The International Cessna^® 170 Association

170C wrote: I seem to remember calculating weight & balance to pass the test, but haven't done so since 1983. Guess I should brush the dust off that old private pilot 3 ring binder and do some studying.

I figure that if the Friendly Aviation Administration makes me carry all that paper, I might as well know what it's for.

Actually, it was quite an eye-opener when I did a few sample loadings. All of the variable weights like people, gas, and luggage are behind the empty CG of the airplane. However, the empty CG is far enough forward that you really have to do some weird things to get the CG aft of limit. However, in my airplane at least, a lightweight pilot (I don't have to worry about THAT anymore) and minimum fuel put the CG forward of the limit.

Miles

I stumbled across this neat little W&B spreadsheet for the 170B while surfing the net.

http://home.new.rr.com/trumpetb/alph/wb170B.html

Very neat, Craig !
Rudy

Craig,

That little spreadsheet is a keeper! Someone really spent some time on it. It's comforting to see that if I change the baggage arm to 249 inches (put it at the tailwheel) that the difference in CG between 0 lbs and 2 lbs is 0.2 inches.

Miles

The calculator is great! Thanks, Craig!

I'll try to get permission to add it to our website when I get a chance.

webmaster wrote:The calculator is great! Thanks, Craig!

I'll try to get permission to add it to our website when I get a chance.

Dale, you might think about removing the default empty weight and CG, if you can, to force folks to go get their real numbers. The author is Robert Booty, one of our members.

Miles

That is a cool program. Some time ago I developed a similar spread sheet in excel for all the 170 models. The graph isn't quite as fancy as the web version. So far I've given at least 50 copies of it away to people who have PM'd me with their email.

cessna170bdriver wrote:Craig,

That little spreadsheet is a keeper! Someone really spent some time on it. It's comforting to see that if I change the baggage arm to 249 inches (put it at the tailwheel) that the difference in CG between 0 lbs and 2 lbs is 0.2 inches.

Miles

Sooooo .... on a percentage basis... .2 versus .26 is a fairly large error.... Who's error is that, Miles?

gahorn wrote:

cessna170bdriver wrote:Craig,

That little spreadsheet is a keeper! Someone really spent some time on it. It's comforting to see that if I change the baggage arm to 249 inches (put it at the tailwheel) that the difference in CG between 0 lbs and 2 lbs is 0.2 inches.

Miles

Sooooo .... on a percentage basis... .2 versus .26 is a fairly large error.... Who's error is that, Miles?

No error whatsoever, George, just a different set of initial conditions. Try my initial assumptions: Go to the calculator, set empty weight at 1600, empty CG at 41, zero out oil pax and fuel, add 2 lbs of baggage (tailwheel core foam) at 259 aft of datum, and voila! New CG is 41.26.

Miles

Awww, I wuz jus kiddin'.
I noticed the original program was developed by someone in UK based on a 172. I wonder how difficult it would be to get the code/program for it. It'd be nice to obtain it for our members. I wish Dale success!

Now I see why the code is so well written. Look at Bob Booty's profile found at http://home.new.rr.com/trumpetb/. It says:

Robert A. Booty,
Bob Booty is a retired Mechanical Engineer in the marine power industry and a serious "recreational musician".

Mixing interests in technology and arts, Bob also maintains and flies his classic Cessna 170B airplane, dabbles in computer graphics/technical illustration, designs and builds audio equipment

Trying to refresh W&B data and am a little confused re the empty weight of a 170. I thought CAR 3 aircraft were weighed absent any fuel or oil? FAR weights include full oil and unusable fuel. I assume I should come up with the latter. Was wondering because I'm coming in a little high at 1370 with 8 qts oil and 5 gal fuel.

Thanks,
Todd

My partner arranged to have our C170B weighed by an A&P who has a reputation for accurate EW & CG calculations. The documented aircraft empty weight and CG before being weighed was 1308 & 38.05. After being weighed the EW and CG became 1376 & 37.26. The empty weight included unuseable fuel and 8 qts of oil. I believe the 8 qts of oil should have been deducted from the EW and the minus moment of the oil added to the total EW moment - otherwise a minus moment weight is included in the total moment as a positive. After correcting, what I believe is an error, the EW and CG are 1361 & 37.89. Even with this correction, if I load the front seats of the aircraft with two 180 lb adults and full fuel - no baggage - no pax, the CG is forward of the forward limits. I did not have this problem with the orginal EW and CG. Anyone else experiencing this W&B problem

Without studying your numbers to see if they are even close to my aircraft some thoughts come to mind.

Since the "accurate" IA seems to have made a mistake with the math in one case could he have done it twice. Could it be he also didn't weight your aircraft correctly? Did you watch it being done?

The total weight of the aircraft doesn't seem to be an issue bu the empty CG does. If The IA did not have the aircraft perfectly level by leveling the upper door jamb or he had his rear scale under the wheel instead of the end of the fuselage at the rudder, the CG would be off. <<-whoops-was thinking of my Cub. A Cessna example has the scale under the tail wheel not the tail post.

Do you have other than stock main gear that would shift the main wheels from other than the stock position? This would do it as well.

The oil is forward of the datum point (firewall), thus it will have a negative moment value. As a note the convention now by aircraft manufacturers is to place the datum point forward of an aircrafts nose (out in space) so that all moments have a positive value to avoid confusion. Whether you remove the oil value or keep it with respect to defining empty weight doesn't really matter as you have to account for it in the end as you probably will take-off with the correct oil level.
My empty weight C of G is 37.94 and the weighing points were the main wheels and the taikwheel. I'm not sure what is being conveyed in the last post as the distances of the weigh points to the datum point are measured for the calculation of the empty weight.
But hey I'm another person that might have mixed this up.