Best Aero Engines

WD and Vortex – thanks for some really helpful stuff. I can’t admit to understanding all of it just yet but I’m working on it!

Vortex, I spent a fair bit of time today looking further into the shaft protection thing in the books. Sensors monitor fan speed compared to LP shaft speed. If the fan speed is slower than the shaft speed then the fadecs read this as a sheared shaft and will auto-shutdown the engine. Unfortunately the system seems to be prone to sensor faults.

thanks for the reply. As to the EPR…the reason i’ve said i see no problem is very simple actually. I think you have two questions there…1)why would you still have thrust, 2) why does the engine keep on flying since pressure in the rear is higher and flow goes “backward”. The first one is very easy to explain, one simply look at the thrust equation and realize that it’s based on the pressure “force” difference (integrated over the area on each face) and the velocity difference. So, even if the pressure force difference is the same, you still have the momemtum (velocity) part. Also, notice that if the areas are not the same, the pressure force is actually different for the EPR=1! So, there’s two answers to part 1. Part 2 is a little bit more complicated, but basically Whiskey Delta was on the right track. Right at the engine exhaust were the measurements were made, the engine air over expanded…this can easily be the case when the air coming in is dense and high pressure while the jet going out overexpands and hot, making the “STATIC” pressure lower than the ambient. If the static pressure is lower than the initial static pressure (which at zero velocity is considered as total pressure), this situation is call over expansion. In this case you would have EPR<1. I think in higher thrust settings this is less likely in high BPR fans since the core jet is mixed signifcantly with the bypass, while in turbojets or low BPR and variable converging-diverging nozzles as in fighter planes, this should be quite common even at high settings…if the pressure measurement is near the engine exhausts. Notice that the RB211 is a three spool engine, so i would assume it’s parameters are quite different if you want to compare them to GE and PW counterparts. Also notice that RR engines tends to duct the bypass with the core while GE and PWs tend to (if not all) dump the bypass directly. Each have their rationale….

Now If I was in a 752 at FL470 doing its typical cruise speed of M.795 and set the EPR to 1.03 I’d be going down at a couple of thousand feet per minute!

I would call that a stall……. 😀 😀 😀 😀

There is a formula for EPR in the link I provided above. I don’t think that a thrust to drag ratio is a good way of putting it though.

Further to the EPR thing –

With both aircraft at MTOW the B752 and the A346 have similar power to weight ratios (I mention this purely to show that neither is underpowered). Today I have just flown a 346 in the cruise across the pond at FL370 and M.83 with the autothrust commanding a target EPR of 1.03. Now If I was in a 752 at FL370 doing its typical cruise speed of M.795 and set the EPR to 1.03 I’d be going down at a couple of thousand feet per minute!

My assumption (which correlates nicely with RB211 operation but not with the Trent) had always been that an EPR of 1.0 represented an engine producing as much thrust as it is producing drag. More than 1.0 meant that thrust was winning the battle and less than 1.0 meant drag was the winner.

Vortex, I spent a fair bit of time today looking further into the shaft protection thing in the books. Sensors monitor fan speed compared to LP shaft speed. If the fan speed is slower than the shaft speed then the fadecs read this as a sheared shaft and will auto-shutdown the engine. Unfortunately the system seems to be prone to sensor faults.

(Edited to correct FL470 to FL370)

My vote as well is for the RR

cant beat the the Mighty RR Merlin, what a beatiful noise this makes ,as for Jets again my vote is for the RR RB211

Kevin

Personally?
The Textron Lycoming O-540-F1B5

That baby just keeps going and going…..kept me dry so far!!

Personally I think Rolls-Royce engines are the best. For me, I find it slightly comforting to look out of an aircrafts window and see the Rolls-Royce badge looking at me. On a development note, has anyone ever seen the turbofan they developed with variable pitch fan blades? If I remember correctly, it was designed to cut down noise for inner-city airports but I guess was shelved. A company called Renishaw used to have the engine in their plant, but I am not sure if it is still there.

Was that the engine originally under develpment for the MD-90 when it was being conceived?

Personally I think Rolls-Royce engines are the best. For me, I find it slightly comforting to look out of an aircrafts window and see the Rolls-Royce badge looking at me. On a development note, has anyone ever seen the turbofan they developed with variable pitch fan blades? If I remember correctly, it was designed to cut down noise for inner-city airports but I guess was shelved. A company called Renishaw used to have the engine in their plant, but I am not sure if it is still there.

Well, from what I can see RR could well be producing the best engines going, and I think a lot of the airlines share the same view (before selecting the GE to power the 777-200LR/300ER many Trent operators wrote to Boeing asking them to choose RR..however in this case I think GE were willing to put A LOT more money into the programme).

I laugh that somebody has mentioned an uncontained engine failure on a RR Trent, because there are numerous examples of similar incidents invloving P&W and GE large fans aswell!

In general the airline orders for engines speak for themselves, and indeed I think RR are renowned for being the leader in R&D for their engines. This goes back to the RB211 which was revolutionary when launched (and nearly bankrupted RR before the Government stepped in following a few teething problems with the engines’ development). P&W have certainly had a rough time in recent years, and RR has certainly edged to push GE at the top…without sitting down and working it out I am not sure who has the larger market share for large fans, but it wouldn’t suprise me if it was RR, and as I say, the orders surely speak for themselves. I honestly think that is why more airlines haven’t ordered the 777-200LR/300ER.

Nothing beats the whirl of a RR Dart!

The data is not incorrect, it’s just that no one has yet been able to explain to me how an EPR of less than 1 doesn’t result in engine surge or stall.

I don’t know if this would help but here’s an online Engine Simulator where you adjust thrust levels and see how it changes different engine perameters.

http://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.html

Change the Output to Engine Performance to see the EPR and other things. At idle you get an EPR less than 1.0.

Basically my guess would be that at idle the mass of the exhaust is at it’s lowest which creates an almost Venturi-type situation since the entry and exhaust air mass is about the same (very little fuel added). Same air mass being accelerated to a higher speed = lower pressure. At higher power settings you are dumping in a bunch of fuel which raises the mass of the air exiting the engine and you end up with a higher EPR.

The fuel rate at idle for different engines would mean some engines would have a <1.0 EPR compared to others that don’t. When I talk about idle I’m only talking about on the ground as inflight “idle” is actually just a very low power setting and increases with altitude. Of course I guess a < 1.0 EPR could happen in flight with the right circumstances.

Disclaimer: I have no experience with EPR as I’ve only used N1 speeds for power setting.

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As for favorite engine I put my vote in for the PW PT6 series. It’s used in just about every highly rated helicopter or aircraft. It’ll go forever and eat just about anything and never lose power.

With the RB211 full chat at sea level gave a max EPR of approx 1.7 IIRC and flight idle was 1.0. With the Trent max EPR comes out at approx 1.2 but flight idle can have indications of around 0.8. I can’t see how a turbine engine can idle properly with a greater inlet pressure to outlet. 1.0 I can understand but less than 1 seems illogical.

Can you elaborate why you think this is a problem? I don’t see it as a problem.

As to the fan speed (I’m assuming they’re not geared so as you said they should be the same as the shaft), I would think two sources are the most likely place. One is the detector themselves. I.e., an optical port may be blocked by deris or soot. Remember the 747 flight around Indonesia during the Phileppine volcano eruptions, the engine computers when out of whack and all shot down simultaneously since a large amount of soot was taken in. I would think a turbine is relatively robust to flameouts in this situation (i.e., turning sands into glass), so i think the computers monitoring the engine speeds just went out of wack from unreliable sensors. The second source is simply the counting, although if the differences in the speed is quite a lot then this is most likely not the case. If the speeds tend to “bounce” between two or few values, this is usually a com link problem.

The ECAM purely displays the data sent from the engines. The data is not incorrect, it’s just that no one has yet been able to explain to me how an EPR of less than 1 doesn’t result in engine surge or stall. The shaft protection loss is purely an engine internal thing and I would imagine a greater worry in higher power derivatives as used in the A330 and the B777.

Thanks.

Thats all I was looking for.

The ECAM purely displays the data sent from the engines. The data is not incorrect, it’s just that no one has yet been able to explain to me how an EPR of less than 1 doesn’t result in engine surge or stall. The shaft protection loss is purely an engine internal thing and I would imagine a greater worry in higher power derivatives as used in the A330 and the B777.

Gawd, you never give it a rest do you? No I’m talking about the info that is displayed in the cockpit regardless of whether the engine is hung on an Airbus, a Boeing or a bleedin’ microlight!

I only asked a question.

You are saying indications in the cockpit are not what they should be, or appear to be incorrect… I naturaly surmised these displays are controlled by the flight computers and I knew about some sort of issue with software on the A346… hence my question. I was only wanting to learn if these issues are possibly related.

If Skycruiser had reported such issue in his mount… I’d have asked the same.

Gawd, you never give it a rest do you? No I’m talking about the info that is displayed in the cockpit regardless of whether the engine is hung on an Airbus, a Boeing or a bleedin’ microlight!

OK…I have some difficulty understanding the logic behind the EPR presentation in the flightdeck. EPR is (simplified) a measure of the pressure between the back end and the front end of an engine. With the RB211 full chat at sea level gave a max EPR of approx 1.7 IIRC and flight idle was 1.0. With the Trent max EPR comes out at approx 1.2 but flight idle can have indications of around 0.8. I can’t see how a turbine engine can idle properly with a greater inlet pressure to outlet. 1.0 I can understand but less than 1 seems illogical.

Also there are some issues with sensing for the system monitoring fan speed and N1 shaft speed. These are monitored and should be the same meaning that the fan has not separated from the shaft. There are known spurious faults with this system and this fault (occuring on 2 separate engines during one pushback) nearly got us stuck in HKG a while ago.

could this be related to a software issue in the flight computers?
I beleive the a340-600 is/was having some issues with engine and fuel software?

OK…I have some difficulty understanding the logic behind the EPR presentation in the flightdeck. EPR is (simplified) a measure of the pressure between the back end and the front end of an engine. With the RB211 full chat at sea level gave a max EPR of approx 1.7 IIRC and flight idle was 1.0. With the Trent max EPR comes out at approx 1.2 but flight idle can have indications of around 0.8. I can’t see how a turbine engine can idle properly with a greater inlet pressure to outlet. 1.0 I can understand but less than 1 seems illogical.

Also there are some issues with sensing for the system monitoring fan speed and N1 shaft speed. These are monitored and should be the same meaning that the fan has not separated from the shaft. There are known spurious faults with this system and this fault (occuring on 2 separate engines during one pushback) nearly got us stuck in HKG a while ago.