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Author Topic: data on power competition planes  (Read 537 times)
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phil alvirez
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« on: May 17, 2016, 09:27:05 AM »

am trying to learn what you guys know about competition free flight power planes, what links to those, plans, 3 views, whatever, that can provide some light to the subject.
particularly to planes with lifting stab. thanks.
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glidermaster
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« Reply #1 on: May 17, 2016, 11:33:13 AM »

Nearly all competition free flight power models have lifting stabs, even those (few) that have symmetrical airfoil stabs.

There are a few drawings on www.faipower.com

What is the nature/reason for your interest, Phil?
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phil alvirez
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« Reply #2 on: May 17, 2016, 12:18:04 PM »

thanks for replying to my message. my interest is in learning if there is data as asked because am beginning to experiment with lifting stabs for sailplanes with e-motor.
i flew free flight including power and all the planes i had-and so all the others-had lifting stab. and the reason is that as the plane climbs under power and the speed increases dramatically, so lift on wing and stab, and the stab compensates for that extra speed. but now all the r/c planes i see have non-lifting stab.
now, about lifting stabs, of course any symmetrical airfoil generates lift when placed at an angle different from zero. but am not talking about stabs that are symmetrical, be airfoiled or flat plates. i mean those that typically have a flat bottom and curved upper surface, like most trainers.
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danberry
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« Reply #3 on: May 17, 2016, 09:05:29 PM »

Lifting stab sections are there to help control power.
FF (term used loosely when referring to auto-surface FF planes which are really remote=controlled planes) often do not use the lifting stab because they can control the plane with a timer or processor.
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phil alvirez
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« Reply #4 on: May 18, 2016, 03:20:10 AM »

i mean, free flight that does not have any device attached that controls or changes the angle of attack of the horizontal tail. be the whole surface or just the elevator. those.
i would like to see if someone can provide data or links that provide 3 views, or plans, that show the designs, and if possible, some of the most recent (that dont have remote controlled elevator or full stabilizer). my interest is on how the design has evolved to actual times. i hope someone here can help me with this.
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phil alvirez
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« Reply #5 on: May 18, 2016, 03:26:39 AM »

thanks. and about this that you said:      Lifting stab sections are there to help control power.
 i guess you mean that when the motor runs at full power and the plane increases its speed, lift increases not only at the wing but at the stab (when it has a lifting airfoil) and compensates or balances the increase of lift of the wing. right?         
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Tapio Linkosalo
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« Reply #6 on: May 18, 2016, 06:40:09 AM »


Most of all, lifting stabs are there to provide dynamic stability.

Full-sized aircraft have the Center of Gravity (CG) quite far forward, and have the tailplane push down to compensate for the nose-down moment of the forward CG. This is probably the most efficient setup, as a rather small tailplane suffices to provide the required static stability. However, such a setup is not dynamically stable: the correction that the tail provides when the plane encounters disturbance it too big compared to the damping effect of the tail, thus the plane over-corrects and enters oscillation. This is easily stopped by the pilot. In a free flight model, however, there is no pilot, so such oscillation would lead to stalling to the ground.

Thus for a free flight model, more dynamic stability is needed. This is provided by a larger tailplane, which resists the plane pitching nose up or down, and dampens the oscillation. Part of the scheme is that the correcting force is also reduced by moving the CG back thus reducing static margin. Consequently you end up with the setup of a Free Flight model: relatively large tailplane, small incidence, thus lifting tailplane.

RC models are somewhere inbetween. They still need some more stability than full-sized, as controls inputs are provided by visually observing the plane attitude, not by the "feel of your pants". To my understanding, typical RC gliders sport roughly non-lifting tailplanes.
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phil alvirez
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« Reply #7 on: May 18, 2016, 08:30:39 AM »

thank you sir. well explained in detail. but 1 thing is that larger stab helps stability just because is larger (hence the name stabilizer), and the other is that a true lifting stabilizer generates lift with the use of a lifting airfoil that has flat under surface and curved upper surface. with this configuration, many high performance airplanes designed for high power (motor or rubber)  or sailplanes with a motor, when climbing at high power increase their speed and both surfaces increase their lift. as the cg moves back, the wing lift (that pulls up, but is located relatively near the cg,) is compensated by the lift of the stabilizer, that is located further to the cg but is smaller than the wing, also increases with the speed, and as is located at the other end of the cg, neutralizes the wing increase.
visualize it: wing: vertical arrow pointing up at left at short distance of cg (now moved back from the aerodynamic center); stab: vertical arrow pointing up at right at long distance from the cg. these distances are the moments of the centers of lift of each airfoil. see an example:      https://www.google.ca/search?q=civy+boy+model+airplane&hl=en&biw=1280&bih=615&site=webhp&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjB9bf95d3MAhWjyoMKHflID-sQsAQILw
regards           
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