Mon Feb 19, 2018 8:35 am
#1591817
Some thoughts...
(1) This isn't the first aeroplane ever lost due to trimmer problems. A powerful trimmer can be very helpful in certain circumstances, but can be a problem.
(2) Seldom is an overweight aeroplane that much of a safety threat. It's being outside of CG limits that really makes a difference.
(3) There's a critical characteristic here called "manoeuvre stability", better understood by its other name of "stick force per g". Section S, the UK microlight code, requires that an aeroplane doesn't exceed its 4g limit load with less than 15lbf on the stick.
(4) A quick calculation suggests that putting the aeroplane 40kg overweight, and pulling on the stick until you pulled the wings off, would take about 21lb of sudden pull if the aeroplane was only just compliant with Section S. The trim input would have had to be consistent with that. [I don't know what the actual manoeuvre stability curve looks like for a Eurostar, so it could be a much bigger number - if it's a small number, somebody somewhere didn't do their job properly.]
(5) Most "group A" aeroplanes use a trim wheel rather than a lever. It's not hard to see how that is much harder to operate inadvertently. Levers are the norm on microlights - most likely because they are lighter to make and install, but you can see the value in a wheel as an alternative design.
(6) You can absolutely see why you want a reasonable amount of friction (and probably a lever that has no sharp corners to catch on anything) at the very least.
(7) I'm not about to criticise the designers of the Eurostar, but it does illustrate well the importance of a broad understanding of airworthiness when approving even a relatively cheap and simple aeroplane like this.
G
(1) This isn't the first aeroplane ever lost due to trimmer problems. A powerful trimmer can be very helpful in certain circumstances, but can be a problem.
(2) Seldom is an overweight aeroplane that much of a safety threat. It's being outside of CG limits that really makes a difference.
(3) There's a critical characteristic here called "manoeuvre stability", better understood by its other name of "stick force per g". Section S, the UK microlight code, requires that an aeroplane doesn't exceed its 4g limit load with less than 15lbf on the stick.
(4) A quick calculation suggests that putting the aeroplane 40kg overweight, and pulling on the stick until you pulled the wings off, would take about 21lb of sudden pull if the aeroplane was only just compliant with Section S. The trim input would have had to be consistent with that. [I don't know what the actual manoeuvre stability curve looks like for a Eurostar, so it could be a much bigger number - if it's a small number, somebody somewhere didn't do their job properly.]
(5) Most "group A" aeroplanes use a trim wheel rather than a lever. It's not hard to see how that is much harder to operate inadvertently. Levers are the norm on microlights - most likely because they are lighter to make and install, but you can see the value in a wheel as an alternative design.
(6) You can absolutely see why you want a reasonable amount of friction (and probably a lever that has no sharp corners to catch on anything) at the very least.
(7) I'm not about to criticise the designers of the Eurostar, but it does illustrate well the importance of a broad understanding of airworthiness when approving even a relatively cheap and simple aeroplane like this.
G
I am Spartacus, and so is my co-pilot.
FLYER Club Member
The trim lever is between the two seats and easily accessible from either seat.