Blackbird
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KC-135 Tanker Wing

Sat Jan 06, 2007 9:17 am

I've been told that it can cruise safely at Mach 0.95 safely, because it features a slightly different wing than the 707-120, and vortex generators along the tail to improve airflow under it.

Was this a modification made during the KC-135 testing period? Because if I recall correctly, the KC-135 and 707 were originally supposed to be basically the same airframe with a large number of parts in common...

I know that to compete with the DC-8, the 707-120 was widened an additional 4.5 inches over the KC-135 before it flew, did that play a role in it being so much slower?

Andrea K
 
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 2:09 am

Yes, the KC-135 has a wing that easily allows it to cruise at .95 Mach. Optimum cruise speed is .88 Mach, and endurance cruise is down around .69 Mach. The wing on the KC-135 is more of a copy of the B-367-80 wing, and slightly different than the wing design on the B-707-100/B-720 series. The wing on the early B-707 was designed for an optimum cruise at .85 Mach, slightly slower than the KC-135.

No, the wing of the KC-135 was not modified, except for the leading and trailing edge flap systems. The B-367-80 wing was selected, as the B-707 wing was not fully developed. Remember, the KC-135 was ordered, and flew before the B-707 did. The early B-707s and the KC-135 each have partial leading edge flaps (the first large jet aircraft to have them), just inboard of the outboard engine struts, but only the KC-135 has fillet flaps (later installed on the B-707-300/-400 series, which also have full leading edge flaps/slats).

The vortex generators (on the KC-135) under the horizontal stabs are to allow better airflow to the elevators. The vortex generators on top of the wing of the B-707-100 series improves airflow to the inboard and outboard airilons.

There are a large number of common parts for both the B-707 and KC-135. But, there are also a large number of different parts that are not interchangeable, too.

The fuselarge crossection of the B-367-80 was 130". This was increased to 144" for the KC-135, and finally to 148.5" for the B-707. No, the wider fuselarges had no effect on the maximum speed of any of the 3 types, but the KC-135 was the fastest of the 3, and the B-367-80 was the slowest (until it was reengined with JT-3D engines, then it matched the speed of the B-707).

Two interesting bits of trivea about the B-367-80. The orginal engines on it were always refered to as J-57s, the military designation. They were never called JT-3Cs. The second thing is it is the only airplane built by Boeing with two side cargo doors, both on the left (port) side. It had a full size cargo door both foreward and aft of the wing.
 
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 2:33 am

The 367-80 was slower? But I thought it had the same wing as the KC-135?

Kamarov, Andrea V
 
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 3:03 am

Quoting Blackbird (Reply 2):
The 367-80 was slower? But I thought it had the same wing as the KC-135?

It did, but the B-367-80 was also heavier, and the fuselarge was not as "clean" as the B-707 and KC-135. The tail plane surfaces were also much thicker than they needed to be. The B-367-80 had a much higher drag factor. Until it was reengined with the JT-3Ds, it also didn't have the thrust. The original engines on the B-367-80 were the J-57-P12s from the B-52C/D, later they were changed to the J-57-P29W used on the early KC-135 and the B-52F/G (later KC-135s got J-57-43WBs). The P-12 engines only produced about 10,500lbs of (dry) thrust, while the P29W engines produced 12,400lbs.

Remember, the B-367-80 was nothing more than a prototype of a completely different design, and it taught Boeing Engineers a lot about commerical versions of jet airplanes. In 1954, this project cost Boeing some $16M, which was close to the net worth of the company at the time. The Engineers did have an experience base to work from, as many worked on the B-47 and B-52 projects.

The first 29 KC-135s ordered by Gen. LeMay, then USAFCOS, paid for the whole project. 29 airplane was the break even point.
 
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 3:16 am

Quoting KC135TopBoom (Reply 3):
The 367-80 was slower? But I thought it had the same wing as the KC-135?

It did, but the B-367-80 was also heavier, and the fuselarge was not as "clean" as the B-707 and KC-135. The tail plane surfaces were also much thicker than they needed to be. The B-367-80 had a much higher drag factor. Until it was reengined with the JT-3Ds, it also didn't have the thrust. The original engines on the B-367-80 were the J-57-P12s from the B-52C/D, later they were changed to the J-57-P29W used on the early KC-135 and the B-52F/G (later KC-135s got J-57-43WBs). The P-12 engines only produced about 10,500lbs of (dry) thrust, while the P29W engines produced 12,400lbs.

You'd also need to define which wing configuration you're referring to on the -80. It had several and ended up with a variation of the 707-320 wing.
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 3:58 am

So it can get up to Mach .95 eh? Ever been above Mach 1 in a dive?  Wink
 
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 6:29 am

The 367-80 was NOT heavier than the KC-135, the KC-135 weighed in at 290,000 lbs, the 367-80 weighed in at 160,000 lbs. The 367-80 may not have had as clean a fuselage, and had a tailplane that was too thick however.

The final wing configuration on the KC-135 appears to have eliminated the inboard aileron, and features a re-designed flap

Andrea K
 
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 5:08 pm

Quoting Blackbird (Reply 6):
The final wing configuration on the KC-135 appears to have eliminated the inboard aileron, and features a re-designed flap

The present day KC-135 has a inboard and outbd ailerons( btw the otbd aileron is interchangable with an 707), are you sure that you have a the wing of a B-52A thru F and B-52G/H mixed up the G/H buffs did away with ailerons and uses spoiler to turn the beast. The 135 OB ailerons are only usable when flaps are set to 50 degrees down due lockouts connected to the flap system.
If you look at the the 367-80 in the Smithsonian it has a 707-300 series wing installed which probably gives it super lift characteristics.

Quoting BladeLWS (Reply 5):
So it can get up to Mach .95 eh? Ever been above Mach 1 in a dive?

Never saw it but have heard of 135's that broke mach 1 which cuases damage to the wingtips making them curl up.
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RE: KC-135 Tanker Wing

Sun Jan 07, 2007 11:58 pm

Quoting Blackbird (Reply 6):
The 367-80 was NOT heavier than the KC-135, the KC-135 weighed in at 290,000 lbs, the 367-80 weighed in at 160,000 lbs. The 367-80 may not have had as clean a fuselage, and had a tailplane that was too thick however.

I think you are talking to different things here. The basic weight of the original KC-135A was 95,000lbs. When I began flying it, that had grown to about 103,000lbs. The original basic weight of the B-367-80 was 105,500lbs, and it eventually grew to the 160,000lbs you mentioned. The original MTOW of the KC-135A was 297,000lbs (growing to 315,000lbs for the KC-135E and 323,000lbs for the KC-135R), but on the original B-367-80 design, I believe it was 255,000lbs and grew to 325,000lbs.

Quoting Venus6971 (Reply 7):
Quoting BladeLWS (Reply 5):
So it can get up to Mach .95 eh? Ever been above Mach 1 in a dive?

Never saw it but have heard of 135's that broke mach 1 which cuases damage to the wingtips making them curl up.

Yes, that was a KC-135A during the Vietnam War. He was told that NVAF Migs were heading for his position. So, they rolled the tanker and made a high speed dash for the ground clutter on the deck. Both wingtips were damaged by their leading edges curling up. But, IIRC, the crew did not notice it as the airplane still appeared to fly just as normal, the damage was found after landing, but the crew had already written the airplane up as exceeding 1.03 Mach (written up for exceeding the manufactures limitation). The wing tips were changed, as were all four engines. There was also a second KC-135A that exceeded 1.01 Mach, but that aircraft had no damage found, that was caused by an autopilot malfunction and slow reaction of the crew to recover the aircraft before hitting the ground. This second aircraft was one of the aircraft that was equipped with a FDR and a SDR (stress data recorder), which provided a lot of information on the health of the fleet.
 
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RE: KC-135 Tanker Wing

Mon Jan 08, 2007 12:01 am

Quoting ZANL188 (Reply 4):
You'd also need to define which wing configuration you're referring to on the -80. It had several and ended up with a variation of the 707-320 wing

Yes, she did end up with a shortened version of the B-707-320 wing. The wing that I was referring to to that she shared with her KC-135 sister was a version of her original wing. My aploigies for any confusion.
 
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RE: KC-135 Tanker Wing

Mon Jan 08, 2007 4:01 am

Quoting KC135TopBoom (Reply 8):
There was also a second KC-135A that exceeded 1.01 Mach, but that aircraft had no damage found, that was caused by an autopilot malfunction and slow reaction of the crew to recover the aircraft before hitting the ground.


I remember that RC-135U's had a nasty habit of dropping 3000 feet suddenly when it was in its orbit with autopilot set with power settings at max fuel endurance
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RE: KC-135 Tanker Wing

Mon Jan 08, 2007 4:07 am

Quoting Venus6971 (Reply 10):
I remember that RC-135U's had a nasty habit of dropping 3000 feet suddenly when it was in its orbit with autopilot set with power settings at max fuel endurance

Yes, the original autopilot (it was the same in all C-135 versions, except the VC-135, wonder why that is?) became very problematic into the early 1980s.
 
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RE: KC-135 Tanker Wing

Mon Jan 08, 2007 2:10 pm

Quoting KC135TopBoom (Reply 8):
Yes, that was a KC-135A during the Vietnam War. He was told that NVAF Migs were heading for his position. So, they rolled the tanker and made a high speed dash for the ground clutter on the deck.

Ok...now I have put on my flack vest for this.

The aircraft you are talking about is supposed to be 60-0333, when I worked on it it was named Triple Trouble, we always called it triple cripple though.

All of the hydraulic shop troops that I knew, had told me that you could not rig the refueling boom using the rig pin holes, because the empennage was bent due to a crew rolling the aircraft inverted and diving away from some pursuing MiG over Southeast Asia in the 1960s, and the folk lore around that incident also mentioned the aircraft possibly going through Mach 1.

Now this is what I heard, it may not be the aircraft in question, but that was always the story surrounding -0333.
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RE: KC-135 Tanker Wing

Tue Jan 09, 2007 11:12 am

Quoting KC135TopBoom (Reply 8):
There was also a second KC-135A that exceeded 1.01 Mach, but that aircraft had no damage found, that was caused by an autopilot malfunction and slow reaction of the crew to recover the aircraft before hitting the ground.

If this is the same incident I'm thinking of, I knew one of the guys from that crew at Grissom - he occasionally wore a "Mach 1 over Michigan" patch that the crew had made up after the flight.
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RE: KC-135 Tanker Wing

Tue Jan 09, 2007 11:36 pm

Quoting Ex52tech (Reply 12):
All of the hydraulic shop troops that I knew, had told me that you could not rig the refueling boom using the rig pin holes, because the empennage was bent due to a crew rolling the aircraft inverted and diving away from some pursuing MiG over Southeast Asia in the 1960s, and the folk lore around that incident also mentioned the aircraft possibly going through Mach 1.

Yes, I beleiev that is the same aircraft.

Quoting Moose135 (Reply 13):
If this is the same incident I'm thinking of, I knew one of the guys from that crew at Grissom - he occasionally wore a "Mach 1 over Michigan" patch that the crew had made up after the flight.

That is the second incident.
 
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RE: KC-135 Tanker Wing

Wed Jan 10, 2007 5:32 am

Quoting KC135TopBoom (Reply 9):
Quoting ZANL188 (Reply 4):
You'd also need to define which wing configuration you're referring to on the -80. It had several and ended up with a variation of the 707-320 wing

Yes, she did end up with a shortened version of the B-707-320 wing. The wing that I was referring to to that she shared with her KC-135 sister was a version of her original wing. My aploigies for any confusion.

Here is a picture of the B-367-80 on her madien flight on 15 July 1954. Notice she is equiped with a wing that has no leading edge flaps/slats, she does not have fillet flaps, and is flying on J-57 engines. Also notice the 3 shiney new KC-97Gs on the ramp.

http://www.boeing.com/commercial/new...04/photorelease/q3/pr_040715g.html
 
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RE: KC-135 Tanker Wing

Mon Jan 29, 2007 4:53 am

Did the KC-135 have worse low-speed performance or the same as the 707-120? (BTW both have leading edge flaps and fillet-flaps, I checked)

Did the 707 have it's wing re-optimized because even with the 367-80 wing, doing Mach 0.88 would produce a higher fuel consumption than the new wing at Mach 0.85?

Andrea K
 
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RE: KC-135 Tanker Wing

Mon Jan 29, 2007 7:12 am

Quoting Blackbird (Reply 16):
Did the KC-135 have worse low-speed performance or the same as the 707-120? (BTW both have leading edge flaps and fillet-flaps, I checked)

The KC-135A/Q had poor low speed performance, but that wasn't because of the wing. It was because of the low power available from the steam jets (J-57s). Once you got her going, though she was very fast.

The low speed performance improved a lot with the "E" or "R" reengineing programs.
 
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RE: KC-135 Tanker Wing

Mon Jan 29, 2007 9:23 am

A couple of points that have been missed here:

1) KC-135s now have horizontal tails removed from scrapped 707s. The horizontal tails the KC-135s were built with were smaller.

2) The KC-135Rs and Ts have a modified leading edge, fitted at the same time that the CFM56s were added.

3) When you talk of "the 707 wing" you have to be careful. There are several. The 707-120, 720 and 707-320 wings are all different.
 
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RE: KC-135 Tanker Wing

Mon Jan 29, 2007 10:22 am

Quoting Aeroweanie (Reply 18):
KC-135s now have horizontal tails removed from scrapped 707s. The horizontal tails the KC-135s were built with were smaller.

That is almost right. The KC-135E modification (that the donor B-707s gave parts to), only got the horizontial tail leading edges, which were bigger. The rest of the tail remained original, including the lower surface vortex generators (which some B-707s did not have there). You are correct, the KC-135R/T got new manufactured horizontial tail leading edges.

The leading edges gave the tails about 15% more surface area than the original tail surface.

Quoting Aeroweanie (Reply 18):
When you talk of "the 707 wing" you have to be careful. There are several. The 707-120, 720 and 707-320 wings are all different

That is also correct, the B-707-120 wing and the KC-135 wing are basicly the same, but there were minor diffences on the KC-135s (such as a thicker wing root).
 
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RE: KC-135 Tanker Wing

Tue Jan 30, 2007 5:05 am

The KC-135 had a thicker wing-root, or the 707-120 did?

Andrea K
 
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RE: KC-135 Tanker Wing

Tue Jan 30, 2007 11:46 am

Quoting Blackbird (Reply 20):
The KC-135 had a thicker wing-root, or the 707-120 did?

It was the KC-135 with the thicker wings, to allow the inboard main wing fuel tanks to carry more fuel. The B-707-120, being medium range airplane didn't need to carry the additional fuel. Sorry for any confusion.
 
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RE: KC-135 Tanker Wing

Thu May 31, 2012 11:46 am

The photo link Topboom posted is broken because parts of it were replaced with periods.

If you're interested in seeing the photo just go to the page that comes up with the link and type 367-80 in the search box.

Arluna
 
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RE: KC-135 Tanker Wing

Thu May 31, 2012 3:39 pm

Here is the Boeing picture of the B-367-80's FF, and a good shot of the wing from below.

http://www.boeing.com/news/releases/...04/photorelease/q3/pr_040715g.html

Here is a later Boeing picture of the B-367-80 with the new (clipped B-707-320) wing, and replaced the JT-3C (J-57) engines with newer JT-3D (TF-33) engines. You can also see the long row of vortex generators on the right wing running from engine #3 to #4. Many of these were later removed.

http://www.boeing.com/history/boeing/dash80.html

Here is a shot of a KC-135A, showing a portion of the left wing, and still sporting the "short tail" about to begin refueling a B-52E.

http://www.boeing.com/defense-space/military/kc135-strat/kc13503.html
 
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RE: KC-135 Tanker Wing

Thu May 31, 2012 5:32 pm

The "Mach 1 Over Michigan" flight involved 305th AREFW KC-135 57-1476 and took place on 2 Nov 82.

The autopilot flipped the airplane to 210 degrees of bank and 70 degrees nose low, dropping from FL330 to 7,600 feet in just under 30 seconds with an average descent rate of approximately 50,000 fpm. The airplane experienced minor stress damage and lost the "boat tails" on the aft edge of the wing root. The airplane remained in service until retired to AMARC on 13 Aug 92. The incident investigation determined that the fault was a freak autopilot malfunction induced when the pilot flying the airplane abruptly snapped the autopilot control knob to the full turn detent. Annoyingly, Boeing faulted the pilot who recovered the airplane for exceeding the g-limits by smoothly reaching 3.5gs [I guess the Boeing engineers would have preferred the pilot not exceed the g limit and instead allowed the airplane to crash...].

Another supersonic flight involved 4950th TW C-135B 61-2662 (later an RC-135S COBRA BALL). Sometime during 1977 the airplane entered a 455 KIAS dive over the Atlantic Ocean dropping from FL310 to 16,000 feet.

Quoting KC135TopBoom (Reply 17):
The KC-135A/Q had poor low speed performance, but that wasn't because of the wing. It was because of the low power available from the steam jets (J-57s). Once you got her going, though she was very fast.

The low speed performance improved a lot with the "E" or "R" reengineing programs.

The engine performance issues were linked more closely with weight than speed, per se. In the J57-equipped airframes at heavy weights there was a flight regime where the airplane under engine-out conditions, could neither climb nor accelerate. Even with four engines operating at full thrust in some hot/high environments with an EWO fuel load the airplane needed the runway overrun to get airborne and would likely not clear contract-specified obstacles.

In light weight situations, however, the J57-equipped airframes performed well at low speeds. An uncommon, and unapproved, pattern training exercise was to pull three engines to just above idle and fly a radar pattern, approach, and landing with just an outboard engine. This demonstrated the asymmetric thrust and yaw habits of the airplane. Engine spool-up time was the limiting factor in any situation: properly anticipated, the J57s provided the necessary thrust to fly safely. However, anytime the pilot "got behind" the power curve in any phase of flight and at any weight the airplane became unresponsive, contributing to a number of fatal accidents. To be clear: this was the result of early jet engine technology, not the KC-135 design.
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RE: KC-135 Tanker Wing

Thu May 31, 2012 5:49 pm

Quoting Venus6971 (Reply 10):
I remember that RC-135U's had a nasty habit of dropping 3000 feet suddenly when it was in its orbit with autopilot set with power settings at max fuel endurance

I don't recall this being a specific problem with the U-model. Because of drag induced by the chin fairing, the airplane could pitch down unexpectedly during air refueling due to changes in the CG, but this was not as dramatic as described here.

Quoting KC135TopBoom (Reply 11):
Yes, the original autopilot (it was the same in all C-135 versions, except the VC-135, wonder why that is?) became very problematic into the early 1980s.

Correct. From the very beginning the KC-135 autopilot was plagued with troubles. During 1955 Air Materiel Command ordered Boeing to utilize the unproven and failure-plagued Lear L-10. It never worked well even after decades. At one point during the 1980s and 1990s use of the autopilot during air refueling was prohibited. As crews had little practical experience with auto-pilot off A/R, especially during heavy weight offloads with multiple changes in CG, they tended to be highly unstable platforms for receivers. During DESERT STORM, for example, fighters had little trouble with their refuelings but heavies that received >100,000 pounds of fuel had real trouble staying in contact as the tanker wandered up and down, often abruptly and dangerously.
KC-135A, A(RT), D, E, E(RT), Q, R, EC-135A, C, G, L, RC-135S, U, V, W, X, TC-135S, W
 
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RE: KC-135 Tanker Wing

Thu May 31, 2012 9:06 pm

Quoting rc135x (Reply 24):
The "Mach 1 Over Michigan" flight involved 305th AREFW KC-135 57-1476 and took place on 2 Nov 82.

I always thought that airplane flew a little funny...  
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Max Q
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RE: KC-135 Tanker Wing

Fri Jun 01, 2012 8:56 am

Very impressive performance, what are the actual VMO / MMO limits on the KC135 ?
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titanmiller
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RE: KC-135 Tanker Wing

Sat Jun 02, 2012 3:15 pm

Quoting Max Q (Reply 27):
what are the actual VMO / MMO limits on the KC135 ?

The R model is .90 Mach above 29,500' PA and has a max KIAS of 373 at 26,500' PA.
 
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RE: KC-135 Tanker Wing

Sun Jun 03, 2012 12:03 am

Quoting rc135x (Reply 24):
. However, anytime the pilot "got behind" the power curve in any phase of flight and at any weight the airplane became unresponsive, contributing to a number of fatal accidents. To be clear: this was the result of early jet engine technology, not the KC-135 design



Well after reading through this thread I realised that all of the answers that I wanted to touch on had been covered already. Bat as far as fatal accidents i do believe that they all stopped after the arrival of the E/R model engines. But the accident rate before that was high and was mainly die to what you touched on and that was the crew getting behind the curve especially during water injection takeoffs. Just had the chance to talk to an older retired military and airline pilot who flew the 135 when they still had the water injection powered left and right instead of inboard and outboard. It took a few fatal accidents from that configuration before it was changed. The amount of 135's of all types lost over the years was a frightening amount but only one one E model and no R models have been lost due to flight related problems.

Quoting Blackbird (Thread starter):
I've been told that it can cruise safely at Mach 0.95 safely



The A model was a rocket at altitude. It just took it a few hours and tons of fuel to get up there.
 
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RE: KC-135 Tanker Wing

Sun Jun 03, 2012 2:35 pm

Quoting titanmiller (Reply 28):
Quoting Max Q (Reply 27):what are the actual VMO / MMO limits on the KC135 ?
The R model is .90 Mach above 29,500' PA and has a max KIAS of 373 at 26,500' PA.

KC-135A/Q is .95 Mach.

Quoting windy95 (Reply 29):
The A model was a rocket at altitude. It just took it a few hours and tons of fuel to get up there.

Correct, but it really didn't take hours to get to that speed.

We departed Thailand for Guam 10 minutes in a KC-135A behind a C-141A flying the exact same route, in 1974, except we were at a higher altitude. We landed at Andersen AFB, Guam about 30 minutes before the Starlifter did. The C-141A carried about 40,000 lbs of cargo, and we had about 30,000 lbs of cargo, plus were dragging 2 F-4s, which were going to Clark AB, Philippines, and had a 150,000 lb fuel load.
 
Max Q
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RE: KC-135 Tanker Wing

Tue Jun 05, 2012 5:56 am

Quoting KC135TopBoom (Reply 30):
KC-135A/Q is .95 Mach.

My scientific response is Awesome !

Quoting KC135TopBoom (Reply 30):

We departed Thailand for Guam 10 minutes in a KC-135A behind a C-141A flying the exact same route, in 1974, except we were at a higher altitude. We landed at Andersen AFB, Guam about 30 minutes before the Starlifter did. The C-141A carried about 40,000 lbs of cargo, and we had about 30,000 lbs of cargo, plus were dragging 2 F-4s, which were going to Clark AB, Philippines, and had a 150,000 lb fuel load.

Very impressive.
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135mech
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RE: KC-135 Tanker Wing

Wed Jun 20, 2012 8:42 pm

Quoting Blackbird (Reply 6):
The 367-80 was NOT heavier than the KC-135, the KC-135 weighed in at 290,000 lbs, the 367-80 weighed in at 160,000 lbs. The 367-80 may not have had as clean a fuselage, and had a tailplane that was too thick however.

The KC-135 weighs a LOT less than 290,000 lbs... with the upgraded engines and all of the current mods most of them weigh on average around 122,000 lbs dry, IF full of fuel they can take off with a MTOW of 322,500 lbs... (worked them for 21 years)
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RE: KC-135 Tanker Wing

Wed Jun 20, 2012 8:56 pm

Quoting rc135x (Reply 25):
During DESERT STORM, for example, fighters had little trouble with their refuelings but heavies that received >100,000 pounds of fuel had real trouble staying in contact as the tanker wandered up and down, often abruptly and dangerously.

One major reason for this was because of the larger airplanes "wake" pushing the smaller KC-135 up and around, I've been on these and a C-5 and 747 will move that little tanker quickly.
135Mech
 
rc135x
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RE: KC-135 Tanker Wing

Wed Jun 20, 2012 10:20 pm

Quoting 135mech (Reply 33):
Quoting rc135x (Reply 25):
During DESERT STORM, for example, fighters had little trouble with their refuelings but heavies that received >100,000 pounds of fuel had real trouble staying in contact as the tanker wandered up and down, often abruptly and dangerously.

One major reason for this was because of the larger airplanes "wake" pushing the smaller KC-135 up and around, I've been on these and a C-5 and 747 will move that little tanker quickly.

This is certainly true when the tanker is a stable platform and the receiver (a C-5 or E-4, for example) is approaching or withdrawing from the tanker. My point, however, is that this "wake" was not the issue as the tanker platform was unstable in pitch and roll because tanker crews had little experience flying autopilot off air refueling with large fuel offloads (>100,000 lbs per receiver) because of the additional pitch instability induced by the changing center of gravity as the tanker body fuel tanks emptied into the receiver. E-3s, E-8s, and RC-135s, for example do not share this "bow wave" effect but had a very hard time staying in contact as the tanker wandered haphazardly all over the air refueling block and the tanker cg ran from 18 (forward) to 32 (aft) and back again. The goal was to get the gas in one contact over about 20 minutes and then get back on station. With the poor ham-fisted tanker flying, it often took 3-4 contacts and 45 minutes to get the gas. No matter how good the receiver pilot, the tanker crews were badly shortchanged in training for autopilot off refueling (it was a minor training item completed in 3 minutes blocks....)
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kc135topboom
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RE: KC-135 Tanker Wing

Thu Jun 21, 2012 1:07 pm

Refueling tanker autopilot off was a currency item for the tanker pilots. But, IIRC it was like a six month requirement to stay current. The KC-135 started getting new digital autopilots around 1989, or so. Units that got their fleets completed did mostly autopilot on refuelings to get the hang of the new autopilot, and work out some of the bugs of the new system. Remember the KC-135 was designed in an era where nothing was digital, so there were some intergration problems. The original autopilot started to become unreliable in the early 1980s, and would sometimes malfunction during refueling, esspecially uncommanded pitch changes due to one axis or another disengaging during refueling. This was very dangerous. Units that had to wait to get more than one airplane modified were stuck with the old autopilot for longer than they wanted. The mod was completed at the depots, it could not be completed locally. Later in the contract depot teams were set up at a few bases just to remove and replace the autopilots and tankers from surrounding units would drop off a tanker there to be modified, that did speed up the process. Airplanes were scheduled by block number then tail number within that block, not by units they were assigned to. So there were a few blocks that could only be modified at a depot base and not at a foreward depot team base.

The 'old' autopilot did 'wander' around in both pitch and yaw (it did not have a yaw dampner), even in cruise, not just during refueling. It was also very slow in keeping the airplane trimmed properly, which is why many heavy weight refuelings had pitch problems.

So, the refueling problems you guys are talking about is not always an autopilot off refueling or the competence of the tanker pilots, it was most likely the aging of the old autopilot system.

For refueling, the E-4 and C-5 created the most challanges for the tanker crew. The Boom Operator would direct the receiver in slowly using the director lights, and at the same time count down the receiver approaching to the tanker pilot over interphone, 50, 40, 30, 20, 10, 5, etc. He/she would also count them as they backed out. The tanker pilot would trim the tanker as the Boom Operator counted. This would help counter the bow wave, perticularly with the C-5, which has the largest bow wave, but the E-4 could also significantly 'push' the tanker around, the KC-10 did too, but to a lessor extent. Airplanes like the EC/RC/KC/WC-135, E-3, E-6, E-8, B-707 (trainer) etc. did not puch us around, nor did the B-52, EC/AC/WC/MC-130, or C-141.

Quoting 135mech (Reply 32):
The KC-135 weighs a LOT less than 290,000 lbs... with the upgraded engines and all of the current mods most of them weigh on average around 122,000 lbs dry, IF full of fuel they can take off with a MTOW of 322,500 lbs... (worked them for 21 years)

Correct. The basic weight of the KC-135A was about 93,000 to 95,000 lbs (original airplane delivered new from Boeing). The unit basic weight, with all the cargo loading equipment, parachutes, life support/survival equipment, live aboard kit (which included the APU and bunks), passenger equipment, life rafts, plywood cargo floor, tail stand, etc. was about 105,000 lbs. The KC-135A/Q had a max ramp weight of 301,600 lbs, and a MTOW of 297,000 lbs., the KC-135E had a MTOW of 315,000 lbs, and the KC-135R/T was 322,500lbs to 325,000 lbs. If all fuel tanks were full the fuel load for all models is 202,000 lbs, not counting the 5,600 lbs of water the KC-135A/Q needed. The KC-135Q was about 1,500 lbs heavier than the KC-135A.
 
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RE: KC-135 Tanker Wing

Fri Jun 22, 2012 5:32 am

Very interesting, as usual. I did not know the KC135 had an APU.



Where is it installed, can it be used in flight ?
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kc135topboom
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RE: KC-135 Tanker Wing

Fri Jun 22, 2012 10:59 am

The APU is installed on the cargo deck, aft, left side. The KC-135R/T actually have two APUs. No, it cannot be used in flight, it is ground ops only.

The KC-135A/E/Q had a single Solar or Air Reach APU that provided cabin heat, elecricity, and noise. The KC-135R/T APU also provides a ground engine start capability.
 
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RE: KC-135 Tanker Wing

Fri Jun 22, 2012 1:46 pm

When I was flying A-models, we weren't even allowed to use the APU on the ground. I think there had been a couple of fires, and they wired the controls shut. We had to rely on a ground cart with hot air on those cold January morning preflights at KGUS...
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windy95
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RE: KC-135 Tanker Wing

Mon Jun 25, 2012 12:12 am

Quoting rc135x (Reply 34):
The goal was to get the gas in one contact over about 20 minutes and then get back on station. With the poor ham-fisted tanker flying, it often took 3-4 contacts and 45 minutes to get the gas. No matter how good the receiver pilot, the tanker crews were badly shortchanged in training for autopilot off refueling (it was a minor training item completed in 3 minutes blocks....)

During the days of SAC I think the crews had more time doing heavy of loads and probably handled them better. We had many a MITO with the BUFF's where we hooked up to them in climbout and dropping 100 to 150K of fuel on the climb and when the offlead was complete we would spin right around and land after giving away all of our fuel. Even with C-5's or the KC-10 I do not remember to many crews having problems with long contacts. I do remember watching the Pilot's working the controls hard as it was a constant adjustment especially with the stab trim wheel.

Quoting KC135TopBoom (Reply 37):
The KC-135R/T APU also provides a ground engine start capability.

And I believe the double APU was for starting all engines at once for Alert.
 
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RE: KC-135 Tanker Wing

Mon Jun 25, 2012 12:44 am

Quoting KC135TopBoom (Reply 35):
the KC-135E had a MTOW of 315,000 lbs, and

The E was the same as the A. The E-model maximum takeoff weight was not increased. The A-model could actually takeoff with more fuel thatn the E-model. The E was just way more efficient which made for the longer range and larger offloads.
 
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RE: KC-135 Tanker Wing

Mon Jun 25, 2012 10:36 pm

Quoting windy95 (Reply 40):
Quoting KC135TopBoom (Reply 35):the KC-135E had a MTOW of 315,000 lbs, and
The E was the same as the A. The E-model maximum takeoff weight was not increased. The A-model could actually takeoff with more fuel thatn the E-model. The E was just way more efficient which made for the longer range and larger offloads.

No sir, none of that is correct. All KC-135s, after airplane #29 (the last of the 1955 models) could carry the same full load, 202,000 lbs, as they all had the same fuel system configueration. The first 29 KC-135As did not have the aft upper deck tank and had one less cell in the foreward body tank, so they maxed out at 180,000 lbs of fuel.

http://en.wikipedia.org/wiki/File:Fi...C-135E_with_TF33_engines_1982.JPEG

The KC-135E modification included much heavier engines. The TF-33-P-102 engines were about 1500 lbs hevier (each) than the J-57-P-59W engines they replaced (some KC-135As had the J-57-P-43W/WB engines), which replaced the 5600 lbs of water and 950 lb water tank*** and pumping/plumbing needed for the water injection takeoffs for the J-57 equipped KC-135A/Qs. The engine struts were also heavier, and these engines added thrust reversers the KC-135A did not have. Other changes were beefier landing gear (to support the gross weight increase), 5 rotor brakes (the KC-135A had 4 rotor brakes), a 15% increase in the size of the horizonltal stabilizer, cockpit equipment, reloacting the APU fuel supply to the #2 main wing tank from the aft body tank, like the KC-135Q (this also added a new fuel pump), and improvements to the the electrical and hydraulic systems. All of this brought the basic operating weight of the KC-135E to 115,000 lbs, add the 202,000 lbs of fuel (full tanks) and you have a max taxi weight of 317,000 lbs giving you a MTOW of 315,000 lbs. The KC-135E was some 17% more efficent than the KC-135A. The KC-135R/T is 25% more efficent than the KC-135A/Q.


***On later KC-135E conversions the water tank was left in place and became a dry bay, as it was cheaper not to remove it and replace the structual components.
 
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RE: KC-135 Tanker Wing

Fri Jun 29, 2012 2:09 pm

Quoting KC135TopBoom (Reply 41):
No sir, none of that is correct. All KC-135s, after airplane #29 (the last of the 1955 models) could carry the same full load, 202,000 lbs,

Yes it is correct. Both the A and the E had the same MTOW. Due ot the heavier engines the E model carried less fuel. Yes the tanks could still hold 202,000lbs but they E model did not use 202,000 as the max fuel load. I participated in many a MTOW flight on the E model and it was never over 297,000lb. Basically 180K was the max fuel loads we put on them. With pax and cargo it was less.

Quoting KC135TopBoom (Reply 41):
KC-135E to 115,000 lbs, add the 202,000 lbs of fuel (full tanks) and you have a max taxi weight of 317,000 lbs giving you a MTOW of 315,000 lbs

Yes the airplane had the capability to carry 202,000 but the MTOW was still the 297,000. The maximum takeoff weight was not increased for the E-model. I spent 10 years a an Air Tech Crew Chief on them and never saw any of what you are talking about.

Quote:
But the maximum takeoff weight was not increased for the E-model

From your own reference on wiki

http://en.wikipedia.org/wiki/KC-135_Stratotanker

Quote:
But the maximum takeoff weight was not increased for the E-model
http://www.thefullwiki.org/KC-135_Stratotanker
 
rc135x
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RE: KC-135 Tanker Wing

Fri Jun 29, 2012 8:03 pm

Quoting windy95 (Reply 42):
Both the A and the E had the same MTOW. Due ot the heavier engines the E model carried less fuel. Yes the tanks could still hold 202,000lbs but they E model did not use 202,000 as the max fuel load. I participated in many a MTOW flight on the E model and it was never over 297,000lb. Basically 180K was the max fuel loads we put on them. With pax and cargo it was less.

Correct.   

A lot of this discussion is "Monopoly Money."

Both the basic KC-135A and KC-135E were operationally limited to a max gross t/o weight (MGTW) of 297,000 pounds under Emergency War Order (EWO) regulations, irrespective of actual potential fuel loads. During flight testing using J57 engines, Boeing decreed that 297,000 was the maximum weight where the airplane could clear an obstacle on takeoff after losing an engine under optimum temperature and pressure altitude conditions. When the KC-135E entered service the Air Force would not pay Boeing for additional testing and validation of heavy weight take off data, and used the same MGTW as the A model, assuming the improved performance would be an added margin of safety benefit rather than an added fuel benefit. Moreover, SIOP fuel offloads were unchanged with the arrival of the KC-135Es; any additional fuel remaining at end-of-offload could be passed to the bomber---especially under VALID RED or similar conditions.

All of the KC-135 variants had an interesting fuel weight limit---maximum in-flight gross weight (MIFGW)---that actually *exceeded* the MGTW. These were airplanes equipped with either the Boeing or the LTV/E-Systems in-flight air refueling (ARR) modification. [I know that all boom-equipped KC-135s could "reverse refuel" in flight, but were limited as to which tanks could be filled by this emergency method, and could therefore not reach or exceed MGTW.] These were usually restricted to 299,000 pounds, although some variants could easily carry over 300,000 pounds. As before, Boeing refused to validate flight data for these extreme weights, again, because SAC refused to pay for the data as a cost-savings measure. Both the prototype KC-135E (59-1514) and the prototype KC-135R (61-0293) were ARR equipped and made multiple test heavy-weight refuelings to in-flight full tanks: because they *could* did not mean that they *did* in an operational environment.

A lot of the Dash One (flight manual) even for the KC-135R is still residue from the original Dash One for the KC-135A. The take-off pitch angle was typically 8.5 degrees no matter what variant or weight because that was the only pitch angle Boeing certified for KC-135A EWO obstacle clearance takeoffs, which is the only scenario that SAC paid for. On the Cherokee Rose, KC-135R 62-3554, Boeing upgraded the F108 engines to full specifications (from 22,000 pounds to 24,000 pounds thrust per engine) AND provided unique validated takeoff data to enable the plane to set four world time-to-climb records, exceeding 8.5 degrees by a wide margin. I took off once in the TC-135S (62-4133) from Eielson AFB, AK, in less than 2,400 feet of runway, rotated to 3-engine climb speed plus 10 knots, and was at FL240 in less than three minutes, with the pitch well above 50 degrees. Using only official or published data, such a climb was not only prohibited but technically impossible.

In my many discussions with Boeing engineers, pilots (including the legendary "Tex" Johnston), and in a robust review of the historical data, I found a consistent theme: despite many examples of what the KC-135 and its variants *could* do, Boeing wore myopic blinders to this potential as it stayed "on-message" from SAC. The KC-135 needed to (1) take off with an EWO fuel load; (2) off load maximum fuel to a single bomber in an EWO environment; and (3) land at absolute minimum weight on unimproved (but paved) airfields to be reconstituted for subsequent EWO sorties. Because this is all the KC-135A was intended to do, this was all that SAC paid Boeing to validate, and anything outside of those parameters is all theoretical.

Naturally there are many exceptions, but, alas, that is a different discussion...
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RE: KC-135 Tanker Wing

Fri Jun 29, 2012 8:13 pm

Quoting rc135x (Reply 43):
I took off once in the TC-135S (62-4133) from Eielson AFB, AK, in less than 2,400 feet of runway, rotated to 3-engine climb speed plus 10 knots, and was at FL240 in less than three minutes, with the pitch well above 50 degrees.

That must have been a sight to behold! I don't know if I would have wanted to be in the back for that ride, but it must have been fun up on the flight deck!
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windy95
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RE: KC-135 Tanker Wing

Fri Jun 29, 2012 11:33 pm

Quoting rc135x (Reply 43):
When the KC-135E entered service the Air Force would not pay Boeing for additional testing and validation of heavy weight take off data, and used the same MGTW as the A model, assuming the improved performance would be an added margin of safety benefit rather than an added fuel benefit.

Which over time the lower accident rate between the A to the E validated using the improved performance for the margin of safety. Having spent 6 years on the A model going to the E really relieved some stress for those heavy loads on a hot day.

Quoting rc135x (Reply 43):
I took off once in the TC-135S (62-4133) from Eielson AFB, AK, in less than 2,400 feet of runway, rotated to 3-engine climb speed plus 10 knots, and was at FL240 in less than three minutes, with the pitch well above 50 degrees. Using only official or published data, such a climb was not only prohibited but technically impossible.

Had a similar experience back in 83/84 with one of our first E's. Dropped off pax for the ANG Golf tournament in Tuscon and departed TUS with 22K on board for the hop to Sky harbor where we spent the long weekend for the TDY. I was in the jump seat and the Colonel flying the jet did the same thing you did. Held it down a bit longer than needed and just aimed high. A fun ride.
 
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RE: KC-135 Tanker Wing

Sat Jun 30, 2012 1:00 am

Quoting windy95 (Reply 45):
Held it down a bit longer than needed and just aimed high. A fun ride.

I believe in either 1991 or 1992 at the RAF Mildenhall air show a colleague of mine flew the EC-135H demo flight. They were very light and he stood on the brakes to allow the thrust to stabilize at full thrust, then "let 'er rip." He held the airplane on the runway to tire placard speed (199 KIAS) minus 10 knots = 189 KIAS instead of the normal rotate speed of around 155 for that weight. The airplane went nearly vertical in pitch, but to level off at 2,000 feet AGL he rolled to the left and sliced the airplane to nearly vertical in roll, causing engines 1 and 2 to compressor stall due to lack of airflow.

The Three-Star watching the departure saw his career come to an end thanks to this major, and there was a "spirited" debriefing after the flight with the general talking and the major listening.

I still have the video from the flight, which is even more interesting after everyone is "well lubricated" and the "WTF were you thinking?" questions get rolling.
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RE: KC-135 Tanker Wing

Sat Jun 30, 2012 2:55 am

Quoting moose135 (Reply 44):
I took off once in the TC-135S (62-4133) from Eielson AFB, AK, in less than 2,400 feet of runway, rotated to 3-engine climb speed plus 10 knots, and was at FL240 in less than three minutes,

I flew aboard a KC-135R out of Elmendorf AFB with a similar profile to this. Our vertical speed indicator was pegged at 6,000fpm the whole way up to our initial level off. Heavy jets are real rockets when lightly loaded.

Quoting rc135x (Reply 46):
I still have the video from the flight,

You've got to upload that to Youtube and share it with the rest of us. It sounds amazing.
 
windy95
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RE: KC-135 Tanker Wing

Sat Jun 30, 2012 2:12 pm

Quoting rc135x (Reply 43):
Boeing decreed that 297,000 was the maximum weight where the airplane could clear an obstacle on takeoff after losing

One of the worst departures for us in the A model was the Hickam departure with 180 to 190 loads with water when we dragged receivers on the way to Guam. With an 8L or 8R departure we could not overfly the city at all. So after rotation we went into the immediate right hand turn and went for speed not altitude during the turn. We prayed to the water god's all the way through that first few minutes. Never enjoyed that one.
 
135mech
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RE: KC-135 Tanker Wing

Mon Jul 02, 2012 5:10 pm

Quoting rc135x (Reply 46):
I believe in either 1991 or 1992 at the RAF Mildenhall air show a colleague of mine flew the EC-135H demo flight. They were very light and he stood on the brakes to allow the thrust to stabilize at full thrust, then "let 'er rip." He held the airplane on the runway to tire placard speed (199 KIAS) minus 10 knots = 189 KIAS instead of the normal rotate speed of around 155 for that weight. The airplane went nearly vertical in pitch, but to level off at 2,000 feet AGL he rolled to the left and sliced the airplane to nearly vertical in roll, causing engines 1 and 2 to compressor stall due to lack of airflow.
HA! I was in that boom pod for that take off! It was AWESOME!!! May of 1991 Air Fete airshow, [61-0291 EC-135H] 5 days before it was retired back to the states and dismantled for corrosion investigating. We took off with only 25,000 pounds of fuel (just enough to wet the 1-4 main tanks and center tank for CG. The #4 engine compressor stalled on take off and shot a 50' flame out the tail, my head crew chief thought "Oh God, not another one"...he was an assistant crew chief on the Tanker that crashed in the '87 airshow at Fairchild AFB at that time. It, to this day, is the most exhilerating "thrill" I've had!

The crew was awesome and thanks for the rest of the story, we maintainers don't always get told of the "after butt-chewings". They put on a great show!!!

[Edited 2012-07-02 10:18:27]
135Mech

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