Weight & Balance Feature Conundrum

[bobw75087]

If you Google aircraft empty weight, your first return is this:
"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." https://www.faa.gov › mediaPDF Chapter 10: Weight and Balance.

Given that GAMA and FAA agree on that, why does the new W&B feature in iFlyEFB insist that category/tab & the weight of unusable fuel be included... essentially doubling the near-20# offset and forcing an unnecessary calculation error?

Please DELETE the 'Unusable Fuel' category/tab. If you must address it, include an *statement that BEW includes unusable fuel AND full oil.

Please add your UP vote to help make this happen.

 

[Hook]

The W&B calculator is correct for both recent planes that use the GAMA method, and older planes that do not. Set your Usable Fuel Capacity to the correct value in the aircraft profile and set the correct amounts for Total Fuel Capacity and Non-usable Fuel in the W&B for Fuel Tank. There is no error if you enter the values correctly.

If you are quoting chapter 10 of the Pilots Handbook of Aeronautical Knowledge (see here) then note that it refers to two different ways to measure empty weight: "Licensed empty weight" (drainable oil removed) and "Standard empty weight" (aka GAMA empty weight; which has a full load of oil). [For both methods, unusable fuel is part of the calculation.]

Licensed empty weight is the older way to do it (such as for my 1963 Cherokee 180) and in my W&B for the Cherokee I had to add a "station" for Oil. More recent planes, and the handbook, use Standard (GAMA) empty weight, which I believe is what you're quoting.

 

[Adrian]

All that you need to do is edit the aircraft's Weight & Balance template and set the Non-usable Fuel value to 0 gallons. That will remove the unusable fuel item from the calculations.

Of course, it's up to you to ensure that the unusable fuel is included in the Empty Weight.

 

[Hook]

I don't see the problem. Unusable fuel is included in Empty Weight in both methods of calculating W&B, and in iFly's calculator. If you have tanks that have unusable fuel then you should specify it. To do what is suggested above (enter 0 for unusable) is going to make the calculation wrong. I specify the correct 2 gal unusable for the Cherokee, and iFly's W&B calculator exactly matches my official W&B sheet. BTW, iFly's "Real Plan" feature uses unusable fuel in its planning so there's that. And I think a feature was requested for iFly to flag any user-planned flight plan leg that exceeds fuel capacity (which again, would take into account unusable fuel).

Note that you must specify Unusable Fuel both in the aircraft profile and the W&B profile.

It might help if you gave specific numbers. Maybe a photo of your plane's W&B sheet and then a screenshot/photo of what iFly comes up with.

 

[Adrian]

I should have clarified that that the fuel capacity for the tanks should be set to the usable quantity, not the total tank capacity.

 

[bobw75087]

I don't see the problem. Unusable fuel is included in Empty Weight in both methods of calculating W&B, and in iFly's calculator. If you have tanks that have unusable fuel then you should specify it. To do what is suggested above (enter 0 for unusable) is going to make the calculation wrong. I specify the correct 2 gal unusable for the Cherokee, and iFly's W&B calculator exactly matches my official W&B sheet. BTW, iFly's "Real Plan" feature uses unusable fuel in its planning so there's that. And I think a feature was requested for iFly to flag any user-planned flight plan leg that exceeds fuel capacity (which again, would take into account unusable fuel).

Note that you must specify Unusable Fuel both in the aircraft profile and the W&B profile.

It might help if you gave specific numbers. Maybe a photo of your plane's W&B sheet and then a screenshot/photo of what iFly comes up with.

Actually, entering ZERO for Unusable 40 for Total Cap in W&B did work perfectly, as Adrian said. If I enter 43 for total and 3 unusable, it actually calculates 37 gal usable vs 40. Why, I'm not sure. But I didn't want to get into changing the BEW as calculated on the manifest + a half dozen amendments and/or put it in disagreement with official docs.
Just thought this should at least be optional, and while you can ADD stations Hook, you can't delete the Unusable field preset...and I was unable to get the ZERO entry to work the first time around. Thanks Hook also for clarifying about the older aircraft and LEW vs BEW.

 

[Brian]

Bobw - I'm glad Adrian's method works for you -- and this is as designed. If you want to include your unusable fuel into the Empty Weight (and hide it from iFly), this can be done by setting Unused Fuel to 0, as you have done.

However, the other works too - if you wanted to do it. I think you are mis-entering the "gallons" -- you should be entering 43 gallons, not 40, because the fine print below the box says "Enter Total Fuel (include non-usable)." as shown here:



I'm guessing that you are entering only 40 gallons here, right? Thus it thinks you are 3 gallons shy of full. If this is the case, you are the 2nd person to have missed this critical detail -- which indicates to me that we need to make this print bolder, so as to not be missed.

 

[bobw75087]

Brian: if you are going to change that, I think it should read: "Enter TOTAL fuel, including Unusable, UNLESS already included in Basic Empty Weight. Check your POH!

 

[Don Maxwell]

Bobw - I'm glad Adrian's method works for you -- and this is as designed. If you want to include your unusable fuel into the Empty Weight (and hide it from iFly), this can be done by setting Unused Fuel to 0, as you have done.

However, the other works too - if you wanted to do it. I think you are mis-entering the "gallons" -- you should be entering 43 gallons, not 40, because the fine print below the box says "Enter Total Fuel (include non-usable)." as shown here:

View attachment 44

I'm guessing that you are entering only 40 gallons here, right? Thus it thinks you are 3 gallons shy of full. If this is the case, you are the 2nd person to have missed this critical detail -- which indicates to me that we need to make this print bolder, so as to not be missed.

Brian, I still like bobw75087's initial idea--that empty weight includes unusable fuel. I know this was debated earlier in the old beta forum, and somehow the opposite condition became Law, just because some old American airplanes got grandfathered in. It seems logical to me to follow the current convention and put unusable fuel in the EW--which is where it logically belongs. Because that's logical. It's intuitive, too, so that's also logical. I could say it a few more ways, but surely that's enough. Pilots of those old planes are the ones who should make the adjustment, not the rest of the world. That's also logical. Sorry--but not sorry!

 

[Cobra]

Shrug. There are lots of "those old planes" still flying. No matter which way you pick, it's going to feel "wrong" to a large fraction of the flying community, and they'll wish it were different.

I don't feel strongly about which approach is better.

 

[Hook]

People are confused here. Unusable fuel is included in empty weight for both methods, old and new. Read the posts above. And/or read the handbook. The only diff between old and new is whether full or just unusable oil is included in EW.

There is nothing wrong with the design of the calculator. It accommodates both methods. And unusable fuel is not the issue anyway.

Bobw was not using the calculator correctly. Sorry to be blunt. Multiple times I said to put the unusable fuel in both the profile and the W&B. It works fine if you give it correct data. I'm not dissing on him, he can do what he wants, but he wasn't using it as designed.

 

[Adrian]

There is a potential, albeit small, error that could sneak into in the method where the total fuel (usable + unusable) is used as the fuel quantity. The total fuel method assumes that the unusable and usable fuel have the same moment arm. That is not necessarily the case.

 

[Hook]

There is a potential, albeit small, error that could sneak into in the method where the total fuel (usable + unusable) is used as the fuel quantity. The total fuel method assumes that the unusable and usable fuel have the same moment arm. That is not necessarily the case.

Good point. However, the W&B profile/calculator accommodates that. Put the correct figures for the whole aircraft in the aircraft profile. In the W&B profile you'll create multiple fuel tanks, at the right arms, that have their own individual total/unusable quantities. (Of course, those totals & unusable's need to add up to the total & unusable in the aircraft profile).

 

[Brian]

In 12.1.3 Beta, I changed the Default "Unusable Fuel" for each template to 0 gallons -- so if you WANT to use this, you can set it. By default, you won't see this until you edit the Fuel Tank's capacity... and there you'll see the default setting of '0' unless you change it.

For the next Beta, I am changing the text beneath this box to also suffix with ".. unless it's part of BEW..." as suggested bobw.

I was defaulting this value to 2 gallons before... which was usually not correct ... so people always had to edit this value anyways. So it seems that defaulting it to '0' will instead make it so that "about half" of the pilots can "leave as is" because it's already part of the BEW. Thus, '0' is a better default, it seems. And then most of this issue goes away, and both preferences are still accommodated.

 

[bobw75087]

In 12.1.3 Beta, I changed the Default "Unusable Fuel" for each template to 0 gallons -- so if you WANT to use this, you can set it. By default, you won't see this until you edit the Fuel Tank's capacity... and there you'll see the default setting of '0' unless you change it.

For the next Beta, I am changing the text beneath this box to also suffix with ".. unless it's part of BEW..." as suggested bobw.

I was defaulting this value to 2 gallons before... which was usually not correct ... so people always had to edit this value anyways. So it seems that defaulting it to '0' will instead make it so that "about half" of the pilots can "leave as is" because it's already part of the BEW. Thus, '0' is a better default, it seems. And then most of this issue goes away, and both preferences are still accommodated.

Thank you for listening.

 

[Brian]

Thank you for listening.

And thank YOU for bringing it up. I'm guessing that your suggestion here inspired a change that benefitted at least half of the pilots who plan to use our W&B feature.

 

[CozyB]

Bobw - I'm glad Adrian's method works for you -- and this is as designed. If you want to include your unusable fuel into the Empty Weight (and hide it from iFly), this can be done by setting Unused Fuel to 0, as you have done.

However, the other works too - if you wanted to do it. I think you are mis-entering the "gallons" -- you should be entering 43 gallons, not 40, because the fine print below the box says "Enter Total Fuel (include non-usable)." as shown here:

View attachment 44

I'm guessing that you are entering only 40 gallons here, right? Thus it thinks you are 3 gallons shy of full. If this is the case, you are the 2nd person to have missed this critical detail -- which indicates to me that we need to make this print bolder, so as to not be missed.

Just a note for anyone else like me who is reading this several months after the discussion happened, the snapshot Brian shared above in post #7 showing the fuel entry blank text saying "include Non-usable" has now changed to say "Enter Fuel not included as part of BEW." I didn't see this change noted in the changes log so I thought I would point it out since it is different than it used to be. v/r, cab