A lot of people know I am a all about weight guy. I have been bashed and chastised for this for a long time. But here is a interesting experiment.

This is for electrics as it will be easy to do and remain the same weight. Pick a airplane of any type full body. Build the tail as light as you possibly can. (sand it out inside) Finish it light. Put the battery up close to the motor so the moment of inertia is low. (whatever that means) Now take solder and wrap the tail wheel until you get it to balance not plan balance, but trim balance. Note the feel of how the plane flies. Should do nice rounds and groove well, if you did your job right and built it straight and light it should turn well. Remember note the feel!

Now take the weight (solder) off the tail wheel set it aside. Move the battery back and add the same weight you took off to the nose and make sure it balances in the exact same spot. It remains the same weight. Note the feel.

It should do nice rounds and groove well along with have a super snappy feel. Remember note the feel!

This is not a debate its a experiment I have done. Please don't come one here with some math formula saying I am wrong just try it and Note the feel!

Oh and please when you find out how it felt make sure to tell us and be sure to note the the feel!
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You'll have reduced the moment of inertia. Folks generally think that will make it fly better.  

But battery and motor and now 5 inches apart? You said it was lower when they are close together.

Is it easier to lever 6.5 ounces or 16? That's to the extreme as the battery is still there but closer to the fulcrum.

Please remember this is not a debate its a experiment you will need to try so you can see what I feel.

It works and its magic LOL.

I watched Viper fly at least 5 times this past weekend and since I launched for you every time, I watched each flight closely and I was really impressed. That plane is special!!!

At least now I have a direction I want to follow. To each his own some like caddy's I like sports cars. Tom Warden said it best about his Continental with the long nose "this flies like a lowered 49 Merc"

I build most of my planes as light as I can. This is a real world example of the plane I have now. Its a experiment not a formula on paper. Nose length remained the same I did not cut it off.

Moved to the bottom so as not to be confusing.

Wing loading is the same. Why because the plane weighs the same. 55 ounces my scale and 53 on contest scale (if that counts Ill take the lighter one) Read the experiment close you are adding the same weight back you took off the tail wheel only to the nose and it balances in the same spot. SAME Same.

I can't feel a piece of paper on the desk but you can feel it in the plane. Read the experiment close. Its all about the feel!

Brett you have tried to interject some hypothetical scenario of a plane that does not exist mine does and this is what has been done to my airplane. So any formula you come up with is just that. I can feel the difference in the way it flies with the concentrated weight shifted closer to the CG while remaining the same CG as before.

If I could build it at 40 ounces I would (light airplanes do fly) but with today's wood and the size of the planes this will not be possible. There is already 27 ounces of fixed weight.

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Next one will be 1 inch less cord thus shortening the whole plane for even faster clock time. It also could end up with a shorter nose too. Then I will need to build the tail even lighter.

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I am not sure how the 16 ounce figure came to be set in stone it was hypothetical example. That's immaterial what are the facts is I did this and it does work and I can feel the difference.

I also think you confirmed Ted's experiments with the super light plane he had years ago. If he would have added the same weight that he added to the cg to the nose and tail (balanced at the same point) the plane would not have flown as well as it did with the weight at the cg. I am not going to get into the lighter is always better argument with you. I believe that there is an appropriate weight for every design, I know this because I have had a plane that was too light and so has my dad. I don't think it is possible to build an electric too light, like you said there is 27 oz of fixed weight...

Derek

I can feel the concentrated weight close to the spinner. Its all about feel, trust me when I say I can feel the concentrated weight shifted, and anyone who tries this will too. This is fact and not a debate. I'm done debate away. This thread will not come down because I know it for a fact! Not a guess so debate away. I'm out.

I think it is easy to see that the moment of inertia of the second experiment will be less than that of the first. And that agrees with everything you have been saying! All else being equal, the model with the lower moment of inertia will turn more quickly and will STOP turning more quickly as well. Your empirical, real-world testing is simply supported by the physics of the situation! SHAZAAM!

Imagine that

That's what I have said all along but Howard said it was lower with the motor and battery close together both here in print and on the phone.

As to differing designs. The Viper has been around sense mid 80Ty's and the first 3 flew like what I like. But as they got bigger and adapted to modern power they started taking on the feel I don't like. Now comes electric and I am headed back to the feel I do like with some experimenting. All because of the drive train weights and placements.

I built some different designs to see if this feel was engineered out by someone. But you can't engineer out the weights.

I don't remember who said it but it was said on this forum its easy to build a light airplane, Not!

It takes the best of wood and the best of thought and layout and the best of skills. If the person reading who said this reads this please show me how easy it is and post the results here.Its all about the feel. when I said its all about weight I guess I should have said concentrated weight

Be sure to tell Ron the next time you see him that a 48 ounces Tucker will fly better than a 38 ounce Tucker. I am sure he will tell you what he thinks. I am not saying that particular plane didn't fly better but you have to think maybe something else was wrong with it. At least I do. No mater how many you build or how careful you are a mistake in alignment can sneak in and you not catch it. Quote Bill Werwage from the Man and his Museum tape.

I don't disagree with you or Billy but it is a hard comparison to make. What Ron thinks flies well may be different than what Ted thinks. I speak from personal experience, I had a Nobler that weighed 31 oz. and it was almost unflyable. After a decade of collecting oil it gained a little weight and it flew better. Now, I can say that my 62 oz. Cutlass flies MUCH better than my 73 oz. Matrix...

Derek

Robert, I think you are correct that Brett was thinking of a different experiment than the one you proposed.  Your proposal was a good experiment: you held weight constant, you held propeller position constant, you held everything else in the airplane constant.  All you changed was moment of inertia.  Moving the battery aft and moving the weight in the tail forward reduced the moment of inertia of both about the CG.  And no, you didn't catch me in a condradiction.  Had you gone on to move the motor back and the battery forward until they were together, while keeping the CG the same, you would have reduced the moment of inertia even more.  That would have changed the prop position relative to other stuff, though, so it throws in another variable.

Bill showed how we'd look at it.  You can also plug numbers into the little spreadsheet I posted here awhile back and have it do the calculation.  That can also give insight.   I think your intuition is leading you astray.  Moment of inertia (the barbell effect, the resistance to starting and stopping a turn) of each piece of mass about the CG is its mass multiplied by its distance from the CG, then multiplied again by its distance from the CG.  So distance from the CG is a big deal.    

Brett you have tried to interject some hypothetical scenario of a plane that does not exist mine does and this is what has been done to my airplane. So any formula you come up with is just that. I can feel the difference in the way it flies with the concentrated weight shifted closer to the CG while remaining the same CG as before.

  The "hypothetical" 6.5 and 16 ounces was *from your own example*, straight out of the post. You are simply incorrect about this particular point. And changing the argument halfway through.

    In my example, you first talk about light weights on long sticks versus heavy weights on short sticks and which one is easier to stop/start. For a given airplane, and assuming that is all you change, it's not a debate and you don't get to have an opinion about what it does to the physics, since it is an immutable law of physics.

 In fact, as I mentioned the first time (something like 10 years ago), what you are doing is the exact opposite of what you have "analyzed" and stated as a fact. Maybe you prefer something with a disproportionately large moment of inertia and don't actually like high entry and exit accelerations, that I can't determine for you.

   Then, you say you build the airplane as light as possible all the time. If you do that, you are not comparing apples to apples in the physical argument. If you reduce mass of the back half of the airplane, then your example is invalid, because you are not keeping everything else the same and changing the one thing you suggested. The "balance moment" is not longer constant and so the argument (both your original one, and my example) is not possible to resolve. You say you like the "feel", and I wouldn't dispute that. It's almost certainly wrong and most everyone else who actually understands the engineering thinks otherwise, but if it fits your needs (right now...) then obviously, build it as you want.

    But one bit of advice, and I mean this with absolutely no malice, because I have seen people thrash and thrash many times over the years, and also seen them get out of it.  I think you are a good guy and I hate to see it when the solution is clear.

   Sometimes you have to change what you are doing to make advances. You have been building every airplane you could as light as you can for, well, ever. You also have been mired in the "not quite a qualifier" area for a similar amount of time. Numerous people have tried their level best to give you good advice and assistance. I can give examples if you like.

    I will also admit to declining it in one case, the night before the 2006 Walker Flyoff, I had to decline to test-fly your airplane (when you asked Crist Rigotti to ask me). I think the reason is obvious, and I offered to do it after the competition.

     If you are going to improve, doing what you have always done, just more extreme, is not going to cut it. You are going to have to accept, at some point, that *a lot of people know a whole lot more about making, trimming, and flying stunt planes than you do*.  In some cases, VASTLY more. And many people with *vastly more* of your vaunted "experience", too. 

    There's nothing shameful or embarrassing about it, it's the nature of the game. You would to well to listen and actually be willing to make changes and evaluate them fairly. Not go out of your way to pick fights and alienate the very people attempting to get you out of the deep rut you are currently in.

     I expect you will sputter on about the rest of is "not getting it" and edit/delete/lock the post, but at some point you are going to have to decide what you want out of this event. If it's to be a website impresario and a gadfly, then you are going about it right, if it's to become competitive in stunt contests, you need to listen to other people's advice and make it work for you. Just exactly like everyone else.

     Brett

This is for electrics as it will be easy to do and remain the same weight. Pick a airplane of any type full body. Build the tail as light as you possibly can. (sand it out inside) Finish it light. Put the battery up close to the motor so the moment of inertia is low. (whatever that means) Now take solder and wrap the tail wheel until you get it to balance not plan balance, but trim balance. Note the feel of how the plane flies. Should do nice rounds and groove well, if you did your job right and built it straight and light it should turn well. Remember note the feel!

Now take the weight (solder) off the tail wheel set it aside. Move the battery back and add the same weight you took off to the nose and make sure it balances in the exact same spot. It remains the same weight. Note the feel.

I'm kinda reiterating what Brett and Howard have said, but hopefully more succinctly:

I'm not arguing with the results of your experiment, but you are neglecting the effect of that tail weight in your analysis of moment of inertia.  Basically, that tail weight changes the moment of inertia.  Since you're putting it on the end of the longest stick available, it changes the moment of inertia a lot for the amount of weight.

You should say: "Put the battery up close to the motor so the moment of inertia is low.  Now put in tail weight to balance and make the moment of inertia higher.  Fly.  Now move the tail weight to the nose and move the battery back to make the moment of inertia lower.  Fly."

If you're sitting there looking at the plane, with weight in hand, and you're bound and determined to end up with the same plane weight and balance and the least possible moment of inertia, then the thing to do is to put the weight about halfway between the battery and the motor, and adjust the battery.  But the difference will be slight compared to putting the weight in the nose.

Weird?  Yes.  But it's the result you get if you start with the definition of the moment of inertia and work out what to do with what you have.

Robert,

I read some of what you wrote and some of the replies. Sorry I didn't read every word in the Thread.

In all honesty, I'm not really sure where any of this is going?

But I will tell you this.

If I go electric, and I expect somewhere along the line I will, I'll place whatever parts/weight I can clustered/nested around the CG. For every model, not just stunt models.

I would be hard pressed to think anyone will change my mind about that. But I will listen.

Congratulations on your efforts and experimentation. There's always something to gain from it.

Charles

What I find interesting is that sparky never smiles in his photos. "Why so serious" LOL

Derek

That is his smile.

Charles

I feel your pain, Igor.
But the underlying goal, for you, was to build a nose that was as short as possible while achieving proper balance.
This one time you missed by just a little. 

Dean P.

Igor,
So you were trying to get the propellor farther away from the wing?
Dean

Igor,
So you were trying to get the propellor farther away from the wing?
Dean

No, it is not because of distance, however it could be important to make some investigation around. If the AoA in corner is ~8 degrees, the the long nose can keep prop exactly on tangent point, so the yaw comming from P factor can be minimized ... or used to cancel precession? :- ))) I do not know, worth to think about it little 

The reason for longer nose is only to better balance side area, nothing else. My previouse model had too short nose designed for heavy IC motor, so I elongated it little bit knowing that I have elecro motor and battery position is not fixed to motor position. Probably I will do it even longer by 10mm on next model.

No, it is not because of distance, however it could be important to make some investigation around. If the AoA in corner is ~8 degrees, the the long nose can keep prop exactly on tangent point, so the yaw comming from P factor can be minimized ... or used to cancel precession? :- ))) I do not know, worth to think about it little 

The reason for longer nose is only to better balance side area, nothing else. My previouse model had too short nose designed for heavy IC motor, so I elongated it little bit knowing that I have elecro motor and battery position is not fixed to motor position. Probably I will do it even longer by 10mm on next model.

Igor, if I'm not mistaken, precession is a torque on the airframe.  It doesn't matter where it is applied, it will take the same amount of a reverse torque to correct.

The idea of extending the nose to put the prop on a tangent to the loop would put the prop more squarely to the airstream.  That would tend to minimize the difference between AOA of the prop blades and minimize P effect, at least on a two bladed prop.  If the prop is inside the path of the loop the down-going blade would be at a greater angle of attack and the up-going blade at lower AOA, causing more P effect.

But just sketching it out, it looks to me that extending the nose puts the prop further away from the flight path, exaggerating the difference.  Making the nose as short as possible puts the prop closer to the flight path.

If the AOA in a corner is 8 degrees, then the AOA of the descending blade is increased by 8 degrees in relation to the relative wind and the AOA of the ascending blade is decreased 8 degrees.  This results in a difference in AOA between the two blades of 16 degrees, and an associated thrust differential resulting in yaw due to P-factor. The length of the nose moment should have no effect on this phenomenon.  It is strictly a factor of the difference between the chord line and the relative wind, I.e., AOA.

The AoA is not the same on all parts of fuselage, we are on circular path in corner, and the tangent point (means 0 AoA) is somewhere on nose. That is why we need so large elevator to keep such small angle as 8 dergrees necessary for corner.

Look pic, you can see that tail is at aproximately at 15 degress if model goes tangent to path on LE of wing. In that case motor will be at aproximately half of that angle but NEGATIVE angle ... means -8 degrees, so plus some AoA for corner and you see that little longer nose will move prop to 0 AoA (means tangent) position.

The AoA is not the same on all parts of fuselage, we are on circular path in corner, and the tangent point (means 0 AoA) is somewhere on nose. That is why we need so large elevator to keep such small angle as 8 degrees necessary for corner.

Look pic, you can see that tail is at approximately at 15 degrees if model goes tangent to path on LE of wing. In that case motor will be at approximately half of that angle but NEGATIVE angle ... means -8 degrees, so plus some AoA for corner and you see that little longer nose will move prop to 0 AoA (means tangent) position.

Good reflection!