Wing design question

[ChthonicPowers]

Hello everyone,

I have noticed that some aircraft manufacturers attach the wings to the lower side of the fuselage, such as Mirage 2000, while others design it towards the upper part of the fuselage such as on F-22 raptor. Can anyone tell me the pros and cons of these two approaches? Which one do you prefer?
Secondly, What are the major factors taken into consideration while designing the wings of a fighter? I heard on Discovery that the larger the wing area, the better an aircraft becomes at dog fight. So why is it that some modern aircrafts have such small wing areas, such as F/A 18? What are the trade-offs or limits to the size of the wings? I imagine weight is one problem, but ignoring the weight, could there be other problems if we increase the wing area by too much?

Third, How would u rate the JF-17 wing design? They look small to me. Whats ur view :?2

I am a casual defense enthusiast, so pls try to keep the terminology as simple as possible and fill in any possible blanks in my post.


Many thanks

 

[rjmaz1]

Aircraft wing design and fluid dynamics is a very interesting topic.

Wings are all about compromise. There is no perfect wing only the best compromise.

Lift, drag and wing area all go hand in hand, increase one and you decrease the other two. An F-22 wing for example is designed for high speed flight because of this the amount of lift it puts out at low speed is very poor. Its only the F-22's thrust vectoring that allows it manuver good as it can direct its insane amount of thrust. If the F-22 had no thrust vectoring and also had the same power to weight ratio as an F-15 eagle then the F-15 would be more agile than an F-22 in a low speed dogfight.

The wing of an A-10 for example is designed to provide very high lift at low speed, the side effect of this is that the wing produces ridiculous amounts of drag at high speed.

The hornet that you mentioned is at the half way point between an A-10 wing and the F-22 in wing shape. Its shape is designed for very high lift at low speed because of this it doesn't have to be as big. This is also the reason why the Hornets are slower than other fighters the high lift wing produces too much drag at supersonic speed. Thats why the F-15 could always travel Mach 2.5 where as the Hornet always had Mach 1.8 listed. The difference between Mach 1.8 and 2.5 is not small either, drag increases exponentially to the speed. So Mach 2.5 would have more than twice as much wind resistance compared to Mach 1.8 which really shows how much drag the hornet wing must produce.

A Hornet wing is only 37 square metres but can lift 24,000kg off the ground at 130 knots.
A F-22 wing area is 78 metrres square but can lift only 28,000kg at 150knots.
The F-22's wing is 100% bigger yet it only provides 20% more and needs 20knots more airspeed.

However comparing the F-22 and hornet at high speed. The F-22 can travel without afterburners at the same speed as a Hornet can with full afterburner. The F-22's wing at supersonic speeds would probably have around half the drag as hornets smaller wing. The F-22 in this case will be burning a fraction of the fuel so its ideal for traveling to the target very quickly. Where as the hornet gets excellent fuel economy traveling to and from the target at subsonic speed. Its probably also worth noting that the F-22's wing is a Mach 3 wing. The USAF has just speed limited the aircraft to save on maintenance due to long term heat problems.

Regarding the Mach 3 thing. If we look at all fighters in history when afterburners are used the engine thrust is increased by 30-40%, the top speed of the aircraft is increased from 50-70% in nearly every aircraft in history. Even using the worst case increase with afterburners the F-22 will be traveling at foxbat speeds.

On a different note swing wing fighters were popular a few decades ago as they allowed the wing to change its profile from high lift/drag to low lift/drag. However this had a huge weight penalty which offsets any performance advantage from a swing wing.

Leading and trailing edge flaps are now where its at. These are light weight and allow the aircraft to change the cord of the wing to increase lift or decrease drag. They dont change the lift and drag as much as a swing wing but then you dont have the weight increase. We have learnt pretty much all there is to know when it comes to conventional wing design and thats what we see in the JSF and F-22.

Now lets compare the JSF and F-22.
F-22 Fuel: 10 tone, Wing area: 78, Max takeoff: 60,000lb
JSF Fuel: 10 tone, Wing area: 42.7, Max takeoff: 50,000lb

Now the JSF is much more similar to the hornet when it comes to wing design. Its smaller wing is a high lift wing designed for high subsonic speed. The F-22 is a low lift wing design for supersonic speed. The reason why the JSF has a subsonic wing is for the following reasons.

Close air support requires low speed agility, JSF doens't have thrust vectoring or the raw power so it needs a low speed wing.
Longer endurance and longer range is provided.

To look at the range difference, the F-22 and JSF both at 100% military thrust without afterburner the JSF will be sitting at around Mach 1, the F-22 will be sitting at Mach 1.8. The F-22 is traveling much quicker and remember that the F-22 has two engines so will be consuming twice as much fuel. As the JSF and F-22 have the same fuel capcity the F-22 will run out of fuel in half the time. However the F-22 travels 1.8 times further in any given time than the JSF. So the JSF needs that extra time to cover the same distance, and in the end the JSF will travel slightly further than the F-22 before running out of fuel.

The JSF has twice the endurance over the battlefield and slightly more range.

If you want an F-117 replacement, to travel to the target slowly drop a bomb and return the JSF is the ideal replacement. If you want an aircraft to stay above the battlefield for 5 hours the JSF is the ideal solution. If you need to take off slowly from an aircraft carrier or fly slowly through mountains the JSF is the ideal solution.

If you need to intercept an Su-27 enemy fighter that is 200 miles infront of you, the JSF will use all its fuel just catching up, the F-22 is the ideal solution. If the AWAC warns that enemy fighters are approaching and you have assets that cant defend themseleves who can get there the quickest? The F-22.

The best part of the F-22 will be Reconnaissance, would be ideal for a country like Australia but it doesn't look like we will be ever getting F-22. US has enough satelites and UAV's to take pictures of the enemy.

As you can see the wing of both the F-22 and JSF is the ideal compromise for their mission. The JSF NEEDS the F-22 to operate to its full potential.

Also the F-16 and YF-17 both had small-ish high subsonic wings. Not as low speed as the hornet but not as high speed as the F-15.

Also on another note, engine design is similar. You can have an engine optimised for subsonic speed or supersonic speed. The JSF uses a F-22 engine with a higher bypass ratio, this improves thrust at lower speed and improves fuel consumption by a few percent. People who say "oh the next model F-22 will use the higher power JSF engines" dont have a clue

 

[Big-E]

I heard on Discovery that the larger the wing area, the better an aircraft becomes at dog fight. So why is it that some modern aircrafts have such small wing areas, such as F/A 18?

Because no one cares about dog fights anymore, it's all about BVR.

 

[Magoo]

So why is it that some modern aircrafts have such small wing areas, such as F/A 18?

It's not just the main wing area that you take into consideration. There's also the wing area in relation to the aircraft's weight and length.

The F/A-18 also has HUGE horizontal stabilisers AND two large vertical stabs, not to mention the leading edge wingroot extension which goes from the wing root to up past the cockpit sill. The Hornet therefore has the equivalent of a 'flying surface' from the cockpit all the way back to the jetpipes!

Magoo

 

[old faithful]

Well done guys! a good read!

 

[Sea Toby]

I have noticed that the faster fighters have a greater sweep angle of the front leading edge of the wings. For example, the F-15 has about a 45 degree sweep whereas the F-16 will have about a 40 degree sweep, while the F/A-18 is more like 20 degree sweep. An F-111 or F-14 fastest speed is when their wings are swept back, for landing and take-off their wings aren't swept back.

 

[ChthonicPowers]

Very informative post rjmaz1. Thanks. Though I am afraid I still don't quite understand the reasons behind different positioning of the wings relative to the fuselage. I am interested in knowing the specific pros and cons. For instance, is it better to place the wings at the bottom if u want better lift etc...?

Edit: R u saying that an F-15 fitted with F-22's radar/avionics/TVC engine will beat F-22 in a dogfight?

And what about JF-17...No opinions?


I don't know if I should open a separate thread but one more question:

Whats the science behind having vertical tail fins? I read somewhere the designers of F-16 tested it with two vertical fins and dropped the idea cuz they made the plane unstable? Generally speaking, are two fins better than one?

Hope I am not bothering anyone with my newbie questions! :

 

[rjmaz1]

I have noticed that the faster fighters have a greater sweep angle of the front leading edge of the wings. For example, the F-15 has about a 45 degree sweep whereas the F-16 will have about a 40 degree sweep, while the F/A-18 is more like 20 degree sweep. An F-111 or F-14 fastest speed is when their wings are swept back, for landing and take-off their wings aren't swept back.

Swept back wing allows for less drag for any given surface area. Looking from the front a swept wing only sticks out a few metres even though its area is quite large. The reduction of the frontal section reduces drag and increases speed.

Its also probably worth noting that the shock wave when traveling at supersonic speed increases in angle the higher the speed goes, so a greater sweep angle is prefered as the speed goes up. 45degree sweep angle is prefered for Mach 1 cruising, where as 30degree sweep is prefered for Mach 2 cruising. This is why higher the faster aircraft in history also have a very swept wing. This also plays a part with the lift/drag/area compromise, which is probably the more important part.

If we didn't have swept back wings to get low drag and large area then the wings would have to be like a F-104 and be absolutely tiny and have little room for fuel.

Though I am afraid I still don't quite understand the reasons behind different positioning of the wings relative to the fuselage. I am interested in knowing the specific pros and cons.

Most delta wing aircraft have low mounted wings, most conventional wing aircraft have a higher mounted wing. This is from experience of being the best option at high angles attack, it allows air be directed over the wings easier. Wingroot extensions further enhance this and its easier to place wingroot extensions with the middle/high mounted wing.

A delta wing doesn't suffer from these problems more so with the use of canards infront of the wing as these provide lift to offset any stalling in the wing. At high angles of attack the vortices become unstable with a delta wing this is why canards help dramatically. With a conventional wing the horizontal stabs actually push the rear of the plane down to make the front move up. Canards provide lift to pull the nose up this is a pretty good idea to use with a high speed delta wing.

The delta/canard versus conventional wing design is the bigger argument. I would have thought that an aircraft with the F-22's intended mission would have been a delta wings aircraft like the experimental F-16 cranked arrow wing.

Edit: R u saying that an F-15 fitted with F-22's radar/avionics/TVC engine will beat F-22 in a dogfight?

Well the F-15 being lighter would actually have a higher thrust to weight ratio. But what i meant is that the F-22 without thrust vectoring or raw power would have pretty average handling at low speed. However in real life the F-22 wing could completely stall and it could still make sharp turns. When the wing stalls the F-22 just needs to use its thrust to compensate by pointing the aircraft upwards so it doesn't loose altitude, the thrust vectoring then makes up for the loss of air flowing around the control surfaces.

And what about JF-17...No opinions?

Its a good average design, medium angle sweep, medium size wing, medium drag wing, wing root extensions to prevent the wing from stalling at high angles of attack. Similar to the F-16 wing in most aspects, its a fairly even compromise between low speed lift, wing area and high speed drag which is ideal for a multirole aircraft allowing for excellent transonic performance while still having good low speed lift to give excellent agility offering a quicker instantaneous pitch/roll rate than the F-15 which is designed for higher speed combat.

In the decades ago people compared the wing loading of aircraft to determine its agility. Based on that the F-16 would have pretty poor agility. These days its a bit harder the comparison used are now trimmed lift coefficient and trimmed drag coefficient at a given angle of attack.

 

[ChthonicPowers]

The delta/canard versus conventional wing design is the bigger argument. I would have thought that an aircraft with the F-22's intended mission would have been a delta wings aircraft like the experimental F-16 cranked arrow wing.

Hmmm..so delta wings r more relevant in today's aircrafts, u reckon? Personally, I love the aesthetics of the conventional wing, especially the diamond shape of F-22. Delta wings just look weird to me, so its kinda sad to know that Deltas paired up with canards r more effective


I think I read somewhere that the designers of F-22 also tinkered with a canard but didnt find it too effective. Not sure, let me try and find the link.

Well the F-15 being lighter would actually have a higher thrust to weight ratio. But what i meant is that the F-22 without thrust vectoring or raw power would have pretty average handling at low speed. However in real life the F-22 wing could completely stall and it could still make sharp turns. When the wing stalls the F-22 just needs to use its thrust to compensate by pointing the aircraft upwards so it doesn't loose altitude, the thrust vectoring then makes up for the loss of air flowing around the control surfaces.

K. Since all that is hypothetical, how abt the rafale Vs F-22 or Eurotyphoon v F-22?

I am sure its already beaten to death.

Its a good average design, medium angle sweep, medium size wing, medium drag wing, wing root extensions to prevent the wing from stalling at high angles of attack. Similar to the F-16 wing in most aspects, its a fairly even compromise between low speed lift, wing area and high speed drag which is ideal for a multirole aircraft allowing for excellent transonic performance while still having good low speed lift to give excellent agility offering a quicker instantaneous pitch/roll rate than the F-15 which is designed for higher speed combat.

Average design? Lets hope future modifications make it more than an average design.

In the decades ago people compared the wing loading of aircraft to determine its agility. Based on that the F-16 would have pretty poor agility. These days its a bit harder the comparison used are now trimmed lift coefficient and trimmed drag coefficient at a given angle of attack.

trimmed lift coefficient. Yeah yeah..I know all about THAT.


















Thanx again for the replies. I'll make a seperate thread for vertical fins question.

 

[rjmaz1]

Average design? Lets hope future modifications make it more than an average design.

No you got me wrong, the F-16 and F-17 design is excellent.

What i meant that the A-10 is a low speed wing, the F-22 is a high speed wing. The F-16/17 wing is half way between these which i meant by "average"

Instead of the word average i should have say that the wing of the F-16 and F-17 is an excellent compromise between low speed handling and high speed cruising.

Also the comparision between F-22, Eurofighter and Rafale has nothing to do with the design of the wing. Todays combat is ruled by the aircraft that detects its enemy first and can shoot first. Being able to turn quick is the least important, but with the F-22 they decided its better to be safe and added thrust vectoring.

 

[ChthonicPowers]

Thanks rjmaz1. I guess That pretty much answers most of my wing design questions. Keep up the good work.

 

[Wooki]

Thanks rjmaz1. I guess That pretty much answers most of my wing design questions. Keep up the good work.

If you are seriously interested in wing design CP, check out NASA's websites. Just do a google and you will find all sorts of educational packages that start at the basics and go up from basic foil simulators you can download to discussions about hypersonic flight. Its all quite useful. I actually used the kiddy foil simulator to quickly check a sail design for a 60 foot yacht, and it worked great.

There are also 2 start up companies that are trying to get funding for a Supersonic Biz jet

http://www.saiqsst.com/index.html

http://www.aerioncorp.com/

I think you might find it interesting comparing the two, as both are trying to achieve the same thing with different designs.

cheers

W

 

[crobato]

Factors in maneuverability and performance. Please note everything is compromise.

Wing Loading = Ratio of wing area vs. plane weight. The lower, generally more maneuverable, especially at high altitudes. Enables tighter turn. Disadvantage, greater drag. Higher Wing Loading allows smoother ride at lower altitudes and high speeds.

Wing Aspect ratio = This is measured by the ratio of wing span vs. chord. Generally, a plane with long thin wings have a high aspect ratio, while that with a short stubby wings have a low aspect ratio. High aspect ratio, better L/D efficiency at lower speeds. Low aspect ratio, better Lift/drag efficiency at higher speeds, as well as faster roll but higher pitch stability, which tends to negate maneuverability. Airliners and cargo planes favor high aspect ratio, while fighters generally favor low aspect ratios.

Anhedral/Dihedral = An Anhedral wing is one where the wingtips are lower than the wing root, or the wing looks angled downwards. A Dihedral wing is where the wingtips are higher than the wingroot, or the wing looks angled upwards. WWII fighters, now modern jetliners tend to be dihedral. Modern fighter and attack jets are either flat or anhedral. Other military aircraft, including bombers and cargo planes, also tend to be anhedral. Dihedral wings tend to be stable at roll, or resist roll, while anhedral wings favor faster roll.

more later

 

[crobato]

The FC-1 wing looks fine to me, though in an F-16ish style of way. As the plane is rather light, it should have lower wing loading even than an F-16A, though the wing dimensions are similar.

My opinion is that the FC-1 is optimized well for maneuverability for medium to high subsonic speeds, and at low to medium altitudes. It should roll pretty quickly, as the first prototypes did during their first flights. The newer prototypes with the expanded LERX may give it better stability and less drag at high angles of attack which I suspect was a problem among the earlier prototype.