How much justifies obsession?

[RC Storick]

The last few days I have been detailing the plane I am trying to finish. Sanding around hatches and doors. I have sanded around the fillets three times. I think they are done and go back and do it again. The way it looks I will be painting grey to save weight. I hate grey planes. But after talking to Bob and Randy I am convinced a light plane would be better and I would hate to ruin my first electric plane due to it being a pig.

So the idea hit me. If I took the wing out and drilled some holes in it. Then measured epoxy by weight and filled them back up. Reinstalled the wing and used leather fillets and then sprayed it with polycrilic and dusted house paint rustoleum paint on it I could save a gram or too. What do you think would this border on obsession?

I don't mean to ruffle anyones cackle,its just my shot at levity and humor as I sit and read all this stuff.

[Mike Keville]

Not sure where I heard this <chuckle> but boring a bunch of holes in it may save you a gram or two.

[RC Storick]

I am a mechanic and just love to take stuff apart.

[Tim Wescott]

Replace the wing skins with tapered, chemically etched unobtainium.  That stuff has negative density, so it'll make the structure lighter than it is.  Moreover, it can be polished to a high shine, and depending on the direction that the surface is oriented when you polish it, it'll come out different colors.  (I can't remember exactly what comes with which, but you get bright red for north and bright blue for south).

[Steve Helmick]

Being a mechanic, you should know that if you take it apart, you are sure to have stuff left over after you put it back together. That always results in a weight savings. If you can install some holes while you have it apart, all the better. Ace Hardware stores have a 20% discount on holes tomorrow, so you can buy some extra holes for your next "ElectricGlide".  Steve

[David Russum]

When you charge the batteries, use an upstairs outlet, or even an attic outlet (the higher the better).  It is a little known fact that only the lighter, more energetic electrons can go up the vertical wire runs in a house.

[Paul Walker]

Myself, I use balsa for fillets. That DOES save weight. And, the paint sticks well.

[wwwarbird]

 Ahh, potentially succumbing to what I call the "overthinkers".

 Whenever in doubt, I always go with the old saying, "Keep It Simple Stupid". There are good reasons so many things in our hobby have worked so well for so long. I think we're all obsessed, that's why we're all here on the forum.

 Just stick with your normal program Sparky, it'll come out real good.

[Mike Griffin]

I think you should fill it with Helium Robert. 

Mike

[Randy Cuberly]

deleted

Hey...I thought we agreed not to delete posts...a lot of valuable information could be lost here. 

Randy C.

[John Sunderland]

Hey...I thought we agreed not to delete posts...a lot of valuable information could be lost here. 

Randy C.

 Well Randy I was just going to wish him luck...after all, since he has gone to the "dark side" and electrified, he may as well learn how to rub out Rustoleum, Duplicolor, over dope and top coated with any number of clear coats that no longer must be fuel proof!

[Steve Helmick]

PolyCrylic does have a mighty nice shine to it...with just a little Bufferin. 

[Larry Fernandez]

Myself, I use balsa for fillets. That DOES save weight. And, the paint sticks well.

Hi Paul how are ya??

I have thought about balsa fillets more than once, especially on a PT-19 or P-40, where the fillets get quite large toward the aft part of the wing I just cant invission how to go about doing it right.
Do you happen to have any pictures of of your fillets as you put them on??

Larry, Buttafucco Stunt Team
 

[Vincent Corwell]

Make sure the holes are 3.14" in diameter..............hee hee 


Vincent

[Mike Griffin]

I would be interested in seeing them too Paul.   I have really no idea how to start to use balsa fillets..

Mike

[FLOYD CARTER]

I don't know why people are so concerned with weight in an electric stunter. 

You go to great lengths to build a super-light structure, with minimum paint...

AND THEN PLOP IN A 16 OUNCE BATTERY!

(ouch!)

[Rick Bollinger]

When you charge the batteries, use an upstairs outlet, or even an attic outlet (the higher the better).  It is a little known fact that only the lighter, more energetic electrons can go up the vertical wire runs in a house.

And when you charge the batteries only fill them 75%. you will lose one flight out of the charge but you will gain a savings of 25% On the weight of the batteries.

[Joe Just]

I have two complete sets of "Instant Holes" ranging from 1/2" to 3" in size.  I have thougt about putting them on Ebey, but I am willing to sell them directly for $1100 for a complete set.  Also because they have no weight I will sell them without any postage or handling fee. PayPal only please!
Joe

[Brett Buck]

I don't know why people are so concerned with weight in an electric stunter. 

You go to great lengths to build a super-light structure, with minimum paint...

AND THEN PLOP IN A 16 OUNCE BATTERY!

(ouch!)

    It is better to plop a 16 oz battery in a 48 ounce airplane, or a 56 ounce airplane?

    There's a legitimate point to whether having an electric VS IC is more valuable than whatever compromise you make with rigidity to keep the weight in range.  But simple dead weight with no purpose is never to your advantage. Most current competitive IC airplanes weigh in the low 70 ounce range when they have fuel in them, all you have to do is beat that.

     When you figure in the fuel weight, there's no significant weight advantage to IC any more.

     Brett

[Douglas Ames]

Uncontrolled OCD is a bad thing, and sometimes funny.

[Steve Fitton]

Put a PA-75 in it?

[Derek Barry]

One of the big advantages of IC is the fact that it does lose weight as the flight goes on. By the time you get to the more complicated maneuvers you have a lighter plane than you started with and all the weight comes off the nose giving you more control authority for those more complex maneuvers. Ha Ha one point for IC.

Derek

[Randy Powell]

Keep in mine that weight isn't an absolute. It's a matter of weight range to design. For instance, I built a lot of high aspect ratio planes. They didn't fly well when too light. They needed to be within a certain weight range. Too much lift in certain areas of the pattern caused them to be unstable unless carrying a certain amount of payload. So figuring out the weight envelope for a particular design is important.

[William DeMauro]

If I recall properly, you have a triple cored foam wing in your new plane which is almost the same type of wing that I am using in my new stunter. I don't know about you but I also ordered the foil insert that sits in that third hollow part of my wing and goes the length of my wing. This insert is then filled with helium to produce a lighter plane than I would normally have. This may be an easy solution for you as you would only have to remove the wingtips to insert the foil tube and leave a small pinhole in a wing tip and use a basketball filler pin to fill it with helium. If you put the filler mechanism in the outboard wing(I would) the fill mechanism can double as tip weight and not add to the final weight of your plane.

[John Sunderland]

I lost a beautiful GeoBolt triple cored foam wing last year....call it a depression!   I bought them from Bob in 2011 ...ready for bellcrank, spar slots cut,  perfect ply half ribs installed, basswood gear mounts installed, TE installed (ready to sand), almost ready to be sheeted. It was painful to lose. A MOVING accident.

[RC Storick]

   It is better to plop a 16 oz battery in a 48 ounce airplane, or a 56 ounce airplane?

    There's a legitimate point to whether having an electric VS IC is more valuable than whatever compromise you make with rigidity to keep the weight in range.  But simple dead weight with no purpose is never to your advantage. Most current competitive IC airplanes weigh in the low 70 ounce range when they have fuel in them, all you have to do is beat that.

     When you figure in the fuel weight, there's no significant weight advantage to IC any more.

     Brett

Your right the weight advantage is with the electric models. This plane ended up at 61 oz full of fuel. If you took away the 7-8 oz of fuel needed for a piped engine that means its the equivalent of a 52 to a 53 oz plane. bringing the wing loading way down if that is factored in like we do with a IC stunt-er. or 11.74 dry wing loading. As opposed to 13.29 full of fuel.

[Derek Barry]

Hi Derek:

This is not intended as a "shot," but this is where the electric model has a distinct advantage in my humble opinion. I think we will all agree that throughout our flying careers we have all had to fly from time to time in a lot of wind. I'm sure we would all also agree that the overhead eight maneuver and the cloverleaf entry loop are two areas where the wind makes things "interesting." Having the pitch CG where it was when the flight started is a huge advantage in flying those maneuvers in the wind. Not convinced? Try this: Go out on a blustery day. Fill your tank, and start the engine. Take off and go right up into an overhead eight. Report back here...

What you will find is that the model tracks through that maneuver much better with the CG where it is supposed to be. Penetration is key in the overhead eight in the wind. A tail heavy ship just does not penetrate as well as one in which the CG is more forward. The ship with the forward CG will have much better control authority. Perhaps the math types will chime in here with the "why" of it all.

This was seriously not meant to start any kind of fight; it is just an observation that I have made after having flown electric models for seven and a half years...  I feel that electric models have a distinct advantage over IC models in the wind in all respects, but especially during the overheads and the clover entry.

Later - Bob Hunt 

Hey Bob,

No offence taken here nor do I think you are trying to start a fight. I cannot argue the points about the overhead and the clover entry either...

Watching your plane fly in the wind last year I have to say that it handled it just fine. That being said, my Dreadnought has flown respectable patterns in some of the worst conditions imaginable too. In hindsight I wish I would have been flying it last year in that terrible wind.

Derek

[Avaiojet]

If saving weight is really an issue from the get go, I personally would never use an Epoxy to sheet foam wings.

I've taken many sets of foam wings to the local cabinet shop and had them spray their contact adheasive on the sheeting and the foam.

Incredible glue!

I know others who have done the same. Sure, years ago, nothing's changed.

Could get a bit complicated with "wrapped" LE sheeting, but I'm sure that could be worked out.

No, I'm not giving advice. I'm stating a fact.

I've done this and I know others who have also.

Charles

[Steve Fitton]

I'm going to try putting a bunch of 7.62 milimeter diameter holes in my wing and see if it lightens it any...

[Avaiojet]

I'm going to try putting a bunch of 7.62 milimeter diameter holes in my wing and see if it lightens it any...

Steve,

Did you ever see those honeycomb foam wings that were available years ago?

Were light and strong, guys used them for years.

Charles

[Crist Rigotti]

Bob is correct about using epoxy (not that he needs my confirmation!).  That is all that I use when I build my wings.  Now, you do have to use the right epoxy.  5 minute epoxy won't work!  Finishing or long cure epoxy is used because it is thinner.  I'm sure Bob will weigh in on what epoxy he uses.  Bob has posted many times THE technique on skinning wings.

[john e. holliday]

Well that explains the reason  the sheeting on a slow rat core was layin on the floor when I started moving out of the basement to the shop.   I had used contact cement to sheet the core, but never got the wing into a plane.  The cores were still hanging on the hook by the leadouts and the cores were still joined in the middle with the epoxy I used.   Never used contct cement again except on that one wing, as Bob says it is heavy.

[Douglas Ames]

I'm going to try putting a bunch of 7.62 milimeter diameter holes in my wing and see if it lightens it any...

Soft nose or Boat tails?

[Doug Moon]

....

What you will find is that the model tracks through that maneuver much better with the CG where it is supposed to be. Penetration is key in the overhead eight in the wind. A tail heavy ship just does not penetrate as well as one in which the CG is more forward. The ship with the forward CG will have much better control authority. Perhaps the math types will chime in here with the "why" of it all.



Later - Bob Hunt 

Hello Bob,

If you have the electric model's CG set at 25% of the MAC with the battery installed then it will be the same at the end of the flight, correct?

The IC model's CG is set at 25% MAC dry.  Putting in fuel moves it forward some and it comes back near the initial setting towards the end of the flight.  Bringing it back to the "correct" CG per the dry setting.  "Correct" is really only whatever the final setting is for the model to fly at its best performance throughout the flight.  Of the two planes the IC plane is flying the entire pattern with a more nose forward CG than the electric plane with the CG set at the same MAC % with the battery installed.

I think this, along with the fact the main weight of the electric drive train is closer to the CG, helps to explain the reason why we are seeing some of the electric planes with longer noses.  And that is certainly not a problem of any kind just a design specific need. In fact it probably helps with installation of components and stuff. 

I can see with the static load of the battery keeping the CG constant might make it a little easier to trim the plane for final CG position. But I am thinking probably it takes about the same amount of test flights and adjustments to get it correct for both types of models.

I am out to mold some top blocks..... 

[Doug Moon]

Hi Doug:

 Perhaps it's the fact that the center of the mass of the weight that is balancing the ship is closer to the CG than with a glow ship due to the weight distribution of the electric versus glow components.

Later - Bob 

That is exactly why you carry a further forward CG without any ill effect!!  With the heavier part of the mass being closer to the CG is easier for the elevator to move it and stop it.  It would only make sense that you can run the CG further forward for stability without losing any of the control authority. 

[Dan McEntee]

  OK this is kind of interesting. Paul Walker has mentioned in a thread over on Stuka that he is flying a much farther forward CG and liking it. Given the information in the previous posts, what is the "typical" total weight of the battery and motor? I haven't ever heard anybody get specific about battery weights, and the weight of motors has to be significant in the equation. It's hard to comprehend just what is being talked about if you are not up on the technology. If you run a PA.75, pretty much the whole free world knows what you are talking about and can relate to what kind of weight is in the nose, or even an OS LA.46 or Fox .35. So the question is, what is a "typical" size model for this day and age, and what is a "typical" motor and battery set up, and what do they weigh? I would imagine the timer, wire, connectors, switches and such add up also and it seems the generally accepted weight is usually in the 59 to 65 ounce range. So , the mass that is the power plant (motor battery, etc.) might weigh the same (or more?) and an I/C set up, but be spread out over the length of the nose moment? Once there is more experience with the systems and things evolve some more, will this affect the design of models that are specifically electric?
   Time marches on!
   Dan McEntee

[Mark Scarborough]

I'll take that question
my setup,, Hacker A30, the motor weighs about 6.5 ounces,, I use a 4S setup,, 4000 mah,,, the batteries weigh 12.2 to 13 ounces,, ( there are two types) I have 25C and 35C packs,, the 35C packs weigh more. I have looked at 5 S setups,, It appears that the motor I am looking at is a slight bit heavier,, almost 7 ounces,, but the packs , 5S 2700, are about 11 ounces,,

[Doug Moon]

I have been thinking....  OUCH!!  I should stop doing that.  

But here goes.

Several years ago I had a model with a Saito 72 in the nose and about 1.5 oz of lead in the tail on a 14" two blade.  The model was pretty much a dog.  Sluggish in the turns and heavy on the handle as you gave it more input. CG set at 25-26% MAC. I tried the usual fixes and it just wasn't coming around.  I started a trimming thread on SS and received an enormous amount of help from the usual suspects.  But there was one explanation in particular that turned out to be the issue.  I will explain in a moment.

The last thing I tried on that model was to remove the tail weight and replace the 72 with a 56 thus removing nearly 2 oz out of the nose.  The 56 ran the same prop and in the CG machine it was in the same exact place, 25-26% MAC, as it was with the 72.  My initial thought was this would never work.  Boy was I wrong.  Right out of the gate that plane was a beast!!!  All issues were solved.

Ted and others spent alot of time in that thread explaining the "moment of inertia."  Even with the CG in the same spot the 72 caused there to be more concentrated amount of weight in the nose of the plane vs the 56 setup.  With the 56 on board the moment was shortened enough to allow the model to perform as intended.

In the case of the electric models with the larger portion of weight from the drive train located in the battery compartment and NOT in the very nose of the model it would only make sense that a farther forward CG would be helpful in flying characteristics and overall stability.  It would almost be a must as without the more forward CG the model could feel a little tail heavy or light on the lines in flight even though the CG on paper looks to be in the correct place.  Which is the exact opposite of what I had run into with my 72 setup.  On paper the 72 setup was spot on in bench trim, believe me I went over it what felt like a million times.  Further field trimming resulted only in wasted fuel.  Shorten the moment and BOOM!!  A beast was born. 

This is all very interesting yet logical at the same time.....imagine that.....

[Dan McEntee]

    Hi Doug;
      I'm familiar with the moment of inertia principals and I think I remember that thread. I'm assuming you designed that airplane around the Saito .72 with an appropriate nose moment. I just did a quick check on line to see what the engines weigh on Horizons web site, and man they are working on getting those puppies lighter! Anyway the vintage of Saito .72 you used was probably at least 16 ounces or a bit more, and the .56 you replaced it with was less, with the same CG. You said you used the same prop. How much different was the RPM? And what pitch/diameter?
    Using Mark's numbers above as a for instance, his set up is pushing a total of 18 to 20 ounces depending on battery, and I still think you need to factor in the weight of the wire, timer, switches, plugs etc.  And to get the desired CG location, you have the capability to put the battery as far forward as you need to. You still have a lot of weight out there on the end of the nose, but it is spread out a bit.
    Now, if I have my thought lined up, how much difference do you think prop RPM played in your results with the 4-strokes? I know you ran the same size prop, but I have to think that you had to spin the .56 up a bit, and the .72 was making a bit more torque and maybe more gyro effect to overcome. Do you remember the RPM range?
   Now, along the same line of thought, most everyone is running CCW props on their electric set ups. How much of an effect is that having on where the final CG gets placed? Now you have motor torque affecting the air frame in flight differently. If you are putting the CG a considerable amount forward, how much change do you make in lead out position and over all line rake? I'm thinking you need to move the lead outs forward by a good bit, correct? I don't think I've read where anyone talks about lead out position yet.
    I guess what I'm getting at is, this forward CG location is the sum of several parts that just happen to compliment each other. Take any one out, and what happens? Like, what if we couldn't get any reverse pitch props. Or, what if you could put the reverse rotation gear in the Saito .56 and what would you have then with the original model that you mention? I think this reverse pitch prop is a pretty big deal.
    Now, looking down the road to the next big advancement in batteries, and say you get to run the same number of cells and amps, but suddenly, the pack only weighs 6 ounces. Initially, you would probably just ballast up the nose for the same CG. But for next years airplane, would you design a longer nose so you won't have to add on that extra dead weight, and then that upsets the aerodynamic applecart for the rest of the airplane? In the last couple of years, I have noticed lots of electric motors and batteries being bought and sold in the forum classifieds, and it's obvious that a lot of the electric guys are still finding their way through what's out there, and then throw in the fact that the technology and hardware keeps changing so fast. I guess that's why I'll just keep lumbering along with what I have in I/C power plants. I don't have the time to get into the electric technology and the experimentation it will require, and it doesn't seem to me that the "Fox .35" or 'VF.40" of electric motor set ups has been determined yet. I do find it interesting, and don't think that it's going to ever go away, but it will be interesting to watch over the next 5 years to see how things "settle"  or if any kind of leveling off or plateau is reached, and what brands and such become more common place.
    Now my head hurts!
    Type at you later,
     Dan McEntee

[Doug Moon]

Hello Dan,

    Hi Doug;
      I'm familiar with the moment of inertia principals and I think I remember that thread. I'm assuming you designed that airplane around the Saito .72 with an appropriate nose moment. I just did a quick check on line to see what the engines weigh on Horizons web site, and man they are working on getting those puppies lighter! Anyway the vintage of Saito .72 you used was probably at least 16 ounces or a bit more, and the .56 you replaced it with was less, with the same CG. You said you used the same prop. How much different was the RPM? And what pitch/diameter?

When I was running the 72 the optimum speed for that prop was 8800 rpms.  The prop in question was a Brian Eather 14x6 2 blade with medium under camber.  I had to run the smallest venturi for the UHP manifold to keep that RPM.  I also had to run 1.5 oz of tail weight.  This tail weight was right at the very back end of the plane so I would have to use as little as possible.

When I decided to switch the 56 I tested it on the stand with that prop.  I wanted the comparison to be as close as possible to prove out the moment of inertia theory.  I was able to achieve the same RPM using the biggest venturi available for the 56.  I wasn't sure it would turn that prop in the air but I was mistaken.  The 56 is quite an animal and had no troubles swinging that prop.  I also REMOVED the 1.5 oz of tail weight.  That is how I was able to get the same CG location.

So the take off RPMs were the exact same on the same prop.  This is what made me think it was the moment of inertia as there was no other change. 

Incidentally, I had tried more tail weight with the 72 but it created the barbell effect.  I as at the max tail weight and the plane just didn't fly well.  I didn't have the right moment arms and tail size for using a 72 and still getting the feel I wanted.  It may not be possible. I don't know as I didn't pursue the 72 anymore. 

    Using Mark's numbers above as a for instance, his set up is pushing a total of 18 to 20 ounces depending on battery, and I still think you need to factor in the weight of the wire, timer, switches, plugs etc.  And to get the desired CG location, you have the capability to put the battery as far forward as you need to. You still have a lot of weight out there on the end of the nose, but it is spread out a bit.
    Now, if I have my thought lined up, how much difference do you think prop RPM played in your results with the 4-strokes? I know you ran the same size prop, but I have to think that you had to spin the .56 up a bit, and the .72 was making a bit more torque and maybe more gyro effect to overcome. Do you remember the RPM range?

As mentioned above the RPMs were the same.  I don't think there was more gyro effect in my case since I was using the same prop and RPMs.

   Now, along the same line of thought, most everyone is running CCW props on their electric set ups. How much of an effect is that having on where the final CG gets placed? Now you have motor torque affecting the air frame in flight differently. If you are putting the CG a considerable amount forward, how much change do you make in lead out position and over all line rake? I'm thinking you need to move the lead outs forward by a good bit, correct? I don't think I've read where anyone talks about lead out position yet.
    I guess what I'm getting at is, this forward CG location is the sum of several parts that just happen to compliment each other. Take any one out, and what happens? Like, what if we couldn't get any reverse pitch props. Or, what if you could put the reverse rotation gear in the Saito .56 and what would you have then with the original model that you mention? I think this reverse pitch prop is a pretty big deal.
    Now, looking down the road to the next big advancement in batteries, and say you get to run the same number of cells and amps, but suddenly, the pack only weighs 6 ounces. Initially, you would probably just ballast up the nose for the same CG. But for next years airplane, would you design a longer nose so you won't have to add on that extra dead weight, and then that upsets the aerodynamic applecart for the rest of the airplane? In the last couple of years, I have noticed lots of electric motors and batteries being bought and sold in the forum classifieds, and it's obvious that a lot of the electric guys are still finding their way through what's out there, and then throw in the fact that the technology and hardware keeps changing so fast. I guess that's why I'll just keep lumbering along with what I have in I/C power plants. I don't have the time to get into the electric technology and the experimentation it will require, and it doesn't seem to me that the "Fox .35" or 'VF.40" of electric motor set ups has been determined yet. I do find it interesting, and don't think that it's going to ever go away, but it will be interesting to watch over the next 5 years to see how things "settle"  or if any kind of leveling off or plateau is reached, and what brands and such become more common place.
    Now my head hurts!
    Type at you later,
     Dan McEntee

I am not really sure on the CCW props as I have no experience with them.  I think Bob Reeves as CCW Saito that he says is AWESOME! 

I agree with you that all the items in the drive train have to be accounted for when setting the CG.  But the main part of the weight being closer to the CG can have an effect on design theory.  With the ever changing electric environment I am thinking it will be a long while before there is a "Fox .35" and or a "PA 65" of electric setups.  I am not sure that will ever happen.  There are so many more ways to skin the "electric" cat.  I suppose one day I will try and tackle it.  But I don't have the time or resources to cover such a quest.  But as the electric pioneers forge ahead they make it that much easier for those of us in the wings to swipe their findings and put them to good use....

[RC Storick]

can anyone say concentrated mass (weight) closer to the center of gravity? the weight of my new planes engine is 6.7 oz (fox .35 weight) as opposed to 12.5. out on the end of the stick. Body in motion tends to stay in motion unless acted upon an equal and opposite force. What take less opposite force 6 or 12? Hum no brainier.
True the fuel is a little heaver but is not out on the end of the stick its closer to the CG and the difference is only 4 oz and that can be pulled into the wing if the plane is light enough in gross weight. There is that word again weight. I said this on SSW when I first came back (and boy was I hammered) baseline characteristics are set in weight and most will find this out eventually.

What I guess I am trying to say is its better to have a long nose light weight engine than a short nose heavy engine both planes of the same gross weight. This is just my opinion but who am I.

[Doug Moon]

Hello Robert,

I remember when you came on SSW taking about weight and getting blasted. Wasnt your angle that lighter was always better no matter what?  

That is not the same thing as moving weight on the airframe to different areas, example electric motor vs IC engine at almost twice the weight. Before the electric movement we didnt really have much choice did we?

[RC Storick]

Hello Robert,

I remember when you came on SSW taking about weight and getting blasted. Wasnt your angle that lighter was always better no matter what?  

That is not the same thing as moving weight on the airframe to different areas, example electric motor vs IC engine at almost twice the weight. Before the electric movement we didnt really have much choice did we?

No this should be a good change. I would rather have a light plane than a heavy one. Lighter is always better for me.

[Dan McEntee]

can anyone say concentrated mass (weight) closer to the center of gravity? the weight of my new planes engine is 6.7 oz (fox .35 weight) as opposed to 12.5. out on the end of the stick. Body in motion tends to stay in motion unless acted upon an equal and opposite force. What take less opposite force 6 or 12? Hum no brainier.
True the fuel is a little heaver but is not out on the end of the stick its closer to the CG and the difference is only 4 oz and that can be pulled into the wing if the plane is light enough in gross weight. There is that word again weight. I said this on SSW when I first came back (and boy was I hammered) baseline characteristics are set in weight and most will find this out eventually.

What I guess I am trying to say is its better to have a long nose light weight engine than a short nose heavy engine both planes of the same gross weight. This is just my opinion but who am I.

    Hi Bob;
     Yeah, your motor only weighs 6.7 ounces, but the 12 or 13 ounce battery pack is sitting right behind it. Add in all the extra hardware required, and you may have a higher total weight in the nose, but it is spread out. And, if the forward CG effect is desired, then to balance the model accordingly, you move the battery as far forward as needed or practical. It would be the cat's pajamas if you could put the battery right on the balance point, but then what would the nose moment look like, and how much ballast would you need to balance? This electric stuff is an experimenter's dream is you have the time and understanding to find your set up, and what will it do for airframe design? Like I said before, the next 5 years or so will be interesting to watch the development of things, including, motor technology, battery technology, and air frame design. And after all that we have seen in the last 25 years or so, prop development seems to be at the bottom end of equation, with the exception of the ease of running reverse rotation. To me , that is the biggest advantage. There are ten times more props available for CCW electric use, than there is for CW I/C use.
    Type at you later,
      Dan McEntee

[Dan McEntee]

  Hi Doug;
     I have been playing with a Top Flite Score with a Saito .56 in it for the last 3 or 4 years or so, and have been following Bob Reeves recipes for four strokes. At first, I could see why some guys loved them and why some guys use them for paper weights, but Bob's set up got me the consistency that I was looking for. I got one of the reverse rotation gears, and another Saito.56 that I want to install it in, and set that engine up as identical to the other as I can. Then I'll head to the flying field and put up three flights with it one way, then swap out the engine and try it the other way. The biggest issue I have right now is finding left handed props like I want and the spare time to do the work. I have been curious about the CCW effect for a long time, and always wanted to do a twin with counter rotating props, using a typical OS.25 engine, but getting a left hand crank is not the easiest thing to do. There are props out there I could use for this project, and you do have the advantage of getting the engine weight closer to the balance point. Walt Brownell's twin electric model got me reved up on the idea again when he was flying his second model. It was impressive!
     Well, back to cleaning the garage. This is a whole lot more fun but the garage is a disaster!
   Type at you later,
     Dan McEntee

[FLOYD CARTER]

Robert.  You really don't have to live with grey!  You can dribble some blue into the grey can to liven it up a bit.

Or.  Red covers nicely in one coat.

Floyd

[Howard Rush]

Too much lift in certain areas of the pattern caused them to be unstable unless carrying a certain amount of payload. So figuring out the weight envelope for a particular design is important.

Understanding the actual phenomenon you experienced is more important.  See Igor's article in the latest Stunt News.

[Howard Rush]

That is exactly why you carry a further forward CG without any ill effect!!  With the heavier part of the mass being closer to the CG is easier for the elevator to move it and stop it.  It would only make sense that you can run the CG further forward for stability without losing any of the control authority.  

can anyone say concentrated mass (weight) closer to the center of gravity? the weight of my new planes engine is 6.7 oz (fox .35 weight) as opposed to 12.5. out on the end of the stick. Body in motion tends to stay in motion unless acted upon an equal and opposite force. What take less opposite force 6 or 12? Hum no brainier.
True the fuel is a little heaver but is not out on the end of the stick its closer to the CG and the difference is only 4 oz and that can be pulled into the wing if the plane is light enough in gross weight. There is that word again weight. I said this on SSW when I first came back (and boy was I hammered) baseline characteristics are set in weight and most will find this out eventually.

What I guess I am trying to say is its better to have a long nose light weight engine than a short nose heavy engine both planes of the same gross weight. This is just my opinion but who am I.

It would be the cat's pajamas if you could put the battery right on the balance point, but then what would the nose moment look like, and how much ballast would you need to balance?

I'm familiar with the moment of inertia principals...

Really?

Yes, reducing the moment of inertia in the pitch axis makes a airplane dynamically more stable.  However, your intuition is letting you down on how to calculate moment of inertia. Here's how: http://en.wikipedia.org/wiki/Moment_of_inertia .  Look for "Moment of inertia about an axis".  Here is a spreadsheet that will do the calculation for you.  It calculates moment and moment of inertia for a bunch of parts.  You can fiddle with it to see what configuration has what moment of inertia for the same CG.  To compare one configuration to another, fiddle with distances from the CG until both have the same moment: the same contribution to CG.  Then read the moment of inertia.  You will see that Doug's .56 has less moment of inertia that the .72 at the same distance from the CG plus the tail weight it took to balance it (use a negative number for distance behind the CG).  You will also see that having the battery and motor at the same distance from the CG gives you less moment of inertia than having them separated.

The second attachment is a motor-battery example.  Configuration 1 is approximately the motor (part 2) and battery (part 1) locations in my current plane.  Configuration 2 is what would happen if I moved the battery aft 2 inches and moved the motor forward to have the CG come out the same.  

[Pat]

In this thread, I saw someone mention "unobtainium" I build and race front engine dragsters, and it seems that I use a similar alloy we like to call ucantaffordium...

Pat

[Dan McEntee]

   Hi Howard;
     First, let me clarify my statement about me understanding moment of inertia principles, in that I understand them in a basic way. I'm a welder/fabricator/maintenance technician  and math has never been one of my strengths. And I know I'm getting into something that is probably over my head, but I find this forward CG phenomena that Bob has been talking about and what I have read in Paul's thread over on Stuka kind of interesting. I'm not arguing a point, just throwing out some questions as this all relates to my level of understanding.
    From what Paul and Bob are saying, they have been flying with a significantly forward CG that what they have in the past. I don't know the exact parameters of each airplane but Paul's model looks to be what I call a"typical" stunt model for these times so let's use his model. You may know the moment numbers, but I'm just going to shoot from the hip and see if I can get my question out correctly.
    First, I think we need to establish the far end of the nose moment, and I'm going to call that the back of the spinner back plate. And for an I/C engine we'll use the Saito .56 we talked about before, mainly because I just looked up the weight and it's 15 ounces. This engine weighs 15 ounces, and that weight, for calculation purposes, is concentrated in one specific point that I think you would call it's center of mass, correct? And that point is a given distance from the CG when installed in the model, and four ounces of fuel (which I think is typical for a Saito.56) weighs a little over 3 ounces, and it's behind the engine for a total of 18 ounces. It gets lighter as the flight progresses. I'm going to guess that the center of mass of the engine is at least two and a quarter inches behind the spinner back plate and the center of mass of the fuel tank is maybe four inches behind that. How much does that 3 ounces of fuel factor in to the moment of inertia equation as it is burning off? And I guess we had better put a location on the CG, and I would guess that it would be around 28 to 30% of the wing cord?
    Now lets put the electric set up in, and I'll use the numbers in your spread sheet because they are probably closer than what I could guess, and that's 9 ounces for the motor and 13 ounces for the battery. The motor is probably mounted typically of at outrunner, and attached right behind the nose ring and the spinner back plate. It's 9 ounces, and it's center of mass could be an inch to an inch and a quarter in front of the center of mass location for the Saito. And the battery weighs 13 ounces and is located behind the motor, and this is where I hope I can state this correctly. You have the same nose length in either case to put the components in, and to achieve the forward CG location that is being desired, your only option is to put the battery as far forward as necessary to achieve the desire balance point. The balance point is around 25% of the wing cord now, maybe less as Bob has put it "north of that" as he says. I guess you really need battery dimensions to locate it's center of mass so this all may be a worthless discussion, but if you have that 9 ounce motor 1 inch or more further forward than the 15 ounce engine, and the 13 ounce battery potentially further forward than the 3 ounces of fuel that is decreasing as the flight progresses, you have theoretically more total weight in the nose of the electric model? Again, I'm having a hard time explaining what I think I have in my head, but if the CG or balance point is being significantly moved forward, and you haven't moved that back side of the spinner back plate that locates the forward point of the nose moment, and the collective total weight of the electric components being maybe four ounces more than the I/C components, that doesn't affect the moment of inertia? I guess I'm thinking of it as an "average"?
     I know I'm not making this very clear, but I have to make the wild ass guess that the reverse rotation prop is making a significant contribution to the electric set up? I know the moment of inertia is significant, but if Bob and Paul (or anyone else flying an electric set up) were limited to CCW rotating props, would they be getting the same results as far a CG location? Does the motor design have anything to do with it? In other words, would anyone be flying electric if they had to use what is now old fashioned DC can motors with cobalt magnets (read heavy!) to achieve the same power? And not to mention battery technology. The electric set up is truly the sum of it's parts I think, and if one component was not available, would anyone be using it? I just have a feeling that the CCW prop is a significant part of the plan and now that some of you guys have progressed to a certain critical point with it, I would be interested in hearing how your current model flies with a CW turning prop. And if a I/C engine set up with a similar balance point and a CCW turning prop could produce similar results? Maybe not equal, but similar?
    Most of us have been flying CCW and it is the normal mode for a whole lot of us, and stunt model design and power plants and prop design have been dealing with "P" factor and gyroscopic pression  (and all the other effects that are over my head and I get into trouble trying to talk about) for all these years. Has the advances in electrics and prop technology made it possible for us to take advantage of all or some of these properties and effects? And where are lead out locations in all of this compared to before? I don't think I've heard that mentioned or discussed.
    In Doug's Saito .72 powered model, would a 1 inch shorter nose moment and a CCW turning prop made a significant change in it's performance?
    I gotta go to bed, I can't believe how long it took me to think this out and type it!
   Type at you later,
   Dan McEntee