Per-engine overheat protection

[Van Disaster]

MJ has a throttledown to protect engines from excess heat - is there something that will do this on a per-engine basis via thrust limiting? much like Davon or TCA do for orientation.

[Svm420]

[quote name='Van Disaster']MJ has a throttledown to protect engines from excess heat - is there something that will do this on a per-engine basis via thrust limiting? much like Davon or TCA do for orientation.[/QUOTE]
Wouldn't that lead to an imbalance in thrust?

[Van Disaster]

[quote name='Svm420']Wouldn't that lead to an imbalance in thrust?[/QUOTE]

Could do, unless it reads/you assign symmetrical pairs or it balances the remaining engines to manage.

[Svm420]

[quote name='Van Disaster']Could do, unless it reads/you assign symmetrical pairs or it balances the remaining engines to manage.[/QUOTE]
How is that different than throttling all the engines down anyway :huh:

[Van Disaster]

[quote name='Svm420']How is that different than throttling all the engines down anyway :huh:[/QUOTE]

Because throttling one engine to 50% and slightly adjusting the others so the thrust vector is in the same place is not the same as throttling all engines to 50%. Additionally, different types of engines overheat at different rates. Edited November 23, 2015 by Van Disaster

[Svm420]

[quote name='Van Disaster']Because throttling one engine to 50% and slightly adjusting the others so the thrust vector is in the same place is not the same as throttling all engines to 50%. Additionally, different types of engines overheat at different rates.[/QUOTE]
How can you move the vector to exactly to where it was if all engines aren't throttled equally? The vector won't be the same unless they all are reduced proportionally. :huh:

[Van Disaster]

Simple illustrative case 1:
[list]
[*] I have four engines on an aircraft, two per side
[*] The inner ones overheat faster than the outer ones
[*] Thrust reducing the inner engines will result in more total thrust than reducing all engines ( and this is obviously the same for a rocket cluster )
[/list]

Slightly less simple with unoptimised illustrative working. If all the engines are the same it doesn't matter what the actual max thrust is.
[list]
[*] You have two pairs of engines of the same thrust, one pair 5m from centre, one pair 8m from centre ( lets assume they're planar )
[*] One inner engine needs throttling to 50% because a radiator fell off, the other is running at 100%
[*] Max thrust per engine is X
[*] Torque ( yaw force ) for the side with the failing engine is Tf =((X*0.5)*5)+(X*8)
[*] Thrust reduction Y for *both* engines on the other side to balance torque is Y = Tf/(5+8)*X ( in this case you'll find it's about 69% )
[/list]

And so on. Edited November 23, 2015 by Van Disaster

[Svm420]

Ahh I didn't consider having all the engines planar to the CoM. You are right in that case. Also what engines do you find you need this with out of curiosity. I have never had an engine overheat so I have no experience to go off of.

[Van Disaster]

Most recent example, Whiplash paired with Rapiers. Rapiers can get to Mach 5 or so before they're in danger of cooking, but they suck before they start working as ramjets - meanwhile the Whiplash starts baking at about Mach 3, just when Rapiers are starting to work properly.

They only need to be planar with each other to avoid pitch complications, but even if they aren't I'm pretty sure it's just a more complicated balance procedure rather than having to throttle the lot - eg if there's four engines in a square with CoM in the middle, you only need to throttle the opposite diagonal ( or to put it another way, you can always have one engine running at 100% ). If they're all in a fairly central cluster the torque imbalance is going to be pretty small anyway. Edited November 23, 2015 by Van Disaster