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Author Topic: Static Roll Moment in Indoor Electric Flight  (Read 1333 times)

Offline Matt Piatkowski

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Static Roll Moment in Indoor Electric Flight
« on: January 07, 2018, 04:27:19 PM »
Hello,
The attachments show my indoor stunt model called Wasp. It is built using 3 mm. Depron Aero and weights RTF 235 grams.
Wasp has the wing area 10% larger than typical indoor bees weighting 210-220 grams therefore the wing loading is approximately the same.
 
Wasp flies the entire pattern quite well but the outside wing tip is a bit down in level flight w/r to the horizontal plane.
I suspected the wing warp but usual method (outside wing tab deflected down 3, 5 and finally 10 degrees) did not work.

Then, I have changed the propeller from CCW to CW and the outside wing tip... stayed a bit down like before, ignoring the fact that the motor torque acting on the model charged the sign.

I temporarily gave up and kept flying as this "bit down" was really minimal.

It was only recently that I looked at the model from the front and saw the reason for this behavior.

There exists a constant static roll moment in level flight generated by the way in which the bellcrank, leadouts and the battery are installed.

Specifically, the bellcrank is 1/4" below the wing, the leadouts exit is 0.05" below it and the 2S 800 mAh battery CG is 0.30" above the wing.

When the model flies level, the moment of the centrifugal force acting on battery w/r to the model CG has the same sign as the moment of the lines tension and this causes the roll until both forces act along the line through the model CG.

I am considering moving the bellcrank and the leadouts exit to the top of the wing to eliminate the roll moment.
 
Happy Flying from the MP Stunt Academy in Toronto.
M
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Offline Crist Rigotti

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Re: Static Roll Moment in Indoor Electric Flight
« Reply #1 on: January 07, 2018, 06:48:20 PM »
I think what your seeing is a vertical CG problem.  Bellcrank location isn't the problem.  It's where the lead outs exit the wing.  Do a search for more details.
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Offline pmackenzie

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Re: Static Roll Moment in Indoor Electric Flight
« Reply #2 on: January 07, 2018, 09:55:47 PM »
Quote from: Matt Piatkowski on January 07, 2018, 04:27:19 PM

I am considering moving the bellcrank and the leadouts exit to the top of the wing to eliminate the roll moment.
 


Why not move the battery to the bottom of the wing?

Pat
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Offline Matt Piatkowski

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Re: Static Roll Moment in Indoor Electric Flight
« Reply #3 on: January 08, 2018, 05:16:51 AM »
Hi Crist,
Yes. It is the vertical CG problem.
As long as the b-crank is relatively close (and it is) to the wing, it's location is indeed secondary considering the free body forces and moments diagram.   

Hi Pat,
I have considered moving the battery below the wing and it would be my first choice but there is a supporting structure there.
Because I have increased the wings area when compared to the R/C ARF I bought, both wings were twisting in flight and I had to stiffen them torsionally, using the elaborate combination of Depron and carbon composite rods. In addition, the Wasp's wings are trapezoidal and the lines tension, even so small as it is, was causing the leadouts exit point to go down about 0.2". At the same time, the outside wing was twisting the other way with the tip aft corner going up 1/8".

Original indoor bees have elliptical wings that are less prone to twisting due to smaller surface area and better support from the wheels Depron pants and the connecting Depron pieces that create the frame surrounding the wings.

Another choice is to leave the battery and the b-crank where they are and move the leadouts exit point about 0.1-0.15" above the inner wing tip. This is technically possible and I will think about it.

Thanks,
M
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Offline Igor Burger

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Re: Static Roll Moment in Indoor Electric Flight
« Reply #4 on: January 08, 2018, 05:33:05 AM »
That battery on wing must kill 1/4 of outer wing lift. Put it to fuselage and you can vertically adust CG position.
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Offline Matt Piatkowski

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Re: Static Roll Moment in Indoor Electric Flight
« Reply #5 on: January 08, 2018, 06:44:20 AM »
Hi Igor,
The battery is sitting in the heavily turbulent zone of the flat wing producing the lift only by the angle of attack so there is no way to quantify this effect. The drag is increased for sure what, by the way, is quite convenient because Wasp does not have the purposely built air brakes like your indoor bees. It does have, though, so many Depron and carbon composite stiffeners that they act like air brakes, giving me at this moment 4.9 sec. lap times with still enough tension to fly five consecutive, narrowing cones between 45 and 20 deg. from the vertical.

The battery was installed on the outside horizontal fuselage part close to the model X-Z plane but the model needed 12 grams of the tip weight. I have moved the battery outside and removed the tip weight. The overall pattern performance is, in my humble opinion, good except the top two corners of the hourglass. I do not have your active timer installed in this model and it is loosing the maneuverability when forced to make the hourglass corner #3 the way it suppose to be. Keith Renecle's timer I am using has the gain parameter set to 5 but I do not see nor feel any difference in the model dynamics when I set it to 1. Perhaps when my "pattern feel" improves, I will feel this difference.

Thanks,
M

 
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Offline Igor Burger

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Re: Static Roll Moment in Indoor Electric Flight
« Reply #6 on: January 08, 2018, 07:22:28 AM »
The problem is, that the battery is there asymmetric, only on upper surface, it can cause exactly what you described.
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Offline Matt Piatkowski

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Re: Static Roll Moment in Indoor Electric Flight
« Reply #7 on: January 20, 2018, 08:46:58 AM »
Hello Everybody,
Please see the attached.
The vertical CG problem has been fixed by using 1/4 oz. outside wing tip weight mounted as shown.
The offset of this 1/4 oz. from the wing center plane is 2", therefore this 1/4 oz. has the roll moment equal to the battery roll moment but its sign is opposite. These moments cancel each other and the wing stays now in the horizontal plane while flying level and inverted.

The addition of 1/4 oz. as shown improved also the hourglass and the outside loops.

Greetings from MP Stunt Academy in Toronto,
M

 
 
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