Avoid reentry effects on launch

[Superluminaut]

Steep launch, low acceleration, I can't avoid reentry effects. How slow do you have to go?

Edited June 25, 2015 by Superluminaut

[Venusgate]

By "effects" I assume you mean the visual sound barrier wave/heat wave?

Atmo is logistical with altitude, so different speeds at different altitudes will have different amounts of drag.

For launch, if im below 240m/s @ 10km, no effects,

below 500m/s @ 20k, no effects.

Out of curiosity, why are you trying to avoid them?

[Snark]

We all learned how to fly rockets anew with 1.0.2. You've gotten used to doing that, now 1.0.4 is out and you're finding that you're getting "reentry" effects on the way up-- after you get to the "10-12 km and 45 degrees, so floor it" stage of your climb, up to the 20-25km zone, amirite?

My observation has been that you don't have to worry about it. I find that the rockets I designed in 1.0.2 can still get to orbit about as well as they did in 1.0.4; I don't have to change either my design or my flying technique. I get more visual f/x than I used to, but if I just ignore them the flight goes fine.

[Kaezan]

We all learned how to fly rockets anew with 1.0.2. You've gotten used to doing that, now 1.0.4 is out and you're finding that you're getting "reentry" effects on the way up-- after you get to the "10-12 km and 45 degrees, so floor it" stage of your climb, up to the 20-25km zone, amirite?

the new patch is 1.0.3

1.0.4 isnt out yet

[OddFunction]

the new patch is 1.0.3

1.0.4 isnt out yet

1.0.4 is definitely out. In fact, we'll see 1.0.5 tomorrow.

[annallia]

Edit- Ninja'd

[Superluminaut]

By "effects" I assume you mean the visual sound barrier wave/heat wave?

Atmo is logistical with altitude, so different speeds at different altitudes will have different amounts of drag.

For launch, if im below 240m/s @ 10km, no effects,

below 500m/s @ 20k, no effects.

Out of curiosity, why are you trying to avoid them?

I'm talking about shock heating effects. At those speeds gravity losses would be astounding.

We all learned how to fly rockets anew with 1.0.2. You've gotten used to doing that, now 1.0.4 is out and you're finding that you're getting "reentry" effects on the way up-- after you get to the "10-12 km and 45 degrees, so floor it" stage of your climb, up to the 20-25km zone, amirite?

My observation has been that you don't have to worry about it. I find that the rockets I designed in 1.0.2 can still get to orbit about as well as they did in 1.0.4; I don't have to change either my design or my flying technique. I get more visual f/x than I used to, but if I just ignore them the flight goes fine.

This was also a problem in 1.0.2. I know the effects don't do anything but they look terrible. Rockets don't do that going up.

[Sharpy]

I think the mach effects (the white "shrouds") change the color to flame-like at altitudes above 20k-something, no matter the speed. And they are not to be worried about. Unless you're getting a full-blown flame shroud, the little "flames" skirting the surface are normal.

[NathanKell]

Nope, transition from white to orange is purely mach-based.

llanthas: that may keep your rocket controllable, but sadly it's horribly inefficient. Unless you're seeing temp gauges, you're losing more to gravity than you gain through lowered drag. Even then the reason to slow down is so you don't blow up, not because you're being inefficient.

[Warzouz]

Anoter way to avoid renetry effect is to go straighter to space. But that's very inefficient in dV (maybe 20 to 40% more ?). 1.04 reduced the cost to go to space. It's even more efficient to stay longer in atmo to do the gravity turn.

In 1.0.2 a good LKO launch was around 3400m/s. In 1.0.4, it's 3300m/s. I think I even did a 3250m/s. Tested with 100T and 240T payload.

[Red Iron Crown]

I can confirm NathanKell's assertion. Drag is trumped by gravity, the sooner you can get accelerating horizontally the better. I've made some rockets for my payload fraction challenge that just barely make orbit, and only if they go fast enough in atmo to see the reentry effects. If I make a steeper ascent that avoids the effects it runs out of fuel. (This is for reasonably aerodynamic designs, it might change if the rocket is severely draggy.)

As someone once put succintly, if a bit simplistically: Vertical speed is eventually lost to gravity, but horizontal speed is yours to keep forever.

Edited June 25, 2015 by Red Iron Crown
Closing parentheses matter.

[imaspacestation]

I see the moderator tag... I see the rep... But what you're saying goes against everything I know about launching....

I must research this.

I think you may be thinking about the advice to keep under supersonic while below 10km. As far as I know, that still holds, with the atmosphere being much too thick below 10km, but once you are at around that altitude, you should floor it to gain horizontal velocity.

[Warzouz]

I think you may be thinking about the advice to keep under supersonic while below 10km. As far as I know, that still holds, with the atmosphere being much too thick below 10km, but once you are at around that altitude, you should floor it to gain horizontal velocity.

Hmmm, I'm not even sure. I did that on my first launches in 1.0.2. Then I realized I got more fuel left in LKO by pushing the throttle to 100%. Sure if you have too much TWR that's maybe no true, but it's a design flaw, not a flight flow.

[Superluminaut]

Anoter way to avoid renetry effect is to go straighter to space. But that's very inefficient in dV (maybe 20 to 40% more ?). 1.04 reduced the cost to go to space. It's even more efficient to stay longer in atmo to do the gravity turn.

In 1.0.2 a good LKO launch was around 3400m/s. In 1.0.4, it's 3300m/s. I think I even did a 3250m/s. Tested with 100T and 240T payload.

Even when I go straight up with a low twr I still get shock heat.

I've noticed that with altitude my dynamic pressure drops off sharply, and only after that do the effects show up. Does this make any sense?

[maccollo]

I think you may be thinking about the advice to keep under supersonic while below 10km. As far as I know, that still holds, with the atmosphere being much too thick below 10km, but once you are at around that altitude, you should floor it to gain horizontal velocity.

Nonsense. Even this puny thing with a TWR of 2.7 never manages to get past terminal velocity, and the really big rockets have terminal velocities around 800 m/s right off the pad. Basically just floor it all the way to orbit.

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Edited June 25, 2015 by maccollo

[NathanKell]

I suggest flying an ascent with Mechjeb's Ascent Stats window open. That will break down your losses to gravity, drag, and cosine (steering), and tell you the total delta V expended. It's really a necessity for optimizing ascents.

Your drag losses will almost certainly be below 500m/s, while gravity losses are in the 1000m/s range. (2000m/s orbit in SRF, plus 1000 from gravity, plus 500 from drag, =3500 expended. But drag will probably be more like 200 or less).

[Superluminaut]

So I've been watching more numbers and that plasma blowtorch outside my rocket is causing a convection heat flux of 0.2 watts.

Seems legit.

[Superluminaut]

I wonder if the problem is that the vapor cone effect and the shock heating effect are the same thing without any break in between.

[Nich]

I noticed this with my space plane attempts. Trying to punch out of the atmophere at 45-55 degrees adn 450 m/s wasn't nearly as good as a nice 30 degrees and 1100 m/s and burning like crazy.

[Superluminaut]

Tried it last night, and everything flipped - with tail fins on the bottom, and not top-heavy. I can't seem to make the turn without flipping below 10k, unless I throttle down to around 200m/s. Anything faster just flips, no matter how the rocket is built. Maybe it works differently with mods, but it's not worth the trouble to me.

Your angle of attack is probably too large. If you can't pilot it by hand try initiating pitch over at the start of the launch, then lock SAS to your surface vector and let it fly itself till you reach the thinner region of the atmosphere.

[Zeo]

Tried it last night, and everything flipped - with tail fins on the bottom, and not top-heavy. I can't seem to make the turn without flipping below 10k, unless I throttle down to around 200m/s. Anything faster just flips, no matter how the rocket is built. Maybe it works differently with mods, but it's not worth the trouble to me.

You want the rocket to be top heavy. Like a dart. As you burn fuel your CoM moves towards the bottom and the rocket becomes less stable. Transfer fuel from the bottom to the top to maintain stability. Scott Manley made a very helpful video about this recently.

[Superluminaut]

I made a video on the issue.