RCU Forums - View Single Post - Top Flite B-25 ARF (Tecnical, tips, suggestions)
Old 10-15-2007, 05:18 PM
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Default RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)

Here is my second post in this thread about the Top Flite B-25 ARF. It contains suggestions on how to prepare the MonoKote covering on your new ARF when it comes out of the box. All of these techniques were developed using Top Flite MonoKote, but may also apply to other brands of covering as well. (Be careful--some types/brands of covering require less heat.) For the most part, the covering job on todays ARFs is fantastic and better than most modelers could do, but the bottom line is this; you should probably expect to do a little preparation work to the covering on an ARF--I feel this is part of the trade off you accept when purchasing a model that has been mass-produced. With the B-25 for example, you should expect to spend one to two hours using the following techniques to go over the covering to bring it up to perfection. You will be rewarded with a model that will look good and should stay looking good as long as you own it. Occasionally, it may be necessary to bring it back into the work shop for touch-up, but the better the job you do now and the more time you take up front, the less that will have to be done later;

How to tighten MonoKote covering on ARF models:

Tightening the covering over control surfaces that have ribs and open structure (such as elevators and ailerons) requires different techniques than tightening covering over sheeted areas. For this process it will be helpful to have two covering irons—one with a protective covering sock, and another without a covering sock. Both irons should be set to approximately 320 – 350-degrees F.

For this example an elevator from a Top Flite B-25 ARF will be used. But the same techniques apply to any control surface that has ribs.

Photo 1. Use a tissue dampened with naptha (lighter fluid) to clean off any adhesive left from masking tape that may have been used to hold the parts together during shipping. This will not hurt the MonoKote and easily wipes the glue away.

Photo 2. When tightening covering on a control surface that has open structure with ribs, the covering must first be SECURELY bonded to the trailing edge and tips. Otherwise, when tightening the rest of the covering on the top and bottom, it may pull away. First, use the iron with a covering sock to bond the covering to the trailing edge. Press hard and make sure the covering is thoroughly attached.

Photo 3. The next thing is to make vent holes in the bottom of the covering which will allow heated, expanding air to escape. Otherwise, during the shrinking process, the air inside will expand, thus stretching the covering—exactly the opposite of what you are trying to achieve! Use a pin to poke small holes in the covering between each rib. (For future reference, the next time you are building a kit, a small (1/16” – 1/8”) brass tube sharpened on the end can be used to cut vent holes in each rib and another vent hole cut in the tip or root end to allow air to escape.)

Photo 4. After the covering has been bonded to the trailing edge and tips and the vent holes have been punched, the covering may be tightened. A covering iron with a protective covering sock is preferred, but sometimes does not transfer enough heat. If unable to remove all the wrinkles, use a covering iron without a covering sock. (Here, a Top Flite iron is set to about “2-1/2”.) Use care NOT to let the iron contact the trailing edge—otherwise, the covering may loosen and pull away. Once the covering has been tightened with the bare iron, go back over it again with the other iron that has the sock. Press down to bond the covering to the ribs and any other structure underneath.

Tightening covering over sheeted areas requires a different technique…

Photo 5.
The covering must be securely tightened and bonded to the sheeting. Use the iron with the covering sock. First, without applying pressure, glide the iron over the wrinkle. Once the wrinkle disappears, go over the spot again this time applying pressure to bond the covering to the sheeting. If a bubble forms, allow the area to cool for a few seconds and go over the spot again this time pressing down harder and moving the iron faster so less heat is transferred. In some cases vent holes must be punctured in the covering over the bubble. Use a sharp, new #11 blade to poke vent holes, then go over the area again with the iron.

In some cases, where the sheeting is thin or soft and over unsupported areas (such as between wing ribs or between stringers and bulkheads), the sheeting will bend inward when pressing down on the iron. This stretches the covering as the sheeting bows inward—again, exactly the opposite of what is trying to be achieved. In these areas, glide the iron over the covering using little or no pressure. If you still cannot get the wrinkles to disappear, use an iron without a protective sock set to higher heat. This will shrink the covering and remove the wrinkle. Then go back over the area with your iron with a covering sock applying little or no pressure to bond the tightened (but “floating”) covering to the sheeting.

Photo 6. Where necessary (and possible), reach inside the model and push outward on the sheeting allowing you to press hard on the iron and bond the covering to the wood.
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