Hoerner wing tip project.

[rodsmith]

Gathering materials to make 15" wide hoerner style wingtips. I've done a fair amount of fiberglass/composite work but nothing on this scale. I plan on using carbon fiber, I'm thinking 5 to 6 layers. Would like advise on style and weight of cloth. Also advise on type of epoxy to use, I have always used West Systems which seems to work well for smaller projects. Also any advise on a good place to buy materials. I know there must be cheaper options than AS.

[svyolo]

There are a lot of epoxies out there, including a lot that I have never tried. I used a lot of West many years ago. It is good but not my favorite for laminating. I prefer thinner epoxies for that. I use mostly System 3, and have also used MAS. I haven't tried any of the aerospace ones. They don't cost any more than the Marine ones, but most don't have dispensing hardware for small time users like us.

I even had to formulate my own about 10 years ago. I was working in China and the only epoxy locally available was pure epoxy. Super thick and unusable for laminating so I had to practice thinning it and seeing if it worked. At least it was cheap, at about 25 dollars a gallon. I did manage to build a 14' paddle board out of it, with the absolute worst junk plywood you have ever seen or used.

Wing tips have a lot of curvature to them giving them a lot of natural stiffness no matter what material you use. I doubt you would need more than 2 layers of 5 oz cloth but that is just a guess.

[svyolo]

I guess if you were making a bunch of big laminations, pouring large amounts of epoxy out of gallon (or 5 gallon) cans is OK. For small stuff, I prefer to use pumps that mount to the cans. That is why I am still using the marine brands.

[geraldmorrissey]

Bear in mind that the majority of weight in a homebuilt composite laminate is resin. Whatever you end up using for resin, if you do not carefully control how much resin goes into the laminate then the advantages of using carbon fiber goes away. Most homebuilders use way to much resin and the parts come out heavy. A well thought out fiberglass laminate with a 40 to 45% resin content by weight could out preform a carbon laminate at 50-60% resin content at a much lower cost. I would make some 12"x12" test coupons using various weights and weaves of fiberglass and learn how to use a squeegee to remove excess resin. Mix less and less resin to laminate each subsequent panel. When your down to the absolute minimum and getting a good surface finish, scale it up to the area of your parts. Its sort of like welding, you get better with practice. A few simple test coupons will give you valuable insite. Curing under a vacuum bag and bleeding the laminate will really help to remove excess resin. I would look for a resin with a long cure cycle so the bag can do its work.
Gerry
Patrol #30

[rodsmith]

Good point on the cost of carbon, I need to evaluate if the extra cost is justified. I will be doing test pieces including mini wing tip shaped before I try laminating the wing tips. Would vacuum bagging a wing tip be effective? I'm thinking it wouldn't draw epoxy from both top and bottom due to the relatively sharp edge.

[Nev]

Mike Patey has some good videos showing how he made the cowlings for Draco using carbon fiber.

[rodsmith]

Thanks, I have watched his videos building Scrappy, will check that out

[Bdflies]

Food for thought; Glasair wings are quite thin and sharp at the tips. The tips are 2 piece units (top skin and bottom skin), bonded at the sharp edges and tape laminate at the front. Their rule was 3 layers of glass were adequate for items that saw airstream forces. Considering the size of the Bearhawk tips, I'd do 3 layers plus a 1/4” foam core with 1 layer over the foam. Making top and bottom pieces would be an easy vacuum bagging project. With molds, this wouldn’t be difficult.
I have a buddy who bought a CNC Bridgeport mill. I spoke with him about milling foam blocks, to make wingtip molds. He agreed it would be a great project. BUT, he hasn’t learned enough about the mill to do the project yet. I guess I should nudge him, huh?

Bill

[rodsmith]

Another option to consider, thanks Bill.

[Mark Goldberg]

There are two different builders working on Hoerner style tips that each should end up an option for other builders who want Hoerner tips. One is a little "fatter" on the leading edge as the wingtip is being built for a certain brand of wingtip recognition lights. The other is pretty much standard Hoerner style. My intention is for someone already flying to do a before and after test of just the wingtip change. Then we'll see what the benefit is and whether the results merit putting them into production as an option for customers. I am hoping the results will be good. Mark

[rodsmith]

I assume these will be for the "B" airfoil, which would also work for the Patrol and Companion?

[Mark Goldberg]

Correct Rod. I have heard of one person who used Model B wingtips on their original BH wings. So it might be possible although I can not promise they would work. MG

[Ed Welfred]

I have just completed making my doors from per impregnated carbon fiber (that was past it’s expiry date) so it was free, but the glue used added up to a fair bit of money. I guess nothing is free but learned a few things. The epoxy in the prepreg that I used, required baking in an oven at 275 degrees for 2 to 3 hours. I read somewhere that even room temperature curing epoxy will benefit from a higher temp cure, but be safe and always check the materials data sheet. If you live in the sunny south perhaps a solar box may work. What ever curing heat you choose to use, the layers of stretch plastic used to vacuum bag has to take the heat.
Jarald is correct, the epoxy is where the weight is and the only way to get just the right amount of epoxy is to vacuum bag. Vacuum bagging consists of stretchy plastic release material on the finished side. Then a porous plastic release layer on the other side that lets excess epoxy bleed through into a fussy breather material. Then a top layer of stretchy plastic is used to seal up the complete unit. A vacuum fitting is attached to this outer layer of plastic.
You want the finished surface to be as smooth as possible in order to reduce finish time and reduce the weight of the smoothing filler material. This requires a smooth female mold.
A male mold could work but it would need to be strong and not compressible as vacuum bagging exerts a lot of pressure. The porous release layer would need to be on the outer finished surface because it is compressible. The finished surface area would not be as smooth but still usable.
Attached are some pictures of small angle pieces that I vacuum formed, then glued to reinforce the corner joints on the doors.

[Bcone1381]

Ed, can you tell us about how you will hinge the door?

[Nev]

Very interested in this idea, I plan to do the same. How do you plan to attach the windows, will they be bonded ?

[Ed Welfred]

The doors hinge at the top. I am just starting the wings now so I do not have the wing struts in place to be sure the doors will clear the struts. The height of the lower door frame was determined by rough measuring the 20 to 1 front page drawing. Hopefully the door will clear.

Yes, I am planning to bond the windows.

[geraldmorrissey]

Second most everything Ed said, to give some perspective, aerospace quality laminates used as class one structure on airliners and fighters have a resin content of about 32% +/-2% by weight. 75-78% of the volume of the laminate is fiber. Thats not much resin. But those laminates are consolidated in an autoclave at 250-350 degrees F and 60-90psi. Be careful applying heat to room temp resins, you are now in unknown territory. Never deviate from the data sheets.
Gerry
Patrol #30

[Ed Welfred]

Jareld your correct, a careless statement could send a reader in the wrong direction. Ed

[svyolo]

Bear in mind that the majority of weight in a homebuilt composite laminate is resin. Whatever you end up using for resin, if you do not carefully control how much resin goes into the laminate then the advantages of using carbon fiber goes away. Most homebuilders use way to much resin and the parts come out heavy. A well thought out fiberglass laminate with a 40 to 45% resin content by weight could out preform a carbon laminate at 50-60% resin content at a much lower cost. I would make some 12"x12" test coupons using various weights and weaves of fiberglass and learn how to use a squeegee to remove excess resin. Mix less and less resin to laminate each subsequent panel. When your down to the absolute minimum and getting a good surface finish, scale it up to the area of your parts. Its sort of like welding, you get better with practice. A few simple test coupons will give you valuable insite. Curing under a vacuum bag and bleeding the laminate will really help to remove excess resin. I would look for a resin with a long cure cycle so the bag can do its work.
Gerry
Patrol #30

I concur with all of this. Using male molds it is difficult to get a beautiful part that needs surface finishing. Surface finishing fiberglass sucks but it is easy. Carbon fibers are actually much worse, and dangerous.

Making scrap carbon parts gets expensive fairly quickly.

I have done lots of glass work, and a small amount of carbon. I know using heat to post-cure makes room temp epoxy a bit stronger, but I was alway afraid of the part getting mis-shapen. I personally wouldn't do it unless someone tells me it works without distorting the shape of the part. I just don't know. It might need to be done in the mold, under pressure.

[rodsmith]

I'm thinking the only way to make female molds for the wingtip, top and bottom, would be to make a male mold first. What materials would be used to make a female mold strong enough for vacuum bagging?

[Bdflies]

If one were to have foam molds, either pulled from a male or machined, a 'female surface' would need to be several layers thick and very smooth. The vacuum bag would only compress to the 'mold surface'. It only squeezes to the first tight surface. Remember, it produces ambient pressure, equally distributed, to the mold surface, not the thickness of the mold.
I hope this makes sense...

[Mark Goldberg]

Rod, if I were doing a "one off" set of wingtips I would glue or attach some rigid foam to the outboard rib. Then carve or shape it to what you want. Then lay the fiber glass on top of it. Bit of a challenge getting the two sides the same shape, but seems possible. Mark

[geraldmorrissey]

About 35 years ago I was working as a contract engineer at Beech on the Starship. It was months of 7 days a week trying to build tooling, the first airplane and train the Beech workforce. It was 3 steps forward and 2 back. One morning about 3:30 AM a bleary eyed Beech engineer walked into a meeting, held up a piece of aluminum sheet metal and proclaimed "I predict someday all airplanes will be built from this material".
Gerry
Patrol #30

[quadra]

I have done thousands of lamination in both glass and carbon, they are equally hazardous, but I would choose carbon; not just for the weight to strength, but because the resin choices are much better. A male plug mold will be your fastest option ( and can be carved out or disolved when you are done ) and finishing with some light filler and paint will take way less time than a set of female molds..deep draw lamination.. and vacuum autoclaving

[rodsmith]

I have done thousands of lamination in both glass and carbon, they are equally hazardous, but I would choose carbon; not just for the weight to strength, but because the resin choices are much better. A male plug mold will be your fastest option ( and can be carved out or disolved when you are done ) and finishing with some light filler and paint will take way less time than a set of female molds..deep draw lamination.. and vacuum autoclaving

What would be a good resin/epoxy to use with carbon? I have no idea what deep draw lamination means.

[svyolo]

CF doesn't do tight radius very well without vacuum bagging. Glass does it better. If you don't want to set up for V bagging you can cheat on the tight radius with soft foam and either duct tape or weights to apply pressure. If you are not going to V bag I would stick to glass.

Epoxy is your choice but ones sold for laminating will wet out easier. Glass or CF doesn't matter. I think deep draw means "Resin-infusion".

[quadra]

I would look at the offerings available through aircraft spruce or one of the online composite supply vendors, selection is really dependant on application, a fast curing resin that generates a lot of heat might be fine in a thin panel layup but in a heavy sectional like a rib or strut reinforcement would create so much heat it might overheat, blister, delaminate between the fiber layers and compromise the intended product. All of the work I do is vacuum bagged and as a result I generally use lower viscosity resins designed to wet out the layup quickly,with relatively short pot life or working time. There are some great videos on youtube that do a good job of showing the process in general terms. I would not recommend even trying these techniques unless you are willing to work under vacuum as most laminating epoxy resins are intended to be used. Deep draw refers to the process of forming a part into a negative or female mold, this is the technique that allows the final products surface finish and dimensions to be very tightly controlled.... a positive male pattern of the intended part is made and precisely finished and a negative mold made from that so that the negative or female mould can be used to create the final product. The challenge in trying to lay up the material, vacuum bag and ensuring the resin fully wets out, without dry spots or resin pooling becomes more challenging in a female mold that requires a deep draw vs a shallow nose bowl or curved panel.