PW JT3C on Boeing 707

[72linerlover]

Hi to everybody.

Does anyone exactly know how is arranged the exhaust section.

In particular:

from the pictures I know there are no visible vanes or flaps or anything else, providing thrust reversing. Perhaps is there something inside for the purpose and the gases come out from what apparently are grids, just before the 21-tube exhaust?

Has anyone good drawings about?

T.i.a.

Euge

[majortomski]

Euge, the JT3/J-57 engines never had thrust reversers. A 707 had nothing but breaks to get it stopped.

[72linerlover]

Euge, the JT3/J-57 engines never had thrust reversers. A 707 had nothing but breaks to get it stopped.

I'm afraid they had, if these sources are reliable.

http://yarchive.net/.../kc135_707.html

http://www.airliners...ain/158452/1/#1

Thanks anyway for responding.

Euge

[TheFlyingDutchman]

I assume you have seen this photo already, the description says this one has NO thrust reverse. I think this is the engine with the grid in front of the multiple tube exhaust you were talking about.

http://www.airliners.net/photo/West-Winds/Boeing-720-022/0772071/L/&sid=b9da131240fb1928a80b1692f4f2b1f1

Do you have photos of the specific aircraft you want to build?

[72linerlover]

Hi Jelle.

Thanks for your help.

Well, "build" is a too great word, at the moment. I'm playing with the idea with some wood and plastic.

I love this one.

Looking at the photo you linked, I suspect there is a reverser, even if the description states there isn't.

Everyone may be right or wrong. Still waiting for an expert.

Euge

[TheFlyingDutchman]

Well keep in mind that thrust reversers are kind of overrated. They are absolutely not essential to bring a jet airliner to a full stop. In fact, they don't do really much and are only useful on short runways that are also contaminated by ice or snow. In this case the wheel brakes still do about 80% of all work. So it won't surprise me if the early 707's did not have them!

I can't think of any way to reverse the engine on the photo I linked. The hot section comes out at the back and there are no clamshell doors to reverse them. On modern turbofans only the cold bypass air is reversed and the old turbojets did not have any bypass, or very little.

Edited January 11, 2013 by TheFlyingDutchman

[Jennings]

Turbojet powered 707s did *not* have thrust reversers. Of that I am 100% certain.

[Jeff Jarvis]

Greetings!

Jennings, I am very surprised at your statement!!!!

While the turbojet powered 707-120, -220 and -320 were pretty simple in their slow speed wing high lift devices, they ALL were equipped with thrust reversers from their date of entry into service and were certificated with them.

On the JT3C-6 (also the JT3C-7/12 of the 720) as well as the JT4A engines, the rear of the cowling with the sound suppressor mounted on it had a venetian blind grille which had blocker doors inside the tail pipe that closed, thus redirecting the thrust through the grilles.

I would also disagree totally with the statement that thrust reversers do not do much. They are VERY effective on some aircraft, achieving up to 70% effectiveness on the 727, and allow airplanes to be backed up in many applications. Even the target type reverser found on the DC-9, 737-200 and many others are capable of producing at least 40% of the effective forward thrust in reverse. When you land a DC-8-63F at 275,000 lbs it is tempting to get on the brakes immediately since you're up around 150 kts, but I always used heavy reverse and stayed off the brakes until I was below 100 kts (if possible) so I could park the airplane and know I was not going to thermal any tires.

If they did not work, they would not be installed. The KC-135R model had them deactivated as part of the installation of the CFM-56, and the guys who flew the C/KC-135E which had reversers on its JT3D (TF33) engines will tell you they wish they had them on the R model.

Regards,

Jeff Jarvis

Edited January 11, 2013 by Jeff Jarvis

[Jeff Jarvis]

I assume you have seen this photo already, the description says this one has NO thrust reverse. I think this is the engine with the grid in front of the multiple tube exhaust you were talking about.

http://www.airliners.net/photo/West-Winds/Boeing-720-022/0772071/L/&sid=b9da131240fb1928a80b1692f4f2b1f1

Do you have photos of the specific aircraft you want to build?

What do you think the grille is in front of the sound suppressor?

It's a thrust reverser!

[bzn20]

If they fit a heavy piece of kit like a reverser you can bet your last pound its because they are needed.I've never landed in any airliner where the the thrust reversers we not used.

Thrust reversers also save the brakes/heatpacks and are therefore cooler.Saves the tyres from deflating and/or wheel fuse plugs melting.You cant do a turn 'round and take off within an hour/90 minutes with hot brakes.

The JT-3C thrust reverser was fitted just in front of the petal/noise reduction assembly as in the photo link above.Bucket/door actuators were at the 12 and 6 o'clock position.

Edited January 11, 2013 by bzn20

[majortomski]

Turbojet powered 707s did *not* have thrust reversers. Of that I am 100% certain.

So was I till I found a web page on the history of the JT3C and that 1961 article said they DID have TR's. But there is the possibilty that they where never used. Even to day on our "new" Challengers and Lear 60s TR's are one of the highest maintenance headaches.

Edited January 12, 2013 by majortomski

[Jeff Jarvis]

So was I till I found a web page on the history of the JT3C and that 1961 article said they DID have TR's. But there is the possibilty that they where never used. Even to day on our "new" Challengers and Lear 60s TR's are one of the highest maintenance headaches.

No, there is not any possibility that they were never used. Quite the contrary, they were practically ALWAYS used. Now, if they landed on a 12,000 foot long runway and the terminal was located at the far end.....

[TheFlyingDutchman]

Well I could be wrong about the effect of thrust reverse on early jet airliners (what this thread is all about, so excuse me :blush:/>) , but they do not very much on MODERN airliners. In fact, airlines operating on EHAM (Amsterdam Schiphol) are requested to not use them in normal weather conditions as the runways are long enough and to reduce noise emission. The manuals of the Airbus A320 family even state the effect of thrust reverse cannot be taken into account when calculating the landing distance, as they reduce the rollout distance by only 10 tot 20% in conditions where the wheel brakes are least effective. Of course wheel braking systems have become much more efficient over the last years because of anti-skid and the development of carbon discs that can absorb a lot more heat than steel.

Sorry guys, times have changed and operational habits from the 707/727 era are not applicable anymore.

Edited January 12, 2013 by TheFlyingDutchman

[bzn20]

Maxeret braking system (antiskid) came out in the 50's and have been widely used ever since.Carbon fibre brakes are a new ish developement and are fantastic in converting mechanical energy to heat energy and dissipating the heat energy very fast.This means they have greater braking efficiency.All of this means that reverser function times are reduced.Reversers arent/werent used (VC-10,707-400,DC-8-40)for as long as much more than 20 seconds anyway,unless there is in an emergency situation.

There was a restriction on reverser operation times,something like 20 secs in 1 hour.You couldnt use the reversers again for 1 hour after a 20 sec reverser operation.

[72linerlover]

Thanks so much to all for the news and suggestions.

Regards

Euge

[Jeff Jarvis]

Greetings!

Well......... Where do I start?

First, there is a LOT of misinformation in these posts. I am NOT talking down to anyone, but your "Facts" need correcting.

My employer gave up on carbon brakes on the 757 because they are so expensive compared to the steel brakes (note the spelling of "Brakes"), and they were only getting at best about 40-45% of the brake life they were promised, yet the brakes cost more than 10 times what the steel ones did. They tried to get better life by reducing the use of autobrakes and placing more emphasis on judicious use of reverse thrust, but it only helped a little. After years and years of promises made and never kept, they gave up on them a little more than 2 years ago. On my aircraft, the A300F4-622R, we do have carbon brakes, but there is a 300 degree temperature restriction for takeoff, thus I ALWAYS use the brake cooling fans after landing so as to avoid the "Bong" and the ECAM message "Hot Brakes" which inevitably follows almost every landing with even minimum autobrakes. I then also use the cooling fans on taxi out. At DEN, if I leave the cargo ramp and taxi to Rwy 8R, I WILL have hot brakes upon reaching the runway if I do not use the brake cooling fans. Brake cooling fans must be "OFF" for takeoff.

So much for carbon brakes.

While there are restrictions on the use of reverse thrust, not one airplane I have ever flown had any time limit on the use of reverse in the limitations. This would include the 707, 727, 747, DC-10, DC-8 or the A300. None of the aircraft my company operates (757, 767, 747-400, MD-11 or A300-600 currently) have any such restrictions. However, we are not supposed to use reverse thrust to back up the airplane, and we should use no more than idle at speeds below 60kts so as to prevent FOD or compressor stalling. Note, these are company policies. We are also supposed to comply with restrictions on night use of reverse where noise restrictions apply, such as most European airports. These noise restrictions are out the window in cases of operational necessity, and I would point out that they are only in effect at airports with extremely long runways, such as FRA. Airports where runway length would preclude normal ops without the likely need of reverse thrust are generally not open at night. Some companies (Eastern Airlines was one) have used reverse thrust to power back from gates, and the 757 was one of these types approved for it, along with the DC-9 and 727. If the reversers don't do much, how do you explain backing airplanes out of gates with it?

You are correct in saying that the use of reverse thrust is never considered in runway stopping requirements. It never has been and is likely to remain that way.

Reverse thrust is still an important player in MODERN airliners whether or not they have carbon or steel brakes, and antiskid systems are a given on jet aircraft, and they always have been because it's the only way to obtain maximum effectiveness in braking without locking up the brakes and blowing the tires. You cannot feel a skidding tire in the cockpit. And, I might add, how do you think you are going to stop a heavy jet with an antiskid failure? That's right, you'll use HEAVY reverse thrust followed by manual braking techniques below 80kts. The DC-8, C5 Galaxy and the HS Trident all used inflight reversing for emergencies and/or quick descents too.

No, I just can't agree with the statement that thrust reversers don't do much and are not an important player in MODERN airliners.

To get back to the OP question, yes the 707/720 with turbojet engines had thrust reversers. Look at photos such as that 720 photo above to see what they looked like. Inside the tailpipe there are 2 vertically attached doors which rotate closed. The covers for the mechanisms can be seen above and also below the sound suppressor (the curved piece underneath), and the grille ahead of the sound suppressor on each side of the cowling directs the exhaust gases forward and outward. The 367-80 prototype did not have reversers on its original engine configuration, but ALL 707 airliners were built with them.

And that's all I have to say on this subject......

Regards,

Jeff Jarvis

Edited January 12, 2013 by Jeff Jarvis

[bzn20]

Jeff

The RR Conways (I was refering to) did have operating time restrictions.Which is why I stated VC-10,707-400 and DC-8-40 aircraft,these models were RR Conway powered.

The Super VC-10 had brake cooling fans fitted originally but when the RAF got the ex EAA aircraft they werent fittied.

Carbon brakes,cost and life etc.....As a pilot didnt you notice any difference in opperation between the two types?

[Jeff Jarvis]

Greetings bzn20!

Well, I never did fly a Conway powered 707 or DC-8, but a friend of mine did fly the DC-8-43. He is now almost 74 and has been retired since 1999. He flew a couple of ex Alitalia and CPAir airplanes out of MIA, but he never mentioned any time limits on the use of reverse, and I don't think that there could be any on the DC-8-40 series because they would not be practical as reverse is normally used inflight and it would be necessary for it to be available for a lot longer than 20 seconds. If I get the chance, I'll ask him about it, but he flew them in the early 1980's and that is a long time ago.

As far as carbon brakes go, they are supposed to last much longer than steel brakes do, but the engineering people I have talked to have told me that in most cases the extended life is largely a myth. They are incredibly expensive, however. Part of the expense is due to being very complicated in how the layers of fibers are laid out and bonded, and then there's the extremely long curing time, which can take a couple of years. They are supposed to take high heat levels better than steel brakes, do not fade when hot like steel brakes do, and are generally smoother and pretty much chatter free, although my experience does not indicate this to be true. I really feel that I can't accurately describe how they differ in use though because I have no experience flying one aircraft type fitted with both different brake types to compare them. I can tell you that the brakes on the A300 make a lot of noise and are somewhat jerky when I'm trying to smoothly come to a stop in my parking spot. We have temperature indications for every wheel and, strangely enough, the brakes on the right main are always hotter than those on the left, and it is not just me. They are always like that. Maybe it's because most of us are right handed and apply the right brakes heavier? I don't know, but then when you use the autobrakes on landing, the right ones are still always hotter.

If I make an autoland (or just manually land at BUR or ROA), or the runway is short or wet, or for whatever reason I elect to use "Medium" on the autobrakes, LOOKOUT! Be strapped in TIGHT, because once the wheels spin up, the brakes are applied NOW and the nose comes crashing down on the runway so hard you'll think you must have cracked the fuselage, and before you even get max reverse in you'll be down near 100kts. Those brakes work very well at stopping on a dime on a dry runway, but then you will immediately have the "BONG" and the ECAM message "HOT BRAKES" so you'll have to use the brake cooling fans. Applying full up elevator and timing it perfectly helps to alleviate the nose crashing down. A selection of "Minimum" on the autobrakes for landing gives about a 10 second delay in brake application and a more gentle deceleration, but you'll still get hot brakes if you don't turn on the brake cooling fans when clearing the runway.

Thrust reverser usage helps to alleviate the wear and tear on the brakes, but my gut feeling is that the benefits of carbon brakes, if any, are more than offset by their incredible expense. As for the A300 carbon brakes, it may be that we are stuck with them as I'm not sure that there are alternatives. As far as tires (Tyres to you Brits!), the only tire I have ever seen on our A300 fleet is made by Michelin.

Regards,

Jeff Jarvis

[Jeff Jarvis]

Greetings!

One more thing about carbon brakes is that they wear more quickly if you misuse them. Misusing them means constantly applying, then releasing, then reapplying them. In other words, using the autobrakes on landing is actually, in theory at least, better for brake life than not using autobrakes would be, but there is really not much that can be done about the stopping and starting that is part of taxiing around a modern and busy airport, especially when in line for takeoff, or after clearing the runway and trying to get to a parking spot with all of the taxiing involved.

Regards,

Jeff Jarvis

[bzn20]

Thanks Jeff.

Reversers in flight,amazing!The VC-10 didnt,I went on all the post major airtests 73-81.Even when we were going for the 1st stall test with full flap,slat and U/c down they never did it with reversers.Maybe because the engine position shrouds the tail plane,you wouldnt want a VC-10 stall,we just went to the stall warning and stick push.My dad was a flight eng on BOAC 707-436/465/336 and VC-10 i'll ask him later.Great info. Jeff,thanks again.

[Jeff Jarvis]

Greetings bzn20!

No, I'm sure the VC-10 did not ever use reverse in flight because it used spoilers/speedbrakes instead. On the DC-8 the flight spoilers were only operable with the landing gear extended and were only there to increase roll authority. Normally they never deployed because the outboard and inboard ailerons were adequate for roll control and the control wheel deflection was never great enough to cause the flight spoilers to kick in. The only time you would be likely to see the flight spoilers extend is during the flight control check as part of the before takeoff checklist on taxi for takeoff. The flight spoilers would be the spoilers outboard of the non sweptback part of the wing trailing edge, the outer 3 panels on each wing.

The use of inflight reversing on the DC-8 was restricted to the clean configuration, inboard engines only to the stops (DC8-62/63) or the EPR limit (all other models), and only to a minimum IAS of 190kts. The aircraft should not be trimmed to less than 0 degrees in pitch to avoid a huge trim change upon cancelling reverse. It worked very well, but shook like hell when applied at high entry speeds, so I always tried to slow down to 250kts or less before applying reverse, then letting the speed build up if necessary. One place it was commonly necessary was going into Maiquetia (Caracas) Venezuela from MIA because Curacao would not clear you for a descent when you were ready and asked for it, then when handed off to Maiquetia, they would not clear you down until they had you on radar and there was no traffic below you, so sometimes you might find yourself starting down 40 miles or more late, but with other traffic precluding any maneuvering to lose altitude, so you had no choice but to use reverse.

Reversing was not commonly used inflight on the DC-8 in passenger operations because of the shaking and noise, but it did work well when it was needed. On the other hand, using the spoilers to slow or descend on the 707 inflight required a logbook writeup and a required maintenance inspection because the inboard sections caused extreme vibrations on the horizontal stabilizers which led to cracking in the spars and that ultimately led to a crash when one failed back in the early/mid 1970's on a Donaldson (?) ex Pan American 707-321.

Regards,

Jeff Jarvis

[bzn20]

(I think) That was a cargo Dan-air 707 at lusaka G-BEBP.All dead.One of the crew's son was an apprentice at Dan-air early ish 80's.Couldnt believe it when he told me.Anyway I was working on a Tradewinds 707 at the time and we had to strip out the Tail plane weights for NDT and remove the fin,called up during the lusaka crash inquiry.Thats what they told us! I was RAF at the time doing some moonlighting!

Edited January 13, 2013 by bzn20

[Jeff Jarvis]

(I think) That was a cargo Dan-air 707 at lusaka G-BEBP.All dead.One of the crew's son was an apprentice at Dan-air early ish 80's.Couldnt believe it when he told me.Anyway I was working on a Tradewinds 707 at the time and we had to strip out the Tail plane weights for NDT and remove the fin,called up during the lusaka crash inquiry.Thats what they told us! I was RAF at the time doing some moonlighting!

I couldn't remember for sure whose airplane it was, but that it was in Africa, an ex Pan American 707-321 freighter conversion and the left horizontal stab failed. It led to a whole bunch of emergency AD's on the 707, and they found that the cracks would not always show up with conventional testing, so new methods were quickly developed. When they checked Pan American's remaining fleet of about 90-95 707s, about 60 of them had the cracks! Needless to say, we tried our best to avoid using the boards in descents and instead used the landing gear more often, but that also shakes and makes a lot of noise like the reversing does on the DC-8. One of the things that I think was more disconcerting to passengers when making these fast descents was the nose down attitude of the airplane.

Ah, well.... Six of one and a half dozen of the other! I can tell you, flying the DC-8 or the 707 requires that you be a thinker, slightly more so on the DC-8 because landing gear and flaps are not available for use above 230kts, but on the 707 the gear can be extended up to 270kts, and once the gear doors are closed again speed can be increased up to 320kts, but I don't remember the M limit. I admire a smooth 707 or DC-8 driver a lot more than I do anyone flying todays electric jets with their magic doodads to save your *** when you don't think a lot.....

Regards,

Jeff Jarvis

[bzn20]

G-BEBP was a 707-321c ex N765PA.

[Jeff Jarvis]

Yes, I did some looking and I saw that it was an IAS Cargo operation and the right stab is the one that came off, year was 1977, 6 people killed.

Boeing was lucky many times with 707 accidents. This one was a 707-321C freighter, and the discovery of the rudder hydraulic support structural faults in the vertical stab occurred on training flights with simulated engine failures, so loss of life was low in all of them.