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Hot-Stream Thrust Reversers  
User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Posted (14 years 6 months 4 weeks 1 day 16 hours ago) and read 1540 times:

The L-1011 and DC-10 originally had thrust reversers for the "hot stream" of their engines in addition to reversers for the fan air. The hot stream components were later deleted because of maintenance problems and as a weight savings. What was the resulting increase in the landing field length?

17 replies: All unread, jump to last
 
User currently offlineJet Setter From , joined Dec 1969, posts, RR:
Reply 1, posted (14 years 6 months 4 weeks 1 day 15 hours ago) and read 1363 times:

I believe hot-stream thrust reversers are also much noisier.

Are the hot stream thrust reversers identified by the following on early L1011s, 2 small pylon-like structures protruding from the rear of the tail pipe, and, on the DC-10 a flat plane in the jet pipe?
None of these airliners have them now, and they can only be seen on prototype/early production photos.

James 


User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 2, posted (14 years 6 months 4 weeks 1 day 13 hours ago) and read 1352 times:

I can't answer from a practical point of view, but theoretically I don't believe reverse thrust is factored in landing field length data.

There is still a wide range of application of reverse thrust. Some use a little; some use a lot. Regardless of how it is used, it is most effective on landing at high roll out speeds as opposed to lower speeds at the end of the landing roll out.

Best Regards,

Buff


User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Reply 3, posted (14 years 6 months 4 weeks 1 day 7 hours ago) and read 1323 times:

Yes, Jet Setter, what you described belong to the hot stream reversers. The L-1011 was a clamshell setup. I'm not sure how the DC-10 worked, but I believe those plates spread out into the exhaust stream. Once the reversers were deleted on the L-1011 they went to a more efficient afterbody which only stuck a little ways out of the back of the engine.

Reverse thrust isn't used to come up with landing field length? Interesting. But it sounds reasonable considering the takeoff run is what uses up the most runway. I understand the USAF E-3, a version of the 707-300B, doesn't even have reversers.

But I am still wondering how much more runway those aircraft use without the hot stream.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3701 posts, RR: 34
Reply 4, posted (14 years 6 months 4 weeks 1 day 5 hours ago) and read 1317 times:
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On modern a/c with Carbon brakes the reversers aren't used as the brakes are sufficient on their own. This of course saves wear & tear on th engines.

On the 747-400 the landing gear are fitted with torque limiters to limit the braking force as the brakes would overstress the gear if they were allowed to be used to their full capabilities


User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Reply 5, posted (14 years 6 months 4 weeks 1 day 2 hours ago) and read 1311 times:

Some of the airlines, on long runways, reduce the takeoff power and go for a longer roll to save wear and tear on the engines. So I guess it would follow that you do the same thing during landing. I was on an F-100 that took off from DFW with no flaps and the pilots said it was done because they didn't have to run the engine thrust as high.

There was another set of messages talking about the -146 and the fact that it doesn't have reversers. Very surprising to me, but the trend of the future?


User currently offlineJim From United States of America, joined Jul 1999, 455 posts, RR: 1
Reply 6, posted (14 years 6 months 4 weeks 1 day 2 hours ago) and read 1311 times:

No reversers on landing because the aircraft has carbon brakes?
No flaps on take-off to save engine wear?

Sorry gents, but I would need someone to substantiate those claims.

Reversers would be used on landing unless 1) you're talking corporate jets or 2) you're landing at Edwards or some other 15,000' runway. Think about the Space Shuttles; DC-9 size, no reversers, just an airbrake, takes FOREVER to stop after landing. Anything 777 size would need all the stopping power it could get.

Flaps increase the lift of the wing, making take-off and landing speeds lower. Therefore, the aircraft can get off the ground at a lower speed. Therefore, the drag of the gear on the runway and in the air prior to retraction is reduced faster. Therefore, the engines would work LESS with the flaps out. Also, transport aircraft are certified with flaps, and the FAA sure would be interested in a revenue take-off without flaps, especially since there have been numerous crashes blamed on improper flap position!!!

-Jim


User currently offlineB727-200 From Australia, joined Nov 1999, 1051 posts, RR: 3
Reply 7, posted (14 years 6 months 4 weeks 22 hours ago) and read 1303 times:


I too do not think we have seen the last of thrust reversers, particularly on large aircraft. The only time I have seen thrust reversers not used is on long runways or international flights that arrive prior to curfew at SYD.

I was returning once from Bali and (due to the noise reduction program) we touched down on 34L ( 13,000' ) and rolled 3/4 the length of the runway using wheel and wing brakes only. Also landing in HKG we did not use reverse thrust.

I still think it would be essential for wet landings or shorter strips though. As you can can tell I am not a great expert on this, so this is just my opinion.

Rgds,
B727-200.


User currently offlineDC-10 From , joined Dec 1969, posts, RR:
Reply 8, posted (14 years 6 months 4 weeks 19 hours ago) and read 1302 times:

The tristar did have a hotstream exhaust reverser but the DC-10 didn't...What the early DC-10s did have was a splitter fairing that was a sort of external acoustic noise dampening component......I really don't think that removing the hotstream reverser from the tristar really made any difference in landing roll performance....pretty insignificant i'd venture....Most of the air is cold fan air anyways....

User currently offlineDnalor From Australia, joined Mar 2000, 369 posts, RR: 0
Reply 9, posted (14 years 6 months 4 weeks 17 hours ago) and read 1294 times:

Yes NO reverse thrust.... see BASI (Australia) re Qantas's crew memo regarding this and how it attributed to a over run.

User currently offlineDnalor From Australia, joined Mar 2000, 369 posts, RR: 0
Reply 10, posted (14 years 6 months 4 weeks 17 hours ago) and read 1293 times:

I'd have to agree that the lack of hot reverse would have very little effect cos lets remember that the bypass ratio even on early engines is 5 to 1, so the percentage of reverse thrust lost would be insignifigant :-)

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3701 posts, RR: 34
Reply 11, posted (14 years 6 months 4 weeks 12 hours ago) and read 1298 times:
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The operator I work for has not been using T. Revs on its -400 for about 18 months. Carbon brakes work more efficiently at high temp and at these temps wear alot less. Since instigating this policy, studies have found that brake wear has been reduced by 15% and in addition to less stress on the engines there are also benifits in less noise on landing, less buffeting of the Thrust Rev structure & L.E. Flaps.

The only downside is slightly increased tyre wear.

The company is trialing this policy on the A340 now.

The foregoing, of course, does not preclude the use of reversers if the crew feel it necessary.

Regarding Flapless T.O.'s is suggest you look at the post "No Flaps Departure? Scared The @#%^ Out Of Me". Use the search facility.



User currently offlineAdam84 From United States of America, joined Jul 1999, 1400 posts, RR: 2
Reply 12, posted (14 years 6 months 4 weeks 7 hours ago) and read 1292 times:

I was on a NW Airlink flight from MSP-DLH on a BAE-146 and they didnt use thrust reversers, or the plane didnt have them, to stop, it seemed like it took forever to stop.

User currently offlineJim From United States of America, joined Jul 1999, 455 posts, RR: 1
Reply 13, posted (14 years 6 months 3 weeks 4 days ago) and read 1285 times:

It helps kill the taste of crow.

I had never imagined that anything bigger than a Cub would even attempt to get airborne with out flaps to at least 15 units.

And I guess I just don't know enough about these carbon brakes yet (even thought I'll be teaching that section in about a month)!

MEA CULPA, MEA CULPA, MEA CULPA

-Jim


User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Reply 14, posted (14 years 6 months 3 weeks 3 days 16 hours ago) and read 1274 times:

The flapless takeoff was done at DFW with nice long runways. Aircraft are tested in all sorts of configurations for takeoff and landing distances, and the pilots have all that info available. So they would tailor their aircraft configuration to conditions. Not every airport or payload is suitable to flaps up takeoff or reverser-less landing. The accidents refered to happened because the flaps were not in the proper position for the airspeed and angle of attack; if you know you are departing without flaps then you have already adjusted your procedure accordingly.


User currently offlineJim From United States of America, joined Jul 1999, 455 posts, RR: 1
Reply 15, posted (14 years 6 months 3 weeks 3 days 1 hour ago) and read 1273 times:

Today I talked at length with Rick, who is one of DALs 'MEL men' about this topic. He really helped me understand what it is all about.

Basically, the FAA does not consider T/Rs as a method of stopping the aircraft. They have no bearing on the certification process. Braking is the only method the FAA recognizes.

As to the Flaps, he was suprised when I repeated what many, many people had written. All he could add was that to the best of his knowedge, DAL procedures call for a minimum of 15 Units on TO. He doesn't know of any procedure where DAL would allow less than that.

I guess I am a victim of living a sheltered life. It just shows me that there is much out there I don't know!

Jim


User currently offlineDash8 From New Zealand, joined Aug 2005, 2 posts, RR: 0
Reply 16, posted (14 years 6 months 3 weeks 2 days 23 hours ago) and read 1265 times:

Buff was right in his post.
Thrust reversers aren't used in calculation of any normal landing distance calculations. Only high drag devices and wheelbrakes.
Thrust reversers are an aid to decelleration of the plane. The crew have this additional braking device as an extra option.

As to flapless TO's, it pretty harmless on conventional wings (with the cross-section we've all seen in private pilot courses). But do not try this with any supercrytical wing as you're sure to perform a high speed taxi right off the end of the runway.
I beleive the 727 was the last commercial airliner to use a modified conventional wing. All others have supercritical wings. All have slats.....SLATS.
If you plane has a leading edge device and THOSE aren't deployed for TO, then you're deep in the "boo boo" !!!!!!!!!
Flaps are just a matter of increasing speed. Slats are a matter of lift production and of diar importance.

Sincerely,

Dash8


User currently offlineDnalor From Australia, joined Mar 2000, 369 posts, RR: 0
Reply 17, posted (14 years 6 months 3 weeks 2 days 20 hours ago) and read 1262 times:

The 727 has an ultra super critical wing*LOL* its has 26, yes 26 leading and trailing lift devices in total and it needs everyone of them to take off


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