Does the stock Aeris 4A have its fuel tanks mixed up? If not, why's it like that?

[tfabris]

I wanted to take a space plane to orbit and back, and the stock Aeris 4A craft says, in the flavor text, that this is possible with that craft. So I tried it. The problem is that it kept running out of fuel, having flame outs because the rocket was starved for oxidizer.

When I looked closely at the stock design, I see that the jet engines were attached to rocket-style fuel tanks, and that the rocket engine had one large rocket fuel tank as the main fuselage and one small jet-engine fuel tank directly attached to it. It's as if, in the design, the jet and rocket engines were accidentally reversed. Like this:

    R
    R
    R
    R
    R
    R
R   J   R
R   J   R
R   J   R

I was never able to get that design to orbit, and I think it was because the fuel was all wonky. So I made my own variant of the Aeris 4A, re-doing the tanks so that the jets had jet fuel and the rocket had all rocket fuel. Like this:

    R
    R
    R
    R
    R
    R
J   R   J
J   R   J
J   R   J

And also I assigned Toggle Engine commands for the Jets and Rocket to custom action groups (1=Jets 2=Rocket) and put the jets and rocket in their own stage. With that design, I was able to orbit the craft, and also to have enough of both the jet fuel and the rocket fuel to de-orbit and land a perfect 3-point landing at the Space Center runway. It took a lot of tries, and I was only able to orbit the craft by going very fast and very high with the jets alone, before firing the rocket for the first time. I had to get the jets accelerating the craft fast enough at high altitude so that flames were coming off the body of the craft. Very exciting! :-)

But anyway, what I'm wondering is, was the original Aeris 4A designed that way on purpose, with the fuel tanks wonky like that? If so, what is the method to that madness that allows the stock craft to reach orbit?

[Sirine]

Aeris 4A, design in away that, It use rocket more than Jet. And its means to be refuel at LKO (Lower Kerbin Orbit) fuel station.

And yes, It is fine in getting to LKO, it is your skill that need improving, not the craft.

[tfabris]

Can you give more details about how the fuel works in that situation, then? I don't understand how attaching oxidizer tanks to the jet engines is supposed to be useful (and vice-versa).

You say that my skill needs improving. That's understandable, but what is it that I'm doing wrong with the stock craft then? What's the correct procedure to orbit it? For instance, do I use different amounts of throttle at different altitudes, and if so, what are the amounts and altitudes? And what angles of attack should I be going for at various altitudes?

Knowing that the plane was not designed to have enough fuel to return on its own, but rather get refuled in LKO, is important information. I'm proud that I was able to alter the ship design such that it didn't need the refuel. :-)

[Sirine]

Check the fuel line.

[Sirine]

Can you give more details about how the fuel works in that situation, then? I don't understand how attaching oxidizer tanks to the jet engines is supposed to be useful (and vice-versa).

You say that my skill needs improving. That's understandable, but what is it that I'm doing wrong with the stock craft then? What's the correct procedure to orbit it? For instance, do I use different amounts of throttle at different altitudes, and if so, what are the amounts and altitudes? And what angles of attack should I be going for at various altitudes?

Knowing that the plane was not designed to have enough fuel to return on its own, but rather get refuled in LKO, is important information. I'm proud that I was able to alter the ship design such that it didn't need the refuel. :-)

Its a bit complicated to answer your questions...give me a minutes to sort it out.

1) Can you give more details about how the fuel works in that situation, then? I don't understand how attaching oxidizer tanks to the jet engines is supposed to be useful (and vice-versa).

It use the fuel line to transfer fuel. It just the design. Nothing is useful in this. You should make it better like what you already did.

2) What's the correct procedure to orbit it? For instance, do I use different amounts of throttle at different altitudes, and if so, what are the amounts and altitudes? And what angles of attack should I be going for at various altitudes?

I've not knowing the "correct procedure". I use 100% all the way. Altitudes 20km switch to rocket. Angle of attack should be around 35~40. (If for normal SSTO, Jet base it should be 1~5 until maximum air ceiling. Remember it is rocket base.).

3) Congratulation on your new Improved Aeries 4A!!!

Edited October 14, 2013 by Sirine

[tfabris]

Ah, I see the fuel transfer lines now, as shown in your screen shot. They were hidden on the bottom. I see how that means the fuel in the side tanks gets consumed first, and that means the overall amount of fuel plus oxidizer should balance out to equal in the end. That design requires that the jets and the rocket are used simultaneously. The reason I was getting flameouts is that I was overthinking it, trying to keep the rocket engine deactivated until I needed it. I see that just using all three engines at once was the original design intent.

*Edit* Nope, even using it as-is without trying to change the activation order of the engines, it still runs out of oxidizer early. I must be doing something wrong.

(Awaiting your edits to the post above to see your solution.)

Edited October 14, 2013 by tfabris

[Sirine]

Ok. You may 'advance edit' the 1st thread to make it "answer".

Anyhow...some extra information for you...I've manage to land it with the 88.44 liquid fuel left on the plane (picture show above.).

You just need to Alt+Click on the both fuel tanks to transfer the fuel.

88.44 units of fuel is consider plenty for Jet engine.

Edited October 14, 2013 by Sirine

[tfabris]

Ah, turns out there's a Wiki entry on it:

http://wiki.kerbalspaceprogram.com/wiki/Tutorial:Aeris_4A_mission

Didn't see this before, had to dig a bit to find it.

[Dispatcher]

Here is a video on the Aeris 4A and some modifications:

[tfabris]

Thanks!

After viewing the information in this thread, the tutorial on the Wiki, and that video, I now clearly understand the intended design and use of the Aeris 4A. I tried doing an orbital flight based on the Wiki tutorial and still couldn't do it when trying to follow those particular instructions exactly to the letter, but I think that if I had tried harder to get more horizontal speed before switching to rockets, I could have done it.

Both the video and the Wiki make mention of needing to manually transfer fuel before deorbiting. The wiki calls that a "Construction Mistake", so I see that I wasn't entirely off-base in wondering if there was indeed something fishy there. I think the whole point of the design was to allow the craft to share the fuel in the tanks between the jets and the rockets over the course of the mission. That's the part I didn't understand when analyzing the original design, and which was never quite explained in any of the stuff above. Now that I see all of those elements together, I think I understand it, even though that part was never quite spelled out anywhere.

There's also the issue where the strange fuel design means that you might, at any given point, run into a mismatch of oxidizer and liquid fuel, where you've used up all of the one you need at that moment, but you've got some of the other left over. It seems to be designed so that the fuel-to-oxidizer ratio comes out close in the end, but the pilot's percentage of jet use to rocket use will always make that a random variable.

In the end, I prefer my modified version of the Aeris with the jet fuel and rocket fuel kept strictly separate. I was able to get to orbit easier with it, and I didn't need to transfer fuel. I didn't have the luxury of being able to use some of my leftover rocket liquid fuel to power the jets, but that didn't turn out to be an issue.

[iDan122]

The Aeris 4A is bad and good:

It doesn't have over the top jet fuel, one tank is more than enough.

It needs a little more intakes, it should have action groups to close them after shutting the jets.

The rocket engine is not the best, it is long and not very efficient, gets easily scraped off during

takeoff, I replaced it with an aero spike, the best alternative.

Need more smaller fuel tanks instead of whose ones, better fuel displacement(to change center of mass).

It's center of lift is a little messy.

Anyway I saw people get It into orbit so it's possible.