Swept wings advantages
Thread Starter
Joined: Mar 2005
Posts: 1,339
Likes: 1
From: My house
Swept wings advantages
Hello all,
Just ran a search on the advantages of swept wings and found only 1, the increase in Mmo, higher cruise speeds.
Are there any others as teh Ryanair assesment guys love the topic apparantly.
Many thanks
Nick
Just ran a search on the advantages of swept wings and found only 1, the increase in Mmo, higher cruise speeds.
Are there any others as teh Ryanair assesment guys love the topic apparantly.
Many thanks
Nick
Joined: May 2008
Posts: 377
Likes: 82
From: Mars
Increased lateral stability (though too much and it ain't an advantage, you'll need to offset too much stability with anhederal)
Have a look at the CL curves and min drag info on one of those aero sites you find all over the web, they may reveal a little more.
Many disadvantages too - may well be part of your answer. Example high sweep equals hi AOA for same lift therefore high pitch attitudes (Concord!)
Have a look at the CL curves and min drag info on one of those aero sites you find all over the web, they may reveal a little more.
Many disadvantages too - may well be part of your answer. Example high sweep equals hi AOA for same lift therefore high pitch attitudes (Concord!)
Joined: Jan 2005
Posts: 2,315
Likes: 10
From: France
nick14,
I can think of one other 'advantage' : you can get rid of the horizontal tail!
A swept-back wing can be longitudinally stable on its own, without needing a horizontal tailplane as a straight wing does.
Think of examples like the Messerschmitt Me-163, or the Northrop flying wings, or the B-2, or the F7U Cutlass They don't rely on artificial stability.
Just try with a few paper aeroplanes, if you don't believe me. A rectangular piece of paper by itself flutters down, because it's unstable. Folded into the right shape, it'll glide.
You don't always want to delete the horizontal tail surface (see present-day jet airliners), most of all because you complicate the control in pitch.
For a start, you'll now have to control the aircraft in pitch with the ailerons, which become elevons, with a far smaller moment arm.
Secondly, IIRC, you have a far smaller CG margin, which is not a good idea on an airliner, unless you have an efficient fuel transfer system, as did Concorde.
But....
If the wing itself is already longitudinally stable it will mean you can to a large extent "offload" the horizontal tail in cruise, and only use it for control and trim.
This is the opposite of a straight wing, where longitudinal stability is obtained using a horizontal tail with a negative incidence relative to the wing, hence a down-force, resulting in increased drag.
CJ
I can think of one other 'advantage' : you can get rid of the horizontal tail!
A swept-back wing can be longitudinally stable on its own, without needing a horizontal tailplane as a straight wing does.
Think of examples like the Messerschmitt Me-163, or the Northrop flying wings, or the B-2, or the F7U Cutlass They don't rely on artificial stability.
Just try with a few paper aeroplanes, if you don't believe me. A rectangular piece of paper by itself flutters down, because it's unstable. Folded into the right shape, it'll glide.
You don't always want to delete the horizontal tail surface (see present-day jet airliners), most of all because you complicate the control in pitch.
For a start, you'll now have to control the aircraft in pitch with the ailerons, which become elevons, with a far smaller moment arm.
Secondly, IIRC, you have a far smaller CG margin, which is not a good idea on an airliner, unless you have an efficient fuel transfer system, as did Concorde.
But....
If the wing itself is already longitudinally stable it will mean you can to a large extent "offload" the horizontal tail in cruise, and only use it for control and trim.
This is the opposite of a straight wing, where longitudinal stability is obtained using a horizontal tail with a negative incidence relative to the wing, hence a down-force, resulting in increased drag.
CJ
Joined: Jan 2005
Posts: 2,315
Likes: 10
From: France
Good one, Hoppy.
You can also directly try:
Horten Ho 229 - Wikipedia, the free encyclopedia
Clicking through from there to the other articles about "flying wings" and "tailless aircraft" will give you more info.
CJ
You can also directly try:
Horten Ho 229 - Wikipedia, the free encyclopedia
Clicking through from there to the other articles about "flying wings" and "tailless aircraft" will give you more info.
CJ
Ecce Homo! Loquitur...
Joined: Jul 2000
Aviation Qualifications: Spotter
Posts: 24,682
Likes: 7,366
From: Peripatetic
Joined: Jan 2005
Posts: 2,315
Likes: 10
From: France
ORAC,
Nice article! I bookmarked the site, may come in useful again.
It won't help nick14 much, since it quotes the advantages and disadvantages of forward vs aft swept wings, but not those of swept wings as such.
CJ
Nice article! I bookmarked the site, may come in useful again.
It won't help nick14 much, since it quotes the advantages and disadvantages of forward vs aft swept wings, but not those of swept wings as such.
CJ
Joined: Feb 2002
Aviation Qualifications: AME
Posts: 4,182
Likes: 1,116
From: UK
Also one of the articles mentions that's one way of getting longitudinal stability:
hang the CG way below the center of lift!
hang the CG way below the center of lift!
Joined: Jul 2001
Posts: 1,611
Likes: 0
From: Gold Coast
And as mate of mine said in the technical part of his Qantas interview in the 80's, "so you can fit more in the hangar!"
He didn't get the job and I met him flying Twotters in PNG. Great bloke though.
He didn't get the job and I met him flying Twotters in PNG. Great bloke though.
Joined: May 2008
Posts: 204
Likes: 0
From: Japan
Wikipedia has this to say:
Swept wing - Wikipedia, the free encyclopedia
Well out of my area of expertise (geologist), so I'll let others judge the validity.
Swept wing - Wikipedia, the free encyclopedia
Well out of my area of expertise (geologist), so I'll let others judge the validity.
Thread Starter
Joined: Mar 2005
Posts: 1,339
Likes: 1
From: My house
Many thanks for all your replies, I do love this forum.
Ok so far we have: High speed
Stability (or disadvantage)
Dispensing with the tail
In terms of modern Pax/cargo jets, If asked, "what are the advantages of wing sweep besides the higher Mcrit?" I would still be stuck for an answer.
I always thought that wing sweep created the Dutch Roll problem (obvious disadvantage) And I cannot see boeing/airbus chopping off the tail any time soon.
Thanks again guys and girls
N
Ok so far we have: High speed
Stability (or disadvantage)
Dispensing with the tail
In terms of modern Pax/cargo jets, If asked, "what are the advantages of wing sweep besides the higher Mcrit?" I would still be stuck for an answer.
I always thought that wing sweep created the Dutch Roll problem (obvious disadvantage) And I cannot see boeing/airbus chopping off the tail any time soon.
Thanks again guys and girls
N
Joined: Jan 2005
Posts: 2,315
Likes: 10
From: France
Originally Posted by nick14
In terms of modern Pax/cargo jets, if asked, "what are the advantages of wing sweep besides the higher Mcrit?" I would still be stuck for an answer.
What's more, pretty well everything that does not need to get up to Mcrit has a straight wing.
I always thought that wing sweep created the Dutch Roll problem (obvious disadvantage)
Check "Dutch roll" in Wikipedia : better write-up than I could do. (BTW, I don't know who does the aeronautical write-ups in Wikipedia, but generally they are quite good.)
Oh, and I see they only quote the "polite" explanation for the origin of the term (i.e., it looks the motion of a Dutch skater). The more likely explanation is that it's like a drunken Dutch sailor making his way from the pub back to his ship....
- then go on about less fuel burn and getting the pax in on time.
Nemo Me Impune Lacessit
Joined: Jun 2004
Posts: 4,103
Likes: 5
From: Chabanais, France
Starting at the very beginning, take a straight wing and fly it through the air, the airflow will pass over and under it at 90 degrees and generates lift for the time that the airflow is in contact with the wing chord. Now sweep that same wing back, (same chord), and the airflow passes over the wing in a diagonal direction and remains in contact with the wing longer = more lift for same chord which can then result in all of the above answers you already have! Draw it out on a piece of paper. That is a very, very simple swept wing 101 and interviewers may expect more!
See Handling The Big jets, third edition, page 90, fig.5.5, also, same book, page 84, 'Sweep'.
See Handling The Big jets, third edition, page 90, fig.5.5, also, same book, page 84, 'Sweep'.
Joined: Jan 2000
Posts: 168
Likes: 0
From: Europe
Critical mach increased: Dont sweat the small stuff
In my own words, same thing and,......
Also from handling the big jets,
" the velocity vector normal to the leading edge
is made less than the chordwise resultant "
What's important ? In my humble opinion.
" the airpeed can can be increased before the effective chordwise component
becomes sonic.
Thus the CRITICAL MACH NUMBER IS RAISED.
Curious Nick14 why look for other things ?
when the interviewer may be asking for your knowledge on things such as local speed, compressiblity, transonic speeds, wing thickness chord ratio, shock waves, longitiudinal stablity.
I wouldnt go too deep or you could get yourself into a hole. you are not expected to be an expert on aerodynamics
Maybe I am wrong. What the hell do I know.
What about the disadvantages
For me a swept wing is worse with a heavy crosswind. I remember that flying the 727.
Which airliner had the highest sweepback and has now ?
Why is a swept wing thin etc ?
Duch roll ?
Also from handling the big jets,
" the velocity vector normal to the leading edge
is made less than the chordwise resultant "
What's important ? In my humble opinion.
" the airpeed can can be increased before the effective chordwise component
becomes sonic.
Thus the CRITICAL MACH NUMBER IS RAISED.
Curious Nick14 why look for other things ?
when the interviewer may be asking for your knowledge on things such as local speed, compressiblity, transonic speeds, wing thickness chord ratio, shock waves, longitiudinal stablity.
I wouldnt go too deep or you could get yourself into a hole. you are not expected to be an expert on aerodynamics
Maybe I am wrong. What the hell do I know.
What about the disadvantages
For me a swept wing is worse with a heavy crosswind. I remember that flying the 727.
Which airliner had the highest sweepback and has now ?
Why is a swept wing thin etc ?
Duch roll ?
Last edited by Mach trim; 1st November 2008 at 21:01.