Current large twin performance question
 

Can anyone give me a rough number for the minimum runway length needed for a 787 and an A350 at maximum takeoff weight, sea level and 30 deg C?
Cheers
Steve

Do you have specific variants in mind, or do you want the data for all ?

I'm just looking at comments elsewhere (i.e. other media not PPrune) about this Heathrow 3rd runway argument, and wondering why they think they need 3500m. Wondering whether a modern twin used for long haul flights would actually need that much.

I think it’s a bit moot: the existing longer runways can be used for departures, and the shorter runway primarily for arrivals. See NRT, LAX, among many others.

It's something that bugs me as well. There's room for a 2500m runway without moving the M25 so why do they need to spend billions of pounds extra to get a third intercontinental runway. A 2500m runway is perfectly adaquate for short/medium routes.

No dog in this fight, but for an international hub, 2500m (8,200ft) is somewhat limiting for a widebody. You’d be able to lift most anything off a 3500m (11,500ft) runway. If you need to make an emergency landing, the longer runway is obviously better as well (reduced need to dump fuel etc).

One of the main drivers for having the third runway full-length is that it will supposedly allow a symmetrical operation that would provide predictable, equal respite for communities under all three approaches.

If the new runway could only be used principally for arrivals, then distributing the respite equitably would not be possible.

Having said that, even a full-length third runway would mean that communities under the current approaches would have respite one-third of the time, instead of the current 50%.

I’ll never understand the noise obsession. Modern airplanes are basically whisper quiet.

Then why are there noise abatement procedures?

A longer runway would allow higher derates for takeoff therefore less noise, so it makes sense in most respects. You can lift a surprising amount off shorter runways if you have to but it increases the maintenance costs and noise footprint.

If you’re going to have a runway, making it 1000m longer if you have the space and budget is a bit of a no-brainer. It also allows more in the way of ‘land after’ clearances and LVPs for big/heavy aircraft.

From the B787 FCOM, roughly: flaps 15 at sea level, temperature 30°C

B787/8 RR 1000AE about 228 tons requires a 3000 m runway, but climb-limited at about 214 tons.

B787/9 RR 1000D about 247 tons requires a 3200 m runway, but climb-limited at about 237 tons.

B787/9 GE about 252 tons requires a 3200 m runway, but climb-limited at about 249 tons.

228,247,252 are around MTOW.But because the temperature is as high as 30°C, it still cannot take off at MTOW (due to the climb limit).

But if there are icing conditions and the various anti-icing systems have to be turned on or wet, contaminated and whatever, a 3200 m runway may not be sufficient even lower temperature . (All affected condition) Therefore, a runway length of 3500 m or more would be required to cover all cases (field length limit).

Thanks Noknoipobin, very useful.

One of the many things I don't believe about Heathrow's "need" is that the existing runways are more than adequate for all traffic from LHR that needs that much runway. What possible projected increase in long range traffic can they anticipate that would use the capacity of 3 runways ALL that length, especially with the cost and disruption associated with the M25 to accomodate it?

Off topic - who remembers operating off the PREVIOUS third LHR runway? I say: just reinstate 23L! It was always fun!
According to wikipedia (!) it was not decommissioned until 2005 and in another thread Topbunk says "The last approach I flew to LHR 23 (SRA) was 1st Feb 2002 in A319 G-EUOD as BA363 from LYS in VERY strong SW winds ar about 2200Z." So only just over 21 years ago..... might be quicker than the arguments they're having now!

For A350-900 (with ETOC) it’s about 2700m in these conditions

Bit of circular logic, but I’ll answer your question. They came about when 707s, A300s and DC8s were flying around.

Most anything flying around today (and especially LHR) is very quiet.

Tens of billions have been spent since the ‘60s on developing, certifying and fielding quiet aircraft, but we’re still saddled with procedures developed from “water wagon” 707s. Landing aircraft noise footprint may not be engines but flap and wing noise. An A220 taxis by and you hear the APU over the engines.

I can't think what's stopping them.

https://cimg6.ibsrv.net/gimg/pprune....09242768df.png

Quieter yes, but very quiet? I don't think so.

I still think 2500m would be more than adaquate for 50% of Heathrow traffic, ie. European, north Africa and near East destinations.
Build T6 and move all the European airlines there. You then have 27C and 27R for that traffic and 27L and 27C for everyone else.

My thinking along the same lines too, dixi188

One thing I learned while looking at 'noise abatement' procedures was somewhat counter-intuitive. Specifically, doing a derated takeoff didn't reduce the noise footprint - it actually made it larger (there is a db limit that defines the 'footprint', although I don't recall what it was).
What happens with a derated takeoff is that you make less noise, but you spread it over a larger area because you climb slower. So the peak noise goes down, but the 'noise footprint' doesn't reflect peak noise - just the area exposed to the noise level above the footprint threshold.