Today I learned... (inverted flight)

[Lace]

The Mud Hen doesn't like sustained inverted flight.  Around 10 seconds to double engine flameout at 300ft made for an interesting end to that particular sortie.  I guess that's one reason the Thunderbirds use Vipers.

[veggy432]

did the same yesterday!! ahaha funny! fortunately I managed to restart the engines during the glide... cool stuff! maybe there are some boost pumps that need to be activated to allow inverted flying, just guessing!

[Mr_Blastman]

This begs the question... what is the manual engine restart procedure in flight?  I had this happen yesterday but could not crank the engines like I would in the Viper...

 

[sirrah]

Just wondering; is this correct behavior, or simply part of EA WIP?

And if it is realistic, is this related to the CFT's on the Mudhen, or do the albino's suffer from the same? Although other than for airshows, sustained inverted flight might not be actually usefull, still I find it kind of odd for a "modern-ish" fighter jet, not being able to do this.

[GGTharos]

It is correct behavior, and it applies to most jets.

[sirrah]

2 hours ago, GGTharos said:

It is correct behavior, and it applies to most jets.

Ah ok, I see

Only familiar (also irl) with the F-16, so I suppose I was a bit "spoiled" then

 

[Holbeach]

The engine is fed with oil to the pump by gravity, therefore without gravity it doesn't get fed and will go bang.

!0 secs max is neg G limit. (Same as a RR Merlin and for the same reason)

..

Edited August 23, 2023 by Holbeach

[Swift.]

7 hours ago, sirrah said:

Just wondering; is this correct behavior, or simply part of EA WIP?

And if it is realistic, is this related to the CFT's on the Mudhen, or do the albino's suffer from the same? Although other than for airshows, sustained inverted flight might not be actually usefull, still I find it kind of odd for a "modern-ish" fighter jet, not being able to do this.

Most fighters cant sustain negative G. As Holbeach mentioned, the engines are gravity fed oil. Which is fine because negative Gs hurt the pilot so its not something that will be done often.

[sirrah]

4 hours ago, Holbeach said:

The engine is fed with oil to the pump by gravity, therefore without gravity it doesn't get fed and will go bang.

!0 secs max is neg G limit. (Same as a RR Merlin and for the same reason)

..

 

Ah that makes sense. Thanks for clarifying  

I was only thinking about fuel (and at least in the Viper with its siphoning system, inverted flight shouldn't be an issue), but I didn't consider engine oil feed limitations.

In my defense, I was an airframe bloke back in my RNLAF days. Apart from removal and installation we didn't do anything with the engines

 

@Swift.; I know, the human in the jet, as usual, is the limiting factor . I was just a bit surprised about the mechanical aspect.

 

So, when flying inverted for over 10sec in negative G, the engines are cut off automatically as a safety measure, to prevent them from running dry (oil wise) and overheating the bearings? Did I understand that correctly?

Or will the bearings already have run dry by then, resulting in major damage/engine fail?

Edited August 23, 2023 by sirrah

[Theodore42]

When I was a kid in the '90s, probably not even 10, I went to an airshow and saw the most amazing thing: An F-15C do a high-G NEGATIVE turn, for real. I'll never forget it because I couldn't imagine something so painful.

Does the F-15C have this restriction? Doesn't it take more than 10 seconds to do 360 degrees in an F-15C at negative 6Gs? I've always wondered about that because I haven't found documentation for a negative high-G turn during a demo, nor have I found any airshow videos of the maneuver.

[Rainmaker]

Its all a bunch/game of hypotheticals, but it also keeps people from being able to do dumb stuff. No different than mach limits, G limits, etc. Like it or hate it, but there is some essence of attempting to implement some realism into to things and not allowing the jet to be flown as if it was confined to the same limits of an aircraft in Ace Combat or whatever flavor of an ‘arcade’ title you want to choose as an example. 

[Theodore42]

1 minute ago, Rainmaker said:

Its all a bunch/game of hypotheticals, but it also keeps people from being able to do dumb stuff.

Ok so maybe they added an automatic cutoff making the high negative-G turn impossible which is why I haven't seen it since the '90s.

[Rainmaker]

3 minutes ago, Theodore42 said:

When I was a kid in the '90s, probably not even 10, I went to an airshow and saw the most amazing thing: An F-15C do a high-G NEGATIVE turn, for real. I'll never forget it because I couldn't imagine something so painful.

Does the F-15C have this restriction? Doesn't it take more than 10 seconds to do 360 degrees in an F-15C at negative 6Gs? I've always wondered about that because I haven't found documentation for a negative high-G turn during a demo, nor have I found any airshow videos of the maneuver.

Would be willing to bet there are some inaccuracies to what you recall TBH. There is definitely not going to be anything done ‘high G’ in a negative G sense.  And the turn circle of what could be tolerated BY ANYONE doing negative g’s would be in the 10s of miles wide and not anything capable at an airshow. 

[Rudel_chw]

From the manual of the real F-15E:

"Baffles in the feed tanks provide limited fuel supply for the left and right main boost pumps during negative g or inverted flight."

and

"NEGATIVE G FLIGHT 

Negative g flight is limited to 10 seconds at all power settings,"

[GGTharos]

4 hours ago, Theodore42 said:

When I was a kid in the '90s, probably not even 10, I went to an airshow and saw the most amazing thing: An F-15C do a high-G NEGATIVE turn, for real. I'll never forget it because I couldn't imagine something so painful.

Does the F-15C have this restriction? Doesn't it take more than 10 seconds to do 360 degrees in an F-15C at negative 6Gs? I've always wondered about that because I haven't found documentation for a negative high-G turn during a demo, nor have I found any airshow videos of the maneuver.

You didn't see what you think you saw.  The F-15 airframe is -3g rated and they're not going to exceed that in an airshow, nor are they going to fly something they don't train, which is -gz.  I don't know where you got -6G.  

[Rudel_chw]

4 hours ago, Theodore42 said:

Does the F-15C have this restriction?

yes, exactly the same: no more than 10 sec of negative G

[Nealius]

Just for additional information, demonstration teams like the Thunderbirds and Blue Angels do modifications to allow longer periods of inverted flight.

[sirrah]

8 hours ago, Theodore42 said:

When I was a kid in the '90s, probably not even 10, I went to an airshow and saw the most amazing thing: An F-15C do a high-G NEGATIVE turn, for real. I'll never forget it because I couldn't imagine something so painful.

Does the F-15C have this restriction? Doesn't it take more than 10 seconds to do 360 degrees in an F-15C at negative 6Gs? I've always wondered about that because I haven't found documentation for a negative high-G turn during a demo, nor have I found any airshow videos of the maneuver.

Are you sure it was an Eagle? Considering you were young, could it perhaps be that you saw a different aircraft type with a false canopy painted on it, like this:

I've been to many airshows in my life and negative G turns are quite common during airshows, yet I've never seen a "high" negative G turn.

[Kercheiz]

It's a fuel issue, too, in most jets.

The fuel pump(s) are designed to work in negative G conditions, and have a small fuel buffer for this (mini feeders). But said fuel buffer has a limited capacity of a couple of seconds depending on fuel rate. Past this, feeding from the main fuel tanks to the mini feeders is generally not possible.

Designing the fuel tanks for sustained negative G flight is possible, but adds complexity and is fully useless besides air shows. And useless complexity is bad.

I don't know the F-15E specifics, though.

Edited August 24, 2023 by Kercheiz

[Hazardpro]

What's simulated in the game seems much more like fuel starvation than oil. 

[GGTharos]

Because it is fuel starvation.  The engine feed tanks are not designed to feed the engines for all (-gz) conditions.

[Theodore42]

16 hours ago, GGTharos said:

You didn't see what you think you saw.  The F-15 airframe is -3g rated and they're not going to exceed that in an airshow, nor are they going to fly something they don't train, which is -gz.  I don't know where you got -6G.  

ok. I may have conflated -6Gs from a prop plane demo at that airshow with the F-15C demo. That would make sense because at that age I was only interested in the military aircraft but I surly would have noticed anyone doing high negative-G maneuvers. And those prop pilots do some insane negative-G work.

I've looked for any negative G maneuvers in US military airshows and never found anything other than inverted flight.

Edited August 24, 2023 by Theodore42

[Rainmaker]

5 hours ago, Hazardpro said:

What's simulated in the game seems much more like fuel starvation than oil. 

Fuel/oil…it can all be problematic. In the state its in, you have a chance for recovery vs bearing seizing for example, which could be catastrophic.  Same as over-g modeling (stressing the wing tip vs flat ripping the wing off).  There was some actual forethought put into what could be considered ‘fair’ from a gameplay perspective when limits get exceeded.   

[GGTharos]

1 hour ago, Theodore42 said:

I've looked for any negative G maneuvers in US military airshows and never found anything other than inverted flight.

-gz are not useful.  They will destroy your +gz tolerance as well ... keep the gz positive.

[Rainmaker]

I can invite you to go fwd and lat stick in both the C and the E in DCS and see what awaits you.   Can assure you it doesnt turn out well. Haha.