Re your post 58

Thanks John - you learn something every day!

1106

Hi,

Because of my narrow mind I thought that Vr for OEI should be higher because of the reduced acceleration. I was reading an article (Bombardier) and it was mentioned (for 3 times) that same Vr is used for AEO and OEI conditions.

It was also mentioned in the same article that Vlof-oei is lower than Vlof-aeo and the time from Vr to Vlof is similar for AEO and OEI takeoffs.
Again because of my narrow mind I thought Vlof-oei should be higher and the time from Vr to Vlof is higher for OEI takeoff because of the lower thrust.
It will be nice if someone can post an explanation.

Thank you.
Regards

I thought that Vr for OEI should be higher because of the reduced acceleration.

That's a fair observation and comment.

However, we only want ONE set of speeds for takeoff. Things get sufficiently busy during a critical takeoff failure without having to do a mental rescheduling of the speeds. Hence we take the more critical case (OEI) for the speed schedule and live with the speed overshoot during the routine AEO takeoff case.

It was also mentioned in the same article that

... haven't read the article so I'm doing a bit of reading between the lines here ..

Vlof-oei is lower than Vlof-aeo

.. mainly associated with the rotation rate and acceleration to achieve the appropriate incidence after a sensibly constant time delta.

and the time from Vr to Vlof is similar for AEO and OEI takeoffs.

a function of the rotation rate which generally is constant regardless of whether there is a failure or not

I thought Vlof-oei should be higher

given that the wing doesn't know too much about what the engines are doing, why should this be so ? (I suspect a slight delta but not overly significant)

and the time from Vr to Vlof is higher for OEI takeoff because of the lower thrust

(This would be so if the liftoff OEI is precisely at the same speed as for AEO) I suggest that the comment is driven more by the rotation rate (constant so a sensibly constant time delta to the lift off incidence). The reduced thrust is going to have the OEI aircraft at the lift off attitude in the same sort of time delta as AEO .. but a slightly lower speed due to the thrust delta. This ignores the probability that the AEO/OEI incidence required may be a little different due to the speed delta but I suspect that that will be a small difference.