aguilo
Posts: 237
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Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 8:16 am

Many of USAirs 733 and all 727s don't have engines with cowlings that open once reverse thrust is applied. So how does this work? With no openings in the cowl where does the reversed thrust go if the engine is still sucking in air through the fan?
 
futureualpilot
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RE: Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 8:19 am

Im sure they can, but the pilots may not have selected reverse thrust for those particular landings. It is not always needed to stop the aircraft.
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aguilo
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RE: Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 8:24 am

futureualpilot: I know its not always necessary to use reverse, but I think its pretty obvious that they are in fact using reverse thrust when you can feel and hear the reverse thrust, but are sitting right next to the engine (on a 733) and not seeing the cowling open up.

Seems that the opening cowls are found on newer engines primarily (DC9 MD80 excluded)

So the question remains: Where does the thrust go?
 
futureualpilot
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RE: Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 8:36 am

it is obvious when they go into reverse, what you probably heard and felt was the spoilers coming up into the slipstream and slowing the aircraft down.

If you have any pictures of these cowlings without reversers, post them because I have never heard of engines such as that, and it may help somebody else give you a better answer than just my .02!

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BA
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RE: Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 8:39 am

Reverse thrust is simply not possible without cowl movement.

There are different types of cowel movements, you have the sliding cowls which is most common such as those on the CFM56s on the 737s, you have the petal cowels such as those on the CFM56ss on the A340-300s and A320 family, and you have the clamshell reversers such as those on the JT8Ds on the DC-9 and MD-80 series.

The 717's BR715 has a unique looking petal reverser which misleads people to think it is a clamshell reverser when it is not.

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L-188
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RE: Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 8:41 am

Do you see those grates that are on the aft ends of the cowls on the 727.

The buckets are under them.

The reverse thrust passes through the grates.
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boo25
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RE: Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 9:59 am

If its a long runway, i believe piolts are told to be prudent in using rev thrust, as brakes are a whole lot cheaper than the complex rev mechanisms Big grin
 
Fly2HMO
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RE: Reverse Thrust With No Cowl Movement: How?

Thu Apr 08, 2004 12:04 pm

Spoilers make a hell lot of noise, only slightly less than reverse, that's what you heard.
 
doug_or
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Current Build

Thu Apr 08, 2004 12:28 pm

L-188 is right on with the 727s, and all 737 classics use pretty much the same model and coweling for their CFM56s. they use blocker doors to reverse fan air through the cascade vanes and out.... The coweling. sorry.


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reverse vanes are the bits on top and bottom on 1&3 and sides of 2. internal doors block mixed core and fan air.
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SlamClick
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RE: Reverse Thrust With No Cowl Movement: How?

Fri Apr 09, 2004 12:09 am

US 737s have the standard CFM reverser system shown in the photo above. It would be difficult to spot the reversing mechanism when it is in the forward thrust mode, but the "translating sleeves" slide aft and the blocking doors get levered out into the fan shroud and direct fan air forward. It all disappears when the reversers stow.
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DC-10Tech
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RE: Reverse Thrust With No Cowl Movement: How?

Fri Apr 09, 2004 4:52 pm

The turbojet powered 737's and 727's use what is basically an internal clamshell reverser. It works just like the DC-9, you just can't see the clamshells opening.
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747Teach
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RE: Reverse Thrust With No Cowl Movement: How?

Fri Apr 09, 2004 8:54 pm

Aguilo: If you look closely at this photo,
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you can see the louvers that redirect the reverse thrust airflow. They are the grill-like areas on the right side of the no. 2 engine aft cowl (you can't see the louver on the left side in this picture), and the upper and lower louvers on the no. 3 engine aft cowl. As L-188 says, the pivoting reverser doors ("clamshells" or "buckets") are under the louvers. In forward thrust, the buckets pivot outward until they are flush with the inside of the exhaust, closing off the louvers and allowing the airflow to exit out the back of the engine. In reverse thrust, the buckets pivot inward until they meet. This opens the louvers, and at the same time blocks the airflow from exiting the rear of the engine. The airflow then has nowhere else to go, so flows out through the louvers. The louvers are angled forward, so this forward flowing air tends to push the aircraft aft, for reverse thrust. Regards,

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