Variable intake ramp(s) (questions)

[ValhallaAB]

Hello!

I never seen or knew that this mechanic actually had a model/visual difference in DCS. Just amazing...

My questions are now: If the P&W-TF-30 engines made it necessary to diffuse the air into slower meals for the engine to reduce damage to the engine face etc, why does the F-110 GE-400 engines need it, is it just safer and not necessary to remove? Would I be wrong in saying the F-110 has a much stronger ''face'' that the engine simply could have ignored this system?

 

The F-16 has used practically the same engine but doesn't have these ramps, is it because the F-16 simply uses a different solution or never was intended to fly that fast? (solutions like a submerged intake or a twin curved intake, etc)

[BreaKKer]

For the F-16 comment, this article should answer your question. 

Perhaps someone more knowledgeable in aerodynamics could chime in on the F110 ramp question. From my understanding, supersonic air is not great to have go through your intakes, due to the shockwaves generated, which can cause you to chuck compressor blades. Even the F-15EX of today with it's fancy engines still use intake ramps to diffuse the air coming into the intake.

Edited February 1, 2023 by BreaKKer

[RustBelt]

3 hours ago, BreaKKer said:

For the F-16 comment, this article should answer your question. 

Perhaps someone more knowledgeable in aerodynamics could chime in on the F110 ramp question. From my understanding, supersonic air is not great to have go through your intakes, due to the shockwaves generated, which can cause you to chuck compressor blades. Even the F-15EX of today with it's fancy engines still use intake ramps to diffuse the air coming into the intake.

 

You must slow air to subsonic speed for any jet. For passenger aircraft this is done by the simple converging/diverging intake duct, because even though they only go about M0.8 the intake air can become transonic in the fan and compressors. Shockwaves in the Compressor is bad BAD news. 

Even the SR-71 had to slow its intake air to subsonic speed before it got to the compressor. The nose cones sticking out the front of the engine moved in and out to adjust the shockwave, as well as dump doors along the intake allowed for over pressure to be released. 

The TF-30 was more picky about intake flow direction due to Angle of Attack. It was never meant to be in such a big wide honker of an intake, and instead preferred the kind of duct you see on the F-111. So high AoA coming into the intake made the TF-30 extra angry. 

[stuart666]

1 hour ago, RustBelt said:

You must slow air to subsonic speed for any jet. For passenger aircraft this is done by the simple converging/diverging intake duct, because even though they only go about M0.8 the intake air can become transonic in the fan and compressors. Shockwaves in the Compressor is bad BAD news. 

Even the SR-71 had to slow its intake air to subsonic speed before it got to the compressor. The nose cones sticking out the front of the engine moved in and out to adjust the shockwave, as well as dump doors along the intake allowed for over pressure to be released. 

The TF-30 was more picky about intake flow direction due to Angle of Attack. It was never meant to be in such a big wide honker of an intake, and instead preferred the kind of duct you see on the F-111. So high AoA coming into the intake made the TF-30 extra angry. 

And even then it had unstarts, or compresser stalls as I guess they probably were. There is a remarkable bit in the Ben Rich book talking about how they had dangerous unstarts in flight, so they finally figured out that, rather than fix the problem, they just automatically dropped the opposite engine thrust by a similar amount, and then the pilot could press autostart the unstarted engine.

Didnt always work though...

https://www.historynet.com/unstart-over-murmansk/

[The_Tau]

3 hours ago, RustBelt said:

The TF-30 was more picky about intake flow direction due to Angle of Attack. It was never meant to be in such a big wide honker of an intake, and instead preferred the kind of duct you see on the F-111. So high AoA coming into the intake made the TF-30 extra angry. 

TF30 at F14 introduction was always seen as "5 years tops" solution. Grumman knew TF30s were horrible choice but thats what Navy wanted and paid for. But they designed F-14 in a way that it was easy to do engine upgrade on it. Too bad USN waited 12 years to actually fund the thing though. If only USMC stick to original F-14 procurement plans... 

[ValhallaAB]

2 hours ago, The_Tau said:

TF30 at F14 introduction was always seen as "5 years tops" solution. Grumman knew TF30s were horrible choice but thats what Navy wanted and paid for. But they designed F-14 in a way that it was easy to do engine upgrade on it. Too bad USN waited 12 years to actually fund the thing though. If only USMC stick to original F-14 procurement plans... 

What were the differences in the USMC plan if they invested early? I know very little of this. I am guessing Grumman had a problem with budgets and sale orders until the Iranian sale made it possible to continue alot better. 

[DD_Fenrir]

F-14 was slated to replace the F-4 in Marine service - so in some regard you can thank the Marines for the Ground Attack options on the RIOs Armament Panel cos they were gonna use it as a fighter bomber!

That was going to mean lots of extra $$$ for Grumman. Then the rug got pulled and suddenly Grumman were in a financial crisis... the sale of F-14s to Iran bailed  Grumman out of a real bad situation financially.

[LanceCriminal86]

The problem with the TF-30 replacement was that it was tied with the Air Force's F100 program, which itself was having issues. When reliability couldn't meet what was specified the Air Force apparently lowered the required hours, but the Navy wouldn't accept it. So the Air Force pressed on with the F100 in the F-15A which had its own issues, and the Navy kept the TF-30 as the Tomcat program was already under heavy scrutiny and embattled and I guess the Navy wasn't about to start over again trying to get a new engine.

The proposed F100 based engines (F401) would, on paper, have had almost the same uninstalled numbers as the GE F110 at 16.5K dry in Mil and 28k in AB. But looking at how much the Air Force had to deal with before their F100s were improved by the 80s in the F-100-PW-200 and later 220 updates. It's funny how much <profanity> is talked about the F-14s engines while the Air Force was dealing with almost the same issues in the Eagle, including the afterburners stalling the engine out, and didn't have a "fix" until the early-mid 80s themselves. But in that light had we gotten the F401s for the F-14, there's a decent chance it would have had the same problems. However, the same remedies for the Air Force could likely have been applied as those updates to the F100 could be applied to existing engines, and the Navy would have been updating F401s instead of having to find another motor.

[lunaticfringe]

Also important to keep in mind- there was a two-plus year period where excess F100s couldn't be had for all the money in the world.  Production was so slow that the USAF was receiving brand new F-15s off the line in St. Louis, performing expedited acceptance, flying them out to recipient commands, and immediately having the engines pulled and trucked back to McDonnell.  Now throw the F-14's production volume on top of that.  

It took years of F100 and F-15 production to get everything stabilized.  Adding the Tomcat, even without the F100s own teething issues, would have left both services without viable numbers of airframes.  So, TF30 it was. 

[cheezit]

What kills me is that the F101-DFE experiment started in 1980 or 1981, did some test flights demonstrating mil-power cat shots and limited supercruise, then immediately got shelved for something like six years until it was restarted as the F110 project that eventually was used in the F-16 '0' blocks, F-14B/D, export F-15s, etc.  The whole thing probably could have been done much sooner if it weren't for the fiscal pressure on the program in that particular year, and the recent failure of the Navy's part in the ATE/P&W F100 program.

 

This is the same timeframe when the Navy dramatically reduced planned purchases of spares for the F-14 in a penny-wise/pound-foolish attempt to save money.  I don't know if I can pull it up now but there was a Q&A segment of one of the defense appropriations hearings transcripts where the Navy either demonstrated complete ineptitude or lied through their teeth to Congress about the long-term costs of purposefully not buying enough spares.

[Raisuli]

5 hours ago, LanceCriminal86 said:

<snip>

It's funny how much <profanity> is talked about the F-14s engines while the Air Force was dealing with almost the same issues in the Eagle, including the afterburners stalling the engine out, and didn't have a "fix" until the early-mid 80s themselves.

<snip>

I wasn't in the Air Force back then, but it's interesting how much <profanity> I heard second hand about the TF30 without anyone bothering to explain the reasoning behind the decision to use them.  It's really amazing how much I've learned around here, because those decisions were so 'obviously' stupid at the time, but the people making them weren't. 

Something didn't add up.

Absolutely ridiculous how much knowledge is on these boards.  Thanks for all that!

[ValhallaAB]

Yes, thank you all very much for your input, it has been very interesting, If you want do discuss more engine history, corruption, decisions, feel free to continue but if somebody says: STAY ON TOPIC, it wasn't me who made that decision. I could do this all day so please feel free to continue in this thread (or ask for a new thread if you feel it's necessary). 

[Whiskey11]

23 hours ago, BreaKKer said:

For the F-16 comment, this article should answer your question. 

Perhaps someone more knowledgeable in aerodynamics could chime in on the F110 ramp question. From my understanding, supersonic air is not great to have go through your intakes, due to the shockwaves generated, which can cause you to chuck compressor blades. Even the F-15EX of today with it's fancy engines still use intake ramps to diffuse the air coming into the intake.

 

It is my understanding the GE F110's had different intake ramp scheduling to accommodate the air intake requirements of the engine.  In doing so they optimized airflow for better transonic performance.  I'm not sure why they couldn't do "it all" given they were programable.  Maybe lack of space for the code to accomplish it.  The claim is the Mach 1.88 "top speed" of the B and D is because of safety issues with an engine failure.  My guess is the risk of engine flameout increased drastically due to airflow in the intake not slowing down enough at high Mach. 

[r4y30n]

Getting back to OP, check out the position of the 3rd ramp (the furthest back) the F-14A vs B at subsonic speeds. The bypass slot is a lot bigger on the TF-30 because, as mentioned by others, the intake was oversized for that engine.

And, to be more clear about the ramp function, yes, the goal is to slow the air to subsonic speed so the engine can function but it’s important to note that slowing the air increases pressure, which is good for power. And compression via shock wave is far more efficient than doing it in the engine. That’s why ramjets and scramjets can reach such high speeds, they rely entirely on shock compression.

It’s another one of those things that’s technically ideal but adds expense, complication and weight to the platform, kinda like the wing sweep system.

[ValhallaAB]

3 hours ago, r4y30n said:

Getting back to OP, check out the position of the 3rd ramp (the furthest back) the F-14A vs B at subsonic speeds. The bypass slot is a lot bigger on the TF-30 because, as mentioned by others, the intake was oversized for that engine.

And, to be more clear about the ramp function, yes, the goal is to slow the air to subsonic speed so the engine can function but it’s important to note that slowing the air increases pressure, which is good for power. And compression via shock wave is far more efficient than doing it in the engine. That’s why ramjets and scramjets can reach such high speeds, they rely entirely on shock compression.

I need to check that position on the 3rd ramp.

Does the F-14 ramp system + engine just form a kind of ramjet engine but with a compressor face and blades lol, really cool similarities.

Compressed air on the ramps must then form higher pressure and thus reduce the use of the compressor stage in the engine and thus reducing fuel consumption or fuel flow right? Fuel per mile must then be very high, high up that is. 

I recently read that the engine ramps could over-collapse to make the intake as open as can be to make landing and takeoff easier. 

[RustBelt]

No the denser air means you can pack it even MORE! Meaning more fuel, meaning more THRUST! 
 

The Tomcat isn’t RamJetting. It’s not at all fast enough for that. As well as there being an engine in the way. The spill is there to prevent that. 

Otherwise you end up like the MiG25s that can basically send so much dense air down its gullet it overheats due to how much gas it can burn and how fast hot and hard it’s blasting the turbine. Goes wicked fast, but the engine becomes a consumable. 
 

For hybrid ramjets you need a bypass system that routs air around the engine core and then throws it through the afterburner. Which because the core isn’t doing the work, means you need a different fuel control system to match afterburner fuel flow to throughput density. 

[r4y30n]

Compressed air on the ramps must then form higher pressure and thus reduce the use of the compressor stage in the engine and thus reducing fuel consumption or fuel flow right? Fuel per mile must then be very high, high up that is. 

In a sense, the engine compressor doesn’t know the ramps are there. It just multiplies whatever pressure is coming in by its overall pressure ratio, about 20:1 in the TF-30 and about 30:1 in the F110.

[ValhallaAB]

3 hours ago, r4y30n said:

In a sense, the engine compressor doesn’t know the ramps are there. It just multiplies whatever pressure is coming in by its overall pressure ratio, about 20:1 in the TF-30 and about 30:1 in the F110.

Yeah, that is better worded. The overall HP bypass on the TF-30 is 18-1 and 31-1 on the F110 from what I read, not that it makes huge difference from your words. 

I also read that the F110 GE-400 had a 32% higher thrust and it's lean fuel burn rate makes the jet CAP loiter time 34% higher, it's radius in MIL power increased it's mission radius to 62% and it's time to high altitude by a whopping 61%. 

[WarthogOsl]

I've wondered....did the F110 powered F-14's even need the ramps?  Given that it was limited to less than Mach 2.0 anyway, why didn't they just fix the ramps or remove them (and the associated actuator hardware)?  Having a fixed inlet doesn't seem to have hurt the 110 powered F-16s.

[Nealius]

16 minutes ago, WarthogOsl said:

Having a fixed inlet doesn't seem to have hurt the 110 powered F-16s.

It's my understanding that the curve in the F-16's intake serves the purpose of the F-14's intake ramps. Could be wrong, though.

[Naquaii]

7 hours ago, WarthogOsl said:

I've wondered....did the F110 powered F-14's even need the ramps?  Given that it was limited to less than Mach 2.0 anyway, why didn't they just fix the ramps or remove them (and the associated actuator hardware)?  Having a fixed inlet doesn't seem to have hurt the 110 powered F-16s.

You can't draw direct comparisons between the F-16 and F-14 like that. The F110 absolutely had them.

[WarthogOsl]

6 hours ago, Naquaii said:

You can't draw direct comparisons between the F-16 and F-14 like that. The F110 absolutely had them.

Sorry....the F110 had what?

[Naquaii]

1 minute ago, WarthogOsl said:

Sorry....the F110 had what?

The F-14 F110 had variable intake ramps. As per the thread subject.

[WarthogOsl]

51 minutes ago, Naquaii said:

The F-14 F110 had variable intake ramps. As per the thread subject.

Yeah wasn't saying it didn't.  Just speculating whether it actually needed variable ones.  For example, if the money were available, could they have shaped the inside of the intake so as not to require them, saving some weight and maintenance issues.

Edited February 4, 2023 by WarthogOsl

[Lurker]

14 hours ago, WarthogOsl said:

I've wondered....did the F110 powered F-14's even need the ramps?  Given that it was limited to less than Mach 2.0 anyway, why didn't they just fix the ramps or remove them (and the associated actuator hardware)?  Having a fixed inlet doesn't seem to have hurt the 110 powered F-16s.

Just because the F16 didn't have variable intake ramps doesn't mean it didn't deal with the supersonic air in another manner. 

https://en.wikipedia.org/wiki/Diverterless_supersonic_inlet