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Author Topic: Paul Walkers Impact at the the Nats  (Read 7586 times)

Offline Dennis Toth

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Re: Paul Walkers Impact at the the Nats
« Reply #50 on: July 28, 2011, 02:47:52 PM »
John,
The electrics seem to be able to accept the additional control input needed to complete the corner and recover smoothly compared to the IC's. By holding speed through the maneuver there is extra pulling power to overcome the additional drag of the increased control surface deflection with the forward CG location. Even with the modern larger tails over 25% of the wing area the forward CG give you that little extra help out the bottom to avoid the bounce.

It is worth giving it a try on your own ship, one thing I would recommend is when you move it bring it up to at least the 15% MAC point. I had been balanced at 23% and moving my CG only 1/8" to 1/4" and it was not that noticeable but moving it 3/4" (14% MAC) made a difference. To get the full benefit you also need to adjust the leadouts forward to maintain position relative to the CG.

Best,             DennisT
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Offline Dean Pappas

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Re: Paul Walkers Impact at the the Nats
« Reply #51 on: July 28, 2011, 03:28:38 PM »
Hi All,
John, if anything, the moments of inertia are less for an E-ship with the same CG position.
In a fully fueled wet setup, more than 2/3 of the powerplant mass is in the engine bay, while for an E-ship only 1/3 is at the very nose.

The observation that we should run more noseheavy became evident in the first conversion of Bob Hunt's Genesis Extreme.

Regards,
  Dean
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Offline John Witt

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Re: Paul Walkers Impact at the the Nats
« Reply #52 on: July 29, 2011, 12:43:13 PM »
Just as another thought to throw into the mix.  If you look at the dynamics of helicopter rotors (complicated), perhaps there are some clues for what is needed for stunt props.  One of the things that occurs to me is that for a control input (analogus to turning the stunt plane) there is a 90 degree phase lag in the control reaction of the rotor, if the rotor is freely hinged at the hub. This phase lag becomes smaller as the hub stiffness is increased, to about 65 degrees (as I remember) for a "rigid" hub.

As we go to larger diameter and more or less flexible props, wouldn't this same set of dynamics occur, to a different degree.  I guess that this is the source of some of what is attributed to P effect, which is normally thought of as just a gyroscopic precession.  Perhaps I am calling the same thing by two different names here, not sure, but I think the helo guys have shown it to be different than pure gyro precession.  It means an opposite hand roll and yaw depending on which way the nose rotates, but how much?

John
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Offline RC Storick

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Re: Paul Walkers Impact at the the Nats
« Reply #53 on: July 30, 2011, 12:17:26 AM »
Full circle. Ron was over tonight while I was installing my ELE set up. We discussed Paul's next set up. He said smaller motor (lighter) and a slightly longer nose so the plane will balance. Would it not make more sense to make the tail shorter? (lighter) I guess we are headed back to where we have always belonged. Lighter (less concentrated wight) is always better!

Flame away but you'll figure it out sooner or later  f~

Oh and by the way the CG has not changed. You just never balanced your plane with the tank full.
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AMA 12366

Offline Air Ministry .

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Re: Paul Walkers Impact at the the Nats
« Reply #54 on: July 30, 2011, 04:13:57 AM »
Was talking to a aero enginner about ' a ' prop ' , he was saying it wouldnt work.
As we walked out his door he got a face full of the end of a chopper blade, almost
End On . Funny , it was identical , and it was his helicoptor.
allways take anything with a grain of salt .
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Offline Dennis Toth

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Re: Paul Walkers Impact at the the Nats
« Reply #55 on: July 31, 2011, 07:16:52 AM »
Robert,
Your point on the fuel tank CG is something that most fliers don't check, I agree it will move the CG forward but for the equivalent size ship our battery weight is about double the fuel load of an IC set up. The IC will also have a constantly changing CG. If you have an IC with a 46 you use about 5 oz of fuel our batter is a 3900 mah @ 12oz, but our motor is 6oz so we have the higher weight components closer to the CG. The 5oz fuel load would move the CG about half as much so it goes from say 25% dry to 20% full. BH/PW are at 12-14% all the time. I tried this on my electric profile, I moved it from 23% to 15% (I could only move the battery 3/4" forward in the mount) and felt the difference on the first flight. This goes back to the barbell analogy (see Olympic article). Point being it did flatten the bottoms and improve the wind penetration with no big change in control input. Seems this works.

Best,         DennisT
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