Yet Moar Spaceplane Woes

[capi3101]

Odd...the plane I'm flying still has Standard Canards for tail fins; located on the inboard edge of the dorsal outboard wings. I'll check to see if for some reason the fins got removed.

I would like help with fixing the issues. Bottom line, though - the current flight is unsalvagable? At least not without putting some of the fuel I delivered back into it? That is a possibility - my quicksave is set to where I'm still docked to the pier.

[Claw]

My bad. I looked where they used to be, then zoomed in to mess with the CoM/CoL. They are indeed still there. Having them that far out has it's own set of challenges, but might be okay if it turns out to be a CoL/CoM/Canard problem.

[Claw]

Bottom line, though - the current flight is unsalvagable? At least not without putting some of the fuel I delivered back into it? That is a possibility - my quicksave is set to where I'm still docked to the pier.

I would say that it seems pretty tough to recover your plane without taking on some fuel to balance the CoM a little more.

My recommendation for recovery, if you want to keep as much fuel in space as possible...

1) Put only as much fuel/oxidizer as you need in the NERVA tanks for reentry. Any excess in there isn't helping much.

2) Put about 580 fuel and 700 oxidizer in the main orange tank.

3) Fill the forward RCS tank.

4) Put 75+ units of liquid fuel in the forward Mk-1 nacelle tanks (that feed your tricouplers). That should give you some gas to control it, and helps the CoM.

5) All the other tanks should be empty. If you have monopro in the cylindrical side tanks it will help but isn't necessary.

6) Maintain below 10 AoA during reentry. You might have enough control authority once you get down below 10km to help keep it under control if you exceed 10 AoA.

Running your engines at a low throttle setting as you pass 18k down to 12k might help control with thrust vectoring. Up to you.

I didn't fly this config (that's what you're getting paid for), but I think that should give you enough control to recover it for design modifications.

Good luck!

Edited February 12, 2014 by Claw

[Claw]

I would like help with fixing the issues.

So I played with your plane some more to help the design itself (separate from recovering your existing flight).

The simplest recommendation I have is to modify the canards in one of two ways:

(I would recommend this if you have plenty of pitch authority with the changes, which I think you will.)

1) Remove two sets of canards. Either the top and bottom set, or the bottom two sets.

2) Keep your 675-700 units of monopro in the forward tank, and fill your NERVAs as required. Transfer the liquid fuel from NERVAs to forward MK-1s when needed.

3) You should be able to fly just about any AoA, but I would stick with 45 deg or less due to limited yaw stabilizers.

-OR-

(Do this if you find you need more pitch authority.)

1) Remove one set of canards and move the other two back as close to the solar panel as you dare. The bottom set is the best candidate for removal.

2) Keep your 675-700 units of monopro in the forward tank, and fill your NERVAs as required. Don't take excess oxy if you don't have to, but take extra liquid fuel. Transfer the liquid fuel from NERVAs to forward MK-1s when needed.

3) Fly your return profile to maintain below 15 AoA. This config is still susceptible to the control surface bug.

[capi3101]

So I transferred some fuel back from docking pier - left it at 70% full (amounted to about 10% of the Liquid Fuel and 15% of the Oxidizer). Filled the foremost jet fuel tanks to full, filled the NERVA tanks, set the center tank to flow out. Attempted to land. This happened:

Obviously my ILS needs a few more markers. But overall I'm not complaining too loudly.

I did go ahead and take the wheels off; they were indeed throwing the center of mass forward in the SPH. In truth, with the original fuel configuration the center of lift was 100% aligned with the center of mass, and there's only so much accuracy you have with the SPH tweakables. I probably was trying to fly with the CoL ahead of the CoM and didn't know it.

Okay...so on to your last two posts. Basically, the landing went about like what you recommended. I may have had more fuel aboard, but nevertheless, that's about how I handled it. I did make the mistake of pulling up too hard and stalled; I was able to recover it, though. Was a bit hairy there for a second.

Second post - I needed the pitch authority; the stupid thing was acting like a lawn dart with two sets installed. It was only after I added the third set that it finally took off. That may have still been when I had the control surfaces outboard; I'll go ahead and play around with it a bit.

The forward RCS tank is empty at takeoff to shift the CoM further back; are you saying I should go ahead and fill it up?

Since I'm now free to make further tweaks, would there be any utility in either moving the fins out to the edge of the wings or adding another set out there?

[Claw]

Awesome! It made my day to know you were able to save it.

For your lawn dart comment, I would give it another shot with a set of canards removed. I remember having pitch problens with the original file when I flew, but it might have been from all that wing flex.

For the forward RCS tank, I meant to leave it empty on takeoff but put the monopro in it in space (like you have been). That last post was meant for how to configure your plane for reentry. However, you can also fly it like this from an initial takeoff for testing. (I.e. set up the tanks like you're reentering and then launch it.)

If you want to add more vertical tails, then go right ahead. Put some on where you like and give it a try. I don't know if I misled you. I don't mean to say "do not add more tail," just that adding more tail wasn't going to address all your original problems. Adding tail fins can help your stability during several points in your flight, so if you think you need it or want to try then do it!

Also, as an alternative to deleting canards, you can add some angled tail fins and play around with the CoL. Adding an angled tail can offset the aero AoA control surface bug (so the CoL won't move as much forward with AoA). Be sure to lock out the pitch and roll portion for the angled fins though. Angled fins bring their own set of funny charachteristics, but they can help.

Incidentally, adding control surfaces anywhere to the back of the plane can counteract the AoA bug induced by the canards. But you'll still have to contend with CoL placement.

So many options, so little time...