Zero Fuel weight and 135 question

Aztec Driver

Aztec Driver

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Bryon
I have a question that I can't find the answer to. On the Aztec I fly, it has a zero fuel weight limit, basically the maximum amount of weight you can put into the cabin before you load fuel. I am trying to figure out what on the aircraft this limit is based on. I had originally thought cabin structure or wing root structure, or landing gear structure, but there is an increase of 100 pounds when operated with turbo-charged engines. Since none of the other structures are changed for that, I assume that can't be it. Is it the distribution of the weight along the wing spar or is there something I am completely missing? I assume it has to be some item on the aircraft unable to handle the load factor above a certain weight, but why would it change with turboed engines?

Second question. Since it is manditory to carry along a manifest on each charter for a multi-engine aircraft, is it permissible that this manifest be in paper form, or can I have an electronic plate that I have to do all the calculations quickly? (assuming one has a written copy back at the office)
 
I'm guessing here, but I _believe_ it's based on wing root strength, and is based on the worst case scenario with the wings being nearly empty with a heavy load in the center.

Having bigger/heavier engines out on the wing structures may actually reduce the stress placed on the wing root as the fuel burns off.
 
Aztec Driver said:
I have a question that I can't find the answer to. On the Aztec I fly, it has a zero fuel weight limit, basically the maximum amount of weight you can put into the cabin before you load fuel. I am trying to figure out what on the aircraft this limit is based on. I had originally thought cabin structure or wing root structure, or landing gear structure, but there is an increase of 100 pounds when operated with turbo-charged engines. Since none of the other structures are changed for that, I assume that can't be it. Is it the distribution of the weight along the wing spar or is there something I am completely missing? I assume it has to be some item on the aircraft unable to handle the load factor above a certain weight, but why would it change with turboed engines?
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Could be the stresses created by the landing gear but I suspect it's simply the wing structure limits. The airplane has to be able to sustain 3.8 gs without yielding and 1.5 times that without failure. With the empty airplane loaded to the ZFL the stress on the wings is higher than it would be if some of that same weight was inside the wings. The turbo engines probably add weight on the wings when empty which has a similar stress effect as adding fuel.

Second question. Since it is manditory to carry along a manifest on each charter for a multi-engine aircraft, is it permissible that this manifest be in paper form, or can I have an electronic plate that I have to do all the calculations quickly? (assuming one has a written copy back at the office)
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My guess is that as long as you can show the electronic copy on a ramp check and there's a copy with dispatch you'd be OK, but part 135 is all about following your Ops specs AFaIK. I'd think you'd want to have that detail spelled out there. This is just a guess, I've never been part 135 qualified, just commercial.
 
Interesting you should ask!! AOPA answered this in this month's new issue (Feb 2009); pages 82/83, when discussing the various types of W&B issues that more advanced aircraft have.

The next calculation is maximum zero fuel weight (ZFW) or the maximum amount of people and bags that can be carried, period. Any weight beyond this maximum can only be fuel. This structural restriction exists because fuel in the wings does not contribute to the twisting motion of the wing--especially at the tips--as much as does fuel in the fuselage. No math games are allowed on this one, so the pilot may never exceed the maximum ZFW by taking on less fuel, for example. To determine an aircraft's maximum allowed payload for crew, passengers, bags, and fuel, simply subtract the standard empty weight from the maximum ZFW.
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It seems to me the last sentence is in error. That arithmetic would give you the maximum allowed payload for crew, passengers, and bags, but by definition (zero fuel weight) it would not be "and fuel."

Wikipedia expands on this explanation a bit:

Wing bending relief

In an airplane, fuel is usually carried in the wings. This weight does not contribute as significantly to the bending moment in the wing as does weight in the fuselage. This is because the lift on the wings and the weight of the fuselage bend the wing tips upwards and the wing roots downwards; but the weight of the wing, including the weight of fuel in the wing, bend the wing tips downwards, providing relief to the bending effect on the wing.

When an airplane is being loaded the capacity for extra weight in the wing is greater than the capacity for extra weight in the fuselage. Designers of airplanes can optimise the Maximum Takeoff Weight and prevent overloading in the fuselage by specifying a Maximum Zero Fuel Weight. This is usually done for large airplanes.

Most small airplanes do not have a Maximum Zero Fuel Weight specified among their limitations. For these airplanes, the loading case that must be considered when determining the Maximum Takeoff Weight is the airplane with zero fuel and all disposable load in the fuselage. With zero fuel in the wing the only wing bending relief is due to the weight of the wing.
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Pilot humor:

Q - What does ZFW stand for?

A - The weight the aircraft becomes when all the fuel tanks suddenly become full of air (which can be somewhat annoying if airborne).
 
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TangoWhiskey said:
Interesting you should ask!! AOPA answered this in this month's new issue (Feb 2009); pages 82/83, when discussing the various types of W&B issues that more advanced aircraft have.



It seems to me the last sentence is in error. That arithmetic would give you the maximum allowed payload for crew, passengers, and bags, but by definition (zero fuel weight) it would not be "and fuel."

Wikipedia expands on this explanation a bit:



Pilot humor:

Q - What does ZFW stand for?

A - The weight the aircraft becomes when all the fuel tanks suddenly become full of air (which can be somewhat annoying if airborne).
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Now how did I miss this from the magazine?

Great explanation, thanks.
 
as far as the manifest question, i suspect you could do it that way, would just have to wrangle some wording into your opspecs to allow for it.
 
...And now for a little trivia...:smilewinkgrin:

There are a couple of airplanes that I know of for which some fuel is actually included in the ZFW.:yikes: Believe it, it's true...When Mitsubishi built the Diamond jet, it only had wing fuel tanks. Branson came up with an aftermarket fuel tank that they put in the aft fuselage, but since the wing structure is the same, the fuselage fuel had to be treated just like passengers and bags, and included in the ZFW.

When Beech bought the design and called it the Beechjet 400, they also bought rights to put the Branson tanks in as standard equipment from the factory. Still had the requirement to include this fuel in the ZFW.

Then for the 400A (now the Hawker 400XP), they redesigned the way the fuel feeds such that it automatically burned the fuselage fuel first, and so it's not considered part of the ZFW in 400A's and 400XP's.

Just thought I'd mention that, in case anybody had insomnia ;)

Fly safe!

David
 
Aztec Driver said:
Second question. Since it is manditory to carry along a manifest on each charter for a multi-engine aircraft, is it permissible that this manifest be in paper form, or can I have an electronic plate that I have to do all the calculations quickly? (assuming one has a written copy back at the office)
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Sounds legal, but better check first with the 135 operator's POI at the FSDO for official interpretation to seal the stamp of approval. As Lance pointed out, you can check your OpsSpecs, but I would highly doubt you'd find this specific provision without asking the POI first and including his/her approval in a revision. All of our crews carry a physical copy of the manifest in the form of a trip sheet for each leg (on our single engines as well) so we don't really run into this scenario at all.
 
Aztec Driver said:
Second question. Since it is manditory to carry along a manifest on each charter for a multi-engine aircraft, is it permissible that this manifest be in paper form, or can I have an electronic plate that I have to do all the calculations quickly? (assuming one has a written copy back at the office)
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It's whatever is written in your FAA-approved ops manual. If you can sell them on an "electronic plate," you're good to go, but the method you use (paper form, electronic device, whatever) must be in the manual and approved by your POI, and you must do it that way and that way only.
 
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