Thrust Reversers
 

Hello, I'm new to this forum and I have a question about TRs. What is the average time that it takes to fully deploy a clam shell type thrust reverser, and approx how much in percentage will they decrease landing distance? Thanks in advance.

To the best of my knowledge, for the clamb-shell type, you have imediate deployment which provides aerodynamic braking, and then the (apx.) 6 seconds for spool up time. But then again, one system varies from the next.

Somebody chime in if I am way off...

Citation Encore takes about 4 seconds to deploy enough that some reverse thrust is noted at low speeds (taxiing), and about 2 seconds to deploy enough that aerodynamic braking occurs at high speeds (landing). Either way, it takes about 4-5 seconds before the "clam-shell" doors have fully deployed and additional thrust can be added.

Don't know about how much they decrease the landing distance, but have seen regarding the following corrections to landing distance figures with the TRs inop (these come from the CRJ performance manuals and factory approved procedures):

one or both TR(s) inop: increase required distance by factor of 1.10 (10%) for landing and 1.15 (15%) for takeoffs.
Thrust reverser inop operations limited to Dry/Damp (non-contaminated) runways only.

Example:

Performance charts for TRs operative indicate landing distance of 3500 feet.
If TR's are inoperative, multiply distance by 1.10 for an inop distance of 3850'.

i know it saves the brake pads.... a few pounds extra burned is alot cheaper than runnin thru braking equip

Also for airline ops where you want to turn the plane around quickly the TR's are important because if you land without them, the brakes will get VERY hot and it can take an hour+ for them to cool down to the point where you can take off again...

The Sabreliner takes about 3-4 seconds to deploy the reversers. Once they are out, they take about 3 more seconds to spool. Honestly, this is the first aircraft that I have flown with a clamshell type reverser and find them relatively poor. The brakes are much more effective. Speaking only from a pilots perspective, a cascading reverser is MUCH more effective (with a clamshell you are limited to around 70-75 percent N1 and they will burn the paint off the pylon if left out too long, but the cascading reverser gives you 100% N1 and you can use them to slow the airplane while taxiing. The amount of power you can use depends on the stow time vs. the spool down time of the engine.)
The positive thing is that Clamshells come out everytime and never when you don't want them too. Not the same with a corporate jet with a cascading system.

Take Care!

In the ERJ at the operation I flew at we hardly ever used them. Supposedly new generation brakes work best at high temperatures.
I have read in the Turbine Flight Manual text that reversers typically dont do much. They may decrease rollout by a small percentage but have been used to reduce (older generation) brake wear.
I talked once with a retired L-1011 capt. where I asked him the same question. He laughingly relpied "I thought they (reversers) just made noise."


It is obvious, however, that brakes do the most work along with spoilers.

There is a great article in Business and Commercial Aviation this month about how thrust reversers work (and how they don't.) The FAA's new stance is that people should not count on them when doing landing numbers. Read the article, it's pretty good!