Is VR always and necessarily higher than V1?
Posted by new_name_needed@reddit | aviation | View on Reddit | 32 comments
Just curious: is there a particular reason why VR is typically higher than V1, besides the constraints of runway length? I’d have thought that ensuring the option of aborting a flight would be useful all the way until rotation if possible
Dangerous_Mud4749@reddit
It may be possible to re-land after rotating. As someone has said, you could consider a 20 mile long runway, which is 200m or more wide with no obstacles anywhere nearby.
However, no airliner is certified to do that. The certification standards exist to ensure that it is always safe either to stop or to continue. Or, not and. Certification requires one single determinative outcome: if you do A B and C, the results you get will be D E and F, always and without exception. Certification doesn't require multiple different ways of achieving safe outcomes depending on pilot's preference.
Therefore, if you continue the take-off upon reaching Vr and getting an engine failure - that is, if you do not attempt to abort after Vr - you will keep the aircraft safe. No-one requires the manufacturer to assess whether stopping might also be an option, so it's an uncertain outcome, so pilots don't try it.
Think of the certification standards not as "anything else will cause a crash", but rather as "this way is definitely safe, and anything else is simply unknown, so we won't try it."
V1 is limited by many different variables, but one of the simplest to understand is that once rotation commences, rejecting the take-off is uncertified and therefore uncertain.
pillowcase718@reddit
Can you wait to rotate past VR?
If VR is 150 kts can you wait until 160 to do so?
If so and if you had a long enough runway where you can stop in time at 165 kts could it be theoretically possible?
I know in practice this would never be done because why wait to rotate and the rejection decision would get way more complex.
Far-Yellow9303@reddit
Vr always comes after V1 because once you've started to rotate, it's a very bad idea to try putting the nose back down and coming to a stop within the runway remaining. You're already a few seconds away from flight so abandoning the takeoff is best done by going around and landing again
skylaneguy@reddit
Thanks for summarizing what I already said by making it longer and more wordy…
ProcyonHabilis@reddit
Every thread like this I've ever seen on Reddit has duplicate answers because people start commenting at the same time or just bother to check for other comments before firing off an answer. This is the first time I've seen someone take it personally like this though. So congratulations, you're petty and pathetic even by reddit standards. That's honestly impressive.
Far-Yellow9303@reddit
Spot on lmao, when the original post came across my feed, it was 2 minutes old with zero comments. I wrote my comment, posted it and got back to work. Grief I had no idea it would cause mini drama lmao.
new_name_needed@reddit (OP)
Can confirm, was weird
new_name_needed@reddit (OP)
I suspect they had already reached VR by the time you had sent your comment.
PilotBurner44@reddit
And even more importantly, the braking distance required to stop in time is severely compromised when you start adding tons of lift to the wings during rotation, lessening the braking ability.
That being said, under certain circumstances you can still abort above V1 and even at Vr. The recent UPS crash would be a good example of this. The pilot's obviously didn't have all the information at the time, but I assume if they did, fear of inability to fly probably would have been an appropriate consideration.
sarahlizzy@reddit
When I did my ppl it was in a Cessna 152 on a 1900 metre runway.
I think we were a few minutes feet up before we passed V1.
idkblk@reddit
As long as you still have engines or a landing gear at least
Apprehensive_Cost937@reddit
You have to realise that for the vast majority of takeoffs, there is a range of V1 speeds available (that might be, or might not be selectable by the crew, depending on the policy of the operator), depending on whether you want to be go-minded or stop-minded.
For example, you could have a V1 range between 140 and 150 kts available for that particular runway, weight and weather conditions. If for example, you are departing a dry runway, with high terrain with a complex engine out SID, you might elect to be more stop minded, and select a higher V1 (up to 150 kts in this case). If you are departing say a short, contaminated runway, with no terrain around, you might elect to be go-minded, and select a lower V1 (down to 140 kts) in this case.
Generally, for a stop-minded scenarios (all other factors permitting), you might see V1 being close to or equal to VR. This is usually the case where stopping is less of a concern (dry runway, no slope or upslope, stopway available, etc.). When the scenarios are more adverse, such as wet/contaminated runway, downslope, no stopway available, tailwind, etc., the V1 speed will usually be lower, and can be a lot lower than VR (even 30+ knots), but as others have pointed out, it can never be lower than Vmcg (which in turn will depend on the amount of thrust used for takeoff, as well as outside temperature), since you need to be able to have directional control on the ground, if you wish to continue takeoff above V1.
Ancient_Narwhal_9524@reddit
In one of the aircraft I fly the performance data offers V1 Min (accelerate stop is less than accelerate go), Balanced Field (accelerate stop = accelerate go) and V1 Max (accelerate go is less than accelerate stop)
At lighter weights it can’t do balanced field so the FMS will default to V1 Min. You can pick V1 Max if you want but V1 Min usually gives the shortest runway required if you are light.
If the runway is contaminated it can be beneficial to pick V1 Min.
Charlie3PO@reddit
There are many cases, depending on type, where Vr = V1.
But in any case, V1 can never be higher than Vr because once you start rotating and becoming airborne, a rejected takeoff would be far too dynamic to certify.
I mean sure it could be done in theory on a very long runway, but the risk of aborting and landing back on the runway, then stopping, is going to be higher than just committing to the takeoff.
old_righty@reddit
Yeah, if it was a 20 mile long runway you could always settle back down
Only_Razzmatazz_4498@reddit
Maybe one of those stol competition planes that can take off over a couple of meters lol.
pattern_altitude@reddit
Vr/V1 aren't a thing in aircraft like that.
Only_Razzmatazz_4498@reddit
It was a joke.
eitilt@reddit
VFastAndFurious
vortex_ring_state@reddit
You just reminded me on an incident where that happened. Not engine failure related though.
https://www.canada.ca/en/air-force/corporate/reports-publications/flight-safety-investigation-reports/cc130342-hercules-epilogue.html
Aerobaticdoc@reddit
In twins that aren’t certified to give you a positive single engine rate (lots of the non-turbine heavier twins like the Crusader, the Aztec, etc) you don’t have a V1 for that very reason, and a lot of those pilots actually brief a rejected takeoff to include landing the aircraft back on existing runway up to a certain point (often Vyse and gear/flaps up) since it’s safer to crash at ground speed at the end of the runway than to try to drag out an impossible climb and stall over a residential neighborhood.
Mean_Passenger_7971@reddit
[EASA-land response]
V1 is an "on the ground" decision speed. In some type of operations you don't have a V1, because your decision point is after you take off. We are talking about MEPs here, not CS-25 jets.
When I was instructing MEP, we had a decision point which is "runway available". While you had runway available, in case of engine failure, you were to pitch down, and land on it. During the climb out, you would called "insufficent Runway", reduce from take off power to climb power and from that moment onwards, in case of engine failure you were expected to continue.
in short, our decision point was AFTER Vr.
skylaneguy@reddit
It’s not. Sometimes V1 and Vr are the same speed.
V1 is never more than Vr because that assumes that you’d be rejecting a takeoff while already airborne and that doesn’t make any sense.
EbbyRed@reddit
Thanks for summarizing what Far-Yellow wrote but with an additional unnecessary snark comment.
skylaneguy@reddit
I wasn’t summarizing anything because I was the first comment on the post.
PaisaLover@reddit
Your parents must be proud!
new_name_needed@reddit (OP)
Makes sense, I get why V1 > VR wouldn’t work but was curious about VR = V1
Wonderful_Virus_6562@reddit
V1 is the speed to which you HAVE to take off and can’t hit brakes on runway to abort a takeoff.
VR is the speed in which you pull the yoke back to get airborn
vatamatt97@reddit
The comments here are correct, but as always, there is an exception to the rule. I know of a supplement for a STOL aircraft which, to improve its ground roll, permits an airborne V1. It is certified but requires specific approval to use. But, to be clear, this is for an aircraft certified under FAR23. This would never be allowed under FAR25.
22Planeguy@reddit
Vr can equal V1, but once you rotate, it becomes much safer to take off and come back around single engine. Some kind of weird post-rotation reject would be very dangerous. Modern jets are honestly just safer in the air than at high speeds on the ground.
There are probably situations where you could rotate before your v1 and get into the air. That would be insane though because you have no idea when (or if) it does become possible to do so, and you would invalidate all of the climb out data.
poser765@reddit
It kind of makes sense. Once you rotate you’re pretty much committed to flying and v1 is a takeoff abort speed. One can’t really reject the takeoff after the takeoff.
Some might argue that after takeoff, with a sufficiently long runway, it might be better to “reject” in certain conditions and put the aircraft back on the ground. And they would be right. Sort of. What they are missing is those certain conditions I can imagine would necessitate an immediate landing because the airplane will not continue flying.
At the end of the day these aircraft fly perfectly safe on one engine and it’s almost always a better idea to continue the takeoff after v1.
SuperSaint77x@reddit
Performance figures are amongst other things based on regulations. V1 must not be less than Vmcg nor greater than Vr or Vmbe (brake energy)