info on molded leading edges wanted

[muss51]

on some of the expensive build up planes like the graphite,omega,zenit,etc. have a molded leading d tube type construction and balsa ribs carbon capped.

so what i'm asking is : is there a premolded leading edge you can buy or do you have to make them yourself , and if you have to make them how do you go about it.

i'm looking to do a one of type of construction of about a 130" span using either a 7037 or mh32 airfoil

[Ollie]

As far as I know, you have to make them yourself. They can be made of kevlar or carbon woven cloth cut on the bias.

One way is to make a rigid, closed cell polystyrene, male form the length of a wing panel. Cover the form with a smooth release film cut from a polyethylene garbage bag. Lay up the cloth and epoxy over the film. Compact the layup by pressing it into a U-shaped box, lined with foam rubber that presses against the layup against form all over. Instead of the U-shaped box lined with foam rubber, you could use a vacuum bag to compact the layup.

[muss51]

thanks for the feed back,but i puzzeled about what foam you use for the female foam box. also with the garbage bag bit wouldn't you have to sand the inside to get the spar and ribs to stick.

[Ollie]

The female box can be made from plywood of suitable thickness or even MDF. It can be lined with a variety of foam rubbers such as the foam rubber used in upholstry or some foam rubbers used for rug padding or even the foam rubber (expensive) sold in hobby shops for padding receivers. The foam rubber should be thick enough and shaped to the aproximate shape of the form so that it presses against the form all over when the form is inserted.

Where a textured surface is desired for gluing, you can use a teflon coated fiberglass release cloth or polyester peel ply over the polyethylene sheet covering the form.

[davidleitch]

According to the manufacturers of the Graphite and Organic, possibly the first guys to popularise the technique, the D box can be made in a mold.

Following picture is taken from manufacturer site.

http://airplane-model.com/technology.htm

[Bernie Wolfard]

I am not sure this construction technique lends itself to home building very well. The D-tube is force fit into a CNC cut aluminum mold, which is then heated to cure the epoxy. The epoxy used needs to be thermal cured. This type of epoxy is much stronger and stiffer that room temperature cured epoxy. Also one of the things not mentioned much about the 7037 and the MH32 and most other modern low Reynolds # airfoils is that they are hypercritical. This means that surface accuracy needs to be at least to the 1000th of an inch especially within the first 20% of the cord or performance will be degraded significantly.

If I were going to make a D-Tube wing I would build a more conventional balsa D-tube wing with a built up carbon spar with a more forgiving and probably higher performance Drela aifoil. Information on both of these is obtainable at the Charles River RC website http://www.charlesriverrc.org/. A wing built like this could be stronger and lighter than an force-molded D-tube wing and certainly quicker and easier to build.

[muss51]

i know this all sounds like alot of work,but i love the way they look. and yes i could go with a glass over balsa for the leading edge but it would not be the same.
what it all comes down to is i got the time and not the money for a built plane. so would i be wrong in trying to get the info and building a one of.
oh, by the way i do like the mh32 and 7037 cause i've used them and they work,but the drala foils i don't have any experience and i have not herd reports on them other than in handlaunch stuff which would not be in the same class as a unlimited.
by the way Ollie i like your foam method.

THANKS: for replying

[Ollie]

Taking the foam method a step farther:

1. Cut full foam cores about 0.005 inches undersize.
2. Make a vertical cut in the foam at the centerline of the spar, dividing the core into front and back pieces.
3. Use the front piece, mounted on its back edge to a flat and mold bias cut carbon cloth directly over the foam for the D-tube.
4. Take the aft piece. Add a thin 1/8 inch wide precured carbon strip at the trailing edge. Vacuum bag uni-carbon caps top and bottom overlapping the trailing edge where you want ribs.
5. Assemble carbon spar caps to vertical grain balsa shearwebs and wrap with a layer of bias cut 2 ounce glass cloth ala Dr. Drela's spar design.
6. Remove foam 1/2 the fore and aft depth of the spar from the front and back core assemblies.
7. Assemble the core subassemblies to the spar sub assembly using the core beds for alignment.
8. Cut away the excess foam in the rib bays between the spar, trailing edge and rib caps.
9. Cover with your favorite plastic film.

If you make the spar height to just fit between the back edges of the D-tube and the front ends of the rib caps, you will have an accurate, strong and light weight wing that will perform very well indeed. Oh, don't forget to make the rib spacing close enough to seriously limit covering sag. The accuracy will be limited only by your craftsmanship.

[Ollie]

Badger,

What kind of foam were you using? How wide were your carbon rib caps?

[muss51]

it sounds like we got a plan for the wing,except i'm a little short of understanding a couple of points.
1. after you cut the cores and seperate the leading edge at the spar cl and then mold the leading edge on with the carbon /kevlar leading edge, how do you get a sharp line on the carbon/kevlar cause every time i cut molded kevlar i get freys and then i usually ca and sand and it leaves a hard to sand and still freys alittle. plus how do you clear out an area for half the spar and not hurt your molded leading edge and have a good surface to join the 2(spar and leading edge).
2.i plan to put flaps and ail. on this wing and was planning on building up the flaps and ail from balsa capped with .007 carbon and using 1/8 x1/4 carbon for the trailing edge and the face of the flap and ail would be balsa (?) and be capped(?)
3. the section between the spar and the ail. flap area would be balsa capped with .007 carbon and have a rear edge of balsa (?) and carbon(?)

for all of this it sounds like maybe 3/32 balsa would be a good choice for the ribs,but is there a easy way to cap the .007carbon on the balsa with out getting your self all glued up and also is there a easy way to strip the carbon?

[Ollie]

You can solve item one by just using woven carbon cloth without any kevlar. You can trim kevlar cleanly with a good pair of scissors which have been resharpened at a cuting edge angle of 85 to 90 degrees.

You will need a sub spar to hinge the flaps and ailerons to.

Dow hiload 60 or Spyder foam capped with unicarbon will make much better ribs than balsa. The denser foam will do the job if it is about 3 times thicker than the eight pound balsa you would use. The pink foam isn't dense or stiff enough for this application. With one or one and a half inch rib spacing the wing will be quite strong enough. Instead of using precured 0.007 thick carbon, you could use 0.005 inch thick smooth uniweb (2.9 ounce fabric in a wet layup). This will greatly simplify construction because there won't be any internal stresses from bending precured carbon. The smooth unidirectional fabric cuts easily with scissors or a roller cutter. This will allow you to easily vary the rib thickness from 1/8 or 3/16 at the tip to 1/2 inch or so at the root. By wetting the rib cap strips on paper and blotting off the excess epoxy before applying the strips to the mylar molding sheet a lot of messiness and excess epoxy in the layup can be avoided. The trailing edges can also be done with the same material top and bottom at the same time as can the aileron support sub spar cap and the aileron leading edge spar caps. The trailing edge carbon can be tqpered from 1/2 inch at the root to 1/4 inch at the tip. These strips must overlap the rib caps in the corners of the rib bays to avoid the foam carrying all the racking forces. This will save a lot of work by eliminating all balsa. After the wing panel is out of the bag, the ailerons are cut away with an exacto knife or razor saw.

The foam removal for the spar can be done with a dremmel or similar tool and a router attachment. Alternatively it can be done with a sanding block sized to the height of the spar with stops on the sides to control depth of sanding. The spar can be set into the foam with a thick mixture of epoxy and microballoons to take care of any voids.

Teaching yourself new construction techniques requires developing detailed work proceedures. There are many possible variations and a certain amount of trial and error may be involved. The proceedures for vacuum bagging wings have been evolving for over 15 years and are still evolving. There are many more materials available now than 15 years ago. The razor blade carpentry of balsa wood has been evolving for over 65 years. That's one reason it is as refined as it is.

[F3X]

[QUOTE]Originally posted by muss51
[B]on some of the expensive build up planes like the graphite,omega,zenit,etc. have a molded leading d tube type construction and balsa ribs carbon capped.

Now you can see why the models cost what they do, it is very possible for the home builder to "copy" the designs and processes used by the manufacturers but what usually happens is a lot of money and time are spent without the same results. Not everyone can pull it off but that shouldn't stop anyone from trying. Just don't expect to clone a 500.00 wing by spending a few bucks and a few hours in the garage, it’s a long process and steep learning curve and once you get it right you will be a better modeler for it.

Good luck with your project and let us know how it turns out.

[muss51]

ollie:
it doesn't sound like where on the same page, cause what apperance i want is the balsa rib bit. it's not that i disapprove of your method and it does sound interresting but the out come is not what i was looking for. so do you have any ideas of how to do the balsa rib bit.
in using your method it sounds like alot of time is needed to do all this work at one sitting. so now i would like to know what resin you would recomend,cause what i have been using is the west system (206 hardener) with a 25-35 min working time.

f3x:
i'm not out to copy a design ,but only looking to learn a new building method for myself. and yes i know the process is going to be long and frustrating the way it sounds. but when i started to get the idea a couple of flying buddies said they herd of the molded leading edges could be purchased and i have not been able to run into any info. so now my thoughts have processed to going the hole way and make my own from the start. this is because i have decided to do a blend of foils of which i like, so if you have any imput i would like to hear it.

[Ollie]

West 209 hardener will give you an hour of working time.

See:
https://www.cstsales.com/Epoxy_&_Molding/mgs.htm
MGS has a hardener with four hour pot life. It also has the advantage of post cure hardening as do some other epoxies.

Get everything ready, mix the epoxy on a disposable aluminum plate so the pot life will be extended, then do the wet out. The assembly after wet out doesn't have to be within the pot life time. This is an example of the method of work details you will learn or develop yourself.

See:
http://groups.yahoo.com/group/Allegro-Lite/?yguid=108420033
Dr. Drela's Allegro Lite and Bubble Dancer designs use balsa ribs. The airfoils are designed to avoid covering sag and give performance equal to or better than all molded wings. The spars are strong enough to break most winch lines. All this at weights considerably lighter that any molded wing. The Bubble Dancer has a dead air duration of over 11 minutes from a winch launch. It will work smaller weaker thermals than any molded ship. It is a challenge to gather the parts and build it.

Dr. Drela's precision, tangential sanding methods can produce airfoil accuracy in balsa wood that comes very close to molded wings. The laser cut rib and shearweb sets from Laser Arts for the Bubble Dancer come with leading edge templates for every rib station along the span.

[Kestrel]

Does anyone know how they put that thin c/f capstrip on the balsa ribs? The craftmanship of those models is amazing. I have built a few models, and when I look at a Graphite, I am in awe at the time and labor that goes into building them.