By: Bill Miles

There is no doubt that more than ever, that Pro-bond glue is probably the most controversial none-R/C product to come along in awhile (at least on the I.M.A.C. mailing list). It seems everyone has their own technique for using this glue and everyone has their theories. I will give you my method and opinion on the glue and also go through some simple tests between odorless C.A., epoxy, 3m 77 spray, and contact cement. I will cover odorless C. A. because any of these glues can also be used for capping stabs and wings.

First, Probond is a product made by Elmers.  It is found in most do-it-yourself super stores like Lowes, Home Depot, and even Wal-Mart. It comes in a black, white and gold bottle. It comes in two sizes, oz. and the large bottle oz. (in the long run-cheaper if you do a lot of wings and I do). It has the consistency of pancake syrup. It is a little thicker than some of the finishing resins out there, so it doesn’t soak into the wood or foam quite as quickly. It is water-soluble so it’s easier to work with than epoxy. With epoxy I usually have to have a bottle of alcohol, latex gloves and baby powder standing by (that’s right-baby powder). Along with epoxy, Probond is easy to take off of your hands with baby powder and if you just don’t want glue to ever touch your hands, I guess you may want to still use the gloves. But at any rate, it’s easier to wash off. As with epoxy however, you never want to let this stuff spill on your wood building surface. You will never scrap it off or pull it up without pulling up some of your building board.

Everybody who has used it out there has his or her own theory for using it. First of all, the directions on the bottle say to wet the surface before you use it. I have found that this is not necessary. The humidity here in S.C. is usually enough to negate the use of water. I first start with the usual for sheeting wings. A large (depending on the size wing panel) flat clean building surface, wax paper, the glue, masking tape, and whatever form of weight that you want to use. I use several sheets of particleboard leftover from jigs that I built for fuselages.

It is heavy in several sheets and it disperses the weight evenly over the entire wing surface. I usually take some form of sticky backed sandpaper and stick it to one part of my building surface in a long sheet. Great Planes makes great sandpaper for they’re sanding bars. I use this to edge sand the balsa so that all the sheets are even. The best method that I have heard of is to use T-pins to hold all of the sheets together in one stack and then run the stack up and down the sandpaper to make an even edge. After edge sanding (if I have to) I then tape the sheet together using masking tape, with the edges of the sheets butted together.

You then have an option with Probond (and this is probably the neatest part). To glue or not to glue, that is the question! What I mean by this is either you can edge glue the sheets or leave them taped together (believe it or not)! Do all wing skins in this fashion. Lay down the first saddle. You now have an option of putting wax paper down or not. If you do not glue the sheet together, you should probably wax paper the entire saddle. There is a chance of the glue coming out between the sheets. It is a very slim chance and it wouldn’t ruin the panel if it did, but it just adds time to the building when you have to pick or sand foam off of your wing.

Now lay in the first wing skin. You can put glue on the skin before or after you do this. I do it after. I usually start at one corner of the skin and then go back and forth diagonally about 2 inches apart at a 45 deg. Angle all the way lengthwise down the wing. Then I go back in the opposite direction. This creates a waffle pattern on the wing. I then take a squeegee or similar item and smooth out the glue.

Keep in mine that the more weight that you can put on the wing, the less glue you have to use. I have done tests to prove this theory. I then lay the panel onto the wing skin. Put glue on the other skin in the same fashion and lay on top. Put more wax paper on and lay the other saddle on top.

I then place the particleboard on top of the wing. I usually use 4 sheets the same exact size of the panel. I then place everything heavy that I can find in my shop on top of the panel. I even have old plastic soda bottles that I have filled with water to place on top of the particle board. Now, because of the wax paper you can actually move around the panel in the saddle to get it lined up properly (another advantage of fully sheeting the saddle with wax paper). I have only let the panel dry for about 3-5 hours before pulling up and cutting the sheeting, but I usually let it dry overnight.

I have also used this glue for capping the wing off. There is one word of caution however, excess. Don’t put a lot of glue on your caps. I usually put the glue on and then use my finger to squeegee most of the glue back off. If you don’t do this, the glue has a natural tendency to foam-up and may push the caps off of the wing panel to far; creating a wing panel that may not be square on the tip, etc.

Let’s talk about what tests have proven. First, Probond has a tendency to seep down into the foam about &Mac189; inch into the foam. You will not get this with contact cement. Epoxy seeps down into the foam but not as far and is heavier. Spray 77 is easy to use and light but tests have shown that in the sun and on larger planes it has a tendency to delaminate. Obviously because of time-to-work reasons, odorless C.A. is not good for sheeting large surfaces such as wings but may be better for wing tip capping and small areas.

Keep in mind that the object here is to use as little glue as possible and as much weight as possible. Remember that for a 1000 sq. in. wing panel, that 1000 lbs. is only 1 lb. per sq. in.!!!! Remember also that you must put in your phenolic tube support before sheeting your wing! Yep, that’s right I have done it. Not on a customers plane of course. Another tip, have all of your items that you will need ready and be totally prepared before starting your wing sheeting project. There is nothing worse than starting and not realizing that you don’t have enough weight ready or that you don’t have enough glue. I hope that your next project goes well and remember, “We build, You fly!” If you have any questions send us an email.

by: Jim Bronowski

To start with, many idle problems with non-pump equipped engines can often be traced to an improperly positioned fuel tank or a fuel tank that is too far from the engine. The center-line of the fuel tank should never be any higher than the center-line of the fuel jet and preferably 1/4 to 3/8 inches below. This helps decrease the siphoning action with a full tank of fuel.

The make of the glow plug also plays an important role. Any older design, cross-flow scavenged (ported) two-stroke engine should use an idle bar glow plug. Most of the newer Schnuerle ported two-stroke engines do not require an idle bar plug, but if idle problems are experienced, an idle bar plug should be used. If you aren’t sure whether the engine is cross-flow or Schnuerle ported, just look into the exhaust. If there is a baffle on the far side of the piston, the engine is cross-flow ported. If there is no baffle, it is Schnuerle ported. Some engines do have better idle characteristics than others due to differences in porting, timing, compression ratio, etc.

When it comes to the actual adjustment, there are two basic methods. The first is to start with the fuel tank half full and the idle speed set in the 2,500-2,700 rpm range. This is where a good tachometer comes in handy and is something every toolbox should contain, not just for setting idle speed but for proper richening of the top end as well. Then, use the “pinch test” (i.e. pinch the fuel line). If the engine dies immediately, the idle mixture is too lean and needs to be opened in 1/8-inch increments. If the engine speeds up and the idle improves, the mixture is too rich and the adjustment should be turned in or leaned.

If the engine is cowled in and the fuel line to the carburetor is not easily accessible, with a tricycle gear ship, lower the tail. If the engine dies immediately, the mixture is too lean. If the idle improves, the mixture is too rich. Remember to always make any idle mixture adjustments in 1/8-turn increments—not one or two turns at a time.

With a tail-dragger, make the mixture adjustments with the tail raised to a level position, being careful not to go so high as to have the propeller hit the ground. Then, lower the tail following the same procedure as with the tricycle gear model.
For the final check, accelerate the engine to full throttle. If it slows and sags and has a weak sound, the mixture is too lean and needs richening. If the engine sputters and spits out a lot of smoke, the mixture is too rich and should be leaned.

After a satisfactory idle and acceleration have been established, you can try lowering the idle speed to the point where the engine will remain idle for a prolonged period with good acceleration to full throttle. Again, the idle speed should be set with a tachometer and not by ear.

Many cases of an engine dying at idle are simply because of pilots who try to idle the engine too slow. It is nice to watch an engine tick over at 1,800 rpm, but an idle speed in the 2,200-2,500 rpm range is more practical and reliable.
Also remember, the heavier the propeller and the larger the diameter, the better the flywheel action. Increased flywheel action is always beneficial to a slow and reliable idle.

By: Andrew Benjamin

Even though I have plenty of new planes around in various stages of completion, I enjoy acquiring used airplanes whenever I find one I like. It’s the flea market mentality in me I guess. Problem is, many times these planes aren’t completely straight like the Pica P-51 (was) I’m working on that I bought at the local club auction. I didn’t have an opportunity to check the incidences before I bid on it and then I put it away until now.  I just discovered it has a warped wing.

Here’s what I do if I find a warped wing and I thought I’d tell you about it in case you buy one (or build one) that isn’t exactly perfect. The Pica Mustang, like the majority of warbirds are made up of balsa sheeting over ribs and formers. In my case one wing tip was 1 degree positive over the other one. This isn’t a lot and some might ignore it, but I can’t live with any plane that isn’t real close to being perfectly straight. I not only bugs my sense of inner peace, but I don’t like necessary trim changes over the speed envelope.

I have a large dead flat and level work table I work from and I use digital and laser incidence meters mounted on homemade brackets of various sizes. I put the plane on it’s back with the wing secured and shimmed it level. Then I firmly secured the plane so it couldn’t move. I checked to see that the good wing half was at O degrees, the I went over to the warped side and cut an X through the bottom sheeting (built up wing) from the leading edge root to the trailing edge tip and from the trailing edge root to the leading edge tip. I accomplished this with a number eleven exacto blade and I purposely cut into the ribs underneath about a 1/4 inch. NOT THE SPAR THOUGH!

I put the digital incidence meter back up on the warped wing tip and twisted the now pliable wing tip until it read 0 degrees and noted the movement in the “X” for reference. I then flipped the incidence meter upside down on the wing with the brackets near one end so that the long home made aluminum extrusion extended beyond the leading edge about 2.5 feet. I hung a 1/4 full gallon paint bucket on the right place of the aluminum extrusion to leverage the twist out of the wing in the opposite direction a little beyond the 0 degrees I was aiming for and went to bed to let the wing undergo “traction therapy” all night.

This morning I took the warped wing half out of “traction” and it measured a perfect 0 degrees like the other one. I then generously wicked thin CA in the “X” cut lines in the sheeting and now I have a perfectly straight wing that’s just as strong as before. I just need to sand the glue joints a little and no one needs to know the difference (except the world wide web) after it’s finished. This method works on sheeted foam wings also, but one doesn’t need to cut an X . A \ cut in the correct orientation will work to straighten it and be sure to use foam compatible CA in the later case. Of course the best bet is to build the wing straight in the first place. Thought I’d share this old trick in case anyone want’s to loose that asymmetrical aileron trim.

PS. Some say the test of a good builder is not how well he builds the first time but how well he fixes his mistakes! I still prefer to get it right the first time however but I also like to know how to fix mistakes.

by: Gene Davis

Petroleum jelly often has been used on pinned hinges to prevent epoxy glue from sticking to the hinge joint; however, it is difficult to get just the right amount on the hinge and to make sure the hinge is completely coated.

A very cool way is to melt the petroleum jelly in a small dish such as a dessert dish (an oven safe type, of course). Use only enough to melt to a depth of about 1/6 of an inch. Fold the hinge and dip the pinned end into the melted jelly.

Remove and touch the hinge to a paper towel to remove excess. In a couple seconds, the petroleum jelly cools and has penetrated the hinge. You now have a completely coated hinge joint that epoxy will not stick to.