Weight & Balance

[ghostflyer]

The 170 , 180 and the 185 are very different animals. I have done "many" hours in a 180 and a few hours in a 185 and find flying the 170A is like being in a pocket rocket. Its lighter ,cheaper to maintain and uses a lot less fuel and a heaps more fun. Most of my flying is by myself or the wife comes along for a ride. Why haul all that extra metal around? . I get paid to fly a near new Cessna 182 around [ The owner flys it on a annual basis for a couple weeks.I fly it around to keep the rust out of the bores] . But I still prefer the 170A. The 170 is not the perfect plane but damm close.

[KS170A]

I know it just depends on personal desires, and the 170 is truly a classic airplane. I know the later model 182s are real pigs when it comes to empty weight (as are pretty much all the new Cessna single-engine planes, with their beefed up seating requirements, sound proofing, etc...). My hangar mate has been working on me to sell my 170 to upgrade to 180...was considering it until I had to move his empty airplane out of the way to get mine out. Uh...no thanks, for many of the reasons listed!

[N3188A]

First off I justed wanted to say thanks for all the comments and support!

So I just got the final report back and the measurements are as follows - weights are with full fuel and aircraft was leveled on upper door sill.

Left wheel: 781 lbs
Right wheel: 729 lbs
Tail wheel: 116 lbs

Firewall to center of main axles: 18.5" (measured)
Firewall to center of tail wheel: 249.375" (measured - Gar Aero TW)

Correcting for fuel (subtracting off 42 gallons at 48" and adding 5 gal unusable at 46" per the TCDS) leaves a final empty weight of 1404 lbs at a moment of 46146.5 and a CG of 32.9"

I'm exploring a LW starter and alternator - this could shave off about 12 lbs. up front but I'll still need to add about 15 lbs. in the tail to be able to fly with two full sized adults in the front seats (380 lbs. total) with my Gar Aeor tires which includes my 40 lbs survival pack at the very back of my extended baggage (about 136").

I've dug around up front thinking that one of the previous owners may have stored his gold somewhere in the engine compartment but haven't found any yet! My brother-in-law suggested I install a LW starter and alternator and put the current starter and alternator in the back so I'll always have a spare...

[blueldr]

It really doesn't matter where you put the scales to take the weight of the airplane. If the calculations are done properly, the CG will be the same.

[blueldr]

A guy has to be dedicated to work on small GA airplanes. The "Big Iron" is where the money is.

The same thing is true in flying them. I've flown small airplanes for pay, scimpy as it was. When I was a Captain flying the DC-6 I made $18.38 per block time hour and the FAA allowed us to fly 1000 hours per year. Talk about cutting a fat hog in the butt! We also got $.70 per hpur per diem away from the domicile. Thats $16.80 per day and all we had to pay for was our meals, laundry, and hotel room. Damn, but those were the good old days!
I never told the company, but I loved flying their old rattlers enough that I probably would have paid THEM out of my military retirement pay just to let me fly them.

[canav8]

First off I justed wanted to say thanks for all the comments and support!

So I just got the final report back and the measurements are as follows - weights are with full fuel and aircraft was leveled on upper door sill.

Left wheel: 781 lbs
Right wheel: 729 lbs
Tail wheel: 116 lbs

Firewall to center of main axles: 18.5" (measured)
Firewall to center of tail wheel: 249.375" (measured - Gar Aero TW)

Correcting for fuel (subtracting off 42 gallons at 48" and adding 5 gal unusable at 46" per the TCDS) leaves a final empty weight of 1404 lbs at a moment of 46146.5 and a CG of 32.9"

I'm exploring a LW starter and alternator - this could shave off about 12 lbs. up front but I'll still need to add about 15 lbs. in the tail to be able to fly with two full sized adults in the front seats (380 lbs. total) with my Gar Aeor tires which includes my 40 lbs survival pack at the very back of my extended baggage (about 136").

I've dug around up front thinking that one of the previous owners may have stored his gold somewhere in the engine compartment but haven't found any yet! My brother-in-law suggested I install a LW starter and alternator and put the current starter and alternator in the back so I'll always have a spare...

N3188A, Your situation is very unique. It is an interesting example of how to make our aircraft function in the most extreme ends of the envelope. I also did not notice if you stated that you were full of oil. That will add weight in the wrong direction as well. I have done a number of mods to lighten up the forward CG issue.
You might consider the F.Atlee Dodge Battery Tray and Optima Battery will save 13 lbs. The other thing you can do is relocate the battery to the back of the aircraft. It will add weight with longer cables but it will allow you to operate without the addition of the survival kit possibly. Just some ideas you may or may not have considered. D

[ghostflyer]

N3188A , I have a similar problem and compared your figures with mine. My aircraft is 28lbs heavier,but has the same characteristic of a heavier side but your aircraft is 4 lbs heavier on the same heavier side . My aircraft is a 1/2 in longer. My C of G is just insde of the line for forward Cof G . Thank-goodness I went for the fixed pitch prop. As stated before my stall is about 4 knots faster. One point I have found is that with a forward C of G it flies faster. My controls are very sensitive over all. However this is also because I am flying faster also. With a 60in pitch prop and at 2500 rpm I am at just under 117 kts.

[Bruce Fenstermacher]

I've run your numbers and I don't get what you came up with. First you corrected by subtracting 42 gal at 48. This is not the most accurate calculation given the info we have. The simple fuel loading info we have says usable fuel has an arm of 48. There is only 37 gal usable. Unusable fuel has an arm of 46. So I believe it is more correct to correct the weighed number by subtracting 37 gal at 48 and then subtracting 5 gal at 46 to remove the fuel. Here is what I came up with.

Screen Shot 2013-11-29 at 10.45.01 AM.png (22.69 KiB) Viewed 13490 times

You will notice that my numbers don't ad up to your numbers. And unfortunately my numbers show your CG even more forward that yours.

[hilltop170]

I haven't checked anything on these posts and it may not apply in this case but I found a years-old error on my C-195 which showed a rearward CG that I intuitively thought too far back but the numbers calculated to be correct until I discovered why. The problem was an incorrect arm value was used. In that case, the arm for the leading edge of the wing was used instead of the axle centerline. You might double-check all the arms for accuracy on these calculations.

[ghostflyer]

The problem could be the weight and balance is being done from a incorrect datum point . It was stated the firewall was used ,I am under the impression the center of the axles should be used as the measurement datum point .

[Bruce Fenstermacher]

The datum for all models according to the TCDS is the front face of the firewall.

[BEEZERBOY]

Cessna has you measure the distance between wheel weigh points, then convert to datum later in the calculation. as long as you keep all the numbers straight during the weigh, get a total, then convert the distances, you are OK. the original weight & balance form that has the weighing procedure takes it step by step, but assumes no fuel and no oil.... weigh the aircraft, then after you calculate the basic w&b, you convert to datum. then you add unuseable fuel and full oil for the "licensed empty weight" using arms from datum.

if you weigh with full fuel.... remove all fuel mathematically after the weigh point numbers are converted.... use the TCDS/Spec for the arm of the fuel. then the unuseable fuel is added back in. it's only unuseable in flight, in some attitude (it is the fuel left in any tank when the engine sputters during any maneuver the aircraft is allowed to do in the category it's certified in). it's not as accurate to do it this way... only more convenient

I usually weigh with full oil and make note in the weighing record. realistically, it's no different than any piece of fixed equipment, and all the adverse load calculations, etc. require full oil anyway

you can also use the weigh points as measured from datum and skip the formula.... same results and is easier to follow. btw, the metal Pipers are the same, the rag ones are worse, uses the same formula, but have 2 datums

[hilltop170]

Just thinking here and sometimes that can be dangerous but wouldn't you want the CG as far forward as possible when it's empty? Since the datum is the firewall, everything you load in the plane will move the CG aft. The plane is never going to go flying by itself so why worry that it is not in range when empty?

That just gives more latitude in loading and the pilot still makes the decision what to carry and where to load it based on whatever the final LOADED CG is going to be. I have a fairly stock plane (weight-wise anyway) and its empty CG is right at the front at 49.9 Index Units, right where I want it to get full usage of the CG range when loaded.

Am I missing something here?

[hilltop170]

Thanks Arash!!! That is what I was missing!

[c170b53]

I am under the impression the center of the axles should be used as the measurement datum point .

Likely that was a senior moment and highly unlikely the reason that you were unable to mount a C/S .....but mounting a C/S was not an issue for me and I believe has not been a unsolvable issue for a few others.