"empty" weight

[Soulyss]

Is there a commonly accepted definition of what constitutes an aircraft's empty weight?  I would assume that it means a production airframe with all standard equipment and armament minus things like fuel, oil, hydraulic fluid, ammunition, and crew.  I noticed what could be a discrepancy in some of the AH numbers but I wanted to try and do a little research to see if I'd just be crying wolf or not.

The first question is if "empty" weight is more or less measured the same or if it's going to vary from source to source.

[Wmaker]

The definitions varied between countries and the most certain way to do comparisons is to have a detailed weight table from a primary source ie. from the aircraft's manufacturer for example. As the weight tables aren't always readily available, the best way is to initially compare the normal takeoff weight from fairly credible sources and see if there's a discrepancy and go from there.

[Soulyss]

I'll look for normal take off weight, my thought in using empty weight was to try and eliminate variables like fuel and ammo.

[Wmaker]

my thought in using empty weight was to try and eliminate variables like fuel and ammo.

Understand, but it becomes problematic with pilot, oil, trapped oil, coolant, etc.

Here's an example of AH's Ki-61 weights which I tired to nail down: http://bbs.hitechcreations.com/smf/index.php/topic,297618.15.html

Obviously, the most ideal situation is to have a document like this from the aircraft you are trying to research:


I recall that you have America's Hundred Thousand. That is a great source for the weights of the US fighters.

If you don't want to mention the aircraft you are looking at publicly, shoot me a pm and I'll see if I can help you by checking the sources I have.

[MachFly]

Empty weight includes the airplane weight, unusable fuel, all operating fluids with maximum oil quantity.

[Soulyss]

What I was looking at was the B-25C, I was reading up n the ventral turret that existed on the early models.  I have a copy of "North American B-25 Mitchell the Ultimate Look: From Drawing Board to Flying Arsenal" by William Wolf on the shelf here which seems to be a well researched tome of B-25 factoids.  

I came across a passage that said the ventral turret weighed in at 392 pounds excluding guns and ammo (which he says was another 300 lbs, which seems really high to me).  Since we don't have the ventral turret I was curious if it was subtracted out of the AH model or how HTC handled that weight.  Skipping forward Wolf lists the "empty" weight at 20,300lbs  for the C/D models.  Going into game I selected the glass nosed B-25 as that would have the "standard" armament for that model, the same armament Wolf lists on the same table.  Took off, fired off all the ammo, and upped the fuel burn to 10 till the engines conked out.  Looking at the E6b I get 23,041lbs.  Seems like a bit of a difference but there's a lot of variables to try and account for like crew weight (if that's modeled), plus all the other fluids other than fuel.  All that's assuming that Wolf's numbers are accurate which I'd want to check against other sources.

So that's about where I'm at, not ready to pronounce that something is amiss, but I think the game is afoot.

[Oldman731]

Is there a commonly accepted definition of what constitutes an aircraft's empty weight? 

"Empty weight means the weight of the airframe, engines, propellers, rotors, and fixed equipment.  Empty weight excludes the weight of the crew and payload, but includes the weight of all fixed ballast, unusable fuel supply, undrainable oil, total quantity of engine coolant, and the total quantity of hydraulic fluid."

14 CFR Section 119.3.

- oldman

[bozon]

Empty weight includes the airplane weight, unusable fuel, all operating fluids with maximum oil quantity.

pilot and his gear? oxygen?

[MachFly]

pilot and his gear? oxygen?

Pilot and gear would be a part of useful load. If by oxygen you mean portable oxygen bottles than it's not included either, if you mean a system that makes it's own oxygen (like on the F-22) than I don't know, it probably is.

[Soulyss]

Discovering just how much fun this sort of research can be.  I found a copy of the flight manual online, it's broken into parts to make the downloads smaller so I'm assuming that all the parts are in fact from the same manual.

Here' a crude shot from the page in the manual that lists the weight breakdown.



Totaling the basic airframe, oil, nose, pilot, navigator, radio/turret compartments, and tail compartments you get 23,606.  Compared to the AH Glass nose/bomber B-25C weight with no fuel and all ammo of 23,041 it looks like HTC is right in the ball park if you remove the ventral turret from the equation. 

[Raptor05121]

FAR 25.29 says usable fuel is the only fluid not counted

[colmbo]

Empty weight includes the airplane weight, unusable fuel, all operating fluids with maximum oil quantity.

On older aircraft empty weight does NOT include oil.

[MachFly]

On older aircraft empty weight does NOT include oil.

Yeah, your right. I did not think about that.

[Oldman731]

On older aircraft empty weight does NOT include oil.

Still doesn't (except for the undrainable stuff).

That probably makes a fairly noticeable difference on radial engine planes.  They tank up a lot of oil.

- oldman

[colmbo]

Still doesn't (except for the undrainable stuff).

That probably makes a fairly noticeable difference on radial engine planes.  They tank up a lot of oil.

- oldman

On a single engine Cessna the oil is 15 pounds.  The B-17 and B-24 have a 38 gallon oil tank for each engine.