W&B chart in TCDS

A place to relax and discuss flying topics.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

Post Reply
ole' blue
Posts: 16
Joined: Sat Dec 04, 2010 3:56 am

W&B chart in TCDS

Post by ole' blue »

I have a question about the W&B chart in the TCDS. It doesn't look anything like the electronic W&B charts floating around here. The number at the bottom of the chart says "Index Units" and the scale is from 40-120. What unit is that? A few searches of Weight and Balance info didn't reveal what I was looking for. Thanks,.
ole' blue
Posts: 16
Joined: Sat Dec 04, 2010 3:56 am

Re: W&B chart in TCDS

Post by ole' blue »

So after looking around for hours, I posted my question. As soon as I clicked "Submit", I looked down at my TCDS and saw the loading graph below has a note that says "Index Units= Moment/1000"! That was easy... :roll:
User avatar
Bruce Fenstermacher
Posts: 10418
Joined: Tue Apr 23, 2002 11:24 am

Re: W&B chart in TCDS

Post by Bruce Fenstermacher »

There you go. Once again the forum has proved it's weight in gold. Had it not been around you wouldn't have had anything to click thus forcing you to look down at the note in the TCDS. :lol:
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
Bruce Fenstermacher
Posts: 10418
Joined: Tue Apr 23, 2002 11:24 am

Re: W&B chart in TCDS

Post by Bruce Fenstermacher »

The TCDS has what I would consider a normal scale of actual weight and arm as can be seen below for the A and B model. The '48 looks the same but the CG range is slightly different
Screen Shot 2013-06-15 at 7.40.25 AM.png

In the Owners Manual however, in a effort to make the math easier, Cessna developed a graph using an index number. Using this method the degree of angle of the line on the graph does the more complicated multiplication required weight using the weight and arm method. Using the index graphs only requires addition and subtraction. It works well once you understand it until you have weight added or subtracted that is not on a line in the index graph.

Index= Moment/1000 so here is an example of an item 10 lbs on the floor in front of the rear seat at +60 inchs from the datum. The moment of the item would be 10 x 60 or 600 and the index would be 600/1000 or .6. The weight of 10lbs and the .6 would then be added to all the other weights and indexs and plotted on the graph.

Here is the graphs from the '53 B model.
Screen Shot 2013-06-15 at 7.43.05 AM.png
Screen Shot 2013-06-15 at 7.43.27 AM.png
You do not have the required permissions to view the files attached to this post.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Post Reply
Cessna® is a registered trademark of Textron Aviation, Inc. The International Cessna® 170 Association is an independent owners/operators association dedicated to C170 aircraft and early O-300-powered C172s. We are not affiliated with Cessna® or Textron Aviation, Inc. in any way.