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W&B Configuration

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philperry9

Joined: 23 Nov 2011
Posts: 381

Posted: Sun Mar 26, 2017 6:08 pm Post subject: W&B Configuration

I'm about to zero in on having this thing on the scales in the next couple of days.  



Reading the FAA circular, they mention that the sumo should be full. (12 Qts in my case).   Vans Section 5 is a little more vague.  



I have a hard time seeing myself ever filling the sump with 12, just to watch it get pumped right overboard and settle in around 8-9 on the stick.  



What have you all done with regards to sump capacity when running your W&B?  I'm tempted to run it with full lines and 8 on the stick. 



But I'm just curious to know what most of you have done with yours?



Sent from my iPhone

rv10flyer(at)live.com
Guest

Posted: Sun Mar 26, 2017 6:26 pm Post subject: W&B Configuration

I thought through how I would fly the plane (aka 8qts) and did the W&B based on that assumption.

--

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Sun Mar 26, 2017 6:33 pm Post subject: W&B Configuration

Do it on a measured 8 qts. The quantity to full is known. You likely 

will run it between 6 and 8 qts, depending on whether you have an 

air/oil separator or not.

You can then prepare a separate W&B with full sump.

I also recommend you weigh it with fuel tanks dry, because you won't 

know what the exact full quantity is, much less its weight that depends 

on temperature.



On 3/26/2017 7:06 PM, Phillip Perry wrote:

 	  Quote: 	
		   



 I'm about to zero in on having this thing on the scales in the next couple of days.



 Reading the FAA circular, they mention that the sumo should be full. (12 Qts in my case).   Vans Section 5 is a little more vague.



 I have a hard time seeing myself ever filling the sump with 12, just to watch it get pumped right overboard and settle in around 8-9 on the stick.



 What have you all done with regards to sump capacity when running your W&B?  I'm tempted to run it with full lines and 8 on the stick.



 But I'm just curious to know what most of you have done with yours?



 Sent from my iPhone

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

Dave Saylor

Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA

Posted: Sun Mar 26, 2017 7:27 pm Post subject: W&B Configuration

I do W&Bs in the most common empty configuration.Â  So I'd weigh it with 8 or 9 qts.



If you want the data for "just in case", weigh it with 8 and then add 2 quarts.Â  That should be enough to see the weight on a decent scale.Â  Record all your weights again and you'll have the data to extract the exact arm of the oil.Â  It's easy on a spreadsheet.

Same goes for pilot, pax, and baggage.Â  Plop down in the seat while it's still on the scales and you get the most accurate arm for your own self.Â  Put 50# in the center of the baggage compartment, and you can get that arm too.

Another thing to consider is to make the datum an easy-to-find spot, like the wing leading edge or the instrument panel or the front of the door.Â  Then when you want to actually measure something important some day, you don't have to mess with some imaginary point out in front of the plane.

--Dave

On Sun, Mar 26, 2017 at 7:06 PM, Phillip Perry <philperry9(at)gmail.com (philperry9(at)gmail.com)> wrote:

 	  Quote: 	
		  --> RV10-List message posted by: Phillip Perry <philperry9(at)gmail.com (philperry9(at)gmail.com)>

 

 I'm about to zero in on having this thing on the scales in the next couple of days.

 

 Reading the FAA circular, they mention that the sumo should be full. (12 Qts in my case).Â  Â Vans Section 5 is a little more vague.

 

 I have a hard time seeing myself ever filling the sump with 12, just to watch it get pumped right overboard and settle in around 8-9 on the stick.

 

 What have you all done with regards to sump capacity when running your W&B?Â  I'm tempted to run it with full lines and 8 on the stick.

 

 But I'm just curious to know what most of you have done with yours?

 

 

 

 Sent from my iPhone

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--Dave
KWVI

Lew Gallagher

Joined: 04 Jan 2008
Posts: 402
Location: Greenville , SC

Posted: Sun Mar 26, 2017 8:05 pm Post subject: W&B Configuration

Hey guys,

  

 Just curious here.  Did I understand correctly that heating fuel  changes the weight ... ??  If so, could someone explain why that would  be?

  

 Thanks, â€“ Lew

_________________
non-pilot
crazy about building
NOW OFICIALLY BUILDER #40549
Fly off completed !

jdriggs49(at)MSN.COM
Guest

Posted: Sun Mar 26, 2017 8:25 pm Post subject: W&B Configuration

When you add heat for all practical purposes it adds mass to the object (liquid fuel).

 There is a formula that shows this but since my iPad doesn't do "powers" I won't repeat it here. In actuality the added mass is so small as to be of virtually no easily measurable consequence. Heating causes an easily discerned  expansion however.

 

 Sent from my iPad

 

 On Mar 26, 2017, at 11:11 PM, "lewgall(at)charter.net (lewgall(at)charter.net)" <lewgall(at)charter.net (lewgall(at)charter.net)> wrote:

 

 

  	  Quote: 	
		      Hey guys,

  

 Just curious here.  Did I understand correctly that heating fuel changes the weight ... ??  If so, could someone explain why that would be?

  

 Thanks, â€“ Lew

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Sun Mar 26, 2017 8:34 pm Post subject: Re: W&B Configuration

 	  Lew Gallagher wrote: 	
		  Hey guys,

  

 Just curious here.  Did I understand correctly that heating fuel  changes the weight ... ??  If so, could someone explain why that would  be?

  

 Thanks, â€“ Lew 	




Nearly all materials (water being different) expand when heated. So one gallon of gas at some temperature might weigh exactly 6 pounds. Heat it up, it expands and overflows the container. There is now less (by weight, or number of molecules) gas in the one gallon container. In real life the aluminum fuel tank will also expand, but it's an order of magnitude less than the expansion of the gas. This is one reason jets (that carry huge amounts of gas) usually keep track of the actual weight.

Strictly speaking the statement should be "Heating decreases the density (mass per volume)".

_________________
Bob Turner
RV-10 QB

Lew Gallagher

Joined: 04 Jan 2008
Posts: 402
Location: Greenville , SC

Posted: Mon Mar 27, 2017 4:15 am Post subject: W&B Configuration

Volume, obviously yes.  Weight?  Sounds like "Trump science" to me   

Keep trying, not sure I believe it yet.  Fuel consumption or 

expansion/contraction changing COG; changing volume with overflow;  density, 

I can understand.  Maybe that's the deal -- does the expansion with heat 

shift the weight, not change the weight?  As I said, it doesn't really 

matter, just curious.



Later, - Lew



Nearly all materials (water being different) expand when heated. So one 

gallon of gas at some temperature might weigh exactly 6 pounds. Heat it up, 

it expands and overflows the container. There is now less (by weight, or 

number of molecules) gas in the one gallon container. In real life the 

aluminum fuel tank will also expand, but it's an order of magnitude less 

than the expansion of the gas. This is one reason jets (that carry huge 

amounts of gas) usually keep track of the actual weight.



--------

Bob Turner

RV-10 QB

_________________
non-pilot
crazy about building
NOW OFICIALLY BUILDER #40549
Fly off completed !

Lew Gallagher

Joined: 04 Jan 2008
Posts: 402
Location: Greenville , SC

Posted: Mon Mar 27, 2017 4:28 am Post subject: W&B Configuration

Then there's this:  "Water expands about four percent when heated from room 

temperature to its boiling point".  Hence more issue of rising ocean levels 

from global warming of ocean temperature than from melting ice caps.



Never mind, I'm just giddy from South Carolina making it into the Final Four 

.. who would have thunk that!!

Do NOT archive.



Later, - Lew

"Nearly all materials (water being different) expand when heated. So one 

gallon of gas at some temperature might weigh exactly 6 pounds. Heat it up, 

it expands and overflows the container. There is now less (by weight, or 

number of molecules) gas in the one gallon container. In real life the 

aluminum fuel tank will also expand, but it's an order of magnitude less 

than the expansion of the gas. This is one reason jets (that carry huge 

amounts of gas) usually keep track of the actual weight."



--------

_________________
non-pilot
crazy about building
NOW OFICIALLY BUILDER #40549
Fly off completed !

Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Mon Mar 27, 2017 4:54 am Post subject: W&B Configuration

Don't worry Lew, it's just that many people are better pilots that they are scientists. It is true that the fuel will expand when it is warm. But considering there will be the same number of molecules, they will not weigh differently when they are warm.  Yes, the fuel tanks will overflow if they are all the way full to the top, so warm fuel would weigh less in that situationâ€¦ If it overflowed some of the fuel. But, if you have your fuel tanks filled to 2 inches from the top, on a cold day, and then you take your plane out on a warm day, and the fuel is up to the top, it will not weigh less. It may in fact weigh a minuscule amount more, due to additional dissolved gases.  The comment about Jets calculating fuel in pounds is accurate, but that would not simply be because fuel weighs less when it is warm. It would have more to do with that it has less volume when it is warm , for the same given amount of fuel in molecules. So you are not going crazy.

Either way, the warm fuel versus cold fuel is a small enough number has to be pretty much insignificant when calculating your weight and balance. Sure, it may weigh a few pounds more if you feel to the exact same spot on a cold day as on a warm day, but I don't think a weight and balance needs to be calculated to that Precision.

Tim



 	  Quote: 	
		   On Mar 27, 2017, at 7:14 AM, <lewgall(at)charter.net> <lewgall(at)charter.net> wrote:

 

 

 

 Volume, obviously yes.  Weight?  Sounds like "Trump science" to me   Keep trying, not sure I believe it yet.  Fuel consumption or expansion/contraction changing COG; changing volume with overflow;  density, I can understand.  Maybe that's the deal -- does the expansion with heat shift the weight, not change the weight?  As I said, it doesn't really matter, just curious.

 

 Later, - Lew

 

 

 

 Nearly all materials (water being different) expand when heated. So one gallon of gas at some temperature might weigh exactly 6 pounds. Heat it up, it expands and overflows the container. There is now less (by weight, or number of molecules) gas in the one gallon container. In real life the aluminum fuel tank will also expand, but it's an order of magnitude less than the expansion of the gas. This is one reason jets (that carry huge amounts of gas) usually keep track of the actual weight.

 

 --------

 Bob Turner

 RV-10 QB

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Mon Mar 27, 2017 6:10 am Post subject: W&B Configuration

The weight per gallon of avgas varies approx. 0.1% per degree C.

So at 15C it is 6.01 lbs per gal. At -40 it is 6.41 lbs/gal, and at 35C 

it is around 5.88 lb/gal. A swing of .53 lbs/gal. That would be 

somewhere in the 32 lb range for full tanks. Yes, it is mostly very 

close to the C.G. I wouldn't call it insignificant. Yes, the difference 

between 10 and 30 C is around a 2% change, not big. Then you have 

difference between individual tanks that may be a gallon or two, for 

another 12 lb difference.

However, why worry about it when it is easy to weigh the plane with 

tanks empty?

I don't advocate calculating weight to a couple decimals, nor c.g. by 

more than about 1 decimal, but you should be aware that if you are 

fueling in Phoenix in the summer, that 120 lbs of baggage will affect 

c.g. more than it will at International Falls in Jan.



On 3/27/2017 5:53 AM, Tim Olson wrote:

 	  Quote: 	
		   

 C.G.

 Don't worry Lew, it's just that many people are better pilots that they are scientists. It is true that the fuel will expand when it is warm. But considering there will be the same number of molecules, they will not weigh differently when they are warm.  Yes, the fuel tanks will overflow if they are all the way full to the top, so warm fuel would weigh less in that situationâ€¦ If it overflowed some of the fuel. But, if you have your fuel tanks filled to 2 inches from the top, on a cold day, and then you take your plane out on a warm day, and the fuel is up to the top, it will not weigh less. It may in fact weigh a minuscule amount more, due to additional dissolved gases.  The comment about Jets calculating fuel in pounds is accurate, but that would not simply be because fuel weighs less when it is warm. It would have more to do with that it has less volume when it is warm , for the same given amount of fuel in molecules. So you are not going crazy.

 Either way, the warm fuel versus cold fuel is a small enough number has to be pretty much insignificant when calculating your weight and balance. Sure, it may weigh a few pounds more if you feel to the exact same spot on a cold day as on a warm day, but I don't think a weight and balance needs to be calculated to that Precision.

 Tim

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Mon Mar 27, 2017 6:52 am Post subject: W&B Configuration

As long as you understand that nearly the entire reason that

the fuel has a different "weight" per gallon is that the

actual QUANTITY of fuel molecules in that gallon is less

as it gets warmer, then you're right on.  It's a VOLUME

issue, not a weight issue.   If you took hot fuel

of a given weight, and cold fuel of a given weight, and

brought them to the same temperature, they would still

weigh the same but have different VOLUMES.



And, I will say that I do consider it to be pretty irrelevant

regarding the weight of fuel, despite the 32lbs of

difference.  The reason I say it's irrelevant is because

I know of no person who flies small planes like RV's, who

would calculate their W&B for a given day of flying and

actually compensate for the weight of fuel THAT DAY

based on temperature.



But you're right, just weigh it with the tanks empty, or

if you wish, after adding some fuel and draining everything

but the unusable fuel.  In the RV-10/14 the unusable fuel

is also such a small quantity that it really isn't a significant

number for practical purposes.  I have flown my tanks to

dry in testing and there is about 1 cup, 2 max, left

in the tank when flown to empty.



So my personal summary is:  The weight difference of fuel

is not significant in PRACTICAL terms for anything,

AFTER you have done an accurate airplane weighing.  You're

not likely to ever need to consider that added or

decreased weight due to temperature when planning any

flight.  And, for practical purposes, in the RV-10/14

models, useable fuel = total fuel, so you don't need to

mark your tanks with a label like "60 Gallons, 59 usable"

or anything like that.



I personally have never, other than during fuel tank

capacity testing, ever flown with less than 5 gallons in

a tank.  I think the risk of fuel unporting during

turns in the pattern would be too high if you get much

lower than that.



And, I think weighing with tanks empty is the way to go.



Tim

On 03/27/2017 09:08 AM, Kelly McMullen wrote:

 	  Quote: 	
		   



 The weight per gallon of avgas varies approx. 0.1% per degree C.

 So at 15C it is 6.01 lbs per gal. At -40 it is 6.41 lbs/gal, and at 35C

 it is around 5.88 lb/gal. A swing of .53 lbs/gal. That would be

 somewhere in the 32 lb range for full tanks. Yes, it is mostly very

 close to the C.G. I wouldn't call it insignificant. Yes, the difference

 between 10 and 30 C is around a 2% change, not big. Then you have

 difference between individual tanks that may be a gallon or two, for

 another 12 lb difference.

 However, why worry about it when it is easy to weigh the plane with

 tanks empty?

 I don't advocate calculating weight to a couple decimals, nor c.g. by

 more than about 1 decimal, but you should be aware that if you are

 fueling in Phoenix in the summer, that 120 lbs of baggage will affect

 c.g. more than it will at International Falls in Jan.



 On 3/27/2017 5:53 AM, Tim Olson wrote:

> 

> C.G.

> Don't worry Lew, it's just that many people are better pilots that

> they are scientists. It is true that the fuel will expand when it is

> warm. But considering there will be the same number of molecules, they

> will not weigh differently when they are warm.  Yes, the fuel tanks

> will overflow if they are all the way full to the top, so warm fuel

> would weigh less in that situationâ€¦ If it overflowed some of the fuel.

> But, if you have your fuel tanks filled to 2 inches from the top, on a

> cold day, and then you take your plane out on a warm day, and the fuel

> is up to the top, it will not weigh less. It may in fact weigh a

> minuscule amount more, due to additional dissolved gases.  The comment

> about Jets calculating fuel in pounds is accurate, but that would not

> simply be because fuel weighs less when it is warm. It would have more

> to do with that it has less volume when it is warm , for the same

> given amount of fuel in molecules. So you are not going crazy.

> Either way, the warm fuel versus cold fuel is a small enough number

> has to be pretty much insignificant when calculating your weight and

> balance. Sure, it may weigh a few pounds more if you feel to the exact

> same spot on a cold day as on a warm day, but I don't think a weight

> and balance needs to be calculated to that Precision.

> Tim

jesse(at)saintaviation.co
Guest

Posted: Mon Mar 27, 2017 7:23 am Post subject: W&B Configuration

This whole discussion cracks me up. The weighing issue is that you have to do it with empty tanks or full tanks. That's the point made that started the expansion of fuel when heated discussion. If you use full tanks, the plane is lighter if the fuel is warm because it's bigger. If you fill it up with cold fuel and it warms up, the expansion will send fuel out the vents onto the ground, making the plane lighter. At half tanks it makes no difference in weight, but you can't weigh at half tanks because you don't know exactly how much fuel you have to calculate it back out for an accurate empty weight. 



The actual best way to get empty weight is to disconnect the fuel line at the engine and pump it out, leaving the unusable fuel in the tanks. 



Jesse Saint

Saint Aviation, Inc. 

jesse(at)saintaviation.com

C: 352-427-0285

F: 815-377-3694



Sent from my iPhone



 	  Quote: 	
		   On Mar 27, 2017, at 8:14 AM, <lewgall(at)charter.net> <lewgall(at)charter.net> wrote:

 

 

 

 Volume, obviously yes.  Weight?  Sounds like "Trump science" to me   Keep trying, not sure I believe it yet.  Fuel consumption or expansion/contraction changing COG; changing volume with overflow;  density, I can understand.  Maybe that's the deal -- does the expansion with heat shift the weight, not change the weight?  As I said, it doesn't really matter, just curious.

 

 Later, - Lew

 

 

 

 Nearly all materials (water being different) expand when heated. So one gallon of gas at some temperature might weigh exactly 6 pounds. Heat it up, it expands and overflows the container. There is now less (by weight, or number of molecules) gas in the one gallon container. In real life the aluminum fuel tank will also expand, but it's an order of magnitude less than the expansion of the gas. This is one reason jets (that carry huge amounts of gas) usually keep track of the actual weight.

 

 --------

 Bob Turner

 RV-10 QB

flyboy(at)gmail.com
Guest

Posted: Mon Mar 27, 2017 7:26 am Post subject: W&B Configuration

On Mon, Mar 27, 2017 at 8:43 AM, Tim Olson <Tim(at)myrv10.com (Tim(at)myrv10.com)> wrote:

 	  Quote: 	
		  --> RV10-List message posted by: Tim Olson <Tim(at)MyRV10.com>

 

 As long as you understand that nearly the entire reason that

 the fuel has a different "weight" per gallon is that the

 actual QUANTITY of fuel molecules in that gallon is less

 as it gets warmer, then you're right on.Â  It's a VOLUME

 issue, not a weight issue.Â  Â If you took hot fuel

 of a given weight, and cold fuel of a given weight, and

 brought them to the same temperature, they would still

 weigh the same but have different VOLUMES. 	




Uhm, no.Â  If you take a pound of cold fuel and pound of hot fuel, they're going to have the same volume *and* weight once you equalize the temperature.Â  This is one of the many reasons we fuel airliners by weight.

rv10pro(at)gmail.com
Guest

Posted: Mon Mar 27, 2017 7:31 am Post subject: W&B Configuration

On the long cross country flights from the West Coast to AirVenture I would swear the bugs get bigger and their weight becomes a factor as we approach Wisconsin.

Will need to tweak my W&B formula.

JohnÂ 

On Mon, Mar 27, 2017 at 7:43 AM, Tim Olson <Tim(at)myrv10.com (Tim(at)myrv10.com)> wrote:

 	  Quote: 	
		  --> RV10-List message posted by: Tim Olson <Tim(at)MyRV10.com>

 

 As long as you understand that nearly the entire reason that

 the fuel has a different "weight" per gallon is that the

 actual QUANTITY of fuel molecules in that gallon is less

 as it gets warmer, then you're right on.Â  It's a VOLUME

 issue, not a weight issue.Â  Â If you took hot fuel

 of a given weight, and cold fuel of a given weight, and

 brought them to the same temperature, they would still

 weigh the same but have different VOLUMES.

 

 And, I will say that I do consider it to be pretty irrelevant

 regarding the weight of fuel, despite the 32lbs of

 difference.Â  The reason I say it's irrelevant is because

 I know of no person who flies small planes like RV's, who

 would calculate their W&B for a given day of flying and

 actually compensate for the weight of fuel THAT DAY

 based on temperature.

 

 But you're right, just weigh it with the tanks empty, or

 if you wish, after adding some fuel and draining everything

 but the unusable fuel.Â  In the RV-10/14 the unusable fuel

 is also such a small quantity that it really isn't a significant

 number for practical purposes.Â  I have flown my tanks to

 dry in testing and there is about 1 cup, 2 max, left

 in the tank when flown to empty.

 

 So my personal summary is:Â  The weight difference of fuel

 is not significant in PRACTICAL terms for anything,

 AFTER you have done an accurate airplane weighing.Â  You're

 not likely to ever need to consider that added or

 decreased weight due to temperature when planning any

 flight.Â  And, for practical purposes, in the RV-10/14

 models, useable fuel = total fuel, so you don't need to

 mark your tanks with a label like "60 Gallons, 59 usable"

 or anything like that.

 

 I personally have never, other than during fuel tank

 capacity testing, ever flown with less than 5 gallons in

 a tank.Â  I think the risk of fuel unporting during

 turns in the pattern would be too high if you get much

 lower than that.

 

 And, I think weighing with tanks empty is the way to go.

 

 Tim

 

 

 On 03/27/2017 09:08 AM, Kelly McMullen wrote:

  	  Quote: 	
		   --> RV10-List message posted by: Kelly McMullen <kellym(at)aviating.com (kellym(at)aviating.com)>

 

 The weight per gallon of avgas varies approx. 0.1% per degree C.

 So at 15C it is 6.01 lbs per gal. At -40 it is 6.41 lbs/gal, and at 35C

 it is around 5.88 lb/gal. A swing of .53 lbs/gal. That would be

 somewhere in the 32 lb range for full tanks. Yes, it is mostly very

 close to the C.G. I wouldn't call it insignificant. Yes, the difference

 between 10 and 30 C is around a 2% change, not big. Then you have

 difference between individual tanks that may be a gallon or two, for

 another 12 lb difference.

 However, why worry about it when it is easy to weigh the plane with

 tanks empty?

 I don't advocate calculating weight to a couple decimals, nor c.g. by

 more than about 1 decimal, but you should be aware that if you are

 fueling in Phoenix in the summer, that 120 lbs of baggage will affect

 c.g. more than it will at International Falls in Jan.

 

 On 3/27/2017 5:53 AM, Tim Olson wrote:

  	  Quote: 	
		   --> RV10-List message posted by: Tim Olson <Tim(at)MyRV10.com>

 C.G.

 Don't worry Lew, it's just that many people are better pilots that

 they are scientists. It is true that the fuel will expand when it is

 warm. But considering there will be the same number of molecules, they

 will not weigh differently when they are warm.Â  Yes, the fuel tanks

 will overflow if they are all the way full to the top, so warm fuel

 would weigh less in that situationâ€¦ If it overflowed some of the fuel.

 But, if you have your fuel tanks filled to 2 inches from the top, on a

 cold day, and then you take your plane out on a warm day, and the fuel

 is up to the top, it will not weigh less. It may in fact weigh a

 minuscule amount more, due to additional dissolved gases.Â  The comment

 about Jets calculating fuel in pounds is accurate, but that would not

 simply be because fuel weighs less when it is warm. It would have more

 to do with that it has less volume when it is warm , for the same

 given amount of fuel in molecules. So you are not going crazy.

 Either way, the warm fuel versus cold fuel is a small enough number

 has to be pretty much insignificant when calculating your weight and

 balance. Sure, it may weigh a few pounds more if you feel to the exact

 same spot on a cold day as on a warm day, but I don't think a weight

 and balance needs to be calculated to that Precision.

 Tim

 	
	
 ====================================

 -List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigator?RV10-List

 ====================================

  FORUMS -

 eferrer" target="_blank">http://forums.matronics.com

 ====================================

 WIKI -

 errer" target="_blank">http://wiki.matronics.com

 ====================================

 b Site -

 Â  Â  Â  Â  Â  -Matt Dralle, List Admin.

 rel="noreferrer" target="_blank">http://www.matronics.com/contribution

 ====================================

rene(at)felker.com
Guest

Posted: Mon Mar 27, 2017 7:37 am Post subject: W&B Configuration

I did mine, full lines and 9 on the stick. I am changing my starter and will

be redoing it in May.  I am going to 8 this time.  I almost always run

within a Quart of that.  Never over 9 and as low as 6 is what I have seen in

my 700 hours.



Rene'

801-721-6080



--

rene(at)felker.com
Guest

Posted: Mon Mar 27, 2017 7:49 am Post subject: W&B Configuration

Great idea.

 

Do not archive.

 

Rene'

801-721-6080

 

From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of John Cox

Sent: Monday, March 27, 2017 9:31 AM

To: rv10-list(at)matronics.com

Subject: Re: Re: W&B Configuration

 

On the long cross country flights from the West Coast to AirVenture I would swear the bugs get bigger and their weight becomes a factor as we approach Wisconsin.



 



Will need to tweak my W&B formula.



 



John 

 

On Mon, Mar 27, 2017 at 7:43 AM, Tim Olson <Tim(at)myrv10.com (Tim(at)myrv10.com)> wrote: 	  Quote: 	
		  

--> RV10-List message posted by: Tim Olson <Tim(at)MyRV10.com (Tim(at)MyRV10.com)>



As long as you understand that nearly the entire reason that

the fuel has a different "weight" per gallon is that the

actual QUANTITY of fuel molecules in that gallon is less

as it gets warmer, then you're right on.  It's a VOLUME

issue, not a weight issue.   If you took hot fuel

of a given weight, and cold fuel of a given weight, and

brought them to the same temperature, they would still

weigh the same but have different VOLUMES.



And, I will say that I do consider it to be pretty irrelevant

regarding the weight of fuel, despite the 32lbs of

difference.  The reason I say it's irrelevant is because

I know of no person who flies small planes like RV's, who

would calculate their W&B for a given day of flying and

actually compensate for the weight of fuel THAT DAY

based on temperature.



But you're right, just weigh it with the tanks empty, or

if you wish, after adding some fuel and draining everything

but the unusable fuel.  In the RV-10/14 the unusable fuel

is also such a small quantity that it really isn't a significant

number for practical purposes.  I have flown my tanks to

dry in testing and there is about 1 cup, 2 max, left

in the tank when flown to empty.



So my personal summary is:  The weight difference of fuel

is not significant in PRACTICAL terms for anything,

AFTER you have done an accurate airplane weighing.  You're

not likely to ever need to consider that added or

decreased weight due to temperature when planning any

flight.  And, for practical purposes, in the RV-10/14

models, useable fuel = total fuel, so you don't need to

mark your tanks with a label like "60 Gallons, 59 usable"

or anything like that.



I personally have never, other than during fuel tank

capacity testing, ever flown with less than 5 gallons in

a tank.  I think the risk of fuel unporting during

turns in the pattern would be too high if you get much

lower than that.



And, I think weighing with tanks empty is the way to go.



Tim



On 03/27/2017 09:08 AM, Kelly McMullen wrote: 	  Quote: 	
		  

--> RV10-List message posted by: Kelly McMullen <kellym(at)aviating.com (kellym(at)aviating.com)>



The weight per gallon of avgas varies approx. 0.1% per degree C.

So at 15C it is 6.01 lbs per gal. At -40 it is 6.41 lbs/gal, and at 35C

it is around 5.88 lb/gal. A swing of .53 lbs/gal. That would be

somewhere in the 32 lb range for full tanks. Yes, it is mostly very

close to the C.G. I wouldn't call it insignificant. Yes, the difference

between 10 and 30 C is around a 2% change, not big. Then you have

difference between individual tanks that may be a gallon or two, for

another 12 lb difference.

However, why worry about it when it is easy to weigh the plane with

tanks empty?

I don't advocate calculating weight to a couple decimals, nor c.g. by

more than about 1 decimal, but you should be aware that if you are

fueling in Phoenix in the summer, that 120 lbs of baggage will affect

c.g. more than it will at International Falls in Jan.



On 3/27/2017 5:53 AM, Tim Olson wrote: 	  Quote: 	
		  

--> RV10-List message posted by: Tim Olson <Tim(at)MyRV10.com (Tim(at)MyRV10.com)>

C.G.

Don't worry Lew, it's just that many people are better pilots that

they are scientists. It is true that the fuel will expand when it is

warm. But considering there will be the same number of molecules, they

will not weigh differently when they are warm.  Yes, the fuel tanks

will overflow if they are all the way full to the top, so warm fuel

would weigh less in that situationâ€¦ If it overflowed some of the fuel.

But, if you have your fuel tanks filled to 2 inches from the top, on a

cold day, and then you take your plane out on a warm day, and the fuel

is up to the top, it will not weigh less. It may in fact weigh a

minuscule amount more, due to additional dissolved gases.  The comment

about Jets calculating fuel in pounds is accurate, but that would not

simply be because fuel weighs less when it is warm. It would have more

to do with that it has less volume when it is warm , for the same

given amount of fuel in molecules. So you are not going crazy.

Either way, the warm fuel versus cold fuel is a small enough number

has to be pretty much insignificant when calculating your weight and

balance. Sure, it may weigh a few pounds more if you feel to the exact

same spot on a cold day as on a warm day, but I don't think a weight

and balance needs to be calculated to that Precision.

Tim 	
	


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Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Mon Mar 27, 2017 7:50 am Post subject: W&B Configuration

Hey Berck,



I, like Jesse, am getting a chuckle out of this whole discussion.



I read what you said here, and I think we're basically saying

the same thing.  Of course, a pound of fuel hot and a pound

of fuel cold will have the same volume and weight, when

temperature equalizes.  I think that is what I was trying

to say, but I just didn't do it eloquently enough. 



The weight of the fuel is due to the molecular structure

of the fuel itself having that weight per fuel molecule.

It just happens to be that if you heat things up, the

molecules become further apart and less dense, so the

volume changes.  But, a the number of molecules and

weight doesn't change.

Now, if you really want to get a pressure/volume/density

problem that confuses people, try explaining why moist

air is LIGHTER than dry air.  Everyone always says stuff

like "the air was so heavy and wet today".  The funny

thing is, moist air weighs less than dry air.



That's why the dangerous factors in flying are

"Hot, High, and Humid".... the air is less dense.



If moist air was heavier than dry air, we'd be in

a constant state of ground fog, and clouds wouldn't

be up high in the sky. 



Tim



(I think I just caused worse thread creep than original.)



On 03/27/2017 10:25 AM, Berck E. Nash wrote:

 	  Quote: 	
		  

 On Mon, Mar 27, 2017 at 8:43 AM, Tim Olson <Tim(at)myrv10.com

 <mailto:Tim(at)myrv10.com>> wrote:



     



     As long as you understand that nearly the entire reason that

     the fuel has a different "weight" per gallon is that the

     actual QUANTITY of fuel molecules in that gallon is less

     as it gets warmer, then you're right on.  It's a VOLUME

     issue, not a weight issue.   If you took hot fuel

     of a given weight, and cold fuel of a given weight, and

     brought them to the same temperature, they would still

     weigh the same but have different VOLUMES.

 Uhm, no.  If you take a pound of cold fuel and pound of hot fuel,

 they're going to have the same volume *and* weight once you equalize the

 temperature.  This is one of the many reasons we fuel airliners by weight.

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Mon Mar 27, 2017 9:16 am Post subject: Re: more drift

 	  Tim Olson wrote: 	
		  Hey Berck,



I, like Jesse, am getting a chuckle out of this whole discussion.

If moist air was heavier than dry air, we'd be in

a constant state of ground fog, and clouds wouldn't

be up high in the sky. 



Tim



(I think I just caused worse thread creep than origine] 	




More thread creep: Moist air doesn't rise because it's moist. In the lower atmosphere there's very good mixing. If that weren't true all the oxygen would be down low, and at higher altitudes it would be all nitrogen. What changes is the amount of water in the vapor state depends on temperature. As the air cools as it rises, you reach the dew point - where no more water can evaporate, so you start having liquid drops.



I thought an early post was referring to Einstein's theory of special relativity: E=mc2(squared). Strictly speaking a sealed container of anything should weigh more as energy (heat) is added. But the speed of light squared is such a big number that you can't measure it under most circumstances.

_________________
Bob Turner
RV-10 QB

Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Mon Mar 27, 2017 10:14 am Post subject: W&B Configuration

Thread creep again....water...

It's amazing when you think of the design of things as simple as

water, in our world.

Think of ice...since water hits its greatest density at above

freezing, we can drive on lakes and go ice fishing.

If water followed other molecules pattern, the ice would

form and sink to the bottom of a cold lake, and eventually the

entire lake would turn into a giant ice block.

There are so many things that were designed just perfectly,

that they amaze me all the time.

Tim

do not archive

On 03/27/2017 12:16 PM, Bob Turner wrote:

 	  Quote: 	

 Tim Olson wrote:

> Hey Berck,

>

> I, like Jesse, am getting a chuckle out of this whole discussion.

> If moist air was heavier than dry air, we'd be in

> a constant state of ground fog, and clouds wouldn't

> be up high in the sky. 

>

> Tim

>

> (I think I just caused worse thread creep than origine]

 More thread creep: Moist air doesn't rise because it's moist. In the lower atmosphere there's very good mixing. If that weren't true all the oxygen would be down low, and at higher altitudes it would be all nitrogen. What changes is the amount of water in the vapor state depends on temperature. As the air cools as it rises, you reach the dew point - where no more water can evaporate, so you start having liquid drops.

 I thought an early post was referring to Einstein's theory of special relativity: E=mc2(squared). Strictly speaking a sealed container of anything should weigh more as energy (heat) is added. But the speed of light squared is such a big number that you can't measure it under most circumstances.

 --------

 Bob Turner

 RV-10 QB

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 http://forums.matronics.com/viewtopic.php?p=467694#467694

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