Best altitude to fly?

[col1948]

I was reading an old thread on another forum that got me thinking, one poster said just because the ceiling height of an aircraft is xxx ft doesn't mean it has to fly at that.
I have noticed when I do an ai flight plan I sometimes just do a random height, I think if it is a short journey by the time it reaches the assigned altitude it will be descending again so I set it low.
Sometimes I do look at the ceiling height and set it to that or slightly lower, so my question is what is the best altitude to set for best performance?
I know different aircraft have different service ceilings I mean is it bet to set it slightly lower for best performance, also on this subject 'Speeds' comes in to play?

I have seen flight plans where all the aircraft speeds were set at 200, I've read that the ai engine ignores this and the ai aircraft will fly at what is in the aircraf.cfg, some put the @ sign in to make it arrive at the designated time, I myself don't use the @ sign as I like the times to be a bit random.

I've set speeds in the the flight plan and the aircraft sometimes flies faster and/or slower that the speed I've set, again what is the best thing to do?

Your thoughts and advice welcome.

Col.

[Firebird]

For civvie aircraft the aircraft will always try to fly at optimum cruise altitude. This is the one that gets the best fuel consumption. In real life this will depend on the weight of the aircraft and is the reason why aircraft always try to climb higher as they get lighter.

For mil aircraft it entirely depends upon their mission. For example a cargo flight from the US to Europe is going to follow the same guidelines as a civvie airliner.

For fighter/attack aircraft it will depend on what they are simulating. For MP aircraft they will transit at high/medium and loiter at low level. For AEW they will operate at the optimum height for radar operations. For AAR generally speaking FL200-FL240 but if you are refueling low and slow or helos you will be a lot lower.

However, these are guidelines rather than hard and fast.

We always use the aircraft cruise speed and a tool like AIFP to work out the flight time.

One final thing I should mention about real life. Even back in my day MIl pilots cruised according to Mach number at medium/high altitude and I would not be surprised if airline pilots did the same. At low level mil pilots will always fly in multiples of 60kts as it makes navigating to turn points a lot easier.
Neither of these things can actually be achieved in game.

[ahs06]

Normally aspirated piston aircraft and non pressurized aircraft tend to stay below 12,500 as they suffer performance setbacks in thinner air and the crew would need supplemental air. Turboprops are most efficient in the FL 20-25. Jets are usually operated between FL30-40 on normal flights. Military fighters usually operate in the high teens up to the highest flight levels depending on the mission. To Firebird's point, in the US, mach numbers are used at en route air traffic control centers for all aircraft in class A airspace.

[col1948]

Thanks it was more of a guideline I was looking for, thats great. I also read these private jets can fly a very high altitude as well.

Col.

[Victory103]

Col, great suggestions for accurately planning your AI flights. Mil fighters are not allowed up way high without a wavier here in the US, then for transits they go up to biz jet levels. You could plan to have them low to simulate flying on a low level route. Mil helos are going to be low as well, even on IFR flights, they are like GA with oxygen limits (I think the AI pilots are ok without). Mil transports have the ability to go high, but with cargo that drops them back in the 20s.

[VulcanDriver]

Here in the UK most combat aircraft fly below 10,000 ft usually a lot lower and usually in uncontrolled airspace I live under uncontrolled airspace and we often have combat jets and mil copter flying around.

[col1948]

Thank you all again, it would be nice to have a little table to work off when doing ai plans, I may have to put one together it will help me and a few others too I think.

[swp53]

From past experience you can have your combat aircraft down at 2000ft and providing the flightplan is IFR the aircraft will always keep itself 2000ft above the terrain so no problems with mountains.
It may be 1000ft I can't remember now but there is a lower limit. I planned a few flights and followed them to prove it works including Lossie to St Mawgan so plenty of mountains to clear.
This was in FS9 not sure if it's the same in FSX/P3D

[col1948]

@swp53, Yes I did a test not long ago with some helicopters and set the flight plan altitude low, I had them fly in a mountainous area and ATC directed them higher to avoid them.
I posted on here about it, I had the plan as IFR, but if I set it to VFR they flew in to the mountains.

[col1948]

On the subject of speeds: I picked this one out at random but if you were to set a speed for this aircraft what would you set it as?

[REFERENCE SPEEDS]
FLAPS_UP_STALL_SPEED= 190.000
FULL_FLAPS_STALL_SPEED= 110.000
CRUISE_SPEED= 520.000
MAX_INDICATED_SPEED=375.000000
MAX_MACH=0.879980

[Firebird]

Cruise_Speed