Why aren't flaps automated and completely incremental
Why aren't flaps automated and completely incremental
Having just had a strange and possibly very fuel-inefficient landing with KQ in ADD, I started wondering why are flaps so crude, nonlinear and set so far in advance of their need? Presumably for any given airspeed there is an optimal flap setting which provides just enough lift ? I remember being surprised by the tale of the BA B-777 which crashed due to iced fuel supply at LHR. The captain ‘averted disaster’ by raising flaps from 30 to 25. I thought at the time, that if raising the flaps 5 degrees didn’t cause a stall, then why were at 30? They obviously were causing ‘unnecessary' drag. So given modern electronics and incredibly reliable systems, why not just let the wing configure itself for minimum drag ?
why not just let the wing configure itself for minimum drag ?
(I apologise ahead of time for what is a highly simplistic answer).
Presumably for any given airspeed there is an optimal flap setting which provides just enough lift ?
The min drag stuff is fine in the descent for fuel economy but nearer the ground other factors take priority. We try very hard not to fly the final approach itself with the engines at a low idle RPM ( certainly below 1000 feet) because if you need them to spool up in a hurry (e.g. if a Go around is needed) it can take quite some time from a low RPM. So you've got to have some power on...which leads to the problem that with the engines running at anything much above idle on a typical 3 degree glideslope many aircraft, even with the gear down, will accelerate ..which is not a good thing as you head down the glideslope....so you've get some drag from somewhere....and "minimum drag" no longer applies.
In the B777 Hatton cross case the guys had a normal flap setting for what they planned to be a normal powered landing (with the engines spooled up away from idle until the flare) ...the equation for them changed when they became a glider..
(FWIW there are aircraft around, or least used to be, that were flown down the approach and landing with speedbrake out to deliberately be "draggy"..if you'll excuse the term)
Last edited by wiggy; 18th Aug 2017 at 13:00.
Vey interesting, thanks. I realise that a big lump of metal moving very fast and very high has to shed a lot of energy for it to come to a halt on the ground. But there seem to be plenty of tweaks during a typical descent, and configuration must rarely be 'fuel optimal' during climb. Today it felt like a lot of power was applied with a lot of flaps late in the descent and we ended-up dragging through the sky in a very nose-up attitude, which must have been very inefficient. I had not thought of the desirability of keeping engines turning fast enough to ensure a rapid response if needed.
Interesting musings.....thanks
Interesting musings.....thanks
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Today it felt like a lot of power was applied with a lot of flaps late in the descent and we ended-up dragging through the sky in a very nose-up attitude, which must have been very inefficient.
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The lower flap settings allow additional lift whilst the higher settings largely supply drag. I don't think there is a such a thing as an optimal setting. Sometimes the Pilot will choose not to use full flap, say because of particularly gusty conditions. I certainly wouldn't describe a modern aeroplane's flaps as 'crude'.
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Not flaps, and very far from an airliner, but the Morane we use for towing gliders has aerodynamically driven slats. There are no controls for them in the cockpit, they are extended by springs and simply blown back by the airflow at higher airspeeds.
https://en.wikipedia.org/wiki/SOCATA_Rallye_family
Munich Akaflieg fitted their Mü 28 with automatic and continuous flaps. Their deflection is automatically adjusted to be optimal for current the combination of airspeed and wingloading. This was built in 1973 and subsequently copied for a small number of other experimental one-shots.
I could not find details on the system after a very cursory search, but I believe it to be a simple mechanical thing, too.
So the idea is not completely new.
https://en.wikipedia.org/wiki/SOCATA_Rallye_family
Munich Akaflieg fitted their Mü 28 with automatic and continuous flaps. Their deflection is automatically adjusted to be optimal for current the combination of airspeed and wingloading. This was built in 1973 and subsequently copied for a small number of other experimental one-shots.
I could not find details on the system after a very cursory search, but I believe it to be a simple mechanical thing, too.
So the idea is not completely new.
And not confined to GA aircraft - the supersonic F-100 Super Sabre had a similar arrangement.
And I have experienced a few extremely 'wobbly' take-off runs, with dramatic side-to-side forces, which started with a very gungho turn onto the runway, immediately into a rolling take-off run. I suspect that was caused by the differential engine pick-up when one engine was already providing significant thrust and the other was idling.
Come to think of it, I have not experienced that for a few years, have procedures changed?
Come to think of it, I have not experienced that for a few years, have procedures changed?
And I have experienced a few extremely 'wobbly' take-off runs, with dramatic side-to-side forces, which started with a very gungho turn onto the runway, immediately into a rolling take-off run. I suspect that was caused by the differential engine pick-up when one engine was already providing significant thrust and the other was idling.
Come to think of it, I have not experienced that for a few years, have procedures changed?
Come to think of it, I have not experienced that for a few years, have procedures changed?
As for the side-to-side forces, that would just be the pilot using the rudder to straighten the aircraft as it turns onto the runway and possibly over correcting it. Bit like a sharp turn on the road and accelerating at the same time!
Thrust is always set to stabilise N1 in both engines at equal values before take-off thrust is set. It's very unlikely one engine was spooled up and the other at idle when the thrust was increased, a sharp turn/jerk to one side would be felt, presumably followed by the take-off run being immediately rejected.
Hope this helps
It does. Thanks. As some background to these possibly odd observations, I spend a ludicrous amount of my life, as a passenger, in aircraft ranging from Cessna Citation X's to A380's. I have strong interest in systems/engineering, so inevitably start to analyse things in those terms.
(As a tiny example. It amuses and pleases me to see that the tray-table release catch works 2-ways in every row except the emergency exit row (my favorite row of course), where it only works if turned against the way human traffic would flow in an emergency. I love that someone has thought of that detail - and implemented it. I occasionally point it out to my neighbor to be met by blank incomprehension)
(As a tiny example. It amuses and pleases me to see that the tray-table release catch works 2-ways in every row except the emergency exit row (my favorite row of course), where it only works if turned against the way human traffic would flow in an emergency. I love that someone has thought of that detail - and implemented it. I occasionally point it out to my neighbor to be met by blank incomprehension)
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Not flaps, and very far from an airliner, but the Morane we use for towing gliders has aerodynamically driven slats. There are no controls for them in the cockpit, they are extended by springs and simply blown back by the airflow at higher airspeeds.
https://en.wikipedia.org/wiki/SOCATA_Rallye_family
Munich Akaflieg fitted their Mü 28 with automatic and continuous flaps. Their deflection is automatically adjusted to be optimal for current the combination of airspeed and wingloading. This was built in 1973 and subsequently copied for a small number of other experimental one-shots.
I could not find details on the system after a very cursory search, but I believe it to be a simple mechanical thing, too.
So the idea is not completely new.
https://en.wikipedia.org/wiki/SOCATA_Rallye_family
Munich Akaflieg fitted their Mü 28 with automatic and continuous flaps. Their deflection is automatically adjusted to be optimal for current the combination of airspeed and wingloading. This was built in 1973 and subsequently copied for a small number of other experimental one-shots.
I could not find details on the system after a very cursory search, but I believe it to be a simple mechanical thing, too.
So the idea is not completely new.
Laurence
Last edited by l.garey; 20th Aug 2017 at 08:45.
It does. Thanks. As some background to these possibly odd observations, I spend a ludicrous amount of my life, as a passenger, in aircraft ranging from Cessna Citation X's to A380's. I have strong interest in systems/engineering, so inevitably start to analyse things in those terms.
(As a tiny example. It amuses and pleases me to see that the tray-table release catch works 2-ways in every row except the emergency exit row (my favorite row of course), where it only works if turned against the way human traffic would flow in an emergency. I love that someone has thought of that detail - and implemented it. I occasionally point it out to my neighbor to be met by blank incomprehension)
(As a tiny example. It amuses and pleases me to see that the tray-table release catch works 2-ways in every row except the emergency exit row (my favorite row of course), where it only works if turned against the way human traffic would flow in an emergency. I love that someone has thought of that detail - and implemented it. I occasionally point it out to my neighbor to be met by blank incomprehension)
I had no idea...you learn something every day!
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Basically flaps are not installed for efficiency. They are there to allow slow flight and to provide drag. Having more fuel efficient flaps would negate one if their uses, that of providing drag. Then there is the useage. Each flap setting, even zero, has a minimum, optimum and maximum speed and 'g' loading limits. So new regimes would have be dreamed of up to deal with indicating these as they would be buggers to remember throughout the range. Go arounds would also be interesting. Which setting would be used? A variable system would result in the optimum setting but how would this be annunciated to the pilots? This would have to be known beforehand otherwise how would we know it had been selected? The same goes for the speed. I'll also assume that any flap movement would automatically elevator compensation. Not having such a thing might make it unpleasant to fly. These are not insurmountable problems but ones that would have to be dealt with before implementation. However, the big question is how much fuel would be saved and what would such a system cost?
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