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747classic
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KC-10, KC-135 Tankers With Winglets.

Mon Jan 04, 2010 9:13 am

Searching on the Internet for some winglet answers, I found the following very interesting article about putting winglets on military aircraft.
Two aircraft types in the USAF inventory came forward as the prime candidates for modification with winglets, the KC-10 and the KC-135.
Seen the long remaining service time in the USAF-fleet of both types and the promising fuel savings (up to 6-7%) , it's remarkable that nothing has been done with this indepth study of 2007.

IMO especially the KC-10 is a prime candidate seen the very low flight hours/cycles of all aircraft and the very limited aging aircraft costs on high hour/cycles DC-10's, compared with several Boeing models.
Together with the hopefully positive decision of the KC-10 CUP (cockpit upgrade program) in may 2010, this produces a very competitive tanker for years to come.

http://www.nap.edu/openbook.php?record_id=11839&page=R1

You can read the article by pressing the fwd buttons or you can download the entire article in PDF. (left hand site of page)
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RE: KC-10, KC-135 Tankers With Winglets.

Mon Jan 04, 2010 1:59 pm

Boeing tested the KC-135 with winglets a few years ago but the idea didn't get approval for funding of the fleet. Don't recall why unless it was a lack of defense dollars.
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RE: KC-10, KC-135 Tankers With Winglets.

Mon Jan 04, 2010 3:21 pm

Quoting EBJ1248650 (Reply 1):
Boeing tested the KC-135 with winglets a few years ago but the idea didn't get approval for funding of the fleet

In the 1980's testing was done on KC-135 aircraft, equipped with winglets.
see for full report (30 MB, pdf file):
http://ntrs.nasa.gov/archive/nasa/ca...asa.gov/19840019618_1984019618.pdf

However at present we have a new situation, more advanced winglets are available (blended winglets) and higher fuel prices. That is why this new (2007) report is made. In this latest report the idea is to install the 737NG blended winglet on the KC135, via an adapted wing extension. This has been done before with the present 757 blended winglet retrofit.

[Edited 2010-01-04 07:38:48]
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RE: KC-10, KC-135 Tankers With Winglets.

Mon Jan 04, 2010 4:39 pm



Quoting 747classic (Reply 2):
Quoting EBJ1248650 (Reply 1):
Boeing tested the KC-135 with winglets a few years ago but the idea didn't get approval for funding of the fleet

In the 1980's testing was done on KC-135 aircraft, equipped with winglets.
see for full report (30 MB, pdf file):
http://ntrs.nasa.gov/archive/nasa/ca...asa.gov/19840019618_1984019618.pdf

However at present we have a new situation, more advanced winglets are available (blended winglets) and higher fuel prices. That is why this new (2007) report is made. In this latest report the idea is to install the 737NG blended winglet on the KC135, via an adapted wing extension. This has been done before with the present 757 blended winglet retrofit.

The 1980s flight tests of the winglets on the KC-135A did show a 7% fuel comsumption improvement, but the program never got the go ahead approval mostly for two reasons back then.
1. The two reengining programs (KC-135E with JT-3D-17/-19 engines and KC-135RE [later changed to KC-135R] with CFM-56-2B engines) provided a much better fuel savings, some 15% on the KC-135E and 25% on the KC-135R over the then KC-135A.
2. The then winglet design greatly decreased the cross wind take-off and landing capability to around 15 knots. The KC-135A, with the tall tail had a cross wind capability over 40 knots, but SAC had a limitation of 25 knots.

I have not read all of the 2007 study. But I wonder what operational effect it would have on KC-135Rs and KC-10As equipped with WARPs. The wing tips of both types will need to be changed out and a new wingtip with the blended type winglet made. That will include modifing the reserve fuel tanks, part of the fuel vent system, some minor plumbing changes, electrical wiring for fuel valves and navigation lights, and wingtip strobe lights on the KC-10A. They may also want to add wingtip strobe lights to the KC-135R/T.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Mon Jan 04, 2010 7:34 pm



Quoting KC135TopBoom (Reply 3):
But I wonder what operational effect it would have on KC-135Rs and KC-10As equipped with WARPs.

That is the real problem. The dry weight of the 900E pod alone is around 1300lbs, add winglets further outboard and that would be another 100-150 lb per side. That is a lot of additional bending moment for the wing to handle.
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RE: KC-10, KC-135 Tankers With Winglets.

Mon Jan 04, 2010 9:55 pm



Quoting Zeke (Reply 4):
Quoting KC135TopBoom (Reply 3):
But I wonder what operational effect it would have on KC-135Rs and KC-10As equipped with WARPs.

That is the real problem. The dry weight of the 900E pod alone is around 1300lbs, add winglets further outboard and that would be another 100-150 lb per side. That is a lot of additional bending moment for the wing to handle.

I agree. Additionally the KC-135 MPRPs are very close to the wingtips. Is there an aerodynamic effect with a blended wingtip for the drogue? I don't think the effect would be much on a receiver aircraft, but it could make a trailing drogue fly around and make contact with it more difficult. This is less of a problem with say the KC-30 as the WARPs are much further inboard from the winglet.

Since Boeing has had drawings of their proposed KC-767 with blended winglets, and the WARPs, although not as far out towards the wing tips as the KC-135 wing has, it is still further outboard, by a significant amount compared to the A-330MRTT. Perhaps Boeing would need to offer raked wingtips on the KC-767 instead of blended winglets? On the KC-10A, the MPRPs are slightly more than half way between the underwing engines and the wingtip, even less of a distance thatn what it looks like on the KC-767, although I do not have the exact measurments for either the KC-10 or KC-767.

The wing bending/flexing you mentioned might be a problem on the KC-135 and KC-10 as both have stiffer wings and spars than either the KC-767 or the huge wing flex on the KC-30. I know the KC-135 wing is designed to flex, as with all large jet transports, just not nearly to the degree on many of the designs of today, or even airplanes designed in the 1980s.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 7:55 am

As shown in the common A330/A340 wing (two versus four engines) the extra weight of WARPs reduces the average wing load in flight conditions, only different loads are present at other locations of the wing box and must be calculated. Only during ground operations the extra weight of WARPs comes into effect.
Both the KC10A and KC135 wing need only extended wiring and strengthening of the wing to counteract the twisting moment of the winglet modification. and the increased lift production of the wing. The strengthening will even be less than with an aircraft without WARPs.
With the present computer models and experience with the blended winglets by API (APB), it must be possible to adapt the wing extension in a way, to keep the modification at the present wingtip to a minimum.
All above has been demonstrated by the adaption of the 737NG winglet on the 757.
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 8:29 am



Quoting KC135TopBoom (Reply 5):
Is there an aerodynamic effect with a blended wingtip for the drogue?

Yes, it alters the wing tip vortex. It would require requalification of the hose and the aircraft that use it.

Quoting 747classic (Reply 6):
As shown in the common A330/A340 wing (two versus four engines) the extra weight of WARPs reduces the average wing load in flight conditions, only different loads are present at other locations of the wing box and must be calculated.

The mass of an A340 engine is around 2600 kg, the mass of an A330 engine is around 6500 kg, and the wing pod 560 kg, the KC-30 wing sees the highest load (pod locations are 9.37m and 19.6 m off the axis).

The moment on the 340 wing is
9.81*(2400*9.37+ 2400*19.6) = 682069 N.m

The moment on the 330 wing is
9.81*6500*9.37 = 597478 N.m

The moment on the KC-30 wing is
9.81*(6500*9.37+ 590*19.6) = 710920 N.m

As the weight on the A330 is lower than the A340 by about 43,000 kg at MTOW, the lift on the A330 wing is also lower.
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 10:25 am



Quoting Zeke (Reply 7):
Quoting KC135TopBoom (Reply 5):
Is there an aerodynamic effect with a blended wingtip for the drogue?

Yes, it alters the wing tip vortex. It would require requalification of the hose and the aircraft that use it.

The wingtip vortex is moving away from the center line of the WARPs, due the wing extension + winglet. So probably the vortex will be far less for the receiver aircraft, flying on the WARPs centerline behind the tanker.
However the real difficulty is the F..... word, the wing flutter behavior will be altered and must be calculated carefully and test flown.

Quoting Zeke (Reply 7):
The moment on the 340 wing is
9.81*(2400*9.37+ 2400*19.6) = 682069 N.m

The moment on the 330 wing is
9.81*6500*9.37 = 597478 N.m

The moment on the KC-30 wing is
9.81*(6500*9.37+ 590*19.6) = 710920 N.m

All depends on the counteracting lift moment of the wing. In general the in flight wing bending will be relieved, when placing a weight (WARPs) further outboard than the wing lift point.
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 12:04 pm



Quoting 747classic (Reply 8):

All depends on the counteracting lift moment of the wing. In general the in flight wing bending will be relieved, when placing a weight (WARPs) further outboard than the wing lift point.

No, the wing will be stressed for the maximum positive and negative g.

I have not idea what you mean by "wing lift point", it is not a term used in aircraft design.
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 12:39 pm

Quoting Zeke (Reply 9):
I have not idea what you mean by "wing lift point", it is not a term used in aircraft design.

To make it not to complicated :
Lift is generated over the entire wing, and generates a wing root moment.
For easy understanding you can replace the total lift by a single vector on a calculated distance from the wing root to give the same wing root moment.(=wing lift point)

Any additional weight underneath the wing (or in the wing : fuel) will decrease the wing root moment. The effect will be larger when the distance to the wing root increases.

Example : 747-200/300 with wing 6.(maximum capable MTOW of 747-200/300.)
MTOW, with full wing tanks is 833.000 lbs/377.800 kgs, however if the specific gravity of the fuel is below a certain value (low fuel weight, volumetric full) the MTOW is limited proportional until 820.000 lbs/371.900 kgs., due wing root bending limitations.

[Edited 2010-01-05 05:29:30]

[Edited 2010-01-05 05:33:56]
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 2:00 pm



Quoting 747classic (Reply 10):
Lift is generated over the entire wing

Correct, but it is not a uniform distribution.

Quoting 747classic (Reply 10):
and generates a wing root moment.

and shear and torsion.

Quoting 747classic (Reply 10):
For easy understanding you can replace the total lift by a single vector on a calculated distance from the wing root to give the same wing root moment.(=wing lift point)

You can have a point load at the centroid of the lift distribution to generate the same bending moment if you assume a uniform lift distribution over a uniform beam. That does not give you the same shear force diagram or the same forces at the wing root as the lift distribution is not constant, nor is the "beam" that the wing is often simplified as.

Quoting 747classic (Reply 10):

Any additional weight underneath the wing (or in the wing : fuel) will decrease the wing root moment. The effect will be larger when the distance to the wing root increases.

Incorrect, wings are stressed for positive AND negative g limits.

Quoting 747classic (Reply 10):
Example : 747-200/300 with wing 6.(maximum capable MTOW of 747-200/300.)
MTOW, with full wing tanks is 833.000 lbs/377.800 kgs, however if the specific gravity of the fuel is below a certain value (low fuel weight, volumetric full) the MTOW is limited proportional until 820.000 lbs/371.900 kgs., due wing root bending limitations.

No, that is MZFW limit. You can fly a 747 with 10t in the tanks or 100t in the tanks, but you cannot go past MZFW.
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 4:23 pm



Quoting Zeke (Reply 11):

No, that is MZFW limit. You can fly a 747 with 10t in the tanks or 100t in the tanks, but you cannot go past MZFW

I am aware of the fact that you can not exceed the MZFW.
I have been involved in the (structural)modification of the full passenger KLM 747-206B(SUD) aircraft PH-BUO,-BUP and -BUR, from 820.000 lb to 833.000 lbs, all with wing 6 installed. So I remember very well that the MTOW can also be restricted by fuel density. Also all factory built 833.000 lb MTOW 747-200/300's, with this wing had the same (not very well known) restriction.
See also "limitations" of the OM 747. (from MP, couldn't find the relevant KL documents)
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 6:00 pm



Quoting Zeke (Reply 7):
Quoting KC135TopBoom (Reply 5):
Is there an aerodynamic effect with a blended wingtip for the drogue?

Yes, it alters the wing tip vortex. It would require requalification of the hose and the aircraft that use it.

That's what I thought. I know the size growth, duration, and lenght of the wingtip vortex behind the current wingtip of the KC-135, but thought the the shape and sizing increase (as distance behind the wingtip increases) would be significantly different behind a KC-135 wing equipped with wingtips.

For tankers, with maybe the exception of the A-330MRTT, I would think a raked wingtip would be better. A raked wingtip extends the wingtip much further out from the original and the vortex would also have a different shape. The benefits of raked wingtips and blended winglets are about the same for reducing drag and increasing fuel economy. The one downside I see with a raked wingtip over a blended winglet, or standard winglet would be reduced parking seperation spacing (and maybe overall reduced number of tankers on a given ramp size), an increase in of the empty weight of the tanker due to the raked wingtip, extra wing strenght or stiffing, and possibly strenghting of the outer portions of the center wing box (that would depend on the tanker type, it may not be needed on the KC-135, but will be needed on a KC-10).

In the early 1980s when the USAF and NASA were flying the winglet KC-135 testbed, the estimated costs to modify each KC-135 was around $2m each, IIRC. With that type of winglet, the KC-135 center wing box (which was very well over built) did not need strenghting, but the outer wing sections out board of the outboard engines did need strenghting.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Tue Jan 05, 2010 10:13 pm



Quoting 747classic (Reply 12):

That graph to looks like the aircraft will reach its fuel volume limit in the tanks at a SG below 0.78 kg/l, nothing too uncommon about that, all aircraft are the same, they have finite amount of fuel volume that can by carried in each tank.
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RE: KC-10, KC-135 Tankers With Winglets.

Wed Jan 06, 2010 9:29 am

I don't want to deviate to much from topic (winglets on KC-10A and KC135), but :

Quoting Zeke (Reply 14):
That graph to looks like the aircraft will reach its fuel volume limit in the tanks at a SG below 0.78 kg/l, nothing too uncommon about that, all aircraft are the same, they have finite amount of fuel volume that can by carried in each tank.

The graph is not a volume/weight fuel tank graph, relevant maximum tank QTY table below :



If you are at MTOW (377.8 tons) with the 747-200/300, always all wing tanks are full.(volumetric), the weight of the total wing fuel depends on the SG.
MZFW = 268.000 kgs.(freighter)
The wing root bending moment reaches the max certified value (when the aircraft becomes airborne) when the specific gravity is .78.
NOW 377.8- 102.6 (see table) = 275.2 tons max allowable weight MZFW + Center Wing tank fuel (total fuselage weight).

If you load your aircraft with fuel with a SG of 0.777 the following weight distribution will occur :
total fuselage weight = 275.6
wing fuel weight = 102.2 (see table)
MTOW = 377.8

More weight in the fuselage and less weight in the wing fuel tanks.
Now the max. wing bending moment is exceeded and the max allowable structural TOW must be reduced to 377.4 tons (see graph reply 12.)

[Edited 2010-01-06 01:31:18]
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RE: KC-10, KC-135 Tankers With Winglets.

Wed Jan 06, 2010 9:59 am

Two things. One, the government does not care about cost minimization necessarily. Any costs are paid by taxpayers. Therefore there is not "pressure" to modify aircraft just for cost reduction, which is not seen as an advantage really.

Second, the aircraft may not be used intensively enough to pay off. Sure the KC-10 flies a good amount, but does it fly 11 hours per day like a United Airlines 757? I really really doubt it. So, the savings stream might pay for winglets on a United jet, but not on a KC-10.

But it still would be very interesting and nice looking.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Wed Jan 06, 2010 10:54 am

Flighty, did you read the article, mentioned in thread starter? I takes a lot of time, i know.
The entire article is a recommendation to the USAF for economic viable winglet retrofit candidates.
Only two were selected as most promising candidates.
If you start reading at page 57 all pros and cons are mentioned.
The only that is not taken into account is the delaying effect the upgrade will have in procuring a successor., eg. the need to replace the winglet equipped aircraft will also move further back, because the difference in operational cost also becomes less between a winglet equipped aircraft and the successor aircraft.
So by implementing the winglets you can also delay the selection of a successor by a few years.
That the airforce brass and politicians are eager to come forward with a brand new replacement aircraft is another story.
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RE: KC-10, KC-135 Tankers With Winglets.

Wed Jan 06, 2010 11:03 am



Quoting 747classic (Reply 17):
The entire article is a recommendation to the USAF for economic viable winglet retrofit candidates.
Only two were selected as most promising candidates.

According to wiki the 135R fleet is used only 2 hours per day (2006). I cannot imagine it justifies millions of dollars to fit winglets to a plane that only flies 2 hours per day. Airlines wouldn't do it. Having looked at the finances of winglets, I doubt whether a 2 hour utilization can support winglets.

Considering a mil customer, this seems to be a capability and range buy, not really a financia move. The USAF honestly does not care about saving such a modest amount of fuel. This is an organization that wastes billions without blinking an eye.

They might want it to look cool and extent the loiter time of the jets. That's all I am seeing here. Maybe the KC-10 flies more hours, but honestly I would expect FedEx to go for them LONG before the USAF, if the financials were sound.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Wed Jan 06, 2010 2:46 pm



Quoting Flighty (Reply 16):
Second, the aircraft may not be used intensively enough to pay off. Sure the KC-10 flies a good amount, but does it fly 11 hours per day like a United Airlines 757? I really really doubt it. So, the savings stream might pay for winglets on a United jet, but not on a KC-10.



Quoting Flighty (Reply 18):
According to wiki the 135R fleet is used only 2 hours per day (2006). I cannot imagine it justifies millions of dollars to fit winglets to a plane that only flies 2 hours per day. Airlines wouldn't do it. Having looked at the finances of winglets, I doubt whether a 2 hour utilization can support winglets.

Considering a mil customer, this seems to be a capability and range buy, not really a financia move. The USAF honestly does not care about saving such a modest amount of fuel. This is an organization that wastes billions without blinking an eye.

They might want it to look cool and extent the loiter time of the jets. That's all I am seeing here. Maybe the KC-10 flies more hours, but honestly I would expect FedEx to go for them LONG before the USAF, if the financials were sound.

You have to realize that any possible fuel savings is only one part of a military equasion. There also does have to be an added military benefit or operational need. In the case of winlets, or raked wintips added to the current USAF tanker fleet there is a strong military operational benefit, if it is ever needed. that is a possible increase in fuel that can be offloaded to receiver aircraft. A 7% increase to a bomber, recce, or transport aircraft will increase range and/or payload by a like 7%. To a fighter or fighter bomber aircraft it would mean an increase of about 14% in a weapons load or loiter time over/near a target area. To put it simply the less fuel the tanker burns increases a possible offload capability. This adds to the force multiplier role of the tankers.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Wed Jan 06, 2010 11:52 pm



Quoting KC135TopBoom (Reply 19):
This adds to the force multiplier role of the tankers.

Yup, that's all a black box to me, but it sounds reasonable. If we figure each new gallon of fuel is worth $11 or perhaps more, then those winglets start paying off, especially vs dispatching additional KC-10s or KC-135s to the scene to give additional fuel.

But, it's not for me to say if it makes sense. It's a hard calculation. But my instinct says no, it's not worth it. Like re-engining the B-52, it seems reasonable until you see how little they fly.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Thu Jan 07, 2010 3:38 pm



Quoting Flighty (Reply 20):
Quoting KC135TopBoom (Reply 19):
This adds to the force multiplier role of the tankers.

Yup, that's all a black box to me, but it sounds reasonable. If we figure each new gallon of fuel is worth $11 or perhaps more, then those winglets start paying off, especially vs dispatching additional KC-10s or KC-135s to the scene to give additional fuel.

But, it's not for me to say if it makes sense. It's a hard calculation. But my instinct says no, it's not worth it. Like re-engining the B-52, it seems reasonable until you see how little they fly.

I don't have the current numbers, but when I flew the KC-135A/E/Q the costs to deliver each gallon of fuel to a reciver was about $25 per gallon.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Fri Jan 08, 2010 2:00 pm



Quoting 747classic (Reply 15):
If you are at MTOW (377.8 tons) with the 747-200/300, always all wing tanks are full.(volumetric), the weight of the total wing fuel depends on the SG

Yes, the mass of the fuel is dependent on the volume by SG.

Quoting 747classic (Reply 15):
The wing root bending moment reaches the max certified value (when the aircraft becomes airborne) when the specific gravity is .78.

I would hope not, the wing would be stressed for +2.5g to --1.0g flaps up, and +2.0g to 0.0 g flaps down.

Quoting 747classic (Reply 15):
MZFW = 268.000 kgs.(freighter)

267570 ?

Quoting 747classic (Reply 15):
wing fuel weight = 102.2 (see table)

Is that not just the SG by the volume of the wing tanks ?

Quoting 747classic (Reply 15):
Now the max. wing bending moment is exceeded and the max allowable structural TOW must be reduced to 377.4 tons (see graph reply 12.)

That just looks like a reduction of the MTOW by wing volume*(0.78-actual SG) when below 0.78 ?
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RE: KC-10, KC-135 Tankers With Winglets.

Fri Jan 08, 2010 2:30 pm

Zeke, do you think blended winglets or raked wingtips for the KC-10 and KC-135 fleet would be best? To me it looks like raked wingtips would be much better as they could be designed to be lighter in weight and would not stress the original design of the wings and center wing box, which were designed in an era where winglets or raked wingtips were no envisioned as a possibility.
 
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RE: KC-10, KC-135 Tankers With Winglets.

Sat Jan 09, 2010 2:32 am



Quoting KC135TopBoom (Reply 23):
Zeke, do you think blended winglets or raked wingtips for the KC-10 and KC-135 fleet would be best?

Neither, it is a poor investment in my view and why I think the USAF did not go with it in the first place.

It would require a lot more money to design and certify the modification (which is a modification to a modification), and then having to requalifiy the tanker and receivers. The engine upgrade on the KC-135R a lot more capability over the E, more than wing tip devices would have provided.

It could have made sense to do this when the were re-skinning the wings, but that is not required again for another 8-10 years.

For the little amount of time that these tankers fly, I cannot see any business case for it. I would think that the fuel burn would be less than 25% of the operating cost of these tankers. If improved wing tip devices gave say a 5% improvement, overall that would only be about 1% reduction in the operating cost of the airframe.
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RE: KC-10, KC-135 Tankers With Winglets.

Sat Jan 09, 2010 11:47 am



Quoting Zeke (Reply 24):
Quoting KC135TopBoom (Reply 23):
Zeke, do you think blended winglets or raked wingtips for the KC-10 and KC-135 fleet would be best?

Neither, it is a poor investment in my view and why I think the USAF did not go with it in the first place.

A business case model can be created to establish the viability of a winglet retrofit program for a fleet of airplanes. Independent variables in the assessment include the following:

Winglet unit price ($/airplane),

Fuel burn reduction (%),

Cost of fuel ($/gallon or lb),

Interest rate (%),

Inflation rate (%),

Fleet size (number of airplanes),

Fleet utilization (hours/year),

Retrofit rate (airplanes/year), and

Current Life span remaining (years).

Extension of Economic and Operational Lifespan, delaying introduction of successor aircraft. (years)


In the thread starter I mentioned the following :

Quoting 747classic (Thread starter):
IMO especially the KC-10 is a prime candidate seen the very low flight hours/cycles of all aircraft and the very limited aging aircraft costs on high hour/cycles DC-10's, compared with several Boeing models.
Together with the hopefully positive decision of the KC-10 CUP (cockpit upgrade program) in may 2010, this produces a very competitive tanker for years to come

I didn't bring forward the KC135. IMO this aircraft has to much uncertaincies about aging aircraft issues, especially in the wings. This is also mentioned in the report as a potential drawback. The remaining expected lifespan is however not as short as some people think.
According the 2007 report the last KC135 will be retired in 2040.


About the KC-10(A) the following :


The KC-10 is a military derivative of the McDonnell Douglas DC-10 commercial aircraft. Winglets were successfully flight tested on the DC-10 aircraft and were later successfully incorporated into the derivative MD-11 aircraft. There are currently 59 KC-10 aircraft in the Air Force inventory, and they are flown extensively. The KC-10 fleet is quite young, with the oldest aircraft having approximately 22,000 flight hours and 14,000 flight cycles. For comparison, the older DC-10 still in service had over 131,000 flight hours and 45,000 flight cycles as of September 2006.

The MD-11 experience indicates that a successful winglet can be incorporated into the DC-10-based wing design. The DC-10 flight test program that was conducted identified approximately 3 percent cruise efficiency improvement, which was later replicated on the MD-11 design.2 In addition, recent winglet design experience using modern CFD methods and high Reynolds number (RN) wind tunnels may provide lessons that could have applicability for winglet designs that may be more effective on the KC-10. With new multidisciplinary design and optimization methods available, it is likely that an even more efficient and simpler design could be feasible for this aircraft family. Expected fuel saving with a new generation blended winglet design could lead to a 5% saving in cruise efficiency.

The cost of installation a set of winglets (incl. certification for 59 aircraft) could range from 1,5- 3.0 milj USD for one aircraft.

In the KC-10 best-case scenario (low investment- high fuel saving, high fuel price) net savings become positive 8 years after starting the modification program. All 59 aircraft in the inventory are modified. Total net savings to the Air Force are approximately $221 million (FY07$).

In the KC-10 worst case scenario, net savings become positive 23 years after starting the modification program. Only 53 of the 59 aircraft in the inventory are modified---the others are not modified because they are expected to be retired from the inventory before reaching the ends of their payback periods. Total net savings to the Air Force are approximately $12 million (FY07$).

In all calculation the Extension of the lifespan of the KC-10 and a later introduction (= large investment) of a successor is NOT taken into account and could produce an additional (very large) saving.
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kc135topboom
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RE: KC-10, KC-135 Tankers With Winglets.

Sat Jan 09, 2010 8:10 pm



Quoting Zeke (Reply 24):
Quoting KC135TopBoom (Reply 23):
Zeke, do you think blended winglets or raked wingtips for the KC-10 and KC-135 fleet would be best?

Neither, it is a poor investment in my view and why I think the USAF did not go with it in the first place.

That could be. Perhaps the best case would be just putting MD-11 type winglets on the 30-45 newest/youngest KC-10As only.

Quoting 747classic (Reply 25):
A business case model can be created to establish the viability of a winglet retrofit program for a fleet of airplanes. Independent variables in the assessment include the following:

Thanks.
 
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747classic
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RE: KC-10, KC-135 Tankers With Winglets.

Sun Jan 17, 2010 11:14 am

Boys, I found a very accurate follow-on report (June 2009) about the KC135 with winglets.
It gives a lot of additional back ground information (plus pictures) about the actual modification costs and fuel saving possible.

Conclusion :

Because there is not a developed winglet modification kit for the KC-135R, the cost of modifying the aircraft was determined by best estimates based on historical information from the NASA KC-135A test during the late 1970s and current winglet modification prices on similar sized aircraft. These winglet studies concluded that the winglet modification of the KC-135A with the AFFDL/Boeing winglets would cost an estimated $66,000 per unit based in 1977 dollars. Adjusted for inflation, that estimate would be about $230,000 in 2009. Personnel at the Business Development office at the Boeing Company, Integrated Defense Systems quote a price of $1M for their version of a winglet modification.
The cost estimates for APB's Blended WingletTM modification of commercial transport aircraft comparable in size to the KC-135R are also calculated.. According to the APB website, these cost estimates include the Blended WingletsTM, wing modification kit; all other necessary materials, parts and fasteners; data; software; manuals and technical documentation; proprietary installation tooling, installation job cards/planning, as well as on-site installation technical support. With these values in mind, the cost-benefit analysis developed two options with different prices for the KC-135R winglet modification: Option A uses $1M for the cost while Option B assumes $1.5M for the cost, both based in 2009 dollars.

With the overall break even points for both options of the three scenarios well within the expected life cycle of the KC-135R aircraft, it is implied that the winglet modification would be cost effective. This analysis quantified the effectiveness of the modification to a dollar value which senior leaders can use in making their decision on future winglet programs. With the three scenarios, the potential savings of the winglet modification ranged from over $1.1 billion seen in the best case scenario to just over $177 million found in the worst case scenario. Focusing on the most likely case scenario options, the potential savings obtained from the modification ranged from over $703 million for Option A to over $582 million for Option B. That is a potential savings of 289 percent above the $242 million invested and a savings of 159 percent above the $364 million invested for Options A and B, respectively. Considering these are estimates based on stated assumptions, any additional operating years beyond 2042 would increase the savings obtained.

http://handle.dtic.mil/100.2/ADA505062
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kc135topboom
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RE: KC-10, KC-135 Tankers With Winglets.

Sun Jan 17, 2010 12:52 pm

My biggest concern for winglets is the effect they have on weather vaning in high cross winds. The DEN crash/runway excursion of CO-1404 a B-737-500 equipped with winglets. They may have also played a role in the recent AA B-737-800 crash, too.

That is mainly why I see raked wingtips a better option. USAF tankers often need the high cross wind capability they currently have for operational missions.

http://www.aviationweek.com/aw/blogs...=blogScript&plckElementId=blogDest
 
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RE: KC-10, KC-135 Tankers With Winglets.

Sun Jan 17, 2010 1:10 pm

Quoting KC135TopBoom (Reply 28):
That is mainly why I see raked wingtips a better option. USAF tankers often need the high cross wind capability they currently have for operational missions.

That's the trade-off the USAF has to make : raked wingtips occupy more space on the ground (greater wingspan) or slightly reduced X-wind limitations with blended APB winglets.
The original AFFDL/Boeing winglets, as tested on the KC-135, however are effected less by X-wind.

[Edited 2010-01-17 05:11:56]

[Edited 2010-01-17 05:12:50]
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