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Reverse Thrust Limit During An RTO?  
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Posted (10 years 9 months 2 weeks 1 day 14 hours ago) and read 3856 times:

Hi guys.

A few months ago in this forum it was explained that on a certain type of airliner (I can't remember which type  Laugh out loud), the thrust reversers (TR's) are automatically stowed after landing once the airliner has slowed down to 100 knots to help prevent any engine damage (FOD) from being caused by the reverser's air blowing up any debris from the runway which could be injested into the engine's intake.

My question is ........

During a rejected takeoff (RTO), if the pilots really need to use "full reverse thrust" and braking to prevent themselves from overshooting the end of the runway, can the 100 knot TR limit be manually or automatically removed?

I believe that the last thing pilots would be worried about during an RTO while trying not to run off the end of a runway and into approach lights, trees, etc, is engine FOD.


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Thanks,

Chris  Smile


"Just a minute while I re-invent myself"
12 replies: All unread, jump to last
 
User currently offlineMusang From United Kingdom, joined Apr 2001, 864 posts, RR: 7
Reply 1, posted (10 years 9 months 2 weeks 1 day 13 hours ago) and read 3794 times:

Agreed, Spaceman. FOD would become second priority, to stopping it at all costs.

If I remember correctly, the 737 idle reverse is just that, Normal Reverse is 75% thrust, Max Reverse is 85%. Since it ejects at a 45 degree angle approximately, the actual stopping effort is nothing like the acceleration at the same levels of forward thrust.

The common misconception that reverse thrust is brutally effective is due to the fact that if a pilot IS using a lot of reverse, he's SIMULTANEOUSLY pounding the brakes (or the Auto-brake system is). Its actually the wheelbrakes which fling you forward in your seat, the deceleration from reverse is comparatively gentle.

But in the context of your original question - every little bit helps.

Regards - Musang


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 2, posted (10 years 9 months 2 weeks 1 day 13 hours ago) and read 3786 times:

Hello Musang.

Thank You for your reply and for the numbers regarding the different reverse thrust settings on a B737.

Unfortunately I can't remember what type of airliner was being discussed when it was explained that at 100 knots or less during landing rollout the reversers automatically retract. It was that aircraft (or any others with this TR safeguard system against FOD) that I was curious about with regards to whether or not the pilots could overide the TR's 100 knot restriction system.

I'm sure that if a flight crew's jet was still rolling forward when only 50 feet from the end of a runway after an RTO or problem during landing, they would want every little bit of help they could get. Even if it was to just prevent the nose gear tires from sinking into the grass off the end.

I understand that some jet airliners can use reverse thrust when moving slower than 100 or so knots. All I have to do is think of MD-80's (I believe) pushing themselves out of a gate with reverse thrust.

I agree with you that many people don't understand that it's not the ground spoilers or TR's that bring an airliner to a stop (although they help), it's the aplications of the brakes.

Question .....

On landing rollout, does the Boeing 737 have a TR speed restriction to prevent FOD?

Chris  Smile






"Just a minute while I re-invent myself"
User currently offlineSovietjet From Bulgaria, joined Mar 2003, 2609 posts, RR: 16
Reply 3, posted (10 years 9 months 2 weeks 1 day 13 hours ago) and read 3767 times:
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Probably none of the tail-mounted engines have that because there is almost no chance of FOD period.

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 4, posted (10 years 9 months 2 weeks 1 day 12 hours ago) and read 3722 times:

Hello Sovietjet.

That's a very good point. I never thought of that.  Laugh out loud I guess I can rule out those types of jets with regards to having a TR speed limit during rollout.

Has anyone ever seen a jet with wing mounted engines push itself backwards out of gate? Probably not.

You can see in these 2 photos which aircraft type's mechanics need to be more worried about FOD.


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By the looks of these photos, if any type of airliner's mechanics should be worried about FOD while the thrust reversers are working, it's the 737. Their engines are very close to the ground. Meanwhile, they probably don't have a speed limit for TR use!


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Chris  Smile





"Just a minute while I re-invent myself"
User currently offlineOkie From United States of America, joined Jul 2003, 3041 posts, RR: 3
Reply 5, posted (10 years 9 months 2 weeks 1 day 10 hours ago) and read 3612 times:

I can not imagine T/R closing when decelerating through 100 knots automatically while engines are spooled up.
Even stowing the buckets before the turbines spool down causes unexpected acceleration. Trust Me.


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 6, posted (10 years 9 months 2 weeks 1 day 8 hours ago) and read 3554 times:

Hello Okie.

Thanks for your reply.

I appreciate your comments. What you are saying about the unexpected acceleration even makes sense to me.

Would this acceleration still occur if the reversers were not buckets/clamshells? Would this happen with every type of TR?

I think the aircraft involved was something like a 767 or 777 ...... maybe!

I will tell you this however, I will find the thread (even if it takes me a week) where it was explained that on a certain airliner the TR's stow automatically after 100 kts. That way you (and everyone else) won't think I'm imagining things. Perhaps I was (we were) taught something incorrect.

I do trust you! Big grin


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineSxmarbury33 From United States of America, joined Oct 2000, 445 posts, RR: 0
Reply 7, posted (10 years 9 months 2 weeks 1 day 8 hours ago) and read 3532 times:

No regular comercial airliner that i know of has an auto shutoff type device on the TR's. It is SOP for a lot of airlines though to have them at idle reverse at aound 70 and stowed at 60. This is totally up to the discretion of the pilot however. There was a copule pics of i think the little rock AA MD80 with the buckets still deployed. It might have been another A/C though.

User currently offlineAJ From Australia, joined Nov 1999, 2391 posts, RR: 24
Reply 8, posted (10 years 9 months 2 weeks 1 day 7 hours ago) and read 3481 times:

Mr Spaceman, I can assure you the 767 doesn't 'autostow' at 100kts. If we needed it we would use reverse thrust until stationary to prevent injury to passengers and crew.

Full reverse is much more effective at high speed, the effect reducing as the aircraft decelerates.


User currently offlineOkie From United States of America, joined Jul 2003, 3041 posts, RR: 3
Reply 9, posted (10 years 9 months 2 weeks 1 day 5 hours ago) and read 3453 times:

Mr Spaceman

Maybe you are thinking of a Speedbrake automatically stowing on some particular aircraft? Tail type as on an F-100 or ARJ, just a thought.


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 10, posted (10 years 9 months 2 weeks 10 hours ago) and read 3371 times:

Hi guys.

Thank You very much for getting back to me on this subject.

You guys have made it very clear that there are no Auto Shutoff or Autostow devices for any commercial airliners's TR's. Thanks for drilling this into my head. I still have not been able to find the thread were this was mentioned (I'm not insane), but I will.

I'm not perfect, perhaps my memory has betrayed me. Although I dought it. I'm a very smart guy and I have a great memory. I hope you guys have been enjoying teaching me and everone else about what makes these gorgeous machines tick. I Thank You.  Big thumbs up

> Sxmarbury33, you stated .......

It is SOP for a lot of airlines though to have them at idle reverse at around 70 and stowed at 60.

I understand that it's the pilot's decision and that it's not automatic. However, It does sound like the TR's are stowed at 60 to prevent FOD. Is this the case?

> AJ, I'm sure you would do anything you had to sir.

> Okie, Thanks for the thought, but this question does not have anything to do with speedbrakes.

Chris  Smile




"Just a minute while I re-invent myself"
User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4490 posts, RR: 21
Reply 11, posted (10 years 9 months 2 weeks 5 hours ago) and read 3336 times:

Chris,

I seem to recall that certain models of the 747 have leading-edge slats that retract at least partially upon reverser activation to prevent FOD...maybe this is what you're thinking of?



I got my head checked--by a jumbo jet
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 12, posted (10 years 9 months 2 weeks 3 hours ago) and read 3335 times:

Indeed, the 'ole B707 had complete leading edge device auto-stow upon selection of engine reverse thrust...to prevent slush from being driven up/under the leading edge kruger flaps...and when reverse was de-selected, leading edge devices deployed once again.
An old design which worked good.


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