My Eve Ascent Vehicle Doesn't Work

[BenKerman]

Hi,

 

I have a specific question.  Do wings always provide lift in KSP?  Take a look at my specific case...oh, looks like I can't add photos.  I got that screenshot for nothing then...Well, just imagine an awkward looking spacecraft.  It is short and fat with multiple parallel stages (like the Soyuz launcher, not like Falcon 9).  On its bottom is one of those inflatable 10m heat shields.  On its top is a tail fin.  The tail fin is attached to the spacecraft via a grabbing unit.  The tail fin is composed of three "Big S Delta Wings" spaced 135 degrees from each other.  Overall the whole assemblage looks rather like a bomb that is meant to point down as it falls.

The purpose of the spacecraft is to enter Eve's atmosphere.  The heat shield is supposed to detach and fall away eventually, and the tail fin will also detach and fall away.

Unfortunately this setup does not always work.  During atmospheric entry (say around...50km?  40km?  30 km? altitude in Eve's atmosphere) the craft flips around so the heat shield is not facing the direction of travel, said craft quickly disintegrated.  That is -- this is USUALLY what happens.  One time the setup worked.  The tail fin kept the craft pointing in the right direction the whole time, and it would have "landed" except it was heading for Eve's ocean (at that point I just reverted to an earlier save).

What I'm wondering is if those Big-S Delta Wings are providing lift?  I don't want them to provide lift; I just want them to provide guidance and stability.  I was looking for an option to change the curvature of the wings to eliminate lift, but didn't find any.

I've tried a couple of other things trying to keep my large-ish spacecraft oriented properly as it heads to Eve's surface.  I tried adding more and larger reaction wheels (didn't work) and I tried adding a weird parachute/heat shield thing.  The weird heat shield parachute thing was three of those 10m inflatable heat shield facing the wrong way, attached to the top of the spacecraft like the tail fin in my current setup.

How do I keep my big Eve Ascent Vehicle (which obviously has yet to even attempt said ascent) from flipping over during landing on Eve?

 

Thanks,

Ben

PS I'm playing on Xbox with no mods.

 

I made a website in Google Sites to upload this picture of my spaceship.

[HebaruSan]

15 minutes ago, BenKerman said:

On its bottom is one of those inflatable 10m heat shields. 

three of those 10m inflatable heat shield facing the wrong way, attached to the top of the spacecraft

One 10m heat shield at the bottom and one at the top worked for me, and I think it's a fairly typical solution that folks stumble upon.

[king of nowhere]

those three wings are providing stability. unfortunately, a 10 m heat shield makes for a lot of drag, it takes more than that to counteract.

20 minutes ago, HebaruSan said:

One 10m heat shield at the bottom and one at the top worked for me, and I think it's a fairly typical solution that folks stumble upon.

in fact, this is a common solution. although one has to be careful, when i tried it the ship tilted sideways and disintegrated.

now my eve landers include heat shields both on top and bottom, and other things to increase drag at the top and keep the ship correctly oriented. here's an example

you can see i also built the top shields on top of high towers, that to push them farther behind the center of mass and give them more leverage.

eve's atmosphere increases in density abruptly shortly below 50 km, a ship gets 10 g of deceleration, that part is absolutely brutal. it's not easy to make something that survives that.

[Singhnaut]

When it comes to landing, Eve can be one of the biggest pain in the necks.

A solution: get mechjeb, your craft doesn't appear to have it (unless its built in i have mechjeb 2. If u play on console switch if u can. PC is a more immersive experience). If you can't get mechjeb then DM Matt Lowne. For some reason, he loves landing on Eve, he even made a movie about it! Hope this helps.

 

I love how just now i had 66 posts. Only true SW fans get that joke

[Gargamel]

Moved to gameplay questions. 

[Guest]

About the pictures, most of us upload them to imgur and link from there. The one you uploaded isn't visible, probably because you haven't enabled sharing -- I'm seeing a 403 Forbidden when looking at it.

To answer your specific question: no, wings do not always produce lift. The lift they produce is a function of angle of attack, and there is a point in that function where the generated lift is zero. However, wings (and indeed all parts) have such a function, and generate lift in the right conditions.

Your difficulty is that the 10 m heat shield produces a tremendous amount of drag right at the nose of the craft. This moves the centre of pressure forward, and once it's forward of the centre of mass, your craft will want to flip. 

There are two ways you can attempt to address this problem. 

1. Design your craft to have the centre of mass as close to the heat shield as possible.
2. Add a stabiliser. It doesn't necessarily need to be that big, but it needs to have a long lever arm. Imagine a long, thin rail going waaaay back, with a couple of tailfin parts on it. 

So without seeing a picture of your craft, I think the problem isn't that the Big-S wings are producing lift; it's that your stabiliser isn't far enough back -- you describe your craft as "short and fat." If the Big-S wings are there only for stability, I think you would do better with less mass by replacing them with a detachable, light, but long tail, with much smaller stabilisers at the tip. If your heatshield is on the nose and the craft enters nose-first, you would detach the tail after you're through the dangerous part of entry; the drag from the heat shield will cause the craft to flip into tail first orientation. Then you can detach the heat shield, causing your craft to fall away from it. And once you're at a safe distance from it, deploy parachutes and float down.

 

[BenKerman]

I tried posting a picture of my ship to imgur, here is a link:

https://imgur.com/6vM4Inn

Edited April 28, 2021 by BenKerman

[OHara]

I would have thought that craft would be stable on reentry.  The heavy fuel is near the heat shield, and those big wings would tend to swing downwind as you want.

The nav-ball is pointing retrograde (probably because the command pod will be pointed forward for the return journey) .  SAS doesn't know that you are flying backwards, so won't know to tilt the elevons appropriately.  So SAS would be commanding those big elevons in the wrong direction, and that might be enough to flip in Eve's atmosphere.

If those elevons are always used when flying backwards (relative to the command pod) you can reverse their actuation by setting a negative 'Authority Limiter' in their right-click menus.  Or, you can set 'Control Point: reversed' on the command pod on the way down, if you remember to restore that setting before going back up.