Overspeeding and fuel efficiency

Hi all,
I’m new to the game and just have a couple of questions about overspeeding and fuel efficiency.
Firstly what constraints change what the overspeeding limit is. sometimes generally in airlines the overspeed limit changes meaning it won’t let me get to a proper cruising speed. This kind of ties into my next question how do I achieve cruising speed without a: overspeeding or B: burning through all my fuel instantly?

(Also on that note, is there a way to turn the overspeed warning off)

The main indicator for speed is an airspeed indicator. The higher you fly the less air density, therefore the airspeed indicator will show less than your real speed.

Cruising speed for airliners is defined by the Mach number, whereas Mach 1 = speed of sound. The Cruising speed for the A320 is around Mach 0.78, the 747 around Mach 0.90.

You will see that the airspeed for overspeeding will decrease the higher you fly, as you get closer to the maximum Mach number for that type of aircraft. In real life it would literally mean that parts of your airframe start reaching supersonic speed (typically starting at the wingtips, as due to the sweep of the wings the air speeds up when it flows along it).

The overspeed warning is crucial, and there’s no way to turn it off.

Edit: there’s a lot more when it comes to the different types of speeds that you see, especially in airliners, but this is the basics of the basics. I hope it helps a little to understand!

In regards to the A320 here is a few things I have noticed (I’m not a pilot, I’m a beginner so this may not be correct)

Your maximum speed before over speeding has a few factors.

Throttle position and altitude

The throttle has a few positions it can be placed which will be indicated on the actual throttle.
Climb mode - Maximum speed of 220KIAS regardless of altitude
Auto thrust position - 250 KIAS below 10k ft above 10k I think you can achieve maximum cruise speed

Having flaps deployed can also reduce your maximum KIAS potential.

As I say I’m no professional so take this with a pinch of salt. Just my observations.

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Ok so you’re saying if I switch it to Mach units instead of feet it will move it up? Sorry if I’m being stupid.

The 747 cruises at typically Mach 0.84 to 0.86, getting slower now due to fuel costs.

At low altitude, say below 20,000ft, your upper limit (VMO) is determined by aircraft structural limits (think of the chicken cannon test for birdstrikes) and lower limit is stall. ATC will typically limit aircraft to 250kts or below for traffic management, but exceptions can exist. For example a heavy 747 may have a higher minimum manoeuvring speed than 250kts with flaps retracted, so they may “request high speed” from ATC.

Because of lower air density at high altitudes you’re travelling further for a given indicated airspeed, in addition the local speed of sound drops as temperature decreases when you get up high. As such you get much closer to the sound barrier. As you cross the critical mach number (Mcrit), some parts of the aircraft may exceed the sound barrier before the rest. You can exceed Mcrit by a little bit before experiencing real drag & controllability problems, so your upper limit is your maximum mach number (MMO). MMO is usually below 0.9 Mach, and the lower limit is stall.

For airliners, the typical transition from airspeed to mach is 28,000ft.

There are other issues to consider as well, such as crew and maintenance costs per hour of operation. If fuel is cheap and crew/maint is expensive, fly faster. If fuel is expensive, fly slower. That’s where the cost index value in the flight management computer comes in.

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Hmm ok I’m not sure I understand what all the pieces of equipment you mention there are I think I get the basic idea. It may have been a bug but when I was flying the a320 at 39,000 ft (probably not the right altitude it was an educated guess) the overspeed limit was jumping around 360 ft per second all the way down to the landing overspeed zone of like 280 feet per second. And, when I tried to throttle up regardless I wasn’t getting very fast and my fuel was burning way faster than I think it should have been. Although, again, I’m new so I’m not really sure how fast it should be draining.

(If it helps I was trying to fly from Faaa to Honolulu in the a320 and by the time I got a third of the way I only had 30% fuel left starting from 90% which the game said was plenty)

TL;DR:

A320:

747-8

Source: Eurocontrol

Ignore the initial climb bit, climb at V2+15 (so somewhere between 145 to 175kts) to 1,500 ft above the airport, then lower the nose, retract flaps and accelerate to 250kts. Climb with constant climb power at 250kts to 10,000ft. Stop climbing at 10,000ft but maintain climb power and accelerate to 280-320kts, then start climbing again.

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Ok great got it I’ll give it a go thanks