the f-22s main engineering flaw - Square exhaust

[Scorpion1alpha]

does the F-25 currently incorporate/have that ability?

Wait, we have an "F-25"!?!?

Ooohhh...can I see it?

<joke post>
http://www.macross2.net/m3/macrossf/vf-25f.htm
</joke post>

It still has a main engineering flaw - Square exhaust.

Must be a Lockheed / P&W product.

[Scorpion1alpha]

does the F-25 currently incorporate/have that ability?

Wait, we have an "F-25"!?!?

Ooohhh...can I see it?

Yes, afraid you can't see it though. Only me and a select few others, like my 9 year old son Nicholas Maximus. Mach 8 supercruiser, zero radar/infrared due to plasma stealth and an engine with no moving parts. Engine nozzels can morph from circular to flat as the situation calls for it..

Sounds impressive. It still would pale in comparison to what we have at Area 51:



Notice the perfect circular nozzles on it and we've had it since the 80's! But don't tell anyone...it's just between you and me.

[popcorn]

Death Blossom!

[mixelflick]

Wow that pic from area 51.

You should read the warning regarding classified information sticky!!

[f119doctor]

One thing that has to be considered for thrust vectoring is what happens when one of the nozzle actuators decides to misbehave.

On the F119 nozzle, the upper and lower convergent nozzle actuators and divergent actuators are independently controlled. If one convergent actuator control is lost, it is designed to drive open, while the actuator on the other side continues to try to maintain exit area as best it can with the stroke limits of the actuator. The divergent actuator position themselves as required to maintain the requested vector angle and area ratio with the unbalanced convergent section.

A failure in the divergent actuators is different, in that unbalanced actuators will result in an uncommanded vector input. If loss of divergent actuator control is detected, a normally powered solenoid on both actuators is depowered, which hydraulically drives both actuators to mid stroke as their fail safe position.

f119doctor,

Excellent points. Sometimes it works some of the time... and things can fail.

A bit off topic but if there is a convergent/divergent malfunction, are the control surfaces on the F-22 large enough to offset? Are the control surfaces tied into the thrust vectoring? Can they be "disconnected"?

I suspect a malfunction on both nozzles would be rare. Bring the "bad" engine to idle and power up the working engine to maintain thrust? Cross control the instability out with stick and rudder movements?

Can you share with us how much thrust is left on the table with the flat thrust vectoring nozzles of the F-22?

The fueldraulic actuators on the F119 use fluidic Electro Hydraulic Servo Valves (EHSV) to convert FADEC electrical position commands to the hydraulic muscle that moves the pistons to position the nozzle segments, and Linear Variable Differential Transducers (LVDT) to provide actuator position feedback to the FADECs. The usual failures are either in the electrical signals to / from the EHSV or LVDT, or contamination binding inside the EHSV. It takes an extreme mechanical binding or loss of fueldraulic pressure to prevent the actuator from going where it is commanded.

As noted in my previous response, the failure accomodation for losing scheduled control of one divergent actuator is to depower the failsafe solenoid, which removes the EHSV from command of the actuator and opens a hydraulic circuit that centers the actuator at mid stroke. This is done with both upper and lower divergent actuator to result in zero vector on that engine. The other engine will continue to vector when commanded by the flight controls as long there is no divergent actuator failures on that engine, which would also go to zero vector angle in that event.

The engine controls on the F-22/F119 are an integral part of the Integrated Flight / Propulsion Control (IFPC) system, with the various systems talking to each other on the dedicated IFPC bus. The flight controls ask for certain amount of thrust vector depending on the pilot stick input and where it is in the flight envelope, and the engine responds with how much was achieved. There is no "Vector Off" switch in the production aircraft. I believe the flight controls would compensate for any unknown asymmetric drag or uncommanded flight control force, within certain control authority limits, without needing any pilot cross control input.

On the topic of the F119 2D nozzle impacting thrust: Nozzle performance is quantified by a parameter known as Coefficient of Discharge, with a CoD of 1.00 being perfect expansion of the engine exhaust pressure to ambient. No nozzle is perfect, and a square nozzle is likely to have a slightly lower CoD than a round one, all else being equal, likely due to "dead" flow areas in the corners of the nozzle and larger surface area than a round nozzle. During F119 development it was discovered that the early EMD nozzles did not meet the specification CoD during wind tunnel tests. Investigation found that there were a lot of flow leakage areas in the design, some caused by straight sections of the nozzle bulging under pressure loads. Many components were stiffened and leakage areas were better sealed, and the production nozzle meets the specification for CoD. There is no 10-15% loss in thrust due to the "square" nozzle as seen in the reported Russian demonstration tests

The other big advantage is that actively controlled divergent segments to enable thrust vectoring, the nozzle convergent to divergent area ratio can also be actively controlled. This allows the nozzle to properly expand the airflow over a wide range of throttle settings and areas of the flight envelope, reducing drag and increasing thrust. "Square" nozzles also also integrate better with closely spaced twin engines than round nozzles, reducing base drag and turbulence around the aft end of the aircraft.

[milosh]

Soviet flat nozzle design was quite different from what F22 have.

So maybe their design have 10-15% loss, from what I understood they didn't go for TVC that much but for noticeable IR reduction.

Also drop in thrust wouldn't be big deal because it was planned to be coupled with big R179 (200kN engine):

http://www.leteckemotory.cz/motory/r-79/r179_04.jpg

that is why nozzle it look hilarious on Su-27 testbed:

[jessmo112]

Ok I'm not sure the OP thought this thread through. Yes there is something flawed, but it's not the F-22 nozzel.

[avon1944]

The designers of the F-22 felt vectored or diverted thrust would be most effective by limiting the thrust to just the vertical plane. That the way the Russian used vectored was less efficient at some angles more than the other directions. The F-22A was designed to have its thrust be most effective at specific angles and the vertical and horizontal controls handle the needed flight changes for other situations.

[allesmorobranna]

Soviet flat nozzle design was quite different from what F22 have.

So maybe their design have 10-15% loss, from what I understood they didn't go for TVC that much but for noticeable IR reduction.

Also drop in thrust wouldn't be big deal because it was planned to be coupled with big R179 (200kN engine):

http://www.leteckemotory.cz/motory/r-79/r179_04.jpg

that is why nozzle it look hilarious on Su-27 testbed:

This flat nozzle was originally made for the S-32 (later what was turned to be Su-47) project. The 1:1 size wooden mockup from 1984 had already this feature:

https://pbs.twimg.com/media/EL4o3qIWsAE ... name=large