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Post  getback Thu Jun 10, 2021 7:29 am

I don't see why you didn't get more Rs out of the engine or maybe i am thinking 4" props ? Was looking for the weight and looks like ur in the neighborhood one guys say 11 oz. but all are saying lacks on performance other than round and round . https://stunthanger.com/smf/12-a-building/weight-of-hyper-viper-and-cox-chipmunk/ Hopefully it will carry itself for you to get some laps .
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Post  batjac Thu Jun 10, 2021 9:18 pm

Eric, I’d say it’s a combination of 6” prop, non-optimized head, and fit and finish. I’m going to play around with it more.  I don’t have a lot of time at the moment.  We’re re-doing the floors and carpet, so that’s taking most of my free time for a few weeks.

I took the plane to the field today to try it out.  Not an impressive start.  I ran five bladders of fuel yesterday through the engine, and the needle stayed where I set it each time (when it ran).  The needle has the standard spring with the black plastic spray bar seal.  I’ve always had a pretty good track record with these seals, so I just went with it as is, since it did so well on the test runs.  I thought about using the washer/fuel tube method to hold the needle, but since it was no problem, I passed.  Big mistake! At the field, the needle started drifting.  It would rotate back and forth about a quarter of a turn.  Not a big deal on a normal product engine, but when your tuning range from slobbering rich to over-lean is only a little over a half turn, this is devastating.  The engine just kept surging and sagging, and the plane just limped around the circle.  Ah, well.  I’ll take the plane back apart and install the tubing and washer.

I did start the camera and video the flight, but it doesn’t do any good if you forget to take off the lens cap…


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What a friend gave me. - Page 3 Empty Styrene and poly styrene adhesives

Post  jmendoza Sun Sep 26, 2021 1:48 pm

Nice Viper repairs. I have one NIB, never had the time to fly it.

For Cox planes, there are several products available that will chemically weld the polystyrene plastic very effectively. They are not glues in the ordinary sense, like Testors, but are actually very thin solvents that wick into the cracks and joints and melt the plastic, thereby fusing it back together. It is a cold weld process.

The most available is a product called Plastex, which comes in a kit with the Acrylic Monomer solvent, plastic dust ( for filling gaps and reinforcing), and a piece of rubberized molding material that can be heated and softened in hot water and then pressed over the part you want to duplicate and make a mold. The kits come with a variety of the plastic powder: clear, white, and dark grey, which has glass and carbon fibers in it to make it more structural.

For clean breaks and cracks, you can simply clean the part and then apply the solvent, allowing it to wick into the break by capillary action. It helps to tape the pieces together so they will not move. It takes several hours for it to set up, overnight for a full cure. If the break need reinforcement, you can saturate a piece of glass cloth or fiber mesh with a mixture of the desired plastic powder and solvent and apply it to the break after abrading the surfaces for better adhesion.

Another product you can buy from a chemical supply is called Methylene Chloride. It is a solvent for polycarbonate plastics (lexan) ABS ( a styrene ) and polystyrene plastic. Again, it is not a glue, it is a solvent that melts and fuses the two broken pieces back together. So, the joint must be clean and fit as closely together as possible with no gaps.

For missing pieces, or filling holes that are stripped, the Plastex powders are used. The rubber material from Plastex is heated in hot water and pressed over and around a good part to make an impression/ mold of it. After it has cooled the mold is removed and filled with the desired plastic powder and solvent to make a soft paste. Solvent is applied to the edges of the original part that has a missing piece, and then the mold placed over the part that has the missing section and allowed to cure for several hours before removing the mold.

I have a PT-19 that split the fuselage on top from the engine mount to about an inch behind the rear cockpit. It also broke the plastic in front of the cylinder. I used the solvent to repair it, and reinforced the underside of the section in front of the cylinder with glass cloth and the grey fiber plastic powder. It has held for years now and had many more crashes and flights.

BTW, Testors plastic cement does contain acrylic monomer and methylene chloride, but in very small percentages and it is also mixed in with a thickening agent to make it easy to apply to surfaces without running. But, it will not penetrate cracks very well, and has limited ability to penetrate and full dissolve the plastic, so it is not as strong structurally.

Hope That Helps, as back in the old days, we could never find any adhesive that would fix a broken Cox plane effectively.

Jay
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