Using FAR, how do I know when I've hit Max Q

[jarmenia]

Is there a way to tell when using FAR when I've hit Max Q so I can go full throttle with my engines? Currently I keep the TWR at about 1.25 until I get to 7 KM but this seems inefficient at times.

[Th3F3aR]

AFAIK there is no way to tell that, but otherwise i can't see why your ascend should be ineffective. Why don't you try with a TWR 1.5 ? The main reason for rockets to flip is that your AoA is to high, this can be coped by never leaving the prograde marker.

[jarmenia]

Thanks for the response. Its not the flipping I am worried about but instead the rocket exploding because of DRE and FAR if I'm flying too fast in the lower atmosphere.

[Th3F3aR]

Well okay, i for my self try to stay lower than 70 m/s till 5 km - 7 km then lower than 200m/s till 15 km and then throttle it up to slowly increase speed and get most of the circularization done, my experience showed that it's not that ineffective to do so

[Hodo]

AFAIK there is no way to tell that, but otherwise i can't see why your ascend should be ineffective. Why don't you try with a TWR 1.5 ? The main reason for rockets to flip is that your AoA is to high, this can be coped by never leaving the prograde marker.

A TWR of 1.5:1 with FAR+DRE is a bit excessive. Most you want is around 1.2:1.

The trick is keep your throttle pretty low till about 10-12km, then you can start to throttle up to full. I generally start my gravity turn at 100m/s or 1000m AGL. If my TWR is around 1.2:1 I start at 100% throttle then throttle back once I hit the target speed to about 80-90%. After I hit 10-12km I throttle back up.

[Th3F3aR]

A TWR of 1.5:1 with FAR+DRE is a bit excessive. Most you want is around 1.2:1.

At that point i didn't know he uses DRE, my advice was given for FAR only

[Jouni]

I'd say that a good launch TWR in FAR+DRE is 1.2 to 1.4. Higher TWRs also work, but the launch may be a bit inefficient, if you can't do the gravity turn quickly enough. Throttling down is completely unnecessary, unless the rocket starts to wobble due to an extremely high TWR (usually above 3 or so).

It's also quite difficult to get the dynamic pressure high enough to cause any trouble. Assuming that your rocket is reasonably sane, it takes bad piloting or deliberate effort to get aerodynamic failures. The only effect DRE has on launches is that it makes some engines like the Mainsail prone to overheating.

[Van Disaster]

Pop open the FAR flight data dialogue, watch the Q figure, and when you explode you've hit your max Q

I don't currently use DRE & I've hit six figure Q without breaking parts off an aircraft, FAR's breaking-things isn't based solely on that. I'd imagine DRE would probably be the culprit in any rocket exploding, unless the rocket is unstable & gets sideways.

[MarvinKitFox]

Is there a way to tell when using FAR when I've hit Max Q so I can go full throttle with my engines?

Sure. That's when the pieces start flying off.

Safe Max-Q is about 1% lower than that.

Seriously though: in Far, just open your info display. One of the many data displayed is you current Q factor.

Max Q is, by definition, when this is, well, max. But you can choose when, and how much, you actually experience.

Don't trim your TWR so far, just dip the throttle while when your current Q reaches a dangerous level (will depend on your vehicle components, layout, your piloting skill etc..)

As it starts dropping because you are exiting the denser layers of atmosphere, you gradually throttle up such that your current Q stays at or near your *chosen* max-Q

[Empiro]

I've never had any issues with Deadly Reentry and FAR when going up, and I often launch with TWRs around 1.6. Unless you pitch over too much, you won't come anywhere close to burning up or destroying your rocket.

[MarvinKitFox]

I've never had any issues with Deadly Reentry and FAR when going up, and I often launch with TWRs around 1.6. Unless you pitch over too much, you won't come anywhere close to burning up or destroying your rocket.

You need about 2.1-2.3 TWR to go fast enough for DRE to kill you.

If you have just FAR, a bit more is possible. About 2.4 TWR at launch will guarantee FAR disassembly at t=100 or so.

[Van Disaster]

I have launched a FAR rocket with a twr of 12, and made it to orbit at full throttle - there's no hard rule for "it will fall apart at this speed", if it doesn't go sideways & it's got enough bracing to withstand the crazy drag you'll generate, it isn't going to blow up from pressure ( generally ).

[NathanKell]

If you have just FAR, a bit more is possible. About 2.4 TWR at launch will guarantee FAR disassembly at t=100 or so.

Err, depends on how long that TWR lasts. An SSTO that starts at 2.4? Bad news. An LV with boosters that go 2.4->3.0 over the course of 30 seconds, then back to 1.2 after separation? Not a problem at all.