YF-22 vs YF-23

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zero-one

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Unread post29 Jul 2019, 08:55

disconnectedradical wrote:Since your link was broken I had to go find it. It may be that specifically for X-32, four tails was chosen because of weight.

Okay thats fair.

disconnectedradical wrote:The F-3 final configuration is NOT even finalized yet, so how can you say it's the best way to move forward?

Yes but since they studied both designs and ultimately proceeded with the F-22's tail for prototype stage. Then there is a bigger chance that that will be the finalized tail design. Its also an indication that that was the best design they saw.

disconnectedradical wrote:A v-tail is not going to be the best solution for every design


Yes its not, and heres where the debate is.
Some think that the pelican tail design offers a far lower RCS return for a slight disadvantage in maneuverability.
Basically a better overall design than the conventional tail.

I on the other hand happen to think that the advantages of the Pelican tail, weather RCS or whatever it is, is simply too small to justify it's disadvantages. Case and point, if it was so good, why has the conventional tail won on most Stealth designs

Disadvantages I can see are:
-You cannot use the tail for both pitch and yaw at the same time
-Using them for pitch may decrease yaw stability\control and using them for yaw may likewise decrease pitch stability\control
-Weight increase (possibly unique to the X-32's design but also possibly inherit to the pelican tail design)

and if the perceived Stealth advantage is too small, then it explains why most have gone with the conventional tail.
Last edited by zero-one on 29 Jul 2019, 10:16, edited 2 times in total.
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eloise

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Unread post29 Jul 2019, 10:13

zero-one wrote:I on the other hand happen to think that the advantages of the Pelican tail, weather RCS or whatever it is, is simply too small to justify it's disadvantages. Case and point, if it was so good, why has the conventional tail won on most Stealth designs

There are quite a few stealth design with V-tail
F-117A
F-117A.jpg

Avenger-C
Avenger-C.jpg

MQ-25
boeing-mq-25.jpg

XQ-58
XQ-58.jpg

NGF
NGF.jpg

GFF
DVjPV.jpg

nVtBC.jpg
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zero-one

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Unread post29 Jul 2019, 10:40

Those are nice but we also have:
F-22
F-35
Su-57
ATD-X
Most if not all K-FX concepts
J-31
FC-3
HAL-AMCA mockup
TAI-TFX mockup
and many others.

What I noticed is that most of the designs that use V tails only, without horizontal stabs seem to have little to no emphasis on performance. Most, not all. Designs that usually emphasize Stealth and performance together, seem to favor conventional tail designs
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sferrin

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Unread post29 Jul 2019, 13:32

zero-one wrote:Those are nice but we also have:
What I noticed is that most of the designs that use V tails only, without horizontal stabs seem to have little to no emphasis on performance.


Depends how you define, "performance". Or do you consider the YF-23 not a performance aircraft? (It met the same set of performance requirements the YF-22 did BTW.)

Also, almost all of your examples simply ripped off the F-22 configuration because they know it works. Had they YF-23 been selected they'd all look like that.
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Unread post29 Jul 2019, 14:33

sferrin wrote:Depends how you define, "performance". Or do you consider the YF-23 not a performance aircraft? (It met the same set of performance requirements the YF-22 did BTW.)

Well thats why I very carefully added the word "most". The X-32 was designed to either have a conventional tail or a pelican tail, specifically when the Navy requested to have increased agility. So the pelican tail can certainly be adopted to a high performance design.

Likewise the Conventional tail also met the USAF's requirements for super-cruise and RCS.

sferrin wrote:Also, almost all of your examples simply ripped off the F-22 configuration because they know it works. Had they YF-23 been selected they'd all look like that.


Hey thats not fair, we don't know that for sure. For all we know the Japanese may have extensively tested both designs in wind tunnels and static pole testing for RCS returns. Ultimately they went with the Raptor's tail in the prototype stage. That speaks volumes.
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Unread post29 Jul 2019, 14:40

“...specifically when the Navy requested to have increased agility.”

No, (as we’ve discussed before) because the Navy actually expected the jet to meet CV approach/handling requirements at the ship.
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sferrin

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Unread post29 Jul 2019, 14:51

zero-one wrote:Hey thats not fair, we don't know that for sure. For all we know the Japanese may have extensively tested both designs in wind tunnels and static pole testing for RCS returns. Ultimately they went with the Raptor's tail in the prototype stage. That speaks volumes.


No, it doesn't.
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Unread post29 Jul 2019, 15:07

zero-one wrote:I on the other hand happen to think that the advantages of the Pelican tail, weather RCS or whatever it is, is simply too small to justify it's disadvantages. Case and point, if it was so good, why has the conventional tail won on most Stealth designs

Disadvantages I can see are:
-You cannot use the tail for both pitch and yaw at the same time
-Using them for pitch may decrease yaw stability\control and using them for yaw may likewise decrease pitch stability\control
-Weight increase (possibly unique to the X-32's design but also possibly inherit to the pelican tail design)

and if the perceived Stealth advantage is too small, then it explains why most have gone with the conventional tail.


You're treating the whole v-tail vs conventional tail as a contest where whichever has the most aircraft using is the "winner". That's NOT how statistics work, and it ignores the engineering decisions for requirements that specific to an aircraft. In designing aircraft it's not a contest of seeing what is the most popular or how many bullet points of pros and cons you list off, that's NOT how engineering is done.

A v-tail will have significantly better stealth especially from the side, but not as much from front. If your stealth requirements are more for the front and not as much for the side, then stealth benefit of v-tail probably isn't as important. Also, tail design should not be look at as something you can just plug and play to any design, it may work for one fuselage design and not the other, it's the overall package that counts.

Even v-tail aircraft have different performance. For example, compare X-32 and YF-23. YF-23 v-tails are much more back from the wing than X-32, so in high AOA it's not as blanked out by fuselage. Downside is the distance between main landing gear and tail is also longer, so for carrier landing it's not suitable since it's more likely to tail strike.
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Unread post29 Jul 2019, 15:26

Also important is to look at if the V-tail is using Ruddevators or all flying Stabilators. X-32 was the former, YF-23 was the later. If using a V tail the individual surface has to be larger which means a more robust mounting (and in the case of an all flying stab, actuating) component. Personally I am a fan of flying V tails, but I am also a fan of flying wings. The effect of the control being blanked out by the win during landing is a real concern, but not insurmountable. Clearly the YF-23 did it.
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Unread post29 Jul 2019, 15:31

quicksilver wrote:
No, (as we’ve discussed before) because the Navy actually expected the jet to meet CV approach/handling requirements at the ship.


Well thats not what the official statement was. What I did see was this:
However, eight months into construction of the concept demonstrator aircraft, the JSF's maneuverability and payload requirements were refined at the request of the Navy and Boeing's delta wing design fell short of the new targets.

https://en.wikipedia.org/wiki/Boeing_X-32
Wiki's source was the Nova documentary on the JSF program. If you haven't seen it, its a good watch. The Boeing team was seen huddled around a room discussing how they can meet the revised maneuvering requirements. No mention of carrier suitability was said.

Furthermore we have this:
http://www.defense-aerospace.com/articl ... ts-(feb.-6).html
Dec. 2 successfully completed low-speed approach CV tests. U.S. Navy Commander Philip Yates, the government Joint Test Force lead pilot, said, "I continue to be impressed with the X-32A's flying qualities in the carrier mode configuration

So the original X-32 with delta wings already had "impressive" low speed Carrier approach handling qualities.


disconnectedradical wrote:You're treating the whole v-tail vs conventional tail as a contest where whichever has the most aircraft using is the "winner". That's NOT how statistics work, and it ignores the engineering decisions for requirements that specific to an aircraft


Not exactly, since we do not have the actual RCS measurements of the YF-22 and YF-23 we need to split hairs. Both met the USAF's requirements. So are they equally good, of course not. A lot of you are saying that it is far better than the conventional tail in RCS measurements while offering similar maneuvering and slightly superior drag performance. But of course you cannot conclusively prove that. Unless you have access to the actual results.

My argument is it offers only slightly better RCS returns while offering considerable disadvantages in some maneuvering aspects (yaw and pitch at the same time) and in weight growth. Likewise I cannot conclusively prove that.

So we let the experts decide and see what they think. So far whenever the Pelikan tail and conventional tail has been pitted in a head to head comparison to see what they prefer to be put in a high performance stealth fighter, the conventional tail has always been selected. The YF-23 is actually the only time a manufacturer selected it for their high performance stealth fighter prototype.

But I'm not simply relying on which is more often preferred thats just a measuring stick I like to use.
I am also arguing that some limitations of the Pelikan tail may contribute to its unfavorable views with designers

-Can't pitch and yaw at the same time
-Using them for pitch may decrease yaw stability\control and using them for yaw may likewise decrease pitch stability\control
-Weight increase (possibly unique to the X-32's design but also possibly inherit to the pelican tail design)
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Unread post29 Jul 2019, 19:45

“Maneuverability” in this case was CV-specific approach/handling. The Navy upped the bring back requirement (weight) and held the approach speed constant — which the existing design wasn’t going to meet. Correction: they actually specified an approach speed which had not been the case before JIRD 3 was issued in 1998.

They didn’t do a full flight test program with these demonstrators and thus there would be little basis to make a ‘...need more UA maneuverability’ case that would force that degree of change in the design.

Here’s the way Bill Sweetman described it on page 71 of his book, Ultimate Fighter, Zenith Press, 2004 —

“The most influential requirement was the Navy’s insistence on a large bring-back payload. By the time JIRD 3 was issued in 1998, the Navy had increased the total bring-back weight comprising fuel and weapons from 8,000 pounds to 9000 pounds and specified an approach speed, which had previously been left to the contractors discretion.”
“Lockheed could and did deal with this problem by enlarging the carrier-based JSF’s wing, gaining low-speed performance at the expense of transonic acceleration and speed. Boeing’s tailless delta was in a more difficult position. The Navy’s requirements drove the size of the trailing-edge controls upwards, but as Boeing sought to increase pitch authority with larger elevens, the weight of the actuation system became unacceptable.”
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Unread post29 Jul 2019, 20:24

quicksilver wrote:... but as Boeing sought to increase pitch authority with larger elevens, the weight of the actuation system became unacceptable.”

Makes me wonder how it would have been with an all flying tail. It's all in the past now.
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Unread post29 Jul 2019, 22:12

One of the complications on the YF-23 all Flying V Tail surfaces was the actuators needed for these large control surfaces. The solution was a stepped piston actuator. Only the smaller inner diameter was used at slow speeds where the dynamic loads were low and large / fast tail movement was necessary. At high speed where high force was needed to move the tail surfaces, the actuator shifted to use the larger diameter of the stepped piston. The smaller surface deflections at high speed allowed the limited flow capacity hydraulic pumps to keep up in this high force / large piston condition. A hydraulic system flow capacity increase (pump sizes, line diameters, coolers, heat rejection, etc) had unacceptable trade offs to use a single large diameter actuator for both conditions.

One of the Northrop flight control challenges was to manage the shift of the actuator from the large deflection mode to the high force mode as the aircraft acellerated and maintain acceptable handling characteristics during the shift. I believe that they were mostly successful, although the test pilots did report that the shift point was noticeable.
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Unread post29 Jul 2019, 22:30

That's actually quite brilliant. Thanks for teaching me something new today.
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Unread post30 Jul 2019, 02:40



THE best.
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