What is the fastest climbing aircraft? And the best at sustained turn? Which is the nastiest to land..and the nicest? And what is it about a particular aircraft’s design that gives it these qualities? Armed with these questions and many more, I went to pester Jim Smith, a man with significant technical roles in the development of the UK’s leading military aviation programmes, to get answers.
Fortunately, his answers were far longer than I expected and instead of a one-off article, we will be sharing a fascinating series.
Over to Jim for the introduction.
Why are aircraft the shape they are?
“This question arises from a discussion between Hush-Kit and I about using specific aircraft as examples to illustrate how various requirements drive aircraft size, shape, wing planform, thrust-to-weight ratio and so on. In best Hush-Kit style, I’ve been asked to look for ‘best and worst’ in a number of categories, for example: High Alpha flight; Acceleration; Sustained turn rate; Instantaneous turn rate; Climb Rate; Agility and manoeuvrability at high and low altitude; nicest and nastiest to land. And of course, the desire is to focus on fighter aircraft.”
“I’ll explore how different parameters drive aircraft design by considering not only fighter aircraft, but also other types of aircraft, noting that individual performance requirements are not the only requirements that drive aircraft configuration design. We’ll start a discussion of requirements for military aircraft, before looking at specific point performance and other requirements that influence their design.
Mission and Point Performance Requirements.”
“In general, even fighter aircraft today are likely to be designed to meet a number of mission profiles, coupled with point performance parameters as constraints. So, requirements might be summarised as “deliver missions 1 through 5, while also achieving stated maximum g-loading, climb rate, sustained and instantaneous turn ratesâ€. Each of the missions will have been matched to realistic operational scenarios, such as an interception from Quick Reaction Alert (QRA); an interception from Combat Air Patrol (CAP); an extended duration patrol; and perhaps also surface strike missions with differing weapons fits.
These mission requirements will generally determine the sensors and crew required (one or two-seat for the majority); the weapons, auxiliary sensor and targeting pods and tanks that may be carried externally; and, in the case of stealthy aircraft, what sensors and weapons must be carried internally.”
“Taken together, these reference missions will allow the ‘payload-range’ of the combat aircraft to be established, and this along with the determination of whether one or two engines is required, will define the size and (largely) the weight of the aircraft.
Point performance requirements will also be set. In some cases, these will be expressed as constraints, rather than targets, and they should also reflect the operating concept of the aircraft, and be coherent with the mission requirements. There is no point specifying a mission requiring extreme range, for example, and at the same time require that the cruise speed of the aircraft be supersonic at low level. If you do this – oh dear – you end up with a TSR2, where low-level supersonic range was apparently an enormous cost driver.”
“One of the reasons that point performance parameters are often set as constraints, is that the turning performance of typical fighter aircraft could easily exceed the tolerance of a human pilot, typically 9g, even with a ‘g-suit’. Consequently, many of today’s fighters are designed structurally to 9g loadings, which effectively means they deliver the same instantaneous turn rate as each other, at least at low to medium altitudes. Sustained turn rates are generally less likely to be structurally limited, and may vary rather more, dependent on wing sweep, aspect ratio, and thrust to weight ratio.
Point performance requirements are likely to include such items as climb rate, field requirements, maximum speed and operating altitude, the structural ‘g’-limit, and possibly others, depending on the role. There will also be plenty of system and reliability and maintainability requirements and targets, but these will not need to be covered here. (For a discussion of BVR combat requirements see my Hush-Kit article here)
The current multi-dimensional approach to combat aircraft requirements has not always been the approach. The Fifties were a period when huge advances had been made in the understanding of aerodynamics and in jet engine design, enabling great leaps in performance. So much so, that the capabilities of the aircraft could outstrip the thinking behind the military requirements being proposed.
The best example of this is the Douglas A-4 Skyhawk. The Navy had in mind a 30,000-lb twin jet attack aircraft, with a 2,000-lb bomb load. What they got from Douglas was the Skyhawk, eventually with an empty weight around 10,000 lb and max TO weight of 24,000lb, able to carry up to 8,000lb of stores, at high subsonic speeds. (Picture)
In looking at specific requirements, I’ll use some of the older point-driven designs to illustrate the configuration trades being made, and indicate which current aircraft may provide best or worst examples. In addition, some civilian operations also require some fairly extreme configurations, so I’ll also consider some of those.
Click here for part one.
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“Without a doubt the first mission in the Operation Protector over Libya. It was the first time in 50 years that Sweden was abroad with the Air Force in a conflict and I had the opportunity to lead our first mission into the area. Even though the memories of most of the following missions in the operation have faded, it feels like I remember every minute of that first one, better than any of them. It wasn’t very exciting per-se, and the mission went as planned, but it was uncharted territory psychologically. It was a little extra exciting as I had our squadron commander as my wingman and the mission could not fail, for many reasons, both military and political. It started with a very exciting air refuelling were we had to connect right after take-off due to fuel incompatibilities on the Sigonella base (don’t ask..). The bingo fuel warning alarm went off almost right away and creative manual calculations had to take its place. There were a few refuelling misses involved, the Air Force Chief looking back at us from the tanker, which was a C-130 that was really just a trainer, and me having to do a few short cuts through the Fighter Area of Responsibility to get on station on time and with enough fuel. But other than that, quite uneventful as we were just doing Defensive Counter Air for the tanker fleet. Psychologically it turns out that live missions are very similar to training ones, even pulse wise, but I didn’t know that before taking off. Train as you fight works.”
Switzerland is a small landlocked nation with powerful neighbours. It has not fought since its civil war of 1847, and has not fought a foreign nation since 1815. Today the neutral nation defends its sovereignty with a small air force of frontline F/A-18s supported by F-5Es. It now seeks to replace both — and an evaluation of five candidates has begun.Â
Five fighter types are being pitted against each to compete for a lucrative order for 30-40 aircraft for the Swiss Air Force. From Europe, the 
To assess the most likely candidate we need to understand a little about the Swiss Air Force and their concept of operations (abbreviated as CONOPS). The Swiss CONOPS prioritises local air policing, against the possibility of a high-end threat, to protect Swiss Neutrality. Their basing model involves hardened and dispersed airfields.
Historically they have not been shy to pay for high-end capability. They’ve tended to go for expensive and complex systems in the past, notably getting the Falcon missile integrated onto the Mirage IIIS, and adding Electronic Counter Measures and Radar Warning Receivers to the normally austerely equipped Hawker Hunter. More recently they chose the McDonnell Douglas F-18 Hornet over the F-16 because of its radar/weapon combination. They make long-term investments in their aircraft (their Hunters served until 1994 and their F-5Es are still operational) so choose mature but modern systems. They prioritise credible and survivable options, and can afford them when needed. They also dropped any air-ground tasking a few years ago. That means aircraft optimised or compromised by air-to-ground performance are at a disadvantage. That’s a big factor with the F/A-18E, and to a lesser extent with Rafale. The F/A-18E’s big advantage of commonality with its forebear, the legacy Hornet, may not be as tempting as it first seems as the older fleet will be completely withdrawn – though familiarity and a good reputation could help its case. Typhoon is the most capable option in pure air-to-air performance, and unlike the earlier evaluation, AESA radar should be available from the outset – an option Switzerland would be likely to go for. But Typhoon is expensive to purchase and operate. The choice between Rafale and Typhoon revolves around a mixture of cost and how much air-to-air performance is required. Typhoon has a premium performance at a price (though investigations in India have highlighted that the oft-quoted price advantage of Rafale may not be all it seems). The Rafale is a capable aircraft that could serve Switzerland well, but is probably more capable and costly than is necessary.
Switzerland’s defensive posture is about credible deterrence in the situation of a European War — and avoiding being a transit zone for others. The Swiss Government is not happy when NATO assets take short-cuts through their airspace, as sometimes happened during conflict in the Balkans. A fast-climbing fighter with good readiness and availability is vital if the SwAF wishes to deter such intrusions.
The Swiss military is also mindful of Russian influence in subverting politics in parts of Eastern Europe, and they’re wary. The perceived high-end threat threat is thus likely to be a ‘Flanker’ derivative with a long-range BVR weapon. This puts the Super Hornet in the outsider position, mostly down to it being the poorest air-to-air performer, and the oldest technology airframe. The reach of an air-to-air missile is closely tied to the specific excess power (SEP) of the platform in the supersonic manoeuvre when launching, a good sustained turn rate is also vital. The Super Hornet has less SEP at higher Mach than the original and a poor STR compared to its rivals.
Jim Smith had significant technical roles in the development of the UK’s leading military aviation programmes. From ASRAAM and Nimrod, to the JSF and Eurofighter Typhoon. In his life he has provided technical assessments of the YF-22 and YF-23, we wondered what he would make of the Lippisch P 13, an exceptionally ambitious wartime concept for a supersonic interceptor of bizarre appearance powered by a coal-fuelled ramjet.
“Hush-Kit has asked me for an assessment of the extraordinary Lippisch L13a. A bold and innovative concept, which, although it did not get to fly, was wind tunnel tested, and was also trialled in glider form. Before I give my thoughts on the aircraft I’ll start by quoting verbatim the Wikipedia entry:
Who are you — and what is your relationship with helicopters?
“I’m an editor with the helicopter industry magazine Vertical, which means I spend an inordinate amount of time writing and thinking about helicopters. I also fly them, although not as regularly these days as I would like! I hold FAA commercial pilot and flight instructor certificates with helicopter and instrument ratings, and have also held commercial helicopter pilot licenses in Canada and Australia.”
Which types have you flown?
“Most of my flight time is in Robinson R22s and R44s, since I learned to fly in Robinsons and spent about 800 hours instructing in them. I also have a fair amount of time in the Airbus AS350 series, the Bell 407, and various Bell mediums (UH-1B/H, Bell 205 and 412).
Then I’m lucky enough to have anywhere from 30 minutes to 20 hours in another 20 different helicopter types, ranging from the two-seat Guimbal Cabri G2 to the mighty Columbia Model 234 Chinook, which I flew as co-pilot on a powerline construction job for one of my more interesting story assignments.
For anyone who’s curious about the other 18 models, they are the Airbus EC120, EC155, and H215; Bell 206B, 206L, 505, and AH-1F; Enstrom 480B; Kaman HH-43 Huskie and K-1200 K-MAX; Leonardo AW139; MBB Bo.105; MD 500 and 902; Mil Mi-24D; Robinson R66; Schweizer 300; and Sikorsky S-55. I’ve flown simulators of a few other aircraft, but maybe the only one worth mentioning is the AW609 tiltrotor.”
What is your favourite helicopter, and why?Â
“I have to say the K-MAX, which is a single-seat heavy-lift helicopter with twin intermeshing main rotors that eliminate the need for a tail rotor. It’s not the most attractive helicopter (it has been described as two broomsticks, um, copulating in a dumpster) and neither is it the most modern (its rotor blades are actually made out of wood). But I’ve been fascinated by it since I first saw one landing on a fire helibase in 2005.
The single seat means that your first flight in the aircraft is also a solo, which is a little intimidating, especially since the intermeshing rotor system gives it somewhat different handling characteristics than a conventional helicopter. But Kaman prepares you pretty well for this by first giving you around five hours of dual flight instruction in the HH-43 Huskie, which has a similar rotor design. Getting to fly a K-MAX in 2014 was a huge thrill, and I was also the first woman to fly the model. It tells you something about the helicopter industry that it took 20 years from the certification date of the aircraft to reach that milestone, but better late than never.”
What is your opinion of the S-97?
“The compound helicopter that Sikorsky is pitching as the U.S. Army’s Future Attack Reconnaissance Aircraft? It still has a long way to go to prove itself, and it remains to be seen how it will stack up against the competition, but generally speaking I’m a total fangirl.
In particular, I’m really excited about the potential for the rear-mounted pusher propulsor to completely transform the way we fly — for example, by permitting rapid accelerations or decelerations in a level altitude, or the ability to maintain a stationary hover while pointing your nose to look up or down. These are revolutionary capabilities that go against everything that helicopter pilots today understand instinctively about how to fly. If anyone from Sikorsky is reading this, I hope they decide I’m the perfect person to write a pilot report on it.”
Please tell us about your experience with the Mi-24?
Sure. The Mi-24 — the fearsome Russian attack helicopter — isn’t something that those of us in the U.S. see very often, but in 2017 I had the opportunity to fly a privately owned Mi-24D in Lancaster, Texas, for a story. It’s one of three owned by the same person, two of which are operational and also available to the U.S. military for adversary orientation training.
Whenever I have a chance, I try to learn as much as possible about an aircraft before I jump in and fly it, even if it’s only for a short demo. Generally speaking, all helicopters have been designed to present a common flight control architecture to the pilot, so without understanding the underlying systems, it’s hard to render any judgment more meaningful than “Yep, flies like a helicopter.â€
In this case, I was able to get my hands on a couple of different versions of the Mi-24D flight manual, and I spent a few weeks before my flight studying up on it. I did a double take when I read that prior to engine start-up the throttle (which is a twist grip like a motorcycle throttle) should be closed full left, away from the pilot — so, similar to a motorcycle throttle, but exactly opposite to the throttle in Western helicopters.
Now, there are also some differences with the pedals in the Hind compared to U.S.-designed helicopters, due to the different rotational direction of their main rotors. So in the Mi-24, which has a clockwise-rotating main rotor system, right pedal increases tail rotor thrust, whereas in something like a Huey, the left pedal is the power pedal. But many Airbus helicopters also have a clockwise-spinning main rotor system and right power pedal, and it’s really not a big deal. Right pedal still points the nose to the right, and left pedal points the nose to the left, so if you happen to input the wrong pedal, you’ll notice and instinctively correct, as long as you’re flying smoothly.
However, in certain circumstances, if you were to inadvertently roll the throttle in the wrong direction, you could potentially hurt yourself or the aircraft before you had a chance to recover. So that really caught my attention!
On the day of my flight, my instructor pilot, John Totty, put me through an abbreviated version of the adversary orientation training that he provides to the U.S. military. This was really interesting, because it took that understanding of aircraft systems to the level of tactical application. So, for example, the Mi-24D’s stub wings make it very fast, but also limit its banking ability. If you were facing off against the Hind in a slower but more manoeuvrable helicopter, how could you exploit this to your advantage? I ended our class feeling much more prepared for a Red Dawn scenario.
We combined my demo flight with an air-to-air photo shoot with the other Mi-24D and two R44 camera ships. I rode in the co-pilot/gunner compartment up front, and during our photo shoot there wasn’t much for me to do except marvel that I was flying in a Hind over Texas! Talk about Red Dawn.
Then we broke off to give me a chance to fly the aircraft. The Mi-24D isn’t meant to be flown from the front; the co-pilot/gunner has only basic flight instruments to allow them to make it home in an emergency. Also, the co-pilot’s flight controls are generally stowed: the cyclic is tucked forward, and the pedals are hidden in the sides of the compartment. The controls move into position through hydraulic pressure after the co-pilot squeezes a lever on the collective. Since they’re not designed for routine use, they’re not very ergonomic! So I can’t say it was a very comfortable flight, but I loved every minute of it. And yes, it flies like a helicopter.”
9. Sikorsky UH-60 Black Hawk (1974): the bestselling successor to the Huey, which embodied a new emphasis on crashworthiness and survivability.
8. Aérospatiale AS350 (1974): the hugely versatile, bestselling successor to the Alouette series (which did not embody an emphasis on crashworthiness, unfortunately).
7. Boeing CH-47/Model 234 Chinook (1961): the most successful tandem-rotor helicopter, which continues to have important military and civilian applications.
6. Mil Mi-8 (1961): the world’s most-produced helicopter, with all of the far-reaching, wide-ranging impacts that implies.
5. Bell UH-1 Huey (1956): the iconic helicopter of the Vietnam War, which created a generation of pilots and mechanics who would shape the industry for decades to come.
4. Sud Aviation Alouette II (1955): the first production helicopter to be powered by a gas turbine engine and one whose derivatives, notably the SA 315B Lama, pioneered high-altitude operations.
3. Sikorsky H-19/S-55 (1949): a pioneering military transport helicopter that helped define air mobility, medevac, and search-and-rescue operations.
2. Bell 47 (1945): the first helicopter certified for civilian use, and consequently essential to the development of the civil helicopter industry.
Vought-Sikorsky VS-300 (1940): Igor Sikorsky’s first practical helicopter, and the one that established the single main rotor and tail rotor configuration that has dominated the industry since.
What is the 
“I foresee a bifurcation of the industry. On the high end, new designs like the Bell V-280, Sikorsky S-97 and SB-
1, and Airbus Racer will deliver incredible speed and performance to military and other customers who have the need and the budget for them. Meanwhile, I expect that cost-effective electric VTOL aircraft will take over many missions, like passenger transport, that are currently being performed by light helicopters. There will still be a market for conventional helicopters, but it will be squeezed at both ends.
Autonomy will undoubtedly be a big part of our future, too. As someone who spends a lot of time writing about the tragic consequences of human error in helicopters, I don’t think this is a bad thing. But getting to the point where vertical-lift aircraft are routinely flying themselves in congested airspace is going to be hugely challenging. New autonomous systems are going to introduce new failure modes that may be difficult to anticipate, and as the recent 737 MAX crashes illustrate, human pilots don’t have a great track record of compensating for failures in complex systems that are largely opaque to them. There are a lot of smart people working on this problem, but they have a lot of hurdles to overcome.”
What advice would you give to new helicopter pilots?
“Well, if they haven’t already entered the helicopter industry, I would advise them to think long and hard before doing so. The civil helicopter industry in particular is not generally conducive to healthy relationships or work-life balance. Part of this is a necessary consequence of the unique work that helicopters do in hard-to-reach places. However, the industry also has a long history of taking advantage of people’s passion — flying helicopters is incredibly addictive, and there is always someone who is willing to put up with almost anything for the chance to do it.
But if you’re absolutely committed to being a helicopter pilot, then my advice is to constantly be looking to expand your horizons. There’s a tremendous amount of knowledge and talent in the helicopter industry, but it’s largely siloed. For example, depending on where you train and begin your career, you may really need to go out of your way to find instructors who are skilled in mountain flying. It’s worth seeking them out! Every new skill you pick up, every new perspective you expose yourself to will make you a better pilot, and along the way you’re likely to make connections that will open doors for you down the road. This curiosity should extend to every mechanical system on your aircraft, too, because the more you understand about how your helicopter works, the better position you’ll be in to keep yourself safe.”
What is the greatest myth about helicopters?
“A lot of people still seem to believe that helicopters can’t glide if they have a power failure. In fact they can in a manoeuvre called an autorotation, although the glide path is closer to, say, a turkey’s than an eagle’s. In an autorotation, air flowing upward through the rotor system drives the rotor blades, and the pilot maintains full controllability, as long as the helicopter continues to go generally down. It’s something that helicopter pilots practice extensively during their training, although the success of the manoeuvre in real life depends on a lot of different factors, including what you happen to be flying over when your engine quits. The one advantage that helicopters have over airplanes in this respect is that they don’t need as much real estate for a safe emergency landing.”
Tell me something I don’t know about them.
“How about the origin of the word helicopter? It’s derived from the Greek words helikos (spiral) and pteron (wing). Of course, the impulse of English speakers today is to divide it into “heli†and “copter,†which masks that etymology.”
What do you think about the way 
They do seem to