Flight Question Glider Launch Flight Path

[PaulG]

Hi. I'm actually asking two questions here with the first question focused around the mechanics, the why, the how come, the scientific rationale. The second simply polls what people do.

In a vessel such as the shuttle, or any other similar rocket, it launches from a pad, straight up for a few then banks and starts a steady climb. With the DGIV it starts horizontally, takes off like an airplane.

Which of the following methods is "best" in terms of efficiency, time, realism, limitations, etc. The more you can provide sound reasoning, the better.

1) Take off like an airplane, turn gently toward the direction you need to orbit and then start your ascent.

2) Take off like an airplane, pitch up to 90 degrees, gain altitude then roll toward the orbit angle and start the gradual ascent like a shuttle/rocket.

3) Some others?


The second question is simply, which method do you use and why?

Thanks.

 

[Cras]

The DGIV actually has its own sort of hybrid way of getting into orbit. It takes off like an airplane, then gets on heading, then pulls straight up and goes up very very high until it is out of the atmosphere until finally starting its gravity turn.

Orbital velocity is very high, so you are best if you start getting to that as soon as possible. The Space Shuttle went up a bit before really pitching hard over for the turn because you can't start going too fast when still in the thick air, so you have a trade off of needing to get high enough quick enough so the air is thin and your dynamic pressure will not be as great as you start to really gain speed.

Another way is look how you get up in the G42. That operates on a very steady climb, slowly but surly getting faster and faster.

 

[PaulG]

Is that the most efficient and realistic route for the DGIV? Why wouldn't it pitch up and gain both altitude and orbital velocity at the same time?

The DGIV actually has its own sort of hybrid way of getting into orbit. It takes off like an airplane, then gets on heading, then pulls straight up and goes up very very high until it is out of the atmosphere until finally starting its gravity turn.

 

[Cras]

Is that the most efficient and realistic route for the DGIV? Why wouldn't it pitch up and gain both altitude and orbital velocity at the same time?

I dont think so, but it is probably the most stable....for the AP anyway. But watch as how the AP takes the ship up, it does not really care about horizontal velocity until you are way way up and out of the atmosphere. Now watch the Space Shuttle, you are pretty much rolling and pitching over as soon as possible, you are at already a 40 degree pitch by SRB sep.

 

[Enjo]

The trick is to use the glider's lift (which the rockets don't have) to counter gravity and get horizontal velocity with as little drag as possilble, which can be monitored with surface mfd. Keep the dynamic pressure less than 20kPa and you're done. You can verify which method is best by simply comparing the remaining fuel after insertion.

Also, Launch MFD has a feature that supports this kind of ascent. Just disable pitch control with shift+i and control vessel's trim manually too keep the dyn. pressure below 20. Then extend the orbit, exit the atmosphere to reach apoapsis and circularise.

 

[C3PO]

Is that the most efficient and realistic route for the DGIV? Why wouldn't it pitch up and gain both altitude and orbital velocity at the same time?

The wings on the DGIV are not very efficient, and they need quite a bit of air density to keep it in the air. This means that you are going to have relatively high ambient pressure during the climb. The engines have lower ISP if the ambient pressure is above vacuum, and you'll fly for a longer period with low engine efficiency if you use the wings during the initial climb.

So the most efficient way to launch is to get out of (most of) the atmosphere ASAP to get the most out your engines during acceleration to orbital speed.

 

[Enjo]

PaulG:
When in doubt, make measurements.

 

[PaulG]

Thanks for the responses everyone.