Aircraft Vs Thread 5

[F-ZeroOne]

Northrop Grumman NGB - now with (retractable?) canards.

So I guess the reply to the classic line "The best place for canards is on someones elses aeroplane!" is "Now you see 'em... "

[David Hingtgen]

Coolest looking plane (and it's stealthy): YF-23

Retractable canards---why does everywhere act like this is new? The Tu-144 did it years ago. And the Tu-144's *canards* had double-slotted flaps and slats. They really were little wings.

[buddhafabio]

something just to make a plane unreliable and high in maintenance costs. like what my dad keeps saying about f-111s

[Retracting Head Ter Ter]

OK, someone beat me to it again about the YF-23.

I am actually hoping that the PLAAF will copy the YF-23's lines instead of the probabe F-22 clone it will be.

Edited March 27, 2009 by Retracting Head Ter Ter

[edwin3060]

Coolest looking plane:

New school: YF-23

Old School: F-14

Both of which had Grumman's hand in making (YF-23 as Northrop Grumman/MDD, F-14 as Grumman).

Ugliest plane ever:

Boeing X-32

Retractable canards= maintenance hell. I don't see the issue with the B-2 having to refuel to it's maximum fuel load just after takeoff. Many other aircraft do that as part of SOP (like the SR-71)

Speaking of the SR-71, I wouldn't really call it stealth, given the thermal signature and the radar return off the exhaust, even if there were some LO features built into the geometry of the aircraft.

[Retracting Head Ter Ter]

Ugliest plane ever:

Boeing X-32

Speaking of the SR-71, I wouldn't really call it stealth, given the thermal signature and the radar return off the exhaust, even if there were some LO features built into the geometry of the aircraft.

X-32 is ugly but there is definitely a lot of really other fugly planes out there. Esp. from the pre-40s.

I suppose SR-71 isn't 'stealth' in the 5th gen sense but its one of the very first operational planes with active measures being taken to reduce its signature. (dumping chemicals into the exhaust etc).

Back to the F-35. With the blended design, internal weapons carriage and that kind of thrust, I am surprised it does not supercruise. Was that some deliberate downgrade to make sure F-22 sales would not be affected?

[miles316]

X-32 is ugly but there is definitely a lot of really other fugly planes out there. Esp. from the pre-40s.

I suppose SR-71 isn't 'stealth' in the 5th gen sense but its one of the very first operational planes with active measures being taken to reduce its signature. (dumping chemicals into the exhaust etc).

Back to the F-35. With the blended design, internal weapons carriage and that kind of thrust, I am surprised it does not supercruise. Was that some deliberate downgrade to make sure F-22 sales would not be affected?

The Air force when it released the info for the competition for the JSF, they told the competitors they were not to exceed the performance of the F-16. They did not want to give any one in the bureaucracy an excuse to cut the F-22.

Edited March 27, 2009 by miles316

[Nied]

The Air force when it released the info for the competition for the JSF, they told the competitors they were not to exceed the performance of the F-16. They did not want to give any one in the bureaucracy an excuse to cut the F-22.

That's flat out wrong. The original requirement asked for JSF designs to meet or exceed F-16 performance. Supercruise was not included in the performance specs because it would have increased the cost of any design by quite a bit which ran counter to the JSF's whole reason detre, though I don't doubt competition with the F-22 was considered as well.

[edwin3060]

X-32 is ugly but there is definitely a lot of really other fugly planes out there. Esp. from the pre-40s.

I suppose SR-71 isn't 'stealth' in the 5th gen sense but its one of the very first operational planes with active measures being taken to reduce its signature. (dumping chemicals into the exhaust etc).

Back to the F-35. With the blended design, internal weapons carriage and that kind of thrust, I am surprised it does not supercruise. Was that some deliberate downgrade to make sure F-22 sales would not be affected?

While the F-35 has tonnes of thrust, because of the internal weapons bays, the frontal cross sectional area of the aircraft is actually quite big. That is probably a factor. Also, the F-135 achieves that kind of thrust with a similar core to the F-119 by having a larger bypass fan, whereas for supersonic performance having a smaller bypass ratio is better. That means that overall exhaust velocity is lower, hence the F-35 can't supercruise. Imagine a 747's engine-- tonnes of thrust, but high bypass ratio and low exhaust velocity.

Well, the stealth measures didn't work that well on the SR-71 I guess, though it's a baby step. But for accidental stealth, look up the Avro Vulcan. Because of it's shape and the massive delta wings, the massive bomber could basically disappear from radar at certain angles other than directly side on (due to the tailplane)-- and the British weren't even designing it to be stealthy!

Actually, on the issue of stealth, I've read quite a few times that having canards on an aircraft is detrimental to the RCS, but I can't quite understand why. If the canards conform to the planform arrangement + other stealth design requirments, why can't a canard aircraft be stealthy as well? Do canards affect the stealth performance more than tailplanes/elevons? Why?

Also, I've read that delta winged aircraft bleed off more energy in turns than a more conventional arrangement. Can someone explain why this is so?

Edited March 27, 2009 by edwin3060

[Nied]

Actually, on the issue of stealth, I've read quite a few times that having canards on an aircraft is detrimental to the RCS, but I can't quite understand why. If the canards conform to the planform arrangement + other stealth design requirments, why can't a canard aircraft be stealthy as well? Do canards affect the stealth performance more than tailplanes/elevons? Why?

That's only partially true. Canards work best on fighters when they're set slightly above the level of the wing like on a Typhoon or Gripen this allows them to direct airflow over the top of the wing at high angles of attack more efficiently which is the whole reason canards are being fitted to many 4th and 5th generation designs. The problem is that in stealth designs you want all horizontal control surfaces to be on the same level for edge alignment purposes (both the F-35 and F-22 have horizontal stabs along the same plane as their wings, and the Raptor's stabs are even set into the wing a little) so the two requirements are at cross purposes. That's not to say that canards are impossible to use on a stealthy design (both the Rafale and Su-30 have their canards mounted level with their wings) but it does make the design work more difficult.

Also, I've read that delta winged aircraft bleed off more energy in turns than a more conventional arrangement. Can someone explain why this is so?

Simple aerodynamics, when an aircraft with a big delta wing (like say a Mirage 2000) makes a hard turn it's going into a high angle of attack just like any fighter, however since it's got a bigger wing it's exposing a much larger surface area to the airstream, and that big high lift delta turns into a barn door. It gets even worse because the way the control surfaces used to pull into a hard turn actually reduce the lift of the wing, so it has to pull even higher AoA to compensate causing even more of that barn door effect. Newer canard deltas like the Typhoon, Gripen, and Rafale mitigate this effect greatly by using their canards instead of the control surfaces at the back of the wing, also their previously mentioned effects on airflow over the top of the wing helps reduce the AoA needed for a given turn.

[edwin3060]

That's only partially true. Canards work best on fighters when they're set slightly above the level of the wing like on a Typhoon or Gripen this allows them to direct airflow over the top of the wing at high angles of attack more efficiently which is the whole reason canards are being fitted to many 4th and 5th generation designs. The problem is that in stealth designs you want all horizontal control surfaces to be on the same level for edge alignment purposes (both the F-35 and F-22 have horizontal stabs along the same plane as their wings, and the Raptor's stabs are even set into the wing a little) so the two requirements are at cross purposes. That's not to say that canards are impossible to use on a stealthy design (both the Rafale and Su-30 have their canards mounted level with their wings) but it does make the design work more difficult.

Simple aerodynamics, when an aircraft with a big delta wing (like say a Mirage 2000) makes a hard turn it's going into a high angle of attack just like any fighter, however since it's got a bigger wing it's exposing a much larger surface area to the airstream, and that big high lift delta turns into a barn door. It gets even worse because the way the control surfaces used to pull into a hard turn actually reduce the lift of the wing, so it has to pull even higher AoA to compensate causing even more of that barn door effect. Newer canard deltas like the Typhoon, Gripen, and Rafale mitigate this effect greatly by using their canards instead of the control surfaces at the back of the wing, also their previously mentioned effects on airflow over the top of the wing helps reduce the AoA needed for a given turn.

Hmm but wouldn't the higher lift result in a generally lower wing loading and thus better turn performance? Or, to take it another way, two identical aircraft, one with a delta wing and one with a normal wing, and both can even have tailplanes (MiG-21 is an example of a delta with a tailplane) so control surfaces are not the issue here. Would the delta wing still have poorer performance?

Good point about stealth. So then for the Northrop Grumman NGB posted earlier in this thread, where the canards are on the same level as the main wing, theoretically doesn't need retractable canards if they are designed properly?

Also, the Rafale's canards are higher than the main wing. Or at least according to the 1/72 model sitting in front of me

Edited March 28, 2009 by edwin3060

[David Hingtgen]

Delta wings always have extreme taper and sweep--that reduces their max lift coefficient. Also, at higher alpha they start generating/relying on vortex lift, which increases induced drag (so now you've got both raw skin drag and induced drag to deal with). They simply produce less lift and more drag overall--they NEED to have a huge area to compensate. Except when flying "flat and fast"----0.5 degrees AOA at M2.0 at 50,000ft. (like a Concorde--does very well because it spends 90% of its time doing that---but fighters don't, they "live" at 30,000ft at M0.9)

Delta=speed. It sucks for everything else. Canards are a band-aid for the delta's problems IMHO.

[edwin3060]

Delta wings always have extreme taper and sweep--that reduces their max lift coefficient.

Hmm that doesn't have to be the case, does it? I mean, the Avro Vulcan has a pretty moderate sweep, and the B-2 can basically be thought of as a massive flying delta as well.

Also, at higher alpha they start generating/relying on vortex lift, which increases induced drag (so now you've got both raw skin drag and induced drag to deal with).

And yet most modern fighter jets with a conventional layout use LERXes to generate vortices, which is supposed to aid maneuverability at high alpha so what's the difference then?

They simply produce less lift and more drag overall--they NEED to have a huge area to compensate.

See my point about the B-2--- it seems that this problem is due to the tailoring of a delta to high speed flight and not inherent to the delta planform, am I right to say that?

Except when flying "flat and fast"----0.5 degrees AOA at M2.0 at 50,000ft. (like a Concorde--does very well because it spends 90% of its time doing that---but fighters don't, they "live" at 30,000ft at M0.9)

Delta=speed. It sucks for everything else. Canards are a band-aid for the delta's problems IMHO.

Hmm good points. Thanks for all the input, people! Actually my quest is to understand why European fighters seem to favour the delta+canards arrangement while American fighters favour a more common planform.

[David Hingtgen]

B-2 so doesn't count as a delta for most things. Anyways---the LEXs on an F-18 etc don't even "start to work" until very high alpha, while a delta is generating drag all the time in even moderate turns/alpha. (that's part of the reason for the big slots cut in a Hornet's LEXs---to allow air to flow through under most conditions, bypassing the LEX and reducing drag) And the vortices from a LEX/strake are "stabilizing" vortices, usually to reinforce the flow along the tail to maintain control----not to generate lift like a delta wing LE does. Even airliners have vortex generators and strakes, not for high alpha nor lift-generation, but to make little "reinforcements" to the flow at certain points.

[Vifam7]

Actually my quest is to understand why European fighters seem to favour the delta+canards arrangement while American fighters favour a more common planform.

That's what I'd like to understand too.

B-2 so doesn't count as a delta for most things. Anyways---the LEXs on an F-18 etc don't even "start to work" until very high alpha, while a delta is generating drag all the time in even moderate turns/alpha. (that's part of the reason for the big slots cut in a Hornet's LEXs---to allow air to flow through under most conditions, bypassing the LEX and reducing drag)

Didn't they fill in those slots later?

[David Hingtgen]

Partly, but they're still there and let a lot of air through. You'll see the entrance is hidden by the splitter plate, which is why it's very hard to see from the sides (and even below). But when the plane's flying straight---the air goes right through. My own pic:

[Vifam7]

Partly, but they're still there and let a lot of air through. You'll see the entrance is hidden by the splitter plate, which is why it's very hard to see from the sides (and even below). But when the plane's flying straight---the air goes right through. My own pic:

That's one neat photo from an angle I've never seen before.

Thanks David!

Edited March 29, 2009 by Vifam7

[David Hingtgen]

Give me a camera and unrestricted access to a plane, and you can be sure of unusual angles showing lots of "secrets" of a plane's design.

[edwin3060]

Haha interesting pic, thanks David. Didn't the F-18 (A-D) have a problem with the vortices from the LERXes hitting the tail and causing increased fatigue? They had to add a fin on top of the LERX to solve that problem, IIRC. Also, every time I read about LERXes I see the words "vortex lift" in there somewhere so surely there must be a lift element in having LERXes and not just maintaining control of the airflow around the tail.

Either way, besides the B-2, the British had a whole series of V bombers with low-sweep delta wings, so surely the problems associated with deltas are more due to the high sweep, which can affect highly swept normal wings as well? Granted, the nature of the delta lends itself to a higher sweep than normal wings.

Back to the canards and stealth-- I get that the wings should be on the same level for better stealth performance, but surely canards can't be that bad? The vertical stabilizers of the F-22 are (for obvious reasons) not on the same plane as the main wings, but it still achieves LO by the planform geometry.

Anyway, reading about the Vulcan bomber I was struck by how it could disappear from radar even though it wasn't designed to be stealth. It seems that a delta winged platform would lend itself better to stealth.

[David Hingtgen]

The F-18's LERX vortex tended to burst right at the v.stabs, causing damage. The LERX strake reinforces the main LERX vortex, allowing it to get past the v.stabs before bursting.

Stealth---well if you believe Boeing and Eurofighter, the head-on RCS is everything, so an above-the-wing mounted canard up front is very bad.

[F-ZeroOne]

Actually my quest is to understand why European fighters seem to favour the delta+canards arrangement while American fighters favour a more common planform.

I'm almost tempted to say "2-3-5" here... (Europeans, as a rule, tend to be footballing nations... )

[Bri]

Actually my quest is to understand why European fighters seem to favour the delta+canards arrangement while American fighters favour a more common planform.

I think it has a lot to do with the time these fighters were developed. The Rafale, Typhoon and Grippen all have their early design work down in the late seventies/early eighties. At the time the Delta configuration with Canards may have looked like the best option. The F-16 XL that lost to the F15 E for the ETF competition also had a delta wing. The "US teens" were conceived based on late 60s/early70s research while the YF22/YF23 had their roots in the late 80s.

I wouldn't be surprised if the shape of these fighters followed the advances in computer-processing-power and windtunnel testing.

Edited March 30, 2009 by Bri

[Nied]

Back to the canards and stealth-- I get that the wings should be on the same level for better stealth performance, but surely canards can't be that bad? The vertical stabilizers of the F-22 are (for obvious reasons) not on the same plane as the main wings, but it still achieves LO by the planform geometry.

No, Boeing and the Eurofighter consortium aside, they are very bad. The reason the F-22 and F-35s vertical stabs are OK is because they are aligned along a different plane (in both cases with the underside of the fuselage) and are at a proper angle for advantageous radar reflection. Canards slightly above the wing would form a nice 90 degree box that from any angle other than dead on would be a huge radar reflector (that's why the Super Hornet's boxy diamond shaped intakes are stealthy, while the F-15's or F-14's big square intakes have an enormous RCS).

[Phyrox]

Either way, besides the B-2, the British had a whole series of V bombers with low-sweep delta wings, so surely the problems associated with deltas are more due to the high sweep...

Just because I'm a stickler...

I could be misunderstanding you, but there were only 3 V-bombers as far as I know, and only one (the previously mentioned Vulcan) had a delta wing.

[David Hingtgen]

Yeah, if you look head-on, you'll see how few planes the F-22 has. When you REALLY look, both the YF-23 and F-22 are pretty amazing in how everything lines up--especially compare "trailing edge of A to leading edge of B"---basically, EVERYTHING lines up with something else--it just may not be near or associated or obvious--but there are overall *very* few skew lines---everything's parallel.

[Retracting Head Ter Ter]

Yeah, if you look head-on, you'll see how few planes the F-22 has. When you REALLY look, both the YF-23 and F-22 are pretty amazing in how everything lines up--especially compare "trailing edge of A to leading edge of B"---basically, EVERYTHING lines up with something else--it just may not be near or associated or obvious--but there are overall *very* few skew lines---everything's parallel.

So an 'Ideal' stealth shape would be a flying diamond with a 'no-opening' anti-gravity propulsion?

[David Hingtgen]

B-2 is a bunch of diamonds arranged like tangram, from above.

News: Even Airbus is now saying they may have to scrap the entire A400 program. "It is better to put an end to the horror than have horror without end."---CEO of Airbus

[edwin3060]

Sweet I learnt alot! Thanks guys!

Yep you're right Phyrox, my bad. The Vulcan was just the most famous of the V-bombers I guess.

Bri: The funny thing is that the US went with a mix of deltas and normal aircraft in the 1950s-60s (F-102, F-106 deltas, F-86, F-100, F-101 swept wings) with the deltas generally being interceptors and the swept wings generally being air-superiority fighters. Then from the 60s-70s with the teen fighters they went with swept wings for the combined interceptor/air-superiority role. Then there was a slight deviation for the F-16XL, but basically from the 70s onwards US fighters went with swept wings rather than deltas.

The Europeans, on the other hand, stuck with deltas all the way, from the Mirage 3 to the Rafale, Viggen to Gripen etc, adding canards somewhere in the 70s, and with some flirtation with swept wings (English Electric Lightning 50s, Mirage F1 60s, Tornado 70s) about once every decade-- but all their newer designs from the 80s onwards are delta-canards.

So, both the US and the Europeans have ample experience with both swept wings and delta wings but the US went for swept wings and the Europeans went for delta wings for aircraft which are basically supposed to do the same job. I wonder why?

[edwin3060]

News: Even Airbus is now saying they may have to scrap the entire A400 program. "It is better to put an end to the horror than have horror without end."---CEO of Airbus

Ouch. I guess after Germany indicated pullout from the programme and France was iffy the other participating nations would be re-considering their decision as well.

[F-ZeroOne]

Hotelicopter to start "aerial cruises":

http://www.engadget.com/2009/03/30/hotelic...hrough-the-air/

"S.O.S! Mr. Tracy, the Western World is calling... "

Edited March 30, 2009 by F-ZeroOne

[David Hingtgen]

The funny thing is that the US went with a mix of deltas and normal aircraft in the 1950s-60s (F-102, F-106 deltas, F-86, F-100, F-101 swept wings) with the deltas generally being interceptors and the swept wings generally being air-superiority fighters. Then from the 60s-70s with the teen fighters they went with swept wings for the combined interceptor/air-superiority role. Then there was a slight deviation for the F-16XL, but basically from the 70s onwards US fighters went with swept wings rather than deltas.

They went with deltas in the 60's for their sheer speed due to extreme sweep angles. As you said---pure interceptors were deltas, air superiority fighters were not. Mach 2 could only be achieved then by having very little wave drag (and polishing the planes until they gleamed). Nowadays anything can hit Mach 2 through sheer power (except a Hornet) so no more US deltas generally. The F-16XL is a delta for range---the sheer area of the wing increases the lift/drag ratio and increases the internal fuel capacity.

[Bri]

The Europeans, on the other hand, stuck with deltas all the way, from the Mirage 3 to the Rafale, Viggen to Gripen etc, adding canards somewhere in the 70s, and with some flirtation with swept wings (English Electric Lightning 50s, Mirage F1 60s, Tornado 70s) about once every decade-- but all their newer designs from the 80s onwards are delta-canards.

So, both the US and the Europeans have ample experience with both swept wings and delta wings but the US went for swept wings and the Europeans went for delta wings for aircraft which are basically supposed to do the same job. I wonder why?

There wasn't much of a joint European effort until the mid 60s. At that time the only two counties with experience in building advanced jets were Britain and France. Afaik Dassault was part of the early design stages for the Eurofighter before they started on the Rafale. Most of their designs were deltas and I'm sure their experience weighed in.

The Swedish defense efforts were separate from the rest of Europe as a neutral country. Maybe their need for interceptors made deltas the most likely choice. Thats pure specualtion though.

[David Hingtgen]

After Dassault left the Eurofighter program and made the Rafale, the EF-2000 had "defeat the Rafale" as a design goal---as they knew France would sell to everybody, and they figured the odds were good the Typhoon might have to fight the Rafale. Very VF-25 vs VF-27 esque in that regard.

Except that the Rafale did amazingly poor export-wise. (I still don't know why, it's a good plane, and carrier capable--not that many can take advantage of the latter)

[Vifam7]

After Dassault left the Eurofighter program and made the Rafale, the EF-2000 had "defeat the Rafale" as a design goal---as they knew France would sell to everybody, and they figured the odds were good the Typhoon might have to fight the Rafale. Very VF-25 vs VF-27 esque in that regard.

Except that the Rafale did amazingly poor export-wise. (I still don't know why, it's a good plane, and carrier capable--not that many can take advantage of the latter)

Perhaps India might buy the Rafale? Provided they get that carrier finished by the Russians...

I would guess sales of Rafale was hurt by having 2 competing delta canard fighters and the availability of cheap F-16s.

[David Hingtgen]

3 competing Eurocanards (Rafale, Typhoon, Gripen).