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Weight and Balance

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Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Fri Mar 30, 2007 2:21 pm Post subject: Weight and Balance

Hey Gang,



I am about ready to record the W&B of Ms Dixie. So I am asking questions from others and gathering as much info as possible about the correct proccedre for this. John W was so kind to send me a spread sheet on his results as well as Mark G. on how he did his. Thanks guys! I have learned one thing for sure, one cant ask to many questions from to many people to learn how to do a task. You only need to be smart enough to do whats right for you so that you understand the task at hand. In this case I also asked a good friend to help explain this to me and thought I might share his thoughts with the list and future builders. 



"Just wanted to send this after we talked.

The datum is any point on the airplane where all measurements will be

taken from, in your case the nose with a plumb bob to the floor.

An arm is simply a distance from the datum to another point where you

are taking a weight, ie, center of the main wheel axles and the center

of the tailwheel with the plane in the level flight position.

The moment is the multiplication of the weight at any point times the

distance aft of the datum to that point,ie, distance X weight = moment

add the total weight and the total moments then divide the total

weight into the total moment the resultant number is the CG or where

the airplane will balance if you put the fuse across a bar or

2x4.expressed in inches aft of the datum.

when you know the empty balance point you can do some weight and

balance calculations for different loadings using the same formula.

You will need to know the distance in inches of the center of the

front seat aft of the datum,center of the rear seat,center of the

fuel tank and any other place you might add or take off weight at some

time. like a cargo compartment.

Then make up a maximum weight you might ever put there, or use your

weight if you wish. do the weight aft of the datum x the distance to

the seat and the other two measuerments you did already using the

wheels. add all together and divide and you have the new CG with this

configeration. do it with full fuel (at) 6 pounds per gallon for a full

tank and one with almost empty. if you stay in the envelope you r

gold.then do it for someone in the rear seat and do it the same way.

You will have to watch the useful load so you dont load over gross.

Please send $500,000.00 for this advice

Tom"

Hope this may help someone and if any see any holes in this as you can tell very expensive advice have at it!

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_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

ceengland(at)bellsouth.ne
Guest

Posted: Sat Mar 31, 2007 9:14 pm Post subject: Weight and Balance

Paul Petty wrote:

 	  Quote: 	
		   

 

 Hey Gang,

 

 I am about ready to record the W&B of Ms Dixie. So I am asking questions from others and gathering as much info as possible about the correct proccedre for this. John W was so kind to send me a spread sheet on his results as well as Mark G. on how he did his. Thanks guys! I have learned one thing for sure, one cant ask to many questions from to many people to learn how to do a task. You only need to be smart enough to do whats right for you so that you understand the task at hand. In this case I also asked a good friend to help explain this to me and thought I might share his thoughts with the list and future builders. 

 

 "Just wanted to send this after we talked.

 The datum is any point on the airplane where all measurements will be

 taken from, in your case the nose with a plumb bob to the floor.

 An arm is simply a distance from the datum to another point where you

 are taking a weight, ie, center of the main wheel axles and the center

 of the tailwheel with the plane in the level flight position.

 The moment is the multiplication of the weight at any point times the

 distance aft of the datum to that point,ie, distance X weight = moment

 add the total weight and the total moments then divide the total

 weight into the total moment the resultant number is the CG or where

 the airplane will balance if you put the fuse across a bar or

 2x4.expressed in inches aft of the datum.

 when you know the empty balance point you can do some weight and

 balance calculations for different loadings using the same formula.

 You will need to know the distance in inches of the center of the

 front seat aft of the datum,center of the rear seat,center of the

 fuel tank and any other place you might add or take off weight at some

 time. like a cargo compartment.

 Then make up a maximum weight you might ever put there, or use your

 weight if you wish. do the weight aft of the datum x the distance to

 the seat and the other two measuerments you did already using the

 wheels. add all together and divide and you have the new CG with this

 configeration. do it with full fuel (at) 6 pounds per gallon for a full

 tank and one with almost empty. if you stay in the envelope you r

 gold.then do it for someone in the rear seat and do it the same way.

 You will have to watch the useful load so you dont load over gross.

 Please send $500,000.00 for this advice

 Tom"

 

 

 Hope this may help someone and if any see any holes in this as you can tell very expensive advice have at it!

 

 --------

 Paul Petty

 Kolbra #12

 Ms Dixie

 Final assembly!

A few quick thoughts.
	


Datum needs to be a known distance from the wing. Is the nose 

pre-drilled to the frame? If not, you could move the datum quite a bit 

meaning the CG might not fall where you expect on the chord of the wing. 

(It would be like using the tip of the spinner on a tractor type plane 

but not specifying the spinner length.)



Do the Kolb plans specify attitude when you do the W&B? Most planes are 

weighed in flight attitude & perfectly level from side to side. Tail 

weight can vary a *lot* depending on whether the plane is level. Using 

one scale would mean a platform the height of the scale for the other 

main wheel. Most procedures specify ramps to get the mains on the 

scales. That's 'cause if you pick up the plane & lower it on the scales, 

  the side load as the mains try to spread out again can affect the 

scale readings.



Weighing should be inside with doors shut, no wind, fans, etc (affects 

scale readings).



The Kolb might fly fine without these details, but it's SOP on homebuilts.



FWIW,



Charlie

Fly it up to Slobovia when you get your A/W cert.

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Arty Trost

Joined: 25 May 2006
Posts: 205
Location: Sandy, Oregon

Posted: Sun Apr 01, 2007 6:19 am Post subject: Weight and Balance

Following up on Charlie's remarks:



The type of scales you use will also make a

difference.  I used two bathroom scales - semi-good

ones that cost about $40 each. I raised the tail for a

level attitude.  (My Drifter is a taildragger.)   I

discovered that the placement of the wheel on the

scales made a different - unless the tire was exactly

in the middle of the scale, the weight could vary by

5-8 lbs./wheel.  So I noted the weight on each side,

then swapped the scales, weighed again, and took an

average of the two for each side. 



Our club is going to be discussing weight and balance

this Tuesday, and we'll also discuss buying calibrated

scales for club members' use.  



Arty Trost

Sandy, Oregon

--- Charlie England <ceengland(at)bellsouth.net> wrote:



 	  Quote: 	
		   Do the Kolb plans specify attitude when you do the

 W&B? Most planes are 

 weighed in flight attitude & perfectly level from

 side to side. Tail 

 weight can vary a *lot* depending on whether the

 plane is level. Using 

 one scale would mean a platform the height of the

 scale for the other 

 main wheel. Most procedures specify ramps to get the

 mains on the 

 scales. That's 'cause if you pick up the plane &

 lower it on the scales, 

   the side load as the mains try to spread out again

 can affect the 

 scale readings.

 

 Weighing should be inside with doors shut, no wind,

 fans, etc (affects 

 scale readings).

 

 The Kolb might fly fine without these details, but

 it's SOP on homebuilts.

 

 FWIW,

 

 Charlie

 Fly it up to Slobovia when you get your A/W cert.

 



 browse

 Subscriptions page,

 FAQ,

 http://www.matronics.com/Navigator?Kolb-List



 Web Forums!



 

 

 

 


	




www.LessonsFromTheEdge.com



"Life's a daring adventure or nothing"

                      Helen Keller



"I refuse to tip toe through life just to arrive safely at death."

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pj.ladd(at)btinternet.com
Guest

Posted: Sun Apr 01, 2007 7:00 am Post subject: Weight and Balance

The type of scales you use will also make a difference.  I used two bathroom 

scales >>



Hi,

When I weighed my Challenger I took the bathroom scales I used to a 

department of the local Council which was responsible for ensuring that 

tradesmen and shopkeepers used `approved` weights and measuring devices and 

they checked my scales against  `certified` weights. At least then I had an 

`approved` starting point.



The `level` of everything is important too. The floor, the plane, the scales 

and if you are only using one scale you must trig the wheels up level . If 

using more than one scale they should be swapped around and averaged  out.



Here in the UK the use of bathroom scales etc is beginning to be frowned on 

by the authorities and the use of `proper` measuring devices is being 

pushed. Not too serious yet but it is coming.



In the UK the weight of the plane is the main factor in deciding if the 

plane is an ultralight or not so although getting the weight and balance 

wrong could kill you using a little imaginative weighing technique could 

keep you in the ultrlight category.



Cheers

Pat



do not archive

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John Williamson

Joined: 10 Jan 2006
Posts: 146
Location: Arlington, TX

Posted: Sun Apr 01, 2007 8:05 am Post subject: Re: Weight and Balance

Hi Paul, Arty and All,



I have only been dioing weight and balance for the last 37 years and still am able to find something new every time.



You normally can't go wrong by using the FAA guidance. Here is the link to the 2007 version on the "Weight and Balance Handbook": 

http://www.faa.gov/library/manuals/aircraft/media/FAA-H-8083-1A.pdf



If you use a set of bathroom scales, it will work better if you place a 3/4" board between the tire and the scale to spread the weight across the scale. 



I use two scales under each main wheel and one under the tail wheel, all at the same time so the airplane stays level. On the main wheels, I put the scales very close together but not touching. I lay a 2"X'6"X18" board across them that has some small chocks attached to it. I zero the scales with the lumber on them and proceed to do the weighing.



Good luck.

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_________________
John Williamson
Arlington, TX

Kolbra, 912ULS, 1640 hours
http://home.tx.rr.com/kolbrapilot

Russ Kinne

Joined: 27 Jan 2006
Posts: 182

Posted: Sun Apr 01, 2007 11:28 am Post subject: Weight and Balance

Some time ago a Kolb pilot's wife gave  birth to a daughtger at a  

fairly remote fishi g camp. They had to use the same scales they  

weighed the freshly-caught fish on. The little girl weighed 47 pounds.

Talk about fat ultralights!



On Apr 1, 2007, at 10:59 AM, pat ladd wrote:



 	  Quote: 	
		   



 The type of scales you use will also make a difference.  I used two  

 bathroom scales >>



 Hi,

 When I weighed my Challenger I took the bathroom scales I used to a  

 department of the local Council which was responsible for ensuring  

 that tradesmen and shopkeepers used `approved` weights and  

 measuring devices and they checked my scales against  `certified`  

 weights. At least then I had an `approved` starting point.



 The `level` of everything is important too. The floor, the plane,  

 the scales and if you are only using one scale you must trig the  

 wheels up level . If using more than one scale they should be  

 swapped around and averaged  out.



 Here in the UK the use of bathroom scales etc is beginning to be  

 frowned on by the authorities and the use of `proper` measuring  

 devices is being pushed. Not too serious yet but it is coming.



 In the UK the weight of the plane is the main factor in deciding if  

 the plane is an ultralight or not so although getting the weight  

 and balance wrong could kill you using a little imaginative  

 weighing technique could keep you in the ultrlight category.



 Cheers

 Pat



 do not archive

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Arty Trost

Joined: 25 May 2006
Posts: 205
Location: Sandy, Oregon

Posted: Sun Apr 01, 2007 9:15 pm Post subject: Weight and Balance

Thanks, John.



I'm swapping out my two 5-gal. gas tanks for two

30-liter (7.92 gal.) gas tanks, so will be doing a new

weight and balance.  I've used a board across the two

scales for the main wheels, but never used two scales

for each main.  I'll try it.



See you at MV -



Arty Trost

Sandy, Oregon

--- John Williamson <kolbrapilot1(at)tx.rr.com> wrote:



 	  Quote: 	
		   

 <kolbrapilot1(at)tx.rr.com>

 

 Hi Paul, Arty and All,

 

 I have only been dioing weight and balance for the

 last 37 years and still am able to find something

 new every time.

 

snip
	




www.LessonsFromTheEdge.com



"Life's a daring adventure or nothing"

                      Helen Keller



"I refuse to tip toe through life just to arrive safely at death."

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