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kitplane01
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Medium Sized 4-engine aircraft

Mon Mar 20, 2017 1:35 am

There are no modern efficient new jet engines in the 35,000-62,000 pound thrust class. But suppose I want to make a new airplane of medium size, that might use a pair of 40,000 or 50,000 pound thrust engine. Instead of paying a manufacturer to design and build such and engine (complete with support infrastructure), I could just use 4 engines from an A320neo/B737max. The result would be an airplane about the size of a KC-135 or a B757 or an A300.

PRO
- Saves on time (the engine is ready NOW, and not in 6 years)
- Saves on support costs (these engines can be overhauled everywhere)
- Saves on money (no need to design a new engine)
- Saves on risk (what if the new engine is late, or does not meet spec)
- No worries about ETOPS

CON
- Need to maintain 4 small engines instead of 2 bigger ones
- Might burn more fuel (smaller engines can be less efficient)

It would seem that for a small but reasonable production run, this would produce better economics that a new engine design.

What is the fuel penalty for 4 small engines instead of 2 bigger ones?
 
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rotating14
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 1:44 am

Weight penalty of the extra engines as well as the drag.
 
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alex0easy
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 1:49 am

So what you're describing is a smaller A340-200neo or a DC-8-70neo?
Doesn't sound like a good idea to me.
 
tomaheath
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 1:57 am

Boeing 707MAX!
 
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kitplane01
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:02 am

alex0easy wrote:
So what you're describing is a smaller A340-200neo or a DC-8-70neo?
Doesn't sound like a good idea to me.


No one is proposing to re-engine a plane designed and built with 1965 or 1991 technology. I don't know that it would fulfill the same role of very long range aircraft. But it might be the same size and general shape sort of maybe.
 
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flee
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:02 am

The simple answer is A340-200neo. But we already have the A330-800 - so how can a 4-engined A340-200neo be more efficient?
 
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NameOmitted
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:03 am

tomaheath wrote:
Boeing 707MAX!


I'll bet Boeing is wishing it hadn't gotten rid of the tooling NOW!
 
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kitplane01
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:09 am

flee wrote:
The simple answer is A340-200neo. But we already have the A330-800 - so how can a 4-engined A340-200neo be more efficient?


It would be a new plane, not one designed with 1991 technology. And it might fulfill a different mission. The A340-200 had a range of 8,100 miles, which might not be what this plane needs. Also, a 340-200 has 130,000 pounds of thrust, and this plane might have (maybe) 100,000 pounds of thrust.

In comparison with the A330, this plane would be significantly smaller. An A330neo has 140,0000 pounds of thrust, and this proposed plane would only have (maybe) 100,000 pounds of thrust. I agree that if you want an A330neo/787 sized plane, existing planes and engines probably meet your needs.
 
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rotating14
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:10 am

kitplane01 wrote:
There are no modern efficient new jet engines in the 35,000-62,000 pound thrust class. But suppose I want to make a new airplane of medium size, that might use a pair of 40,000 or 50,000 pound thrust engine. Instead of paying a manufacturer to design and build such and engine (complete with support infrastructure), I could just use 4 engines from an A320neo/B737max. The result would be an airplane about the size of a KC-135 or a B757 or an A300.

PRO
- Saves on time (the engine is ready NOW, and not in 6 years)
- Saves on support costs (these engines can be overhauled everywhere)
- Saves on money (no need to design a new engine)
- Saves on risk (what if the new engine is late, or does not meet spec)
- No worries about ETOPS

CON
- Need to maintain 4 small engines instead of 2 bigger ones
- Might burn more fuel (smaller engines can be less efficient)

It would seem that for a small but reasonable production run, this would produce better economics that a new engine design.

What is the fuel penalty for 4 small engines instead of 2 bigger ones?



The current aircraft with 4 engines, A380, A340-600, A340, 744, are falling out of favor to the twin engined crowd. You're describing the engines and how 4 are better than 2 but why do you need 4 engines when an engine of greater thrust exists to accomplish the mission in mind?

4 35k engines on a 737 or a A320 will not work. You need to beef up the wing to support the extra engine. All this does is add weight. Weight that airlines stay away from.
 
zrh177
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:13 am

Sounds a little bit like a Kawasaki P-1 to me. Although, the P1 is a military aircraft...

https://en.wikipedia.org/wiki/Kawasaki_P-1
 
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Aesma
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:17 am

You need 2*40Klbs engines so you'll use 4*30Klbs engines instead. Yep, seems logical.

If you need 2*40Klbs the correct engine power for an equivalent quad would be 4*15Klbs or thereabout. Think Embraer E175-2 engines : Pratt & Whitney PW1715G.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
rg787
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:17 am

What I understand the OP is actually proposing is what is the feasibility of making the MOM a 4 engine aircraft, because there are no engines available for the thrust range proposed by him. It is not an A342, it is rather a new 757/DC8.

I would imagine that it is possible, considering the Avro RJ was a four engine aircraft when it probably didn't need to be.
 
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ikolkyo
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:17 am

Not happening, with the time it would take to build a clean sheet plane (Few years) an engine could also be developed in that time span.
 
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thebatman
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:36 am

How about a BAe-146 MAX-10! If I had my choice, I would design a new, stretched Boeing 727 MAX. Make it out of carbon fiber, give it a 787-style cockpit and avionics, and give it a 4500nm range. There's your new MoM aircraft. Of course I would be doing this purely for sentimental reasons...
Aircraft mechanics - because pilots need heroes too!
 
QueenoftheSkies
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:37 am

I don't know what's more absurd, this thread or the whole circular runway nonsense one.
 
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Btblue
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:45 am

I like your idea and the possibilities - but the cost benefits would be short-lived if even realised. Give it a few years and you'd have an engine capable of doing the job with two instead of four on the wing, pretty much like the A340/30. If you can hold off on your plane and maybe lease for the time being :airplane: come 2025 you may be able to get your hands on a EE UltraFan :)
 
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kitplane01
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 3:30 am

Btblue wrote:
I like your idea and the possibilities - but the cost benefits would be short-lived if even realised. Give it a few years and you'd have an engine capable of doing the job with two instead of four on the wing, pretty much like the A340/30. If you can hold off on your plane and maybe lease for the time being :airplane: come 2025 you may be able to get your hands on a EE UltraFan :)


Developing a new engine would cost maybe billions. If you're only going to produce 500 aircraft, that might not be the economic thing to do regardless of timeline.

Also, if you're only going to produce 500 airplanes, I doubt the Ultrafan will be made in your thrust range.
 
Bald1983
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 3:33 am

kitplane01 wrote:
There are no modern efficient new jet engines in the 35,000-62,000 pound thrust class. But suppose I want to make a new airplane of medium size, that might use a pair of 40,000 or 50,000 pound thrust engine. Instead of paying a manufacturer to design and build such and engine (complete with support infrastructure), I could just use 4 engines from an A320neo/B737max. The result would be an airplane about the size of a KC-135 or a B757 or an A300.

PRO
- Saves on time (the engine is ready NOW, and not in 6 years)
- Saves on support costs (these engines can be overhauled everywhere)
- Saves on money (no need to design a new engine)
- Saves on risk (what if the new engine is late, or does not meet spec)
- No worries about ETOPS

CON
- Need to maintain 4 small engines instead of 2 bigger ones
- Might burn more fuel (smaller engines can be less efficient)

It would seem that for a small but reasonable production run, this would produce better economics that a new engine design.

Con, much more expensive to operate. Therefore, not going to happen.
What is the fuel penalty for 4 small engines instead of 2 bigger ones?
 
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Spacepope
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 3:49 am

Aesma wrote:
You need 2*40Klbs engines so you'll use 4*30Klbs engines instead. Yep, seems logical.

If you need 2*40Klbs the correct engine power for an equivalent quad would be 4*15Klbs or thereabout. Think Embraer E175-2 engines : Pratt & Whitney PW1715G.

Yep, the math doesn't work. We clearly need a trijet. Mini narrowbody L1011. What could possibly go wrong?
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Flighty
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 4:23 am

thebatman wrote:
How about a BAe-146 MAX-10! If I had my choice, I would design a new, stretched Boeing 727 MAX. Make it out of carbon fiber, give it a 787-style cockpit and avionics, and give it a 4500nm range. There's your new MoM aircraft. Of course I would be doing this purely for sentimental reasons...


How about a 727-700 with 2 under-wing turbofans... 5 engines. This is a lot more efficient than the 7 engine option.
 
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kitplane01
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 6:23 am

Spacepope wrote:
Aesma wrote:
You need 2*40Klbs engines so you'll use 4*30Klbs engines instead. Yep, seems logical.

If you need 2*40Klbs the correct engine power for an equivalent quad would be 4*15Klbs or thereabout. Think Embraer E175-2 engines : Pratt & Whitney PW1715G.

Yep, the math doesn't work. We clearly need a trijet. Mini narrowbody L1011. What could possibly go wrong?


There are two constraints on minimum engine power
1) The need to climb away from the airport after an engine failure
2) The need to achieve a reasonable cruise altitude while the engines are operating in very thin air. This is the top-of-climb requirement.

The result is that a 4 engine plane needs about as much installed thrust as a two engine plane. For example (thrust/weight ratios)
787-9: 0.271
747-8: 0.270

A330-200: 0.242
A340-200: 0.204

In particular, if your plane needs 2x40,000 pounds thrust, you probably need 4x20,000 or maybe 4x16,000. And that is in the PW1700 series. A nice modern available engine. And if your plane needs 2x50,000 pounds thrust, the four engine equivalent is probably 4x25,000 or 4x22,000 which is still a PW GTF.
 
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flee
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 6:46 am

A tri-jet should be more economical than a quad. So maybe an all CFRP B727 Max10 might be feasible.

3 x 27,000 lbs (PW GTF or CFM LEAP) or 3 x 34,000 lbs (PW GTF or CFM LEAP)
 
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 6:57 am

- 4* A320 engine : DC8-70/A340
- AN-70TK?
- Dash 7?
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kitplane01
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 7:00 am

flee wrote:
A tri-jet should be more economical than a quad. So maybe an all CFRP B727 Max10 might be feasible.

3 x 27,000 lbs (PW GTF or CFM LEAP) or 3 x 34,000 lbs (PW GTF or CFM LEAP)


Is that true? I understand that 3 engines is fewer than 4 engines, but I *thought* that the problems of mounting the third engine outweighed the benefit. I'm willing to be corrected. Of course, Douglas and Lockheed agreed with you ...
 
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PatrickZ80
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 7:09 am

What you don't add to your calculations is that adding an engine means adding weight to the aircraft, so you need more thrust just to get the engine moving. That makes it very uneconomical. Plus there already are engines available that offer enough thrust to get a plane that size moving with two engines or even with one if it needs to be.

The A340 has been discontinued for a reason, the reason was that the A330 was more popular because it had 2 engines instead of 4. That makes the A330 more efficient than the A340.
 
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flee
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 7:15 am

kitplane01 wrote:
flee wrote:
A tri-jet should be more economical than a quad. So maybe an all CFRP B727 Max10 might be feasible.

3 x 27,000 lbs (PW GTF or CFM LEAP) or 3 x 34,000 lbs (PW GTF or CFM LEAP)


Is that true? I understand that 3 engines is fewer than 4 engines, but I *thought* that the problems of mounting the third engine outweighed the benefit. I'm willing to be corrected. Of course, Douglas and Lockheed agreed with you ...

I think that the weight and balance issues should be easier to solve with CFRP bodies. I also think that any tri-jet should have similar layout to the L-1011 Tristar for it to be less of an engineering challenge. Having all the engines at the back like the B727 might be too much as the weight of modern engines is way above that of the previous generations.
 
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flee
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 7:18 am

PatrickZ80 wrote:
What you don't add to your calculations is that adding an engine means adding weight to the aircraft, so you need more thrust just to get the engine moving. That makes it very uneconomical. Plus there already are engines available that offer enough thrust to get a plane that size moving with two engines or even with one if it needs to be.

The A340 has been discontinued for a reason, the reason was that the A330 was more popular because it had 2 engines instead of 4. That makes the A330 more efficient than the A340.

I think one of the reasons why twins are more efficient is because they are inherently over-powered due to the one engine out take off requirements. As such, these engines do not have to work so hard when cruising. With quads, the smaller engines may each have to work harder to deliver cruising thrust.
 
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keesje
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 8:11 am

To have the same thrust as a 2x50k lbs twin, you'll need a quad of 4 x 15-17 klbs. For a tri-jet you would need 3x 20-25k lbs.
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richcam427
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 8:15 am

I wouldn't dismiss four-engine aircraft that fast. Don't twins have a problem with most hot and high airports? JNB immediately comes to mind. AFAIK, even 77Ls and 77Ws are restricted when flying out of it, and is one of the reasons why SAA has kept their A340s while the rest of the world couldn't get of them fast enough.
 
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Aesma
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 8:56 am

If you think about it there is only one successful widebody with more than 2 engines, it's the 747. All the others only sold in the hundreds.

Tris and quads only exist because technology at the time didn't allow for powerful and reliable enough engines.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
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Mortyman
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 9:40 am

Boeing 707-300neo :-)
 
LightningZ71
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:26 pm

Does anyone have a chart that shows the weights of the various PW1000G family members? While I don't imagine that the weight spread between the PW1700G and the PW1135G is too great, there has to be some sort of difference. The PW1715G has only a 56 inch fan and a shorter HP/Hot core than the PW1715G and it also has a necessarily smaller and lighter reduction gear box. That is a non-trivial difference in mass.
 
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Spacepope
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:34 pm

flee wrote:
A tri-jet should be more economical than a quad. So maybe an all CFRP B727 Max10 might be feasible.

3 x 27,000 lbs (PW GTF or CFM LEAP) or 3 x 34,000 lbs (PW GTF or CFM LEAP)


I like the way you think! I was also leaning towards a TU-154NEOxwb myself.
The last of the famous international playboys
 
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kitplane01
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:38 pm

PatrickZ80 wrote:
Plus there already are engines available that offer enough thrust to get a plane that size moving with two engines


There are *not* new modern engines available in the 35,000-60,000 pound thrust range. That's false.
 
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Blimpie
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 2:49 pm

Two engine designs seem like they are working just fine. I see no reason to revert back to four engines. :crazy:

Mortyman wrote:
Boeing 707-300neo :-)


Would that be the airliner equivalent of retro styling that was popular with cars a few years ago (eg, the retro Mustangs, PT Cruiser....) :gnasher:

QueenoftheSkies wrote:
I don't know what's more absurd, this thread or the whole circular runway nonsense one.


Amen brother. I think I'm going to start on thread for an MoM proposal, and call it the 747-50. We cut the entire back of a 474-8i from the hump back ala A380 mini (double deck, full length) and make an argument for it. :idea:
Now get the hell off of my lawn your dang kids!
 
QueenoftheSkies
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 3:55 pm

Blimpie wrote:
Two engine designs seem like they are working just fine. I see no reason to revert back to four engines. :crazy:

Mortyman wrote:
Boeing 707-300neo :-)


Would that be the airliner equivalent of retro styling that was popular with cars a few years ago (eg, the retro Mustangs, PT Cruiser....) :gnasher:

QueenoftheSkies wrote:
I don't know what's more absurd, this thread or the whole circular runway nonsense one.


Amen brother. I think I'm going to start on thread for an MoM proposal, and call it the 747-50. We cut the entire back of a 474-8i from the hump back ala A380 mini (double deck, full length) and make an argument for it. :idea:


Brilliant!
 
LightningZ71
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Re: Medium Sized 4-engine aircraft

Mon Mar 20, 2017 6:16 pm

I mean, seriousl, seriously! Why don't we just go back to modern four engine turboprops for mid sized transatlantic hauling?!?! So what if it takes 10-14 hours to get from JFK to LHR, it's a good 7% more efficient and can go 11 abrest with the same economics as a 6 abrest narrowbody! Heck, the dash-8 proved that a modern turboprop can reach near jet speeds in a commercial airliner! What about a widebody TU-95 version? There must be a way to make those turboprops noise compliant!!!

SMDH...

(In case anyone needs to know, that was sarcasm...)

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