Posts about: "Flameout" [Posts: 9 Page: 1 of 1]¶

Hi Stilton, that is a question that we all used to ask ourselves; not having an APU was a major pain in the butt for the fleet, particularly at charter destinations, where air start trucks, GPU's and air conditioning trucks would all have to be pre-arranged.
One problem with 'Conc' was always one of weight, (for every extra pound you carried, another pound of fuel was required) so any APU installation would have to have been light, and worth the extra weight. But the main problem was one of 'where to put the darned thing. The only suitable space available for an APU was in the tailcone, aft of the tail wheel. Now a ready supply of fuel would have been available either from the aft trim tank, #11, or from one of the two trim galleries. (For stability reasons, tank 11 was invariably left empty during ground transits). The real crunch however, was how to arrange pneumatic services from an APU: Tank 11 was directly forward of the tailcone, so this would have meant either ducting the pneumatics THROUGH the fuel tank (not a particularly good idea ) or externally around the fuselage, which would have been 'draggy' to say the least.
You could still have had an APU powering hydraulics, and in essence electrics too (the emergency generator was powered from the Green System), but without pneumatics for engine starting and air conditioning, it would really have been a waste of weight. Still, it really is a shame that there was no APU.
Historically, there were 'sort of' aux power units fitted to development aircraft: The prototypes had two GTS's (Gas Turbine Starters), one in each nacelle pair, that could start the engines without an air start truck, but these never saw the light of day in later aircraft. The most unusual unit of all was the MEPU (Monogol Emergency Power Unit), located in the tail cone. This was manufactured by Sundstrand, and was fitted to all of the development aircraft. (A derivation of a unit fitted to the X-15!!). The idea was that if you had a four-engined flameout at Mach 2, this thing would fire up, power Green and Yellow hydraulics (plus the emergency generator, again from the Green system), and give you power and control down to a safe relight altitude. The MEPU was powered by Hydrazine rocket fuel (unbelievably unstable) and I seem to remember that the thing would run for about 8 minutes. There was no way that this monstrosity would ever be acceptable on a commercial aircraft, and so a conventional RAT was developed by Dowty for the production aircraft. (Also, the windmilling engines would give you full electrics down to Mach 1.1, and Hydraulics down to about Mach 0.7, so the thing had little practical use when supersonic anyway).
I hope this extended blurb helps answer your query Stilton.

Yes, M2dude , but how long could you remain above M1.1 with a four-engine flameout while drifting down? I presume you would driftdown above M0.7. BTW, the RAT on the F-16 is hydrazine powered as was the ME 162 rocket interceptor.

M2dude

Thanks for the reply, Concorde expertise is always interesting. I should not have called the F-16 Emergency Power Unit a RAT, it is indeed not. The Concorde RAT was located aft between the engine pods, correct?

What I found interesting is that the AC generators would remain on-line at all; they drop instantaneously at subsonic speeds and the associated N2 rpm. I believe the hydraulics on the 747 will power flight controls down to a pretty low IAS.

Four engine flameout is a very unlikely event, unless one runs into a volcanic cloud.

Hi M2Dude - keep it coming! I missed all this stuff from the early days......

Tim00 - good question, and very relevant.

It takes a lot to incapacitate a Flight Engineer - beer, cigars and scary women were no issue - they were definitely the most relaible part of the operation. (And arguably the least attractive.....)

If the unthinkable happened the First Officer would find himself on the FE's seat. We practised it less often than you might think, but thought about it a great deal. Especially the fuel system management.

Which brings me to your second point - yes, there was a preset for the 'automatic' fuel transfer system, although that wasn't the mechanism used for the pilots to 'take control' of the CG. The critical thing was to be able to get the CG forward if a rapid decel had to be made - for this reason there was an override switch above the First Officer which used various pumps and valves to txfr fwds - primarily by txfring from tank 11. It would be used in various recall checklists (supersonic 4-engine flameout and Continuous Ssurge at M>1.3 seem to register from the dim past) until the FE was able to take over the txfr system himself.

I didn't ever need it - in the surges I encountered the FE was always ready to manage the txfr before we needed the override.

Oooooooh!!!! There's a new topic for someone: Surges.

Theoretically the correct checklist to call for was the "Continuous Engine surge above M 1.3 Conditional Procedure, please". In reality the call was always much more succinct.

Monosyllabic, in fact................

I'm off to the pub, but I bet Bellerophon can speak with erudition on the operational aspects, and if M2Dude is who I suspect he is, I KNOW he'll be able to cover the technical aspects in great depth!

WOK

The deceleration would be like very hard braking after landing, so - yes.

The drag incurred flying supersonic was once described to me as like flying through wood, not air. The only times I ever closed all 4 throttles at M2 was dealing with surges (see earlier posts on the subject). While not quite like flying into teak, the decel was very impressive - it more than once resulted in a member of cabin crew appearing in the flt deck in a semi-seated position, grimly trying to stop a fully loaded galley cart.......

As for four-engine flameouts - perish the thought. The checklists, like many, depended on flight phase;

Above M1.2 it was expected that windmilling would provide adequate eletric and hydraulic power so the c/list aimed to start a fuel txfr forward, use the spare hydraulic system to drive half the PFCUs, ensure a fuel supply to the engs and ensure cooling to equipment.

Below M1.2 the RAT would be deployed, it was less likely that the standard means of fuel txfr would work so valves were overridden and the hydraulic fuel pumps brought into use, and the Mach fell further the PFCUs were put on half-body use only, using the stby hydraulic system.

You weren't far from the ground, in time, at this stage so it was a good time to get an engine relit!

Given the Olympus' auto-relight capability a four engine loss was going to be caused by something fairly drastic.

Mr Vortex
Not quite; remember that the N1s and N2s in the E SCHEDULE graph are non-dimentional. ie. they vary with temperature. As the temperature rises (with increasing Mach Number) the scheduled spool speeds increase. What really happens (I did not explain it correctly first time) is that the much lower N1 demanded by the use of E LOW at high speed results in a much further closed primary nozzle than normal, pushing up TET (and EGT) and we run hard into the EGT limiter, which claws fuel flow off, to the extent that the ramps and spill doors come down to their preset limits, almost as if there is a flame-out. The net result is a huge reduction in thrust. The condi was formed as the primary nozzle naturally took up a near fully open position in supersonic cruise and the wide open secondary nozzle buckets completed the picture. The schedule used here was E HIGH. I've noticed a couple of errors on the graph, the main one being that E HIGH is used with reheat off but with Vc > 220 KIAS
Apart from being set as a variable limit, EGT normally played no role in the control loops (there were 2 loops, the 'governor' and 'positioner' loops). P7 played no part whatsoever in any case, the main variables were; N2, throttle valve position, throttle transmitter position, T1, total pressure and static temperature..

Feathers McGraw
Oh nooooo... I've been outed
Best regards

Dude

The "venom" is in the tail of your question.....
Best glide angle for Concorde is in the order of 1:10, so with an multiple failure at 40,000ft (7.5 miles) your "nearest airport" would have to be well within a distance of 75 miles.
(BTW, I think somebody earlier already mentioned that a large part of the actual descent from top-of-descent was with the engines barely above idle, so that it was much like a glide. It was during the final hold, approach and landing, that it was preferable to have a few engines left.....)

Four-engine surges have happened a few times during flight testing, but I don't think there ever has been a four-engine flameout.

Re the SAAB Draken, I would think a dead-stick landing would be possible, but only IF you could arrive 'overhead' at about 10,000ft and IF you were well aware of the horrendous sink rate 'on the back of the drag curve' once you committed to the final approach and landing.
Even the F-104G, not known for its gliding qualities, could be and has been landed dead-stick - there is a section on the subject in the flight manual. On the 104, things were further complicated by the fact that without an engine you also lost the "blown flaps", so your landing speed was a lot higher.

In Western Europe, with its densely populated areas on the one hand, and a lot of airbases on the other hand, there were certainly cases where you thought twice before 'punching out'.

CJ

Hah.

I'm pretty sure my memory isn't betraying me too far when I say I seem to remember a case, in the dim and distant past, of a management pilot (no less) taking a Concorde sector and... mismanaging things... badly. In fact they came so close to a four engine flameout (with no volcanic cloud in sight) that the thing was unable to be disembarked after landing for... CoG reasons... if you take my meaning!

Someone confirm?

R1

Thanks for the reply, Concorde expertise is always interesting. I should not have called the F-16 Emergency Power Unit a RAT, it is indeed not. The Concorde RAT was located aft between the engine pods, correct?

What I found interesting is that the AC generators would remain on-line at all; they drop instantaneously at subsonic speeds and the associated N2 rpm. I believe the hydraulics on the 747 will power flight controls down to a pretty low IAS.

Four engine flameout is a very unlikely event, unless one runs into a volcanic cloud.