Search found 25 matches

by Farsight
Thu Jul 04, 2019 8:56 pm
Forum: Technical/Operations
Topic: Jet buzzsaw noise
Replies: 17
Views: 1794

Re: Jet buzzsaw noise

What is fan & N1 shaft imbalance?

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by Farsight
Thu Jul 04, 2019 7:27 pm
Forum: Technical/Operations
Topic: Jet buzzsaw noise
Replies: 17
Views: 1794

Re: Jet buzzsaw noise

masi1157 wrote:
Engine fan and N1 shaft imbalance, it has nothing to do with buzzsaw noise.


Gruß, masi1157



?? What question was this the answer too?

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by Farsight
Thu Jul 04, 2019 4:08 pm
Forum: Technical/Operations
Topic: Jet buzzsaw noise
Replies: 17
Views: 1794

Re: Jet buzzsaw noise

Its interesting to me that at cruise engine settings...you are in the correct RPM range to create the buzzsaw sound, but you can no longer hear it. Throughout the cruise the engines will still be going 'grrrrrrrr'. You can notice it especially on a 757 during cruise, you can't really hear it anymore...

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by Farsight
Thu Jul 04, 2019 4:02 pm
Forum: Technical/Operations
Topic: Jet buzzsaw noise
Replies: 17
Views: 1794

Re: Jet buzzsaw noise

As for the posters original question, why does the buzzsaw sound gradually reduce....I think its mostly due to masking by the wind noise, which becomes the predominate sound you hear at cruise due to increased speed.

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by Farsight
Sun Jun 30, 2019 4:40 pm
Forum: Technical/Operations
Topic: Fuel efficiency vs Noise reduction
Replies: 9
Views: 1640

Re: Fuel efficiency vs Noise reduction

This is what I don't understand, if the engines are already meeting noise regulations, why bother making them quieter at the expense of fuel economy??

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by Farsight
Sun Jun 30, 2019 3:34 pm
Forum: Technical/Operations
Topic: Fuel efficiency vs Noise reduction
Replies: 9
Views: 1640

Re: Fuel efficiency vs Noise reduction

Thats what I'm getting at. Chevrons on the 787 was a surprising example of prioritising noise suppression over fuel consumption. That case is especially strange considering the engines were probably also within current noise regulations without the chevrons.... And although yes it is correct to say ...

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by Farsight
Sun Jun 30, 2019 1:09 am
Forum: Technical/Operations
Topic: GE9X Record Breaker
Replies: 60
Views: 9774

Re: GE9X Record Breaker

Well...i can’t wait to see the new record figures, im going with 131,000lbs

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by Farsight
Sun Jun 30, 2019 1:01 am
Forum: Technical/Operations
Topic: Silly question
Replies: 9
Views: 1860

Re: Silly question

Yes, very statutish. Shame we will never get to test this out. I don’t think mythbusters have the budget.

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by Farsight
Sun Jun 30, 2019 12:54 am
Forum: Technical/Operations
Topic: Fuel efficiency vs Noise reduction
Replies: 9
Views: 1640

Re: Fuel efficiency vs Noise reduction

And...if we were to come up with some new technology that boosted fuel effiency by 20% but took us back to pre hush kit 727 sound levels (acceptable in the 70’s apparantly), would we ease noise regulations to accomodate it?

My question is long winded but hopefully you can see where im going!

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by Farsight
Sun Jun 30, 2019 12:42 am
Forum: Technical/Operations
Topic: Fuel efficiency vs Noise reduction
Replies: 9
Views: 1640

Fuel efficiency vs Noise reduction

Hi I was looking into unducted fans the other day and it got me thinking... Where is the line drawn between increased fuel efficiency and noise? Fuel efficiency is obviously crucial, and in an age where were spending tens of millions in R&D to eak out a 5% advantage...is a subsequent 10% increas...

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by Farsight
Sun Jun 30, 2019 12:22 am
Forum: Technical/Operations
Topic: Silly question
Replies: 9
Views: 1860

Re: Silly question

Thankyou for the responses, I feel slightly more satisfied now...

So perhaps 450ish MPH?

If indeed we did add some downward elevator deflection, is it possible the tail would rise up off the ground at high enough speed? Pushing the nosewheel into the ground?

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by Farsight
Fri Jun 28, 2019 4:21 am
Forum: Technical/Operations
Topic: Silly question
Replies: 9
Views: 1860

Silly question

Here goes: Forgetting tire limits and runway length, what do we reckon would be the maximum speed of a commercial turbofan powered plane on the runway if it was to never liftoff? I randomly wandered this the other day, did a google search but to no avail. There must be a maximum speed at which engin...

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by Farsight
Fri Apr 19, 2019 4:39 am
Forum: Technical/Operations
Topic: 747-8 vs 777-9x
Replies: 4
Views: 1743

Re: 747-8 vs 777-9x

Ps: goofy answers along the lines of ‘make more money’ etc are NOT welcome :)

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by Farsight
Fri Apr 19, 2019 4:36 am
Forum: Technical/Operations
Topic: 747-8 vs 777-9x
Replies: 4
Views: 1743

747-8 vs 777-9x

Hey All

Fun question:

What exactly can a 747-8i do that a 777-9x cannot do?

Freighter discussion is welcome too...

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by Farsight
Thu Apr 18, 2019 7:25 pm
Forum: Technical/Operations
Topic: Runway Aquaplaning
Replies: 9
Views: 1932

Re: Runway Aquaplaning

I suppose the general geometry of aircraft landing gear (2 mains, 1 nose) adds inherent stability kind of like a rail dragster with the big wide rears and skinny front tires too.

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by Farsight
Thu Apr 18, 2019 7:23 pm
Forum: Technical/Operations
Topic: Runway Aquaplaning
Replies: 9
Views: 1932

Re: Runway Aquaplaning

Interesting, thank you for the replies! So aquaplaning/hydroplaning DOES happen occasionally. It seems like if an aircraft were to start sliding to one side I can't imagine the nosewheel steering having enough authority to correct. I've searched youtube hoping for some examples but haven't found any...

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by Farsight
Wed Apr 17, 2019 7:40 pm
Forum: Technical/Operations
Topic: Runway Aquaplaning
Replies: 9
Views: 1932

Runway Aquaplaning

Hi All

What stops planes from aquaplaning in wet conditions? I know that the rudder can minimise this above a certain speed and add stability, but I am surprised it doesn't seem to happen more often. Aircraft tires seem remarkably simple (in comparison to automotive tires). Am i missing something?

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by Farsight
Wed Apr 17, 2019 7:34 pm
Forum: Technical/Operations
Topic: Quad engines and reverse thrust use
Replies: 42
Views: 3851

Re: Quad engines and reverse thrust use

I believe the A380 doesn't have reversers installed on the 1 & 4 engines due to those engines being so far from centreline, putting them at risk of foreign object damage.

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by Farsight
Wed Mar 06, 2019 8:15 pm
Forum: Technical/Operations
Topic: Trent/CF6 Question
Replies: 10
Views: 1840

Re: Trent/CF6 Question

Yep, 'Combustor Howl', caused by combustion instability. Same thing that causes that bassy sound during startup when the igniters are switched on. Shame we won't hear it anymore: the noise stems from a less than perfect combustion regime. See here for full paper (Paywalled). http://proceedings.asmed...

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by Farsight
Wed Mar 06, 2019 6:05 pm
Forum: Technical/Operations
Topic: Trent/CF6 Question
Replies: 10
Views: 1840

Re: Trent/CF6 Question

Yes Masi1157 Thanks for the relevant interesting reply! I always thought it sounded like a 'resonant' type of sound. However I didn't think 'resonant' sounds would pitch up and down in a chamber with a fixed geometry, ie a jet engine combustion chamber, but rather have a fixed note that fades in and...

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by Farsight
Thu Feb 28, 2019 5:00 pm
Forum: Technical/Operations
Topic: Trent/CF6 Question
Replies: 10
Views: 1840

Re: Trent/CF6 Question

Actually that's not true at all. All sound is generated by some type of physical process, we can actually 'predict' what type of sounds certain processes will generate. There is a whole field dedicated to researching this, and its useful. The way my voice sounds is a result of the complex interplay ...

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by Farsight
Thu Feb 28, 2019 4:32 pm
Forum: Technical/Operations
Topic: Trent/CF6 Question
Replies: 10
Views: 1840

Trent/CF6 Question

Hi All I've noticed that all Trent engines make a distinctive 'wooing' noise under certain circumstances. The sound only occurs whilst advancing throttles through the lower rpm range and will stop as soon as throttles are left static, it never occurs whilst retarding throttles through the same rpm r...

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by Farsight
Thu Feb 28, 2019 1:59 pm
Forum: Technical/Operations
Topic: GE9X Record Breaker
Replies: 60
Views: 9774

Re: GE9X Record Breaker

Thanks for the replies...

I think we can safely assume then that the GE9X has been heavily overloaded during testing, way past the 105,000lb rating. Anyone care to speculate on any maximum thrust figures?

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by Farsight
Wed Feb 27, 2019 11:30 pm
Forum: Technical/Operations
Topic: GE9X Record Breaker
Replies: 60
Views: 9774

Re: GE9X Record Breaker

Thanks for the replies..

Then how was the 127,000lbs figure achieved during GE90 testing?

The design brief was fixed at 115,000...so why did they exceed it so dramatically? What was the purpose?

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by Farsight
Wed Feb 27, 2019 8:32 pm
Forum: Technical/Operations
Topic: GE9X Record Breaker
Replies: 60
Views: 9774

GE9X Record Breaker

Hi All

Feels good to finally join after a decade+ of observation!

My question is...how likely is it that GE will attempt to beat the GE90 thrust record any time soon? Could a test GE9X be 'turned up to 11' and put out a few 1000lbs extra...just for bragging rights of course!

Many thanks.

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