Had my plane weighed today

Luvjet · Post by **Luvjet** » Wed Sep 11, 2013 8:22 pm

Always wanted to see how accurate the weight and balance was after all these years, so two of us, both 170 owners, '50 A and a 55 B just had it done a couple of hours ago. His empty weight went up about 80 lbs, and mine went up 93 lbs. This is with the tanks drained dry and the tail up level and the other plane ('55) with the tanks full. Everything was pulled out of my plane including what was in the back of the seat pockets. Anybody else have the same experience? I really do believe the guy doing the weighing knows what he is doing. I was there when they did it. I guess I'll have to go on a diet to get back some of the useful load.

170C · Post by **170C** » Wed Sep 11, 2013 9:57 pm

Don, its like others have said in the past. Our planes, like their owners, tend to pick up some pounds as we/they get older. You probably just forgot to unload all those packages of SW Peanuts you had in there

canav8 · Post by **canav8** » Wed Sep 11, 2013 10:38 pm

When you say the tail was up and level what was the tops of the doors doing? Proper weight and balance is to assure the top of the door frame is level not the tail! you will get a different cg. D

bigrenna · Post by **bigrenna** » Wed Sep 11, 2013 11:28 pm

delete

Post by **GAHorn** » Wed Sep 11, 2013 11:41 pm

My airplane gained weight but it's not clear exactly why since all (or most) of the sheet metal was replaced in the restoration.
I suspect it is due to extensive epoxy poliamide primer installed as a "marinizing" process to prevent corrosion. (The restorer worked for Bell Helicopter and had access to all the processes they do to marinize helicopters for the Navy.)

Anyway, it left the factory around 1245 lbs and is now almost 100 lbs heavier.

Wed Sep 11, 2013 11:57 pm

Remember, we really don't know what the aircraft weighed when it left the factory. We only know what it was calculated to weigh. Most aircraft leaving the factory are not actually weighed. My 170 has never stepped on a scale and isn't likely to any time soon. At least official scales

.

While it is true the level of the aircraft is critical to determine the CG. It is not critical to determine the weight which when all scales are added together will be the same no matter the level of the aircraft.

canav8 · Post by **canav8** » Thu Sep 12, 2013 2:33 pm

After I replaced my battery to an Optima and used F. Atlee Dodge's Battery tray and several other mods to put the aircraft on a diet, I got the Weight below original manufacturers Weight and Balance numbers. Yes, it was weighed by the manufacturer.
The aircraft is not as sensitive to weight as much as it is sensitive to CG. That is why it is so critical to make sure the top of the door frame is used. Using improper W&B data can put the operater in a dangerous controllability condition if it is misloaded using the Aircraft Owners Manual chart with the wrong C of G calculated. D

Luvjet · Post by **Luvjet** » Thu Sep 12, 2013 2:54 pm

I do have the Atlee-Dodge rear seat conversion but not the battery conversion. I think that might be in my future. How has that battery conversion worked for you? The airplane was leveled for the check.

Luvjet · Post by **Luvjet** » Thu Sep 12, 2013 3:03 pm

Besides the seat mod which saved 18.5 lbs I removed the original starter which saved a net of around 8-9 pounds I really don't have much in the plane in the way of radios (KLX 135 a Garmin 320A x-ponder , and a interphone box) I really do think this guy doing the W/B knew what he was doing. Apparently this is not uncommon when the plane gets weighed. Nice to know the correct C/G, but still.......

canav8 · Post by **canav8** » Thu Sep 12, 2013 3:35 pm

Luvjet wrote:I do have the Atlee-Dodge rear seat conversion but not the battery conversion. I think that might be in my future. How has that battery conversion worked for you? The airplane was leveled for the check.

The Battery has been going for 5 years now. Hasnt missed a beat. The total weight savings was 18 lbs if I remember correctly. D

cessna170bdriver · Post by **cessna170bdriver** » Thu Sep 12, 2013 7:30 pm

Bruce Fenstermacher wrote:...
While it is true the level of the aircraft is critical to determine the CG. It is not critical to determine the weight which when all scales are added together will be the same no matter the level of the aircraft.

I don't think I'd bother to weigh my airplane if I didn't also plan on calculating a center of gravity.

BEEZERBOY · Post by **BEEZERBOY** » Fri Sep 13, 2013 8:46 pm

to get the most accurate balance you should weight the aircraft EMPTY and add in the unusables later. the undrainable fluids (residual) and unuseable fuel are considered part of the aircraft the empty weight, just as if there are not there. and yes, you can probably use most (or even all) of the unusable fuel in level flight. unuseable fuel in a particular tank is determined by when the engine sputters during any maneuver the aircraft is allowed to do in whatever category it is certified in. the position of that fuel is almost never in the normal position that is given for the fuel tank.... I can think of only one airplane where it is (Piper T-hawk). what that means is if you weigh the plane with full fuel, you have to subtract the weight and moment of all fuel and then add back the unusable, which is always listed in Note 1 on the Spec or TCDS. that still does not account for the undrainable, but that's pretty small. as long as you do it right, you can get pretty close, but I have also seen guys try to weigh the plane with the unusable on board.... but that's not actually possible because of the position of the fuel.

for instance, if you have a straight 170, fuel is located at 45".... but unusable fuel is at 53"...

From Note 1, C170 Specification:

"The certificated empty weight and corresponding center of gravity location must include unusable fuel at 19 lb. at (+53) for Model 170 and 30 lb. at (+46) for Model 170A and Model 170B (above values are included in total fuel capacity). When Item 113, 18 gallon auxiliary fuel tank, is installed an additional 3 lb. unusable fuel at (+99) must be included."

Note 1 always has the unuseable fuel if there is any. if there is no unusable... there is no mention in the Note. they don't come out and tell you that, it is simply omitted.

KS170A · Post by **KS170A** » Sat Sep 14, 2013 11:44 am

I was also of the understanding that airplanes of our vintage were supposed to have the empty weight calculated to reflect unusable fuel (as previously indicated) and NO oil in the engine (the weight of which is to be added when doing W&B calculations). Full oil was later (can't remember when, not enough coffee yet) added as part of the empty weight of the airplane. At the end of the day, whether weighing with full or empty oil and gas, as long as appropriate calculations are made, probably not going to vary much...certainly not as much as being 90# off between previous and new weighings!

BEEZERBOY · Post by **BEEZERBOY** » Sat Sep 14, 2013 8:22 pm

I think the no oil thing was because the wide spread use of Radial engines back in the day with their huge oil tanks.... bit of a moot point really since every W&B I've ever seen eventually has you putting in full oil. it was changed with the advent of the FARs. Part 23 aircraft are weighed with full oil.

truth is when I weigh a CAR certified airplane I use full oil and make note on the W&B data (unless the owner wants to use the OEM W&B sheets). some owners like to run 7 qts instead of 8 for instance, so I jut put a can of oil on top of the engine

T. Gandy · Post by **T. Gandy** » Sat Sep 14, 2013 10:22 pm

BEEZERBOY wrote: some owners like to run 7 qts instead of 8 for instance, so I jut put a can of oil on top of the engine

BEEZERBOY, do you take into account the weight of the can?

The International Cessna 170 Association