Weighing my 170B Couple Questions

How to keep the Cessna 170 flying and airworthy.

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nippaero
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Weighing my 170B Couple Questions

Post by nippaero »

Hi guys,

I am planning on weighing my plane this Saturday so I am getting all my information together. I read through the FAA handbook to brush up and have been looking through others W&B sheets. I had a couple questions that I think I know the answer to but want a sanity check.

Question 1
I should not include the engine oil in the 170 empty weight. Aircraft certified under CAR 3 do not include the engine oil. So I should subtract the engine oil from the empty weight right? I think the best way to accomplish this will be to fill the engine to 8 quarts and subtract 60lbs @ -20 (7.5lbs x 8quarts).


Question 2
Fuel. Looks like I need to include the unusable fuel in the empty weight. The TCDS says 5 gallons or 30lbs @ +46. Trying to decide whether to drain the tanks or top them off. I think it is probably easier to top off both tanks and subtract 37 gallons from the empty weight. So 6lbs x 37 gallons = 222lbs @ +48

Then make sure all the required equipment is in the airplane and weight it.

Am I overlooking anything?
1952 170B
N8180A s/n 25032
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canav8
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Re: Weighing my 170B Couple Questions

Post by canav8 »

nippaero wrote:Hi guys,

I am planning on weighing my plane this Saturday so I am getting all my information together. I read through the FAA handbook to brush up and have been looking through others W&B sheets. I had a couple questions that I think I know the answer to but want a sanity check.

Question 1
I should not include the engine oil in the 170 empty weight. Aircraft certified under CAR 3 do not include the engine oil. So I should subtract the engine oil from the empty weight right? I think the best way to accomplish this will be to fill the engine to 8 quarts and subtract 60lbs @ -20 (7.5lbs x 8quarts).


Question 2
Fuel. Looks like I need to include the unusable fuel in the empty weight. The TCDS says 5 gallons or 30lbs @ +46. Trying to decide whether to drain the tanks or top them off. I think it is probably easier to top off both tanks and subtract 37 gallons from the empty weight. So 6lbs x 37 gallons = 222lbs @ +48

Then make sure all the required equipment is in the airplane and weight it.

Am I overlooking anything?
Okay. Answer to question 1. Oil should not be included in Empty Weight. It is added later. If you look on the weight and balance graph on the AFM it will show a small line in the bottom corner from the Origin that is the oil line to be figured when doing your Weight and balance when loading the aircraft.

Answer to Question 2. You must have all drainable fuel out of the aircraft. requirement is technically no more then 12% in the tank but by draining all usable is draining all useable fuel. 1.6 gallons is considered unusable in each tank in the Cessna 170 a total of 5 gallons in the lines gascolator, fuel bowl. I would drain all the available fuel from the fuel valve(the lowest point) and the gascolator. Get your numbers then fill the fuel tanks totally full then weigh it and get the numbers. This serves two purposes, One knowing how much useable baggage and people you can take with full fuel as a hardline number not a calculated number. also you might find a blockage in the fuel system(mechanics rag) ask me how I know?

Answer 3 to question you did not ask. Aircraft is leveled by placing a level at the top of the door sill. Make sure you measure tare weight before you set the aircraft on the scales. If aircraft is not level you will get wild numbers. Also run a plum bob from the firewall and measure the distance from the main wheels and the plum bob. Also measure the distance to the tailwheel from the main wheel centerlines. Those are the gotchas
Regards, D
52' C-170B N2713D Ser #25255
Doug
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nippaero
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Re: Weighing my 170B Couple Questions

Post by nippaero »

Hi Doug, thanks for taking time to explain.

I know about the oil not being part of the empty weight. I guess my question would be is simply subtracting the oil weight mathematically "good enough" and deemed acceptable? Obviously, if I drained it, there would be some amount of oil left in the engine. I would rather not drain the oil so I am gathering that subtracting it from the numbers would be "ok". Just wondering what overs have done.

On the fuel. I like your idea of weighing it both ways. I had thought about that but I thought I might be over complicating things. It seems like draining the fuel would produce the most accurate numbers. Any fuel left in the plane becomes part of the empty weight. The TCDS says you have to include 30lbs unusable fuel. I may get two different numbers like you say. What would the "legal" number be?

Do you think it will make a difference in how much fuel drains out if the plane is level vs. tail on the ground?

requirement is technically no more then 12% in the tank but by draining all usable is draining all useable fuel.
I am wondering where this comes from?
Last edited by nippaero on Fri Jan 26, 2018 2:42 am, edited 1 time in total.
1952 170B
N8180A s/n 25032
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Kyle Wolfe
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Re: Weighing my 170B Couple Questions

Post by Kyle Wolfe »

If it were me, I’d subtract 15 pounds for the oil (7.5 lbs to the gallon). :!:
Kyle
54 B N1932C
57 BMW Isetta
Best original 170B - Dearborn, MI 2005
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canav8
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Re: Weighing my 170B Couple Questions

Post by canav8 »

nippaero wrote:Hi Doug, thanks for taking time to explain.

I know about the oil not being part of the empty weight. I guess my question would be is simply subtracting the oil weight mathematically "good enough" and deemed acceptable? Obviously, if I drained it, there would be some amount of oil left in the engine. I would rather not drain the oil so I am gathering that subtracting it from the numbers would be "ok". Just wondering what overs have done.

On the fuel. I like your idea of weighing it both ways. I had thought about that but I thought I might be over complicating things. It seems like draining the fuel would produce the most accurate numbers. Any fuel left in the plane becomes part of the empty weight. The TCDS says you have to include 30lbs unusable fuel. I may get two different numbers like you say. What would the "legal" number be?

Do you think it will make a difference in how much fuel drains out if the plane is level vs. tail on the ground?

requirement is technically no more then 12% in the tank but by draining all usable is draining all useable fuel.
I am wondering where this comes from?

This comes from AC 43.13-1B Chapter 10 para 10-16 I think. It’s in there somewhere. Legal is removing the oil. The reason why is because it will influence CG not so much total weight.
52' C-170B N2713D Ser #25255
Doug
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canav8
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Re: Weighing my 170B Couple Questions

Post by canav8 »

Also if you are doing weight and balance for informational purposes that’s one thing but if you are doing it officially, caution it may cut down your useful load. Over time accumulation occurs in these planes and reweighing the aircraft usually yields heavier. Once it is officially done, it is to late and becomes permanent aircraft record. Only way to reduce it is go under the panel get all the old wire out, get all the oil from under the floor and pull all the debris out of the corners then weigh it again. I got my bird down to 1339 lbs. Lighter then original W&B when manufactured.
52' C-170B N2713D Ser #25255
Doug
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nippaero
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Re: Weighing my 170B Couple Questions

Post by nippaero »

Yeah. This will be official. I recently had the plane completely apart for restoration and painting.
1952 170B
N8180A s/n 25032
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mit
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Re: Weighing my 170B Couple Questions

Post by mit »

Where is your A&P?
Tim
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nippaero
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Re: Weighing my 170B Couple Questions

Post by nippaero »

mit wrote:Where is your A&P?
Lol. He's around somewhere. Probably drinking coffee...

No seriously. I am finding if you ask 10 mechanics how to do this you will get at least 4 different answers.
1952 170B
N8180A s/n 25032
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Ryan Smith
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Re: Weighing my 170B Couple Questions

Post by Ryan Smith »

You can't do a W&B before you put your wheel pants back on. :wink:
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lowNslow
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Re: Weighing my 170B Couple Questions

Post by lowNslow »

This book has some good info on W&B.
http://www.faa.gov/regulations_policies ... 8083-1.pdf
Karl
'53 170B N3158B SN:25400
ASW-20BL
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cessna170bdriver
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Re: Weighing my 170B Couple Questions

Post by cessna170bdriver »

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

“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne
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edbooth
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Re: Weighing my 170B Couple Questions

Post by edbooth »

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 ?
Ed Booth, 170-B and RV-7 Driver
Metal Master
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Re: Weighing my 170B Couple Questions

Post by Metal Master »

The numbers that are in the first post make no sense?
Engine oil is 7.5 lbs. / gallon
Which is a total of 15 lbs. oil at 8 quarts
Installed at -20 (minus 20 inches) X -15 lbs. (Minus 15 lbs.) = 300
Where:
Minus 20 inches equals the distance (Arm) forward of the fire wall.
Minus 15 lbs. equals the weight of the oil removed.
300 equals the calculated moment for the weight and balance.
Using the numbers I think you are trying to get at.
Jim
Last edited by Metal Master on Thu Feb 01, 2018 1:19 pm, edited 1 time in total.
A&P, IA, New owner C170A N1208D, Have rebuilt some 50 aircraft. So many airplanes, So little time!
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cessna170bdriver
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Re: Weighing my 170B Couple Questions

Post 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.
Miles

“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne
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