While in the A319 you can mostly hear the engines, in the 175 or 190 it is mostly aerodynamic noise. Especially if you're seated in front of the engines. There is virtually no engine noise on an A319 in cruise. It is almost exclusively boundary layer noise (with a bit of air cond) in front of the w...Jump to post
The GE90-115 being the most powerfull engine by a significant margin, could it be that due to its intrinsically high air flow, the noise resulting from the jet mixing is simply higher than for any other engine? Also, has the exhaust speed any effect on the low frequency noises? Of course a more pow...Jump to post
I have always thought the RR powered -200ER was really noisy in the cabin, even forward of the L2 door. Sounds like a buzz saw and quite unpleasent at times. That is called buzzsaw noise (really!) and I am perfectly sure it occurs during climb (on all aircraft, some noisier, some less) but not duri...Jump to post
I agree with you, compared to 772 (PW4077), 77E (RR Trent 892) and 773 (RR Trent 892) I have flown with the 77W is more noisy in the cabin. Being noisier in the cabin does not necessarily mean it is also noisier when heard from the ground. It may be a hint, but it surely is not related 1 to 1. Perh...Jump to post
If you are talking about a 77W at FL310 the A330/A350/A380 would be at FL370 at the same corresponding fraction of actual weight/MTOW. At MTOW a 77W will only get to FL290 normally, the A350 straight to FL350. That would give 1.2dB and 1.6dB difference. As I said, still below 2dB and inaudible if n...Jump to post
I guess its an inverse square law thing (been 11 years since I did the acoustics at uni) so (37/33)^(1/2) = 1.058. Not sure how that equates to dB but I'm sure you are right. It is not "^(1/2)" but simply "^2". And the sound pressure level difference is 10*log((37/33)^2) or 20*l...Jump to post
It may well be louder because its lower and therefore closer to you. Flying at FL330 instead of say FL370 would make a 1dB difference. That is the smallest noise difference to distinguish in a direct comparison. But hearing them several minutes/hours/days apart you would not be able to notice any d...Jump to post
What happens at the expansion valve is cavitation I would not call it cavitation but rather vaporization: The fluid, all the fluid, turns into a gas and stays a gas for a while. But it does not have the local and very explosive and destructive formation and collapse of gas bubbles inside the fluid....Jump to post
On aircraft where air is used to pressurize the reservoir, we measure and regulate air pressure, not hydraulic pressure, in terms of head pressure. In a way you control both simultaneously. What you want to achieve is a certain pressure in the fluid on the low pressure side of the system. What you ...Jump to post
In an aircraft hydraulic system, we refer to head pressure as the air pressure in the reservoir. Which is of course the same as the pressure of the hydraulic fluid in the reservoir. Lower pressure means lower boiling temperature, so I think temperature may still the cause of the boiling. Don't thin...Jump to post
Hamburg: HAM, XFW, LBC (well, at least Ryanair called it Hamburg) Berlin: TXL, SXF, THF (now closed) London: LHR, LGW, LTN, STN Paris: CDG, ORY Reykjavik: KEF, RKV Tenerife: TFS, TFN New York: JFK, EWR Buenos Aires: EZE, AEP And a few "current and former" airports: München: MUC (Erding) an...Jump to post
I think it must one of the last adventures and challenges to do such flights on such a plane over water for such a long time...is that the longest route of a Dash 8 Q 400? Air Iceland operates quite a number of flights from RKV to west Greenland, some of them even with Dash8-200. Those are over wat...Jump to post
You often hear the cabin ventilation go silent before engine start so that would suggest that they are off. That doesn't mean the cabin fans are off. Turning off the packs would leave the cabin fans blowing 1/2 of the air into the cabin, which would reduce the flow noise by (theoretically) 18dB. An...Jump to post
What is fan & N1 shaft imbalance? What do you not understand here? The fan is sitting on the N1 shaft, so they both rotate at the same frequency. An imbalance of the fan or the shaft and the inhomogenuous flow condition across the fan inlet introduce a vibration at that same frequency, that is ...Jump to post
It was an answer to your post immediately before it. The imbalance of the fan and shaft also have (of course) the same fundamental frequency as buzzsaw noise would have, but the generating mechanism is completely different. Other than the frequency it has nothing to do with it.
[but what is the mechanism of producing energy at higher than BPF from shocks? There probably is one, but either way the acoustic energy of harmonics above BPF is much lower than that at BPF or 1/rev or 2/rev. The 1000th engine order is not of much interest generally. The mechanism is simply from t...Jump to post
That’s exactly what I said. “And its harmonics up to blade passing frequency” You said "also". Only the shaft frequency and its harmonics are created by supersonic blade tip speed and are perceived as buzzsaw noise. And the harmonics of the shaft frequency reach far beyond the BPF. Gruß, ...Jump to post
So does this buzzsaw sound disappear in-flight because of external wind noise or because thrust on the aircraft is gradually reduced? There are a number of reasons why buzzsaw noise changes during the climb. The reason why it disappears at cruise is primarily the helical tip speed dropping to subso...Jump to post
This is something I've been trying to research for years. This article contained the most logical and detailed explanation, even if it's a little confusing to understand :D https://www.southampton.ac.uk/engineering/research/projects/buzz_saw_noise_and_non_linear_acoustics.page That is only the abst...Jump to post
I've never seen any research yet that indicated bearings are a substantial source of noise on turbofans. Perhaps it has just not been considered but... If they were, they would have been considered. And if they really would generate any considerable noise I would not worry about the noise but rathe...Jump to post
DocLightning wrote:However, waves in and of themselves do not cause drag..
Waterbomber2 wrote:What evidence is there that shocks eat up other shocks? I can't imagine how that can happen at all.
Every blade is shaped very slightly differently, no matter how hard the manufacturer tries to make them all identical. This causes subtle changes in shock strength and shape generated by each blade resulting in an irregular sine wave with a fundamental harmonic of the rotational speed of N1. It is ...Jump to post
Why do they have to be on the same axis? Props on different axes are still imparting torque to the aircraft. You are right, for the "static" torque the need not. I was taken away by "dynamic" in the thread title and was thinking about imbalance and vibration, which could in fact...Jump to post
Will anybody here try to discuss the content of the Youtube video, or just the fact it is in german?
It is to balance out the forces. You have less vibrations that way. you can observe this on helicopters, if the rotor in the back fails the cabin start to turn counter to the rotation of the blade. The same force applies on the nacelle of the propeller engine. To balance that our you have counter r...Jump to post
KUZAWU08 wrote:Sometimes what you observe literally is what you think it is!
Here some informations about the Electric Taxiing project developped by Safran (the objective is an EiS by 2022). That is the one I was talking about earlier. It drives a wheel of the main landing gear and it is being developed. I think this is a useful system for short-haul aircraft, that do sever...Jump to post
I remember reading about them a decade ago; however I don't believe there was much interest or rage to speak of. As I said earlier, such a system is currently being studied and developed. It wil drive a wheel of the main landing gear, not the nose gear. An earlier version had been tested, but it mo...Jump to post
RMP convert Kinectic energy from pressurized system and convert it kinetic as energy, who will be transformed on rotary energy, converting it late on Hidraulics, (for instance) for yellow system Again: That system is called PTU. It has been discussed in hundreds of threads in this forum. But this t...Jump to post
EMBQA wrote:APUs do not even come close to offering enough thrust to move an aircraft
What's the deal with the CS100/A220 "humpback whale" noise? I never heard an A220 from close, so I don't know what noise you are talking about. Does it occur during climb and is it rather continuous? Then I would assume it is the so called buzzsaw noise.But that is not exclusive to A220, ...Jump to post
During flight tests, the blankets reduced overhead noise levels by morethan 2 dBa. An optional treatment for flight deck windows two and three reduces ambient noise by an additional 1.5 dBa. [....] Source : AERO First-Quarter 2003—January, page 21 So that would make >3.5 dB(A) together? That would ...Jump to post
When describing the current date I would say "It is March 11th, 2019" not "It is the 11th day of March in the year 2019" or "It is the year 2019, the third month March and the eleventh day." or something similar. That again depends on the language. In german we say &qu...Jump to post
Why even bother to defend the european format over the US format? They're both bad. No sense in saying "I'll stick with bad format #2", when you clearly have another superior format at hand. Huh? I use yyyy-mm-dd quite frequently, for file numbering and things like that. But I live in a c...Jump to post
It is NOT the exact reverse of ISO 8601. If it were, you would write today's date as "11-30-9102". BTW, how do you tell time in Europe? ss:mm:hh, right? That would align with your date format, so logically you should be expected to leverage that. I hope you did understand though, what I w...Jump to post
One area that would be a bit tough is swimming (I'm a swimmer). In most of the world, the two competitive swimming pool formats are either short-course or long-course meters (25 or 50m). In the US, there is a third format, 25 yards (short-course yards) that is used for high school and NCAA swimming...Jump to post
If you use miles or kilometers, gallons or liters, Celsius or Fahrenheit doesn't matter at all. It doesn't matter anyway. That is all easily converted and it seems everybody except you can do that. Where the unit system does matter a lot is obviously out of your scope, so you will be fine. Gruß, mas...Jump to post
Who cares? In "irish pubs" in Germany you can order something called a "pint of Guinness". It may actually be close to a pint, but legally it is 0.568l (± whatever the legal tolerance in the EU may be). It won't be much different from that in the UK (at least for the next 3 week...Jump to post