[Michael Burbidge]

I'm going from a Sky-Tec LS starter to a B&C starter. The B&C starter is about 3.5 lbs. heavier.

Unfortunately my fuel tanks are full. To do a from scratch weight and balance would require that I empty the tanks! Ugh!

It seems that mathematically you could calculate a new weight and balance using the change in weight and position.

Is that true? Is that legal?

Thanks,
Michael-

 

[rstory]

Here is the link to the FAA's handbook. It looks like page 7-5 should take care of what you need.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-1.pdf

 

[az_gila]

....

Is that true? Is that legal?

Thanks,
Michael-

Yes and yes.

Make sure you get the correct location of the center of gravity for both starters to put that into the formula as well, not just the weight change.

 

[Michael Burbidge]

Thanks!

Great thanks for the answers and reference!

 

[Fast Eddie B]

Incrementally is normally how it's done.

An example from my Sky Arrow:

As an aside, shows the gains possible from switching to a lithium-iron battery!

 

[az_gila]

Incrementally is normally how it's done.

An example from my Sky Arrow:

As an aside, shows the gains possible from switching to a lithium-iron battery!

And although no-one has mentioned it yet, do it in an Excel spreadsheet to keep the mathematical calculations correct...

And I see the image above was created in Excel.

 

[Michael Burbidge]

In Excel

My original W&B is in Excel, so I can just go from there.

The B&C starter shows the CG for the starter in the drawings. The Sky-Tec does not. I'll just figure that out myself with some experimenting.

Michael-

 

[az_gila]

My original W&B is in Excel, so I can just go from there.

The B&C starter shows the CG for the starter in the drawings. The Sky-Tec does not. I'll just figure that out myself with some experimenting.

Michael-

This CG location came from a Sky-Tec supplementary installation document -

Weight and Balance Calculation
Fore-Aft CG: Half the distance between the front and rear starter mounting holes (starter datum)

http://lib.store.yahoo.net/lib/stylespilotshop/sky-tec-starter-install.pdf

 

[Michael Burbidge]

Thanks!

I figured it was somewhere. I didn't see that document. Thanks!
Michael-

 

[Bubblehead]

Is there really 3.5 lbs difference? I checked the B&C website but could not find the weight of their starters.

 

[Michael Burbidge]

2.4

So it looks more like 2.4 lbs difference.