"I don't know about your atmospheric conditions or altitude, but I will say that the three of us that fly them together here have had only minor problems. The stock plane flies well, with good line tension throughout the flight hemisphere. We are using the stock engines running Byron 1/2a fuel (25% Nitro, 20% all castor, 55%methanol) and using the supplied Cox prop, although we all have several of the Cox recommended APC props to try. The three of us are all using the supplied dacron lines and handles, as well, but all of us have 35'x .008" cables that we'll be using soon, as the dacron is becoming oil soaked and sticky. The only modifications (?) we've made are:

1. Add a Nickel (5¢) to the weight hole on the bottom of the outboard wing for a bit more tip weight and cover the hole with a piece of 2" wide clear tape.

2. Install the leadouts one hole to the rear of the position suggested in the plans.

The other problems we have had are:

1. Two of the three fuel tanks were improperly joined to the point that air would not exit the tank when blowing into the fuel outlet. Cox/Estes replaced the tanks with no problem. We were not the first to have this problem, and we checked the tanks before assembling the planes.

2. One plane lost its canopy on every flight until the owner taped the front to the fuselage. We're going to find some "Goop" to fix that problem permanently.

We decided, contrary to the stereotypical male image, to read and follow the directions that came in the box. The only reason we installed the leadouts/lines about 1/16" to the rear of the position indicated in the directions was that one of us already had a HyperViper and had flown it at his winter home in Reno (at a much higher elevation than here) with good results. He found that variance to be worthwhile while flying there. He also discovered the advisability of that Nickel more tip weight at that time.

We also broke the engines in a bit, again following the break-in instructions with the plane, by running three tanks on the ground, leaning the mixture on all three runs until the engine would hold a strong, high RPM. None of us are engine gurus or designers, but this process works!! The engines have continued to gain power with additional runs while flying.

On none of the flights I've watched or flown have I seen any of the problems you and other folks have described. We are not expert level fliers, but we do know a fairly decent airplane when we see or fly one. While I'm certain that the mods done by Larry and others will provide better performance, the plane does pretty well stock.

Did you read Larry Renger's review? It's the first post in this thread. In it, he wrote, "...Don't even dream of trying to fly with .012 lines, unless you just want to climb, dive, and fly level I also found that I needed extra tip weight (everyone seems to be finding the same), and it has now been added....." This might be your biggest problem so far. Has your engine been properly broken in?

I admire the excellent TD .049 installation shown here as well, but I'm not convinced that it is needed. As far as replacing tail feathers and sealing the bottom of the fuselage with balsa, I would ask, "Why?" If one is going to all that trouble, why not go all the way and throw away everything but that foam wing and possibly the landing gear and build the rest of the plane from appropriately sized balsa. That's what I would do if I wanted the ultimate in performance from that wing.

Finally, as I wrote previously, I'm not an expert flyer who would be able to obtain the performance you might be seeking, but for my money ($40.00 at the LHS) the HyperViper is a good machine as it comes from the factory. I have 1/2a planes that I've built that fly much better, as they are larger and much lighter, but when I consider the cost of balsa, finishing materials, tank, engine, wheels and all the other bits required, to say nothing of my time (if I considered it as a cost), those probably cost at least double, if not considerably more, the price of the HyperViper."