drag and weight question

[Zacspace]

1 hour ago, camacju said:

(If you're not doing some funny stuff with fairings as your craft's hull, you always want a 5 degree incidence, since that gives the best lift to drag ratio. If you are doing funny stuff with fairings then technically -22 degree wing incidence is "best" but that's probably outside the scope of this thread)

This has to be when your craft has the optimal amount of wing for its mass, right? I can't imagine trying to run anything I've built with 5 degrees, even the stuff without fairing tricks, but then I usually just build wings that look cool.

As far as the scope of this thread, is there a better one? I've been noticing players confused about SSTO stuff around the place lately and I'm never sure where to send them. It seems like knowledge about how to design  and fly efficiently is spread pretty thin around the forum and mixed with a good amount of well meaning nonsense. I guess I'm guilty of that myself with my 1 degree comment earlier.

[camacju]

14 minutes ago, Zacspace said:

This has to be when your craft has the optimal amount of wing for its mass, right

Yes, it's when you have a well balanced wing area. For a super high performance craft, you'll want at least 6 tons per unit of wing area.

15 minutes ago, Zacspace said:

As far as the scope of this thread, is there a better one?

I'm not aware of one - maybe @Lt_Duckweed could make a video about advanced SSTO design for his next Kerbal University video? He knows this stuff better than I do.

[miklkit]

That editor thingy is only compatible up to 1.12.2 but it seems to work ok. 

This planes wings are at 5 degrees.  It seems that holding "shift" while tilting the wing puts it there.  I also got a lot of other stuff along with that mod and don't know what they do.  Anyway, it does fly differently now and more flying time is needed to get used to it.  So far, once the Rapiers are set to closed cycle it does better when pointed up steeply until it gets over 30,000m, then hit prograde and turn off the Rapiers.  Hitting prograde earlier just has it pushing air and burning fuel.

The only fairing trick I'm using is on the nose and that is for its heat resistance and pointy looks.  I also had to change the tail (vertical elevator?) for heat resistance.

[miklkit]

Further testing shows that 5 degrees is too much for this plane.  The extra drag is noticeable and causes it to be sluggish taking off and it slows down quicker when landing.  It is at 2 degrees now (I think) and takes off better and lands smoother.  Gotta try these tricks on an ore carrier next as they have to land smoothly or they lose their load.

[18Watt]

8 hours ago, miklkit said:

Further testing shows that 5 degrees is too much for this plane.

The term ‘optimized’ can mean a lot of things.  For my personal use, an ‘optimized’ SSTO design is not very useful.

My SSTOs tend to have a lot (LOT) more wing area that what would be considered ‘optimal’.  For me, I plan for a departure from somewhere on Laythe or a remote area of Kerbin, where I don’t have a long, flat runway.  For me, getting airborne quickly in a short distance is more important than being optimized for a departure from the KSC runway.

That means more wing area, and 5 degrees of incidence becomes counter-productive.  I actually get worse performance with 5 degrees of incidence than with 0 to 3.5 degrees.  My definition of ‘worse performance’ is that I reach orbit with less dv remaining.

As a pilot by profession, I am also squeamish about using every inch of runway for a takeoff.  However, an ‘optimized’ design would use every inch of KSC’s runway, after all that’s free lift!  In real life I wouldn’t fly a plane that required every inch of runway, so the SSTOs I make lift off before using about 66% of the KSC runway.  Again, that requires more wing area than what is optimal.

It sounds like you are fairly far along in your design.  At some point, you will need to test your designs and try some different ascent profiles.  Find a combination that gets you to orbit with the most dv remaining, while still having a plane that performs well in the other situations you need it to.

If 5 degrees is too much, dial it’s back until you find what works well.  Again, the planes I use have a LOT more wing area than what is ‘optimal’, and 5 degrees is too much for me.

If you only need to depart and arrive at the KSC runway, you can creep up on a more optimal design by increasing weight or reducing wing area.  When your plane will just barely get airborne at the end of the runway, I suspect that 5 degrees ( or possibly more) incidence will yield better performance.

For reference, my spaceplanes usually lift off at 85 m/s or so, and reach that speed about 2/3 down the KSC runway.  That’s probavly more (initial) thrust than optimal, and a much lower speed.  A more optimized design would hit the end of the runway at about 120 m/s, and be just barely able to fly at that point.

[miklkit]

Yeah I'm petty much set on a single basic design now.  All the new ones are variations on a theme.  The lighter ones lift off before the end of the runway and fly well, while the heaviest one struggles until it hits 165 m/s or so, then flies itself.  Just added more wing to that one. 

How it does on the runway is not a concern to me as it is used for takeoffs only.   How they take off and land on rough ground is much more important.  And yes, I have been experimenting with different ascent profiles and have been getting some interesting results.  Returning with more Ox than LF is strange. 

[camacju]

18 hours ago, 18Watt said:

However, an ‘optimized’ design would use every inch of KSC’s runway, after all that’s free lift!

Funnily enough, many designs are even more optimized than this. Some plane designs can't quite maintain level flight at the end of the runway, so you have to dive down to sea level to pick up the required amount of speed. Going further into optimization land, there are planes that can't take off from the runway at all, so they accelerate on the flats around KSC. Even further are the hills near KSC, where you roll down the hill and accelerate across the flats, picking up speed. And finally, for when you really really need minimal wing area, I've seen people use the polar ice caps as an incredibly long runway, where the plane can only attain level flight after accelerating across the entire ice cap.

If you're just talking about lift, a 5 degree angle provides a great lift to drag ratio, so it's great if you don't need higher lift than that. If you do, then it might be better to use more wing and fly at a lower angle of attack, knowing that you can pitch up and get lots of lift for a good L/D ratio, like you said for Laythe.

(My most recent Laythe SSTO struggles for this reason - I have to dive down the slope of the crater lake island, and use the nuclear engine as a bit extra thrust, in order to pick up enough speed to stay level).

[miklkit]

On 3/4/2022 at 2:57 PM, Zacspace said:

I gotta shout out Editor Extension Redux again here. It lets you select a bunch of different angles to snap to, even just 1 degree at a time,  instead of just being snap or don't snap.

On all my good SSTOs the wings have either 1 or 2 degrees of incidence. The one I linked earlier had 1. The sweet spot for wing incidence should keep your fuselage facing directly into the airstream to minimize drag while still producing enough lift with your wings to ascend at an agreeable rate.

Sorry to clutter this thread with this, but it is relevant. 

Installed Editor Extension Redux and all the stuff that comes with it.  Everything seems to be ok except that now the skybox is fracked.  I use Pood's skybox and now the dynamic dimmer is on and can't be turned off except by leaving an SOI.  Then it returns to normal, for a while.  This results in a completely black sky. 

I've tried tinkering with other things and possibly Bizzy's thingy has something to do with it.  Or not.  Will continue tinkering with things I don't know anything about.

[Zacspace]

3 hours ago, miklkit said:

Sorry to clutter this thread with this, but it is relevant. 

Installed Editor Extension Redux and all the stuff that comes with it.  Everything seems to be ok except that now the skybox is fracked.  I use Pood's skybox and now the dynamic dimmer is on and can't be turned off except by leaving an SOI.  Then it returns to normal, for a while.  This results in a completely black sky. 

I've tried tinkering with other things and possibly Bizzy's thingy has something to do with it.  Or not.  Will continue tinkering with things I don't know anything about.

I've never had any conflicts between EER and any of the other mods I use, certainly none of the graphics mods, so I can't really help you out with that. I'll tell you that you can delete blizzy's toolbar if you installed it for this, though. That's an old thing from back when KSP didn't have it's own toolbar, lots of mods support it, but no mods as far as I know require it anymore. All editor extensions requires is click through blocker and toolbar controller by linuxgurugamer.

The whole sky dimming thing sounds to me like it could be from the mod planetshine, but I don't know if you're using it or what could be going wrong if you are.

Not much help, sorry. If you make a post on the technical support subforum for modded installs you might get some better help. Be ready to provide your KSP.log and a list of the mods you're using.

[miklkit]

I deleted everything except the Editor and now have the skybox back.   One of them was a distant objects thingy.  Maybe that was the one.