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Just looking at an Extra 400 in the hanger and again wondering about aircraft engine thrustline. Who on earth works this stuff out ?!? On the Extra the engine is noticeably off line and off centre as is the tail. The engine is also off pitch, as in it is angled slightly up wards. I get it ish and why, to deal with prop rotation, airflow etc... But who and how does this stuff?
Now a picture is a thousand words, just need to get a couple up.
Ps suppose similar to offset hubs and different length spokes etc..
A lot is probably learning from previous iterations of the aircraft type. Although these day’s it’s probably all 4D computer modelled, too.
Ah,,, thought so guess work and intuition..
If 4D (think I need to look that up) then someone programmed the computer? Or I’m I really showing how out of date I am now?
Just looked it up
‘ 4D, or fourth dimension, is essentially the same as 3D with the addition of time dimension. The physical object becomes unified with space and time in a 4D continuum. That is spacetime.’
I'd imagine that as the engine is a rotating mass, then the thrust won't be entirely evenly distributed in a linear fashion from the exhaust and so the angle will be to account for this?
I could be talking pish mind. 😂
Have a look at how Concorde’s engines curve to point up at the back.
It’s almost like the design called for some canards to lift the front that got missed in the final version*.
*I am not an aeronautical engineer.
The basic positioning is relatively simple to calculate - relative to the centre of gravity, work out how the forces are acting (torque, thrust etc), and balance them with the tail and the wings. Then iterate from there.
When I was at university (Aero Eng), we’d all beaver away to solve problems like this using equations of motion and all sorts of ‘cutting edge’ computer systems to prove what the lecturer had worked out after 5 minutes using a pencil from behind his ear and a scrap of paper.
All designs like this are compromises. It will likely only be an ideal solution for a small part of the flight envelope but should be tailored to the use that the aircraft is designed for.
Aero Engineers also get this stuff wrong. A400M has a number of problems related to the wash from the TP400 engines and their specific pattern of flow. Multi engine is tough, twin engine is a real PITA.
I assume that simplistically the engines pitch up at the back so they are horizonal when cruising, as the nose of the plane pitches up by a few degrees during cruise. This would ensure that the thrust is translating to forward motion rather than a component of it working to create lift as would be the case if they were installed horizontally (the rear would then face downwards with cruise AOA).
*No actual knowledge about the above 🙂
Back in the day, you stuck the engine in, built up the prototype, and flew it roudn the block, noting how much trim you had to apply to the controls and in what direction, but when under power, and in a "glide". That told you the difference between your engine thrust offset and the basic aerodynamic trim of the aircraft. Then you got out your pack of shims and blockers, and stuck them under the engine mounts, at a best guess. Then it's round the loop once more, return and re-set. repeat till it's good enough.....