If I understand correctly, V1 refers to the speed at which an airplane is committed to takeoff because there is insufficient length of runway, at that point, for the airplane to safely abort takeoff afterwards. In other words, if the airplane tries to abort after V1, it will overrun the end of the runway.
But if the runway is an exceptionally long one, might the airplane reach V2 takeoff speed long before it reaches V1? In fact, with a (hypothetically) infinitely long runway, would an airplane never reach V1?
V1 is the decision speed to either brake or attempt a take-off. Above V1 is less safe to try and stop than attempt a take-off.
V2 is the take-off safety speed i.e. the speed where it’s safe to take-off with only one engine.
No, not normally. The reason is that the V1 is never greater than Vr (rotate speed) and normally Vr is slower than V2. The only time I can think of that Vr might be faster than V2 is when using an increased Vr as part of precautionary wind-shear procedures. However even when using an increased Vr for wind-shear, the original V1 applicable to the aircraft weight limited Vr is still used. In short, V1 is a speed that occurs while you are on the ground, once you have lifted off you are, by definition, past your V1.
This is all for multi-engined transport category aircraft. When it comes to single engined aircraft or light twins that aren’t required to meet the regulatory performance requirements as larger aircraft, if you loosely define V1 as being the decision speed where you can either land ahead or are committed to climbing out then you could say that your “V1” could be faster than your V2, but the terms V1 and V2 aren’t really used for light aircraft.
Some further info: There is often a range of V1 speeds with the lowest being the lowest speed you could continue the take-off and the fastest being the fastest speed at which you could abort the take-off. The fastest is limited by Vr and obviously runway length, the slowest is limited by minimum control speeds on the ground (Vmcg) and aircraft performance. Any speed within the range is a safe and valid V1. Depending on how the take-off performance is presented to the pilot, they might not be aware of any range, for example it may be an electronic system where you enter the data for the take-off and the software spits out numbers back at you. In our case we use tabulated paper charts which gives us some awareness of the available V1 speeds. Where there is a range available to us, we are required to use the lowest. The thinking is that, particularly for a four engined jet, we are safer continuing the take-off than attempting a high speed abort.
V1 & V2 are regulatory concepts, NOT physics concepts.
To be sure, they *are *rooted in physics. But they are defined by the government to achieve certain macro levels of statistical safety under certain non-physics more or less arbitrary assumptions. And one of the sub-rules embedded in the required method for calculating V1 is that it must be less than V2 and hence will be adjusted downwards as necessary to achieve that result. There is another sub-rule which limits the amount by which V1 can be less than V2. Again these are government fiat law, not physics.
In the USAF we used an entirely different system for takeoff calculations that did not have V1 or V2. Instead we calculated the maximum possible abort speed (i.e. the “max stop” speed). And we calculated the minimum continue speed after an engine failure (i.e. the “min go” speed). And separately we calculated the liftoff speed and the speed to climb away at. Both of which were completely unrelated to either stopping or going.
On long runways on cool days it was possible for the max stop speed to be above the liftoff or even climb speed. And vastly more than the min go speed. Which is exactly the scenario the OP posits. IOW, the OP’s thinking is good physics, but bad regulatory compliance for a civilian aircraft subject to V1 / V2 regs.
On icy short runways or at stupid heavy wartime liftoff weights it was possible for the max stop speed to be less than the min go speed. In that situation, if an engine failure occurred between those speeds you were 100% committed to crashing; the only remaining choice was exactly where and going how fast.
Civilian V1 & v2 calculations implicitly require that max stop be faster than min go. Starting a takeoff with a built in must-crash segment is illegal. Said another way, if the calculation leads you to that conclusion then you need a longer runway, a lighter airplane, or you wait until conditions improve.
Depends on the length of the runway?
So, uh, if it came to that, you’d want to eject before the jet, loaded with bombs and fuel, skids off the edge of the runway?
I’ve read that ejecting doesn’t destroy an aircraft, so could you engage the brakes and then eject, hopefully saving the aircraft if it gets lucky when it leaves the end of the runway?
I guess you’d look like an asshole if the charts were wrong and the aircraft came to a safe stop right before the end of the runway.
It’s probably not very common, but consider the odd case of this F-106.
Why would you look like an asshole if the charts were wrong? The chart maker would be the one, no?
Generally speaking there’s no way to apply wheel brakes and have them remain engaged after the pilot(s) eject. Ordnance will 99.9% *not *explode during the prompt accident sequence. It will eventually if it sits in the post-crash fire long enough.
With the background out of the way, there are several cases to consider.
In a single engine fighter if the engine quits during takeoff you’re not going flying today. Unless you’re about to lift off anyhow, the drill is apply max braking, extend the emergency tail hook, radio for the departure end cable to be raised it isn’t already, and generally be thinking eject if you run out of runway at any speed above a brisk jog. F-16s particularly have a very small wheelbase and will topple upside down & catch fire if they end up in even fairly firm grass. You don’t want to be trapped in the overturned aircraft. So eject just as it leaves the pavement even if it’s trundling along at 15 knots. If you are almost at liftoff speed, skip the braking, zoom, eject near the apogee & plan one swing in the 'chute before arriving at the ground. Ideally some distance from the fireball that was your jet.
In a two-engine fighter it’ll usually fly on the one remaining engine or stop in the runway remaining. But there are lots of ways for an engine to fail that damage the other one, and few reasons to fail that leave the other 100% intact. So the decision making is similar although you may get a more robust zoom if the other engine keeps running awhile.
Tankers, transports, and bombers are the ones who spend a bunch of time during takeoff roll in the no mans’ land of too fast to stop, to slow to go. Tankers especially.
Tankers and transports don’t have ejection seats. So the drill is max braking and steer for something soft. See Runway safety area - Wikipedia & Engineered materials arrestor system - Wikipedia for ways airfields try to arrange for something soft.
B1s & B2s have ejection seats. So stop if you can get slow enough to hit something soft enough, or plan to zoom & eject.
B52s have 5 crewmembers now. 3 eject upwards, 2 downwards. Makes for a morally challenging decision tree.
Man, those should all be retrofitted to go upwards.
Not practical. The B-52 has a double-deck cockpit, with the flight crew upstairs behind the windshields and the bombardiers (loosely speaking) downstairs directly beneath them.
If the USAF ever retires the B52 it’s a good bet the replacement won’t have downward firing ejection seats.
Does a safety system stop the downward firing ejection seats from activating if the bomber is too low/on the ground?
For that matter, if the upwards firing seat crew hit their eject levers, is this tied to the lower ones (and vice versa), or is it in separate banks (so if the lower guys see a clear path to eject they won’t kill the upper guys, and vice versa, by hitting their own eject levers)
Good question. I checked the B52 owner’s manual available at an cool online site.
The B52 manual says there’s no such safety system to prevent downward (or upward) ejection outside of survivable parameters. I’ve never heard of such a system on a fighter-type either.
In most two-seat fighters & fighter-like trainers the seat controls *are *interlocked so launching one launches both with appropriate delays to prevent a post-ejection collision.
The B52 manual says it doesn’t have a system like that. Each seat control fires itself and only itself. There is a nice EJECT light to advise the guys downstairs that a pilot upstairs has departed the aircraft so they may consider doing so themselves post haste.
So if an impact, depressurization, g forces, etc knock someone out, they are a goner.
Depends on the scenario. There are also provisions for manual bailout since they sometimes carry more crewmembers than they have ejection seats. The extra crewmembers wear conventional parachutes and jump out one or more hatches installed for that purpose. That would be more a peacetime scenario.
In airplanes where folks can physically reach each other’s seats inflight there was/is a common view that “I will sacrifice an arm to save your life” by reaching over & firing your seat if you’re unconscious, probably ripping my hand or arm off in the process, rather than simply abandoning you to your fate & punching out myself.
That of course presupposes a scenario where we all have time to think about it and I see your condition before I punch. The interconnected seats in two-seat aircraft are a mechanical manifestation of the same instinct.
There are certainly scenarios where the wounded could end up left behind.
I notice a trend to your various questions about aviation and other topics which seem to amount to trying to achieve a path of zero possible defects through any plausible scenario, and many implausible scenarios as well. My observation is not intended as a criticism, just an observation.
As a software developer myself I get the idea of trying to produce zero defect code and writing to anticipate every conceivable normal and abnormal condition. But the real world can throw far more jokers than even the best man-made code (or hardware) can handle.
And unlike the software industry, aviation doesn’t have the luxury of being granted twice the capability every 18 months. We’re still very hemmed in by materials and practices that haven’t advanced but a few percent in my 50+ year lifetime. Particularly in the military, there’s an understanding that this stuff is inherently dangerous and some losses are simply the cost of doing business. Safety in design and procedure is taken very seriously. But getting from 99.9999 to 100 is a very very long and very costly road. And one mostly not taken.
After you eject the plane weighs less and thus will stop sooner.
I know this one. For tire : ground interactions, the weight of the vehicle is mostly independent of stopping distance.
That’s because the force of friction is proportional to the contact normal which is proportional to the vehicle weight.
If you had a wheeled vehicle braking to a halt, and you jettisoned half the weight from the vehicle mid-maneuever, it would come to a halt at the same place, theoretically.
For big rig trucks, they train drivers that empty trucks tend to take longer to stop because the “bounciness” of the empty truck trailer keeps some of the wheels from fully contacting the ground during a hard stop.
One confounding factor here is that a heavy vehicle stopping will result in hotter brakes during the maneuver, and overheated brakes are less effective.
I think **Desert Nomad **was making a joke.