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Do Prop-jets Have Thrust Reversers

Thu Oct 12, 2000 9:29 am

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RE: Do Prop-jets Have Thrust Reversers

Thu Oct 12, 2000 10:13 am

This topic has been discussed ad nauseum! Yes, the props can be feathered then reversed. Please use the search function before asking questions. Please also check the Tech Ops board for information such as this.

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RE: Do Prop-jets Have Thrust Reversers

Thu Oct 12, 2000 10:15 am

When I'm at BOS, I can hear thrust reverse from every DHC-8, and SAAB 340 that lands, although they aren't used for very long, maybe 5 seconds.

« On ne voit bien qu'avec le cœur. L'essentiel est invisible pour les yeux » Antoine de Saint-Exupéry
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RE: Do Prop-jets Have Thrust Reversers

Thu Oct 12, 2000 1:15 pm

There are two levers that control thrust in most propjet aircraft making a total of four for two engines.

One lever sets the speed of the jet engine, rpm's, the amount of fuel supplied to the engine.

The other lever sets the amount of blade pitch. This lever is used more than the engine speed lever.

During the takeoff run, the engine speed lever is set at maximum, the pitch lever is set for the maximum "bite" for forward thrust.
Once in cruise flight, the engine speed is backed down to cruise and the speed is adjusted using the pitch lever.

Upon landing, the length of the runway, how fast the aircraft must clear the runway is taken into consideration of the pitch and engine speed settings.

Short runway= Increasing engine speed while setting the prop pitch to reverse and pushing the brake pedal.

Long runway, light traffic= Maybe increase engine speed some while setting the props for reverse, might not even touch the brake pedal.

On the Saab 2000, there are two levers only, one for each engine. The levers control both engine speed and prop pitch combined.

The worst possible situation is where an engine fails and the props cannot be feathered. The means set for the least resistance against the moving air.

The happens ever so rarely. You have one of two large props creating so much drag on one side of the aircraft that it goes into a sharp turn on dives till it hits the ground. Most if not all propjets have "Auto-Feather". If one engine fails, it will automatically feather the dead prop. This is most important when the aircraft rotates, i.e., leaves the ground.
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RE: Do Prop-jets Have Thrust Reversers

Thu Oct 12, 2000 1:50 pm

Most prop-jets do for the most part have reverse pitch to aid in slowing the aircraft.
Some like the Dash-8 with a huge diameter prop don't usually need alot of reverse on landing, especially if the are using a large runway. After landing the crew will put the props into a sort of discing mode which is not reverse, but like a zero blade angle. The large surface of the spinning prop (flat plate) is usually enough to slow the aircraft, and it does sound similar to reverse.
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RE: Do Prop-jets Have Thrust Reversers

Thu Oct 12, 2000 2:04 pm

To be precise on this issue it is true that turoboprops have two sets of engine control levers, power levers and prop levers.
The prop levers have settings between feather and high rpm (low pitch). Generally in flight this levers are used to adjust rpm, and are adjusted to high rpm on final approach for good power response. After this the next time they are touched is on shutdown.
Reverse thrust is a function of prop pitch, however it is selected using the power levers. After the flight idle gate (minimum airborne thrust) the power levers are raised over a gate into beta mode which readjusts the prop pitch stops to allow selection of reverse. This is the growling noise turboprops make on landing and whilst taxiing. Continuing to bring the power levers back applies reverse thrust to a set limit. Continuous reverse thrust is limited due to the possibility of foreign object damage to the props and engines, however it can be used to back the aircraft on the ground.
I hope this helps.