Climb profile

[Lace]

I remember seeing somewhere that an 'ideal' climb profile in the Viper is 350kts until M0.8, then hold the mach number until TOC.  My question is - is this correct, and what is the power setting (assume MIL, but haven't seen it stated)?

[cmbaviator]

i guess there is different climb profile depending on the situation like Economic climb for optimal range, Fast climb for interception.....

[skywalker22]

Check here: https://www.f-16.net/forum/viewtopic.php?t=4840

[Lace]

20 minutes ago, skywalker22 said:

Check here: https://www.f-16.net/forum/viewtopic.php?t=4840

So interpolate between...

MIL Power
------------
Drag Index (DI) = 0:
450 KIAS until Mach 0.88

DI = 300:
300 KIAS until Mach 0.72

It would be nice if the loadout section in preflight/mission planner gave the DI.

[ASAP]

Mil power is probably what they use single ship and VFR the vast majority of the time. If they are doing a trail departure through the weather everyone would set FTIT at 750 degrees so they are all getting identical engine performance. Or if the lead needs to give wingmen an energy advantage.  Otherwise everything you said sounds correct as I understand it.

[Frederf]

There are various optimum trajectories based on what parameter you're optimizing (minimizing), e.g.:

• Minimum time to climb (2)
• Minimum fuel to climb
• Minimum time to distance
• Minimum fuel to distance (3)
• Balance of minimum fuel and time to distance (1)

The commonly defined climbs are the (1) MIL climb schedule, (2) MAX AB climb schedule, and (3) HOME schedule. As the name implies MIL/HOME schedule is the most efficient trade of fuel for position (range and altitude) and rely on using maximum dry thrust, aka military power, aka MIL power. In any jet airplane the most economical trajectory is at MIL power. The HOME profile is the actual (or best attempt) at minimum fuel and it's slower than MIL schedule. MIL schedule is slightly less economical than true minimum fuel but it's faster. They figure out how to use 103% or 110% or whatever of the true minimum fuel required and then figure out how fast can it be done with this reduced economy. So instead of climbing at 330 knots for 100% minimum fuel burned you climb at 440 knots for 105% (numbers for example only).

MIL climb is based solely on drag index. More drag, more slow. I made a cheat sheet because it's faster to reference than the manual's big diagram.

From drag index at bottom go up to the blue line and look left for airspeed, look right for Mach. To do the climb put engine in MIL and pitch to do the lower of the two speeds (airspeed will be lower to some altitude then follow Mach).

For MAXAB climb (usual for interception mission getting up high fast) it's about riding the PSmax curve which is essentially M0.9 always so just full burner and pitch for M0.9. The fun one is to get a friend at 200 knots, 10,000' right beside you and have a race up to 35,000'. He will start climbing and you will descend first (to get on M0.9) and still beat him to altitude.

[Lace]

That's great, thanks.

[cmbaviator]

whats the drag index ?

So i want to climb to FL 200 with the least fuel during the climb, what speed/mach should i use ?

[Lace]

26 minutes ago, cmbaviator said:

whats the drag index ?

So i want to climb to FL 200 with the least fuel during the climb, what speed/mach should i use ?

That's the issue, DI is dependent on stores loaded.  It is something which needs to be calculated for each flight, zero being a clean jet, up to very draggy TERs, pods, etc.  Unfortunately DCS does not show it in the mission planner (yet!).

 

Edit - the 350KIAS/0.8Mach mentioned in the original post is bang in the middle of the chart for a DI of 200, so probably a good ballpark for most 'normal' loadouts.

Edited September 7, 2022 by Lace

[cmbaviator]

1 minute ago, Lace said:

That's the issue, DI is dependent on stores loaded.  It is something which needs to be calculated for each flight, zero being a clean jet, up to very draggy TERs, pods, etc.  Unfortunately DCS does not show it in the mission planner (yet!).

i see, thanks

[Mr_sukebe]

This is a really interesting area.

Within DCS, I've previously climbed at say 300knots, assuming that to be efficient.

I was watching something a little while ago, which talked about jet engines by their nature like going fast, because that gives them more air to intake.  So instead of climbing at 300knots, I tried accelerating to mach .8 at say FL200, then climb just to maintain that .8 mach speed.  It's certainly faster to higher altitudes, though I've no idea if it's more fuel efficient.

[cmbaviator]

2 minutes ago, Mr_sukebe said:

This is a really interesting area.

Within DCS, I've previously climbed at say 300knots, assuming that to be efficient.

I was watching something a little while ago, which talked about jet engines by their nature like going fast, because that gives them more air to intake.  So instead of climbing at 300knots, I tried accelerating to mach .8 at say FL200, then climb just to maintain that .8 mach speed.  It's certainly faster to higher altitudes, though I've no idea if it's more fuel efficient.

for me if you want to be fuel efficient during the climb, is to climb at MIL power which the max climb angle so that you can reach cruise altitude faster

[Mr_sukebe]

So maybe the answer is mil power to mach .8 at FL200, then climb at mil power, maintaining mach .8 to whatever altitude you're intending to cruise at?

 

I say mach .8, as that appears to be a nice balance between the significantly increasing levels of drag as you get towards mach 1.  Additionally, aircraft like the F18 and Mirage F1 seem to suggest that as a good number to shoot for.

[cmbaviator]

4 minutes ago, Mr_sukebe said:

So maybe the answer is mil power to mach .8 at FL200, then climb at mil power, maintaining mach .8 to whatever altitude you're intending to cruise at?

 

I say mach .8, as that appears to be a nice balance between the significantly increasing levels of drag as you get towards mach 1.  Additionally, aircraft like the F18 and Mirage F1 seem to suggest that as a good number to shoot for.

;that seems like a good compromise

[Lace]

7 minutes ago, cmbaviator said:

for me if you want to be fuel efficient during the climb, is to climb at MIL power which the max climb angle so that you can reach cruise altitude faster

Max climb angle (i.e ft per nm) is for terrain clearance, max climb rate (i.e ft per minute) is quickest  to TOC.

[cmbaviator]

1 minute ago, Lace said:

Max climb angle (i.e ft per nm) is for terrain clearance, max climb rate (i.e ft per minute) is quickest  to TOC.

they are quite similar i would guess, if your vertical speed is 20K/min,  the climb angle must be very important. 

[Lace]

1 minute ago, cmbaviator said:

they are quite similar i would guess, if your vertical speed is 20K/min,  the climb angle must be very important. 

Indeed, but best climb 'angle' is 90deg straight up vertically, given enough power.  The definition is best angle, not rate.  In a lot of lower powered aircraft the figure can be similar (can't vertical climb in a C172!), but there is a reason for the two distinct terms.

[cmbaviator]

2 minutes ago, Lace said:

Indeed, but best climb 'angle' is 90deg straight up vertically, given enough power.  The definition is best angle, not rate.  In a lot of lower powered aircraft the figure can be similar (can't vertical climb in a C172!), but there is a reason for the two distinct terms.

yes indeed, in a civil aircraft, for terrain avoidance, if you want the max climb angle, you will generally climb at a lower speed and your vertical speed could be lower than normal

[Frederf]

If you want true min fuel you can set CRUS HOME for a waypoint thousands of miles away (to minimize the effect of the descent segment and finite trip length). It will change based on what SMS thinks is on the plane. In a way one could back-calculate DI with cruise info.

It's a common error to climb too slow and steep. It's often better to get there early with an efficient climb and them hold at max endurance (if no threat). Less than 350 isn't good unless you have the draggiest load possible.