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AND NOW - HOw do those Jet engines REVERSE upon landing?

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AND NOW - HOw do those Jet engines REVERSE upon landing?

 
Old 03-14-2019, 07:56 AM
  #21  
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Originally Posted by VatorMan View Post
According to FPD, you've now killed everyone on board because you've "unsettled" the aircraft.
According to DaNN, you've also pivoted the rear wheels off the ground because you've "cobbed" the brakes.
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Old 03-14-2019, 09:43 AM
  #22  
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Old 03-14-2019, 09:55 AM
  #23  
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Does the braking system work on a treadmill???
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Old 03-14-2019, 10:21 AM
  #24  
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Some questionable explanations in here. I'm waiting until Gixxer weighs in before determining the correct answer.
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Old 03-14-2019, 10:57 AM
  #25  
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What chiefttp said.
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Old 03-14-2019, 11:01 AM
  #26  
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They don't make any straight jet engines anymore. At least not for modern aircraft.
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Old 03-14-2019, 11:31 AM
  #27  
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Originally Posted by VatorMan View Post
According to FPD, you've now killed everyone on board because you've "unsettled" the aircraft.
Damn it!
Originally Posted by dvarapala View Post
Modern aircraft have a special treadmill that they deploy below the wheels on landing which makes the plane stop.
Beat me to it!
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Old 03-14-2019, 12:03 PM
  #28  
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Originally Posted by jcsperson View Post






These pictures show what is happening rather well.

What has changed in the last 30+ years is the engines now have a High Bypass Ratio which means that up to 70+% of the thrust of the engine comes from the air that bypasses the actual engine. That is why the cowls are so much larger than the old engines as seen in the second picture above. Hell, the engine cowl on a 777 is as big in diameter as the fuselage of a 737. The HBR engines are also much quieter than the old engines because of all the airflow around them muffles the noise.

The old jet engines used the clamshell to redirect the engine thrust as shown in picture 2 above. All the others show what is happening when the bypass air is redirected to slow the aircraft.
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Old 03-14-2019, 12:11 PM
  #29  
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Originally Posted by JetMechZ16 View Post
They don't make any straight jet engines anymore. At least not for modern aircraft.
Gay engines?
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Old 03-14-2019, 12:24 PM
  #30  
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Originally Posted by grandpawmoses View Post
Gay engines?
Turbo jets, turbo fans, turbo props, turbo shafts. The majority of passenger/airline winged aircraft are turbo fans and the bypass air on these turbo fans has grown as Silverback has pointed out.

The last straight jet engine that I worked on was in the EA6B which was a Pratt & Whitney J52-P-408A like the one pictured here.





Just for you though, here's the Turbo ghey engine.

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Old 03-14-2019, 12:48 PM
  #31  
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they just run the treadmill backwards
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Old 03-14-2019, 01:03 PM
  #32  
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Originally Posted by JetMechZ16 View Post
Turbo jets, turbo fans, turbo props, turbo shafts. The majority of passenger/airline winged aircraft are turbo fans and the bypass air on these turbo fans has grown as Silverback has pointed out.

The last straight jet engine that I worked on was in the EA6B which was a Pratt & Whitney J52-P-408A like the one pictured here.


Well since you mentioned the distinction, could you explain the difference between a "jet" engine versus a turbofan or turboprop in language even an ignoramus can understand?
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Old 03-14-2019, 01:07 PM
  #33  
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Originally Posted by VegasJen View Post
Well since you mentioned the distinction, could you explain the difference between a "jet" engine versus a turbofan or turboprop in language even an ignoramus can understand?
As I understand it, a jet's thrust is from the exhaust only. Turbofans and turboprops use the shaft at the center of the engine to spin a fan or propeller to also make thrust.

Jet:



Turboprop:



Turbofan:


Last edited by Meh; 03-14-2019 at 01:10 PM.
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Old 03-14-2019, 02:49 PM
  #34  
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Originally Posted by Meh View Post
As I understand it, a jet's thrust is from the exhaust only. Turbofans and turboprops use the shaft at the center of the engine to spin a fan or propeller to also make thrust.

Jet:



Turboprop:



Turbofan:

OK, so I get the "jet" engine. No problem.

I kind of thought the turboprop was as described. I assume that's like the engines for something like the C-130 were it's a jet engine that drives the props. Correct me if I'm wrong.

Now, on to the turbofan. So is that what a conventional commercial airliner uses? Is the jet engine actually providing any significant thrust? Or is the fan the primary source of thrust?
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Old 03-14-2019, 02:54 PM
  #35  
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On all Airbus and Boeing commercial planes they use turbofan engines. As a rule of thumb you can assume that 70% of the thrust comes from the fan and the remaining 30% comes from the jet engine.
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Old 03-14-2019, 03:02 PM
  #36  
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Originally Posted by Silverback51 View Post
On all Airbus and Boeing commercial planes they use turbofan engines. As a rule of thumb you can assume that 70% of the thrust comes from the fan and the remaining 30% comes from the jet engine.
OK. So what's the advantage as opposed to a straight jet engine? More efficiency/economy? Better power to weight? Complexity?
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Old 03-14-2019, 03:06 PM
  #37  
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Jet engine operation simplified:

SUCK - SQUEEZE - BLOW - GO!

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Old 03-14-2019, 03:13 PM
  #38  
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A friend of mine, back in HS (early 1970's) had a jet boat, that was maybe 17 feet long, but had an Olds 455 engine. Being a jet boat, you could instantly put it into reverse (as this was just re-directing the outlets under the boat, to face forward). It was incredible how fast that thing would come to a stop. (And top speed was not bad, either, over 65, IIRC...)
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Old 03-14-2019, 03:15 PM
  #39  
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Originally Posted by VegasJen View Post
OK. So what's the advantage as opposed to a straight jet engine? More efficiency/economy? Better power to weight? Complexity?
The thrust rating of a 777 engine is in excess of 100,000 pounds. It would take a very large pure jet engine to produce that thrust. Also the air from the fan significantly quiets the roar of the jet engine. Also a lot of time and effort is input into the design of the chevrons where the jet exhaust and the fan air meet. Once again this is to make them quieter.

So they are more efficient, quieter, and have a better power to weight ratio. The only downside is that they are more complex, but in the end not that much.
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Old 03-14-2019, 03:30 PM
  #40  
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Originally Posted by Silverback51 View Post
The thrust rating of a 777 engine is in excess of 100,000 pounds. It would take a very large pure jet engine to produce that thrust. Also the air from the fan significantly quiets the roar of the jet engine. Also a lot of time and effort is input into the design of the chevrons where the jet exhaust and the fan air meet. Once again this is to make them quieter.

So they are more efficient, quieter, and have a better power to weight ratio. The only downside is that they are more complex, but in the end not that much.
While this engine is technically a turbo fan not much additional thrust is provided by the fan. The actual bypass air area is no where near that of a commercial airliner. I'm just showing this as an example of the wide variety of turbofans that are out there.

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