soholingo

ok guys, I don't have a vacuum bagger, yet. I wondering if anyone has ever thought about the following technique to get a plane wing that should be pretty close a hollow molded plane.

The spar will will be spruce or some sort of hardwood. Strengthened with epoxy, kevlar, carbon, etc...

Ribs made out of balsa, and set up on the spar. Like a standard kit.

The next part is where the technique should yield similar to a regularly molded plane. The outer surface of the wing will be balsa, and a thin layer of fiberglass, which is epoxied and painted using mylars. For the weight, I would epoxy these skins to the ribs, and hold them down with bags of sand or cement. Enough so that the skin confroms to the ribs, but not enough to break the ribs.

The bottom skin would be done the same way.

If this isn't clear post questions, if it is let me know how this will fair...

thanks,

Jay

Darrinc

My Feedback: (5)

???? I guess I'm not following you. You seem to want either build a very heavy wing, or your just glassing the wing like the warbird guys do.

The hardwood spar does not need to be reinforced and is 3 to 4 times heavier than a balsa spar reinforced with the same width using uni carbon. Epoxying the ribs in is also about 3 to 4 times heavier than CA. I've heard of guys that can glass a wing and have it come out lighter than covering, but they tend to have been doing this for years. Another trick to try is using water based polyurathane to glass a wing and they come out pretty light. You should be able to have the skins already layed up and painted before thay are applied since a wing is a simple shape. (I hope your only using 1/16, 8lb density contest balsa for the skin and ribs, anything more is overkill)

I always wanted to try painting the mylars with epoxy paint, 3M the 0.5oz glass to the wing and putting them together while the paint is B-staged. (just getting tacky)

Personally, if I was trying to make a lite built up wing, I would use the lightest balsa spar I could find reinforced with uni. Only cap the D-box and at the aileron. I've covered the balsa to use. And use some of the new lightweight coverings with balsarite on the leading and trailing edge. If you picked that wing up it would be so lite, it would be scary, but incredibly strong!!!!

But hey, try it. I love being wrong!

soholingo

this was just the information I was looking for. I like the idea 3m'ing the clothe to the balsa.

As for the balsa spar, I didn't think it would be strong enough, this is for a high g application. I can CA the ribs to the spar, but I was worried about the ca being able to hold the sheeted wing the spar and the ribs.

Lastly, how would you apply the carbon to a ribbed/sheeted dbox?

Thanks

Jay

davidfee

I've seen people use pre-cured fiberglass skins over a built-up balsa (or composite) inner structure. I think this is similar to what you're suggesting, but you're using balsa as part of the skin. I think the best way to do the skinning would be to cut saddles out of foam (like the offcuts from a foam wing core) so you can get even pressure applied to the skin for bonding to the ribs. Sandbags will just buckle the unsupported areas between the ribs. I think vacuum bagged glass over foam will be much easier. Probably lighter, too.

For the spar, use spruce or carbon. Pick one. If you laminate carbon over the spruce, the carbon will carry all of the load and the spruce will just be extra weight. This is because the carbon is an order of magnitude stiffer than the spruce. If you want to see how to make some very strong (unbreakable) glider spars, check out the Drela designs on the Charles River RC website. Matt at CST has made a very nice step by step photo tutorial also, at https://www.cstsales.com/How_to_Arti...arBuilding.htm .

good luck,
David

KC-135

My Feedback: (3)

Another is to have aflat surface like a pane of glass .Wax the glass then pour your resin out spreading it out then lay your glass on top rolling it till it is satruated then lay another pane on top or mylar, roll out again, let dry, peel off a thin fiberglass sheet .Glue to foam or open bays.There was a article years ago on this method and I think aerospace composite sold pre made ones.

KC-135

My Feedback: (3)

Another is to have aflat surface like a pane of glass .Wax the glass then pour your resin out spreading it out then lay your glass on top rolling it till it is satruated then lay another pane on top or mylar, roll out again, let dry, peel off a thin fiberglass sheet .Glue to foam or open bays.There was a article years ago on this method and I think aerospace composite sold pre made ones.

Darrinc

My Feedback: (5)

You say it need to handle high G's. What is the application? Definately not a 3D plane, 200mph pylon racer maybe???

soholingo

hotliner sailplane... I expect it to go to 100 mph+ in dives, I would like to be able to pull up without having the wing shatter...

As for the fiberglass skinning material, I like that idea... That has merit with a heavier glass I wouldn't need the balsa....

thanks,

Jay

Darrinc

My Feedback: (5)

For that application just hotwire out your wings out of foam, Blue foam at the root and 1lb white foam halfway out at the tips. Put Uni down for the spar wrap in glass. DJ Aerotech used to prep and paint the mylar halves with the trailing edges taped together. Then layup on this using one piece of glass, wrap around your foam core and place wing back in the saddle that you made when you cut the wings out. Normally you would bag this, but I guess you could pile a bunch of weights on it.

Make sure the mylar does not overlap at the leading edge or else the wing will not sit square in the saddle. When your done there is just a little sanding on the leading edge and your ready to fly.

soholingo

Good technique, however I want to control the planform with the skin. So that calls for a piece of balsa or a hardned piece of fiberglass...

davidfee

Jay, what do you mean by "control the planform with the skin?" What Darrin described for you is more or less the standard method of vacuum bagging composite skins on a foam core wing (a pretty good way of doing a hotliner wing).

-David

soholingo

Dave,

If I use that method, the wing takes the shape of the foam core, which is generally several pieces of foam glued together to form straight angles. I want an elliptical LE so I would need either a balsa skin or a heavy glass to be able to get an elliptical LE.

Jay

Darrinc

My Feedback: (5)

soholingo,

I think you need to do research on foam wings. Your completely wrong on what a foam core wing is.

davidfee

Jay,
You're basically right that foam core wings with multiple tapers are made from several smaller sections glued together. However, you can take it a step further if you want. Elliptical planforms ARE possible with "normal" foam core wings. They just take more work. You have to assemble the small sections, then blend them together with gentle sanding using templates to check accuracy. The number of sections you need depends on how much curvature you want. I'll attach a pic of a vac-bagged wing I did almost 2 years ago. It has a pseudo-elliptical leading edge planform. It's made from 4 panels (2 per side). I've also seen elliptical foam wings (Spitfire) cut by a sequence of passes of the hot wire on a single foam core, using a bunch of templates. The multi-panel method is probably easier.

For the elliptical planform, your sheeting needs to take a compound curve. This is next to impossible with a pre-cured sheet of glass, or even balsa. They bend one way, but not two ways. In a real molded wing, you have atmospheric pressure holding the skin down into the mold, helping with the compound curves.

On a foam core wing, the fabric can drape over the compound curves before the epoxy has set. Vacuum (atmospheric pressure) holds the fabric and mylars in place, as with the molded wing.

I really think a foam-core wing is the best way for you to go on this project... unless you like cutting a lot of ribs and doing a lot of planking and filling and sanding (sounds heavy).

-David

js3

My Feedback: (3)

Years ago I read an article about how to cut an elliptical foam core wing. The process involved using weights to bend the foam in a certain way to allow the straight hot wire to pass through the foam. When the weight is removed, the foam returns to its original position and the formerly straight hot wire cut is now curved. It was an interesting article however, I never tried it.

soholingo

Where am I wrong regarding what a foam wing is? I don't know what you mean.

As for the other guys, the elliptical leading edge is what I want. I would prefer the elliptical LE be done in the foam core, but It seems to be easier to get that LE by using a balsa skin. The only reason I suggested ribs is because I know I can do those rather easily...

Darrinc

My Feedback: (5)

You could just cut out templates for a constant chord wing, once the wing is cut out, you can hand cut thr shap of the leading edge and sand the rounded leading edge. The wing should now have a taper in it along with your rounded leading edge.

Something worth trying. I like simple.

soholingo

I guess I don't know much about tapered wings. My thought was that thickest portion of the wing (height) would be swept back in a tappered wing. If I make a constant chord wing, then the thickest portion of the wing is consistant. Meaning the airfoil is changing as you go our to the tips? These are just my assumptions. How should the the thickest portion of the wing resolve itself through out the entire width of the wing?

thanks

jay

davidfee

The location of the high point along the span will depend on the planform you choose. A tapered TE with an elliptical LE will not give you a straight line for the high point. Only a straight wing or plain double taper will do that for you. My wing pictured above has a slightly swept forward 1/4 chord line. If you look at a modern F5B with the swoopy tips, those are fairly straight along the 1/4 chord, but that 1/4 chord line flows rearwards towards the tip. The aerodynamic reasons for doing this at the tip are complicated and actually under dispute. Structurally, having a straight 1/4 chord line gives you the strongest wing because the spar is straight.

As for the airfoil, it is very common to use a different airfoil at the tip (or a series of different airfoils) to adjust for lift distribution and Reynolds number changes. But to do it right is complicated and probably not worth the effort the first time around while you're learning the construction techniques. Pick an airfoil, like the MH-30, and just use it for the whole wing.

-David

davidfee

Jay,
I just went back and read your opening post again. You don't have a vacuum bag setup yet, so you're trying to build the strongest, stiffest, smoothest hotliner wing you can without bagging. Is this correct? What I'd suggest is that you build a balsa ribbed wing with carbon spars and fully sheet it with balsa. But you won't be able to do the glass/balsa panels without vacuum, so you'll need to either cover with iron-on film, use tissue and dope, or glass the outside and then fill/sand to a paintable finish.

Basically, the vacuum pump is an indispensable tool for most composite work. Maybe try looking for a used one... or go to an appliance repair shop and see if they have any old refrigerator compressors. These make good vacuum pumps. Just add a regulator.

-David