch your ribs (top and bottom) to match the spar location and glue them in place from the spar back. I don't do the front yet. It's easier to do this when the rear section is dry as you can use something like UHU POR as a contact adhesive and pull the foam up to the ribs whilst keeping the rear section weighted to your board.

 

Then add your top spar, and some spar webbing. You can use foam in between the spars, or balsa glued to them conventionally. Balsa is stronger, naturally. Add a dihedral brace (I use ply, probably 1/8") and fit to one wing.

 

I use a second spar as it helps support the skins and hold the airfoli. It's not there for strength, so you can fit it between your ribs. Add this at around 60% chord, and you can use a couple of thicknesses of foam. I understand this wing is 3Ch, so you don't need to worry about ailerons.

 

Curve your upper skins as per the lower, but a bit more aggressively. Take your time or you'll crack the foam. I sand the insides of the trailing edges top and bottom to get a thinner trailing edge.

 

Then the tricky bit; contact adhesive on all the contact points, and take a deep breath and whack it on! Line up the trailing edge as there will be a bit of overhang at the leading edge, which we'll manage later. Keep the wing pressed hard against the board (with a bit of packing under the leading edge of the prifile) and it should stay straight.

 

You now have most of a wing (probably within an evening!). You need now to trim the leading edges to align. I now add a few laminates of foam for the leading edge, and sand to shape. You can use soft balsa for a bit more tougness.

 

You can do both wings and join last, but it's tricky to clamp the dihedral brace. I use various methods, depending on the size. You can join once you have finished one wing, but before adding the top skin to the other. Makes it a bit of a handful, but you'll get a good strong join. Or split the skin and cut a section out where the brace is and add this bit back in after joining. It makes little difference to strength. to be honest.

 

So you now have a wing. I have covered in PVA/ Brown paper with success (although not great if you leave the paper on foamboard as the heat can loosen and bubble it). My new favourite method, and probably most suitable for you, is to glass cloth using 25 gsm cloth and water based varnish from, again, B&Q. (I don't work for them, btw...). This is a great method and super easy. You just paint the stuff on. A couple or three coats and you'll have a good tough finish. You can then paint with your choice of paint, but I'd avoid solvents as they will probably still damage the foam underneath. You will obviously then need some fuel proofer. I don't have much experience here, but some have used the same water based varnish I hear with some success. I have used it over emulsion to protect the finish, but my models are electric.

 

The wings are quite strong, but not as stiff as a balsa wing. Don't let this put you off trying; it costs peanuts if it doesn't work.

 

I hope that helps David, please feel free to drop me a line, or have a chat.

 

Some pics of the wing of my Regianne. I did this a year or so back and have got better since, but this model is still flying.

 

Graham

 

Graham

[J D 8 - Moderator]

Given what Barron's seemingly do, that being crash a lot. Recon Correx would be a more suitable materiel. 😁

[Simon Chaddock]

David

Perhaps the thing to remember is that a Depron wing on its own is unlikely to be as strong and crash resistant as a conventional as balsa one as by volume Depron is at least 5 times lighter than balsa.

Thin foam sheet can be used as a skin provided the structure within is suitable for the purpose. Being so light a Depron skin can be much thicker which can have advantages in both providing a smooth profile and for physical handling but be aware many foams do not like methanol or petrol.

On the plus side Depron is much cheaper than balsa and is easier to repair.

Using Depron comes down to a choice between the benefits and disadvantages for each particular application. 

 

Foam as a constructional material really comes into its own when its benefit of light weight is used in the appropriate areas of the whole airframe rather than just say a wing. Light weight reduces the power to fly, reduces  airspeed and thus the energy of any impact. 

[Don Fry]

Comment on Grahams very informative wing build post above. Love it, I’m getting a lot more curious about foam, balsa, carbon mixes. I too am a I/c methanol user  One certainty, use somethingg like Rustins plastic coating. 2 pack, fuel proof and foam safe. Foam, acrylic paints need proper protection against. The system has its origins in the furniture industry for varnishing tables and the like from steam, food, and provide longevity.

[john davidson 1]

Use sign shop self adhesive vinyl to cover the depron, make ribs and a depron spar , use one sheet for top and bottom with the top wider to allow for the top curve, Cover in one piece flat,  groove the fold point then fold with a batten to support the depron. There is a tutorial on U tube by Graeme Dorschel. the result is an extremely strong ding proof wing ideal for your purpose. Not sure if vinyl is fuel proof though.

[Mike Chantler]

12 hours ago, Graham Davies 3 said:

My current favourite (cheapskate) method is to use 6mm square pin from B&Q, one top, one bottom.

Graham,

Lovely wing and technique 🙂 am tempted. But what is the "6mm square pin"

M

[Graham Davies 3]

9 hours ago, Mike Chantler said:

Graham,

Lovely wing and technique 🙂 am tempted. But what is the "6mm square pin"

M

Sorry, 6mm square PINE. I obviously lost interest half way through that word!

 

Give it a go Mike; it's dead easy, costs peanuts, and with a bit of lateral thought, produces great results. I flew these two yesterday; both look great in the air, fly incredibly well, and are considerably lighter than a standard build. This results in really decent flight times. The Regianne is 55" span and I get over 8 minutes in 4S 3300; the spitfire is 74" and I get 5 minutes from a 6S 3300 pack. 

 

Graham

 

[Simon Chaddock]

David

It may need some thought. The Baron wing is a constant chord plank with a moderately high aspect ratio. The Spitfire elliptical wing is a much better structural shape.

As suggested the only way is to try and see using spar(s) similar to your current wing design. Nothing ventured nothing gained

[Mike Chantler]

Thanks David 🙂 very tempted, esp for elliptical wings as I spent ages hotwiring and shaping fiddly 6 section spitfire wing.

And I like the cost factor  🙂 

[Graham Davies 3]

The whole project for the 1/6 scale spitfire including servos, retracts, wheels and a load of detailing stuff from Mick reeves was about £250. The actual airframe part was probably less than £40...