Nose heavy or tail heavy - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 04-22-2015, 10:08 AM   #11
Eye Can Fly
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Re: Nose heavy or tail heavy


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Last tail heavy one I flew reminded me that the "Throttle" can be used as another control surface. Like mentioned before, set up the plane as per the instructions, get it up to a safe altitude and see how it flies. If it displays (some experience really helps here) tail heavy you have to find the throttle position where it flies like a plane.

I wouldn't wish a tail heavy flight on anyone, no matter if it is a foamy or a giant scale. Tail heavy is hard on the pocket book, and harder on the confidence.
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Old 04-22-2015, 11:14 AM   #12
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Re: Nose heavy or tail heavy

Quote:
Originally Posted by kip51035 View Post
The centre of gravity should be between 23% and 33% of the "Mean Average Cord". That is any aircraft except a canard style aircraft.
Sorry for my ignorance but what exactly does this mean?
I have a cheapo Cessna 55" wingspan foamy that does not have the center of gravity in the instructions and can't find any information as to the correct C of G anywhere.
So what would be a good starting point?
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Old 04-22-2015, 11:54 AM   #13
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Re: Nose heavy or tail heavy

On a constant cord wing (no taper) measure the width of the wing, leading edge to trailing edge. This distance will be your cord. Then figure out what 25% would be from the leading edge. This will be your starting point for the CG. Another good rule of thumb, though not always, is that the CG will be on the main spar. Like the guys say check your instructions.

Example 24" chord 25% would be 6". so you CG will be 6" from the leading edge.


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Old 04-22-2015, 12:13 PM   #14
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Re: Nose heavy or tail heavy

Here is the simple aircraft center of gravity calculator.

Or the full aircraft C.G. calculator.
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Old 04-22-2015, 01:07 PM   #15
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Re: Nose heavy or tail heavy

Excellent link! Thanks!

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Old 04-27-2015, 09:21 AM   #16
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Re: Nose heavy or tail heavy

Quote:
Originally Posted by horwood View Post
In flight, how does a slightly heavy nose plane fly compare to a slightly tail heavy plane? Hopefully it is not too badly balance that you can bring it down and do some adjustments!
Horwood
What kind of airplane is it?

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Old 04-10-2016, 01:25 PM   #17
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Re: Nose heavy or tail heavy

THere is a say, a nose heavy plane fly badly a tail heavy plane fly worst...
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Old 04-10-2016, 01:51 PM   #18
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Re: Nose heavy or tail heavy

Once!
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Old 07-08-2016, 04:35 PM   #19
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Re: Nose heavy or tail heavy

Welcome to the hobby

Last edited by jsparky; 07-09-2016 at 04:58 AM.
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Old 07-08-2016, 11:46 PM   #20
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Re: Nose heavy or tail heavy

Wing and tail airfols, incidence angles, etc. do *not* influence the CG location.

The CG must be ahead of the aircraft neutral point in order for the airplane to be pitch stable. The aircraft neutral point is determined by the wing planform, the stab planform, the distance between the 1/4c of the wing and stab, and the effect of the wing wake on the airflow velocity at the stab (usually a small factor). Airfoils and incidence angles do not affect the CG location.

Quote:
Originally Posted by kip51035 View Post
The centre of gravity should be between 23% and 33% of the "Mean Average Cord". That is any aircraft except a canard style aircraft.
This is just wrong. Most free flight gliders fly just fine all by themselves with the CG at 55% to 90% of the wing chord. And it is not because they have a cambered airfoil on the stab. A cambered stab will have lower drag if the aircraft configuration requires the stab to lift upward all the time. They would fly the same with a symmetrical stab airfoil, or even an inverted cambered stab, but the drag would be slightly higher. If a free flight glider is stable and flies fine with the CG at 90% of the wing chord, shouldn't an RC airplane of the same layout also be pitch stable?

http://www.johnanthonymodeldesign.co.../timeline3.pdf

Most RC sailplanes are flown with CGs well aft of the supposed "magic" 33%. They have long tail arms that move the aircraft neutral point back, and therefore for the desired static stability margin the CG will be well aft as well. And the stab on an RC sailplane typically lifts slightly up or down in different flight regimes.

This is the best CG calculator I know of (short of running AVL), and will handle almost any aircraft configuration. It will also allow you to move all the equipment weights around to forecast where the actual CG will be even before you build the airplane. I find it very useful, but it does take some time to understand:

www.rcgroups.com/forums/showthread.php?t=1106300

An airplane with a large static margin (15% or larger, CG well forward of the aircraft neutral point), will be less responsive to the elevator, may run out of up elevator control for landing. Moving the CG back requires decreasing the elevator throw, since the elevator will become more powerful. An airplane with the CG at the neutral point may diverge up or down when disturbed, and will have no tendency to return to a trim speed. Most discus launch gliders are flown neutrally stable. A decent RC pilot can usually fly an airplane with decent pitch damping, like a sailplane, with the CG behind the neutral point.

The best test is to roll the airplane inverted, and see how much down stick is required to hold the flight path straight. A neutrally stable airplane will not require any down elevator input. A nose heavy airplane will require a lot of down stick. Aerobatic airplanes are usually tested on a 45 degree up-line.

A dive test also works, but is harder to interpret. Basically trim for a nice glide, and pitch the nose down. Release the elevator stick and observe how long it takes for the airplane to pitch up. If it pitches up quickly, it is very stable (forward CG). If it just continues along the line, it is neutrally stable (CG near the aircraft neutral point). From Dr. Mark Drela, famous MIT aero prof:

http://www.charlesriverrc.org/articl...GMarkDrela.htm

Kevin
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