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Building Tips and technical articles. => Building techniques => Topic started by: Will Moore on October 30, 2006, 09:26:43 PM
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My next project will be a size 60 stunt ship, built for electric . Would there be any advantages
in building the motor's thrust line to go through the center of the wing and stab - set up
0 - 0 - 0. I've noticed most all ships with thrust lines going above the wing and below the stab.
Why is that - so the inverted engine would not expose the head of the cylinder so much ?
Was it for prop clearance ? Was it for appearance sake ? What if everything were in line ? What are the advantages and disadvantages aerodynamically ?
Thanks, Will Moore
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There have been quite a few stunt ships designed that are "Inline". It seems to be a personal preference and some top level flyers have reported trimming problems, while others love it. I know Billy Werwage dwesigned a smaller Junar that is all 0-0-0. I built one and it flew really nice with equal inside-outside turn rates.
Bill <><
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Will,
Others may go into more detail, but for starters:
Wings create downwash when they create lift. The flow off the TE aims 'down' compared to the direction of lift aiming 'up.'
Theoretically, then, a 0-0-0 layout has the downwash miss the horizontal tail. But, consider: stunters have enormous lifting capacity for their weight, so in level flight, straight tracks, and even round figures, the downwash does not make an extreme angle coming off the TE, and it smooths back as it moves aft of the wing TE...
Also, the 'masses' (weights considered in view of their momentum/inertia) of wing, fuselage and tail being in line, there should be a more equal ability to turn both ways. However, with thrust line on wing and tail chordline, only a sidewinder engine mount, and no landing gear - or retracts - keeps those masses "centered" in that sense.
The "normal" layout: inverted engine, thrustline above wing chordline and below stab/elev chordline, works well. Personal opinion - 0-0-0 full stunters look a bit odd, IMO not as attractive as we can do with the "normal" layout. 0-0-0 looks sort of scrunched up, like a guy ducking his head into his shoulders... IMO.
0-0-0 fuselages may create some interesting complications for engine and tank installation, control linkage routing, and landing gear.
The "normal" layout allows a shorter landing gear, usually, which looks better inverted than a pair of stilts reaching upwards...
With the longer control horns we use these days, there may be problems keeping them indoors at the back end with 0-0-0. Also, raising the wing chordline can make the slope of the pushrod from flap to elevator much more severe. That DOES have an effect on neutral and rate of angle change at the elev. A 'cobra' type flap-to-elev horn becomes more crucial.
NEXT?
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You got all the high points Lou. Slightly raised thrustline, slighty lowered wing, slightly raised stab gives just about the best balance possible for all the variables involved.
You'll notice too that all the RC pattern guys use the same setup. Apparently it gives the least variation in aero forces over all the regimes the plane flys in. Since CL stunters hit just about every combination of sideslip, yaw, and wind angle possible on every lap, we want a setup that minimizes those reactions.
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Guys, thanks for the info - I greatly appreciate it
Will Moore
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Roughly half of a judged PA flight is inverted, so I never can understand arguments which seem to pertain to the plane flying upright.