LRC

[mfclearner]

I a confused about Long Range Cruise. Does LRC give you (close to) Maximum Distance in given amount of fuel or Does it give you maximum endurance (time)
When is LRC Speed used? Is LRC speed single engine speed or OEI (One Eng Inop) Speed?

[Keith.Williams.]

For MAXIMUM range fly at VMRC....... Velocity MAXIMUM Range Cruise.

But VMRC is not very fast (about 1.32 Vmd) and it is possible to fly a bit faster without incurring a very lage increase in fuel burn.

VLRC........Velocity Long Range Cruise is typically about 5% faster than VMRC but it does burn more fuel, so the range is less than maximum.

VLRC gives about 99% of Maximum range.

For maximum endurance you must fly at the maximum endurance speed. For jets this is Vmd.

[mfclearner]

Thanks

Thanks for the answer. Further I would like to know after one engine failure once I go to drift down altitude do I cruise with LRC or any other speed? As per my knowledge LRC is AEO (all engine operating speed) and not OEI (One engine Inop) speed. am I right?

[Keith.Williams.]

You are correct in saying that the VMRC and VLRC speeds are AEO speeds.

Logically there will be comparable speeds (which give best range and best trade off between fuel and speed), for the OEI case.

But after an engine failure you may have more important things to think about. If clearing obstacles becomes problematic with OEI you will need to fly at a speed which maximises (or at leats increases) your cruise altitude. You will also probably want to get to an airport and land as soon as reasonably possible.

[mfclearner]

Thanks Keith

That helps alot Keith .. thanks

[Spendid Cruiser]

Just to add to Keith's reply, OEI LRC altitude capability assumes max continuous thrust and a residual rate of climb. A 737 at a heavyish weight OEI LRC with anti-ice on could be as little as 7,000' AMSL and about 20,000' AMSL at driftdown speed (approx 230kts). Quite a difference.

During planning, ETOPs flights may be predicated on the OEI LRC to meet the diversion time requirements.