SSG: Spy/Spec-Ops Group discussion

Place for random tidbits of aviation knowledge to hover

Cabin crew can unlock toilets from the cabin.

And lock them too.

The TU-95 BEAR turboprop bomber/long range maritime reconnaissance aircraft is said to be one of the loudest planes in service, due to engine and propeller noise. The crew have to wear ear defenders constantly during flights in order to avoid becoming deaf in the long run.

You actually have a scene in the movie HUNT FOR RED OCTOBER that shows the crew of a TU-95 on a patrol. You can clearly see them wearing ear protection and the movie did capture the noise from the engines and props.

Uh, what is W.H.&S, if I may ask?

Question! Does it take more fuel & engine effort for a jet to cruise at extremely super-high altitude, or less?

The problem, as exemplified by the U-2 spy plane, was that, the higher you flew, the higher the minimum speed needed becomes, even when you have extra-long wings. The U-2 maximum speed was in fact barely higher than its stalling speed at high altitude, making it very tricky to pilot. The cold and rarefied air at very high altitude also made it easier for jet engines to flame out.

Nice answer but didn't answer the question. I think it's more fuel efficient to fly at higher altitudes, but as alluded to at a certain height the lack of air particles to generate lift begin to negate this.

That being said, I have done physics since senior school so I'm sure the real life pilots / physics high school teachers will correct me soon.

Haven't* done physics. English could probably do with a dust up too.

Lolz

Yes, someone else spoke to me about the obvious 'lack of air' at high altitude; which I had been assuming made high speed easier to attain at less engine thrust--because, (my thinking ran) if there's less air then that means less friction and drag, the craft should glide with the ease that spacecraft enjoy. But my advisor said no; less air particles in the case of a jet plane means more thrust needed! The engines work harder! So I want to get it straight. Which is it?

Well, in the case of the U-2, at the least, it had to keep its turbojet engine at near maximum thrust while cruising at very high altitude, which is never economical for a turbojet. Funnily enough, the engine type that is the most efficient at high altitude and high speed (especially above Mach 2) is the ramjet engine. The SR-71 BLACKBIRD Mach 3 reconnaissance plane had hybrid turbojet-ramjet engines (they then called them 'variable bypass ratio turbofans'). it was mostly on ramjet mode at Mach 3+ cruise. They also discovered that the faster you went past Mach 2.2, the more economical those ramjet engines became in terms of liters of fuel per mile flown. As for pure turbofan type engines, they are very efficient at low and medium altitude (0-30,000 feet), but perform less well at very high altitude (60,000+ feet). So, in my humble opinion, the answer would be that more fuel and engine effort went to fly at very high altitude. As you can see from this, Feliks, the answer varies depending on the type of engine used and the cruising speed (high subsonic, supersonic or high supersonic/hypersonic).

Well done! So to make my question more specific, let's focus only on commercial passenger airliners. I see a lot of planes where I reside (near JFK airport). Naturally they are all stacked at different heights, but I can't fathom just what kind of airliner seems to cross overhead at such extraordinary heights, (as a few of them do) really just the size of a pinprick. Isn't fuel conservation paramount for airliners? They glide along with seemingly little effort compared to their brethren lumbering along below.

That's because the rarefied air at medium altitude (yes, that is considered medium altitude if you talk to a U-2 or SR-71 pilot) creates less drag, thus allows the turbofans that typically equip airliners these days to run at an economical cruise setting, just below the speed of sound (most often at Mach 0.85 to 0.92).