702 Kit Bash / Twin Arrow

[sandman]

I was inspired to bash the Arrow kit 702 when I ran across these plans for Twinster on Outerzone. I chopped 2" off the tail and will go from 28" to 30" wing span. The booms will be on a 9" centerline and I have some counter rotating 6.5" props off a long forgotten Wright flyer.

Question: Should I build the stabilizer flat or use the ribs and make it lift?

[Bill Gaylord]

Neat subject. The undercambered horizontal stabilizer section is probably intended as a "lifting stab", allowing for a further aft CG. My guess is the designer is trying to avoid adding excessive nose ballast, along with other possible reasons for the design.

[davidchoate]

I was recently asking a similar question, but mine was "does an aifoil tail get added as wing area". Then I found out that certain competition rules have limits on wing area, and also I made aware of how it can be used to "lighten the tail" So to speak. I don't know Sandman. Definitely something to consider. It is a mighty big Stabilizer. I think I would stick with the airfoil lifting tail. I was not pleased with My Arrows. I built several trying different tweaks on each one, and I can not say It did not Fly good, but considering it is not a scale model, and purposely designed for long Rubber FF, It did not Fly any longer than the Scale FF planes I have made. I think it has a too short Wing Chord, and I am no expert in FF what soever, but I did 1 with the undercamber wing, and it was an improvement. The Guillows in a bag. That one We used to buy as kids with the solid balsa wong on a stick is a good example. Those things Fly better than any Kit They have, and its got that under camber Wing. I do not know the physics of it, but airfoils are going to become an area of flight I am ready to start learning about.

[sandman]

Thanks for the suggestions gentlemen. Both plans have a lifting stabilizer and although it would be easier to start with a flat I think I will go with the original design intent and make the stabilizer lift. I made some blueprints at work for the modified wing and stabilizer. The two fuselages are almost done except for the prop stops and landing gear which I will be adding after I set the wing and stab. The fuselages weigh 6.5 grams each. This plane will be FF and I plan on sliding pins into coffee straws glued to the nose to hold the props till im ready to launch ROG. More next week!

[David Lewis]

A lifting stabilizer means the CG is pretty far back and there's no decalage (zero-zero setup). You can use either a flat plate or flat bottom stabilizer airfoil. The stabilizer angle of attack is low enough that I don't think you'll see much difference in performance.

[sandman]

Thanks for the info Mr. Lewis but im a little worried now. I have my lifting stabilizer done but it wont be adjustable and I built in some negative incidence of a degree or two based on past experience. I also shortened the fuselage by two inches and with those beefy twin props up front I might be nose heavy. Hopefully I can come in at under 60 grams and this thing will be a real floater. I like the way my prop stops turned out and hope they work as good as they look.