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Re: Weighing my 170B Couple Questions
Posted: Thu Feb 01, 2018 4:21 am
by cessna170bdriver
Metal Master wrote:The numbers that are in the first post make no sense?
Engine oil is 7.5 lbs. / gallon
Which is a total of 21 lbs. oil at 8 quarts
Installed at -20 (minus 20 inches) X -21 lbs. (Minus 21 lbs.) = 420
Where:
Minus 20 inches equals the distance (Arm) forward of the fire wall.
Minus 21 lbs. equals the weight of the oil removed.
420 equals the calculated moment for the weight and balance.
Using the numbers I think you are trying to get at.
Jim
Easy mistake to make. He used 7.5 lb/quart rather than per gallon. We 170 drivers don’t normally think of oil in terms of gallons. Your mistake was math. 8 quarts is 2 gallons, or 15 pounds.
Re: Weighing my 170B Couple Questions
Posted: Thu Feb 01, 2018 4:31 am
by cessna170bdriver
edbooth wrote:cessna170bdriver wrote:I had mine weighed with full fuel and subtracted the weight of 37 gallons of fuel to determine the empty weight. That way I know what it weighs with full fuel regardless of what the actual unusable fuel is.
Miles, how did the new W&B compare with the old one ?
She went from 1358 lb to 1383, a gain of 25 lb. Most of that is probably the 2-3 gallons of epoxy primer on the interior of the skins.
Re: Weighing my 170B Couple Questions
Posted: Thu Feb 01, 2018 3:11 pm
by edbooth
cessna170bdriver wrote:edbooth wrote:cessna170bdriver wrote:I had mine weighed with full fuel and subtracted the weight of 37 gallons of fuel to determine the empty weight. That way I know what it weighs with full fuel regardless of what the actual unusable fuel is.
Miles, how did the new W&B compare with the old one ?
She went from 1358 lb to 1383, a gain of 25 lb. Most of that is probably the 2-3 gallons of epoxy primer on the interior of the skins.
Interesting......mine has not been weighed since leaving the factory. I'm almost afraid to weigh it.....however it still gets off the ground.
Re: Weighing my 170B Couple Questions
Posted: Thu Feb 01, 2018 6:48 pm
by GAHorn
cessna170bdriver wrote:.... We 170 drivers don’t normally think of oil in terms of gallons. ....
Since you've replaced your engine recently Miles .... you have forgotten how much these damn things leak! I have no problem thinking in terms of gallons and cases of quarts.
Re: Weighing my 170B Couple Questions
Posted: Wed Jul 17, 2019 4:36 pm
by iowa
my understanding was that full oil was included in
the empty weight of an airplane.
but my weight and balance out of the factory
shows 15lbs (for 2 gallons; or 8 quarts) at arm of -20
i take it that full oil was not included in the empty weight?
dave
'iowa'
Re: Weighing my 170B Couple Questions
Posted: Thu Jul 18, 2019 2:47 pm
by GAHorn
“Empty Weight” is the airplane’s weight with unuseable/undrainable fuel and oil. This is the standard for “small aircraft”.
Empty weight for “large aircraft” includes necessary operating fluids such as hydraulic fluids, etc. The definition is determined by the manufacturer and is usually referred to as “Manufacturers Empty Weight” (MEW). Large aircraft often use a modified version of “Empty Weight”, known as Basic Operating Weight (BOW) for operational purposes. BOW includes fluids needed for normal operations, Crew Weight, and even includes necessaries such as galley supplies and crew manuals, etc.
The “Empty Weight” used for Weight and Balance purposes is calculated from MEW. The Cessna method for the 170 is defined in the AFM/OM and includes unuseable fuel/oil.
(Notice that brake fluid is not mentioned.)
Hope that helps.
Re: Weighing my 170B Couple Questions
Posted: Thu Jul 18, 2019 11:28 pm
by n2582d
gahorn wrote:“Empty Weight” is the airplane’s weight with unuseable/undrainable fuel and oil. This is the standard for “small aircraft”.
What George meant to say was, "this is the standard for
older 'small aircraft.'" It's true for aircraft like the C-170 which was certified under CAR 3. It does not apply to aircraft certified under FAR 23. This quote is from the
FAA's Weight & Balance Handbook, page 3-4:
Oil
The empty weight for aircraft certificated under the Civilian
Air Regulations (CAR) part 3 does not include the engine
lubricating oil. The oil must either be drained before the
aircraft is weighed, or its weight must be subtracted from
the scale readings to determine the empty weight. To weigh
an aircraft that does not include the engine lubricating oil
as part of the empty weight, place it in level flight attitude,
then open the drain valves and allow the oil to drain out.
Any remaining is undrainable oil and is part of the empty
weight. Aircraft certificated under Title 14 of the Code of
Federal Regulations (14 CFR) parts 23 and 25 include full
oil as part of the empty weight. If it is impractical to drain the
oil, the reservoir can be filled to the specified level and the
weight of the oil computed at 7.5 pounds per gallon. Then,
its weight and moment are subtracted from the weight and
moment of the aircraft as weighed. The amount and arm of
the undrainable oil are found in Note 1 of the TCDS, and
this must be added to the empty weight.
Re: Weighing my 170B Couple Questions
Posted: Fri Jul 19, 2019 2:05 pm
by iowa
great clarification guys!!
my daughter is a algebra I teacher
and wants to do a W&B calculation
before we go to Oshkosh this year
thanks
dave
'iowa'
Re: Weighing my 170B Couple Questions
Posted: Sun Jul 21, 2019 11:58 am
by GAHorn
That was kind, Gary. Actually, I’d forgotten Parts 23/25 made that change. Thanks.
Re: Weighing my 170B Couple Questions
Posted: Fri Aug 02, 2019 9:47 pm
by iowa
how does one drain the fuel
before an empty plane is weighed?
is it while the plane is level as in flight?
dave
Re: Weighing my 170B Couple Questions
Posted: Fri Aug 02, 2019 10:14 pm
by Bruce Fenstermacher
iowa wrote:how does one drain the fuel
before an empty plane is weighed?
is it while the plane is level as in flight?
dave
This is the problem. It is very difficult to drain all the fuel unless you disassemble stuff.
This is why folks fill the tanks, weigh the aircraft, then subtract the fuel if empty fuel calculations are desired.