YF-22 vs YF-23

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mityan

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Unread post30 Oct 2014, 12:27

Forgot to say that the RCS value for UCAV is taken from the chineese article "The Assessment Method for Multi-Azimuth and Multi-Frequency Dynamic Integrated Stealth Performance of Aircraft" and is a result of simulation
http://www.intechopen.com/books/aeronautics-and-astronautics/the-assessment-method-for-multi-azimuth-and-multi-frequency-dynamic-integrated-stealth-performance-o

But the UCAV has a very stealthy shape and is made using radio absorbing materials. Its RCS value should be less than that of ATF.
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popcorn

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Unread post30 Oct 2014, 14:20

Why "should' it? Just because it "looks" stealthier or is of more recent vintage doesn't mean anything. Again, these are different aircraft designed/ built to different specifications.
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Unread post30 Oct 2014, 15:13

A vlo design is all well and good, but final RCS is determined by the bucks the developer throws at manufacturing tolerances and RAM coating.
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mityan

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Unread post30 Oct 2014, 15:16

sprstdlyscottsmn wrote:A vlo design is all well and good, but final RCS is determined by the bucks the developer throws at manufacturing tolerances and RAM coating.

And are there any physical limitations that could set a lower bound of RCS?

And the second question. Could we trust this chineese estimations?
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Unread post30 Oct 2014, 16:40

I'm sure are is a physical limitation but I wouldn't know what it is or how limiting it is. The 172ft wide B-2 is often referenced as having an RCS ranging from .1 to .001. I don't know if one of these is an "overall" reference while the other is "frontal" but operationally I know it is for all intents and purposes "not there" on radars of the 90s-2000's.
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Unread post31 Oct 2014, 09:05

sprstdlyscottsmn wrote:I'm sure are is a physical limitation but I wouldn't know what it is or how limiting it is.

You may look at US patent for example.
http://www.freepatentsonline.com/5164242.pdf
Figure 7 shows that maximum of signal loss is greater than 20 dB for frequencies near 8 gHz - where fighter radars act, and for 14-15 gHz for active missile seekers.
Building a RAM is a great trade off between attenuation and its mechanical properties.
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Unread post31 Oct 2014, 09:14

popcorn wrote:Again, these are different aircraft designed/ built to different specifications.

So you have no doubt on the value itself? But have you any guess about specifications?
As I've heard X-47 is just a navy variant of X-45 which has been developed for suppression of enemy air defense. So for its greate survivability it requires to be even more VLO cause ground radars are more powerful and in a much wider band cause there are a lot of them from UHV to X band.
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Unread post31 Oct 2014, 10:03

It seems like they modeled just X-47 (and X-45), but F-22 RCS comes from that USAF quote about metal marble size RCS. A lot depends on how accurate the X-47 model really is as even slight differences to actual aircraft can lead to rather large differences in RCS. It seems to me that they used pretty crude models in their analysis. Also they do not mention modeling effects of RAM and RAS and this leads to rather large difference as those can lower the actual RCS by a factor of 10 to 100 (10 to 20 dB) depending on frequency range. So to me it seems like it's entirely possible that X-47 actually has equal or smaller RCS than F-22 if the model is relatively correct and X-47 has modern RAM and RAS.
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Unread post31 Oct 2014, 11:47

mityan wrote:
popcorn wrote:Again, these are different aircraft designed/ built to different specifications.

So you have no doubt on the value itself? But have you any guess about specifications?
As I've heard X-47 is just a navy variant of X-45 which has been developed for suppression of enemy air defense. So for its greate survivability it requires to be even more VLO cause ground radars are more powerful and in a much wider band cause there are a lot of them from UHV to X band.

X means experimental and was intended to lead to a follow-on design which never happened. No,sense trying to guess specs.,without credible documentation it's all speculation and assumptions on what the designs might have evolved into.
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Unread post31 Oct 2014, 13:01

hornetfinn wrote:A lot depends on how accurate the X-47 model really is

Yeah. I scrolled the article again with much more attention and realized that I understood nothing.
No frequencies, no material, not clear where the pictures come from (may be taken from other researches with unknown conditions). They (chineese) concentrated on air defence area penetration and probabilities of detection.
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Unread post07 May 2015, 12:05

Guys, I now have a range of YF-23 related gifts for sale, the proceeds of which will help to keep my site running...

http://www.redbubble.com/people/yf-23
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Unread post16 Jul 2015, 20:32

Well I just read all 28 pages and am surprised that there is not much data about the engine competition that was going on.

I also tried to search for any topics with the YF-119 vs YF-120 as the main topic but did not find any.

So I hope none of you mind if I post it down here?

How did the the prototype YF119 compare against the YF-120 anyway.
From what I read on this page, it looks like the YF-120 was the better performing engine.

Although Im sure the 119 met the requirements otherwise it wouldn't of been selected, but was is selected simply because it was the safer, cheeper, less risky option, or where there performance metrics where it outperformed the YF120?

Looking at the F100 vs F110 series, it seems that GE just builds better engines.

Looking here
http://foxtrotalpha.jalopnik.com/how-to ... 1682723379

a viper pilot describes that most PW powered aircraft are good performers but not great, however most GE powered aircraft are "absolute beast" the PW powered block 52 was the only excemption and made it into the beast category.

IIRC all GE powered Vipers have larger intakes, which could explain the performance advantage.

If this is true, then PW should be given tremendous credit for matching the Block 50's performance on their block 52 even with the smaller intake. Were PW engines ever installed on big mouth vipers?

Anyway we're veering off, mainly I just wanted to ask if there were any released statements (official or from someone's cousin's brother's neighbor's gardener who knows somebody who knows somebody) about any performance comparison of the YF-119 against the YF-120.

And what led to the YF-119 getting the nod? Since it looked like the 120 clearly had performance advantages.
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Unread post16 Jul 2015, 20:48

I've updated the Wikipedia page on the F119, and most of the information came from the book Advanced Tactical Fighter to F-22 by Aronstein and Hirschberg. It's the definitive book on the ATF. So I'll quote myself below.

The F119 resulted from the Joint Advanced Fighter Engine (JAFE) program in the early 1980s aimed at supplying the powerplant for the Air Force's Advanced Tactical Fighter (ATF). Detailed design of Pratt & Whitney's submission, designated internally as PW5000, began when the JAFE request for proposals was released in May 1983. Advances in technology allowed the design to do more work with fewer stages, with the PW5000 having only 6 compressor stages compared to the F100's 10 compressor stages. The high pressure and low pressure turbines were vaneless and single stage and counter-rotating, thus shortening the engine and saving weight. The fan and compressor stages use integrally bladed rotors (IBRs, similar to GE's blisk) to reduce weight and cost and improve performance. To meet the requirement for high specific thrust for supercruising, the design would have very high core temperature. The original RFP called for maximum thrust in the 30,000 lbf class.

Pratt & Whitney and General Electric were selected to make prototype engines, designated YF119 and YF120 respectively, for demonstration and validation. The ATF's increasing weight required more thrust to meet the performance requirements, and required max thrust increased by about 20% to 35,000 lbf class. Pratt & Whitney's design changed to incorporate a 15% larger fan, increasing bypass ratio from 0.25 to 0.30. However, the larger fan was not test flown on the ATF flight demonstrators to avoid potential reliability issues that may arise. Instead, the revised fan was extensively ground tested at Wright-Patterson Air Force Base. As a result, both the YF-22 and YF-23 had lower performance with the YF119s compared to the YF120s.

On 3 August 1991, Pratt & Whitney was awarded the EMD contract for ATF engine. While the YF119 was a more conventional designed compared to the General Electric's variable cycle YF120, Pratt & Whitney accrued far greater number of test hours and emphasized lower risk. One thing to keep in mind is that the performance levels of the YF120 was very close to what the production F120s would've been.

As a side note, after further examining the F-23A EMD, compared to the YF-23, the EMD aircraft would be longer by about 3 feet, and may have smoother volume distribution, but the cross-sectional area towards the middle definitely bulked up compared to the YF-23. The F-23's rounded off tops of the nacelles in the back is an improvement though, it should increase lift in that area. Speed wise the F-23 may not be very different from the YF-23, though that's not a bad thing at all.
Last edited by disconnectedradical on 16 Jul 2015, 21:01, edited 1 time in total.
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slapshot!

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Unread post16 Jul 2015, 21:01

zero-one wrote:Well I just read all 28 pages and am surprised that there is not much data about the engine competition that was going on.

I also tried to search for any topics with the YF-119 vs YF-120 as the main topic but did not find any.

So I hope none of you mind if I post it down here?

How did the the prototype YF119 compare against the YF-120 anyway.
From what I read on this page, it looks like the YF-120 was the better performing engine.

Although Im sure the 119 met the requirements otherwise it wouldn't of been selected, but was is selected simply because it was the safer, cheeper, less risky option, or where there performance metrics where it outperformed the YF120?

Looking at the F100 vs F110 series, it seems that GE just builds better engines.

Looking here
http://foxtrotalpha.jalopnik.com/how-to ... 1682723379

a viper pilot describes that most PW powered aircraft are good performers but not great, however most GE powered aircraft are "absolute beast" the PW powered block 52 was the only excemption and made it into the beast category.

IIRC all GE powered Vipers have larger intakes, which could explain the performance advantage.

If this is true, then PW should be given tremendous credit for matching the Block 50's performance on their block 52 even with the smaller intake. Were PW engines ever installed on big mouth vipers?

Anyway we're veering off, mainly I just wanted to ask if there were any released statements (official or from someone's cousin's brother's neighbor's gardener who knows somebody who knows somebody) about any performance comparison of the YF-119 against the YF-120.

And what led to the YF-119 getting the nod? Since it looked like the 120 clearly had performance advantages.


For the F16, I dont believe there was any real performance gain for the F100-229 with the big mouth. The F110 just required more air. From what I could see, the YF119 and YF120 were fairly similar in most aspects, its just the YF120 was variable-cycle. Variable-cycle is just a way of saying it could vary its bypass ratio, thus having big improvements to fuel consumption. It was an early version of the ADVENT or AETD engines being worked on now and apparently only added ~10lbs.

Nonetheless, the YF120 was deemed "risky" and not picked up. 25 years later we are looking back at the technology for application in the F35 and other future aircraft.
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Unread post17 Jul 2015, 06:57

slapshot! wrote:Nonetheless, the YF120 was deemed "risky" and not picked up. 25 years later we are looking back at the technology for application in the F35 and other future aircraft.

In retrospect a wise decision. The F-22 program had a tumultuous gestation and the last thing it needed would be the additional challenges that would come wih the variable engine approach.
"When a fifth-generation fighter meets a fourth-generation fighter—the [latter] dies,”
CSAF Gen. Mark Welsh
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