VNAV - Vertical Navigation

old topic has been/will be shut, permission from a mod for this

VNAV?! What’s VNAV, you might ask. It stands for Vertical Navigation. But what does it do? You probably know what LNAV is (Lateral Navigation), and that it basically follows your flight plan for you. Well VNAV is similar, but slightly different. When you see your FPL, it is from a top-down perspective. Now imagine looking at it from a side perspective. The lines would show the altitude of the aircraft, not location.E.g
image
Ignore the reserves part

Here you can see the pilot climbed, leveled off, climbed again, cruises, step climbed (explained later) and then descended, leveled off and landed. Simply, VNAV controls your climbs and descent.

But why is this useful? Climbing only takes 15 mins and I’ll set an alarm to remind me to descend

Aha! You see, VNAV is less useful for initial climbs or the final descent, but more for step climbing and climbing/descending during the middle of your flight when you aren’t with your device.

But why would I climb or descend in the middle of my flight? And what’s step climbing?!

Simple. Imagine you’re on an airway with certain cruising altitudes and transition to a different one with different altitudes, or cruising one direction and turning around requiring a different altitude (SWEVENNEODD). You would set VNAV to climb/descend at that waypoint to the correct altitude.

Step climbing: On long flights, with very fuel-heavy aircraft that weight alot, the ceiling (and therefore cruise altitude) is restricted to lower, thicker air where the wings have enough lift to keep from stalling. When some of this fuel burns, it is important to climb so you aren’t cruising to low and wasting fuel, so VNAV climbs for you. Let’s see an example. We are EY878, an a340 from OMAA-RJAA. As we are so heavy, for the first half of the trip we can only cruise at FL290, but as we pass over Tibet (China) we can go up to FL350. As we may not be by our devices at this point, VNAV would make the climb for us.

I suggest to set a VNAV profile you click on a waypoint in your fpl (either in map or fpl) and set an altitude for it. Then you could have an ALT view along with the map, map/FPL and FPL views we have currently that shows the vertical profile.

In summary, VNAV would help a lot with fuel efficiency through step climbing and also help on routes that change direction, as well as increasing realism a lot.

Totally needed !!! I was wondering if anything like this exited.
Gave my vote.

45 Likes

I just removed a vote to vote for this. We definitely need this in Infinite Flight. It would be so useful!

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Shouldn’t it be a side perspective?

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MaxSez: L/ VNAV are not stand alones, there sud-systems of RNAV autonav system. RNAV+ programs are used in a Flight Management System/Director (FMS/D) as found on modern airliners. The votes here should be for an IF RNAV+ FMS/D with L/VNav sub-systems. Here’s a system summary from airliner.com. V

"RNAV is short for ‘Area Navigation’. In the old days you used to have to fly directly over the navigation aids on the ground (VOR, NDB etc) to make your route. It meant a slightly zig-zag course for your flight as you couldn’t get the navaids in a perfect line between every possible city pair. Then when computers started getting into planes, it was possible for the computer to ‘create’ an imaginary navigation aid based on a direction and distance from a real one on the ground. So you could draw a straight line from your origin to destination, and create the waypoints based on the computer figuring the direction and distance from some nearby navaids (usually VORs) and using that to fly a straight route. Nowadays, RNAV is also loosely used to describe any ‘straight line’ navigation method like GPS, as well as the old RNAV method too.

LNAV and VNAV are parts of the flight guidance system, and are acronyms for ‘Lateral Navigation’ and ‘Vertical Navigation’. I don’t know the 737 very well, but I’d bet the 767 I fly is very similar.

LNAV is the route you fly over the ground. The plane may be using VORs, GPS, DME, or any combination of the above. It’s all transparent to the pilot, as he enters his route as specified in the clearance and flight plan into the FMS (Flight Management System). The route shows up as a magenta line on the lower flight display, and as long as the autopilot is engaged in the LNAV mode, it will follow that line across the ground. LNAV however does not tell the plane what altitude to fly, and that is where…

VNAV comes in. Vertical Navigation is where the specified altitudes at particular waypoints are entered into the FMS, and the computer figures the best way to accomplish what you want. For instance, if you are flying with the autopilot on in VNAV mode at cruise altitude, you can enter what speed you desire to make a descent at, and what altitude you wish to cross a particular point, and the computer will figure out where to bring the throttles to idle and begin a descent, to allow you to cross to that point in the most economical manner. VNAV also works in climb. There are airspeed restrictions at various altitudes, and if you are in VNAV, it will fly the plane at the desired power setting and angle to achieve the speed (and efficiency) you wish.

In reality, we spend most of our flying with both LNAV and VNAV engaged. If the autopilot is off, LNAV and VNAV still send their signals to the flight director so we can hand fly the plane the way the autopilot would if it were flying.

So in summary, RNAV is a method of navigation, and LNAV/VNAV are subsystems of the autoflight system. LNAV is the course (in 2 dimensions) across the ground, and VNAV is the flight path (in 2 dimensions) up and down. Of course we can do it by other methods which worked well for many, many years. But I’ve found the computer can almost always do it better and smoother. A word of caution is always given to pilots when first learning the LNAV/VNAV system though; it’s best to study well and always keep an eye on what it’s doing. It is only as good as the person punching the buttons, and the most common thing heard in today’s modern cockpits is "What’s it doing now???“I”. (airliner.com)

That’s my opinion and I’m sticking to it! For me I prefer KISS Systems, (GPS/GNSS) ! Regards

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Honestly I don’t know how this would work because a lot of the stuff is driven off of cost indexes, and routing restrictions which we don’t have at all in IF. Once we get those implemented VNAV would be very nice to have.

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Great thinking @Insertusernamehere
Definitely have my LAST vote Great Feature

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Really well put together, and it might not seem like much, but in FSX I use it nearly every flight. Would be great to see this along with LNAV in Global!

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This is a feature which would be very useful to go alongside VNAV. It wasn’t in the list of features for this update so ill doubt it will be added for the initial global update but it would be very useful for future updates to help fuel save etc.

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Would love to see this

Very useful for step climbs and altitude restrictions as mentioned

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I just see this, it would be fantastic, more time to sleep 😴, 😆 Joking, now seriously, this would be awesome, definitely you’ve got my vote

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This is soooooo cool… I can’t wait

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Yes! This would be perfect for IF Global!

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Yes, yes, yes! I was thinking this would be helpful just the other day.

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Nice bump. We really need VNAV. Sadly I’m out of votes :(

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Really nice topic for an essential feature. You have my vote.

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Voted! This a must for global, calculating decent manually is quite tricky with VNAV it’ll be a walk in the park!

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I can only speak for the Airbus, but when climb we usually climb in two modes, “Open Climb” which sets Climb thrust and uses pitch to maintain airspeed, the other is VS but that mainly used in Paris and London area so we don’t set off TCAS… Also for step climbs I hope people understand VNAV or Managed Climb will never auto step climb, it will calculate it for you, but it has to be initiated by flight crew, for numerous reasons including ATC and level busts . Decent is slightly different, the MCDU calculates based on loads of factors, to give a continuous decent profile and gives a top of decent, we “manage” the decent for that one “VNAV” if you like and honestly i can can see that feature being handy to some guys who struggle with decent profile, but in order to have an VNAV you’d almost need an MCDU/FMS in game and that’s just really complicated.

Regards,

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Yeah this would be an awesome feature. Aerofly 2 already have it.

This is a great idea! I hope the devs consider this. Maybe we can see it before the end of 2018? Hint hint

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