The International Cessna^® 170 Association

I just purchased my ragwing, and it was absent a weight and balance. As part of the purchase agreement the previous owner had a new one done, but as it turns out it was really just "weighing but no balancing". In other words, I got all the wieights but no CG. I have never gone through this process before from scratch, and I am hoping some of you can help me figure out the CG. I know the datum is the firewall, but does anyone know the figures for each wheel? Any help will be much appreciated. Thanks! Kevin

Are you an Association member? There was a really good article about doing a new weight & balance in the Q2/2003 issue of The 170 News. I know, I wrote it.
When you say the "figures for each wheel", I assume you mean the arm (distance from datum?). I can tell you what the factory figures were -- mains at +22",tailwheel at +249"-- and what mine were (with 180 gear legs)-- mains at +18.5",tailwheel at +249.5"-- but you really should measure the arm for the wheels on your own airplane.
In case you didn't know, the weight at each wheel must be determined with the airplane in a level position-- it will be different than when the airplane is sitting on all three wheels. It also needs to be level when you measure the arm of the wheels.
Get a copy of the article ("Wait and Balance") from Velvet at Association headquarters,after reading it this post will make a lot more sense to you.

Eric

Thanks for the info Eric. I am an association member, but am brand new. When the plane was weighed it was leveled. What I am missing is a clear picture on how to figure the arms and CG. My ragwing has stock legs with PPonk mod (I'm not sure if that mod makes any difference in their position). My weights are as follows: R=747, L=675, tail=122 less 201 for full fuel comes out to a total of 1343. Thanks again for your help!

Kevin
I'll be sending my W&B spread sheet to you later today when I'm home. It's not set up to enter the weights as the aircraft is weighed but we can help you get that done.

The Pponk mod won't change the wheel position. Are you sure the aircraft was level at the top of the door? This is essential to get the cg.

The weight and balance is calcuated the same way as that taught in ground school The formula is the sum of all the moments - (arm times the weight) divided by the weight to give the CG location. In this case, the values are (22*(747+675)+122*249 - 45*201)/1343 = 39.2 inches aft of the fire wall (empty weight) and with full fuel at 39.9 inches aft of the fire wall. I would double check these numbers to make sure there are no math errors. The arms are: 22 inches for the main wheels, 249 inches for the tail wheel and 45 inches for the fuel.

Okay, that makes sense. I think I have been making things more difficult than they need to be. Does 39.2 seem in the normal ballpark for a ragwing? Thanks much to all for the help! Kevin

Your airplane's empty weight of 1,343 pounds with a CG of 39.2" doesn't sound out of line. With the rear bench seat installed, mine weighs 1,332 pounds empty with a CG of 39.1". With the single rear jump seat installed in place of the bench seat, it weighs 1,310 pounds empty with a CG of 38.4".

Eric

I dont know offhand what my figures are at cause im not home, however my empty weight came in at 1362. A friend came ip with a excel program that all I have to do is add in the weights for each wheel and it computes the rest. If you like I could send it to you to take a look at. One thing I never realised is the foward cg moment with just two HUSKY? adults up front You can check out the level job at the web site .
http://www.sandhillaviation.com/weight.html