Darrinc

My Feedback: (5)

A fiberglass wing will tweak in the sun ,even if it is a symetrical layup. It is just it's TCE and the TG of a roomtemp layup. (It's easy to test this with a couple of heat lamps and a 36" long, 1/8"x2" piece) As David Free stated, post curing does help this problem, it raises the TG.

There are expensive reflective paints out there that allows different choices, but the easiest way is to paint the top of the wing a lite color and the bottom a dark color. The lite side is in direct sunlight and will somewhat reflects the heat, and the dark side will absorb it, hopefully by doing this the wing heats up evenly and does not twist. You can add carbon ribs that offer a low TCE, and it is a good thermal conductor, so it will help transfer the heat to the bottom of the wing.

Darrinc

My Feedback: (5)

rcairplanenut,

I just reread the post and found that you are upset because I suggested to you to hot wire your foam out thinner and that it is hard to beat balsa for lightness in another post. I'm sorry if you were offended. I've just been doing this for a long time and have tried everything.

I have talked to the yellow aircraft people and some of the other "high tech" rc guys and they said, "what is core???".

As far as you just receiving your BS, I work, and have worked, for a lot of good engineers in my life, I have found that experiance and lack of attitude make the best engineers. Arrogent engineers usually last 6 months because the shop guys have had it with them. To bad because they are probably very talented, they just won't listen to the guy who does it everyday and knows instictively what will and will not work. He or she may not know how to run the numbers, but they are typically right.

Everyone has something to offer, as long as we listen and apply it to our situation.

rcairplanenut

About the thickness issue.

I worked the thinner shell problem on Catia, both shells are of the same outside dimension, the one on the left has a ½” thickness the one on the right has 1/8” thickness. This is what I found.

The Volume of the thicker shell is 67.675 in3

The Volume of the thinner shell is 21.25 in3

The density of white foam is 1 lb / ft3

Or .009259 oz / in3

The weight of the thicker shell is 67.675 X .009259 = .6266 oz.

The weight of the thinner shell is 21.25 X .009259 = .1967 oz.

The difference between the to is .429 oz.

Less then one half of an oz. savings on a 10 lbs plane may be worth the effort to you, I would rather have a slightly more damage resistant plane, go fly and have fun.

SGG BSAE ERAU

Darrinc

My Feedback: (5)

I keep forgetting that your dealing with small planes. It's much more critical with GS airplanes since they have came out with a new breed of superlight engines. Trying to get the plane stretched as much as possible and still balance with a lite engine has called for a radical new approach and ideas where every oz counts.

Have you tried to do the whole fuse in foam? Shape gives stiffness so a nice rounded fuse should be stiff and lite. Oh, and it would look cool too.

rcairplanenut

A round fuse is also easy to make a mold and shells with.

The plane in the picture is called the Falcon, it is a prototype 2+2 ship of my own design. Everything is built up, future generations of the plane will need to go together quicker, I am planning on a glass fuse, and built up tube connected wings and H stabs.

This is the closest I have come so far as to building an all round fuse with foam and glass. It is 2 half ellipse shells sitting on the top and bottom of a sheeted truss.

The next generation will have a fuse built from molds; the first will be built BVM exe style to get the ball rolling. The next I will probably use your suggestion of glass / balsa core / glass in a vacuum bag, all using the same molds. I know I can get the BVM / Yellow Aircraft style of lay-up on the first shot then I can experiment with cores.

I will go to the standard tube supported wing, rather then the interlocking Box beam, to save time, effort and weight.

The 2 big issues I need to figure out is the hinge support for the Rudder and the access hatch for the radio, fuel tank, and wing attachment. A balsa insert would work good for the rudder and a smaller access hatch would be better for strength.

SG

Darrinc

My Feedback: (5)

Looking good!

One nice thing about honeycomb core is that you can pack the hard points with epoxy/micro, then drill them out without adding any other structure. It works well for wing tube areas and such. I'm also a big fan of iso grid structures, so you can use thin strips of nomex and pan them down and only give stiffness were you need it. With our applications I have not seen a need for the tow that goes along, but then, maybe you only need the tow. I have not tried that yet.

Darrinc

My Feedback: (5)

One way to handle the hatch poblem is to layup your whole fuse, then cut out your hatches. Lay your fuse back in the mold and place your hatches back in with thin double sided tape (3M spray might work better). Pull the fuse back out and release your hatches(teflon tape works well here) with your favorite mold release. Place the fuse back in and fill in the cracks between the fuse and hatch with epoxy/cabosil, then layup 1" tapes over the edges of the hatch (split the difference). Once cured, pop the fuse from the mold, pop the hatches and they should perfectly fit in your fuse.

CZM

Hey Guys, I want to vacum bag my fuselage after laying up. Molds are in two halves, left and right. I have a couple of questions on which I require some help.

When should I release the vacum and remove the bagging materials from the molds ? Also when should I trim the excess cloth around the seam ?

I am also used to baking the molds for 20 minutes after laying up. Can I bake it after adding vacum to the molds. I plan to hold the nylong bagging film on the mold flange with sealent tape. Any help or step by step photos on laying up a fuselage and vacum bagging it would be welcome.

Thanks.

CZ

rcairplanenut

The hatch idea sounds good,

Im planing on the fuse plug to have the cowl, hatch and Vstab / rudder all conected to it.

Darrinc

My Feedback: (5)

You can do the cowl the same as the hatch, or layup the parts seprately in the molds, trim them and release them and put them back in the molds and then do the layup over them. (don't forget the cabsil/epoxy around the edges)

This will give you a all most seamless look to your fuse.

blkbird68

My Feedback: (19)

Darrin...I wish you gave classes in composite construction.....

By the way, that 1/4 panel I got from you worked great....that thing was less than half the weight of a panel I got from another place and it is much stiffer.

Thanks;
Dan

rcairplanenut

Good advice,

Can you use cabosil as a replacement for cotton fibers as "flox"?

Darrinc

My Feedback: (5)

We always use flox where we need toughness, like if you have hatch that you will be removing a lot. (Cabosil is brittle and will crack from repeated use)

A little bit of cabosil mixed in first makes the flox mixture a lot smoother for some reason.

Darrinc

My Feedback: (5)

Dan,

The only way to really learn is the hard way![&o]

I'm glad you liked the Nomex Panel! I really am proud of those panels! They really are as n'th degree as you can get! (I actually mean that) I haven't had the heart to sell the other two panels, I just know that I'll have a project around the corner that they will be perfect for and then I will be out of those panels. I don't have access to that type of equipment anymore so I better use them wisely.

BFoote

You learn by screwing up. Took me 7 tries till I got a vacuum baggin system / Mold for laying up prepreg carbon fiber I-beam spars for SAE Aero Design Heavy Lifters... It didn't help that for the first 4 tries I was too CHEEP to buy Nylon bagging and tried to use Polyethylene... HAH what a cheep schmuck... guess what! It worked like it also. In composites I learned the hard way WASTE that epoxy, Waste that FILLER, Waste that extra Carbon so as to leave excess to trim instead of having to "refill" and FILL and FIll in some more.

Cheers,

Honycomb is the bomb... Anyone who has ever taken Structural Mechanics will know what I mean for Strength to Weight ratio.

DarrinC is in the Strength to Weight ratio business; thus why RcPlaneNut and he don't get "along" or have missunderstandings... I am in the same boat{Strength to weight raio is king}... Most RC'rs don't care about weight except those who are racing, so doing multi layers which saves weight and is stronger doesn't make as much sense as several thick layers that saves time to the normal RC'r

Best class for Composites is asking the Tech Reps From Hexcell and other companies... or FiberLay here in Seattle how to do it and screweing up a bunch of times. If you are lucky you know someone in the layup/ vacuum bagging business, and if you are lucky know someone that has a nice LARGE ciruclating oven that allows you to use prepreg and high temp expoies. Room Temp epoxies that you buy in your hobby shop are Trash = cheepest common denominator. Havnen't found a good 1:1 epoxy yet... Any decent epoxy will be at least a 2:1 or higher ratio epoxy.

Brian

BFoote

To do Honeycomb correctly you need a vacuum pump capable of at least 24 inches of Mercury, 28 is desireable otherwise Press it together. Put extra expoxy next to the honeycomb side of things if you plan on using it so that it won't 'peel' on you.

Brian
Most common vac pumps that composites places sell you will pull 25 inches 12psi equivelant

CZM

Guys,

I am looking for a source of epoxy containing aluminium to use near the seam in my molds to make it sharp and virtually indestructible. Do you think epoxy mixed with aluminum dust would give me the same results. I have been informed that this mixture is stronger and more resilent than tooling resin.

CZ

BFoote

Are you talking a sharp 90 degree corner in a mold or a seam in a mold that will have to withstand a lot of abuse like impact resistance.
If impact resistance use chopped kevlar or S-glass fibers in a resin.
If a sharp corner is your aim, then aluminum in epoxy may or may not work. There are a bunch of epoxies that won't adhere to aluminum very well which is more important when its filler in a matrix form. For Bombproof corners, I would install super thin sheet steel. IF you want a bombproof complex corner, then I am not sure what would be better than tooling resin. A phenolic resin with chopped carbon fibers might be a pretty good bet... 1/4" to 1/2" fibers. Phenolic Resin is rather brittle, but very hard, not sure if its as hard as your "tooling resin". It could be the same thing.

Muddying the waters.

Brian Foote

davidfee

Brian,
I'm pretty sure CZ is asking about an aluminum-filled epoxy system. Basically, it is aluminum powder mixed into a high quality tooling resin. I have used "Epoxyd-Formbauharz-System EP 262/EPH 460-A" from http://www.bacuplast.de/ . I have also made my own using aluminum powder, steel powder, etc. mixed in with my tooling resin. Another one is Larit L-280 from Lange-Ritter, http://www.lange-ritter.de

I'm sure there are US suppliers... not sure about in India.

-David

rcairplanenut

What is your education level BFoote?????????

Just what kind of a bee hive are you trying to stir up with me BFoote?

I also know the advantages of honeycomb, it’s a mater of logistics not every modeler in universe has vacuum bags and all this other high tech equipment. Its about the resources that the individual has to use. In other words not every one has a Jhon Deer 5020 to mow their lawn with!

I just happened to graduate from the most difficult major offered by the highest ranked Aerospace / Aeronautical University in the country Embry Riddle Aeronautical University.

I took structural mechanics from the man that wrote the book on it, Howard Curtis.

I also am a full size pilot and I have worked on full-scale aircraft for the past 7 years, RC aircraft for the past 12 years. I also though ERAU have worked with Gulf Stream, they are currently working on an idea that my team and I came up with. I know the game from all angles!!!!!!!!!

I am in the strength to weight AND logistics business.
If you want to talk Strength to Weight ratio you start by maximizing the cross sectional moment of inertia. Not by a construction method, that is later down the line. Also Bfoote there are other methods other then Honeycomb that will achieve high strength to weight ratios such as Balsa as suggested by Darric and many materials books, documents, and computer programs.

I build many full balsa aircraft; some are fully aerobatic while maintaining a 6.2 oz/ft2 wing loading!!!!!!!! And wing loading stands side by side with strength ratio in terms of its significance to aircraft design. E/row is another important propriety. There are many ratios to look at not just one.

If you want to accurately define the misunderstanding that I had with Darric it was Ideal composite construction methods VS. Logistics. We are now brainstorming rather then arguing, don’t mess it up, Bfoote.

Bfoote I am NOT going to get “walked on” by you!

SGG

BFoote

Hey, someone who knows the names of the epoxies and has used them! How did those aluminum/steel filled epoxies work? Do they smooth out nicely? If so I would love to try using them, a million epoxies in this world just waiting to be tried... What is their hardness by the way? Do you know?

Questions Questions eternal Questions

Brian

BFoote

Wow, dude, you are way too touchy. I was giving out info on how to make and use tpes of composites and construction techniques. Jeepers man grow a thicker skin. No one is trying to force one to use different techniques here. I am a Mechanical Engineer who has taught himself Aerodynamics by reading every text book I can find along with applying it to Competitions for SAE by construcing a plane that weighed in at 5.3lbs when every other plane at that competition weighed in at 6.5lbs or More. I have also designed, machined, heat-treated, etc a Variable pitch propeller that works on a K&B .61.... That is a first as far as I know. It weighed in at .26lbs.

I swear everyone in these forums nit picks and self pontificates themselves way too much, when all I have been doing is stating a different way things can be done. I am perfectly aware that when designing things for Strength:Weight that Section modulas is what you are interested in.
I just wish I had a job designing the real planes

Brian

davidfee

Yes, they work quite nicely. They should be degased after mixing, prior to application. They are pourable, yet still highly viscous. It's usually a good idea to use a brush to get the resin into the nooks and craneys around the part line. After 24 hours at room temperature, the finished mold should be post-cured, usually about 15 hours at 120-140F.

I don't actually have the physical data handy but I can tell you that they are very hard and very tough. That is why they are great for mold edges.

I've also used a great silicon carbide-filled surface coat made by Ciba-Geigy. For most molds though, just a blend of graphite and colloidal silica fillers makes a really nice surface coat.

-David

CZM

David,

While I am looking for suppliers in India, would like to know the results you had in mixing aluminium powder in tooling resin. I would like to mix it with epoxy and try it . What ratio should I mix it in. Is there any efect on the curing period.

CZ

davidfee

Mixing the aluminum in is no problem. It slows the curing down quite a bit because the metal takes heat away from the reaction, as well as just keeping the epoxy spread out a bit.

You need to use a lot of aluminum because you don't want it to "settle" and separate into layers. You should probably make an experiment first to test the mix ratio, before you start making a mold. It will usually end up being quite thick, so you need to be careful when mixing to make sure you scrape the sides and bottom of the container to get everything mixed.

good luck,
-David