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Questions about 4 * 40 mods

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Old 06-23-2004, 08:55 AM
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Connery
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Default Questions about 4 * 40 mods

With all the recommendations people have given on here, I went with the 4*40 as my first low wing plane and I have a couple of questions. I like all the mods I've seen so far, expecially what I saw on Tom Pierce's web site. So I'm going to do a balsa cowl, sheet the turtle deck, and the canopy mod. My questions are in regards to the wings and tail surfaces.

1. What are the pros and cons of making the wing shorter by one bay?

2. How much should the rudder and elevators be extended?

3. Should the vertical stab height be increased at all?

4. With the additional surface area of the rudder and elevators, should any aerodynamic counterbalances be built in?

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Old 06-25-2004, 08:10 AM
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Default RE: Questions about 4 * 40 mods

Another question. When you increased the size of the elevators and rudder, did you reduce the size of the stabs to keep the flying surface the same, or just extended the control surfaces?
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Old 06-25-2004, 08:46 AM
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Ed_Moorman
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Default RE: Questions about 4 * 40 mods

Removing 1 rib from each side has little, if any, down side. The plane rolls faster and doesn't float like a trainer on landing. To a person, everyone I have talk to who has done this mod, likes it.

The 4*s tend to have small tails from the get-go. Enlarging the horizontal area has no real adverse effect. It gives you a wider CG placement and left the plane snap and spin better.

The rudder is woefully small. I would say to add an inch to the rudder chord-make it wider. Going too large on vertical area can get you into what is called, "spiral instability." And this will take more than an inch on the rudder. I mean, look at the tails on Sticks.

If you are in a spiral dive, adding up elevator will tend to tighten the spiral, increasing the bank as opposed to raising the nose. You have to roll out first to recover. On a trainer, for example, after you establish a bank and add elevator for a turn, the plane will tend to roll out during the turn. You tend to add a little aileron as you go through the turn to "touch up" the bank. A plane that has spiral instability will tend to increase the bank during the turn instead of rolling out. It isn't violent or anything and I have had it on a couple of my planes while experimenting with rudder area. On a plane with spiral instability, you tend to touch up the bank in the other direction. You may have had this condition before and not known what it was.
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