V2+10 climb plus more - huh?

[Trolltuner]

I need some help trying to figure this out from you bizjet experts out there.

Here's my example: A Gulfstream III (Stage 2) airplane AFM says that its certificated noise levels at max gross takeoff mass and at V2+10 are 103.4 EPNdb (sideline), 91.1 EPNdb (takeoff or flyover), and 97.3 EPNdb (approach).

Now let's reduce the takeoff weight. Obviously, the flyover and approach measures will both be reduced, and so will cumulative noise levels. Good news for the environmentalists.:D

However, at lower weights, V2 is decreased. This means the time duration at V2+10 for the sideline measure will increase and the sideline noise will therefore increase as well.:eek:

Solution? The noise regs allow us to use V2+10 to V2+20 for noise demonstrations. Fine. We schedule a climb airspeed transition to (for example) V2+18 instead. That means no noise increase at all, so the noise police folks are happy and accept the notion of "no acoustical change". :D

Bottom line questiuon: How do you feel about the new restriction of climbout at V2+18 vs. V2+10? Are there any operational downsides in your view? Or might it even be better (perhaps closer to Vy, improved climb)?

Your thoughts appreciated.

Cheers,

Tom

[I.R.PIRATE]

Why not climb at V2?

[FrankR]

Why not follow the procedure as it is written?

[Green Cactus]

If you fly the procedure as instructed (V2+10), you are not going to spent more time flying that speed when you reduce the takeoff weight.
You will be climbing at a lower speed but steeper, you will reach your desired altitude in less time.

And that equals less noise on the ground....

GC
(I hope I understood the question correctly.....)

[Trolltuner]

I.R.PIRATE sez: "Why not climb at V2?"

Cannot. For certification, both ICAO and FAA noise regs call for (applicant's choice) between V2+10 to V2+20.

FrankR sez: "Why not follow the procedure as it is written?"

I should have been more clear. Sorry. This is NOT a noise abatement procedure at all. It is a standardized certification procedure, not at all the best way to fly neighborly.

Green Cactus sez: "If you fly the procedure as instructed (V2+10), you are not going to spent more time flying that speed when you reduce the takeoff weight. You will be climbing at a lower speed but steeper, you will reach your desired altitude in less time. And that equals less noise on the ground...."

Yes, this is true for the takeoff or flyover measurement, since most of the noise reduction on the ground is due to a longer distance now away from the microphone. However, it is not true for the sideline measurement which must be made at the noisiest point perpendicular to the takeoff path 450 meters away. How come? It's because the noise measurements are in effective perceived noise level units which take into account the time of exposure to the noise. Slower TAS, higher noise.

Summing all this techno trash up, high gross weight = higher takeoff and approach noise, but lower sideline noise. Low gross weight = lower takeoff and approach noise, but higher sideline noise given a lower climb TAS.

My goal is to not increase sideline noise at lower weights, hence I must climb at more than the newly calculated V2+10. And that's the question. All mumbo jumbo aside, from an operational standpoint, do you feel that a climb airspeed restriction (at lower weight) of say, V2+18 has advantages/disadvantages over V2+10? When considering the question, remember that V2+10 at gross weight is equal to V2+18 at the lower weight.

(And for the purists out there, yes I know "mass" is more correct, but let's just all agree we're in an American assumed 1G environment, OK? :):))

Tom

[mutt]

Assuming you are talking about ALL ENGINE performance, it will take you approx 2 seconds to accelerate from V2+10 to V2+18, this is the equivalent of "Improved climb" or "Overspeed", with the slightly higher rate of climb your exposure to the noise monitors should be lower. However, why +18? Why not +20, or a canned speed like 170 or 180?

My assumption is that in the event of an engine failure, you will ignore the noise restrictions and fly as per the AFM.

If you are within the Stage 3 limits, why are you seeking a lower noise foot print? If your attempt is to reach the lower limits of certain airports (Paris), then without certified paperwork to prove these lower limits, the French DGAC wont accept your procedure.

Mutt

[mutt]

Find (http://noisedb.stac.aviation-civile.gouv.fr/find.php) Unfortunately this database doesn't have your G3, but you might find it interesting anyway.

Mutt

[Trolltuner]

mutt, yes, I am indeed talking about all engine performance. Normally, the airplane will take off at max gross, retract the gear while still IGE, and stabilize in a full power first segment climb, flaps 10, at V2+10. The sideline noise measurement occurs during this stable segment. But at lower weights, if I fly the new V2+10, that means a lower TAS and an increased noise exposure time. (I know that's counter-intuitive, but if you review official sideline noise cert data, given the same TO configuration, the lower weight version almost always has a higher sideline noise level due to the extra time exposure).

You infer that the equal-weight climb rate at V2+18 will be higher than at V2+10. Is that right? I know Vy increases with weight, but not really clear as to its comparison with V2 in general.

I used V2+18 just as an example. The point is, if my TAS is reduced, the noise police will demand a full flight test regime. (Read = costly and impractical). By showing no change in TAS, they'll accept NAC (No Acoustical Change) and I'll avoid actual testing.

Yes, in case of OEI, all bets are off. Fly per the AFM, noise be damned.

You wrote: "If you are within the Stage 3 limits, why are you seeking a lower noise foot print? If your attempt is to reach the lower limits of certain airports (Paris), then without certified paperwork to prove these lower limits, the French DGAC wont accept your procedure."

I agree with your notion. But we're actually talking about a Stage 2 airplane undergoing some mods and involving a lower weight limitation. An acoustical change, other than a noise decrease needs to be avoided. Hence the higher TAS requirement. Thrust reduction is not an option until a later second segment climb, during which a much lower noise level will occur. That one, final level, is the only one of any real practical interest, as it is the one most US municipalities are concerned about as they consider Stage 2 curfews and other restrictions. (And they typically measure in a simple dBA, single highest event, scale - not the complex EPNdB time-relative scale).

So, re-stating the question. My GIII weighs 65,000 lbs at takeoff, not the 69,700 for which it was certified. Based on 65,000 lbs, I calculate my V2 and I climb at V2+10. Next takeoff, same weight, same V2, I decide to climb at V2+20 (or whatever higher increment you choose). What will be the performance change, advantages or disadvantages? :)

PS: Thanks for that link, mutt. Very interesting, and I hadn't seen that before. :ok:

Cheers,

Tom

[I.R.PIRATE]

V2 can easily change by 10 knots or more depending on your weight, so for a MAUW take off, the V2 could quite easily be the equivalent value as V2+10 for a lighter weight - or am I missing the point totally. Who polices the exact V2 for the specific take off profile?

[Trolltuner]

I.R., no, I do not think you're missing the point at all and I agree with your premise regarding V2 variation with weight. Nevertheless, I still seek an answer to the "re-stated" question in my last post above. Hope you or someone else here can chime in with answers. :)

As far as your "who polices" question, the noise certification regs (FAA or ICAO/EASA) specify that the climb is to be at V2+10 to V2+20, applicant's choice. So, if I specify a "lower than gross TO mass", at, say, V2+20 and that turns out to equal the original "max gross TO mass" airspeed of V2+10, I'm OK because there will be no change in sideline noise levels, That is, (V2+10)HW = (V2+20)LW, where HW is "higher weight" and LW is "lower weight". See where I'm coming from?

The only things I'm unsure about are the operational consequences of flying at V2+20 instead of V2+10.

Cheerio,

Tom

[I.R.PIRATE]

I would think that that only operational consequences would be a slightly flatter second segment climb and the question would be in the case of a failed engine would be whether you are still be able to make the minimum climb gradient assuming V2+20? Although, who cares about noise in an emergency situation?

[mutt]

slightly flatter second segment climb I would say that its the opposite as this is the basis of improved climb or optimized V-speeds.

Trolltuner, not sure if you have an airline background, but improved climb is where we basically are limited by the climb limit weight but have plenty of runway, by increasing the speed on the runway and achieving a higher V2, we obtain a higher second segment climb gradient. This is the same as you are trying to do.

As you cannot prove that you are quieter by using any other procedures, I can only guess that you are trying not to ring the noise bells, if you have any airport in particular, it might be worth adopting a special procedure for that airport.

This airport has one of the most interesting noise abatement procedures that I have seen.

Boeing Company (http://www.boeing.com/commercial/noise/john_wayne.html)

I compared the noise figures that you provided with the European limit, you are about +10 EPNdB above Stage 3 accumulative limits, I know that you are operating a Stage 2 aircraft, but what exactly did you achieve with the limiting takeoff weights and acoustical improvements.

Mutt

[I.R.PIRATE]

"I would say that its the opposite as this is the basis of improved climb or optimized V-speeds."

Interesting - would you mind commenting on why this would be? Assuming 2nd segment to be from 35ft to 400 ft.

[mutt]

2nd segment is up to a minimum of 400 feet, or limited by your takeoff thrust, 5 or 10 mins. But in this case it would be to the point where the aircraft changes configuration, we use 1500 feet for thrust reduction and 3000 feet for flaps. (Noise abatement)

Mutt

[I.R.PIRATE]

Ok, I buy that then with 400 ft stated as minimum.

[mutt]

The great thing about digital flight manuals is that they make things like this easy to prove, unfortunately it isnt for the Gulfstream :)


Change Gross Speed
DEG Grad. KIAS
------- ----- -----
Screen Height .0 2.7 153.5
Gear-Up .0 2.9 153.5
Level-Off .0 2.7 153.5
Start Final Climb .0 3.9 225.0


But if we increase the V2 by 10 knots without changing anything else....


Change Gross Speed
DEG Grad. KIAS
------- ----- -----
Screen Height .0 3.2 165.0
Gear-Up .0 3.4 165.0
Level-Off .0 3.3 165.0
Start Final Climb .0 3.9 225.0



You can see that with the higher V2 the climb gradient increases, the figures above are single engine AFM data, but the same should apply for all engine performance.

It will all depend on which noise monitor he is trying to avoid :)

Mutt

[Trolltuner]

mutt and I.R., thanks very much for your thoughts, they're appreciated.

mutt, sure wish I had a digital flight manual for the GIII. I have the original AFM, but interpolating across the many graphs is a bit painstaking and subject to error. Anyone know if such a manual is available for the Gulfstream? I found a very nice one for the Pilatus PC-12 at the Apple App Store (free, no less :ok:), and downloaded it to my iPad.

mutt, thanks for the example. As I.R. suggested, I too thought the higher climb airspeed would result in a lower gradient. Why is it improved? Is it because we're getting closer to Vy, or??

BTW, no real airline background here, just mostly GA & some bizjet avionics and certification endeavors.

Let me know if any out there have further thoughts or examples, and thanks to all so far for your help.

Cheers,

Tom

[maralinga]

As stated at the begining of the post, its all certification and doesnt provide the lowest footprint in the real world.

Flying at those deck angles is a great way to point the engines at the noise monitors. Talking to those who maintain the noise programs at these airports can give you some valuable insights.

Then again, at those angles, your passengers probably wont fly with you again anyway, so no more noise problem!

[mutt]

Then again, at those angles, your passengers probably wont fly with you again anyway, so no more noise problem! Can you please give us the cabin angles for a GIII at V2+10 and V2+20? You point is valid and is the reason we dont fly V2+10 with all engines, however we have a wide margin below stage 3 limits, for airports that have stricter limits, we would follow the certified procedures to achieve the lowest noise footprint, and if this required V2+10, then so be it.

Trolltuner, do you have a noise document for the G3?

Mutt

[Trolltuner]

"Trolltuner, do you have a noise document for the G3?"

Yes, it's entitled "Noise Standards" and is in the AFM at Section 6, Performance. I've posted a .PDF copy of it here:

GIII Noise - Trolltune Corporation (http://www.182stc.com/GIII-Noise)

As you can see, the procedure is full throttle, flaps 10, at MTOM at V2+10. Thrust is cutback at 2562 ft for the second segment climb and is the only config change allowed (i.e., flaps 10, V2+10) until reaching the flyover measuring point 6500 meters from brake release. I want to figure out the airplane's altitude at that point. Then I want to know the altitude at the same point at weight 61,500 using the same config except now at V2+20 (this is still the same 164 KIAS). Change in TAS during the climb and weight of fuel burned are not material.

By comparing the two reference altitudes I can predict the noise reduction by an inverse square law process.

Cheers,

Tom

P.S.: I do understand that EASA requires a specific "Noise Certificate", but that is not used in the US with "N" registered aircraft. The "Noise Standards" page from the AFM is a substitute, but not all European authorities, nor "N" operators have fully understood this fact. :D

[maralinga]

Hi Mutt....I have no experience with the G3 so I cant help you there unfortunately.

But as an example, the initial pitch for a GLEX is 17 degrees which is quite high in itself. Following the V2 +10-20 profile will give a pitch attitude substantially higher than this. Combine low weights, isa...blah blah bla, it can be pretty scary for unseasoned pax.

[Trolltuner]

I don't know, maralinga, but it sounds more like fun to me. Then again, you're quite right - the CEO and his mistress in the aft cabin might not find it so unless properly briefed in advance.

So, how much (approximately) does the new GLEX deck angle change atwixt MTOM and say 8000 lbs less at V2+10 vs. V2+20, say at ISA?

Also, you wrote that the higher deck angle was a "great way to point the engines at the noise monitors", and I suppose you're suggesting an increased deck angle may increase the noise level over that of a flatter climb. Is that just intuitive, or do you know of evidence to that effect?

Either way, I do appreciate your inputs.

Bests,

Tom

[RainingLogic]

I don't have the airplane manuals in front of me, but from memory I seem to recall that sideline noise levels and such measured at certification based on SOP flight profiles as set forth by certification for climb performance, etc. If those numbers exceeded the airport noise levels...seems reduced thrust departures, if safe, possible, might be the next 'tool' to use...personally I'd consider telling the boss, 'do you want a high deck angle or a noise fine'...which would probably lead to a discussion, options, and the obvious solutions. Reduced power, high deck angle...

[Trolltuner]

Hi RainingLogic. I agree reduced thrust TO (flex thrust, etc.) will certainly reduce noise. From a non-certification or operational level, however, sideline noise is (I believe) almost never measured because that measurement must be at THE point of highest noise, laterally 450 meters away. So, for an airport authority, it would be impractical to decide where along the takeoff path to actually put the microphone(s) for different aircraft.

I am more concerned about the takeoff or flyover measurement taken at 6500 meters from brake release and the effect reduced weight has upon it. Naturally, the higher the altitude (read: further away because of better climb) the airplane is at that point, the lower the noise. (Even though it has at least been inferred in this thread that a higher deck angle may increase noise somewhat. I'm not sure there's evidence of this).

So, let me summarize in statement form some of what those responding to this thread have indicated. Please anyone, copy and correct any of these if you can confirm, if you disagree or have something to add:

A. Given all engine climb (AEO) at V2+10, both the deck angle and climb angle will increase as will climb rate compared with a same configuration climb at V2.

B. Given all engine climb (AEO) at V2+20, both the deck angle and climb angle will increase as will climb rate compared with a same configuration climb at V2+10.

C. AEO deck angles at V2+10 or V2+20 will be excessive, or at least may be uncomfortable for PAX.

D. V2 varies with weight, but A thru C above are still valid.

Remember we're talking about a twin engined biz-jet in the Gulfstream class. Thoughts welcomed.

Cheers,

Tom

[Gulfstreamaviator]

Many years ago:

I was busted for exceeding the permitted noise levels at LGW.

The formal letter arrived, and we were invited to the airport noise monitorint office at the airport, to explain why we exceeded the levels, and be prepared to pay the fine.

No quite sure why on PA28 (140, not even a 180) managed to exceed even a 1-11's scream, but the monitor man did laugh, and decided that our fine was cancelled.

As I understand it the monitor did not filter any frequencies, and our little puddle jumper had a spike in its audio spectrum.

Was also invited one day to discuss why we did not follow the SID / Min noise when operating between Gatport and Redhill.....

glf

[RainingLogic]

Fortunately I haven't had to deal with noise issues, haven't been in the plane/airport combination to have this consideration.... But it reminds of guys I knew looking for jets for their boss, passing on 5 million dollar GIIs for 20 million dollar GIVs mainly because of noise abatement issues and some nod to range, even though they never took the plane anywhere with more then a half tank on board. I found it funny that some weak pilot could get some very smart guy, who's DNA is wired for making money, to part with $15 mil. more then he had to, because no one asked the question: 'So why don't we go to the airport three minutes away that doesn't have noise abatement?' Or - 'Why don't we drop a half mil. on a hush kit? or 'Why do you have to do an F16 carrier departure?

[JChallenger]

I know in the states, there is only a few airports that will actually fine you. Most of them just send you a nasty gram...