Dubai AirShow DAS2017 | Updates And Discussion

[The Eagle]

@Khafee @Taygibay (A fuel transfer after Gs?)

 

[Gomig-21]

@Khafee @Taygibay (A fuel transfer after Gs?)

Do you mean fuel dump? It looks like it but I highly doubt they would allow any fuel dumping during an airshow demonstration. Plus there is no need for it since they limit the fuel load extensively for these show performances. It was probably the SNECMA engine afterburner adjusting to some excess fuel from the pilot aggressively using the afterburner and pushing the throttle back and forth. Maybe some trapped fuel that automatically burns away with the throttle.

 

[The Eagle]

Do you mean fuel dump? It looks like it but I highly doubt they would allow any fuel dumping during an airshow demonstration. Plus there is no need for it since they limit the fuel load extensively for these show performances. It was probably the SNECMA engine afterburner adjusting to some excess fuel from the pilot aggressively using the afterburner and pushing the throttle back and forth. Maybe some trapped fuel that automatically burns away with the throttle.

Yes that burn which is obviously not fuel dump as prohibited and also, they do fly with limited quantity during airshow. Commentator says nothing to worry but fuel transfer after Gs.

 

[Khafee]

Do you mean fuel dump? It looks like it but I highly doubt they would allow any fuel dumping during an airshow demonstration. Plus there is no need for it since they limit the fuel load extensively for these show performances. It was probably the SNECMA engine afterburner adjusting to some excess fuel from the pilot aggressively using the afterburner and pushing the throttle back and forth. Maybe some trapped fuel that automatically burns away with the throttle.

YES!

Yes that burn which is obviously not fuel dump as prohibited and also, they do fly with limited quantity during airshow. Commentator says nothing to worry but fuel transfer after Gs.

YES!

 

[Gomig-21]

Yes that burn which is obviously not fuel dump as prohibited and also, they do fly with limited quantity during airshow. Commentator says nothing to worry but fuel transfer after Gs.

Ah yes, I couldn't hear at first what he said but I stuck my ear right up to my laptop speakers and then I heard what he said and it makes sense now because prior to that happening, the Rafale was performing that terrific negative G pushover and then he said "it's because of the fuel transfer from the negative G" which essentially means the bit of trapped, excess fuel. His use of the word "transfer" was the "non-alarming" way of saying "trapped fuel" lol. Good spot, though.

You can see the negative G pushover the French pilot does prior to that from 35:31 - 35:39.

 

[Taygibay]

Temporary blockage of a post-combustion channel
that pops open is one guess although on the image
one wonders if there isn't a plume from below visible.

I don't think it's anything related to Gs since the fuel
is pumped in under pressure to allow inverted et al.

A hiccup in all cases but nothing spectacularly worrisome
unless it happens with regularity.

Have a good day gang, Tay.

 

[Gomig-21]

Temporary blockage of a post-combustion channel
that pops open is one guess although on the image
one wonders if there isn't a plume from below visible.

Funny you should mention that. There isn't the conventional flaming plume but there is a fuel plume (if that's what you were referring to.) If you look at the still that @The Eagle posted, the fuel plume is probably ignited by the hot flame and gases of the left afterburner as it's shutting down (the right afterburner is a bit delayed in shutting down) but once that fuel flashes, the fuel plume continues for half a second or so. If you watch the video, there is definitely a release of quite a bit of fuel from that left nozzle. From minute 35:46 - 35:48 that fuel plume comes out of the bottom left edge of that left nozzle.

So there might be something to this "fuel transfer" as a result of that negative G maneuver that fella was talking about?

I tried looking for any info on such a procedure from the SNECMA M88 but couldn't find anything beyond all the standard info. Or even something in the nozzle that would show an area where that fuel could be released from, but no luck either, other than some gadgets near the nozzles that don't appear to be part of the flares ejectors (those are in a different area) or any MAWS (those are also different than those two receptacles near the nozzle in the pic below.)

Or to the left of this nozzle in the bottom corner appears to be some type of pipe that might be plumbing for fuel release/dumping.

 

[The Eagle]

Funny you should mention that. There isn't the conventional flaming plume but there is a fuel plume (if that's what you were referring to.) If you look at the still that @The Eagle posted, the fuel plume is probably ignited by the hot flame and gases of the left afterburner as it's shutting down (the right afterburner is a bit delayed in shutting down) but once that fuel flashes, the fuel plume continues for half a second or so. If you watch the video, there is definitely a release of quite a bit of fuel from that left nozzle. From minute 35:46 - 35:48 that fuel plume comes out of the bottom left edge of that left nozzle.

So there might be something to this "fuel transfer" as a result of that negative G maneuver that fella was talking about?

I tried looking for any info on such a procedure from the SNECMA M88 but couldn't find anything beyond all the standard info. Or even something in the nozzle that would show an area where that fuel could be released from, but no luck either, other than some gadgets near the nozzles that don't appear to be part of the flares ejectors (those are in a different area) or any MAWS (those are also different than those two receptacles near the nozzle in the pic below.)

Or to the left of this nozzle in the bottom corner appears to be some type of pipe that might be plumbing for fuel release/dumping.

As per my knowledge only, I will refer to an example here that when you push throttle a lot and so aggressively, then sometimes mechanical engine use to give a spark out of silencer chamber which basically originated by the plugs while having even a dot of dust or such kind of particle. What is being referred to Gs is actually, as per my understanding, it was merely due to extreme push of aircraft not some worrisome thing as @Taygibay mentioned, which actually and rately too I must say, just took out useless particle of fuel mixed with air and all that seems to be happened in combustion.

Side note: (Me feeling of expert here, .... surprised though is just because many of you knowledgeable and experienced personnel and it could be only me wrong on this account).

 

[Gomig-21]

What is being referred to Gs is actually, as per my understanding, it was merely due to extreme push of aircraft

Indeed, but he referred to the aircarft pushing negative G's and not just G's. That's when the moving aircraft is forcing the pilot out of his seat instead of into it. So the aircraft is turning into the direction of its belly. If an AC is flying straight but upsidedown, then it tries to gain altitude, it's creating negative G's like at minutes 35:31 - 35:39. The aircraft's fuel is positioned in its tanks and is subject to gravity even though it is pressurized prior to fuel flow and injection into the combustion chamber. So it's mostly on the bottom side and when it's forced into negative G, the fuel gets pushed to the top side of the tanks and so it makes sense what he said that after the aggressive negative G pushover move, the M88's computer automatically releases some of that fuel & air to restore the balance of the fuel in the tanks that got pushed into the top areas and possibly created unwanted air pockets and pressure from the effects of the negative G.

 

[Taygibay]

OK! An image is worth a thousand words they say, so :

​

At the end of the central channel one sees the post combustion injectors' nozzles
with that radial layout best visible on the previous images. You can imagine the
blockage The Eagle and I referred to in one of the lower left injectors on the left
engine producing this upon release / after clearing up.

The fuel dump is different because one must differentiate what we mean by that.
Fuel dumping as in making the aircraft light enough to land safely is rare and of
course forbidden above a civilian crowd or even ground.
Fuel release as in small quantities of fuel possibly "lost" in the circuits is different.
While the dump is definitive on fuel tanks with the valve staying open afterwards,
there is an electrically controlled plumbing fixture akin to a spigot or faucet on the
fuel circuits of a jet.
This could have been a result of the inverted maneuvers and necessitate a release.
That would come from below left too and follow the fuselage due to the position of
the aircraft and sparked by the normal hot flow into this little firework effect.

A simple view from the rear would solve our problem in deciding which.

Read you soon, good day, Tay.

 

[Gomig-21]

@Khafee @Taygibay (A fuel transfer after Gs?)
View attachment 437298

Saw this yesterday while chatting with someone about the Russian RD33MK engine and I thought of this thread and what we were discussing. This is obviously a different situation but a bit along the same lines and besides, I thought it was a pretty cool pic to share.

 

[Taygibay]

Nice find, Gomig mate but that one could be a ground trial.
The starboard engine doesn't seem to function at all?
And the guy in front of the port motor might be an engineer?

So a full reheat test with a tire stop only on the left, brakes on?

What do you think?

Have a great day, Tay.

 

[Gomig-21]

Nice find, Gomig mate but that one could be a ground trial.
The starboard engine doesn't seem to function at all?
And the guy in front of the port motor might be an engineer?

So a full reheat test with a tire stop only on the left, brakes on?

What do you think?

Have a great day, Tay.

I think this is called "Russian Engine Start-up"! lol

So after the left engine has starter, the right one starts the same way, Russian style!

I think what's happening here is we're seeing "manual" startups of the two engines because the left (or port) engine is starting first, then the right (or starboard as you mentioned.) With automatic engine startups, the APU calls for the right engine to start up first, at least this is what the MiG-29 start-up brochures indicate.

As far as the flameouts, I think it's common with these Russian engines on manual start-ups. The APU drives the engines between 35% to 50% RPM until they can be ignited. Once the pilot pushes down the start button and depresses it, that bit of fuel that's injected into the engine under pressure creates that flameout once the engine is ignited, probably the result of fuel and excessive fumes building up prior to being ignited. Then the other engine starts up the same way and the gearbox synchronizes both engines. At least this is how I understand it.

Reminds me of a 4-barrel carburetor, when fuel is being dumped into it at startup and the linkage is stuck and not opening the choke to let in air, so fuel builds up in the carb until the linkage frees up and you get a slight "boom" and flameout in the carb, then engine starts up.

In this video of a Malaysian Su-30MKM, you can see both engines ignite exactly that way with each one flaming out. Left engine @ 1:15 and right one @ 1:54. You can hear the turbines turning and reaching that certain RPM percentage before igniting and then they're put in idle by the gearbox until they're ready to taxi.

 

[Gomig-21]

@Taygibay , I don't know if you've seen this video before, but related to our discussion here, and speaking of Russians, check out what happens with this MiG-31 and even at the end with the photographer just nonchalantly filming all the spewing fuel.