Question for the physics experts re; nose lengths

[Russell Bond]

Here's a question for the physics experts in regard to nose lengths. (Model nose!!!)

You have a plane with the tail moment and design which works well for you.
Are you better off having a shorter nose with the battery right up close to the motor or is it better to have a bit longer nose with the battery further back closer to the balance point?
Of course keeping the balance point the same on the model in both scenarios.
Which setup would be better to keep the corners snappy?
In other words, which one causes less inertia in the corners?

Unless there is no difference of course. 

[Howard Rush]

Shorter nose, but not so short that you need to add ballast.  It's not obvious.  Here's a calculator, at post 20, I think: http://stunthanger.com/smf/index.php/topic,30303.msg300702.html#msg300702 .

You also want to allow for lights and other bling in the nose.

[Igor Burger]

and may be one hint more ... aerodynamics is also physics 

[Russell Bond]

Yeah Howie, you and your "bling"!!!!!!!! hahaha
I was blinded by it at the World's, is it designed to blind the judges so you get a better score??? Hahahaha. 

Seriously, I modified my older Bandolero the other day by removing 1/2 oz of nose weight, moving the battery forward to right behind the motor and fitting a lighter motor to balance the model in exactly the same place as before and now it turns snappier in squares than it did before........................

Gee, did I answer my own question? 

[Jim Thomerson]

Moment of inertia is weight x distance ^2.

[Howard Rush]

and may be one hint more ... aerodynamics is also physics 

I assumed a constant propeller position, of course.  The motor in the short nose would connect to the prop with a long, massless shaft.

[Tim Wescott]

I assumed a constant propeller position, of course.  The motor in the short nose would connect to the prop with a long, massless shaft.

I dunno, Howard, those massless shafts can get pretty flexible, not to mention delicate.

[Howard Rush]

Seriously, I modified my older Bandolero the other day by removing 1/2 oz of nose weight, moving the battery forward to right behind the motor and fitting a lighter motor to balance the model in exactly the same place as before and now it turns snappier in squares than it did before.

I'd guess that the weight reduction would have more effect than the reduced moment of inertia.

[Russell Bond]

I was wondering about that as well Howard as I saved 3 oz. 

[bill bischoff]

If you reduce the weight ahead of the CG, and the plane balances the same, doesn't that mean the nose moment arm/ polar moment of inertia INCREASES? This is what would happen when the battery is moved forward.

[Howard Rush]

If you reduce the weight ahead of the CG, and the plane balances the same, doesn't that mean the nose moment arm/ polar moment of inertia INCREASES? This is what would happen when the battery is moved forward.

Yes.  Russell changed the experiment from moving the battery and motor at constant total weight to changing the motor weight and (I presume) leaving it where it was, then moving the battery forward to keep the CG the same.  Here's the calculator with some made-up numbers showing the effect of reducing motor weight 3 oz. and moving the battery forward to keep CG the same.

[RC Storick]

.  Here's the calculator with some made-up numbers showing the effect of reducing motor weight 3 oz. and moving the battery forward to keep CG the same.

It's all about weight? Huh Howard? I think I said that years ago with resistance from everyone. I don't care what moment is involved IMO better to have a longer nose and lighter motor than a short nose heavy motor. Battery is King.

This mans experiments are exactly what I have been trying to illustrate for years.

[Steve Helmick]

Uh-oh!  Steve

[Howard Rush]

...IMO better to have a longer nose and lighter motor than a short nose heavy motor.

I think so, too.  Once you pick a battery and a motor, though, for a given CG the combination will have minimum moment of inertia with the battery crammed up against the motor.  You probably don't want to design for that: it's nice to leave a little margin for moving the battery forward, rather than adding ballast, when you want to move the CG forward.  Also, I take it from Igor's cryptic comment above that having the prop way far forward is good, and may be more important than minimizing moment of inertia.

[RC Storick]

I think so, too.  Once you pick a battery and a motor, though, for a given CG the combination will have minimum moment of inertia with the battery crammed up against the motor.  You probably don't want to design for that: it's nice to leave a little margin for moving the battery forward, rather than adding ballast, when you want to move the CG forward.  Also, I take it from Igor's cryptic comment above that having the prop way far forward is good, and may be more important than minimizing moment of inertia.

Well I might know something then. But it was not math just practical experience.

[Brett Buck]

It's all about weight? Huh Howard? I think I said that years ago with resistance from everyone. I don't care what moment is involved IMO better to have a longer nose and lighter motor than a short nose heavy motor. Battery is King.

This mans experiments are exactly what I have been trying to illustrate for years.

 You are cherry-picking the comments you like and not addressing the others. No one ever said there wasn't a potential tradeoff between weight and moment of inertia, just that your understanding of the effects of moment of inertia and weight is wrong. Which I expect is still the case.

    Brett

[Douglas Ames]

Maybe Duke Fox had it right years ago with the Long-shaft FOX .59 ?

[Tim Wescott]

There have been a number of cautionary tales here and elsewhere, about how designing a good stunt ship is an exercise in balancing a number of different factors, and about how giving any one preeminence over all the others usually ends up with a non-competitive ship in the hands of a wild-eyed, optimistic babbler.

Yes, you can latch onto ONE aspect of the whole, and optimize the plane for just that one thing -- but you may have to give up so much else that it doesn't matter.

On moment of inertia, the moment of inertia of any solid body is simply the sum of the weights of all of the particles in that body, multiplied by the square of their distance from the center of gravity.  That "simply" is in the mathematical sense -- it's not at all intuitive until you've spent a year or so doing the math over and over again, and have beaten your brain cells into submission.

If you're purely interested in minimizing the moment of inertia, then use an infinitely heavy motor of infinite density, located an infinitesimal distance in front of the center of gravity.  For any given balancing effect, this will give the minimum moment of inertia to the airframe.  Failing that (I believe that infinitely small, infinitely heavy motors are stocked in the "Theoretical Physics Store" right next to infinitely light, infinitely rigid shafts), just use a motor that weighs five pounds.  Then see how much snappier your airplane goes around the corners!

[RC Storick]

You are cherry-picking the comments you like and not addressing the others. No one ever said there wasn't a potential tradeoff between weight and moment of inertia, just that your understanding of the effects of moment of inertia and weight is wrong. Which I expect is still the case.

    Brett

No I am not! This is what I always said and because you think I am a nobody I must be wrong. Guess what? I'm not.

This term moment of inertia means squat to me. I have built enough airplanes to feel the difference. This is what I have always said.

After flying with bricks in the nose and being schooled on what to look for in other peoples flights, I can not only feel it but I can see it.

[Tim Wescott]

No I am not! This is what I always said and because you think I am a nobody I must be wrong. Guess what? I'm not.

I believe that you are at least partially referring to this thread,
http://stunthanger.com/smf/index.php/topic,32892.0.html, where no one argued at all about your experimental results, but did attempt to correct your interpretation of those results in terms of moment of inertia.  My recollection is that it followed on another thread where you were also making claims about moment of inertia, but were messing up your analysis by assuming that you could declare that a plane without a battery and the same plane with a battery mounted off the CG would have the same moment of inertia.

You were then, and are now, venturing into engineering territory, and your work is being judged by an engineer as if you were an engineer.  No one's judging you by your name, or whether your brother-in-law is the company president -- that's what they do over in Sales.

Brett is judging what you say, alone and irregardless of you.  That's how any good engineer is going to behave toward another's work.  This isn't Brett judging you, this is about an engineer dispassionately judging another engineer's work.  If you don't like your work being criticized so, don't make pronouncements about things you don't understand.

The way to get personally judged among engineers is to get hostile when some helpful person tries to correct your analysis.  Think about that.

[RC Storick]

Well I don't have the skill or time to type out a long winded explanation of how it feels. Math means nothing what means something to me is how it feels on the end of the lines. If a person builds 1 plane every 10 years and gets accustomed to it fine by me. I know what I am looking for.

It took someone who is world champ to say the same thing to what I already knew to light for some.

Slow learners I guess.

Here's another insight. If everyone would just drop some weight off the nose they would not need to try exponential control horns and huge bell cranks and horns. There would be no need to leaver the sinker (Engine-Motor-battery) with mechanical advantage. The plane would just turn with ease because of less stored energy in the nose.   Of course I'm wrong

[Howard Rush]

Yes, you can latch onto ONE aspect of the whole, and optimize the plane for just that one thing -- but you may have to give up so much else that it doesn't matter.

I worked for a company like that once.

[Derek Barry]

I don't know about the "feel" you are looking for but I can say that you looked better with that heavy old PA 75 in the nose than you did with any of the electrics I saw you fly.

Just sayin...

Derek

[Randy Cuberly]

Maybe Duke Fox had it right years ago with the Long-shaft FOX .59 ?

Maybe Mr Belko has it right, now!

[Howard Rush]

I don't know about the "feel" you are looking for but I can say that you looked better with that heavy old PA 75 in the nose than you did with any of the electrics I saw you fly.

Just sayin...

I hear what you're sayin'
And don't think I'm lyin'.
The JCT looks good
Whatever we're flyin'.

[RC Storick]

I don't know about the "feel" you are looking for but I can say that you looked better with that heavy old PA 75 in the nose than you did with any of the electrics I saw you fly.

Just sayin...

Derek

Been flying that pane for 7 years (just like a old shoe) It was said to me in Memphis "I think you found your groove" when I flew the Minado. Its 10 ounces lighter than the XL and lot of that is in the nose. Same airplane in numbers. That being said its still not exactly what I am looking for but it's better.

My electric program is on hold until I can figure out the issue with them. (omitted)

[Derek Barry]

Been flying that pane for 7 years (just like a old shoe) It was said to me in Memphis "I think you found your groove" when I flew the Minado. Its 10 ounces lighter than the XL and lot of that is in the nose. Same airplane in numbers. That being said its still not exactly what I am looking for but it's better.

My electric program is on hold until I can figure out the issue with them. (omitted)

Good deal, I hope to see you and the Minado at the Nats!

Derek

[RC Storick]

Good deal, I hope to see you and the Minado at the Nats!

Derek

doubtful but thanks

[john e. holliday]

Where is that article about the bar bell effect on model planes.   It was something on the order of taking a bar bell like the weight lifters use.   Equal weights on each end.   You lift in the middle with no problem, but if you get off center it takes more effort to lift the weight that is farther from you.   Also when you get it started to move it takes jut as much effort or more to stop the movement.   If a person can design, build and fly a plane that needs no weight adjustment front or rear I think has did a miricle, especially if he/she can fly a great pattern with the plane.  Don't forget the wing tip weights also.

[Curare]

That's not an idea analogy.

It stands to reason (even without maths) that if you have a bar (or a fuselage) and you put heavy weights at the extremites, it will balance somewhere. If you move the weights closer into the pivot point it will still balance, but they lever effect from the pivot of the weights is altered.

The next effect of doing this is that it will take less force, to move the bar with the weights closer to the centre, than if they're out at the ends. Correspondingly it will take less force to stop them moving, or damping the movement.


This explains the change in feel that Robert is experiencing. I'm sure we all agree on that.

So if you have all the weight of your engine, tank and battery all right out at the pointy end of the nose, you'll find that the plane will be harder to start cornering, and harder to stop than a similar plane with the weight around the CG. Of course to do this you'd need a tail that weighs nothing. I guess here's the rub though: whats worse, a plane that has the majority of it's weight closer to the CG, and is heavier to balance that tail and keep your battery on CG you'd need to add some ballast, or one that has all the weight out at the front, but is lighter (using all the available heavy things to their best STATIC advantage).

Robert's getting around the CG issue by building ultra-light tails, but for mere mortals like me, I still have to balance that tail with something.

[RC Storick]

Robert's getting around the CG issue by building ultra-light tails, but for mere mortals like me, I still have to balance that tail with something.

Light tails are good but less paint is better.As gross weight goes down (less paint) it becomes less tail heavy.

Now I must say this with regret the plane I flew at the last NATS is no light weight and it is the plane at that time I flew best but it's not what I like. I have sense built the same plane (same wing and numbers only 10 ounces lighter) That flies better and is more enjoyable to fly.

[Howard Rush]

Why didn't you fly the plane you flew last year?  It looked like it flew very well.

[RC Storick]

Why didn't you fly the plane you flew last year? 

Its all I had ready to fly. My electric program was and still is not quite right.

[Tim Wescott]

So if you have all the weight of your engine, tank and battery all right out at the pointy end of the nose, you'll find that the plane will be harder to start cornering, and harder to stop than a similar plane with the weight around the CG. Of course to do this you'd need a tail that weighs nothing. I guess here's the rub though: whats worse, a plane that has the majority of it's weight closer to the CG, and is heavier to balance that tail and keep your battery on CG you'd need to add some ballast, or one that has all the weight out at the front, but is lighter (using all the available heavy things to their best STATIC advantage).

Robert's getting around the CG issue by building ultra-light tails, but for mere mortals like me, I still have to balance that tail with something.

I think you're saying what if you start with a plane that has all the weight concentrated at the CG but doesn't balance, then add weight to the nose until it does.  If you do that, then I'm pretty sure that when you're done you'll have a plane that has a higher moment of inertia around the CG than if you took your hypothetical plane and rearranged the mass within the fuselage (i.e., moved the battery) until it balanced.

The best way, strictly from the perspective of moment of inertia, would be to build the plane with whatever wing and tail structure it needed to fly right and look good, then built the nose just long enough so that with the motor and battery shoved as close together as possible, the thing balanced right.

However, that ignores the mysterious comments by the multiple world-champs winner who keeps suggesting that perhaps there's some other reason for wanting a long nose.

[RC Storick]

However, that ignores the mysterious comments by the multiple world-champs winner who keeps suggesting that perhaps there's some other reason for wanting a long nose.

I'm not a wold champ and a few think I don't know anything but I have the ability to build quickly and have built both long and short nose airplanes. I don't know the math and I cant explain the science behind it but a longer nose with the battery moved back as far as needed to balance feels better on the end of the lines then a short nose with battery moved forward to balance. Crisper start and stop in the turn. I don't need the math or a spread sheet I just build them and feel them fly.

My guess is most will learn and follow suit some will not.

[Trostle]

Where is that article about the bar bell effect on model planes.   It was something on the order of taking a bar bell like the weight lifters use. 

(Clip)

  

I think you are referring to the Bob Gialdini article on his Olympic in the 1963 American Modeler Annual.  It is one of those articles that should be in every stunt flier's library

Keith.

[Russell Bond]

"but a longer nose with the battery moved back as far as needed to balance feels better on the end of the lines then a short nose with battery moved forward to balance. Crisper start and stop in the turn."


Robert, that's what I mean. Is it better to have a long nose with the battery back further, or is it better to have a shorter nose with the battery up close to the motor?
You seem to have had success with the longer nose. 

[Tim Wescott]

I think there's some confusion in the original question, however:

Which setup would be better to keep the corners snappy?
In other words, which one causes less inertia in the corners?

The engineers in the group see "inertia" and immediately think you mean "moment of inertia", and get off on that tangent.

But Igor is making his mysterious statements about longer noses, and Robert's giving us his empirical evidence, which seems to indicate that something other than just keeping the moment of inertia at a minimum is what's important.

I dunno.  I'm going to build a Legacy to the plans, put Marvin the Martian in the cockpit, and call it good.  Uh, I mean, I'm going to call it "Illudium Phosdex", but I'm going to call the plane good.  Damn, that's still confusing -- at any rate, I'm not going to change the nose length.

[RC Storick]

"but a longer nose with the battery moved back as far as needed to balance feels better on the end of the lines then a short nose with battery moved forward to balance. Crisper start and stop in the turn."


Robert, that's what I mean. Is it better to have a long nose with the battery back further, or is it better to have a shorter nose with the battery up close to the motor?
You seem to have had success with the longer nose.  

Less weight stuck all the way out on the end of a long nose is easier to leaver than a heavy weight on a short nose. Both balanced at the same CG. It will turn faster and stop faster. One draw back is clock time.

Before I hear any pie times radius square just build one and see.

[RandySmith]

There is another part of this equation that not many want to talk about, or at least it seems mentioned seldom, that is the part that has to turn and stop the nose, that is the elevator/stab. and its moment. A very powerful large stab and elevator will do a great job of stopping and turning the mass up front, a small area stab/elev.  will NOT do nearly as well. Plus remember balance in the size of the stab/elev , in relationship to what it needs to move is very important. Too little and you have to run a tail heavy ship, or suffer turn, and stability in the turn and stop is also due to the proper size.
I personally do not want anything over 10 or so inches at the nose on 60 sized ships, and 9 inches or so on 35 sized ones. I have flown 60 size ships with near 10 inch nose moments and have 16.5    (17, 17.5, 18, 18.5, 19, 20, 21 )to 22 inch tail moments (the way modelers measure nose and tail) you can make them all work, but they work best with percentages varied along with aspect ratio weight etc..
 NOTHING is simple !!

Randy

[Howard Rush]

I've seen many cases here of a guy who makes a good experimental observation, then invents a bogus, scientific-sounding explanation for it.  A technically trained person reads it and reacts to the bogus explanation.  This doesn't mean that the observer was wrong about what he saw.  

Igor has long noses on his airplanes and writes about long noses having side area forward of the CG and minimizing p effect.  That's sideways stuff; Robert's observation was about pitch.  It looks like if the nose is long enough, the destabilizing effect of angle of attack on the prop disk would be overcome by the stabilizing effects of flying on a curved path and by reduced upwash in front of the wing.  For an easy-to-calculate example, for a ten-foot-radius turn and an angle of attack of 7.5 degrees, not counting the upwash effect, putting the prop disk 15" in front of the CG would cause the curved-air angle to cancel the angle of attack, hence the air would be blowing perpendicular to the prop disk.  And you thought that the reason for Igor's long nose was to hold up his enormous sunglasses.

[Curare]

For the purposes of arguing hypotheicals, what would be the effect of a short nose with a lot of forward area? Deep fuselage, canopy forward or a rhino rudder?

Would the effect be the same?

What about adding stators behind the prop to direct propwash?

[Howard Rush]

There is another part of this equation that no many want to talk about...

Or not many want to listen about.

[Howard Rush]

For the purposes of arguing hypotheicals, what would be the effect of a short nose with a lot of forward area? Deep fuselage, canopy forward or a rhino rudder?

Would the effect be the same?

What about adding stators behind the prop to direct propwash?

Good questions, I think.  Igor's long, deep forward fuselage seems wrong to me, yet I've seen him do square eights upwind.

[Igor Burger]

Igor's cryptic comment

and will anyone (especially the author of orriginal question) believe depanted guy? 

[Russell Bond]

 

[Avaiojet]

My new stunt design, the Mean Lean Stunt Machine, has a nose moment of only 9.5" with a span of 54".

[Phil Hawkins]

I think you are referring to the Bob Gialdini article on his Olympic in the 1963 American Modeler Annual.  It is one of those articles that should be in every stunt flier's library

Keith.

Here is this from SSW   http://clstunt.com/noselong.htm