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CJ6A: stations for CG calculation

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Tue Jan 31, 2006 6:51 am Post subject: CJ6A: stations for CG calculation

I am doing the W&B on a CJ6A for a friend. I am trying to find a full

set of stations for doing the calculation without having to go back to

the Chinese book and figure it out all over again.



I was looking through the archives where we had a big discussion of this

(and one of the famous McCoy/Lloyd flamefests) in May of '02. The

problem is, I can't find a complete set of stations from a standard

datum plane that includes the rear skid or tailcone for the placement of

lead to get the CG back in range.



Yes, I could go back out to the airplane with a tape measure and plumb

bob to figure it out but I suspect that there are a couple of people on

this list who could just answer the question and save me the time and trip.

-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

cjpilot710(at)aol.com
Guest

Posted: Tue Jan 31, 2006 9:20 am Post subject: CJ6A: stations for CG calculation

Some 11 year ago when I  got the CJ-   IA Bill Freeze at DRV did mine and I have used this ever  since.

  

 The Zero Datum is 70  inches in front of the first vertical bulk head ("second  firewall")

  

 Oil tank at  +57"

 Pilot  at      +114"

 Pax  at        +161"

 Fuel  at       +133.5"

 L main gear  +128.75

 R main gear  +128.75

 Nose  gear     +40.25

 Tail cone (where I keep  the ballast ) +335"

 C/G range    +111.2" to +116.1"

  

 Hope that's a  help.

  

 Jim "Pappy"  Goolsby

  

 --> Yak-List message posted by: Brian Lloyd  <brian-yak(at)lloyd.com>



I am doing the W&B on a CJ6A for a  friend. I am trying to find a full

set of stations for doing the calculation  without having to go back to

the Chinese book and figure it out all over  again.



I was looking through the archives where we had a big discussion  of this

(and one of the famous McCoy/Lloyd flamefests) in May of '02.  The

problem is, I can't find a complete set of stations from a  standard

datum plane that includes the rear skid or tailcone for the  placement of

lead to get the CG back in range.



Yes, I could go back  out to the airplane with a tape measure and plumb

bob to figure it out but I  suspect that there are a couple of people on

this list who could just answer  the question and save me the time and trip.

-- 

Brian Lloyd                           361 Catterline Way

brian-yak at lloyd dot com           Folsom, CA 95630

+1.916.367.2131 (voice)              +1.270.912.0788  (fax)

Ernie

Joined: 11 Jan 2006
Posts: 513

Posted: Tue Jan 31, 2006 9:40 am Post subject: CJ6A: stations for CG calculation

I have a datum 24" forward of the prop axial plane. You could easily

just use the prop as the datum and subtract 24" from all the stations.



Prop = 24"

engine = 45"

Nosewheel=57"

accessory section=60"

oil = 69"

front seat=123"

jack point = 129"

front spar = 131.5"

main wheels = 146.5"

fuel = 149"

rear seat = 174"

avionics rack = =188"

battery box = 199"

adf rack = 214"

tail skid = 338"



Forward CG limt 127.93" (Front of MAC +11.7")

Aft CG limit = 132.80"     (fron of MAC + 16.57")

front of MAC = 116.23"



CG range = 4.9"



Ernie

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Tue Jan 31, 2006 12:44 pm Post subject: CJ6A: stations for CG calculation

Ernest Martinez wrote:

 	  Quote: 	
		   Prop = 24"

 engine = 45"

 Nosewheel=57"

 accessory section=60"

 oil = 69"

 front seat=123"

 jack point = 129"

 front spar = 131.5"

 main wheels = 146.5"

 fuel = 149"

 rear seat = 174"

 avionics rack = =188"

 battery box = 199"

 adf rack = 214"

 tail skid = 338"

 

 Forward CG limt 127.93" (Front of MAC +11.7")

 Aft CG limit = 132.80"     (fron of MAC + 16.57")

 front of MAC = 116.23"

 

 CG range = 4.9"


	


Well, so far everyone looks consistent.



Brian

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Tue Jan 31, 2006 12:44 pm Post subject: CJ6A: stations for CG calculation

cjpilot710(at)aol.com wrote:



 	  Quote: 	
		   */The Zero Datum is 70 inches in front of the first vertical bulk head 

 ("second firewall")/*

 *//* 

 */Oil tank at +57"/*

 */Pilot at      +114"/*

 */Pax at        +161"/*

 */Fuel at       +133.5"/*

 */L main gear +128.75/*

 */R main gear +128.75/*

 */Nose gear     +40.25/*

 */Tail cone (where I keep the ballast ) +335"/*

 */C/G range   +111.2" to +116.1"/*

 *//* 

 */Hope that's a help./*


	


Works beautifully. Thank you.

mgdimarco

Joined: 20 Apr 2006
Posts: 23
Location: Kissimmee, FL

Posted: Sun Dec 28, 2008 12:37 am Post subject: Re: CJ6A: stations for CG calculation

I have to admit some confusion on this issue. The w/b I had done has most of the station numbers matching the 70" from firewall datum.  However the oil my guy used is at 48".  The pilot station seems a bit aft when using 114.3. Seems to measure out at around 104.  Etc., Etc. and none of this matches the CJ manual which seems to use the nose gear axle or the Leading edge of MAC.



What is the real answer on stations?



What is the MAC?



What is the LE of MAC station?



And what are the % LE of MAC limits really?



Thanks in advance

Mike

_________________
Michael Di Marco
China Blue

mgdimarco@yahoo.com
407-608-3290

cjpilot710(at)aol.com
Guest

Posted: Sun Dec 28, 2008 7:22 am Post subject: CJ6A: stations for CG calculation

Mike,

  

 I am away from home right now and not near my books.  But the 70"  measurement is from the vertical (or second) firewall.  IF my memory  services me right the oil tank is about the 48" mark.  The Chinese used a  different method of figuring C/G.  I get home on the 1st or 2nd and will be  able to help you.  But I'm sure others on this list have gone though this  before.

  

 Jim "Pappy" Goolsby

  

  In a message dated 12/28/2008 3:38:24 A.M. Eastern Standard Time,  mgdimarco(at)yahoo.com writes:

  	  Quote: 	
		  -->    Yak-List message posted by: "mgdimarco" <mgdimarco(at)yahoo.com>



I    have to admit some confusion on this issue. The w/b I had done has most of the    station numbers matching the 70" from firewall datum.  However the oil my    guy used is at 48".  The pilot station seems a bit aft when using 114.3.    Seems to measure out at around 104.  Etc., Etc. and none of this matches    the CJ manual which seems to use the nose gear axle or the Leading edge of    MAC.



What is the real answer on stations?



What is the    MAC?



What is the LE of MAC station?



And what are the % LE of MAC    limits really?



Thanks in advance

Mike



--------

Michael Di    Marco

China Blue



407-348-4798





Read this topic    online    here:



http://forums.matronics.com/viewtopic.php?p=221448#221448

	




One site keeps you connected to all your email: AOL Mail, Gmail, and Yahoo Mail=emlcntaolcom00000025">Try it now.

  [quote][b]

Dabear(at)damned.org
Guest

Posted: Sun Dec 28, 2008 8:52 am Post subject: CJ6A: stations for CG calculation

Michael,



There is some discussion on the stations.  However the MAC location, LE of 

MAC, and limits really provided.  I did a spreadsheet and put it on the RSPA 

website if you want to down load it (and are a member).  I built that after 

gathering W/B information from 10 CJ pilots and a few A/Ps.  I also did some 

more measurements on the scales with known weights and positions.  The 

Spreadsheet also allows you to calculate the w/b of your aircraft from scale 

points.  Call me to discuss the process if you want.



Randy "DaBear" DeVere

571.213.4344

---

wlannon(at)persona.ca
Guest

Posted: Sun Dec 28, 2008 2:58 pm Post subject: CJ6A: stations for CG calculation

Mike:



 MAC is the "mean aerodynamic chord" of the wing.  If the wing has no taper, 

no sweep and no variation in airfoil properties over the span the MAC and 

the measured chord are one and the same.  If the same plank wing is swept 

the effective chord length is increased (relative to airflow direction). The 

MAC is therefore longer and the position of the MAC leading edge has moved 

aft. Taper also changes position and length of the MAC.

In the plan view the MAC location of a tapered and/or swept wing will be 

located somewhere around the mid half-span point. This is of no interest for 

weight and balance. We are concerned only with it's location in the 

elevation view.



That location is shown by fig. 1.3, pg. 6 of the CJ6 Tech. Specs. manual. 

The MAC leading edge is located 769 mm (30.27") forward of the main wheel 

center line. It's length is 1747 mm (68.78").



The MW center is the primary reference point. It is not convenient to use as 

the DATUM point for W&B which can be at the reference or at any point 

established from it.

I use 125" forward of the MW center line as the DATUM. That keeps all 

moments positive and greatly simplifies the math.



With that DATUM the LE of the MAC is at + 94.73"  (125-30.27)



The forward limit  (17% of MAC or 11.69") is at + 106.4" with the landing 

gear DOWN

The aft limit  ( 24.1% MAC or 16.57")         is at  + 111.3"  "     " 

"         "     UP



With the gear UP the CG moves aft by 0.48".



As noted you can use any datum point but you MUST determine the MAC L/E 

point from that datum.



The aircraft must be level (canopy rails).  Should be levelled by jacking 

NOT by deflating the nose oleo.  That changes the MW to NW dimension which 

you need for calculation. That dimension is given in Fig. 1.3 as 2233 mm 

(87.9")



Use a clean floor, chalk line, masking tape and plumb bob, etc.  Transfer MW 

C/L to the aircraft C/L on the floor and establish DATUM from there. 

Transfer cg of all load items to the floor for accurate measurement.



Cheers;

Walt





---

mgdimarco

Joined: 20 Apr 2006
Posts: 23
Location: Kissimmee, FL

Posted: Sun Dec 28, 2008 5:23 pm Post subject: Re: CJ6A: stations for CG calculation

My understanding is making real progress.  Thanks for the definition of MAC, but I was looking for a value and the best I could determine was 68.8 which is right in line with the 68.78 answer.  



Is the 94.7 LE of MAC the same as the datum of 70" forward of the firewall?



Anyone see the Pilot station as being closer to 104"  than 114.3" from that datum?



Thanks for the confirmation of the oil tank at 48" on the 70" datum.



How about the "cargo" compartment.  Would you use the battery location or just aft of it as the center?



In case anyone is interested, what started this was my head scratching as to why I could not but a 240# pilot and a 280# co-pilot in a 2412# airplane with only 140# of gas and 25# of oil.  I kept getting a 116.7" C.G. (out of limit aft).  It is not the case if the pilot station is at 104 (as I measure it) vs. 114.3 which seems to be the standard answer. 



Thanks again in advance for the help and your replies.



Mike

_________________
Michael Di Marco
China Blue

mgdimarco@yahoo.com
407-608-3290

Dabear(at)damned.org
Guest

Posted: Mon Dec 29, 2008 7:33 am Post subject: CJ6A: stations for CG calculation

Michael,



Who wieghed your CJ?  Who did the initial W/B calcualtions or are you just 

using the information in the manual without actually putting the CJ on 

scales?  Also, please check the past conversations on the yak-list as you 

will find that many people had the exact same W/B calculation sheet (same 

weights for everything) down to the same signature in the xerox copy.  That 

led many here to re-do their W/B themselves or have their local shop do it. 

If you haven't done it yourself or had a good shop do it, please go get it 

done before your next flight.



If you are using the 94.7 inches in front of the Main Nose Wheel then the 

pilot station I have is 101.81.  I've seen as much as 9 inches difference 

from the other cj pilots calculations.  Now, you will also find if you put 2 

different known weight pilots in the front seat and re-weigh the airplane, 

you will find there will be difference in the pilot station due to the 

weight difference of the "legs vs. body" between the two pilots.  I took an 

average of 3 people (170lbs, 210lbs, and 250lbs) in my caluclation.  Rather 

than just a measurement off the seat pan.



I don't believe (but can not confirm because I didn't measure) the inner 

firewall station being 70"  It sounds wrong.



Walt using 125 MWcenter, what do you have as the firewall station?



Using the 94.7" forward of the MW Center as the DATUM, the oil station 

becomes 47.81

Using the 94.7" forward of the MW Center as the DATUM you get the following 

stations depending on the length of your baggage compartment:

Avionics bay  161.28

Battery Box   178.19

ADF Electronics Tray 200.19



Again,  if the CJ W/B is still a xerox copy of someone else's information, 

you haven't watched the shop do the W/B from scratch, then please have it 

re-done before you fly.



I'll forward the spreadsheet I did in case you are interested.  However it 

is only good if you weigh your airplane and input the 3 wheel weights and 

initial measurements.



Version 3 of the sheet will be coming out in the next few weeks as I've 

found out I didn't put a "DATUM" location explaination in the sheet.  Some 

may want that.  If there is anyone out there that would like to see changes 

to the sheet, please let me know before Feb 1.



DaBear



---

CJ_WB.xls

Description:

Download

Filename:

CJ_WB.xls

Filesize:

38.5 KB

Downloaded:

459 Time(s)

mgdimarco

Joined: 20 Apr 2006
Posts: 23
Location: Kissimmee, FL

Posted: Mon Dec 29, 2008 6:56 pm Post subject: Re: CJ6A: stations for CG calculation

This latest reply from Mr. Dabear has really muddied the waters.  



When I say 70" Datum, I'm referring to what many are using as datum to be 70" forward of the vertical firewall. And yes the airplane was put on scales but the stations were from the commonly publicized 70" datum. 



Examining your spreadsheet it is great for dynamic calculations, but the numbers/stations  are way different from the "standard" I've been finding and not consistently different.  Stations vary from 4" to over 10" from what I've been seeing.  What you quote as the C.G. range also deviates significantly from everything I've seen so far.



So it is back to the drawing board for finding a consistent answer/standard.  Oh the joys of experimental aircraft.



Mike

_________________
Michael Di Marco
China Blue

mgdimarco@yahoo.com
407-608-3290

wlannon(at)persona.ca
Guest

Posted: Mon Dec 29, 2008 7:13 pm Post subject: CJ6A: stations for CG calculation

Randy & Mike;



I use a DATUM point of 125" forward of the manufacturers specified reference 

point which is the MAIN wheel C/L.

All measurements are taken from the DATUM.  For weight and balance purposes 

the DATUM is located at STATION "0"

The figure 94.7" is not a datum, it is the station at which the leading edge 

of the MAC is located.

That information is necessary ONLY to translate %MAC fore and aft limits 

into hard dimensions

relative to the DATUM.  Beyond that it is meaningless and irrelevant.



 	  Quote: 	
		  From the above DATUM I get the following;


	


Oil (est. cg)  -- 47"

Pilot   "         -- 101.5"

Pass.  "         -- 150.5"



The "standard" man in the "standard" aircraft seat has his CG located at his 

belly button. Hmmm-- that was the 165 lb standard man of many years 

ago-----??????



Walt



---

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