Aircraft measurement convention(s)

[pigsty]

Is there a standard convention for measuring aircraft dimensions?  I'm fairly sure there's only one way to measure span, or two for VG wings.  But length and height both seem subject to variables like whether the subject is on its wheels, and whether to include the propeller.  Length is also sometime quoted as "excluding probe", which is OK so far as it goes, except that you can't say whether all the others do or don't.  So, is there a standard configuration you should have in mind when reading data?  Or, worse, more than one?

[malpaso]

Good question.  I seem to recall reading that length and height were (by convention) measured with the aircraft in flying attitude or along the fuselage datum line.  In other words a taildragger's length would be measured with its tail up on a trestle.  Whether anyone actually ever bothered to measure a plane like this rather than accept what the manufacturer said is a different discussion altogether!

And then there's what sticky out bits are to be included in the dimensions - pitots, aerials, guns and all the other interesting items.

Cheers 

Will 

[Truro Model Builder]

Whatever they are, you can be sure that kit manufacturers will use the biggest measurement to put on the outside of the box for scale purposes.

 

I wonder if the guys who do that use the same criteria to measure other items? Though I imagine that is a different topic altogether.

 

[PhantomBigStu]

its a bit confusing, hence youcan end up with Hobbyboss 1/76 Rafale, where they took the quoted length as including the nose probe when they downscaled it

[lasermonkey]

Many years ago, I was talked into doing a review/comparison between the 1/72 ICM Bf 109E and the Tamiya example. Whilst I was doing the research, I stumbled across the likely reason between the discrepancy in the length of the two kits.

Several people had commented that they thought the Tamiya kit was too short. I took the most reliable measurements I could find at the time, converted into 1/72 and measured the Tamiya kit. It was spot-on! So why was it shorter than the other kit and the (highly regarded) drawings I was using? t was only when I looked at the drawing of the aircraft on its undercarriage that it dawned on me. When I took the measurements from the aircraft at rest (i.e. dropping a plumb line from the tip of the nose and the very end of the rudder) the measurements were again bang-on. The ICM kit fitted the drawing very well, while the Tamiya kit must have been scaled so the measurement was taken along the thrust line and consequently ended up being a bit short.

Now, I'm pretty sure that the Tamiya kit is short, the main reason being that when you use markings of a known size and you position them referenced to the prominent fuselage panel lines, they end up going out of datum, due to the error being spread along the fuselage length. To me, it was one of those once you've seen it, you can't un-see it" moments.

 

What this means is that we need to know exactly how the aircraft is measured. I suspect the plumb line method is easiest, since it is easily repeatable and consistent. Good ol' gravity!

 

Cheers,

Mark.

[Tailspin Turtle]

15 hours ago, pigsty said:

Is there a standard convention for measuring aircraft dimensions?  I'm fairly sure there's only one way to measure span, or two for VG wings.  But length and height both seem subject to variables like whether the subject is on its wheels, and whether to include the propeller.  Length is also sometime quoted as "excluding probe", which is OK so far as it goes, except that you can't say whether all the others do or don't.  So, is there a standard configuration you should have in mind when reading data?  Or, worse, more than one?

 

Once upon a time, I came across the Navy instructions for preparation of Standard Aircraft Characteristics charts. Unfortunately, I can't find it. The configuration of the aircraft (fuel load etc) for which the dimensions were to be provided was quite specific, for one thing. Suffice it to say, length data without a side view depicting what the number represents can be misleading. For more, see http://tailhooktopics.blogspot.com/2012/05/accurate-three-view-drawings.html