How does Elon Musk’s G650 land and T/O on a 4,800’ runway?

geezer said:
But backing off thrust on the good engine would bring you back under control, possibly with enough thrust to continue the departure.

The examples we are looking at here, the aircraft has a large surplus of thrust, due to the low takeoff weight. Heavier departures would not have the same option.

The sort of decision that is hard to get right, even if mentally prepared for the possibility.
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True, but that's not how things are done in big airplane world. All that would be taken care of on the ground before hand and you would launch with valid takeoff data and know that you had full controllability even with an engine failed.

When I started flying KC-135s, there was no approved takeoff data software. All takeoff data was manually computed by the copilot by chasing spaghetti charts found in a 500-page performance manual. This was a huge ordeal at first, but after a while, good copilots could probably bang out a set of data in less than 10 minutes. The issues became when you would get into some of the corner cases like above. You'd get close to the end and come up with invalid numbers and would have to go back and start again using different flap settings or thrust values.

The takeoff data in the early (A and E) model tankers always assumed full thrust for Vmc numbers, even though we could do reduced power takeoffs. This would put you into binds because you'd run into an issue like above where you couldn't get your Vmc speeds lower than S1 or Vrot, but there weren't charts for reduced power Vmc numbers, so you were just stuck. When the R-model tankers came along, we got Vmc charts that took into account reduced thrust takeoffs, so you could mitigate some of those issues, but not always.

If we were doing data for our nuclear alert sorties (EWO data), it became a different animal altogether. With that data, since we were presumably launching to refuel B-52 headed to the Soviet Union, there was an assumption that we wouldn't lose an engine. All the data was 4-engine data. All we were coming up with was the max tailwind that we could take and still make it off of the runway at max gross weight. Luckily we never had to put that data to the test.
 
Sluggo63 said:
Maybe we're misunderstanding each other.

When we ran takeoff data, we had to ensure that V1 (we actually use S1 in the KC-135, slight difference, but essentially the same for these purposes) was greater than or equal to Vmcg. We also had to ensure that Vto (takeoff speed... essentially a few knots after rotate) was greater than Vmca.

To me that all makes sense. If Vmcg was greater than S1, then you could be in a position where you could lose an engine just above S1, by definition are then committed to the takeoff, but yet be below Vmcg which means you don't have directional control.

Same with Vmca and Vrot/to. If your takeoff speed is less than Vmca, that would mean you could conceivably get airborne, but yet be too slow to have directional control with an engine failure.
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V1 may be a lot of things, especially in the context of a military airplane (which is probably why they use a different term…it IS different), but per Part 25 (and CAR4 reads substantially the same), V1 must be no less than 1.05xVmca, and Vr must be no less than V1.

again, the same general effect.
 
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Years ago I met a Brit who had flown 707s for Danair. At one point, Idi Amin of Uganda leased on from them as his private plane.

This guy had been the Captain. Hauling a dozen people, without much luggage and fuel for internal Uganda flights (a couple of hours max), he was operating out of 5,000 foot runways.
 
MauleSkinner said:
Technically it’s V1 that has to be above Vmca. With Vr at or above that, the effect is as you said.
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MauleSkinner said:
V1 may be a lot of things, especially in the context of a military airplane (which is probably why they use a different term…it IS different), but per Part 25 (and CAR4 reads substantially the same), V1 must be no less than 1.05xVmca, and Vr must be no less than V1.

again, the same general effect.
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Thanks for making me dive back into Part 25. ;)

V1/S1 are essentially the same.

What you're saying doesn't make sense though. Think about it... Why would V1 need to be greater than 1.05xVmca? V1 becomes essentially a stopping issue. For example, a heavywieght 777 is taking off from Chicago going to Hong Kong. It's snowing in Chicago. Your V1 is going to be pretty low, because getting 760,000 pounds of airplane stopped on a snowy runway is going to take a lot of distance. There's no way that low V1 is going to be 1.05xVmca. Vmca is going to be much higher than V1. You'll have a huge split between V1 and Vr during the takeoff roll.

If you re-look at Part 25, it says exactly what I said earlier:

Sluggo63 said:
...V1 ... was greater than or equal to Vmcg. We also had to ensure that Vr was greater than Vmca.
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(I changed Vto to Vr. Again, essentially the same, just converting AF talk to FAA terms).

If you look at Part 25.107(a)(1):
V1 must be established in relation to VEF as follows ... VEF must be selected by the applicant, but may not be less than VMCG determined under § 25.149(e). (emphasis mine)

And also at Part 25.107(e)(1):
VR ... may not be less than - V1; 105 percent of VMCa (emphasis mine).

The only difference between what I said we did in the AF and what the FAA is saying is that our Vr just had to be greater than Vmca, we didn't have the 105% rule, but the idea is the same, you can't rotate and become airborne slower than your min controllable airspeed.

So, V1 >= Vmcg and Vr >= 1.05 Vmca.
 
Sluggo63 said:
Thanks for making me dive back into Part 25. ;)

V1/S1 are essentially the same.

What you're saying doesn't make sense though. Think about it... Why would V1 need to be greater than 1.05xVmca? V1 becomes essentially a stopping issue. For example, a heavywieght 777 is taking off from Chicago going to Hong Kong. It's snowing in Chicago. Your V1 is going to be pretty low, because getting 760,000 pounds of airplane stopped on a snowy runway is going to take a lot of distance. There's no way that low V1 is going to be 1.05xVmca. Vmca is going to be much higher than V1. You'll have a huge split between V1 and Vr during the takeoff roll.

If you re-look at Part 25, it says exactly what I said earlier:

(I changed Vto to Vr. Again, essentially the same, just converting AF talk to FAA terms).

If you look at Part 25.107(a)(1):
V1 must be established in relation to VEF as follows ... VEF must be selected by the applicant, but may not be less than VMCG determined under § 25.149(e). (emphasis mine)

And also at Part 25.107(e)(1):
VR ... may not be less than - V1; 105 percent of VMCa (emphasis mine).

The only difference between what I said we did in the AF and what the FAA is saying is that our Vr just had to be greater than Vmca, we didn't have the 105% rule, but the idea is the same, you can't rotate and become airborne slower than your min controllable airspeed.

So, V1 >= Vmcg and Vr >= 1.05 Vmca.
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At least I knew 1.05 was in there somewhere! ;)
 
Sluggo63 said:
All good, brother! I did not know about the 1.05 thing, so I was glad to get into that part and do some learning! Cheers!
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When guys start talking about “two seconds above V1” during the oral that I tell them it’s probably not a place they want to go right then, but otherwise it’s definitely good for me to realign and increase my understanding of this stuff.
 
Is that original figure the balanced field length? If so, that plane needs much less runway to get wheels off ground. Also, landing distances may not include use of reversers.
 
My military experience is in fighter/attack. We calculated separate Accelerate and Stop and Accelerate and GO speeds. All takeoffs were full power.

If GO speed was less than Stop speed, this was called Condition 1 and a very good thing. It gave you options. And time to decide.

If they were the same, it was Condition 2, and meant no decision, less than it, you stopped, more you go. Civilian transports use reduced thrust take offs, and adjust so that they have the single number, called V1.

In the military, if the Go speed was higher than the Stop speed, that was Condition 3, and only used in war time emergency. No decision with the either. If past stop speed, you were going to crash.
 
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