A Study in Contrasts

By lex, on May 17th, 2009

Flew twice yesterday, a pair of nice young couples, the first from Northern Idaho, near Coeur D’Alene, and the other from Laguna Beach more closely to hand. As Earl the Pearl was engaged in a thirty minute learn-to-fly before the first dogfight, and had to be to San Diego International shortly after the second, I briefed both flights. Which meant, in the rich custom of our enterprise, the ladies went flying with your host, and the gentlemen with Pearl.

Like rank, briefing has its privileges.

These dogfights take the experience of two years and roughly 300 hours of Navy flight training and whittle them down to their bare essentials. The guest pilots do not need to know how to start the aircraft, take-off, land or talk on the radios. They will need to know a little about fighting them however, which really is the best part.

Some discussion of aerodynamics is therefore invoked, the four forces acting on a machine in flight; lift opposed by gravity, thrust by drag, their perfect balance in an aircraft that is level at a constant speed. The concepts of energy both kinetic (airspeed) and potential (altitude), and how one may be traded for the other, at least until the either the hard deck is reached or the aerodynamic limits of the craft are explored. At 1200 pounds of twisted steel and sex appeal, the Varga 2150A Kachina is no FA-18 Hornet, but just as a Hornet flies well against another Hornet, so too does a Varga compare favorably to another Varga. The differences are chiefly of proportion, max g available and thrust-to-weight: The FA-18′s GE engines yield over 16,000 pounds of static thrust each in full reheat, and the wings are stressed to 7.5 g’s with an engineering margin. In the Varga, at 3 g’s the aircraft feels like it weighs 3600 pounds and you’ll never get more than 150 horses out of the Lycoming engine.

Something has to give.

We don’t do overhead aerobatics in the Varga for reasons of cost and simplicity (and to save from cleaning up the messes), but a relatively flat, two-circle fight is fully possible, turning across the opponent’s tail and exchanging altitude for airspeed, airspeed for g, and g for turn rate, so that’s the fight we choose. A rate fight is a matter of turning more degrees per second than your adversary, which over time arrives you at a position five hundred to a thousand feet at his 5 to 7 o’clock, ready to execute a simulated gun attack. The alternate fight would be a so-called “one circle”, or radius fight, but it’s more complex to execute, brings the adversaries closer to each other throughout and is, frankly, more dangerous.

We don’t fight the Vargas one-circle.

The first lady was all open smiles and enthusiasm, and had wished as a child to fly F-15s. This flight was a gift from her husband, a contractor in Iraq come home for a thirty day celebration of everything they’d missed together over the past year, and a partial realization of her dream. This was about as close as she could ever come to realizing it – she had been subject in childhood to a severe case of scoliosis of the spine. A deep and painful looking scar ran down between her shoulder blades below the top of her halter. That scar was now fully healed, but bore mute testimony to an invasive surgery and prolonged recovery whose agonies can only be dimly appreciated. This she spoke about as openly as she did the challenge of raising a five year old daughter with autism, with no sense of victimization or self-pity. It was just the way the world was and we all have our crosses to bear.

In a fighter aircraft, we talk about “corner airspeed,” which is the minimum speed at which maximum rated g may be obtained. Below corner in a maximum performance turn you will stall the jet before you get to peak g, above that airspeed you may overstress the machine if you’re not careful. Corner – so called because it corresponds to a square-shaped peak on the energy/maneuverability diagram – is a kind of decisional pivot point. Above corner, a turn at a “sustained” turn – constant g at a given airspeed and altitude – will in turn enable a given turn rate in degrees per second. If you can turn 10 degrees per second while your opponent turns 8, after 20 seconds you will have a forty degree advantage.

All aircraft turn at the same rate at a given g, altitude and airspeed, fighters and airliners – it’s a simple matter of physics. Put another way, a 747 pulling 4 g’s at 350 knots at 15,000 will turn exactly as many degrees per second as will a Hornet (or a Flanker) under the same conditions. The difference between the fighter and the airliner is excess available thrust, wingform and how many people get sick in the back. The airliner will lose airspeed more rapidly than the fighter and either have to yield altitude to maintain airspeed, or stall.

Alternatively, airspeed above corner may be traded for instantaneous advantage down to corner, but below that number turn rate falls rapidly and it’s time to re-define the fight away from rate to radius. In similar aircraft, regardless of type, it all comes down to piloting. Everything scales.

In general aviation aircraft the concept is the same, but the terminology is different. Plane Operating Handbooks reference Va, or maneuvering airspeed, and pilots are warned to avoid rapid control movements or turbulence above Va, since the airframe may be over-stressed to failure. In actual practice, the airspeed band between never exceed speed (Vne), Va and stall (Vs) is much narrower in GA aircraft than it is in fighters. You don’t have as much trade space.

The extra $39.955 million has to buy you something.

If our first guests were stout examples of survivor stock from a harsh climate, our second pair were almost breathtakingly beautiful. California blond, raised in a privileged place, immaculately dressed. He was fashionably thin, she was graced with a form that would never be unfashionable, each of them with perfect complexions. They would neither have been out of place as elves in Peter Jackson’s Lord of the Rings, nor as extras on the set of 90210.

The young man was an avid surfer, and gatherer of experiences, the lady his experiential partner. She had anticipated a trip south for dinner and some fine wine, he had – once again, I gather – surprised her. The last go-around it was hang-gliding at the Torrey Pines gliderport, now it was to be dogfighting in the Varga. She was no particular fan of small aircraft and – although she correctly (and to my candid astonishment) identified a Citation I business jet sitting on the ramp at Montgomery not merely by make but also by model – she was nervous as we briefed and taxied out of the flight line.

The key to winning a two circle fight against a similar aircraft is patient aggressiveness. Since the curve for turn degrees per second is relatively flat above corner, it’s important to grab a bite at the first merge and put the adversary on the defensive – make him react to you – but not to get so greedy that you bleed down below corner, or worse yet, stall. You’re still turning above stall angle of attack (especially in a swept-wing aircraft) but performance is woefully inefficient, and altitude is lost more quickly than would otherwise be necessary. Eventually the over-aggressive pilot will find himself on the hard deck; out of altitude, airspeed and ideas.

We spend ten to fifteen minutes in each flight letting our passengers get a feel for just flying the aircraft, how she turns, climbs, descends. Demonstrating the academic aspects of flight in practice; how g affects turn rate, how to exchange altitude for airspeed. After that there’s a “demo dogfight,” with one aircraft as a non-maneuvering target, and the other free to maneuver to advantage, after which we swap roles. Finally, three dogfights “mano à mano” with coaching as required from the front seat. It’s an odd number of fights for a reason. In air combat, someone always comes home the winner. Ties are not allowed.

For my first guest pilot yesterday, I was forced to put the “stick limiter” in effect during the actual engagements, my hand cupped about the stick to prevent excursions. She may have been all smiles and cheeriness on the deck, but in the aircraft it was all “Ride of the Valkyries.” My second passenger took a tentative turn or two at low bank angles early in the “learn to fly” phase of the flight, before telling me that she was quite content to let me do the flying, she would watch.

I asked if she was feeling all right. Some people take a while to get used to the maneuvering and it’s supposed to be fun.

“Fine, perfectly fine.”

“Would you like us to win, or to let your friend win?”

“Oh, I want to win,” she replied.

And so, of course, we did.

Both passengers declared that they had a wonderful time. The first set would return to fly later that afternoon in the open cockpit biplane with Bronco Chuck. The second promised to think about it for their next trip down. The first pair promised a re-match. The second asked if I could recommend a good restaurant on the road back north.

I draw no conclusions from any of this. I only make observations.

 

Advertisements

1 Comment

Filed under Best of Neptunus Lex, by lex, Uncategorized

One response to “A Study in Contrasts

  1. Pingback: Index – The Best of Neptunus Lex | The Lexicans

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s