Airshow and military jets

Factual Questions
1

We went to the airshow yesterday and I need my ignorance fought. First, the low altitude, high speed pass is one of my favorite parts of the show. You see this completely silent F/A- 18 moving at what seems to be incredible speed very close to the ground (or in this case, water) until the sound catches up and you see and feel the afterburners at work. Just how fast might the jet be going? Is it teetering on breaking the sound barrier? How fast can it go w/o the burners, assuming level flight at sea level? How fast could a 777 go at sea level? I would love to see a supersonic low pass but I’m too old to join the Navy.

Speaking of afterburners – I assume the jet continues to accelerate towards maximum speed as long as they are lit – is that correct? If so, how long does it take to get to maximum speed from, say, 350 kts? During what I think is call a “maximum performance turn” (burners lit, 360 degree turn banked at what looks like 70 degrees or more) is the pilot constantly tightening the turn as the speed increases to keep the circle shape or is angle of bank constant with an increasing diameter of the turn?

Can afterburners be lit at any throttle setting or is it necessary to be at full throttle first? I know –why would you add burners if you weren’t already going as fast as you could? But could you?

Lastly, there was an F-22 demo. It didn’t appear to be as nimble as the F/A- 18 but did some pretty cool maneuvering, especially at very low airspeeds. Neat for airshows but how does that translate into combat flying? How do they do against F-15/16s in mock dogfights? Any better than the F-35? Is it a matter of stealth/ better weapons systems as opposed to maneuverability?

2

Even commercial airliners go at close to the speed of sound (IIRC, about Mach 0.9) once they’re cruising. There’s a reason it’s called the sound “barrier”: It’s easy to get close to the barrier, but breaking through is hard. The unusual (and impressive) part is just going that fast while they’re that close to you.

You’re not going to see an actual supersonic pass at an air show, because those tend to break windows and otherwise get people really upset.

3

They’ll get close, though. First time I saw a near-supersonic pass was at an air show at NAS Pt. Mugu.

I think it was the 50th anniversary of the forming of the U.S. Air Force (seems kind of late – could have been a few years before that) that I saw Chuck Yeager go supersonic in an F-15 at Edwards AFB. They were at 50,000 feet, and the ‘boom’ was plenty loud.

4

Generally, sure. Some engines have afterburner stages, which most has to do with how much fuel is being dumped into the hot parts.

I don’t know precisely, but it really isn’t a lot of time. The response on modern jet engines, even from low speed to full military power (non-afterburning max power) is very… enthusiastic. The acceleration definitely pushes one back into the seat.

Not fully sure if I’m understanding the question, but at a given bank angle, increasing speed will increase the radius of the turn. To decrease the radius of the turn, one can increase the bank, but beyond a certain point, you need to slow the aircraft down to further decrease the radius.

The throttle has a notch that the lever must pass to engage afterburners. You need to push the throttle to 100% and then beyond a bump to engage the afterburner. Think of the bump as being the resistance that you feel when you use the turn signal in your car – you push it one way, it meets resistance, and you push a wee bit harder and then the lever goes beyond the stop.

As a general rule, the F-22 has beaten its opponents with a stick in simulated dogfights. But the huge part of that advantage is that the F-22, because of its stealth, can detect and fire a missile at an opponent before the opponent knows the F-22 is there.

In simulated dogfights where the opponent somehow survives that first shot, or dogfights where each aircraft starts off within visual range of each other, the F-22 has been beaten by good pilots in older aircraft. It is certainly not at a disadvantage in such close combat, but it is probably better to say that the F-22’s major advantage of stealth is eliminated, which is a big deal.

There was a recent F-16/F-35 exercise where the F-16s beat the F-35s in this kind of close aerial combat. There is controversy over the significance of this outcome. Critics of the F-35 contend that it is not as maneuverable as it should be. Defenders of the F-35 contend that the aircraft isn’t fully operational and was without the benefit of some technologies that will be inserted later. Not wishing to start a debate on the relative merits of each argument, I will leave it there.

5

My non-expert recollection is that the F-22 has plenty of maneuverability where it counts: at speed, and at high altitudes. Low altitude, tight turn radius maneuvers look nifty but are generally useless in air combat. It’s better to have a higher turn rate, to faster get the nose pointed in the direction it needs to be, while maintaining as much energy (altitude or speed) as possible.

AFAIK, in all air combat exercises so far, the F-22 comes out on top, handily beating 4th gen fighters like the F-15 (though obviously there haven’t been many tests against Russian and Chinese 5th gen fighters). Though perhaps the F-22 loses its advantage in more contrived situations, e.g. low speed gun only battles.

(Was the F/A-18 designed to have good low-speed maneuverability to help its air combat performance, or is that something of a side effect of needing good low-speed control authority for carrier landings?)

eta: Ninja’d by someone with real expertise! At least I don’t have anything embarrassingly wrong to delete…

6

Straight from the hornet’s mouth (see question #31):

For reference, the speed of sound at sea level on a pleasant day (~70F) is about 760 MPH.

For your amusement, here’s a waterfront sneak pass that stirred up beachgoers’ belongings. :smiley:

7

Hornet can fly just above the speed of sound at sea level. It needs afterburners to break through the speed of sound, but should be able to cruise without them when not carrying any weapons and low on fuel. And it should take less than a minute to reach this speed.

Maybe somebody will correct me, but at maximum rate of turn, the aircraft should be loosing speed.

8

The F-22 is supposed to be highly maneuverable, using a new-ish technology called “thrust vectoring” – basically, turning/deflecting the jet engine blast so it’s not coming straight out the back but at an angle.

The key things I have absorbed from many episodes of Dogfights on the military channels and from much reading on the topic of aerial combat: performance is dynamic, advantage is relative, and technology changes these conditions rapidly.

Plane performance is dynamic. A given aircraft turns, rolls, accelerates, climbs, and dives differently at different altitudes and weather conditions. In WWII, the huge lumbering P-47 Thunderbolt fighter was somewhat less maneuverable than its German opponents at low altitude, but more maneuverable at very high altitudes, because its huge supercharger and big engine gave it the power to do things in thin air that its opponents could not. A German pilot who assumed he could still turn inside a '47 at high altitude was in for a rude shock.

Advantage is relative to whom/what you are fighting. What matters in aerial combat is less “my plane is good at x” than it is “my plane is better than his at x.” But better at x under certain conditions – performance is still dynamic. Ace pilots often say things like “I knew my plane could turn inside his at this speed,” “At that altitude, my plane’s supercharger gave me the power my opponent lacked,” and so on.

This also changed over time – later in conflicts, different technologies had different relative strengths. A classic example of change over time is the American P-40 Warhawk and its variants. Against early war opponents, the P-40 was (relatively) fast and powerful but lacked the maneuverability to turn with opponents, and was used as an “energy fighter,” making high-speed passes and breaking off. Later in 1942-3 in North Africa, the same plane was by then significantly slower than its current adversaries but had a much better turn radius, and pilots would maneuver defensively and dare opponents to close in for a turning fight. Same plane, totally different relative strengths as opposition technology changed.

9

The engines have to be set to full throttle, but you don’t have to be going as fast as you possibly could. You could even be perfectly stationary, such as on the deck of an aircraft carrier before a catapult launch. The reason why you wouldn’t use afterburners routinely is they are extremely fuel inefficient; you’re essentially dumping raw fuel into the exhaust for the added thrust.

10

I know that airliners approach Mach speed at altitude but how fast could they go in the thick air found at sea level?

11

Depending on who you talk to, one of the planes that hit the WTC on 9/11 was doing 510 knots (586 MPH, about 0.77 Mach) at impact. There’s certainly a lot more aero drag at such low elevation than at normal cruising altitude, but the engines also produce more thrust, and the aircraft may have been descending too.

12

AFAIK, it is something like 350 or 400 knots. But this would put a lot of fatigue stress on the airframe.

13

The manufacturers recommend they not be flown faster than that (at low altitude), but this does not mean the aircraft itself is incapable of going faster.

14

Fairly recent post on point: http://boards.straightdope.com/sdmb/showpost.php?p=18563884&postcount=6

15

Way cool, I was there for the same show and thought Yeager’s pass was pretty cool

16

Could be either. Essentially it’s a balancing act between G-forces which are trying to slow the aircraft and engine thrust which is trying to accelerate it. Assuming a reasonable starting altitude & speed, the pilot can pull enough Gs to just offset thrust and if so the speed and turn radius remain constant.

Or he could increase G and immediately tighten the turn, plus begin to lose speed which will further decrease the turn radius and as the speed continues to decrease over time, so will turn radius.

Or he could decrease G and immediately loosen the turn, plus begin to gain speed which will further increase the turn radius and as the speed continues to increase over time, so will turn radius.

Bank angle is independent of this; it’s entirely a matter of thrust versus how hard the pilot is pulling back for more or less G. Having said that, whether the maneuver gains or loses altitude depends on the bank angle. If he’s in balanced turning flight and pulls more G, the airplane will climb unless he increases bank an offsetting amount. And just the same, if he decreases bank the aircraft will climb unless he decreases G to match.

In high performance aircraft maneuvers we really don’t think about bank angle; it’s just not a very informative POV. All turns are really loops. They’re either loops in a vertical plane, loops in a horizontal plane, or loops in a diagonal plane which is a compromise between vertical and horizontal. You play off speed, thrust, and G to achieve the turn radius and rate required, and alter the plane of maneuver with roll.
It seems like everybody else did a fine job on the other points.

17

They certainly can, but usually it is during a dive, or the speed was built up during an earlier dive. Do you know what the maximum sustainable speed in level flight would be?

18

I saw (actually, heard) several "low-altitude’ super-sonic passes. As a small child a few miles from WPAFB in the 50’s.

Then the Air Force got tired of buying people new windows, and prohibited them below 40,000’ MSL.

Above FL400 (40,000 MSL), the boom does not reach the surface.

If a plane not specifically designed for trans-sonic flight were to reach Mach 1, I would expect the wings and/or tail to fail.
The Concode was the result of trying to turn an airliner into a SST - it largely didn’t work.

19

There was an F-14 broke Mach 1 during the opening pass at the Miramar airshow back in the early/mid '80s. Blew the windows out on a local radio station’s mobile studio, as well as a number of windows in nearby La Jolla. I was in the grandstands at airshow center and the concussion nearly blew me over. Pilot lost his wings over that one.

20

Sure they do.

I lived in Lancaster, and I was on the Space Shuttle Support Team at Edwards. I heard the double sonic boom of the Space Shuttles many times as they did Mach 1.5 at 60,000 feet on their landing approaches.