blobby3
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Why No Lighter Seats?

Tue Sep 10, 2013 10:00 pm

Hi everyone

First time starting a thread so please be kind.

Every time I get on an aircraft I wonder about this and finally feel compelled to ask....

Manufacturers spend billions on designing new aircraft, more recently formed from ultra-modern composite materials, equipment on the aircraft seems optimised for minimising weight and maximising efficiency (take the 787 battery system as a well discussed example). Inside the aircraft however it always seems a different story. The seats are usually made of aluminium or other metal and look very bulky and heavy and also seem very low tech with chunky legs and other heavy looking and bulky components. The seats in economy seem pretty similar to those used 20 years ago in aircraft.

With such a large number of seats on some aircraft (which have to be carried whether or not they have a bottom sitting in them) and long in service lives I presume any weight saving would be financially quite substantial over the life of an aircraft. I wondered therefore why you never seem to see high tech, light and strong materials being used in new and ultra modern seat designs?

I thought perhaps in relation to the overall weight of the aircraft any weight saving would not be substantial enough relative to the materials cost of using (say) CFRP but other than that I am stumped as to why?

Many thanks
 
FriendlySkies
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RE: Why No Lighter Seats?

Tue Sep 10, 2013 10:04 pm

Quoting blobby3 (Thread starter):
The seats in economy seem pretty similar to those used 20 years ago in aircraft.

You must not have seen the recent trend toward slimline seats. They are indeed lighter...and thinner...and more uncomfortabler. All in the name of profits though!

I'm not sure how much weight could be saved over the latest designs (which are aluminum I believe, but someone correct me) if CFRP were used, especially versus the added cost.
 
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Polot
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RE: Why No Lighter Seats?

Tue Sep 10, 2013 10:12 pm

Don't automatically assume bulky=heavy. Aluminum is fairly light, that is why many automakers are frequently turning towards it.
 
blobby3
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RE: Why No Lighter Seats?

Tue Sep 10, 2013 10:20 pm

Did think about this Polot and maybe that perhaps I think they are very heavy but you could lift one with one finger - never tried as they always screw then down!! Then I though that parts like armrest, tray table, footrest etc not only look bulky but are also relatively heavy for their size.

Maybe someone knows the all up weight of a typical economy seat??
 
nomadd22
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RE: Why No Lighter Seats?

Tue Sep 10, 2013 10:37 pm

Those seats have to hold up under impacts almost strong enough to kill a person. There's a reason almost everybody survived the recent 777 crash in SF. And, if you've ever picked a modern one up you'd know they were already extremely light.
Anon
 
blobby3
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RE: Why No Lighter Seats?

Tue Sep 10, 2013 10:53 pm

I haven't ever picked one up so going from how they feel, look and the bits you touch - if they are already very light then that probably answers the question and means not a lot to save.

I was thinking about the survivability aspects but figured they are making fuselages and other components from CFRP now and also in non aviation circles design things like F1 cars, Yachts, from very strong composite materials. Not arguing the point but would have thought it was possible to design something as comparatively survivable as current designs in aluminium. Suppose fire could also be an issue.
 
Viscount724
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RE: Why No Lighter Seats?

Tue Sep 10, 2013 11:14 pm

Quoting blobby3 (Thread starter):
With such a large number of seats on some aircraft (which have to be carried whether or not they have a bottom sitting in them) and long in service lives I presume any weight saving would be financially quite substantial over the life of an aircraft. I wondered therefore why you never seem to see high tech, light and strong materials being used in new and ultra modern seat designs?

New seats are much lighter. LH and OS have replaced all their seats on their A320 family and B737 aircraft over the past couple of years with new lightweight Recaro seats that are between 1.5 kg and 5 kg lighter per seat. The lightweight, thin back constructiion also permits at least one more row of seats to be installed without reducing effective legroom, meaning several thousand more seats to generate revenue.

Excerpt from a 2011 document re the new LH/OS narrowbody seat change:

In total, Lufthansa will receive 32,000 new airplane seats while Austrian Airlines has agreed to purchase 4,600 units. Compared to the seats currently in use, this conversion will reduce the aircrafts’ total weight by 60 tons.

Many other carriers are making similar changes.
 
roseflyer
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RE: Why No Lighter Seats?

Tue Sep 10, 2013 11:27 pm

Economy seat weight has been dropping.

http://www.beaerospace.com/products/seating_main_cabin.htm

http://www.weberair.com/seating-systems/economy-class.htm

http://www.flightglobal.com/news/art...ght-of-economy-class-seats-341294/

The seats still have to meet the 16G requirements, so they do need to have a strong aluminum frame. Seats have to be stronger than before when they were only certified to 9Gs.

Business and first class is where weight is going up. It's not abnormal to have the new suite seats was over 150 lbs. However an economy seat is closer to 20 pounds.
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Starlionblue
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RE: Why No Lighter Seats?

Wed Sep 11, 2013 12:29 am

Quoting FriendlySkies (Reply 1):
You must not have seen the recent trend toward slimline seats. They are indeed lighter...and thinner...and more uncomfortabler.

Don't immediately assume they're less comfortable. For example the new CX monkey class seats are lighter and thinner but also way more comfortable than the ones they replaced.

Quoting nomadd22 (Reply 4):
Those seats have to hold up under impacts almost strong enough to kill a person.

Actually more than would be survivable in some cases. 16G but I don't know if that's instantaneous or not. Having said that, impacts vary and as in the Asiana case the seat can collapse before the person.

Quoting blobby3 (Reply 5):
I was thinking about the survivability aspects but figured they are making fuselages and other components from CFRP now and also in non aviation circles design things like F1 cars, Yachts, from very strong composite materials. Not arguing the point but would have thought it was possible to design something as comparatively survivable as current designs in aluminium.

Sure, but CFRP for this application is probably still rather expensive for the strength required. There's also the issue of scuffing and bumps from the self-loading cargo. I do imagine composites will play a bigger role in the future.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Mender
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RE: Why No Lighter Seats?

Wed Sep 11, 2013 8:29 am

You'd be surprised what already goes into reducing the weight of the seats already. It's not unusual for the leather seat covers to be made from the hide of an animal other than a cow such as kangaroo hide.

Kangaroo leather is lighter and stronger than the hide of a cow or goat. It has 10 times the tensile strength of cowhide and is 50% stronger than goatskin. (http://en.wikipedia.org/wiki/Kangaroo_leather)

Plus it already has a pocket in the front.
 
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Starlionblue
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RE: Why No Lighter Seats?

Wed Sep 11, 2013 8:37 am

Kangaroo leather is used for high-end motorcycle suits for the same reason.

Quoting Mender (Reply 9):
Plus it already has a pocket in the front.

        
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citationjet
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RE: Why No Lighter Seats?

Wed Sep 11, 2013 2:28 pm

Quoting roseflyer (Reply 7):
Economy seat weight has been dropping.

While the weight of the average economy passenger has been increasing.....
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yeelep
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RE: Why No Lighter Seats?

Wed Sep 11, 2013 6:01 pm

To give some idea of an actual weight. The seats that SWA uses as a basis for the new Evolve seats weighs anywhere from 80lbs for a narrow seat row, 87lbs for a standard seat row to 101lbs for a seat row with in armrest tray tables.
 
bjorn14
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RE: Why No Lighter Seats?

Sat Sep 14, 2013 2:14 pm

Quoting Starlionblue (Reply 8):
Kangaroo leather is lighter and stronger than the hide of a cow or goat. It has 10 times the tensile strength of cowhide and is 50% stronger than goatskin. (http://en.wikipedia.org/wiki/Kangaroo_leather)

I've heard salmon fish leather is just as good if not better.
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Starlionblue
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RE: Why No Lighter Seats?

Sun Sep 15, 2013 12:25 am

Quoting bjorn14 (Reply 13):
Quoting Starlionblue (Reply 8):
Kangaroo leather is lighter and stronger than the hide of a cow or goat. It has 10 times the tensile strength of cowhide and is 50% stronger than goatskin. (http://en.wikipedia.org/wiki/Kangaroo_leather)

I've heard salmon fish leather is just as good if not better.

Cool. However I imagine this advantage is negated by the much greater amount of stitching to get a seat cover.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
MD11Engineer
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RE: Why No Lighter Seats?

Sun Sep 15, 2013 11:48 am

Quoting Starlionblue (Reply 8):
Don't immediately assume they're less comfortable. For example the new CX monkey class seats are lighter and thinner but also way more comfortable than the ones they replaced.

Not in my experrience. E.g. you can´t tilt the backrest backwards anymore, instead the seat pan slides forward and a part of the backrest comes forward with it. For myself I found them too uncomfortable to sleep in for a longer period of time (more than 15 minutes, then I would wake up with cramps). Since the seatbacks don´t really recline, I´m also sure that they reduced the seat pitch, making it difficult for me to stow my legs (I´m 6 feet tall, so just average for central Europe).

Jan
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Starlionblue
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RE: Why No Lighter Seats?

Sun Sep 15, 2013 12:52 pm

Quoting MD11Engineer (Reply 15):
Quoting Starlionblue (Reply 8):
Don't immediately assume they're less comfortable. For example the new CX monkey class seats are lighter and thinner but also way more comfortable than the ones they replaced.

Not in my experrience. E.g. you can´t tilt the backrest backwards anymore, instead the seat pan slides forward and a part of the backrest comes forward with it. For myself I found them too uncomfortable to sleep in for a longer period of time (more than 15 minutes, then I would wake up with cramps). Since the seatbacks don´t really recline, I´m also sure that they reduced the seat pitch, making it difficult for me to stow my legs (I´m 6 feet tall, so just average for central Europe).

Actually, those are by now the old seats and I agree they are quite poor. CX is replacing them with seats that do actually recline. I sat in one for 13 hours a couple of weeks ago and it was quite tolerable; a definite improvement over the old ones.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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bikerthai
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RE: Why No Lighter Seats?

Mon Sep 16, 2013 1:36 pm

Not a seat designer, but had some insight into seat loading when working some interiors stuff.

The 16 G dynamic forward loading drives the seat design strength.

16 G seats are designed to fail is a controllable way in order to absorb the energy of a crash. You can not have the seat too strong or too stiff because then the passenger body would end up absorbing the crash energy.

Aluminum is great for absorbing energy through material deformation. If you design a composite seat you may have to build in shock/strut to perform that function.

Note that most of the passenger load will go through the seat belt and into the lower part of the seat. So the seat back is where you can target the composite. Lower seat frame structure is still aluminum because it is also less expensive to fabricate than CFRP, which is also important on a 300+ seat airplane.

The other key word is controllable. Material failure of aluminum is really well defined and predictable. With CFRP, not so much. You can not stand the variation is failure load in CFRP when you are trying to control the energy absorption aspect of the failure.

Same reason why you still have steel seat belt buckles and straps forever. No one have figure out a way to make it better.

bt
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soon7x7
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RE: Why No Lighter Seats?

Tue Sep 17, 2013 7:46 pm

Quoting bikerthai (Reply 17):
16 G seats are designed to fail is a controllable way in order to absorb the energy of a crash. You can not have the seat too strong or too stiff because then the passenger body would end up absorbing the crash energy.

I just finished the certification of 16G seats for one of our customers...the 16G certification is torture when compared to 9G. The seat weight may not be all that different as the foam build ups may add weight to a rather light frame. The engineering differences between the two is obvious. The complexity of the seat...a fully articulating seat when compare to a static seat is the real weight culprit. Seats in private jets have all kinds of goodies tucked in them while commercial rows of 3 & 4 seats can actually be picked up by one medium sized individual. First class, a different story. In short, the more crap, the more weight. CFRP's might not pass the "Fire blocking" Tests. I am not sure of that.
 
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bikerthai
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RE: Why No Lighter Seats?

Tue Sep 17, 2013 9:07 pm

Quoting soon7x7 (Reply 18):
CFRP's might not pass the "Fire blocking" Tests. I am not sure of that.

This is a very good point. It's not the fire blocking test. It's the smoke toxicity requirements.

Stringent smoke toxicity requirement prevent us from using epoxy systems inside the passenger cabin (with exceptions of small quantities).

Graphite phenolic could be used, but it's not as strong or as easy to fabricate complex seat parts.

bt
Intelligent seeks knowledge. Enlightened seeks wisdom.
 
soon7x7
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RE: Why No Lighter Seats?

Wed Sep 18, 2013 11:37 am

Quoting bikerthai (Reply 19):
Graphite phenolic could be used, but it's not as strong or as easy to fabricate complex seat parts.

Now that you mention it I have never even seen phenolic used on a seat...the only plastics I have seen are "Kydex". That is pretty much it.

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