John, that is so Flite Streaky.  You should receive a letter of censure from the Brotherhood of the Ring.

I go through Bloomington twice a year or so.  We should visit and fly a little electric stunt. 

Robert, you have said this many times, but I sincerely don't understand it.   What do you mean by concentrated weight?  I take it that you consider the battery concentrated weight, but do you consider the motor concentrated weight?  When you say "weight added to balance" above, do you mean weight in the tail?  If so, I think conventional science agrees with you; the misunderstanding is perhaps in how the problem is stated.

Something interesting came up when I recently talked to Robert.  He suggested distributing the battery weight.  What if you distributed it out the wings?  One example would be on a twin.  Should you have one battery in the middle or one at each motor? 

Something interesting came up when I recently talked to Robert. He suggested distributing the battery weight. What if you distributed it out the wings? One example would be on a twin. Should you have one battery in the middle or one at each motor?  

Hello Allan,
Hello All,
Allan, we have to solve two problems (at least) at one time: you want to minimize the pitch inertia and the plane must balance.

The tail moment is selected for handling characteristics, and the nose length is selected for balance.
I'm not kidding: that's all that noses are for.
That, and I cannot imagine why you'd change the tail moment (which affects handling) just to get balance.
That's almost as bad as changing the length of the tail so that the fuse sides fit in the kit box ... and the stories about that are legend!

Propellers are destabilizers, and putting them farther forward just gives them more leverage to do that unhelpful job.

Keeping the battery and motor close together, in a nose that is juuuust long enough to get balance,  minimizes the rotational inertia as Tim and Howard astutely point out.
It also means that the nose will be just long enough to balance ... and no longer.

So if you want an airplane that balances and has low pitch inertia, build the tail light like Sparky said, and make the nose as short as possible while still getting the battery far forward enough to balance.
Come to think of it ... just build light! Less "barbell" in pitch is always better.
It's nice when the theory and the practical agree, right Sparky?
That means that the theory isn't based on incomplete thinking and that the practical experiment controlled all the necessary variables.

Now, just to be a troublemaker, let me add another dimension to this design question.
Just a few weekends ago, I was at the RC field with my buddy Matt.
He has been working busily this last year on gasoline engines for F3A and has finally gotten the powerplant handling characteristics to the point where they are competition-worthy.
All the development had been done with existing airplanes that were overweight (due to the weight of the gassers) and carried tons of tailweight to compensate.
As a result, the test ships flew like barbells, and we accepted the deficit carried on.
Eventually, Matt built a ship that met the 5 kilogram (11 pound) weight limit with a 3 pound engine.
It sure has a short nose, and a monstrous percentage of the planes mass is right up in the end of the nose.
This is the first plane in the development process that balances properly and isn't overweight, so flight bcharacteristics are now being evealuated seriously ...
Flown smoothly, it handles well, but try to make a tight square corner, and the plane feels sluggish.
It behaves noseheavy for quick pitch changes and behave like it is properly balanced for moderate corners and rounds.
Matt and I came to the conclusion that the plane's center of percussion is very far forward of the center of gravity.
This is a consequence of having nearly one third of the planes mass in one lump at the very end of the nose.
For those, who have never heard the term, the center of percussion is the center of rotational inertia ... and yes that is different than the C of G.
The sweet spot of a baseball bat is defined by its center of percussion.

Any comments?
Howard?

Regards,
  Dean

Howard   , Keep in mind that I scored a D in freshman college physics back in 1950!! 

This subject seems a bit complicated to me. If you have mass concentrated in the nose and tail regions I can understand that the inertia is different from concentrating the mass near the CG even as the total mass remains the same (that assumes that the CG is a kind of pivot point for changes in flight attitude). It strikes me that in a violent corner maneuver first the inertia must be overcome and then the momentum must be canceled to return to a given flight path.

Will the location of the mass (peripheral vs central concentration) make difference in way the model reacts to these changes in the flight path.

Flown smoothly, it handles well, but try to make a tight square corner, and the plane feels sluggish.
It behaves noseheavy for quick pitch changes and behave like it is properly balanced for moderate corners and rounds.
Matt and I came to the conclusion that the plane's center of percussion is very far forward of the center of gravity.

Now here's a thought, by changing the elevator flap ratio are we effectively moving the net force application point to align with a point relative to the centre of percussion?