I flew the Big Sexy KC-10 super-tanker and I will miss it
The KC-10 did not require modification to carry the SR-71’s special JP-7 fuel, as it had fuel tanks that could be isolated (if desired) and only delivered to the boom. Those tanks could also hold regular JP-8 and feed it to the engines if needed.
Last week, the KC-10 Extender, a superb aerial refuelling aircraft, retired. We spoke to a KC-10 pilot to learn about ‘Big Sexy’.
The best KC-10 was its versatility and the flexibility of its crews. Unlike the KC-135, the KC-10 was ready to refuel probe or drogue receivers without any extra work or attachments needed before launch. With the ability to be refuelled itself, the KC-10 could be launched and flexed to almost any refuelling mission quickly.
The worst thing about the KC-10 was taxiing it around on smaller airfields. The nosewheel sits 20+ feet behind the pilots, so you must be very careful about turning sharp corners or trying 180° turns. In these cases, we’d often have a boom operator open the forward doors, lay on their stomach & hang out of the aircraft; they were on the intercom, relaying the position of the main and nose wheels to the pilots, keeping us from crunching taxi lights or ending up in the grass (which we sometimes did anyway).
Based on overall capacity, the KC-10 was better than the KC-135; it could take off with a much higher fuel load. While it burned more per hour, there was still significantly more fuel available for receivers. The ‘135 also couldn’t do Drogue receivers unless the boom was modified ahead of time (which meant it couldn’t do probe receivers) or if you attached pods to the wings. The KC-10 was ready for either at any time (and we could put our own pods on the wings, if needed).
The empty weight of the KC-10 was about 250,000 lbs. Maximum takeoff weight was 590,000 lbs…so about 340,000 lbs of fuel, if you weren’t carrying cargo. All of it could be offloaded, other than what we needed to save to get ourselves home…and sometimes we pushed that limit! In one case, I pushed a little too far – we got back to our deployed base, and it was fogged in. We couldn’t even attempt an approach.
We were getting close to diverting, which would have been painful, but another KC-10 arrived. They took up a holding pattern over the base, a couple thousand feet above us. We started coordinating between ourselves to balance fuel out so nobody had to divert, then just did it. At one point, there were four of us in the pattern, talking to each other, and passing fuel so that everyone got to sleep in their own bunks. The fog eventually lifted, and we all made it in.
The KC-10 was actually pretty easy to take off and land. It was very stable and large, and bumps that would affect smaller jets didn’t have much impact on us. The controls were pretty straightforward. On landing, you’d start the process of “flaring” just after the 50’ radar altimeter callout.
You rarely landed smoothly, though, as the centre gear touched down first on crowned runways. It shook & rattled, so there was always some of that, except in the rare instance you’d land with the centre gear retracted.
There weren’t many foibles to the jet; it handled well. It was just very large. When refuelling with KC-135s years ago, the bow wave of a heavy KC-10 could hit a sensor in the 135’s tail, disconnecting their autopilot. If they weren’t watching it, you’d suddenly end up with a face-full of KC-135 as their autopilot kicked off and the nose dropped. They eventually fixed that problem, if I recall.
One peculiar aspect was that the number 2 engine in the tail was angled down at about 2.5°. We tried not to use it for taxiing, as we were already worried about blowing things over…some would limit how much they used it when air refuelling, too, as a big input could push the nose down.
Something you may not know about the KC-10: well, it had a large space under the cargo floor that was just empty. I think it was the galley on the DC-10, but the Air Force had no need. We called it “The Pool Room”; I was told it was because you could put a pool table in there, and have room to play. Getting into it was a hassle.
You could access the KC-10 through the nose gear. We occasionally had to do that; you’d climb up & shimmy through the avionics compartment, eventually ending up in the cockpit. It was a tight fit!
The newer KC-46 is a decent aircraft. It’s had teething issues, but they will eventually sort it out. The problem is that losing the KC-10 still represents a major loss of overall capacity, as there will be less fuel in the air at any given time. The Air Force already can’t meet all its demand for Air Refueling, and I’m afraid that is much worse today.
My favourite aircraft to refuel was the B-1; it wasn’t particularly cool or anything, but when it showed up on your schedule in Afghanistan, they were going to take about 100k lbs of fuel…and your day just got a lot shorter!
My least favourite aircraft to refuel was the A-10. It doesn’t have the power of other jets and flies pretty slowly; we had to use slats and sometimes flaps to get slow enough. Above certain weights, it was just not possible.
The deck angle when refuelling A-10s could be in excess of 5° nose up…almost feels like you are setting up for a power-on stall. We had a procedure to help called a “Toboggan”…we’d enter a slight descent at around 300 feet per minute. That gave the A-10 the help it needed to get on the boom, but you only had 1,000’ below you before you’d be outside of your protected airspace, so you’d only get 3 minutes or so. Then you’d have to climb up & do it again.
Nobody was necessarily bad at meeting the tanker, and we went out of our way to come to them. It didn’t always work, but we usually managed to end up 1-3 miles in front of them. Many fighter types referred to the KC-10 as the “mothership” because it was so large and was just there, in front of you.
Occasionally, the AWACs would control our rejoins. They didn’t seem to have much practice doing so; I can recall them vectoring us to our bomber, and vectoring the bomber to us…AWACs handed us off nose to nose at around 3 miles, closing at probably 600-700 knots. We were separated by 1,000’, so it wasn’t unsafe, but AWACs kind of said, “There you go,” and we immediately shot past each other in opposite directions. It was funny…we took over & directed a mutual turn on the same magnetic heading, which at least put us abeam each other & fixed it from there.
The KC-10 set the bar for tanker ops, hands down. As we discussed, the flexibility to do any Air Refueling mission at any time was key, and our ability to be refuelled meant we could be doing it for long hours.
We also had a significant cargo capacity. You could load up support troops and their equipment, then drag multiple fighters across an ocean. When you landed, you were almost your own little Air Force and could start operations quickly.
1A good tanker crew got to be a mini family. We didn’t use ranks in the KC-10 while flying, but rather, first names. We wanted every member of the crew to feel like they could speak up if they saw something wrong; everyone knew who the Aircraft Commander was, but that wasn’t something you wanted to flex on your crew – doing so may mean you win the battle, but you’re losing the war.
A good crew got to the point where they knew what everyone else needed, and they were ready before anyone asked. They understood the bigger picture, and took care of each other; you could complain, but my only rule was that the complaints better be funny because there wasn’t a lot we could do about most of it…it was better to laugh about it than to make each other miserable.
Big Sexy was the most common name, yes. Sometimes referred to as Gucci, but the official name was the Extender.
Three engines weren’t particularly unusual, no. The tail engine was exactly like the other two, but with a longer cowling. It was angled down slightly, though, as I mentioned.
If you had an engine failure (like we did in the simulator every quarter), you hoped it would be the tail engine. There was no asymmetrical thrust; the loss of one of the wing engines caused a lot of asymmetrical thrust, which required a lot of rudder to counteract.
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The debate on single versus twin engines for fighter aircraft continues. Paul Stoddart* follows Gen Chuck Horner and David Baker, PhD into the ring.
The choice of engine is a fundamental design driver for any aircraft – both the type and the number. One or two engines and one or two seats are fundamental choices for fighter aircraft. However, while a second seat can be spliced into even smaller designs, the number of engines is fixed (the metamorphosis of the twin F-5 into the cancelled single-engined F-20 is an exception).
After decades of study and experience, the debate on one versus two engines continues. General Charles Horner, USAF, offered his views in the October ’98 issue of Air Forces Monthly, with Dr David Baker adding to the debate in the June ’99 issue of Air International.
![Thrust vector nozzles (TVC) of Sukhoi Su-30SM Flanker-C jet engines [3862 × 2575] : r/WarplanePorn](https://i0.wp.com/i.imgur.com/Phhlu9o.jpg?w=830&ssl=1)
General Horner emphasised the increasing reliability of engines and the lower cost of single-engine designs. Dr Baker balanced that approach by highlighting the unique performance advantages of twin-engine layouts. Two engines have a safety advantage over singles, but they are not major advantages, and the price paid for them is high. Indeed, General Horner argued convincingly that even with its likely higher lifetime losses due to engine failure, the single-engine fighter fleet would still work out cheaper. But will the superior aerodynamic performance of the twin help it gain air supremacy? If so, the extra cost will be money well spent – there is nothing more expensive than a second-rate fighter. Of course, there is more to air supremacy than manoeuvrability. Radar and missile performance are crucial, effective command and control is a force enhancer, and signature control is increasingly important.
Over the next few decades in the West, we may well see the service entry of the twin-engined GCAP, FCAS and whatever the US goes for. The current twin-engined designs are the F-15, Super Hornet, Rafale, Typhoon and F-22; the F-35, F-16 and Gripen represent the single-engine design school.
When a new aircraft is chosen, the engine number will be one of several fascinating design drivers. While a second seat can be spliced into even the smaller designs (Gripen and F-16) engine number is almost invariably fixed (F-20 weirdness aside). Cost and survivability are leading factors in the engine number debate, but there are two other issues: availability and commonality. Specifically, which engine types are available for use, and which do you already use? These points largely arise from the cost question but should be examined in their own right.
It is beyond argument that twin-engined fighters cost more to buy and support than their single-engine equivalents. The twin-engine proponents claim improved survivability in peace and wartime flying, justifying the extra expense. A commonly quoted statistic is that the extra engine buys around 15% lower attrition in combat. General Horner quoted the loss rates for US fighter aircraft from the ’50s to the ’90s (presumably peacetime losses). He correctly emphasised the major improvement for both types but then stated that the difference has narrowed significantly. The difference in raw numbers has fallen from a high of 5 in the ’60s to one in the ’90s. However, the proportional difference, i.e. the relative likelihood of losing an aircraft, should also be considered. In that respect, a twin was little better in the ’50s than a single, suffering 90% of the latter’s loss rate. However, for the following four decades to the late 1990s, the twins had an average loss rate of 64% of the single.
As the General pointed out, the lower lifetime cost of the single-engine fighter can more than offset its higher lifetime loss rate. There are, however, three counterarguments. Firstly, many nations buy fighters in small numbers and use them for long periods, two decades or more. The lower loss rate of the twin will better sustain fleet size, whereas the single could decline into ineffectiveness. Readers may remember the period in the mid-90s when the USAF lost five F-16s in quick succession owing to engine failure. The failure, resulting from a manufacturing defect, was not in itself catastrophic and a twin could have got home on its remaining engine. Although the USAF could absorb such losses, most nations could not.
The twin-engined option, being a larger aircraft, will have more potential for upgrade of new weapons and systems. Thirdly, when second-hand aircraft are procured, the extra purchase cost of the twin-engined fleet versus the single option is unlikely to be a showstopper, and the higher lifetime cost may be acceptable given the preceding two arguments. Incidentally, the General’s second experience of engine loss involved a contained failure of a turbine blade in an F-15. He shut down that engine and recovered on the remaining unit. Had that happened in an F-16 the aircraft would almost certainly have been lost. Coincidentally, at the time of writing, the Taiwan Air Force had just grounded its F-16A/B fleet for the second time within a few months. An F-16 was lost in August with an apparent engine problem; this followed three other engine-related accidents since March 98. Issues with the P&W F100 turbofan previously caused the grounding of the US and Israeli Air Force F-16 fleets.
Sometimes, we use two engines because we have no choice. Airframes are designed around engines, but aircraft start as a collection of performance requirements. The speed, range and so forth that the customer wants are distilled into a number of engine parameters with thrust remaining a priority for fighters. If there is an engine that meets those targets in a solo installation then, on cost grounds, it will probably win. If not, then the huge cost of engine development will likely be prohibitive and will rule out the single option. A twin-engine selection could well be the only choice. The F-22 has two 35,000 lb (wet thrust) P&W F119 engines. There is no 70,000 lb class alternative in the military engine class. Both the Lockheed and Boeing JSF contenders use a single engine – a derivative of the F119 is sufficiently powerful and is the obvious choice for these projects where low cost is a crucial design goal.
Similarly, the Saab Gripen needs 12,250 lb dry and 18,100 lb wet thrust to achieve its performance requirement; a single RM12 (F404 –GE-400) makes sense. Puzzlingly, the AIDC A-1 Ching-Kuo uses two TFE1042-70 turbofans to provide similar thrust and roughly equal performance to the Gripen. Perhaps the specification emphasises survivability (or there is some export limitation).
There is a strong argument that air forces should choose a high-low mix of aircraft. The more capable fighters are costly and can only be procured in small numbers, whereas the cheaper aircraft will lack certain capabilities. Buying some of each should provide sufficient force size and capability to produce a truly effective fleet. If both types use the same engine, then large savings in maintenance, training, facilities and spares will accrue. Generally, the high-end fighter will be larger than its low-end partner. If both use a single engine then, to achieve reasonable performance, those engines must be of different types, and the duplication of support effort will be expensive. The best example of the common engine, high-low mix is the F-15 and F-16, both of which use the P&W F100. The later F-22 and JSF do not share a common engine, the 
Saab’s Gripen E-series has adopted the F414-GE-39E turbofan, suggesting a good high-low mix, partnering it with the F/A-18E/F Super Hornet. The Russian MoD would ideally would like a future force of Su-57Ms twins and single-engined Su-75s both powered by the AL-51F-1. Interestingly, the 
An extension of this idea of community may be that a next-generation European ‘Loyal Wingman ‘-like the project would benefit from engine commonality with either Typhoon, Rafale or Gripen E, or perhaps more expensively, engine commonality with the next generation. Fitting a larger UCAV with an existing generation engine (such as the EJ200) may be a good move, as well as insurance against a cancelled ‘high’.
Paul Stoddart served as an engineer officer in the Royal Air Force for eight years. He now works for the Defence Evaluation & Research Agency (DERA). This article is his personal view on the subject and does not necessarily reflect RAF, Ministry of Defence or DERA policy.
NOTE: *The original article has been updated to reflect its date of 1998. I just found it sitting in the WordPress drafts folder many years after Paul sent it to me.
Rivers were covered in coal, cities blacked-out, factories disguised as great towns (with even drying laundry put out on weekly cycles) and radio navigation signals mimicked. Saving your own air force was vital for survival. Decoy or ‘dummy’ aircraft placed as tempting targets for enemy air attacks have saved many lives and aircraft. Creating decoy aircraft wastes enemy resources and confuses their estimates of your strength. Wasting enemy weapons and time is a good thing, and the decoy aircraft are bloodless heroes. 
Score: 8.6/10
