Elevator Tip Finishing

A forum in which to discuss topics specific to the assembly of the RV 8/8A
bmurrish
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Elevator Tip Finishing

Post by bmurrish »

I am trying to finish my fiberglass elevator tips. Still haven't decided what is the best route here. Should I leave it with the counterweight exposed, or grind down the weight a little more and fiberglass over it? Curious as to what others are doing.
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Elevator Tip Finishing

Post by Spike »

I would either throw a layer of cloth over it or maybe something like a body filler. I find it interesting that yours do that. The 9 tips completely enclose the weight so that none of it is visible.
 
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I am trying to finish my fiberglass elevator tips. Still haven't decided what is the best route here. Should I leave it with the counterweight exposed, or grind down the weight a little more and fiberglass over it? Curious as to what others are doing.
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bmurrish
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Post by bmurrish »

Thomas, are your elevator tips open on the front end also? I have seen some older -7 kits that are enclosed also. I thought about putting some filler to make a smooth transition from the fiberglass to the weight, then I also thought about taking off a little more of the weight and fiberglassing the forward end.
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4kilo
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Post by 4kilo »

Don't forget that you need to ballance the surfaces after painting. Since the paint will move the CG of the surface aft a little bit, you need to leave the weight heavy enough to compensate. I am planning to leave mine quite a bit heavy so that after painting I can just drill out enough lead to ballance. The resulting hole can be glassed over to match the rest of the tip.

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Elevator Tip Finishing

Post by Spike »

Are the RV8 rudder weights enclosed? On the RV-9 the counterweight is not accessible once you rivet the rudder together. Is that also true for the 8? I wonder if its because gravity works parallel to the axis of pivot. Any thoughts?


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Don't forget that you need to ballance the surfaces after painting. Since the paint will move the CG of the surface aft a little bit, you need to leave the weight heavy enough to compensate. I am planning to leave mine quite a bit heavy so that after painting I can just drill out enough lead to ballance. The resulting hole can be glassed over to match the rest of the tip.

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mustang
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Post by mustang »

Spike,
The RV-8 elev tips are as the picture above. I've glassed over one weight but not the other. I may still do both. I'm wrestling with the rudder tip right now and the rudder bottom. I'm gonna make my bottom fairing removeable because of the nav light and strobe combo being installed there. I will use plate nuts on the inside aluminum strip and countersunk tinnerman washers and screws on the outside.

Cheers, Pete
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Post by 4kilo »

Spike,

The rudder weight on the RV-8 is not really accessable once the rudder tip is completed, but I will leave a hole so that I can drill it if neccessary.

The ballancing is not actually a weight issue; it is a mass issue (mass ballance). Different aircraft have different needs for mass ballance, but Van designed the RV series for simplicity, so simply ballancing the empanage surfaces on the hinge line for weight will do the trick.

Mass ballance has many different effects on the aircraft, but probably the most important in our application is flutter damping. Since I don't know how critical the mass ballance on the rudder is, I will try to make it as close as possible. Someone else (best source would be an engineer at Van's) may be able to tell us just how much tolerance there is. Probably lots, but I am still going to try for perfect.

Pat
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bill murrish

Post by bill murrish »

The plans call for you to cut away about 1/2" of the weight, but I am planning on not shaving it down until the tail is painted. For that reason, I am going with the platenuts so the tips can be removed.

Bill

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Post by tshort »

Mine are open on the ends, too.

So you're gonna make the elevator tips removable? That seems like a lot of work ... it also may be a lot harder to smooth out the junction between the tip and the elevator rather than doing like Dan Checkoway and others have done. Do you think there will be any reason to remove them after paint / balance?

Thomas

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Post by arffguy »

There are two styles to the pre-made elevator counterweights. The old style (RV-6, older 7, 8 and the 9) and the new ones. The one pictured above is the new style. When asking how another person did it make sure they know which style you have.
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bmurrish
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Post by bmurrish »

TShort wrote:Do you think there will be any reason to remove them after paint / balance?
I wouldn't have any reason to open it once painted. However, I think I will be flying a naked plane for a while until I get it painted. I guess it would be just as easy to drill out the rivets to gain access to tweak the weights after it is painted.
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Post by mustang »

If you have the open type pictured above, you can install the tips pemanently and then still drill out some lead either through the lightly glassed over end cap or from the inside which remains naked for eternity.

I don't think the rudder will balance like the elevators. At least mine won't. Its already tail heavy without paint. The mass balance will still do it's job even if not perfectly balanced however. Consider that the "4" has no mass balance at all on the rudder. So, some mass balance weight is better than no mass balance. Balance weight on the rudder was one of the things Van did when upping the Vno on the 7's and 8's from 200 to 230mph.

Cheers, Pete
Peter Marshall
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You wanna draw, ....against the fastest rivet gun in the West??? LOL

bmurrish
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Post by bmurrish »

Can you use any fiberglass kit found locally in an automotive or marine store or is there something specific to use on aircraft?
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Post by bmurrish »

Anyone going with West Systems epoxy or will a regular fiberglassing kit from Home Depot work?
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mustang
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Glassing 101

Post by mustang »

Bill,
Yes, for the wing, stab, and surfaces tips you can use the stuff available in hardware stores or car places. These parts are made of polyester resin, readily identified by it's sickly sweet odor on the inside of the parts.

However, Van recommends using epoxy resin to glass over the tips, to attach the lead weights to the aluminum counterweight cover etc. Use epoxy like J B Weld for laminating aluminum strips on the inside of your tip pieces to be drilled out and riveted onto the tips of the aluminum structure. Use thinner, laminating epoxy for glassing the end caps onto the lead weights also.

The rule works like this: You can use epoxy to stick to polyester resin parts, but never use polyester resin to stick to epoxy parts. (It doesn't!) So, any glassing you do, should be done with epoxy resin, especially around the lead weights. Pound for pound, epoxy is almost twice as tough as polyester and as far as I am concerned, polyester should not even be used to make aircraft parts. It is brittle, cracks easily and basically is the shits. I am frankly shocked at the lack of quality in Van's fiberglass parts. The parts have been shoddily made, pulled out of the mold before cured, do not fit well, and are basically not very good. At the minimum, they should have been made with epoxy resin and "S"-Glass for strength. Polyester is heavy and a poor product for aircraft use. No commercial aircraft that I know of uses polyester resin for parts.

AIRBUS and Boeing use composites made of special epoxy, not polyester.

You can order aircraft grade epoxy from Aircraft Spruce at reasonable prices. I just received an order a couple of days ago. I ordered the one quart kit of Aeropoxy and a pint kit of the thicker Aeropoxy for glueing metal to fiberglass. (A lot cheaper than J B Weld, similar stuff) The West System Epoxy has long been a standard for boat and aircraft builders, also available at Aircraft Spruce. I have probably 5 gallons of Epoxy in my basement left over from model aircraft days, but it is all 15 years old or more, so I'm updating my stock for this airplane. Hey! I'm gonna be in this one!!!

This is a long winded answer, but yes, you can use hardware store polyester resin, but I recommend using epoxy to cover your lead weights with a couple of layups of glass, you will be happy.

As you might guess, I have a lot of glassing experience. So, I will pass on a couple of tips.

GLASSING 101

Lets say you are going to lay up some glass over the ends of your lead weights and tie in the ends of the fiberglass elevator tips at the same time. Grind away the gelcoat, that is the white stuff that covers the fiberglass parts that Van sends us. This stuff is non-structural and does nothing but add weight. Grind it back from the end of the tip about one inch so that the raw fiberglass is visible and tapered out to nothing at the forward tip. Round off the corners of the lead weight so that there is not a sharp corner any more but a smooth rounded corner. Glass, does not like to be molded around sharp corners. See if you can buy some four once glass cloth. Six ounce is common for boat repairs but four ounce is easier to mold around corners. Try a Hobby store and see if they have any crowsfoot weave glass. Cut some pieces to fit over the roughed up glass and around the tip and over the glass on the other side. Because of the shape, you will have to slit the glass to make it lay down around the end cap. You NEVER want a fold in any layup. Now mix up some epoxy and let it stand for a while. Epoxy needs a certain amount of time to mingle before using. Use a metal can for this mellowing time, it transfers heat out of the resin. (OF course, this mellowing time does not apply to Fast Cure epoxies like 5 minute epoxy) You can mix the epoxy first, and cut the fiberglass while waiting for the resin molecules to shake hands. Use good sharp scissors for cutting the glass. Using a paste brush, coat the end of the lead weight and fiberglass roughed up area with epoxy. Wearing rubber gloves, layup the cloth onto the end caps and paint it down with resin. Have lots of paper towels and 99% alcohol ready for wipe ups. Epoxy is alcohol soluble and alcohol can even be used to "THIN" epoxy, or cool it, if it starts to "cook-off" Now that your layup is daubed onto the job, paint it with epoxy so that the glass is wetted out and no air bubbles exist under the glass.

You now have a soggy mess of a glass job, dripping with excess epoxy. To keep it light and strong we need to remove excess resin but keep the layup lying down on the job with NO AIR BUBBLES. To do this we take a roll of single layer toilet paper, (Avoid double layer paper if you can) and roll it over the job. The first thing that happens, is that the layup sticks to the paper and comes off the part. YIKES! This is not good. Stick the glass back onto the job and begin so that the rolling procedure rolls towards the edges, not away from the edges. You will notice when you roll away from an edge, the toilet paper will try to pick up the layer of glass again. You must also position the roll so that the paper does not simply unroll onto the job!!! As you roll the toilet paper, it will absorb copious quantities of resin. As it does, strip off the saturated paper and start with a clean sheet always. The discarded paper will find it's way onto the bottom of your running shoes very shortly! Continue to roll until very little resin is transferring onto the paper. That is the correct amount of resin to complete the layup. Inspect the layup and if required, daub a little resin if you spot any airbubbles. Roll it again Sam.

It is possible with experience, to do more than one layer of glass at one time, but I recommend that you just do one. When the layup has cured to "GREEN", you can trim any overlapping extraneous pieces off with an exacto knife. When the layup is fully cured, sand it lightly to remove any sharp prickly bits and repeat the glassing process again. Continue until you are satisfied with your layup for strength and shape. After curing thoroughly, (keep it warm to cure, but not hot) sand to shape and prime a few times, sanding between coats to eliminate pinholes. You now have a strong, light layup that is far tougher than Van's parts.

If you find that doing the whole end cap at once is too weird for you, then just do one half of a cap, then do the other side when the first side has cured. Overlap the layups in the center of the lead weight area. First one side, then the other and so on. Remember to sand lightly before the second layup. The prickly bits can catch on the next layup and cause air bubbles! Yikes!

This whole process is called the male mold technique and commonly used by one-off builders where they carve a part from foam, glass it as described above, then dissolve the foam out from underneath the glass and VOILA! a perfect hollow part! The bad part about this process is the heavy workload to finish the outside of the part. In our case, there isn't much to do so it's not too bad.

If you mixed a lot of epoxy and left it in the can for a long time, it will go nuclear and cook-off. If your paint brush was standing in the can of epoxy, it is still there, preserved for eternity. The chemical reaction that changes the liquid into a solid creates heat. The heat hastens the chemical reaction. The chemical reaction speeds up and creates more heat. We are now in a meltdown situation people! If you catch this early enough, you can add some 99% alcohol and it will cool the epoxy and slow down the process. You can also transfer the warming liquid to a cooler metal container. You can also pour it into a wider container to thin out the mass. Either, or both methods will slow the process down but you are out of loiter time. Finsh the job as quickly as possible. OH! And remove the brush and clean it out! This meltdown thing is strictly a characteristic of MASS, and you will notice that the layup has not cured at all. This is because it is a thin layer, whereas in the can is a very thick layer.

Hope this is of some help.
Peter Marshall
Newbie RV-8 builder.

You wanna draw, ....against the fastest rivet gun in the West??? LOL

bmurrish
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Post by bmurrish »

Thanks Peter, this is some really good information. I am going to check out a couple boat stores to see if I can find the West System products and some 4 oz glass. I would rather buy it locally since I read you have to pay hazmat when having it shipped. Not sure how much that would be. I do have a couple questions. Will the mixture and glass adhere to the lead weights on the elevator or will I be able to seperate it once it is cured? I would like to make the tips removable until I paint the plane. I bought some carvable foam from a crafts store to use inside the tips while glassing, then I planned on removing the foam after everything was set. If I go this route, is there anything I can use (like wax paper) over the foam to keep the resin from sticking to the foam? Thanks for your advice.
Bill Murrish
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Filling the counterweight arm

Post by Guest »

Peter Marshall
Would you fill in or have you filled in the inboard side of the elevator counter weight arm? (the side opposite from the fiberglass tip.) Thank you
Lyle
Emp -8

bmurrish
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Post by bmurrish »

Lyle, are you thinkig about making a rib to go inside this area or glassing it in?
Bill Murrish
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Post by Guest »

Yes, I was thinking of putting a foam or balsa plug in there and then glass over it just like what the instructions call for on the stabilizers. I have heard of concerns about mosture getting traped in there. I don't see how it could get traped any more than on the stabilizers. Thanks
Lyle
-8
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bmurrish
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Post by bmurrish »

Lyle, My question is, how would you glass it in? The inboard sections are aluminum. Will the fiberglass adhere there? It seems like you would have to make a rib and rivet it in.
Bill Murrish
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