The F-35 Thread

[GGTharos]

Yeah, that makes a little more sense ;)

[Sticky]

Mystery solved then :)

[RIPTIDE]

(in fact, the MiG-25's empty weight is close to the F-15C's combat weight, and the F-15 has more powerful engines).

 

True about the weight, but remember the difference in power of the engines is really small. IIRC like 1% diff with the -220 engines?

[GGTharos]

I think it is a little more than that, especially since you can tune the 220's up to some 25000lbs these days.

 

But I digress; the point is the F-15 has a superior TWR, and so do its engines. The MiG-25 has engines built for supersonic cruise, and they do their job. Consequently they give up subsonic performance/subsonic fuel consumption.

 

IIRC, the Raptor has a similar shortcoming at least in fuel performance, but not quite as bad.

 

Difference between low/high bypass engines, basically.

 

True about the weight, but remember the difference in power of the engines is really small. IIRC like 1% diff with the -220 engines?

[4c Hajduk Veljko]

DoD, Lockheed Agree to 32 F-35 Lightning II Fighters in LRIP-4 Purchase

[mikoyan]

I still think that this fifth generation birds are too expensive; at this point there would be no nation able to afford loses on any type of conflict let alone accidents. Now another think I don't like is that lockheed is involved in too many weapons programs. Why rely in one company to produce most of your weapons and if you as a government are giving so many contracts to this companies; shouldn't you expect this company to give you better prices.

How are they going to replace the f-16 with this if it is not an affordable fighter like the f-16 was when launched back in the 70's

[GGTharos]

It was an affordable fighter back in the 70's because it lacked much of what it can do today. F-15's weren't 'affordable' either.

 

As far as I can tell, F-35's are about right where you might expect a brand new fighter to be priced at in 'today dollars'. Newer stuff = more cost.

The superiority of an F-35 over current opponents is what makes it worth while. The fact that THEY are the ones who have to play catch-up, not you.

[4c Hajduk Veljko]

From the same article, quote:

 

"The DoD has stated before that the cost of the F-35 program from inception to retirement could cost the U.S. taxpayers as much as $382 billion."

 

End of quote.

 

Some may think money grow on trees. $382 billions of dollars!! Who's gonna pay for that? As of today, the poverty level in USA is the highest since the records started being taken. In addition, quote:

 

Food Stamp Usage Across the Country

The number of food stamp recipients has climbed by about 10 million over the past two years, resulting in a program that now feeds 1 in 8 Americans and nearly 1 in 4 children.

 

End of quote.

 

I don't think it is prudent to spend so much money on ONE military program while there are other problems (read above) we need to take care about.

[nscode]

at this point there would be no nation able to afford loses on any type of conflict let alone accidents.

 

 

a good thing, if you ask me ;)

[GGTharos]

This is a cost estimate over a 30-40 year span. It is quite typical for any fighter.

 

Some may think money grow on trees. $382 billions of dollars!! Who's gonna pay for that? As of today, the poverty level in USA is the highest since the records started being taken. In addition, quote:

[hitman]

 

Difference between low/high bypass engines, basically.

Im curious...which aircraft has high bypass? IIRC smaller aircraft arent capable of being high bypass due to size restrictions. I hear high bypass, I think turbofans on C-5's.

[mvsgas]

High bypass engine ( turbofan) are like the ones on the A-10, C-5, etc. Low bypass are like the ones on the F-15, F-22, etc. The bypass, as the name implies, is relative to how much air bypasses the core or N2, the core being where the higher compression occurs and where the combustion chamber is located.

 

But I thought Mig-25/31 did not use turbofans, I thought they use turbojet, which has not bypass air. Someone showed me along time, on this very forums, why they are better at high altitude and speed... That's when I first got here and I still thought I knew a lot about aircraft ( ignorance and cockiness is a bad combination :D)

 

Correction:

Disregard, MIG-31 uses turbofans (Soloviev D-30)

Edited September 27, 2010 by mvsgas

[GGTharos]

Yep, the more you fill in the engine with core, the closer to a turbojet you get which gives you higher exhaust temp/pressure IIRC, but also requires heat shields and whatnot .. against IIRC.

 

As long as you can feed it subsonic air and not exceed some temp limits (ie. thrust), you can use a turbofan with a ramjet engine ... your afterburner ;) (Again, IIRC)

[mvsgas]

Yep, the more you fill in the engine with core, the closer to a turbojet you get which gives you higher exhaust temp/pressure IIRC, but also requires heat shields and whatnot .. against IIRC.

 

Well I have never worked on turbojets, so I'm just guessing, but I'm not sure if you get higher exhaust pressure. You get higher temps because the is no relatively cool air to mix with combustion chamber exhaust to cool components. I may get higher pressures on a turbofan because afterburner area in a turbofan should have more oxygen available for combustion and relatively cooler air (more store energy for expansion...right?) again, just guessing.

 

 

As long as you can feed it subsonic air and not exceed some temp limits (ie. thrust), you can use a turbofan with a ramjet engine ... your afterburner ;) (Again, IIRC)

What do you mean by;"temp limits (ie thrust)?

 

You can use turbojets with ramjets, isn't that the way the J58 worked?

 

I think the coolest thing of the F119 and F135 is that n1 and n2 rotate in different direction or counter rotate, I wonder if there are any other jet engine that use this system.

[Pilotasso]

High bypass, means bigger fan, means more turbine stages to power the fan. i.e. more losses at the exhaust gas speed (higher is better for top speed).

 

It also means that the bigger fan is not so good for supersonic speed. It gradually looses in its contribution to total thrust as speed and altitude increases, until, it too will act as an air-brake.

 

On the other hand pure turbojets are terrible for acceleration. Think of turbofans as lower gears in your car while turbojet higher gear.

 

If you start your car with 5th gear you will take forever to speed up but once you get there... :) --->turbojet

 

Similarly if you start with 1st or 2nd gear, you will accelerate faster but you will also reach its speed limit quicker.--->turbofan

 

The compromise is the 3rd or 4rth gear. This is analogous to current jet fighters.

Edited September 27, 2010 by Pilotasso

[GGTharos]

Well I have never worked on turbojets, so I'm just guessing, but I'm not sure if you get higher exhaust pressure. You get higher temps because the is no relatively cool air to mix with combustion chamber exhaust to cool components. I may get higher pressures on a turbofan because afterburner area in a turbofan should have more oxygen available for combustion and relatively cooler air (more store energy for expansion...right?) again, just guessing.

 

I meant higher exchaust gas speed - as per what Pilotasso wrote, sorry.

 

What do you mean by;"temp limits (ie thrust)?

 

Your best indicator of thrust produced is the engine temp. The problem is that, IIRC, turbofans are not quite as resistant to heat damage as turbojets - for example, the F-15 can go M2.3+ only for about a minute, and then it requires hot boresite inspection, again, IIRC. If you run it above that speed for longer, you will destroy engines in-flight, possibly causing an engine fire.

 

Similarly F-15's with the -100 used to have a V-max switch which would allow scheduling of higher tems in the engine, allowing more thrust for a short period of time above M1.1. Again, your Crew Chief would chew you out for using it ... until the -220 came along, and thanks to some redesign and new materials, it can provide more thrust without damaging the engine, so a -220 equipped eagle has a better performance envelope despite that -220 delivering 'less rated thrust' (in fact, it can be tuned up to deliver enough thrust that the USAF isn't worried about the recent flanker engine upgrades).

 

You can use turbojets with ramjets, isn't that the way the J58 worked?

 

Yep. I think the J58 is a very interesting and exceptional engine though.

[mvsgas]

Your best indicator of thrust produced is the engine temp. The problem is that, IIRC, turbofans are not quite as resistant to heat damage as turbojets - for example, the F-15 can go M2.3+ only for about a minute, and then it requires hot boresite inspection, again, IIRC. If you run it above that speed for longer, you will destroy engines in-flight, possibly causing an engine fire.

 

Similarly F-15's with the -100 used to have a V-max switch which would allow scheduling of higher tems in the engine, allowing more thrust for a short period of time above M1.1. Again, your Crew Chief would chew you out for using it ... until the -220 came along, and thanks to some redesign and new materials, it can provide more thrust without damaging the engine, so a -220 equipped eagle has a better performance envelope despite that -220 delivering 'less rated thrust' (in fact, it can be tuned up to deliver enough thrust that the USAF isn't worried about the recent flanker engine upgrades)

 

I was reading some manuals at work and I do not thing the best indication for thrust is EGT/FTIT temp. Maybe engineering side, that I have no Idea, but most manuals basically look more into rpm range ( "X' throttle position should have "Y" RPM) I remember working on 404 when on hot day you would have higher temp and less power.

 

F100-PW-100 engines were terrible in many ways, I never worked them, but all the old timer told me stories about how hard they were to work on. 200 and 220 had their share of bad years also. AB no lights, multiple low hours bore scope that where 95% bad.

 

Anyway, the F135; I thought this engine exhaust is based in the MNPK Soyuz R-79, I wonder how similar they are? Anyone got good photos of the Yak-141 engine?

[Rhen]

FTIT or EGT is a Great!! indicator of thrust. It usually stabilizes out faster than RPM, and has little variation between OAT/conditions in comparison to the same engine installed on another jet.

 

For example, if I'm flying and want to give someone else my approximate thrust setting (actual thrust produced) then giving them the FTIT will give them a better approximation of the same amount of thrust that I'm producing in my jet. This is great to use for exercises where we keep our power set, and the other aircraft must use cutoff to remain in position (no throttle).

 

Also if I'm shooting an approach, I know that if I set an FTIT, I'll keep a certain speed. It's a good control instrument for power.

 

FTIT/EGT probably doesn't mean as much to a maintainer during an engine run, as long as they don't exceed their max values. However, in the air they're a better indicator of thrust, without varying with the condition of the air mass when compared to the same engine installed in another aircraft, and vary less than RPM, or fuel flow for that matter - which varies significantly with the temp and quality of the airmass (humidity, etc.) - coming up initial at Luke vs Tyndall.

[mvsgas]

I guess that is the difference between frying them and fixing them. Obviously on the ground parameters are different, I just did not realize how different. F-117 was terrible for this since ambient temperature had such a direct impact on EGT. I was looking at -1 for F-16 block 42 here and FTIT is not mention as much as RPM. I guess is just confusing since on the ground FTIT varies so much to us. RPM we have set numbers ranges at set engines while FTIT, like you said, we are only looking for it not to pass Max temp. So, FTIT is more stable? What engine do you fly with?

 

I wish I could post active T.O. without going to jail. Conversation would be more interesting.

 

I was reading the A10 manual posted here, since this one can be access by everyone, on page 1-3, it talks about this subject. Does this relate to High bypass turbofans only or to other engine as well?

 

 

At any rate thank for the info. Does anyone have photos of the YAK-141 engine? How does it compare to the F135? I looked but can't find that much info, maybe I'm asking Google the wrong questions :D

Edited September 29, 2010 by mvsgas

[hitman]

high bypass. no other turbine is more efficient than high bypass...what else is there? torque producers dont create thrust, and blah...

[zakobi]

Seems Denmark might not buy it now.

[Rhen]

high bypass. no other turbine is more efficient than high bypass...what else is there? torque producers dont create thrust, and blah...

 

Yeah, because so many mach capable fighters use a high bypass turbofan.... no wait! :smilewink:

 

Care to guess again? :smartass:

[hitman]

thats not exactly efficient..the way engines are rated in efficiency is how much heat isnt used for thrust. a jet engine like a low bypass are about 75% efficient, while the latest GE90 high bypass turbofan is 90% efficient. in this case its how much fuel is used to heat up the compressed air. high bypass turbofans produce a LOT more thrust than low bypass engines that dont have an afterburner, which then they consume 500% more fuel too.

[Rhen]

Oh, come on now! Just because I'm a pilot, don't treat me like a no-nothing idiot! :smilewink:

 

Jet engine efficiency can be described several ways:

Cycle efficiency, which is what you're talking about.

Propulsive efficiency, which I'm talking about, is based on how well the thrust of the engine approximates the airspeed of the jet - so a jet flying at M1.3 would have a high propulsive efficient engine if the airspeed of the exhaust equals M1.3 - something a high-bypass turbofan will never ever get to.

Energy efficiency, which is the product of Cycle efficiency x Propulsive efficiency.

 

While high-bypass turbofans might have a high cycle efficiency, they can never be propulsive efficient at high speed. Also, an afterburning section is no longer required to sustain mach speeds.

Edited October 3, 2010 by Rhen

[nscode]

Anyway, the F135; I thought this engine exhaust is based in the MNPK Soyuz R-79, I wonder how similar they are? Anyone got good photos of the Yak-141 engine?

 

hmm.. hard to find. there is some info at the manufacturers web site: http://www.amntksoyuz.ru/engines/airengines/history/#r79v-300/

 

but even there they only show the nozzle. btw, its bypass ratio is 0,81

 

 

edit - here's one:

Edited October 3, 2010 by nscode