akgreg wrote:..... I know of too many planes that are way off on what they really weigh and the owners still swear by their calculated W&B. "My 170 with an O-360 on 31" bushwheels only weighs 1360 lbs" I call BULLSHIT!

What he said!

Alpina23 wrote:.........I found two W&B sheets in the plane this is the newest one. I went through the complete logs and cant find anything that declares that it was actually weighed so I have no idea if this is anywhere close to accurate or if it was updated when the battery was moved etc. I can't image any modifications would have been done off the books (wink wink). ....

The battery was probably moved aft as part of the O-340 conversion. Your W&B numbers don't look out of line to me, but that doesn't mean anything. As far as loaded CG, I HATE the Cessna "index" system. Look on the C170B TCDS
http://rgl.faa.gov/Regulatory_and_Guida ... /A-799.pdf
and you'll find the CG limits listed along with a CG chart, in INCHES rather than Cessna's index figures.

I use the old fashioned weight x arm = moment, total moment divided by total wt = CG.. Not sure if your 170 uses the same stations but my 180 puts fuel @ 48", pilots @ 36", pax @ 70", and baggage @ 95". Here's a sample loading scenario for your airplane:

empty wt 1428 / 40.31" CG / 57,562 moment
30 gal fuel 180 @ 48" = 8,640
pilots 350 @ 36" =12,600
ditty bag 20 @ 95" =1,900
loaded wt 1,978 / 40.79" CG / 80,702

1978# @ 40.79" is well within the normal category CG limits shown on the TCDS.

Now to address the change in CG from moving the battery.
Measure the arm from the firewall to the centerline of the existing battery box. Determine best as possible the weight of the battery, batt box, and (probably) master solenoid.
Estimate the weight of the battery cable.These are your deducts.
Use the firewall/battery measurement for the arm on the battery, box, & solenoid; use half that arm for the batt cable.
Determine the weight of the Odyssey battery, whichever mounting box / bracket you want to use, the master solenoid, & add a couple pounds for a new batt cable. These are your adds-- use about 2-1/2" (just ahead of the firewall) for the arm on these. Do the math as per the loading example in my last post. This will give you a pretty good idea of where the new empty CG will be. Do a few loading examples to see if this will be a good thing.

And finally.... missing W&B sheets are a pet peeve of mine. I think every time a new W&B is determined, it not only should be noted on a W&B sheet revision, but should also be noted in the airframe logbook. Logbooks do get lost, but not nearly as often as W&B sheets. Of the four airplanes I've owned, my 180 is the only one that seems to still have all the old W&B sheets. It really helps to have all the old data, esp when changes are calculated, not weighed,

Yes, don't get the index confused with CG Arm in inches, it looks like that's been covered. If that W&B sheet is accurate 40.31 looks fine to me and not nose heavy at all, infact my 170 with the standard C-145 is more nose heavy than that. I don't have my W&B sheet handy but I know the empty CG was 38.xx something when we weighed it last September. With that CG I can load full fuel, my wife, daugter, dog, and myself plus 120lbs in the baggage area and 50lbs in the extended baggage are and still be in limits.

I do agree you should do a new W&B on the airplane so you know what it really weighs and what the empty CG is. Your current sheet is over 17 years old and looks like it was calculated not actually weighed. Who knows how accurate it really is.

This thread reminds me of a question I've always had but have never found the answer to. The arm for the pilot and co-pilot seats is 36 inches. In what seat position is that calculated from? The stock seat rails have 6 holes each spaced 1 inch apart. So obviously the CG of the pilot or copilot will change depending on which hole they're locked into. If you have McFarlane seat rails like I do then there are 2 more holes allowing the seat to be placed 2" further aft than the stock rails when locked into the aft hole. This is the seat position I always use since I'm a tall guy. This means my real arm for the pilots seat is 38 inches or possibly even further aft. Something to think about when you're calculating your W&B

Rob,

I was told by a Cessna rep some years ago, that the arm given for the pilot/copilot seats assumes the middle position of the seat. In my experience, the seats are typically at or close to the most forward position.

Bottom line is this: You can worry yourself blue over precisely where everything is in your plane. Consider this: where is the "center" of the baggage or extended baggage compartment?

The appropriate answer is: Who gives a shit?

Frankly, close is good enough. And, he has an old outdated weight and balance??? I got some news for you: there are a LOT of airplanes out there flying every day with really old weight and balance sheets.

You need to be close, and in fact, when you get right down to it, the only thing that really matters when it comes to C/G is whether you're within (or really close to) the aft limit.

FWIW, I'd have it weighed, just for peace of mind. But, that's me.

MTV

In my experience, it's pretty tough to get a Cessna 100 series too far out of balance, at least with the 2 pilots and gear configuration I most often run in. They do have an amazingly long CG range.

mtv wrote:Rob,

I was told by a Cessna rep some years ago, that the arm given for the pilot/copilot seats assumes the middle position of the seat. In my experience, the seats are typically at or close to the most forward position.

Bottom line is this: You can worry yourself blue over precisely where everything is in your plane. Consider this: where is the "center" of the baggage or extended baggage compartment?

The appropriate answer is: Who gives a shit?

Frankly, close is good enough. And, he has an old outdated weight and balance??? I got some news for you: there are a LOT of airplanes out there flying every day with really old weight and balance sheets.

You need to be close, and in fact, when you get right down to it, the only thing that really matters when it comes to C/G is whether you're within (or really close to) the aft limit.

FWIW, I'd have it weighed, just for peace of mind. But, that's me.

MTV

I hear what you're saying, but as a Loadmaster in the Air Force, W&B is a big part of my job and I can't help thinking about these things. I do consider exactly where all the weight is positioned in my airplane when it's loaded. And I do a agree with Zane that it's pretty tough to load a Cessna out of limits. I know what the worst case scenario is for aft limits and always load it in a way that I know I'm good without actually calculating the CG, unless I know I'm close.

Zzz wrote:In my experience, it's pretty tough to get a Cessna 100 series too far out of balance, at least with the 2 pilots and gear configuration I most often run in. They do have an amazingly long CG range.

I rarely do a balance calculation with any Cessna 4 place. I've done enough of them over the years that I know that if I weigh what is put in, it'll be within the envelope. I do make a point, when I'm hauling my camping gear and pup dog, of keeping heavier stuff forward to the extent possible, and when I carry 3 pax, I put the heaviest in the front seat. But it's unusual to feel any real effect from any loading, as long as it's within weight limits.

Cary

Thanks for all the input.
The summary sounds something like this to me: weight the plane just because its nice to know. Do the mods I want because its not likely to be a problem. If its a problem, throw in some survival gear aft.
Got it.
Zzz: I also normally fly either solo or with one front seat passenger. I've never felt like the camping gear I pack on the rear floor is a problem (I have jump seats so the whole rear floor is available).
I mentioned in the beginning that I was guessing I had an aft weight problem because of the significant differences in how this 170B and my Stinson wheel land. Zzz suggested it might just be the nut thats holding the yoke. Well, I think he's probably right. I've been off work all week so I've been flying quite a bit out of my house and to other airports (grass). I put out an extra effort with 170 on my wheel landings and it was fine (just different than the other plane). Today I made great wheel landings in the 170 that could be held as long as desired as long as I shove the yoke far forward and brake harder as it slows. As long as I shove the yoke forward I was even able to just simply taxi around with the tail up with a little power added back in.
So, as usual, the problem is the pilot.
The plane needs a starter for sure anyway (hot start problem) and I dont like the looks of the battery, so I'll be replacing them both. I just want the battery on the firewall so that the cable are shorter and I have the option of extended baggage if I want.
Thanks again guys. You can bet it will take while for me to get this all done but I'll share the new W/B when it is just in case anyone still care by then.

Don't forget if you do add an extended baggage that it does add a considerable amount of weight. So if you do go with the firewall mounted battery some of the CG change would be offset by the extended baggage. The Selkirk fiberglass extended baggage for a 170B weighs 11lbs.

robw56 wrote:

mtv wrote:Rob,

I was told by a Cessna rep some years ago, that the arm given for the pilot/copilot seats assumes the middle position of the seat. In my experience, the seats are typically at or close to the most forward position.

Bottom line is this: You can worry yourself blue over precisely where everything is in your plane. Consider this: where is the "center" of the baggage or extended baggage compartment?

The appropriate answer is: Who gives a shit?

Frankly, close is good enough. And, he has an old outdated weight and balance??? I got some news for you: there are a LOT of airplanes out there flying every day with really old weight and balance sheets.

You need to be close, and in fact, when you get right down to it, the only thing that really matters when it comes to C/G is whether you're within (or really close to) the aft limit.

FWIW, I'd have it weighed, just for peace of mind. But, that's me.

MTV

I hear what you're saying, but as a Loadmaster in the Air Force, W&B is a big part of my job and I can't help thinking about these things. I do consider exactly where all the weight is positioned in my airplane when it's loaded. And I do a agree with Zane that it's pretty tough to load a Cessna out of limits. I know what the worst case scenario is for aft limits and always load it in a way that I know I'm good without actually calculating the CG, unless I know I'm close.

I hear you, Rob. That said, the load range in a C-5 or a C-17 to that of a 170 is a very different kettle of fish. Consider the cargo bay length of the cargo plane compared to the total length of the plane, then consider the same for the 170. The length of the seat rails in the Cessna is pretty tiny compared to the cargo bay of a cargo plane.
I'm not saying it doesn't matter, but using the center of the tracks is a reasonable compromise. Consider also that a load in the baggage compartment of the 170 does not necessarily act exactly at the center point of the baggage space, but that's the arm we use. This stuff can make you crazy if you worry about it too much.

MTV

Alpina23 wrote:....The plane needs a starter for sure anyway (hot start problem) .....

I put a Skytec flyweight starter on the 150/150, great starter-- Spruce has them for about $380.
That said, I have a Prestolite starter that has very little time on it since it was gone through, I'd sell it for $50.

mtv wrote:

robw56 wrote:

mtv wrote:Rob,

I was told by a Cessna rep some years ago, that the arm given for the pilot/copilot seats assumes the middle position of the seat. In my experience, the seats are typically at or close to the most forward position.

Bottom line is this: You can worry yourself blue over precisely where everything is in your plane. Consider this: where is the "center" of the baggage or extended baggage compartment?

The appropriate answer is: Who gives a shit?

Frankly, close is good enough. And, he has an old outdated weight and balance??? I got some news for you: there are a LOT of airplanes out there flying every day with really old weight and balance sheets.

You need to be close, and in fact, when you get right down to it, the only thing that really matters when it comes to C/G is whether you're within (or really close to) the aft limit.

FWIW, I'd have it weighed, just for peace of mind. But, that's me.

MTV

I hear what you're saying, but as a Loadmaster in the Air Force, W&B is a big part of my job and I can't help thinking about these things. I do consider exactly where all the weight is positioned in my airplane when it's loaded. And I do a agree with Zane that it's pretty tough to load a Cessna out of limits. I know what the worst case scenario is for aft limits and always load it in a way that I know I'm good without actually calculating the CG, unless I know I'm close.

I hear you, Rob. That said, the load range in a C-5 or a C-17 to that of a 170 is a very different kettle of fish. Consider the cargo bay length of the cargo plane compared to the total length of the plane, then consider the same for the 170. The length of the seat rails in the Cessna is pretty tiny compared to the cargo bay of a cargo plane.
I'm not saying it doesn't matter, but using the center of the tracks is a reasonable compromise. Consider also that a load in the baggage compartment of the 170 does not necessarily act exactly at the center point of the baggage space, but that's the arm we use. This stuff can make you crazy if you worry about it too much.

MTV

It can make a difference though. My empty CG is 38.38", if I put two 200lb people in the front seats at 36" I am out of limits on the forward end of the envelope. If the 36" is at the middle hole on the stock rails that would be either the 3rd or 4th hole. The McFarlane rails using the 8th hole would either be 40" or 41". Using 40" instead of 36" moves the CG back 0.8" with 400lbs in the front seats, this puts me back in limits.

robw56 wrote:..... My empty CG is 38.38", if I put two 200lb people in the front seats at 36" I am out of limits on the forward end of the envelope. ....

Is that with empty fuel? What's the arm for fuel? On my 180 it's at 48". Doesn't take much fuel to start shifting the CG aft.