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Old Jan 19, 2013, 04:10 PM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
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Quote:
Originally Posted by eflightray View Post
Are you saying that an airplane with a symmetrical airfoil would always pitch up with increased throttle ?, not matter how it is set up ?

That it will react the same as a positive cambered wing with increased throttle ?

Perhaps I have just always got it wrong, that the reason for using a symmetrical section as used by pylon racers, aerobatic model etc, was that they don't noticeably change pitch with throttle.
I wasn't saying anything. I was asking a question. But since you brought it up, yes, a zero camber symmetrical wing will pitch up with increased throttle just like a cambered airfoil. That is with the caveat that the airplane has positive longitudinal stability. If it has neutral longitudinal stability then it will not pitch up with increased throttle. But then, neither will a cambered airfoil with neutral longitudinal stability.

As far as using symmetrical wings on aerobatic models and pylon racers is concerned, aerobatic models use them so they fly basically the same inverted as they do upright. Aerobatic models are also usually set up with neutral longitudinal stability so the pitch angle doesn't change with throttle change. Pylon racers would use thin symmetrical airfoils to reduce drag. A symmetrical airfoil has the best lift to drag ratio. Pitching up with increased throttle is eliminated on pylon racers basically by setting up the relative angle between the wing and the horizontal stabilizer, sometimes called decalage but more properly known as longitudinal dihedral, so that the plane flies level at full throttle. In that case it would tend to pitch down strongly with decreased throttle.

Larry
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Last edited by Lnagel; Jan 19, 2013 at 04:19 PM.
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Old Jan 19, 2013, 06:45 PM
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Australia, ACT, Kambah
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Last edited by scirocco; Jan 19, 2013 at 06:53 PM. Reason: fat fingers
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Old Jan 19, 2013, 06:50 PM
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Australia, ACT, Kambah
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Quote:
Originally Posted by Lnagel View Post
Are you saying then that an airplane that has a wing with a symetrical airfoil would not pitch up with increased throttle?

Larry
No. The wing's pitching moment will not change, but if the tail is carrying a down load eg trimmed for show flight or a fwd CG, or the thrust line is below the wing etc the acft will pitch up if not retrimmed. That's not to say that a well set up model can't exhibit minimal pitch change with power and speed, they clearly can! But just as clearly the Op's model is not set up that way.
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Old Jan 19, 2013, 06:54 PM
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I agree with Larry 100%. Good explanation!.
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Old Jan 19, 2013, 11:51 PM
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Australia, WA, Perth
Joined Aug 2012
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Quote:
Originally Posted by rcmaverick View Post
Hmm no..

I can leave the elevator alone at about 50% throttle - the plane flies level - If I now want to speed it up to 80% - 90% it starts going vertical.

Perhaps I need to trim the elevator for a higher throttle position.
i only usally notice this when i have a heavy cambered wing, i guess you should trim in elevator. not really any other way to fix it
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Old Jan 20, 2013, 03:50 AM
Grumpy old git.. Who me?
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+2 on what Larry just posted, exactly what I've been trying to say all along but maybe Larry said it better.
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