Hacker News Reader

Comment by londons_explore | Hacker News Reader

We currently use a complex system of trying to weigh everything that goes onto the plane - baggage, cargo, fuel, and estimate the weight and distribution of the people.

Sure, estimates are good... But why not just weigh the whole plane just before takeoff?

Simple strain gauges in the suspension struts would give you all the info you need. And then you can still use the old system of weighing all the stuff you put on the plane as a backup/sanity check if you want to.

View on HN

My father used to work in a manufacturing plant where they would weigh the trucks coming in and out. The scales had to be in a fully enclosed garage or any breeze would throw the reading completely off.

I have a hunch that this same issue might be even more of a problem for an airplane.

I don’t think the plane needs a high level precision for the weight. I’m sure it could be off by a couple thousand pounds without any issue, and winds wouldn’t affect the weight that much.

a 130kt (~the stall speed) wind over the wings would pretty much remove the entire weight of the aircraft. Okay, lift is proportional to the square of the airspeed, but it's still going to be a huge factor and make it really unreliable

I'd be even more concerned with crosswinds indicating uneven loading length-wise!

My impression is there is a sensor to accomplish this already.

Source: Just supposition, but I was on a completely full flight (on an Embraer 175) last week and they held us on the tarmac while ground crews drove a 200lb ballast weight to us which was placed in the forward cargo area. To decide this was an issue after having pulled away from the gate implies to me that the issue was raised by instruments on the plane.

Generally the computer / flight crew does those calculations based on location of passengers, cargo and fuel. They probably missed something and requested more weight.

Source: I was personally loading cargo on an Embraer 175 two days ago. Also this link gives a good overview of weight sensors in planes.

https://aviation.stackexchange.com/questions/1850/do-some-ai...

This sounds less like total weight, and more like a differential / CG problem.

Where would these struts go? I assume in the landing gear suspension, and if so does that provide enough feedback to adequately understand the load and distribution? That's usually only 3 points of contact across the whole of the aircraft, isn't it?

You can still work out the total weight and the location of the center of mass (in 2D) from the strain on the three landing gear struts. It's a linear system of 3 equations and 3 unknowns.

As another commenter has pointed out, there may be an issue with wind, as the whole point of the airplane is that it efficiently converts a relative air velocity into an apparent change in weight.

3 points is exactly what you need to know the total weight, forward-back weight distribution, and left-right weight distribution.

You don't get to know the top-bottom weight distribution, but that is rarely an issue in aviation.

Fair enough, I assumed there might need to be more consideration in where the weight in in terms of where along the wing it is, stuff like that, but I guess not.

Isn’t that pretty much what they do?

Only a few planes have landing-gear based weight systems, mostly large military transports that won't be necessarily able to estimate weight well under fire.

Reply on news.ycombinator.com