Un-usable Fuel

[cdoughty]

Thanks for all the comments. I am confident there is no definitive statement from Cessna/FAA as to usable fuel. Hard to prove a negative to a bureaucrat and you are back to arguing which ambiguous rules to apply and how--and you can't really win those arguments.

That said as PIC you should have a number for un-usable fuel of course and mine is John C's above--keep at least one tank out of the red. The red zone seems to be a placard just like "no spins with flaps down" and since every landing might end as a takeoff/go around I interpret it as "no landing" too.

As to what it would be under the current regs. Hard to see that "normal maneuvers" doesn't include 30 deg pitch and 60 bank but those aren't easy values to reach on the ground. I would point out that coordinated 60 degree bank turn is 0 degree as far as the fuel is concerned. I wonder what the un-usable would be flying a 60 degree knife edge--would probably exceed 3 gals though (at least for bottom tank).

I think the red zones are very conservative. When I drained the tanks on the ground in 3pt attitude fuel flowed well into the red and I decided the un-usable was a couple of gallons. But I wasn't trying to be super accurate-it could have been 1.5 or 2.5. So I think its safe to be at the top of the red, especially if you avoid a really steep climb out-but why bother?

As to weight. I doubt there are many lighter 140s. Ours is 907 empty. They were legal.

[6643]

I have run a tank "dry" (engine quit) in level flight. When I landed I tried to sump that tank (the lowest point in the tank, right?) The amount that came out would have had to be measured in drops, so...

The only fear I have of doing that is if the selector valve breaks when you try to switch tanks. Of course, that could be a problem even if both tanks had fuel in them...

[maverick_fa]

As to what it would be under the current regs. Hard to see that "normal maneuvers" doesn't include 30 deg pitch and 60 bank but those aren't easy values to reach on the ground. I would point out that coordinated 60 degree bank turn is 0 degree as far as the fuel is concerned.

Normal Attitude are part of the 1st flight lesson that we are getting over here. It's called ''Attitude & Movement" aka exercise #5 (in Canada).

Normal Pitch Attitude include:
-Best Angle Climb (Vx)
-Best Rate of Climb (Vy)
-Normal Climbing
-En Route Climbing (Vcc)

Normal Banking Attitude include:
-Gentle Bank: 0° to 15°
-Medium Bank: 16° to 30°

Pitch at 30° or bank at 60° is considered as ''Steep Attitude" & use as part of upset recovery &/or escape maneuvers (in Canada).
I can also climb at 90° when I'm doing an Hammerhead or banking at 90° when I'm doing a Wingover with an A152 (aerobat) but this is considered aerobatic or upset recovery. I can also easily kill the engine if I do -G's.

Most of the time the regulations are really similar between FAA, EASA & TC.

It make sense what you are saying for the fuel in the tank during a bank attitude... it's something that I want to test now when my airplane will be back in service. Please don't forget the 30° slip turn that can be part of the flight test!

As to weight. I doubt there are many lighter 140s. Ours is 907 empty. They were legal.

I don't have have the data for your airplane. With # provided by your DPE, I'm getting overweight (see picture).
You are right, 907 is extremely light... mine was 974... I hope to be around 930.

I think the red zones are very conservative. When I drained the tanks on the ground in 3pt attitude fuel flowed well into the red and I decided the un-usable was a couple of gallons. But I wasn't trying to be super accurate-it could have been 1.5 or 2.5.

I did/think the same but I'll never talk about that topic during a flight test & this is something I wont teach to my students.
We just need to stay on the conservative/safe side during the the flight test.


We need an updated POH for the C120/140!!


I hope this will help.

[cdoughty]

Agree with your W&B, but at 1450 gross you can only carry 7.5 gals (your 1481-31 lbs, 5 gals). 30 mins reserve (at 6/hr), unusable at 2 and you cant go far

[simonlowther]

You have overloaded the baggage area by 10 lbs (I see 90 vs 80), also isn't oil in basic empty weight? That leaves 6 lbs each for the people to loose, easily done by flying naked!

Si

[cdoughty]

You are right actually that oil is included. Not that I want to discourage flying naked.

At least my weighed W&B includes oil. The original 1946 factory one did not, so if you are still using a derived W&B it might.

[maverick_fa]

You have overloaded the baggage area by 10 lbs (I see 90 vs 80)

The DPE didn't believe this. He then asked him to do W&B for 190, 210 lb occupants and 90 lbs of baggage (already illegal) and didn't believe that you could only go about 20 miles legally.

Due to the question of the DPE...
I believe he was looking for an answer like: Baggage exceed max capacity & the MTOW is exceeded.

isn't oil in basic empty weight

Back in the days, the engineers considered that the oil wasn't part of what we called today the ''Basic Empty Weight''
You can use the official W&B from the website. We need to add the oil during our W&B calculations.
You can found in the FAA documentation (TC as well) this method is called ''Licensed Empty Weight''.
In the AC43-13 under the W&B section, there is a note mentioning that we need to subtract the oil from the ''Basic Empty Weight'' when it's applicable like our C140.

See attached file for more details.
Official W&B sheet from this website
Official AW W&B from Cessna (1947)

[maverick_fa]

Here is the reference from the FAA...

REF. : PHAK Chapter 10 - Page 10-5
Licensed empty weight
The empty weight that consists of the airframe, engine(s), unusable fuel, and

undrainable oil

plus standard and optional equipment as specified in the equipment list. Some manufacturers used this term prior to GAMA standardization.

VS

Standard empty weight (GAMA)
Aircraft weight that consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the aircraft, including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.


REF. : FAA-H-8083-1 - 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.

[maverick_fa]

Reference from the FAA AC43.13-1B

g. The oil system should be filled to the
quantity noted in the TCDS or Aircraft Specifications.

NOTE: On Civil Aeronautics Regulations (CAR-3) Certified Aircraft, the
weight of the oil was subtracted
mathematically to get the empty
weight. In 14 CFR, part 23 aircraft,
the weight of the oil is included in the
empty weight.

When weighed with full oil, actual empty
weight equals the actual recorded weight less
the weight of the oil in the oil tank( oil weight
= oil capacity in gallons x 7.5 pounds). Indicate on all weight and balance reports whether
weights include full oil or oil drained. (See figure 10-9.)

Here is the oil capacity & moment in our TCDS under Empty Weight C.G. Range

[6898]

This is Great question with a lot of knowledge for answers. Thank You for the question and to our Moderators and others to always help out, So much better than the crazy unreliable comments you get from your phone apps. I hope your son gets back in and passes from this.